Bo Wang

Tailored photonic spin-orbit interactions (SOIs) in structured nanophotonic systems provide a powerful platform for controlling spin-dependent light-matter interactions. By engineering structural symmetry or geometric phases in photonic crystals and metasurfaces, photonic SOIs give rise to spin-dependent dispersion, spin-momentum locking, spin-textured dynamics, and nontrivial topological states. In this review, we first discuss the design principles of emerging spin-engineered nanophotonic structures, particularly geometric-phase photonic crystals, within a general perturbative framework. We then review representative spin-valley functionalities enabled by integrating these structures with transition metal dichalcogenide monolayers, where intrinsic spin-valley locking establishes versatile interfaces for coherent manipulation of both photonic spin and electronic valley pseudospin. Finally, we briefly discuss emerging opportunities for integrated quantum light sources enabled by photonic SOIs. These developments establish photonic SOIs as a versatile route toward coherent, nonlinear, topological, and quantum nanophotonic devices.

We report that optical quasisymmetry groups emerge from the commutation between mirror operation and spin-orbit interaction (SOI) of light. Contrary to the principle of symmetry inheritance in free-space optics—where the symmetry of any structured field is strictly constrained by that of its source—we show that strong SOI enables quasi-symmetry-protected formation of topological lattices even when the underlying optical sources violate the nominal rotational symmetry. By analyzing the Hermiticity of the electric-dipole radiation amplitude in a circular polarization basis, we derive an effective mirror operator acting only on a subset of C 3 polarized dipole emitters, forming a quasisymmetry group that commutes with SOI. This quasisymmetry guarantees exact C 3 merons and gives rise to a robust polarization zone within which continuously varying input polarizations generate identical topological textures. Our work establishes quasisymmetry as a fundamental principle in optical physics and opens pathways to engineered topological structures of light beyond conventional symmetry constraints.

Ultrafast manipulation of polarization provides a powerful approach to controlling light–matter interactions on femtosecond timescales. Here, we demonstrate the generation of photon spin‐waves—spatiotemporal oscillations of the spin angular momentum of light—arising from the beating of non‐degenerate orthogonally polarized modes in photonic crystal cavities. To capture this phenomenon, we develop a polarization‐dependent quasi‐normal‐mode (QNM) theory to describe the temporal polarization dynamics of pulsed excitation in anisotropic nanocavities, predicting ultrafast oscillations of the Stokes parameters. Numerical simulations confirm that slight structural perturbations lift the degeneracy, producing sub‐picosecond spin oscillations that are tunable by cavity geometry. Remarkably, the oscillating spin is coupled to the far field, giving rise to propagating photon spin‐waves at the tails of transmitted pulses. We further verify the generality of this mechanism by investigating photon spin‐wave generation in square‐lattice photonic crystals. Our work reveals a compact and versatile platform for engineering ultrafast spin dynamics of light, with promising applications in chiral light–matter interaction, ultrafast magnetism via the inverse Faraday effect (IFE), photonic spin angular momentum information processing, and ultrafast spin‐lasers.

Cavity quantum electrodynamics (cQED) harnesses light-matter interactions to produce nonclassical light states. However, a fundamental challenge lies in simultaneously achieving Purcell enhancement and tailored wave front control within a single cavity, due to conflicting resonator requirements. Here, we overcome this limitation by demonstrating triggered single-photon emission with customizable wave fronts from semiconductor quantum dots embedded in geometric-phase metacavities. These monolithic devices-only 200 nm thick-deliver Purcell-enhanced emission alongside spin-momentum-locked radiation, vortex beams, and holographic patterns depending on the design. The meta-atom lattice provides high-Q optical confinement, while spatially modulated orientations of the elliptical holes enable efficient outcoupling of photons with designed states. This Letter establishes a new paradigm for intrinsically multiplexing metasurface-based wave front shaping with cQED, enabling high-performance quantum light sources from subwavelength-scale monolithic platforms.

Optical nonlinear processes are fundamental to numerous applications, from frequency conversion to quantum technologies. Although subwavelength integrated photonic structures can enhance nonlinear interactions, they rarely exploit the broad oblique wavevector components of tightly focused pump beams, restricting the nonlinear conversion efficiency. Here, we demonstrate efficient second-harmonic generation (SHG) pumped by tightly focused beams containing broad oblique wavevector components in thin-film lithium niobate (TFLN) moiré superlattice microcavity. Specifically, we experimentally achieve flatband enhanced SHG in a 4.41°-twisted moiré cavity with a high quality (Q) factor of ∼1100 and a normalized SHG conversion efficiency of (2.1 ± 0.4) × 10^–4 cm²/GW at an extremely low pump power density of 1.1 ± 0.2 MW/cm². The synergy of high Q, flatband dispersion, and broad angular acceptance maximizes pump utilization, enabling high-efficiency nonlinear conversion. This breakthrough establishes TFLN moiré superlattices as a versatile platform for compact, integrated nonlinear photonics and next-generation quantum light sources.

High-speed thin-film lithium niobate (TFLN) electro-optic modulators are essential for next-generation photonic integrated circuits. We demonstrate a high-performance TFLN Mach–Zehnder modulator on a thick silica buried layer using periodic capacitively loaded traveling-wave electrodes. Our design simplifies fabrication compared to undercut silicon or quartz substrates while enhancing modulation efficiency. The fabricated device achieves a modulation efficiency of 1.25 V·cm in the C-band with only 1.3 dB roll-off at 67 GHz, successfully overcoming the voltage-bandwidth trade-off. This work provides a streamlined, scalable approach for high-performance TFLN modulators, supporting advanced optical communications and signal processing.

We introduce quasi-symmetry groups in optics emerging from the commutation between mirror operation and the spin-orbit interaction (SOI) of light. Contrary to the principle of symmetry inheritance in free-space optics, where the symmetry of any structured field is strictly constrained by that of its source, we show that strong SOI enables quasi-symmetry-protected formation of meron lattices even when the underlying optical sources violate the nominal rotational symmetry. By analyzing the Hermiticity of the electric-dipole radiation amplitude in a circular polarization basis, we derive an effective mirror operator acting only on a subset of C3 polarized dipole emitters, forming a quasi-symmetry group that commutes with SOI. This quasi-symmetry guarantees exact C3 merons and gives rise to a robust polarization zone within which continuously varying input polarizations generate identical topological textures. Our work establishes quasi-symmetry as a new fundamental principle in optical physics and opens pathways to engineered topological structures of light beyond conventional symmetry constraints.

We present a novel photonic Ising machine based on Sidon set, which demonstrates a record-high coupling resolution. These results pave the way toward Ising machines capable of faithfully modeling real-world optimization problems.

Brownian systems are characterized by spatiotemporal disorder, which arises from the erratic motion of particles driven by thermal fluctuations. When light interacts with such systems, it typically produces unpolarized and uncorrelated fields. Here we report the observation of a large-scale spin-locking effect of light within a Brownian medium. In an observation direction perpendicular to the incident wave’s momentum, scattering naturally divides into two diffusion regions, each associated with an opposite spin from the Brownian nanoparticles. This effect arises from the intrinsic spin–orbit interactions of scattering from individual nanoparticles, which ubiquitously generate radiative spin fields that propagate through the Brownian medium with multiple incoherent scattering. It offers an experimental platform for exploring macroscale spin behaviour of diffused light, with potential applications in precision metrology for measuring various nanoparticle properties. Our findings may inspire the study of analogous phenomena for different waves from unusual spin–orbit interactions in complex disordered systems.

Ising machines have emerged as promising platforms for efficiently tackling a wide range of combinatorial optimization problems relevant to resource allocation, statistical inference and deep learning, yet their practical utility is fundamentally constrained by the coarse resolution of spin-spin couplings (Jij). Current implementations, relying on direct modulation of physical parameters, achieve at most 256 discrete coupling levels, which severely hinder the faithfully modeling of arbitrary real-valued interactions in realistic applications. Here we present a novel photonic Ising machine that encodes spins in random lattices while programming couplings in the momentum space of light. By introducing the Sidon set-a mathematical structure ensuring pairwise difference uniqueness - and employing the Erdos-Turan bound, we establish an optical framework in which each spin pair can be assigned a unique Jij. This approach decouples the resolution limit from hardware modulation to the spatial precision in the momentum space of light. Experimentally, we demonstrate a record-high coupling resolution of 7,038 on a simple photonic platform, surpassing previous Ising machines. Our results highlight the power of uniting discrete mathematics with momentum-space photonics, paving the way toward scalable Ising machines capable of faithfully modeling real-world optimization problems.