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A depolarizer or depolariser is an optical device used to scramble the polarization of light. An ideal depolarizer would output randomly polarized light whatever its input, but all practical depolarizers produce pseudo-random output polarization. Optical systems are often sensitive to the polarization of light reaching them (for example grating-based spectrometers). Unwanted polarization of the input to such a system may cause errors in the system's output. ==Types== ===Cornu depolarizer=== The Cornu depolarizer was one of the earliest designs, named after its inventor Marie Alfred Cornu. It consists of a pair of 45 degree prisms of quartz crystal, optically contacted to form a cuboid. The fast axes are 90 degrees apart and 45 degrees from the sides of the depolarizer (see figure). Any ray entering the prism effectively passes through two wave plates. The thickness of these wave plates and therefore their retardance varies across the beam. The phase shift is given by : .〔 〕 For an input beam of uniform polarization the output polarization will be periodic in . The phase shift is also dependent on wavelength due to dispersion. The use of two prisms means that the output is essentially coaxial with the input. At the interface between the prisms refraction does take place, as the refractive indices are exchanged. There is therefore some separation of the components of the output beam. This device is not commonly used today, but similar designs are commercially available. ===Lyot depolarizer=== The Lyot depolarizer is another early design. It was invented by Bernard Lyot. It consists of two wave plates with their fast axes 45 degrees apart, with the second plate twice the thickness of the first. The output is periodic as a function of wavelength and as a function of the wave-plates' thickness. Special considerations are needed when this depolarizer is to be used for a particular application, because the optimal wave-plate thicknesses depend on the signal wavelength and optical spectrum with which it is to be used. It is commercially available for broadband visible applications. This device is especially attractive in fiber-optics where two pieces of correct length of polarization-maintaining optical fiber spliced together at a 45° angle are used instead of the wave-plates, thus no other components such as beam splitters are required. ===Wedge depolarizer=== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Depolarizer (optics)」の詳細全文を読む スポンサード リンク
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