The Concept and Working Principle of Optical Amplifier
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The concept of passive optical amplifier
Optical amplifier refers to a device that amplifies the optical signal and increases the power of the optical seat. Since the transmission span of the optical fiber communication system is limited by the optical loss, the traditional optical fiber long-distance transmission system needs to be equipped with a regenerative repeater every certain span, and the traditional relay amplification method is in the optical/electrical/optical relay mode. The emergence of the optical amplifier overcomes the bottleneck of these electrical regeneration methods. The relay amplifier reshapes the signal pulse, re-clocks and regenerates the clock, that is, the photoelectric relay amplifier has 3R power. Obviously, 3R is closely related to the form of the signal and the signal code rate. Its circuit complexity is quite high. When the transmission link needs to increase the code rate, the relay amplifier will be restricted by the response speed of the electronic device, forming a bottleneck effect, which is precisely the limitation that the direct signal amplification by an optical amplifier helps to overcome.
The working principle of optical amplifier
The optical amplifier is different. It directly amplifies the optical signal without optical/electrical/optical conversion. As long as the wavelength of the optical signal falls within the effective gain region of the optical amplifier, it can be amplified. In other words, the optical amplifier is transparent to the optical signal. At present, optical amplifiers used in optical fiber communication systems mainly include non-linear optical fiber amplifiers, erbium-doped optical fiber amplifiers, which have the advantages of simple structure and easy connection with optical fiber lines, and have the incomparable advantages that traditional optical relay amplifiers don’t have. However, due to the transparent amplification function of the optical fiber amplifier, it also has some shortcomings that the traditional optical amplifier does not have, such as the gradual accumulation of dispersion broadening, the excitation of fiber nonlinear effects, and the accumulative noise of the concatenation system caused by the polarization effect. The other is based on the nonlinear effect of optical fiber, that is, the direct amplification of light is achieved by the stimulated scattering mechanism, such as optical fiber Raman TV station amplifier and optical fiber Brillouin amplifier
The main functions of optical amplifiers in the optical fiber communication domain are as follows:
1. Power amplification; put the optical amplifier at the front end of the transmitter to increase the optical power into the fiber;
2. Online relay amplification, replacing repeaters;
3. Pre-amplification: the weak light signal is pre-amplified before the photoelectric detector at the receiving end to improve the receiving sensitivity.
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