Abstract: Based on the characteristic of fiber Bragg grating used as sensing element as well as light-transmitting element, and on the linear relationship between the strain and deflection of the elastic element on simply supported condition, a novel measurement of relative displacement between the two curved surfaces in narrow curved space whose clearance is less than 1 mm is presented. Through the fiber Bragg wavelength modulated by strain of elastic element, the linear relationship between the Bragg wavelength shift and displacement of curved surface is obtained. The cross-sensitivity due to temperature is eliminated by using strain differential of elastic element. Results indicate that, when the range of relative displacement between the two curved surfaces is 0.35~0.85 mm, the displacement sensitivity of measuring system is 2.54 nm/mm, and its linearity is less than 1%.

Key words: Displacement measurement, Fiber Bragg grating sensing, Guide wave and fiber optics, Temperature compensate