Polarizers and Retardation Plate

Most hquid crystal optical devices make use of the birefringence of the liquid crystal in combination with a multitude of optical elements to control, modulate, or switch 

For +7i/2 or -nil (i.e., quarter wave) phase shift, the two components add up to a circularly polarized light. For n or -n phase shift, the light is again linearly polarized, but along a direction that is 90° with respect to the incident linear polarization direction. For other values of the phase difference, the light acqrrires elliptical polarizations. 

Note on conventions In this book, we use the convention typically nsed in optics texts— from the observer s point of view with light propagating towards the observer to denote the handedness of the circular or elliptical polarizations. Also, unless otherwise specifically stated, we express a plane propagating wave as e where 

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The first application arising as a result of Eqs. (3) and (4) is in optical filters. Here the selective transmission or reflective properties are used to select a narrow spectral band [9, 181-183], i.e., notch filters, or even a wide spectral band [184], of optical frequencies. As a result of the circular polarization properties, this also leads to the production of polarizers and retardation plates [181]. The light reflected from a planar or Grand-jean texture is either right- or left-handed cireularly polarized at normal incidence. The eombination of two such films of opposite handedness leads to notch and band pass filters capable of selecting bandwidths of a few nanometers or so, depending on Eqs. (3) and (4) from an unpolarized spectrum, i.e.. 

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