LED-based visible light communication for color image and audio transmission utilizing orbital angular momentum superposition modes

Twisted light has recently gained enormous interest in communication systems ranging from fiber-optic to radio frequency regimes. Thus far, the light-emitting diode (LED) has not yet been exploited for orbital angular momentum (OAM) encoding to transmit data, which, however, could open up an opportunity towards a new model of secure indoor communication. Here, by multiplexing and demultiplexing red, green and blue (RGB) twisted beams derived from a white light emitting diode, we build a new visible light communication system with RGB colors serving as independent channels and with OAM superposition modes encoding the information. At the sender, by means of theta-modulation, we use a computer-controlled spatial light modulator to generate two-dimensional holographic gratings to encode a large alphabet with 16 different OAM superposition modes in each RGB channel. At the receiver, based on supervised machine learning, we develop a pattern recognition method to identify the characteristic mode patterns recorded by CCD cameras, and therefore, decoding the information. We succeed in demonstrating the transmission of color images and a piece of audio over a 6-meter indoor link with the fidelity over 96%.