A Study on the Feasibility of a Silica-on-Silicon Blue Upconversion Laser Fabricated by Flame Hydrolysis Deposition Thesis submitted for the degree o f Doctor of Philosophy from the Faculty of Engineering, University of Glasgow © Marcos Vinicius Dias Vermelho September 1999 ProQuest Number: 13833921 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a com plete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 13833921 Published by ProQuest LLC(2019). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C ode Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 GLAs g ; IfBRAnv Abstract The use of compact blue laser light source is showing a remarkable technological improvement in certain applications, which include devices such as optical data storage, laser printers, and colour displays, to mention a few. Therefore, these applications are requiring more reliable laser sources. Factors such as compactness, robustness, long-term stability, suitability for large-scale integration and possibility of mass-production can be decisive for the choice of the kind of blue laser source as part of a practical tool. Planar lightwave circuits provide practical solutions for such optical devices. A combination of the Flame Flydrolysis Deposition (FHD) and Reactive Ion Etching (RJE) is by now a mature technology, and it has produced planar lightwave circuits for telecommunications applications. In using these analogous technologies, the aim of this work is to study the feasibility of fabrication of compact blue upconversion laser sources. Before proceeding to the study of the blue upconversion process, the research concentrates on the optimisation of the glass host, investigating an alternative approach to reduce the ion-ion interaction in a heavily rare earth doped matrix using sodium ions. The characteristics of the waveguides employed as cavity lasers for the devices fabricated in this planar form also demand accurate numerical modelling for optimisation. Thus, a numerical procedure is developed to complete this general optimisation. The laboratory facilities and availability of experimental data were decisive in the choice of the erbium ion as active material for this first part of the research. The blue upconversion process investigation is initiated by considering two rare earth doping composition for the SiCb-PiOs glass: a single thulium and a thulium doped sensitised with ytterbium ions. Blue upconversion is examined in both glasses considering future diode lasers pump wavelength. The wavelengths at 800 nm and 980 nm demonstrated to be the potential choices for pumping the Tm/Yb glass. The inclusion of ytterbium ions in the glass composition enhanced the blue upconversion process using the pump wavelength at 800 nm* however the population inversion for laser threshold was not predicted by; the modelling. The pump wavelength at 980 nm is applied to the numerical model to study the feasibility of the fabrication of this blue upconversion laser. The preliminary results, which do not correspond to the optimised laser structure design, predicted performance comparable to the results of the employment of optical fibre based devices which have been reported so far. Resumo O uso de fontes de radia 9 ao laser operando na regiao de comprimentos de onda correspondente ao da luz azul tern proporcionado uma notavel melhoria tecnologica em certas aplica 9 oes, incluindo dispositivos tais como os usados para armazenamento optico de informa 9 oes, impressoras a laser, e mostradores opticos, para citar apenas alguns. Estes dispositivos necessitam de lasers que sejam confiaveis em termos de funcionamento. Alem disso, fatores como compacidade, robustez, estabilidade em uso prolongado, alta capacidade de integra 9 ao e possibilidade de produ 9 ao em massa podem ser decisivos na escolha do tipo de fonte de luz azul a ser empregado no dispositivo pratico. Circuitos opticos planares (“Planar Lightwave Circuits” - PLC) apresentam solu 9 oes praticas para estes dispositivos opticos. A combina 9 ao do metodo de fabrica 9 ao de vidro por chama hidrolisada (“Flame hydrolysis Deposition”) e de fabrica 9 ao de guias de ondas denominada “Reactive Ion Etching” e no momento uma tecnologia estabelecida que produz circuitos opticos para aplica 9 oes em teIecomunica 9 oes. Esta pesquisa tern por objetivo estudar a viabilidade de aplicar tecnologia analoga para fabrica 9 ao de fontes laser de luz azul produzida por conversao ascendente de freqiiencia em guias de ondas dopados com Ions terras raras. Anteriormente ao estudo da conversao ascendente de freqiiencia, a pesquisa dedica­ se a buscar uma forma altemativa de reduzir o efeito prejudicial da intera 9 ao entre os Ions terras raras em amostras com alta dopagem, estudando a influencia da inclusao de ions de Sodio na composi 9 ao do vidro. Tendo em vista as caracteristicas dos guias de ondas a serem utilizados como as cavidades laser, foi desenvolvido tambem um modelo visando otimiza-las atraves de simula 9 oes numericas. Desta forma, a altemativa para melhoria do vidro hospedeiro e o modelo matematico para simula 9 ao formam um conjunto instrumental para a otimiza 9 ao dos dispositivos. Fatores concementes a estrutura laboratorial disponivel e a disponibilidade de resultados experimentais para fiituras compara 9 oes foram decisivos na escolha de vidros dopados com ions de Erbio nesta primeira etapa. A conversao ascendente de freqiiencia em vidros SiC^-PzOs e feita considerando duas composi 9 oes com ions terras raras: amostras dopadas somente com ions de Tulio e amostras com ions de Tulio e Iterbio. A conversao ascendente de freqiiencia e investigada levando-se em considera 9 ao futuras aplica 9 oes com comprimentos de ondas de bombeamento disponiveis em laser de diodo. Os comprimentos de ondas em 800 nm e 980 nm demonstraram ser os de maior potencial para bombeamentos em amostras em vidros dopados com Tm/Yb. A inclusao de ions de iterbio aumentou a eficiencia da conversao ascendente de freqiiencia nos vidros com dopagem composta para comprimento de onda em 800 nm, todavia a simula 9 ao nao previu a inversao de popula 9 ao necessaria para gera 9 ao de luz coerente (laser). O comprimento de onda em 980 nm e entao definido para o estudo da viabilidade de fabrica9 ao dos lasers por conversao ascendente de freqiiencia. Os resultados preliminares, que nao correspondem ao de uma estrutura laser otimisada, preveem performance comparavel aos resultados reportados ate entao utilizando dispositivos com fibras opticas. Acknowledgements I would like to thank my academic supervisor Professor J. S. Aitchison for his constant support and advice during the development of this work, and in particular at the important initial stage of this project, prior to my scholarship award. The members of the staff of the Department of Electronics and Electrical Engineering are acknowledged for the use of its facilities. My thanks are due to the colleagues of the optoelectronic group, specially to Paulo Marques for his preliminary assistance on the use of the Flame Hydrolysis Deposition laboratory; Dr. Amr Saher for his friendship and generous help by handing over the lab space at a crucial period in the fmalisation of this work. I wish to express my thanks to my office-mates during this time at the department. Among them, Dr. Ulf Peschel must be thanked for assisting me in numerous occasions, and Dr. Eugene Avrutin for, among other “helps”, his critical reading in this work. The Cleaning Room staff are also thanked, in particular Joan and Margaret. Thanks also go to the whole “team” of the mechanical workshop, for their receptive warmth and professionalism. I wish to express my to thank to Professor Artur da S. Gouveia Neto, from the Department of Physics - UFAL/BR, for his continuous support and encouragement during part of my academic life. Professor Jandir M. Hickmann from the same Department is also acknowledged for introducing me to the Department of E&E Eng., University of Glasgow. I would like to thank my friends in Glasgow for their care in the bleak moments of homesickness, for supporting our national football team in the last World Cup, for having pints over enjoyable conversations, and much more: Alexandra Muller, Mario Gon 9 alves, Flavio and Vania Marques, Luis and Margarete Avanci, Hemerson Gama, Helio and Waleska Lira, Jose Figueiredo, Sofia Figueiredo, Marcelo Vieira. I would like to include in this list my friend and brother-in-law Ilbert Cavalcanti (who followed us to Glasgow by heart) for his “Friday Family Report” e-mails which kept us up-to-date with the hottest news and sustained our good mood. I would like to say a very special ‘thank you’ to Ildney Cavalcanti: companion, wife, and friend. I would like to thank my parents Americo and Maria Vermelho, and sisters and brother Maria, Americo, Juares and Cristina, and their families, for understanding my long absence. My financial support was provided by the Brazilian Agency - Conselho Nacional de Desenvolvimento Cientifico e Tecnologico - CNPq, which is gratefully acknowledged Contents CHAPTER 1 - INTRODUCTION 1.1 The Blue Laser Technology 1 1.2 Different Approaches to Obtain Blue Laser