基于Kogelnik理论模型，以平面波为入射光，分析了双体布拉格光栅(VBG)的反馈特性。理论分析表明，采用双VBG结构，通过控制两个VBG的中心波长差，可以使光栅反馈的效率提高，带宽加宽。对于由两块带宽100 pm、衍射效率20%的VBG组成的双VBG反馈系统，中心波长相同时，衍射效率最大(33.3%); 中心波长相差84 pm时，其带宽为单VBG带宽的1.8倍(180 pm)。由于VBG的中心波长存在温度漂移特性，因此通过改变双VBG结构中VBG的温度可以实现衍射效率和带宽的改变，为泵浦源的优化提供有效可行的方法。

Assuming the incident light was a plane wave, the feedback characteristics of double volume Bragg gratings (VBGs) were studied based on Kogelnik’s theory. According to the analysis, with the structure of the double VBGs, the bandwidth could be broadened and the diffraction efficiency could be improved through choosing the wavelength differences between the two VBGs. For a system consisting of two VBGs whose bandwidth and diffraction efficiency were 100 pm and 20% respectively, the diffraction efficiency was 33.3% when their central wavelengths had the same value, and the bandwidth could be tuned to 1.8 times (180 pm) of a single VBG’s bandwidth. Since there was a thermal shift in VBG’s central wavelength, changes in diffraction efficiency and bandwidth could be realized by adjusting the VBGs’ temperature. External cavities with double VBGs offers an efficient method for optimizing pumping source.