| Compared with traditional solid-state lasers,fiber lasers have many advantages,including small size,low cost and high conversion efficiency.The 2μm fiber laser located in the safe band of human eyes has important applications in high-speed space optical communication,biomedicine,material processing,gas detection,scientific research,etc.Furthermore,thulium-doped,holmium-doped,thulium-holmium co-doped fiber lasers have also become the focus of laser research in the field of laser technology.However,the 2μm band all-fiber ultrafast laser is very different from the 1.55μm and 1μm band all-fiber ultrafast laser,so it can’t be put to practical application yet.Therefore,in view of some problems existing in the existing 2μm all-fiber ultrafast laser,the key technologies of the laser are studied,and the complex dynamic characteristics of the laser are discussed,which has a very important role and scientific value in promoting the 2μm band laser technology and its application.Comprehensive domestic and foreign research present situation,the current 2μm band of passively mode-locked fiber laser research is focus on thulium doped fiber laser and thulium holmium doped fiber laser,the research on soliton characteristics of holmium doped fiber laser is still relatively scarce.The main reason is that for holmium doped fiber,the selection of pump and the loss of mode-locking device increase the system complexity.In order to solve the above problems,passively mode-locked holmium and thuliumdoped fiber lasers have been studied by using nonlinear polarization rotation mode-locking and nonlinear amplifying loop mirror mode-locking techniques.Stable mode-locking operation has been achieved and a variety of solitons have been obtained,which is helpful for the study of solitons dynamics at 2μm band.Specific research contents are as follows:1)2.1μm holmium doped fiber pump source was studied.According to the energy level structure and gain principle of holmium doped fiber,in order to achieve high pump conversion slope,the holmium doped fiber was pumped by in-band pumping.An allfiber continuous output thulium-doped laser with tunable wavelength was experimentally constructed as the pump seed source.The effect of the pumping mode on the gain of holmium doped fiber was studied.The optimal pumping wavelength and pumping mode of holmium doped fiber was obtained by studying the effect of pumping mode on the gain of holmium doped fiber.2)The conventional soliton characteristics of anomalous dispersive cavity at 2.1μm band are studied.Based on the nonlinear polarization rotating mode-locking technique,a conventional soliton single-pulse mode-locking state was obtained by using this structure.Secondly,conventional solitons with tunable wavelength are obtained by adjusting the pump power and the polarization state of the resonator.In addition,the phenomenon of multiple solitons,including soliton clusters and harmonic mode-locking states,appears.Finally,dissipative soliton resonance pulses and noise-like pulses were also obtained by constructing holmium-doped fiber lasers based on nonlinear amplification loop mirror mode-locking,and the single pulse energy of noise-like pulses can reach 1.99 n J.3)The soliton characteristics of dispersion management cavity at 2μm band are studied.Based on the nonlinear polarization rotation-mode-locking technique,an ultra-high numerical aperture fiber is used to compensate for the dispersion in the cavity,and the stretched pulse of near zero dispersion region is obtained.The characteristics of the pulse with the variation of pump power are also analyzed.Dissipative soliton mode-locked pulses can be obtained by further optimizing the dispersion in the cavity to compensate it to a net positive dispersion.Finally,based on the principle of chirp pulse amplification,the pulse amplification of the dissipative soliton in the previous section is studied,and the laser pulse output with wide spectrum and high energy in the order of 100 m W is obtained. |
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