Chiral valley edge states based on Dirac mass engineering.

Valleytronics has emerged as a promising platform for energy-efficient and high-speed information processing. However, backscattering-induced valley depolarization remains a fundamental limitation, making valley-polarized waves with backscattering-free propagation highly desirable. Here, we demonstrate a general approach to realize chiral valley edge states in topological photonic crystals, which integrates the robust chiral edge states with valley degree of freedom. By controlling the valley Dirac masses, we selectively confine the chiral edge band around a single valley, enabling backscattering-free propagation while inducing valley polarization. Via engineering Dirac masses in both momentum and real spaces, we propose valley multiplexing as a novel functionality that enables independent and arbitrary control over waves with distinct valley polarizations. Moreover, two key components for valley multiplexing are demonstrated: a valley (de-)multiplexer and a valley-locked waveguide crossing, facilitating low-crosstalk signal routing. By establishing the interplay between topological quantum Hall and valley Hall phases, our work offers a new framework for robust valley-based information processing.