18.2 A 4x64Gb/s NRZ 1.3pJ/b Co-Packaged and Fiber-Terminated 4-Ch VCSEL-Based Optical Transmitter.

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.