In the case of optical fiber transmission link, LED’s and LASER’s are used as ______

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RRB ALP CBT 2 Electronic Mechanic Previous Paper: Held on 23 Jan 2019 Shift 1

Answer 1

Being a single wavelength light source with uniform phase:

For fiber optics with glass fibers, light in the infrared region is widely used which has wavelengths longer than visible light, typically of 850, 1300, and 1550 nm.
Transmitters (Lasers or LEDs) emit in infrared regions and are used as a light source for fiber transmission.
The laser acts as the best source in optical communication because it is a single wavelength light source.
Ordinary light contains many different wavelengths of light, differences emerge in the speed of the transmission, reducing the number of signals that can be transmitted in any set time.
Receivers (photodetectors) at these particular wavelengths are also easy to construct.

Notes:

We use infrared because the attenuation of the fiber is much less at those wavelengths.
The attenuation of glass optical fiber is caused by two factors, absorption, and scattering.
Absorption occurs in several specific wavelengths called water bands due to the absorption by minute amounts of water vapor in the glass.