Chikara Watatani

25.8Gbps direct modulation of BH AlGaInAs DFB lasers with p-InP substrate for low driving current

1.3µm-band BH AlGaInAs DFB lasers with p-InP substrate are fabricated for 100GbE (25Gbps × 4 wavelengths). Very high mask margin of over 30% is achieved at 50oC under 25.8Gbps modulation with low operation current.

40G RZ-DQPSK transmitter monolithically integrated with tunable DFB laser array and Mach-Zehnder modulators

A 40G RZ-DQPSK transmitter monolithically integrated with a tunable DFB laser array and Mach-Zehnder modulators was developed for the first time. The optical waveform of 40Gb/s DQPSK was successfully demonstrated.

Uncooled directly modulated 1.3-μm AlGaInAs-MQW DFB laser diodes

We have proved that short cavity length and large coupling coefficient structure can increase the relaxation oscillation frequency of directly modulated 1.3mm DFB-LDs for 10Gb/s operation. The grating with large coupling coefficient can be made of high refractive index InGaAsP material (=narrow band gap energy material), which has to be fabricated in the n-type InP cladding layer to prevent large hole and electron accumulation in the grating layer. By using this grating, 1.3mm AlGaInAs quarter lambda phase shifted DFB-LDs successfully revealed excellent eye diagrams with over 10% margin for OC-192 mask at the temperature range of 25-95 deg.C. Furthermore, we newly propose multi-phase shifted gating to 10Gb/s quarter lambda phase-shifted DFB-LDs to suppress the deterioration of eye diagrams due to non-uniform longitudinal distribution of light intensity and carrier density.

25Gbps × 4ch photodiode array with high responsivity for 100Gbps Ethernet

Four-channel surface-illuminated photodiodes monolithically integrated in one array chip are fabricated for 100Gbps Ethernet. The photodiode with an optimized distributed Bragg reflector has a 3dB bandwidth of 25GHz and the highest responsivity of 0.92A/W at a 1.3µm wavelength.