High efficiency reflective liquid crystal polarization gratings

Abstract

We experimentally demonstrate a reflective-mode liquid crystal polarization grating with high reflectance, small grating period, and subms switching times. This switchable optical element can diffract ∼100% into a single order, have highly polarization-sensitive first orders, and have a polarization-insensitive zero order. Here we introduce an absorbing layer that overcomes the reflection of the (ultraviolet) holographic beams, which otherwise prevents high quality fabrication. At a grating period of 2.1 μm, we report 98% diffraction efficiency, 90% reflectance, ∼600:1 contrast-ratio, and ∼3000:1 polarization contrast. These elements can therefore be configured as polarization-independent modulators or switchable polarizing beam splitters, for use in telecommunications, displays, spatial-light modulators, and polarimetry.

One-Step Holographic Photoalignment for Twisted Nematic Liquid Crystal Gratings

“…Generally, light propagating inside the diffractive optical element is diffracted by inducing a phase difference to the light propagating through a medium whose shape or isotropic refractive index is periodically modulated. In addition, anisotropic diffractive optical elements in which the optical anisotropy is periodically modulated have been reported [1][2][3][4][5][6][7][8][9][10]. Anisotropic diffractive optical elements show the polarization controllability which the diffraction efficiency and polarization states depend on the polarization states of the incident beams.…”

“…Therefore, with simultaneously induced photoisomerization reactions depending on a direction of incident polarized light, a periodically modulated anisotropic structure is fabricated by exposure of azobenzene polymer films to the orthogonal polarization interference field. In addition, liquid crystal (LC) gratings, in which LC directors are periodically modulated by periodically aligned films, are mentioned as an example of anisotropic diffractive optical elements [2][3][4][5][6][7][8][9][10]. Photoalignment by holographic exposure [2,4,8,9], photo-masking exposure [3], microrubbing method [5], and using an interdigitated electrode [6] are the common methods of the fabrication methods of LC gratings.…”

“…In addition, liquid crystal (LC) gratings, in which LC directors are periodically modulated by periodically aligned films, are mentioned as an example of anisotropic diffractive optical elements [2][3][4][5][6][7][8][9][10]. Photoalignment by holographic exposure [2,4,8,9], photo-masking exposure [3], microrubbing method [5], and using an interdigitated electrode [6] are the common methods of the fabrication methods of LC gratings. Photoreactive polymer LCs are mentioned as materials to use for alignment films other than azobenzene-containing material [2][3][4][7][8][9][10].…”

“…Photoalignment by holographic exposure [2,4,8,9], photo-masking exposure [3], microrubbing method [5], and using an interdigitated electrode [6] are the common methods of the fabrication methods of LC gratings. Photoreactive polymer LCs are mentioned as materials to use for alignment films other than azobenzene-containing material [2][3][4][7][8][9][10]. LC gratings can be applied to optical switching elements by applying a voltage [2,[4][5][6].…”

“…Photoreactive polymer LCs are mentioned as materials to use for alignment films other than azobenzene-containing material [2][3][4][7][8][9][10]. LC gratings can be applied to optical switching elements by applying a voltage [2,[4][5][6]. Moreover, control of diffraction properties and wavelength selection properties is realized by birefringence control in LC gratings using temperature control [10].…”