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Description
Rice grain exposed to excessive or insufficient moisture is susceptible to quality deterioration and microbial contamination, highlighting the need for a highly sensitive moisture sensing system to ensure food safety. This study presents the development of a graphene oxide (GO)-coated optical fiber sensor based on a hybrid Single-Mode Fiber–Multimode Fiber–Single-Mode Fiber (SMF–MMF–SMF) structure integrated with a Fiber Bragg Grating (FBG) for rice moisture level detection. Rice samples with varying moisture levels were prepared through controlled drying and steaming processes. To evaluate the influence of the hybrid fiber configuration, the MMF length was varied from 3.0 cm to 5.0 cm, while single-, double-, and triple-layer GO coatings were deposited on the spliced regions between the MMF and FBG. The sensor performance was investigated at operating wavelengths of 1310 nm and 1550 nm using an optical power meter and an optical spectrum analyzer (OSA), with the sensing probe directly immersed in the rice samples. Material and optical characterizations of the GO coating were conducted using X-ray diffraction (XRD), X-ray fluorescence (XRF), and UV–Vis spectroscopy. The results demonstrate that the sensor incorporating a 5 cm MMF section produced the highest output power of -65 dBm. Furthermore, the combination of a double-layer GO coating and a 1550 nm operating wavelength exhibited the optimum sensing performance, yielding a 9.11% higher output power than the 1310 nm wavelength when detecting rice samples with different moisture levels. These findings demonstrate the potential of the proposed GO-coated hybrid SMF–MMF–SMF–FBG sensor as a reliable and cost-effective approach for rapid rice moisture monitoring, contributing to improved food quality assurance and safety.
