We demonstrate a 60-GHz-bandwidth O-band electro-absorption modulator (EAM) on a Si photonics platform. The EAM consists of an InGaAlAs multiple quantum well with a lateral p-i-n junction, and is fabricated by heterogeneous integration technique. Clear eye opening for 100-Gbit/s non-return-to-zero signal is demonstrated.

A product-sum photonic integrated circuit consisting of SOI-based cascaded microring modulators and a 4×1 multimode interference coupler is proposed for CNN computing. A basic product-sum operation is numerically demonstrated for 2×2 matrix.

We fabricated the first compact 100-gigabit Ethernet (100GbE) transmitter optical sub-assembly (TOSA) using a directly modulated DFB laser (DML) array monolithically integrated with an optical multiplexer. Specially designed InGaAlAs/InGaAlAs multiple quantum wells make it possible to obtain a large gain in the 1295-1310-nm wavelength range and to operate at a high temperature of 55 degrees C. The four-channel DML array chip is only 2.0 mm x 2.4 mm in size, and the fabricated TOSA is only 7.2 mm(W) x 14.3 mm(L) x 6.5 mm(H), which fits a CFP2 or smaller 100-GbE transceiver. For all the lanes, the 3-dB bandwidths of the TOSA exceeded 17 GHz, and it could operate at 25.8 Gb/s. With 25.8-Gb/s x four-channel simultaneous operation, error-free transmissions over a 30-km single-mode fiber were demonstrated for all the lanes.

We have developed a compact hybrid-integrated four-lane x25.8 Gb/s transmitter optical sub-assembly (TOSA) for a 100 Gb/s transceiver for 40-km transmission. The TOSA has a simple configuration in which a four-channel electroabsorption modulator integrated distributed feedback (EADFB) laser array is directly attached to the input waveguide end-faces of a silica-based arrayed waveguide grating (AWG) multiplexer. We integrated a lateral tapered spot-size converter for the EADFB laser to achieve a high optical butt coupling efficiency between the EADFB lasers array and the AWG multiplexer. We confirmed that the TOSA, which is 19.9 mm x 6 mm x 5.8 mm, achieved error-free operation for a 40-km transmission with a high average optical output power of over 0.3 dBm at an operating temperature of 55 degrees C.

A compact hybrid-integrated 100 Gb/s (4 lane x 25.78125 Gb/s) transmitter optical sub-assembly (TOSA) has been developed for a 100 Gb/s transceiver for 40-km transmission over a single-mode fiber. The TOSA has a simple configuration in which four electro-absorptionmodulator-integrated distributed feedback (EADFB) lasers are directly attached to the input waveguide end-face of a silica-based arrayed waveguide grating (AWG) multiplexer without bulk lenses. To achieve a high optical butt coupling efficiency between the EADFB lasers and the AWG multiplexer, we integrated a laterally tapered spot-size converter (SSC) for the EADFB laser and employed a waveguide with a high refractive index difference of 2.0% for the AWG multiplexer. By optimizing the laterally tapered SSC structure, we achieved a butt-coupling loss of less than 3 dB, which is an improvement of around 2 dB compared with a laser without an SSC structure. We also developed an ultracompact AWG multiplexer, which was 6.7 mm x 3.5 mm in size with an insertion loss of less than 1.9 dB. We achieved this by using aMach-Zehnder interferometer-synchronized configuration to obtain a low loss and wide flat-top transmission filter spectra. The TOSA body size was 19.9 mm (L) x 6.0 mm (W) x 5.8 mm (H). Error-free operation was demonstrated for a 40-km transmission when all the lanes were driven simultaneously with a low EA modulator driving voltage of 1.5 V at an operating temperature of 55 degrees C.

We developed a flip-chip interconnection technique that is suitable for an EADFB laser array transmitter operating at more than 100 Gb/s (4 x 25 Gb/s). The flip-chip interconnection technique provides a good thermal flow comparable to that of the conventional wire interconnection technique but with a higher modulation bandwidth and lower electrical crosstalk. For a flip-chip interconnection 112-Gb/s (4 x 27.9 Gb/s) module, the OTU4 mask margin is only 4% worse for simultaneous four-channel operation than for single-channel operation. For a flip-chip interconnection 400-Gb/s (8 x 50 Gb/s) module, we obtained clear eye openings for all eight lanes with simultaneous eight-channel operation.

We fabricated a lumped-electrode type EADFB laser module using a flip-chip interconnection technique which provides a large modulation bandwidth. We obtained clear 56-Gbaud 4-PAM signal after 10-km SMF transmission with no equalizer using this module.

Using a lumped-electrode EADFB laser with a modulation bandwidth of similar to 59 GHz, we demonstrated single-wavelength single-polarization direct-detection 4-PAM transmission with the record net data rate of 200 Gbit/s.

We have developed a novel electroabsorption modulator (EAM)-integrated distributed feedback laser (EA-DFB laser), in which an EAM functioning as an external modulator is integrated in a Mach-Zehnder interferometer (MZI). The MZI-type EAM (MZEA) modulates light intensity by both optical absorption and interferometric extinction. As a result, it improves the extinction ratio (ER) of a conventional EAM, which allows us to reduce the modulation voltage (V-m), and thus reduce the power consumption of the driver circuit. A fabricated MZEA-integrated DFB laser (MZEA-DFB laser) exhibited high-ER operation and an output power of about 8 dBm, which is comparable to that of a conventional EA-DFB laser, with a 100-mA laser current. Thanks to the high ER and sufficient output power, the MZEA-DFB laser operating at half the V-m of a conventional EA-DFB laser is able to generate optical signals with a given optical modulation amplitude, and we achieved a 25.8-Gb/s 40-km transmission with the novel laser at a V-m of 1V(pp).

We fabricated a 400-G flip-chip interconnection eight-channel EADFB laser array module. The flip-chip interconnection technique provides a higher modulation bandwidth and lower electrical crosstalk than the wire interconnection technique. The 3-dB bandwidth of the flip-chip interconnection subassembly was about 50 GHz. And the electrical crosstalk of the flip-chip interconnection module was suppressed to less than -20 dB below 35 GHz. We obtained clear eye openings for all eight lanes under eight-channel 50-Gb/s simultaneous operation after a 10-km SMF transmission.

We have achieved the 100-Gb/s/lambda operation of a flip-chip interconnection 1.3-mu m lumped-electrode electroabsorption modulator integrated with a distributed feedback laser module for the first time. The flip-chip interconnection provides a flatter frequency response characteristic and a higher modulation bandwidth. Clear eye opening was achieved for 103-Gb/s nonreturn to zero and equalizer-free 56-GBd 4-pulse-amplitude modulation operation after a 10-km single-mode fiber transmission.

A transmitter optical subassembly (TOSA) has been developed for a 100-Gbit/s Ethernet system for a long optical transmission distance over a 40-km single-mode fiber (SMF). To obtain a high optical output power and a high dynamic extinction ratio, the TOSA consists of two two-channel distributed feedback laser diode array chips integrated with electro-absorption modulators (EADFB laser array chips) with a 2 x 1 multimode interference (MMI) optical coupler and a polarization beam combiner for wavelength multiplexing. The TOSA is 8.7 mm x 28.7 mm x 6.5 mm including an LC-type receptacle. The TOSA has a twin collimator path for two EADFB laser array chips. The wavelength multiplexer consists of a mirror, a half-wavelength plate, and a polarization beam combiner. The TOSA could improve the optical output power by around 2 dB compared with a TOSA with a four-channel EADFB laser array chip and a 4 x 1 MMI optical coupler. An optical modulation amplitude of over 0.5 dBm and a mask margin exceeding 21% were obtained for each lane when all lanes were operated simultaneously with an EA modulator driving voltage of 1.5 V at a bit rate of 25.78125 Gbit/s, which fully satisfies the 100GBASE-ER4 specifications. We demonstrated error-free operation for an SMF transmission of over 40 km. Moreover, we confirmed that the TOSA was capable of error-free SMF transmission over 60 km with a power penalty of less than 1.4 dB.

The first directly modulated InGaAsP DFB laser module using the flip-chip mounting technique was fabricated for 25.8-Gb/s operation. The fabricated laser chip has p-and n-electrodes on the surface side. This structure is suitable for flip-chip mounting, which provides a high modulation bandwidth. The fabricated module provided clear eye opening with a dynamic extinction ratio of over 4 dB when operated 25.8 Gb/s.

The flip-chip interconnection 8-channel EADFB laser array module is developed. The flip-chip interconnection technique provides low crosstalk. After 10-km transmission, clear eye opening is obtained for all eight lanes under 8 x 50-Gb/s simultaneous operation.

We present a high-linearity avalanche photodiode (APD) for 28-Gbaud PAM4, namely, 56 Gbit/s/X. With an optical receiver incorporating the APD, a 40-km transmission with-17 dBm receiver sensitivity was successfully demonstrated for the first time.

We developed a compact hybrid-integrated 100 Gbit/s TOSA using an EADFB laser array with a spot-size converter and a silica-based AWG multiplexer. Error-free operation for a 40-km transmission was demonstrated at an operating temperature of 55 degrees C.

We have proposed and developed a new type of electroabsorption modulator (EAM) that employs both optical absorption and interferometric extinction. The EAM operates at a record low voltage of 0.2 V at 25.8-Gbit/s modulation, which can reduce optical transmitter power consumption and allows the adoption of cost-effective CMOS drivers. (C) 2014 Optical Society of America

We developed an InP-based 4x1 transversal filter (TF) with multi-mode interference couplers (MMIs) as a compact wavelength multiplexer (MUX) 1700 mu m x 400 mu m in size. Furthermore, we converted the MMI-based TF to a reflection type to obtain an ultra-compact MUX of only 900 mu m x 50 mu m. These MUXs are made with a simple fabrication process and show a satisfactory wavelength filtering operation as MUXs of monolithically integrated light source arrays, for example, for 100G bit Ethernet. (C) 2014 Optical Society of America

The first compact electroabsorption modulators integrated with distributed-feedback (EADFB) laser array module using flip-chip interconnects have been fabricated for a 400 Gbit/s transceiver. Eight 50 Gbit/s EADFB lasers and an optical multiplexer were monolithically integrated on one chip in an area of only 3.2 x 4.8 mm. The flip-chip interconnects provide a higher modulation bandwidth. Clear eye opening was achieved for all eight lanes under 50 Gbit/s operation.

The first compact and high-performance optical transmitter using flip-chip interconnects has been developed for a 112-Gbit/s transceiver. The flip-chip interconnects provide lower crosstalk and a higher modulation bandwidth than wire interconnects. The flip-chip interconnection module has 3-dB frequency bandwidths of over 30 GHz. This value is up to 5 GHz better than that of a wire interconnection module. Under four-channel simultaneous operation, the OTU4 mask margins for all four lanes of the flip-chip interconnection module exceed 37%. These values are degraded up to only 4% compared with those for single-channel operation. In addition, an error-free transmission through 10 km of single-mode fiber at 112 Gbit/s is demonstrated.

We developed a new type of EAM-integrated DFB laser that employs both optical absorption and interferometric extinction. And, we achieve a 25.8-Gbit/s 40-km transmission with the novel laser at a modulation voltage of 1 V-pp.

We fabricated an eight-channel EADFB laser array sub-assembly using a flip-chip interconnection technique that provided a low crosstalk. We achieved clear eye openings for all eight lanes with 8 x 50-Gb/s simultaneous operation.

A compact transmitter optical sub-assembly (TOSA) has been developed for a 100 Gb/s Ethernet system with a long transmission distance of 40 km over single-mode fiber. The TOSA consists of electro-absorption modulator integrated distributed feedback laser diode arrays and a polarization beam combiner for wavelength multiplexing to obtain a high optical output power and a high dynamic extinction ratio. We confirmed that the TOSA successfully achieved an error-free four-lane x 25.8 Gb/s transmission, i.e., a total bit-rate of 100 Gb/s, over 40 km.

A compact transmitter optical sub-assembly (TOSA) has been developed for a 100 Gb/s Ethernet system with a long transmission distance of 40 km over single-mode fiber. The TOSA consists of electro-absorption modulator integrated distributed feedback laser diode arrays and a polarization beam combiner for wavelength multiplexing to obtain a high optical output power and a high dynamic extinction ratio. We confirmed that the TOSA successfully achieved an error-free four-lane x 25.8 Gb/s transmission, i.e., a total bit-rate of 100 Gb/s, over 40 km.

A 4 x 25-Gb/s electroabsorption modulator integrated with a distributed feedback (DFB) laser (EADFB laser) array monolithically integrated with a low-loss optical multiplexer (MUX) is developed for 100 GbE transmitters for the first time. A cascaded Mach-Zehnder (MZ) filter, which has no intrinsic loss, is used as the MUX. The design and fabrication of the MZ-MUX for 100 GbE are thoroughly described. The measured loss of fabricated MZ-MUX is 2-3 dB, which is improved by 4 dB compared with that of the conventional 1 x 4 multimode interference MUX. The MZ-MUX is monolithically integrated with a four-EADFB-laser array and the output power of the chip is increased by 3 dB compared with that of a conventional 4 x 25-Gb/s monolithically integrated chip. With the folded layout, the size of the chip is similar to that of the conventional chip. The fabricated chip is packaged into a very compact transmitter optical subassembly (TOSA). The system requirements are satisfied with semi-cooled operation, and very clear eye openings are obtained after 10-km single-mode-fiber transmission. The adjustment of filter spectra by current injection is also shown, and fine tuning is possible with very low injection current.

The first ultracompact transmitter optical subassembly for long-distance, beyond-100-Gbit/s data communication systems based on a monolithically integrated light source is developed. The light source consists of four InGaAlAs-based electroabsorption modulator integrated DFB lasers (EADFB lasers) and their optical multiplexer and these components are monolithically integrated on one chip, resulting in very small chip size of 2.4 x 3.3 mm(2). This small chip makes it possible to reduce the size of the transmitter module. Very small transmitter optical subassemblies (TOSAs), using the chip and employing three-dimensional interconnection board, is fabricated, whose volume is only 1.82 cc. By using the TOSA, 40-Gbit/s x 4 operation with the clear eye openings up to 10-km single mode fibre transmission is demonstrated. Electrical crosstalk under the multi-lane operation is also evaluated, and the error-free transmission is achieved with the power penalty to the discrete operation of 1 dB. (C) 2013 Optical Society of America

The first uncooled operation (5-85 degrees C) at 50 Gbit/s of a 1.3 mu m electroabsorption modulator integrated with a DFB laser is achieved and 10 km transmission on singlemode fibre with very clear eye openings is demonstrated.

The first ultra-compact transmitter optical sub-assembly (TOSA) has been developed for the metro-area 100 Gbit/s Ethernet (100 GbE) system. Four DFB lasers integrated with electro-absorption modulators (EADFB lasers) operated at 25.8 Gbit/s and an optical multiplexer are monolithically integrated on one chip. The chip was assembled in the compact TOSA using a three-dimensional (3D) RF circuit board supported by a spacer. The new structure provides compact and high-density interconnection with low crosstalk between RF signal lines. The TOSA is very small at just 8.0 mm × 35 mm × 6.5 mm including the receptacle and the flexible printed circuit (FPC) and could be installed in next-generation small form 100 GbE transceivers. In addition, an error-free transmission is demonstrated through 40 km of single-mode fiber at 100 Gbit/s with a modulation voltage of 2 V. © 1983-2012 IEEE.

We developed a reflection-type 4x1 transversal filter (TF) on an InP substrate as a compact and low-loss wavelength multiplexer (MUX) for monolithically integrated light source arrays. The filter has a satisfactory MUX function and is very compact of about 900 mu m x 50 mu m which is one twentieth of a size of a conventional 4x1 TF. It is suitable for a MUX of a monolithically integrated light source array thanks to its compactness and input/output-port arrangement.

We developed the first compact 100GbE optical transmitter to use flip-chip interconnects for the first time. The flip-chip interconnects provide low crosstalk and a high modulation bandwidth. Under four-channel simultaneous operation, the 100GBASE-LR4 mask margin of the flip-chip interconnection module was improved by 10% to 27% compared with that of a wire interconnection module. © 2013 IEEE.

We have proposed and developed a new type of electroabsorption modulator (EAM) that employs both optical absorption and interferometric extinction. The EAM operates at a record-low voltage of 0.2 V at 25.8-Gbit/s modulation, which can reduce optical transmitter power consumption and allows the adoption of cost-effective CMOS drivers.

A 1.3-mu m, 4 x 25-Gbit/s, EADFB laser array module with large output power and low driving voltage is developed for 100GbE. A novel rear grating DFB laser is introduced to increase the output power of the laser while keeping the single mode lasing, which is desirable for a monolithic integration. Also, InGaA1As-based electroabsorption modulators make very-low-driving-voltage operation possible due to their steep extinction curves. With the module, very clear 25-Gbit/s eye openings are obtained for four wavelengths with the driving voltage of only 0.5 V while securing the dynamic extinction ratio required by the system. These results indicate that the presented module is a promising candidate for energy-efficient future 100GbE transmitter. (C) 2011 Optical Society of America

The mechanisms of increased output power and stable single-mode lasing characteristics of novel rear-grating laser are both theoretically and experimentally investigated and its application to uncooled light source is demonstrated for the first time. (C)2012 Optical Society of America

Recent progress in electroabsorption modulator integrated lasers for high-speed data communications is reviewed. The design of discrete components for high-speed operation and low-power-consumption as well as their large-scale-integration technologies are described. © 2012 IEEE.

The first ultracompact transmitter optical subassembly for long-distance, beyond-100-Gbit/s data communication systems based on a monolithically integrated light source is developed, and 40Gbit/sx 4 operation with the clear eye openings up to 10-km single mode fibre transmission is demonstrated.

An extremely compact 1.3-mu m, 4x25-Gbit/s TOSA was made by using monolithically integrated EADFB laser array with rear-grating DFB lasers. The dynamic extinction ratio and optical modulation amplitude are high enough for 10-km 100GbE.

The first ultracompact transmitter optical subassembly for long-distance, beyond-100-Gbit/s data communication systems based on a monolithically integrated light source is developed, and 40Gbit/sx 4 operation with the clear eye openings up to 10-km single mode fibre transmission is demonstrated.

A compact electroabsorption modulators integrated distributed feedback (EADFB) laser array module has been developed for 100-Gb/s Ethernet. Four 25-Gb/s EADFB lasers and an optical multiplexer are monolithically integrated on one chip in an area of only 2 mm x 2.6 mm. As a result, a compact 12 mm x 20 mm EADFB laser array module is achieved. A bridge-type RF circuit board is employed to transmit high-frequency, 4 x 25-Gb/s, electrical signals effectively in a narrow package and improve the electrical/optical response of the module. The module has a 3-dB frequency bandwidth of 20 GHz for the four lanes assigned in 100-Gb/s Ethernet. Furthermore, the possibility of realizing low-driving voltage operation is investigated to reduce the power consumption of the module. An error-free transmission through 10 km of single-mode fiber at 100 Gb/s with a modulation voltage of only 1 V is demonstrated.

High-performance 1.3-mu m electroabsorption modulators integrated with DFB lasers are developed for long-reach 100 Obit Ethernet. The dynamic extinction ratio of over 8-dB with the voltage swing of 2 V are achieved for the four LAN-WDM lanes (14 nm wavelength range) used in 100 Gbit Ethernet with the same modulator structure. The fabricated devices are packaged in butterfly modules and four-lane 40-km single mode fiber transmission at 25-Gbit/s operation is demonstrated. Further, a can-type transmitter optical subassembly is fabricated to reduce the cost and size of transmitter modules. The use of a low-dielectric-constant liquid crystal polymer transmission line makes the 3-dB bandwidth larger and enables 25-Gbit/s operation with CAN-TOSA module.

A 1.3 mu m, 50 Gbit/s electroabsorption modulator integrated with a DFB laser for future parallel LAN, the total data rate of which is over 100 Gbit/s, is developed. Very clear eye openings after 40 km transmission under 50 Gbit/s operation on singlemode fibre are demonstrated for eight wavelengths with discrete packages for the first time.

A 1.3-mu m monolithically integrated light source for metro area 100-Gb/s Ethernet is developed. Four 25-Gb/s electroabsorption modulators integrated with distributed-feedback lasers and their multiplexer are monolithically integrated on one chip. A shallow ridge waveguide is used for lasers and modulators for large modulation bandwidth, and a deep ridge waveguide is used for the multiplexer region due to its low bending and radiation losses. The integration of hetero-waveguide devices enables the very small chip size of 2 x 2.6 mm(2). With the device, 100-Gb/s (4 x 25-Gb/s simultaneous) operation is demonstrated with the clear eye-openings, and error-free 40-km single-mode fiber transmission is achieved for the first time.

We have developed 1.3-mu m, 50-Gbit/s EADFB lasers for future 400Gbit Ethernet. 10-and 40-km SMF transmission with clear eye openings over 14-nm wavelength range under 50-Gbit/s operation are demonstrated for the first time.

A large-output-power 1.3-mu m, 4x25G, EADFB laser array with a novel rear grating DFB laser is developed for 100GbE. Ultralow-driving-voltage operation (0.5 V-pp) is achieved for the first time with clear eye openings after 10-km transmission.

A 1.3-mu m, 4x25G, EADFB laser array with a novel rear grating DFB laser was developed and packaged in a compact module. It provides enough dynamic extinction ratio and averaged optical power for 10-km 100GbE.

High-performance 1.3-mu m InGaAlAs electroabsorption modulators integrated with DFB lasers are developed for long-reach 100-Gbit/s Ethernet system. Four-channel, 40-km SMF transmission at 25-Gbit/s operation is demonstrated for the first time.

We have developed 4x25-Gbit/s, 1.3-mu m, monolithically integrated light source for 100-Gbit/s Ethernet (100GBASE-LR4) for the first time. Error-free transmission of 10-km on SMF under 100Gbit/s (4x25-Gbit/s simultaneous) operation is demonstrated.

We developed a 4x25.8-Gbit/s EADFB laser array module for use as a 100-Gbit/s Ethernet transceiver. We demonstrated error-free transmission over a 10-km single-mode fiber at 100-Gbit/s with a modulation voltage of 1 V.

We propose an optically clocked transistor array optoelectronic integrated circuit (OEIC) for both serial-to-parallel and parallel-to-serial conversion (demux/mux), enabling an interface between high-speed asynchronous burst optical labels and CMOS circuitry for optical label swapping. Dual functionality of the OEIC reduces size, power, and cost of the optical label swapper. The capability for greater than 20-Gb/s conversion operation is demonstrated.

Asynchronous optical packet switching (OPS) is a promising solution to support the continuous growth of transmission capacity demand. It has been, however, quite difficult to implement key functions needed at the node of such networks with all-optical approaches. We have proposed a new optoelectronic system composed of a packet-by-packet optical clock-pulse generator (OCG), an all-optical serial-to-parallel converter (SPC), a photonic parallel-to-serial converter (PSC), and CMOS circuitry. The system makes it possible to carry out various required functions such as buffering (random access memory), optical packet compression/decompression, and optical label swapping for high-speed asynchronous optical packets.

We present two types of optoelectronic time-domain packet switches, a photonic add-drop multiplexer, and a 4 x 4 packet switch, for high-speed asynchronous burst optical packets. They employ all-optical serial-to-parallel converters, optical single clock-pulse generators, and photonic parallel-to-serial converters that enable utilization of a compact highly functional complementary metal-oxide-semiconductor circuitry for label processing, packet switching, and buffering for contention resolution. We have experimentally confirmed basic operation of the packet switches for 40-Gb/s 16-bit asynchronous optical packets.

An ultrashort electrical pulse with a pulse width of 3.3 ps was generated successfully from an ordinary metal-semiconductor-metal photodetector simply by adding an input resistor and hold capacitor. The new detector not only provides ultrashort fall time, but also has other advantages such as ease of fabrication, high sensitivity, and low-bias operation.

We propose an optically clocked transistor array which performs both serial-to-parallel and parallel-to-serial conversion (time demux/mux) of incoming/outgoing packets, enabling a low cost, low power, compact optical label processor for asynchronous burst optical packets. (c) 2004 Optical Society of America

A novel scheme for time-domain programmable label swapping for burst-mode asynchronous optical packets is described. Label recognition of input signals and generation of output signals with corresponding new labels are achieved by a complementary metal-oxide-semiconductor circuit sandwiched between input and output interfaces (all-optical serial-to-parallel and photonic parallel-to-serial converters, respectively) for fast serial-bit optical labels. Accurate synchronization in operating these interfaces is accomplished with an optical single-clock-pulse generator. Self-routing with 16-bit label swapping of 40-Gb/s optical packets is demonstrated.

We propose a novel optical packet compressor-decompressor. It is based on an optoelectronic memory that employs a complementary metal-oxide-semiconductor memory sandwiched between all-optical serial-to-parallel and photonic parallel-to-serial converters. Its optoelectronic scheme makes it possible to handle a long optical packet, and provides ultrafast burst-mode operation and flexible choice with regard to the center wavelength and/or spectral bandwidth of the output packet. We demonstrated both the 40-to-80-Gb/s compression and 40-to-10-Gb/s decompression of 32-bit optical packets.

We propose a burst optical packet generator based on a novel photonic parallel-to-serial conversion scheme, and demonstrate 40-Gbit/s 16-bit optical packet generation from 16-ch parallel low-voltage TTL data streams. It consists of electrical 4:1 parallel-to-serial converters that employ InP metal-semiconductor-metal photodetectors, and an optical time-domain multiplexer with electroabsorption modulators. The proposed optical packet generator is suitable for burst optical packet generation and overcomes the electronic bandwidth limitation, which is prerequisite for achieving high-speed photonic packet switched networks. In addition, it can be driven by simple low-cost low-power CMOS logic circuits, and is compact and extensible in terms of the number of input channels due to the effective combination of electrical and optical multiplexing.

We present a photonic random access memory (RAM) that can write and read high-speed asynchronous burst optical packets freely by specifying addresses. The photonic RAM consists of an optical clock-pulse generator, an all-optical serial-to-parallel converter, a photonic parallel-to-serial converter, all developed by us, and a complementary metal-oxide-semiconductor RAM as a storage medium, and features large capacity, long-term storage, random access at an arbitrary timing, low power consumption, and compactness. We experimentally confirm its basic operation for 40-Gb/s 16-b optical packets.

We present a photonic random access memory (RAM) that can write and read high-speed asynchronous burst optical packets freely by specifying addresses. The photonic RAM consists of an optical clock-pulse generator, an all-optical serial-to-parallel converter, a photonic parallel-to-serial converter, all developed by us, and a CMOS RAM as a storage medium. Unlike conventional optical buffers, which merely function as optical delay lines, the photonic RAM provides various advantages, such as compactness, large capacity, long-term storage, and random access at an arbitrary timing for ultrafast asynchronous burst optical packets. We experimentally confirm its basic operation for 40-Gbit/s 16-bit optical packets.

To cope with the explosive growth of IP traffic, we must increase both the link capacity between nodes and the node throughput. These requirements have stimulated research on photonic networks that use optical technologies. Optical packet switching (OPS) is an attractive solution because it maximizes the use of the network bandwidth. The key functions in achieving such networks include synchronization, label processing, compression/decompression, regeneration, and buffering for high-speed asynchronous optical packets. However, it is impractical to implement such functions by using all-optical approaches. We have proposed a new optoelectronic system composed of a packet-by-packet optical clock-pulse generator (OCG), an all-optical serial-to-parallel converter (SPC), a photonic parallel-to-serial converter (PSC), and CMOS circuitry. The OCG provides a single optical pulse synchronized with the incoming packet, and the SPC carries out a parallel conversion of the incoming packet. The parallel converted data are processed in the smart CMOS circuit, and reconstructed into an optical packet by the photonic PSC. Our system makes it possible to carry out various functions for high-speed asynchronous optical packets. This paper reviews our recent work on high-speed optical packet processing technologies such as buffering, packet compression/decompression, and label swapping, which are key technologies for constructing future OPS networks.

We developed compact high-power photonic millimeter-wave emitter (PME) modules for 60-GHz fiber radio links. The PME chip is a monolithic integration of a unitraveling-carrier photodiode (UTC-PD) and an antenna. One module was fabricated by attaching the chip and a plastic housing to a metal substrate, and the equivalent-isotropic radiated power (EIRP) of over 8 dBm was obtained with weak directivity of the radiated pattern. This module is suitable for point-to-multi-point communication. It is very compact, 29 x 24 x 6 mm. A module whose antenna gain was increased by attaching a dielectric lens to it was also fabricated, and the estimated EIRP of 18 dBm was obtained. This type of module is suitable for point-to-point communication and it too is compact, 29 x 24 x 17.5 mm. We achieved high-speed error-free data transmission of 1.25- and 2.5-Gbit/s phase-shift keyed (PSK) signal. The maximum distances of free-space propagation were estimated to be 18.2 and 8.9 m at bit rates of 1.25 and 2.5 Gbit/s, respectively.

A new electrical parallel-to-serial converter (PSC) is proposed for optical communication networks. The PSC uses a simple circuit scheme that markedly reduces the fall time of a ordinary MSM-PD without degrading either its sensitivity or ease of fabrication. An InP-based 4:1 PSC is shown to convert 4-ch parallel electrical signals into a serial 10-Gbit/s 4-bit electrical signal when MSM-PDs in the PSC are optically triggered. It has several advantages including support of burst signal input, low driving voltage, compactness, ease of fabrication, and low power consumption. The electrical PSC is used in a new photonic PSC. By effectively combining electrical multiplexing with optical multiplexing, the photonic PSC can generate a 40-Gbit/s 16-bit optical packet from 16-ch parallel electrical signals with frame rates of 40 MHz. The electrical PSC is also applied to a label comparator for bypass/drop self-routing of optical packets. The label comparator, consisting of the 4:1 PSC and an electroabsorption modulator (EAM), properly processed 10-Gbit/s burst optical packets with no preamble even when a local address was changed at 40 MHz.

A novel and simple electrical parallel-to-serial converter for high-speed label comparison is developed using conventional metal-semiconductor-metal photodetectors. The 1 x 2 bypass/drop self-routing of 10 Gbit/s burst optical packets is demonstrated using the 4:1 converter.

We propose novel ultrafast photonic interfaces for use in storage networking based on all-optical serial-to-parallel and photonic parallel-to-serial conversion. We confirm their operation with 40-Gbit/s 16-bit optical data using compact modules and a potential bandwidth of over 100 Gbit/s. We realize a photonic random access memory (RAM) by sandwiching a CMOS RAM with these two interfaces and achieve the storage and read-out of 40-Gbit/s 16-bit optical data. We also discuss the advantages of the interfaces and their possible applications to storage networking such as the real-time remote back-up of huge quantities of data, disaster recovery and video communication systems.

In this paper, we have demonstrated the ultra-short electrical pulse generation using a normal metal-semiconductor-metal photodetector circuit (MSM-PD) at low bias voltage. The circuit using MSM-PD has much shorter fall time at the cost of repetition time and also provides high sensitivity and ease of fabrication. This circuit is very suitable for the PSC which is the key technology of photonic packet switching. © 2003 IEEE.

A uni-traveling-carrier refracting-facet photodiode. a short-stab bias circuit, and a patch antenna are monolithically integrated to make a compact and low-cost photonic millimeter-wave emitter for fiber-radio applications. The device emits the maximum effective radiation power of 17 +/- 3 d Bm at 60 GHz including a directive gain of the patch antenna.

We developed a compact photonic emitter module for a 60 GHz fiber radio downlink with an estimated equivalent isotropically radiated power of 18 dBm. Phase-shift keyed data transmission is experimentally demonstrated at 2.5 Gbit/s.

A compact optically-fed radio access point module was developed that consists of a uni-traveling-carrier refracting-facet photodiode, a patch antenna, and an optical input interface. An output power from the photodiode was 1.4 dBm at a frequency of 5.88 GHz without any bias voltage.

10-Gbit/s monolithic receiver OEIC's for 1.55-mu m optical transmission systems were fabricated using a stacked laver structure of p-i-n photodiodes and HEMT's grown on InP substrates by single-step MOVPE. A receiver OEIC with a large O/E conversion factor was obtained by adding a three-stage differential amplifier to a conventional feedback amplifier monolithically integrated with a surface-illuminated p-i-n photodiode. The circuit configuration gave a preamplifier a transimpedance of 60 dB Omega. The receiver OEIC achieved error-free operation at 10 Gbit/s without a postamplifier even with the optical input as low as -10.3 dBm because of its large O/E conversion factor of 890V/W. A two-channel receiver OEIC array for use in a 10-Gbit/s parallel photoreceiver module based on a PLC platform was made by monolithically integrating multimode 'WGPD's with HEMT preamplifiers. The side-illuminated structure of the WGPD is suitable for integration with other waveguide-type optical devices. The receiver OEIC arrays were fabricated on a 2-inch wafer with achieving excellent uniformity and a yield over 90%: average transimpedance and average 3-dB-down bandwidth were 43.8 dB Omega and 8.0 GHz. The two channels in the receiver OEIC array also showed sensitivities of -16.1 dBm and -15.3 dBm at 10 Gbit/s. The two-channel photoreceiver module was constructed by assembling the OEIC array on a PLC platform. The frequency response of the module was almost the same as that of the OEIC chip and the crosstalk between channels in the module was better than -27dB in the frequency range below 6 GHz. These results demonstrate the feasibility of using our receiver OEIC's in various types of optical receiver systems.

A multimode waveguide p-i-n photodiode (WGPD) and a distributed baseband amplifier consisting of high-electron mobility transistors (HEMT's) were monolithically integrated on InP substrate using a stacked layer structure for both components. The multimode WGPD has a 3-dB bandwidth of 49 GHz. The distributed baseband amplifier has a 3-dB bandwidth of 47 GHz, though its 0.5-mu m gate-length HEMT's have modest cutoff frequencies f(T)/f(max) Of 47/100 GHz. The receiver optoelectronic integrated circuit has a bandwidth of 46.5 GHz. It was packaged into a fiber-pig-tailed module, and the WGPD in the module has a high responsivity of 0.62 A/W for 1.55-mu m wavelength. The module achieves a sensitivity of -22.7 dBm at 40 Gb/s and exhibits a clear eye-opening at 50 Gb/s.

A uni-traveling-carrier refracting-facet photodiode, a short-stub bias circuit, and a patch antenna were monolithically integrated to make a compact and low-cost millimeter-wave photonic emitter for fiber-radio applications. The device emits the maximum effective radiation power of 17±3 dBm at 60 GHz.

The optical response of InAlAs/InGaAs HEMT's under illumination with modulated light from a 1,3-mu m semiconductor laser diode onto the backside of the substrate is measured by using an optical-signal analyzer. It is clear that the response is composed of two signals, One signal is dominant at a low frequency and is due to the photovoltaic effect that causes excess holes photogenerated in the InGaAs channel to accumulate in the source region, This accumulation thus causes a decrease in the threshold voltage of the HEMT's. To explain this mechanism, a theory is given which connects the change in threshold voltage with that in the Fermi energy of the two-dimensional electron gas (2-DEG), The other signal is dominant at a high-frequency and is due to the photoconductive effect in the InGaAs channel beneath the gate. In this case, a large optical gain is produced since electrons at the source region are replenished in the gate channel. This leads to the first clear observation of a photoconductive signal. The bandwidth due to the photovoltaic effect is as low as 45 MHz and is dominated by the lifetime of the excess holes, The bandwidth due to the photoconductive effect is as high as 37 GHz and is dominated by the gain-bandwidth product of transistors rather than the intrinsic transit-time of electrons.

A long-wavelength monolithic photoreceiver has been fabricated using a multimode waveguide pin photodiode and an HEMT loss-compensated distributed amplifier. It provides an O/E conversion factor of 105V/W and a 3dB-down bandwidth of 52GHz, which is the largest bandwidth for any integrated photoreceiver reported to date.

A high-efficiency uni-travelling carrier (UTC) photodiode has been developed which employs an edge-illuminated refracting-facet photodiode (RFPD) structure. The fabricated UTC-RFPD shows a maximum responsivity of 0.48A/W even with an absorption layer as thin as 2808nm, and a high output peak-to-peak voltage of 1.5V at 40Gbit/s.

A high-speed monolithic receiver, consisting of a waveguide pin photodiode and an HEMT distributed amplifier, was packaged in a fibre-pigtailed module. It achieved a sensitivity of -22.7 dBm at 40 Gbit/s and a clear eye-opening at 50 Gbit/s. Such a performance is a first for a monolithic photoreceiver module.

The current-voltage (I-V) characteristics of InAlAs/InGaAs high electron mobility transistors (HEMT's) under illumination are investigated. The change of the drain current caused by the illumination can be explained by using the photovoltaic effect so that the excess holes photo-generated in the InGaAs channel lager accumulate at the source-electrode region and cause an effective decrease in the potential barrier for electrons between the source and the channel, The basic equations describing this phenomenon are derived on the basis of the experimental results. In addition, our experimental results are shown to support the barrier-induced hole pile-up model in which holes generated by the impact ionization accumulate in the InAlAs barrier on the source side and cause the kink effect in InAlAs/InGaAs HEMT's.

A large bandwidth monolithically integrated photoreceiver for 1.55-mu m wavelength operation was fabricated using a stacked structure of waveguide p-i-n photodiode layers and InAlAs-InGaAs high-electron mobility transistor (HEMT) layers grown using a single-step metal-organic vapor-phase epitaxy. The monolithic receiver optoelectronic integrated circuit (OEIC) consists of a waveguide p-i-n photodiode with a high responsivity of 0.5 A/W and a HEMT distributed amplifier. It has a bandwidth of 46.5 GHz, which is the largest yet reported for a long-wavelength receiver OEIC, and exhibits a clear eye opening at 40 Gb/s. This excellent performance is very attractive for use in high-speed optical transmission systems and millimeter-wave fiber-radio systems.

A monolithic photoreceiver module using a waveguide p-i-n photodiode/HEMT-distributed-amplifier OEIC has been developed. It achieves a sensitivity of -22.7 dBm at 40 Gbit/s and a clear eye-opening at 50 Gbit/s. Such performance is a first for a monolithic photoreceiver module.

A monolithic photoreceiver OEIC for lambda = 1.55 mu m consisting of a waveguide pin photodiode and an InAlAs/InGaAs HEMT distributed amplifier has been fabricated using a single-step MOVPE growth technique. It has a 3dB-down frequency of 2OGHz and operates at 20Gbit/s with a sensitivity of -10.4dBm.

A monolithic receiver OEIC with a record bandwidth of 46.5 GHz is described, It consists of a waveguide p-i-n photodiode with a high responsivity of 0.5 A/W and a HEMT distributed amplifier. A fabricated OEIC operates at 40 Gbit/s with a clear eye opening.

Two-channel side-illuminated receiver OEIC arrays comprising waveguide p-i-n photodiodes and InAlAs-InGaAs-HEMT transimpedance amplifiers were fabricated with good uniformity on a 2-in wafer. The performances of the two channels were measured by on-wafer probe measurements and showed well-matched 3-dB bandwidth of 8.0 GHz, transimpedance of 155 Omega, and crosstalk less than -20 dB, The OEIC array operates at 10 Gbit/s with sensitivities of -16.1 dBm and -15.3 dBm for each channel for a bit error rate of 10(-9) at a wavelength of 1.55 mu m This is the highest bit rate yet reported for a long-wavelength monolithic photoreceiver array.

Tunable wavelength conversion of a 10 Gb/s signal over a broad wavelength range of about 90 nm is achieved by using a super structure grating distributed Bragg reflector laser. The extinction ratio dependence of converted signal light on input signal light power and bias current to the laser active region is discussed. The extinction ratio becomes large when the input signal light power increases and the bias current decreases. Bit error rate measurements shaw that error-free, penalty-free wavelength conversion is achieved when the extinction ratio is large (12.5 dB) and that the bit rate which error-free wavelength conversion is possible increases as the input signal light power increases. Twenty Gb/s signal wavelength conversion is also demonstrated.

This paper proposes a novel model for estimating power dissipation of optical/electrical interconnections as a function of transmission bit error rate. This model is applied to a simplified optoelectronic transmitter and receiver configuration in which a photodetector is directly connected to the decision circuit. It is analytically verified that this configuration can achieve error-free operation with low power under practical operating conditions. A comparison between optical and electrical interconnections based on this simplified configuration is performed. This result shows the interconnection length and bit rate at which optical interconnection is superior in terms of power dissipation to electrical interconnection. Only optical interconnections achieve error-free operation with 40 mW power dissipation at a transmission bit rate of 10 Gb/s and an interconnection length over 7 m.

The wavelength conversion device whose frequency response is evaluated analytically and experimentally in this work has a saturable absorber region, which acts as an optical gate, within the active region. The 3-dB bandwidth of this device was measured to be 800 MHz and found to be limited by the frequency response of the saturable absorber region. To speed up this device, the electrodes of the saturable absorber and the gain regions were connected electrically so that the device would act as a unidirectional-output distributed Bragg reflector (DBR) laser. When the active region (saturable absorber and the gain regions) of this DBR laser were biased above threshold condition, the 3-dB bandwidth was more than 10 GHz, and clear eye patterns were observed when the input TM-polarized light intensity was modulated by a 10-Gbit/s pseudo-random NRZ signal. These results show that high-speed wavelength conversion can be achieved when the device is operated as a laser diode.

Two-channel receiver OEIC arrays comprising waveguide p-i-n photodiodes and transimpedance amplifiers have been fabricated on 2-inch wafer with god uniformity. Two channels show well matched 3-dB bandwidth of 8.0GHz and crosstalk less than -20dB with on-wafer-probe measurements. The OEIC array operates at 10Gbit/s with a sensitivity of -16.1dBm and -15.3dBm for each channel for a bit error rate of 10^<-9>. This is the highest-bit-rate demonstration yet reported for a longwavelength monolithic photoreceiver array.

A novel optical frequency conversion device that successfully demonstrates optical frequency conversion and unidirectional transmission of optical signals has been designed and fabricated. The device is composed of a gain region and saturable absorber region with monolithically integrated distributed Bragg reflector (DBR) mirrors with different coupling coefficients. The device structure is optimized to achieve three functions: 1) unidirectional light output, 2) converted-light wavelength tuning, and 3) optically triggered optical frequency conversion. The output power of converted light from the light input-end facet of the device is 30 dB smaller than that from the output-end racet, and the converted light wavelength can be scanned over 4 nm without a bias current to the input-end DBR region, and it is widened to 7.8 nm by injecting current to that region. The device emits converted light only when light input is injected and optical signals are unidirectionally transmitted, and its response frequency is estimated to be 0.8 GHz.

The authors report the tunable wavelength conversion of a 10Gbit/s signal over a broad wavelength range of similar to 90nm using a superstructure grating distributed Bragg reflector (DBR) laser.

The frequency response of a unidirectional-output optical frequency conversion device is measured. The device has a saturable absorber region within the active region, which acts as an optical gate for converted light. The 3-dB bandwidth of the device with saturable absorber region is measured to be 800 MHz, and is found to be limited by the frequency response of the saturable absorber region.
To operate the device faster, lasing mode intensity modulation by input light is attempted by using the device in a laser diode mode. In this case, the electrodes of the saturable absorber and the gain regions are connected electrically, and the saturable absorber region is also biased far above the threshold condition at the same time with the gain region. The 3-dB bandwidth of the device increases to over 10 GHz, and the 10 Gb/s nonreturn-to-zero (NRZ) eye pattern can be observed when the input TM-polarized light intensity is modulated by a 10 Gb/s NRZ pseudo-random signal.

An optical-frequency conversion device is fabricated, using monolithically integrated distributed Bragg reflector (DBR) mirrors with different coupling coefficients at the outer sides of the active and the saturable absorber regions. The input-end DBR mirror has higher coupling coefficient than that of the output-end DBR mirror. The converted light is reflected by the input-end DBR mirror and is emitted only from the output end of the device. This device successfully performs optical frequency conversion when the input TM-polarized light has a wavelength within the wavelength range for which the reflection of the input-end DBR mirror is fairly high for TE-polarized light. The ratio of the converted-light output power for TE-polarized light from the input end to that from the output end is less than -30 dB.

Ion Bernstein wave (IBW) heating at ion cyclotron half-harmonic frequencies was performed in hydrogen (H) discharges in the WT-3 tokamak. The bulk ion temperature increase was measured by a charge exchange analyser and a spatially scanning polychrometer. The latter diagnostics can provide radial ion-temperature profiles. The incremental ion temperature has shown a peak at the exact location where the IBW frequency omega equals 3/2 of the ion cyclotron frequency, indicating the nonlinear direct acceleration of H ions. The wave electric field was measured by a Langmuir probe in the scrape-off layer. The electric field at the second harmonic of the excited IBW frequency was observed to vary depending on the power level and the toroidal magnetic field. These experimental results are compared with the theoretical prediction of nonlinear IBW damping. The measured dependences of the ion heating and the wave amplitude at 2omega on the toroidal magnetic field are in reasonable agreement with the prediction.

Wavelength dependence was measured for a one-directional output optical frequency conversion device that has an asymmetric-coupling-coefficient (kappa) distributed-Bragg-reflector (DBR) structure. The output power of converted light from the light input end is 30 dB smaller than that from the output end. The injected light wavelength and polarisation dependence of converted light power has also been investigated. The converted light wavelength scanning range is confirmed to be the design value of 4 nm, which is the widest ever reported.

The spectral linewidth of a multiple-quantum-well (MQW) distributed feedback (DFB) laser is measured when intensity-modulated orthogonally-polarized (transverse magnetic (TM) mode) light is injected into the laser. The spectral linewidth does not change when the modulation frequency is higher than several hundred megahertz and is almost the same as without light injection. However, it broadens when the injected orthogonally polarized light modulation frequency is close to zero. The line shape of the MQW DFB laser's lasing light becomes non-Lorentzian in shape below a modulation frequency of 500 MHz.

Gain saturation coefficients of unstrained- and strained-layer multiple quantum-well lasers were measured experimentally. These coefficients were higher in lasers that had compressive strain in their active-layer wells: 2.45 x 10(-17) cm3 with unstrained wells and 12.6 x 10(-17) cm3 with strained wells. The higher gain saturation coefficient in lasers with strained active-layer wells is related to their higher linear TE mode gain coefficient. The linearity factor (K factor) between a laser's damping constant and the square of the laser's resonant frequency decreased slightly with introducing the strain in laser's active layer wells. This factor, however, took the value of about 0.2 x 10(-9) s for each of these lasers. The a parameter of these lasers was also estimated: 3.1 for an unstrained-layer multiple quantum-well laser and 1.1 for a laser with compressive strain in the active-layer wells.

The gain saturation coefficients are measured for strained and unstrained multiple quantum-well distributed feedback lasers. The gain saturation coefficient depends on the deviation of the laser's TM mode gain peak wavelength from its TE mode gain peak wavelength delta-lambda, which is concerned with the strain on the active-layer wells. It is also found that the gain saturation coefficient increases with strain on the active-layer wells.

The Balmer line intensities of atomic hydrogen from the WT-III tokamak plasma have been observed and interpreted in terms of the collisional-radiative model. The atomic and molecular hydrogen densities are deduced together with the electron density. Going from the plasma centre to the edge region along the minor radius, the atomic hydrogen density increases slightly and molecular hydrogen is found only in the periphery. In the edge region, the atomic hydrogen density reaches 1 × 1016 m−3 and the molecular hydrogen density 4 × 10l7 m−3The electron density distribution is consistent with that determined by infrared laser interferometry. © 1989 IOP Publishing Ltd.