Study On Femto-Second Laser Pulse Propagation In Tapered Holey Fibers

Photonic Crystal Fiber (PCF) is a special fiber which has a two-dimensional and periodic structure. Owing to the adjustable structure parameters, PCF has so much strange characteristics such as dispersion and nonlinear effects that the traditional optical fibers do not have. Tapered holey fibers are manufactured by drawing the PCFs, there will be more different characteristics because the pitch and core change along with the axis. Therefore, tapered PCF has become an important medium to investigate the interactions between the ultrashort laser pulse and micro–nano structured fiber. This paper numerically studies the nonlinear propagation of femtosecond laser pulse in the tapered photonic crystal fiber. The major work we have done is as follows:Firstly, research status and development trends of photonic crystal fiber are clarified. The method of tapered holey fiber fabrication and study are introduced.Secondly, the equation of pulse propagation in holey fibers have been explained and studied by an adaptive split-step Fourier method. Meanwhile, showed how to use it in tapered holey fibers。Thirdly, a linear and a convex tapered holey fibers have been proposed, the characteristics of dispersion and nonlinear have been studied, the result shows that the pulse have been compressed in both tapered holey fibers and the convex one is better to compress pulse than the linear one. Furthermore, a multi-to-single mode converter has been observed in convex tapered holey fiber. We also considered the affect of power in the convex one.Finally, the phenomenon of supercontinuum in As₂S₃ tapered holey fiber have been obtained, moreover the ultra-flat of mid-infrared supercontinuum is about 5500 nm. Supercontinuum has great significance for spectrum analysis, pulse wave form measurement, fiber parameters measurement, optical communication and so on.