Optical amplifier-EDFA-How to work
EDFA, also known as Erbium-doped Fiber Amplifier, is a special kind of optical fiber, in which the rare earth element erbium (Er) is injected into the fiber core, so that under the action of the pump light source, the optical signal of a certain wavelength can be directly amplified.
Its birth is a revolutionary breakthrough in the field of optical fiber communication. It makes long-distance, large-capacity, and high-speed optical fiber communication possible. It is an disposable and important device for DWDM systems, future high-speed systems, and all-optical networks.
This time the notes will focus on introducing the relevant content of EDFA.
How EDFAs work
The erbium-doped fiber amplifier is actually a rare earth element doped with bait in the core of the silica fiber, and the bait ion, as we know, has three working energy levels, namely E1, E2 and E3. Among them, the E1 energy level has the lowest energy and the largest number of particles, while the E3 energy level has the highest energy and the least number of particles. The blue line in the middle corresponds to the E2 energy level. Among the three energy levels, because the E1 energy level is the lowest, the number of particles is the largest, and the most stable, we also call it the ground state, that is, the most stable state; while the E3 energy level has the highest energy, and the particles of this energy level are the least stable, we also call it an excited state. The middle E2 energy level is between the ground state and the excited state, we call it a metastable state. It is more active than the ground state and more stable than the excited state. The number of particles in the metastable state is relatively stable and can maintain a stable state for a period of time.
Knowing the composition of the three energy levels of bait ions, how does EDFA achieve light amplification?
For example, the light to be transmitted through the optical fiber is relatively weak. After passing through the EDFA amplifier, the output is amplified strong light. How is it realized?
First of all, for the three energy levels of the erbium-doped fiber amplifier, we add a pump light source. The purpose of the pump source is to input energy to the material, so that the particles of the low energy level E1 absorb the energy of the pump light and then jump up to the E3 energy. Level, that is, the excited state, we call this process the electron absorption pump light transition.
The particles on the E3 energy level are in an excited state and are very unstable, so in the absence of external particle excitation, they will jump down one after another to the E2 energy level, which is a metastable state. We call this process For The non-radiative transition, there is no external particle excitation, and the particles at the high energy level automatically and spontaneously transition down to the low energy level.
Because the E2 energy level is in a metastable state, the particles on this energy level can be kept for a period of time, so that the inversion distribution state of the number of particles can be realized between E2 and E1 (about the inversion distribution state of the number of particles we As mentioned in the previous notes, it means that the particle distribution of matter is abnormal, so that the number of high-energy particles is more, while the number of low-energy particles is less).
At this time, if there is an excitation of an external photon, and this light happens to be the optical signal to be amplified, the optical signal at this time is a weak light, and the number of photos contained in it is relatively small. As an external excitation photon between E1 and E1, the process of stimulated emission is greater than the process of stimulated absorption between E2 and E1 in the reversed distribution state, and new identical photons are generated, thereby achieving light amplification, then from The light output matter is intense light.
This is how Erbium-doped fiber amplifiers work. We can know from the principle that for an erbium-doped fiber amplifier, there must first be a section of optical fiber doped with erbium, a rare earth element, and secondly, this section of optical fiber must be activated because it needs to be in the particle number Inversion distribution state, then how to be activated, which requires an external excitation source – pumping light source. These two parts are the most important parts that make up the erbium doped fiber amplifier .
On the basis of understanding the working principle, next time we will introduce its classification and characteristic parameters.