Research On High-power Narrow-linewidth Laser Seed Source Technology Based On Super-fluorescence White Noise Phase Modulation

High-power narrow-linewidth fiber lasers have important applications in high energy laser weapon,laser ranging and laser gravitational wave detection.At present,the power enhancement of narrow-linewidth fiber lasers is limited by the nonlinear and thermal effects of the fiber,among which stimulated Brillouin scattering(SBS)effect is concerned by research institutions due to its low threshold and strong destructivity.The seed based on single-frequency laser phase-modulated broadening is one of the ideal schemes to suppress the SBS effect of high-power narrow-linewidth lasers.In this paper,the single-frequency laser phase modulation broadening technique based on super-fluorescence white noise is studied and applied to the high-power narrow-linewidth laser,which effectively inhibits the SBS effect.The occurrence process,threshold model and suppression methods of SBS effect in optical fiber are analyzed theoretically.Based on the basic principle of single-frequency laser phase modulation,the simulation models of sinusoidal phase modulation and white noise phase modulation are established.According to the principle of ytterbium-doped super-fluorescent light source,the theoretical model of white noise based on the relative intensity noise of super-fluorescent light source is established.Theoretically,the amplitude of white noise is proportional to the power of super-fluorescent light source and inversely proportional to the bandwidth of the light source.The bandwidth of white noise is limited by the photodetector.According to the characteristic that the relative intensity noise of super-fluorescence source is white noise on photodetector,the super-fluorescence white noise is produced.Based on the simulation analysis of the output characteristics of ytterbium-doped super-fluorescent light source,the one-way reverse structure wideband super-fluorescent light source is prepared.The working principle,response characteristics and noise characteristics of indium gallium arsenic(In Ga As)PIN photodetector are analyzed theoretically.Ytterbium-doped super-fluorescent light source and In Ga As PIN photodetector are used to produce the white noise source.The amplitude characteristics of the super-fluorescent white noise are experimentally verified,and the 10 GHz bandwidth super-fluorescent white noise is obtained.In order to verify the effect of super-fluorescence white noise on the linewidth of single-frequency laser,the phase-modulated broadening experiment of single-frequency laser with linewidth less than 1k Hz is carried out using super-fluorescence white noise.The two-stage white noise cascade structure is used in the broadening unit.By changing the amplitude and bandwidth of the super-fluorescent white noise,different linewidth broadening effects are implemented.Finally,the line width of the single-frequency laser is expanded to0.14 nm(10 d B linewidth)by using the 10 GHz+100 MHz super-fluorescence white noise cascade modulation scheme.The SBS suppression effect of super-fluorescence white noise phase-modulated seed source in high-power fiber amplifier is verified by an experimental platform with four-stage main oscillation power amplification(MOPA)structure.Consequently,the output power is pushed up to 2 k W with linewidth of 0.15 nm(10 d B).No obvious spectral broadening and SBS phenomena are observed during the amplification process.