Optical switch (Optical Switch, OS) is a device with one or more selectable transmission windows that can perform mutual conversion or logical operation on optical signals in optical transmission lines or integrated optical paths. The basic form of the optical switch is 2X2, that is, there are two optical fibers at the input and output ends, which can complete two connection states, parallel connection and cross connection, as shown in Figure 2. Larger space division optical switching units can be composed of basic 2X2 optical switches and corresponding 1X2 optical switches in cascade and combination.

Optical switches play a very important role in optical networks. In Wavelength Division Multiplexing (WDM) transmission systems, optical switches can be used for wavelength adaptation, regeneration, and clock extraction. In the Division Multiplex (OTDM) system, the optical switch can be used for demultiplexing; in the all-optical switching system, the optical switch is a key component of the optical cross-connect (OXC) and an important component of wavelength conversion. According to the number of input and output ports of the optical switch, it can be divided into 1×1, 1×2, 1×N, 2×2, 2×N, M×N, etc. They have different uses in different occasions. Its application scope mainly includes: optical network protection switching system, light source control in optical fiber test, real-time monitoring system of network performance, optical device test, construction of the switching core of OXC equipment, optical add/drop multiplexing, optical test, optical Sensing system, etc.