Directional bending sensor with temperature insensitivity using a sampled chirped fiber Bragg grating

A simple and practical scheme for a directional bending sensor based on a sampled chirped fiber Bragg grating is proposed. The proposed sensing method has temperature insensitivity. The wavelength spacing in the reflection spectrum of a sampled chirped fiber Bragg grating is changed by bending because of the modification of the chirp ratio. As positive or negative bending is applied to the sampled chirped fiber Bragg grating embedded on a flexible cantilever beam, the wavelength spacing increases or decreases because of the induction of the tension and the compression strain gradient along the fiber grating. However, the wavelength spacing is not changed by the applied temperature. Since the effect of the temperature variation along the grating length remains the same, the chirp ratio is independent of the applied temperature change. Regardless of temperature change, it is therefore possible to measure the direction and the variation of bending.