Beam Engineering for Advanced Measurements Company , Orlando , Florida 32810 , United States.
Department of Medico-Surgical Sciences and Biotechnologies , Sapienza University of Rome , Corso della Repubblica 79 , 04100 Latina , Italy.
ACS Appl Mater Interfaces. 2018 Apr 18;10(15):13107-13112. doi: 10.1021/acsami.8b02821. Epub 2018 Apr 4.
Dynamic diffraction gratings that are hidden in the field-off state are fabricated utilizing a room-temperature photocurable liquid crystal (LC) monomer and nematic LC (NLC) using holographic photopolymerization techniques. These holographic LC polymer-dispersed LCs (HLCPDLCs) are hidden because of the refractive index matching between the LC polymer and the NLC regions in the as-formed state (no E-field applied). Application of a moderate E-field (5 V/μm) generates a refractive index mismatch because of the NLC reorientation (along the E-field) generating high-diffraction efficiency transmission gratings. These dynamic gratings are characterized by morphological, optical, and electrooptical techniques. They exhibit a morphology made of oriented LC polymer regions (containing residual NLC) alternating with a two-phase region of an NLC and LC polymer. Unlike classic holographic polymer-dispersed LC gratings formed with a nonmesogenic monomer, there is index matching between the as-formed alternating regions of the grating. These HLCPDLCs exhibit broad band and high diffraction efficiency (≈90%) at the Bragg angle, are transparent to white light across the visible range because of the refractive index matching, and exhibit fast response times (1 ms). The ability of HLCPDLCs not to consume electrical power in the off state opens new possibilities for the realization of energy-efficient switchable photonic devices.
利用全息光聚合技术，通过使用室温可光固化液晶（LC）单体和向列相 LC（NLC）制造出在关态下隐藏的动态衍射光栅。这些全息 LC 聚合物分散 LC（HLCPDLC）处于隐藏状态，因为在形成状态（未施加 E 场）下 LC 聚合物与 NLC 区域之间的折射率匹配。施加适度的 E 场（5 V/μm）会产生折射率失配，因为 NLC 重取向（沿 E 场）产生高衍射效率传输光栅。这些动态光栅通过形貌、光学和电光技术进行了表征。它们表现出由取向的 LC 聚合物区域（含有残留的 NLC）交替排列的形态，与 NLC 和 LC 聚合物的两相区域交替排列。与使用非介晶单体形成的经典全息聚合物分散 LC 光栅不同，光栅的形成交替区域之间存在折射率匹配。这些 HLCPDLC 在布拉格角处表现出宽带和高衍射效率（≈90%），由于折射率匹配，在整个可见光范围内对白光透明，并且具有快速响应时间（1 ms）。HLCPDLC 在关态下不消耗电力的能力为实现节能型可切换光子器件开辟了新的可能性。
