Polymerized tunable chiral nematic liquid crystals

Chiral liquid crystals (CLCs) are known to self-organize into helical structures with periodicities of a few hundred nanometer. As such they exhibit a reflection band for a certain wavelength interval ∆λ (= ∆nP) with P the period and ∆n the birefringence. Since the photonic band gap (PBG) can be controlled by external stimuli (electricity, heat, light, elasticity), CLCs can potentially be used as switchable optical devices such as polarizers, shutters, modulators, diffraction gratings, reflectors, notch- and band-pass filters, reflective displays, and lasers [1]. In this work, we report a wide shifting of the photonic band gap with a range of 126 nm. The shifting is performed by applying an electric field. The material that is used is a mixture of photopolymerizable and nematic LC including a chiral dopant. The transmission spectra of the sample are measured when electric field is applied on the film from 0 to 248 V/µm (Fig. 1). The center of PBG is shifted from 876 nm to 750 nm. The shifting range of the PBG from IR to visible light is more than reported before. By selecting the appropriate chiral dopant concentration, it is possible to make devices for different operation wavelengths