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were replaced with optical fibers and so too went local data transmission soon after. To date,
even copper interconnects in modern computers are becoming inadequate and ways are
being sought to replace them with an optical architecture. The principles of SOP that
encompass codesign, cointegration, and ultraminiaturization are timely for the task at hand.
In this chapter we offer an up-to-date view of various attempts to introduce optoelectronic
architecture in modern information networks in order to stay ahead of the information
bandwidth, and we will attempt to make sensible predictions on near-term trends.

6.1 Introduction
Optoelectronic SOP is based on the principles of miniaturization and cointegration to
bring about a higher-performance system at a lower cost. Optoelectronic SOP accomplishes
this goal by embedding thin-film optoelectronic components in digital and analog circuits
to achieve high functional density. Examples of thin-film optoelectronic components may
include lasers, detectors, waveguides, gratings, microlenses, micromirrors, and optical
amplifiers, all of which can comfortably exist within a thickness of 30 μm. This chapter
describes the evolution toward optoelectronic SOP from the board-to-board and chip-to-
chip optical interconnects being developed today through the integration of discrete
components, into a highly integrated multiprocessor optical network. The advantages of
optoelectronic SOP, even in its early stages of evolution, as described in this chapter are
higher performance at lower cost for the system as a whole through the use of simplified
materials, simplified digital integration, expanded architectural options enabled by the
independence of optical bandwidth on distance, and miniaturization.
Optoelectronic SOP systems rely on a strategy of codesign and cointegration of
optical, digital, and radiofrequency functions. Each laser, photodetector, amplifier, and
passive waveguide interface operates at peak performance, and no compromises are
made because of limitations due to incompatibilities with the integration process. At
the same time, SOP designers and integrators seek ways to increase functionality by
ultraminiaturization. This usually means developing and implementing thin-film
optical technology in the form of thin-film lasers and thin-film photodetectors as well
as thin-film flexible optical transceivers and full color organic light-emitting diodes
(OLEDs), high-resolution displays that can be embedded in low-power cell phones,
PDAs, and wireless mobile image processors that can be folded four ways and can fit
neatly into a vest pocket. Clearly, conventional flex copper interconnects are subject to
severe crosstalk limitations, particularly at higher bandwidths. Shielded copper lines
and surface-mount components with large capacitance values, often used for electrical
isolation, become less practical because of the high interconnect density and low power
requirements of portable digital electronics.
While optoelectronic SOP is most commonly associated with highly miniaturized
consumer and sensor products, the SOP concepts can also be applied to larger systems
since they promote miniaturization, expanded design options, and greater packing
efficiency. For example, in a copper data bus one may replace copper lines with optical
waveguides. This can support longer data links with no appreciable signal degradation,
narrower buses with increased bit carrying capacity per line, less crosstalk, less shielding,
and fewer decoupling capacitors, all on an inexpensive substrate with fewer vias. However,
the system is still not fully optimized because this architecture does not take into consideration
the advantages and strengths of integrated optics. In order to optimize the system, one can
remove, from the processor, the power-hungry electronic serializer-deserializer and the