Research On 1 ?m Square Wave Based On NPR And Its Raman Fiber Laser

In recent years,fiber laser has attracted much attention because of its good stability,high beam quality and low comprehensive cost.It is widely used and has great development potential in the fields of electronic information,industrial processing,biomedicine,national defense science and technology.At present,the main research directions of fiber lasers are high power,ultra short pulse and wide spectrum.Among them,ultrashort pulse passive mode locking technology has developed rapidly in the fields of nonlinear pulse dynamics,near and mid infrared.For dissipative soliton resonance and Raman frequency shift,a 1 ?m near infrared passively mode-locked fiber laser is studied based on nonlinear polarization rotation(NPR)technique.High repetition rate and high energy square wave pulses are obtained and Raman frequency shift is performed.The specific work is as follows:1.Based on the propagation equation of optical pulse in fiber,the influence factors are analyzed,including dispersion,nonlinear effect and gain.Based on the nonlinear Schrodinger equation,the coupled Ginzburg Landau equation is obtained by considering the two polarization components in the birefringent fiber.We established a Using Jones matrix,a mode-locked model based on NPR technique is established.Based on the nonlinear polarization rotation technique,the square wave pulse is simulated and its evolution process is analyzed.The formation mechanism of square wave pulse is studied,the evolution process is simulated,and the influence of pump power and cavity length on square wave pulse is analyzed.2.Based on nonlinear polarization rotation(NPR)technology,passively modelocked ring resonators with cavity length of 61.5 m and 111.5 m are built respectively.When the cavity length is 61.5 m,different mode locking states are obtained.It includes mode locking of dissipative soliton and square wave pulse working in the region of dissipative soliton resonance.The pulse width of the square wave pulse is tunable from3.15 ns to 5.7 ns,and the repetition rate is 3.18 MHz.By adjusting the polarization controller at the same pump power,a square wave pulse with tunable pulse duration time from 3.85 ns to 5.5 ns is obtained.Then the cavity length reached to 111.5 m,the nonlinearity in the cavity is enhanced,the threshold of square wave pulse is reduced,and the pulse width is significantly improved.The repetition frequency is 1.77 MHz,the pulse width is tunable between 2.6 ns and 13.3 ns,and the output power is 15 MW.3.The wide pulse width square wave pulse is amplified based on the main oscillation power amplification technology,and the maximum output power of 3.4 W is obtained after one-stage amplification,and the spectrum does not change,the pulse does not appear distortion due to amplification,the pulse width and repetition frequency are maintained,only the peak power is increased.Raman scattering is studied theoretically,and Raman frequency shift experiment is carried out based on amplified spontaneous Raman scattering to make up for the wavelength range of Yb doped fiber.The influence of pump power and length of Raman gain fiber on first-order Stokes conversion is studied.