Monolithically integrated detector chip for a two-channel unidirectional WDM link at 1.5 μm

The fabrication and operation of a monolithically integrated InGaASP/InP wavelength division multiplexing (WDM) detector chip is reported. It consists of a Y-branch grating demultiplexer and two p-i-n photodiodes. Polarization-independent operation for two closely spaced channels (Δλ=3.6 nm) at λ=1.5 μm was obtained. In polarization-independent operation, 1.3-mm-long Bragg gratings on buried waveguides showed a peak crosstalk attenuation of 15 dB and a stop bandwidth of 0.2 nm at -10 dB. These values show the high potential of Bragg grating devices for dense wavelength division multiplexing applications. The static electrical properties of the monolithically integrated p-i-n photodiodes (dark current of 2-5 nA at -10 V, breakdown voltage of 45-65 at a 10 μA leakage current) approach the values obtained for discrete devices. The bandwidth of 420 MHz enables operation in the 600-Mbaud region. The external quantum efficiency of the complete detector chip (η=0.08) is still rather small. However, it could be considered sufficient for the operation of such devices in local networks with distances of a few kilometers