New multi-channel visible light communication system uses a single optical path

The new design saves cost and space, could lead to light-based compact computer processors

WASHINGTON — Researchers have demonstrated a new visible-light communication system that uses a single optical path to create a multi-channel communication link over the air. This approach could be used as a backup communication link or to connect IoT devices.

Caption: Researchers have created a multi-channel communication system using a single optical path. It contains blue-emitting MQW III nitride diodes placed between two green diodes in a single optical path. A coating on each diode chip blocked blue light while letting green light through, creating separate green and blue optical paths. T: transmitter, R: receiver, PRBS: pseudo-random binary sequence.

Image Credit: Yongjin Wang, Nanjing University of Posts and Telecommunications

“Today’s free-space optical communication systems typically use two separate links with separate optical paths to establish two channels,” said research team leader Yongjin Wang from the University of Posts and Telecommunications. from Nanjing in China. “This new mode of communication can save half the channel space, cost and energy by using a single link.”

The researchers describe their new approach in the journal Optica Publishing Group Optics Letters. It is based on devices called multiple quantum well (MQW) III-nitride diodes that can emit and detect light at the same time.

“This technique could allow light-based communication functions to be highly integrated on a chip, which could also be used to reduce the size of printed circuit boards, making them cheaper and more portable,” Wang said. . “Ultimately, we would like to develop a photonic processor based on this mode of communication.”

Crosstalk cancellation

MQW III-nitride diodes are on-chip devices that exhibit a region of overlap between the wavelengths they emit and sense. This allows them to be used simultaneously as a transmitter and receiver in a light-based wireless communication system. These diodes also have a variety of emitting, transmitting, modulating, and light sensing functions that make them useful for this application.

In the new work, the researchers used blue- and green-emitting MQW III nitride diodes to create a single-link communication system capable of transmitting and receiving information over multiple channels. This required figuring out how to prevent crosstalk from occurring between the different optical signals.

They achieved this by designing a setup with two blue-emitting MQW III nitride diodes placed between two green diodes in a single optical path. Each diode chip was coated with a Distributed Bragg Reflection (DBR) coating that blocked blue light while letting green light through. This created a green optical path with one green diode acting as the emitter and one as the receiver while the blue light remained between the blue diode emitter/receiver pair.

Demonstration of two channels

To test the system, the researchers carried out different types of optical characterizations. For example, they showed that when the blue diode operated as an emitter, light emission increased as the injection current increased from 10 mA to 30 mA, converting energy and information from the electrical domain to the domain optical. They also demonstrated that the emission and detection spectra of the blue light chip overlapped by approximately 37 nm, confirming simultaneous emission and detection. Overall, these tests confirmed that a single optical path full-duplex optical communication link could be stably formed using two pairs of MQW III nitride diodes, delivering a data rate of 100 bits per second.

“Through this new mode of communication, we have shown the saving of channel space and cost and the strong integration of communication,” Wang said. “This is of great importance for the miniaturization and integration of photonic chips in the future.”

Researchers are now working to better understand the simultaneous emission and detection properties of MQW III nitride diodes to fabricate even more integrated and multifunctional optoelectronic chips. They are also working to improve the detection capabilities of the new communication system.

Article: Article: K. Fu, X. Gao, Q. Yin, J. Yan, X. Ji, Y. Wang, “Full-duplex visible light communication system using single channel”, Opt. Lett., 47.18, 4802-4805 (2022).

DOI: 10.1364/OL.470796.

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