Fiber Optic Faraday Rotators Information
Fiber optic Faraday rotators take the output from single-mode optical fibers and rotate the polarization by a specified amount. They eliminate the state of polarization (SOP) variations that can occur in standard single-mode optical fiber due to thermal and mechanical perturbations. Faraday rotators can compensate for these fluctuations that are often undesirable in sensitive fiber optic systems requiring a precise SOP.
Faraday rotators have many applications ranging from polarization control in fiber laser systems to polarization sensitivity elimination in bulk diffraction grating systems. Polarization-induced fluctuations can be eliminated with Faraday rotators in fiber based interferometers, fiber sensors, Brillouin amplifier systems, remote fiber optic antenna systems, and other fiber laser systems.
Fiber optic Faraday rotators rely on a magnetic field to alter the polarization of a light beam. A magnetic field is imposed upon light passing through a transparent medium by a surrounding magnet. The polarization of the light is rotated by a total angle depending on the length of the transmitting medium, the Verdet constant of the medium, and the magnetic flux density along the direction of propagation.
The process can be understood by considering the beam of light as a superposition of two circularly polarized beams. A difference in phase velocity between the two components is created by the magnetic field, with the resulting change in linear polarization direction corresponding to the relative phase shift.
The following specifications are important when selecting a fiber optic Faraday rotator:
- Center wavelength (nm)
- Wavelength range (nm)
- Insertion loss, typical (dB)
- Insertion loss, maximum (dB)
- Faraday rotation angle (°)
- Rotation angle tolerance @ 23° C
- Rotation angle wavelength dependence
- Reflection polarization dependence
- Maximum optical power
- Fiber type
- Operating temperature range (°C)
- Storage temperature range (°C)
RP Photonics Encycopedia—Faraday Rotators