Fig. 4
From: Pseudo-spin–valley coupled edge states in a photonic topological insulator
Topological Y-junction operating as valley filter with valley-splitting wave transport. a Schematic of the Y-junction formed by three domains. Energy is injected via port 1. Ports 2 and 3 only support K′ and K-polarized waves, respectively. The spin down state is indicated by the subscript ↓. The lower panel shows Chern numbers in three regions and the supported edge modes along the direction of the arrows. b, d The region in the red box functions as a beam filter that only passes signals carrying specific valley index. In b, the triangles inside the red box are upright, so that the \(\varphi _{K^\prime }^ \downarrow\) state can propagate freely in the direction of the arrow. d When these triangles are inverted the beam filter only supports the \(\varphi _K^ \downarrow\) state. All transmission profiles are simulated at 21 GHz. c, e Comparison of experimental valley-dependent transmission from port 1 to ports 2 and 3. Blue and red lines indicate the intensities at port 2 and port 3, respectively. Light red and light blue shaded regions indicate the bandgap of the rod-triangle region and collars-up-down region
