Precise tailoring of acoustic velocity in optical fibers by hydrogenation and UV exposure

Abstract

Tailoring of acoustic properties in solids has many potential applications in both acoustics, i.e. acoustic gratings and waveguides, and photon-phonon interactions, i.e. stimulated Brillouin scattering (SBS). One immediate application is in the area of SBS suppression in optical fibers. We demonstrate, for the first time, a post-processing technique where hydrogen is diffused in to a fiber core and then locally and permanently bonded to core glass by a subsequent UV exposure. It is discovered that local acoustic velocity can be altered by as much as ~2% this way, with strong potential for much further improvements with an increased hydrogen pressure. It is also found that the large change in acoustic velocity is primarily due to a reduction in bulk modulus, possibly as a result of network bonds being broken up by the addition of OH bonds. It is possible to use this technique to precisely tailor acoustic velocity along a fiber for more optimized SBS suppression in a fiber amplifier. Change in Brillouin Stokes frequency of ~320MHz at 1.064μm was observed.