Research On Narrow-linewidth Fiber Laser Based On Cascade Four-wave Mixing

Narrow-linewidth fiber lasers have broad application prospects in optical coherent communication,high-precision ranging,coherent radar detection,military and national defense due to their promising performances of compact all-fiber configuration,simple thermal management,high monochromatism and ultra-high coherence.However,these applications are severely hampered by the difficulty in scaling up the output power of single-channel narrow-linewidth lasers due to the low threshold of SBS for narrow linewidth.Therefore,wider linewidth can not only improve the output power,but also meet the requirements of industrial and military.Besides,the linewidth broadened by nonlinear effects has the characteristics of stable broadening effect and relatively simple implementation.This paper focuses on the linewidth broadening of narrow-linewidth fiber laser based on CFWM.The research contents and the main results are as follows:(1)The evolution of CFWM pumped by continuous wave is analyzed and simulated theoretically by coupled mode theory and GNLSE.Firstly,the four-coupled equation is used to model and simulate FWM,and the influences of different factors on the efficiency of FWM are discussed.Secondly,combined with GNLSE and an appropriate numerical model,the evolution of CFWM pumped by continuous wave is simulated,and on this basis,the cascading is predicted with different interaction lengths and pump powers.(2)Study on narrow-linewidth fiber laser based of CFWM double-pumped by dual-cavity is as follows.Firstly,the wavelength-space tuning is implemented by adjusting the wavelength of two single-frequency fiber lasers(SFFL1 and SFFL2)through changing cavity temperature from 16 to 34 ? and employing piezoelectric effect.SFFL1 with tuning range from 1063.895 to 1064.045 nm and SFFL2 with tuning range from 1063.879 to 1064.032 nm are considered as two input frequency components to activate additional frequency components.And their temperature sensitivity is 8?9 pm/?.Driven by piezoelectric electricity,the wavelength micro-drift within 1 pm within the voltage of 3 V is achieved.And the natural linewidths of SFFL1 and SFFL2 are 6.2 k Hz and 19 k Hz,respectively.Secondly,the linewidth of narrow-linewidth fiber laser is broadened by tunable pump source and CFWM.The linewidth is broadened to 9.58 GHz pumped by power of 890 m W.And the linewidth becomes smaller when the wavelength spacing is shortened.(3)Study on narrow-linewidth fiber laser based of CFWM double-pumped by single-cavity is as follows.Firstly,the wavelengths of the dual single-frequency laser are1063.72 nm and 1064.07 nm,respectively,and the SNR is more than 66.2 d Bm.The output power of 11.5 m W fluctuates within ±1.3% for 15 min.Secondly,the dual single-frequency laser is amplified and sent into photonic crystal fiber as the pump source of CFWM.The linewidth of narrow-linewidth fiber laser is broadened by CFWM.And the linewidth is 15.8GHz when the mixing power is 858 mW.