Hybrid OAM Multiplexing using Butler Matrices toward over 100 Gbit/s Wireless Transmission

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This paper presents a hybrid analog-digital architecture design of orbital angular momentum (OAM) multiplexing transmission system. Adequate function allocation to analog and digital processing can reduce the amount of digital signal processing and device expenses, so we implemented wideband Butler matrices with uniform circular arrays (UCAs), which were analog components in our hybrid system worked as discrete Fourier transform (DFT) processors to generate and separate OAM waves. Then, we introduced the mode isolation index to evaluate the performance. Consequently, our implemented Butler matrices have roughly 20 dB modes isolation, and can generate five and seven OAM modes simultaneously on 28 GHz and 40 GHz bands, respectively. Lastly, we summarize our experimental demonstrations including more than 100 Gbit/s wireless transmission using the Butler matrices on 28 GHz and 40 GHz bands.