Polarization-independent and high-diffraction-efficiency Fresnel lenses based on blue phase liquid crystals

Abstract

A polarization-independent and high-diffraction-efficiency Fresnel lens is developed based on blue phase liquid crystals (BPLCs). The optically isotropic characteristic of BPLCs is used to produce a polarization-independent Fresnel lens. The small optical phase shift of BPLCs that is induced by the Kerr effect is sufficient for the BPLC Fresnel lens to have high theoretical and experimental diffraction efficiencies of 41% and ∼34%, respectively. An electrically erasable memory effect in the focusing diffraction at an electric field E>4.44 V/μm is observed. The electro-optical properties of the BPLC Fresnel lens are analyzed and discussed.

Fast-Response Liquid Crystal Microlens

“…Firstly, due to the existence of polymer network, it is more difficult for the LC molecules to reorient in accordance to the electric field. Thus, a relatively high voltage is needed to drive the BPLC devices [16,29]. Secondly, in most tunable LC lenses, it is the variation of refractive index, rather than induced birefringence of LCs, determines the dynamic range of the focal length.…”

“…Polymer-stabilized blue phase liquid crystal (PS-BPLC) microlenses [28][29][30][31][32][33][34] have been developed with several attractive features: (1) submillisecond response time, (2) alignment-free, and (3) polarization insensitive. Blue phase [47][48][49][50] exists over a narrow temperature range (1-2 °C) between chiral nematic and isotropic phases.…”

“…To increase the dynamic range, Fresnel type BPLC lenses have been developed [28,29]. Figure 16 shows the configuration and working principle of the Fresnel BPLC lens [29].…”

“…Two major technical challenges have severely limited their practical applications and commercialization: polarization dependency and slow response time (several seconds or hundreds of milliseconds). The former can be solved by using residual phase modulations [26,27], and optical isotropic materials, such as blue phase LC [28][29][30][31][32][33][34], double-layered structure [35][36][37], or axially symmetric photoalignment [38]. Due to the intrinsic speed of NLCs, the response time of a LC microlens is usually in the order of 100 ms, which is obviously not fast enough for image processing, optical communication, etc.…”

Switchable Two-Dimensional Liquid Crystal Grating in Blue Phase

“…Blue phase liquid crystal (BPLC) has been developed recently for optoelectronic applications in photonics, light modulation, and displays [19][20][21][22], because of its unique characteristics including a fast response time and no requirement for an alignment layer. Under an external electric field, the Kerr effect is exhibited by local reorientation of the LC directors and electrostriction in BPLC [23].…”