The present invention relates to optical fibers useful for the transmission of electromagnetic energy at such high levels of power that stimulated Brillouin scattering (SBS) may be of importance. One aspect of the present invention is an optical fiber for the propagation of optical radiation having an optical wavelength, the optical fiber and optical wavelength having an SBS acoustic wavelength associated therewith, the optical fiber comprising a core having a geometrical center and an outer perimeter; and a cladding surrounding the core; wherein the core is rare earth doped and substantially free of germanium, the optical fiber has a refractive index profile such that the core is guiding for optical radiation having the optical wavelength, and the optical fiber has an acoustic index profile such that the core is antiguiding for an acoustic wave having the SBS acoustic wavelength.