The Fiber Optic circulator has multiple ports and its working principle is similar to that of the optical isolator. It is a single transmission device, mainly used in single fiber bidirectional transmission systems and optical splitter multiplexer. The principle of the Optical Circulator for single-fiber bidirectional transmission system: the optical signal input on port 1 is only output on port 2, and the optical signal input on port 2 is only output on port 3.