"Version: 20231001"--Title page verso.Includes bibliographical references.1. Motivation -- 1.1. PIN-photodiode and APD receivers -- 1.2. SPAD receivers -- 1.3. Quantum image sensors -- 1.4. The principle of ultra-sensitive PIN and avalanche photodiode receivers2. Basics of photodiodes -- 2.1. Optical absorption and photogeneration -- 2.2. Drift and diffusion -- 2.3. Width of space-charge region…