The types of optical amplifiers mainly include semiconductor amplifiers and optical fiber amplifiers. Semiconductor amplifiers are divided into resonant type and traveling wave type; fiber amplifiers are divided into rare-earth-doped fiber amplifiers and nonlinear optical amplifiers. Non-linear optical amplifiers are divided into Raman and Brillouin fiber amplifiers.
The fiber amplifier is to dope rare earth ions (such as erbium, praseodymium, thulium, etc.) into the optical fiber as the laser active material. The gain bandwidth of each dopant is different. The gain band of erbium-doped fiber amplifier is wide, covering the S, C, and L bands; the gain band of thulium-doped fiber amplifier is S-band; the gain band of praseodymium-doped fiber amplifier is around 1310nm.
The Raman optical amplifier is an optical amplifier made by using the Raman scattering effect. After the high-power laser is injected into the fiber, the nonlinear effect of Raman scattering will occur. In the process of continuous scattering, the energy is transferred to the signal light, so that the signal light is amplified. The Raman optical amplifier is a distributed amplification process, that is, gradually amplifies along the entire line. Its working bandwidth can be said to be very wide, almost unlimited. This optical amplifier has begun to be commercialized, but it is quite expensive.
The semiconductor optical amplifier generally refers to a traveling wave optical amplifier, and its working principle is similar to that of a semiconductor laser. Its working bandwidth is very wide. However, the gain range is slightly smaller, making it more difficult to manufacture. Although this kind of optical amplifier has been put into use, the output is very small.
In a WDM optical transmission system that uses an optical amplifier in its transmission path, a semiconductor optical amplifier is used to monitor and control the operation of the amplifier and a monitoring signal channel that is spectrally separated from the data transmission, and can be multiplexed with data. It discloses the structure of an amplifier that can be upgraded with the upgrade of the transmission system in order to increase the data processing capacity, such as increasing the data transmission in the band or in the opposite direction. However, it is not necessary to disconnect the data transmission path through the amplifier to be upgraded. This structure is implemented by using channel drop and insert filters. These filters are configured to extend the amplified data transmission path and pass the drop and insert channels of these filters.