An optical circulator is a special fiber-optic component that can be used to separate optical powers that travel in opposite directions in one single optical fiber, analogous to the operation of an electronic circulator. An optical circulator is a three-port device that allows light to travel in only one direction?from port 1 to port 2, then from port 2 to port 3. This means that if some of the light emitted from port 2 is reflected back to the circulator, it is directed not back to port 1, but on to port 3. Circulators can also be used to achieve bi-directional transmission over a single fiber. Because of its high isolation of the input and reflected optical powers and its low insertion loss, optical circulators are widely used in advanced communication systems and fiber-optic sensor applications.
Optical circulators are non-reciprocal optics, which means that changes in the properties of light passing through the device are not reversed when the light passes through in the opposite direction. This can only happen when the symmetry of the system is broken, for example by an external magnetic field or a material with optical activity. A Faraday rotator is another example of a non-reciprocal optical device.
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