On-chip valley-conserved dual-polarization photonic crystal router

Photonic crystals serve as a powerful platform for guiding light in ultra-compact geometries. However, in two-dimensional photonic crystals, overlapping transverse electric (TE) and transverse magnetic (TM) bandgaps cannot be realized with identical permittivities. Here, we achieve a complete photonic bandgap on a chip by exploiting the difference in two-dimensional effective permittivities for TE and TM modes in lossless silicon photonic crystal slabs with hexagonal air holes arranged in a honeycomb lattice. We leverage the valley degree of freedom to design dual polarization waveguide modes that exist below the light cone and achieve field confinement within the photonic crystal slab. This waveguide also offers broadband transmission for both polarizations, unlike traditional narrowband TE-polarized-only valley photonic crystal with triangle air holes. We further utilize the valley-conserved properties of TE-polarized waveguide modes to design and fabricate an on-chip polarization router through interfacial engineering. Our work demonstrates one of the first experimental realizations of a dual TE/TM polarized valley photonic crystal waveguide, enabling polarization-multiplexed functionality for integrated THz photonics. This progress enables high-performance on-chip and inter-chip interconnects, underpinning future AI systems, data center scalability, and emerging 6G communication systems.