In photonic integrated circuits, topological photonics offers previously unknown possibilities for manipulating the direction of light flow.
A one-way street for light is possible in photonic crystals (PhCs) and other platforms with the addition of non-trivial topological phases. Light cannot be reflected in these unusual structures, similar to a strictly enforced one-way traffic lane.
However, due to inadequate topological protection, such one-way light transmission at the visible and near-infrared wavelengths may not be resistant to severe fabrication flaws. High-density topological photonic integrated circuits cannot be developed due to inadequate mode confinement and constrained bandwidth.
Tianji Liu from the Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) of the Chinese Academy of Sciences, Satoshi Iwamoto from the University of Tokyo, and Yasutomo Ota from Keio University worked together to solve these issues in a recent study published in ACS Photonics.
They numerically demonstrated the above 1,000-fold enlargement of topological bandgaps in epsilon-near-zero (ENZ) magneto-optical (MO) PhCs in comparison with the reported results gathered previously.
Triangular MO prisms with a honeycomb lattice encased in a silicon plate comprise the proposed two-dimensional MO-PhC. The opening photonic bandgaps acquire non-trivial topological characteristics when a magnetic field is introduced.
Due to very weak reactions in naturally occurring MO materials, the topological size gap is often quite tiny at visible and near-infrared wavelengths.
On the other hand, using synthetic metamaterials, MO responses can be improved by lowering the diagonal permittivity constant components of MO materials. The topological gap widths are significantly enlarged in MO-PhCs with ENZ diagonal permittivity elements as an extreme case.
Combining two ENZ-MO-PhCs with opposed magnetizations created a one-way light path. At the interface between two PhCs, numerical results for immune unidirectional and backscattering light transport were obtained. Additionally, even with substantial flaws and acute bends, the transport performance remained unaltered.
This study contributes to the understanding of certain fundamental topological photonics processes as well as the potential for improving one-way light transport performance.
Liu, T., et al. (2022) Topological Band Gaps Enlarged in Epsilon-Near-Zero Magneto-Optical Photonic Crystals. ACS Photonics. doi:10.1021/acsphotonics.1c01942.