Jianbin Fu | Searcharxiv

arXiv2025

High-bandwidth photodetector enabled by frequency-domain equalization

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.

physics.optics↗

arXiv2024

Silicon modulator exceeding 110 GHz using tunable time-frequency equalization

Silicon modulators have garnered considerable attention owing to their potential applications in high-density integration and high-speed modulation. However, they are increasingly challenged by the limited 3 dB bandwidth as the demand for modulation speed in optical communications continues to rise, impeding their ability to compete with modulators made of thin-film lithium niobate. This bandwidth limitation arises because of the parasitic resistance and capacitance in the PN junction of the silicon modulators. This study demonstrates the first silicon modulator exceeding 110 GHz without any resonant structure using a tunable time-frequency equalization technique. This substantial breakthrough enables on-off keying modulation at a rate of 140 Gbaud without digital signal processing. These accomplishments represent the highest bandwidth and maximum baud rate achieved without digital signal processing in an all-silicon modulator, reaching the testing limitations of the experimental system. This opens the possibility of attaining modulation rates of up to 200 or even 300 Gbaud by adopting design strategies such as slow light and technologies such as digital signal processing. This advancement extends the speed capabilities of silicon modulators to the level of thin-film lithium niobate modulators, thereby promoting their application in the broader array of fields, such as linear-drive pluggable transceivers.

physics.optics↗