气体传感理论和实验研究已成为当今光纤传感领域的热点之一。波长调制法和有源内腔法是提高气体传感灵敏度的两种有效方式。结合上述两种气体传感方法，构建一个基于波长调制技术的内腔式气体传感系统。讨论气体吸收光谱二次谐波分量与气体浓度之间的函数关系，从理论和实验两方面确定系统的最佳参数。利用提取多条吸收谱线的二次谐波分量，采用平均算法进一步提高系统灵敏度，进行乙炔气体传感的灵敏度可达7.5×10-5。以光纤光栅作为波长参考，建立系统的波长电压响应曲线，进而检测气体的吸收波长值。进行乙炔气体传感时吸收波长检测的绝对误差不超过0.445 nm。

Theoretical and experimental research of gas sensing technique is one of the focus in modern fiber sensing area. Wavelength modulation and active intra-cavity methods are two effective ways which increase the sensitivity obviously. Combined with these two methods, an intra-cavity gas sensing system based on wavelength modulation technique (WMT) is established. The relationship between the second-harmonic component of gas absorption spectra and concentration is investigated. And then the optimized parameters of the system are obtained theoretically and experimentally. The second-harmonic components of several gas absorption spectra can be detected. And the average algorithm is used to increase the sensitivity further. The sensitivity of acetylene can be less than 7.5×10-5. With fiber Bragg grating (FBG) as wavelength reference, the wavelength-voltage relationship model of the system can be established. This model can be used to detect the absorption wavelength of different gases. When the system is used to measure acetylene, the maximum absolute error of the detected absorption wavelength is less than 0.445 nm.