H-Shaped plastic optical fiber sensor based on surface plasmon resonance for ammonia gas detection

This study delineates the utilization of polished H-shaped plastic optical fibers (H-shaped POFs) as a sensor for the detection of ammonia (NH3) concentration in the air for pollution monitoring. We tested the built sensor's performance by looking at things like its signal-to-noise ratio (SNR), sensitivity, resolution, and figure of merit. Resonance of surface plasmons, the SPR response curves for different amounts of NH3, were recorded, and they showed that the location of the resonance intensity changed. The value of the resonance intensity changes with each change in time and, as a result, with each change in NH3 concentration. Three different sensors with different gold nanoparticle (Au-NP) thicknesses were used to test how the thickness of the GNP layer and the size of the grains affect the sensitivity and other properties of the SPR sensor when it is used to find NH3 particles in concentrations of parts per million (ppm). The H-shaped plastic optical fiber-based SPR sensor had an Au-NPs layer thickness of 365.5 nm and a grain size of 52.061 nm for the H-shaped sensing region. The sensitivity was 0.057 nm/ppm (R 2 =0.99) for the S1 sensor, 0.119 nm/ppm (R 2 =0.99) for the S2 sensor, and -0.22198 nm/ppm (R 2 =0.75) for the S3 sensor. The results show that the S2 sensor, which has an Au-NPs layer thickness of 556.2 nm and a grain size of 60.438 nm, is more sensitive and has a lower limit of detection (LOD) of 4.54 ppm. The S3 sensor, on the other hand, has an Au-NPs layer thickness of 727.6 nm and a grain size of 63.631 nm in the H-shaped sensing region. This gives it a different sensitivity profile than the S1 and S2 sensors, making it very sensitive but with a higher LOD of 31.92 ppm. The results of the SPR response curve show that the S2 sensor has the highest intensity, -1.16 a.u., at high NH3 concentration in comparison with the S1 and S3 sensors. The plastic optical fiber used in this study had a core diameter of 980 μm, a cladding thickness of 20 μm, and a numerical aperture of 0.51.