Simultaneous Temperature and Strain Measurement Based on Hollow-Core Fiber Sensor with Multi-Phenomenon

A fiber optic sensor for simultaneous measurement of temperature and strain by observing transmission and reflection spectra is proposed and demonstrated. The sensor connects a hollow-core fiber in series with two single-mode fibers, and the transmission and reflection spectra are observed simultaneously by a demodulator. Anti-resonance phenomenon and Mach-Zehnder interference are observed in the transmission spectrum, and Fabry-Perot interference and Vernier phenomena are observed in the reflection spectrum. The anti-resonance phenomenon is sensitive to temperature, and the Fabry-Perot interference is sensitive to both strain and temperature. Since the responses of the two phenomena are different, a fiber optic sensor for simultaneous measurement of temperature and strain is proposed, achieving a sensitivity of 22.32 pm/°C for temperature and
$1.62\ \text{pm}/\mu\varepsilon$
for strain by using wavelength drift of Fabry-Perot interference. Currently, the spectral intensity of Mach-Zehnder interference is too low for three-parameter measurements. In the future, the MZI spectral intensity can be enhanced by improving the fiber structure (e.g., using hollow Bragg gratings) or fusion parameters. It is possible to utilize the anti-resonance and Mach-Zehnder phenomena in the transmission spectrum and the Fabry-Perot and harmonic phenomena in the transmission spectrum at the same time, thus achieving simultaneous four-parameter measurements.