Introduction to the working principle of optical isolator

Optical isolators mainly use the Faraday effect of magneto-optical crystals. The Faraday effect is the first observation by Faraday in 1845 that a non-optically active material rotates the polarization direction of light passing through the material under the action of a magnetic field. It is also called the magneto-optical rotation effect. For polarized light transmitted in the direction of the magnetic field, the rotation angle θ of the polarization direction and the product of the magnetic field strength B and the length L of the material are proportional.

For the signal light incident in the normal direction, it becomes linearly polarized light after passing through the polarizer. Together with the external magnetic field, the Faraday gyromagnetic medium rotates the polarization direction of the signal light by 45 degrees to the right, and makes the low loss pass 45 degrees with the polarizer. Degree of analyzer placed. For reverse 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 polarization direction of the reverse light is orthogonal to the direction of the polarizer, completely blocking the transmission of reflected light .

The Faraday magnetic medium usually adopts yttrium iron garnet (YIG) single crystal with low optical loss in the wavelength range of 1 μm to 2 μm. The optical isolator of the new pigtail input and output has quite good performance, the minimum insertion loss is about 0.5dB, the isolation is 35-60dB, and the highest can reach 70dB.