Etched circular waveguide-based on-chip silicon mode-order converters

Mode-order converters act as the vital higher-order mode sources for on-chip multimode applications. Here, we propose a silicon-based mode-order conversion scheme by leveraging etching slots on the circular waveguide. Through designing and optimizing the etching slots and circular waveguide, the mode-order conversion from input T E 0 mode to output T E 1 mode has been achieved with the mode conversion efficiency of 99.1%, modal crosstalk of − 25.7 d B , and insertion loss of 0.21 dB, respectively, in a mode conversion size of ∼ 8 µ m × 8 µ m ( T E 0 - T E 1 ). For the device fabrication, only one-step lithography and etching processes will be required, and the requirements of slot width (600 nm) and slot gap (1.49 µm) would be very beneficial for the device fabrication. Moreover, the proposed device scheme can also help achieve other higher-order mode conversions, such T E 0 - T E 2 and T E 0 - T E 3 , where their structural parameters and performances are also analyzed. With these features of relatively good device performance, compact size, easy fabrication, and functional scalability, we believe the proposed scheme would be applied in the on-chip multimode applications to enhance their transmission capacities.