Abstract: A measuring device including at least one optical fiber which contains a series of Bragg gratings distributed between first and second ends of the fiber. A light source is arranged to emit a luminous flux at multiple wavelengths incident on the first end of the fiber, and an instrument connected to the second end of the fiber measures the power of the light transmitted at each emitted wavelength, enabling implementation of the method. In the method the power of the light transmitted by the optical fiber in a spectrum including wavelengths is measured.