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Research On All-normal-dispersion Mode-locked Fiber Lasers

Posted on:2011-10-03Degree:MasterType:Thesis
Country:ChinaCandidate:H ZhaoFull Text:PDF
GTID:2198330338483539Subject:Photonics technology
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During the past two decades, mode-locked fiber lasers have been developed to be a promising branch of ultrashort pulse laser technologies due to their compact sizes, superior performances, flexible structures and diverse mode-locking mechanisms, causing wide-spread academic and applicational interests. The recently proposed all-normal-dispersion (ANDi) mode-locked fiber lasers have even simpler structures due to the exclusion of negatively dispersive intracavity elements, and introduce a new mode-locking mechanism into mode-locked fiber lasers with their dissipative-process-dependant shaping of intracavity pulses, the key of which is the spectral filtering effect. In this thesis, theoretical, numerical and experimental research concerning this novel kind of mode-locked fiber lasers has been demonstrated.The theoretical research started with a fairly detailed illustration of how the three key features of a fiber laser, containing dispersion, nonlinearity and gain, affect the optical pulse individually. Based on this, the Ginzburg-Landau equation which describes the propagation of optical pulses inside a mode-locked fiber laser was derived. Also the specific mechanism and the pulse properties of the ANDi mode-locking regime were discussed.Numerical simulations were performed using the split-step Fourier method for the ANDi mode-locked fiber laser. A clear image of the intracavity dynamic process was achieved, which was followed by a discussion of how the output pulse characteristics change when the length of the intracavity single-mode fiber was altered. The impact of the fiber gain on the output pulse properties was also discussed.A ring-cavity Yb-doped ANDi mode-locked fiber laser was experimentally constructed. Single pulse energies of 3.5nJ, 12nJ and 20nJ were obtained when operating at repetition rates of 26.6MHz, 6.66 MHz and 5.05 MHz, respectively. The energy of the 5.05 MHz-repetition-rate pulse was further increased up to 32 nJ by optimization of the gain fiber length, and the extracavity compression was performed utilizing a grating pair. The experimentally observed variation tendency of output pulse parameters with the change of total cavity length was in agreement with simulation results.
Keywords/Search Tags:all-normal-dispersion mode-locked fiber laser, spectral filtering, nonlinear polarization rotation, Ginzburg-Landau equation, split-step Fourier method, single pulse energy
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