Faraday isolator

An optical isolator, or optical diode, is an optical component which allows the transmission of light in only one direction. It is typically used to prevent unwanted feedback into an optical oscillator, such as a laser cavity.

The operation of [some of] the devices depends on the Faraday effect (which in turn is produced by magneto-optic effect), which is used in the main component, the Faraday rotator.

The main component of the optical isolator is the Faraday rotator. The magnetic field, ${\displaystyle B}$, applied to the Faraday rotator causes a rotation in the polarization of the light due to the Faraday effect. The angle of rotation, ${\displaystyle \beta }$, is given by,

where, ${\displaystyle \nu }$ is the Verdet constant of the material (amorphous or crystalline; solid, liquid, or gaseous) of which the rotator is made, and ${\displaystyle d}$ is the length of the rotator. This is shown in Figure 2. Specifically for an optical isolator, the values are chosen to give a rotation of 45°.

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