High-output-current, high-speed Ge-on-Si waveguide photodetector with four-port evanescent coupling

Abstract We propose and demonstrate a novel four-port evanescently coupled Ge-on-Si photodetector (PD) designed to overcome performance limitations under high optical power. This study aims to mitigate the space-charge effect that causes photocurrent saturation and bandwidth degradation in conventional Ge-on-Si PDs. In our device, the input optical signal is divided into four waveguides that evanescently couple light into a central Ge absorption region from four sides. This configuration effectively distributes the optical intensity, thereby reducing the space-charge effect. The fabricated PD exhibits a linear responsivity of 1.08 A W −1 , a large maximum photocurrent of 54 mA, and a 3 dB bandwidth of approximately 15 GHz at an output current of 15 mA. These results indicate that the proposed PD offers a promising solution for high-power and high-speed applications, demonstrating strong potential for advanced radio-frequency photonics.