Development of a Tunable Laser Based Bragg Grating Demodulation System Laurie Chappell A thesis submitted in wnfdtywith the requirements for the degree of Master of Applied Science Graduate Department of Aerospace Engineering University of Toronto O Copyright by Laune ChappeU 1998 National Library Bibliothèque nationale du Canada Acquisitions and Acquisitions et Bibliographie Services services bibliographiques 395 Weltington Sireet 395. rue Wdlingtm Ottawa ON K1A ON4 OttawaON KIAON4 Canada Canada The author has granted a non- L'auteur a accorde une licence non exclusive licence allowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, distriiute or seil reproduire, prêter, distribuer ou copies of this thesis in microform, vendre des copies de cette thèse sous paper or electronic formats. La forme de microfiche/nlm, de reproduction sur papier ou sur format électronique. The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts f?om it Ni la thèse ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. A novel Bragg grating demodulation system based on the use of a tunable gain-coupled distributeci feedback (GC-DFB) semiconductor laser is developed and demonstrated. The laser, donated by Norte1 Technologies, is packageci and characterizcd, including wavelength tuning, power curve and temperature dependence characteristics. A current driver is developed to precisely ramp the injection current of the tunable laser given selactable user inputs. Severai data acquisition programs are written to facilitate the different system modalities, and are combined into a final, all-encompassing product. The sys~is demonstrated to demodulate Bragg grating signals with a resolution of M.8 pe over a strain range of 6070 W. Demodulation of wavelength division multipiexed and parallel multiplexed signals is demonstrateci, for both sec and dynamic signals. A hybrid serial / paraliel muitiplexed is demonstrated to simultaneously demodulate 12 separate Bragg grating signals. A tradeoff between system measurement range and measurement bandwidth is discussed. An estirnate of the theoretical maximum number of channels simultaneously adcimisable by the system is presented. Demodulation of pultnided Bragg grating senson is presented. Suggestions for future systems are given. Acknowledgements htand foremost, 1 would like to thank my supervisor, Dr. Raymond M. Measuns, for the academic support thai enabled me to complete this thesis. I would also like to thank Dr. Shangyuan Huang, Dr. Myo Ohn, and Trent Coroy. for always king there to answer "just one more question." 1 would like to thank Gregory Fishbein for his pncision craftmanship and Jake Unger for his invaluable knowledge of electronics. I would also like to thank the other students in the FOSS Lab, past and present, for helping me out in numerous different ways. 1 wodd üke to acknowledge ISIS Canada and Photonics Research Ontario (forrnerly Ontario Laser and Lightwave Research Center) for their financial support. Without this funding my thesis project could not have been completed Finaliy, 1 would iike to thank Dr. ED.Chik and Dr. R Kriegler af Norte1 Technologies for generously donating the GC-DFB laser that made this work possible. LIST OF FIGURES ........................................................................................................................VI 1.1 Fiber Optic Sensors for Smart Structures .................................................................................................. 1 1.2 Development of Fiber Optic Sensors ........................................................................................................ 1 1.3 Thesis Objective ................................................................................................................................... 2 1.4 Thesis Organization ................................................................................................................................ 2 2 THEORETICAL............................................................................................................................ 4 2.1 Fiber Bragg Gratings ................................................................................................................. ...,..... 4 2.1.1 The Bragg condition ......................................................................................................................... 5 2.1.2 Grating Rtsponse ............................................................................................................................. 6 21.21 Strain Sensitivity .................................. ..... ............................................................................................................. 7 2.1.2.2 Tan- Seasitivity ......................................................................................................................................... 9 2.1 -3 Grating Reflection Spectrurn ............................................................................................................. 9 2.1.4 Grating Bandwidth ......................................................................................................................... 10 2.2 Multiplexing Techniques for Fibcr Bragg Graciag Scnsors ............ .... .....................................................Il 2.2.1 Wavelength Division Multiplexing (WDM) ...................................................................................... 11 2.2.2 Time Division Multiplexing (TDM) ............................................................................................. 12 2.2.3 Parailel Mu1 tiplexing .............. .... ........................................................................................... 13 2.2.4 Hybrid Systcms ............................................................................................................................. 14 2.3 Overview of Bragg Grating Demodulation Techniques ........................................................................... 16 2.3.1 Broadband Source / Wavelength-Sclective Component Schemes ......................... ...... .............. 16 2.3.1.1 Passive Raîiometric Appmach ....................... ,... ....................................................................................... I6 23.12 Waveleagth Division Coupla ............................................................................................................................ 17 23.1.3 ScaMing Fabry-Paot Fiter .. ....................................................................... ................................................. 18 23.1.4 Ac0wtd)pcic Tiurable Pilter (AO..................... ,, ......................................................................................... 19 23.15 fnt#fc~omcûicDetection Technique.......... ... ........... ...... ................................................................................ .. ......20 23.1.6 Quantum Wcii Eieccroabsorption Filtaing Detector ............................ .................................................................. 21 2.3.2 Nanowband TunabIt Source / Broadband Recciver Systems ......................... .... ......................... 22 23.2.1 ninable Laser Basai ï)umduMon of Frbcr Bragg Graihg Sensors .................................................................... 22 3 SYSTEM COMPONeNTS ......................................................................................................... ...24 3.1 The Norte1 GC-DFB Laser .............. .. ................................................................................................. 24 3.1.1 Tùtory of Operation ...................................................................................................................... -24 3.1.1.1 Hïscory of the DFB taser ............................. ,, ..................................- .................................................. ............. 24 3.1.1.2Tbe Gain-Coupiai DFB Laser .................................................................................................................. ............. 25 3.1.13 Theoieticai Analysis .... ............. -...... "............... ................................................... ....-........... -........................*. 26 3.1.1.4'Ihning ...... -....,..-. .. ............ ....................... ................................................ .................................................. .. ....... 26 3.1.2 Packaging ...................................................................................................................................... 27 3.2 Curreat Supply .................................................................................................................................. 28 3.3 Bragg Gratings............................... ....................................................................................................... 29 3.4 Data Acquisition / LabVIBW Program.................................................................................................... 30 3.4.1 Data Acquisition Boards ........................................................................................................... 30 3.4.2 LabVIEW Program ........................................................................................................................