Free Space Optical Communication by Hemani Kaushal V. K. Jain & Subrat Kar

Author:Hemani Kaushal, V. K. Jain & Subrat Kar
Language: eng
Format: epub
Publisher: Springer India, New Delhi

3.1 Optical Transmitter

The optical transmitter including the choice of laser, concept of ATP system, and various types of modulation schemes and coding techniques used in FSO communication system are discussed in this section. Further, the details of communication and beacon detectors in FSO receiver are also discussed. The transmitter converts the source information into optical signals which are transmitted to the receiver through the atmosphere. The essential components of the transmitter are (i) modulator, (ii) driver circuit for the optical source to stabilize the optical radiations against temperature fluctuations, and (iii) collimator that collects, collimates, and direct the optical signals toward the receiver via atmospheric channel. The optical sources that are used for FSO transmission lie in the atmospheric transmission window that is ranging from 700 to 10,000 nm wavelength. The wavelength range from 780 to 1064 nm is most widely used as beacon operating wavelength. The 1550 nm wavelength is commonly used as data operating wavelength due to following reasons: (i)Reduced background noise and Rayleigh scattering: The absorption coefficient of the Rayleigh scattering has functional dependence with the wavelength λ as λ −4. Consequently, there is almost negligible attenuation at higher operating wavelengths as compared to those at the visible range.

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