Experimental demonstration of a 200-Gbit/s free-space optical link by multiplexing Laguerre-Gaussian beams with different radial indices.

We demonstrate a 200-Gbit/s space-division multiplexing system using two Laguerre-Gaussian (LG) beams with different radial indices (LG_ℓ=0,p=0 and LG_ℓ=0,p=1). With a proper design of the radial change of the demultiplexing pattern, the channel crosstalk could be minimized and both channels could achieve a bit error rate of 3.8×10^-3. Moreover, the multiplexing of four LG beams with different azimuthal indices and different radial indices (e.g., LG_ℓ=0,p=0, LG_ℓ=0,p=1, LG_ℓ=1,p=0, and LG_ℓ=1,p=1 beams) is also demonstrated with a <-12  dB channel crosstalk, potentially enabling a 400-Gbit/s data transmission.