Ultra-broadband Tunable and Chirality Invertible Bragg-Berry Optical Vortex Generators Based on Molecular-Motor-Doped Cholesteric Liquid Crystals

Zhi-Qun Wang^1*, Yan-Song Zhang¹, Chia-Rong Lee¹

¹Department of Photonics, National Cheng Kung University, Tainan, Taiwan

* Presenter:Zhi-Qun Wang, email:l78101024@gs.ncku.edu.tw

We demonstrate an advanced planar phase modulator called Bragg-Berry optical vortex generator (BBOVG) based on molecular-motor-doped cholesteric liquid crystals. The BBOVG can generate reflected vortex beams in the wavelength range of photonic bandgap (PBG). The photoisomerization of the molecular motor induced by UV light can drive the pitch change of the liquid crystal molecules, which can regulate the photonic bandgap in a wide range, and even reverse the overall spiral, making the sign of orbital angular momentum (OAM) opposite. In this manuscript, we measured the reflectance spectrums, polarized optical microscopy (POM) images, and the Michelson interferograms of the BBOVG under the control of UV light and applied voltage, and verified that the BBOVG can generate optical vortex beams of the corresponding wavelength and spiral direction under a fixed external stimulus.

Keywords: photonic crystal, cholesteric liquid crystal, optical vortex, molecular motor, planar phase device