The book focuses on optical wireless communication systems. It summarises the author's work on optical wireless communication during the implementation of relevant scientific research plans. The main contents include the research status and progress of optical wireless communication, including the author's own work in this field and the research progress of domestic and foreign scholars in related fields. The key technologies, key components, modulation and coding methods, influencing factors of coherent optical communication, underwater optical communication, visible light communication, and orbital angular momentum involved in wireless optical communication are analysed, and their research progress and development trends are presented.