Simultaneous Measurement of Temperature and Pressure Based on Ring-Shaped Sensing Structure With Polymer Coated No-Core Fiber

A ring-shaped structure based on polymer coated no-core fiber (NCF) is presented for simultaneous temperature and pressure measurements. The sensing structure is fabricated by splicing the partially coated NCF between single-mode fibers and bending it into a loop. The anti-resonance effect is formed in the NCF and the resonant dips have wavelength shift responses to the temperature and displacement variations. It should be noted that the increase of temperature leads to a decrease in the polymer coating refractive index and changes the displacement measurement sensitivity, thus, the compensation algorithm is required to resolve this cross-sensitivity problem. Combining the ring-shaped structure with the elastic diaphragm encapsulation can convert seawater pressure into structural deformation displacement to achieve pressure measurement. The experimental and simulation results show that this sensor offers a high temperature sensitivity of −5.098 nm/°C with the resolution of
$2\times 10^{-4}$
°C and a pressure sensitivity of −2.368 nm/MPa with the resolution of
$0.4\times 10^{-3}$
MPa. In addition, the sensing performances could be changed by adjusting the NCF size and the ring-shaped structure diameter, which enables this sensing structure to have a broader application potential for seawater parameter measurement.