Polarisation properties of long-period grating inscribed in pure-fused-silica photonic crystal fibre

The first measurements of polarisation properties of a long-period grating inscribed in an endlessly singlemode photonic crystal fibre are reported. Strong modulation in the spectra of polarisation-dependent loss and differential group delay with periods of 2.6 and 1.3 nm, respectively, were found. As such an effect has not been observed in standard optical fibres, it is believed that this is due to the specific mode structure of the holey fibre used for grating fabrication