提出了一种基于级联体光栅(VBG)的谱组束方案,组束阵元数可随级联体光栅的数目倍增。给出了一个双光栅级联谱组束系统实例,将组束阵元按波长分为两组,利用具有相应波长选择性的体光栅分别对它们进行组束,由于两个级联体光栅的角度选择性互不重叠,所有光束经第二个体光栅后都沿其布拉格(Bragg)角方向出射,实现近场和远场的功率叠加。为保证各光束传播方向的一致性,采用严格耦合波理论推导出了准确计算光束入射角的解析式。数值计算结果表明各光束的平均衍射效率优于80％,在入射角偏离理论值不超过±5′(≈2.424×10-5 rad)的条件下组束光中所有光束的传播方向偏差小于4×10-7 rad。

A new spectral beam combination scheme based on cascaded volume Bragg gratings (VBG) was presented. The number of beams can be multipled with the number of cascaded gratings. A system as example based on two cacaded VBGs was given. All the beams were firstly divided into two groups according to their wavelength. Each group was then combined by a VBG with corresponding central wavelength. Because the angular selectivity of the two VBGs are not overlapped, all the beams can be steered to propagate in the direction of the Bragg angle of the second VBG. The power of all beams can then be added at the near and far fields. In order to assure the consistency of the propagating direction of all beams, a formula to accurately determine the incident angle of all beams was derived using rigorous coupled-wave theory. Numerical results show that the average diffraction efficiencies of all beams are higher than 80%, and the deviation of the propagating direction of all diffracted beams are less than 4×10-7 rad when the incident angle of all beams deviates from their theoretical value less than ±5′.