A relative humidity (RH) sensor based on in-fiber Michelson interferometer (MI) is proposed, which consists of a short piece of graded-index multimode fiber (GIMMF) followed by a 2-core fiber (2CF), whose end face is terminated by a thick aluminum film. The GIMMF excites cladding modes into the pigtail 2CF via the mismatched-core splicing interface. The core-cladding modes are reflected back by the aluminum film and recoupled to the core of lead-in SMF through the GIMMF. A well-defined interference pattern is obtained as the result of core-cladding mode interference. The experimental results show that a configuration with a 10 mm pigtail 2CF at a wavelength of 1552.78 nm has a good linear response to relative humidity with the sensitivity of – 0.044 dB/%RH in the range of 35–95%RH. Meanwhile, the selected monitoring peak provides a better temperature sensitivity of 65 pm/℃ in the range of 35 –85 ℃. In addition, the aluminum film is manufactured by physical vapor deposition (PVD), which greatly enhances the compactness of the film and improves the contrast of the interference fringes; the manufacturing method has high repeatability.

提出了一种基于光纤内迈克尔逊干涉仪（MI）的相对湿度（RH）传感器，该传感器由一小段渐变折射率多模光纤（GIMMF）和其端面为2芯光纤（2CF）组成。由厚铝膜终止。GIMMF 通过不匹配的纤芯拼接接口将包层模式激发到尾纤 2CF 中。纤芯-包层模式被铝膜反射回来，并通过 GIMMF 重新耦合到引入 SMF 的纤芯。纤芯-包层模式干涉的结果是获得明确的干涉图案。实验结果表明，具有 10 mm 尾纤 2CF 的配置在 1552.78 nm 波长下对相对湿度具有良好的线性响应，在 35-95%RH 范围内灵敏度为 – 0.044 dB/%RH。同时，所选监测峰值在35 – 85 ℃范围内提供了65 pm/℃的更好温度灵敏度。另外，铝膜采用物理气相沉积（PVD）技术制造，大大增强了膜层的致密性，提高了干涉条纹的对比度；该制造方法重复性高。