Transverse load sensing by use of pi-phase-shifted fiber Bragg gratings

The birefringence of a pi-phase-shifted fiber Bragg grating an be determine d with high accuracy by measurement of the polarization-induced spectral sp litting of its narrow central transmission window. The use of this feature for sensing of a load applied in the direction transverse to the optical fi ber is demonstrated. A distributed force resolution of 1.4 x 10(-3) N/mm wa s obtained, which corresponds to a difference in the principal strains of t he fiber core of 0.5 mu epsilon. We also show that the transverse load resp onse of the sensor is insensitive to temperature.