A fiber laser sensor for liquid level and temperature based on two taper structures and fiber Bragg grating

A fiber laser sensor for simultaneous measurement of liquid level and temperature is proposed and demonstrated experimentally. The sensor is based on two taper structures and a fiber Bragg grating (FBG). The two taper structures form a novel fiber interferometer, which is fabricated by cascading two tapers in a section of single-mode fiber (SMF). The FBG and the interferometer serve as the filters of the laser cavity. Corresponding to the two filters, the laser outputs are stable dual-wavelength outputs, which have different characteristics to the liquid level and the temperature. The wavelength produced by the FBG is not sensitive to the liquid level. The temperature sensitivity of the wavelength produced by the FBG is 0.0123 nm/°C. The wavelength produced by the interferometer is sensitive to the liquid level and the sensitivity is up to 0.2294 nm/mm. The temperature sensitivity of the wavelength produced by the interferometer is 0.0648 nm/°C. According to the different spectral responses of the liquid level and the temperature, simultaneous measurement can be realized. Furthermore, the proposed sensor has the advantages of less detection limit (DL), higher resolution and higher sensitivity compared to other optical fiber sensors.