Presented By: Electrical and Computer Engineering
High-Speed Back Emitting VCSEL for AI Scale-up Optical Interconnects
Connie Chang-Hasnain, High-Speed Back Emitting VCSEL for AI Scale-up Optical Interconnects Berxel Photonics Co. LTd.
Abstract
High bandwidth-density and energy-efficient optical links are required to interconnect accelerators, memory, and switches in AI scale-up systems. Back-emitting (BE) vertical-cavity surface-emitting laser (VCSEL) are promising for this application because of its two-dimensional (2D) topology facilitating large array, simultaneous operation using flip-chip addressable architecture. The wavelength of interests ranges from 940- to 1060-nm wavelength regime. In this talk, we review BE-VCSEL at both wavelengths, showing their suitability for high-speed multi-mode fiber (MMF) transmission. For the 940-nm BE-VCSEL with a monolithically integrated high-contrast- metalens (HCM) at the back of the substrate to enable high efficiency MMF coupling with a large tolerance. A 106-Gb/s PAM4 link over 30-m OM2 fiber operates below the KP4-FEC threshold was obtained. The 940-nm flip-chip device exhibits an approximately 40-K lower junction temperature than a reference 850-nm top-emitting VCSEL at 9 mA, supports an open 106-Gb/s PAM4 eye at 110 °C, and achieves error-free 25-Gb/s NRZ transmission at 140 °C. A 16-channel near-package-optics transmitter provides clear 106-Gb/s PAM4 eyes across all channels, corresponding to an aggregate capacity of approximately 1.6 Tb/s. For the 1060-nm BE-VCSEL, we show a 3-dB modulation bandwidth of 43.97-GHz at 7 mA, limited by instrumentation. The device has a low 0.4-mA threshold current and intensity noise of -149.6 dB/Hz at 7 mA. It further supports 212-Gb/s PAM4 transmission over 30-m OM2 and 50-m OM5 fibers under the stated transmitter and receiver equalization conditions. We believe these results attest to BE-VCSEL array for high-lane-rate, two-dimensionally scalable optical engines for cost-effective AI scale-up interconnects through conventional MMF over a wide wavelength range between 940~1060 nm.
Bio
Connie Chang-Hasnain is Chairperson of Berxel Photonics Co. Ltd. and X.Q. Deng Presidential Chair Professor at the Chinese University of Hong Kong (Shenzhen). Dr. Chang-Hasnain received her Ph.D. in Electrical Engineering and Computer Science (EECS) from UC Berkeley in 1987. She was a Member of the Technical Staff at Bell Communications Research (1987–1992) and Assistant Professor at Stanford University (1992–1995). She joined UC Berkeley as Professor of EECS in 1996. She was Whinnery Distinguished Chair Professor since 2006; Chair of the Nanoscale Science and Engineering Graduate Group 2006-2017; and Associate Dean for Strategic Alliances of College of Engineering 2014-2019. She retired from UC Berkeley and is Whinnery Chair Professor Emerita since 2020.
Prof. Chang-Hasnain’s research interests range from semiconductor optoelectronic devices to materials and applications. Over the past 40 years, she worked on many aspects of VCSELs including planar VCSEL structure, MEMS-VCSEL for wavelength tuning, and VCSEL arrays for 3D imaging. She has been honoured with the 2024 IEEE Nick Holonyak Jr. Medal, 2018 Okawa Prize, 2015 UNESCO Medal For the Development of Nanoscience and Nanotechnologies, and 2011 IEEE David Sarnoff Award. She was the Editor-in-Chief of Journal of Lightwave Technology 2007-2012, a member of IEEE LEOS Board of Governors, OSA Board of Directors, and the 2021 President of Optica. She is member of the US National Academy of Engineering.
High bandwidth-density and energy-efficient optical links are required to interconnect accelerators, memory, and switches in AI scale-up systems. Back-emitting (BE) vertical-cavity surface-emitting laser (VCSEL) are promising for this application because of its two-dimensional (2D) topology facilitating large array, simultaneous operation using flip-chip addressable architecture. The wavelength of interests ranges from 940- to 1060-nm wavelength regime. In this talk, we review BE-VCSEL at both wavelengths, showing their suitability for high-speed multi-mode fiber (MMF) transmission. For the 940-nm BE-VCSEL with a monolithically integrated high-contrast- metalens (HCM) at the back of the substrate to enable high efficiency MMF coupling with a large tolerance. A 106-Gb/s PAM4 link over 30-m OM2 fiber operates below the KP4-FEC threshold was obtained. The 940-nm flip-chip device exhibits an approximately 40-K lower junction temperature than a reference 850-nm top-emitting VCSEL at 9 mA, supports an open 106-Gb/s PAM4 eye at 110 °C, and achieves error-free 25-Gb/s NRZ transmission at 140 °C. A 16-channel near-package-optics transmitter provides clear 106-Gb/s PAM4 eyes across all channels, corresponding to an aggregate capacity of approximately 1.6 Tb/s. For the 1060-nm BE-VCSEL, we show a 3-dB modulation bandwidth of 43.97-GHz at 7 mA, limited by instrumentation. The device has a low 0.4-mA threshold current and intensity noise of -149.6 dB/Hz at 7 mA. It further supports 212-Gb/s PAM4 transmission over 30-m OM2 and 50-m OM5 fibers under the stated transmitter and receiver equalization conditions. We believe these results attest to BE-VCSEL array for high-lane-rate, two-dimensionally scalable optical engines for cost-effective AI scale-up interconnects through conventional MMF over a wide wavelength range between 940~1060 nm.
Bio
Connie Chang-Hasnain is Chairperson of Berxel Photonics Co. Ltd. and X.Q. Deng Presidential Chair Professor at the Chinese University of Hong Kong (Shenzhen). Dr. Chang-Hasnain received her Ph.D. in Electrical Engineering and Computer Science (EECS) from UC Berkeley in 1987. She was a Member of the Technical Staff at Bell Communications Research (1987–1992) and Assistant Professor at Stanford University (1992–1995). She joined UC Berkeley as Professor of EECS in 1996. She was Whinnery Distinguished Chair Professor since 2006; Chair of the Nanoscale Science and Engineering Graduate Group 2006-2017; and Associate Dean for Strategic Alliances of College of Engineering 2014-2019. She retired from UC Berkeley and is Whinnery Chair Professor Emerita since 2020.
Prof. Chang-Hasnain’s research interests range from semiconductor optoelectronic devices to materials and applications. Over the past 40 years, she worked on many aspects of VCSELs including planar VCSEL structure, MEMS-VCSEL for wavelength tuning, and VCSEL arrays for 3D imaging. She has been honoured with the 2024 IEEE Nick Holonyak Jr. Medal, 2018 Okawa Prize, 2015 UNESCO Medal For the Development of Nanoscience and Nanotechnologies, and 2011 IEEE David Sarnoff Award. She was the Editor-in-Chief of Journal of Lightwave Technology 2007-2012, a member of IEEE LEOS Board of Governors, OSA Board of Directors, and the 2021 President of Optica. She is member of the US National Academy of Engineering.
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