Chemical and Optical Studies of the Hydrogen-Exchanged Optical Waveguides in Lithium Niobate

Foad, Abdel Majeed Ali (1988) Chemical and Optical Studies of the Hydrogen-Exchanged Optical Waveguides in Lithium Niobate. MSc(R) thesis, University of Glasgow.

Abstract

Integrated optics is a key technology for many optical applications like communications, signal processing, optical sensors and instrumentation. The hydrogen-exchange "proton-exchange" is a new technique for fabricating large refractive index difference optical waveguides. The aim of this thesis is to investigate the stability of these waveguides, especially using [2H]-hydrogen incorporated from benzoic acid by [2H] hydrogen-exchange, with respect to the surrounding environment at room and elevated temperatures. The possibility of fabricating waveguides with superior performance and larger change in refractive index using phosphorus containing acids was investigated. This possibility is of particular interest in non-linear optics applications. The crystal change in stoichiometry and crystal structure of the widely used ferroelectric lithium niobate were described. The available techniques for fabricating optical waveguides on lithium niobate were described with emphasis on the hydrogen-exchange technique. The methods of preparation of the [1H] and [2H]-hydrogen labelled benzoic and phosphoric acids were described. Infrared spectroscopy has been used to determine the extent of the exchange reactions and to monitor the incorpor- ation of [1H] and [2H] hydrogen into lithium niobate crystals under various conditions. Atomic absorption spectroscopy has been utilized to detect and determine the lithium out-diffused from the crystal into the acid. The prism-coupling technique has been used to measure the mode angles and hence to determine the refractive indices/depth profiles of the waveguides. The stability of the [2H] hydrogen-exchanged waveguides has been investigated by the exposure of x- and z-cut LiNbO3 waveguides to [1H] water vapour at room temperature. The z-cut [2H] hydrogen-exchanged waveguides showed reversible behaviour when exposed to [2H]-hydrogen labelled water vapour successively, unlike the x-cut waveguide which exhibited non-reversible behaviour. Isotopic-exchange reactions were also examined at elevated temperatures and incorporation of [1H] and [2H] hydrogen was observed when slow flow rates were used. The stability of the effective refractive indices of the [2H] hydrogen-exchanged waveguides was monitored during the period of exposure to water vapour in ambient air. Lithium detected in the acids after the exchange reactions was smaller in the [2H]-hydrogen labelled acids than in the [1H]-hydrogen acids and a relationship was established between the quantity of benzoic acid used in the reaction and the extent of the reaction. The extent of the reaction deduced via spectroscopic and optical measurements has been established for z-cut waveguides fabricated in ortho and pyrophosphoric acids. X-cut lithium niobate waveguides have been successfully fabricated, for the first time using pyrophosphoric acid at 200

• Item Type: Thesis (MSc(R))
• Qualification Level: Masters
• Keywords: Physical chemistry
• Date of Award: 1988
• Depositing User: Enlighten Team
• Unique ID: glathesis:1988-77736
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Jan 2020 11:53
• Last Modified: 14 Jan 2020 11:53
• URI: https://theses.gla.ac.uk/id/eprint/77736