Intensity-modulated liquid-level and temperature sensor based on cascaded air bubble and fiber Bragg grating interferometer

An intensity-modulated liquid-level and temperature sensor based on the air bubble (AB) cascaded fiber Bragg grating (FBG) is designed and presented. The sensor is composed of the AB, single-mode fiber (SMF), no-core fiber (NCF) and FBG. The AB is formed by the discharge between SMF and NCF, which makes the sensor sen-sitive to temperature. The liquid-level and temperature ranges of experimental measurement are 0-18 mm and 30-70 degrees C, respectively. The results show that one characteristic peak (i.e., peak 1) at 1545 nm is sensitive to liquid-level and temperature. The liquid-level sensitivity and linearity of peak 1 are-0.68987 dB/mm and 0.9903, respectively, and the temperature sensitivity and linearity are-0.14872 dB/degrees C and 0.99368, respec-tively. Thus, the intensity modulations of liquid level and temperature can be realized by monitoring the peak 1. The other characteristic peak (i.e., peak 2) produced by FBG at 1549.7 nm is sensitive to liquid level but insensitive to temperature. The liquid-level sensitivity and linearity of peak 2 are-0.62687 dB/mm and 0.98322, respectively, but the temperature sensitivity is almost 0. A temperature-insensitive liquid-level sensor can be archived by monitoring the peak 2 with the intensity modulation. The sensor has high sensitivity, good linearity, easy demodulation, and can be applied in the small liquid-level and temperature monitoring fields.