Optical fiber system in broadband communication consists of a transmitter, receiver and a transmission medium. The transmission medium consists of a pair of wires, a co-axial cable or a radio link through free space down in which the signal is transmitted to the receiver. It transforms into the original electrical information signal before passing to the destination.
Optical Fiber System
In any transmission medium, the signal attenuation suffers loss because of contamination by random variables and noise. The distortions imposes the mechanisms within the medium itself.
The information source provides an electrical signal to the transmitter comprising an electrical stage, which drives an optical source to give modulation of the light wave carrier.
The optical source provides the electrical-optical conversion, which may be either a semiconductor laser or LED.
The transmission medium consists of an optical fiber cable and the receiver consists of an optical detector, which drives a further electrical stage and hence provides demodulation of the optical carrier.
Photodiodes, Phototransistors and photoconductors utilizes the detection of optical signal and the optical electrical conversion.
Elements of Optical Fiber system
Transmitter:
At the optical transmitter, an electric signal is applicable. The optical transmitter consists of a driver circuit, the light source and fiber fly lead.
- Driver circuit uses drive the light source.
- Light source converts the electrical signal to optical signal.
- Fiber fly uses lead to connect optical signal to optical fiber.
Transmission channel:
It consists of a cable that provides mechanical and environmental protection to the optical fibers contained inside. Each optical fiber acts as an individual channel.
- Optical splice is used to permanently join two individual optical fibers.
- Optical connector is for temporary non-fixed joints between two individual optical fibers.
- Optical coupler or splitter provides signal to other devices.
The Repeater converts the optical signal into electrical signal using optical receiver. It passes it to electronic circuit where it is reshapes and amplifies as it attenuates and distortes with increasing distance. The scattering, absorption and dispersion in waveguides again converts into optical signal by the optical transmitter.
Receiver:
Optical signal applies to the optical receiver which consists of photo detector, amplifier and signal restorer.
- Photo detector converts the optical signal to electrical signal.
- Signal restorers and amplifiers improves signal to noise ratio of the signal.
- Because of the presence of noise, the signal uses photo detectors.
- For short distance communication the main elements are required.
Source- LED
Fiber- Multimode step index fiber
Detector- PIN detector
- For long distance communication main elements are there is need for couplers, beam splitters, repeaters, optical amplifiers.
Source- LASER diode
Fiber- single mode fiber
Detector- Avalanche photo diode (APD)
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