Multiparameter sensing with fiber Bragg gratings

This paper describes the design of a fiber optic sensor capable of sensing temperature and three independent components of strain simultaneously in a single, short gage length device. The sensor utilizes two fiber Bragg gratings at widely spaced wavelengths (1300 nm and 1550 nm) written at a single location in polarization maintaining optical fiber. When a broad-band light source is used to illuminate the gratings, the reflected spectrum will contain four peaks corresponding to the two polarization states for each of the two gratings. If the fiber is subjected to a change in temperature or strain, the resulting change in wavelength of the reflected peaks can be used to determine the magnitude and direction of the perturbation. In theory, the four peaks can be used to simultaneously determine the grating temperature, and three independent components of strain in the fiber.