Light-Driven Pitch Tuning of Self-Assembled Hierarchical Gratings

Yuan-Hang Wu,Jing-Ge Wang,Sai-Bo Wu,Wei Hu,Rui Yuan,Chao Liu,Qing-Gui Tan,Ling-Ling Ma

doi:10.3390/cryst11040326

Yuan-Hang Wu, Jing-Ge Wang + Show 6 more

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https://doi.org/10.3390/cryst11040326

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Abstract

Gratings are of vital importance in modern optics. Self-assembled cholesteric liquid crystal (CLC) gratings have attracted intensive attention due to their easy fabrication and broad applications. However, simultaneously achieving arbitrary patterning and delicate tuning of CLC gratings remains elusive. Here, light-driven pitch tuning is accomplished in hierarchical gratings formed in a molecular switch doped CLC. We fabricate a checkerboard hierarchical CLC grating for a demonstration, whose pitch is optically tuned from 4.6 µm to 10.7 µm. Correspondingly, the first-order diffraction angle continuously changes from 9.4° to 4.8° and a significant polarization selectivity is also observed. In addition, hierarchical CLC gratings with triangular wave pattern, Archimedean spiral, and radial stripes are also demonstrated. This work creates new opportunities for soft-matter-based intelligent functional materials and advanced photonic devices.

Highlights

We report a light-driven pitch tuning of hierarchical cholesteric liquid crystal (CLC) gratings generated by photopatterning a photo-responsive CLC doped with chiral molecular switches
The CLC mixture is composed of 99.54 wt.% nematic liquid crystal E7
The CLC mixture is stirred in the isotropic phase (73 ◦ C) and capillary filled into the cell

Summary

Introduction

Optical gratings are key components of spectrometers, sensors, tomography, media storage, and beam steering devices widely adopted in nanofabrication, biological medicine, and military areas. They can be made by physical techniques, such as mechanical ruling, electron beam ablation, lithography, and holography, or by bottomup chemical nanofabrication [1,2,3,4]. These methods are often complicated and limited to producing gratings with a fixed grating constant. Thanks to the high responsiveness to diverse external stimuli, LC gratings have played important roles in tunable optical components for light manipulation [8,9,10]

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