Reflective liquid level sensor based on modes conversion in thin-core fiber incorporating titled fiber Bragg grating.

A simple and compact reflective liquid level sensor based on modes conversion in the thin-core fiber incorporating one tilted fiber Bragg grating (TFBG) is proposed and experimentally demonstrated. A piece of thin-core fiber containing one TFBG ensures the modes conversion between the core mode and cladding modes. The external liquid can induce the cladding modes covert to the radiation modes and lead to the decrement of the collected cladding modes power, then the liquid level can be measured from the collected cladding modes power. The modes conversion in the proposed structure is theoretically analyzed. The experimental results show the high liquid level sensitivity and temperature immunity of the proposed sensor, and its significant advantage is that the measurement range is not limited to the length of the TFBG itself.