Temperature-Insensitive 2-D Pendulum Clinometer Using Two Fiber Bragg Gratings

A novel two-dimensional (2-D) clinometer has been demonstrated by attaching two fiber Bragg gratings (FBGs) on a deliberately designed pendulum composed of a tapered cylindrical beam and a mass. Due to the nonuniform tilt-induced strain field applied along the length of the FBGs, the bandwidths of their reflection spectra vary linearly with the applied inclination. By monitoring the reflected optical powers of the two FBGs, temperature-independent measurement of 2-D tilt angle is realized. In the experiment, a high sensitivity of 1.96 μW/degree over the inclination range from - 4° to 4° is achieved, and the accuracy for tilt angle measurement is ±0.125°.