The use of apodised in-fibre Bragg gratings in the measurement of both strain and strain gradient is discussed. A system of two Bragg gratings of similar but slightly displaced Bragg wavelength, joined using a 3dB coupler was used with a specially designed spectrum analyser of approximately nine picometers wavelength resolution. This consisted of a scanning Fabry Perot interference filter and photodiode detector unit interfaced to a PC. The reflection spectrum of both gratings, one exposed to strain, the other used as a temperature-referencing channel, was constructed using a Voigt type deconvolution. A directed evolution software algorithm was used as a line fitting routine to extract both the Bragg wavelengths and linewidths of the light back reflected from the gratings. A cantilever type strain rig in a temperature-controlled environment was used to create known strain and strain gradient fields. The variations in the Bragg wavelength with strain over a -400 to +600 microstrain range was measured from which the strain sensitivity of 0.962 ± 0.002 pm/microstrain, at ~1300nm was determined. The
temperature sensitivity was also evaluated. The linewidth of the back reflected spectrum from the Bragg grating was measured as a function of strain gradient (g) over the range - 1.0 to +1.5 microstrain per mm and was'fitted to a quadratic in g . This functional form was explained using a model based on coupled mode theory applied to apodised gratings.