Hajime Shoji

Evaluation of differential gain of 1.3 /spl mu/m AlGaInAs/InP strained MQW lasers

Differential gain (dg/dn) of AlGaInAs strained MQW lasers was estimated from relaxation oscillation frequency (fr), and compared with that of GaInAsP lasers. The estimated dg/dn of the AlGaInAs laser was 1.1/spl times/10/sup -15/ cm/sup 2/ at 25/spl deg/C, which was 1.4 times larger than that of the GaInAsP laser. The AlGaInAs laser also showed less temperature dependence of dg/dn. The degradation of dg/dn in 25-85/spl deg/C was only 28%, while that of the GaInAsP laser was 51%.

High-power and low phase noise full-band tunable LD for coherent applications

High output power and low noise performances of CSG-DR-LD have been investigated. Kink-free fiber output power > 60 mW over C-band with high SMSR have been demonstrated. Measured phase noise is lower than 170 kHz, exhibiting excellent noise properties as a monolithic and single stripe tunable LD. These characteristics reveal that CSG-DR-LD is a promising light source for the future digital coherent applications.

Well-thickness dependence of high-temperature characteristics in 1.3-μm AlGaInAs-InP strained-multiple-quantum-well lasers

Well-thickness dependence of temperature characteristics of 1.3-/spl mu/m AlGaInAs-InP strained-multiple-quantum-well lasers was investigated. Higher characteristic temperatures of threshold current density were obtained for thicker wells up to 6 nm. Fabricated ridge-waveguide lasers with 6-nm-thick wells exhibited characteristic temperature of as high as 125 K. Relaxation-oscillation frequency reduced by only 13% between 25/spl deg/C and 85/spl deg/C.

InP-Based p-i-n-Photodiode Array Integrated With 90

This paper reports on the performance of an InP-based p-i-n-photodiode array monolithically integrated with a 90° hybrid consisting of multimode interference structures using the butt-joint regrowth and its application to compact 100 Gb/s coherent receivers. A responsivity including total loss of 8.2 dB in the waveguide was as high as 0.14 A/W, and responsivity imbalance of all channels was less than ±0.5 dB. The wide 3-dB bandwidth of 26 GHz at a low reverse bias voltage of 1.6 V was obtained under high optical input power conditions (photocurrent = 2.5 mA). The stable dark current was achieved in the accelerated aging test (test condition: -5 V at 175 °C) over 2000 h. Finally, the excellent common mode rejection ratio with low loss imbalance of 90° hybrids (less than -20 dB up to 25 GHz) and demodulation of 128 Gb/s dual polarization quadrature phase-shift keying modulated signals were demonstrated for the compact coherent receiver (package body size: 15 mm × 26 mm × 5.5 mm).

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We demonstrate sub-millisecond tuning of a prototype parametric tunable dispersion compensator (P-TDC) based on cascaded polarization-diverse four-wave mixing (FWM) process with a fast tunable and highly wavelength-stable pump light source. The pump light source is developed using a tunable distributed amplification chirped sampled grating distributed reflector laser that is fully wavelength tunable by on-chip heaters with a 3-dB frequency response of 45 kHz, resulting in fast dispersion tuning of less than 50 μs without additional timing jitter. The P-TDC is developed as the first prototype to satisfy essential requirements for practical network uses: stable input-polarization diversity, input-wavelength preservation, and seamless dispersion tunability for entire C-band input wavelengths are simultaneously achieved.

Hybrid Using Butt-Joint Regrowth for Compact 100 Gb/s Coherent Receiver

We demonstrate an autonomous fast parametric dispersion compensator with a fast TDA-CSG-DR laser and a dispersion monitor based on spectral shearing interferometer. A response time of less than 17 ms, potentially sub millisecond, is achieved.

Sub-millisecond timing-jitter-free tuning of parametric dispersion compensator.

6.25GHz-spaced optical-comb-line selection either by low-coherence injection-locked laser (LC-ILLD) or with a combination ultra-narrow-filter and low-noise-fiber-amplifier (UNF-FA) is assessed. In a 144Gbps DP-64QAM transmission the LC-ILLD outperforms the UNF-FA approach for comb-OSNR-levels below 30dB.

Dynamic parametric dispersion compensation using FPGA pump controller and dispersion monitor

The InP-based pin-photodiode array monolithically integrated with a 90° hybrid and spot-size converters was realized using selective embedding regrowth for compact 100Gb/s coherent receivers. The low dark current of less than 500 pA up to 85 °C was attained by InP passivation effect in four-channel pin-photodiodes. As a receiver using these photodiode arrays, a receiver responsivity including total loss of 6.7 dB in the 90° hybrid and intrinsic loss of 3 dB in the polarization beam splitter was higher than 0.060A/W between −5 °C and 85 °C through the integration of the spot-size converter. Responsivity imbalance of the In-phase and Quadrature channels was also less than 0.5 dB over the C-band.

Optical-comb-line selection from a low-power/low-OSNR comb using a low-coherence semiconductor laser for flexible ultra-dense short range transceivers

We demonstrate dynamic parametric optical dispersion compensation in dynamic optical path networks (DOPNs). A fully automatic parametric tunable dispersion compensator (P-TDC) based on four-wave mixing process is developed with a fast tunable distributed amplification chirped sampled grating distributed reflector laser, a field-programmable gate array (FPGA) pump controller, and a fast dispersion monitor based on spectral shearing interferometer. The dispersion monitor detects a change in the dispersion of a path, and the monitoring signal is fed forward to the FPGA controller. The fast tunable laser sets its wavelength accordingly for the dispersion compensation through parametric process. A response time of <;17 ms is demonstrated in a testbed of DOPN. The autonomous P-TDC has a potential response of submillisecond.

High receiver responsivity and low dark current of InP-based pin-photodiode array monolithically integrated with 90° hybrid and spot-size converter using selective embedding regrowth

Summary form only given. High-temperature operation of 1.3-/spl mu/m semiconductor lasers is required for optical subscriber systems. AlGaInAs-InP strained multiple quantum well (MQW) lasers are promising devices because of their superior temperature characteristics. In this work, we investigated the dependence of threshold current density and characteristic temperature (T/sub c/) on well thickness. Ridge waveguide lasers with 6-nm-thick wells exhibited high T/sub c/ of 125 K.