A partially PDMS-encapsulated microfiber Bragg grating for simultaneous temperature and strain measurement

This paper proposes a sensor for simultaneously measuring temperature and strain using a microfiber Bragg grating (MFBG), half of which is coated with polymer polydimethylsiloxane (PDMS) and encapsulated inside a couple of U-shape glass grooves, while the other half is bare. Due to the different thermal-optic coefficient, elastic-optic coefficient, and cross section structural dimension, the two reflection bands from the encapsulated part of the MFBG and the bare MFBG section show different behaviors to temperature and strain. The sensitivity to temperature varies significantly between the two peaks, the reflection wavelength shifts in the opposite direction, capable of effectively detecting temperature variations. The strain is almost all concentrate on the bare MFBG (BMFBG) as the cross-sectional area of the encapsulated MFBG (EMFBG) is much larger than that of BMFBG. The experimental results show that the temperature sensitivities of -31.92 pm/degrees C and 10.31 pm/degrees C and strain sensitivities of similar to 0 pm/mu epsilon and 6.24 pm/mu epsilon are achieved, respectively. The sensor has the advantages of high sensitivity and simple structure and can measure strain and temperature simultaneously.