Photonic Liquid Crystal Fibres for Temperature and Electric Field Sensing Applications

Abstract

Four commercially available index-guiding photonic crystal fibres (PCFs) were infiltrated with nematic mixture MLC-6204 creating photonic liquid crystal fibres (PLCFs). The PLCFs were placed in a cell to allow the application of an electric field across the fibre and 534.5nm laser was launched into them. The effect of electric fields (0V-140V) and temperature (25 ̊C to 120 ̊C) on the PLCF's light guiding properties were observed, the fibres were determined to behave as anti-resonant reflecting optical waveguides (ARROWs) with periodic transmission minima. The variables determining the response of the fibres were found to be the hole diameter, the extraordinary refractive index of the liquid crystal and the magnitude of the angle between the nematic director and the capillary axis. The nematic structures formed by MLC-6204 when confined to capillaries of diameters from 2micro metre to 20micro metre were examined. The liquid crystal is seen to exhibit escaped radial and planar polar structure when a homeotropic alignment layer is applied to the capillaries, when left untreated parallel alignment is seen. By comparing simulated and observed polarising microscopy textures, the anchoring conditions in the escaped radial case were determined to be strong in 20micro metre capillaries and weak for smaller capillaries. The electric field within the PLCFs is simulated showing up to 40% variation in field strength between the micro-capillaries within the PLCFs, also shown is the variation in field strength with different axial alignment of the fibre with respect to the electrodes.A device was created utilising a programmable microcontroller and the PLCF system to measure the voltage applied across the electrodes to an accuracy of ±0.5VRMS over therange +30VRMS to +60VRMS.

Date of Award	1 Aug 2012
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Helen Gleeson (Supervisor)