High-bandwidth photodetector enabled by frequency-domain equalization

Abstract

High-bandwidth germanium (Ge) photodetectors are crucial for silicon photonic integrated circuits. However, their bandwidth is restricted by carrier transit time and parasitic parameters. In this work, we propose an equalization photodetector (EqPD) utilizing the frequency response of a high-bandwidth photodetector PDA to subtract the frequency response of a low-bandwidth photodetector PDB. With the response of PDB attenuating more severely than PDA at high frequency, the differential frequency response (the response of EqPD) can get higher values at high frequency than at low frequency, flattening the overall frequency response and expanding the bandwidth. Experimental results show that the EqPD has a bandwidth exceeding 110 GHz with a responsivity of 94 mA/W. A 100 Gbaud non-return-to-zero (NRZ) operation without digital signal processing is also demonstrated. To the best of our knowledge, this represents the highest bandwidth in a vertical Ge photodetector, providing a promising solution for high-speed photodetection in next-generation optical communication.