Characteristics and applications of fiber-doped amplifiers

The gain coefficient g(z) is related to the difference in the number of particles between high energy levels and low energy levels and the pump power. By integrating the gain coefficient g(z) over the entire length of the erbium-doped fiber, the gain GE of the fiber-doped fiber amplifier can be obtained. Therefore, the gain of the amplifier should be related to the pump intensity and the length of the fiber.

The g-in curve of erbium-doped silicon fiber is shown in Figure 3-27. It can be seen from the figure that the gain coefficient varies with different wavelengths.
Optical fiber has a bandwidth of 200nm in the 1.55μm low-loss region, while the currently used EDFA gain bandwidth is only about 35nm.

Several applications of optical amplifiers are shown in the figure. Depending on the location of the optical amplifier in the optical link, its applications can be divided into 3 types:

 

 

(1) EDFA is used as a line amplifier. EDFA is used as a line amplifier.

Line amplifier is an important application in optical fiber communication systems. In a single-mode optical fiber communication system, the dispersion of the optical fiber has a small impact. The main factor limiting the transmission distance is the attenuation of the optical fiber, so the optical amplifier can be used to compensate for the transmission loss. It is suitable for ultra-long distance transmission systems, as shown in the figure.

(2) EDFA is used as a preamplifier

Due to the low noise characteristics of EDFA, it is very suitable to be used as the front end of a receiver.
amplifier. Preamplification refers to the position of the optical amplifier at the end of the optical fiber link and before the receiver, as shown in the figure. Amplifying weak signals before the photodetector suppresses the signal-to-noise ratio degradation caused by thermal noise in the receiver.

(3) EDFA is used as a power amplifier

The power amplifier places the EDFA directly after the optical transmitter to increase the output power. As shown in the figure, it can generally increase the transmission distance by 10 to 100km. If the preamplifier is used at the same time, 200-250km non-relay submarine transmission can be achieved. Since the power amplifier is placed directly behind the optical transmitter, its input power is higher and the required pump power is also higher. Its input is generally above -8dBm, and its gain must be greater than 5dB.