2024/03/03 更新

写真a

ハラヤマ タカヒサ
原山 卓久
所属
理工学術院 先進理工学部
職名
教授
学位
博士

研究分野

  • 数理物理、物性基礎
 

論文

  • Universal Single-Mode Lasing in Fully Chaotic Billiard Lasers

    Mengyu You, Daisuke Sakakibara, Kota Makino, Yonosuke Morishita, Kazutoshi Matsumura, Yuta Kawashima, Manao Yoshikawa, Mahiro Tonosaki, Kazutaka Kanno, Atsushi Uchida, Satoshi Sunada, Susumu Shinohara, Takahisa Harayama

    Entropy   24 ( 11 )  2022年11月

     概要を見る

    By numerical simulations and experiments of fully chaotic billiard lasers, we show that single-mode lasing states are stable, whereas multi-mode lasing states are unstable when the size of the billiard is much larger than the wavelength and the external pumping power is sufficiently large. On the other hand, for integrable billiard lasers, it is shown that multi-mode lasing states are stable, whereas single-mode lasing states are unstable. These phenomena arise from the combination of two different nonlinear effects of mode-interaction due to the active lasing medium and deformation of the billiard shape. Investigations of billiard lasers with various shapes revealed that single-mode lasing is a universal phenomenon for fully chaotic billiard lasers.

    DOI

    Scopus

    4
    被引用数
    (Scopus)
  • Chaotic laser based online physical random bit streaming system and its application to high-throughput encryption

    Kenichi Arai, Susumu Shinohara, Peter Davis, Satoshi Sunada, Takahisa Harayama

    Optics InfoBase Conference Papers   2018   Tu3G.3 - 3  2018年  [査読有り]

     概要を見る

    We developed a high-speed entropy source using a compact chaotic laser module for streaming unpredictable random bits. It achieved 4 Gbps streaming of random bits to an encryption application via a general-purpose API.

    DOI

    Scopus

  • Universal single-mode lasing in fully chaotic two-dimensional microcavity lasers under continuous-wave operation with large pumping power [Invited]

    Takahisa Harayama, Satoshi Sunada, Susumu Shinohara

    PHOTONICS RESEARCH   5 ( 6 ) B39 - B46  2017年12月  [査読有り]

     概要を見る

    For a fully chaotic two-dimensional (2D) microcavity laser, we present a theory that guarantees both the existence of a stable single-mode lasing state and the nonexistence of a stable multimode lasing state, under the assumptions that the cavity size is much larger than the wavelength and the external pumping power is sufficiently large. It is theoretically shown that these universal spectral characteristics arise from the synergistic effect of two different kinds of nonlinearities: deformation of the cavity shape and mode interaction due to a lasing medium. Our theory is based on the linear stability analysis of stationary states for the Maxwell-Bloch equations and accounts for single-mode lasing phenomena observed in real and numerical experiments of fully chaotic 2D microcavity lasers. (C) 2017 Chinese Laser Press

    DOI

    Scopus

    9
    被引用数
    (Scopus)
  • Self-adjustment of a nonlinear lasing mode to a pumped area in a two-dimensional microcavity [Invited]

    Yuta Kawashima, Susumu Shinohara, Satoshi Sunada, Takahisa Harayama

    PHOTONICS RESEARCH   5 ( 6 ) B47 - B53  2017年12月  [査読有り]

     概要を見る

    We numerically performed wave dynamical simulations based on the Maxwell-Bloch (MB) model for a quadrupole-deformed microcavity laser with spatially selective pumping. We demonstrate the appearance of an asymmetric lasing mode whose spatial pattern violates both the x-and y-axes mirror symmetries of the cavity. Dynamical simulations revealed that a lasing mode consisting of a clockwise or counterclockwise rotating-wave component is a stable stationary solution of the MB model. From the results of a passive-cavity mode analysis, we interpret these asymmetric rotating-wave lasing modes by the locking of four nearly degenerate passive-cavity modes. For comparison, we carried out simulations for a uniform pumping case and found a different locking rule for the nearly degenerate modes. Our results demonstrate a nonlinear dynamical mechanism for the formation of a lasing mode that adjusts its pattern to a pumped area. (C) 2017 Chinese Laser Press

    DOI

    Scopus

    7
    被引用数
    (Scopus)
  • Random Number Generation from Intermittent Optical Chaos

    Andreas Karsaklian Dal Bosco, Naoki Sato, Yuta Terashima, Shoma Ohara, Atsushi Uchida, Takahisa Harayama, Masanobu Inubushi

    IEEE Journal of Selected Topics in Quantum Electronics   23 ( 6 )  2017年11月

     概要を見る

    We propose a method to generate physical random numbers based on intermittent optical chaos. Intermittent chaotic output is produced in a semiconductor laser subjected to optical feedback embedded in a photonic integrated circuit. This dynamics is characterized by a temporal waveform organized in a succession of laminar regions of low amplitude and bursts of high amplitude. The temporal randomness ruling the alternation of successive laminar regions and bursts is used as an entropy source to generate sequences of random bits. We compare the performances of the exclusive OR and reverse methods implemented in the bit generation process and evaluate the quality of the random bits with the Rabbit test of TestU01 for different bit sequences lengths.

    DOI

    Scopus

    20
    被引用数
    (Scopus)
  • Dynamics-dependent synchronization in on-chip coupled semiconductor lasers

    Shoma Ohara, Andreas Karsaklian Dal Bosco, Kazusa Ugajin, Atsushi Uchida, Takahisa Harayama, Masanobu Inubushi

    PHYSICAL REVIEW E   96 ( 3 )  2017年09月  [査読有り]

     概要を見る

    Synchronization properties of chaotic dynamics in two mutually coupled semiconductor lasers with optical feedback embedded in a photonic integrated circuit are investigated from the point of view of their dynamical content. A phenomenon in which the two lasers can show qualitatively different synchronization properties according to the frequency range of investigation and their nonlinear dynamics is identified and termed dynamics-dependent synchronization. In-phase synchronization is observed for original signals and antiphase synchronization is observed for low-pass filtered signals in the case where one of the lasers shows chaotic oscillations while the other laser exhibits low-frequency fluctuations dynamics. The experimental conditions causing the synchronization states to vary according to the considered frequency interval are studied and the key roles of asymmetric coupling strength and injection currents are clarified.

    DOI PubMed

    Scopus

    10
    被引用数
    (Scopus)
  • Dynamics Versus Feedback Delay Time in Photonic Integrated Circuits: Mapping the Short Cavity Regime

    Andreas Karsaklian Dal Bosco, Shoma Ohara, Naoki Sato, Yasuhiro Akizawa, Atsushi Uchida, Takahisa Harayama, Masanobu Inubushi

    IEEE PHOTONICS JOURNAL   9 ( 2 )  2017年04月  [査読有り]

     概要を見る

    We report a comprehensive experimental investigation of the nonlinear dynamics yielded in five photonic integrated circuits, each consisting of a semiconductor laser with optical feedback from a short external cavity. The external cavity lengths are different for each laser and range from 1.3 to 10.3 mm, allowing analysis of the dependence of the dynamical scenario on the feedback delay time. We draw two-dimensional bifurcation diagrams and study the relative predominance of the different dynamics exhibited in each laser when the feedback strength and the laser injection current are varied. We identify that, in the commonly termed short cavity regime, small variations of the external cavity length can result in totally different dynamical distributions, suggesting the possibility to use the feedback delay time as a means to control laser behaviors.

    DOI

    Scopus

    12
    被引用数
    (Scopus)
  • Chaotic laser based physical random bit streaming system with a computer application interface

    Susumu Shinohara, Kenichi Arai, Peter Davis, Satoshi Sunada, Takahisa Harayama

    OPTICS EXPRESS   25 ( 6 ) 6461 - 6474  2017年03月  [査読有り]

     概要を見る

    We demonstrate a random bit streaming system that uses a chaotic laser as its physical entropy source. By performing real-time bit manipulation for bias reduction, we were able to provide the memory of a personal computer with a constant supply of ready-to-use physical random bits at a throughput of up to 4 Gbps. We pay special attention to the end-toend entropy source model describing how the entropy from physical sources is converted into bit entropy. We confirmed the statistical quality of the generated random bits by revealing the pass rate of the NIST SP800-22 test suite to be 65 % to 75 %, which is commonly considered acceptable for a reliable random bit generator. We also confirmed the stable operation of our random bit steaming system with long-term bias monitoring.

    DOI PubMed

    Scopus

    22
    被引用数
    (Scopus)
  • Real-time fast physical random number generator with a photonic integrated circuit

    Kazusa Ugajin, Yuta Terashima, Kento Iwakawa, Atsushi Uchida, Takahisa Harayama, Kazuyuki Yoshimura, Masanobu Inubushi

    OPTICS EXPRESS   25 ( 6 ) 6511 - 6523  2017年03月  [査読有り]

     概要を見る

    Random number generators are essential for applications in information security and numerical simulations. Most optical-chaos-based random number generators produce random bit sequences by offline post-processing with large optical components. We demonstrate a real-time hardware implementation of a fast physical random number generator with a photonic integrated circuit and a field programmable gate array (FPGA) electronic board. We generate 1-Tbit random bit sequences and evaluate their statistical randomness using NIST Special Publication 800-22 and TestU01. All of the BigCrush tests in TestU01 are passed using 410-Gbit random bit sequences. A maximum real-time generation rate of 21.1 Gb/s is achieved for random bit sequences in binary format stored in a computer, which can be directly used for applications involving secret keys in cryptography and random seeds in large-scale numerical simulations.

    DOI PubMed

    Scopus

    64
    被引用数
    (Scopus)
  • One-port ring refractive index sensor with attached sub-ring

    H. Okayama, H. Takahisa, M. Tsutsui, M. Mendez-Astudillo, H. Nakajima

    OPTICAL REVIEW   24 ( 1 ) 11 - 16  2017年02月  [査読有り]

     概要を見る

    In this report, we propose a ring resonator with one port for surface normal input/output attached with another ring resonator. A resonance generated by one of the ring resonators is used for sensing and that by the other as a reference. The device characteristics were examined using the FDTD simulation.

    DOI

  • Photonic integrated circuits unveil crisis-induced intermittency

    Andreas Karsaklian Dal Bosco, Yasuhiro Akizawa, Kazutaka Kanno, Atsushi Uchida, Takahisa Harayama, Kazuyuki Yoshimura

    OPTICS EXPRESS   24 ( 19 ) 22198 - 22209  2016年09月  [査読有り]

     概要を見る

    We experimentally investigate an intermittent route to chaos in a photonic integrated circuit consisting of a semiconductor laser with time-delayed optical feedback from a short external cavity. The transition from a period-doubling dynamics to a fully-developed chaos reveals a stage intermittently exhibiting these two dynamics. We unveil the bifurcation mechanism underlying this route to chaos by using the Lang-Kobayashi model and demonstrate that the process is based on a phenomenon of attractor expansion initiated by a particular distribution of the local Lyapunov exponents. We emphasize on the crucial importance of the distribution of the steady-state solutions introduced by the time-delayed feedback on the existence of this intermittent dynamics. (C) 2016 Optical Society of America

    DOI

    Scopus

    24
    被引用数
    (Scopus)
  • Photonic integrated circuits unveil crisis-induced intermittency

    Andreas Karsaklian Dal Bosco, Yasuhiro Akizawa, Kazutaka Kanno, Atsushi Uchida, Takahisa Harayama, Kazuyuki Yoshimura

    OPTICS EXPRESS   24 ( 19 ) 22198 - 22209  2016年09月  [査読有り]

     概要を見る

    We experimentally investigate an intermittent route to chaos in a photonic integrated circuit consisting of a semiconductor laser with time-delayed optical feedback from a short external cavity. The transition from a period-doubling dynamics to a fully-developed chaos reveals a stage intermittently exhibiting these two dynamics. We unveil the bifurcation mechanism underlying this route to chaos by using the Lang-Kobayashi model and demonstrate that the process is based on a phenomenon of attractor expansion initiated by a particular distribution of the local Lyapunov exponents. We emphasize on the crucial importance of the distribution of the steady-state solutions introduced by the time-delayed feedback on the existence of this intermittent dynamics. (C) 2016 Optical Society of America

    DOI

    Scopus

    24
    被引用数
    (Scopus)
  • Long-path formation in a deformed microdisk laser

    Susumu Shinohara, Takehiro Fukushima, Satoshi Sunada, Takahisa Harayama, Kenichi Arai

    PHYSICAL REVIEW A   94 ( 1 ) 013831  2016年07月  [査読有り]

     概要を見る

    An asymmetric resonant cavity can be used to form a path that is much longer than the cavity size. We demonstrate this capability for a deformed microdisk equipped with two linear waveguides, by constructing a multiply reflected periodic orbit that is confined by total internal reflection within the deformed microdisk and outcoupled by the two linear waveguides. Resonant mode analysis reveals that the modes corresponding to the periodic orbit are characterized by high-quality factors. From measured spectral and far-field data, we confirm that the fabricated devices can form a path about 9.3 times longer than the average diameter of the deformed microdisk.

    DOI

    Scopus

  • Long-path formation in a deformed microdisk laser

    Shinohara, Susumu, Fukushima, Takehiro, Sunada, Satoshi, Harayama, Takahisa, Arai, Kenichi

    Physical Review A - Atomic, Molecular, and Optical Physics   94 ( 1 )  2016年07月

     概要を見る

    © 2016 American Physical Society.An asymmetric resonant cavity can be used to form a path that is much longer than the cavity size. We demonstrate this capability for a deformed microdisk equipped with two linear waveguides, by constructing a multiply reflected periodic orbit that is confined by total internal reflection within the deformed microdisk and outcoupled by the two linear waveguides. Resonant mode analysis reveals that the modes corresponding to the periodic orbit are characterized by high-quality factors. From measured spectral and far-field data, we confirm that the fabricated devices can form a path about 9.3 times longer than the average diameter of the deformed microdisk.

    DOI

    Scopus

  • Signature of Wave Chaos in Spectral Characteristics of Microcavity Lasers

    Satoshi Sunada, Susumu Shinohara, Takehiro Fukushima, Takahisa Harayama

    PHYSICAL REVIEW LETTERS   116 ( 20 )  2016年05月  [査読有り]

     概要を見る

    We report an experimental investigation on the spectra of fully chaotic and nonchaotic microcavity lasers under continuous-wave operating conditions. It is found that fully chaotic microcavity lasers operate in single mode, whereas nonchaotic microcavity lasers operate in multimode. The suppression of multimode lasing for fully chaotic microcavity lasers is explained by large spatial overlaps of the resonance wave functions that spread throughout the two-dimensional cavity due to the ergodicity of chaotic ray orbits.

    DOI

    Scopus

    24
    被引用数
    (Scopus)
  • N-1-20 光集積回路における間欠性ルートとカオス(N-1.非線形問題,一般セッション)

    カルサクリアン・ダル, ボスコ アンドレアス, 秋澤 康裕, 菅野 円隆, 内田 淳史, 原山 卓久, 吉村 和之

    電子情報通信学会基礎・境界ソサイエティ/NOLTAソサイエティ大会講演論文集   2016   358 - 358  2016年03月

    CiNii

  • Cycles of self-pulsations in a photonic integrated circuit

    Andreas Karsaklian Dal Bosco, Kazutaka Kanno, Atsushi Uchida, Marc Sciamanna, Takahisa Harayama, Kazuyuki Yoshimura

    PHYSICAL REVIEW E   92 ( 6 )  2015年12月  [査読有り]

     概要を見る

    We report experimentally on the bifurcation cascade leading to the appearance of self-pulsation in a photonic integrated circuit in which a laser diode is subjected to delayed optical feedback. We study the evolution of the self-pulsing frequency with the increase of both the feedback strength and the injection current. Experimental observations show good qualitative accordance with numerical results carried out with the Lang-Kobayashi rate equation model. We explain the mechanism underlying the self-pulsations by a phenomenon of beating between successive pairs of external cavity modes and antimodes.

    DOI

    Scopus

    11
    被引用数
    (Scopus)
  • Secret-Key Distribution Based on Bounded Observability

    Jun Muramatsu, Kazuyuki Yoshimura, Peter Davis, Atsushi Uchida, Takahisa Harayama

    PROCEEDINGS OF THE IEEE   103 ( 10 ) 1762 - 1780  2015年10月  [査読有り]

     概要を見る

    This paper reviews an approach to secret-key distribution based on the bounded observability (BO) model. First, the information-theoretic framework of secret-key agreement from a correlated random source is reviewed. Next, the BO model is introduced. In the context of this model, the BO condition is presented as a necessary and sufficient condition for the possibility of secret-key distribution. This condition describes limits on the information obtained by observation of a random object, and models the practical difficulty of completely observing random physical phenomena. Finally, an implementation of secret-key distribution based on BO in an optical fiber system is described.

    DOI

    Scopus

    15
    被引用数
    (Scopus)
  • Secret-Key Distribution Based on Bounded Observability

    Jun Muramatsu, Kazuyuki Yoshimura, Peter Davis, Atsushi Uchida, Takahisa Harayama

    PROCEEDINGS OF THE IEEE   103 ( 10 ) 1762 - 1780  2015年10月  [査読有り]

     概要を見る

    This paper reviews an approach to secret-key distribution based on the bounded observability (BO) model. First, the information-theoretic framework of secret-key agreement from a correlated random source is reviewed. Next, the BO model is introduced. In the context of this model, the BO condition is presented as a necessary and sufficient condition for the possibility of secret-key distribution. This condition describes limits on the information obtained by observation of a random object, and models the practical difficulty of completely observing random physical phenomena. Finally, an implementation of secret-key distribution based on BO in an optical fiber system is described.

    DOI

    Scopus

    15
    被引用数
    (Scopus)
  • Ray-wave correspondence in chaotic dielectric billiards

    Takahisa Harayama, Susumu Shinohara

    PHYSICAL REVIEW E   92 ( 4 )  2015年10月  [査読有り]

     概要を見る

    Based on the reformulation of the boundary integral equations recently derived by Creagh, Hamdin, and Tanner [J. Phys. A: Math. Theor. 46, 435203 (2013)] together with semiclassical (short wavelength) approximation, we theoretically show that low-loss resonances of a fully chaotic dielectric billiard can be related with ray dynamical orbits whose intensities are weighted by the Fresnel reflection and transmission coefficients. In addition, it is revealed that intensity localization spots observed in the phase-space representation of an individual resonance wave function are ray-dynamically correlated.

    DOI

    Scopus

    20
    被引用数
    (Scopus)
  • A-2-17 光集積回路における自己パルス生成とダイナミクス(A-2.非線形問題,一般セッション)

    アンドレアス カルサクリアン・ダル・ボスコ, 宇賀神 上総, 菅野 円隆, 原山 卓久, 吉村 和之, 内田 淳史

    電子情報通信学会総合大会講演論文集   2015   48 - 48  2015年02月

    CiNii

  • A-2-15 相互結合された半導体レーザを有する光集積回路を用いたカオス同期の周波数依存性(A-2.非線形問題,一般セッション)

    小原 翔馬, 宇賀神 上総, 高橋 里枝, 原山 卓久, 吉村 和之, 内田 淳史

    電子情報通信学会総合大会講演論文集   2015   46 - 46  2015年02月

    CiNii

  • Transverse Magnetic Emissions of GaAs Unstrained Quantum-Well Microcavity Lasers

    Takehiro Fukushima, Susumu Shinohara, Satoshi Sunada, Takahisa Harayama, Koichiro Sakaguchi, Yasunori Tokuda

    2015 17th International Conference on Transparent Optical Networks (ICTON)   2015-August  2015年  [査読有り]

     概要を見る

    We investigated the polarization characteristics of emissions from two-dimensional microcavity laser diodes. For an unstrained single-quantum-well active layer structure, an argument based on the interband optical transition usually leads to the lasing of transverse electric (TE) rather than transverse magnetic (TM) modes. Indeed, we observed TE-polarized emissions for the excitation of modes quantized along a one-dimensional (Fabry-Perot) orbit. However, when selectively pumping modes quantized along a diamond-shaped ray orbit, we observed TM-polarized emissions. These unusual TM-polarized emissions can be explained by the fact that the incident angles of the diamond-shaped orbit are very close to the Brewster angle, making corresponding TE modes too leaky to be excited. This mode-dependent polarization leads us to propose a microcavity laser diode with the function of polarization switching.

    DOI

    Scopus

  • Compact Two-Dimensional Multipass GaAs Optical Cavity with a Long Path Length

    Takehiro Fukushima, Susumu Shinohara, Satoshi Sunada, Takahisa Harayama, Kenichi Arai, Kazuyuki Yoshimura, Koichiro Sakaguchi, Yasunori Tokuda

    Frontiers in Optics 2014    2014年10月  [査読有り]

     概要を見る

    We fabricated and tested a compact multipass GaAs optical cavity with a round-trip path length of approximately 3.7 mm. The optical light injected into the cavity was found to propagate along a stable ray trajectory. © OSA 2014.

    DOI

    Scopus

  • Efficient optical path folding by using multiple total internal reflections in a microcavity

    Susumu Shinohara, Satoshi Sunada, Takehiro Fukushima, Takahisa Harayama, Kenichi Arai, Kazuyuki Yoshimura

    APPLIED PHYSICS LETTERS   105 ( 15 )  2014年10月  [査読有り]

     概要を見る

    We propose using an asymmetric resonant microcavity for the efficient generation of an optical path that is much longer than the diameter of the cavity. The path is formed along a star polygonal periodic orbit within the cavity, which is stable and confined by total internal reflection. We fabricated a semiconductor device based on this idea with an average diameter of 0.3 mm and achieved a path length of 2.79 mm experimentally. (C) 2014 AIP Publishing LLC.

    DOI

    Scopus

    2
    被引用数
    (Scopus)
  • A compact chaotic laser device with a two-dimensional external cavity structure

    Satoshi Sunada, Takehiro Fukushima, Susumu Shinohara, Takahisa Harayama, Kenichi Arai, Masaaki Adachi

    APPLIED PHYSICS LETTERS   104 ( 24 ) 241105  2014年06月  [査読有り]

     概要を見る

    We propose a compact chaotic laser device, which consists of a semiconductor laser and a two-dimensional (2D) external cavity for delayed optical feedback. The overall size of the device is within 230 mu m x 1mm. A long time delay sufficient for chaos generation can be achieved with the small area by the multiple reflections at the 2D cavity boundary, and the feedback strength is controlled by the injection current to the external cavity. We experimentally demonstrate that a variety of output properties, including chaotic output, can be selectively generated by controlling the injection current to the external cavity. (C) 2014 AIP Publishing LLC.

    DOI

    Scopus

    12
    被引用数
    (Scopus)
  • Fast physical random bit generation with photonic integrated circuits with different external cavity lengths for chaos generation

    Rie Takahashi, Yasuhiro Akizawa, Atsushi Uchida, Takahisa Harayama, Ken Tsuzuki, Satoshi Sunada, Kenichi Arai, Kazuyuki Yoshimura, Peter Davis

    OPTICS EXPRESS   22 ( 10 ) 11727 - 11740  2014年05月  [査読有り]

     概要を見る

    We generate random bit sequences from chaotic temporal waveforms by using photonic integrated circuits (PICs) with different external cavity lengths. We investigate the condition for generating random bits at different sampling rates of single-bit generation method with the PICs. We succeed in generating certified random bit sequences by using the PIC with 3, 4, 5, or 10-mm-long external cavity, whereas random bits cannot pass all the statistical tests of randomness when the PIC with 1 or 2 mm-long external cavity is used. (C) 2014 Optical Society of America

    DOI

    Scopus

    56
    被引用数
    (Scopus)
  • Lasing of TM modes in a two-dimensional GaAs microlaser

    Takehiro Fukushima, Susumu Shinohara, Satoshi Sunada, Takahisa Harayama, Koichiro Sakaguchi, Yasunori Tokuda

    OPTICS EXPRESS   22 ( 10 ) 11912 - 11917  2014年05月  [査読有り]

     概要を見る

    We fabricated and tested an unstrained GaAs single-quantum-well microlaser which has a two-dimensional cavity shape known as the Penrose unilluminable room. The cavity exhibits quasi-one-dimensional modes, namely axial, diamond-shaped, and V-shaped modes. In contrast to previous observations of TE-polarized emission in GaAs microlasers, we observed TM-polarized emission. We explain this observation as being the result of lasing of the diamond-shaped modes whose incident angle at the cavity interface is very close to the Brewster angle. (C)2014 Optical Society of America

    DOI

    Scopus

    4
    被引用数
    (Scopus)
  • Anticorrelated bidirectional output of quasistadium-shaped semiconductor microlasers

    Susumu Shinohara, Takehiro Fukushima, Satoshi Sunada, Takahisa Harayama, Kenichi Arai, Kazuyuki Yoshimura

    Optical Review   21 ( 2 ) 113 - 116  2014年03月  [査読有り]

     概要を見る

    Time-domain properties of the output from quasistadium-shaped microcavity semiconductor lasers are studied. Ring modes generating a bidirectional output are selectively excited by partial pumping. We observe a high anticorrelation between the two beams output from the ring modes. This can be considered as the generalization of alternate oscillations reported previously. We find that the outputs exhibit a robust slow modulation of 4-10 MHz, and explain it by the quasi-degeneracy of the resonator modes. © 2014 The Optical Society of Japan.

    DOI

    Scopus

    2
    被引用数
    (Scopus)
  • Selective excitation of lowest-order transverse ring modes in a quasi-stadium laser diode(共著)

    T. Fukushima, S. Shinohara, S. Sunada, T. Harayama, K. Arai, K. Sakaguchi, Y. Tokuda

    Optics Letters   38 ( 20 ) 4158 - 4161  2013年10月  [査読有り]

    DOI

    Scopus

    3
    被引用数
    (Scopus)
  • Stable single-wavelength emission from fully chaotic microcavity lasers

    Satoshi Sunada, Takehiro Fukushima, Susumu Shinohara, Takahisa Harayama, Masaaki Adachi

    Physical Review A - Atomic, Molecular, and Optical Physics   88 ( 1 ) 013802  2013年07月  [査読有り]

     概要を見る

    We experimentally and numerically show that single-wavelength emission can be stably observed for a fully chaotic microcavity laser with a stadium shape under continuous wave condition. The emission pattern is asymmetric with respect to the symmetry axes of the laser cavity, and it cannot be explained by a single cavity mode. On the basis of numerical analysis, we interpret such a lasing as the result of frequency-locking interaction among several low-loss cavity modes. Moreover, we experimentally investigate the optical spectral properties of the laser under pulsed-pumping condition, and discuss the pulse-width dependence on the number of lasing modes. © 2013 American Physical Society.

    DOI

    Scopus

    11
    被引用数
    (Scopus)
  • Ray dynamical simulation of penrose unilluminable room cavity

    Takehiro Fukushima, Susumu Shinohara, Satoshi Sunada, Takahisa Harayama, Koichiro Sakaguchi, Yasunori Tokuda

    Optics InfoBase Conference Papers    2013年

     概要を見る

    We performed ray dynamical simulations for a cavity having a two-dimensional shape known as the Penrose unilluminable room. The cavity is shown to have the potential to lase with a rich variety of resonator modes. © OSA 2013.

    DOI

    Scopus

  • Physical random number generation using photonic integrated circuit with mutually-coupled semiconductor lasers

    Rie Takahashi, Yasuhiro Akizawa, Atsushi Uchida, Takahisa Harayama, Ken Tsuzuki, Satoshi Sunada, Kazuyuki Yoshimura, Kenichi Arai, Peter Davis

    Optics InfoBase Conference Papers    2013年

     概要を見る

    We propose a photonic integrated circuit with mutually-coupled semiconductor lasers for fast physical random number generation. The random bit sequences generated at 5.56 Gb/s pass statistical tests of randomness. © OSA 2013.

    DOI

    Scopus

  • Noise amplification by chaotic dynamics in a delayed feedback laser system and its application to nondeterministic random bit generation

    Satoshi Sunada, Takahisa Harayama, Peter Davis, Ken Tsuzuki, Ken-ichi Arai, Kazuyuki Yoshimura, Atsushi Uchida

    CHAOS   22 ( 4 )  2012年12月  [査読有り]

     概要を見る

    We present an experimental method for directly observing the amplification of microscopic intrinsic noise in a high-dimensional chaotic laser system, a laser with delayed feedback. In the experiment, the chaotic laser system is repeatedly switched from a stable lasing state to a chaotic state, and the time evolution of an ensemble of chaotic states starting from the same initial state is measured. It is experimentally demonstrated that intrinsic noises amplified by the chaotic dynamics are transformed into macroscopic fluctuating signals, and the probability density of the output light intensity actually converges to a natural invariant probability density in a strongly chaotic regime. Moreover, with the experimental method, we discuss the application of the chaotic laser systems to physical random bit generators. It is experimentally shown that the convergence to the invariant density plays an important role in nondeterministic random bit generation, which could be desirable for future ultimate secure communication systems. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4754872]

    DOI

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    29
    被引用数
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  • Randomness in a Galton board from the viewpoint of predictability: Sensitivity and statistical bias of output states

    Kenichi Arai, Takahisa Harayama, Satoshi Sunada, Peter Davis

    PHYSICAL REVIEW E   86 ( 5 ) 56216  2012年11月  [査読有り]

     概要を見る

    The Galton board is a classic example of the appearance of randomness and stochasticity. In the dynamical model of the Galton board, the macroscopic motion is governed by deterministic equations of motion, and predictability depends on uncertainty in the initial conditions and its evolution by the dynamics. In this sense the Galton board is similar to coin tossing. In this paper, we analyze a simple dynamical model which is inspired by the Galton board. Especially, we focus on the predictability, considering the relation between the uncertainty of initial states and the structure of basins of initial states that result in the same exit state. The model has basins with fractal basin structure, unlike the basins in coin tossing models which have only finite structure. Arbitrarily small uncertainty of initial conditions can cause unpredictability of final states if the initial conditions are chosen in fractal regions. In this sense, our model is in a different category from the coin tossing model. We examine the predictability of a small Galton board model from the viewpoint of the sensitivity and the statistical bias of final states. We show that it is possible to determine the radii of scatterers corresponding to a given predictability criterion, specified as a statistical bias, and a given uncertainty of initial conditions.

    DOI

    Scopus

    6
    被引用数
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  • Fast Random Number Generation With Bandwidth-Enhanced Chaotic Semiconductor Lasers at 8 x 50 Gb/s

    Yasuhiro Akizawa, Taiki Yamazaki, Atsushi Uchida, Takahisa Harayama, Satoshi Sunada, Kenichi Arai, Kazuyuki Yoshimura, Peter Davis

    IEEE PHOTONICS TECHNOLOGY LETTERS   24 ( 12 ) 1042 - 1044  2012年06月  [査読有り]

     概要を見る

    We propose a scheme for fast random number generation with bandwidth-enhanced chaotic semiconductor lasers. Chaotic laser intensity output and its time-delayed signal are sampled at 50 GigaSample per second and converted into eight-bit values. The order of the eight-bit samples of the time-delayed signal is reversed, and bitwise exclusive-or operation is executed between the bit-order-reversed samples and the original eight-bit samples. With this method, it is not necessary to eliminate any of the bits in eight-bit samples in order to obtain good-quality random bit sequences. The equivalent generation rate of 8 x 50 Gb/s is achieved in an experiment using bandwidth-enhanced chaotic semiconductor lasers.

    DOI

    Scopus

    72
    被引用数
    (Scopus)
  • Lowest-order axial and ring mode lasing in confocal quasi-stadium laser diodes

    Takehiro Fukushima, Satoshi Sunada, Takahisa Harayama, Koichiro Sakaguchi, Yasunori Tokuda

    APPLIED OPTICS   51 ( 14 ) 2515 - 2520  2012年05月  [査読有り]

     概要を見る

    We investigated the lasing modes of quasi-stadium laser diodes that have confocal cavity geometries, with stripe electrode contacts formed either along the cavity axis or a diamond-shaped trajectory. It was clearly demonstrated that by using narrow electrode contact patterns of 2 mu m width, the lowest-order axial and ring modes were excited selectively. On the other hand, the second-lowest-order axial and ring modes were excited by using broad electrode patterns of 14 mu m width. Experimentally obtained far-field patterns for lasers with broad and narrow electrode contact patterns agree very well with the simulation results obtained using an extended Fox-Li mode calculation method. (C) 2012 Optical Society of America

    DOI

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    11
    被引用数
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  • Theory of fast nondeterministic physical random-bit generation with chaotic lasers

    Takahisa Harayama, Satoshi Sunada, Kazuyuki Yoshimura, Jun Muramatsu, Ken-ichi Arai, Atsushi Uchida, Peter Davis

    PHYSICAL REVIEW E   85 ( 4 )  2012年04月  [査読有り]

     概要を見る

    We theoretically show that completely stochastic fast physical random bit generation at a rate of more than one gigabit per second can be realized by using lasers with optical delayed feedback which creates high-dimensional chaos of laser light outputs. The theory is based on the mixing property of chaos, which transduces microscopic quantum noise of spontaneous emission in lasers into random transitions between discrete macroscopic states.

    DOI

    Scopus

    30
    被引用数
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  • Secure Key Distribution Using Correlated Randomness in Lasers Driven by Common Random Light

    Kazuyuki Yoshimura, Jun Muramatsu, Peter Davis, Takahisa Harayama, Haruka Okumura, Shinichiro Morikatsu, Hiroki Aida, Atsushi Uchida

    PHYSICAL REVIEW LETTERS   108 ( 6 ) 070602  2012年02月  [査読有り]

     概要を見る

    We propose a secure key distribution scheme based on correlated physical randomness in remote optical scramblers driven by common random light. The security of the scheme depends on the practical difficulty of completely observing random optical phenomena. We describe a particular realization using the synchronization of semiconductor lasers injected with common light of randomly varying phase. We experimentally demonstrate the feasibility of the scheme over a distance of 120 km.

    DOI

    Scopus

    123
    被引用数
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  • Theory and experiments of fast non-deterministic random bit generation using on-chip chaos lasers

    Satoshi Sunada, Takahisa Harayama, Kenichi Arai, Jun Muramatsu, Kazuyuki Yoshimura, Ken Tsuzuki, Peter Davis, Atsushi Uchida

    IUTAM SYMPOSIUM ON 50 YEARS OF CHAOS: APPLIED AND THEORETICAL   5   190 - 194  2012年  [査読有り]

     概要を見る

    We report physical random bit generation with on-chip chaos lasers. The design of the laser device is based on a theoretical model for non-deterministic random bit generation by amplification of microscopic noise. It is shown that the bit sequences generated at rates up to 2.08 gigabit per second (Gbit/s) pass a standard statistical test suite of randomness. (c) 2012 Published by Elsevier Ltd. Selection and/or Peer-review under responsibility of Takashi Hikihara and Tsutomu Kambe

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    2
    被引用数
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  • Estimation of entropy rate in a fast physical random-bit generator using a chaotic semiconductor laser with intrinsic noise

    Takuya Mikami, Kazutaka Kanno, Kota Aoyama, Atsushi Uchida, Tohru Ikeguchi, Takahisa Harayama, Satoshi Sunada, Ken-ichi Arai, Kazuyuki Yoshimura, Peter Davis

    PHYSICAL REVIEW E   85 ( 1 )  2012年01月  [査読有り]

     概要を見る

    We analyze the time for growth of bit entropy when generating nondeterministic bits using a chaotic semiconductor laser model. The mechanism for generating nondeterministic bits is modeled as a 1-bit sampling of the intensity of light output. Microscopic noise results in an ensemble of trajectories whose bit entropy increases with time. The time for the growth of bit entropy, called the memory time, depends on both noise strength and laser dynamics. It is shown that the average memory time decreases logarithmically with increase in noise strength. It is argued that the ratio of change in average memory time with change in logarithm of noise strength can be used to estimate the intrinsic dynamical entropy rate for this method of random bit generation. It is also shown that in this model the entropy rate corresponds to the maximum Lyapunov exponent.

    DOI

    Scopus

    40
    被引用数
    (Scopus)
  • Chaos-assisted emission from asymmetric resonant cavity microlasers

    Susumu Shinohara, Takahisa Harayama, Takehiro Fukushima, Martina Hentschel, Satoshi Sunada, Evgenii E. Narimanov

    PHYSICAL REVIEW A   83 ( 5 ) 053837  2011年05月  [査読有り]

     概要を見る

    We study emission from quasi-one-dimensional modes of an asymmetric resonant cavity that are associated with a stable periodic ray orbit confined inside the cavity by total internal reflection. It is numerically demonstrated that such modes exhibit directional emission, which is explained by chaos-assisted emission induced by dynamical tunneling. Fabricating semiconductor microlasers with an asymmetric resonant cavity, we experimentally demonstrate the selective excitation of the quasi-one-dimensional modes by employing the device structure to preferentially inject currents to these modes and observe directional emission in good accordance with the theoretical prediction based on chaos-assisted emission.

    DOI

    Scopus

    20
    被引用数
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  • Random optical pulse generation with bistable semiconductor ring lasers

    Satoshi Sunada, Takahisa Harayama, Kenichi Arai, Kazuyuki Yoshimura, Ken Tsuzuki, Atsushi Uchida, Peter Davis

    OPTICS EXPRESS   19 ( 8 ) 7439 - 7450  2011年04月  [査読有り]

     概要を見る

    We experimentally show that a random optical pulse train can be generated by modulating a bistable semiconductor ring laser. When the ring laser is switched from the monostable to the bistable regime, it randomly selects one of two different stable unidirectional lasing modes, clockwise or counterclockwise modes. Non-deterministic random pulse sequences are generated by driving the switch parameter, the injection current, with a periodic pulse signal. The origin of the nondeterministic randomness is the amplified spontaneous emission noise coupled to the counter-propagating lasing modes. The statistical randomness properties are optimized by adjusting the relative strength of amplified spontaneous emission noise sources for the two lasing modes. It is also shown that it is possible to generate optical pulse sequences which pass a standard suite of statistical randomness tests. (C) 2011 Optical Society of America

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    33
    被引用数
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  • Chaos laser chips with delayed optical feedback using a passive ring waveguide

    Satoshi Sunada, Takahisa Harayama, Kenichi Arai, Kazuyuki Yoshimura, Peter Davis, Ken Tsuzuki, Atsushi Uchida

    OPTICS EXPRESS   19 ( 7 ) 5713 - 5724  2011年03月  [査読有り]

     概要を見る

    We report a novel chaos semiconductor laser chip in which a distributed feedback (DFB) laser, two semiconductor optical amplifiers (SOAs) and a photodiode (PD) are monolithically integrated with a passive ring waveguide. The ring-type structure with the two separate SOAs achieves stronger delayed optical feedback compared to previous chaos laser chips which use linear waveguide and facet-reflection. The integrated PD allows efficient detection of the optical signal with low optical loss. A rich variety of dynamical behaviors and optical signals can be selectively generated via injection currents to the two separate SOAs. In particular, the strong optical feedback makes possible the generation of strong broadband optical chaos, with very flat spectrum of +/- 6.5 dB up to 10 GHz. The stability and quality of the chaotic mode is demonstrated using strict statistical tests of randomness applied to long binary sequences extracted by sampling the optical intensity signal. (c) 2011 Optical Society of America

    DOI PubMed

    Scopus

    70
    被引用数
    (Scopus)
  • Fast nondeterministic random-bit generation using on-chip chaos lasers

    Takahisa Harayama, Satoshi Sunada, Kazuyuki Yoshimura, Peter Davis, Ken Tsuzuki, Atsushi Uchida

    PHYSICAL REVIEW A   83 ( 3 )  2011年03月  [査読有り]

     概要を見る

    It is shown that broadband chaos suitable for fast nondeterministic random-bit generation in small devices can be achieved in a semiconductor laser with a short external cavity. The design of the device is based on a theoretical model for nondeterministic random-bit generation by amplification of microscopic noise. Moreover, it is demonstrated that bit sequences passing common tests of statistical randomness at rates up to 2.08 Gbits/s can be generated using on-chip lasers with a monolithically integrated external cavity, amplifiers, and a photodetector.

    DOI

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    92
    被引用数
    (Scopus)
  • Fresnel filtering of Gaussian beams in microcavities

    Susumu Shinohara, Takahisa Harayama, Takehiro Fukushima

    OPTICS LETTERS   36 ( 6 ) 1023 - 1025  2011年03月  [査読有り]

     概要を見る

    We study the output from the modes described by the superposition of Gaussian beams confined in the quasistadium microcavities. We experimentally observe the deviation from Snell's law in the output when the incident angle of the Gaussian beam at the cavity interface is near the critical angle for total internal reflection, providing direct experimental evidence on the Fresnel filtering. The theory of the Fresnel filtering for a planar interface qualitatively reproduces experimental data, and a discussion is given on small deviation between the measured data and the theory. (C) 2011 Optical Society of America

    DOI

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    10
    被引用数
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  • Manifestation of ray chaos in optical cavities

    Susumu Shinohara, Takahisa Harayama

    Trends in Nano- and Micro-Cavities     62 - 108  2011年

     概要を見る

    The correspondence between ray and wave descriptions for twodimensional chaotic open billiards describing optical cavities is reviewed. Focusing on the stadium-shaped cavity, which is well-known for its fully chaotic ray dynamics, we show how ray chaos is manifested in emission patterns, or eigenfunctions of resonances (decaying eigenmodes). The flux phase-space distribution is introduced, which not only enables one to understand the relation between ray dynamics and emission directionality, but also provides a suitable stage to study the ray-wave correspondence. We observe intrinsic localization phenomenon in each resonance, which causes discrepancies with the ray description. Nonetheless, we demonstrate that the average of many low-loss resonances reproduces the ray description very well, where one can clearly observe that signature of ray chaos (i.e., long-term effects of stretching and folding) is embedded in resonance eigenfunctions. © 2011 Bentham Science Publishers Ltd.

    DOI

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    1
    被引用数
    (Scopus)
  • Fast physical random number generation with bandwidth enhancement of chaotic semiconductor lasers

    Taiki Yamazaki, Yasuhiro Akizawa, Atsushi Uchida, Takahisa Harayama, Satoshi Sunada, Kazuyuki Yoshimura, Peter Davis

    Optics InfoBase Conference Papers    2011年

     概要を見る

    We experimentally demonstrate random bit generation using multi-bit samples of bandwidth-enhanced chaos in semiconductor lasers. The bit generation rate of 75 Gigabit per second is achieved. FIO/ LS Technical Digest © 2011 OSA.

  • Selective Excitation of Lowest-Order Axial and Ring Modes in Confocal Quasi-Stadium Laser Diodes

    Takehiro Fukushima, Satoshi Sunada, Takahisa Harayama, Koichiro Sakaguchi, Yasunori Tokuda

    2011 13TH INTERNATIONAL CONFERENCE ON TRANSPARENT OPTICAL NETWORKS (ICTON)    2011年  [査読有り]

     概要を見る

    We fabricated and investigated two confocal quasi-stadium laser diodes: one has a narrow electrode contact pattern along its cavity axis and the other has a narrow electrode contact pattern along a diamond-shaped trajectory. The lowest-order axial and ring modes were selectively excited. The resonator modes of the laser diodes were calculated using the extended Fox-Li mode calculation method. Although some deformation of the far-field emission pattern was observed in experiments, the numerically calculated far-field emission patterns agree well with the experimentally observed far-field patterns.

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  • Chaos-Assisted Directional Light Emission from Microcavity Lasers

    Susumu Shinohara, Takahisa Harayama, Takehiro Fukushima, Martina Hentschel, Takahiko Sasaki, Evgenii E. Narimanov

    PHYSICAL REVIEW LETTERS   104 ( 16 ) 163902  2010年04月  [査読有り]

     概要を見る

    We study the effect of dynamical tunneling on emission from ray-chaotic microcavities by introducing a suitably designed deformed disk cavity. We focus on its high quality factor modes strongly localized along a stable periodic ray orbit confined by total internal reflection. It is shown that dominant emission originates from the tunneling from the periodic ray orbit to chaotic ones; the latter eventually escape from the cavity refractively, resulting in directional emission that is unexpected from the geometry of the periodic orbit, but fully explained by unstable manifolds of chaotic ray dynamics. Experimentally performing selective excitation of those modes, we succeeded in observing the directional emission in good agreement with theoretical prediction. This provides decisive experimental evidence of dynamical tunneling in a ray-chaotic microcavity.

    DOI

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    124
    被引用数
    (Scopus)
  • Fast random bit generation with bandwidth-enhanced chaos in semiconductor lasers

    Kunihito Hirano, Taiki Yamazaki, Shinichiro Morikatsu, Haruka Okumura, Hiroki Aida, Atsushi Uchida, Shigeru Yoshimori, Kazuyuki Yoshimura, Takahisa Harayama, Peter Davis

    OPTICS EXPRESS   18 ( 6 ) 5512 - 5524  2010年03月  [査読有り]

     概要を見る

    We experimentally demonstrate random bit generation using multi-bit samples of bandwidth-enhanced chaos in semiconductor lasers. Chaotic fluctuation of laser output is generated in a semiconductor laser with optical feedback and the chaotic output is injected into a second semiconductor laser to obtain a chaotic intensity signal with bandwidth enhanced up to 16 GHz. The chaotic signal is converted to an 8-bit digital signal by sampling with a digital oscilloscope at 12.5 Giga samples per second (GS/s). Random bits are generated by bitwise exclusive-OR operation on corresponding bits in samples of the chaotic signal and its time-delayed signal. Statistical tests verify the randomness of bit sequences obtained using 1 to 6 bits per sample, corresponding to fast random bit generation rates from 12.5 to 75 Gigabit per second (Gb/s) (= 6 bit x 12.5 GS/s). (C) 2010 Optical Society of America

    DOI PubMed

    Scopus

    179
    被引用数
    (Scopus)
  • Ray-wave correspondence in limaçon-shaped semiconductor microcavities

    Susumu Shinohara, Martina Hentschel, Jan Wiersig, Takahiko Sasaki, Takahisa Harayama

    Physical Review A - Atomic, Molecular, and Optical Physics   80 ( 3 )  2009年09月

     概要を見る

    The limaçon-shaped semiconductor microcavity is a ray-chaotic cavity sustaining low-loss modes with mostly unidirectional emission patterns. Investigating these modes systematically, we show that the modes correspond to ray description collectively rather than individually. In addition, we present experimental data on multimode lasing emission patterns that show high unidirectionality and closely agree with the ray description. The origin of this agreement is well explained by the collective correspondence mechanism. © 2009 The American Physical Society.

    DOI

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    68
    被引用数
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  • Linewidth properties of active-passive coupled monolithic InGaAs semiconductor ring lasers

    Muhan Choi, Tomoko Tanaka, Satoshi Sunada, Takahisa Harayama

    APPLIED PHYSICS LETTERS   94 ( 23 ) 231110  2009年06月  [査読有り]

     概要を見る

    We report linewidth properties of active-passive coupled monolithic InGaAs semiconductor ring lasers with various length of passive waveguide. It is experimentally confirmed that the linewidth of the lasers is proportional to the square of the ratio of the length of active part of the cavity over the total length of the cavity. The lasers are applicable for communication and sensing devices, which need the narrow linewidth.

    DOI

    Scopus

    3
    被引用数
    (Scopus)
  • Improvement in size distribution and optical properties of InAs/GaAs QDs by post growth thermal treatment

    Shanmugam Saravanan, Takashisa Harayama

    Physica Status Solidi (B) Basic Research   246 ( 4 ) 725 - 728  2009年04月

     概要を見る

    We investigated the effect of rapid thermal annealing from 700 °C to 950 °C on stacked InAs/GaAs quantum dots (QDs) covered with GaAs and In0.19Ga0.81As layers. Large blue-shift of the energy positions nearly 380 meV (1187 nm to 870 nm) have been observed in InGaAs capped samples together with improvement in the photoluminescence integrated intensity of more than five times. The strong narrowing of the photoluminescence line-width in both GaAs (as narrow as 8 meV) and InGaAs capped samples show an improvement of the size distribution of the QDs. In addition, a significant reduction of the energy spacing (ΔE2-1) between ground state and first excited state emissions were found in both GaAs and InGaAs capped quantum dots due to interface inter-diffusion induced by thermal treatment. The excited state filling experiments for InGaAs capped sample annealed at 950 °C exhibits quantum well like behavior where as, the GaAs capped sample shows a shoulder in high energy side might be due to first excited state of QDs. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

    DOI

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    2
    被引用数
    (Scopus)
  • Photoluminescence properties of annealed InAs quantum dots capped by InGaAs layers

    Shingo Hiratsuka, Shanugam Saravanan, Takahisa Harayama, Naoki Ohtani

    Physica Status Solidi (C) Current Topics in Solid State Physics   6 ( 1 ) 189 - 192  2009年

     概要を見る

    We have investigated the annealing-temperature dependence on photoluminescence (PL) properties of InAs quantum dots (QDs) fabricated on GaAs substrate. The annealing temperatures were varied from 700 to 1000°C. The observed PL spectra were drastically changed by changing the annealing temperature. The PL peaking-wavelength of non-annealed sample is around 1200 nm. However, the peaking-wavelength is drastically blue-shifted with increasing annealing temperature. The strongest PL intensity is observed from the sample annealed at 875°C. This PL intensity is more than seven fold compared with that of the non-annealed sample. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA.

    DOI

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    1
    被引用数
    (Scopus)
  • Ring-laser gyroscope without the lock-in phenomenon

    Satoshi Sunada, Shuichi Tamura, Keizo Inagaki, Takahisa Harayama

    PHYSICAL REVIEW A   78 ( 5 ) 53822  2008年11月  [査読有り]

     概要を見る

    We theoretically and numerically study the effect of backscattering on rotating ring lasers by employing the Maxwell-Bloch equations. We show that frequency shifts due to the Sagnac effect incorporating the effect of backscattering can be observed without lock-in phenomenon, if the strength of backscattering originating in the bumps of the refractive index is larger than a certain value. It is also shown that the experimental results corresponding to the theoretical ones can actually be obtained by using a semiconductor fiber-optic ring laser gyroscope.

    DOI

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    37
    被引用数
    (Scopus)
  • Dependence of far-field characteristics on the number of lasing modes in stadium-shaped InGaAsP microlasers

    Muhan Choi, Susumu Shinohara, Takahisa Harayama

    Optics Express   16 ( 22 ) 17554 - 17559  2008年10月

     概要を見る

    We study spectral and far-field characteristics of lasing emission from stadium-shaped semiconductor (InGaAsP) microlasers. We demonstrate that the correspondence between a lasing far-field emission pattern and the result of a ray simulation becomes better as the number of lasing modes increases. This phenomenon is reproduced in the wave calculation of the cavity modes. © 2008 Optical Society of America.

    DOI

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    14
    被引用数
    (Scopus)
  • Alternate oscillations in quasistadium laser diodes

    Muhan Choi, Takehiro Fukushima, Takahisa Harayama

    PHYSICAL REVIEW A   77 ( 6 ) 063814  2008年06月  [査読有り]

     概要を見る

    We found alternate oscillations in AlGaAs/GaAs single-quantum-well quasistadium laser diodes (QSLDs). Unlike the alternate oscillations in conventional ring lasers, which are explained by interaction between two counterpropagating modes, the alternate oscillations in QSLDs arise from two nearly degenerate cavity modes due to its geometric structure. The lasing signals in QSLDs are directly obtained from the emitted beams which spread over the space without the use of waveguides. We also showed that the alternate oscillation frequencies decrease linearly as the amplitudes of the two different cavity modes increase.

    DOI

    Scopus

    8
    被引用数
    (Scopus)
  • Light emission patterns from stadium-shaped semiconductor microcavity lasers

    Susumu Shinohara, Takehiro Fukushima, Takahisa Harayama

    PHYSICAL REVIEW A   77 ( 3 ) 033807  2008年03月  [査読有り]

     概要を見る

    We study light emission patterns from stadium-shaped semiconductor (GaAs) microcavity lasers theoretically and experimentally. Performing systematic wave calculations for passive cavity modes, we demonstrate that the averaging by low-loss modes, such as those realized in multimode lasing, generates an emission pattern in good agreement with the ray model's prediction. In addition, we show that the dependence of experimental far-field emission patterns on the aspect ratio of the stadium cavity is well reproduced by the ray model.

    DOI CiNii

    Scopus

    32
    被引用数
    (Scopus)
  • Investigation of in<inf>x</inf>Ga<inf>1-x</inf> As strain reducing layers effects on InAs/GaAs quantum dots

    Shanmugam Saravanan, Takashisa Harayama

    IEICE Electronics Express   5 ( 2 ) 53 - 59  2008年01月

     概要を見る

    Optical and morphological properties of self-assembled InAs quantum dots (QDs) covered by InxGa1-xAs strain reducing layers (SRL) with different thicknesses (2. 4, 6 and Snm) and compositions (x-0.13, 0.1.8 and 0.30) were investigated. Photolumincscencc from InAs QDs shows the dependence on indium mole fraction and thickness of the overgrown InxGa 1-xAs SRL. Improvement in PL intensity and narrowing of PL width up to 26 meV occurred together with a red shift of up to 138 nm when the QDs were coved with 6 nm of In0.18Ga0.82As. Also, we found that when the total amount of InAs deposited to form the QDs and the SRL was larger than a critical value of around 6MLs, the surface roughness increased and the PL intensity decreased drastically. © IEICE 2008.

    DOI

    Scopus

    4
    被引用数
    (Scopus)
  • Nonlinear dynamics in deformed microcavity lasers

    Takahisa Harayama

    Optics InfoBase Conference Papers    2008年

     概要を見る

    We report a theory and demonstration of lasing in several deformed microcavities which are rigorously known to be chaotic. We also discuss their applications to optical switching and sensing devices. © 2008 Optical Society of America.

    DOI

    Scopus

  • Convergence of far-field characteristics upon ray dynamics in stadium microlasers

    Muhan Choi, Susumu Shinohara, Takehiro Fukushima, Takahisa Harayama

    Optics InfoBase Conference Papers    2008年

     概要を見る

    We study spectral and far-field characteristics of lasing emission from stadium-shaped semiconductor microlasers. We demonstrate that the correspondence between far-field emission patterns and ray simulation results becomes better as the number of lasing modes increases. © 2008 Optical Society of America.

    DOI

    Scopus

  • Earth's rotation rate detection using an extremely-large semiconductor fiber optic gyroscope extending over 10,000 m2

    Keizo Inagaki, Shuichi Tamura, Tomoko Tanaka, Hiroyuki Noto, Takahisa Harayama

    Proceedings of SPIE - The International Society for Optical Engineering   7004  2008年

     概要を見る

    We detect the Earth's rotation rate using a semiconductor fiber optic gyroscope (S-FOG), which is an active ring laser gyroscope that consists of a semiconductor optical amplifier (SOA) and a fiber optic ring resonator. Four different optical fiber layouts with different scale factors in rotation rate measurement are configured and measured. Expected Sagnac beat signals proportional to the scale factors are observed. The maximum layout of S-FOG is extended over 10,898 m2, which, to our knowledge, is the largest active ring laser gyroscope ever built.

    DOI

    Scopus

    4
    被引用数
    (Scopus)
  • Lasing emission patterns from monza-shaped semiconductor microcavities

    Yutaka Nakae, Tomohiro Miyasaka, Takahiko Sasaki, Susumu Shinohara, Takahisa Harayama

    Proceedings of 2008 10th Anniversary International Conference on Transparent Optical Networks, ICTON   4   258 - 259  2008年

     概要を見る

    We fabricated Monza-shaped semiconductor microcavity lasers and evaluated their far-field characteristics. From the ray dynamical point of view, the Monza-shaped cavity belongs to a special class of fully chaotic cavities; its phase space is decomposed into two independent chaotic components, which yield two different emission patterns. In the present paper, we discuss which ensemble of ray trajectories (i.e., phase space measure) can reproduce far-field emission patterns observed in experiments. ©2008 IEEE.

    DOI

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    2
    被引用数
    (Scopus)
  • Sagnac effect and frequency splitting in rotating optical microcavities

    Takahisa Harayama, Satoshi Sunada

    ICTON 2008: PROCEEDINGS OF 2008 10TH ANNIVERSARY INTERNATIONAL CONFERENCE ON TRANSPARENT OPTICAL NETWORKS, VOL 4   4   38 - 38  2008年  [査読有り]

     概要を見る

    The Sagnac effect in rotating microcavities is Studied theoretically and numerically. The frequency splitting due to the Sagnac effect Occurs as a threshold-like phenomenon for the angular velocity in a rotating microcavity. Above the threshold, the eigenfunctions of a rotating microcavity become rotating waves while they are standing waves below the threshold.

    DOI

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  • Improvement of accuracy of angular velocity detection in semiconductor fiber-optic ring laser gyroscope

    Tomoki Ishida, Shuichi Tamura, Satoshi Sunada, Keizo Inagaki, Shigeru Saito, Takahisa Harayama

    19TH INTERNATIONAL CONFERENCE ON OPTICAL FIBRE SENSORS, PTS 1 AND 2   7004  2008年  [査読有り]

     概要を見る

    A semiconductor fiber-optic ring laser gyroscope (S-FOG) consists of a semiconductor optical amplifier (SOA) and optical fiber to form a ring cavity. The fiber ring cavity enables larger sizes and smaller scattering, while the SOA gain is shared by the clockwise (CW) and counterclockwise (CCW) propagating modes. When the S-FOG is rotated, a new beat signal called the Sagnac beat frequency is observed. We investigated the effect of the fiber ring cavity's length on detection characteristics. Detection sensitivity was not dependent on the number of laps of fiber ring cavity. However, when the cavity length became longer, the linewidth of Sagnac beat became narrower, and then accuracy of angular velocity detection improved. The relation between the linewidth Delta v of the Sagnac beat and cavity length P was proved to be Delta v approximate to p(-1.86).

    DOI

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    5
    被引用数
    (Scopus)
  • Light beam output from diamond-shaped total-internal reflection modes by using intracavity air gaps

    Takehiro Fukushima, Susumu Shinohara, Takahisa Harayama

    OPTICS EXPRESS   15 ( 25 ) 17392 - 17400  2007年12月  [査読有り]

     概要を見る

    We propose a novel method for extracting light beams from diamond-shaped total-internal reflection modes in two-dimensional microcavity laser diodes by the use of intracavity air gaps. By fabricating such a laser diode, we experimentally demonstrate that the direction and longitudinal mode spacing of the output beams are in good accordance with theoretical calculations. (c) 2007 Optical Society of America.

    DOI

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    4
    被引用数
    (Scopus)
  • High-quality lowest-loss-mode lasing in GaAs quasi-stadium laser diodes having unstable resonators

    Takehiro Fukushima, Tomoko Tanaka, Takahisa Harayama

    OPTICS LETTERS   32 ( 23 ) 3397 - 3399  2007年12月  [査読有り]

     概要を見る

    We obtained high-quality lowest-loss-mode lasing in quasi-stadium laser diodes having unstable resonators that consisted of two curved end mirrors and two straight sidewall mirrors. The laser diodes were fabricated by applying a reactive ion etching technique to a metal-organic chemical-vapor deposition-grown graded-index separate-confinement heterostructure single-quantum-well GaAs/AlGaAs structure. The electrode contact area of the laser diodes was formed along unstable periodic orbits, along which the optical beams are localized. Highly directional fan-out beams corresponding to the numerically obtained lowest loss mode were emitted from the end mirrors under CW operation at room temperature. (C) 2007 Optical Society of America.

    DOI PubMed CiNii

    Scopus

    6
    被引用数
    (Scopus)
  • Design of resonant microcavities: application to optical gyroscopes

    Satoshi Sunada, Takahisa Harayama

    OPTICS EXPRESS   15 ( 24 ) 16245 - 16254  2007年11月  [査読有り]

     概要を見る

    We study theoretically and numerically the effect of rotation on resonant frequencies of microcavities in a rotating frame of reference. Cavity rotation causes the shifts of the resonant frequencies proportional to the rotation rate if it is larger than a certain value. Below the value, a region of rotation rate exists where there is no resulting the frequency shifts proportional to the rotation rate. We show that designing cavity symmetry as C-nv (n &gt;= 3) can eliminate this region. (c) 2007 Optical Society of America.

    DOI

    Scopus

    52
    被引用数
    (Scopus)
  • Signature of ray chaos in quasibound wave functions for a stadium-shaped dielectric cavity

    Susumu Shinohara, Takahisa Harayama

    Physical Review E - Statistical, Nonlinear, and Soft Matter Physics   75 ( 3 )  2007年03月

     概要を見る

    Light emission from a dielectric cavity with a stadium shape is studied in both ray and wave models. For a passive cavity mode with low loss, a remarkable correspondence is found between the phase space representation of a quasibound wave function and its counterpart distribution in the ray model. This result provides additional and more direct evidence for good ray-wave correspondence in low-loss modes previously observed at the level of far-field emission pattern comparisons. © 2007 The American Physical Society.

    DOI

    Scopus

    42
    被引用数
    (Scopus)
  • Progress of Theoretical Physics Supplment: Preface

    Katsuhiro Nakamura, Takahisa Harayama, Kazuo Takatsuka

    Progress of Theoretical Physics Supplement   ( 166 )  2007年

  • Experimental investigation of Sagnac beat signals using semiconductor fiber-optic ring laser gyroscope (S-FOG) based on semiconductor optical amplifier (SOA)

    Shuichi Tamura, Keizo Inagaki, Hiroyuki Noto, Takahisa Harayama

    Proceedings of SPIE - The International Society for Optical Engineering   6770  2007年

     概要を見る

    We are conducting research to confirm the performance of a semiconductor fiber-optic ring laser gyroscope (S-FOG) featuring a semiconductor in its laser cavity. This S-FOG consists of a semiconductor optical amplifier (SOA) as a gain medium, a polarization-maintaining fiber to make a ring cavity, and a directional coupler to take part of the optical power out of the cavity. One of the advantages of the S-FOG is the adaptability of the laser cavity, which allows us to examine many cases of S-FOG applications easily. In the first case, we observed that the S-FOG generated Sagnac beat signals whose peak frequency was proportional to the rotation rate when it rotated. In the second case, we changed the area surrounded by the ring cavity (the fiber) and its perimeter and maintained a near-fixed oscillation wavelength of the ring laser. In this case, all of our experimental results were in good agreement with theoretical calculations, within a few percent. In the third case, we changed the oscillation wavelength and fixed the shape of the ring cavity. In this case, our results were also in good agreement with theoretical calculations. In the fourth case, we examined the Sagnac beat spectrum generated by the S-FOG in detail. The linewidth of the Sagnac beat spectrum increases as the area bounded by the optical path in the ring cavity becomes smaller, or as the length of the cavity becomes shorter. Our experimental results show that the S-FOG works as a gyro and that there exists practical potential for a semiconductor ring laser gyro.

    DOI

    Scopus

    8
    被引用数
    (Scopus)
  • Ray-wave correspondence in stadium-shaped optical cavities

    Susumu Shinohara, Takahisa Harayama

    Proceedings of 2007 9th International Conference on Transparent Optical Networks, ICTON 2007   4   188 - 189  2007年

     概要を見る

    We study light emission from a stadium-shaped optical cavity by ray and wave descriptions. A remarkable ray-wave correspondence is revealed by investigating phase space distributions that describe how the light is transmitted outside the cavity. © 2007 IEEE.

    DOI

    Scopus

  • Rotating optical microcavities

    Takahisa Harayama, Satoshi Sunada

    2007 PACIFIC RIM CONFERENCE ON LASERS AND ELECTRO-OPTICS, VOLS 1-4     914 - 915  2007年  [査読有り]

     概要を見る

    The Sagnac effect in rotating microcavities is studied theoretically and numerically. The frequency shift due to the Sagnac effect occurs as a threshold-like phenomenon for the angular velocity in a rotating microcavity Above the threshold, the eigenfunctions of a rotating microcavity become rotating waves while they arc standing waves below the threshold.

    DOI

    Scopus

  • Generalized sagnac effect in rotating optical cavities

    Satoshi Sunada, Takahisa Harayama, Tomohiro Miyasaka

    ICTON 2007: PROCEEDINGS OF THE 9TH INTERNATIONAL CONFERENCE ON TRANSPARENT OPTICAL NETWORKS, VOL 4   4   158 - +  2007年  [査読有り]

     概要を見る

    We study the effect of rotation on resonances of an optical cavity in an accelerated frame of reference. We show that, even when the resonant modes of an optical cavity are wave-chaotic, degenerate resonant frequency of those modes split into different frequencies due to the rotation of the cavity. The frequency difference is proportional to the rotation rate, although the splitting resonant modes are still wave-chaotic, which do not have any corresponding counter-propagating waves as well as ray-dynamical counterparts.

    DOI

    Scopus

  • Chaos and multi-attractors in rilly chaotic 2D microcavity lasers

    Takahisa Harayama, Takehiro Fukushima, Satoshi Sunada, Kensuke S. Ikeda

    PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT   166 ( 166 ) 104 - 111  2007年  [査読有り]

     概要を見る

    Multi-mode lasing in stadium-shaped cavities which are rigorously known to be fully chaotic is investigated both theoretically and experimentally. By a nonlinear dynamical model, it is shown that there exist multi- attractors of limit cycles and chaos corresponding to the final lasing states for large microst.adiums. We also show that the envelopes of the far field patterns of the actual microstadium laser diodes are excellently approximated by fully chaotic ray-dynamics.

    DOI

    Scopus

    1
    被引用数
    (Scopus)
  • Axis and Ring Mode Switching in Multi-Electrode GaAs Quasi-Stadium Laser Diodes

    Takehiro Fukushima, Takahisa Harayama

    2007 CONFERENCE ON LASERS & ELECTRO-OPTICS/QUANTUM ELECTRONICS AND LASER SCIENCE CONFERENCE (CLEO/QELS 2007), VOLS 1-5     2338 - +  2007年  [査読有り]

     概要を見る

    We fabricated and tested mufti-electrode quasi-stadium laser diodes having GaAs/AlGaAs GRIN-SCH-SQW structures. Axis and ring mode switching was achieved under CW operation for output powers up to 15 mW by selecting the electrode used. (C) 2007 Optical Society of America

    DOI

    Scopus

    2
    被引用数
    (Scopus)
  • Theory and applications of 2D microcavity lasers

    Takahisa Harayama, Takehiro Fukushima

    ICTON 2007: PROCEEDINGS OF THE 9TH INTERNATIONAL CONFERENCE ON TRANSPARENT OPTICAL NETWORKS, VOL 3   3   42 - +  2007年  [査読有り]

     概要を見る

    We report a demonstration of lasing in a two-dimensional (2D) microcavity which is a semiconductor diode structure with a stadium shape finely formed by reactive-ion-etching technique and pumped by electric current injection. The laser exhibits output over a wide angle, although the fundamental lasing modes have highly complex wave structures which do not correspond to any simple set of rays inside the cavity. The applications of 2D microcavity lasers are also discussed.

    DOI

    Scopus

  • Alternate oscillations with pi phase difference in quasi-stadium laser modes

    Muhan Choi, Takehiro Fukushima, Takahisa Harayama

    2007 PACIFIC RIM CONFERENCE ON LASERS AND ELECTRO-OPTICS, VOLS 1-4     1141 - 1142  2007年  [査読有り]

     概要を見る

    We found alternate oscillations in AlGaAs/GaAs single-quantum-well (SQW) quasi-stadium laser diodes (QSLD). The alternate oscillations in QSLD can be well explained by the interactions of two different cavity modes due to the geometrical symmetry of QSLD. We also showed the alternate oscillation frequencies are inversely proportional to the amplitudes of two different cavity modes.

    DOI

    Scopus

    1
    被引用数
    (Scopus)
  • Two mode interactions in quasi-stadium laser diodes

    Muhan Choi, Takehiro Fukushima, Takahisa Harayama

    ICTON 2007: PROCEEDINGS OF THE 9TH INTERNATIONAL CONFERENCE ON TRANSPARENT OPTICAL NETWORKS, VOL 4   4   166 - +  2007年  [査読有り]

     概要を見る

    We found alternate oscillations in AlGaAs/GaAs single-quantum-well (SQW) quasi-stadium laser diodes (QSLD). The alternate oscillations in QSLD can be well explained by the interactions of two different cavity modes due to the geometrical symmetry of QSLD. Unlike the alternate oscillations in semiconductor ring lasers that need the waveguides to extract the light signals, the alternate oscillation signals in QSLD are obtained from the emitting lights spreading over the space. We also showed the alternate oscillation frequencies are inversely proportional to the amplitudes of two different cavity modes. This result is consistent with the theory of locking of two modes explaining the locking phenomenon between two nearly degenerated modes due to the nonlinear interactions in an active medium.

    DOI

    Scopus

  • Optical control of ring modes using tandem quasi-stadium laser diodes

    Takahiko K. Sasaki, Yutaka Nakae, Muhan Choi, Takehiro Fukushima, Takahisa Harayama

    ICTON 2007: PROCEEDINGS OF THE 9TH INTERNATIONAL CONFERENCE ON TRANSPARENT OPTICAL NETWORKS, VOL 4   4   151 - +  2007年  [査読有り]

     概要を見る

    In order to demonstrate controlling directional emissions corresponding to the ring trajectory modes by using external optical injection, we fabricate the AlGaAs/GaAs single-quantum-well tandem quasi-stadium laser diodes consist of the front slave and the rear master laser diodes. The geometry of the laser cavities have been defined by using a lithography system and a reactive-ion-etching technique. The optical injection is performed from the master laser to the slave laser. The ring mode control with the optical injection is evaluated by far-field patterns for the output from the curved end mirror.

    DOI

    Scopus

  • Beam mode observation in quasi-stadium laser diodes

    Yutaka Nakae, Hiroki Takehana, Takahiko Sasaki, Takehiro Fukushima, Takahisa Harayama

    ICTON 2007: PROCEEDINGS OF THE 9TH INTERNATIONAL CONFERENCE ON TRANSPARENT OPTICAL NETWORKS, VOL 4   4   162 - +  2007年  [査読有り]

     概要を見る

    We fabricated quasi-stadium laser diode which has a 'window' on the top of cavity by ion-etching technique to epitaxial wafer and demonstrated to observe direct lasing mode observation. In the carrier poor region, bright line can recognize. On the other hands, in the rich carrier region, lasing pattern was recognized as dark line. Both lines well fit extended Fox-Li simulation. From these results, it can understand that the lasing pattern condition depend the carrier density.

    DOI

    Scopus

  • Classical phase space revealed by coherent light

    Tomoko Tanaka, Martina Hentschel, Takehiro Fukushima, Takahisa Harayama

    PHYSICAL REVIEW LETTERS   98 ( 3 ) 033902  2007年01月  [査読有り]

     概要を見る

    We study the far-field characteristics of oval-resonator laser diodes made of an GaAs/AlxGa1-xAs quantum well. The resonator shapes are various oval geometries, thereby probing chaotic and mixed classical dynamics. The far-field pattern shows a pronounced fine structure that strongly depends on the cavity shape. Comparing the experimental data with ray-model simulations for a Fresnel billiard yields convincing agreement for all geometries and reveals the importance of the underlying classical phase space for the lasing characteristics.

    DOI

    Scopus

    46
    被引用数
    (Scopus)
  • Sagnac effect in resonant microcavities

    Satoshi Sunada, Takahisa Harayama

    PHYSICAL REVIEW A   74 ( 2 )  2006年08月  [査読有り]

     概要を見る

    The Sagnac effect in two-dimensional resonant microcavities is studied theoretically and numerically. The frequency shift due to the Sagnac effect occurs as a threshold phenomenon for the angular velocity in a rotating microcavity. Above the threshold, the eigenfunctions of a rotating microcavity become rotating waves while they are standing waves below the threshold.

    DOI

    Scopus

    42
    被引用数
    (Scopus)
  • Control of directional emission in quasistadium microcavity laser diodes with two electrodes

    M Choi, T Tanaka, T Fukushima, T Harayama

    APPLIED PHYSICS LETTERS   88 ( 21 ) 211110  2006年05月  [査読有り]

     概要を見る

    We fabricated the AlGaAs/GaAs three quantum well quasistadium laser diodes with two electrodes and succeeded in controlling directional laser emission by applying different currents to each electrode. We showed the ratio of laser emission with two different directions is proportional to the ratio of currents injected into two electrodes. These devices are applicable for beam switching and splitting. (c) 2006 American Institute of Physics.

    DOI

    Scopus

    18
    被引用数
    (Scopus)
  • Ray-wave correspondence in the nonlinear description of stadium-cavity lasers

    Susumu Shinohara, Takahisa Harayama, Hakan E. Türeci, A. Douglas Stone

    Physical Review A - Atomic, Molecular, and Optical Physics   74 ( 3 )  2006年

     概要を見る

    We show that the solution of fully nonlinear lasing equations for stadium cavities exhibits a highly directional emission pattern. This directionality can be well explained by a ray-dynamical model, where the dominant ray-escape dynamics is governed by the unstable manifolds of the unstable short periodic orbits for the stadium cavity. Investigating the cold-cavity modes relevant for the lasing, we found that all of the high- Q modes have the emission directionality corresponding to that of the ray-dynamical model. © 2006 The American Physical Society.

    DOI

    Scopus

    32
    被引用数
    (Scopus)
  • Unidirectional beam emission from confocal Quasi-Stadium laser diodes

    Takehiro Fukushima, Tomoko Tanaka, Takahisa Harayama

    Optics InfoBase Conference Papers   1   574 - 576  2006年

     概要を見る

    Unidirectional beam emission was obtained from strained InGaAsP multiple-quantum-well quasi-stadium laser diodes. The unidirectional beam emission can be explained by the phase locking of two resonator modes with different symmetry classes. © 2005 Optical Society of America.

    DOI

    Scopus

  • Nonlinear Sagnac effect for ring laser gyroscopes

    Takahisa Harayama, Satoshi Sunada, Shuichi Tamura, Keizo Inagaki, Hiroyuki Noto

    Optics InfoBase Conference Papers    2006年

     概要を見る

    We propose a novel ring laser gyroscope that gives the Sagnac beat frequency as the oscillation frequency of the amplitude of the only unidirectional propagating mode instead of the coupled counter-propagating laser lights in the conventional ring laser gyroscope. © 2006 Optical Society of America.

    DOI

    Scopus

    1
    被引用数
    (Scopus)
  • Sagnac beat signals observed in semiconductor fiber-optic ring laser gyroscope

    Keizo Inagaki, Shuichi Tamura, Hiroyuki Noto, Takahisa Harayama

    Optics InfoBase Conference Papers    2006年

     概要を見る

    A semiconductor fiber-optic ring laser gyroscope, which consist of a semiconductor optical amplifier as a gain medium and polarization-maintaining fiber to form a ring resonator, generate Sagnac beat signals demonstrating good agreement with theoretical calculations. (35 words) © 2006 OSA/OFS 2006.

    DOI

    Scopus

    10
    被引用数
    (Scopus)
  • Highly directional emission in stadium-cavity lasers

    Susumu Shinohara, Takahisa Harayama, Hakan E. Türeci, Douglas A. Stone

    2006 International Conference on Transparent Optical Networks   4   137  2006年

     概要を見る

    In two-dimensional microcavity lasers, as a way to extract highly directional emission, it has been proposed to deform the cavity shape smoothly from perfect circularity [1]. As a result, rays start to exhibit a variety of dynamics from integrable to strongly chaotic, which is tunable by the deformation. The ray picture has been providing a simple and intuitive method to explain experimental observations of emission directionality. For example, emission directionality has been associated with the existence of a periodic ray orbit with a particular geometry [2], drastic shape dependence of emission directionality has been successfully explained by the difference of phase space structure [3], and the far-field intensity patterns have been closely reproduced by ray-tracing simulations [4]. Among various cavity shapes the stadium is a simple geometry for which ray dynamics has been proven to become strongly chaotic [5]. That is, for almost all initial conditions, a ray trajectory explores the entire phase space uniformly. Even for such a strongly chaotic cavity, a ray model can generate highly directional emission patterns as a consequence of the openness of the cavity. Namely, strongly chaotic dynamics and highly directional emission are compatible, as was demonstrated by Schwefel, et al. [3] In this presentation, we report evidence for the ability of a ray model to describe the lasing states of the stadium-cavity lasers. Earlier work has focused on establishing a relationship between the ray model and a few quasi-bound state solutions of the linear wave equation without pumping or gain. In this case, however, there remains an intrinsic arbitrariness about which modes to choose, although plausibility argument can be made based on their Q values. Here we show that the solution of the full nonlinear lasing equations [6] for a stadium cavity, uniquely determined by the pumping conditions, exhibits highly directional emission pattern in good agreement with the ray model. Moreover, we reveal the property of cold-cavity modes that allows the robust appearance of the emission directionality in the lasing states.

    DOI

    Scopus

  • Sagnac effect in resonant microcavities

    Satoshi Sunada, Takahisa Harayama

    ICTON 2006: 8TH INTERNATIONAL CONFERENCE ON TRANSPARENT OPTICAL NETWORKS, VOL 1, PROCEEDINGS   74   92 - 92  2006年  [査読有り]

     概要を見る

    We report the Sagnac effect in resonant microcavities. The Sagnac effect is the phase and frequency difference between two counter propagating laser beams in a rotating ring resonator, and has been studied for a long time [1, 2]. It forrns the basis for the optical gyroscopes, such as ring laser gyroscope or fiber optic gyroscopes [1-3]. Conventional theoretical approach for the Sagnac effect has been derived from the assumption that the light propagates one-dimensionally and the wavelength of the light is typically much smaller than the cavity length. However, nowadays, micro-fabrication techniques are developed enough that the cavity size can approach the size of the wavelength of the light [4-6]. The conventional formalism for the Sagnac effect, therefore, breaks down and needs to be replaced.
    We derive the Sagnac effect in resonant microcavities theoretically and numerically without the conventional assumption and show that the frequency shift due to the Sagnac effect occurs as a threshold phenomenon for rotation velocity in a rotating microcavity by employing perturbation theory typically used in quantum mechanics. The threshold exists even in the absence of the backscattering, which causes the lock-in phenomenon [2, 3], and depends on the geometric shape and the symmetry of resonant cavities.
    It is also shown that the eigenfanctions of a rotating microcavity become rotating waves above the threshold while they are standing waves below the threshold.
    Our theoretical approach can be applied to the resonant cavities of arbitrary shapes and can make it possible to design compact optical gyroscopes that have a low threshold.

    DOI

    Scopus

    42
    被引用数
    (Scopus)
  • Mode switching by optical injection in tandem quasi-stadium laser diodes

    Takehiro Fukushima, Takahisa Harayama

    Conference on Lasers and Electro-Optics and 2006 Quantum Electronics and Laser Science Conference, CLEO/QELS 2006    2006年  [査読有り]

     概要を見る

    We demonstrate mode switching in tandem quasi-stadium laser diodes. Switching is achieved by optical injection between lasing in the cavity axis and the closed ring trajectory of a quasi-stadium laser resonator. © 2006 Optical Society of America.

    DOI

    Scopus

  • Ray-wave correspondence in an unstable quasistadium laser resonator

    Takehiro Fukushima, Takahisa Harayama, Jan Wiersig

    Physical Review A - Atomic, Molecular, and Optical Physics   73 ( 2 )  2006年  [査読有り]

     概要を見る

    The relation between unstable periodic orbits and resonator modes in a fully chaotic open-sided two-dimensional laser resonator is theoretically investigated in the short wavelength limit. We derive a periodic-orbit-sum formula for eigenvalues of the resonator modes by applying the semiclassical approximation to the extended Fox-Li mode calculation method. With this formula, we show that the complicated wavelength dependence of the power-coupling coefficients of the fully chaotic quasi-stadium laser resonator can be explained by a few kinds of unstable periodic orbits. © 2006 The American Physical Society.

    DOI

    Scopus

    17
    被引用数
    (Scopus)
  • Directional emission patterns from the oval-billiard microcavity laser diodes

    Tomoko Tanaka, Martina Hentschel, Takehiro Fukushima, Takahisa Harayama

    ICTON 2006: 8TH INTERNATIONAL CONFERENCE ON TRANSPARENT OPTICAL NETWORKS, VOL 4, PROCEEDINGS   4   121 - +  2006年  [査読有り]

     概要を見る

    We investigate the lasing characteristics of oval-resonator laser diodes made of AlGaAs/GaAs quantum wells both experimentally and theoretically. The resonator shapes are various oval geometries, thereby probing chaotic and mixed classical dynamics. The far field pattern shows a pronounced fine structure that strongly depends on the cavity shape.

    DOI

    Scopus

  • Control of directional emission in two-dimensional quasi-stadium micro-cavity laser diodes with two-electrodes

    Muhan Choi, Tomoko Tanaka, Takehiro Fukushima, Takahisa Harayama

    ICTON 2006: 8TH INTERNATIONAL CONFERENCE ON TRANSPARENT OPTICAL NETWORKS, VOL 4, PROCEEDINGS   4   117 - +  2006年  [査読有り]

     概要を見る

    We fabricated the AlGaAs/GaAs 3QW quasi-stadium laser diodes with two-electrodes and succeeded in controlling directional laser emission by applying different currents to each electrode. We showed the ratio of laser emission with two different directions is proportional to the ratio of currents injected into two electrodes. These devices are applicable for beam switching and splitting.

    DOI

    Scopus

  • Lowest order ring mode lasing in confocal quasi-stadium laser diodes

    Takehiro Fukushima, Takahisa Harayama

    2006 IEEE LEOS ANNUAL MEETING CONFERENCE PROCEEDINGS, VOLS 1 AND 2     931 - +  2006年  [査読有り]

     概要を見る

    We succeeded in selectively lasing only the lowest order ring mode of a confocal quasi-stadium laser diode by optimizing the electrode contact area shape. The lasing mode had excellent agreement with the numerically calculated mode.

    DOI

    Scopus

    6
    被引用数
    (Scopus)
  • Morphological dependence of emission patterns from oval-billiard microcavity laser diodes

    Tomoko Tanaka, Martina Hentschel, Takehiro Fukushima, Takahisa Harayama

    2006 IEEE LEOS ANNUAL MEETING CONFERENCE PROCEEDINGS, VOLS 1 AND 2     729 - +  2006年  [査読有り]

     概要を見る

    We investigate the lasing characteristics of oval-billiard microcavity laser diodes made of AlGaAs/GaAs single-quantum well both experimentally and theoretically. Experiments with various oval-billiard microcavity laser diodes enable us to observe chaotic and mixed classical dynamics.

    DOI

    Scopus

  • Ring and axis mode switching in quasi-stadium laser diodes with multi-electrodes

    Yutaka Nakae, Takehiro Fukushima, Tomoko Tanaka, Takahisa Harayama

    ICTON 2006: 8TH INTERNATIONAL CONFERENCE ON TRANSPARENT OPTICAL NETWORKS, VOL 4, PROCEEDINGS   4   132 - +  2006年  [査読有り]

     概要を見る

    Mode switching operation of multi-electrode strained InGaAsP multiple-quantum-well quasi-stadium laser diodes is reported. Far-field patterns exhibit highly directional emission along the laser cavity axis for current injection at the axis electrode and highly directional emission at angles +/- 19 degrees from the cavity axis for current injection at the ring electrode.

    DOI

    Scopus

  • Locking of two modes and unidirectional beam emission in quasi-stadium laser diodes

    Takahiko Sasaki, Takehiro Fukushima, Tomoko Tanaka, Takahisa Harayama

    ICTON 2006: 8TH INTERNATIONAL CONFERENCE ON TRANSPARENT OPTICAL NETWORKS, VOL 4, PROCEEDINGS   4   134 - +  2006年  [査読有り]

     概要を見る

    We present locking of two modes in GaA/AlGaAs single-quantum-well quasi-stadium laser diodes and unidirectional emission from InGaAsP multiple-quantum-well quasi-stadium laser diodes.

    DOI

    Scopus

  • Ring and axis mode switching in multielectrode strained InGaAsP multiple-quantum-well quasistadium laser diodes

    Takehiro Fukushima, Tomoko Tanaka, Takahisa Harayama

    Applied Physics Letters   87 ( 19 ) 1 - 3  2005年11月  [査読有り]

     概要を見る

    We describe the mode switching operation of multielectrode strained InGaAsP multiple-quantum-well quasistadium laser diodes. Far-field patterns exhibit highly directional emission along the laser cavity axis for current injection at the axis electrode and highly directional emission at angles ±19° from the cavity axis for current injection at the ring electrode. These directions correspond to the axis mode and the ring trajectory mode of the laser cavity. We also succeeded in obtaining single peak output beams using narrow curved end mirrors of 40 μm width. © 2005 American Institute of Physics.

    DOI

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    18
    被引用数
    (Scopus)
  • On the boundary element method for billiards with corners

    Y. Okada, A. Shudo, S. Tasaki, T. Harayama

    Journal of Physics A: Mathematical and General   38 ( 30 ) 6675 - 6688  2005年07月

     概要を見る

    The boundary element method is one of the reliable numerical schemes to solve the eigenvalue problem of the Helmholtz equation, which is justified by the Fredholm theory for domains with a smooth boundary. When a domain has corners, however, the corresponding integral equation is singular, so that the boundary element method lacks its well-established base. Employing a cutoff technique, we here formulate a well-grounded version of the boundary element method, and also give a certain justification to the standard boundary element method even for domains with corners. © 2005 IOP Publishing Ltd.

    DOI

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    6
    被引用数
    (Scopus)
  • Theory of two-dimensional microcavity lasers

    T Harayama, S Sunada, KS Ikeda

    PHYSICAL REVIEW A   72 ( 1 ) 13803  2005年07月  [査読有り]

     概要を見る

    We present theoretical models of two-dimensional (2D) microcavity lasers. The relation between stationary lasing modes and resonances or metastable states is elucidated for arbitrary shapes of 2D resonant microcavities.

    DOI

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    56
    被引用数
    (Scopus)
  • Chaotic behavior in quantum transport devices

    S. Harada, N. Kida, T. Morimoto, M. Hemmi, R. Naito, T. Sasaki, N. Aoki, T. Harayama, J. P. Bird, Y. Ochiai

    AIP Conference Proceedings   772   475 - 476  2005年06月

     概要を見る

    We have studied transport properties in the low-temperature magnetoresistance through the ballistic narrow path restricted by a short width metallic gate on the 2 dimentional electron gas (2DEG) system. An alternate and systematic variation between a Lorentzian line fitting and a cusp-like line fitting in the zero-field peaks has been observed, as sweeping the gate voltage. It indicates a possibility of existence of chaotic and regular paths on the short gated ballistic/tunneling transport. We will discuss on the quantum chaos behavior on the systematic variation between the Lorentzian and the cusp-like peakshape based on the disordered path system under the short gate. © 2005 American Institute of Physics.

    DOI

    Scopus

  • Unidirectional beam emission from strained InGaAsP multiple-quantum-well quasistadium laser diodes

    Takehiro Fukushima, Tomoko Tanaka, Takahisa Harayama

    Applied Physics Letters   86 ( 17 ) 1 - 3  2005年04月  [査読有り]

     概要を見る

    We present unidirectional emission from strained InGaAsP multiple-quantum-well quasistadium laser diodes, whose resonators consist of two confocal end mirrors and two long, straight, sidewall mirrors. Far-field patterns exhibit highly directional emission at a 20° angle from the cavity axis. This angle corresponds to a unidirectional ring trajectory inside the resonator. We also report that the unidirectional emission can be explained by the phase locking of two resonator modes with different symmetry classes based on the extended Fox-Li mode calculation method. © 2005 American Institute of Physics.

    DOI

    Scopus

    13
    被引用数
    (Scopus)
  • Multimode lasing in two-dimensional fully chaotic cavity lasers

    Satoshi Sunada, Takahisa Harayama, Kensuke S. Ikeda

    Physical Review E - Statistical, Nonlinear, and Soft Matter Physics   71 ( 4 )  2005年04月

     概要を見る

    Multimode lasing in a fully chaotic cavity is investigated numerically by using a nonlinear dynamics model. We report a transition process from single-mode lasing to multimode lasing and reveal interactions among the lasing modes. In particular, both mode-pulling and mode-pushing interactions are shown to decrease the number of effective lasing modes. In addition, coexistence of different types of attractors of the final lasing states is numerically confirmed. © 2005 The American Physical Society.

    DOI

    Scopus

    25
    被引用数
    (Scopus)
  • 'Can one hear the shape of a drum?': Revisited

    Y. Okada, A. Shudo, S. Tasaki, T. Harayama

    Journal of Physics A: Mathematical and General   38 ( 9 )  2005年03月

     概要を見る

    A famous inverse problem posed by M Kac 'Can one hear the shape of a drum?' is concerned with isospectrality of drums or planer billiards, and the first counter example was constructed by Gordon, Webb and Wolpert (1992 Invent. Math. 110 1). Here we present pieces of numerical evidence showing that 'One can distinguish isospectral drums by measuring the scattering poles of exterior Neumann problems'. This is based on the observation that the Fredholm determinant appearing in the boundary element method admits a factorization into interior and exterior parts. © 2005 IOP Publishing Ltd.

    DOI

    Scopus

    16
    被引用数
    (Scopus)
  • Mode expansion description of stadium-cavity laser dynamics

    S Shinohara, S Sunada, T Harayama, KS Ikeda

    PHYSICAL REVIEW E   71 ( 3 ) 36203  2005年03月  [査読有り]

     概要を見る

    The lasing dynamics of a stadium-cavity laser is studied by using a mode expansion model which is a reduction of the Schrodinger-Bloch model. We study the properties of stationary lasing states when two cavity modes are selectively excited, while examining the validity of the mode expansion model by comparing its results with those of the Schrodinger-Bloch model. Some analytical results are obtained for single-mode and two-mode stationary lasing states for the mode expansion model.

    DOI

    Scopus

    7
    被引用数
    (Scopus)
  • Stadium and quasi-stadium laser diodes

    Takehiro Fukushima, Takahisa Harayama

    IEEE Journal on Selected Topics in Quantum Electronics   10 ( 5 ) 1039 - 1051  2004年09月  [査読有り]

     概要を見る

    We present theoretical and experimental studies on two-dimensional microcavity laser diodes with stadium and quasi-stadium shapes. We report a demonstration of lasing for the first time in a fully chaotic microcavity - a stadium-shaped cavity which is rigorously known to be fully chaotic. We also present systematic studies on quasi-stadium laser diodes for three types of resonator conditions: stable, marginally stable, and unstable. Morphological dependence of lasing characteristics of quasi-stadium laser diodes is elucidated. We also show examples of the application of quasi-stadium laser diodes to beam switching operation and optical signal distribution by using patterned electrodes and the phase locking phenomenon between two resonator modes.

    DOI

    Scopus

    70
    被引用数
    (Scopus)
  • Fractal behavior in magnetoconductance in coupled quantum dot systems

    Nobuyuki Aoki, Li Hung Lin, Takahiro Morimoto, Takahiko Sasaki, Jun Feng Song, Koji Ishibashi, Jonathan P. Bird, Agung Budiyono, Katsuhiro Nakamura, Takahisa Harayama, Yuichi Ochiai

    Physica E: Low-Dimensional Systems and Nanostructures   22 ( 1-3 ) 361 - 364  2004年04月

     概要を見る

    Fractal behavior in magnetoconductance fluctuations in coupled quantum dots has been studied by means of exact and statistical self-similarity. The fractal dimensions from the different features are not coincident exactly but show the similar gate voltage dependences, where the values increase with increasing negative gate voltage. Moreover, results of statistical fractal dimensions obtained from two types of dot-array samples show the same dependence on the gate voltage variation. It seems a common feature of coupled-dot systems that the fractal dimension increases by decreasing the inter-dot coupling. © 2003 Elsevier B.V. All rights reserved.

    DOI

    Scopus

    1
    被引用数
    (Scopus)
  • Nonlinear whispering-gallery modes in a microellipse cavity

    S Sunada, T Harayama, KS Ikeda

    OPTICS LETTERS   29 ( 7 ) 718 - 720  2004年04月  [査読有り]

     概要を見る

    We study theoretically the effect of deformed microelliptical cavities on lasing characteristics. We show that the transition of stationary lasing states from unidirectional rotational waves to a mixture of clockwise and anticlockwise rotational waves occurs when the shape of a disk is deformed to that of an ellipse. (C) 2004 Optical Society of America.

    DOI

    Scopus

    13
    被引用数
    (Scopus)
  • Ray-wave correspondence in a fully chaotic quasi-stadium laser resonator

    Takehiro Fukushima, Takahisa Harayama, Jan Wiersig

    OSA Trends in Optics and Photonics Series   97   845 - 846  2004年

     概要を見る

    The relation between resonator modes and unstable periodic orbits in a fully chaotic quasi-stadium laser resonator is investigated. The complicated wavelength dependence of the power-coupling coefficient is explained by a simple coupling model, which considers some unstable periodic orbits. ©2003 Optical Society of America.

  • Morphological dependence of lasing modes in two-dimensional quasi-stadium laser diodes

    Takehiro Fukushima, Takahisa Harayama, Tomohiro Miyasaka, Pablo O. Vaccaro

    Journal of the Optical Society of America B: Optical Physics   21 ( 5 ) 935 - 943  2004年  [査読有り]

     概要を見る

    Three types of quasi-stadium laser diodes, which have confocal, concentric, and geometrically unstable end mirrors, were fabricated by a reactive-ion-etching technique. It is shown that the experimental results on the lasing characteristics of these lasers excellently correspond to the theoretical results by the extended Fox-Li mode calculation method. The morphological effects on lasing modes are discussed from the viewpoint of raywave correspondence. © 2004 Optical Society of America.

    DOI

    Scopus

    43
    被引用数
    (Scopus)
  • Asymmetric stationary lasing patterns in 2D symmetric microcavities

    T Harayama, T Fukushima, S Sunada, KS Ikeda

    PHYSICAL REVIEW LETTERS   91 ( 7 ) 073903  2003年08月  [査読有り]

     概要を見る

    Locking of two resonance modes of different symmetry classes and different frequencies in 2D resonant microcavity lasers is investigated by using a nonlinear dynamical model. The patterns of stationary lasing states and far fields are asymmetric in spite of the symmetric shape of the resonant microcavity. The corresponding phenomenon is actually observed in the experiment of a 2D semiconductor microcavity laser diode.

    DOI

    Scopus

    68
    被引用数
    (Scopus)
  • Quasi-stadium laser diodes with an unstable resonator condition

    Takehiro Fukushima, Takahisa Harayama, Peter Davis, Pablo O. Vaccaro, Takehiro Nishimura, Tahito Aida

    Optics Letters   28 ( 6 ) 408 - 410  2003年03月  [査読有り]

     概要を見る

    We have observed lasing in a complicated eigenmode of a quasi-stadium laser diode with an unstable resonator consisting of two curved end mirrors obeying an unstable resonator condition and two straight side-wall mirrors. The laser was fabricated by application of a reactive-ion-etching technique to a molecular beam epitaxy - grown graded-index separate-confinement heterostructure single-quantum-well GaAs/AlGaAs structure. The far-field pattern shows that the lasing mode corresponds to the complicated lowest-loss mode obtained numerically by an extended Fox - Li method. © 2003 Optical Society of America.

    DOI

    Scopus

    11
    被引用数
    (Scopus)
  • Stable oscillations of a spatially chaotic wave function in a microstadium laser

    Takahisa Harayama, Peter Davis, Kensuke S. Ikeda

    Physical Review Letters   90 ( 6 ) 4  2003年02月

     概要を見る

    A fully nonlinear dynamical treatment of lasing in a fully chaotic cavity was shown to give single-mode oscillation of a spatially chaotic wave function. For the cavity shape, Bunimovich's stadium was chosen, and for the laser model, the Schrödinger-Bloch model was employed. Furthermore, it was illustrated that the spatially chaotic wave function of the stationary lasing oscillation excellently corresponds to the quasistationary state of the resonance obtained by an extended boundary element method.

    DOI

    Scopus

    7
    被引用数
    (Scopus)
  • Lasing on scar modes in fully chaotic microcavities

    Takahisa Harayama, Tekehiro Fukushima, Peter Davis, Pablo O. Vaccaro, Tomohiro Miyasaka, Takehiro Nishimura, Tahito Aida

    Physical Review E - Statistical, Nonlinear, and Soft Matter Physics   67 ( 1 2 ) 152071 - 152074  2003年01月

     概要を見る

    The lasing on scar modes in fully chaotic microcavities was discussed. The scar wave functions in a fully chaotic cavity was found to be obtained numerically by an extended Fox-Li method. The laser on scar modes was found to be observed in a semiconductor microcavity with a selective excitation of different scars controlled by corresponding shape of electrodes for current injection.

  • Can One Determine the Shape of a Quantum Billiard Table through the Eigenenergies and Resonances?

    Yuichiro Okada, Akira Shudo, Takahisa Harayama, Shuichi Tasaki

    Progress of Theoretical Physics Supplement   150   397 - 400  2003年

     概要を見る

    The quantum billiard problem, that is the Dirichlet problem for the Helmholtz equation, can be rewritten as a Fredholm integral equation of the second kind and the eigenenergies can be characterized as the zeros of the Fredholm determinant on the positive real axis. However the Fredholm determinant also has complex zeros corresponding to the resonances when the billiard table is regarded as a scatterer against the exterior wave function. That naturally leads us to a new question "Can one determine the shape of billiard table through the interior eigenenergies and exterior resonances, i.e., all zeros of the Fredholm determinant?" instead of the famous Kac's question "Can one hear the shape of a drum?", which was solved negatively.

    DOI

    Scopus

  • Asymmetric beam emission from a symmetric confocal quasi-stadium laser diode due to locking of two ring-trajectory modes

    Takehiro Fukushima, Takahisa Harayama, Peter Davis, Pablo O. Vaccaro, Takehiro Nishimura, Tahito Aida

    OSA Trends in Optics and Photonics Series   88   1284 - 1285  2003年

     概要を見る

    Lasing modes in a two-dimensional quasi-stadium resonator with confocal curved end-mirrors were investigated. Asymmetric output beam emission was obtained by the locking of two modes of different symmetry classes corresponding to a closed ring-trajectory. © 2000 Optical Society of America.

  • Lasing on scar modes in fully chaotic microcavities

    T Harayama, T Fukushima, P Davis, PO Vaccaro, T Miyasaka, T Nishimura, T Aida

    PHYSICAL REVIEW E   67 ( 1 ) 015207  2003年01月  [査読有り]

     概要を見る

    Scar wave functions in a fully chaotic cavity are obtained numerically by an extended Fox-Li method. Lasing on the scar modes are observed in a semiconductor microcavity with a selective excitation of different scars controlled by corresponding shape of electrodes for current injection.

    DOI CiNii

    Scopus

    5
    被引用数
    (Scopus)
  • Deterministic diffusion in flower-shaped billiards

    Takahisa Harayama, Rainer Klages, Pierre Gaspard

    Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics   66 ( 2 )  2002年08月

     概要を見る

    We propose a flower-shaped billiard in order to study the irregular parameter dependence of chaotic normal diffusion. Our model is an open system consisting of periodically distributed obstacles in the shape of a flower, and it is strongly chaotic for almost all parameter values. We compute the parameter dependent diffusion coefficient of this model from computer simulations and analyze its functional form using different schemes, all generalizing the simple random walk approximation of Machta and Zwanzig. The improved methods we use are based either on heuristic higher-order corrections to the simple random walk model, on lattice gas simulation methods, or they start from a suitable Green-Kubo formula for diffusion. We show that dynamical correlations, or memory effects, are of crucial importance in reproducing the precise parameter dependence of the diffusion coefficent. © 2002 The American Physical Society.

    DOI

    Scopus

    17
    被引用数
    (Scopus)
  • Ring and axis mode lasing in quasi-stadium laser diodes with concentric end mirrors

    Takehiro Fukushima, Takahisa Harayama, Peter Davis, Pablo O. Vaccaro, Takehiro Nishimura, Tahito Aida

    Optics Letters   27 ( 16 ) 1430 - 1432  2002年08月  [査読有り]

     概要を見る

    We fabricated quasi-stadium laser diodes whose resonators consist of two concentric curved end mirrors and two straight sidewall mirrors. We observed two lasing modes that correspond to different beam propagations along the cavity axis and along a ring trajectory, and different far-field patterns with wide angular separation. The modes can be selected by control of an electrode pattern. We also show that the far-field patterns numerically obtained by the extended Fox-Li mode calculation method are in good agreement with the experimental results. © 2002 Optical Society of America.

    DOI

    Scopus

    28
    被引用数
    (Scopus)
  • Quantum-classical correspondences of the Berry-Robnik parameter through bifurcations in lemon billiard systems

    H. Makino, T. Harayama, Y. Aizawa

    Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics   63 ( 5 )  2001年

     概要を見る

    The quantum level statistics affected by bifurcations in classical dynamics is studied by using a one-parameter family of lemon billiard systems. The classical phase space of our system consists of regular and irregular regions. We determine an analytic solution of the phase volume for these regions as a function of the system parameter and show that the function reveals a cusp singularity at the bifurcation point. The function is compared with its quantum mechanical counterpart, the Berry-Robnik parameter. By estimating the semiclassical regime from the effective Planck constant that validates the quantum-classical correspondence of the Berry-Robnik parameter, we determine a region of the system parameter where the cusp can be reproduced by the statistical properties of the eigenenergy levels. © 2001 The American Physical Society.

    DOI

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    26
    被引用数
    (Scopus)
  • Diffusion of particles bouncing on a one-dimensional periodically corrugated floor

    T. Harayama

    Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics   64 ( 3 ) 16 - 3621516  2001年

     概要を見る

    We report on a class of spatially extended mechanical systems sustaining a transport process of diffusive type. These systems consist of a point particle subject to a constant vertical acceleration and bouncing on a one-dimensional periodically corrugated floor. We show that the deterministic dynamics of these systems is chaotic with small elliptic islands for many parameter values. The motion of particles perturbed by a small noise has a horizontal diffusion that is normal. In such a case, we show that the diffusion coefficient oscillates periodically as the energy of particles increases. In the absence of noise, there still exists an effective numerical value for the diffusion coefficient and this value has an irregular dependence on energy. © 2001 The American Physical Society.

    DOI

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  • Numerical validities of the Berry-Robnik's surmise for quantum oval billiard

    Hironori Makino, Takahisa Harayama, Yoji Aizawa

    Progress of Theoretical Physics Supplement   ( 139 ) 477 - 488  2000年

     概要を見る

    We studied the energy level statistics for one parameter family of quantum oval billiards. The classical phase space of this system consists of a mixture of both regular and irregular regions. We analyzed localization phenomenon of the wavefunction on the phase space structures and verified numerically the validity of the Berry-Robnik formula which is based on the Berry-Robnik's surmise.

    DOI

    Scopus

    9
    被引用数
    (Scopus)
  • Whispering gallery mode lasers

    Takahisa Harayama, Peter Davis, Kensuke S. Ikeda

    Progress of Theoretical Physics Supplement   ( 139 ) 363 - 374  2000年

     概要を見る

    The lasing of the whispering gallery modes of the microdisc are investigated theoretically by solving the Maxwell equation with the nonlinear effect of the light field on the polarization due to the lasing medium as well as the circular boundary condition. The light of the lasing modes are trapped inside the microdisc even in the case that the angle of incidence of the light to the disc boundary is smaller than the critical angle.

    DOI

    Scopus

    8
    被引用数
    (Scopus)
  • A functional equation for semiclassical Fredholm determinant for strongly chaotic billiards

    Takahisa Harayama, Akira Shudo, Shuichi Tasaki

    Progress of Theoretical Physics Supplement   ( 139 ) 460 - 469  2000年

     概要を見る

    We derive a functional equation for the Fredholm determinant of the boundary element method. By assuming that the functional equation holds for the semiclassical Fredholm determinant for strongly chaotic billiards, we obtain a real function whose zeros are the semiclassical eigenenergies. We also show by the numerical experiment of concave triangle billiards that the semiclassical eigenenergies are very close to the exact eigenenergies.

    DOI

    Scopus

    1
    被引用数
    (Scopus)
  • Semiclassical Fredholm determinant for strongly chaotic billiards

    Takahisa Harayama, Akira Shudo, Shuichi Tasaki

    Nonlinearity   12 ( 4 ) 1113 - 1149  1999年07月

     概要を見る

    We investigate the "semiclassical Fredholm determinant" for strongly chaotic billiards derived from the semiclassical limit of the Fredholm determinant of the boundary element method. We show that it is the same as a cycle-expanded Gutzwiller-Voros zeta function when the bounce number of the periodic orbit with the billiard boundary corresponds to the length of the symbolic sequence of its symbolic dynamical expression. A numerical experiment on a "concave triangle billiard" shows that the series defining the semiclassical Fredholm determinant does not converge absolutely in spite of the absolute convergence of the series defining the Fredholm determinant. However, the series behaves like an asymptotic series, and the finite sum obtained by optimal truncation of the series defining the semiclassical Fredholm determinant gives the semiclassical eigenenergies precisely enough such that the error of the semiclassical approximation is much smaller than the mean spacing of the exact eigenenergies.

    DOI

    Scopus

    9
    被引用数
    (Scopus)
  • Nonlinear whispering gallery modes

    Takahisa Harayama, Peter Davis, Kensuke S. Ikeda

    Physical Review Letters   82 ( 19 ) 3803 - 3806  1999年

     概要を見る

    The stationary lasing of the modes in a microdisk is formulated as a nonlinear eigenvalue problem for a nonlinear Maxwell equation. It is shown that whispering gallery modes can be obtained as stationary lasing solutions with finite pumping thresholds. Further, it is discovered that whispering gallery lasing modes can exist even though the angle of incidence to the disk boundary is smaller than the critical angle for total internal reflection. © 1999 The American Physical Society.

    DOI

    Scopus

    36
    被引用数
    (Scopus)
  • Effects of bifurcations on the energy level statistics for oval billiards

    H. Makino, T. Harayama, Y. Aizawa

    Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics   59 ( 4 ) 4026 - 4035  1999年

     概要を見る

    We studied the energy level statistics for one parameter family of oval billiards whose classical phase space consists of some regular and some irregular components. As the parameter is varied, a transition from an integrable system to a strongly chaotic one occurs with successive bifurcations. We applied the Berry-Robnik formula to the level-spacing distributions for a variety of shapes of quantum oval billiards and found some striking effects of bifurcations in the classical mechanical systems on the level-spacing distributions. The validity of the Berry-Robnik formula is also checked for those shapes of the oval billiard for which there exist two separated chaotic components in the phase space. © 1999 The American Physical Society.

    DOI

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    25
    被引用数
    (Scopus)
  • Chaos mirror for free-space links

    Takahisa Harayama, Peter Davis

    Optics Letters   23 ( 18 ) 1426 - 1428  1998年09月

     概要を見る

    We propose a novel reflector, called a chaos mirror, designed by use of the principles of chaotic reflection. A feature of the reflector is that it converts a one-dimensional spread of incident rays into a two-dimensional spread of reflected rays. This can be useful for making free-space optical beam links by sweeping a transmission beam in only one dimension. © 1998 Optical Society of America.

    DOI

    Scopus

    10
    被引用数
    (Scopus)
  • Zeta function derived from the boundary element method

    Takahisa Harayama, Akira Shudo

    Physics Letters A   165 ( 5-6 ) 417 - 426  1992年06月

     概要を見る

    A Selberg type zeta function is derived from the semiclassical limit of the boundary element method. It implies that the boundary element method with replacing the Hankel function by its asymptotic form can be interpreted as a type of resummation of the periodic orbit sum. © 1992.

    DOI

    Scopus

    13
    被引用数
    (Scopus)
  • Periodic orbits and semiclassical quantization of dispersing billiards

    T. Harayama, A. Shudo

    Journal of Physics A: Mathematical and General   25 ( 17 ) 4595 - 4611  1992年

     概要を見る

    Periodic orbits in a dispersing billiard system consisting of three circular arcs are studied numerically by using a partial coding rule together with an efficient method for enumerating periodic orbits on the real billiard plane. By examining several statistical measures, it is shown that the length spectrum and the stability exponents are highly uncorrelated. The validity of the semiclassical trace formula is also tested, and a remarkable agreement of the semiclassical and quantum density of states is obtained at least for about the lower 15 levels.

    DOI

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    21
    被引用数
    (Scopus)

▼全件表示

共同研究・競争的資金等の研究課題

  • 光多重化によるフォトニックコンピューティングデバイスの変革

    日本学術振興会  科学研究費助成事業 学術変革領域研究(A)

    研究期間:

    2022年06月
    -
    2027年03月
     

    砂田 哲, 原山 卓久, 丸山 武男, 犬伏 正信

  • 波動カオスとレーザー媒質による2重非線形性が導く普遍則の探求

    日本学術振興会  科学研究費助成事業

    研究期間:

    2021年04月
    -
    2025年03月
     

    原山 卓久

     概要を見る

    2次元微小光共振器を用いたレーザーは2次元全方位に光を出射することのできる新しいタイプのレーザーである。微小光共振器の2次元形状を工夫することで出射方向を調整でき、様々な応用が提案・期待されている。また、共振器形状によっては光線軌道が不規則でカオスを示すことがあり、そのような形状における共鳴波動関数の性質は波動カオスとして基礎物理学の観点から注目されている。本研究では、光線軌道が完全カオスを示すような共振器形状として、スタジアム形、D形、および、カージオイド形を用いて、多数の共鳴波動関数を数値的に求め、共鳴波動関数同士の類似度を調べる指標であるオーバーラップの値が中心0.77、分散0.05で正規分布することを明らかにした。異なる共振器形状で同じオーバーラップの値分布となることにより、これが2次元微小光共振器の共鳴波動関数の普遍則であることを示した。これに対して、円や楕円など光線軌道が規則的な完全可積分となるような形状では、中心0.4、分散0.3で正規分布する。この理由は、完全可積分共振器の共鳴は2つ量子数により指定され、それらに対応して共鳴波動関数は局在して棲み分けることができるためである。これに対して、カオティック共振器では、光線カオスを反映してすべての共鳴波動関数が共振器全体に広がるため棲み分けることができず、必ず他の共鳴波動関数との重なりが大きくなる。さらに、この共鳴波動関数の普遍測はさらにレーザー発振特性の普遍測を導くことを明らかにした。即ち、共鳴波動関数は、レーザー発振するとレーザー媒質を通じて相互作用するが、重なりが大きいほど相互作用が大きくなり、モード競合の結果、1つのモードだけが発振し、他はすべて消滅することが2次元微小光共振器レーザーの普遍則であることを解明した。

  • 光の波動カオス現象に基づく情報処理と動的深層学習

    研究期間:

    2020年04月
    -
    2023年03月
     

     概要を見る

    脳のような高度で柔軟な情報処理システムの構築には,外部からの刺激に対して多様に応答し,並列分散的に処理する機構が不可欠である。本研究では,そのような多様で並列的な処理機能を“波動カオス”と呼ばれる光の物理現象に担わせることで,分類・予測処理を高効率かつ高速に実行する光情報処理系を創出する。更に,深層学習と動的システムの最適制御との類似性に基づき,”動的深層学習”という新しい概念を導入する。この概念に基づき,光の動的システムを制御することで,深層学習を光の物理現象によって実行させるような処理機能を実現する

  • 無限エルゴード理論と大偏差解析による弱いカオス拡散の特性指数の決定

    研究期間:

    2013年04月
    -
    2016年03月
     

     概要を見る

    非定常域のカオス現象はハミルトン系の異常拡散、間欠性、および無限エルゴード性など、未解決の問題が多い。本研究では、それらの多様な現象と統計法則をいくつかの非線形力学モデル【格子ハミルトン系、マッシュルームビリアード系、散逸無限エルゴード系、非カオス的ストレンジアトラクター系、光共振器モデル系、生物の群れ力学モデル系】を用いて明らかにすると共に、実際の地震現象のデータを用いて、地震時系列に埋め込まれている間欠性法則を取り出す分析手法についても具体的に探求し、多くの新しい成果を得ることができた

  • ハミルトン系におけるエルゴード特性の微細構造

    日本学術振興会  科学研究費助成事業

    研究期間:

    1997年
    -
    2000年
     

    相澤 洋二, 宮坂 朋宏, 原山 卓久

     概要を見る

    本研究では、ハミルトン力学系の相空間に潜む未知の精密微細構造の発見に取り組み、軌道のエルゴード論的・運動論的複雑さのもつ普遍的法則の解明を目標とした。研究対象は、古典系から量子系まで、また少数自由度系から多自由度系にまで及んだ。運動論的法則の探求においては、多粒子系のクラスター化、緩和現象及び異常拡散現象などの理解の基礎となる力学的描像を理論化することに挑戦した。さらにハミルトン系研究の理論的手法が適用できる具体的実験系であるレーザー発振の光学系の解析も並行して進め、本研究の基礎的成果が技術・工学の分野にまでも拡大・適用できる可能性を追及した。具体的には、以下の成果をあげることができた:(1)トーラス・カオス共存系のフラクタル構造と臨界現象の解明トーラス崩壊現象において、トーラス-カオスの転移点が真性特異点として普遍的な臨界現象を伴うことを、理論および数値シミュレーションで明らかにした。これらの成果を基礎に非双曲系の統計則を決定し、Weibull分布とLog-Weibull分布という、高次元系特有のアーノルド拡散と一致するスケール則を生み出すことを明らかにした。(2)KAM条件の破れに伴う普遍則の解明KAM条件を破るハミルトン系において、相空間構造を系統的に調べる新しい手法を提案し、リコネクション現象やシアーレストーラスの構造の精密な解析に成功した。また、大域的カオス発生の臨界点をパラメータ空間全域において決定し、臨界点の集合がフラクタルになることを明らかにした。(3)微細構造の生み出す量子カオス効果の解明非可積分ビリヤード系の量子レベル統計におけるベリー・ロブニックパラメータの決定法を新たに提案し、それによって最近接レベル間隔分布関数が、半古典領域ではほぼ完全に決定できることを示した。古典系の分岐現象に伴う微細構造変化が、量子レベル統計の変化に直接反映することを解明した

  • 格子振動系の1/fゆらぎを生み出すカオス力学的機構の解明

    日本学術振興会  科学研究費助成事業

    研究期間:

    1994年
    -
    1996年
     

    相澤 洋二, 原山 卓久, 宮坂 朋宏

     概要を見る

    ハミルトン系が1/fスペクトルのゆらぎを生み出す機構について、古典系及び量子系の双方にわたって研究した。最近の結果は、以下の1-4である。1.ノンツイスト条件下における最安定トーラスのスぺクトル構造を決定し、ツイスト条件下のくり込み構造と違うことを示した。2.高次元系のトーラスの崩壊に伴い、f^<-μ>(1【less than or equal】μ【less than or equal】2)型のゆらぎスペクトルが発生することを、4次元シンプレクティック3.散乱カオスの長時間緩和機構が、正曲率領域における位相安定性に由来することを示し、さらに共鳴状態における新しい緩和機構を明らかにした。4.間欠性カオスを示す量子ビリヤード系が、ウィグナー分布に近いレベル統計に従うことを計算によって示した。1/fスペクトルの発生とレベル統計の詳しい対応は今後の課題として残されたテーマである。本研究によってハミルトン系の微細構造についての新しい知見が他にも多く得られており、一部の結果については、既に学術誌に報告されている

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Misc

  • Two-dimensional microcavity lasers

    T. Harayama, S. Shinohara

    Laser and Photonics Reviews   5 ( 2 ) 247 - 271  2011年03月

    書評論文,書評,文献紹介等  

     概要を見る

    Advances in processing technology, such as quantum-well structures and dry-etching techniques, have made it possible to create new types of two-dimensional (2D) microcavity lasers which have 2D emission patterns of output laser light although conventional one-dimensional (1D) edge-emitting-type lasers have 1D emission. Two-dimensional microcavity lasers have given nice experimental stages for fundamental researches on wave chaos closely related to quantum chaos. New types of 2D microcavity lasers also can offer the important lasing characteristics of directionality and high-power output light, and they may well find applications in optical communications, integrated optical circuits, and optical sensors. Fundamental physics of 2D microcavity lasers has been reviewed from the viewpoint of classical and quantum chaos, and recently developed theoretical approaches have been introduced. In addition, nonlinear dynamics due to the interaction among wave-chaotic modes through the active lasing medium is explained. Applications of 2D microcavity lasers for directional emission with strong light confinement are introduced, as well as high-precision rotation sensors designed by using wave-chaotic properties. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

    DOI

  • Efficient Physical Random Bit Generation with Lasers

    Takahisa Harayama, Atsushi Uchida, Kazuyuki Yoshimura, Peter Davis

    ICTON: 2009 11TH INTERNATIONAL CONFERENCE ON TRANSPARENT OPTICAL NETWORKS, VOLS 1 AND 2     791 - 791  2009年

     概要を見る

    We discuss the role of physical fluctuations in physical random bit generators focusing on the practical limits of generation rates. First we present a brief review of existing random bit generators, their mechanisms and performance characteristics. Then we discuss in detail random bit generation by chaotic lasers. It has recently been shown that bit sequences which passed statistical tests of randomness could be generated at fast rates up to 1.7 Gbps using chaotic semiconductor lasers. This is faster than any previous report of physical random sequence generation passing the same tests. In this paper it was reported that the chaotic state of the lasers gave better performance than the steady state noise. We show that one reason for the relatively good performance of the chaotic state versus the steady state is due to the drift of the threshold in the analog-to-digital converting (AD) device. Accordingly, we conclude that it is possible to generate random bit sequences by the steady state in the following alternative ways: (a) introducing another stage of broadband amplifier to amplify the steady state noise, (b) improving the stability of the threshold of the AD device by an order of magnitude. These results show that the chaotic laser is an efficient and robust mechanism for use in physical random bit generation in the sense that it did not require either (a) or (b). Moreover, the relative efficiency can be measured as the minimum amplification required to meet the randomness criteria, and the robustness can be measured as the maximum threshold variation which can be tolerated.

    DOI

 

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他学部・他研究科等兼任情報

  • 理工学術院   大学院先進理工学研究科

学内研究所・附属機関兼任歴

  • 2022年
    -
    2024年

    理工学術院総合研究所   兼任研究員

特定課題制度(学内資金)

  • 2次元マイクロキャビティレーザーを用いたリザバーコンピューティング

    2022年  

     概要を見る

    リザバーコンピューティングとは、人工ニューラルネットワークを利用した機械学習の一つであり、学習が著しく速いことが特徴である。本研究では、リカレントネット部分を、複雑なダイナミクスを呈するスタジアム形状の2次元マイクロキャビティ内の光の伝搬で代用する。スタジアムキャビティの端面の複数の点で出射光強度を測定し、それらに結合の重みを付けて和を取ったものを最終的な出力とし、この出力がターゲットとできるだけ近くなるように結合の重みを調整することによって学習が行われる。これにより、蔵本・シバシンスキー方程式に従う化学乱流を数値的に求めたものを入力・ターゲット信号として用いて、複雑な振る舞いをする時系列であっても予測可能であることを示した。

  • 2次元微小光共振器における共鳴波動関数のオーバーラップの普遍性に関する研究

    2021年  

     概要を見る

    2次元微小光共振器を用いたレーザーは2次元全方位に光を出射することのできる新しいタイプのレーザーで、形状を工夫することで出射方向を調整でき、様々な応用が提案・期待されている。また、共振器形状によっては光線軌道がカオスを示す。本研究では、光線軌道が完全カオスを示すような共振器形状として、スタジアム形、D形、および、カージオイド形を用いて、多数の共鳴波動関数を数値的に求め、共鳴波動関数同士の類似度を調べる指標であるオーバーラップの値が0.77を中心に正規分布することを明らかにした。異なる共振器形状で同じオーバーラップの値分布となることにより、これが普遍則であることを示した。

  • カオティックビリヤードレーザーにおけるシングルモード発振の解明

    2020年  

     概要を見る

    幾何光学として完全カオスであることが数学的に厳密に証明されているカージオイド形状、Bunimovichのスタジアム形状、およびD形状という異なる形状を用いて、完全カオス2次元マイクロキャビティレーザー(カオティックビリヤードレーザー)では、共振器サイズが発振波長よりも十分に大きく、利得媒質への注入エネルギーが十分に大きくなると、1つの共鳴波動関数だけがレーザー発振するシングルモード発振が普遍的に生じる現象であることを明らかにした。さらに、この普遍的シングルモード発振が光線軌道の完全カオスの波動光学的性質としての顕在化であり、共鳴波動関数の量子エルゴード性に起因していることを解明した。

  • 非対称2次元微小光共振器における光線・波動対応

    2019年  

     概要を見る

    2次元形状を有する微小光共振器は、従来の1次元形状のものにはない全く新しいレーザーとしての機能が期待されており、さらに、波動カオスという基礎物理学研究の舞台としても注目されている。本研究課題では、波動カオスにおけるカイラリティについての研究を推進した。完全に非対称な微小光共振器の固有状態の一種である共鳴の波動関数は、一方向の回転成分を多く含むカイラリティという性質がある。完全カオスであることが数学的に厳密に証明されている2種類の2次元形状の微小光共振器の共鳴を境界要素法を用いて数値的に多数求め、光線動力学の不変分布と比較し、波動・光線対応を解明し、光線動力学でもカイラリティが生じることを明らかにした。

  • 2次元マイクロキャビティレーザーの波動・光線カオスと非線形ダイナミクスの研究

    2018年   篠原晋

     概要を見る

    完全カオスを示す2次元マイクロキャビティレーザーとして、D型およびスタジアム型マイクロキャビティレーザーを数値的に詳しく研究し、両者に共通するレーザー発振特性として、注入電流が十分に大きくなると単一モード発振となることを解明した。また、完全可積分系である楕円型マイクロキャビティレーザーに関しても同様に研究し、注入電流が大きくなっても複数のモードが発振することを解明した。これらの数値的な研究と理論研究によって、単一モード発振が完全カオス型2次元マイクロキャビティレーザーの普遍則であることを明らかにした。

  • 完全カオスビリヤードレーザーにおける発振モードの非線形ダイナミクスの研究

    2018年   篠原晋

     概要を見る

    対称性を全く持たない完全非対称なリマソン型マイクロキャビティについて研究し、発振モードの候補となる共鳴には、近縮退するものがカイラルモードペアとして2つ組で存在し、それらが共に時計回りの回転波を主成分とすることを解明した。さらに、この共振器を用いたレーザー発振を数値的に研究し、発振時には、カイラルモードペアがロックすることを解明した。そして、2つの共鳴波動関数の位相の関係により、時計回りだけでなく、反時計回りのモードが発振することも可能であることを明らかにした。

  • 2次元マイクロキャビティレーザーの波動・光線カオスと非線形ダイナミクスの研究

    2017年   篠原晋

     概要を見る

    2次元マイクロキャビテイレーザーの光線軌道のエルゴード性が共鳴波動関数およびレーザー発振に及ぼす効果を解明した。光線軌道の定常確率分布と共鳴波動関数の分布を比較し、Q値の高い多数の共鳴波動関数の平均が光線軌道の定常確率分布と一致することを明らかにした。また、光線軌道がカオスを示す場合には、カオスでない場合よりも、共鳴波動関数の重なりが非常に大きくなることを明らかにした。さらに、レーザー発振に関して、光線軌道がカオスを示す場合にはシングルモード発振となり、そうでない場合はマルチモード発振となることを解明した。

  • カオティックビリヤードレーザーに関する波動・光線対応の研究

    2016年   鈴木慎, 関口峻矢, 小山廣英, 川嶋悠太, 折原眞児, 外崎真広, 中村友彦, 鈴木裕一郎, 吉川真生

     概要を見る

    カオティックビリヤードレーザーを舞台に、乱流状の複雑な共鳴波動関数と予測不可能な光線軌道の対応を研究した。光線軌道が完全カオスとなるような微小光共振器の場合、光線軌道のエルゴード性を反映して、すべての共鳴波動関数の重なりが大きいことを明らかにした。これに対して、光線軌道が予測可能な可積分微小光共振器では、共鳴波動関数は局在するため、重なりが小さいことを明らかにした。共鳴波動関数はレーザー媒質を通じて相互作用を及ぼすが、その大きさは重なりによって決定される。このため、可積分微小光共振器では、共鳴波動関数は別々の場所に局在し、レーザー発振モードはマルチモードとなる。これに対して、完全カオスビリヤードレーザーでは単一モード発振となることが明らかとなった。

  • 2次元マイクロキャビティレーザーにおける光線と波動の対応

    2014年  

     概要を見る

    規則的な光線軌道とカオティックな光線軌道の両方が混在するような2次元マイクロキャビティを外部キャビティとして用い、入力レーザー光をそのカオティックビリヤードキャビティ内部で多重反射させることで長い光路を伝搬遅延した後、レーザーに戻すことで、レーザー光源を不安定化させ、レーザー出力光のカオティックな変動を実現した。この場合のカオティックビリヤードキャビティは、光線波動対応確認のために細長い形状を用いた。この方法が機能することを実験で確認できたため、さらに、円形に近い形状を用い、全反射の利用により反射損失を低減し、戻り光レーザーカオスに必要な長い光路が可能となるように改良した。

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