Introduction to Polarization rotator
As the name suggests, a polarization rotator is basically an optical device that rotates the axis of propagation of a linearly polarized beam of light by an angle of choice. These types of devices are based on the Faraday effect, on total internal reflection, or on birefringence. The rotator of linearly polarized light has found wide application in modern optics because laser beams are linearly polarized and it is often necessary to rotate the original polarizer to its orthogonal substitute.
A Faraday operator basically consists of an optical material in a magnetic field. When the light propagates or travels through a material, interaction with the magnetic field results in the right and left-handed circularly-polarized waves propagate having a slight difference in the phase velocities. Although, wan describe the linearly-polarized wave as a combination or superposition of left- and right-handed circularly polarized waves, the difference in phase velocity causes the polarization direction of a linearly-polarized wave to rotate as it travels through the material. The beamsplitter coating and glass mirror coating both are done on polarization rotators to improve its efficiency. The direction of the rotation is decided by whether the propagation of light is done with or against the direction of the magnetic field: a rotation generated by passing through the material cannot be reversed by making it pass through the material in the opposite direction. It can be used to create an optical isolator.
Qualter-wave plates and half-wave plates keep changing the polarization of light due to the principle of birefringence. Their performance is wavelength-specific: a fact that can be a limitation. We can also use the Ferro-electric liquid crystals, liquid crystals, or magneto-optic crystals in order to manufacture switchable wave plates. We can also use this device to instantly change the angle of polarization in the response to an electrical field and can be used for polarization state analysis (PSA) or polarization state generation (PSG) with high accuracy. In particular, PSGs and PSAs created with magneto-optic (MO) switches were successfully used to analyse polarization mode dispersion (PMD) and polarization-dependent loss (PDL) with precision in rotating waveplate methods is thanks to the binary nature MO switch. In addition, the generation of the differential group delay for PMD compensation and PMD emulation applications has also been successfully adopted by the switches.