| Due to the merit of high optical coherence,narrow-linewidth lasers have great application value in many areas such as laser radar,fiber sensing,gas detection,nonlinear frequency conversion,etc.In order to generate narrow-linewidth,high-power,wavelength-tunable near-infrared lasers,and provide useful laser sources for gas detection in the near-infrared waveband,this thesis demonstrates narrow-linewidth fiber lasers based on the rare-earth doped fibers and the nonlinear principle successively.At last,we have obtained a series of 2 ?m narrow-linewidth fiber lasers and 1.65 ?m narrow-linewidth fiber lasers,making up the deficiency and blank of the lasers in these two wavebands.Firstly,this thesis emphasizes the application value of 2 ?m and 1.65 ?m narrow-linewidth lasers in gas sensing.And it also indicates the deficiency of current lasers,highlighting the necessity of developing new narrow-linewidth fiber lasers in these two wavebands.Then this thesis simply introduces the origin of laser,the basic knowledge of fiber laser,cladding pumping and different kinds of pumping structures.Secondly,we have proposed a high-power wavelength-fixed single-longitudinal-mode(SLM)thulium-doped fiber laser(TDFL)by combining a fiber Bragg grating and a segment of un-pumped thulium-doped fiber as saturable absorber.The central wavelength,maximum output-power and linewidth of the SLM laser are 1957 nm,>400 mW and-20 kHz,respectively.In order to enable the laser to have the ability of tuning wavelength,we then have proposed a widely wavelength-tunable SLM TDFL using a tunable filter based on the principle of Fabry-Perot cavity.The wavelength tuning-range and linewidth of the SLM laser are 1920 nm-2020 nm and<10 kHz.respectively.Furthermore,in order to enable laser cavity to output high-power 2?m wavelength-tunable narrow-linewidth laser directly,we have proposed a widely wavelength-tunable SLM TDFL which pumped by a 790 nm high-power laser diode.This TDFL used a segment of double-cladding thulium-doped fiber as gain medium and is optimized appropriately.The wavelength tuning-range,linewidth and direct output power-range of the SLM laser are 1920 nm-2040 nm,-20 kHz and 0.4 W-1.07 W,respectivelyThirdly,in order to obtain 2 ?m laser with narrower linewidth,we have proposed a 2 ?m widely wavelength-tunable SLM Brillouin fiber laser(BFL)using a segment of highly germania-doped fiber as gain medium.This SLM BFL is pumped by the homemade widely wavelength-tunable SLM TDFL as mentioned above.The wavelength tuning-range of the SLM BFL is 1920 nm-2030 nm.The linewidth of BFL decreases to less than 0.9 kHz due to the linewidth-narrowing effect in the Brillouin ring cavity.Finally,in order to meet the need of methane gas detection,we have proposed a 1.65 ?m narrow-linewidth Raman continuous-wave(CW)fiber laser using a segment of highly nonlinear fiber as gain medium.A 1541 nm CW pump is used to amplify a 1.65 ?m narrow-linewidth laser seed via the stimulated Raman scattering effect.The central wavelength,maximum output-power and-20 dB linewidth of the narrow-linewidth Raman CW laser are 1653.7 nm,726 mW and 0.18 nm,respectively.Furthermore,in order to measure the spatial distribution of the methane gas,we then have proposed a 1.65 ?m wavelength-tunable narrow-linewidth Raman pulsed fiber laser using a segment of highly germania-doped fiber as gain medium.A 1541 nm pulsed pump is used to amplify and modulate a 1.65 ?m narrow-linewidth laser seed simultaneously via the stimulated Raman scattering effect.The wavelength tuning-range,repetition-rate,pulse-width,peak-power and linewidth of the narrow-linewidth Raman pulsed laser are 1652.0 nm-1654.0 nm,100 kHz,31 ns,30.85 W and<0.08 nm,respectively. |
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