Inverse-Designed Broadband and Compact $TE_{N}$ to $TE_{0}$ Mode Converters via Optimized Bezier Curves

Abstract

We present a scalable design strategy for compact, broadband mode converters capable of transforming arbitrary high-order transverse electric ($TE_{N}$) modes into the fundamental $TE_{0}$ mode on a silicon-on-insulator platform. The architecture employs a “split-phase-combine” mechanism: the higher-order mode is spatially separated into fundamental mode components, phase-synchronized, and subsequently recombined. The device comprises a $1\times (N+1)$ input splitter, an adiabatic phase shifter, and a multimode interference (MMI) combiner. By parametrizing the device geometry with optimized cubic Bezier curves, we achieve a compact footprint with large operating bandwidth, while effectively maintain low losses. We validate the scalability of this approach by designing converters for $TE_{1}$, $TE_{2}$, and $TE_{3}$ modes. The optimized devices exhibit mode conversion efficiencies of 98.3%, 95.8%, and 86.8%, respectively, across a broad 100 nm bandwidth (1500–1600 nm). Tolerance analysis further confirms the robustness of the designs against systematic fabrication deviations of $\pm 10$ nm, suggesting their suitability for high-density mode-division multiplexing in next-generation optical interconnects.