Direct UV-writing of waveguides

The research presented in this Ph.D. thesis is concerned about fabrication of waveguide structures in photosensitized germanosilica thin films by exposure to Ultra-violet (UV) radiation. Using a high pressure loading system and a waveguide fabrication setup, planar waveguiding structures with an UV induced refractive index change of more than 10−2 have been obtained. New insight, with respect to understanding the UV induced index change obtained by direct UV writing, has been provided, through experiments conducted with such high-pressure loaded germanosilica samples. This include measurements of the UV induced refractive index change, and spectroscopic measurements of the defect distribution, for various fabrication parameters. A method to measure the concentration of molecular hydrogen in thin film planar waveguide samples is established, and validated for hydrogen loading at up to 12 mole%. The solubility of molecular hydrogen is hereby found not to depend on the loading pressure. Modelling the diffusivity of molecular hydrogen in such samples shows the expected diffusion behavior only when loading at a pressure below 200 bar. The work has mainly been carried out at the COM Center, Technical University of Denmark, under supervision of Mikael Svalgaard and Martin Kristensen. The work related to luminescence spectroscopy have mainly been carried out at Université de Paris-Sud XI (France) under supervision of Professor B. Poumellec. Resume Denne Ph.D. these omhandler fabrikation af bølgeleder strukturer ved en teknik kendt som Direkte UV-skrivning, hvorved en fotofølsom tyndfilm best̊aende af germanium doteret silica belyses med en fokuseret ultraviolet (UV) laser str̊ale. Herved kan man inducere en lokal forøgelse af brydnings indekset og s̊aledes forme bølgeledere ved at translatere filmen under UV str̊alen. For at opn̊a rimelige bølgeleder egenskaber kræves en relativ stor ændring i brydnings indekset, hvilket kun har vist sig muligt for det anvendte tyndfilms materiale hvis det indeholder en mængde molekylær brint. Den inducerede brydnings ændring har s̊aledes vist sig at være stærkt afhængig af brintkoncentrationen under UV belysningen, hvorfor denne sammenhæng har været et gennemg̊aende tema i afhandlingen. Rent praktisk er der blevet installeret højtryksudstyr p̊a COM centret som muliggør indiffusion af molekylær brint i silica tyndfilms materialer, i koncentrationer p̊a helt op til 20 mol%. Herved har det været muligt at fremstille bølgeledere med en UV induceret brydnings indeks ændring p̊a over 2 × 10−2. Der har dog ogs̊a vist sig en del nye problemer iform af en s̊akaldt ”tærskel effekt”, en ikke monoton sammenhæng mellem indeks ændring og brint koncentration, komponent asymmetri og en forøget uddiffusion ved høje koncentrationer. Mange af disse fænomener er forsøgt belyst i denne these gennem beskrivelser af observationer, eksperimenter og tilhørende m̊aleresultater. Acknowledgements First I would like to thank my supervisors Mikael Svalgaard and Martin Kristensen for being very helpful and inspiring during my study. I also wish to thank Bertrand Poumellec and the people working at Laboratoire Physico-Chimie de L’etat Solide, Université de Paris-Sud XI, for the great help during my work in Paris. I have also had a large benefit from working together with Anders Harpøth, Tue Rosbirk, Michael Galili and Marc Andersen in the UV-lab. I owe thanks to Christian Rosberg, Rasmus Kjær, Mikkel Strange, Clement Lessel and Thomas Nielsen, who has helped me with several smaller projects related to my thesis. The people at NKT integration and Koheras also deserves a big thank for supplying us with samples, equipment and for helping in other practical aspects. I wish to thank the people in the ILC group: Karin Andersen, Peter Carøe, Karsten Rotwitt, Haiyan Ou, Søren Agger, Jørn Hedegaard, Hugh Philipp and Morten Dyndgaard. Other people that have been of great help are: Jesper B. Jensen, Carl-Johann Marckmann, Henrik Rokkjær, HansJürgen Deyerl, Jacob Fage, Rune Shim. Frank Persson and Jan Mortensen from the workshop at EMI should also have credit for their support with fabricating small parts for the different setups. I wish to thank the following people from MIC: Jörg Hübner, Winnie Svendsen, Rasmus Sandberg, Christian Mikkelsen and Ole Hansen. Finally my wife Louise (and the little guy she is carrying) deserves thanks for the waiting during the long nights of conducting experiments and thesis writing.

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