Abstract
In this work, an accurate numerical modeling of the diffraction properties of transmission holographic polymer dispersed liquid crystal (H-PDLC) gratings is presented. The method considers ellipsoid geometry-based liquid crystal (LC) droplets with random properties regarding size and location across the H-PLDC layer and also the non-homogeneous orientation of the LC director within the droplet. The direction of the LC director inside the droplets can be varied to reproduce the effects of the external voltage applied in H-PDLC-based gratings. From the LC director distribution in the droplet, the permittivity tensor is defined, which establishes the optical anisotropy of the media, and it is used for numerically solving the light propagation through the system. In this work, the split-field finite-difference time-domain method (SF-FDTD) is applied. This method is suited for accurately analyzing periodic media, and it considers spatial and time discretisation of Maxwell’s equations. The scheme proposed here is used to investigate the influence on the diffraction properties of H-PDLC as a function of the droplets size and the bulk fraction of LC dispersed material.
Highlights
Holographic polymer dispersed liquid crystal (H-PDLC) gratings are formed by the interference of light on a mixture of liquid crystal (LC), monomer and dye.During the recording process of holographic polymer dispersed liquid crystal (H-PDLC) gratings, a separation between polymer-rich and LC-rich areas is produced in the so-called photo-polymerization-induced phase separation process (PIPS) [1].In this process, the polymerization generates areas in which the LC is concentrated, forming droplets.This LC domain has the same period as that of the recording interference pattern
The curves are consistent and show the over-modulated behavior commonly perceived in some holographic applications [36,37]. These results demonstrate the potential of the scheme, since it offers the possibility to analyze the complex structure formed in an H-PDLC accurately and realistically
Is the creation of the H-PDLC sample that is composed of a set of randomly-placed and -sized LC droplets inside the LC-rich region of the grating
Summary
Holographic polymer dispersed liquid crystal (H-PDLC) gratings are formed by the interference of light on a mixture of liquid crystal (LC), monomer and dye (which shows sensitivity to light). The main problem derived from applying finite-difference schemes to periodic media is related to the spatial discretization of Maxwell’s equations This discretisation forces a limit on the extent of the simulation grid. PBCs show low accuracy for oblique angle plane wave sources in the standard FDTD scheme due to the phase variation across a unit period of the structure and the time-domain nature of the method. In both works previously mentioned [2,3], the drawbacks related to the application of the standard FDTD formulation to periodic media without periodic boundary conditions are shown [19]. The results show that this model sets up a reliable numerical solution for predicting the behavior of H-PDLC
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