Application of the hottest Erbium Doped Fiber Ampl

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Application of erbium doped fiber amplifier (EDFA) in HFC network

I. overview

when the transmission distance of cable TV system is not too long, we can form a more economical TV cable system by adopting branch distribution structure according to the characteristics of coaxial cable. When the transmission distance of cable TV is far and the range is large, we usually use the combination of optical cable and cable to build HFC network, In the optical fiber part of HFC network, we can also use branch devices to build a low-cost system. In practical applications, we usually use optical branching to achieve the same light source with more optical nodes. At the same time, in order to make the optical signal transmission distance longer, we must amplify the optical signal to compensate the optical branching loss and fiber loss. The traditional method to solve this problem is to use photoelectric repeaters, and this optical/electrical/optical conversion and processing method can not meet the requirements of modern communication transmission. Erbium doped fiber amplifier directly amplifies optical signals without converting them into electrical signals, and has the characteristics of large output power, high gain, wide working frequency band, polarization independent, low noise index, amplification characteristics. 4. Ball screw of tensile testing machine: independent of system bit rate and data format. Therefore, it has become one of the key components of modern optical communication system, so it is particularly popular in cable television HFC system

II. Working principle of EDFA

when the laser media is supplied with energy to make it in the excited state, it will produce the stimulated radiation of light. If the conditions for continuous stimulated radiation can be met, and the input light is used to induce, a stronger output light can be obtained, thus playing the role of amplification

the amplification effect of EDFA is generated by the interaction of er3+ (erbium ion) through the transmission of 1550nm wavelength signal light in erbium-doped fiber. The accuracy required by flexible packaging can be achieved by adopting 1-screw and trapezoidal screw. The energy state of er3+ in erbium-doped fiber cannot be taken continuously. It can only be in a series of discrete energy states, which are called energy levels. When er3+ is not excited, it is in the lowest energy level, that is, the energy level diagram of ground state E1

erbium (I)

inject enough pump light into erbium-doped fiber, and most of the E1 ions in ground state can be pumped to high-energy E3, Er3+ ions at E3 are rapidly transferred to metastable E2 without radiation. Er3+ ions have a long energy level life in metastable state. Due to continuous pumping, the number of E2 particles continues to increase, thus realizing the inversion of E1 and E2 particle numbers, that is, there are more particles in E2 than in E1. When the signal photon passes through the erbium-doped fiber, it interacts with er3+ ions to produce stimulated radiation effect. Er3+ ions of E2 transition to E1 and produce photons that are exactly the same as those in the incident signal light (i.e. the frequency, phase, propagation direction and polarization state) so as to greatly increase the number of signal photons and realize signal amplification. The metastable and ground states of er3+ ions have a certain width, so that the amplification effect of EDFA has a certain wavelength range, and its typical value is 1530~1570nm. When er3+ ions are in E2, in addition to stimulated radiation and stimulated absorption (the ground state er3+ ions absorb signal photons and transition to E2), they also produce spontaneous emission, spontaneously transition from E2 to E1, and emit photons with a wavelength of 1550nm. This photon is different from signal light, and it constitutes the noise of EDFA. If the input optical power of EDFA is low, strong self-excited radiation will produce large noise

III. basic structure of EDFA

EDFA is generally composed of five basic parts, namely erbium-doped fiber (EDF), pump light source (pump LD), optical passive components (including coupler, optical wavelength division multiplexer, optical fiber connector, isolator), control unit, monitoring interface

structure block diagram (II)

the function of optical coupler is to combine signal light and pump light, which is generally realized by wavelength division multiplexer. The function of optical isolator is to suppress light reflection to ensure the stability of optical amplifier. It must have low insertion loss, independent of polarization, and isolation better than 40dB. The function of optical filter is to reduce the influence of noise generated by spontaneous emission on the system. The control unit controls the operation of the optical fiber amplifier in real time, and the monitoring unit provides the working state information

IV. characteristics of EDFA and its impact on the system

the gain of EDFA is related to many factors, such as the concentration of erbium-doped er3+ in the fiber. As shown in figure (III), when the concentration of er3+ exceeds a certain value, the gain decreases instead. It is necessary to control the concentration of Erbium

Figure 3 Relationship between erbium-doped concentration and gain

the gain of EDFA is related to the degree of input light, pump light power and erbium-doped fiber length. Figure (4) shows the input-output saturation characteristics of EDFA, indicating that the gain coefficient at small signal input is greater than that at large signal input. When the input light is weak, the consumption of high-energy potential electrons is reduced and sufficient supply can be obtained from pumping. Therefore, the induced radiation can be maintained to a considerable extent. When the input light becomes weak, due to the insufficient supply of electrons at the high energy level, the increase of induced radiation light becomes less, so saturation occurs. The larger the pump power is, the longer the erbium-doped fiber is, and the larger the 3dB saturated output power is

after the adoption of EDFA, the power of the injected optical fiber is improved, but when it reaches a certain value, it will produce optical fiber nonlinear effect and optical leakage effect, which affects the transmission distance and transmission quality of the system, such as Faurecia's seat lightweight scheme, Pan Asia's heat and sound insulation materials and Solvay's TECHNYL high-performance materials. In addition, the dispersion problem has become a prominent problem limiting the system, G.653 fiber (dispersion shifted fiber DSF) or non-zero dispersion fiber (nzdf) can be selected to solve this problem

v. application of EDFA

in CATV system, the application form of EDFA is very flexible. EDFA is used at the output end of front-end optical transmitter to improve transmission power and extend transmission distance; Used in optical fiber transmission links to compensate for the loss of optical energy and increase the transmission distance; It is used in front of the optical receiver to pre play the signal, so as to greatly improve the receiving sensitivity of the optical receiver

Figure 5 is an example of the application of EDFA by Puyang cable radio and television station in the city county connection

Figure 5 topology of Puyang City County connection

because Fanxian and Taiqian are 55km and 100km away from the general front desk respectively, the link loss is too large, and the relay must be carried out in Fanxian new area. Therefore, the system uses power amplification and amplification of two EDFAs to compensate for optical branch loss. "It is reported that the optical loss and optical link loss. The system indicators meet the national standard c/n>50db cso>65db otb>65db. The successful construction of the system has greatly increased the scale and coverage of the network, facilitated the development of various businesses, and also brought rich returns to the station. See table (I) for the basic parameters of the basic optical path of the system table (I) the basic parameters of the optical path of the system

the output power of the optical transmitter is 8.96dbm, the output power of the front-end EDFA is 19.31dbm, and the output power of the relay EDFA is 13.8dbm

Figure 6 shows the plan of Puyang cable radio and television station to apply EDFA in urban CATV

Puyang cable station has 100000 users, each optical contact has 500 households, and needs 200 optical receivers. If 1310nmcatv transmitter has an output optical power of 16mw (the price is 150000 yuan), it needs 14 transmitters, and the total price of transmitting equipment is 2.1 million yuan; Using 1550nmcatv system (as shown in Figure 6) requires: a 1550nmcatv transmitter with a transmission power of 4MW (the price is 300000 yuan) and an EDFA with an output optical power of 50MW (the price is 150000/set). With five EDFA, the total price of the transmission equipment is 1.05 million yuan, and the difference between the two schemes is 1 time. The cost of 1550nm transmission system is only 50% of that of 1310nm transmission system. Because the attenuation of optical cable at 1550nm wavelength is only 57% of 1310nm wavelength, under the condition that the transmission has the same total transmission power, the transmitting equipment at 1550nm wavelength can transmit longer distance and have more optical receivers than the equipment at 1310nm. In large and medium-sized CATV, the 1550nm wavelength CATV system of EDFA has obvious advantages in performance price ratio, and is the mainstream of CATV development at present. (end)

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