Study On Supercontinuum Spectrum Generation In Optical Fibers

Because of its many significant potential applications in optical metrology, spectroscopy, biomedical optics, and optical communications, especially in the OTDM and DWDM systems, Supercontinuum (SC) laser source has attracted intensive attentions recently. And Supercontinuum generation in optical fiber is one of the most effective methods to obtain this source. Supercontinuum is such an optical phenomena that when an high power optical pulse is put into an optical fiber, its optical spectrum becomes very broad, much wider than that of the original spectrum. A lot of nonlinear effects between the high power pulse and the fiber contribute to the SC generation. This thesis focuses on the SC generation in the dispersion flattened and dispersion decreasing fiber (DFDF). The results show that both the initial frequency chirp of the pump pulse and the dispersion characteristics of the fibers influence the SC generation significantly. The thesis consists of 5 chapters. The first one is a brief survey, and the second one presents the basic theory of the work. Chapter 3 and 4 are the introduction of the main work of the author. Chapter 5 makes a conclusion of the whole work and shows some prospective views.Chapter 1: Includes the history of the study on the SC generation and the significant development of the SC applications.Chapter 2: Presents the fundamental theory of the whole research, including the basic propagation equation of optical pulses in fibers.Chapter 3: Focuses on the effect of frequency chirping on Supercontinuum generation in dispersion flattened and dispersion decreasing fibers. The results show that initial frequency chirping is very important to the SC generation. A range of optimal positive frequency chirps is identified to obtain the maximized Supercontinuum bandwidth and intensity. The mechanism of this enhancement is also discussed detailedly through the evolutions of temporal and spectral width related to different pre-chirped pulses. It is shown that a range of optimal positive initial frequency chirp compensates the dispersion-induced chirp and enhances the chirpcreated by SPM. As a result the initial pulse compression is enhanced and higher peak power is obtained, and thus a broader and stronger SC spectrum is generated.Chapter 4: Studies the effects of dispersion characteristics on Supercontinuum generation in dispersion flattened and dispersion decreasing fibers. It indicates that the initial dispersion and the fiber dispersion-decreasing rate have significant effects on the SC generation. SC bandwidth changes slowly when these two parameters are within certain threshold values, while it changes drastically when they exceed such values. The results also show that convex dispersion fiber is more favorable than the linear dispersion fiber in the generation of wide SC spectrum, while concave dispersion fiber is not suitable for the generation of wide SC spectrum, A 330nm wide SC spectrum can be generated from a DFDF fiber with optimal dispersion characteristics.Chapter 7: Includes the conclusions and prospective views.