Theoretical Investigating On The Characteristics Of Nonlinear Optical Bistable Switching

The nonlinear optical bistable switching has considerable potentials in optical computation and optical communication fields, such as optical gate operations, signal reshape and regeneration, optical time-division demulplexing, optical memory, all-optical wavelength convertion, etc. The research results have showed that, the nonlinear fiber gratings optical bistable switching, as a typical component of all-optical bistale switching, exists restriction factors for application, for example: The switching-on threshold is so high that it is difficult to realize for the common laser and the fiber grating is easy to be damaged under high incident power; the small width of the hysteresis results in the instability of switching; the steep upper branch is harmful to reshape and restrict amplitude to the pulse, etc. Based on the above considerations, in this paper, the bistable characteristics of nonlinear fiber grating have been investigated further.Standing from the coupled mode theory, a novel method, by introducing chirp in linear negative tapered bragg gratings, is proposed and investigated for improving the bistable performance. The results show that, introducing positive chirp in linear negative tapered bragg gratings is helpful to decrease the switching-on threshold, flatten the upper branch of hysteresis, and widen the bistable wavelength range; and the influence of the grating length on the switching-on threshold, the width of the hysteresis and the on-off ratio of the bistable switching are obvious, the bistable performance can be further optimized by reasonably selecting the length of the linear negative-tapered bragg gratings with positive chirp.Based on the coupled mode theory, the bistability performance of nonlinear bragg gratings is analyzed theoretically in terms of elliptic integration, the analytical expression describing the relation between the input intensity and the output intensity is presented. Consequently, the dependence of the bistability on the gratings inner parameters is investigated numerically. The results show that, the bistability performance of the nonlinear bragg gratings depends on not only the product of the couple coefficient and the grating length but also the couple coefficient and the gratings length respectively.The above results can provide an instructive insight to optimizing the nonlinear bragg gratings bistable switching.