Strain-optic coefficients of individual cladding modes of singlemode fibre: theory and experiment

The different strain-optic coefficients for the effective indices of the core and cladding modes of a standard telecom singlemode fibre are measured by stretching a fibre in which a 4°-tilted fibre Bragg grating has been written. The origin of the modal dependence of the strain-optic coefficient differences is analysed and discussed. Good agreement between theoretical and experimental values of these coefficients is reported.