When the transmission interval is too long (more than 100 km), the optical signal will have a great loss. In the past, people generally used optical repeaters to expand the optical signal. This kind of equipment has certain limitations in practical use, and it has been gradually Instead of optical fiber amplifiers, the working principle of optical fiber amplifiers is shown in the figure below. It can directly expand optical signals without the need to go through the process of optical-electrical-optical conversion. What kinds of fiber amplifiers are there? 1. Erbium-doped fiber amplifier (EDFA) Erbium-doped fiber amplifier (EDFA) is mainly composed of erbium-doped fiber, pump light source, optical coupler, optical isolator and optical filter. In the meantime, erbium-doped fiber is the main component of optical signal amplification, mainly used to complete the 1550 nm The expansion of the band optical signal, therefore, the erbium-doped fiber amplifier (EDFA) works best in the wavelength range of 1530 nm to 1565 nm. Strengths: The pump power utilization is the highest (greater than 50%), and the optical signal in the 1550 nm band can be expanded directly and together, the gain exceeds 50dB, and the noise in long-interval transmission is small. Defects: Erbium-doped fiber amplifier (EDFA) is large in size, and this type of equipment cannot work in harmony with other semiconductor equipment. 2. Raman amplifier The Raman amplifier is the only device that can amplify the optical signal in the 1292 nm~1660 nm band. Its operating principle is based on the stimulated Raman scattering effect in the quartz fiber. As shown in the figure below, when it is in the pump light When the weak light signal in the Raman gain bandwidth is transmitted in the optical fiber together with the strong pump light wave, the weak light signal will be enlarged due to the Raman scattering effect. Advantages: It is applicable to a wide range of bands, which can be used in installed single-mode fiber wiring applications, which can supplement the lack of erbium-doped fiber amplifiers (EDFA), with low power consumption and low crosstalk. Defects: high pump power, messy gain control system, and high noise. 3. Semiconductor optical fiber amplifier (SOA) Semiconductor optical fiber amplifier (SOA) uses semiconductor materials as gain media, and its optical signal input and output have anti-reflection coatings to avoid reflection on the end face of the amplifier and eliminate the effect of the resonator. Advantages: small size, low output power, small gain bandwidth, can be used in a variety of different bands, cheaper than erbium-doped fiber amplifier (EDFA), and can be used with semiconductor equipment, can complete interleaved gain modulation, interleaved phase modulation, wavelength Four non-linear operations of transform and four-wave mixing. Defects: The function is not as high as the erbium-doped fiber amplifier (EDFA), with high noise and low gain.
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