  Stimulated Brillouin scattering (SBS) processes have been allowing important
technological breakthroughs in integrated photonics and nano-optomechanics, by
exploiting light-sound (photon-phonon) interactions at the nanoscale. These
nonlinear processes are created by two main effects: radiation pressure and
electrostriction; however, the former is the predominant one in
high-index-contrast nanowaveguides. In this letter, we derive a simple set of
analytical expressions that can be used for optimizing the radiation pressure
on the waveguide boundaries, for any optical mode, polarization, and
wavelength. We observe a very strong influence of the waveguide geometric
parameters on the optimal radiation pressure value. Furthermore, we explain how
the existence of such optimal geometric dimensions is physically related to the
minimization of the electromagnetic momentum flow in the propagation direction.
This work provides a novel and robust method, yet simple, to optimize the
radiation pressure in dielectric nanowaveguides, which may be of great
relevance for designing integrated photonic-phononic devices.
