Demonstration of 12.8-bit/s/Hz spectral efficiency using 16-QAM signals over multiple orbital-angular-momentum modes

We demonstrate an approach of four-mode multiplexing/demultiplexing using orthogonal Laguerre-Gaussian modes carrying orbital angular momenta. High spectral efficiency of 12.8-bit/s/Hz is achieved using 10.7-Gbaud 16-QAM signals over four Laguerre-Gaussian modes. Crosstalk <;-20 dB and OSNR penalty <;2.4 dB are achieved.