page_title: Polarizer
section_title: Homogeneous circular polarizer
hierarchical_section_title: Polarizer / Circular polarizers / Homogeneous circular polarizer
context_page_description: A polarizer or polariser is an optical filter that lets light waves of a specific polarization pass through while blocking light waves of other polarizations. It can filter a beam of light of undefined or mixed polarization into a beam of well-defined polarization, that is polarized light. The common types of polarizers are linear polarizers and circular polarizers. Polarizers are used in many optical techniques and instruments, and polarizing filters find applications in photography and LCD technology. Polarizers can also be made for other types of electromagnetic waves besides light, such as radio waves, microwaves, and X-rays.
context_section_description: A homogeneous circular polarizer passes one handedness of circular polarization unaltered and blocks the other handedness. This is similar to the way that a linear polarizer would fully pass one angle of linearly polarized light unaltered, but would fully block any linearly polarized light that was orthogonal to it.
  A homogeneous circular polarizer can be created by sandwiching a linear polarizer between two quarter-wave plates.  Specifically we take the circular polarizer described previously, which transforms circularly polarized light into linear polarized light, and add to it a second quarter-wave plate rotated 90° relative to the first one.
  Generally speaking, and not making direct reference to the above illustration, when either of the two polarizations of circularly polarized light enters the first quarter-wave plate, one of a pair of orthogonal components is retarded by one quarter of a wavelength relative to the other. This creates one of two linear polarizations depending on the handedness the circularly polarized light. The linear polarizer sandwiched between the quarter wave plates is oriented so that it will pass one linear polarization and block the other. The second quarter-wave plate then takes the linearly polarized light that passes and retards the orthogonal component that was not retarded by the previous quarter-wave plate. This brings the two components back into their initial phase relationship, reestablishing the selected circular polarization.
  Note that it does not matter in which direction one passes the circularly polarized light.
caption: Homogeneous circular polarizer passing left-handed, counter-clockwise circularly polarized light. (Left-handed as viewed from the receiver.)[11]