利用高频CO2激光在普通通信单模光纤上制作了非对称折变型超长周期光纤光栅(ULPFG), 由于这种光栅具有较高的外界折射率响应灵敏度, 可基于此设计制作高灵敏度湿度传感器。通过在ULPFG的表层涂覆一层具有较强吸水性的新型纳米复合水凝胶, 水凝胶通过吸收空气中的水蒸气而使自身的折射率发生变化, 从而导致ULPFG透射谱的谐振峰发生漂移, 通过检测ULPFG谐振峰的漂移量就实现了对环境湿度参量的传感。实验结果表明, 在38%～96%的相对湿度变化范围内, 光栅谐振峰的最大漂移量可达约30 nm, 比先前一些报道的湿度传感器的灵敏度高出近3倍。

An ultra-long-period fiber grating (ULPFG) with asymmetric refractive index modulation is fabricated in common communication optical fiber by using high-frequency CO2 laser pulses. A highly sensitive humidity sensor based on this grating can be realized due to its high refractive index sensitivity. The ULPFG is coated with a new nano-composite hydrogel, which has strong water capacity. This kind of hydrogel can absorb water vapor in the air substantially to make its own refractive index change, which will induce the resonant peak shift of transmission spectrum of the ULPFG. And such a shift can be used in humidity measurement. The experimental results show that the maximum shift of the resonant peak can reach 30 nm when the surrounding humidity varies in the range of 38%～96%, and such sensitivity is three times higher than that of the humidity sensors reported before. Such novel humidity sensor can be found important applications in humidity measurement of the field of optical fiber sensing.