Graphene-assisted hybrid photonic crystal with a VO 2 defect for switchable reflection and tunable nonreciprocal multi-channel THz absorption

We propose a thermally and electrically tunable terahertz (THz) device based on a graphene–VO 2 hybrid one-dimensional photonic crystal (1DPC) of the form G(AB) N VO 2 (BA) N . Owing to the insulator–metal phase transition of VO 2 , the structure behaves as a high-reflectivity mirror at the insulating phase ( T = 300 K ), while at the metallic phase ( T = 350 K ) it transforms into a reconfigurable multichannel absorber. The number of absorption channels is deterministically governed by the periodicity: for N ≤ 4, each period introduces one resonance; at N = 5, five resonances emerge with four showing absorption above 0.88; for 5 ≤ N ≤ 10, the highest-frequency mode gradually vanishes, yielding N − 1 channels; and for 11 ≤ N ≤ 13, suppression of the lowest-frequency mode results in N − 2 channels, reaching up to eleven modes at N = 13. Removing graphene collapses the response to a single absorption peak, confirming its essential role in multichannel formation through plasmonic loss. The device also exhibits robust angular and polarization stability, preserving high absorption for all channels up to , while TE-polarized modes maintain near-unity absorption for higher-order peaks. In addition to thermal and geometric tunability, electrical gating of graphene enables continuous frequency shifts of 1.6–9.6% per eV and controllable redistribution of modal absorption strength. Furthermore, due to the asymmetric placement of graphene, the structure displays pronounced unidirectional nonreciprocity: forward incidence supports multichannel absorption, whereas backward incidence yields only a single resonance for N = 4–7 and no resonances for other N , demonstrating unidirectional THz absorption without magnetic bias or temporal modulation. By synergistically combining VO 2 phase switching, graphene electro-optic control, and periodicity engineering, the proposed platform enables multifunctional THz operation, ranging from single-mode and multimode absorption to direction-dependent nonreciprocal absorption, within a compact and reconfigurable 1DPC architecture.