镀有敏感膜的长周期光纤光栅NO气体传感特性

为提高长周期光纤光栅(LPFG)化学传感器检测折射率小于1.4介质时的灵敏度,实现对一氧化氮(NO)气体的高灵敏度检测,采用在常规长周期光纤光栅包层外镀上折射率大于包层折射率的SiO2-WO3薄膜的方法,运用四层阶跃折射率耦合模理论,分析长周期光纤光栅谐振波长的光谱特性.当膜厚为最佳值时,谐振波长变化率最大,灵敏度最高.在室温下,用镀有不同膜厚的传感器检测体积分数为2%的NO气体.结果表明,只有镀3层膜的传感器谐振波长红移4.77 nm,灵敏度达3%,元件响应时间10 s,恢复时间20 s,其他膜厚的传感器谐振波长没有变化.

NO gas sensitive effect of long period fiber grating coated with sensitive film

LPFG(long period fiber grating) sensors with different film thicknesses have been prepared by coating different layers SiO2-WO3 films to improve the sensitivity of LPFG chemistry sensor especially for the media with refractive index less than 1.4,and improve the detectability to nitric oxide(NO).The spectral characteristics of LPFG resonant wavelength were analyzed theoretically based on four-layer-step refractive index coupled mode theory.Optimal film thickness corresponded to the maximum values of sensitivity and change rate of resonant wavelength.When LPFG sensors with different film thicknesses were put into NO with 2% volume fraction at room temperature,some changes happen only on the sensor coated with three layers,whose resonant peaks red shift 4.77 nm,gas sensitivity,response time and recovery time reaches 3%,10 s and 20 s respectively.The resonant wavelengths of LPFG sensors with the other film thicknesses are unchanged.