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It is well-known that interconnect issues pose a significant bottleneck with regard to improving the
performance of high-speed integrated systems such as a cluster of computer processing units. Power, speed
(bandwidth), and size all affect the computational performance and capabilities of future systems. High-speed
optical processing has been looked to as a means for eliminating this interconnect bottleneck.
Presented here are the results of a study for a novel optical (integrated photonic) processor which would
allow for a high-speed, secure means for arbitrarily addressing a multiprocessor system. This paper will
present analysis, simulation, and optimization results for the architecture as well as considerations for a
proof-of-concept level system design. The architecture takes advantage of spatial and wavelength diversity
and in this regard may be regarded as a Multiple Input Multiple Output (MIMO) architecture.
A given node to be addressed, rather than having a wired metal contact as an output, has as a radiating laser
source that has been modulated with the data to be conveyed to another point in the system. Each processor
node radiates a different optical wavelength. Each individual wavelength is chosen, for example, to
correspond to the wavelengths associated with a WDM ITU grid. All wavelengths are incident on a
coherent fiber bundle which acts as an array receiver. Unlike conventional phased arrays, the receive
elements are spaced many wavelengths apart giving rise to a large number of grating lobes. It will be
shown that by using appropriate photonic/optical signal processing methods any node of the processor
cluster can be randomly and rapidly addressed using high-speed phase shifters (electrooptic or others) as
control elements. The diversity techniques employed achieve high gain and a narrow beamwidth in the
direction of the desired node and high attenuation with regard to the signals from all other nodes. As is
often the case of MIMO-bases systems, overall performance exceeds that of diffraction limited array
processing.
In addition to the interconnect application discussed, the methods described in this paper can also be
applied to other applications where rapid electrical (non-mechanical) optical beamsteering is required such
as raster scanned laser radar systems and tracking, guidance, and navigation systems.
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