Experimental Investigation of Visible Diffraction in Tilted Fibre Bragg Gratings

Abstract

We present an analysis on the visible diffraction patterns of Tilted Fiber Bragg Gratings (TFBG), with applications to blue-laser fiber sensors. On the basis of our current understanding of a visible diffraction phenomenon called sidetapping, or outtapping, we compare theoretical predictions with experimental results. In order to compare theory to experiment we obtain empirical observations of diffraction angles. A 1550nm-TFBG is connected to a Coherent Spectrum-70C laser source and measurements are taken for several wavelengths including red (647.1nm), yellow (568.2nm), green (514.5nm), blue (488.0nm) and violet (457.9nm) to show that our results are in definite agreement with theory. There are other variables that affect and govern this diffraction behaviour so a comprehensive parameter study is used to relate the input variables to output variables. Output variables are power and longitudinal angles of each radiating diffraction order. Input variables would include the type of fiber used, grating pitch, grating tilt, and wavelength. With information gathered from the input-output analysis, we continue by studying blue light diffraction. Different devices are compared to gain insight into the optimal conditions for a blue light TFBG sensor. The diffraction of blue light in particular is exploited to gain insight on specialized fiber nano-coatings used in biochemical sensors. To start we review the existing methods of TFBG diffraction in the visible spectrum, including Coupled Mode analysis and a brief overview of alternate methods. Generally, depending on the wavelength and other factors there may or may not be coupling to radiation modes. The specific angles of these radiation modes with respect to the fiber axis, called longitudinal angles, are determined by theoretical phase-matching conditions related to the incoming beam wavelength. iii Acknowledgements My immediate thanks go to Dr. Jacques Albert and Dr. Christopher Smelser, my thesis supervisors, for their constant support, encouragement, and professional demeanour throughout my thesis research. You were both always ready to provide invaluable suggestions and to conduct productive discussions. Our lab technician, Albane Laronche was integral to the realization of this project. She was always available for troubleshooting and to help with laboratory equipment and procedures. Ultimately, your professionalism and insights were a major factor in the success of this research and your contribution is duly appreciated. A special thanks goes to Dr. Anatoli Ianoul, Daniel Prezgot and Adam Bottomley of Carleton University's Department of Chemistry for providing the workspace required for the completion of this project and helping me in ways I can only describe as selfless and adept. Similarly, I am infinitely grateful to Penka Matanska and Mike Antunes of the Physics Department for lending a Goniometer, which turned out to be the key to the success of this research. Finally, none of this work was possible without the Department of Electronics, from its Faculty to ...