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

摘要

A theoretical study on the stimulated Brillouin scattering (SBS) in asub-wavelength anisotropic waveguide is conducted. The optical, photoelasticand mechanical anisotropies of the waveguide materials are all taken intoaccount. First, the integral formulae for calculating the acousto-opticalcoupling coefficients (AOCCs) due to the photoelastic and moving interfaceeffects in SBS are extended to an optically anisotropic waveguide. Then, withthe extended formulae, the SBSs in an elliptical nanowire with strongtransverse anisotropies are simulated. In the simulations, the elastic fieldsare computed with the inclusion of mechanical anisotropy. Observable effects ofthe strong transverse anisotropies are found in numerical results. Mostnotably, the SBS gains of some elastic modes are found to be very sensitive tothe small misalignment between the waveguide axes and the principal materialaxes. Detailed physical interpretations of this interesting phenomenon areprovided. This interesting phenomenon implies an attractive way for moresensitive tuning of the SBS gain without significantly changing the phononicfrequency.