Direction change judgment by double circuits and temperature compensation for optical fiber Fabry-Perot cavity liquid level sensor with fringe counting

A method for accurately judging the direction change by usingπ/2 electric RC phase shifter during the interference fringe counting for optical fiber Fabry-Perot cavity liquid level sensor is proposed. Instead of using double optical channels, the structure of the sensor system could be then simplified and be more compact and practical. After analyzing the relationship between the F-P cavity length and temperature, if the materials, initial lengths, and thermal expansion coefficients of the interior and exterior of the cavity were properly chosen, the cavity length change could be kept as small as possible. A novel design for compensating temperature influence on the sensing result by software approach is suggested. The experimental results show that this software technique can effectively compensate the temperature drift impact.