64 Gb/s low-voltage waveguide SiGe avalanche photodiodes with distributed Bragg reflectors

We demonstrate low-voltage waveguide silicon-germanium avalanche photodiodes (APDs) integrated with distributed Bragg reflectors (DBRs). The internal quantum efficiency is improved from 60% to 90% at 1550 nm assisted with DBRs while still achieving a 25 GHz bandwidth. A low breakdown voltage of 10 V and a gain bandwidth product of near 500 GHz are obtained. APDs with DBRs at a data rate of 64 Gb/s pulse amplitude modulation with four levels (PAM4) show a 30%-40% increase in optical modulation amplitude (OMA) compared to APDs with no DBR. A sensitivity of around -13 dBm at a data rate of 64 Gb/s PAM4 and a bit error rate of 2.4 x 10(-4) is realized for APDs with DBRs, which improves the sensitivity by similar to 2 dB compared to APDs with no DBR. (c) 2020 Chinese Laser Press