Mode-locked Yb-doped Fiber Laser Based On The Effect Of Evanescent Field

Ultrafast laser has the characteristics of extremely narrow pulse width,extremely high peak power and wider spectral width.It has been widely used in biomedicine,optical detection,material processing and other fields.The development of ultra-fast optics and ultra-intense laser technology has important academic significance and application value.In recent years,the generation of mode-locked pulses using evanescent field effect of tapered fiber combined with a new type of saturable absorber material(two-dimensional nanomaterials)has become a research hotspot.Due to different the strength of evanescent field at different wavelength,the output of mode-locked pulses based on evanescent field effect is mostly concentrated in 1.5?m band,and the study of mode-locked evanescent field based on 1.0?m band is less now.In this paper,passive mode-locked Yb-doped fiber laser based on evanescent field effect is studied from three aspects: theoretical simulation,experimental research and data analysis.In the first chapter,the purpose and significance of passive mode-locked fiber lasers are discussed.On this basis,the starting mechanism and classification of passive mode-locked fiber lasers are briefly introduced.The development history of passive mode-locked fiber lasers based on two-dimensional nanomaterials and evanescent field effect is reviewed.In the second chapter,the basic principle of mode-locked fiber laser is introduced,and the transmission of optical pulse in the fiber is described in detail.Finally,the effects of dispersion,nonlinearity,gain,loss and the parameters of saturable absorbers on the output characteristics of mode-locked pulses are simulated by MATLAB software,which provides theoretical basis for the experiment.In the third chapter,the structure and characteristics of several two-dimensional nanomaterials and tapered fibers are briefly introduced,and the mode field distribution of tapered optical fibers is simulated by MATLAB software.The influence of tapered waist diameter on mode field distribution and evanescent field strength is analyzed,and the method of enhancing evanescent field effect is proposedIn the fourth chapter,we deposit graphene oxide/ molybdenum disulfide material on tapered optical fibers by mixing with a low-refractive-index silicone elastomer to enhance the strength of evanescent field and obtain stable mode-locked pulse output.The mode-locked pulse generated by graphene oxide saturable absorber has a central wavelength of 1030 nm,pulse width of 103 ps,repetition frequency of 37.3 MHz,spectral width of 0.4 nm,pulse signal-to-noise ratio of 30 dB and an output power of 1.03 mW.The mode-locked pulse signal-to-noise ratio(SNR)of the saturable absorber based on molybdenum disulfide is 25 dB,the repetition rate is 24.7MHz,the pulse width is 135 ps,and the output power is 0.8mW.Through further optimization,it can be used as a seed source of ultra-short pulse amplification to achieve high power mode-locked pulse output.