18.2 A 4x64Gb/s NRZ 1.3pJ/b Co-Packaged and Fiber-Terminated 4-Ch VCSEL-Based Optical Transmitter
Susnata Mondal, Junyi Qiu, Sashank Krishnamurthy, Joe Kennedy, Soumya Bose, Tolga Acikalin, Shuhei Yamada, James Jaussi, Mozhgan Mansuri
Abstract
As bandwidth demand increases, electrical interconnects suffer from limited reach due to channel loss. Multi-mode vertical-cavity surface-emitting laser (VCSEL)-based optical interconnects can enable high-bandwidth connectivity while extending the reach to tens of meters [1] –[3]. Pluggable VCSEL-based optical modules are widely used in data center communication. With VCSELs and their drivers separately mounted on a board, these modules similarly suffer from electrical interconnect limitations when they communicate to computing/switching (XPU/SW) systems; hence, they do not meet stringent system requirements on interconnect latency, bandwidth (BW), or energy efficiency. A co-packaged optical interconnect solution can address the outlined challenges by integrating the optical components with an XPU/SW and satisfy VCSEL temperature and reliability requirements [4]. This paper presents a co-packaged VCSEL-based optical TX solution that integrates a VCSEL driver (VCDRV) IC, VCSEL array, and fiber termination on the XPU/SW package. A complex-zero continuous time linear equalizer (CTLE) is introduced to equalize a complex-pole pair present in the VCSEL optical response and enhance the maximum achievable baud rate for best latency and energy efficiency. A low-power, low-jitter resonant clocking architecture improves system jitter performance and includes a transmission-line (TL)-based resonant distribution and a wide-tuning-range quadrature generation (quad-gen). Finally, a low-power serializer and electrical driver architecture employs pulse-width correction for improved eye symmetry.