The significance of optical skyrmions and the research around them cannot be overstated. Optical skyrmions which are topologically protected spin textures have attracted considerable attention due to their unique properties and potential applications in various fields. The skyrmion is a unified model of nucleons initially proposed by British particle physicist Tony Skyrme in 1962 and behaves like a nano-scale magnetic vortex with intricate textures. Meanwhile, it occupies significant positions in quantum field theory, solid-state physics, and magnetic materials. Skyrmions are widely regarded as efficient information carriers thanks to their unique topological stability, high speed, high density, and low energy consumption. However, generating optically controlled skyrmions remains a significant challenge. Breaking the limitation of topological control for skyrmions will unlock infinite possibilities for the next-generation information revolution, including applications in optical communication, information encryption, and topological phase transitions. This will present new opportunities for the expansion and practical application of advanced fundamental theories of photonics. Optical skyrmions exhibit nontrivial topological structures, robustness against external perturbations, and ultra-fast motion dynamics, serving as promising candidates for the development of novel information storage and processing technologies. Studying optical skyrmions is essential for several reasons. First, optical skyrmions provide a new paradigm for information storage with high-density and low-energy requirements. Their topological nature ensures stability against thermal fluctuations and material defects, which makes them highly reliable for long-term data retention. This property is particularly valuable in the era of big data and cloud computing, where efficient and durable information storage solutions are in high demand. Second, the unique properties of optical skyrmions make them ideal for spintronic applications. Spintronics, which utilizes the spin of electrons for information processing, has emerged as a promising field for the development of next-generation electronic devices. Optical skyrmions provide a means of manipulating and controlling spin currents, thus enabling the design of novel spin-based devices, such as spin transistors, logic gates, and memory elements, with enhanced functionality and reduced power consumption. Furthermore, the study of optical skyrmions can shed light on fundamental physics principles and contribute to our understanding of condensed matter physics. The complex interplay between spin, magnetism, and topology in optical skyrmions poses intriguing scientific challenges and opens up new avenues for exploring new phenomena. Additionally, investigating the formation, dynamics, and interactions of optical skyrmions can provide valuable insights into the fundamental laws governing quantum systems and promote the development of advanced theoretical frameworks. Meanwhile, optical skyrmions hold promise for applications in photonics and optoelectronics. The ability to control and manipulate light at the nanoscale is of significance in fields such as telecommunications, data transmission, and sensing. Optical skyrmions provide a new approach to achieving efficient light modulation, waveguiding, and information encoding, thereby enabling the development of compact and high-speed photonic devices with improved performance. In summary, the study of optical skyrmions is of paramount significance due to their potential applications in information storage, spintronics, fundamental physics research, and photonics. By unraveling the unique properties and behavior of optical skyrmions, researchers can pave the way for innovative technologies that can revolutionize various domains. Continuous exploration of this field will undoubtedly lead to exciting discoveries and transformative advancements in science and technology. In recent years, there has been a continuous emergence of optical skyrmions with different topological structures and vector configurations, including transient field skyrmions, structured medium skyrmions, free-space skyrmions, spacetime skyrmions, and momentum space skyrmions. In particular, spin skyrmions in transient fields and Stokes skyrmions in free space provide valuable references for skyrmion applications. However, the practical applications of optical skyrmions still face a series of challenges. Therefore, it is important and necessary to summarize the existing research achievements and provide more rational guidance for the future development of this field's applications.

We review the current research progress of optical skyrmions, and discuss in detail the topological structure classification of optical skyrmions, the generation and manipulation of optical skyrmions with different vector configurations, and the potential applications of optical skyrmions in micro-displacement measurement and optical communication encoding and encryption. As a result, references are provided for further development in this field. With the flourishing topological optics, the existence of optical skyrmions has been confirmed by the scientific community. In 2018, the research team led by Tsesses first realized Néel-type electric field vector optical skyrmions via surface plasmon interference excited by metal surface hexagonal grating structures [Fig. 4(a)]. Meanwhile, the research team led by Yuan realized Néel-type spin vector optical skyrmions via surface plasmon interference excited by tightly focused vector structured light fields on a metal surface [Fig. 6(a)]. Additionally, they further developed a sub-nanometer optical displacement sensing system by controlling the spin distribution of optical skyrmions on a skyrmion pair (Fig. 13), opening up the path for practical applications of optical skyrmions. In 2023, the research team led by Shen proposed a high-capacity optical communication and secure encryption scheme based on optical topological quasi-particles, with the reliance on Stokes vector optical skyrmions (Fig. 14). Currently, optical skyrmions with different topological structures and vector configurations continue to emerge, providing new ideas and methods for the study of spatio-temporal characteristics of topological structured light fields.

Optical skyrmions have become a major focus in the research on topological optics. Skyrmions can be formed and controlled within optical fields, and the development of high-dimensional structured light provides possibilities for constructing complex topological structures of high-dimensional skyrmions. In conclusion, if the topological limitations of skyrmions can be overcome to achieve freely controllable topological states, infinite possibilities will be posed to the next-generation information revolution. Applications such as optical communication, information encryption, spin-orbit interactions, and topological phase transitions will benefit from the expansion and practical applications of advanced photonics fundamentals.