Robust Optical Mode Conversion in Waveguides by Triplet Supercell

On-chip mode conversion is beneficial in photonic integrations and enables many functionalities for optical signal processing, however, it is still challenging to achieve a robust solution with broadband working wavelengths. Here, by exploring an interesting coupling effect between triplet and singlet waveguides, we propose and realize a robust mode conversion based on an undistributed breathing mode in the waveguide triplet supercell. It is well demonstrated with high efficiency and robustness in the silicon waveguide platform, which shows further extensions to higher-order mode conversions by connecting more elements together. Our approach makes good use of the undisturbed breathing modes in a three level system for robust mode conversions, which is proved to be an effective means and promises further functional elements in photonic integrations.