Study On All-fiber Structured High-power Mid-infrared Supercontinuum Source

All-fiber structured high-power MIR-SC source has some characteristics including ultra-wide spectral range,good spatial coherence and high brightness,which has advantages of good power stability,compact structure and so on.As for practical application,these were extensively used on space freedom communication,industrial process analysis and so on.Therefore,it is of great significance to carry out the research on all-fiber structured high-power MIR-SC source.In this thesis,we not only did some researches on the fundamental theory of SC generation and numerical simulation in ZBLAN fiber was carried out,but also did some work experimentally,such as 2?m seeds laser manufacturing by high efficiency laser wavelength transferring from 1.55?m to 2?m and cascaded Tm-doped fiber amplifier(TDFA)master oscillator power amplifier(MOPA)to further pump the ZBLAN and As₂S₃ fibers to generate an all-fiber structured high-power MIR-SC source,including the output spectrum and power property characterization and analysis.The structure of this thesis is as follows:In the first chapter,we primarily introduced the development history about MIR-SC source.At the same time,the soft glass fibers were adopted as the spectral broadening fiber due to lower losses in MIR region.Furthermore,the research progress about MIR-SC source and application based on ZBLAN fiber and chalcogenide fiber was introduced.Then,the main research contents of the thesis are also illustrated.In the second chapter,the SC generation based on the generalized nonlinear Schrodinger equation(GNLSE)derived from Maxwell equations is reviewed.Then,fiber dispersion and nonlinear effects are detailed introduced.Furthermore,SC numerical simulation for 2?m femtosecond pulse pumping ZBLAN fiber by using Matlab software were performed and the simulation results are analyzed and discussed in detail.In chapter 3,we described the dispersion and nonlinear effects of single-mode fiber(SMF),which was utilized to realize the frequency transferring from 1.55?m to 2?m,eventually,by took some improvement measures,the conversion efficiency was well improved by the amplification method of gain self-absorption that cascaded a piece of single-mode thulium-doped fiber(SM-TDF),obtained the SC seed source covering 1.9?m to 2.4?m.Then,by further adopting the large-mode-area TDFA(LMA-TDFA),the power of 2?m SC source was boosted to above 34 W;the power amplification slope efficiency was improved to 29% and spectral long wavelength edge was extended to near 2.5?m;For better adapting the mode field diameter of silica fiber and ZBLAN fiber,a customized mode-field adapter(MFA)was employed,by matching the mode field diameter between 25/400?m and SM1950 fiber due to the large difference of their fiber core diameter,nearly half of the amplified power was attenuated,so the output power from the SM-1950 fiber is nearly 14 W.Although the high loss of the adapter,power of this level is enough for further ZBLAN fiber MIR-SC generation.In the fourth chapter,we mainly introduce the experimental details on generation of MIR-SC by using the TDFA pumping ZBLAN and As₂S₃ fibers,respectively.In these experiments,we adopted cascaded SM-TDFA system to pump the As₂S₃ fiber,when the output power of SM-TDFA was scaled up to 5 W,the output spectrum output from As₂S₃ fiber covering 1.9?m to3.6?m at power of 0.9 W was obtained,in addition,the power fluctuation standard deviation was also optimized to near 30 mW.Meanwhile,in combination with the three-stages TDFA MOPA system,by pumping a 6 m ZBLAN fiber,we extended the long wavelength edge of MIR-SC spectrum from 2.4?m to 4?m,the spectrum intensity fluctuation of in 2.1?m to 3.54?m was as low as 0.09 dB.At the output power of 5.4 W,we measured the long-term power stability and the measured RMS value of the output power in 2 hours was as low as 0.03%,means a high power stability of this system.The fifth chapter summarizes the experimental results of this research paper.The first step of this experiment was to realize a high quality 2?m SC source by frequency transferring from 1.55?m to 2?m in a piece of SM-28 fiber.The second step is to amplify this seed laser,boosting its power to several tens watts.Then,by using the cascaded TDFA system to pump As₂S₃ fiber and ZBLAN fiber and to realize a spectrum extending to mid-infrared and even longer wavelength range;in addition,the shortcomings of the current experimental scheme and results were proposed,therefore,we come up with the corresponding experimental improvement schemes in the context for further system property optimization.In the near future,we will integrate the high power pump laser with ZBLAN and As₂S₃ fiber spectrum broading module,to further broaden the SC long wavelength components toward far-infrared region.