High-Power Ge/Si Waveguide Photodetector

A lateral germanium/silicon waveguide photodetector with a side-coupling structure is proposed and realized. For the present photodetector, the input light is split into four channels, which are gradually coupled into two parallel germanium waveguides by adiabatic side-coupling. In this way, uniform optical field distribution is achieved and the space-charge effect is eliminated greatly even with high optical power. The experimental results show that the responsivity is still as high as 0.68 A/W even for an input optical power of 28 mW and the saturation photocurrent is more than 19.5 mA. The present photodetector features a broad bandwidth of >40 GHz for detecting low optical power, while the bandwidth is still more than 20 GHz for the input optical power of 12.4 mW (the output current is 10.2 mA). The open eye-diagrams for receiving the 25 and 50 Gbps data are demonstrated with the photocurrents of 16 and 8.5 mA, respectively. The present side-coupling Ge/Si photodetector exhibits excellent performances for high-power detection compared with the conventional one.