In 1985, at the famous University of Southampton in the United Kingdom [Note 1], one of the greatest inventions in optical fibercommunications was born,the Erbium-Doped Fiber Amplifier (EDFA, that is the fiber core through which the signal is doped witherbium ion Er3 + Optical signal amplifier ), simply describe its principle, which is the core of fiber amplifier-ilica fiber [Note 2 isdoped with a small amount of rare earth element erbium(Er) ions to make erbium-doped fiber,and the amplifier with it t iscalled erbium-doped fiber amplifier, and every year from now on,its research work has continuously made major breakthroughs.For example, wDM technology [Note 3] has greatly increased the capacity of optical fiber communication and promoted it tobecome an application. The most widely used optical amplifying device in optical fiber communication.

The three most common ways in real-world applications

l.Power-Amplifier (Power-Amplifier ), after the multiplexer, is used to boost the power of multiple wavelength signals after multiplexing. and then transmit it. since the signal power after multiplexing is generally relatively large,so, The noise figure and gainrequirements of a power amplifier are not very high, but it is required to have a relatively large output power after amplification

2. Line-Amplifier (Line-Amplifier), after the power amplfir, is used to periodically compensate the line transmission loss. General,a relatively small noise index and a relatively large output optical power are required.

Erbium-doped fiber amplifier

3.The pre-amplifier (Pre-Amplifier) located before the demultiplexer and after the line amplifier, is used for signal amplification to improve the sensitivity of the receiver (when the optical signal-to-noise ratio (oSNR) meets the requirements, larger input power it can suppress the noise of the receiver itelf and improve the receiving sensitivity), the noise figure is required to be very small andthere is not much requirement on the output power.

[Note ] University of Southampton (University of Southampton),Royal Honorary University, Soton ,founding member of Russell Uni-versity Group, world University Alliance, Science and Engineering Yugoslavia Alliance,International University Climate AlianceWorld Port City University Alliance,RENKEl member.

[Note 2] ilica fioer is an optical fiber with a pure siica glass material with a high refractive index as the core and an organic orinorganic material with a low refractive index as the sheath.

[Note 3] wDM technology is a technology for channel multiplexing on optical fibers. The bandwidth of an optical fiber can reach25000 GHz, while the bandwidth of an optical signal is usually only a few gigahertz.The principle of wavelength division mutiplex-ing is that the entire wavelength band is divided into several wavelength ranges and each signal occupies a wavelength rangefor transmission. Iin essence,it is a variant of frequency division multiplexing used on optical channels, that is opticalfrequencydivision multiplexing, but the technology and equipment used in optical multiplexing are different from electrical multiplexing, be-cause light waves are in high frequency harmonics. The frequency band has a very high bandwidth, so many channels of wave-length division multiplexing can be realized.