Research On 2 ?m High Repetition Rate Mode-locked Fiber Laser

In recent years,due to the 2 ?m thulium-doped fiber laser operating in the safe range of human eyes in remote sensing,space communication,laser radar technology,photoelectric countermeasures,mid-infrared hypercontinuum spectrum,Many fields,such as the emergence of medicine and so on,have a good prospect of application,which has attracted wide attention of researchers.In the past few decades,there have been many achievements about 2 ?m fiber laser in the fields of high power,Q switching,and wide tuning range etc.Achieving high repetition-rate mode-locking operation at 2 ?m is meaningful because of its potential application in high speed communication,frequency comb and broad signal processing.In this paper,a high repetition-rate mode-locked fiber laser in 2 ?m band is studied.Thulium-doped fiber is used as gain medium.We have done a lot of experiments to study it,and we have developed a lot of mode-locked structures with high repetition rate.The experimental results have been analyzed and improved.The main achievements of the experimental research in this thesis are as follows::1.The spontaneous emission characteristics of thulium doped fiber and its gain spectrum are studied.A high repetition-rate passively mode-locked thulium-doped fiber laser based on nonlinear polarization rotation(NPR)structure is studied.The pulse width is 54.7 ps,the fundamental repetition-rate of the output pulse is 5.05 MHz,and the high-order harmonic mode-locked pulse output with the repetition-rate is 1.02 GHz,and the harmonic order is 202.The central wavelength of the output pulse is 1891.89 nm and the 3 dB line width of the output pulse is 3.1 nm.2.A high repetition rate passively mode-locked thulium-doped fiber laser based on NPR filter structure is studied.The Agiltron manual tunable filter(FOTF-020121333)is added to the NPR structure.The insertion loss is 2.61 dB and the filter bandwidth is 1.508 nm,tuning range is 109 nm.The filter greatly narrows the linewidth of the output pulse,and then increases the repetition-rate of the output pulse.The pulse width is 51 ps,the maximum repetition frequency is 10.3 GHz,and the output of 2039 nd ultra-high order harmonic mode-locked pulse is realized.The central wavelength of the output pulse can be continuously tuned,and the tuning range is 1882-1925 nm.3 dB line width is 0.2 nm.3.A high repetition rate active mode-locked thulium-doped fiber laser based on intensity modulation is studied.All-fiber ring cavity structure is used in the laser.The modulator in the experiment is a 2-micron band electro-optic intensity modulator developed by the laboratory.Its bandwidth is 10 GHz.The pulse width is 50.4 ps,the maximum repetition rate is 10.4 GHz,and the output of 3006 nd ultra-high harmonic mode-locked pulse is realized.The central wavelength of the output pulse is 1967 nm,and the line width of 3 dB is about 0.37 nm.4.A high repetition rate active-passive hybrid mode-locked thulium-doped fiber laser is studied.In order to limit the linewidth of the active mode-locked laser and effectively suppress the super-mode noise of the active mode-locked pulse,an active-passive hybrid mode-locked structure with NPR filter structure is adopted.The high-order harmonic mode-locked pulse output with 470 ps pulse width,519 MHz repetition rate and 135 nd is realized.The central wavelength of the output pulse is 1887.5 nm and the line width of 3 dB is 0.05 nm.