Optical Isolator Magnet – Optical Isolator Working and 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.

The optical isolator is an optical component which allows the transmission of light in only one direction. It can be used to prevent reflected light feedback into the optical device. Optical isolator has been widely used in optical communication and laser field. The optical isolator mainly exploited the Faraday Effect of the magneto-optic crystal, and the Faraday Effect is a kind of magneto-optic effect.

What is magneto-optical effect?
The magneto-optical effect refers to the effect of the strong magnetic field to the interaction between matter and light. The electromagnetic wave will generate several phenomena when propagate through the medium that has been altered by the presence of the quasi static magnetic field. The common magneto-optical effect includes:

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.

Types of Optical Isolator
According to the polarization characteristics, optical isolator can be divided into polarization independent type and polarization dependent type.

The polarization dependent isolator, or Faraday isolator, is made of three parts, an input polarizer, a Faraday rotator, and an output polarizer, called an analyser (polarized at 45°). Polarization dependent isolators are typically used in free space optical systems. This is because the polarization of the source is typically maintained by the system. In optical fiber systems, the polarization direction is typically dispersed in non polarization maintaining systems. Hence the angle of polarization will lead to a loss.

The polarization independent isolator is made of three parts, an input birefringent wedge, a Faraday rotator, and an output birefringent wedge. Typically collimators are used on either side of the isolator. In the transmitted direction, the beam is split and then combined and focused into the output collimator. In the isolated direction the beam is split, and then diverged, so it does not focus on the collimator.

Optical Isolator Magnet – Optical Isolator Working and Applications
Optical isolator is used in many optical applications in corporate, industrial, and laboratory settings. They are reliable devices when used in conjunction with fiber optic amplifiers, fiber optic ring lasers, fiber optic links in CATV applications, and high-speed and coherent fiber optic communication systems. Single polarization fiber optic isolators are also used with laser diodes, gyroscopic systems, optical modular interfaces, and a variety of other mechanical control and testing applications.

Conclusion
From the text, we can get basic Knowledge of optical isolator. It plays an important role in fiber optic system by stopping back-reflection and scattered light from reaching sensitive components, particularly lasers. For more information about optical isolator, you can visit Fiberstore.

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.

The operating principle of the optical isolator base on the nonreciprocity of Faraday rotation. The main part of the optical isolator is the so-called Faraday rotator. The Faraday rotator consists of Terbium Gallium Garnet (TGG) magneto-optical crystal and high performance permanent magnet.

The magneto-optical crystal needs to apply the suitable magnetic field. The permanent magnet should provide enough magnetic field in the space of magneto-optical crystal, then the cost can be reduced through the decrease of crystal. Both SmCo magnet and NdFeB magnet can be served as the optical isolator magnet.

Optical Isolator Magnet

Optical Isolator Magnet

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.

Applications
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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