Simultaneous measurement of liquid level and temperature based on spherical-shape structures and long period fiber grating

A Mach-Zehnder interferometer (MZI) for simultaneous measurement of liquid level and temperature is proposed. It is formed by embedding a long-period fiber grating in the middle of two spherical-shape fiber structures. Two Dips in the interference spectrum are selected to demonstrate the interferometer's responses to the liquid level and temperature, and simultaneous measurement of liquid level and temperature can be realized by means of sensitivity coefficient matrix. The performances of two MZIs with different lengths are investigated. The results show that a high sensitivity of −0.214 nm/mm for liquid level measurement is acquired for the 35 mm sensor, and the temperature sensitivity is 0.059 nm/ °C in the range of 35-70 °C.