Observing 0D subwavelength-localized modes at ~100 THz protected by weak topology

Area of Science:

• Photonics
• Condensed Matter Physics
• Materials Science

Background:

• Topological photonic crystals (TPhCs) offer robust light manipulation, immune to defects.
• Weak topology in TPhCs with dislocations enables protected localized modes.
• Demonstrating weak topology TPhCs at optical frequencies remained a challenge.

Purpose of the Study:

• To experimentally verify mid-bandgap zero-dimensional light localization in a weak topology TPhC at optical frequencies.
• To investigate the effect of dislocation geometry on light localization in such systems.
• To establish a foundation for TPhCs based on weak topology in advanced photonic applications.

Main Methods:

• Utilized scattering-type scanning near-field optical microscopy (s-SNOM) for high-resolution optical measurements.
• Fabricated a TPhC with a nontrivial Zak phase and an edge dislocation.
• Employed full-field simulations to support experimental findings.

Main Results:

• Observed and verified mid-bandgap zero-dimensional light localization near 100 THz.
• Demonstrated that dislocation geometry has minimal impact on the strength of light localization due to weak topology.
• Confirmed the robustness of light localization, consistent with topological protection.

Conclusions:

• First experimental demonstration of weak topology TPhCs at optical frequencies.
• Established strong and robust light localization in TPhCs with dislocations.
• Paved the way for applications in active topological nanophotonics, nonlinear, and quantum optic integrated devices.