PD stands for photodiode, whose fundamental function is to convert received optical signals into electrical signals, enabling signal detection and demodulation. PD chip optical modules are core components in modern high-speed optical communication (HSC) systems. Among them, the “receiver chip” is a critical component responsible for optical-to-electrical. TOSA is used to realize the electro-optical conversion in the optical module, the built-in devices include optical laser, MPD, TEC, isolator, MUX, coupling lens, and so on. It is available in TO-CAN, Gold-BOX, COC (chip on chip), COB (chip on board), and other packaging forms.