15 Jun 2020
CEA-Leti’s optical transmission of 7.7 Gbps positions Li-Fi to replace wi-fi and potential 5G interoperability.CEA-Leti, a technology research institute based in Grenoble, France, say they have broken the throughput world record of 5.1 Gbps in visible light communications (VLC – also known as Li-Fi) using a single GaN blue micro- light-emitting diode (LED).
The published data transmission rate of 7.7 Gbps achieved with a 10 µm microLED "marks another step toward commercialization and widespread use of Li-Fi communication," say the scientists.
Wireless communications technology Li-Fi (short for "light fidelity") offers an alternative or a complementary technology to radio frequency systems such as Wi-Fi and 5G. It is considered to be a promising technology for security-related applications because light propagation can be confined to a room with no information leakage, as opposed to Wi-Fi communication, which penetrates walls.
Li-Fi also looks promising for ultra-high speed data transmission in environments where RF emissions are controlled, like hospitals, schools, and airplanes. Single microLED communications offer an ultra-high data-transmission rate for a variety of opportunities for new applications. These include industrial wireless high-speed links in demanding environments such as assembly lines and data centers, and contact-less connectors, or chip-to-chip communication.
But their weak optical power limits their applications to short-range communications. In contrast, matrices of thousands of microLEDs contain higher optical powers than open mid- and long-range applications. However, preserving the bandwidth of each microLED within a matrix requires that each signal has to be brought as close as possible to the micro-optical source.
“This technology has exciting potential for mass-market applications," commented Benoit Miscopein, CEA-Leti research scientist. "Multi-LED systems could replace Wi-Fi, but wide-scale adoption will require a standardization process to ensure the systems' interoperability between different manufacturers. The Light Communications Alliance was created in 2019 to encourage the industry to implement this standardization.
In addition to a stand-alone Wi-Fi-like standard, there is the possibility of including Li-Fi technology as a component carrier in the downlink of 5G-NR, a radio-access technology for 5G mobile considerations, is also under investigation to bring a large additional license-free bandwidth.
”This may be feasible because its Li-Fi physical layer relies on the same concepts as WiFi and 5G technologies," added Miscopein. "Matrices of thousands of microLEDs could also open the way to mid- to long-range applications, such as indoor wireless multiple access.”
Preserving the bandwidth of each microLED within a matrix requires that each signal is generated as close as possible to the micro-optical source.
“To meet this challenge,” he said, “we expect to hybridize the microLED matrix onto another matrix of CMOS drivers: one simple CMOS driver will pilot one microLED. This will also enable the additional feature of piloting each microLED pixel independently, and that allows new types of digital-to-optical waveforms that could eliminate the need for digital-to-analog converters commonly used in the conventional 'analogue' implementations of LiFi.”
While industry association Light Communications Alliance will promote interoperability between different manufacturers' Li-Fi systems, CEA-Leti will continue its research in two areas: better understanding of the electrical behavior of single LEDs in high frequency regimes and the link between bandwidth and electromigration patterns; and techniques to improve the range and data rate using multi-LED emissive devices. This will require adapting the waveform generation as well as a CMOS interposer to drive the matrix on a pixel basis.
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