The topology-induced phase transition (TPT) in spin-orbit optics refers to a process of topological transition from one kind of spin-orbit interaction (e.g., spin-controlled vortex generation) to another (e.g., photonic spin-Hall effect). However, it is not clear in the TPT how a light beam evolves from a vortex state with a topological charge of ±2 to nonvortex states with spin-Hall shifts. Here, we examine the orbital angular momentum content (vortex harmonics) of a typical TPT process, i.e., the spin-orbit interactions of a light beam transmitted through an optically thin slab, based on vortex mode decomposition. It is found that the two kinds of spin-orbit interactions and the intermediate states can be described in a unified framework by considering the superposition and competition of three vortex modes with topological charges of 2, 1, and 0 (or −2, −1, and 0). These findings provide an alternative perspective for understanding the two spin-orbit interactions of light in a unified form and can be extended to the TPT-like processes in other physical systems.

• Received 19 July 2021
• Accepted 22 October 2021

DOI:https://doi.org/10.1103/PhysRevA.104.053504