Metamaterial-waveguide bends with effective bend radius < λ_0/2

We designed, fabricated, and characterized broadband, efficient, all-dielectric metamaterial-waveguide bends (MWBs) that redirect light by 180 deg. The footprint of each MWB is 3  μm×3  μm and redirection is achieved for single-mode waveguides spaced by 1.3 μm, which corresponds to an effective bend radius of 0.65 μm (<λ₀/2 for λ₀=1.55  μm). The designed and measured transmission efficiencies are >80% and ∼70%, respectively. Furthermore, the MWBs have an operating bandwidth >66 nm (design) and >56  nm (experiments). Our design methodology that incorporates fabrication constraints enables highly robust devices. The methodology can be extended to the general routing of light in tight spaces for large-scale photonic integration.