Page 317 - Introduction to Information Optics

302 6. Interconnection with Optics

Fig. 6.1. Fully embedded optical interconnection using thin-film transmitter and receiver within u
PC hoard.

illustrated in Fig. 6.1. All the elements involved in providing high-speed optical
communications within one board are shown. These include a vertical cavity
surface-emitting laser (VCSEL), surface-normal waveguide couplers, a poly-
imide-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 are all through electrical
vias connecting to the surface of the PC board. In this 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.
The approach described here presents two major opportunities. The first is
to accomplish the requirement of planarization necessary to provide three-
dimensional (3D) on-board interconnect integration through vias to fulfill the
required interconnection density. The board-level optical interconnection
layers can be sandwiched between electrical interconnection layers. Assurance
of the flatness and compatibility of the insertion of optical layers is crucial
to ensure a technology transferable to the computer industry. The second
opportunity is to provide compatible optical-to-electrical and electrical-to-
optical conversions, which are the major concerns for system packaging. This
approach will use fully embedded transmitters (electrical-to-optical) and re-
ceivers (optical-to-receiver) within the 3-D integrated board [9,10, 11]. For a
multilayer interconnection the optical components, including lasers, wavegu-
ides, couplers, and detectors, can be fully embedded. The input electrical signal