All-optical switching characteristics analysis in an optimized nonlinear Bragg grating with a π phase shift

We numerically study the nonlinear switching characteristics of optical transmission through optimized fiber Bragg grating with a π phase shift. The nonlinear coupled-mode equations were solved numerically based on the time-dependent transfer-matrix method. The result shows that the π phase shift grating is superior to the uniform grating in the enhancement, corresponding to the local intensity of the light inside the grating. It shows that the use of π phase shift gratings reduces effectively the switching threshold, but the on-off contrast is generally declined which can be generally improved through the introduction of tapered parameters. In addition, the narrowed transmitted pulse for positive-tapered nonlinear Bragg grating is a Bragg soliton owing to the balance of anomalous group velocity dispersion and self-phase modulation (SPM). It can be found that the tapered nonlinear Bragg grating with a π phase shift is more preferable for achieving the larger on-off contrast.