Efficient Dense Orbital Angular Momentum Demultiplexing Enabled by Quasi-Wavelet Conformal Mapping

Orbital angular momentum (OAM) has recently attracted increasing interest in optical communications for capacity scaling by OAM mode-division multiplexing (MDM). OAM (de)multiplexer is crucial to the success of OAM-MDM communications. Scalable and efficient dense OAM demultiplexing is highly desired, but full of challenges. Here, a quasi-wavelet conformal mapping method is proposed and demonstrated to implement scalable and efficient dense OAM demultiplexing. The OAM mode is divided at the input plane into multiple concentric rings, which are mapped to multiple tilted plane waves and arranged side by side in a line. The engineered transformed light beams with periodic extension and increased length enable narrow focused spot width, reduced beam overlap, and suppressed demultiplexing crosstalk. The quasi-wavelet conformal mapping method is compared with conventional log-polar transformation scheme and hybrid log-polar and fan-out technique, and the crosstalk matrix for OAM demultiplexing is measured. Efficient OAM demultiplexing is demonstrated for 15 OAM modes (OAM(-7) to OAM(+7)) with a maximum crosstalk of -12.1 dB in the experiment. Moreover, the method is also applied to system-level data-carrying OAM-MDM communications with favorable performance. The demonstrated quasi-wavelet conformal mapping method may pave the way for future ultrahigh capacity dense OAM-MDM communications with a large number of OAM modes.