Investigation On The High-performance Single-frequency Thulium-doped Silica Fiber Laser With A Ring-cavity Configuration

Single-frequency thulium-doped fiber laser(TDFL)is one of the major narrowlinewidth laser sources operating at 2 ?m region,which has broad applications in highresolution spectroscopy,remote sensing,coherent LIDAR and so on.For broadening the operating wavelength of high-performance TDFL,a single-mode-multimodesingle-mode(SMS)fiber device is demonstrated and finally the laser operating above 2 ?m is achieved.To further narrow the linewidth of single-frequency fiber laser,a hybrid Brillouin/thulium fiber laser structure is set up and an ultra-narrow linewidth less than kilohertz is achieved in 2 ?m fiber laser.The research contents are as follows:1.The multimode interference effect in SMS fiber devices are numerically simulated,and the influence of input wavelength,length of multimode fiber and core size of multimode fiber on transmission properties are investigated.The capacity of the SMS fiber device serving as band-pass filter is confirmed,and a series of low-loss multimode interference filters are experimentally manufactured.2.The ring-cavity TDFL by utilizing SMS all-fiber device is demonstrated.The laser of 1.9 ?m is suppressed by the introduction of cascaded SMS fiber devices,and the laser operating around 2005 nm is realized.Sagnac loop and saturable absorber are utilized to realize single-longitude-mode operation,and a single-frequency TDFL operating at 2004.9 nm is obtained with maximum output power of 20.9 m W.3.Hybrid Brillouin/thulium fiber lasers are set up based on 793 nm cladding pump and 1570 nm core pump respectively.The influences of output coupling,pump scheme and fiber length on the power and linewidth behavior of Stokes light are experimentally investigated.By optimizing the output coupling,344-m W output power with a narrow linewidth of 0.93 k Hz is obtained from the hybrid Brillouin/thulium fiber laser,whose linewidth is suppressed 43 times of the Brillouin pump.The output power is further boosted to 5.5 W by a one-stage cladding-pumped fiber amplifier,and the corresponding spectral linewidth is broadened to 1.93 k Hz.