Optical integrated reconfigurable mode generator-multiplexer for radio-frequency orbital angular momentum

Radio-frequency orbital angular momentum (RF-OAM) mode multiplexing has received increasing attention in next-generation (6G) wireless communication as a new spatial multiplexing dimension to further extend data capacity. In particular, the circular antenna array (CAA) based RF-OAM generation using photonic methods is a promising approach due to its flexible reconfigurability, low propagation loss, high operating bandwidth, and high pattern quality. However, most current reports focus either on the bulk optics-based implementations or on band-limited delay line-based approaches. In this paper, we present a novel phased array-based integrated photonic RF-OAM generator-multiplexer for a four-antenna CAA system supporting three RF-OAM modes at 16 GHz for both fast mode switching and mode multiplexing. It consists of a specially designed interleaved optical filter and a four-element phased array based on cascaded phase shifters. By changing the pair of wavelengths used, the output RF-OAM modes can be quickly switched between fundamental mode and ±1 modes. A bandwidth of 1 GHz was experimentally demonstrated. Mode multiplexing can be achieved when all three wavelength pairs are loaded.