Broadband low-crosstalk compact waveguides enabled by anisotropic metamaterial substrate.

Reducing crosstalk between waveguides is an essential and viable strategy for enhancing integration density in photonic chips. Traditional approaches to crosstalk suppression primarily focus on engineering cladding layers. Here, we demonstrate that engineering substrate also plays a very critical role in mitigating waveguide crosstalk. We find that properly designed anisotropic metamaterial substrate can significantly suppress evanescent waves within the substrate that couple into adjacent waveguides across a broad wavelength spectrum, thereby facilitating broadband crosstalk suppression. Specifically, two coupled silicon strip waveguides with a center-to-center distance of 840 nm are designed to exhibit crosstalk below -20 dB for the fundamental mode within the wide wavelength range of 1300∼1637 nm. This strategy is also applicable to bending waveguides and waveguide arrays. Our work underscores the substantial influence of metamaterial substrate and paves the way toward ultra-compact integrated photonic chips.