Research On The Technology Of 2.0-?m High-power Low-noise Single-frequency Fiber Laser

The 2.0-?m single-frequency fiber laser(SFFL)has broad application prospects in high-resolution spectroscopy,nonlinear optics,lidar,gravitational wave detection and non-invasive medical treatment.The 2.0-?m single-frequency laser has the advantage of eye-safety to the human and can be used in the field of coherent detection and coherent communication in the atmosphere.The 2.0-?m SFFL has a higher threshold of nonlinear effects than the 1.0-?m one,and it has more potentiality for increasing the output power.In addition,the high-power SFFL can be applied to long-distance coherent detection,and its characteristic of low intensity-noise makes the detection sensitivity higher.In order to meet the increasing demand for laser sources in the corresponding laser application fields,the research on power enhancing and noise suppressing of the 2.0-?m SFFL is of great significance.Based on the distributed Bragg reflector(DBR)single-frequency fiber resonator(seed laser)and the master-oscillator power-amplifier(MOPA)system,this paper has carried out research on the high-efficiency output,power amplification and noise suppression of the 2.0-?m SFFL seed source.The main research results are as follows:(1)Research on high-power and high-efficiency 2.0-?m single-frequency fiber resonator technology:Firstly,a theoretical model of fiber resonator based on the in-band pumping system of Tm³⁺is established,and the influence of the pump wavelength and the length of the active fiber on the output power is studied.Secondly,based on the theoretical simulation,the resonant cavity was designed and optimized,and an SFFL with an output power of 617 m W,a slope efficiency of 42.2%and a wavelength of 1950 nm was achieved.Furthermore,the wavelength of the DBR short-cavity SFFL resonator based on the Tm³⁺-doped germanate glass fiber is expanded.An SFFL is output with a power of 90 m W and a wavelength of 2015 nm;(2)Research on the in-band-and core-pumping amplification technology of 2.0-?m SFFL:Firstly,the theoretical model of the in-band-pumped Tm³⁺-doped fiber amplifier is established,and the evolution of output power and the influence of Stokes light on the increase of signal laser power were theoretically simulated.Secondly,a 1.6-?m fiber laser output with a power of113 W and a signal-to-noise ratio of 65 d B was achieved.Finally,the 1.6-?m fiber laser was used as the pump source to in-band-and core-pump the 9-?m-core-diameter Tm³⁺-doped fiber,and the 1950-nm SFFL with an output power of 55.3 W,a linewidth of 7 k Hz,and the beam quality factors M_x² and M_y² of 1.01 and 1.03,respectively,was achieved;(3)Research on 2.0-?m high-power SFFL and mode field optimization technology:First,a theoretical model of cladding-pumped Tm³⁺-doped fiber amplifier is established,and the power amplifier stage is optimized through theoretical simulation results.Secondly,a 2.0-?m high-power SFFL amplifier was designed to achieve a 1950-nm SFFL with an output power of110 W,a linewidth of 6.3 k Hz,and a polarization extinction ratio of 16.2 d B.In addition,the coupling model of the transverse mode loss and the output laser transverse mode in the large mode field area fiber laser amplifier is established.The rounded-square-coiling fiber sceme is designed to optimize the transverse mode field of the output laser.Based on theoretical simulation analysis,the transverse mode field of the output laser of the amplifier.Finally,a1950-nm SFFL with a power of 316 W,a linewidth of 8.4 k Hz,and beam quality factors of M_x²and M_y² of 1.19 and 1.17 were achieved;(4)Research on the intensity-noise suppression technology of 2.0-?m SFFL amplifier:On the one hand,an all-optical suppression technology of relative intensity-noise based on the nonlinear saturation amplification effect of the fiber amplifier is proposed.The nonlinear saturation amplification state of the bidirectional power-amplifier structure is optimized through the theoretical model,and the maximum noise-suppression ratio in the frequency range of 1-200 k Hz is 24 d B.Finally,a 1950 nm SFFL with a relative intensity-noise of-135 d B/Hz@20-40 k Hz and a power of 5.16 W was achieved.On the other hand,the influence of photoelectric feedback acting on the semiconductor pump source of the pre-amplifier and the power-amplifier on the output laser intensity-noise is explored,and the effective suppression of the relative intensity noise in the 0.2-13 k Hz frequency band is achieved.Finally,a 1950 nm SFFL with relative intensity-noise of-140 dB/Hz@0.6-4 kHz and an output power of 5.86 W was realized.