Experimental observation of metamaterial-enabled high-density waveguides with low crosstalk

Crosstalk in densely spaced waveguides fundamentally constrains the integration density of photonic circuits. Although various strategies exist to mitigate crosstalk for transverse-electric (TE) modes, suppressing transverse-magnetic (TM) mode crosstalk remains challenging due to the weaker optical confinement of TM modes. Here, we address this challenge by introducing an anisotropic metamaterial between waveguide cores and the substrate, which effectively suppresses TM-mode crosstalk and enables dense waveguide integration. This mechanism is confirmed through both proof-of-principle microwave experiments and numerical simulations of on-chip silicon strip waveguides. We show that with a center-to-center separation of 1200 nm—nearly half the distance required by conventional waveguides—the designed silicon strip waveguides exhibit crosstalk below −20 dB for both fundamental TM and TE modes across a broad wavelength range from 1440 to 1555 nm. Our approach not only enhances the performance and integration compatibility of TM-mode-based photonic devices but also provides a viable pathway toward ultracompact, polarization-multiplexed integrated photonic circuits.