Birefringence in fibres with multi-lobe stress region

The dielectric anisotropy in the centre of a weakly guiding fibre with stress region of N (N = 2, 3, 4...) lobes is studied by using the perturbation method. These stress lobes are arranged uniformly along the azimuthal direction in the fibre cladding. In the centre of the fibre, the total change of the dielectric constant induced by the stress is the superposition of that resulted from each lobe stress region individually. The final results reveal that the birefringence for fibres with N = 2 (i.e. bow-tie fibre or Panda fibre) is double that of fibres with the single-lobe stress region, and the birefringence will disappear for all fibres with N > 2.