Ultra-Compact Reflective Waveguide Mode Converter Based on Slanted-Surface and Subwavelength Metamaterials

Mode converter (MC) is an indispensable element in the mode multiplexing and demultiplexing system. Most previously reported mode converters have been of the transmission type, while reflective mode converters are significantly lacking. In this paper, we propose an ultra-compact reflective mode converter (RMC) structure, which comprises a slanted waveguide surface coated with a metallic film and a subwavelength metamaterial refractive index modulation region. The results demonstrate that this RMC can achieve high-performance mode conversion within an extremely short conversion length. In the two-dimensional (2D) case, the conversion length for TE₀–TE₁ is only 810 nm, and the conversion efficiency reaches to 94.1% at the center wavelength of 1.55 μm. In a three-dimensional (3D) case, the TE₀–TE₁ mode converter is only 1.14 μm, with a conversion efficiency of 92.5%. Additionally, for TE₀–TE₂ mode conversion, the conversion size slightly increases to 1.4 μm, while the efficiency reaches 94.2%. The proposed RMC demonstrates excellent performance and holds great potential for application in various integrated photonic devices.