A simple and compact temperature sensor based on a Mach-Zehnder modal interferometer has been fabricated by bending a single-mode fiber into a balloon-like configuration. Three different fiber sections, fiber without stripping, fiber with a stripped-off protective coating and fiber with a polyvinyl alcohol (PVA) coating have been utilized, each with a small bending diameter of 1 cm that mimics a balloon-like shape. The PVA-coated segment sensor structure showed the highest sensitivity of ∼−1.492 nm • C −1 , a fast response time of ∼2.78 ms and a good resolution of ∼3 × 10 −4 • C, for the temperature range 30 • C-55 • C, benefiting from the good thermo-optical properties of PVA. This sensor can potentially be used in various temperature monitoring processes such as food industries, chemical analysis, detection of molecular analysis and label-free biomedicine.

Construction of pH sensors based on optical fiber encapsulated copper (Cu-NPs) has been accomplished. Briefly, a length of single-mode fiber (SMF) of about 25 cm has been wrapped in two rings by twisting one side of the fiber on the other from both ends to form a figure-eight shape. To upsurge the sensitivity, the sensor configuration has been immobilized with copper nanoparticles/polyvinyl alcohol hydrogel (Cu/PVA) composite. The Cu/PVA composite was employed to shape a membrane structure on the sensing active length by laminating it using the dip-coating method. The wavelength interrogation method was employed to evaluate the sensitivity of the fabricated pH sensor. The fabricated fiber pH sensor exhibits a sigmoidal response above a wide range of pH from 1 to 14. The result displays a superior sensitivity of ∼4.8 nm/pH for a range of 1-7 pH and 3.86 nm/pH for the range of 8-14 pH with an excellent linear response. Besides the great sensitivity, the dual-parameters measurement of pH and refractive index was effectively accomplished with perfect stability. The proposed fiber sensor possesses a superior performance compared with the other sensors.

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