A miniature ultra long period fiber grating for simultaneous measurement of axial strain and temperature

Abstract A SMF-MMF-SMF-ultra long period fiber grating (SMS-ULPFG) sensor is proposed for the simultaneous measurement of axial strain and temperature. The all-optical fiber sensor was fabricated by periodically splicing a multimode fiber (MMF) and a single mode fiber (SMF). Due to the strong refractive index (RI) modulation ability of the MMF, the sensor forms two resonant dips with smaller dimensions (the period of 1000 µm and total length of 5 mm). The transmission spectra were obtained by experiments and simulations. The results of the performance tests indicate that the uncertainty values of the SMS-ULPFG structure are 3.26 μe and 0.23 °C over the ranges of 0–1000 μe and 26–118 °C.