Fingerprint Textures And Their Applications Of Light-Manipulated Cholesteric Liquid Crystal

Diffraction gratings are of great importance in modern optics.They are key components of spectrometers,monochromators,tomography,lasers and beam steering devices widely adopted in nanofabrication,biological medicine and military areas.Nowadays,integrating multiple functionalization onto integrated optical products is highly desirable.The new generation of optical diffractive elements also demands precise,tunable,non-mechanical and remote-control capabilities.Thanks to the self-assembly characteristics of liquid crystals(LCs)and the sensitivity to various external stimuli,the self-assembled LC microstructures have attracted much attention and become a wise choice for tunable optical components to manipulate light.In this paper,the photo-patterned alignment induces the cholesteric liquid crystals(CLCs)to self-assemble into desired microstructures with fingerprint textures under a certain electric field.In addition to the generation of photo-patterned grating structures,the continuous photo-tuning of the grating pitch is further achieved through the remote light control,which greatly enriches the species of smart optical grating.Our research are shown as follows:1.Combined with the rational azimuthal angle control of LC directors,two kinds of fingerprint textures(namely,developable modulation DM and growing modulation GM)are created with different cell-gap/pitch(d/p)ratios.Their stripe-growing and pitch-tuning properties are further investigated.Under the blue light illumination,the pitch of photo-patterned DM fingerprint stripes gradually increase and their orientations are switched to a direction perpendicular to the initial,due to the helicity untwisting.The tunability of the photo-patterned GM stripe is also performed with different light sources,including UV light(?=365 nm),blue light(?=450-490 nm),and green light(?=510-560 nm).The grating pitch is tuned attributed to the light-induced HTP changes.Related experimental parameters are optimized to guarantee the design and performance of light-driven tunable diffraction gratings with hierarchical helical structures.2.Based on light-activated liquid crystal gratings with tunable pitches,we obtain hierarchical CLC gratings with a DMD-based photoalignment technique.Through this method,a two-dimensional checkerboard hierarchical grating is created and the grating pitch can be manipulated continuously and reversibly light stimulation(UV light,?=365 nm,E=3?W/cm~2;green light,?=532 nm,E=14?W/cm~2).The maximum tuning range of the grating pitch is from 4.6?m to 10.7?m,which is 2.3 times the initial pitch.The diffraction properties of the checkerboard hierarchical grating are further verified.The first-order diffraction angle can be tuned from 9.4°to 4.8°continuously and the polarization sensitivity of the CLC grating is also investigated.Notably,the polarization-dependent diffraction performances are quite distinct among different diffraction orders(first-order,second-order,third-order and fourth-order)during the variation of incident polarization.The light-driven CLC gratings are formed with a photosensitive-chiral-agent-doped CLCs which can be photo-patterned and photo-tuned due to the HTP variation under the irradiation of light with different wavelengths.This study will open up new ways to create diversified dynamic optical diffraction devices,which are expected to be applied in the fields of beam steering,virtual reality,measurement,optical data storage and communication.It brings new opportunities for soft-matter-based functional materials and advanced photonics.