Large Bandwidth and High Power Germanium/Silicon Photodetector: A Novel Solution for 100 Gb s^–1Microwave Photonic Links

Germanium/silicon (Ge/Si) photodiodes have emerged as highly desirable components in optical communication, sensing, and computing domains owing to their unique integration advantages. However, conventional designs are fundamentally limited by the exponential absorption in the Ge region, causing abrupt performance degradation under high optical power incidence and restricting their applications in high-power scenarios. Herein, we report an on-chip PIN Ge/Si photodetector that for the first time achieves large bandwidth and high-power capabilities via a fully noncustom wafer-scale fabrication process, supporting 100 Gb s^–1 pulse-amplitude modulation 4 (PAM4) reception. The design innovatively adopts a dual-directional mode-evolution coupler strategy, wherein an adiabatic mode-evolution architecture is utilized to precisely manipulate the electric field and homogenize the optical mode. This mechanism fundamentally resolves the power-bandwidth trade-off inherent in traditional Ge/Si photodetectors. The device exhibits an excellent 48 GHz bandwidth and 0.8 A/W responsivity under a −3 V reverse bias and an incident optical power of 5 dBm. At an input power of 12 dBm, an advanced power bandwidth product of 552 GHz·dBm is achieved, surpassing the current state-of-the-art germanium/silicon PIN photodetector. Fabricated via a standard silicon photonics process, the device features competitive performance, cost-effectiveness, and high-yield compatibility, paving the way for high-speed and high-power applications in next-generation microwave photonics and beyond.