Research On 2.8μm And 3.5μm Pulsed Lasers Based On Er³⁺ ZBLAN Fiber Laser

Since the 21st century,mid-infrared fiber lasers have been a research hotspot.And rare-earth ion-doped fiber lasers are important technical means to achieve mid-infrared laser output.Compared with traditional laser technology,it has significant advantages such as high beam quality,excellent heat dissipation,high conversion efficiency,and easy integration.At present,Er³⁺ZBLAN fiber lasers have been able to achieve high-efficiency laser lasing in the two mid-infrared bands of 2.8μm and 3.5μm.However,it is still in its infancy in terms of short pulses and ultrashort pulses,and there are many problems that need to be solved and explored urgently.In this thesis will focus on the broadband lasing potential of Er³⁺ZBLAN fiber in the two bands of 2.8μm and3.5μm,and explore the potential of wavelength tuning under short pulse and ultrashort pulse operation.The main contents include:1.Based on the energy level transition process related to 3.5μm laser lasing in Er³⁺ZBLAN fiber,combined with rate equation and power transmission equation,a laser dynamic model of continuous and pulse pumping is established.Secondly,in the case of continuous pumping,optimize the fiber doping concentration,length,and cavity mirror reflectivity to obtain the optimal parameter range of output efficiency.Finally,in the case of pulse pumping,the influence of the number and concentration of energy level ions on its pulse generation characteristics is analyzed and the influence of the pump repetition frequency on the output pulse characteristics is revealed at the same time.This provides theoretical guidance for the follow-up Er³⁺ZBLAN gain-switched pulsed fiber laser.2.An all-fiber Tm³⁺1981 nm pulsed fiber laser was built as the pump source for the experiment,and obtained a stable pulsed laser output with an output power of 5 W and an adjustable pulse repetition frequency of 20-50 k Hz.Secondly,the gain-switched Er³⁺ZBLAN pulsed fiber laser is built based on the pump source.A pulsed laser output with adjustable wavelength in the range of 3397.1～3690.2 nm was obtained,and it is the first to achieve gain modulation pulse wavelength tuning in the 3.5μm band.Analyze pulses at repetition frequencies of 20 k Hz,40 k Hz and 50 k Hz,respectively.Finally,the experimental data was verified by numerical simulation,and the reasons for the errors in the results were analyzed and resolved.3.An Er³⁺ZBLAN-doped fiber laser based on nonlinear polarization rotation mode-locking was built,and a mode-locked pulsed laser output with a wavelength of2780 nm and a pulse width of about 300 fs was obtained.On this basis,according to the spectral bandwidth and center wavelength of the mode-locked pulse,the Lyot filter is designed based on the Li Nb O₃ crystal.A self-built 2.8μm ASE（amplified spontaneous emission）light source was used to test the filtering characteristics of the filter.Finally,the filter was introduced into the mode-locked laser to realize the soliton tuning with a range of more than 50 nm and a pulse width of less than 300 fs from 2752.4 nm to2807.2 nm,and a dual-wavelength mode-locked pulse output with switchable states.This is the first femtosecond fiber laser in the mid-infrared band.This is a reliable method for the realization of a longer wavelength femtosecond tunable fiber laser in the future.