Temperature and Curvature Measurement Based on Low Cavity Loss FLRD Technology

In this study, we proposed a fiber loop ring-down (FLRD) based method for simultaneous temperature and curvature measurements. A tapered single-mode fiber (TSMF) and a TSMF covered with polydimethylsiloxane (PDMS-TSMF) were used as curvature and temperature sensors, respectively. Owing to the low insertion loss of these sensors, erbium-doped fiber amplifiers were not required to compensate for the intensity of the pulsed light in the FLRD. The insertion loss of PDMS-TSMF decreased as the ambient temperature increased, which decreased the slope of the peak envelope of the ring-down pulse. The results show that the linear relationship between the pulse envelope slope and temperature varied from 1.237 dB/(km °C) to 0.397 dB/(km °C) in the temperature range of 40–70 °C. The insertion loss of TSMF increased with the increase in curvature. The slope-curvature relationship was 51.013 dB/(km m
⁻¹
) from 2.706 to 4.364 m
⁻¹
. The proposed quasi-distributed sensing system has the advantages of low cavity loss, high sensitivity, low cost, and independent measurement of two variables simultaneously. It has potential value in practical engineering applications, especially in building structural health detection, disaster warning.