What is an Optical Fiber Amplifier?

Figure 1: Panasonic FX-301P optical fiber amplifier.

The optical fiber amplifier, also known as the optical fiber ampler (OFA for short), refers to a new type of all-optical amplifier used in optical communication link to realize signal amplification. According to its position and function in the optical communication link, it is generally divided into three types: trunk amplifier, pre-amplifier and power amplifier.

Compared with the traditional semiconductor laser amplifier (SOA), the optical fiber amplifier does not need to go through complex processes of photoelectric conversion, electro-optical conversion and signal regeneration. It can directly amplify the signal all-optically and has good "transparency". It is especially suitable for trunk amplification of long-distance optical communication. It can be said that the optical fiber amplifier has laid a technical foundation for the realization of all-optical communication.

Characteristics of the Optical Fiber Amplifier

Optical fiber amplifiers can be used as a type of light beam or diffuse sensor. The sensing combination of optical fiber amplifier and optical fiber can meet the sensing requirements in complex and changing industrial automation systems. Fiber optics can be easily integrated in space-constrained locations, solving difficult signal collection problems. Optical fiber amplifiers can process signals with high precision and convert different information and output to automated systems or humans.

Optical fiber amplification technology includes erbium doped fiber amplifier (EDFA), distributed Raman fiber amplifier (DRFA), semiconductor optical amplifier (SOA) and optical time division multiplexing (OTDM). This technology, along with dense wavelength division multiplexing (DWDM) technology, has been greatly developed and widely applied in recent decades. Thanks to this, optical fiber communication technology is constantly developing towards higher-speed and larger-capacity communication systems.

Figure 2: ViaLiteHD HRA-4-CB-8T-ZZ-D016-BC Erbium Doped Fiber Amplifier.

The advanced optical fiber manufacturing technology can not only maintain stable and reliable transmission and sufficient redundancy, but also meet the needs of optical communication for large bandwidth and reduce nonlinear damage.

Working Principles of Optical Fiber Amplifiers

Rare earth-doped fiber amplifiers are one of the most commonly used fiber amplifiers. Rare earth elements, which can generate laser light, are doped into the core of the fiber. And the light signal passing through is amplified by the direct current light excitation provided by the laser.

The ions doped in the fiber transition to a metastable highly excited state after being excited by the pump light. Under the induction of signal light, these ions generate stimulated radiation, which forms a coherent amplification of the signal light. This optical fiber amplifier is essentially a special laser, and its working cavity is a section of rare-earth-doped particle fiber. The pump light source generally adopts a semiconductor laser.

Figure 3: Working principles of erbium doped optical fiber amplifiers.

The current optical fiber communication systems operate in two low-loss windows: the 1.55 μm band and the 1.31 μm band. Selecting different doping elements can make the amplifier work in different windows.

Applications of Optical Fiber Amplifiers

In recent years, with the rapid development of information and communication technology, the research and development of optical fiber amplifiers has further expanded the gain bandwidth, and pushed the optical fiber communication system to the direction of high speed, large capacity and long distance. The unique performance of fiber amplifier makes it widely used in DWDM transmission system, fiber cable television (CATV) and fiber access network.

DWDM system has become the mainstream technology in optical fiber transmission system. As one of the core components of the DWDM system, the optical fiber amplifier will develop rapidly in its application. This is mainly due to the sufficient gain bandwidth of the optical fiber amplifier. Combined with wavelength division multiplexing (WDM) technology, it can quickly and easily expand the communication capacity of the existing optical cable system and extend the relay distance.

Figure 4: Schema of how erbium doped optical fiber amplifiers are connected.

The scale of the optical fiber CATV system continues to expand, the transmission distance of its link continues to increase, and the transmission loss of the optical path also continues to increase. The application of optical fiber amplifier in optical fiber CATV system can not only improve optical power, compensate link loss, increase optical user terminals, but also simplify system structure, reduce system cost, and speed up the development of optical fiber CATV.

In the optical fiber access network, although the distance of the user system is short, there are too many branches of the user network. Therefore, it is necessary to use an optical fiber amplifier to increase the power of the optical signal to compensate for the optical loss caused by the optical distributor and increase the number of users. This can reduce the construction cost of the user network.

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