| Smart
Pixel Arrays (SPAs) |
Definition
High speed smart pixel arrays (SPAs) hold great promise as an enabling technology
for board-to-board interconnections in digital systems. SPAs may be considered
an extension of a class of optoelectronic components that have existed for over
a decade, that of optoelectronic integrated circuits (OEICs). The vast majority
of development in OEICs has involved the integration of electronic receivers with
optical detectors and electronic drivers with optical sources or modulators. In
addition, very little of this development has involved more than a single optical
channel. But OEICs have underpinned much of the advancement in serial fiber links.
SPAs encompass an extension of these optoelectronic components into arrays in
which each element of the array has a signal processing capability. Thus, a SPA
may be described as an array of optoelectronic circuits for which each circuit
possesses the property of signal processing and, at a minimum, optical input or
optical output (most SPAs will have both optical input and output).
The name smart pixel is combination of two ideas, "pixel" is an image
processing term denoting a small part, or quantized fragment of an image, the
word "smart" is coined from standard electronics and reflects the presence
of logic circuits. Together they describe a myriad of devices. These smart pixels
can be almost entirely optical in nature, perhaps using the non-linear optical
properties of a material to manipulate optical data, or they can be mainly electronic,
for instance a photoreceiver coupled with some electronic switching.
Smart pixel arrays for board-to-board optical interconnects
may be used for either backplane communications or for distributed board-to-board
communications, the latter known as 3-D packaging. The former is seen as the more
near-term of the two, employing free-space optical beams connecting SPAs located
on the ends of printed circuit boards in place of the current state-of-the-art,
multi-level electrical interconnected boards. 3-D systems, on the other hand,
are distributed board-to-board optical interconnects, exploiting the third dimension
and possibly employing holographic interconnect elements to achieve global connectivity
(very difficult with electrical interconnects).
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