Optical fibers inscribed with Bragg grating are used as strain sensors. The grating consists of a periodic change in the optical index of the fiber. These sensors are glued onto surfaces and measure the surface’s mechanical strain by measuring the optical strain (shift in reflected wavelength divided by the inscribed wavelength). Strain is either sensitive to a change in grating distance (mechanical, sensitivity of ~ 1 ppm/ppm) or grating refractive index (temperature based, ~ 8 ppm/K).
