A compact silicon-based TM₀-to-TM₂ mode-order converter using shallowly-etched slots

Mode-order converter is a pivotal component in the on-chip multimode optical transmissions with different mode orders. In this work, we propose a compact and highly-efficient TM₀-to-TM₂ mode-order converter using shallowly-etched rectangular slots on the silicon-on-insulator platform. The proposed device consists of four same shallowly-etched slots in symmetrical arrangements (two by two) along the light propagation direction and a smaller one between them, which can change the refractive index distribution of the silicon waveguide and add accumulated phase difference through light propagation. With detailed optimizations, we realize the efficient mode conversion from input TM₀ mode to output TM₂ mode, which is different from some reported TE-polarized mode-order converters, and the insertion loss and conversion efficiency of the present device are 0.21 dB and 94.3%, respectively, in a total device length of only 8.97 μm. Meanwhile, the modal crosstalk is lower than −15 dB and the bandwidth can be extended to ∼100 nm. We believe this device could be applied in the on-chip multimode optical transmission systems with different mode orders to further improve the link capacity. (paper)