Indium Phosphide based Integrated Photonic Devices for Telecommunications and Sensing Applications by Ta-Ming Shih M.S. Electrical Engineering Massachusetts Institute of Technology 2007 B.S. Electrical Engineering and Computer Science University of California, Berkeley 2006 Submitted to the Department of Electrical Engineering and Computer Science in partial ful¯llment of the requirements for the degree of Doctor of Philosophy in Electrical Engineering at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY June 2012 °c 2012 Massachusetts Institute of Technology. All rights reserved. Author.............................................................. Department of Electrical Engineering and Computer Science May 18, 2012 Certi¯ed by. Leslie A. Kolodziejski Professor of Electrical Engineering Thesis Supervisor Accepted by . Leslie A. Kolodziejski Chair, Committee on Graduate Students 2 Indium Phosphide based Integrated Photonic Devices for Telecommunications and Sensing Applications by Ta-Ming Shih Submitted to the Department of Electrical Engineering and Computer Science on May 18, 2012, in partial ful¯llment of the requirements for the degree of Doctor of Philosophy in Electrical Engineering Abstract Photonics is an exciting area of study that is situated at the cross-section of physics, material science, and electrical engineering. The integration of photonic devices serves to reduce the size, weight, power consumption, and cost of the photonics- based systems, whose applications can be as disparate in nature as communications and medicine. In particular, an integrated all-optical logic gate and wavelength con- verter for ¯ber-optic telecommunications and an integrated tunable laser for trace-gas sensing are investigated in this thesis. These devices are fabricated in the indium phos- phide (InP) material system, which includes InP and the ternary/quaternary III-V semiconductors that can be grown closely lattice-matched on the InP substrate. The all-optical logic gate is designed as a Mach-Zehnder interferometer with semi- conductor optical ampli¯ers as active nonlinear elements that are optically coupled to the passive waveguides using the asymmetric twin waveguide technique. The device is grown and fabricated monolithically and carrier-dependent optical interference is demonstrated at the 1.55 ¹m wavelength. The tunable diode laser is designed to oper- ate in the wavelength range of 1.55 ¹m { 2 ¹m for trace-gas spectroscopic sensing and comprises of strained InGaAs quantum wells. The laser is monolithically fabricated using mask-less lithography techniques and tuning is demonstrated in Fabry-Perot cavity lasers under continuous-wave operation. A ring-coupled 2 ¹m wavelength laser is designed that will exhibit a tuning range of tens of nanometers. Thesis Supervisor: Leslie A. Kolodziejski Title: Professor of Electrical Engineering 3 4 Acknowledgments I am honored to have had the opportunity to work with and learn from so many talented people during the course of my PhD. It has been an unforgettable experience that I will cherish for the rest of my life. My wonderful time could not have been possible without all of the people I worked with at MIT. I am extremely grateful to my advisor, Professor Leslie Kolodziejski, for all of her guidance throughout the years. Leslie gave me the freedom to chart my own way, while she provided a light for the path. She has taught me the value of teamwork and collaboration, along with the importance of patience. Through all of the ups and downs of the past 6 years, Leslie has demonstrated to me what it means to stay focused on the big picture and smile through it all. And ¯nally, she has shown me how to have fun: I will always remember the parties at her house, at MIT, and even aboard the Spirit of Boston! The great thing about being a graduate student in the Integrated Photonic Devices and Materials group is that one automatically gets to have another advisor: Dr. Gale Petrich. Gale has always been there to help me get to the bottom of anything that was suspicious, broken, or missing. I cannot count the number of times that I knocked on his door with a random question that I knew only he would know. I am thankful to Gale for all of the explanations, advice, and rides to Lincoln Laboratory! I would like to express my sincere gratitude toward my committee members, Pro- fessors Erich Ippen and Rajeev Ram, for their valuable insights and generous guid- ance. Professor Ippen has been a great source of knowledge and advice since I started my studies at MIT. He has always been more than happy to make time for any ques- tions that I had. Rajeev has been a role model for me throughout my PhD. Having taken two of his classes and helped to TA another, I have a lot of respect for his modesty and charisma. The people in the groups of Professors Ippen and Ram have been wonderful to collaborate with, especially Dr. Marcus Dahlem (now Professor), Dr. Ali Motamedi, Dr. Jason Orcutt, and Dr. Joseph Summers. Professor Jaime Viegas has become a true mentor and friend during his stay at 5 MIT and the continued collaboration between our group at MIT and his at the Masdar Institute of Science and Technology. Jaime's humor has never failed to lighten the mood of a meeting, and his candor is something that I admire. I want to thank him for all of the times he sat down with me to help me with my research. No amount of thanks would be enough to give to the folks at the Nanostructures Laboratory (NSL) for all of their help and advice. Professor Henry Smith has always been able to set aside time for me to meet with him. Mark Mondol has been extremely patient with me as I tried my best not to break the e-beam lithography tool. Dr. Tim Savas has never failed to put a smile on my face with his humor. A medal of honor should go to James Daley, who has always been there to answer questions, ¯x equipment, perform evaporations, or just talk to in the cleanroom. Jim has been a mentor in the lab and has become a good friend. Similarly I need to o®er my appreciation to the people at the Microsystems Tech- nology Laboratories (MTL), where a large fraction of my fabrication work was per- formed. I want to thank Vicky Diadiuk for her understanding and all of the technical sta® for their patient instruction. Finally, I want to o®er a warm \Thank you" to Debroah Hodges-Pabon for giving me the opportunity to work as a session chair for the Microsystems Annual Research Conference. The Integrated Photonics Initiative has been a great joint e®ort between the MIT campus and Lincoln Laboratory. The wonderful people at Lincoln have been a matchless source of guidance and encouragement. It has been tremendous to have had the opportunity to work with Dr. Paul Juodawlkis, Dr. Reuel Swint, Dr. Jade Wang, and William Loh. In¯nite thanks to Jason Plant for all of the fabrication assistance and wisdom that he has imparted on me. I also need to thank all of the sta® from 6.007 who have made my two semesters as TA and one semester as instructor some of the best experiences I had at MIT. Thank you to Professor James Kirtley and Dr. Yu Gu (now Professor) for being so supportive. Thank you to Professor Kenneth Wong for trusting me and inviting me to Hong Kong, and for treating me as a friend. And a million thanks to Professor Vladimir Bulovi¶c,for his encouragement and counsel throughout it all, and for giving 6 me the opportunity to lecture as a graduate student. His humble attitude toward teaching will stick with me for the entirety of my career. I want to thank Orit Shamir, with whom I shared an o±ce for 5 years, for being such a great friend and colleague. From the gumball trophy, to the taped-shut mini- fridge, to the carpet-less floor, Orit and I have really made 36-295 an o±ce to call our own. She has been a great person to discuss ideas with, not all of which pertained to research. I will always remember the April fool's day of 2008 when we hacked our group's website and replaced it with \Leslie's Daily Journal," and our never-published research paper, \Analysis of Optimized and Quantized Performance and the Results Obtained." It has been a true pleasure to work with Dr. Sheila Nabanja, a fellow groupmate and next door neighbor. The long days that we spent upstairs in the optics lab as we took pages of data were tolerable because of her optimism and humor. I also need to express my gratitude for her shared interest of taking exercise classes at the gym! During the IAPs of 2009 and 2010 I organized a three-unit seminar class called \Hooked on Photonics" for MIT undergrads. I want to thank everyone who parti- cipated for their selflessness and enthusiasm, especially Dr. Vanessa Wood (now Professor), Dr. Tim Heidel, and Dr. Zheng Wang (now Professor). Course 6.095 could not have been possible without you. There are many other friends at MIT whom I will not be able to mention here. But I absolutely need to express my gratitude to everyone in my group for their fellowship: Pei Chun Amy Chi, Mohammad Araghchini, Dr. Ryan Williams, and Dr. Reginald Bryant. My experience at MIT would not have been the same without the kindness from my friends Adrian YiXiang Yeng, Dr. Sidney Tsai, Allen Hsu, David He, Dr. Amil Patel, Dr. Donald Winston, and Dr. Mahmut Ersin Sinangil. Finally, I want to thank my family for always being there for me.