Optical computing means performing computations, operations, storage and transmission of data using only light. It uses the photons in visible light or infrared(IR) beams, rather than electric current, to perform digital computations. Optical computers, theoretically, transmit data using light from laser or infrared beams as opposed to electronic currents. Instead of silicon chips optical computer uses organic polymers like phthalocyanine and polydiacetylene. Optical technology promises massive upgrades in the efficiency and speed of computers, as well as significant shrinkage in their size and cost. Optical computer would be extremely fast because they wouldn't need physical wires or cables to transmit data.An optical desktop computer is capable of processing data up to 1,00,000 times faster than current models.
Computers have enhanced human life to a great extent. The speed of conventional computers is achieved by miniaturizing electronic components to a very small micron-size scale so that those electrons need to travel only very short distances within a very short time. The goal of improving on computer speed has resulted in the development of the Very Large Scale Integration (VLSI) technology with smaller device dimensions and greater complexity. Last year, the smallest-todate dimensions of VLSI reached 0.08 urn by researchers at Lucent Technology. Whereas VLSI technology has revolutionized the electronics industry and established the 20th century as the computer age, increasing usage of the Internet demands better accommodation of a 10 to 15 percent per month growth rate. Additionally, our daily lives demand solutions to increasingly sophisticated and complex problems, which requires more speed and better performance of computers.
For these reasons, it is unfortunate that VLSI technology is approaching its fundamental limits in the sub-micron miniaturization process. It is now possible to fit up to 300 million transistors on a single silicon chip. It is also estimated that the number of transistor switches that can be put onto a chip doubles every 18 months. Further miniaturization of lithography introduces several problems such as dielectric breakdown, hot carriers, and short channel effects. All of these factors combine to seriously degrade device reliability. Even if developing technology succeeded in temporarily overcoming these physical problems, we will continue to face them as long as increasing demands for higher integration continues. Therefore, a dramatic solution to the problem is needed, and unless we gear our thoughts toward a totally different pathway, we will not be able to further improve our computer performance for the future.
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 traveling on optical fibers or thin films instead of electrons to perform the appropriate functions. In the optical computer of the future, electronic circuits and wires will be replaced by a few optical fibers 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 colors) of light can travel through optical components without interfacing with each others, allowing photonic devices to process multiple streams of data simultaneously.
3. NEED FOR OPTICAL COMPUTING
Optical interconnections and optical integrated circuits have several advantageous over their electronic counterparts. They are immune to electromagnetic interference, and free from electrical short circuits. They have low-loss transmission and provide large bandwidth; i.e. multiplexing capability, capable of communicating several channels in parallel without interference. They are capable of propagating signals within the same or adjacent fibers with essentially no interference or cross-talk. They are compact, lightweight, and inexpensive to manufacture, and more facile with stored information than magnetic materials.
We are in an era of daily explosions in the development of optics and optical components for computing and other applications. The business of photonics is booming in industry and universities worldwide. It is estimated that photonic device sales worldwide will range between $12 billion and $100 billion in 1999 due to an ever-increasing demand for data traffic. According to KMI corp., data traffic is growing worldwide at a rate of 100% per year, while, the Phillips Group in London estimates that the U.S. data traffic will increase by 300% annually. KMI corp. also estimates that sales of dense-wavelength division multiplexing equipment will increase by more than quadruple its growth ;n the next five years, i.e. from $2.2 billion worldwide in 1998 to $9.4 billion 2D04. In fact, Future Communication Inc., London, announced this year to -pgrade their communication system accordingly. The company's goal is to use .va.elength division multiplexing at 10 Gb/s/channel to transmit at a total rate of -ore than 1000 Tb/s.
Most of the components that are currently very much in demand are eectro-optical (EO). Such hybrid components are limited by the speed of their electronic parts. All-optical components will have the advantage of speed over EO components. Unfortunately, there is an absence of known efficient nonlinear optical materials that can respond at low power levels. Most alloptical components require a high level of laser power to function as required. A group of researchers from the university of southern California, jointly with a team from the university of California Los Anglos, have developed an organic polymer with a switching frequency of 60 GHz. This is three times faster than the current industry standard, lithium niobate crystal-based devices. The California team has been working to incorporate their material into a working prototype. Development of such a device could revolutionize the information superhighway and speed data processing for optical computing. Another group at Brown University and the IBM Almaden Research Center (San Jose, CA) have used ultrafast laser pulses to build ultrafast datastorage devices. This group was able to achieve ultrafast switching down to 100ps. Their results are almost ten times faster than currently available "speed limits". Optoelectronic technologies for optical computers and communication hold promise for transmitting data as short as the space between computer chips or as long as the orbital distance between satellites. A European collaborative effort demonstrated a high-speed optical data input and output in free-space between IC chips in computers at a rate of more than 1 Tb/s. Astro Terra, in collaboration with Jet Propulsion Laboratory (Pasadena, CA) has built a 32-channel 1-Ggb/s earth-to-satellite link with a 2000 km range. Many more active devices in development, and some are likely to become crucial components in future optical computer and networks.
The race is on with foreign competitors. NEC (Tokyo, Japan) have developed a method for interconnecting circuit boards optically using Vertical Cavity Surface Emitting Laser arrays (VCSEL). Researchers at Osaka City University (Osaka, Japan) reported on a method for automatic alignment of a set of optical beams in space with a set of optical fibers. As of last year, researchers at NTT (Tokyo, Japan) have designed an optical back plane with free-space optical interconnects using tunable beam deflectors and a mirror. The project had achieved 1000 interconnections per printed-circuit board, with throughput ranging from 1 to 10 Tb/s.
Optics has a higher bandwidth capacity over electronics, which enables more information to be carried and data to be processed arises because electronic communication along wires requires charging of a capacitor that depends on length. In contrast, optical signals in optical fibers, optical integrated circuits, and free space do not have to charge a capacitor and are therefore faster.
Another advantage of optical methods over electronic ones for computing is that optical data processing can be done much easier and less expensive in parallel than can be done in electronics. Parallelism is the capability of the system to execute more than one operation simultaneously. Electronic computer architecture is, in general, sequential, where the instructions are implemented in sequence. This implies that parallelism with electronics is difficult to construct. Parallelism first appeared in Cray super computers in the early 1980's. Two processors were used in conjunction with the computer memory to achieve parallelism and to enhance the speed to more than 10 Gb/ s. It was later realized that more processors were not necessary to increase computational speed, but could be in fact detrimental. This is because as more processors are used, there is more time lost in communication. On the other hand, using a simple optical design, an array of pixels can be transferred simultaneously in parallel from one point to another. To appreciate the difference between both optical parallelism and electronic one can think of an Tiaging system of as many as 1000x1000 independent points per mm2 in the crsject plane which are connected optically by a lens to a corresponding 1000x "000 points per mm2 in the image plane. For this to be accomplished = ectrically, a million nonintersecting and properly isolated conduction channels zer mm2 would be required.
Parallelism, therefore, when associated with fast switching speeds, .vDuJd result in staggering computational speeds. Assume, for example, there are only 100 million gates on a chip, much less than what was mentioned earlier .Ã‚Â¦optical integration is still in its infancy compared to electronics). Further,