A relative humidity (RH) sensor based on a seven-core fiber (SCF) coated with graphene oxide (GO) is proposed. The sensing structure consists of a part of the SCF sandwiched between two parts of no-core fibers (NCFs). The SCF was corroded by hydrofluoric acid until the six outer cores were exposed to air and then coated with a layer of GO. The two NCFs play splitting and coupling roles because of the core diameter mismatch. The center core of the SCF acts as the reference arm, and the outer six cores of the SCF act as the sensing arm to construct a Mach–Zehnder interferometer. When GO absorbs water molecules, its refractive index changes. Consequently, the phase difference between the center core and outer core modes varies, and the resonant dip moves. The experimental results indicate that the RH sensitivity can reach 0.165 nm/%RH in the range of 30% to 100%, and the corresponding linear fitting coefficient is 99.9%.

中文翻译：

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基于氧化石墨烯涂层腐蚀性七芯光纤的相对湿度传感器

提出了一种基于涂有氧化石墨烯 (GO) 的七芯光纤 (SCF) 的相对湿度 (RH) 传感器。传感结构由夹在两部分无芯光纤 (NCF) 之间的一部分 SCF 组成。SCF 被氢氟酸腐蚀，直到六个外核暴露在空气中，然后再涂上一层 GO。由于芯径不匹配，两个 NCF 起到分裂和耦合作用。SCF 的中心核心作为参考臂，SCF 的外部六个核心作为传感臂，构成了一个 Mach-Zehnder 干涉仪。当 GO 吸收水分子时，它的折射率会发生变化。因此，中心纤芯和外纤芯模式之间的相位差发生变化，谐振倾角移动。实验结果表明RH灵敏度可达0。