A Deformable Low-Threshold Optical Limiter with Oligothiophene-Doped Liquid Crystals

Abstract

Optical limiting is a phenomenon widely recognized as the potential application for a protector of human eyes and optical sensors from irradiation with lasers. However, a high optical limiting threshold and low flexibility have restricted such applications. Here, we report that oligothiophene-doped liquid crystals (LCs) function as a low-threshold optical limiter with deformability. Irradiation of dye-doped LCs with a continuous wave (CW) laser beam brings about the formation of diffraction rings, and the number of rings changes depending on the incident light intensity due to their photoinduced molecular reorientation. Utilizing such reorientation enables reversible optical limiting without additional multilayered optical components. In particular, an electric field application to a LC-based optical limiter decreases their optical limiting threshold from 2100 to 25 mW/cm 2 , and the threshold can be tuned by adjusting the applied voltage. Furthermore, the softness of LCs allows for the fabrication of the deformable optical limiter; optical limiting due to the molecular reorientation occurs even in largely bent states. The low-threshold and deformable optical limiter based on oligothiophene-doped LCs thus will enable one to develop the protector of eyes and optical sensors from glaring light-induced damage.

Effect of Host Structure on Optical Freedericksz Transition in Dye-Doped Liquid Crystals

“…Instead of the anthraquinone dyes, Zhang et al reported the usage of oligothiophene dyes to enhance the sensitivity of the LC molecular reorientation [12]. To further decrease the light intensity required for the OFT in oligothiophene-doped LCs, various approaches focusing on the incident light, alignment processing, and materials have been proposed [13][14][15][16][17][18][19]. Recently, we focused on the material design and achieved the effective molecular reorientation by doping oligothiophene dyes with ester moieties [17,18].…”

“…[12]. [13][14][15][16][17][18][19]. Recently, we focused on the material design and achieved the effective molecular reorientation by doping oligothiophene dyes with ester moieties [17,18].…”

Recent Progress in Functional Dye‐Doped Liquid Crystal Devices

“…Usui et al also reported an optical limiter fabricated from oligothiophene dye-doped polymer-stabilized LCs (TR5/ PSLC). [83] Because of the efficient molecular reorientation of the LCs and dichroic dyes, the optical limiter can have both a low threshold and deformability. This nonlinear reorientation induced the spatial change in the refractive index, forming diffraction rings on the screen due to self-focusing and self-phase modulation.…”

Polymer-grafted ZnO nanorods enhance optical nonlinearity of oligothiophene-doped liquid crystals

“…35 The usage of PSLCs delivered optical limiters with a low threshold intensity, and the application of an electric field greatly enhanced their optical limiting threshold. 34 However, this low optical threshold intensity was only achieved by applying an electrical stimulus that can lead to a complex system. Therefore, a new NLO material that can lower the threshold intensity is necessary for developing optical switching, self-modulators, and holographic memory with simple systems.…”

“…We induced the molecular reorientation of oligothiophene dyedoped LCs at relatively low light intensities through polymer stabilization, [29][30][31] surface anchoring, 32 hybrid alignment, 33 and assistance of an electric field. 34 In polymer-stabilized LCs (PSLCs), the threshold intensity was reduced by a factor of six compared to conventional homeotropic LCs. 35 The usage of PSLCs delivered optical limiters with a low threshold intensity, and the application of an electric field greatly enhanced their optical limiting threshold.…”