Mechanism Research Of Polarization Poincaré Sphere Beam Fiber Laser Based On Vortex Half-wave Plate

In recent years,polarized Poincaré sphere beams,represented by high-order and hybrid-order Poincaré sphere beams,have been widely used in the fields such as free space optical communication,optical trap,optical microscopy,encryption,and laser processing due to their unique phase and polarization structure.These numerous applications require compact,high-quality,and high flexibility Poincaré sphere beams lasers,strongly.Fiber lasers have become the preferred choice for producing polarized Poincaré sphere due to their compact structure and high photoelectric conversion efficiency.Therefore,this thesis intends to investigate the mechanism of polarized Poincaré sphere beams fiber laser.The main research contents are as follows:(1)Based on Jones vector and Jones matrix,the mode modulation theory of arbitrary high-order Poincaré sphere beams was studied.A high-order Poincaré sphere beams fiber laser based on cascaded vortex half wave plates was designed.The operating characteristics of the laser were experimentally investigated.The research results indicate that by using a fiber polarization controller to control the polarization state in the cavity,the laser can output arbitrary high-order Poincaré sphere beams.The slope efficiency is 37.64%.The center wavelength is 1029.06 nm,and the maximum output power is 168 m W.The insertion loss of cascaded vortex half wave plates has a negligible impact on the output characteristics of high-order Poincaré sphere beams fiber laser.This laser achieves the output of arbitrary high-order Poincaré sphere beams in the cavity,which improves the controllability of the beam mode in fiber laser cavity and simplifies the system structure of the high-order Poincaré sphere beams fiber laser.(2)The theory of mode modulation of mode-switchable higher-order Poincaré sphere beams is studied.Based on the structure of inserting two quarter wave plates between cascaded vortex half wave plates,the mode-switchable high-order Poincaré sphere beams is achieved.Based on Q-switched technology,a mode-switchable pulses high-order Poincarésphere beams fiber laser was designed and constructed.The operating characteristics of the laser were studied.The operational characteristics of mode-switchable pulsed higher-order Poincaré sphere beams fiber laser was experimentally studied.The slope efficiency of the laser is 33.4%.The central wavelength is 1029 nm,and the pulse repetition frequency and pulse width are 241 k Hz and 360 ns,respectively.The maximum output power is 150.2m W.This laser achieves the output of mode-switchable arbitrary high-order Poincaré sphere beams.This method further improves the controllability of the beam mode in the fiber laser cavity.(3)The mode control theory of arbitrary hybrid-order Poincaré sphere beams is studied.Based on the structure of inserting two quarter wave plates between cascaded vortex half wave plates,a quarter wave plate and a fiber polarization controller are used to control the polarization state in the cavity,which can achieve the conversion between the Pancharatnam topological charge and the polarization topological charge,and mode modulation of arbitrary hiybrid-order Poincaré sphere beams.A hybrid-order Poincaré sphere beams fiber laser was designed and its operational characteristics were experimentally studied.The experimental results show that the laser can achieve the output of arbitrary hybrid-order Poincaré sphere beam.The spatial position of the vortex half wave plate will change the hybrid-order Poincaré sphere where the beam mode is located.The hybrid-order Poincarésphere beams with different mode vectors have different slope efficiency and spectral width when output.The slope efficiency of the beam with mode vector [-4,2,Φ,Θ],central wavelength and 3d B bandwidth of the beam are 27.64%,1030.04 nm and 0.07 nm respectively.The relevant data of the beam with mode vector [-4,-2,Φ,Θ] are 25.85%,1030.41 nm,and 0.08 nm,respectively.This method achieves the output of arbitrary hybrid-order Poincaré sphere beams in the fiber laser cavity for the first time,and improving the diversity of modes generated in the cavity.