Optical Circulator: Working Principle, Uses and Applications in Fibre Optic Networks

An optical circulator is a nonreciprocal passive component with many ports.

Similar to a microwave circulator, an optical circulator blocks light transmission from one port to the previous port while simultaneously transmitting a light wave with maximum intensity from one port to the subsequent port. The nonreciprocal polarisation rotation of the Faraday effect serves as the foundation for optical circulators.

Optical Circulators' Uses

Initially, optical circulators were employed in telecommunications systems to boost the transmission capacity of pre-existing networks. In a bi-directional transmission system, optical circulators can quickly increase the network's transmission capacity without requiring the deployment of more fibres, which has become more costly.

However, the applications of fiber circulators have significantly expanded into not only the telecommunication industries but also the sensing and imaging fields due to the quick development of optical communication technologies and the easy access to inexpensive, high-performing circulators. In sophisticated optical networks like DWDM networks, optical circulators are now a crucial component.

The transmitters and receivers in the conventional bi-directional optical communication system were coupled using a 50/50 (3 dB) coupler, which divides a light beam into two beams of equal intensity. Nevertheless, this type of construction has two primary issues. The first is the requirement for an optical isolator in the transmitters to prevent light crosstalk between the transmitters; the second is the high insertion loss associated with the 50/50 coupler because two couplers must be used, each of which has a minimum loss of 3 dB, resulting in a minimum 6 dB reduction of the system's link budget.

Strong tools for removing optical signals from a reflecting object is an optical circulator. As a result, optical circulators frequently work in tandem with fibre Bragg gratings, which are generally reflective devices. Optical circulators are now one of the essential components of sophisticated DWDM optical networks, along with fibre Bragg gratings. In addition to being used as MUX/DEMUX devices, circulators are also employed in tunable optical Add/Drop, dispersion compensation, and other applications using the fibre Bragg grating.