涂有半导体气敏薄膜的长周期光纤光栅气敏传感特性理论分析

首先利用耦合模理论研究了长周期光纤光栅LPFG折射率敏感特性,数值计算了长周期光纤光栅透射谱谐振波长与环境介质折射率的关系。其次分析了半导体氧化物气敏膜光学特性机理,当气体与薄膜接触时,气体会使敏感膜的消光系数、吸收系数和相应的折射率发生变化。基于上述两点,提出可将气敏膜涂于光栅表面,利用气敏膜的折射率随环境气体成分和浓度变化而变化的特性,从而影响LPFG透射谱谐振波长的变化,通过检测波长的变化达到探测气体成分和浓度的目的。由于长周期光纤光栅对环境介质折射率的灵敏度高于光纤,且其传感信号属于波长调制,测量信号不受光强波动及光纤损耗的影响,因此其灵敏度比强度型光纤气体传感器高。

Theoretical Analysis of Sensing Character ofLong-period Fiber Grating Coated with Gas-sensitive Film

Firstly we studied the sensitivity of long-period fiber gratings (LPFGs) to the re- fractive index of ambient medium using the coupled modes theory. Then we presented numeri- cal calculation based on long-period fiber grating to show the relationship between the reso- nant wavelength of transmission spectrum and the ambient refractive index. Secondly we ana- lyzed the optical mechanics of the semiconductor oxide film with gas-sensitivity and found that when touching the thin film gas can make its extinction coefficient, absorption coefficient and corresponding refractive index change. Thus we can coat the grating surface with gas-sensi- tive film and make use of the character that the refractive index will change with the component and density of ambient gas. Furthermore the change will influence the resonant wavelength of transimssion spectrum of LPFGs therefore we can get information about the gas component and density by way of monitoring changes of wavelength. The LPFGs is more sensitive to ambient refractive index than fiber and the sensed signal is wavelength-modulated so the signal is not reflected by the fluctuation of light intensity and the fiber loss. Therefore the LPFGs is more sensitive than intensity-type fiber gas sensor.