| Recently,high power supercontinuum(SC)all-fiber laser source has been widely applied to areas such as electro-optical countermeasure,laser radar,medical imaging and so on,because of its broadband spectrum,good beam quality,high brightness and compact structure.With the rapid development of pulse fiber amplification technology and the innovation of nonlinear media,the level of SC output power has increased from watts to hundreds of watts,and the SC spectrum has gradually expanded to ultraviolet and infrared waveband.However,with SC fiber laser getting improved in terms of average power and spectral width,the potential problem is also exposed.Although the SC output power has been increased a lot,the corresponding spectrum range is not further widened,but even becomes smaller to the visible-waveband.Also,the visiblewaveband power occupies only a little part of the whole SC.This problem will bring some limitations to the application of SC.In order to solve the issue above,this paper will make a systematical and profound study on high power SC laser source including more visible-waveband power,such a laser source can be called a high power white SC laser source,which is based on the theoretical and experimental aspects.The main contents and results of this paper are as follows:1.Firstly,based on Generalized Nonlinear schrodlinger Equation,the numerical simulation of SC evolution process with picosecond pump pulses in photonic crystal fiber(PCF)was carried out.The simulation results showed that the main mechanism of visible-waveband SC broadening and energy increasing was the dispersion,and the cross phase modulation and the four wave mixing under the soliton capture.Secondly,according to the numerical simulation results,the factors restricting the further enhancement of white SC output power were analyzed and summarized,mainly including: the coupling efficiency between high power pulses pump source and high nonlinear PCF,the nonlinear effects in the high power pump pulses source,and the thermal damage of high nonlinear PCF with the high power operation condition.2.The factors influencing the coupling efficiency between high power pulses pump source and the high nonlinear PCF were analyzed.Mainly including,the mode field mismatch between the output pigtails of high power pulses pump source and high nonlinear PCF,and the optical mode control of pulses fiber amplifier.In this paper,firstly,a theoretical model of mode field adaptor(MFA)based on thermal expansion core technique was established.Then the numerical simulation on optimal thermal expansion time and thermal expansion core region length of the fibers used in the MFA was carried out.Secondly,relying on the numerical simulation results,the high power fiber MFA was fabricated successfully,which had input fiber with 20?m core diameter and output fiber with 6?m core diameter.It could work stably under the incident pulse power of 145 W with high coupling efficiency of 82%.Additionally,the theoretical study on mode control of pulse fiber amplifier with bending fiber methods was carried out.Based on the theoretical calculation of the critical bending radius and the relationship between the bending radius and the loss of the different optical modes in the fiber amplifier,the mode control experiments on single mode fiber amplifier and multi-mode fiber amplifier were conducted.The experimental results showed that through mode control,the amplified pulse beam quality was improved efficiently and the pump pulse energy coupled into PCF was further increased.Meanwhile,the beam quality of 160 W high power pulse after mode control was measured with M2 at 1.12,which means the high power pulse has the near diffraction-limited beam quality.3.A high power white SC fiber laser module was fabricated.In the experiment,the nonlinear effects in the pulse amplification process were restrained by the self-made repetition frequency multiplier.And on the basis of high efficiency coupling between the pulse pump source and PCF,53.3 W high power white SC fiber laser was achieved with spectrum ranging from 430 nm to 2400 nm,spectral width below 10 d B flatness exceeding 1700 nm(except pump wavelength).Also,67.9 W high power white SC fiber laser was achieved with spectrum ranging from 500 nm to 1700 nm,spectral width below 10 d B flatness exceeding 1000 nm(except pump wavelength).In addition,the mechanical design and electronic control design of the laser system were carried out,and the high power white SC laser system was encapsulated into a 50 W white SC module which can be used in practice.Then,the white SC module was operating continuously for 1 hour under full power operating condition,and the test result showed that the working stability of the module can reach ±0.4%.4.The theoretical study and fabricating experiment of(7×1)high power SC fiber combiner was carried out.The(7×1)fiber combiner system model was established,and based on the finite difference beam propagation method,the relationship between combining efficiency and some combiner parameters such as taper ratio,taper length,taper waist length,and output fiber length were stimulated.Relying on the simulation results,the(7×1)high power SC fiber combiner with output fiber of 100?m core diameter was designed and fabricated.After optimizing the manufacture technique of the combiner,the combiner was tested by the 50 W SC module.And the test result showed the average coupling efficiency of the singlearm of the combiner was up to 98.8%.Also,the output SC spectrum had no obvious transmission loss in any waveband,which indicated that the combiner was capable of combing and transmitting the SC spectrum.5.Using the(7×1)high power SC fiber combiner to combine three white SC modules with average power of about 50 W,143.4 W high power combining white SC was successfully achieved. |
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