| The study of single longitudinal mode(SLM)narrow linewidth erbium-doped fiber-lasers(TDFLs)is significant for field where strict and special requirements for linewidth are required in the 2μm band.The laser in this band can be applied to laser radar,medical and health,atmospheric detection,remote sensing technology etc.and is safe for the human eye.Multi-wavelength fiber laser(MWFL)can simultaneously illuminate optical signals of multiple wavelengths,and has the characteristics of compact structure and high beam quality.Therefore,it has wide application prospects in broadband optical fiber communication and optical communication systems.In view of this,this thesis takes SLM,narrow linewidth and multi-wavelength erbium-doped fiber laser(MWTDFL)as the research target,and carries out simulation and experiment on multi-wavelength and SLM,narrow linewidth annular cavity TDFL.The main work and innovative achievements of this paper are as follows:(1)Taking the erbium-doped fiber Giles model as the research background,the theoretical model of erbium-doped fiber amplifier(TDFA)is introduced.According to the rate equation of TDFA and the power transfer equation of erbium-doped fiber ring laser(TDFRL),the theoretical model of multi-wavelength annular cavity TDFL is established,which lays a theoretical foundation for simulation numerical modeling.In the numerical simulation,the second order Runge-Kutta method is used to solve the power transfer equation and rate equation of pump light and signal light,and then analyze the transmission characteristics of multiple wavelengths.(2)Modular analysis of MWTDFL numerical analysis simulation,including erbium-doped fiber gain medium module and comb filter module,and the implementation of these modules in simulation is introduced in detail.Numerical simulation is carried out by using MATLAB.The effects of gain fiber length on multi-wavelength output flatness and output power are simulated under the condition of fixed pump power and cavity loss.The simulation results are analyzed to provide a theoretical basis for the experiment.(3)Propose and experimentally verify a single longitudinal mode(SLM)narrow linewidth annular cavity TDFL,and achieve a stable SLM laser at room temperature by using a special sub-ring cavity and a self-made narrow linewidth fiber Bragg grating(FBG).Signal lasing and narrow linewidth output.The sub-ring cavity consists of three interconnected optical couplers for suppressing dense multi-longitudinal modes and mode hopping.The self-made FBQ as a narrow linewidth filter,finally achieves a stable SLM lasing.In the experiment,the output spectrum of the proposed 2μm band TDFL,optical signal-to-noise ratio(OSNR),stability,single longitudinal mode,linewidth,etc.have been studied and analyzed in detail,and the laser has good stability and higher OSNR.The experimental results show that the laser can obtain a stable signal output with a center wavelength of 1940.6nm and an OSNR of 60dB at room temperature.(4)The mechanism of measuring linewidth based on frequency noise measurement method is studied.The phase noise is measured by the Michelson unbalanced interferometer method based on the 3x3 optical couplers.The data processing is performed on the interferometer detection data to obtain the power spectrum characteristics of the phase noise,and the laser linewidth is calculated.In the single-longitudinal-mode obtained in this paper,when the measurement time is 0.05 s,the linewidth calculated by the frequency noise is about 8kHz. |
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