We theoretically demonstrate the first photonic spin-meron tube lattice in free space using spin-angular momentum vectors. Square-block diffraction creates $C_4$-symmetric beams with $\pi /2$ phase steps. Nonparaxial spin-orbit coupling then forms finite-length meron tubes ($N_{sk}\approx \pm 1/2$), whose length is dependent on diffractive element dimensions. Extending the geometry driven formalism, we show that $C_3$ geometry of triangular block yields spin-skyrmion tubes while effective moiré bilayer results in spin twistronics in free space without the need of strong near-field confinement. Stratton-Chu theory and full-vectorial finite-difference time-domain calculations both support this material-agnostic geometric driven approach as a platform to explore the symmetry-driven free-space topology.

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• Optical interactions with surfaces
• Spin-orbit coupling
• Structured light
• Symmetry protected topological states
• Topological effects in photonic systems
• Topological phase transition