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The Field-Induced Stop-Bands and Lasing Modes in CLC Layers with Deformed Lying Helix

Shubnikov Institute of Crystallography of Federal Scientific Research Centre “Crystallography and Photonics” of Russian Academy of Sciences, Leninskii pr.59, Moscow 119333, Russia
Crystals 2019, 9(9), 469; https://doi.org/10.3390/cryst9090469
Received: 19 August 2019 / Revised: 30 August 2019 / Accepted: 4 September 2019 / Published: 8 September 2019
(This article belongs to the Special Issue Localized Optical Modes in Liquid Crystals)
Waveguide optical properties of a cholesteric liquid crystal (CLC) layer with a deformed lying helix (DLH) have been studied by numerical simulations using the finite difference time domain method. The DLH structure, when the helix’s axis is oriented in plane of a CLC layer, is induced by an electric field in a virtual CLC cell with periodic (planar/homeotropic) boundary conditions at one of the alignment surfaces. This in-plane helical structure is stable only in a permanently applied electric field providing the helix deformation. In this work the polarized light reflectance spectra have been studied at different electric fields and light impingement into a waveguide formed by the DLH layer. It is found that for light propagating along the helix axis the reflectance spectrum has multiple stop-bands centred at wavelengths λ j = 2 p n j , which is different from set of bands located at λ j = p n j , and characteristic of CLC spectra for the Grandjean-plane textures subjected to distortion by an electric or magnetic field perpendicular to the helix axis, where j is a natural number, p is the helix pitch and n is the average refractive index. Each of the higher order (j > 1) bands consists of three polarization-dependent sub-bands. In the case of an amplifying CLC DLH layer, depending on an extent of the helix deformation, the lasing modes can be excited at different edges of the sub-bands. While at the strongest deformation the lasing is preferable at the edges of the central sub-band; a lower extent of deformation makes favourable conditions for the lasing at edges of the two other sub-bands. View Full-Text
Keywords: cholesteric liquid crystals; deformed lying helix; photonic liquid crystals; liquid crystal lasers cholesteric liquid crystals; deformed lying helix; photonic liquid crystals; liquid crystal lasers
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Palto, S.P. The Field-Induced Stop-Bands and Lasing Modes in CLC Layers with Deformed Lying Helix. Crystals 2019, 9, 469.

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