Let's understand the working principle of optical isolators

Optical isolator, also known as optical unidirectional device, is a kind of optical fiber passive device with non-reciprocal transmission of light. In the optical fiber communication system, there are always many reasons for the reverse light. For example, the signal light emitted by the light source in the optical transmitter is usually coupled to the optical fiber line in the form of a movable connector. The gap of the fiber end face at the movable joint will cause about 4% of the reflected light to be transmitted to the light source.

The existence of this kind of reverse light will cause the self-coupling effect in the optical path system, which will make the laser work unstable and produce reflection noise. The gain of the optical amplifier is changed and self-excitation occurs, causing the entire optical fiber communication system to fail to work normally. If an optical isolator is connected to the output end of the laser and the input or output end of the optical amplifier, the problem can be solved.

Therefore, the basic function of the optical isolator is to realize the forward transmission of the optical signal, while the YZ reverse light is irreversible. Under normal circumstances, the optical path of light in an isotropic or anisotropic medium is reversible. Therefore, the design of an optical isolator must consider how to break its reversibility. The current solution is to use the non-reciprocity of magneto-optical materials to adjust the polarization state of light to realize the irreversible transmission of light.