Core Components of an Optical Circulator

An optical circulator is a three- or four-port designed such that entering any port exits from the next. This means that if light enters port 1 it is emitted from port 2, but if some of the emitted light is reflected back to the circulator, it does not come out of port 1 but instead exits from port 3. This is analogous to the operation of an electronic. Fiber-optic circulators are used to separate optical signals. [pdf]