Tunable Fiber Laser With Mid-infrared Wavelength Based On Self-frequency Shift Effect Of Soliton

With the rapid development of the optical fiber field,the broadband tunable fiber laser has the advantages of compact structure,low cost,easy to control and so on,which has become the research hotspot in the field of laser.There are many ways to achieve wavelength tunability.In this paper,we use the most promising scheme,that is,using the soliton self-frequency shift(SSFS)effect produced in the fiber to realize the mid infrared wavelength tunable Raman soliton laser,and make a detailed study of the laser.The main contents of this paper are as follows:1.On the basis of summarizing the physical effects of dispersion and nonlinearity,the propagation equation of light in optical fiber medium is deduced,and the generalized nonlinear Schrodinger equation is solved by using Runge-Kutta method.The formation mechanism of the Raman SSFS effect is further analyzed.The influences of the three core parameters,namely,the peak power of the pump source,the pulse width of the laser and the length of the fiber,on the SSFS phenomenon are studied by numerical simulation.2.On the basis of theoretical research,an all fiber Raman soliton laser consisting of a mode-locked pulse fiber laser and a thulium doped amplification system is constructed.The traditional soliton pulse with strong Kelly sideband is used as signal light in the Raman soliton laser.By simply increasing the pump power of the amplification system,the SSFs effect in thulium doped fiber is enhanced continuously,and the Raman soliton laser with wavelength tuning range of 1953.1~2328.4 nm is realized.When the central wavelength of the Raman soliton is 2194.3 nm,the minimum pulse width is 471 fs.In order to further analyze the specific effect of Kelly sideband strength on SSFS phenomenon,the Lyot filter with a specific filter period is selected to effectively suppress Kelly sideband of traditional soliton pulse.The soliton pulse of weak Kelly sideband is transmitted to the same thulium doped amplification system as signal light.By increasing the pump power,the Raman soliton laser with wavelength tuning range of 1953.1~2375.3 nm is produced.When the Raman soliton red shifts to 2240.6 nm,the pulse time-domain width reaches the narrowest state,which is 381 fs.By effectively suppressing the Kelly sideband of the soliton pulse,the peak power of the pulse itself can be increased,the SSFS effect generated in the fiber can be enhanced,the wavelength shift and soliton energy can be increased,and the femtosecond pulse with narrow time-domain width can be obtained.3.By adding dispersion compensation fiber into the cavity of traditional soliton pulse laser,the nearly zero dispersion dissipative soliton pulse laser output is realized.The mode-locked laser produces a dissipative soliton pulse with a central wavelength of 1940.7 nm and a spectral bandwidth of 36.4 nm,which can well cover the Raman gain spectrum of thulium doped fiber.The pulse has a time-domain width of 279 fs and a maximum output power of 18 mW.A tunable wavelength Raman soliton laser is formed by using the dissipative soliton pulse as the signal input to the thulium doped amplification system.By increasing the pump power of the system,a very strong SSFS effect is produced in thulium doped fiber.Finally,a Raman soliton laser with the center wavelength of 1940.7~2400 nm is obtained,and the pulse width is as narrow as 364 fs.