Winding coupling phase for pseudo-spin-derived topological photonics.

Abstract

Topological phases derived from spin or pseudo-spin typically leverage specific effects like spin-orbit interaction or antiferromagnetism. Here, we propose a flexible theoretical framework capable of designing pseudo-spin-derived topological phases. We reveal that the evanescent coupling between nearby resonators exhibits a <math xmlns="http://www.w3.org/1998/Math/MathML"> <msub><mrow><mi>π</mi></mrow> <mrow><mn>1</mn></mrow> </msub> <mrow><mo>(</mo> <mrow> <msup><mrow><mi>S</mi></mrow> <mrow><mn>1</mn></mrow> </msup> </mrow> <mo>)</mo></mrow> </math> topology characterized by a quantized coupling winding number. By tailoring the coupling winding number in photonic crystals, we propose silicon-on-insulator designs for the spin-valley Hall phase (SVHP), its anomalous variant, the anomalous Hall phase, and anti-helical edge states. Notably, the SVHP is obtained in a non-antiferromagnetic system without the need of time-reversal symmetry breaking, and the anti-helical edge states are designed independently of next-nearest coupling tuning. The results are compatible with conventional fabrication processes, demonstrating the simplicity and versatility of this framework and its potential for applications in spin-valley protected light transport and slow light guiding.