Study On Transmission Of Urtrashort Laser Pulse In The SF57Photonic Crystal Fiber

Spectral broadening and frequency conversion of ultrashort laser pulse in photoniccrystalfiber(PCF)transmissionisahotresearchtopicinthefieldofnonlinearfiberoptics.The dispersion and nonlinearity of the fiber play an important role in the transmissionof the ultrashort laser pulse and in the spectral evolution. Based on the transparencyin the near-infrared and mid-infrared, along with the high linear and nonlinear refractiveindex, non-silicatePCFwillfindbroadapplicationsinthefieldofnonlinearoptics. Inthisthesis, transmission characteristics of the femtosecond laser pulses in SF57glass PCF arestudied both theoretically and experimentally. The main contents of this dissertation areas follows:First,theresearchbackgroundanddevelopinghistoryofthePCFarepresented. Thenthe development status and production process of the non-silicate PCF are described indetail. the main theories and methods involved in the simulation of this thesis are intro-duced systematically: one is the finite element method (FEM), which is used to simulatethe PCF characteristics. The other is the adaptive split-step Fourier method. It can beused to simulate the transmission of the ultrashort laser pulses in optical fibers.Second,thetransmissioncharacteristicsofthefemtosecondlaserwhosecenterwave-length is at1550nm are studied experimentally in the dispersion flattened highly nonlin-ear SF57PCF. A flat and stable supercontinuum from1300nm to1900nm is obtained.Further, the transmission of ultrashort laser pulses in the PCF is numerically simulated.And the spectral broadening mechanism is illustrated at the same time. It is found that theresults of the experiment match well with the theoretical results. The obtained supercon-tinuum has both the high stability and coherence properties.Finally, a lead silicate SF57PCF is designed. The basic characteristics of the fiberis numerically simulated using the FEM. The results show that the normal dispersionexistsinthewholetransparentbandinthisPCF,whichperfectlycombinedwiththehighlynonlinear and transparency in the mid-infrared of the SF57material. The transmission ofultrashort laser pulses in the PCF is simulated by the adaptive split-step Fourier method.And the variations of the output spectrum by varying with the center wavelength andpower of the incident pulse are presented.The results of this paper have certain guidance significance for the design of highly nonlinear SF57PCF and for the generation of supercontinuum with high stability andcoherence when the femtosecond laser is transmitted in this fiber.