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- About Optical Isolator
About Optical Isolator
An optical isolator is an electronic component to which the "Faraday effect" of magnetooptics is applied, transmitting light only in one direction and preventing the penetration of reflected light.
The "Faraday effect" referred to here means the phenomenon where the polarization plane of light is rotated by an applied magnetic field, discovered by Faraday in 1845.
Generally, the LD (Laser Diode) of the optical transmitter is built in the LD module integrated with optical parts such as optical fiber. The optical isolator is located between the LD and optical fiber, and prevents the penetration of reflected light to the LD.
The "reflected light" referred to here means the slight amount of light that is reflected by parts such as the optical connector and returns from among the light radiated from the LD, and the penetration of the reflected light to the LD can result in troublesome noises.
Generally, the oscillation direction (polarization direction) of LD irradiating light used in optical transmitters is to be set in one particular direction.
In this case, a polarization dependent optical isolator with a simple structure is used. Crystal film with the Faraday effect is called a "Faraday rotator".
The basic structure of a polarization type optical isolator is shown below. It is composed of garnet single-crystal film, a magnet for applying a magnetic field, and two polarizer sheets located at the relative angle of 45°.
Basic structure of the polarization type optical isolator
