Study On Key Technology Of Power-Scaling-Up For Fiber Light Sources At 2 ?m

2 ?m light sources are not only important eye-safe sources in applications such as medical care,industrial processing,environment monitoring and nonlinear frequency conversion,but also favorable sources for LIDAR and laser communication,so researchers have paid much attention on them.2 ?m light sources based on all-fiber configuration has become a hot topic currently,since fiber light soucres possess the advantages including convenience for thermal management,good beam quality,high stability and outstanding compactness.However,2 ?m fiber light sources have some limitations,such as the serious intrinsic quantum defect and the immature development of fiber devices,which make it a challenging and popular research subject to obtain 2 ?m fiber light sources with high power,high energy and high beam quality.In this thesis,considering the above demands for research and applications,high power 2 ?m fiber light sources are studied theoretically and experimentally,the main results are listed as follows.1.High power 2 ?m single frequency continuous wave,single frequency pulsed and broadband pulsed Tm-doped fiber amplifier(TDFA)systems are investigated theoretically.Stimulated Brillouin scattering(SBS)process is added into the traditional kinetics model based on rate equations and propogation equations,and the kinetics model for single frequency continuous wave TDFA is built up.SBS process is added into the traditional kinetics model,and parallelizable and bidirectional arithmetic is employed as the calculation method to build up a high efficiency and high precision model for nanosecond pulsed TDFA.The above models are employed to perform simulation on single frequency continuous wave,single frequency pulsed and broadband pulsed TDFA systems,and the simulated and experimental results provide reference for designing parameters of systems with higher output power target.2.High power 2?m fiber sources based on all-fiber configuration are investigated experimentally.Firstly,master oscillator power amplifier(MOPA)configuration is employed to scale up the output power of a seed fiber laser,and the output power of 2?m single frequency continuous wave laser based on all-fiber configuration is increased to 100 W level for the first time.The output power is further improved to 310 W subsequently,which is the highest value demonstrated,as far as we know.Meanwhile,the results of simulation and experiment are compared and discussed,and it is concluded that the experimental system can realize k W level single frequency continuous wave output at 2?m if the pump power and thermal management are properly handled.Secondly,two beams of continuous wave TDFA are combined to one beam via coherent beam combining(CBC).The total output power is 108 W,which is the highest one at 2?m based on CBC.The active phase-locking control can compensate phase noise below 400 Hz effectively in the experiment,which validates the feasibility of obtaining high power laser output at 2?m based on CBC of TDFAs.Thirdly,amplified spontaneous emission(ASE)fiber source with m W-level power is amplified based on multi-stage TDFA.The power of the amplified narrowband tunable ASE source is more than 250 W,which is the first demonstration on 2?m narrowband tunable ASE fiber source at this power level.Fourthly,stable pulse train at 2?m via mode-locking and modulating of relaxiation oscillation are obtained by active phase modulation in line-shape and ring-shap fiber lasers,which indicates that these lasers can be used the seed lasers for high power pulsed TDFAs.At last,a system based on MOPA configuration is used to scale up the power of 2?m nanosecond pulsed seed.When the seed is quasi-single frequency nanosecond pulsed laser,the amplified average output power reaches 100 W level,when the seed is narrowband pulsed laser,the average power reaches 200 W level,when the seed is broadband pulsed laser,the average power reaches 150-238 W level.The above output results are all the highest values as far as we know.3.Tandem-pumping method employing high power Yb-doped Raman fiber lasers(YRFLs)is proposed to obtain fiber laser output at 2 ?m,the highest output records of Tm-doped fiber laser(TDFL)and Ho-doped fiber laser(HDFL)with this pump method are achieved,and resonantly-pumping method is employed to realize high power output of long-wavelength TDFL.Firstly,YRFLs at 1173 nm are used to pump a TDFL,and the output power of the TDFL reaches 96 W.This is the first demomstration on 100 W level TDFL at 2 ?m pumped by high power YRFLs.Secondly,an YRFL at 1150 nm is used to pump a HDFL,and the output power is 42 W,which is highest power from an HDFL pumped by an YRFL.Meanwhile,the 1150 nm YRFL is also used to pump the HDFL to obtain pulsed output at 2 ?m.After properly controlling the parameters of the HDFL system,the average output power can reach 16.1 W.This is the highest average output power from a passively Q-switched HDFL.At last,a 2153 nm TDFL is resonantly-pumped by a 1943 nm TDFL,the output power reaches 24 W.Experimental results show that the temperature and length of the gain fiber in a long-wavelength TDFL should be properly managed to suppress ASE and parasitic lasing effectively,and one can hence increase the output power of the system.This is the first experimental investigation on high power TDFL with wavelength longer than 2.15 ?m,and the output power is also the highest one among the TDFLs and Raman fiber lasers/amplifiers at this wavelength band.By the way,the spectral characteristics of the TDFL are also favorable.The above experimental researches have validated the potential of employing tandem-pumping method to obtain high power fiber laser output at 2 ?m.4.Exploring investigation on the applications of nonlinear effects at 2 ?m is performed,in which single frequency pulses,slow light and multiwavelength laser based on SBS effect are achieved for the first time.Firstly,single frequency pulsed Brillouin-Thulium fiber laser(BTFL)at 2 ?m based on SBS effect is investigated experimentally.Nonlinear polarization rotation and active phase modulation techniques are employed to realize single frequency pulsed BTFL.This is the first demonstration on stable single frequency pulsed BTFL based on SBS effect.Secondly,slow light based on SBS effect at 2 ?m is investigated.Continuous and linear pulse delay can be realized by controlling the pump of Brillouin pump.Theoretical simulating results based on three-wave coupled equations match well with that of experimental ones.This is the first investigation on slow light at 2 ?m.At last,multiwavelength BTFL was investigated experimentally.5 Stokes lights based tandem SBS effects were realized with spacing of about 0.105 nm.This is the first multiwavelength investigation at 2 ?m based on tandem SBS effect.