Scott Lerner

A High-Speed Optical Multi-Drop Bus for Computer Interconnections

Buses have historically provided a flexible communications structure in computer systems. However, signal integrity constraints of high-speed electronics have made multi-drop electrical busses infeasible. Instead, we propose an optical data bus for computer interconnections. It has two sets of optical waveguides, one as a fan-out and the other as a fan-in, that are used to interconnect different modules attached to the bus. A master module transmits optical signals which are received by all the slave modules attached to the bus. Each slave module in turn sends data back on the bus to the master module. Arrays of lasers, photodetectors, waveguides, microlenses, beamsplitters and Tx/Rx integrated circuits are used to realize the optical data bus. With 1 mW of laser power, we are able to interconnect 8 different modules at 10 Gb/s per channel. An aggregate bandwidth of over 25 GB/s is achievable with 10 bit wide signaling paths.

Etendue and optical system design

This paper presents our practical experience with etendue and optical system design. We clarify several different commonly used definitions of etendue. Examples are given that illustrate the applicability of conservation of etendue.