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Recently, communication capacity has increased significantly due to diversification of contents, and online classes and teleworks emerging from the spread of COVID-19. Furthermore, technological development of sixth-generation mobile communication system (6G) has planned in 2030, it is predicted that communication capacity increase more in the future. For the realization of 6G, not only a large capacity of backhaul, but also an all-optical network is required owing to high frequencies. To satisfy these requirements, orbital angular momentum (OAM) in optical wireless communication has been investigated. The OAM is a part of the Laguerre-Gaussian (LG) beam, which possesses modes that are determined by the radial order n and the azimuthal order m. The OAM is modes when the radial order n is equal to zero. Because crosstalk between the modes are inevitable, it is necessary to separate orders during multiplexing. Therefore, the LG mode that has been extended to the radial order n must be used for mode multiplexing in order to achieve large communication capacity. For realizing multiplex communication, the multiplexed signal must be separated into individual detectors. Previous studies have reported a method for separating signals using light as the carrier wave in multiplex communication, by preparing the same number of filters as the number of multiplexes. However, the system becomes more complex and reception efficiency deteriorates as the number of multiplex increases. In this study, we achieved mode-demultiplexing with one filter using kinoform-type computer generated holograms as multiplexed holograms in LG mode multiplex communication.
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