Polarization excited optical switch based on valley topological photonic crystal.

An optical switch, which enables applications covering logical operation, channel conversion control, has attracted extensive research attentions in on-chip optical communication and network. However, in order to construct composite logic operations, traditional wavelength selective optical switches that manipulate the effective refractive index of the light field require complex system design, resulting in a large device footprint. Herein, by using unidirectional coupling excited by a chiral polarized light in the valley topological edge, we propose a 1 × 1 optical switch with a triangular resonant cavity design. The valley topological edge is constructed by breaking the spatial-inversion symmetry of hexagonal photonic crystal, and the unidirectional coupling originates from the locked phase vortex associated with the chiral polarized light (left-/right- handed circularly polarized light), which brings an extraordinary on-off contrast for optical switch. Furthermore, we introduce a 2 × 1 optical switch based on the unidirectional coupling characteristic of chiral polarized light, and verify the logic gates of NOR, AND, NAND, XOR, and OR via unidirectional coupling and frequency resonance. Benefiting from the polarization dependent unidirectional coupling characteristic, our 1 × 1 topological photonic crystal optical switch achieves a high on-off contrast of 22.8 dB. By adjusting the cavity length and implementing symmetrical design of the device, five logic gates based on 2 × 1 optical switches are realized, with logical contrasts of 5.9 dB∼19.3 dB and a footprint of less than 14.76 × 12.78 µm. Compared with traditional thermo-optic or electro-optic intensity control schemes, our proposed polarization conversion strategy opens up what we believe to be a new path and provides a technical foundation for the design of on-chip passive optical networks. This work is expected to leverage the advantages of unidirectional excitation and robustness of topological photonic crystals in device design, and promote the development of on-chip optical computing.