Polarisation characteristics of a side-tunnel fibre

Modal birefringence and polarisation mode dispersion in a single-mode fibre having vacuum pits beside the core are measured in the wavelength region from 0.633 ¿m to 1.52¿m. Both quantities monotonically increase as the operation wavelength becomes large. The magnitudes of birefringence and modal dispersion are evaluated to be 1.0 × 10¿4 at 1.52¿m and 148 ps/km at 1.41 ¿m, respectively. These values are much less than those predicted theoretically for side-tunnel-type optical fibres.