Liquid level and refractive index double-parameter sensor based on tapered photonic crystal fiber

In this article, a liquid level and refractive index double-parameter sensor with single-mode fiber–tapered photonic crystal fiber (TPCF)–single-mode fiber structure is designed. We utilized the temperature-insensitive characteristics of photonic crystal fiber (PCF) to solve the crosstalk caused by temperature. Tapering techniques are adopted to increase the evanescent wave and the sensing region length of the PCF surface and improve the sensitivity and measurement range of the sensor. The liquid level and refractive index can be simultaneously detected through the mode analysis of the sensor's interference spectrum, along with the double-parameter matrix equation. Experimental results show that the maximum sensitivity of the sensor is 0.58466 nm/mm within a liquid level range of 0–10 mm (for an aqueous solution). The maximum sensitivity of the sensor is 195.969 nm/RIU within the refractive index range of 1.336–1.382. The sensor has simple structure and excellent sensing performance, as well as several application prospects in the fields of fuel storage and chemical liquid level measurement.