A plastic optical fiber (POF) temperature sensor with high sensitivity is experimentally demonstrated in this work. The temperature sensor is realized by a combination of macrobending and an unclad region in the fabrication of its sensor head. The POF sensor is bent into a balloon-like structure in order to introduce the effect of macrobending. For the optimization of the sensor performance, the bending radius of the balloon-like structure is varied. Experimental results suggest that the performance is optimized when the bending radius is fixed at 55 mm. With this amount of bending radius, temperature sensitivity of up to 22.2 × 1 0 − 3 ∘ C − 1 can be achieved in the range from 40°C to 80°C, with linearity of 0.99 and resolution of 0.45°C. This technique is found to improve the POF temperature sensitivity in comparison to previous developments.

Optimization of light source wavelength for ammonia detection in surface water is presented in this work. For the ammonia detection, the surface water sample is mixed with sodium chloride and nessler reagent, whereas the sensor head consists of unclad plastic optical fiber. The unclad region has a length of 1 cm and the cladding is removed by immersing it in acetone solution. Experimental results indicate that the output light intensity of the sensor has linear relationship with the ammonia concentration. At the wavelength of 510 nm, the output light increases linearly as the ammonia concentration varies from 0.07 mg/L to 8.97 mg/L. At the same wavelength, the proposed sensor achieves the sensitivity of 0.0139 (mg/L) -1 , accuracy of 99.59% and resolution of 0.72 µg/L. The analysis of light source wavelength reveals that a wavelength range from 450 nm to 580 nm produces the optimized performances. Within this wavelength range, the proposed sensor achieves sensitivity of higher than 0.01 (mg/L) -1 , accuracy of higher than 99% and resolution of less than 1 µg/L.

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This work presents the demonstration of a plastic optical fiber (POF)-based ammonia sensor. The sensor head is formed by bending an unclad fiber optic sensor into a balloon-like structure. The bending radius of the balloon-like bent fiber optic sensor is varied from 1.0 to 2.5 cm. The performance of each sensor is tested using ammonia solution with concentration ranging from 0 to 15 mg/L. Results show that the optimized performances of the proposed sensor occur when the bending radius is fixed at 1.5 cm. At this bending radius, the sensor illustrates the sensitivity of - 0.0024 (mg/L)-1 with linearity of 0.97 and resolution of - 4.17 mg/L. For comparison, the bent sensor is compared to the straight sensor and performances of the former is found to be more superior. In addition, the balloon-like bent sensor is further tested with real water samples. The sensor sensitivity is found to be - 0.0022 (mg/L)-1 with linearity of 0.95 and resolution of - 4.54 mg/L. The result shows that the sensor has comparable performance in the ammonia detection for both pure ammonia and real water samples. In essence, this balloon-like bent sensor functions without additional coating on the sensor head, making it favorable in terms of the simplicity of the design.