Side-Coupled High-Power and High-Speed Ge-on-Si Photodetectors using Lateral Subwavelength Grating Waveguides

High-saturation power Ge-on-Si photodetectors are widely used in analog photonics and microwave photonics, serving as key components to convert optical signals to electrical signals. However, the saturation power of the conventional butt-coupled photodiode is typically constrained by the space-charge effect. Here, two side-coupled Ge-on-Si photodetectors assisted by subwavelength grating (SWG) waveguides are proposed and realized. The present photodetectors adopt the side-coupled method, and the SWG waveguides are optimized to eliminate the space-charge effect with high optical power. One of the side-coupled photodetectors, which has a single SWG input waveguide, demonstrated a saturation current of 53.4 mA. The other has two SWG waveguides with bidirectional optical feed and has a saturation current of 41.1 mA. The device exhibits a bandwidth of 53.4 GHz under 5 mA output current. Under a photocurrent of 1 mA, the high-speed open eye diagram for 112 Gbps nonreturn-zero (NRZ) data transmission is demonstrated. And under the photocurrents of 13 and 20 mA, the open eye diagrams for the 56 and 28 Gbps NRZ data transmission are demonstrated, respectively. The present side-coupled Ge-on-Si photodetector shows excellent performance for high power detection compared with the conventional butt-coupled one.