Silicon Nitride Waveguide-Integrated Ge Photodetector with >110 GHz Bandwidth under 1 mA Operation in the O-Band

Germanium photodetectors (Ge PDs) are widely integrated in optical interconnects, particularly at the receiver, where different data rates impose specific performance requirements. With the commercialization of 200 Gbps-per-wavelength links, the demand for higher data rates continues to rise. For next-generation 400 Gbps-per-lane intensity modulation direct detection systems, the optical power incident on photodetectors may approach 0 dBm, corresponding to photocurrents on the order of 1 mA. However, due to the larger absorption coefficient of Ge in the O-band, conventional Ge photodetectors typically exhibit performance degradation under high optical power. Here, we first demonstrate lateral Ge PDs with cantilevered silicon nitride waveguides positioned over Ge. The integrated device achieves bandwidth of >110 GHz in the O-band under photocurrents ranging from 0.1 mA to 1 mA. Simultaneously, 128, 140, and 150 Gbit/s NRZ and 240, 256, and 280 Gbit/s PAM-4 clear eye diagrams are experimentally obtained. To evaluate the power-handling performance under high-speed data transmission, clear eye diagrams at 112 Gbit/s are also achieved for both NRZ (5 mA) and PAM-4 (3.5 mA). Overall, a high-performance cantilevered Si3N4 waveguide-coupled Ge PD has been demonstrated on a 12-in. CMOS-compatible silicon photonics platform, highlighting strong potential for next-generation 400 Gbit/s-per-lane optical interconnects.