Directional Curvature and Temperature Sensor Based on Side-Polished Fiber Interferometer

A dual-parameter sensor for directional bending and temperature sensing based on side-polished multimode fiber is proposed. In this scheme, a side-polished multimode fiber is spliced between two sections of coreless fiber to form a Mach-Zehnder interferometer. The side-polished structure induces distinct phase changes when the fiber is bent from different directions. The side-polished fiber exhibits wavelength responses of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$3.252 \text{nm}/\mathrm{m}^{-1}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$-1.146 \text{nm}/\mathrm{m}^{-1}$</tex> in <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0^\circ$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$180^{\circ}$</tex> bending, respectively. This same structure is further demonstrated for high-sensitivity temperature sensing by coating it with Polydimethylsiloxane (PDMS). The PDMS-coated sensor shows an improved sensitivity of - <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$-107.9 \text{pm}/^{\circ}\mathrm{C}$</tex> compared to the uncoated sensor which attain sensitivity of 55.7 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{pm}/^{\circ}\mathrm{C}$</tex>. The results of this study demonstrate the sensor's potential for use in multi-parameter sensing applications, including medical wearable devices, soft robotics, and health monitoring of civil and mechanical engineering structures.