Amplification and attenuation of light in a waveguide modulated by a travelling wave

TL;DR

This paper models how light in an optical waveguide interacts with a travelling wave modulation, analyzing different modulation cases and identifying the anti-Stokes resonance as promising for light amplification.

Contribution

It provides a theoretical framework for understanding light modulation in waveguides with travelling wave perturbations, including simple expressions for transmission, reflection, and gain.

Findings

Anti-Stokes resonance offers the best potential for light amplification.

Total gain remains small under realistic parameters.

Different modulation cases are analytically compared.

Abstract

Light propagating in an optical waveguide can gain or lose power through interaction with a travelling acoustic wave or radio-frequency modulation of permittivity. Here, we model this propagation by considering an optical wave interacting with a weak travelling-wave permittivity perturbation whose frequency is much smaller than the optical frequency and whose amplitude decays exponentially along the propagation direction. Four modulation cases are analyzed: instantaneous modulation, synchronous modulation, and the Stokes and anti-Stokes resonances. For these cases, simple expressions are obtained for the carrier and sideband transmission and reflection powers as well as for the total gain and loss powers. Although the achievable total gain remains small for realistic modulation and waveguide parameters, the anti-Stokes resonance is identified as the most promising condition for observing modulation-induced light amplification.