基于光流控技术的光子晶体光纤长周期光栅纳米双层薄膜传感器对甲烷快速灵敏检测研究

Monitoring methane concentration is one of the most effective methods for preventing the gas accident in coal mines. The obtained detection results play an important role in the coal mine safety. In previous studies, in despite of good selectivity, the optical fiber methane sensors based on complexation effect of cryptophane molecules, have some shortcomings such as slow response and low sensitivity etc. To address these problem, this project develops a fast response and sensitive photonic crystal fiber long-period grating(PCF-LPG) methane sensor based on refractive index change of nano-bilayer films formed by optofluidic technology. The nano-bilayer films are composed of bare cryptophane and polysiloxane coated on the inner surface of cladding air holes in photonic crystal fiber (PCF), and a long-period grating (LPG) with high coupling efficiency in photonic crystal fiber is inscribed by high-frequency CO2 laser pulses method under some pressure carrier gas condition. ①The sensing mechanism of PCF-LPG methane sensor is analyzed. The sensing equation involving the resonant wavelength of sensor, the structure parameters of PCF, the LPG grating parameters, the parameters of nano-bilayer films, methane concentration etc., is estabished. ②The new method to form nano-bilayer films on the inner surface of cladding air holes in PCF through a covalent bond is investigated by optofluidic technology. ③Fabrication of high coupling efficiency PCF-LPG methane sensor is studied by high-frequency CO2 laser pulses method under some pressure carrier gas. ④The response time, sensitivity and detection limit of the sensor are evaluated. The feasibility of the sensor for detecting mine gas sample is verified.

监测矿井甲烷浓度是预防瓦斯事故发生的最有效手段，其监测结果对确保煤矿安全生产意义重大。针对目前基于笼形分子的高选择性光纤甲烷传感器存在响应速度慢、灵敏度低等问题，提出采用光流控技术在光子晶体光纤包层空气孔内壁形成快速响应的裸露笼形分子/聚硅氧烷纳米双层薄膜和制作高耦合效率的光子晶体光纤长周期光栅(PCF-LPG)甲烷传感器，从而建立一种响应速度快、灵敏度高的折射率变化型PCF-LPG甲烷传感新方法。①分析PCF-LPG甲烷传感机理，建立传感器谐振波长与PCF结构参数、LPG光栅参数、纳米双层薄膜参数、甲烷浓度等参量间传感方程；②研究光流控技术在PCF包层空气孔内壁共价键合聚硅氧烷、笼形分子以形成笼形分子裸露的纳米双层薄膜新方法；③研究加压载气作用下CO2激光脉冲写入法制作高耦合效率PCF-LPG甲烷传感器方法；④评价传感器响应速度、灵敏度、检出限等特性，探索传感器检测现场甲烷样品可行性。

甲烷是矿井瓦斯主要成分，监测甲烷浓度是预防瓦斯事故发生的有效手段。建立一种含笼形分子A-6Me和静电自组装薄膜的光子晶体光纤长周期光栅（PCF-LPG）甲烷传感方法，采用有限元法和局域耦合模理论分析传感机理，通过气压驱动和静电自组装技术制作PCF-LPG甲烷传感器，研究传感器谐振波长随甲烷浓度变化规律。主要成果包括：. （1）建立光子晶体光纤(PCF)传感器结构模型，利用有限元法分析PCF干涉谱特征波长随薄膜折射率、厚度变化特征，表明膜厚100nm~300nm、膜折射率从1.455减少至1.410时，干涉谱特征波长蓝移。. （2）采用有限元法和局域耦合模理论，研究纤芯基模LP01和包层模LP11电场分布、纤芯基模与包层模有效折射率、耦合系数等，分析PCF-LPG透射谱谐振波长随薄膜折射率、厚度变化规律。表明当膜折射率由1.53降至1.51时，PCF-LPG谐振波长蓝移；当膜厚由50nm增至150nm时，传感器灵敏度增加；对于膜厚150nm的传感器，谐振波长移动量-17.18nm。. （3）通过苄基化反应合成笼形分子框架用二苯甲烷衍生物，通过模板法和直接法合成笼形分子A-6Me、笼形分子E-6Me等，分析甲烷对笼形分子的荧光猝灭性质；在表面处理单晶硅上表征含cryptophanes敏感膜折射率的甲烷响应特性，以无芯光纤/单模光纤组成的反射式光纤甲烷传感器和长周期光纤光栅甲烷传感器验证。. （4）以薄芯光纤为对象，验证静电自组装技术在薄芯光纤表面成膜并形成光纤传感器的可行性；采用气压驱动和静电自组装技术，将含笼形分子A-6Me和静电自组装膜的敏感膜涂覆于包层空气孔内壁以形成PCF-LPG甲烷传感器，膜厚分别为50nm、100nm、150nm。. （5）研究敏感膜厚度对PCF传感器干涉谱特征波长影响，表明甲烷浓度由0%增至3.5%时，敏感膜折射率减小，干涉谱特征波长线性蓝移；对于薄膜厚度240nm的PCF传感器，灵敏度0.513nm/%，探测限0.16%。. （6）研究PCF-LPG传感器透射谱谐振波长随甲烷浓度变化规律，表明甲烷浓度由0%增加至3.5%时，敏感膜折射率减小，传感器透射谱谐振波长线性蓝移。对于膜厚150nm的PCF-LPG传感器，灵敏度1.056nm/%，探测限0.18%；同时，还开展现场瓦斯样品检测，证明PCF-LPG甲烷传感器是可行的。