Anti-Stokes Raman gain enabled by modulation instability in mid-IR waveguides

Abstract

The inclusion of self-steepening in the linear stability analysis of modulation instability (MI) leads to a power cutoff above which the MI gain vanishes. Under these conditions, MI in mid-IR waveguides is shown to give rise to the usual double-sideband spectrum, but with Raman-shaped sidelobes. This results from the energy transfer of a continuous-wave laser simultaneously to both Stokes and anti-Stokes bands in pseudo-parametric fashion. As such, the anti-Stokes gain matches completely the Stokes profile over the entire gain bandwidth. This remarkable behavior, not expected from an unexcited medium, is shown not to follow from a conventional four-wave mixing interaction between the pump and the Stokes band. We believe this observation to be of relevance in the area of Raman-based sensors, which, in several instances, rely on monitoring small power variations of the anti-Stokes spectral component.