Full-color tunable Bragg-Berry vortex generators based on cholesteric liquid crystal smart materials

Abstract

In this thesis an optical element called Bragg-Berry vortex generator (BBVG) was demonstrated based on ferroelectric liquid crystal and cholesteric liquid crystal (FLC-CLC) smart materials The BBVG element was obtained by filling with the FLC-CLC materials into the indium-tin-oxide (ITO) glass cells which were pre-coated with a q-plate-like circularly-symmetric photoaligned pattern After a non-vortex laser beam impinges into the BBVG a reflective optical vortex beam with an azimuthal-angle(Φ)-dependent phase and thus an orbital angular momentum (OAM) will be obtained if the wavelength of the incident laser is included in the Bragg reflection band of the BBVG To obtain optical vortex beams with oppositely-twisted phase structures (carrying with ±OAM) two BBVG elements with FLC-CLC mixtures of right- and left-handedness were prepared The FLC-CLC smart materials can effectively reflect light within the reflection band or photonic bandgap (PBG) which can be easily tune with less sacrifices in reflectance and band shape throughout the full visible region by the application of a low DC voltage range (?3 2 V) around room temperature The oppositely-handed FLC-CLC BBVG elements can generate optical vortex beams with oppositely-handed OAM within the full visible region (400~700 nm) by simply tuning the PBG at specific voltages Herein the oppositely-handed BBVGs were demonstrated to generate oppositely-handed optical vortex beams with red (R) green (G) and blue (B) colors at different voltages if the incident laser beam has 632 8 nm 442 nm and 532 nm respectively The interferograms obtained experimentally based on Michelson interferometer were used to determine the OAM characteristics of the vortex beams including the topological charge number l and the twisting direction of the phase surface which were consistent with the simulated results

Date of Award	2020
Original language	English
Supervisor	Chia-Rong Lee (Supervisor)