Analysis of Brillouin frequency shift and acoustic waves in a hollow optical fiber

We propose and demonstrate a new method to manipulate the Brillouin frequency shift in silica optical fiber by introducing a silica hollow optical fiber (HOF) waveguide structure. Propagation characteristics of acoustic waves guided along the HOF were theoretically analyzed, and the corresponding Brillouin frequency shifts were measured by a Brillouin optical-correlation domain-analysis system. We experimentally observed that Brillouin frequency shift v_B monotonically increases as a function of the central air-hole radius, which showed good agreement with the simulation results. We confirmed that a precise control of Brillouin frequency shift can be obtained by controlling the waveguide parameters of the HOF.