CEA-Leti, a research institute for electronics and information technology has announced that its researchers have broken the throughput world record of 5.1 Gbps in visible light communications (VLC) using a single GaN blue micro-light-emitting diode (LED). Their data transmission rate of 7.7 Gbps achieved with a 10 µm microLED marks a big step toward commercialization and widespread use of LiFi communications.
- VLC, commonly called LiFi (short for "light fidelity"), is an emerging wireless communication system that offers an alternative or a complementary technology to radiofrequency (RF) systems such as WiFi 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 WiFi communication, which penetrates walls. LiFi also holds promise for ultra-highspeed 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 micro LEDs 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. Multi-LED systems could replace WiFi, 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 WiFi-like standard, the possibility to include this new 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. According to Benoit Miscopein, CEA-Leti research scientist, this may be feasible because CEA-Leti's LiFi physical layer relies on the same concepts as WiFi and 5G technologies. Matrices of thousands of micro LEDs 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. Miscopein says that to meet this challenge, researchers 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 analog implementations of LiFi.
While the Light Communications Alliance will promote interoperability between different manufacturers' LiFi systems, CEA-Leti will continue its research in two areas:
- A 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/or increase the data rate using multi-LED emissive devices. This requires adapting the waveform generation as well as a CMOS interposer to drive the matrix on a pixel basis.
