Electro-Optic-Waveguide Frequency-Translators in Lithium Niobate Fabricated by Titanium Indiffusion and Proton Exchange

Wong, Ka Kha (1989) Electro-Optic-Waveguide Frequency-Translators in Lithium Niobate Fabricated by Titanium Indiffusion and Proton Exchange. PhD thesis, University of Glasgow.

Abstract

The work described in this thesis arose as a result of the need for an optical frequency translator in fibre and integrated optical sensors that employ heterodyne detection techniques. The devices were realised in X- and Y-cut LiNbO3 using proton exchange and titanium indiffusion respectively. Chapter 1 provides an outlook in the areas of optical communications, integrated optics and integrated optical sensor technology. The rapid advancement in the state of the art of integrated optical components in LiNbO3 is reviewed with implications to the future development of fibre and integrated optical sensors. A review of all known frequency translation methods using microwave, bulk optics and guided wave optics components was carried out and reported in Chapter 2. This was necessary to establish the performances, advantages and disadvantages of all the known methods. In performing the above review of frequency translators, it was found that the use of the serrodyne (or commonly known as sawtooth) method, which is the main subject of this thesis, is one of two attractive ways to realise a simple, low frequency (a few MHz) and high performance device. The integrated optical device used in this technique was the phase modulator. The other method is the use of the quadrature method in conjunction with an integrated optical Mach-Zehnder interferometer which is capable of generating frequency translations in the GHz regime. Chapter 3 provides the necessary theoretical background to the understanding of the serrodyne technique for frequency translation. The Fourier analysis of the sawtooth waveform with respect to a number of nonideal situations was carried out to predict sideband suppression levels. Examples of three uses of serrodyne frequency translators in fibre and integrated optical sensors are described. Chapter 4 describes in detail the fabrication procedures for the realisation of titanium indiffused phase modulators in Y-cut LiNbO3. A review of the proton exchange technique for realisation of passive and active devices in LiNbO3 was carried out. Problems with waveguides and devices realised by concentrated benzoic acid melts were identified. A possible solution to all the above problems is to realise the waveguides using diluted benzoic acid melts (lithium benzoate being the dilutant used in all the experiments reported in this thesis). A complete fabrication procedure for the realisation of a proton exchange phase modulator is described in detail. The use of various slab and stripe optical waveguide analysis models is described in Chapter 5. Special attention was given to the analysis of slab and stripe proton exchange waveguides. Techniques that were used extensively to characterise the optical performances of the slab and stripe optical waveguides are also described in detail. The experimental evaluations (at 633 nm) of optical waveguides realised by the proton exchange method (both by concentrated and diluted benzoic acid melts) are given in detail. The improved optical waveguide and device performances realised by diluted benzoic acid melts are stated. Chapter 6 outlines the complete design procedures for the optical phase modulators used in this thesis. The test equipment and experimental techniques that were used to evaluate the phase modulators as serrodyne frequency translators are described. The evaluations of the serrodyne frequency translators using commercially available sawtooth waveform generators are presented. The various problems that resulted in the limited performance of the frequency translators are discussed and supported by experimental verifications. The experimental results were compared to the theoretically predicted results. Hence this establishes the main limiting factors for a high performance serrodyne frequency translator. The main results of this work are summarized in Chapter 7. In addition proposals for improving the test procedures and the performances of serrodyne optical frequency translators are stated. Other possible candidates for use as optical frequency translators are discussed with descriptions on their implementations using integrated optical components.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Electrical engineering
• Date of Award: 1989
• Depositing User: Enlighten Team
• Unique ID: glathesis:1989-77807
• 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/77807