Study On High Quality Multi-wavelength And Pulse Laser Seed Sources Used In 2?M Band High Power Fiber Laser

Space optical communication system in 2 ?m band has a bright prospect for the excellent atmospheric window in this band.Wavelength division multiplexing(WDM)technology remains the trend of development in the future.A WDM system demands multi-wavelength fiber lasers which are spacing tunable and flexible in choosing the wavelength and the quantity of the output lasing with high beam quality and stability.Moreover,owing to the strong absorption peaks of OH-in 2 ?m band and the coagulation or vaporization effect of human tissue caused by thermal effect of high power pulsed laser,the 2 ?m band lasers could be used as laser scalpel in the removal or hemostasis of human tissue.Space optical communication system and laser scalpel require high laser power and beam quality,and the master oscillator power amplifier(MOPA)technology could ensure an excellent laser beam quality with high output power.The studies in this dissertation mainly focus on MOPA system using in high quality seed source.In addition,wavelength-and spacing-tunable single polarization(SP)dual-wavelength thulium-doped fiber laser(TDFL)and wavelength-tunable multi-wavelength TDFL are designed for WDM system,and noise like(NL)pulse and SP pulse TDFLs are proposed for laser scalpel.Besides,the realization methods and output characteristics of multi-wavelength and pulse TDFLs are analyzed respectively in detail.The main focuses and innovations of this dissertation are summarized as follows:(1)The filtering characteristics of uniform fiber Bragg grating(UFBG),polarization maintaining fiber Bragg grating(PM-FBG)and polarization maintaining Fabry-Perot(PM-F-P)filters in 2 ?m band were analyzed by numerical calculation.Meanwhile,the center wavelength shift characteristics of UFBG and PM-FBG were studied,the center wavelength shift of UFBG was proportional to the axial stress,the proportional coefficient was 0.15 pm/??.When the axial strain was 2500??,the center wavelength shift of PM-FBG was 3.83 nm.(2)A spacing-tunable dual-wavelength TDFL based on cascaded UFBG was proposed.Using a nonlinear amplifying loop mirror(NALM)to suppress the mode competition in the laser cavity,a dual-wavelength output could be achieved at 1941.33 nm and 1941.72 nm.The optical signal-to-noise ratio(OSNR)was better than 56 dB.A tuning range from 0 to 5.14 nm was achieved for the dual-wavelength spacing by applying static strain;a tunable dual-wavelength TDFL based on PM-FBG was proposed,which had the dual-wavelength output at 1941.40 nm and 1942.21 nm respectively.The OSNR was better than 48 dB,and a 6.93 nm tuning could be realized by adjusting stress;a switchable dual-wavelength TDFL based on PM-F-P filter was proposed.The output wavelengths were 1941.82 nm and 1942.21 nm and the OSNR was better than 51 dB.It had a SP single-wavelength output in two different polarization directions,and the polarization extinction ratio(PER)was higher than 33 dB.(3)A multi-wavelength TDFL based on nonlinear polarization rotation(NPR)and Lyot filter was proposed.17 output channels within 10 dB bandwidth from 1982 to 1998 nm were achieved.The OSNR of multi-wavelength operation was approximately 35 dB.By using the polarization maintaining fiber with the length of 5 m,4.22 m and 2.06 m in the Lyot filters,the wavelength spacing of the multi-wavelength TDFL could achieve 0.975 nm,1.16 nm and 2.38 nm.A multi-wavelength TDFL based on NPR effect and polarization maintaining Sagnac(PM-Sagnac)loop mirror was put forward.A 150 m highly nonlinear fiber could improve the NPR effect in the laser cavity.The fiber laser could achieve 15 output channels within 10 dB bandwidth from 1990 to 2007.5 nm,The OSNR was approximately 30 dB.A multi-wavelength TDFL based on all-fiber phase modulator and PM-Sagnac loop mirror was proposed.By optimizing the loaded sinusoidal signal frequency of phase modulator,the laser could realize 10 wavelengths in the range of 15 dB bandwidth(1982 nm-1998 nm)with the OSNR up to 37 dB.(4)A passively mode-locked TDFL based on NALM was proposed.At a launched pump power of 2.98 W,the central wavelength of the NL pulse was 1990.56 nm,the coherence spike width was 518 fs,and the pulse energy was 26.63 nJ.A mode-locked TDFL based on NPR was come up with to realize NL pulse output by adjusting the length of singe mode fiber in the laser cavity,which is conducive to the optimization of dispersion of the laser.The NL pulse with coherence spike width of 406 fs and pulse energy of 12.342 nJ was generated at a center wavelength of 2003.20 nm.A hybrid mode-locked pulse TDFL was proposed.At a launched pump power of 3.52 W,the SPNL pulse centered at 2007 nm with a coherence spike width of 258 fs and a pulse energy of 42.11 nJ.(5)A switchable SP dual-wavelength mode-locked TDFL using the PM-FBG and semiconductor saturable absorber mirror was proposed.The dual-wavelength pulse lasing operation was obtained at 1940.97 and 1941.73 nm.The OSNR of the pulse laser was 57.36 dB.In the SP single-wavelength pulse lasing state,the SP pulse duration were 3.75 and 3.73 ps.