The Study On Phase-Shifted Fiber Gratings And The Nonlinear Characteristics Of Fiber Gratings

Fiber gratings, as a novel fiber device, have been widely applied with the development of its manufacture technology, and have greatly affected the fiber communication, fiber grating sensors, optical computing and optical information processing because of its practical utilization.In this thesis, the phase-shifted fiber grating and the nonlinear characteristics of the fiber gratings are focused on, and the contents are as follows.The transmitting characteristics of the phase-shifted grating are numerically simulated in theory, and the effects of chirp coefficient and apodizing functions on the reflection spectrums are analyzed. The results show that the reflection spectrums can be broadened by the linear chirp coefficients, and the symmetry of the reflection spectrum will be broken while the spectral window will deviate from the center of the spectrum by the nonlinear chirp coefficients. The effects on side-lobe suppression will be different by chirp coefficients and apodizing functions.The switching characteristics of FBG and LPG are analyzed. The influence of the pump power on the switching rate of FBG is discussed. And the characteristics of the LPG are analyzed in the on-resonance and off-resonance situation, and the transmission processes are compared with different input powers and pulse shapes. The results indicate that the distribution of the pulse energy has a significant impact on the switching characteristics. The slow-light effect of the fiber grating is researched. The principle of slow-light in the fiber grating is expounded. The effects of apodizing functions on slow-light in the apodized fiber grating, and the research that the variations of coupling coefficient and the width of apodized area have great influence on the transmission results. Then the effects of the defect in the gratings on the Bragg solitons are discussed and the influences of modulation depth of the Local refractive index on Bragg solitons are studied according to different velocity parameter. The results indicate that the defects in the fiber gratings have a greater impact on the Bragg solitons with a small velocity parameter.