Investigations on tunabilities of pretilt angle and distributed feedback laser based on liquid crystal cells incorporating with micro- and nano-grooves of polymer

Abstract

This thesis entitled “Investigations on the tunability of pretilt angle and distributed feedback laser based on liquid crystal cells incorporated with micro- and nano-grooves of polymer ” examines the tunability of liquid crystal (LC)-based optical devices with a grooved structure The following two topics are discussed (1) Controllable pretilt angle of LCs with the formation of microgrooves This work investigates the controllability of the pretilt angle of LCs in a cell with an initial vertical alignment through microgrooves induced by the holographic fast-writing method By changing the writing time or intensity of the pumped beam the microgrooves with various surface modulations can form and provide distinct planar anchoring strength for the LCs The pretilt angle of the LCs can be controlled from 18 3° to 89° The writing time of the microgrooves takes less than 25 s which is a two-fold reduction in the time taken in previous investigations using other photoalignment methods (2) Thermally tunable LC distributed feedback laser based on a polymer grating with nanogrooves fabricated by nanoimprint lithography (NIL) This work demonstrates a thermally tunable dye-doped liquid crystal (DDLC) distributed feedback (DFB) laser based on a polymer grating The surface emitting the DDLC DFB laser is supported by the second-order Bragg grating with nanogrooves with periodicity of 360 nm and pre-fabricated by UV NIL The lasing wavelength of the DFB laser can be tuned from 625 1 nm to 606 35 nm if the temperature increases from 10 °C to 50 °C The tunability of the laser is attributable to the temperature-sensitive feature in the effective refractive index of the LCs

Date of Award	2014 Aug 25
Original language	English
Supervisor	Chia-Rong Lee (Supervisor)