Research In All-Polarization-Maintaining Mode Locked Laser With A Figure-9

The mode-locked lasers with high peak power and narrow pulses have important application in many fields such as precision measurement,biomedicine,scientific research,aerospace,and industrial production.Based on passive mode locking Nonlinear amplifying Loop Mirror(NALM)laser is a hot spot in recent years.Using the nonlinear artificial saturable absorption characteristic of the cavity itself,NALM perfectly avoids the disadvantages of the real saturable absorber such as low damage threshold and short life.Therefore,it is one of the most promising methods to realize fiber mode locking.It is of great guiding significance and practical value for the stable pulse output and the controllable pulse performance to study the influence of mode-locking parameters under different conditions and to adjust the state of the cavity on the performance of NALM output pulses.Based on the principle of the NALM interferometer,we explored the mode-locking conditions,output characteristics and regulatory mechanism of the figure-9 cavity fiber laser.The main content of the article is as follows:1.We have explored the basic principles of NALM passive mode-locked lasers and analyzed the mode locking mechanism and property of the existing figure-9 structure.In addition,we built full polarization maintaining figure-9 mode-locked laser based on polarization beam splitting prism,which is a further improvement on the basis of polarization-maintaining figure-9.We obtained the central wavelength of 1573.2 nm,pulse width of 797 fs and repetition frequency of 51.9 MHz,respectively.Moreover,the wavelength tunable range of 7.3 nm also be realized when rotating the wave plate.2.We designed a full polarization-maintaining polarization beam splitter-collimator hybrid device,optimized the figure-9 structure,and improved the stability of the laser cavity.In the same laser cavity,a dual-state mode-locked pulse output of different spectra and output powers is realized with the repetition frequency of up to 86.5 MHz,pulse width of 1.51 ps and 1.71 ps,respectively.Meanwhile,the construction cost of the laser in our work has been greatly reduced than traditional one.Finally,the conditions having impact on the stability of "9" cavity is analyzed from the phase noise.3.By means of Jones matrix,the transmittance of the all-fiber polarization-maintaining figure-9 was analyzed with various parameters in the cavity.We designed and processed the fiber non-reciprocal phase shifter and the fully-polarization-maintaining figure-9 mode-locked fiber laser based on the fiber coupler is built.finally,we successfully realized the output of mode-locked laser under full polarization maintaining fiber structure and the pulse output had periodic modulation in intensity and new periodic comb teeth were generated in the spectrum.Compared with polarization splitting prism figure-9,polarization-maintaining figure-9 fiber laser has many advantages:the compact structure,the smaller volume to move easily,the higher integration,and the stronger ability to resist environmental interference.