Tunable edge states in reconfigurable photonic crystals

We propose a reconfigurable photonic crystal based on split-ring structures, which hosts tunable edge states by controlling the rotation angle of the split-rings. The split-ring structure breaks the inversion symmetry and introduces a nontrivial Dirac mass in the otherwise gapless Dirac photonic spectrum. The sign of the Dirac mass depends on the rotation angle that thus introduces two topologically distinct phases. It is shown that an interface between two split-ring photonic crystals with opposite rotation angles supports gapped edge states. Despite the topologically trivial nature of the split-ring photonic crystal, the dispersion of the edge states is tunable through the rotation angle of the split-ring, making it useful in frequency-selective beam splitters. Our study provides an alternative way for the controlling of edge states and thus can be useful for future integrated photonic circuits.