2.13. Optical Computing

264. Optical computing would provide much higher computing speeds. Developments have centered on devices such as VCSELS (Vertical Cavity Surface-Emitting Lasers) for data input, SLMs (Spatial Light Modulators) for putting information on light beams and high speed APDs (Avalanche Photo-Diodes) for data output. More work remains before digital optical computers will be available commercially.

2.13.1. Data Storage

265. Data storage media will need to improve to keep pace with computer processing power, and may be achieved via optical disk technologies and applications of parallelism. Promising areas involve the use of holographic memory, offering 64 billion bits storage capacity on a laser activated crystal the size of a compact disk. Holographic data storage captures information using an optical inference pattern within a thick, photosensitive optical material. Light from a single laser beam is divided into two separate beams, a reference beam and an object or signal beam; a spatial light modulator is used to encode the object beam with the data for storage. An optical inference pattern results from the crossing of the beams’ paths, creating a chemical and/or physical change in the photosensitive medium; the resulting data is represented in an optical pattern of dark and light pixels. By adjusting the reference beam angle, wavelength, or media position, a multitude of holograms (theoretically, several thousand) can be stored on a single volume.

266. Importance: The theoretical limits for the storage density of this technique are approximately tens of per cubic centimeter. In addition, holographic data storage can provide companies a method to preserve and archive information. The write-once, read many (WORM) approach to data storage would ensure content security, preventing the information from being overwritten or modified. Manufacturers believe this technology can provide safe storage for content without degradation for more than 50 years, far exceeding current data storage options.