| High-power narrow-linewidth linear-polarization single-frequency fiber lasers have important applications in laser radar,gravity wave detection,space optical communications,nonlinear frequency conversion and other fields due to their characteristics such as compact structure,good stability,easy operation,and maintenance-free.In particular,single-frequency lasers in the 1.5 ?m band can be frequency doubled to 780 nm by using nonlinear crystal and frequency stabled by atomic saturation absorption spectrum to obtain long-term frequency-stable rubidium-atom-operated laser,which has important applications in the field of precision measurement.Coupled with its unique advantages such as eye safety,low optical fiber transmission loss,and high atmospheric transmittance,it has attracted extensive attention in recent years.The use of main oscillation power amplification(MOPA)technology is an important method to obtain this laser source.This article mainly focuses on the single-frequency fiber laser of MOPA structure with high power and narrow linewidth in the 1.5 ?m band.The specific work includes:Firstly,based on the rate equation and transmission equation,a theoretical model of the Erbium-Ytterbium co-doped double-clad fiber(EY-DCF)amplifier is constructed,and a cladding-pumped EY-DCF amplifier scheme based on dual-wavelength auxiliary signal injection technology is proposed and demonstrated.The experimental results show that the use of auxiliary signals with wavelengths of 1030 nm and 1040 nm can greatly alleviate the effect of EY-DCF non-uniform gain broadening when a single wavelength signal is injected,which restricts the suppression of potential self-lasing peaks in reverse Yb-ASE.It can not only increase the allowed maximum pump power in the amplification process,but also play its auxiliary pump role at the end of the gain fiber,so that the net output power of the signal light can reaches 13.8 W.Secondly,based on a self-developed 1560 nm single-frequency narrow-linewidth DBR fiber laser,using a waveguide type periodically polarized lithium niobate(PPLN)crystal,a frequency-doubled optical output of 2.8 mW is obtained at a 1560 nm fundamental frequency optical power is 30 mW.Through the use of saturated absorption spectral frequency stabilization technology locks the obtained 780 nm laser to the ultrafine transition spectrum line of rubidium atoms,obtains the laser output of absolute frequency,and stabilizes the frequency fluctuation of the 1560 nm laser within 150 kHz for a long time.Thirdly,the 1560 nm single-frequency low-noise DBR fiber laser made by our laboratory is used as the seed source after the frequency is stabilized by the rubidium atomic absorption line.Through the reasonable design of the amplifier structure,the fiber splicing parameters are optimized,and finally two-stage single-mode fiber amplifier and two-stage double-clad Erbium-Ytterbium co-doped fiber amplifiers are used to achieve high-power,narrow-linewidth linearly-polarized 1560 nm laser light source.Using bulk PPLN crystal for frequency doubling can obtain 780 nm laser output with stable frequency and output power up to 2.25 W.Fourthly,through reasonable mechanical structure design and optical fiber thermal management measures,the 1560 nm high-power and narrow-linewidth MOPA fiber laser source is integrated and packaged in a 4U standard chassis,and the external frequency doubling module can be used for Rb atomic operation.Combined with the sideband locking technology,the frequency of the 780 nm laser can be precisely tuned within the tuning range of 1.2 GHz.Finally,it is possible to obtain cooling laser,repumping laser and atomic interference coherent operation laser simultaneously on a single laser.The above research results have important reference value for the development of high-power,narrow-linewidth,frequency-stable all-fiber MOPA lasers to meet the needs of applications such as nonlinear frequency conversion,atomic precision measurement,gravitational wave detection,Lidar and so on. |
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