Photodetectors, optical communication

In photodetectors (qv) for photocouplers, optical switches, fiber optics, communication, and imaging, the materials used are InGaAs, InGaAsP, and... 

S. R. Forrest, Sensitivity of Avalanche Photodetector Receivers for High-Bit-Rate Long-Wavelength Optical Communication Systems J. C. Campbell, Phototransistors for Lightwave Communications... 

Until recently optical communications were restricted by the lack of fast monochromatic light sources and sensitive photodetectors. Prospects for optical communications improved considerably about two decades ago when a powerful light source became available with the invention of the laser. After that, the transmission medium was the bottleneck of an optical communication system. At that time an intensive search for a new transmission medium was started, particulary because free space propagation could be ruled out for civil use as a consequence of the relative frequent occurrence of atmospheric disturbances. 

Organic Light-Emitting Diodes and Photodetectors for Optical Communication... 

In many applications of practical interest, the total optical ASE noise power given by Eq. (11) is not the most appropriate measure of the noise introduced by the SOA. In optical communications systems, for example, it is more useful to know the electrical noise power that accompanies the signal after detection. Modern communications systems generally employ intensity modulation with direct detection (IMDD), in which the information is represented directly by the power of the optical signal. Upon reception with a photodetector, the signal power is converted into photocurrent. However, since direct detection is a square-law process with respect to the optical field amplitude, conversion of the optical noise into the electrical domain is somewhat more complicated. 

H. Melchior, M.B. Fischer, F.R. Arams Photodetectors for optical communication systems. IEEE Proc. 58, 1466 (1970)... 

Pigure 10 shows the typical commercial performance of LEDs used for optical data communication. Both free-space emission and fiber-coupled devices are shown, the latter exhibiting speeds of <10 ns. Typically there exists a tradeoff between speed and power in these devices, however performance has been plotted as a function of wavelength for purposes of clarity. In communication systems, photodetectors (qv) are employed as receivers rather than the human eye, making radiometric power emitted by the devices, or coupled into an optical fiber, an important figure of merit. 

Bandyopadhyay, A. and Deen, M.J. (2001) Photodetectors for optical fiber communications, in Photodetectors and Fiber Optics (ed. H.S. Nalwa), Academic Press, San Diego, pp. 306-368, Chapter 5. 

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