GeSn/SiGeSn Multiple-Quantum-Well Electroabsorption Modulator With Taper Coupler for Mid-Infrared Ge-on-Si Platform

We propose a taper coupler electroabsorption modulator (EAM) composed of GeSn/SiGeSn multiple-quantum-well (MQW) on Ge-on-Si platform for mid-infrared (2 μm) integrated optical active devices. The epitaxial design is performed by calculating the absorption spectra of GeSn/SiGeSn MQW using many-body theory to investigate the extinction characteristics of GeSn MQW waveguides. Two types of taper couplers are considered for connecting Ge-rib waveguide and GeSn-MQW-highmesa waveguide efficiently. One is an adiabatic taper coupler (ATC) type EAM and it is useful for thin Ge-buffer structure in terms of the extinction ratio. Another is a resonant taper coupler (RTC) type EAM and it is superior to ATC type EAM for thick Ge-buffer. It is confirmed that RTC type EAM can obtain the high extinction characteristics with low-loss and shorter device length (6.87 dB, -3.97 dB, and 215 μm) compared with conventional ATC type EAM for thick Ge-buffer (5.67 dB, -4.9 dB, and 340 μm).