Fiber Optic Circulator Applications

• Add-Drop Multiplexing
• Fiber Sensors
• Bi-directional Pumping
• Bi-directional Signal Transmission Systems
• Coupling In-line Chromatic Dispersion Compensation Devices

Fiber optic circulators are non-reciprocating, one directional, three-port devices that are used in a wide range of optical setups and for numerous applications. An optical circulator is analogous to an electronic circulator and both perform similar functions. An optical circulator is a three-port device that allows light to travel in only one direction. A signal entered to Port 1 will exit Port 2, while a signal entering Port 2 will exit Port 3 all with minimal loss. Light entering port 2 experiences a large amount of loss at port 1, and light entering port 3 experiences a large amount of loss at ports 2 and 1.

Optical circulators are non-reciprocal optics. This means that any change in the properties of the light caused by passing through the device are not reversed by traveling in the opposite direction. Another example of non-reciprocal optics are Faraday rotators which are sometimes used in isolators. Because of its high isolation and low insertion loss, optical circulators are widely used in advanced communication systems as add-drop multiplexors, bi-directional pumping, and chromatic dispersion compensation devices. The example to the right depicts the use of a circulator to drop an optical channel from a DWDM system using a fiber bragg grating. The input DWDM channels are coupled into Port 1 of the device with a FBG device connected to Port 2. The single wavelength reflected off the FBG then reenters the circulator in port 2 and is routed accordingly to Port 3. The remaining signals pass through the FBG and exit on the top fiber.

Circlulators can also be used to send optical signal in two directions down a single fiber. A circulator is located at both ends of the fiber. Each circulator functions to add a signal in one direction while removing the signal in the other. See the example below.