Exploring Optical Circulators: Categories, Functionality, And Benefits

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An optical circulator is designed to transfer light from one optical fibre to another. It is a non-reciprocal device that routes light according to the direction of propagation. Light can be moved forward using either an optical circulator or an optical isolator. However, the optical isolator often loses more light energy than the optical circulator. Optical circulators normally have three ports: two input ports and one output port. Many applications only require two, therefore they can be designed to restrict any light entering the third port.


Technologies for optical circulator components


An optical circulator consists of a Faraday rotator, a birefringent crystal, a wave plate, and a beam displacer. The Faraday rotator employs the Faraday Effect, a phenomenon in which the polarisation plane of an electromagnetic wave is rotated in a material by a magnetic field applied parallel to the propagation direction of the light wave. Light propagation in a birefringent crystal is determined by the polarisation state of the light beam and the crystal's orientation. The beam's polarisation can be ...
... adjusted, or it can be divided into two beams with orthogonal polarisation states. Wave plate and beam displacer are two distinct types of birefringent crystals. A wave plate can be created by cutting a birefringent crystal in a certain orientation so that the optic axis is in the incident plane and parallel to the crystal border. The beam displacer splits an incoming beam into two beams with orthogonal polarisation states.


Categories of Optical Circulators


Polarisation determines whether an optical and Fiber Circulator is polarization-dependent or polarization-independent. The former is utilised for light with a specific polarisation state, whereas the later is not limited to the polarisation state of light. Most optical circulators used in fibre optic communications are designed to be polarization-independent.


Optical circulators are categorised into two types based on their functionality: full circulators and quasi-circulators. As previously stated, full circulators make full use of all ports in a complete cycle. Light travels from port 1 to port 2, then to port 3, and finally back to port 1. Regarding the quasi-circulator, light flows through all ports sequentially, but light from the last port is lost and cannot be sent back to the first port. For most purposes, a quasi-circulator is sufficient.


Optical Circulator Applications: - Duplex Transmitter/Receiver System Optical circulators can be used to achieve two-way transmission over a single fibre. Transmitter 1 sends a signal through Circulator 1's Port 1 and then through the fibre to Circulator 2's Port 2, where it is routed to Receiver 2. The signal from Transmitter 2 travels the opposite direction to Receiver 1.


Double Pass Erbium Doped Amplifier: This approach enables high-gain signal amplification via an erbium-doped fibre amplifier. The signal travels via an optical circulator and an optical amplifier before returning from the fibre optic reflector and passing through the amplifier again. The amplified signal is routed through the return port.


Wave Division Multiplexing System: Optical circulator and Bragg gratings work together to reflect and send certain wavelengths along multiple pathways.

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