题目: Challenges of integrated Bragg gratings in silicon photonics

　　报告人: Sophie LaRochelle (Center for Optics, Photonics and Lasers (COPL), Department of Electrical and Computer Engineering, Université Laval, Québec QC, Canada)

　　时间: 2014年11月6号，上午9:00

　　地点: 中科院半导体研究所图书馆101会议室

　　摘要: In today’s information world, people and devices worldwide are constantly exchanging data through the cloud. This increased connectivity has spurred a quest for high capacity communication links implemented with subsystems that that are low cost/size/power and high density/speed. Integrated circuits in silicon have been the workhorse of microelectronics for decades but photonic integrated circuits (PICs) are barely emerging as a practical solution for these high-speed low-cost data networks. Many integrated devices must thus be developed in order for the silicon photonic designers to have all the building blocks needed to implement a high number of functionalities. One such building block is an optical filter with precisely tailored amplitude and phase responses. In optical fibers, photoinduced Bragg grating filters have been extremely successful at providing accurate filters with elaborate spectral responses for a plethora of applications. In this talk, we examine the challenges in translating these advances in Bragg grating filter design to nanowire waveguides in silicon-on-insulator (SOI).

　　Due to the scaling property of Bragg gratings, when the filter bandwidth needs to be reduced or when the spectral response needs to be precisely tailored, it is necessary to fabricate long integrated Bragg gratings (IBGs) with weak coupling coefficients. Indeed, the grating length needs to be sufficient to implement apodization profiles with adequate resolution. In SOI, long and weak IBGs are difficult to achieve because of two main issues. Firstly, there is a strong overlap of the optical mode with the sidewalls leading to large coupling coefficients, typically > 100 cm-1, even when the grating corrugation amplitude is limited to a few nanometers. The precision of the amplitude apodization is therefore strongly limited by the resolution of the fabrication process. Secondly, long gratings are more prone to spectral distortions introduced by the accumulated phase noise due to sidewall roughness.

　　In this talk, we first describe modeling and characterization of spectral distortions due to phase noise. We quantify through SEM measurement the statistical parameters of sidewall roughness and introduce the values in a noisy IBG emulator to predict device yield. We further propose a strategy to mitigate phase noise by the use of hybrid singlemode-multimode waveguide structures. Finally, we demonstrate two apodization techniques that are robust to fabrication variations. We show unprecedented IBG performance in terms of bandwidth and phase response design. Finally, these apodization techniques are shown to be compatible with IBGs made in spiral waveguides to improve compactness.

　　Lastly, we will briefly present the Center for Optics, Photonics and Lasers (COPL). We will describe its fiber fabrication facility and the testbeds of the optical communication laboratory. We will discuss opportunities for collaboration, student exchange and graduate studies.

　　报告人简历: Professor Sophie LaRochelle received a Bachelor's degree in engineering physics from Université Laval, Canada, in 1987; and a Ph.D. degree in optics from the College of Optical Sciences, University of Arizona, USA, in 1992 under the supervision of Prof. George Stegeman. From 1992 to 1996, she was a Research Scientist at the Defense Research and Development Canada - Valcartier, where she worked on electro-optical systems. She is now a professor at the Department of Electrical and Computer Engineering, Université Laval, where she holds a Canada Research Chair (tier 1) in Advanced Photonics Technologies for Communications. She is a renowned expert in fiber optics components and communications with more than 285 papers published in peer-reviewed journals and conferences. She is the co-author of eight patents (three licenced to the industry). She has served on the advisory or technical committees of many organizations. In career, she has directed the work of more than 60 graduate students and post-doctoral fellows and has led several industry-sponsored projects. Prof. LaRochelle is an IEEE senior member and an OSA senior member.

　　Her current research activities are focused on active and passive components for optical communication systems including optical fibers carrying modes with orbital angular momentum, erbium-doped fiber amplifiers for spatial multiplexing, silicon photonic devices for short range communications, and wavelength converters for packet switched networks. Over the years, she has made contributions in the field of fiber lasers (tunable, multiwavelength, high power, narrow frequency or pulsed), all-optical signal processing (dispersion compensation, photonic code identification, pulse rate multiplication, pulse shaping and beam forming), analog optical transmissions (radio-over-fiber, GPS-over-fiber, ultrawideband-over-fiber), and code division multiple access with frequency encoding.

　　In career, she has published 120 papers in refereed journals, almost exclusively in IEEE or OSA journals, and more than 165 papers in international conference proceedings. Her work has been highly cited, receiving more than 3450 citations according to Google scholar (h-index=29, i10-index=83). Two papers have received more than 300 citations (FFH-CDMA, IEEE J. of Lightwave Technol., 1999, cited 388 times and Multiwavelength laser, IEEE J. of Lightwave Technol., 2000, cited 331 times).

　　Prof. LaRochelle has been very active in developing photonics research in Canada through the program of the Canadian network of centers of excellence Canadian Institute for Photonics Innovations (CIPI). From 1999 to 2012, she has successively been the leader of four major multi-university projects: Fiber optics components and devices, Advanced fibre laser systems, Packet switched networks with photonic code-based processing, and Optical packet-switched architecture and technologies for data centers. She has served on the technical committees of many conferences, and several times as chair of subcommittees, including the Optical Fiber Communication Conference (OFC, OSA/IEEE conference), Bragg Grating, Photosensitivity and Poling in Glass Waveguides (BGPP, OSA topical meeting), Photonics in Switching (OSA topical meeting) and Photonics North (SPIE). She is currently serving on the technical committee of the Confrence on Lasers and Electro-Optics (CLEO). Prof. LaRochelle has also served on the Advisory committee to Quebec’s Minister of Développement économique, de l’innovation et de l’exportation, M. Clément Gignac, for the revision of Québec investment policy in research and innovation (2009-2010) and she is now serving on the board of directors of CMC microsystems.