Abstract of Optical Computer
mantra of our electronic age has been 'faster, smaller, better' for over two decades
now. Today, computer lies at the very core of our society. As we try to squeeze
more from a silver of silicon, the cost of chip making has become prohibitively
expensive. Chip barriers are now down to three or four atoms apart. So far the
ride has been good, but at some point, something has to give. At that point,
incremental approach to silicon technology would not be enough - we will need
a new approach. Many new technologies abound, but the most promising among them
is the use of light. An Optical Computer is a hypothetical device that uses
visible light or infrared beams, rather than electric current, to perform digital
An electric current flows at only about 10 percent of speed
of light. By applying some of the advantages of visible and/or IR networks at
the device and component scale, a computer can be developed that can perform operations
very much times faster than a conventional electronic computer.
The term 'Optical Computer' can also be used in a broader sense; that is an optical computer is a computer in which light is used somewhere. This can mean fiber optical communications between electronic components, free space connections, or one in which light functions as a mechanism for storage of data, logic or arithmetic.
The Need for Optical Computers
Optical interconnections and optical integrated circuits will provide a way out of these limitations to computational speed and complexity inherent in conventional electronics. Optical computers will use photons travelling on optical fibres or thin films instead of electrons to perform the appropriate functions. In the optical computer of the future, electroic circuits and wires will be replaced by a few optical fibres and films, making the systems more efficient with no interference, more cost effective, lighter and more compact. Optical components would not need to have insulators as those needed between electronic components because they don't experience cross talk. Indeed, multiple frequencies (or different colours) of light can travel through optical components without interfacing with each others, allowing photonic devices to process multiple streams of data simultaneously.
In future Terabit speeds (1 Terabit, abbreviated "Tb", is 10 12 , or 1 trillion bits) are needed to accommodate the growth rate of the Internet and the increasing demand for bandwidth-intensive data streams. Optical data processing can perform several operations simultaneously (in parallel) much faster and easier than electronics. This "parallelism" when associated with fast switching speeds would result in staggering computational power. For example, a calculation that might take a conventional electronic computer more than eleven years to complete could be performed by an optical computer in a single hour.
All-optical switching using optical materials can relieve the escalating problem of bandwidth limitations imposed by electronics. In 1998, Lucent Technologies introduced a lithographic submicron technology to further miniaturize electronic circuits and enhance computer speed. Additional miniaturization of electronic components only provides a short-term solution to the problem. There are also physical problems accompanied by miniaturization that might affect the computer's reliability.
Scientist have also developed and tested nanosecond optical switches, which can act as computer logic gates. Such logic gates are members of a large family of gates in computers that perform logic operations such as addition, subtraction and multiplication. They are vital for the development of optical computing and optical communication. The all optical logic gates were made using a thin film of metal-free phthalocyanine compound and a polydiacetylene polymer in a hollow fiber.
The optical computers will result in development of super-fast, super-miniaturized, super-lightweight and lower cost optical computing and optical communication devices and systems.
Structure of optical computers
Modern computer architecture is based on classical Von Neumann computer. In this scheme all the processing logic is contained in the CPU and the memory is located almost entirely in a different unit. Input and output is generally performed by CPU or by a system closely coupled to the CPU in a process called serial addressing. The CPU accesses the memory through a binary addressing unit and memory contents are returned to the CPU through a single or small number of lines. This scheme reduces the number of wires throughout the computer, simplifying the architecture. However storing memory through serial addressing results in a slower response time for a computer since it can direct only one bit of information at a time in and out of the CPU. This limitation on the computing speed is called Von Neumann bottleneck.
The theoretical model of optical computer is based on the modified Von Neumann computer. In this design, all the memory elements are accessible in parallel. By using free space interconnections, the input output part of the CPU can be separated allowing direct parallel communication between all three parts of the computing system. In this way the CPU can process hundreds of problems at a time and the results of all these calculations can be sent to the memory concurrently.
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