Comunication System A general term for the technical systems used to accomplish the process of information transmission. Modern communication systems are mainly realized through the propagation of electromagnetic waves in free space or the transmission mechanism of the guiding medium, the former being known as wireless communication systems and the latter as wired communication systems. When the wavelength of electromagnetic waves reaches the light wave range, such a telecommunication system is specifically referred to as an optical communication system, while communication systems in the other electromagnetic wave ranges are referred to as electromagnetic communication systems, or telecommunication systems for short. Wired optical communication systems are also known as fibre optic communication systems because the guiding medium for light is a special glass fibre. Generally speaking, the guiding medium for electromagnetic waves is a wire, which can be divided into cable communication systems and open-wire communication systems according to their specific structure; wireless telecommunication systems can be divided into microwave communication systems and short-wave communication systems according to the wavelength of their electromagnetic waves. On the other hand, according to the different communication services, communication systems can be divided into telephone communication systems, data communication systems, fax communication systems and image communication systems. As people's requirements for communication capabilities become higher and higher, and the requirements for communication services become more and more diverse, communication systems are developing rapidly in the direction of broadband, and optical fibre communication systems will play an increasingly important role in communication networks.