Optical communication parts are also called optical devices, which are divided into optical active devices and optical passive devices. Optical active devices are the key devices in optical communication systems that convert electrical signals into optical signals or convert optical signals into electrical signals. They are the heart of the optical transmission system; optical passive devices require a certain amount of energy to be consumed in optical communication systems. Devices with a certain function but no photo-electric or electrical-optical conversion function are the joints of the optical transmission system.