Posts Tagged ‘Optical computing

Efficiencies in optical computing

Optical computing is an inherently multidisciplinary subject whose study routinely involves a spectrum of expertise that threads optical physics, materials science, optical engineering, electrical engineering, computer architecture, computer programming, and computer theory. Applying ideas from theoretical computer science, such as analysis of algorithms and computational complexity, enables us to place optical computing in a framework where we can try to answer a number of important questions. For example,which problems are optical computers suitable for solving? Also, how does the resource usage on optical computers compare with more standard (e.g. digital electronic) architectures? The physical principles behind some efficiencies in optical computing are outlined here.

1. Fan-in efficiency

Kirchoff’s Law is well understood in analog electronics as a natural and constant time means of summing the current at the intersection of an arbitrary number of wires. In optics, the same thing is possible by directing several light beams towards a point detector with a linear response to incident light. Such an optical arrangement sums n non-negative integers in O(1) addition steps. On a model of a sequential digital electronic computer this would require n − 1 addition operations and even many typical (bounded fan-in)parallel models, with n or more processors, take O(log n) time steps. Tasks that rely on scalar summation operations (such as matrix multiplication) would benefit greatly from an optical implementation of the scalar sum operation. Similarly, O(1) multiplication and O(1) convolution operations can be realised optically. Very recently, an optics-based digital signal processing platform has been marketed that claims digital processing speeds of  tera (10^12) operations per second.

2. Efficiency in interconnection complexity

As optical pathways can cross in free space without measurable effect on the information in either channel, high interconnection densities are possible with optics. Architectures with highly parallel many-to-many interconnections between parallel surfaces have already been proposed for common tasks such as sorting. Currently, intrachip, inter-chip, and inter-board connections are being investigated for manufacturing feasibility.

3. Energy efficiency

Electrical wires suffer from induced noise and heat, which increases dramatically whenever wires are made thinner or placed closer together, or whenever the data throughput is increased. As a direct consequence of their resistance free pathways and noise-reduced environments, optical systems have the potential to generate less waste heat and so consume less energy per computation step than electronic systems. This has beend emonstrated experimentally with general purpose digital optical processors.

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Optical computing today

The traditional field of optical computing is no longer so active, it is not dead but it has evolved. Applied Optics has no longer an issue per month on the subject, but in each issue there is a section “Information is processing”. “Optical Computing”. However, it should be noted that there are still two conferences organized by the SPIE on the subject: “Optical Pattern Recognition” since 20 years in Orlando in the frame of the SPIE conference “Defense, Security, Sensing”, and “Optics and Photonics for Information Processing” in San ego in the frame of the SPIE conference “Optics and Photonics”. The research on optical correlators is continued by fewer research teams, however it should be noted that the Jet Propulsion Laboratory (JPL) is still working on optical correlators for real time automatic target recognition correlators for real time automatic target recognition. Some of the algorithms developed for pattern recognition initially for optical processing are now used successfully in digital computers. DOEs are now mature and are part of numerous industrial products. All the research on the fabrication of DOEs made possible the fabrication of nano structures and very exciting new fields of research such as nano photonics, nano fluidics and optofluidics. The list of the papers presented in 2009 at the SPIE conference “Optics and Photonics” reflects the growing interest in all the research related to nano science and nano optics. Bio photonics is an exponentially growing field that is largely benefiting from the past research in optical processing. Typical examples are the optical tweezers and the optical trapping. Thanks to the digital holography, where the holographic plate is replaced by a camera, holography is again finding industrial applications particularly for the quality control of manufactured products, for digital holographic microscopy opening completely new fields of applications for optical microscopy. For information processing, optics is also finding a place where it has a unique feature such as the polar metric imaging, or multispectral imaging. Security applications are also a promising field for optical information processing. It is well known that optics is used commonly for the communication systems.

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