Research On The 2 ?m Pulsed Fiber Laser And The Generation Of 3.5 ?m Synchronously Pumped Mode-locked Pulses

The 2?m pulsed fiber laser has a wide range of applications in medical surgery,military,atmospheric detection,lidar,mid-infrared supercontinuum generation,etc,so it has important academic research value and practical application significance.This paper mainly studies the ultrashort pulse generation and the main oscillation power amplification(MOPA)in 2?m band fiber laser,and uses it as a pulsed pump source to achieve 3.5?m synchronously pumped mode-locked fiber laser.The specific contents of the work are as follows:(1)Discuss and introduce the application and development of 2?m band pulsed fiber lasers,focusing on the generation of 2?m ultrashort pulses and the research progress of 2?m pulsed fiber lasers based on MOPA amplification structure,and elaborated the main research content of this paper And innovation.(2)The energy level structure of Tm~3+is analyzed,the formation mechanism of the mode locking and the principle of laser amplification are introduced,and the mechanism of power amplification of the main oscillation is analyzed.(3)Using RP Fiber Power software,a 2?m passive mode-locked fiber laser was numerically simulated,and the effects of the band-pass filter parameters and active fiber length on the spectrum and time-domain characteristics of the passive mode-locked pulse were studied.The simulation results show that,whether it is traditional soliton mode-locking or dissipative soliton mode-locking,by selecting a filter with appropriate center wavelength and bandwidth,a wide range of wavelengths can be tuned for passive mode-locked pulses;by increasing the active length,Stable operation can only be achieved in a smaller tunable wavelength range.This numerical simulation provides theoretical support for the development of a wavelength-matched 3.5?m fiber laser pulse pump source.(4)The generation of a large pulse energy h-shaped mode-locked pulse based on a 9-word cavity is studied.When the pump power is between 0.8 W and 1.8 W,the polarization controller is adjusted to achieve an h-shaped base with a repetition frequency of 240.7 k Hz Frequency mode-locked pulse.At this time,the center wavelength of the spectrum is 1890 nm,and as the pump power increases,the spectral bandwidth gradually decreases.When the pump power is increased from 0.8 W to 1.8W,the pulse width increases from 180 ns to 350 ns,thereby achieving a maximum pulse energy of 1.23?J in the current h-shaped mode-locked pulse.In addition,when the pump power continues to increase,the second harmonic,third harmonic,and fifth harmonic high-order harmonic h-shaped mode-locked pulse output are generated in sequence.(5)A 2?m passive mode-locked thulium holmium co-doped fiber laser based on CNT saturable absorber was developed.By changing the active fiber length(2 m–7 m),it was realized in the wavelength range of 1934 nm–1950 nm.Stable passive mode-locked pulse;by customizing and inserting a band-pass filter with a center wavelength of 1976 nm and a bandwidth of 40 nm,the center wavelength of the mode-locked pulse is moved from 1934 nm to 1976 nm,matching 3.5?m erbium-doped fluoride fiber The maximum absorption peak of the laser.In order to avoid the non-linear spectral broadening caused by low duty cycle pulses during power amplification,a 220 m SMF-28 single-mode fiber is inserted into the output of the mode-locked pulse to pre-chirp it to widen the pulse width from 800 fs to 84 ps,its repetition frequency is 9.841 MHz,and the output power is 2 m W.Furthermore,the 1976 nm picosecond pulse was subjected to 2nd-stage preamplification and 1st-stage large-mode field fiber power amplification,which reduced the nonlinear spectral broadening caused by the small-mode field fiber,and finally achieved an average power of 10.5 W and an optical-optical conversion efficiency of 31.25%of the 1976 nm high-power pulse output,and then the mode field adapter(MFA)was introduced after the large-mode field double-clad fiber to achieve single-mode output,with an average power of 8.5 W.(6)Based on the above-developed 1976 nm high-power picosecond fiber laser and976 nm pigtail output multimode semiconductor laser as the pump source,the dual-band pumped Er3+:ZBLAN fiber is adjusted by accurately adjusting the Er3+:ZBLAN fiber resonator The cavity length is closely matched with the cavity length of the 1976 nm mode-locked resonant cavity.Under the pumping of 10 W 976 nm continuous laser and 7 W 1976 nm picosecond laser,a pulse width of ps and a repetition frequency of 9.841 MHz are achieved.?m synchronous pump mode-locked pulse.