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

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 mu m 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 mu epsilon and 0.23 degrees C over the ranges of 0-1000 mu epsilon and 26-118 degrees C.