Numerical Analysis of Parameter Optimization in Slow Light Phase-Shifted Fiber Bragg Gratings

Abstract

In this paper, we present results of numerical analysis of phase-shifted fiber Bragg gratings aimed at slowing down the group velocity of light propagating through these structures. Using coupled-mode theory and transfer matrix method we model the impact of several parameters such as length of the grating, refractive index modulation depth and phase shift in the periodicity of Brag gratings to calculate transmission spectral properties and to maximize the final group delay. By introducing irregularity into a periodic structure of refractive index, Fabry-Perot like cavity formed in the grating results in a favorable narrow dip in resonance spectra characteristics. Correspondingly, we observe a significant spike in group delay at the same wavelength. Simulations results obtained by numerical approach show a strong need for parameter optimization in process of tailoring gratings behavior. Considerable attention must be put on width of spectral region suitable for large group delay realization and suitable interrogation schemes need to be implemented when adopting studied structures for sensors applications.

Fig. 5 Comparison of group delay for 5 mm uniform and π phase shifted gratings. With selected index modulation we observe a rapid peak centered around 13 × 10⁻⁴, for a phase shift grating. Uniform grating shows stable and predictable increase.