取样光栅滤波的新型光纤甲烷差分检测系统

A Novel Fiber-Optic Differential Absorption Methane Detection System Based on Sampled Grating Filtering Technique

综合应用取样光纤光栅滤波和改进的差分吸收检测技术,实现了对甲烷气体等距分布的多条近红外吸收线的同时测量,完善了差分吸收技术应用于弱气体检测的理论。基于分子光谱学理论对谱带精细结构的分析,结合取样光纤光栅的梳状滤波思想,以1.66μm附近甲烷泛频(2v3)吸收光谱R支中的R4线为中心,同时对R3、R4和R5三条吸收线进行测量。为消除光源功率波动对测量结果的影响,利用两个同类型的取样光纤光栅实现对气体浓度的差分吸收检测。选用中心波长在R4附近的啁啾光纤光栅作为光学带通滤波器,利用PINPD实现对三条吸收线处光强的同时测量,由比值处理消除光源功率波动对测量结果的影响。通过实验验证了系统的可行性。

A novel fiber-optic methane detection system was proposed based on sampled fiber bragg grating（SFBG）filtering technique.By means of SFBG,Near-infrared equal-spaced multi methane absorption lines were detected simultaneously and difference absorption detection theory was developed.The fine structure of methane absorption spectra was analyzed.Using the comb filter characteristic of SFBG,R3,R4 and R5 lines in 2v3 overtone band around 1.66 μm were measured at the same time.In order to diminish the influence of light source instability on measurement result,two SFBGs of same type were used alternately to fulfill the task of difference absorption detection.Chirped fiber grating with its central wavelength around R4 was adopted as optical band-pass filter.The light power corresponding to three absorption lines and three reference wavelengths was detected simultaneously by PIN PD.The influence of light source instability was avoided by ratio treatment and the validity of the system was verified by experiments.