▎ 摘　　要

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 degrees C, 200 degrees C, 300 degrees C, and 400 degrees 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 similar to 380 nm. The bandgap energy was verified between 2.3 and 3.17 eV for 100 degrees C and 400 degrees 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 degrees C and 400 degrees 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. (C) 2022 Optica Publishing Group