Photonic Bilayer Topological Insulators From Two‐Dimensional Waveguide Arrays

Although waveguide arrays are an ideal platform for photonics, their planar geometry constrains realizations beyond two spatial dimensions. To overcome the dimensionality constraint of waveguide arrays, in this work, we exploit birefringence and develop a general framework for realizing photonic bilayer analogs. Based on this framework, we construct the Sublattice‐Rotated Birefringent Honeycomb Photonic Lattice to demonstrate the zero Berry curvature photonic quantum valley Hall effect protected by the valley Euler number and show that the two polarization components are primarily transported in opposite directions within the transverse plane as light propagates along the waveguide axis. Accordingly, this effect has potential applications in topological photonic devices, including topological beam splitters and topological polarization converters.