Multiplexed fiber-optic Bragg stack sensors (FOBSS) for elevated temperatures

A novel fiber-optic technique for the measurement of temperature is demonst rated, By depositing alternating quarter-wave layers of silicon nitrite and silicon-rich silicon nitrite at the end of an optical fiber, we can fabric ate the equivalent of a Bragg grating of a high-temperature material to for m a fiber Bragg stack sensor. When heated, the Bragg stack expands and a ch ange in wavelength of the reflective peak is registered, Thus, the waveleng th of peak reflectivity is a function of temperature, The sensors, which ha ve previously been shown to be capable of surviving temperatures in excess of 900 degreesC, can be wavelength division multiplexed, Using a CCD solid- state spectrometer, we demonstrate the multiplexing of eight temperature se nsors, Crosstalk effects, arising from the side lobes observed in the wave stack spectra, limit the performance of the multiplexed sensors. We show th at this problem can be minimized by apodizing the Bragg stacks during fabri cation, Currently, the sensor system is estimated to have a temperature res olution of 2 degreesC using a CCD spectrometer with a spectral resolution o f 2.1 nm.