Investigation On Slow Light For Nonuniform Photonic Crystal Fiber Gratings

With the rapid development of our society, the requirement for information is exploding and subsequent requirement for communication network capacity is increasing. The development of all optical network makes it possible to have large capacity and high speed communication network. But all optical switching network is one of the bottlenecks for the development of all optical network. Therefore, as one of the key technologies for all optical switching network, all optical buffer technology becomes the current research focus. As fiber grating slow light technology has so many advances, such as simple experiment conditions, easy modularization and distortionless transmission pulse, it has an promising future in practical applications. Compared with conventional fiber gratings, photonic crystal fiber gratings have more excellent properties:larger design freedom, infinite single-mode transmission characteristic and sensitive, structure-tunable dispersion characteristics. At the same time, apodization and chirp can optimize the characteristics of fiber gratings. So the emergence of nonuniform photonic crystal fiber grating opens a new window for the research on slow light of fiber gratings.With the improved full-vectorial effective index method, the coupled mode theory and the transfer matrix method at the core, this paper establishes a set of method to analyze slow light in nonuniform photonic crystal fiber Bragg gratings. In this paper, the cut-off characteristics and dispersion characteristics of conventional hexagonal photonic crystal fiber are first analyzed by improved full-vectorial effective index method, then the effects of structure parameters of photonic crystal fiber on slow light are investigated, at last the influences of apodization and chirp on slow are analyzed as well. The main of our wok is showed as follows:1. After analyzed by improved full-vectorial effective index method, the results show that infinite single-mode transmission condition for conventional hexagonal photonic crystal fiber is d/A<0.4; adding the diameters of air holes d can make the first zero dispersion wavelength to move toward short wavelength, and adding the pitches of the air holes A can make the fire maximum value of dispersion to move toward long wavelength. Based on these results, the fundamental parameters of photonic crystal fiber are set.2. By adjusting the fundamental structures of photonic crystal fiber carefully, the effects of structure parameters of photonic crystal fiber on slow light are investigated. The results show that increasing the diameters of airhole d can decrease the minimum value of group velocity, and decreasing the pitches of air holes A has the same result when the ratio of the diameters and the pitches d/A is a constant.3. For photonic crystal fiber gratings apodized by gaussian function, when the’dc’index change Δ n is big enough, the ratio of the minimum group velocity value and the vacuum value of light V first decreases and then increases with the increase of gaussian apodization G. But when the’dc’index change Δ n is very small, V increases with the increase of G all the time; although chirp can not make the minimum value of group velocity smaller, it generates a good linear area in the group velocity spectra.