In photonic integrated circuits, topological photonics offers virtually unknown possibilities for manipulating the direction of light flow. In photonic crystals (PhCs) and other platforms, a one-way street for light is now possible with the addition of non-trivial topological phases. In these strange buildings, light cannot be reflected, similar to a strictly enforced one-way traffic lane.
However, because of inadequate topological protection, such one-way light transmission at the visible and near-infrared wavelengths may not be resistant to severe fabrication defects. High-density topological photonic integrated circuit development is further hindered by inadequate mode confinement and constrained bandwidth.
In a recent study that was published in the journal ACS Photonics, LIU Tianji from the Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) of the Chinese Academy of Sciences (CAS), Satoshi Iwamoto from the University of Tokyo, and Yasutomo Ota from Keio University worked together to solve these issues by numerically demonstrating the 1,000-fold enlargement of topological bandgaps in epsilon-near-zero (ENZ) magneto-optical (MO) PhCs, in comparison to earlier published findings.
A silicon plate-embedded honeycomb lattice and triangular MO prisms make up 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 gap size at visible and near-infrared wavelengths is often quite tiny.
On the other hand, by lowering the diagonal permittivity components of MO materials, one can improve MO responses with the use of artificial metamaterials. 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 the opposite magnetization creates a one-way light path. Numerical results show that the immunological transmission of light between two PhCs is unidirectional and backscattered. Even with large-size flaws and acute bends, the transport performance remains unaffected.
This study enhances the knowledge of several fundamental topological photonics processes while also demonstrating the potential for improving one-way light transmission performance.
Liu, T., et al. (2022) Topological Band Gaps Enlarged in Epsilon-Near-Zero Magneto-Optical Photonic Crystals. ACS Photonics. doi.org/10.1021/acsphotonics.1c01942.