Liquid crystal phase-only modulator and optical beam steering system

Thesis

This thesis describes the development of a new analogue, phase-only liquid crystal (LC) modulator and an LC-based optical beam steering configuration. To begin with, a new and simple method for the rapid and precise measurement of the flexoelectro-optic performance of large tilt-angle chiral nematic LC is presented. These large tilt angle LCs are then employed in the development and demonstration of a flexoelectro-optic LC phase modulator with >2π phase range and sub-millisecond response. It is shown that the voltage-induced rotation of the optic axis is converted into a phase modulation with the aid of a reflective device configuration incorporating a ∼5 μm LC cell, a polarizer, two quarter-wave plates, and a mirror. It is then demonstrated that the mirror and quarter-wave plate can be replaced with a chiral reflector, which improves the robustness of the system.

Based on the reflective phase modulator, two different transmissive phase modulators are considered, which consist of either adding a half-wave plate in between two LC layers when the electric field applied to the two layers is the same or by applying electric fields of opposite polarity, avoiding the need for an additional half-wave plate. Even though those phase modulators can generate 2π phase modulation with sub-millisecond response time, a key disadvantage is that numerous optical components are required. In order to solve this, a LC phase modulator that combines a flexoelectro-optic LC layer, a polymerized reactive mesogen layer and a mirrored substrate is presented, which demonstrates the potential for making next-generation LC on silicon spatial light modulators. In the final part of this thesis, LC phase modulators are combined with LC polarisation gratings to form a novel beam steering for optical communications.

Authors: Wang, X

• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: integrated device; SLM; fast response; phase modulation; liquid crystal
• Subjects: Engineering