Engineering Spectrum of Mode Converter Based on Cascaded Bragg Gratings

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.