Research On Ultroshort Pulses Propagation In Photonic Crystal Fiber And Tapered Fiber

Supercontinuum(SC) source is a new type of light source with broad spectralbandwidth, high radiation power, and great spatial coherence. This source oftengreatly improves the signal-to-noise ratio in applications that require a broadbandsource, including high-resolution spectroscopy, the characterization of opticalcomponents, or optical coherence tomography. In recent years, the research on howto generate wide bandwidth and great flatness SC becomes an important issue innonlinear optics. The combination of the ultra-short femtosecond pulses andphotonic crystal fiber, tapered fiber of nonlinear effects plays a key role for SCgeneration. Therefore, the propagation characteristics of ultra-short pulses inphotonic crystal fiber, the core and cladding diameter tapered fiber were researchedin this paper. The main content of this paper was listed below:(1) Finite-difference time domain method was achieved based on MATLAB,the effect of structural parameters of photonic crystal fiber on its fundamentaleffective refractive index and dispersion was investigated theoretically. Zerodispersion wavelength in visible region and more than one zero dispersionwavelength can be obtained by changing air hole and pitch diameters of photoniccrystal fiber.(2) Numerical simulation of SC generation during the ultra-short pulsespropagation in photonic crystal fiber was conducted. The characteristics of spectrumoutput in normal and anomalous dispersion regimes were simulated based onsplit-step Fourier method. The flatness of spectrum in normal dispersion regime wasrelatively better than that in anomalous, while the broadening magnitude wassmaller.(3) The characteristics of ultra-short pluses propagation in photonic crystalfiber were experimental investigated. The SC generation in photonic crystal fiberswas recorded with different femtosecond pulses power and different fiber length,respectively. Experimental results were greatly matched with numerical simulations.(4) The characteristics of femtosecond pulses propagation in taperedmultimode fiber were experimental researched. Using discharge-taper system,tapered multimode fibers were fabricated with different length. Adjusting the pump power through attenuator, the output spectra generated by femtosecond pulsespropagation in these tapered fibers were recorded.