Brillouin gain-coefficient measurement for bismuth-oxide-based photonic crystal fiber under significant beam reflection at splicing points

We investigate a six-air-hole bismuth-oxide-based photonic crystal fiber (Bi-PCF) in terms of Brillouin characteristics. One huge challenge in measuring the Brillouin properties of the Bi-PCF is the nonnegligible beam reflection at the splicing points, which can be attributed to the mirroring effect caused by different refractive indices of silica and bismuth fibers. To solve the problem we propose a method that is based on the combination of a pump-probe beat lock-in scheme and a normalized gain curve-fitting technique. Using this method, successful characterization of Brillouin properties for a 1.16-m-long Bi-PCF is experimentally demonstrated. With the measured Brillouin gain coefficient and the known x® nonlinearity parameters, the Kerr nonlinearity figure-of-merit (F_nl-SBS), including the stimulated Brillouin scattering-caused pump-power limit, is also estimated for the Bi-PCF.