Study On Random Characteristics Of Chaotic Output Of Fiber Amplifier

Chaotic laser has the advantages of noise-like,wide bandwidth,strong anti-interference,etc.It is widely used in lidar detection,chaotic secure communication,fiber fault detection and fast physical random number generator,etc.The random characteristics of chaotic laser directly affect its application fields and measurement accuracy.In recent years,chaotic secure communication systems and optical fiber fault detection systems using erbium-doped fiber amplifiers and underwater lidars using ytterbium-doped fiber amplifiers have gradually become research hotspots.Therefore,study of the random characteristics of chaotic lasers during the amplification process can be some guidance for laser applications.The nonlinear Kerr effect in the fiber laser ring cavity realizes the generation of chaotic laser.The erbium-doped and ytterbium-doped fiber amplifiers are used to amplify the chaotic laser.The autocorrelation function is used to monitor the random characteristics of the chaotic laser in real time.The random characteristics of the chaotic laser during the amplification process is measured by analyzing the permutation entropy,skewness and kurtosis of the chaotic time series during the amplification process.The main research contents of the thesis are as follows:1.The paper introduces the purpose and significance of the research,the development and application of chaotic lasers are introduced,the research progress of the random characteristics of chaotic lasers are explained.2.The paper briefly describes the method of generating chaotic laser by fiber laser,and introduces in detail the theoretical model of using the nonlinear Kerr effect in fiber to generate chaotic laser.Then some characterization methods to measure the random characteristics of chaotic laser are introduced,including Lyapunov index,autocorrelation function,permutation entropy,autocorrelation and statistical characteristics.3.The fiber ring cavity structure is used to built a chaotic erbium-doped fiber laser device and a chaotic ytterbium-doped fiber laser device.The random characteristics of the chaotic laser generated by the erbium-doped fiber laser and the ytterbium-doped fiber laser were studied respectively.The experimental results show that:(1)the permutation entropy of the erbiumdoped fiber chaotic laser source is stable around 0.956,and the fluctuation range does not exceed 2‰.Combining the chaotic time series,autocorrelation and spectrogram,it can be found that the random characteristics of the chaotic source are strong and stable.(2)The permutation entropy of the ytterbium-doped fiber chaotic laser source is stable around 0.965,and the fluctuation range does not exceed 1‰.Combining the chaotic time series,autocorrelation and spectrograms,it can be found that the chaotic time series only increases the peak-to-peak value during the increase in the pumping current of the chaotic source.The autocorrelation curves all have good delta-like function characteristics,while the spectrum changes from a single peak to a double peak.From the perspective of permutation entropy,the random characteristics of the chaotic laser light source are very good and very stable.In conclusion,the random characteristics and stability of the ytterbium-doped fiber chaotic laser source are slightly better than that of the erbium-doped fiber chaotic laser source.4.The principle and experimental equipment of erbium-doped and ytterbium-doped fiber amplifiers are introduced.The random characteristics of chaotic laser in the process of erbiumdoped and ytterbium-doped fiber amplifiers are experimentally studied,and the influence of different conditions on the chaotic time series is analyzed.The experimental results show that:(1)regardless of whether an erbium-doped fiber amplifier or a ytterbium-doped fiber amplifier is used to amplify the chaotic laser,the polarization state affects the amplification range of the chaotic laser.When the polarization state has been changed,the amplified signal under the same source pump current condition is not necessarily in a chaotic state.(2)During the amplification process of erbium and ytterbium fibers,the permutation entropy of the chaotic laser increases or decreases with the amplification pump current depending on the polarization state.Furthermore,the statistical properties of the chaotic time series in the time domain,namely the skewness and kurtosis,are also affected by the polarization state.(3)Ytterbium-doped fiber amplification can increase the permutation entropy of the chaotic laser,and whether the erbiumdoped fiber amplification gains the permutation entropy is related to the polarization state of the chaotic laser.