Abstract
This work presents recent results derived from the rigorous modelling of holographic polymer-dispersed liquid crystal (H-PDLC) gratings. More precisely, the diffractive properties of transmission gratings are the focus of this research. This work extends previous analysis performed by the authors but includes new features and approaches. More precisely, full 3D numerical modelling was carried out in all analyses. Each H-PDLC sample was generated randomly by a set of ellipsoid geometry-based LC droplets. The liquid crystal (LC) director inside each droplet was computed by the minimisation of the Frank elastic free energy as a function of the applied electric field. The analysis carried out considered the effects of Frank elastic constants , and ; the anchoring strength ; and even the saddle-splay constant . The external electric field induced an orientation of the LC director, modifying the optical anisotropy of the optical media. This effect was analysed using the 3D split-field finite-difference time-domain (SF-FDTD) method. In order to reduce the computational costs due to a full 3D tensorial analysis, a highly optimised method for high-performance computing solutions (HPC) was developed. The influences of the anchoring and voltage on the diffraction efficiencies were investigated, showing the potential of this approach.
Highlights
Many applications, such as diffraction lenses, optical data storage, image capture devices and solar cell applications, amongst others, are related to holographic polymer dispersed liquid crystals (H-PDLCs)
The higher the anchoring strength is, the lower the effect of higher control voltages is on the grating, thereby maintaining higher diffraction efficiencies even for the highest control voltage considered. These results demonstrate the necessity of applying huge voltages in H-PDLC devices, since it is well known that the surface and anchoring effects on the droplets are quite high [32]
This work shows the results derived from a rigorous numerical analysis of H-PDLC
Summary
Many applications, such as diffraction lenses, optical data storage, image capture devices and solar cell applications, amongst others, are related to holographic polymer dispersed liquid crystals (H-PDLCs). Materials 2020, 13, 3725 contributed significantly to the application of FDTD to H-PDLC It is worth noting the analysis performed in [12], wherein the LC director distribution was computed by means of the application of the Monte-Carlo method, and a two-dimensional FDTD scheme was used for obtaining the light propagation along the grating. A rigorous formalism based on the minimisation of the free energy was used for determining the director distribution of the LC droplets, instead of considering statistical approaches such as the one considered in [19] This solution brings about the opportunity of modelling accurately LC-based devices in a sub-micron regime, taking into account the physical parameters of the media considered, and the external control voltage or the LC constants, for instance. The results presented show the potential of the setup since the scheme provides the diffraction efficiency as a function of the external field amplitude for a different angle of incidence and anchoring conditions
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