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Integrated circuit scaling has enabled a huge growth in processing capability, which necessitates a corresponding increase in inter-chip communication bandwidth. As bandwidth requirements for chip-to-chip interconnection scale, deficiencies of electrical channels become more severe. Optical links present a viable alternative due to their low frequency-dependent loss and higher bandwidth density in form of WDM. Increasing silicon integration leads to better performance in optical links but necessitates a corresponding intimate design strategy of electronics and photonics. In this light, designing optical links with a deep understanding of photonics and state-of-the-art electronics brings their performance to an unprecedented level.
In this talk a 3D-integrated CMOS/Silicon-photonic receiver will be presented. This receiver is designed to effectively take advantage of low-cap silicon photonic photodiodes and advanced 3D-integration technologies. The electronic chip features an integrating receiver based on a low-bandwidth TIA that employs double-sampling and equalization through dynamic offset modulation. This architecture is also implemented in a 4-channel WDM-based parallel optical receiver using a forwarded clock at quarter-rate. Quadrature ILO-based clocking is employed for synchronization and a novel frequency-tracking method that exploits the dynamics of IL in a quadrature ring oscillator to increase the effective locking range.
Next, I will describe some of my research in other primary elements of an optical link: clocking and transmitters. A first-order frequency synthesizer will be presented that is suitable for high-speed optical links as well as on-chip clock generation. This frequency synthesizer is capable of receiving a low jitter optical reference clock generated by a high-repetition-rate mode-locked laser. On the optical transmitter side, two new techniques will be presented. First technique is thermal stabilization of micro-ring resonator modulators through direct measurement of ring temperature using a monolithic PTAT temperature sensor. Second technique is a differential ring modulator that breaks the optical bandwidth/quality factor trade-off known to limit the speed of high-Q ring modulators. This structure maintains a constant energy in the ring to avoid pattern-dependent power droop.
When electronics and photonics are closely integrated they provide a great promise for improving interconnect performance and reduce cost. Holistic design of co-integrated optical interconnects provides a unique opportunity to design entirely new architectures and bring the performance of current systems to unprecedented levels. In this light, I will cover some future directions for my research beyond data communication such as sensors, computing and networking applications.
Saman Saeedi received his double-major B.S. degree in Electrical Engineering and Physics from Sharif University of Technology, Tehran, Iran, in 2010. He received his M.S. and Ph.D. degrees in Electrical Engineering from California Institute of Technology, Pasadena, in 2011 and 2015 respectively. He is currently a member of VLSI research group at Oracle Labs. The focus of his current research is low-power, high-performance mixed-signal integrated circuits with applications in sensing and communication. During the summer of 2012 he was a PhD intern at Apple Inc. where he worked on display driver chipsets. His work during fall and winter of 2014 at Rockley Photonics Inc. enabled a core technology for CMOS/silicon-photonic optical packet switching in data centers.
Dr. Saeedi is a gold medal winner of the National Physics Olympiad and recipient of four years undergraduate fellowship from National Elite Foundation of Iran. He received the Atwood fellowship in Fall 2010 and is the recipient of 2014 Intel/Texas Instruments/Catalyst Foundation CICC Student Scholarship Award and a finalist of 2015 Broadcom Foundation University Research Competition. Dr. Saeedi holds 7 U.S. patents and is serving on the Technical Program Committee of IEEE Optical Interconnect Conference.
