L-band EDFA amplifier system technical scheme

EDFA uses erbium ion-doped fiber as the gain medium, which produces population inversion under pump light. It realizes stimulated radiation amplification under the induction of signal light.
Erbium ions have three energy levels. They are at the lowest energy level, E1, when they are not excited by any light. When the fiber is continuously excited by the pump light source laser, the particles in the ground state gain energy and transition to a higher energy level. Such as the transition from E1 to E3, because the particle is unstable at the high energy level of E3, it will quickly fall to the metastable state E2 in a non-radiative transition process. At this energy level, the particles have a relatively long survival life. Due to the continuous excitation of the pump light source, the number of particles at the E2 energy level will continue to increase, and the number of particles at the E1 energy level will increase. In this way, the population inversion distribution is realized in the erbium-doped fiber, and the conditions for learning optical amplification are available.
When the input signal photon energy E=hf is precisely equal to the energy level difference between E2 and E1, E2-E1=hf, the particles in the metastable state will transition to the ground state E1 in the form of stimulated radiation. The radiation and the input The photons in the signal are identical to the photons, thus significantly increasing the photons' number, making the input optical signal become a strong output optical signal in the erbium-doped fiber, realizing the direct amplification of the optical signal.

2. System diagram and basic device introduction
2.1. The schematic diagram of the L-band optical fiber amplifier system is as follows: