High-temperature performance of femtosecond laser inscribed MgAl 2 O 4 spinel fiber Bragg gratings

This research reports the fabrication and comprehensive high-temperature performance assessment of fiber Bragg gratings (FBGs) inscribed in magnesium aluminum spinel (MgAl 2 O 4 ) single-crystal fibers (MSCFs) using femtosecond (Fs) laser point-by-point (PbP) and line-by-line (LbL) techniques. Individual MSCF-FBGs demonstrated short-term thermal stability up to 1600 °C. A 10-grating cascaded FBG array exhibited stable operation for over 180 h at 1200 °C in ambient air, highlighting its potential for highly multiplexed, quasi-distributed sensing in extreme environments. While 3-cascaded FBGs maintained stability at 1400 °C for approximately 50 h before degradation, this study provides crucial insights into the long-term reliability, operational limits, and degradation mechanisms of MSCF-FBGs under challenging high-temperature and oxidative conditions.