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。

One limitation of the single-stage acousto-optic tunable filter (AOTF) as a bandpass filter is the presence of large sidelobes higher than -9 dB. Multi-stage AOTF for suppressing sidelobes further is studied in this paper. The filter characteristics of single and multi-stage AOTF have been analyzed and compared theoretically and experimentally,and the advantages of multi-stage filters have been demonstrated. First the theory of single-stage collinear and quasi-collinear AOTF were discussed,and then the transfer function of multi-stage filter was obtained. The calculations have shown that multi-stage devices can provide significant improvement not only in sidelobe suppression but also in bandwidth narrowing as compared to single-stage ones. The triple-stage AOTF was measured,and a sidelobe suppression of about -27 dB and a narrower bandwidth were obtained. The experimental results demonstrate multi-stage AOTF is of lower sidelobe and narrower bandwidth.