Enhancing the sensing behavior of a reduced graphene magnetite-based plasmonic optical fiber sensor

The D-shaped optical fiber is a base for the magnetite-based graphene nanocomposite (rGO/Fe₃O₄) for a Pb heavy metal sensing layer. The designed sensor was studied under the effects of rapid annealing, water circulation, and plasmonic tuning. Various annealing temperatures (100°C, 200°C, 300°C, and 400°C) were investigated. The effect of rapid thermal annealing (RTA) temperature on the transmission results were found at a short wavelength of 300 nm and a minimum point of ∼380nm. The bandgap energy was verified between 2.3 and 3.17 eV for 100°C and 400°C, respectively. The sensor results show modification toward a short wavelength by increasing the rapid annealing temperature. Compared with furnace methods, the transmittance shift of the plasmonic effect showed the best performance under the influence of RTA. RTA at 300°C and 400°C offered an acceptable degree of stability at the beginning (1-50 min). The best performance of the proposed sensor was improved by introducing a circulating liquid chamber into the initial design. The resonance shifts due to Pb ion concentration (5, 10, and 15 ppm) were studied for transmission and wavelength shifts. The sensor shift was enhanced by using a free space polarizer controller attached to the second design. The results give detection and sensing potential in the visible range at a possible remarkable response time. The figure of merit was 62.5 a.u., and the maximum sensitivity was 1 a.u./ppm by using a polarizer controller. This article presents the optical characterizations of plasmonic sensor-based rGO/Fe₃O₄ for detecting Pb ions and enhancing the resonance shift. RTA for composite material and water circulation associated with D-shaped optical fiber enhances response time and stability designed using a polarizer controller.