Stability Study of Photo-inscribed Bragg Gratings in Sapphire Fibers at Very High Temperature
Fiber Bragg gratings inscribed by femtosecond laser in sapphire fibers were subjected to thermal cycling up to 1500$\degree$C. Adding a multimode silica fiber reduces modal interference, improves the quality of the Bragg spectrum and the measurement accuracy. The measurement uncertainty is about 1.9$\degree$C at 1500$\degree$C.
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