Oct 30 (Thurs) @ 10:00am: "Energy-Efficient O-Band Coherent Links for Data Centers, Enabled by Electronic-Photonic Codesign," Aaron Wissing, ECE PhD Defense

Location: Henley Hall (HH), Room 1010
Zoom Meeting: https://ucsb.zoom.us/j/2041389251
Research Area: Communications & Signal Processing, Electronics & Photonics
Research Keywords: Silicon Photonics, Low Power, Circuit Design, High Speed/Frequency

Abstract

This dissertation demonstrates energy-efficient, high link budget coherent optical interconnects for data centers. Coherent optical interconnects utilize phase modulation as an additional degree of freedom for scaling data rates to meet the growing demands of data centers, imposed by applications such as AI and cloud-computing. Furthermore, coherent receivers allow for more loss tolerant interconnects, allowing optical switching to be incorporated into the network. Optical switching allows the removal of power-hungry electrical switching layers, while offering dynamic-reconfigurability of the network to promote more energy efficient usage of the transceivers and servers in data centers. Coherent technology has already been deployed in long-haul interconnects using digital signal processing (DSP) with high cost and power consumption, but innovative link architecture is required for coherent links to meet the cost and power requirements of data centers.

An analog coherent link operating in O-band using an optical phase locked loop (OPLL) for carrier recovery avoids the need for coherent DSP, offering a reduction in cost and latency, as well as the large link budget given by an integrated local oscillator (LO) in the receiver. A transimpedance amplifier (TIA) with a phase-frequency detector and O-band coherent silicon photonic integrated circuits (PICs) with heterogeneously integrated tunable lasers were developed to implement an OPLL. The large link budget enabled the first demonstration of a coherent link through a silicon photonics O-band wavelength-selective switch. The link used entirely integrated lasers and no off-chip optical amplifiers were needed. A second approach demonstrated is the Mixed-Domain Coherent (MDC) architecture, utilizing the PAM4 DSP currently available for data centers along with low-cost, uncooled lasers in a self-homodyne configuration, where a forwarded LO is boosted by an integrated semiconductor optical amplifier (SOA) for expanded link budget. Reconfigurability with PAM4 is offered by the MDC receiver, and a low-power 90-nm SiGe TIA was demonstrated in both QPSK and PAM4 links at 100 Gbps. A segmented travelling-wave Mach-Zehnder modulator (MZM) transmitter with monolithically integrated CMOS drivers will be presented, with potential applications in future coherent links. The O-band coherent approaches will be compared based on their data rate, energy efficiency, link budget, and implementation feasibility.

Bio

Aaron Wissing is an Electrical Engineering Ph.D. student in the Schow group. He received an M.S. degree in Electrical Engineering from the University of California, Santa Barbara in 2022, and a B.S. degree in Electrical Engineering from the University of California, Los Angeles in 2020. During the program, he interned at Intel from 2021-2022. His research focuses on energy-efficient coherent optical interconnects for data centers, with co-designed photonic and electronic integrated circuits. 

Hosted By: Professor Clint Schow

Submitted By: Aaron Wissing <aaronwissing@ucsb.edu>