In-situ non-contact high-temperature measurement of an optical fiber up to the glass softening point

The optical fiber itself can function as a partially reflecting concentric cavity interferometer when transversely probed by a focused laser beam. In this study, the thermal response of the fiber heated by a CO 2 -laser beam was characterized by monitoring the back-scattered interference pattern. Simultaneous measurement of the Bragg wavelength shift of an inscribed, high-temperature stable fiber Bragg grating allowed for calibration of the temperature-dependent phase response of the interferometer. The presented technique allows for in-situ non-contact temperature measurements up to the glass softening point.