Functions and Requirements of Optical Amplifiers

Ⅰ. The role of optical amplifiers

The function of the optical amplifier is to amplify the multiplexed optical signal to solve the ultra-long-distance transmission of the system and the insertion loss of the wavelength division multiplexing device in the system. The system generally needs to be equipped with an optical amplifier because the insertion loss of the combiner and the demultiplexer is large, which will greatly reduce the transmission distance of the system and cannot meet the actual needs. Taking a 2.5Gb/s system as an example, the allowable attenuation between transmission and reception is generally about 26dB. After deducting the attenuation of optical connectors, the redundancy of optical cables, and the cost of optical channels, it can transmit about 80km. However, for the system, the insertion loss of the combiner and the splitter must be considered again. Therefore, if the optical amplifier is not used, the transmission distance is only about 20~30km, which cannot meet the actual demand at all. It can be said that without the optical amplifier, there is no practical application of the technology. Optical amplifier applications should be further developed.

Ⅱ. Requirements for optical amplifiers

1. High gain

The so-called gain is the magnification of the optical signal by the optical amplifier. From an attenuation point of view, the larger the value is, the more likely it is to transmit longer distances. The gain of a good optical amplifier can reach more than 33dB.

2. Wide bandwidth

In order to use one optical amplifier to amplify all the optical multiplexing channel signals of the system, the optical amplifier must have a wide enough bandwidth; and its amplification characteristics must be very flat. Only with sufficient bandwidth, it is possible to use one optical amplifier to simultaneously amplify all the multiplexed optical channel signals of the system. Only with flat amplification characteristics can the optical amplifier achieve the purpose of uniformly amplifying all the multiplexed optical channel signals, so as to facilitate the design and implementation of the system.

3. Low noise figure

An optical amplifier is an active device. In addition to optical amplification, it may also generate noise itself, such as the most widely used EDFA will generate spontaneous emission noise. Noise can degrade system performance and reduce the optical signal-to-noise ratio at the receiver. Therefore, it is required that the optical amplifier should have a very low noise figure.