Magnetically Tunable Liquid Crystal-Based Optical Diffraction Gratings

Abstract

We present a theoretical analysis of optical diffractive properties of magnetically tunable optical transmission gratings composed of periodically assembled layers of a polymer and a ferromagnetic liquid crystal (LC). The orientational structure of the LC layers as a function of an applied magnetic field is calculated by minimization of the Landau-de Gennes free energy for ferromagnetic LCs, which is performed numerically and also analytically by using the one-constant approximation and the approximations of the high and the low magnetic fields. Optical diffractive properties of the associated diffraction structure are calculated numerically in the framework of rigorous coupled-wave analysis (RCWA). The presented methodology provides a basis for designing new types of diffractive optical element based on ferromagnetic LCs and simulating their operation governed by the in-plane magnetic field.

Tunable Waveguides Couplers Based on HPDLC for See-Through Applications

“…Holographic polymer-dispersed liquid crystals are known as HPDLCs. In this case, the orientation of the liquid crystal molecules in dark zones can be induced by means of an electric or magnetic field in the case of ferromagnetic liquid crystal [ 19 ] and it produces a refractive index variation which changes the diffraction efficiency. Therefore, the grating develops a dynamic behavior that can be modified by means of an electronic device.…”

Electrically Tuneable Optical Diffraction Gratings Based on a Polymer Scaffold Filled with a Nematic Liquid Crystal

“…To solve the problem analytically, we considered two limiting cases—a high and a low electric field, as in our previous work [ 55 ]. In the limit of the high electric field, it was assumed that θ ( x ) is close to π /2, while in the limit of the low electric field, it was assumed that θ ( x ) is close to zero.…”

“…The rigorous coupled-wave analysis (RCWA) is a semi-analytical method, which is used to describe light propagation in optical grating structures with various grating periodicities and thicknesses. The basic idea of this method is described in our previous work [ 55 ]. To perform the calculation described in this work, we used the Stanford Stratified Structure Solver (S 4 ) [ 76 ], which is the freely available electromagnetic solver for solving Maxwell’s equations in layered periodic structures, based on the RCWA.…”

“…The innovation of this approach is that the polymeric material is present in the volume of the grating structure and not only on its surfaces, as is the case in photoalignment-based LC gratings. The orientational structure of the LC medium, located inside the periodic polymeric scaffold as a function of an applied external electric field, is calculated by minimization of the Landau–de Gennes free energy [ 53 , 54 , 55 ]. The resulting orientational structure is then used for the calculation of optical transmission and diffraction properties.…”

Editorial for the Special Issue “Polymeric and Polymer Nanocomposite Materials for Photonic Applications”

“…D. Bošnjaković et al report on numerical simulation of holographic polymer-dispersed ferromagnetic liquid crystal [ 3 ]. The presented methodology provides a basis for designing new types of diffractive optical elements and their operation under in-plane magnetic fields.…”