Continuous Ring of Unidirectional Guided Resonances Induced by Isotropic Interband Coupling

Area of Science:

• Photonics
• Condensed Matter Physics
• Topological Electromagnetism

Background:

• Unidirectional guided resonances (UGRs) are topological polarization singularities with intrinsic unidirectional radiation.
• Previous research has been limited to achieving only a few discrete UGRs.
• There is a need for robust and continuous UGRs for practical applications.

Purpose of the Study:

• To demonstrate a continuous ring of UGRs.
• To explore the formation mechanism and topological properties of these UGRs.
• To provide a platform for novel photonic devices.

Main Methods:

• Fabrication of a hexagonal bilayer cylinder array.
• Theoretical analysis of isotropic interband coupling.
• Leveraging in-plane inversion symmetry-protected bound states in the continuum (BICs).

Main Results:

• Demonstrated an unprecedented continuous ring of UGRs.
• Formation governed by isotropic interband coupling, ensuring robust unidirectional emission.
• Continuous UGRs acquired topological properties from an enclosed BIC, manifesting as a phase vortex with nontrivial topological charge.

Conclusions:

• The continuous ring of UGRs offers robust, azimuthally continuous unidirectional emission.
• The topological properties derived from BICs enable a global topological charge.
• This provides a robust platform for developing devices like unidirectional vortex lasers.