Photonic Klein Tunnelling in Silicon Topological Materials for Terahertz 6G Interconnects

Topological photonics enables robust light transport along engineered interfaces, but transport across a potential barrier placed within such an interface, and the range of barrier strengths over which it survives, remain largely unexplored. Here we experimentally demonstrate photonic Klein tunnelling in a Complementary Metal-Oxide-Semiconductor (CMOS) compatible silicon valley photonic crystal at terahertz frequencies. A local, inversion-symmetric barrier is introduced into a valley kink channel, with its strength Δ controlled through the geometry of the triangular holes. The barrier strength is calibrated using the local Dirac-frequency shift, establishing a direct relation between photonic crystal geometry and the effective tight-binding potential. We find that transmission remains close to its barrier-free value for Δ below the nearest-neighbour hopping amplitude t, and is strongly suppressed as Δ approaches t. Momentum-space analysis shows valley pseudospin preserved to better than 98% across two cascaded barriers. We further demonstrate Klein-tunnelling transport through multibarrier, Ω-shaped and power-splitter devices, supporting terahertz data transmission at rates up to 100 Gbit s^{- 1}. Our findings underpin a new design framework for resilient and high-capacity terahertz photonic integrated circuits.