Ultracompact Optical Hybrid Based on Standing Wave Integrated With Graphene-Based Photodetector for Coherent Detection

In this paper, we propose a novel scheme to integrate an optical hybrid based on standing wave with graphene photodetector (GPD). Different from optical hybrids based on multimode interference (MMI) couplers, the proposed optical hybrid can be miniaturized by constructing a standing wave field in a silicon strip waveguide. The waveguide-integrated GPD with symmetric electrodes is adopted as an ultrafast self-differential photodetector (SDPD), instead of conventional balanced-photodetectors (BPDs) based on p-i-n photodiodes in a coherent receiver. By placing two sysmmetric interdigitated electrodes of the SDPD at nodes and antinodes of the standing wave, it is convenient to realize the integration of the proposed optical hybrid with the graphene-based SDPD, which can effectively reduce the complexity of a coherent receiver and meet the future demand for wide bandwidth. The finite-difference time-domain method was used to calculate optical absorption for demonstrating operation feasibility. Finally, device bandwidth and effective responsivity have been discussed. In theory, our scheme would provide a feasible way to realize a high-speed compact coherent receiver.