串联双微环湿度传感器光谱特性研究

提出了一种基于串联双微环谐振器的新型聚酰亚胺(Polyimide，PI)湿度传感器，采用传输矩阵法和耦合模的理论计算微环谐振器的传递函数，并对比了传统单微环与串联不同半径的双微环的输出光谱特性。外界湿度变化使得聚酰亚胺SOI波导吸收水汽后折射率发生变化，从而引起微环输出光谱发生漂移，通过探测光谱漂移量来测湿度值，得到了串联双微环传感器的灵敏度和测量范围，并且分析了感湿部位不同时谐振器输出光谱特性。理论结果表明：串联不同半径的微环谐振器的自由光谱范围（FSR）要比单微环有所提高，而且串联双微环谐振器整体感湿比单个微环单独感湿的传感性能更优良，可作为最佳的湿敏元件。与传统的单微环传感器相比，串联不同半径的微环结构可提高系统的测量范围和灵敏度，半径为30和50 μm的串联微环谐振器的FSR可达到0.15 μm，传感器测量湿度范围为10%RH～80%RH，灵敏度可达到0.001 7 μm·(%RH)-1。因此串联不同半径的双微环谐振器为制备成本低、结构简单、高灵敏度、可集成的微型湿度传感器件提供一定理论基础。

Study of Spectrum Characteristic of Humidity Sensor Based on Series Coupled Two Micro-Ring Resonators

A novel humidity sensor of polyimide(PI) based on the series coupled two-micro-ring resonators is proposed in the present paper. The transfer function of the micro ring resonator was calculated by using the transfer matrix method and the coupled mode theory. The authors compared the output spectrum characteristics of the traditional single micro-ring and series coupled two-micro-ring with different radii. The refractive index of the PI waveguide changes with different environmental humidity and this will lead to the drift of the output spectrum of the micro-ring resonator. By detecting the drift of the output spectrum we can measure the humidity, and the sensitivity and the sensing-range of the sensor are acquired accordingly. We also analyzed the output spectrum characteristics of resonators at different humidity sensing part. The theoretical results show the good performance of humidity sensor which could be used as the optimum sensing unit when the whole structure of the series coupled two-micro-ring resonators serves as the sensing part. The sensing-range and sensitivity of the system are improved by series micro-ring resonators of different radii compared to the conventional sensor with single micro-ring resonator. The free spectral range (FSR) of resonator reaches to 0.15 μm, the sensing-range is 10%RH～80%RH, and the sensitivity is 0.001 7 μm·(%RH)-1. Series coupled two-micro-ring with different radii gives theoretical instruction for producing integrated humidity sensor with low-cost, simple structure and high sensitivity.