Brillouin spectroscopy of YAG-derived optical fibers

We present Brillouin spectroscopy of YAG-derived optical fibers. It is found that the addition of yttria and alumina both tend to raise the acoustic velocity when added to silica, with the change due to yttria being much weaker. The temperature-dependence of the Stokes's shift in the YAG-derived fibers is also measured, disclosing a lesser temperature dependence than conventional Ge-doped fibers. These fibers are found experimentally to have a substantially larger acoustic attenuation coefficient relative to that of bulk silica, and assuming a photoelastic constant of amorphous YAG similar to that of pure crystalline YAG, a much-reduced Brillouin gain coefficient as a result. A 40 weight percent yttria and alumina fiber has a Brillouin gain coefficient estimated to be roughly one sixth of pure silica. We also show that the addition of Er to the YAG-derived system decreases the acoustic velocity and broadens the Brillouin spectrum.