Electroinduced Diffraction Gratings in Cholesteric Polymer with Phototunable Helix Pitch

Abstract

For the first time the cholesteric mixture containing nematic polymer with small amount of chiral‐photochromic dopant is used for electroinduced diffraction gratings production. The gratings are obtained by applying electric field to the planar‐aligned cholesteric polymer layer causing its periodical distortion. Material developed permits manipulating supramolecular helical structure by means of UV exposure resulting in helix untwisting. Photo‐controlling of helix pitch brings to change parameters of the electroinduced gratings. Due to macromolecular “nature” of the material one can easily stabilize electroinduced gratings by fast sample cooling. All‐known cholesteric grating types are realized in the studied polymer material. It is observed that the grating vector can be oriented along or perpendicular to the rubbing direction of the cell. It is shown that the diffraction efficiency is dictated by grating type and the amplitude of the applied electric field and can achieve about 80%. Moreover, the period of gratings can be tuned upon UV light illumination. The possibility of 2D gratings creation is also demonstrated. The described material and approach gives an opportunity to easily fabricate a variety of diffraction gratings with flexibly controllable parameters. Such gratings can be potentially applied in optics, optoelectronics, and photonics as intelligent diffraction elements.