Ultra‐Sharp Multi‐Mode Waveguide Bending Assisted with Metamaterial‐Based Mode Converters

Abstract On‐chip multi‐mode communication has attracted much attention for its potential to greatly expand the bandwidth of data transmission. However, the application of multi‐mode transmission is still restricted since the multi‐mode waveguide can't be compactly routed, especially in the sharp bending region. The challenge lies in decreasing the significant inter‐mode coupling in the multi‐mode bending with a small radius. Few works have been reported to achieve multi‐mode bending, but all suffer from the complex fabrication. In this paper, an ultra‐sharp multi‐mode waveguide is proposed, which is assisted with metamaterial‐based mode converters. The sub‐wavelength structures are directly written onto the polymer cladding. By engineering the effective medium index of the metamaterial cladding in the mode converters, the inter‐mode coupling is dramatically inhibited. The fabricated sharp bending with a 30‐μm radius shows that the crosstalk is <−20 dB and the loss is <1 dB over a >80 nm wavelength band.