Geometry-Driven Lattice of Photonic Spin-Meron Tubes in Free Space

Area of Science:

• Optics and Photonics
• Quantum Information Science
• Condensed Matter Physics

Background:

• Photonic topological structures are crucial for advanced optical devices.
• Controlling spin-angular momentum in free space is challenging.
• Existing methods often require near-field confinement.

Purpose of the Study:

• To theoretically demonstrate the first photonic spin-meron tube lattice in free space.
• To explore geometric designs for creating novel topological structures.
• To investigate material-agnostic approaches for free-space topology control.

Main Methods:

• Theoretical demonstration using spin-angular momentum vectors.
• Utilizing square-block diffraction for C4-symmetric beams with phase steps.
• Applying nonparaxial spin-orbit coupling to form meron tubes.
• Extending geometry-driven formalism for different symmetries (C3) and structures (moiré bilayers).
• Validation through Stratton-Chu theory and finite-difference time-domain (FDTD) calculations.

Main Results:

• Successful creation of finite-length meron tubes (Nsk≈±1/2) dependent on diffractive element dimensions.
• Demonstration of spin-skyrmion tubes using C3-symmetric triangular blocks.
• Observation of spin twistronics in free space using effective moiré bilayers.
• Validation of a material-agnostic, geometry-driven approach.

Conclusions:

• Geometric designs offer a powerful platform for creating free-space photonic topological structures.
• This approach enables exploration of symmetry-driven free-space topology.
• The findings pave the way for novel optical devices without near-field confinement.