There is a growing interest in the application of orbital angular momentum (OAM) ranging from optical imaging, optical manipulations to quantum information science. In line with this, interest in optical communication that employs OAM as the information carrier has reinvigorated. The first visible light wireless communication was achieved by Bell in 1880 where he was able to transmit voice over 200m using sunlight. Since then, much has been published, and, with the recent trends in communication technology, demands may exceed the bandwidth of the current laser communication systems hence an alternative ought to be sought.
A plausible plethora of literature exists regarding this matter; however, majority of such work typically focuses on the utilization of commercial laser systems in implementing the optical communication. Specifically, no experimental demonstration that exploits OAM in the visible light communication has been conducted to transmit data with, for example; a white LED source. Therefore, an easier and economical light source, such as LED, should be exploited if we aim to generalize and commercialize the visible light communication technique.
In a recent paper published in Optics Express, researchers at Xiamen University led by Professor Lixiang Chen from the Department of Physics, Jiujiang Research Institute and Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices developed an effective light communication scheme with Red-Green-Blue (RGB) colors serving as independent data channels while with OAM superpositions encoding the information. The research team focused on achieving this by multiplexing and demultiplexing Red-Green-Blue twisted light beams derived from LED.
In brief, the researchers began by assembling the system they proposed and testing its functionality. Next, at the sender, by means of theta-modulation, they used 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. Concurrently, at the receiver, they developed a pattern recognition method to identify the characteristic mode patterns recorded by CCD cameras, and therefore, decoding the information. Lastly, they transmitted color images and an audio file over a 6-meter indoor link so as to test the fidelity of the system.
The authors observed that their system could effectively transmit a tri-circle of the three primary colors and an image of Albert Einstein; i.e. the system was able to send and reconstruct the RGB images effectively. In addition, they noted that their scheme had a fidelity of 96% based on the audio file and imaged transmitted. As such, they showed the potential of twisted light in visible light communication.
In summary, Yuanying Zhang and her colleagues reported successfully a new OAM-based indoor visible light communication system. In a traditional Light Fidelity (Li-Fi) system, the logical state of 1 and 0 is encoded by swiftly controlling the on and off state of LED. In contrast, they used different OAM superposition modes to realize a multi-level data encoding/decoding, and they succeeded in transmitting both the color images and a piece of audio with a relatively high accuracy, and excellent security encryption. Altogether, their work presents bright future for communication systems, although some issues need to be fully addressed before full commercialization of such a communication system.
Yuanying Zhang, Jikang Wang, Wuhong Zhang, Shuting Chen, Lixiang Chen. LED-based visible light communication for color image and audio transmission utilizing orbital angular momentum superposition modes. Volume 26, Number 13 | 2018 | OPTICS EXPRESS 17300.Go To OPTICS EXPRESS