Photonics Maintaining Competitiveness in the Information Era (1988) / Chapter Skim
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3. Opportunities in Information Processing
3. Opportunities in Information Processing
Pages 23-37
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From page 23... ...
The worldwide market for information processing hardware and software, including computer systems, office automation equipment, and input/output (I/O) peripherals (but not including displays, data storage devices, communications equipment, and consumer audio, video, and personal products)
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From page 24... ...
These advantages are technically available, and the existing widespread commercial use of photonics in long-distance telecommunications systems has provided a seed from which the use of photonics in information processing might grow. CURRENT TECHNOLOGICAL STATUS Digital Technology In digital applications, information is coded into binary form, where a voltage near one standard value represents a 1 and a voltage near another standard value represents a 0.
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From page 25... ...
, ensures low cost. Si integrated circuits reliably carry out logic and memory functions despite the variations of the characteristics of individual devices that mass production entails.
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GaAs technology can produce 1-kbit memory chips. For applications that require more speed than Si can provide, GaAs integrated circuits represent the most mature alternative and are commercially available.
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From page 27... ...
For example, in laser printers that have a single laser as the light source, a multifaceted rotating mirror provides a raster scan, while the rotating photosensitive drum that captures the image provides an orthogonal scan. The laser diode is turned on and off, and the lenses keep the beam focused on the surface of the drum (Figure 3.1~.
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From page 28... ...
Present advanced development activities are probing how far into a computer this optical interconnect approach will penetrate; many people feel that optically interconnecting printed circuit boards will become a widespread reality. A closely related advantage of optics for interconnects is freedom from cross talk; i.e., two beams of photons can pass through one another with
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From page 29... ...
Powerful optical analog processing of this type is already being harnessed in practical systems, as described under "Analog Technology" in the "Current Technological Status" section. AREAS RIPE FOR PRODUCT DEVELOPMENT Digital Interconnect Technology As pointed out above, progress in electronic digital computers is being limited by communications considerations.
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From page 30... ...
In light of the relatively well-developed GaAs materials growth and electronic circuit technology and the development of inexpensive sources for the commercial market (e.g., compact disk and laser printers) , it is inherently reasonable to concentrate much of the photonic product development effort on GaAs technology.
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From page 31... ...
These devices, referred to as optoelectronic integrated circuits (OEICs) , could be formed in GaAs and would take full advantage of the state of development of GaAs electronic integrated circuits and optoelectronic components (Figure 3.3~.
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From page 32... ...
But even with the same bandwidth, optical interconnects would lead to a reduction in the drive power requirements for the I/O connections when compared to that required for electrical lines that need to be terminated to prevent reflections. Thus, when power requirements are a limiting factor, optical interconnects have an advantage for chip-to-chip communication at data rates of around 100 Mbit/s or higher.
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From page 33... ...
Digital Interconnect Technology In the area of OEICs, sustained work is needed, especially in the area of light-emitting chips. The development of low-cost, high-yield OEICs with lasers, LEDs, and/or modulators is a challenging area because the optoelectronic and electronic circuits have quite different materials and processing needs that complicate device fabrication.
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From page 34... ...
Available devices will be even more useful if algorithm research intensifies its focus on utilizing the bandwidth, freedom from interference, connectivity, and coherent parallel processing capabilities of photonics. In addition, increased interaction between algorithm and device researchers could lead to invention of devices with special characteristics that algorithm developers request.
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From page 35... ...
Another important direction in optical digital information processing involves neural networks, a concept based on analogies to the central nervous system. Synthetic neural networks are being implemented both in electronics and in optics.~3~4 The basic approach models the behavior of a neural network by using a connection matrix between an array of inputs and an array of outputs and nonlinear feedback to the inputs from all of the outputs to modify the strength of the connections.
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From page 36... ...
This pathway offers the tantalizing, longterm prospect of far more powerful information-processing technology but must be considered speculative until practical optical logic devices are developed. These visions demand that photonics research and development be pursued at a vigorous pace to keep the United States at the forefront of information processing science and technology.
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From page 37... ...
1984. Multiple quantum wells for optical logic.
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