Abstract

Board-to-board and on-board interconnections in high-end digital applications require a combination of low latency, high density, and high bandwidth. There are several problems with metal technology for high-density interconnections running at clock rates at or above several hundred megahertz.¹ Optical interconnects have some unique advantages over metal interconnections and offer a potential alternative solution to the board-to-board interconnect problem. However, this advantage is offset by the long latency and the sensitivity to the switching noise commonly associated with the optical interconnects. One way to reduce latency in an optical link is to remove the encoding and decoding circuits normally associated with serial optical links, and the switching-noise sensitivity of a circuit can be minimized by using a fully differential configuration. Line coding (such as 8B/10B coding) is necessary in conventional optical interconnects in order to maintain the dc balance of the signals so that a constant logic threshold at the receiver can be derived. Therefore other means must be provided for establishing the decision threshold when line coding is eliminated. Also, an uncoded link must be dc coupled if there is no constraint on the lowest-frequency component present in a bit stream.

© 1993 Optical Society of America