High and online tunable sensitivity fiber temperature sensor based on Vernier-effect

•An optical fiber temperature sensor is proposed based on Vernier-effect.•The sensor can achieve an online tunable sensitivity.•The proposed sensor helps to balance the tradeoff between the sensitivity and the dynamic range in fiber sensor. Based on Vernier-effect, a high sensitivity fiber temperature sensor with online tunable sensitivity is proposed and experimentally demonstrated. The sensor is composed of a Sagnac loop Interferometer (SLI) and a Fabry-Perot Interferometer (FPI). The effects of the parallel and the serially cascaded configurations on the temperature sensitivity are analyzed in detail. Experimental results show that the parallel configuration generates much clearer Vernier envelope than the serially cascaded one, thus it is more suitable for temperature sensing. A magnification factor up to 30.74 is demonstrated experimentally. Meanwhile, the parallel configuration also demonstrated a tunable sensitivity with a support of a fusion splicer-assisted FPI and its temperature sensitivity could be tuned to −4.26 nm/℃, −6.93 nm/℃, −9.99 nm/℃, which is 6.26, 10.19 and 14.69 times as high as that of single SLI, respectively. The tuning function makes the sensor more flexible in some cases where high sensitivity or wide measurement range are required. The proposed scheme offers a possibility to overcome the long-standing contradiction between high sensitivity and large dynamic detection range by tuning the temperature sensitivity.