  In the age of information explosion, the conventional optical communication
protocols are rapidly reaching the limits of their capacity, as almost all
available degrees of freedom (e.g., wavelength, polarization) for division
multiplexing have been explored to date. Recent advances in coherent mode
division multiplexing have greatly facilitated high-speed optical
communications and secure, high-capacity information storage and transfer.
However, coherent mode division multiplexing is quite vulnerable to even minute
environmental disturbances which can cause significant information loss. Here,
we propose and experimentally demonstrate a paradigm shift to incoherent mode
division multiplexing for high-security optical information encryption by
harnessing the degree of coherence of structured random light beams. In
contrast to the conventional techniques, our approach does not require mode
orthogonality to circumnavigate unwanted mode crosstalk. In addition, our
protocol has, in principle, no upper bound on its capacity. Thanks to the
extreme robustness of structured random light to external perturbations, we are
able to achieve highly accurate information encryption and decryption in the
adverse environment. The proposed protocol opens new horizons in an array of
fields, such as optical communications and cryptography, and it can be relevant
for information processing with acoustical, matter as well as other types of
waves.
