Compound Angular Lens for Radio Orbital Angular Momentum Coaxial Separation and Convergence

Effective separation of different modes is very important for orbital angular momentum (OAM) multiplexing systems. In this letter, a coaxial separation and convergence scheme for multiple OAM modes is proposed based on a compound angular lens (CAL) module. Whether at the transmitter or the receiver, this CAL module can implement modes division and beams convergence of multiple OAM signals simultaneously along the transmission axis. This scheme does not require the RF links compensation and complex demultiplexing algorithms, which greatly simplifies the structure of the receiver. The experimental results show that the crosstalk between multiple OAM channels can be effectively reduced. This work will have an important implication in the coaxial OAM transmission application such as the fronthaul and the backhaul.