Optical Isolator Working and Its Applications

In the year 1842, Michael Faraday was stated that the optical isolator operation depends on the Faraday Effect. This effect refers to a fact that the polarized light plane turns when the light energy transmits through the glass that can be exposed toward a magnetic field. The direction of rotation mainly depends on the magnetic field as an alternative of the light transmission direction.

The optical devices as well as connectors in a fiber optic system cause some effects like absorption, and reflection of the optical signal on the o/p of the transmitter. So, these effects may cause light energy. These effects may cause light energy to be reproduced back at the supply and obstruct with supply function. To overcome the interference effects, an optical diode or optical-isolator is used.

What is an Optical Isolator?

An optical isolator is also known as an optical diode, photocoupler, an optocoupler. It is a passive magneto-optic device, and the main function of this optical component is to permit light transmission in one direction only. So it plays a main role while preventing unnecessary feedback to an optical oscillator namely laser cavity. The working of this component mainly depends on the Faraday’s effect which is used in the main component like Faraday rotor.

Working Principle

An optical isolator includes three main components namely a Faraday rotator, i/p polarizer, & an o/p polarizer. The block diagram representation is shown below. The working of this is like when light passes through the i/p polarizer in the forward direction & turn into polarized within the vertical plane. The operation modes of this isolator are classified into two types based on the different directions of light such as forward mode & backward mode.


In forward mode, the light enters into the input polarizer then becomes linearly polarized. Once the light beam arrives at the Faraday rotator, then the rod of the Faraday rotator will turn with 45°. Therefore, finally, the light leaves from the o/p polarizer at 45°. Similarly in backward mode, initially the light enters into the o/p polarizer with a 45°. When it transmits throughout the Faraday rotator, rotates continuously for another 45° in a similar path. After that, the 90° polarization light turns into vertical toward the i/p polarizer & cannot depart the isolator. Thus, the light beam will be either absorbed or reflected.

Types of Optical Isolator

Optoisolators are classified into three types which include Polarized, Composite, and Magnetic optical-isolator


Polarized Type Optical-Isolator

This isolator uses the polarization axis to keep light transmit in one direction. It allows light to transmit in forwarding direction, however, prohibits every light beam to transmit back. Also, there are dependent and independent polarized optical-isolators. The latter is more complicated and often used in EDFA optical amplifier.

Composite Type Optical-Isolator

This is an independent polarized type optical-isolator, which can be used in EDFA optical amplifier which includes different components like wavelength-division multiplexer (WDM), erbium-doped fiber, pumping diode laser, etc..

Magnetic Type Optical-Isolator

This type of isolator is also named as the polarized optical-isolator in a new face. It pressures the magnetic element of a Faraday rotator, which is usually a rod designed with a magnetic crystal beneath the strong magnetic field through Faraday Effect.


Optical isolators are used in different optical applications like an industrial, laboratory, and corporate, settings. They are dependable devices while used during conjunction with fiber optic amplifiers, fiber optic links in CATV, fiber optic ring lasers, high-speed logical FOC systems.




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