Choice of Optical Fibers as Communication Channel

Researchers in telecommunication had been in search of a medium that will allow long distance transmission with low loss until they develop optical glass fibers. In optical transmission, a communication channel transports the optical signal from transmitter to receiver without much distortion. Most lightwave systems use optical fibers as the communication channel because silica fibers can transmit light with losses as small as 0.2 dB/km. Optical power reduces to around 1% after 100 km. Fiber losses remain an important design issue that determines the repeater and amplifier locations in longhaul optical networks. One of the important design issues after loss is fiber dispersion. Dispersion leads to broadening of optical pulses as they propagate along the fiber.

If optical pulses spread significantly outside their allocated bit slot, the transmitted signal will be degraded. Eventually, it becomes impossible to recover the original signal with accuracy. The problem is severe in the case of multimode fibers, since pulses spread rapidly because of different speeds associated with different fiber modes.

It is for this reason that most optical communication systems use single mode fibers. Material dispersion, which is related to the frequency dependence of the refractive index still leads to pulse broadening. But it is almost negligible to be acceptable for most applications and can be reduced further by controlling the spectral width of the optical source.

Author: Fiber

Chief Editor of Fiber Optic Mania Magazine

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