Metamaterial‐Based Maxwell's Fisheye Lens for Multimode Waveguide Crossing

Abstract On‐chip multimode transmission has drawn tremendous interest for its ability to expand the link capacity with a single wavelength carrier. The waveguide crossing is a basic component in the on‐chip photonic circuit allowing the routing of a complex network. The situation has arisen where the multimode waveguide crossing is required to achieve the high‐density multimode networks. However, the conventional designs of the waveguide crossing only work for the single‐mode. Some works have been reported which realize the multimode crossing, but all suffer from significant losses. Here a multimode waveguide star‐crossing is proposed using the metamaterial‐based Maxwell's fisheye lens, where four multimode waveguides converge at a single junction. The index‐engineered silicon metamaterial is utilized to obtain the Maxwell's fisheye lens on the silicon‐on‐insulator platform. By combining the Maxwell's fisheye lens and tapered waveguides, both TM 0 and TM 1 modes propagate through the star‐crossing with low losses and cross talk. The fabricated multimode waveguide star‐crossing shows low losses of <0.3 dB and cross talk of <‐20 dB.