Technotes Faraday isolator

Faraday isolator: Working Principle

Effects on the input beam

  • 1 Polarizing beam splitter eliminates the s-polarized portion (typically 1%) of the laser (diode) radiation
  • 2 Faraday crystal in a strong magnetic field rotates the ­input polarization plane 45°
  • 3 Polarizing beam splitter exactly aligned with the output polarization plane, i.e. by 45°with respect to the input polarization

Effects on the back-reflected beam

  • 4 Reflective or scattering surfaces cause polarized or ­depolarized reflected signals 
  • 5 Polarizing beam splitter (3) eliminates the s-polarized portion of the reflected signal 
  • 6 Faraday rotator (2)  rotates the polarization plane by a further 45° so that the polarization plane of the reflected signal is now rotated by 90° from the polari­zation plane of the input beam 
  • 7 Polarizing beam splitter (1) blocks the reflected signal