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Open Access Publications from the University of California

Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2017)

Silicon photonic interconnects hold great promise in meeting the high bandwidth and low-energy demands of next-generation interconnects. System-level driven electronic-photonic co-design is the key to improving the bandwidth density and energy efficiency. In this study, a comprehensive co-optimization framework is developed for high-speed silicon photonic transmitters utilizing compact models and a detailed optical simulation framework. Given technology and link constraints, microring and Mach-Zehnder transmitter designs are optimized and compared based on a unified optical phase shifter model. Non-return-to-zero (NRZ) and pulse-amplitude-modulation-4 (PAM-4) modulation schemes are analyzed and compared for microring-based transmitters. Using the co-design approach, a monolithic 40Gb/s optical NRZ transmitter based on microring modulators is designed and demonstrated in zero-change 45nm CMOS SOI process. Electronic-photonic co-design with the high swing driver enables this transmitter to achieve total energy efficiency of 330fJ/b and the photonics and modulator driver area bandwidth density of 6.7 Tb/s/mm2. This dissertation also discusses the design and demonstration of the first full silicon photonic interconnect on a 3D integrated electronic-photonic platform. These results make the microring-based silicon photonic transceivers an attractive solution for the next-generation inter and intra-rack photonic interconnects. Finally, a short-reach laser-forwarding coherent link architecture is proposed to further improve the energy efficiency of silicon photonic interconnects. The key concepts of the proposed architecture are verified experimentally with microring-based silicon photonic transmitters. The architecture saves the laser power by 6-7.5x and could enable complex modulation schemes for the future short-reach optical links.

    Cover page: Electronic-Photonic Co-Design of Silicon Photonic Interconnects
    • Article
    • Peer Reviewed
    UC Irvine Previously Published Works (2020)
    This paper studies distributed Q-learning for Linear Quadratic Regulator (LQR) in a multi-agent network. The existing results often assume that agents can observe the global system state, which may be infeasible in large-scale systems due to privacy concerns or communication constraints. In this work, we consider a setting with unknown system models and no centralized coordinator. We devise a state tracking (ST) based Q-learning algorithm to design optimal controllers for agents. Specifically, we assume that agents maintain local estimates of the global state based on their local information and communications with neighbors. At each step, every agent updates its local global state estimation, based on which it solves an approximate Q-factor locally through policy iteration. Assuming decaying injected excitation noise during the policy evaluation, we prove that the local estimation converges to the true global state, and establish the convergence of the proposed distributed ST-based Q-learning algorithm. The experimental studies corroborate our theoretical results by showing that our proposed method achieves comparable performance with the centralized case.
      Cover page: Distributed Q-Learning with State Tracking for Multi-agent Networked Control
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2015)
      Data transport across short electrical wires is limited by both bandwidth and power density, which creates a performance bottleneck for semiconductor microchips in modern computer systems--from mobile phones to large-scale data centres. These limitations can be overcome by using optical communications based on chip-scale electronic-photonic systems enabled by silicon-based nanophotonic devices. However, combining electronics and photonics on the same chip has proved challenging, owing to microchip manufacturing conflicts between electronics and photonics. Consequently, current electronic-photonic chips are limited to niche manufacturing processes and include only a few optical devices alongside simple circuits. Here we report an electronic-photonic system on a single chip integrating over 70 million transistors and 850 photonic components that work together to provide logic, memory, and interconnect functions. This system is a realization of a microprocessor that uses on-chip photonic devices to directly communicate with other chips using light. To integrate electronics and photonics at the scale of a microprocessor chip, we adopt a 'zero-change' approach to the integration of photonics. Instead of developing a custom process to enable the fabrication of photonics, which would complicate or eliminate the possibility of integration with state-of-the-art transistors at large scale and at high yield, we design optical devices using a standard microelectronics foundry process that is used for modern microprocessors. This demonstration could represent the beginning of an era of chip-scale electronic-photonic systems with the potential to transform computing system architectures, enabling more powerful computers, from network infrastructure to data centres and supercomputers.
        Cover page: Single-chip microprocessor that communicates directly using lightCreative Commons 'BY-NC-ND' version 4.0 license
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