Influence of air-filling fraction on forward Brillouin scattering in highly birefringent PCF

In this paper, we report on the influence of cladding air-filling fraction on the spontaneous forward Brillouin spectrum in birefringent PCFs. We focused our investigation on a range of birefringent fibers drawn from the same fiber perform and showing roughly the same structure, but with different cladding air-filling fractions. To measure the spontaneous forward Brillouin scattering spectrum we launched light from a linearly polarized CW laser at 45deg with respect to the birefringence axis into 10 m long fibers. The polarization modulation induced by thermally excited phonons was measured using a polarization spectroscopy technique In addition to the experiments, we modelled the optical and acoustic modes of such fibers using a full-vectorial finite element approach. The ability to engineer the forward scattering spectrum by altering the cladding structure is important for the design of efficient acousto-optic devices and in reducing low frequency noise in quantum optics experiments.