Breath, as an important health monitoring indicator, provides valuable diagnostic information for cardiovascular disease and pulmonary function. Humidity can act as a bridge between breath and sensing signals. Current monitoring methods depend on humidity-sensitive material characteristics. In this work, an all fiber-optic flexible humidity sensor for wearable breath monitoring is reported. An eccentric fiber Bragg grating (EFBG) is inscribed in a single mode fiber to excite a stable core mode and sensitive cladding modes. The core mode is shown to maintain stable spectral features under a high-humidity atmosphere and can be used to calibrate the wavelength and power of the system. Importantly, the interface evanescent field of the cladding mode is highly sensitive to the ambient refractive index (RI) and even humidity-induced RI variation. Without combining any sensitized material, EFBG can directly perceive humidity fluctuations during breath with fast response (92 ms) and recovery times (100 ms). Different breathing patterns can be recognized, and breathing frequency can be extracted by sensor responses. The EFBG humidity sensor demonstrates great reproducibility, fast response, high flexibility, excellent robustness, and self-compensation capability, showing promising potential for wearable breath monitoring.

呼吸作为重要的健康监测指标，为心血管疾病和肺功能提供有价值的诊断信息。湿度可以作为呼吸和感应信号之间的桥梁。当前的监测方法取决于对湿度敏感的材料特性。在这项工作中，报告了一种用于可穿戴呼吸监测的全光纤柔性湿度传感器。偏心光纤布拉格光栅 (EFBG) 刻在单模光纤中，以激发稳定的纤芯模式和敏感的包层模式。显示核心模式在高湿度环境下保持稳定的光谱特征，可用于校准系统的波长和功率。重要的是，包层模式的界面渐逝场对环境折射率 (RI) 甚至湿度引起的 RI 变化高度敏感。在不结合任何敏化材料的情况下，EFBG 可以直接感知呼吸过程中的湿度波动，响应速度快（92 毫秒）和恢复时间（100 毫秒）。可以识别不同的呼吸模式，并且可以通过传感器响应提取呼吸频率。EFBG 湿度传感器具有良好的可重复性、快速响应、高灵活性、出色的鲁棒性和自我补偿能力，显示出可穿戴呼吸监测的潜力。