Takafumi Taniguchi

40-Gb/s Direct Modulation With High Extinction Ratio Operation of 1.3-

Direct modulation at 40 Gb/s of a 1.3-mum InGaAlAs distributed feedback ridge waveguide laser is experimentally demonstrated. By combination of the high differential gain of an InGaAlAs multiquantum well active layer, a short cavity length of 100 mum, and a low-resistance notch-free grating, it achieves high bandwidth of 29 GHz and high-extinction ratio of 5 dB at 40-Gb/s modulation. Moreover, the laser operates at a record maximum ambient temperature of 60degC under 40-Gb/s directly modulation. It also achieves 40-Gb/s modulated transmission over 2 km with a low power penalty of 0.25 dB at 25degC .

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Direct modulation at 56 and 50 Gb/s of 1.3-μm InGaAlAs ridge-shaped-buried heterostructure (RS-BH) asymmetric corrugation-pitch-modulation (ACPM) distributed feedback lasers is experimentally demonstrated. The fabricated lasers have a low threshold current (5.6 mA at 85°C), high temperature characteristics (71 K), high slope relaxation frequency (3.2 GHz/mA1/2 at 85°C), and wide bandwidth (22.1 GHz at 85°C). These superior properties enable the lasers to run at 56 Gb/s and 55°C and 50 Gb/s at up to 80°C for backto-back operation with clear eye openings. This is achieved by the combination of a low-leakage RS-BH and an ACPM grating. Moreover, successful transmission of 56and 50-Gb/s modulated signals over a 10-km standard single-mode fiber is achieved. These results confirm the suitability of this type of laser for use as a cost-effective light source in 400 GbE and OTU5 applications.

m InGaAlAs Multiquantum Well Ridge Waveguide Distributed Feedback Lasers

Direct modulation at 12.5 Gb/s of 1.3-/spl mu/m DFB RWG lasers with low-resistance notch-free gratings running at 115/spl deg/C is experimentally demonstrated, for the first time. Moreover, 10-Gb/s modulated transmission over 30 km at 115/spl deg/C was achieved.

Direct Modulation at 56 and 50 Gb/s of 1.3-

We have developed the advanced performance, small-scale InGaP/GaAs heterojunction bipolar transistors (HBTs) by using WSi/Ti base electrode and buried SiO/sub 2/ in the extrinsic collector. The base-collector capacitance C/sub BC/ was further reduced to improve high-frequency performance. Improving the uniformity of the buried SiO/sub 2/, reducing the area of the base electrode, and optimizing the width of the base-contact enabled us to reduce the parasitic capacitance in the buried SiO/sub 2/ region by 50% compared to our previous devices. The cutoff frequency f/sub T/ of 156 GHz and the maximum oscillation frequency f/sub max/ of 255 GHz were obtained at a collector current I/sub C/ of 3.5 mA for the HBT with an emitter size S/sub E/ of 0.5/spl times/4.5 /spl mu/m/sup 2/, and f/sub T/ of 114 GHz and f/sub max/ of 230 GHz were obtained at I/sub C/ of 0.9 mA for the HBT with S/sub E/ of 0.25/spl times/1.5 /spl mu/m/sup 2/. We have also fabricated digital and analog circuits using these HBTs. A 1/8 static frequency divider operated at a maximum toggle frequency of 39.5 GHz with a power consumption per flip-flop of 190 mW. A transimpedance amplifier provides a gain of 46.5 dB/spl middot//spl Omega/ with a bandwidth of 41.6 GHz at a power consumption of 150 mW. These results indicate the great potential of our HBTs for high-speed, low-power circuit applications.

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High-speed InGaP/GaAs heterojunction bipolar transistors (HBTs) with a small emitter area are described. WSi is used as the base electrode to fabricate HBTs with a narrow base contact width and a buried SiO/sub 2/ structure. An HBT with an emitter area of 0.8/spl times/5 /spl mu/m exhibited an f/sub T/ of 105 GHz and an f/sub max/ of 120 GHz. These high values are obtained due to the reduction of C/sub BC/ by using buried SiO/sub 2/ with a narrow base contact width, indicating the great potential of GaAs HBTs for high-speed and low-power circuit applications.

m InGaAlAs Ridge-Shaped-BH DFB Lasers

Direct modulation of 1.3-mum InGaAlAs DFB RWG lasers at 40 Gb/s is experimentally demonstrated. This laser achieves a record extinction ratio of 5 dB under 40-Gb/s modulation. Moreover, it can provide 40-Gb/s modulated transmission over 2 km

115/spl deg/C, 12.5-Gb/s direct modulation of 1.3-/spl mu/m InGaAlAs-MQW RWG DFB laser with notch-free grating structure for datacom applications

A tunable laser based on a medium wavelength selectivity tunable filter named a lateral-grating-assisted lateral-co-directional-coupler was developed. A wide tuning range of over 65 nm with SMSR of over 35 dB was demonstrated at 50°C.

High-speed small-scale InGaP/GaAs HBT technology and its application to integrated circuits

Small-scale InGaP/GaAs heterojunction bipolar transistors (HBTs) with high-speed as well as low-current operation are demonstrated. To reduce the emitter size SE and the base-collector capacitance CBC simultaneously, the HBTs are fabricated by using WSi/Ti as the base electrode and by burying SiO2 in the extrinsic collector region. WSi/Ti metals simplify and facilitate processing to fabricate small base electrodes, and the buried SiO2 reduces the parasitic CBC under the base electrode. The cutoff frequency fT of 156 GHz and the maximum oscillation frequency fmax of 255 GHz were obtained at a collector current Ic of 3.5 mA for the HBT with SE of 0.5 μm×4.5 μm, and fT of 114 GHz and fmax of 230 GHz were obtained at IC of 0.9 mA for the HBT with SE of 0.25 μm×1.5 μm. A 1/8 static frequency divider operated at a maximum toggle frequency of 39.5 GHz with a power consumption per flip-flop of 190 mW. A transimpedance amplifier provides a gain of 46.5 dB·Ω with a bandwidth of 41.6 GHz at a power consumption of 150 mW. These results indicate the great potential of our HBTs for high-speed. low power integrated circuit applications.

High-speed InGaP/GaAs heterojunction bipolar transistors with buried SiO 2 using WSi as the base electrode

Two vertically coupled asymmetric InGaAsP ridge waveguides were fabricated and tested as a tunable dispersion compensator. In this waveguide, two coupled modes, symmetric and antisymmetric, exist simultaneously and have a significant amount of group-velocity dispersion (GVD), making it possible to reduce the size of the dispersion compensators. Since the GVD can be continuously controlled by changing the temperature of the asymmetric coupled waveguide, a semiconductor asymmetric coupled waveguide has great potential as a basis for a compact tunable dispersion compensator. To demonstrate tunable dispersion compensation, we carried out an experiment on the pulse compression of frequency-chirped pulses by using the InGaAsP asymmetric coupled waveguide at various temperatures of the waveguide. We observed a change in the compression ratio, ranging from 42.7% to 84.2%, as the temperature of the waveguide changed from 8to48.9°C. A theoretical study showed that the observed change in the compression ratio was we...

High extinction ratio operation at 40-Gb/s direct modulation in 1.3-/spl mu/m InGaAlAs-MQW RWG DFB lasers

A semiconductor dispersion compensator based on two vertically coupled asymmetric InGaAsP/InP ridge waveguides was designed and fabricated. This device consists of a dispersion-compensation region sandwiched between two mode converters. Two types of coupled modes, symmetric and antisymmetric, simultaneously exist in the dispersion-compensation region and have significant group-velocity dispersion (GVD) with opposite signs, making shrinkage of the device possible. The mode converters serve as mode selectors, exciting only the coupled mode needed for dispersion compensation with a high degree of efficiency. The compression of a 5.4-ps down-chirped pulse was demonstrated by the device; the pulse compression ratio was 55%. A theoretical study showed that the observed pulse compression was explained well by the dispersion compensation caused by the GVD of the coupled modes, and that the selectivity of the mode converter was approximately 80% for the symmetric coupled mode.