Temporal Bragg Gratings: Broadband Reconfigurable Parametric Amplifiers

This article introduces temporal Bragg gratings as a new class of broadband, reconfigurable parametric amplifiers. We present a comprehensive investigation of power amplification in temporal Bragg gratings, spatially periodic structures with refractive index modulated near the Bragg frequency. Through systematic numerical simulations, we explore the effects of modulation location (high-index versus low-index layers), frequency, and amplitude on gain spectra and field dynamics. Both layer types yield significant parametric amplification, with high-index modulation providing higher gain for comparable depths. Amplification is frequency-agile, with gain peaks tunable across a broad range, and exhibits strong asymmetry: the sub-Bragg regime ( $\omega _{\text {m}} \lt \omega _{\text {B}}$ ) requires substantially stronger modulation than supra-Bragg for comparable gain. In the extreme sub-Bragg limit ( $\omega _{\text {m}} \lesssim 0.1\omega _{\text {B}}$ ), the system transitions from discrete sidebands to a broadband gain continuum via multiphase-matching. These results establish a unified framework for designing reconfigurable optical amplifiers, tunable frequency converters, and broadband light sources using temporally modulated photonic crystals.