Rescarch Of DFB-FL And Optimization Of Amplifier

Recent years, fiber laser and fiber amplifier have become emerging technologies. They are widely applied in many fields, such as optical fiber communication, optical fiber sensing, national defense, medical, ranging and so on. Narrow linewidth fiber laser which uses optical amplification to generate laser, has many appealing features, such as narrow linewidth, low noise, high power, small volume and simple structure, strong controllability and good output spectrum. All these advantages make it a very important development direction of fiber laser. Distribute feedback fiber laser (DFB-FL) is an important branch of the narrow linewidth fiber laser, because the laser output is narrow linewidth, high interference and low noise. DFB-FL has many significant applications in fiber communication and sensing. So we consider that analysis and research on DFB-FL is necessary.DFB-FL can be classified to line cavity fiber laser, and its composition method is directly writting a phase-shifting grating to a doped fiber. Its resonant cavity is very short, at centimeter level. However, the output power of DFB-FL is relatively low, so if we choose DFL-FL, it should be equipped with fiber amplifier.According to different materials, fiber amplifier can be devided into rare earth doped fiber amplifier, nonlinear optical fiber amplifer, crystal fiber laser and plastic optical fiber laser. With the rapid development of fiber communication, the application of rare earth doped fiber is considered as the most extensive and convenient. Among rare earth doped fiber, erbium-doped fiber amplifier (EDFA) has experienced rapid growth, there are two main reasons. Firstly, EDFA has many advantages such as high gain, low noise, high output power, wide bandwidth, low coupling loss and polarization insensitive. Secondly, its working wavelength can cover the optimal window for fiber communication.Requirement on EDFA varies with different systems, but they all need high gain, high output power and low noise. Nevertheless, it’s difficult for these three features to reach optimal as the same time. Therefore, in this thesis we optimize EDFA to make DFB-FL have better performances.This thesis makes theoretical analysis for DFB-FL and EDFA. We design a compatible EDFA for DFB-FL.We try to find the most optimal fiber length. The main research is as follows:1. Introduce the basic working principle of DFB-FL, and make a theoretical analysis. Introduce the resonant cavity-FBG in detail. Design two kind of structures:the phase-shifting position asymmtric DFB-FL and refractive index modulation depth asymmtric DFB-FL.2. Study the characteristics of the DFB-FL from spectrum, laser intensity, the output power and the linewidth. Analyze characteristics of the two kind of asymmetric DFB-FL.3. Analyze the working principle of erbium-doped fiber amplifier(EDFA) in theory. Analyze the energy level structure of erbium ions in detail, and according to the energy level transition model we discuss the rate equation and transmission equation and their analytic methods.4. Compare several common EDFA, we find the most suitable EDFA for DFB-FL in this thesis. Make sure the erbium-doped fiber length is optimized designed, in order to achieve optimal EDFA performance.5. Finally, we test many EDFAs which have different lengths and different compound modes. Analyzing the experimental results, we try to find out the best length of erbium fiber, and design the most suitable EDFA for the DFB-FL.