Spatial Frequency Responses of Anisotropic Refractive Index Gratings Formed in Holographic Polymer Dispersed Liquid Crystals

Abstract

We report on an experimental investigation of spatial frequency responses of anisotropic transmission refractive index gratings formed in holographic polymer dispersed liquid crystals (HPDLCs). We studied two different types of HPDLC materials employing two different monomer systems: one with acrylate monomer capable of radical mediated chain-growth polymerizations and the other with thiol-ene monomer capable of step-growth polymerizations. It was found that the photopolymerization kinetics of the two HPDLC materials could be well explained by the autocatalytic model. We also measured grating-spacing dependences of anisotropic refractive index gratings at a recording wavelength of 532 nm. It was found that the HPDLC material with the thiol-ene monomer gave higher spatial frequency responses than that with the acrylate monomer. Statistical thermodynamic simulation suggested that such a spatial frequency dependence was attributed primarily to a difference in the size of formed liquid crystal droplets due to different photopolymerization mechanisms.

Tunable Waveguides Couplers Based on HPDLC for See-Through Applications

“…In our study, the measured quantity was the diffraction efficiency, and the results show a similar behavior of the waveguides to those presented in [ 25 ]. Another interesting aspect of the work presented is that good results (high diffraction efficiency) are obtained for gratings with relatively high spatial frequencies (over 1700 lines/mm) using HPDLC, which is a considerable good result taking into account the decrease of performance with respect to the spatial frequency of this kind of device [ 26 ]. In order to measure the time response of the device, Diao et al [ 25 ] and us [ 27 ] used a square-wave voltage of 1 kHz frequency.…”

Low-Threshold-Voltage and Electrically Switchable Polarization-Selective Scattering Mode Liquid Crystal Light Shutters

“…Moreover, the contrast ratio of the [7:3]-PDLCs NBA107 is ~9. Accordingly, the [7:3]-PDLCs NBA107 with low power consumption has considerable potential to be applied in the various areas of optics [1,2,3,4,5,6,7,8,9,10,11,12]. The scattering performances of the PSMLS mainly driven by in-plane and/or vertical fields with low V th were also demonstrated.…”

“…Optical devices based on polymer-dispersed liquid crystals (PDLCs) have been studied worldwide for several decades because of their electrically switchable light-scattering properties [1,2]. PDLCs can be applied to light shutters, 2D/3D switching, displays, holographic gratings, optical retardations, and so forth [1,2,3,4,5,6,7,8,9,10,11,12]. Polymers and liquid crystals (LCs) with a proper weight ratio are initially well-mixed with each other, and LC droplets can be formed in a continuous polymer matrix through polymerization-induced phase separation (PIPS) after treatment with UV illumination for a certain duration [1,2].…”

Numerical Technique for Study of Noise Grating Dynamics in Holographic Photopolymers

“…Because the observed Bragg-matched noise gratings have structure in both transverse dimensions and the amplification process depends on growth in both depth and time, such a study requires a simulation in three spatial dimensions and time. Conversely, numerical studies of predominantly local effects such as phase segregation in holographic polymers have typically been restricted to a slice through the hologram in the plane of the grating wave vector and time [ 5 ].…”