Research On Supercontinuum Generation By A Femtosecond Fiber Laser

As its many significant potential applications in optical metrology, spectroscopy, biomedical optics, and optical communications, especially in the high speed optical communication systems, Supercontinuum (SC) laser source has attracted intensive attentions recently. Supercontinuum is such an optical phenomena that when ultrashort pulses propagating in nonlinear media, its optical spectrum becomes very broad, much wider than that of the original spectrum. In this paper, we focus on femtosecond acquired in fiber laser and supercontinuum generation in dispersion-shifted fiber pumped by femtosecond pulses.This paper presents two methods of generating femtosecond pulses: stretched-pulse Erbium-doped ring based on nonlinear polarization rotation and figure eight fiber laser based on nonlinear amplifying loop mirror. Erbium-doped fiber with normal dispersion is used to compensate anomalous dispersion of single mode fiber in stretched-pulse Erbium-doped ring fiber laser. The pulses undergo twice stretching and compression, reducing the nonlinear saturation and narrowing the pulses, which leads to the generation of sub-100fs ultrashort pluses. We have proposed reducing the length of nonlinear amplifying loop mirror to acquire femtosecond pulses. In experiments, the ultrashort pulses of 600fs width were observed when the fiber length reach minimum.We carry on research on the supercontinuum generation in dispersion-shifted fiber. High peak power ultrashort pulses as short as 70fs are injected into 1m, 3m, 5m and 10m dispersion-shifted fiber respectively and supercontinuum range from 130nm to 312nm is observed in OSA. We solved the generalized nonlinear Schr?dinger equation by using the split-step Fourier method. The simulation of the evolution in the fiber shows that spectral broadening arises from soliton dynamics when pumping using femtosecond pulses in the anomalous group velocity dispersion regime of the fiber. Furthermore, this paper proposes a new method that dispersion compensating fiber is used to achieve the supercontinuum flattening.