Optical Isolator

The main use of the isolating device is to protect the laser and an unstable system that the reflection of amplifier leads to, and its function lies in high return loss and causes the reflecting energy that is generated where it was a discontinuous medium to reduce its power.

One of common manufacturing methods is to utilize the magnetic field effect of Faraday crystal. As picture show that, at the beginning, the light source is inputted by the left end then the light is formed a very linearly polarization that we assume it is vertical when it passes through the polarizer.

After the Faraday rotator, the polarization is rotated 45 degrees. What follows is being lined by passing the second polarizer of 45 degree. Finally, the light that it has the polarization of 45 degree is outputted.

If we are viewed from reflecting view, as the light source being from the output end enters the polarizer and is lined to 45 degree. Later, it is rotated 45 degree again that causes the backward light is rotated total 90 degree and makes a transition to parallel light. At this time, the polarizations are perpendicular to one another, the front polarizer is vertical and the light is parallel, that it causes no light to pass through the polarizer. In short, the light can not pass through backward because it will be reduced to near zero.

For this reason, we can understand that isolator is an irreversible component and has different insertion loss between forward and backward directions. Generally speaking, it is 0.2 to 2dB forwardly and the backward is 20 to 40dB, and its return loss is greater than 60dB.