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 d Bm at a data rate of 64 Gb/s PAM4 and a bit error rate of 2.4×10^-4 is realized for APDs with DBRs,which improves the sensitivity by^2 d B compared to APDs with no DBR.