Hyperspectral Tunable Filters via Polymer-Stabilized Oblique Helicoidal Cholesteric Liquid Crystals

Abstract

Spectral filters play an important role in sorting specific wavelength information from incident light. However, conventional filters, such as pigment-based color filters, acousto-optic filters, and Lyot filters, have limitations in terms of poor color purity, low tunability, and low transmittance [1,2]. The experimental discovery of oblique helicoidal cholesteric (ChOH) liquid crystals (LCs), with their periodic pseudo-layers, realizes highly tunable Bragg reflectors across a wide spectral range in response to electric field (E) and temperature [3,4].

Here, we report a hyperspectral tunable filter using polymer-stabilized ChOH LCs. Specifically, we broaden reflection bandwidth of ChOH by forming a density gradient of polymer networks which induces gradients on the pitch of periodic oblique helicoidal structures. Additionally, we introduce elasticity into the polymer networks to enable the polymer-stabilized ChOH to be freely tuned by E, leading to tunable reflection wavelengths in a wide spectral range. By preparing bilayer ChOH films that reflect different spectral ranges, a certain wavelength of light is transmitted where both ChOH films do not reflect. The transmitted light shows high level tuning in wavelength with narrow bandwidth (< 20 nm) covering the whole visible range with respect to E. The proposed method has potential in various applic