A method of engineering spectrum of mode converter based on cascaded Bragg gratings is investigated in detail. Due to the cascaded structures, the proposed mode converter owns higher design degrees of freedom comparing with mode converter based on traditional Bragg grating. Meanwhile, thanks to various light responses of gratings, conversion spectrum can be easily tailored by designing grating structures. As examples, mode converters with specific conversion spectra such as single-band pass, double-band pass, multi-band pass, narrow-band backward spectra have been designed. Besides, the same triangle-shaped band pass spectrum is obtained by two converters based on different grating structures with the aid of distribute-layer-peeling algorithm, which further shows the high design flexibility of the proposed method. We think the proposed method gives a new way for advanced mode converter with required conversion spectrum.

中文翻译：

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基于级联布拉格光栅的模式转换器的工程频谱

详细研究了一种基于级联布拉格光栅的模式转换器的工程频谱方法。由于级联结构，所提出的模式转换器与基于传统布拉格光栅的模式转换器相比具有更高的设计自由度。同时，由于光栅的各种光响应，可以通过设计光栅结构轻松定制转换光谱。例如，已经设计了具有特定转换光谱的模式转换器，例如单带通、双带通、多带通、窄带反向光谱。此外，基于不同光栅结构的两个转换器借助分布层剥离算法获得了相同的三角形带通谱，进一步表明了该方法的高设计灵活性。