Light entering the Faraday rotator from the opposite direction has its phase rotated in the opposite direction (relative to the direction of propagation of the light). Light travelling in one direction through a Faraday rotator has its polarisation rotated in one particular direction. The device is symmetric in operation around a circle. Light entering at port 1 leaves at port 2, entering at port 2 leaves at port 3 and so on. Light entering at any particular port travels around the circulator and exits at the next port. The basic function of a circulator is illustrated in the figure below. There are many different designs but the key principle is like that of the optical isolator. Optical circulators are made of an assembly of optical components. Of course if you did something like this you would need to take particular care to minimise reflections on the link.Д«y itself there is no single, simple principle behind the optical circulator. This might be done to save the cost of fiber. For example, a bidirectional link consisting of two fiber strands (one for each direction) is multiplexed onto a single strand of fiber. Optical circulators are very versatile devices and may be used in many applications. Typical devices give a port-to-port loss of between 0.5 dB and 1.5 dB.

One of the great attractions of optical circulators is the relatively low level of loss. For example, if the input to the first port is directly connected to a laser we certainly donвЂ™t want spurious signals to be returned back into it. If we make sure the last port does not circulate around to the first, we can use the device in systems where we do not need (or want) this feature. While this saves some cost this is not the most important reason for doing it. Also, it is common to build an asymmetric version where the last port does not circulate around to the first. Optical Circulators are microoptic devices and can be made with any number of ports but 3 and 4 port versions are most common.

Optical isolator material