Fig. 5: Valley-locked waveguide crossing.
From: Chiral valley edge states based on Dirac mass engineering
a Spatial distributions of \({m}_{K}\left({{\bf{r}}}\right)\) and \({m}_{{K}^{{\prime} }}\left({{\bf{r}}}\right)\), forming a horizontal channel for K-valley waves and a vertical channel for K’-valley waves. b Schematic of the valley-locked waveguide crossing, consisting of two CPCs (blue and pink) and two VPCs (yellow and orange). Insets: Valley Dirac masses of the four constituent photonic crystals. c Simulated transmission spectra of the waveguide crossing with electromagnetic waves excited at port 1. The crosstalk is characterized by the difference between S41 (pink line) and S21 (baby-blue line), signifying a crosstalk level below -16.2 dB. d Measured transmission spectra for port 1 excitation, showing average crosstalk about −9.8 dB. e Measured Ez-field profile at 5.57 GHz for port 1 excitation, demonstrating smooth propagation and negligible crosstalk. f Corresponding Fourier density of the field profile in (e), further confirming the valley-locked feature of the crossing. g, h Simulated and measured transmission spectra when electromagnetic waves are excited at port 3. i, j Measured Ez-field profile and corresponding Fourier density for port 3 excitation, confirming K′-valley polarization and low crosstalk.
