Simultaneous measurement of temperature and liquid level base on core-offset singlemode–multimode–singlemode interferometer

A fiber sensor based on core-offset singlemode–multimode–singlemode (SMS) interferometer for simultaneous measurement of temperature and liquid level is proposed. The sensor is fabricated by a SMS interferometer spliced with a single mode fiber (SMF) in core-offset way. Since the cladding mode of SMF is excited in the core-offset SMS, two different kinds of interference dips which are formed by the SMF and the SMS interferometer respectively are obtained. Using the difference sensitivities to the two parameters of the selected dips, temperature and liquid level can be measured simultaneously. The chosen interference dips are at 1529.632 nm and 1553.18 nm. Experiments indicate that the dip at 1529.626 nm is insensitive to liquid level, the temperature sensitivity is 0.064 nm/°C. The temperature sensitivity of the dip at 1553.18 nm is 0.082 nm/°C. The temperature measurement precision is 0.001 nm/°C. When the liquid is water (n=1.33), the sensitivity of the liquid level is 0.140 nm/mm. When the liquid is sodium chloride solution (n=1.38), the sensitivity of the liquid level is 0.290 nm/mm. The liquid level measurement precision is 0.001 nm/mm. The interferometer also can be applied in other sensing fields.