THERMAL HYSTERESIS OF BRAGG WAVELENGTHS OF INTRACORE FIBER GRATINGS

Bragg gratings written within GeO2 doped-silica-glass fibers were subm itted to increasing temperature steps. Bragg wavelength permanent shif ts induced by heating were measured at room temperature after each ste p using a tunable laser (accuracy of the measurement +/-3 10(-3) nm). Thus, hysteresis could be observed even after a temperature step as lo w as 80 degrees C from room temperature. Through other experiments, th e temperatures of various gratings were progressively increased in sta ges. During each stage, the Bragg wavelength was measured as a functio n of the grating temperature. The thermal evolutions of the Bragg wave length were shown to depend slightly upon the experimental conditions used for the photoinscription of the gratings. These two effects were minimized through a curing profess.