LiFi is particularly suited for secure communications compared to Wi-Fi as light doesn’t penetrate walls...
Researchers at CEA-Leti in Grenoble appear to have made a step closer to achieving LiFi communications as a replacement for WiFi. It claims to have broken the throughput world record of 5.1 Gbps in visible light communications (VLC) using a single GaN blue micro- light-emitting diode (microLED), achieving a data transmission rate of 7.7 Gbps with a 10 µm microLED.
Considered to be particularly suited to security-related applications because light propagation can be confined to a room and doesn’t penetrate walls, VLC, commonly called LiFi (short for “light fidelity”), is an emerging wireless communication system that offers an alternative or complementary technology to radio frequency (RF) systems such as WiFi and 5G. LiFi also holds promise 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 environments such as assembly lines and data centers, and contactless 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.
CEA-Leti’s expertise in the microLED epitaxial process produces microLEDs as small as 10 microns, which it claims is among the smallest in the world. The smaller the emissive area of the LED, the higher the communication bandwidth – 1.8 GHz in the institute’s single-blue microLED project. The team also produced an advanced multi-carrier modulation combined with digital signal processing. This high spectrum-efficiency waveform was transmitted by the single LED and was received on a high-speed photodetector and demodulated using a direct sampling oscilloscope.
According to Benoit Miscopein, CEA-Leti research scientist, this technology has a lot of potential for mass-market LiFi applications. He commented, “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 of including 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 large additional license-free bandwidth. “This may be feasible because CEA-Leti’s LiFi physical layer relies on the same concepts as WiFi and 5G technologies,” said 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, we expect to hybridize the microLED matrix onto another matrix of CMOS drivers: one simple CMOS driver will pilot one microLED,” Miscopein said. “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 the Light Communications Alliance will promote interoperability between different manufacturers’ LiFi systems, CEA-Leti will continue its research in two areas. One is to obtain a better understanding of the electrical behavior of single LEDs in high frequency regimes and the link between bandwidth and electromigration patterns. The second is in 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.