InP-Based Photodetectors Monolithically Integrated with 90^° Hybrid toward Over 400Gb/s Coherent Transmission Systems

抄録

We present InP-based photodetectors monolithically integrated with a 90^° hybrid toward over 400Gb/s coherent transmission systems. To attain a wide 3-dB bandwidth of more than 40GHz for 400Gb/s dual-polarization (DP)-16-ary quadrature amplitude modulation (16QAM) and 600Gb/s DP-64QAM through 64GBaud operation, A p-i-n photodiode structure consisting of a GaInAs thin absorption and low doping n-typed InP buffer layers was introduced to overcome the trade-off between short carrier transit time and low parasitic capacitance. Additionally, this InP buffer layer contributes to the reduction of propagation loss in the 90^° hybrid waveguide, that is, this approach allows a high responsivity as well as wide 3-dB bandwidth operation. The coherent receiver module for the C-band (1530nm - 1570nm) operation indicated the wide 3-dB bandwidth of more than 40GHz and the high receiver responsivity of more than 0.070A/W (Chip responsivity within the C-band: 0.130A/W) thanks to photodetectors with this photodiode design. To expand the usable wavelengths in wavelength-division multiplexing toward large-capacity optical transmission, the photodetector integrated with the 90^° hybrid optimized for the L-band (1565nm - 1612nm) operation was also fabricated, and exhibited the high responsivity of more than 0.120A/W over the L-band. Finally, the InP-based monolithically integrated photonic device consisting of eight-channel p-i-n photodiodes, two 90^° hybrids and a beam splitter was realized for the miniaturization of modules and afforded the reduction of the total footprint by 70% in a module compared to photodetectors with the 90^° hybrid and four-channel p-i-n photodiodes.