Terabus: Terabit/Second-Class Card-Level Optical Interconnect Technologies

In the "Terabus" optical interconnect program, optical data bus technologies are developed that will support terabit/second chip-to-chip data transfers over organic cards within high-performance servers, switch routers, and other intensive computing systems. A complete technology set is developed for this purpose, based on a chip-like optoelectronic packaging structure (Optochip), assembled directly onto an organic card (Optocard). Vertical-cavity surface emitting laser (VCSEL) and photodiode arrays (4times12) are flip-chip bonded to the driver and receiver IC arrays implemented in 0.13-mum CMOS. The IC arrays are in turn flip-chip assembled onto a 1.2-cm² silicon carrier interposer to complete the transmitter and receiver Optochips. The organic Optocard incorporates 48 parallel multimode optical waveguides on a 62.5-mum pitch. A simple scheme for optical coupling between the Optochip and the Optocard is developed, based on a single-lens array etched onto the backside of the optoelectronic arrays and on 45deg mirrors in the waveguides. Transmitter and receiver operation is demonstrated up to 20 and 14 Gb/s per channel, respectively. The power dissipation of 10-Gb/s single-channel links over multimode fiber is as low as 50 mW

I. Introduction

THE bandwidth and density requirements for interconnects within high-performance computing systems are growing fast, owing to increasing chip speeds, wider buses, and larger numbers of processors per system. Some of these trends are highlighted in the most recent update of the International Technology Roadmap for Semiconductors [1] and are summarized in [2]. These trends project that many high-performance chips or modules will be increasingly limited by off-chip or off-module bandwidth. While some relief is expected to come from larger caches and software, there will be an increasing need for technologies that provide improved chip-to-chip or module-to-module interconnections in order to continue the price-performance trends that servers and other high -end systems have shown over the years.