Appendix J: Photodetectors

This appendix explains the background of materials and wavelengths for photodetectors (PDs) and noise in PDs. Operation principles and photon detection mechanisms in p‐i‐n, APD‐, DPD‐, SPAD‐, and Si‐PM‐based commercial products are discussed. The p‐i‐n–based PDs are used in datacom modules, while APD and SPAD arrays are very popular in consumer (mobile) and automotive (LiDARs) industries for single‐photon counting in low‐light ambient at NIR wavelengths. Superconductor‐based PDs with key attributes of noiseless (zero dark counts), sub‐20 picosecond response times with near 100% quantum efficiency is also discussed for long‐range single‐photon detection applications in SWIR and MIR wavelengths.