Thermal hysteresis of Bragg wavelengths of intra-core fiber gratings

Bragg gratings written within GeO/sub 2/ doped-silica-glass fibers were submitted to increasing temperature steps. Bragg wavelength permanent shifts induced by heating were measured at room temperature after each step using a tunable laser (the accuracy of the measurement +or-3*10/sup -3/ nm). Thus, hysteresis could be observed even after a temperature step as low as 80 degrees C from room temperature. Through other experiments, the temperatures of various gratings were progressively increased in stages. During each stage, the Bragg wavelength was measured as a function of the grating temperature. The thermal evolutions of the Bragg wavelength were shown to depend slightly upon the experimental conditions used for the photoinscription of the gratings. These two effects were minimized through a curing process.<>