Design of Bi-level adiabatic mode converters for compact and efficient mode conversions

Abstract

This study investigates the optimal design of bi-level adiabatic mode converters to enhance efficient and compact mode conversion in integrated optics, particularly for applications requiring compatibility with various polarizations and mode orders. As the demand for high-capacity communication increases, conventional waveguides encounter limitations in both bandwidth and mode conversion efficiency. To address these challenges, this study designs bi-level adiabatic mode converters based on the adiabatic mode evolution mechanism, which enables efficient mode conversion. The approach integrates theoretical methods and simulations to evaluate mode conversion in a bi-level ridge waveguide and to identify potential regions of mode hybridization. By leveraging the mechanisms of adiabatic mode evolution, compact bi-level converters with optimized waveguide geometries are proposed. Specifically, four bi-level adiabatic mode converters are designed to facilitate conversion between TE- and TM-polarized waves. Results indicate that the proposed designs offer a more compact footprint compared to conventional linear configurations. Additionally, mode conversion between higher-order TE modes is achieved through the intermediate TM₁ mode; a bi-level adiabatic converter enables efficient conversion between TE₂ and TE₄ modes as well as TE₄ and TE₆ modes, achieving a power conversion efficiency of 96 % within a compact length of just 86 μm. Overall, the developed bi-level adiabatic mode converters demonstrate efficient and compact conversion between TE and TM modes, as well as between higher-order TE modes.