An optical computer is a device that uses photons, thin films, crystals, and optical fibers to perform digital computations. Since the advent of lasers in 1960, researchers have thought of using lasers and fibers for computing. Optical computation is the most feasible technology that can replace electronics, and promises impressive speeds that can enhance processing power and data rate transmission. The recent revival of optical computing technology is due to an ever-increasing need for computational speed and the recent developments in building super "tiny and fast" transistor-like all-optical switches.
Lasers, fibers, and optical components have already proven their reliability and high levels of performance in many applications such as CD-ROM drives, laser printers, photocopiers and scanners, Storage Area Networks (SANs), optical switches, all-optical data networks, holographic storage devices, and biometric devices at airports to track weapons and drugs. At the same time, the promise of optical computing comes from the many advantages that optical interconnections and optical integrated circuits have over their electronic counterparts. Optical computing is immune to electromagnetic interference and free from electrical short circuits. Photons of different colors can travel together in the same fiber or cross each other in free space without interference or cross-talk. Photons have low-loss transmission and provide large bandwidth, offering multiplexing capacity for communicating several channels in parallel without interference. Optical materials are compact, lightweight, inexpensive to manufacture, more facile with stored information than magnetic materials, and possess superior storage density and accessibility compared to magnetic materials. Progress in holographic storage devices can enable storage of the entire U.S. Library of Congress onto a sugar-cube-size hologram. Furthermore, optical parallel data processing is easier and less expensive than electronic. In addition, optical computing systems offer computational speeds more than 107 times faster than the currently fastest electronic systems. This means a computation that takes a conventional computer more than 11 years to solve would take an optical computer less than one hour.
An all-optical system means an optical signal in a logic gate controls another optical signal by switching it on/off without external electronic components. Logic gates are the building blocks of any digital system. The light beam is "on" when the device transmits light and is "off" when it blocks the light. Photonic switches can perform in the picosecond (10-12s) and femtosecond (10-15s) range as has been demonstrated in polydiacetylene .
An all-optical AND logic gate in the nanosecond (ns) (10-9s) range was demonstrated in our laboratory , where the ns Nd:YAG at 532nm modulated a continuous-wave helium-neon (cw He-Ne) laser at 632.8 nm in a metal-free phthalocyanine thin film. The AND logic gate was attributed to the saturation of absorption mechanism in the film. Another all-optical XOR logic gate in the picosecond regime was also demonstrated in our laboratory using a polydiacetylene film, a picosecond Nd:YAG laser at 532nm, and a cw He-Ne laser at 633nm. The switching in the material was attributed, in this case, to excited state absorption. Tens of these logic gates with different physical and optical properties have been demonstrated in different materials and with different speeds .