Optical isolator is a two-port optical device with non-reciprocal characteristics. It has little attenuation to the optical signal transmitted along the forward direction and great attenuation to the optical signal transmitted along the opposite direction, forming a one-way path of light. In the laser and transmission fiber, the optical isolator can effectively suppress the reflected light generated from the optical fiber distal end face and optical fiber connector interface to return to the laser, so as to ensure the stability of the laser working state and reduce the system noise caused by reflected light. This is especially important for high rate coherent optical fiber communication systems. https://www.glsunmall.com/fiber-optic-articles/types-and-working-principles-of-optical-isolators.html