L-band Erbium-doped Fiber Amplifier

Since the 1970s, optical fiber communications has made great progress in ashort period of 30 years. The speed of fiber-optic communication has been growingfrom 45Mbits/s to 40Gbit/s. How to use the existing communication system towiden the communication capability in order to meet increasingly demands hasbecome the hotspot of the optical communication research realm, when all kinds ofdata services require more and more transmission bandwidth. Through combinedwith the traditional C-Band erbium-doped fiber amplifier (EDFA), L-Band EDFAcan widen the original gain bandwidth and improve the channel capacityremarkably. So L-band EDFA has become the key device of the new generationDWDM system, it can be realized or not determines the realization of broad bandDWDM system. Comparing with C-band EDFA, L-band EDFA has its particularcharacter in widen mechanism, gain, how to choose pump wavelength and power,power conversion efficiency and so on. How to optimize the design of L-bandEDFA has become a new request for optical communication. Therefore, thedevelopment of L-Band EDFA has great significance for the enhancement of thefuture fiber communication system capacity.Under this background, the author develops two kinds L-band EDFAinstructed by Processor Guo Yubin during the postgraduate study. Through theintroduction of a single optical fiber Bragg grating (FBG), better gain clampingresults and bigger gain figure were obtained. This paper studied and had carried onthe experiment in the expectation of offering the theory and experiment referencefor the methods of L-band EDFA.First, the thesis introduced the background knowledge such as: theclassification, application of optical amplifiers and the development of EDFA. Atthe same time, the paper carried out the theoretically analysis on the characteristicof Er ion in erbium-doped fiber, especially on the principle of EDFA and itsamplified performance, the Gils model, one of the most used models in theoreticalcalculations, is also derived. Second, several important performance parameters of L-band EDFA isintroduced. The measurement of noise figure is discussed in detail. According tothe following experiments, the reflected spectrum of FBG is measured. Then theamplified spontaneous emission (ASE) spectrum characteristic of the designedconfiguration is studied. According to the ASE spectrum characteristic, adjusted thefiber structure in the experiment to achieve more satisfactory results.Finally, the paper studied linear cavity and ring-shaped cavity L-Banderbium-doped fiber amplifier. The linear cavity L-Band erbium-doped fiberamplifier adopted two sections EDF as gain medium, 1480nm LD as pump laserfor higher efficiency and lower noise figure (NF). When input 1589nm signal, thegain is clamped at 23dB with a variation of 0.5 dB from input signal power of -30to -8dBm for a pump power of 180mW, and NF below 5dB is obtained. As FBGreflects some ASE back into the EDF, the gain enhances 5dB with inputting smallsignal. The saturated output power for 1589nm is 7dBm. At the longer wavelength(1614nm) in L-band higher gain is also obtained.At the same time, the paper studied L-band EDFA based on ring erbium-dopedfiber laser cavity. When input 1589nm signal, the gain is clamped at 17.5dB with avariation of 0.3 dB from input signal power of -30dBm to -12dBm for a pumppower of 180mW, and NF below 5dB is obtained. By adjusting the intra-cavity loss,the gain reaches 19.78dB with inputting small signal. The saturated output powerfor 1589nm is 8.5dBm. At 1614nm, 9.2dB gain is obtained.The main features of this paper are:1. A novel gain-clamped linear cavity L-band EDFA is proposed andexperimented by using a fiber Bragg grating (FBG) at the input end of the amplifier.This design provides a good gain clamping and decreases noise effectively. AsFBG reflects the backward ASE into the EDF, the small signal gain is improved.Comparing with the previous schemes, higher gain is observed at the longerwavelength at L-band.2. The linear cavity configuration adopts two sections of EDF, 20-m-length high concentration EDF combined with 11-m-length common EDF. The commonEDF is used to generate C-band ASE, then this C-band ASE is utilized to pumphigh concentration EDF. The Experiment results show that this configuration canameliorate gain and NF effectively.3. An L-band EDFA based on ring erbium-doped fiber laser cavity isestablished. By adding a FBG at the output end, the FBG can reflect parts forwardASE into the laser cavity, the signal gain can be clamped consequently. Comparingwith related reports, this configuration also has a good gain clamping. Because1480nm LD and high concentration EDF is used in this experiment, the amplifierhas lower noise figure.As a conclusion, this thesis analyzes the principle, design process, debuggingprocess, output characteristic measuration of L-band Erbium-doped Fiber Amplifier.I hope that these researches could provide worthy theories and the techniquesupport for further research and development.