The spin-orbit interaction of light refers to the interaction between the spin angular momentum and the orbital angular momentum of light, which exists in basic optical processes such as reflection, refraction, scattering, diffraction, and focusing. In traditional large-scale classical optics, the influence of spin-orbit interaction can be ignored, but at sub-wavelength scales, strong coupling between spin and orbital angular momentum occurs. This article reviews the basic origins and important applications of the spin-orbit interaction of light. Firstly, two important basic concepts of photon spin-orbit interaction, photon angular momentum and geometric phase theory, are introduced. Secondly, two types of spin-orbit interactions, spin-intrinsic orbit interaction and spin-extrinsic orbital angular momentum interaction, are briefly introduced respectively. Then, the research progress and representative applications of photon spin-orbit interaction are mainly introduced. Finally, the challenges and future research directions of the research on the spin-orbit interaction of light are prospected.

Optical beam can carry both spin angular momentum and orbital angular momentum. Since its concept was proposed by Allen et?al in 1992, optical orbital angular momentum has attracted more and more interests. Optical orbital angular momentum has the characteristics of infinite bandwidth and orthogonal modes, which makes it a promising technology to transmit information. Firstly, the basic concept of optical orbital angular momentum is summarized. And then the generation of orbital-angular-momentum multiplexed entanglement source based on four-wave mixing process in continuous variable system is mainly reviewed, including the deterministic generation of 13 pairs of multiplexed continuous variable entanglement, the implementation of 9 sets of orbital-angular-momentum multiplexed tripartite entanglement and the realization of large-scale quantum network over 66 orbital angular momentum optical modes. Furthermore, the latest application of optical orbital angular momentum multiplexing entanglement source is also introduced, including the realization of 9 channels of all-optical quantum teleportation by utilizing the orbital-angular-momentum multiplexed continuous variable entanglement and the experimental implementation of the orbital-angular-momentum multiplexed quantum dense coding.

The correlation feature of quantum light field is an important subject of quantum optics research. With the in-depth study on the subject, the researchers have also made a series of great progress in the correlation of classical light. Especially, by combining the orbital angular momentum of light, which has drawn much attention in the recent 20 years, a series of counterparts of high-dimensional quantum light have been observed. In this review, the related research of classical optical correlation in orbital angular momentum beams is summarized, the local inseparability in orbital angular momentum and its application are introduced, and the classical optical correlation in spatially separable orbital angular momentum is discussed as well. In particular, as a potential quantum process research platform, the random walk research based on the orbital angular momentum of classical light is also introduced.

Vortex field is a kind of special structured light field with spiral wavefront, which is widely used in optical micromanipulation, large-capacity optical communication and super-resolution imaging due to its physical properties such as phase singularity, orbital angular momentum and central dark core structure. By modulating the traditional physical dimensions of vortex field (amplitude, polarization and frequency), the novel vortex fields with richer modes and wider application can be obtained. In addition, there is a very important regulation dimension of vortex field, that is coherence. Recently, researchers have obtained a novel type of vortex field, namely partially coherent vortex beam, by adjusting the coherence of vortex beam. Compared with fully coherent vortex beam, partially coherent vortex beam has more advantages in some fields, such as higher disturbance resistance to turbulent atmosphere, richer beam shaping, higher self-reconstruction ability and stronger particles trapping ability. In this paper, the research progress of the partially coherent integer vortex beams and the partially coherent fractional vortex beams in recent years is reviewed, and the theoretical model, generation method, transmission characteristics, topological charge measurement and application of partially coherent vortex beam are described in detail.

Photon carries orbital angular momentum (OAM), which manifests as a helical phase distribution in the wavefront. Because of its unique optical field distribution and physically-unbounded OAM state, OAM beam plays an important role in super-resolution imaging, high-density data coding and other fields. The study on the new mechanisms of OAM beam-matter interaction at nano structures is expected to provide new ideas and methods for the fields of modern photonic devices and multidimensional light-matter interaction. The applications of OAM beams in multidimensional multiplexing as well as the detection technologies of OAM topological charges developed by the authors’ group are reviewed, and an outlook onthe application of OAM beams at nanoscale is also presented.

Perfect optical vortex beam (POVB) is a specific kind of vortex beam with radial intensity distribution and radius both independent of the orbital angular momentum (OAM) states, which has been applied in optical manipulation, optical communication, laser material processing and so on. The detection of OAM states of POVB is critical and challenges remain. A diffractive optical neural network (DNN) has been constructed based on the parallel gradient descent algorithm, and the recognition of the POVB with OAM order ranging from-50 to +50 has been realized experimentally. In this process, the diffraction conversion efficiency can reach up to 58%. This work provides a new method for OAM detection of POVB and shows great potential in various POVB-based applications.

Conventional measurements of optical chirality are based on the response difference of material to the left- and right-handed circularly polarized light. Circularly polarized state of light carries spin angular momentum (SAM) of photons. Orbital angular momentum (OAM) introduces a new degree of freedom of light. For chiral measurement, OAM of photons can be exploited in new methods for the study of the chirality of substances. In this review, starting with the basic concepts of SAM, OAM and optical chirality, the chirality measurement methods based on the OAM of photons in recent years are summarized. These latest developments show that the chiral signal of conventional circular dichroism can be enhanced by the light with OAM. On the other hand, based on the spin-orbit coupling effect and the high order interaction between light field and electric quadrupole of molecules, chiral signals can be measured by directly switching the sign of OAM of photons. In addition, light with high-order OAM state is helpful to improve the chiral response of particles with size larger than wavelength. Finally, the recent progress on spatiotemporal optical vortex and its potential applications on chiral measurements are also presented.

Vectorial vortex beam possesses unique advantages in the fields of micro optical manipulation and optical communication. Rotational Doppler effect is usually applied in the researches of topological charges of optical vortex, and analysis of rotational Doppler effect of vectorial vortex beam is meaningful to deduce properties of polarization. Here a method to discriminate the direction of rotation of cylindrical vector beams is proposed based on rotational Doppler effect. In the method, the scattered light of an incident vectorial vortex beam carries beating signal whose intensity changes periodically with time due to Doppler frequency shift. The phase of the beating signal variation function depends on equator angle of vectorial vortex on high-order Poincaré sphere and the slope of the function depends on topological charge of optical vortex. The measurement theory of beating signals of two vectorial vortex beams with opposite handnesses are proposed and experimentally verified, which provides a new effective method to measure the signs of topological charges of cylindrical vector beams.