Research On Narrow-linewidth Single-frequency Fiber Laser At 1560 Nm And Its Frequency Doubling

1.5?m single-frequency fiber lasers have been a research hotspot in the fields of coherent optical communication,distributed optical fiber sensor,terahertz and high-precision spectroscopy,because of the advantages such as narrow-linewidth of k Hz order,high signal-to-noise ratio,excellent beam quality and compact all-fiber structure.Especially for single-frequency fiber lasers operating at 1560 nm band,780 nm single-frequency laser can be obtained by its frequency doubling,corresponding to the transition wavelength of the D₂ line of Rubidium?Rb?atom,which can be applied for quantum information storage,high-resolution lidar,high-precision frequency calibration and laser cooling.Because of the high intensity noise of 1560 nm single-frequency fiber laser as the fundamental laser,the noise performance of the780 nm laser is poor,which seriously limits the resolution and fineness of its application system In addition,it needs higher fundamental laser output power,and it is difficult to achieve high conversion efficiency at the low fundamental laser power.However,limited by the large quantum defect,serious amplified spontaneous emission?ASE?and the low stimulated brillouin scattering?SBS?threshold,it would be difficult to achieve further power scalling of 1560 nm narrow-linewidth single-frequency fiber lasers.To overcome these limitations,this paper focuses on the research of narrow-linewidth single-frequency fiber laser at 1560 nm and its frequency doubling,and the research contents and the main results are as follows:?1?Based on the self-developed DBR single-frequency fiber laser seed oscillator at 1560nm,the MOPA configuration of of three-stage polarization-maintaining amplifier is constructed.In the power amplifier stage,the large-mode-field erbium-ytterbium co-doped double-clad fiber is used as the gain medium,which improves the SBS threshold of the system.The off-peak pumping scheme to 940 nm on Er:Yb LMA fibers has been adopted to enhance the Yb-to-Erenergy transfer efficiency,enable higher ASE threshold and decrease the thermal loading.A 1560 nm linearly-polarized single-frequency fiber laser with 53 W output power and 43%slope efficiency is demonstrated.Its signal-to-noise ratio?SNR?is 64.6 d B,and the laser linewidth is less than 4 k Hz.No ASE have been observed around Yb³⁺and 1.5?m band.By monitoring the backward power,it can be concluded that the SBS threshold is not reached and the power could be further amplified.?2?The high-power 780 nm single-frequency laser with a high conversion efficiency in a SHG configuration is demonstrated by utilizing the high power 1560 nm linearly-polarized single-frequency fiber laser as the fundamental laser,and the Mg O:PPLN crystal with high damage threshold as the frequency-doubling crystal.An maximum power of 6.4 W single-frequency laser at 780 nm is generated under the 32.5 W fundamental laser with a conversion efficiency of 19.7%,and its SNR is more than 52.4 d B.The optimal quasi-phase temperature of the Mg O:PPLN crystal is 115.0?,and the T_FWHM is 4.8?.?3?A broad-bandwidth near-quantum-noise-limited intensity noise suppression of single-frequency fiber laser?fundamental laser?at 1560 nm is obtained by the nonlinear amplification effect of a semiconductor optical amplifier?SOA?.An all fiber low-intensity-noise single-frequency laser at 780 nm by means of frequency doubling in a fiber-coupled PPLN waveguide is developed.The output power of SH single-frequency 780 nm laser can reach 340m W power with maximum conversion efficiency of 19.7%.The wavelength of the SH laser is set at 780.24 nm,and its SNR is more than 55 d B.The RIN of SH 780 nm in the frequency from 0.1 MHz to 5MHz is less than approximate-151 d B/Hz which approaches the quantum-noise-limited?-152.93 d B/Hz@780 nm,1 m W?.