What Is an Optical Isolator?

An optical isolator is a passive optical device that allows only unidirectional light to pass through. Its working principle is based on the non-reciprocity of Faraday rotation. The light reflected by the fiber echo can be well isolated by the optical isolator. Optical isolators mainly use the Faraday effect of magneto-optical crystals. The characteristics of optical isolators are: low forward insertion loss, high reverse isolation, and high return loss. Optical isolator is a passive device that allows light to pass in one direction and prevents it from passing in the opposite direction. The function is to limit the direction of light so that light can only be transmitted in one direction. The light reflected through the fiber echo can be used by the optical isolator. Good isolation to improve light wave transmission efficiency

An optical isolator is a passive optical device that allows only unidirectional light to pass through. Its working principle is based on the non-reciprocity of Faraday rotation. The light reflected by the fiber echo can be well isolated by the optical isolator. Optical isolators mainly use the Faraday effect of magneto-optical crystals. The characteristics of optical isolators are: low forward insertion loss, high reverse isolation, and high return loss. Optical isolator is a passive device that allows light to pass in one direction and prevents it from passing in the opposite direction. Its role is to limit the direction of light so that light can only be transmitted in one direction. Good isolation to improve light wave transmission efficiency

Chinese name

Optical isolator

Foreign name

optical isolator

Types of

Passive optical device

Function

Prevent light path from adversely affecting

Features

High isolation, low insertion loss; high reliability, etc.

Optical isolator introduction

A two-port non-reciprocal optical device. It has a small attenuation for the optical signal transmitted in the forward direction and a large attenuation for the optical signal transmitted in the opposite direction, forming a unidirectional path of light. Connecting an optical isolator between the laser and the transmission fiber can effectively suppress the reflected light from the end of the fiber at the end of the line, the interface of the fiber connector, etc., from returning to the laser, thereby ensuring the stability of the laser working state and reducing the system caused by reflected light Noise. This is even more important for high-speed fiber-optic communication coherent optical fiber communication systems.

Optoisolators are required to have low insertion loss (eg 0.5dB), low isolation reverse loss, or large forward loss (eg 30dB).

There are many types of optical isolators, including block optical isolators, all-fiber optical isolators, integrated optical waveguide optical isolators, and polarization-independent optical isolators.

Optical isolator function

Its role is to prevent the backward transmission light generated in the optical path due to various reasons from generating to the light source and the optical path system.

Optical isolator samarium cobalt magnetic ring

Adverse effects. For example, installing an optical isolator between the semiconductor laser source and the optical transmission system can greatly reduce the adverse effect of reflected light on the stability of the spectral output power of the light source. In a high-speed direct modulation and direct detection optical fiber communication system, the backward transmission light will generate additional noise, which will degrade the performance of the system, which also needs an optical isolator to eliminate it. Installing optical isolators at the two ends of the doped fiber in the fiber amplifier can improve the working stability of the fiber amplifier. Without it, the backward reflected light will enter the signal source (laser), causing severe fluctuations in the signal source. In coherent optical long-distance optical fiber communication systems, installing an optical isolator every other distance can reduce the power loss caused by stimulated Brillouin scattering. Therefore, optical isolators play an important role in optical fiber communication, optical information processing systems, optical fiber sensing, and precision optical measurement systems.

At present, there are many applications in on-chip integrated all-optical paths. Now the research focuses on how to integrate the optical isolator and the on-chip COMS circuit.

Optical isolator features

Optical isolator is characterized by high isolation, low insertion loss; high reliability, high stability; extremely low polarization-dependent loss and polarization mode dispersion.

Optical isolator type

There are many types of optical isolators, including in-line optical isolators, free-space optical isolators, etc.

Optical isolator

Various specifications of optical isolators are used to meet the needs of different application areas. The internal design of 1310/1480 / 1550nm polarization-independent optical isolators is designed for the processing of two orthogonal polarization states in a single-mode fiber to ensure the polarization-independent characteristics of the entire device. Unipolar devices have lower insertion loss, and dual-stage devices have extremely high optical isolation, suitable for different applications, mainly used in fiber amplifiers, fiber lasers, fiber CATV networks, and satellite communications.

Optical isolators are generally distinguished by wavelength, there are many 800-1300nm, and there are some special wavelengths.

Connect the output end of the LD light source to the optical power meter through an optical fiber jumper, and read its output power from the optical power meter, that is, the input power of the optical isolator.

Optical isolator works

Optical isolators mainly use the Faraday effect of magneto-optical crystals. The Faraday effect is that Faraday first observed in 1845 that a material without optical rotation rotates the polarization direction of light passing through the material under a magnetic field. It is also called the magneto-optical rotation effect. For polarized light transmitted in the direction of the magnetic field, the polarization direction rotation angle and the product of the magnetic field strength B and the length L of the material are proportional. The working principle of the optical isolator is shown in Figure 1.

For the signal light that is incident in the forward direction, it becomes linearly polarized light after passing through the polarizer. The Faraday rotator media together with the external magnetic field makes the polarization direction of the signal light turn 45 degrees to the right, and makes the low loss pass through 45 with the polarizer. Placed analyzer. For reversed light, when the linearly polarized light exiting the analyzer passes through the placement medium, the deflection direction is also rotated 45 degrees to the right, so that the direction of polarization of the reversed light is orthogonal to the direction of the polarizer, completely blocking the transmission of reflected light. .

Faraday magnetic medium usually uses yttrium iron garnet (YIG) single crystal with low optical loss in the wavelength range of 1 m to 2 m. The new type of pigtail input and output optical isolator has fairly good performance, with a minimum insertion loss of about 0.5dB, an isolation of 35 to 60dB, and a maximum of 70dB.