基于多层三明治光栅的宽带高效率分束器的研究

The beam splitter includes the polarizing beam splitter and the 1×2 beam splitter which may be widely used in optical communication, integrated optics and optical information processing systems. Conventional beam splitters based on multilayer coatings and birerefringent crystals have disadvantages of low damage threshold and bulky size. Recently, many beam splitters are reported by dielectric gratings. However, on the one hand, the performance will fall with the deviation of the incident wavelength, though the optimized single-layer grating can separate beams for the prescribed wavelength. It is necessary to be further investigated how to improve the broadband property of the beam splitter. On the other hand, most reported beam splitters are surface-relief gratings. Due to the reflection on the grating-air and grating substrate interfaces, the diffraction efficiency is relatively low. The study is desirable in detail to enhance the diffraction efficiency. The project investigates the basic theory and key technique of the multilayer sandwiched grating to obtain the broadband property and high efficiency. The incident wavelength band can be improved by the multilayer grating instead of the single-layer grating. And the efficiency can be enhanced by the sandwiched structure instead of the surface-relief grating. The modal method and rigorous coupled-wave analysis are employed to investigate the physical propagation mechanism in the two-layer sandwiched grating to achieve the merits of the broadband property and high efficiency, which should have important theoretical value and practical prospect.

分束器包括偏振分束和1×2分束等，广泛应用于光通信、集成光学和光学信息处理系统中。传统的分束器基于多层介质膜和双折射晶体，其损伤阈值低和体积大。近来，许多工作报道了基于相位光栅的分束器。但一方面，优化的单层光栅虽然对于给定的入射波长具有分束性能。但实际应用中，入射波长的偏离会引起分束性能的显著降低。如何提高分束器的宽带特性，需要进一步的研究。另一方面，已报道的分束光栅大多基于表面浮雕型。由于入射光在光栅-空气和光栅-基底界面的反射，存在着衍射效率低的缺点。对于如何提高衍射效率，需要深入细致地研究。本项目拟重点研究基于多层三明治光栅的宽带高效率分束器的基础理论和关键技术。根据多层光栅模型代替单层光栅，提高光栅的宽带特性；通过三明治结构代替表面浮雕型，提高光栅的衍射效率。研究中采用模式方法和严格耦合波分析，研究多层三明治光栅的物理传播机理获得宽带和高效率的优点，具有重要的理论价值和实际意义。

研究了基于多层三明治光栅的宽带高效率分束器。通过多层光栅提高分束器的带宽，利用三明治光栅结构增强衍射效率。分束器广泛应用于光通信、集成光学和光学信息处理系统中。传统的分束器基于多层介质膜和双折射晶体，其损伤阈值低和体积大。优化的单层光栅虽然对于给定的入射波长具有分束性能。但实际应用中，入射波长的偏离会引起分束性能的显著降低。再者，已报道的分束光栅大多基于表面浮雕型。由于入射光在光栅-空气和光栅-基底界面的反射，存在着衍射效率低的缺点。基于多层三明治光栅，根据模式方法中的有效折射率的概念初步探索可能存在的光栅参数，利用严格耦合波分析精确设计光栅的占空比、周期、多层光栅的各光栅层深度以及覆盖层的厚度。该光栅比传统光栅适用光谱范围宽，更为重要的是其衍射效率高，具有重要的理论价值和实用前景。