Theoretical study on the stimulated Brillouin scattering in a sub-wavelength anisotropic waveguide: Acousto-optical coupling coefficients and effects of transverse anisotropies

TL;DR

This paper provides a theoretical analysis of stimulated Brillouin scattering in sub-wavelength anisotropic waveguides, extending calculation methods to anisotropic materials and revealing how transverse anisotropies influence SBS gain sensitivity.

Contribution

It introduces extended integral formulas for acousto-optical coupling coefficients in anisotropic waveguides and demonstrates their impact on SBS in elliptical nanowires with strong transverse anisotropies.

Findings

SBS gains are highly sensitive to small misalignments of waveguide axes.

Mechanical and optical anisotropies significantly affect SBS behavior.

Potential for sensitive SBS gain tuning without altering phononic frequency.

Abstract

A theoretical study on the stimulated Brillouin scattering (SBS) in a sub-wavelength anisotropic waveguide is conducted. The optical, photoelastic and mechanical anisotropies of the waveguide materials are all taken into account. First, the integral formulae for calculating the acousto-optical coupling coefficients (AOCCs) due to the photoelastic and moving interface effects in SBS are extended to an optically anisotropic waveguide. Then, with the extended formulae, the SBSs in an elliptical nanowire with strong transverse anisotropies are simulated. In the simulations, the elastic fields are computed with the inclusion of mechanical anisotropy. Observable effects of the strong transverse anisotropies are found in numerical results. Most notably, the SBS gains of some elastic modes are found to be very sensitive to the small misalignment between the waveguide axes and the principal material axes. Detailed physical interpretations of this interesting phenomenon are provided. This interesting phenomenon implies an attractive way for more sensitive tuning of the SBS gain without significantly changing the phononic frequency.