Compact Near-Infrared 3-Dimensional Channel Waveguide Lasers Rose Mary A dissertation submitted for the degree of Doctor of Philosophy Heriot-Watt University School of Engineering and Physical Sciences September 2014 This copy of the thesis has been supplied on condition that anyone who consults it is understood to recognise that the copyright rests with its author and that no quotation from the thesis and no information derived from it may be published without the prior written consent of the author or of the University (as may be appropriate). Abstract This thesis presents the development of ultrafast near-infrared (NIR) waveguide laser sources, through the fabrication of waveguides in Yb-doped bismuthate glass using ultrafast laser inscription (ULI). An integrated linear cavity waveguide laser is demonstrated in the glass with output powers of 163 mW and a slope efficiency of 79%. The laser performance is comparable to bulk systems while providing additional advantages in terms of low threshold ~35 mW and system compactness. The simultaneous achievement of low propagation losses and preservation of the fluorescence properties of Yb ions after the ULI process is key to the outstanding laser performance. Based on the current interest in ultrafast laser development using graphene as a saturable absorber (SA), a systematic study of nonlinear absorption in graphene is presented. The nonlinear optical characterisation of graphene at the wavelengths of 1 µm and 2 µm contributes to the experimental evidence for the wavelength independent absorption saturation in the material. Ultrashort pulse generation from the Yb-doped bismuthate waveguide laser is investigated using SAs based on semiconductor technology and carbon nanostructures. The quasi-monolithic waveguide laser, employing a graphene SA generated ~485 mW output power with a slope efficiency of 49%. The laser generated ~1 ps pulses in a Q- switched mode-locked regime, with the mode-locked pulses measuring a high repetition rate of 1.5 GHz. Ultrafast laser development is also investigated based on a novel evanescent-wave mode-locker device, fabricated by ULI. The device consists of an orthogonal waveguide with the right-angle positioned along its angled facet. The substrate is converted into a mode-locker by depositing carbon nanotube SA at the angled facet. Mode-locked operation is demonstrated by incorporating the substrate in an Er-doped ring laser, generating ~800 fs pulses at 26 MHz. Some preliminary work is done to replicate the device design in an active gain medium, namely, Yb-doped bismuthate glass, for the development of compact laser sources. To my family and friends Acknowledgements My heartfelt thanks to my supervisor Ajoy Kar, for his continued guidance and motivation throughout the course of my studies. His motto of perceiving the positive aspect in every situation has been really helpful and inspiring. I would like to thank him for his infinite patience and encouragement, especially during the thesis writing stage. I would like to thank Robert Thomson, who introduced me to ‘the magic of ULI’. The sheer excitement with which he approaches research has always left me with a sense of awe. Also, thanks for teaching me the few Scottish terms I know. My heartfelt thanks to Graeme Brown who helped me in every stage of my work. Thank you for all the discussions and endless support in preparing papers and talks. Special thanks to Stephen Beecher, for his amazing insights, encouragement and moral support. My thanks to John Macdonald, Nick Psaila, Airan Rodenas, Henry Bookey, Ashleigh Barron and Debaditya Choudhury for their help and support throughout the course of the study. Thanks also to the current members of the nonlinear optics group, Mark Mackenzie, Adam Lancaster, Giorgos Demetriou, Nitin Jha, Anusha Keloth and James Morris. I would like to thank Daniel Jaque, for his contributions to my research, in terms of the microluminescence studies of the sample. I will cherish the vibrant discussions with him and Airan during his visits to Heriot-Watt University. I am grateful to my collaborators at the University of Cambridge: Andrea Ferrari, Zhipei Sun and Daniel Popa. Thank you for your contributions of CNT and graphene saturable absorbers, which formed a vital part of my work. Thanks to Duncan Hand, who provided a ‘story’ version of how they discovered fibre- fuse effect during the course of his PhD. Thanks to Derryck Reid for useful discussions with regard to my work, and for the loan of a number of equipments. Special thanks to the members of physics mechanical workshop, especially Peter Heron, who has come to the rescue countless number of times by designing and machining parts in record time. Thanks to Neil Ross for help with dicing samples. Thanks also to Alex Bell, for his amusing quips on life. Special thanks to Ashleigh Barron for being a great friend throughout and tolerating my music choices. Thanks to Peter Kremer for being a kindred spirit, especially on the topic of food. Thanks to Martin Smith who taught me the beauty of irony. And Nitin, who gives valuable life lessons using puns. Big thanks to Cristtel Ramirez for being the wonderful friend that she is! I will forever cherish all our experiences over the years, right from the Summer School SUSSP ’66, ASSP, Olympics 2012, Korean songs and to whatever the future holds as well. I am always amazed by your boundless enthusiasm about everything. Thanks to all my other friends who has contributed to make my time in Scotland amazing: Ximing, Nabin, Chandra, Ruth, Yingying, Ying Peng, Arun Babu, Tam, Wolf, Diego, Rajiv, Akhil, Hari-mon, Pragati, Hema, Himanshu, to name a few . Special thanks to Joanne, for her support and friendship throughout the years. The Christmas at your place was a fairy tale come true. Thank you. Rishad, Shraddha and Anusha, I love you folks! In my mind, we form the equivalent of ‘F.R.I.E.N.D.S’. Thanks for all the wonderful times, the musical evenings, food appreciation sessions, the umpteen bouts of craziness, and infinite number of insightful discussions including physics. Special thanks to my wonderful friend Supta. I’m truly blessed to have you in my life. Thanks to Adi, Supta and Adwita for adopting me as part of their family, and for the many dinners. Thanks to wee Adwita for being my bestie. Thanks to Swapna maam for her love, care and hospitality. Thanks to Linda Bruce, for her friendship, and for teaching all about Scotland. My thanks to my many friends from back home, who remains a vital part of my life: Tanya, Sonia, Priyamvada, Thomas, Jenu, Nishant, Suchand Sandeep, Manthan, Yedhu, Raji, Abhinav and many more. Thanks to Heriot-Watt University for the opportunities and support in the form of the sports centre, library, the many clubs and most importantly, the Chaplaincy. My thanks to Alistair, Nicky, Fiona, Tillie and Shirley at the chaplaincy for their support and friendship. Thanks to Aftab for helping me get the thesis printed. Thanks to my parents, Abraham and Cicily, for their unconditional love and faith in me. Thanks to my brothers Xavier and George for being my role models, I adore you guys. Sumi C and Santhi C, thanks for being my absolute friends. And thanks to my wee godson Nathan, for being the joy of our lives. Special thanks to my aunt Sr Silvie, for her prayers over the years, I’m truly blessed to have you in my life. Above all, thanks to Lord Almighty for the gift of this wonderful life. Also, thank you for the silver linings. Publications by the Author Peer reviewed journal articles by the author 1. R. Mary, S. J. Beecher, G. Brown, R. R. Thomson, D. Jaque, S. Ohara, and A. K. Kar, "Compact, highly efficient ytterbium doped bismuthate glass waveguide laser," Opt. Lett. 37, 1691-1693 (2012). 2. R. Mary, G. Brown, S. J. Beecher, F. Torrisi, S. Milana, D. Popa, T. Hasan, Z. P. Sun, E. Lidorikis, S. Ohara, A. C. Ferrari, and A. K. Kar, "1.5 GHz picosecond pulse generation from a monolithic waveguide laser with a graphene-film saturable output coupler," Opt. Express 21, 7943-7950 (2013). 3. R. Mary, G. Brown, S. J. Beecher, R. R. Thomson, D. Popa, Z. Sun, F. Torrisi, T. Hasan, S. Milana, F. Bonaccorso, A. C. Ferrari and A. K. Kar, “Evanescent- wave coupled right angled buried waveguide: Applications in carbon nanotube mode-locking,” Appl. Phys. Lett. 103, 221117 (2013). 4. R. Mary, D. Choudhury and A. K. Kar, “Applications of fiber lasers for the development of compact photonic devices,” IEEE J. Sel. Top. Quant. Electron, 20, (2014). doi: 10.1109/JSTQE.2014.2301136. 5. Y. Ren, G. Brown, R. Mary, G. Demetriou, D. Popa, F. Torrisi, A. C. Ferrari, F. Chen and A. K. Kar, “7.8 GHz graphene-based 2 µm monolithic waveguide laser,” IEEE J. Sel. Top. Quant. Electron. doi: 10.1109/JSTQE.2014.2350016. Conference papers by the author 1. R. Mary, S. Beecher, G. Brown, R. R. Thomson and A. K. Kar, "Yb-doped Bismuthate Glass waveguide laser fabricated by Ultrafast Laser Inscription", ASSP - Lasers, Sources, and Related Photonic Devices, OSA Technical Digest (CD) (Optical Society of America, 2012), paper AM4A.14. 30th January 2012. 2. R. Mary, S. J. Beecher, G. Brown, S. Ohara, and A. K. Kar, “Passive Q- switched Mode-Locking in a Ytterbium Doped Bismuthate Planar Waveguide Laser,” Fibre Optic and Waveguides symposia, Photon 12, Durham, 6th September 2012. 3. R. Mary, S. Beecher, G. Brown, Z. Sun, D. Popa, T. Hasan, A. Ferrari, S. Ohara, and A. Kar, "Q-switched modelocking using carbon nanotubes in an ultrafast laser inscribed ytterbium doped bismuthate glass waveguide laser," International Conference on Fibre Optics and Photonics (Photonics 2012, Chennai, India), OSA Technical Digest (online) (Optical Society of America, 2012), Paper T3B.3.