Study Of Vortex Mode-locked Laser Based On Fiber Structure

Vortex beam is a special beam with helical spatial phase and annular spatial intensity,which carries orbital angular momentum.It has attracted lots of attentions and been widely used in imaging,microscopic detection,metrology,astronomy,optical tweezers,quantum information processing,optical communication and so on.In order to support various applications,researchers have developed a variety of vortex beam lasers including gas lasers,solid lasers,diode lasers and fiber lasers to meet different demands.Although recently there have been a few demonstrations,vortex beam laser is still very limited.In this thesis,new-type vortex beam fiber lasers are investigated for higher vortex beam order and longer wavelength.The generation mechanism,transmission characteristics,phase reconstruction and evaluation scheme of vortex beam are introduced.Then the working principle of mode-locked fiber laser is introduced.A hybrid cavity mode-locked vortex beam laser with tunable order is built and characterized.And a 2 ?m mode-locked vortex beam all fiber laser is demonstrated and characterized.This thesis is organized as follows:(1)The theory of vortex beam is introduced.The transmission and interference of vortex beam are simulated,and the measurement and evaluation scheme of vortex beam is further proposed.(2)The operation principle of mode-locked fiber laser based on nonlinear polarization rotation and time-stretch ultrafast measurement method for studying its dynamic characteristics are introduced.(3)A hybrid cavity mode-locked vortex beam lase is built.The vortex beam pulse has a pulsewidth of ?600 fs with vortex order tunable between 1 and 8.The spatial,temporal and spectral characteristics of the output vortex beam pulse are characterized,and the spectral coherence and dynamic establishment process of the pulse are further measured by timestretch technique.(4)A thulium-doped mode-locked fiber laser is fabricated.According to its working wavelength,a mode selection coupler is designed and fabricated to further complete the 2?m mode-locked vortex beam fiber laser,which is also characterized.