LiFi (short for “light fidelity”) 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-high speed data transmission in environments where RF emissions are controlled, like hospitals, schools, and airplanes.
Single microLED communications could deliver ultra-high data-transmission rate for applications such as 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 that 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.
To address this challenge, the researchers aim to hybridize the microLED matrix onto another matrix of CMOS drivers where each CMOS driver will pilot one microLED, so that each microLED pixel can be driven independently, allowing 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.
CEA-Leti’s expertise in the microLED epitaxial process produces microLEDs as small as 10 microns, which 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.
“This technology has exciting potential for mass-market applications,” said Benoit Miscopein, CEA-Leti research scientist. “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.
“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.”
While the Light Communications Alliance will promote interoperability between different manufacturers’ LiFi systems, CEA-Leti will continue its research to better understand the electrical behavior of single LEDs in high frequency regimes and the link between bandwidth and electromigration patterns. The researchers will also develop 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.
CEA-Leti – www.leti-cea.com