Abstract
The spectral response of the dual resonant peaks of a 100 µm period fibre grating to surrounding refractive index (SRI) from n = 1 to 1.74 has been investigated. The two peaks were found to shift in opposite directions over –180 and +300 nm, respectively, as the SRI changed. A novel chemical sensing scheme with enhanced sensitivity based on the measurement of the separation of the two peaks instead of a shift in a single peak is also presented.