A polarization rotator is an optical device that rotates the polarization axis of a linearly polarized light beam by an angle of choice. These rotators are either based on the principle of birefringence or on total internal reflection.
Wavelength specific polarization rotators
Half-wave plates and quarter-wave plates: these rotators work due to the principle of birefringence. Their performance is wavelength specific; a fact that may be a limitation. Switchable wave plates can also be manufactured out of liquid crystals or ferro-electric liquid crystals. These devices can be used to rapidly change the angle of polarization in response to an electric signal.
Broadband polarization rotators
Double Fresnel rhomb: rotates the linear polarization axis by 90 degrees. Works on total internal reflection and it uses four internal reflections. A disadvantage may be a low ratio of useful optical aperture to length.
Broadband prismatic rotator: rotates the linear polarization by 90 degrees. Works on total internal reflection and it uses seven internal reflections to induce collinear rotation. The polarization is rotated in the second reflection, but that leaves the beam in a different plane and at a right angle relative to the incident beam. The other reflections are necessary to yield a beam with its polarization rotated and collinear with the input beam. These rotators are reported to have transmission efficiencies better than 94%. The term broadband indicates that the rotation is independent of wavelength, or achromatic.
Rotators of linearly polarized light have found widespread applications in modern optics since laser beams tend to be linearly polarized and it is often necessary to rotate the original polarization to its orthogonal alternative.
- F. J. Duarte, Tunable Laser Optics (Elsevier-Academic, New York, 2003) Chapter 5.
- F. J. Duarte, Optical device for rotating the polarization of a light beam, US Patent 4822150 (18th of April, 1989).
- J. M. Bennett and H. E. Bennett, Polarization, in Handbook of Optics, W. G. Driscoll and W. Vaughan, Eds. (McGraw-Hill, New York, 1978) Chapter 10.
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