Simultaneous measurement of strain and temperature using a tilted fiber Bragg grating

The strain, temperature and refractive index of a material can be evaluated from the Bragg and cladding modes in the transmission spectrum of tilted fiber Bragg gratings (TFBGs). The strain and temperature of resin-based composite materials are evaluated from the changes of these indicators. The sensitivities of the TFBG were acquired by changing either the temperature or mechanical strain while fixing the other parameter. The TFBG was then surface-mounted in a more practical environment in which both the temperature and strain changed. The test results showed that simultaneous measurement was possible, but the conventional method of extracting arbitrary peaks in cladding mode had low measurement accuracy. To improve this situation, two peaks were non-arbitrarily extracted to minimize the condition number. The proposed extraction method clearly improved the accuracy of strain and temperature measurements by the TFBG.