A Study On Hectowatt Scale Ultra-short Pulse Ytterbium-doped Fiber Amplifier And Supercontinuum Generation

High-power ultra-short pulse fiber lasers have played an important role in various fields due to the advantages,such as good beam quality,high conversion efficiency,good anti-interference performance,all-fiber structure and so on.Based on this,we carried out the research of hectowatt scale ultra-short pulse Yb-doped fiber laser.In this paper,the theoretical analysis and experimental research of the all-fiber polarization maintaining(PM)and non-PM ultra-short pulse Yb-doped oscillator,amplifier,compressor and application in supercontinuum source are demonstrated with high average power and pulse energy.The specific research work and results are as follows:1.Theoretical and experimental research of all-fiber mode-locked oscillator.The physical mechanism and the ways of mode-locking are analyzed theoretically.Passive mode-locked fiber laser are achieved in quasi-three-level system and quasifour-level system by Nonlinear Polarization Rotation(NPR),semiconductor saturable absorber mirror(SESAM)and single wall carbon nanotubes(SWCNTs).Stable modelocked pulses of 567 ps are obtained in a ring cavity by NPR.Commercial SESAMs are employed in PM linear cavities and mode-locked pulses are obtained with different wavelengths(1031 nm and 1064 nm)and different repetition frequency(16.68 MHz and 36.41 MHz).With different periods of material layer,two of the three kinds of homemade SESAMs can achieve stable mode-locking operations.Mode-locking experiments have been achieved in ring cavities by using SWCNTs with diameters of 0.8 nm as saturable absorber(SA)in quasi-three-level system at 979 nm and quasi-fourlevel system at 1032 nm.To our knowledge,this is the first time ever reported in an allfiber Yb-doped mode-locked fiber laser using SWCNTs as SA at 980 nm.2.Theoretical and experimental research of all-fiber hectowatt scale Master Oscillator Pulse Amplification(MOPA)system.Firstly,the principles of amplifier and grating pair compressor are theoretically analyzed.The main amplifier is studied through MATLAB numerical simulation software.The seed source is NPR mode-locked oscillator of 1033 nm,which can be amplified directly without pulse stretching.The signal light is amplified by a two-stage MOPA system using gain fiber of 10/130 μm with length of 6 m,resulting 100 W output power,which is matched with the theoretical simulation results.The pulses with pulse width of 221 ps are compressed to 0.84 ps by transmission-grating as compressor.3.Experimental research of all-fiber PM MOPA amplifier.Linear polarization is the key parameters of ultrafast pulse fiber laser and important characteristic in the applications of high-efficiency frequency-doubling laser generation,biological imaging and laser ranging.The PM SESAM mode-locked oscillator with central wavelength of 1031 nm is adopted as the seed source without pulse stretching.The pulses are amplified with spectral broadening due to the influence of strong nonlinear effects in the amplifier.The signal light is amplified to 35 W with wide spectrum range from 1020 nm to 1700 nm after a two-stage PM MOPA amplifier.4.Experimental research of all-fiber hectowatt scale PM Chirped Pulse Amplification(CPA)system.The main amplifier is studied through MATLAB numerical simulation software firstly.Then we use PM SESAM mode-locked oscillator of 16.68 MHz as seed source and PM single mode fiber(SMF)as stretcher in CPA system.PM highly Yb-doped fiber is adopted in amplifier to reduce the impact of the nonlinear effects.100.8 W linear polarized laser is achieved with peak power of 21.58 k W and single pulse energy of 6.04 μJ,which is matched with the theoretical simulation results.The pulse is compressed to 12.5 ps by grating compressor.To further reduce peak power and nonlinear effects in amplifier,36.41 MHz is adopted in seed source and 100 W is obtained in same amplifier structure,which is good for following compression.5.Experimental research on all-fiber supercontinuum source.An important application of ultrashort-pulsed fiber laser is pumping nonlinear PCF to get supercontinuum.Firstly,supercontinuum generation in seven-core photonic crystal fiber(PCF)with different lengths is simulated by MATLAB software.Then supercontinuum with high power and wide spectrum is obtained in two different length of large mode area seven-core PCF pumped by an all-fiber picosecond pulse MOPA system.The central wavelength is close to the zero dispersion wavelength of sevencore PCF.11.7 W supercontinuum ranges from 620 nm to 1700 nm with and 20.4 W supercontinuum range from 680 nm to 1700 nm are obtained.The supercontinuum source can work stably for a long time and match with theoretical simulation results.