What Is an Optical Computer? An optical computer is a computer that performs its computation with photons as opposed to the more traditional electron-based computation. Optical or photonic computing uses photon produced by laser or diodes for computation. An optical computer (also called a photonic computer) is a device that uses the photons in visible light or infrared (IR) beams, rather than electric current flows at only about 10 percent of the speed of light. This limits the rate at which data can be exchanged over long distances, and is one of the factors that led to the evolution of optical fiber. By applying some of the advantages of visible and/or IR networks at the device and component scale, a computer might someday be developed that can perform operations 10 or more times faster than a conventional electronic computer. Visible-light and IR beams, unlike electric currents, pass through each other without interacting. Several (or many) laser beams can be shone so their paths intersect, bit there is no interference among the beams, even when they are confined essentially to two dimensions. Electric currents must be guided around each other, and this makes three-dimensional wiring necessary. Thus, an optical computer, besides being much faster than an electronic one, might also be smaller.
There are two different types of optical computers:
● Electro-Optical Hybrid computers
● Pure Optical computers Basic Path of Information Through an
Optical Computer:
● Information gets sent in from keyboard, mouse, or other external sources and goes to the processor.
● Processor then sends the information through logic gates and switches to be programmed.
● The information is then sent through different fiber optic cables depending on it’s final location.
● Some information will be sent to the holographic memory, where it will then be saved.
● After information is saved and the program would like to use it, the program sends a command to the processor, which then sends a command to receive the information.
● The program receives the information and sends a signal back to the processor to tell it that the task is complete.
Pure Optical Computers:
● Use multiple frequencies
● Information is sent throughout computer as light waves and packets.
● No electron based systems
● No converstion from binary to optical necessary, greatly increasing the speed.
Building of an Optical Computers:
Building an optical computer will not be easy. A major challenge is finding materials that can be mass produced yet consume little power; for this reason, optical computers may not hit the consumer market for 10 to 15 years. Another of the typical problems optical computers have faced is that the digital optical devices have practical limits of eight to eleven bits of accuracy in basic operations due to, e.g., intensity fluctuations. Recent research has shown ways around this difficulty. Thus, for example, digital partitioning algorithms, that can break matrix-vector products into lower-accuracy sub-products, working in tandem with error-correction codes, can substantially improve the accuracy of optical computing operations. Nevertheless, many problems in developing appropriate materials and devices must be overcome before digital optical computers will be in widespread commercial use. In the near term, at least, optical computers will most likely be hybrid optical/electronic systems that use electronic circuits to preprocess input data for computation and to post-process output data for error correction before outputting the results. The promise of all-optical computing remains highly attractive, however, and the goal of developing optical computers continues to be a worthy one.
Nevertheless, many scientists feel that an all-optical computer will not be the computer of the future; instead optoelectronic computers will rule where the advantages of both electronics and optics will be used. Optical computing can also be linked intrinsically to quantum computing. Each photon is a quantum of a wave function describing the whole function. It is now possible to control atoms by trapping single photons in small, superconducting cavities. So photon quantum computing could become a future possibility. Optical Computing: Optics has been used in computing for a number of years but the main emphasis has been and continues to be to link portions of computers, for communications, or more intrinsically in devices that have some optical application or component (optical pattern recognition, etc). Optical digital computers are still some years away, however a number of devices that can ultimately lead to real optical computers have already been manufactured, including optical logic gates, optical switches, optical interconnections, and optical memory. The most likely near-term optical computer will really be a hybrid composed of traditional architectural design along with some portions that can perform some functional operations in optical mode.
Optical computing was a hot research area in the 1980s. But the work tapered off because of materials limitations that seemed to prevent optochips from getting small enough and cheap enough to be more than laboratory curiosities. Now, optical computers are back with advances in self-assembled conducting organic polymers that promise super-tiny all-optical chips. Advances in optical storage device have generated the promise of efficient, compact and large-scale storage devices. Another advantage of optical methods over electronic ones for computing is that parallel data processing can frequently be done much more easily and less expensively in optics than in electronics.
Optical technology promises massive upgrades in the efficiency and speed of computers, as well as significant shrinkage in their size and cost. An optical desktop computer could be capable of processing data up to 100,000 times faster than current models because multiple operations can be performed simultaneously. Uses of Optics in Computing: Currently, optics is used mostly to link portions of computers, or more intrinsically in devices that have some optical application or component. For example, much progress has been achieved, and optical signal processors have been successfully used, for applications such as synthetic aperture radars, optical pattern recognition, optical image processing, fingerprint enhancement, and optical spectrum analyzers. The early work in optical signal processing and computing was basically analog in nature. In the past two decades, however, a great deal of effort has been expended in the development of digital optical processors. Much work remains before digital optical computers will be widely available commercially, but the pace of research and development has increased through the 1990s. During the last decade, there has been continuing emphasis on the following aspects of optical computing:
● Optical tunnel devices are under continuous development varying from small caliber endoscopes to character recognition system with multiple type capability.
● Development of optical processors for asynchronous transfer mode.
● Development architectures for optical neural networks.
● Development of high accuracy analog optical processors, capable of processing large amounts of data parallel.
In optical computing two types of memory are discussed. One consists of arrays of one-bit-store elements and the other is mass storage, which is implemented by optical disks or by holographic storage systems. This type of memory promises very high capacity and storage density. The primary benefits offered by holographic optical data storage over current storage technologies include significantly higher storage capacities and faster read-out rates. This research is expected to lead to compact, high-capacity, rapid- and random-access, radiation-resistant, low-power, and low-cost data storage devices necessary for future intelligent spacecraft, as well as to massive-capacity and fast-access terrestrial data archives. As multimedia applications and services become more and more prevalent, entertainment and data storage companies are looking at ways to increase the amount of stored data and reduce the time it takes to get that data out of storage. The SLMs and the linear array beam steerer are used in optical data storage applications. These devices are used to write data into the optical storage medium at high speed. The analog nature of these devices means that data can be stored at much higher density than data written by conventional devices. Researchers around the world are evaluating a number of inventive ways to store optical data while improving the performance and capacity of existing optical disk technology. While these approaches vary in materials and methods, they do share a common objective: expanded capacity through stacking layers of optical material. For audio recordings, a 150-MB minidisk with a 2.5-in. diameter has been developed that uses special compression to shrink a standard CD’s 640-MB storage capacity onto the smaller polymer substrate. It is rewritable and uses magnetic field modulation on optical material. The minidisk uses one of two methods to write information onto an optical disk. With the minidisk, a magnetic field placed behind the optical disk is modulated while the intensity of the writing laser head is held constant. By switching the polarity of the magnetic field while the laser creates a state of flux in the optical material, digital data can be recorded on a single layer. As with all optical storage media, a read laser retrieves the data. Along with minidisk developments, standard magneto-optical CD technology has expanded the capacity of the 3.5-in. diameter disk from 640 MB to commercially available 1 GB storage media. These conventional storage media modulate the laser instead of the magnetic field during the writing process. Fourth-generation 8× 5.25 in. diameter disks that use the same technology have reached capacities of 4 GB per disk. These disks are used mainly in ‘jukebox’ devices. Not to be confused with the musical jukebox, these machines contain multiple disks for storage and backup of large amounts of data that need to be accessed quickly. Some Key Optical Components for Computing: The major breakthroughs on optical computing have been centered on the development of micro-optic devices for data input. Conventional lasers are known as ‘edge emitters’ because their laser light comes out from the edges. Also, their laser cavities run horizontally along their length. A vertical cavity surface emitting laser (VCSEL – pronounced ‘vixel’), however, gives out laser light from its surface and has a laser cavity that is vertical; hence the name. VCSEL is a semiconductor vertical cavity surface emitting microlaser diode that emits light in a cylindrical beam vertically from the surface of a fabricated wafer, and offers significant advantages when compared to the edge-emitting lasers currently used in the majority of fiber optic communications devices. They emit at 850 nm and have rather low thresholds (typically a few mA). They are very fast and can give mW of coupled power into a 50 micron core fiber and are extremely radiation hard. VCSELS can be tested at the wafer level (as opposed to edge emitting lasers which have to be cut and cleaved before they can be tested) and hence are relatively cheap. In fact, VCSELs can be fabricated efficiently on a 3-inch diameter wafer. A schematic of VCSEL is shown in Figure 1. The principles involved in the operation of a VCSEL are very similar to those of regular lasers. As shown in Figure 1, there are two special semiconductor materials sandwiching an active layer where all the action takes place. But rather than reflective ends, in a VCSEL there are several layers of partially reflective mirrors above and below the active layer. Layers of semiconductor with differing compositions create these mirrors, and each mirror reflects a narrow range of wavelengths back into the cavity in order to cause light emission at just one wavelength.
Advantages of Optical Computing:
● Small size
● Increased speed
● Low heating
● Reconfigurable
● Scalable for larger or small network
● More complex functions done faster
● Applications for Artificial Intelligence
● Less power consumption (500 microwatts per interconnect length vs. 10 mW for electrical)
Optical technology has made its most significant inroads in digital communications, where fibre optic data transmission has become commomplace. The ultimate goal is so-called photonic network, which uses visible and IR energy exclusively between each source and destination. Optical technology is employed in CD-ROM drives and their relatives, laser printers, and most photocopier and scanners. However, none of these devices are fully optical ; all rely to some extend on conventional electronic circuits and components. Optical technology promises massive upgrades in the efficiency and speed of computers, as well as significant shrink age in their size and cost.
Limiting factors for Optical Computers:
● Optical fibres on a chip are wider than electrical traces.
● Crystals need 1mm of length and are much larger than the current transistor.
● Software needed to design and run the computers.
