Research On Multi-wavelength Mode-locked Fiber Laser Based On Multimode Fiber Saturable Absorber

Multi-wavelength passive mode-locked fiber lasers have a wide range of applications in the fields of wavelength division multiplexing,optical communication and so on.As the core device of passive mode-locked fiber laser,saturable absorbers(SAs)have always been the research hotspot of mode-locked fiber laser.As a new type of SA,the multimode fiber structure SA based on nonlinear multimode interference has the characteristics of filtering and saturation absorption in the state of stretching or bending.In this paper,the multi-wavelength mode-locked pulse lasers are obtained by using a SA based on GIMF structure,which provides a new scheme for the research of multi-wavelength mode-locked fiber lasers.The main work of this paper includes:Firstly,the research background and development history of multi-wavelength mode-locked fiber lasers are introduced,and the core device of passive mode-locking SA is introduced.The working principles and advantages and disadvantages of several commonly used multi-wavelength mode-locking methods are analyzed;Secondly,the multimode interference effect and nonlinear multimode interference effect in multimode fiber are studied.The new SA preparation method based on the GIMF structure is given,and the filtering and saturation absorption effects of the structure device are also studied.The new SA can be used to generate multi-wavelength mode-locked pulses;Finally,multi-wavelength mode-locked laser output was obtained in a ring-shaped thulium doped fiber laser cavity using SA based on single-mode fiber and GIMF structure.In the single-soliton operation,the central wavelength of the spectrum is about 1931 nm,the spectral 3dB bandwidth is about 3.7nm,and the pulse width is 1.2ps.By stretching GIMF,the single soliton laser output with a tuning range of 5.2nm can be obtained.In addition,the multi-wavelength mode-locked thulium doped fiber exciter designed by using multimode fiber structure SA is mainly studied.In different bending state of GIMF,it is easy to obtain the double soliton mode-locked pulse with the spectral interval between 15 nm and 43 nm by adjusting the intracavity birefringence,and other dual-wavelength mode-locked pulses were obtained using GIMF with different lengths.By increasing the pump power and adjusting the intracavity birefringence,the triple-soliton mode-locked pulses are obtained and the spectral center wavelength is 1855 / 1895 / 1933 nm,the spectral 3dB bandwidth is about 3nm,and the pulse width is 1.17/1.22/1.27 ps,respectively.By adjusting the birefringence of the cavity,the triple-soliton mode-locked operation can be converted into a double-soliton mode-locked operation and a single-soliton mode-locked operation.Such a switchable multi-wavelength mode-locked fiber laser with a wide spectral interval has a good application prospect in the fields of wide tunable soliton light source and mid infrared light source.