提出一种基于光子晶体光纤(PCF)的光纤迈克耳孙干涉仪,传感器结构由单模光纤(SMF)与一段PCF熔接构成。SMF与PCF之间的粗锥作为耦合器,既能激发出PCF中的高阶包层模,又能耦合PCF端面反射回的纤芯基模与高阶包层模,形成模间干涉。由于PCF中的空气孔全部暴露在环境中,湿气与光纤充分作用,有效提高了传感器的湿度灵敏度。传感实验结果表明,在30%~90%的相对湿度范围内,传感器的湿度灵敏度为-0.095 dB/%,线性拟合度为0.998;在20~100 ℃的温度范围内,传感器的温度灵敏度为0.008 nm/℃,线性拟合度为0.997,温度引起的湿度测量误差为0.01%/℃;稳定性实验结果显示,该传感器的湿度测量标准误差为0.25%;呼吸测试表明,传感器的响应时间为190 ms。所设计的传感器结构简单、制作简便、灵敏度高、稳定性好、响应快,在湿度监测领域有较好的应用前景。

A fiber-optic Michelson interferometer based on a photonic crystal fiber (PCF) is proposed, constructed by fusing a piece of PCF and a single-mode fiber (SMF). The taper between the SMF and the PCF works as a coupler. It excites the high-order cladding modes and couples the fundamental mode of the core and high-order cladding mode after being reflected by the end face of the PCF to form an intermodal interference. Since all the air holes in the PCF are exposed to the environment, the moisture and the fiber are fully affected, effectively improving the sensor's humidity sensitivity. The experimental results show that the humidity sensitivity of the designed sensor is -0.095 dB/% with a linearity of 0.998 in a 30%-90% relative humidity range. The temperature sensitivity is 0.008 nm/℃ with a linearity of 0.997 from 20 ℃-100 ℃, and error in the humidity measurement, caused by temperature, is 0.01%/℃. The stability experiment indicates a humidity standard deviation of 0.25%, and the human breathing test shows a sensor response time of 190 ms. Importantly, the designed sensor has a simple structure, high sensitivity, good stability, fast response time, and is easy to fabricate, indicating excellent potential in humidity detection applications.