Research On Multi-wavelength Q-Switched Fiber Laser And Its Performance

With human society entering information age,traditional communication technologies are difficult to meet the increasing requirement of communication capacity.Multiple signals of different wavelengths can propagate in the same optical fiber by DWDM technology,which greatly improve the transmission capacity,and become an important method to satisfy the requirement.Multi-wavelength Q-switched fiber lasers have promising applications in dense wavelength division multiplexing optical network,high-precision optical fiber sensor,radar ranging system,biomedicine due to the characteristics of multi-wavelength oscillation and Q-switched simultaneously.It has become one of the research hotspots of researchers in recent years.In this thesis,multi-wavelength Q-switched fiber lasers with three different structures are studied.The contents of the thesis include multi-wavelength passively Q-switched fiber laser and multi-wavelength actively Q-switched fiber laser.The effects of pump power and the parameters of filter on performances of multi-wavelength Q-switched fiber laser are studied,which including intracavity dispersion,filter line-width,wavelength-spacing and phase.The specific works are as follows:Firstly,the multi-wavelength Q-switched fiber laser,which is based on the unpumped erbium ytterbium co-doped fiber(EYDF)served as saturable absorber and Sagnac ring interferometer served as multi-wavelength filter,is studied.The theory of filtering of Sagnac interferometer is analyzed by Jones matrix method.Free spectrum range and transmissivity of the filter are given by the theory.In the experiment,the non-linear characteristics of EYDF-SA are given by the double balanced power detection method.Furthermore,the experimental setup and results are given and analyzed respectively.The influences of pump power and wavelength-spacing of filter on the Q-switched fiber laser are studied.The proposed laser has the advantages of simple structure,variable wavelength number and wavelength-spacing.Secondly,the multi-wavelength Q-switched fiber laser,which is based on EYDF-SA and Wave Shaper is studied.The principle of filtering of Wave Shaper,which is the key device used in the experiment,is introduced briefly.The experimental setup and results of the laser are given and analyzed respectively.Theinfluences of pump power and dispersion on the performances of Q-switched laser are studied,which include spectral line-width,pulse-width,average output power and single pulse energy.The influences of line-width,phase and wavelength-spacing of filter on the pulse-width of Q-switched laser are studied.Thirdly,the actively Q-switched fiber laser,which is based on electro-optic modulator(EOM)and Wave Shaper,is studied.The experimental setup and of results the laser is given and analyzed respectively.The influences of the pump power on the generation of multi-pulse are studied.The effects of frequency and amplitude of the RF signal on the average output power and pulse-width are studied respectively.In addition,we find that the line-width,group delay and center wavelength of the filter also have certain influences on the generation of multi-pulse.