Temperature-insensitive displacement sensing using the chirp effect of fiber Bragg grating

A new approach for displacement sensing based on chirp effect of fiber Bragg grating under strain-gradient is proposed and demonstrated in this paper. Strain gradient chirp of fiber Bragg grating is realized by attaching the grating slantways on a side face of a simple cantilever beam. The strain gradient, which is formed along the grating when the free of the beam is curved, produces a linear variation in the grating pitch The theoretical formulae are derived and the experimental results are given. Because bandwidth of the grating is temperature-insensitive, the cross talk between displacement and temperature is avoided. This device has many characteristics, such as simple configuration, good, noise immunity, and good linearity (about 0.9992). It is promising to be used into in-process displacement measurement.