Polarization-maintaining Passive Mode-locked Fiber Laser Based On Dispersion Compensation

Ultrafast laser has many advantages,such as peak power,very short pulse width,high repetition frequency and ultra-wide spectrum,etc.,which has attracted much attention in many fields such as optical communication,biomedicine and precision processing.Passive mode-locked technology is an important way to generate ultrashort-short pulses.The saturable absorber is relatively mature,but its low damage threshold and low damage threshold seriously affect the output mode-locked pulse characteristics.The laser based on full polarization-maintaining fiber and nonlinear amplification structure has many advantages,such as low construction difficulty,self-starting mode locking,performance of high output pulse,strong anti-environmental interference ability,and has good application prospect and commercial value.At the same time,the dispersion compensation method based on all-fiber structure is easy to realize the ultra-short pulse with shorter response time and more compact structure.Therefore,in this paper,dispersion compensation fiber and chirped fiber grating are used to compensate the dispersion of"9"cavity mode-locked structure,and the dispersion compensation optimization and output pulse characteristics of fully polarization-maintaining passive mode-locked fiber laser are studied.The specific contents are as follows:1.Based on the nonlinear Schrodinger equation and its Fourier solution,the working mechanism of light pulse in mode-locked structure is analyzed by mathematical and physical methods.The propagation of mode-locked pulses in optical fibers with different dispersion media is simulated by Fourier method.The physical mechanism of intracellular dispersion compensation is analyzed by using nonlinear Schrodinger equation,and the relations of transmittance and input pulse light intensity in the following two experimental structures are deduced by combining with the physical mechanism of NALM structure,which improves the theoretical system for subsequent experiments.2.Based on this,a fully polarization-maintaining"9"cavity fiber laser based on dispersion compensation fiber was built.According to the dispersion compensation mechanism,a polarization-maintaining dispersion compensation fiber was added into the resonator for accurate dispersion compensation.The calculated net dispersion value at 1550nm was-0.0106 ps~2,close to zero dispersion.The structure laser realizes self-start mode-locking at pump power of 80m W,and its pulse repetition rate is 22.18 MHz,pulse energy is0.046 n J,and pulse width is 538 fs.After 2000 successful self-starting tests and 10 h laser output tests,it is proved that the structure laser can operate stably for a long time.3.The physical mechanism of chirped fiber grating was analyzed and combined with the mathematical and physical equation of NALM structure,a fully polarization-preserving"9"cavity mode-locked fiber laser based on chirped fiber grating was designed and constructed.The output pulse characteristics of different cavity lengths were analyzed.After optimization,18m cavity length was selected to realize the self-starting broadened soliton pulse mode-locking of 326 m W pump power.That made the average output power was 10.3 m W,the repetition rate was 12.1 MHz,the pulse width was 1.04 ps,and the corresponding pulse energy was 0.85 n J.It is proved that the resonators of the two structures can stably output ultra-short pulses that comparing the mode-locked pulse characteristics of the two structures.