Tunable Flat-Top Liquid Crystal Optical Filter
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United States of America Patent
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Issued Date -
May 16, 2013
app pub date -
Oct 26, 2012
filing date -
Oct 26, 2011
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Abandoned
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Abstract
An optical wavelength filter with flat-top pass-band and tunable center wavelength is presented. The filter uses birefringence wave plates, polarizers, and electrically controlled birefringent (ECB) liquid crystal cells. The filter employs a multistage structure which is composed of a cascade of filter units. Each stage includes two polarizers, two birefringent crystal wave plates and two ECB liquid crystal cells. The pair of the thinnest wave plates have a thickness of L, and the wave plates in the following stages have thicknesses of 2 L, 4 L, . . . , 2(N−1)L. The passband bandwidth is determined by the free spectral range (FSR) of the filter stage with the thickest wave plates (with a thickness of 2(N−1)L). The ECB liquid crystal cells enable the selection of one wavelength in a certain wavelength range and the correction of the variations in retardations which are typically caused by the variation in crystals' lengths. The flat-top liquid crystal filter has a larger 0.5-dB bandwidth as compared with classical Lyot and Solc type filters. The feature of flat-top passband is important for applications in optical network and optical communications. It also has numerous applications in optical instrumentations.
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