Page 363 - Introduction to Information Optics

348 6. Interconnection with Optics

interconnection layer, as shown in Fig. 6.1. Each bus line consists of two
optical waveguides, one OIC per plug-in board, couplings and stub wave-
guides, and power and ground lines (metal traces) to power the OICs.

6.8. SUMMARY

This chapter described necessary building blocks of the board-level guided
wave optical interconnection. All elements involved in providing high-speed
optical communications within one board were demonstrated. These include a
vertical cavity-surface emitting laser (VCSEL), surface-normal waveguide
couplers, a polyimide-based channel waveguide functioning as the physical
layer of optical bus, and a photoreceiver. The driving electrical signal to
modulate the VCSEL and the demodulated signal received at the photoreceiver
can be applied through electrical vias connecting to the surface of the PC
board. In such an approach, all the areas of the PC board surface are occupied
by electronics and therefore one only observes performance enhancement due
to the employment of optical interconnections but does not worry about the
interface problem between electronic and optoelectronic components, unlike
conventional approaches.
A l-to-48 optical clock signal distribution network for a supercomputer
board was described. Further experimental results on a 12-channel linear array
of thin-film polyimide waveguides, VCSELs (42 ^m, can be made as thin as
8 jum), and silicon MSM photodetectors (10 ^m) suitable for a fully embedded
implementation are provided. Two types of waveguide couplers, tilted gratings
and 45° total internal reflection (TIR) mirrors, are fabricated within the
polyimide waveguides. A waveguide bus architecture was presented which
provides bidirectional broadcasting transmission of optical signals. Such a
structure is equivalent to such IEEE-standardized bus protocols as VME bus
and FutureBus.

Authors will like to acknowledge the research contributions from the Lei
lin, Chulchae choi, Yujie Liu, Linghui Wu, M. Dubinovski, Feming Li, Dr.
Bing Li, and Dr. Suning Tang. We also acknowledge the research funds
provided by Radiant Photonics, ONR, BMDO, DARPA, AFRL, the ATP
program of the State of Texas, 3M Foundation, Dell Computer, Cray Re-
search, GE, Honeywell and MCC.