Low-complexity coherent optical receivers

The rapid growth of data-intensive applications in data centers has driven the demand for high-speed, energy-efficient optical interconnects. Traditional intensity-modulation direct-detection (IM-DD) techniques face significant challenges in scaling data rates, making coherent detection a promising alternative for short-reach links. Coherent detection offers higher spectral efficiency by utilizing intensity, phase, and polarization but comes with increased power consumption due to the need for advanced digital signal processing (DSP) engines. This dissertation explores analog signal processing (ASP) techniques for designing low-complexity, power-efficient coherent optical receivers (RXs) tailored for short-reach data center interconnects (DCIs). By minimizing the reliance on power-hungry analog-to-digital converters (ADCs) and complex DSP algorithms, the proposed designs enable more energy-efficient operation. The first part of this work introduces a monolithically integrated, wide-bandwidth, analog carrier-phase recovery (CPR) loop for QPSK coherent RXs, that eliminates the need for external optical feedback loops, enhances phase tracking capabilities and reduces system complexity. Fabricated using a 28 nm CMOS process, the QPSK RX achieves error-free operation at 24 Gb/s, with 10–100 MHz CPR loop bandwidth and 600 MHz frequency tracking range, consuming only 3.2 pJ/bit. The second part extends the QPSK RX and CPR architectures to support 16-QAM formats, addressing the complexities of higher-order modulation. A novel phase detector (PD) design is proposed, leveraging both inner and outer symbols for improved phase tracking of 16-QAM constellations. The 16-QAM RX, also fabricated in a 28 nm CMOS, achieves a bit error ratio (BER) of 1E-10 at 64 Gb/s, with 20 MHz CPR loop bandwidth, while consuming just 1.54 pJ/bit. These innovations highlight the potential for scalable, low-power coherent optical RXs and pave the way for broader adoption of coherent technology in short-reach data center applications.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Electrical & Computer Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2024

Author dc:creator

• Abdelrahman, Ahmed

Contributors dc:contributor

• Hanumolu, Pavan K
• Hanumolu, Pavan Kumar
• Shanbhag, Naresh R.
• Rosenbaum, Elyse
• Schutt-Aine, Jose E.

• Coherent Optical Receivers
• Wireline
• Serial Links
• Transceivers
• Serdes

Statement dc:rights

• Copyright 2024 Ahmed Abdelrahman

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/127487

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F127487