Study on nonlinear characteristics of phase shifted gratings and fiber gratings

      As a new type of optical device, fiber grating has been widely used in many fields, such as optical fiber communication, fiber grating sensing, optical calculation and optical information processing, with the continuous improvement of its manufacturing technology. This paper mainly studies on the nonlinear phase shift grating and fiber grating, mainly including the following aspects: the transmission characteristics of the phase shifted grating is theoretically calculated, analyzed the influence of chirp coefficient and apodization function of the phase shifted grating reflection spectrum. The results show that the linear chirp can broaden the grating reflection spectrum, the nonlinear chirp coefficient will change the symmetry of the reflection spectrum, so the transmission window center of reflection spectrum, and different chirp and cutting selection will suppress the sidelobe of the toe function have different influence on. The optical switching characteristics of Prague gratings and long period gratings are discussed. Analysis of the effect of pump power on Prague grating switching rate; analysis of the switching characteristics of long period grating in the resonant and non resonant conditions, comparison of the transmission input power and pulse shape and pulse in the grating, the results showed that the distribution of the pulse energy has an important effect on the switching characteristics. Slow light effect of fiber grating is studied. Firstly, the principle of slow light FBG is discussed, the influence of apodized grating, linear function, Gauss function and the hyperbolic tangent function of fiber grating slow light effect is discussed, the results show that the variation of coupling coefficient and the width of apodized area is very important for pulse transmission have the. Then discuss the influence of point defect gratings on the Prague solitons, analyzes the different speed parameters, the local refractive index modulation depth effect on the Prague solitons, the results indicate that the defects in the grating has a large effect on the smaller Prague grating soliton velocity parameters.