Electrically Tunable Broadband Oblique Helicoidal Cholesteric Liquid Crystals

Hyperspectral optical filters, which transmit specific wavelength range of the light, play an important role such as self-driving car to precisely identify an object. IMEC linescan filter and Lyot filter are representative hyperspectral optical filters. However, IMEC linescan filter requires physical adjustments to switch transmitted wavelength and Lyot filter reduces transmittance of light due to various polarizing plates. To address these limitations, we propose an electrically tunable broadband oblique helicoidal cholesteric liquid crystal (CLC) based hyperspectral optical filter. The tilted orientation of oblique helicoidal CLCs allows the tunable wavelength controlled by vertical electric field. We assembled two circular patterned indium tin oxide (ITO) coated glasses and fill the cell with twist-bend nematic liquid crystal mixture. By applying vertical electric field, z-directional electric field gradient is induced at the center of circular pattern. Thus, pitch gradient is caused by z-direction electric field gradient, and the broadband gap is obtained. With the method, we can obtain both tunability and a broadband feature without polymerization. Finally, we designed hyperspectral optical filter just simply stacking two electrically tunable broadband oblique helicoidal cholesteric CLC cells.