Optical fiber amplifier refers to a new type of all-optical amplifier used in optical fiber communication lines to achieve signal amplification. According to its position and function in the optical fiber line, it is generally divided into three types: relay amplification, pre-amplification and power amplification. Compared with the traditional semiconductor laser amplifier (SOA), the optical fiber amplifier does not need to go through complicated processes such as photoelectric conversion, electro-optical conversion and signal regeneration. It can directly amplify the signal all-optically, with good "transparency", and is especially suitable for relay amplification of long-distance optical communications. It can be said that the optical fiber amplifier has laid a technical foundation for the realization of all-optical communication.
The technology of the fiber optic amplifier is to dope rare earth elements that can generate laser light into the core of the fiber, and amplify the passed optical signal through the direct current light excitation provided by the laser. Traditional optical fiber transmission systems use optical-electrical-optical regenerative repeaters, which affect the stability and reliability of the system. In order to remove the above conversion process and directly amplify and transmit the signal on the optical path, an all-optical transmission repeater must be used to replace this regenerative repeater.
Erbium-doped fiber amplifier (EDFA) is mainly composed of erbium-doped fiber, pump source, isolator, multiplexer, coupler, detector and control circuit.
The following is the optical amplifier working principle. The erbium-doped fiber is the most basic and key component of the amplifier; the role of the pump source is to provide energy to the erbium-doped fiber to excite the ground state erbium ions (Er3+) to a high-energy state, causing the population to reverse, thereby producing Stimulated radiation realizes the amplification of 1550nm waveband optical signal. The most widely used pump source is 980nm LD; the isolator is mainly used to prevent self-excited oscillation of the amplifier; the function of the multiplexer is to couple the pump light into the erbium-doped fiber, and the coupler is the signal light Separate a part and provide it to the detector in order to realize real-time monitoring of the amplifier's working status.
The amplification principle of erbium-doped fiber amplifier is similar to that of laser generation. The energy difference between the metastable state and the ground state of the rare earth element Er(3+) doped in the fiber is equivalent to the energy of a 1550nm photon. When the pump light energy of the appropriate wavelength (980nm or 1480nm) is absorbed, the electrons will transition from the ground state To an excited state with a higher energy level, then release a small amount of energy and transfer to a more stable metastable state. When the pump light source is sufficient, the electrons of the erbium ion will undergo a population inversion, that is, the metastable state with a higher energy level is lower than the energy level. The number of ground state electrons is large. When an appropriate optical signal passes through, the metastable electrons will have a stimulated emission effect, emitting a large number of photons of the same wavelength. However, because of the vibrational energy level, the wavelength is not single but a range, the typical value is 1530nm~1570nm.