title: Modulational instability in periodic quadratic nonlinear materials.
abstract: We investigate the modulational instability of plane waves in quadratic nonlinear materials with linear and nonlinear quasi-phase-matching gratings. Exact Floquet calculations, confirmed by numerical simulations, show that the periodicity can drastically alter the gain spectrum but never completely removes the instability. The low-frequency part of the gain spectrum is accurately predicted by an averaged theory and disappears for certain gratings. The high-frequency part is related to the inherent gain of the homogeneous non-phase-matched material and is a consistent spectral feature.
authors.affiliation: Department of Informatics and Mathematical Modelling, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark.
authors.forename: J F
authors.initials: JF
authors.lastname: Corney
authors.forename: O
authors.initials: O
authors.lastname: Bang