首次提出了一种基于U型波导耦合的新型单微环结构湿度传感器, 该传感器以聚酰亚胺(polyimide, P1)作为感湿材料, 当外界环境相对湿度变化时, 引起感湿部位折射率的相应变化, 导致传感器的输出光谱发生漂移。根据传输矩阵法推导U型波导耦合单微环结构的传递函数, 重点讨论了不同感湿部位对输出光谱的影响, 通过Matlab理论仿真, 确定以U型波导耦合单微环结构整体作为最佳感湿部位。当U型波导的两个耦合点间的距离为微环周长的整数倍时, 相比于传统的单微环结构, 自由光谱范围(FSR)实现加倍。外界相对湿度从10%RH变化到100%RH时, 传感器的输出光谱漂移量在0.027～0.191 μm之间变化, 灵敏度高达0.001 8 μm/%RH, 相比于具有高灵敏度的光纤光栅类湿度传感器, 灵敏度提高了10~100倍, 实现了在高灵敏度感湿的同时兼顾谐振峰两侧大范围的滤波选频。

The paper proposes a novel high sensitivity humidity sensor based on a U-shaped waveguide-coupled single micro-ring, Polyimide is used as the wet material, the refractive index of humidity-sensing part changes as relative humidity changes, thus leading to a obvious peak drift. The transfer function of the structure is derived basing on transfer matrix method and the paper mainly discusses the influence on the output spectrum with different humidity-sensing parts. Through the theoretical simulation of Matlab, the whole structure of U-shaped waveguide coupled single micro-ring is proved to be the best humidity-sensing part. The free spectral range (FSR) will be doubled compared to the traditional single micro ring structure while the length between the two coupling points of the U-shaped waveguide is an integer multiple of circumference of the micro-ring. When the relative humidity of external environment changes from 10%RH to 100%RH, the output spectrum appears a obvious drift from 0.027 to 0.191 μm and the sensitivity reaches up to 0.001 8 μm/%RH. Compared to FBG humidity sensor with high sensitivity, the sensitivity in this article is increased by 10 to 100 times, achieving a high sensitivity in the sense of humidity when the wide range of filter frequency selection is taken into account.