Optical Electronics

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Optical Electronics

 

a branch of electronics that encompasses problems of using optical and electronic methods for the processing, storage, and transmission of information. Optical electronics came into being in the development of electronics and computer technology, which always tend toward increasing complexity of their systems in improving their informational and technical-economic performance—for example, increased reliability, higher speed of operation, and reduction of size and weight.

The idea of using light for data processing and transmission was put into practice long ago. There exists a large group of photoreceivers that convert light signals into electric signals—for example, photocells, photomultipliers, photoresistors, photodiodes, and phototransistors. There are also devices that convert a sequence of electric signals into a visible image. However, all processing of information in the electric circuits of electronic equipment was formerly carried out by vacuum-tube or semiconductor devices.

Optical electronics is distinguished from vacuum-tube and semiconductor electronics by the presence of an optical member or an optical (photon) link in the signal circuit. The merits of optical electronics derive primarily from the advantages of optical communications over electrical communications, and also from the possibilities of using the various physical phenomena that occur upon interaction of light fields with a solid body.

Since photons are electrically neutral, the electric or magnetic fields that accompany the flow of an electric current are not excited in an optical communications channel. In other words, photons do not cause crosstalk in communications lines, and they ensure complete electric decoupling of the transmitter and receiver, which is, in principle, impossible in electrical communications circuits. The transmission of information by means of a light beam is not accompanied by accumulation or dissipation of electric energy in the line; this results in the absence of any substantial delay of the signal in the communications channel, and also in high speed of operation and a minimum level of distortion of the information carried by the signal.

The high frequency of light vibrations—1014 -1015 hertz (Hz) —is the reason why a large volume of information can be transmitted and why the speed of the operation is high. The corresponding shortness of the wavelengths, down to 10-4 to 10-5cm, facilitates microminiaturization of optical-electronic transmitters and receivers and of the communications line itself. The minimum transverse dimensions of the light beam are of the order of the wavelength λ. The information capacity of the communications channel is extremely high because of the channel’s great band width.

The idea of optical electronics was proposed as early as 1955, but at that time the known means for interconversion of electrical and optical signals and for achieving optical communication could not provide the required efficiency, speed of operation, and power of the light flux and did not lend themselves to microminiaturization. The intensive development of optical electronics did not begin until 1963–65, after the appearance of lasers, semiconductor light-emitting diodes (LED’s), and fiber optics.

The main elements of optical electronics are light sources (lasers and LED’s), active and passive optical media, and pho-todetectors. They are used in various combinations or as self-contained devices or assemblies for independent tasks.

Optical electronics is developing along two paths: the optical path, which is based on the coherent beam of a laser (coherent optical electronics), and the electrooptical path (optronics), which is based on the photoelectric conversion of an optical signal. The essence of optronics is the substitution of optical links for electrical links in communications circuits. Coherent optical electronics deals with new principles and methods used in building major systems for computer technology, for optical communications, and for storage and processing of information. Such systems have no analogues in traditional electronics. This category includes holography, with its extremely great potential for recording, storing, and displaying vast quantities of information; computers with parallel input of information in the form of pictures (machines with pictorial logic); superhigh-speed computer systems, with a data-processing rate of about 109-1011 operations per second; high-capacity memories (1010–1012 bits); and laser television. Coherent optical electronics also opens up far-reaching possibilities for multichannel optical communications systems.

Functional coherent optical electronics, or integrated optics, is the optical analogue of integrated-circuit microelectronics. This branch of optical electronics is based on the use of microwave guides on rigid substrates. These wave guides are used to transmit a light signal from one functional block to another and to convert signals.

Optronics uses specific characteristics that are obtained in various combinations of such components as light sources, transmitting and controlling media, and photodetectors. In Optronics the conversion of signals is achieved by the parametric method. Optronic circuits are much simpler and have a much higher operating capacity than semiconductor circuits. This results from two factors. First, optical coupling introduces galvanic decoupling into the electric circuit, thus eliminating the problem of matching the circuits with respect to impedance, frequency, or voltage; circuit stability is also increased. Second, the conversion of an electric signal into an optical (light) signal and back into an electric signal or the conversion of an optical signal into an optical signal with an intermediate stage of electrical conversion is simple—an optronic circuit can control and be controlled by both electrical and optical signals.

The main structural element of Optronics is the optron. Op-trons are used in solving various circuit problems, such as amplification and conversion of electrical and optical signals, switching, and modulation. They are capable of combining logic functions with the functions of display and indication, if the light source operates in the visible part of the spectrum.

REFERENCES

Svechnikov, S.V. Elementy optoelektroniki. Moscow, 1971.
Fotoelektricheskie iavleniia v poluprovodnikakh i optoelektronika. Collection of articles, edited by E. I. Adirovich. Tashkent, 1972.
Georgobiani, A. N. “Shirokozonnye poluprovodniki AIIBVI i perspektivy ikh primeneniia.” In Uspekhi fizicheskikh nauk, 1974, vol. 113, fasc. 1.

S. V. SVECHNIKOV

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