Optical Amplifier-EDFA-Characteristic Parameters
Continuing from the previous introduction, on the basis of understanding the working principle, next, let’s take a look at the classification and characteristic parameters of EDFA.
Classification of DFA
According to the different pumping methods of the pump light source, EDFA has three different structural forms:
(1) Co-directional pumping structure
Pumping in the same direction: both the pump light source and the input optical signal are injected into the erbium-doped fiber from the same direction.
(2) Reverse pump structure
Reverse pumping: The pump light source and the input optical signal are injected into the erbium-doped fiber from two opposite directions.
(3) Bidirectional pumping structure
Bi-directional pumping: There are both forward pumping and reverse pumping.
The main characteristic parameters of EDFA
1. Power gain
Erbium-doped fiber amplifiers amplify weak light into strong light, and we use power gain to represent the multiple of amplification. The larger the power gain value, the better the amplification capability of the Erbium-doped fiber amplifier. The size of the gain is related to the pump light power and the length of the fiber.
(1) The relationship between the gain and the pump light power
The power gain of the amplifier increases with the increase of the pump power (the stronger the pump light, there will be more low-energy particles absorb the energy of the pump light and jump upwards, so the number of particles with reversed distribution will be more, and the light The amplification effect will be stronger), when the pump power reaches a certain value, the power gain of the amplifier will be saturated, that is, the power gain will basically remain unchanged when the pump power is increased (because the number of particles that can be reversibly distributed is limited after all, When the pump light intensity is already very strong, no matter how much it is strengthened, if the limit of the number of reversed distribution particles is reached, the magnification will not increase any more, so there will be a saturation trend).
(2) The relationship between the size of the gain and the length of the fiber
The fiber here refers to the fiber length of the erbium-doped fiber in the erbium-doped fiber amplifier. The longer the length of the erbium-doped fiber, the greater the available power gain (because the greater the length of the erbium-doped fiber, the longer the active area of the number of particles that can reverse the distribution, and the longer the active area, the greater the power gain of course) , but as the fiber length is further increased, the power gain will decrease instead (this is because the loss will increase if the fiber length continues to increase, the loss is greater than the power gain loss of the amplification, and the final power gain will be reduced. ). Therefore, the magnitude of the gain and the length of the fiber have a process of first increasing and then decreasing, wherein the apex is the best power gain, and the corresponding fiber length is the fiber length of the maximum gain.
2. Output saturation power
is a parameter that describes the relationship between the input signal power and the output signal power.
The power of the input signal is not exactly proportional to the power of the output signal, and there is a trend of saturation (because the input signal continues to increase, the number of particles in the reverse distribution is limited, and the output signal is no longer enhanced, but a saturation trend appears).
The maximum output power of EDFA is usually represented by 3dB output saturation power. When the saturation gain drops by 3dB, the corresponding output power value is 3dB saturated output power, which represents the maximum output capability of the EDFA.
3. Noise figure
The main sources of EDFA noise include the shot noise of the signal light, the beat noise between the signal light wave and the spontaneous emission light wave of the amplifier, the shot noise of the amplified spontaneous emission light, and the beat noise between the light waves of different frequencies spontaneously emitted by the optical amplifier .