PHYSICS AND APPLICATIONS OF PHOTONIC CRYSTAL NANOCAVITIES A DISSERTATION SUBMITTED TO THE DEPARTMENT OF APPLIED PHYSICS AND THE COMMITTEE ON GRADUATE STUDIES OF STANFORD UNIVERSITY IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Hatice Altug December 2006 © Copyright by Hatice Altug 2007 All Rights Reserved 2 I certify that I have read this dissertation and that in my opinion it is fully adequate, in scope and quality, as dissertation for the degree of Doctor of Philosophy. __________________________________ (Jelena Vuckovic) Principal Advisor I certify that I have read this dissertation and that in my opinion it is fully adequate, in scope and quality, as dissertation for the degree of Doctor of Philosophy. __________________________________ (Martin M. Fejer) Academic Advisor I certify that I have read this dissertation and that in my opinion it is fully adequate, in scope and quality, as dissertation for the degree of Doctor of Philosophy. __________________________________ (Shanhui Fan) Academic Advisor Approved for the University Committee on Graduate Studies __________________________________ 3 ABSTRACT The capability to confine and manipulate photons at nanometer scales opens up unprecedented opportunities in classical and quantum information processing technologies, and also in life sciences. There have been various demonstrations of sub-micron light confinement, but yet the most critical issue ahead is the development of new device concepts and technologies that will reliably operate at such length scales. In this thesis, we present our efforts along this direction. The large aggregated bandwidths of the optical interconnects require memory and delay components to launch, buffer, and collect optical signals at the nodes. To realize them we proposed two-dimensional coupled nanocavity array structures, which have flat electromagnetic bands i.e., whose frequency variation with wavevector is minimized in all crystal directions. We then experimentally demonstrate group velocity reduction below 0.008 c. We also show that such structures with reduced rotational symmetries can be used to strongly control polarization of light. The performance of lasers such as their speed and efficiencies can be dramatically enhanced with the use of nanocavities due to the spontaneous emission rate enhancement via the modification of vacuum field density in a cavity. Here, we present ultra-fast lasers with turn on and turn-off times as short as 1-2 ps. We demonstrate direct signal modulation speeds in excess of 100 GHz, which is more than an order of magnitude above semiconductor laser speeds. Such speed enhancements are enabled by up to 75-fold spontaneous emission enhancement. To achieve nanocavity lasers with higher output powers and efficiencies, we invented a new device composed of coherently coupled nanocavity laser array. Our unique design combined with strong cavity quantum effects enabled high differential quantum efficiencies, and orders of magnitude larger output powers while preserving low lasing threshold and high operation speeds. For device realizations, we also present nanofabrication procedures developed for Indium Phosphide and Silicon material systems. Finally, nanocavities can also dramatically increase sensitivity of bio and chemical sensors. Furthermore, a network of such nanocavity detection centers can be integrated with microfluidic circuits for high throughput and compact lab-on-a-chip system. As an initial step along this direction, we present our results on detection of refractive index changes in nanocavities with high sensitivity levels. 4 ACKNOWLEDGMENTS This thesis would have been impossible without the contribution of many colleagues and friends. First of all I would like to acknowledge my advisor, Prof. Jelena Vuckovic. When I decided to continue my PhD in her group she was just starting at Stanford. In our first meeting her great energy and enthusiasm to do exciting research have impacted me. I feel fortunate to be her first student as going through the work to set-up a lab with her was one the most valuable experience that I gained in my PhD. I had access to her whenever I needed to discuss my problems, and her insights have lead to the success of my PhD work. I also want to thank all of my friends in Jelena’s group: Dirk Englund, Ilya Fushman, Edo Waks, Maria Makarova, Bryan Ellis, Andrei Faraon, Hideo Iwase and Yiyang Gong for their help and company. In particular I want to thank Dirk for his collaboration on the ultra-fast nanocavity laser work; his talents and enthusiasm were crucial for the success of this project. I also would like to thank Ilya for working together on biosensors and their integration with microfluidic channels. I would like to thank Mehmet Fatih Yanik and Prof. Shanhui Fan for their collaboration on the bistable laser switch project. Prof. Fan was in my thesis reading committee, examiner in PhD qualification exam and followed my research very closely during my PhD and I thank him for all that. With Fatih, we presented the laser switch and won the first place in the Inventors’ Challenge Competition at Berkeley. It was a very stimulating experience for me to work on projects with high impact. I would like to acknowledge Prof. Martin M. Fejer for being in my defense and PhD qualification exam committees. He was also my academic advisor, and gave me very valuable advices starting at my first day at Stanford. I also did rotation in my first year in his group and his deep knowledge on many topics has greatly inspired me. 5 I would like to acknowledge my ex-advisor Prof. David Miller for having me in his group, where I worked on quantum confined start effect devices and learned many valuable experimental techniques. I would also like to thank his group members, and in particular my collaborator Noah who has introduced me to the cleanroom. I would like to thank Prof. James Harris for accepting to be in my defense committee, and also to be examiner in PhD qualification exam. I am very thankful to Prof. Mark Brongersma for being the chairman of my thesis committee, and to Prof. Alexander Fetter for being in my defense committee. I would like to thank Prof. Steve Harris for accepting me to his group in my first year as a rotation student, and for teaching me electromagnetically induced transparency. I thank in particular Deniz Yavuz, David Walker and GY from his group for their help in my first project at Stanford. I would also like to thank the Intel Corporation for awarding me the Intel Graduate Fellowship, and I would like to acknowledge Dr. Mario Paniccia for being my mentor at Intel. In addition, I would like to thank IEEE LEOS organization for awarding me the Graduate Student Fellowship in 2005. I would like to thank all my teachers in my education that had helped me to recognize my talents and ambitions to do science. I want to express my deep gratitude to Prof. Ekmel Ozbay in Bilkent University (Ankara, Turkey) as I have started my first research in optics in his group and he was the one who has inspired me to pursue a PhD at Stanford University. I would like to thank all the Stanford Nanofabrication Facility staff for their help. In particular, I am deeply thankful to Dr. Jim McVittie for his help and advices in dry-etching. I thank Cesar Boxer and Elmer Martinez for their help on operating plasma quest at high temperatures for InP processing. I would like to James W. Conway for making e-beam systems at Stanford always up and working; Nancy, Uli and Mahnaz for allowing me to use oxidation furnaces, wet-benches and lithography tools with my non-standard wafer sizes. I 6 also want to express my special thank to Eric Perozziello who was always available in the cleanroom to help. I thank Ginzton and Applied Physics staff, in particular Claire Nicholas, Paula Perron, Ingrid Tarien and Yurika Peterman for taking care of administrative work. I would like to thank all of my friends in Ginzton Lab and Applied Physics Department for making Stanford an exciting place to study and a fun place to live. In particular, I would like to thank my friends Erhan Yenilmez, Aydogan Ozcan, Omer Oralkan, Onur Kilic, Ozgur Sahin, Ragip, Ali Kemal, Zheng Wang and many others whose names I forgot to list. I am thankful to my husband Fatih Yanik for his never ending support, love and encouragements throughout my Ph.D. Fatih helped me starting from my first day at Stanford in many aspects. With him, I spent the most beautiful and enjoyable days of my life. I would like to thank my brothers Huseyin and Sedat for their support, they were always proud of my every little success. Finally, I am deeply grateful to my mother and father for their love, care and all the sacrifice they made for my education. Being my primary school teachers they had the most powerful impact in my education, they were the ones who ignited my interest in science. Their thrust on my decisions and their belief that I will be successful whatever I do was the most powerful force that has pushed me forward in any difficulty that I faced in my research and to reach my goals. 7 DEDICATION I dedicate this dissertation to my mother (annem) Gulten and my father (babam) Seref. 8 TABLE OF CONTENTS Chapter 1 Introduction ....................................................................……………..................22 1.1 Photonic crystals ........…...........………………………….....................….…………..22 1.2 Photonic crystals slabs…………………………………………………………………23 1.3 Photonic crystal nanocavities………………………………………………………….26 Chapter