论文部分内容阅读
单级声光可调谐滤波器(AOTF)存在旁瓣过高的问题(-9 dB左右),这给其应用带来了一定的局限性。研究了用多级滤波结构实现旁瓣抑制,通过对单级和多级AOTF滤波特性的理论计算值、实验测量结果的分析比较,说明了多级滤波的优越性。利用耦合模理论分析了单级共线型和单级准共线型AOTF的滤波原理,推导出了多级级联滤波的转换特性表达式。计算结果表明,较之单级滤波,多级级联不仅具有较强的旁瓣抑制能力,还具有良好的带宽压窄作用。实验测量了三级滤波,其旁瓣被抑制到-27 dB左右,并且滤波带宽也得到了压窄。该实验结果说明,多级滤波结构在更为有效地抑制旁瓣的同时也能够很好地压窄带宽。
The single-stage acousto-optic tunable filter (AOTF) has the problem of side lobes being too high (about -9 dB), which brings some limitations to its application. The sidelobe suppression using multilevel filter structure is studied. By analyzing and comparing the theoretical and experimental results of single-level and multi-level AOTF filtering, the superiority of multi-level filtering is illustrated. The coupled-mode theory is used to analyze the filtering principle of single-stage collinear and single-stage quasi-collinear AOTF, and the expression of the conversion characteristic of multi-stage cascaded filter is deduced. The results show that, compared with single-stage filtering, multi-stage cascades not only have strong side-lobe suppression ability, but also have good bandwidth narrowing effect. The third-order filtering was measured experimentally and its sidelobe was suppressed to -27 dB, and the filtering bandwidth was also narrowed. The experimental results show that the multi-stage filter structure can suppress the sidelobes more effectively while narrowing the bandwidth well.