One of the significant challenges in photonics is the on-chip integration of all-optical control, for which polaritonic fluids offer a promising solution. Polaritons enable the condensation of polaritons, which transforms a two-dimensional dilute photon gas into a high-density, highly coherent optical fluid with nonlinear interactions. Throughout the condensation process, the lifetime and coherence of polaritons improve significantly, thus facilitating the observation of their trajectories and the temporal evolution of their spin states. Furthermore, injecting photons with specific spin and momentum into microcavities via resonant excitation allows targeted investigation of photon transport and evolution processes, thereby realizing phenomena such as photonic topological insulators and the Hall effect.

In this paper, we systematically summarize studies pertaining to the spin‒orbit coupling effects of photons and excitons in Fabry‒Perot (F‒P) optical microcavities. Initially introduced in electronic systems, the concept of spin‒orbit coupling has been extended to cold atoms, free space, surface plasmons, metasurfaces, and finally to cavity polaritons. The second section briefly introduces F‒P optical microcavities and exciton polaritons. Subsequently, the third section focuses on the fundamental principles of TE‒TM mode splitting in microcavities, which generates an equivalent photon magnetic field, and summarizes a series of research advances pertaining to spin‒orbit coupling effects induced thereby. Subsequently, recent spin‒orbit coupling mechanisms are detailed, including those induced by external magnetic fields breaking time-reversal symmetry, material anisotropy, and their combined modulation with magnetic fields. These mechanisms yield diverse effective gauge fields corresponding to different photon physical processes and applications. An external magnetic field enhances the oscillator strength of excitonic components in polaritons, thus resulting in Zeeman splitting and breaking time-reversal symmetry; consequently, chiral symmetry breaking is realized via TE‒TM mode splitting. By contrast, anisotropy-induced Zeeman splitting in materials preserves time-reversal symmetry, thus resulting in emergent optical activity. In such microcavity systems, emergent optical activity, TE‒TM mode splitting, and linear birefringence from material anisotropy combine to form an effective photon gauge field. The subsequent section discusses the spin‒orbit coupling of polaritons in potential fields partitioned into confined potential fields, such as open microcavities. Notably, tunable open F‒P optical microcavity systems developed in recent years utilize concave and planar mirrors, thus facilitating their integration with emissive materials and realizing the dual tunability of resonance frequency and spatial position. Compared with two-dimensional photons in planar microcavities, confinement potential fields introduce orbital angular momentum, thus generating optical modes such as LG modes and the polar distributions of spin vortices. TE‒TM mode splitting in bound potential fields is coupled with photon spin, thereby resulting in the spin‒orbit coupling of photons and numerous new physical phenomena. The second section discusses periodic potential fields based on photonic-crystal topological insulators, which control polariton wave functions via spatially periodic optical structures in microcavities.

The spin‒orbit coupling of polaritons in microcavities is affected by several key factors. First, the intrinsic TE‒TM mode splitting within the microcavity creates an effective photon magnetic field. Second, the applied magnetic fields induce Zeeman splitting in polariton excitonic components, thus breaking time-reversal symmetry. Material anisotropy further complicates spin‒orbit coupling by varying the photon gauge field. Additionally, confining and periodic potential fields within microcavities are crucial for manipulating spin‒orbit coupling, which can generate novel photon gauge fields. These factors collectively result in the complex behavior of spin‒orbit coupling in microcavity polaritons, thus offering abundant possibilities for on-chip optical systems.

Notably, strong nonlinear interactions of polaritons enable all-optical manipulation of spin‒orbit coupling effects on-chip. Concentration gradients induce effective photon gauge fields that affect spin‒orbit coupling, thereby altering the system's Hamiltonian. Thus, the spatial modulation of pump light intensity enables the on-chip control of spin‒orbit coupling effects. After polariton condensation, the dissipation rates and concentrated energy are reduced, which can modify the original non-Hermitian system, thus potentially altering or eliminating singular points and achieving non-Hermitian properties in on-chip optical control systems.