Optical communications—the backbone of the internet—use modulated lasers to transmit over a hundred different colored channels (using wavelength-division multiplexing) each with a hundred gigabits per second of speed. Multi-bit encoding modes—instead of just 1s and 0s—have been proven in the lab to increase throughput even further, but all suffer from errors introduced by noise in the channels, especially over free-space channels such as to satellites, submarines or even through living cells, according to researchers at the University of the Witwatersrand (Johannesburg, South Africa). Now Wits’ researchers have demonstrated a mode-division multiplexing (MDM) scheme using a quantitative measure for a vector (polarized) beam’s purity, its vector-quality factor (technically, its polarization separability) as the information carrier that can encode not just 1s and 0s, but countless modes of vector light that are virtually unaffected by channel noise.
