Power-type liquid-level sensor for high refractive index liquid based on long-period fiber grating

Abstract

In order to measure depth of liquid with high refractive index which is greater than that of the fiber cladding, a power-type liquid-level sensor based on reflective long-period fiber grating (RLPFG) is designed and implemented. A mode-transition model for RLPFG between guided mode and leaky mode is established, and spectral and power characteristics under different liquid level are theoretically analyzed. For the liquid level measurement of glycerol, a sensing sensitivity of 0.772 dB/mm is obtained, and its linear correlation coefficient is 0.9959. Then the influence of temperature on the sensor is analyzed. The experimental results are in good agreement with the theoretical results acquired by the above model. Compared with the phase method and the transmission power method, this method is simpler and more practical through detecting the reflected power.