Temperature and Strain Sensing With Femtosecond Laser Written Bragg Gratings in Defect and Nondefect Suspended-Silica-Core Fibers

The spectral behavior in the C-band of fiber Bragg gratings (FBGs) was analyzed as a function of temperature and strain. The FBGs were fabricated in pure silica four-leaf-clover-shaped suspended-core fibers by (DUV) femtosecond laser exposure (3.6 W at 800 nm, 130 fs, 1 kHz frequency tripled to 350 fs, 650 mW at 267 nm). A defect fiber (with a hollow hole in the core) and nondefect fiber were compared both yielding ≈1 pm/με sensitivity to strain but different sensitivity to temperature (from 3.0 pm/°C to 8.4 pm/°C for the defect fiber and 10 pm/°C for the nondefect fiber). The 16% to 70% relative difference between the thermal coefficients of the two fibers, together with their similar strain sensitivity enables the simultaneous measurement of strain and temperature.