InP-Based Butt-Joint Coupled Waveguide Photodiodes Integrated With Various Functions for 100 GBaud Coherent Detection

This paper reports on the performance of an InP-based butt-joint (BJ) coupled waveguide photodiode (PD) for 100 GBaud coherent detection. We adopt a dual-layer absorber comprised of p- and i-type GaInAs absorption layers to enhance the advantage of BJ coupled waveguide PDs which overcome the tradeoff between high responsivity and wide bandwidth. As a result, a responsivity as high as 0.90 A/W over the C-band and a wide 3 dB bandwidth of 71 GHz have been successfully obtained at a reverse bias voltage of 2.5 V. Towards the realization of compact coherent modules without complicated assembly processes, we have also fabricated a compact photonic integrated circuit (PIC) chip (Chip size: 2.6 × 4.1 mm) configured by 12 BJ coupled waveguide PDs and various optical functions, such as 90° hybrids and variable optical attenuators (VOAs) through the InP-based monolithic integration technology. An integrated coherent transmitter-receiver optical sub-assembly (IC-TROSA) employing the PIC has exhibited receiver performance sufficient for 100 GBaud coherent detection.