An optical fiber sensor for the measurement of elevated temperatures

A novel optical technique for the measurement of temperature is proposed. T his is accomplished by depositing alternating 1/4 wave layers of silicon ni tride and silicon-rich silicon nitride at the end of an optical fiber. Thes e layers of alternating refractive index form the equivalent of a Bragg gra ting of a high temperature material. When the fiber and the Bragg grating a re heated, the Bragg stack expands, and there is a change in the reflective peak wavelength of this wave stack. Thus, the wavelength of peak reflectiv ity is a function of temperature. Currently, the 15 nm spectral width of th e Bragg stacks is achieved in our laboratory, which is conveniently monitor ed with a CCD solid state spectrometer and the temperature sensor probes ca n be also multiplexed at separated specific reflection wavelength. In the e xperiment, the temperatures in excess of 1,100 centigrade have been measure d with a resolution of less than 3 centigrade degree.