Integrated All-Fiber Sensor for Simultaneous Measurements of Curvature and Temperature

An integrated all-fiber sensor based on ring-core fiber (RCF)-embedded long-period fiber grating (LPFG) cascaded RCF-Mach-Zehnder interferometer (MZI) for measuring curvature and temperature is proposed and demonstrated experimentally. The RCF-embedded LPFG section is fabricated by periodically embedding hundreds of micrometers sized RCF into SMF by employing the mature, low-cost cleaving splicing method (CSM). Due to the large core diameter mismatch, the energy within the core is exceeded into the cladding mode more effectively, and the periodic refractive index modulation gives our sensor has a compact size with only three-period SMF-RCF structures and a total length of 2.8 mm. To measure curvature and temperature simultaneously, an RCF-based MZI with an RCF length of 1 mm is cascaded behind LPFG by employing the CSM. Thus, there are two dips corresponding to LPFG and MZI occur in the transmission spectrum. The dips show different responses to curvature and temperature changes. The maximum curvature and temperature sensitivities of the two dips are 26.61, −1.67 nm/
$\text{m}^{-{1}}$
, 0.053 nm/°C, and 0.059 nm/°C, respectively. By utilizing a
$2\times2$
matrix, simultaneous measurement of curvature and temperature can be achieved. The integrated all-fiber sensor has a compact size, low cost, and high sensitivity possessing more competitivity in complex, harsh applications.