Fig. 5: Secure communication with OCIS.

a, b Conceptual illustration. OCIS enables secure free-space optical communications between communication parties Alice and Bob. a Alice establishes optical channels between Alice and Bob by sending a laser pulse through the scattering medium. Bob measures the resultant speckle intensity pattern on the remote end to reveal the optical channels between Alice and Bob. b To send a binary message to Alice, Bob streams spatially incoherent optical pulses through different channels of the scattering medium, e.g., logical ones to randomly selected bright channels and logical zeros to randomly selected dark channels. As a result, Alice receives a matched message, while a third person Chuck receives a random message because the channels between Bob and Chuck are uncorrelated with those between Alice and Bob. c, d Experimental demonstration of the OCIS-based free-space secure communication. c A laser beam transmits through a local and a remote diffuser. A photodetector array at the remote end measures the resultant speckle pattern as the map of the optical channels. d An intensity modulator array is used to route the optical pulses to different channels based on the message and the measured channel map. Two photodetectors on the local side record the returned optical pulses. One of the photodetectors is conjugated to the laser, while the other one is placed elsewhere. e–h Experimental results. e Original binary data. f Raw data received by the conjugated photodetector. g Binarized data of (f). h Raw data received by the neighboring photodetector.