Fig. 4: Photonic valley demultiplexer.
From: Chiral valley edge states based on Dirac mass engineering
a Schematic diagram of a photonic valley demultiplexer. Insets: Valley Dirac masses of the three photonic crystals involved. b Simulated Ez-field profile at 5.5 GHz, excited by a point source located on the left (yellow star). c Left: Ez-field (color map) and Poynting vector (black arrows) distribution in the CPC-1@VPC-1 waveguide (framed in green box in (b)). The pink circular arrow indicates an energy vortex at the edge. Right: Measured Ez-field profile. The black circles represent the positions of rods. The asymmetric field distribution about the edge matches well with simulation result, indicating K-valley polarization of the propagating wave. d Left: Ez-field and Poynting vector distribution in the CPC-2@VPC-1 waveguide (framed in brown box in (b)). Right: Measured Ez-field profile. The symmetric field distribution indicates the K’-valley polarization. e Refraction of electromagnetic waves from the valley demultiplexer to the empty-waveguide region at 5.57 GHz. Since the edge modes lie below the light cone of air, two acrylic semi-circular lenses (n = 1.45) are positioned at the two exits to couple the beams outward. Measured Ez profiles are plotted in the right panel, aligning well with simulations. Inset: k-space analysis on the out-coupling waves. The red (blue) circles indicate the K-valley (K’-valley) momentum of edge modes, while the black circles indicate the isofrequency contours of the acrylic lenses. The conservation of the tangential component of the wave vector determines the direction of the refracted beam. f Refraction of the electromagnetic waves in another valley demultiplexer where VPC-1 in (e) is replaced by VPC-2 (orange domain).
