Abstract.
Solids with spatially varying photonic structure offer gaps to light of a wider range of frequencies than do simple photonic systems. We solve numerically the field distribution in a cholesteric with a linearly varying inverse pitch (helical wavevector) using equations we derive for the general case. The simple idea that the position where the Bragg condition is locally satisfied is where reflection takes place is only true in part. Here, reflection is due to a region where the waves are forced to become evanescent, and the rate of variation of structure determines over which distance the waves decay and therefore how complete reflection is. The approximate local Bragg-de Vries schemes are shown to break down in detail at the edges of the gap, and an analytical estimate is given for the transmission coefficient.
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Received: 9 September 2003, Published online: 5 February 2004
PACS:
42.70.Df Optics: liquid crystals - 61.30.-v Structure of solids and liquids: liquid crystals - 78.20.Bh Optical properties of bulk materials and thin films: theory, models, and numerical simulation
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Kutter, S., Warner, M. Reflectivity of cholesteric liquid crystals with spatially varying pitch. Eur. Phys. J. E 12, 515–521 (2003). https://doi.org/10.1140/epje/e2004-00023-6
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DOI: https://doi.org/10.1140/epje/e2004-00023-6