What is Optical Circulator in Optical Communication?

Optical circulator is a multi-port optical device with nonreciprocal property. It is based on the nonreciprocal polarization of an optical signal by Faraday effect. When an optical signal is input from any port, it can be output from the next port sequentially with very low loss, and the loss from this port to all other ports is very large, so these ports are not communicating with each other.

That means that optical circulator is a three- or four-port optical device designed such that light entering any port exits from the next. If light enters port 1 it is emitted from port 2, but if some of the emitted light is reflected back to the circulator, it does not come out of port 1 but instead exits from port 3. This is analogous to the operation of an electronic circulator.

 

Fiber-optic circulators are used to separate optical signals that travel in opposite directions in an optical fiber, for example to achieve bi-directional transmission over a single fiber. Because of their high isolation of the input and reflected optical powers and their 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. A Faraday rotator is another example of a non-reciprocal optical device, and indeed it is possible to construct an optical circulator based on a Faraday rotator.

 

Structure Principle
It consists of a Faraday rotator and two polarizing prisms on both sides. When polarized light passes through a Faraday rotator, its polarization plane can rotate 45°under the action of an external magnetic field. As long as the optical axes of the two polarizing prisms are set at an appropriate angle to each other, the insertion loss of the inter-connected optical paths can be very low and the isolation of the disconnected optical path is very large.

 

The optical circulator can also be formed by utilizing the characteristics of the single-mode fiber will produce the Faraday rotation effect under the action of an external magnetic field. The insertion loss and isolation of the polarization-independent optical circulator are independent of the polarization state of the incident light.

 

Technical Parameters
The technical parameters of optical circulator include insertion loss, isolation, crosstalk, polarization dependent loss(PDL), polarization mode dispersion(PDM) and return loss, etc. The definitions of insertion loss, isolation, polarization dependent loss and polarization mode dispersion of optical circulators are basically the same as those of optical isolators, except that for an optical circulator, it refers to a specific index between two adjacent ports.

What Is Optical Communication?

 Optical communication is any type of communication in which light is used to carry the signal to the remote end, instead of electrical current. The transmitted information is firstly converted into an electrical signal in the transmitting end, and then the electrical signal is modulated onto the laser beam emitted by the light source, so that the light intensity changes with the frequency of electrical signal. Based on the principle of total internal reflection, the light signal is transmitted in optical fiber.

Due to the loss and dispersion of the optical fiber, the optical signal will be attenuated and distorted over a long distance transmission. It is necessary to amplify the attenuated signal at the optical repeater and repair the distorted waveform. At the receiving end, the detector converts the optical signal into an electrical signal after receiving it, the original information will be restored after demodulation. 

 

Advantages of Optical Transmission

• Large Capacity and Long Transmission Distance
• Small Size, Light Weight, Long Life and Low Cost
• High Insulation and High Voltage Resistant
• High Temperature and Anti-corrosion
• Strong Adaptability and High Confidentiality

 

Optical communication consists of a series of optical communication devices. There are active devices and passive devices. Optical active devices are key devices in optical communication systems that convert electrical signals into optical signals or convert optical signals into electrical signals. Optical passive devices mainly include optical fiber patch cables, wavelength division multiplexers(WDM), optical splitters, optical switches, optical circulators and optical isolators, etc.

 

Optical fiber patch cord is a fiber optic cable with connectors at both ends to realize the connection of optical path. The cable with only one connector is called pigtail.

In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths. This technique enables bidirectional communications over a single strand of fiber, also called wavelength-division duplexing, as well as multiplication of capacity.

 

A optical splitter is an optical device that splits a beam of light in two or more. There are two types of splitters: FBT couplers and PLC splitters.

 

Optical Switch is a device that switches or amplifies optical signals. It is mainly used to realize the physical switching of optical signal or other logical operation in optical path, and is often used as the key device of optical cross connection (OXC) technology to switch optical path.

An optical circulator is a three- or four-port optical device designed such that light entering any port exits from the next. This means that if light enters port 1 it is emitted from port 2, but if some of the emitted light is reflected back to the circulator, it does not come out of port 1 but instead exits from port 3.

 

An optical isolator is an optical component which allows the transmission of light in only one direction. The working principle is based on the non-reciprocity of Faraday rotation. Optical Isolator is typically used to prevent unwanted feedback into an optical oscillator, such as a laser cavity.