Local orbital-angular-momentum dependent surface states with topological protection

Area of Science:

• Photonics
• Condensed Matter Physics
• Electromagnetism

Background:

• Valley photonic crystals in honeycomb lattices host unique edge states.
• Chirality and orbital angular momentum (OAM) are key properties influencing wave propagation.

Purpose of the Study:

• To demonstrate and characterize chiral surface states along the zigzag edge of a valley photonic crystal.
• To investigate the influence of OAM on the unidirectional propagation of these states.
• To explore the robustness of unidirectional propagation around structural bends.

Main Methods:

• Decomposition of local electromagnetic fields into orbital angular momentum (OAM) modes.
• Quantification of propagation directivity based on local OAM.
• Analysis of chiral surface state propagation through sharp bends.

Main Results:

• Chiral surface states exhibit OAM-dependent unidirectional propagation.
• Propagation directivity is controlled by the chirality of both the source and the surface states.
• Unidirectional propagation is maintained through sharp bends due to topological properties.

Conclusions:

• Demonstrated engineered control of unidirectional electromagnetic energy flow without ancillary cladding.
• Validated the role of topology in maintaining directional propagation in chiral photonic systems.
• Opened avenues for novel photonic devices with tailored energy transport.