Ultrafast 2 × 2 Green Micro-LED Array Driving
Simultaneous Growth of Smart Displays and Communications

The collaboration among Dr. Gong-Ru Lin 林恭如 (Professor of NTU’s Graduate Institute of Photonics and Optoelectronics and the Dept. of Electrical Engineering), Dr. Hao-Chung Kuo 郭浩中 (Professor of National Yang-Ming Chiao-Tung University), and Dr. Chih-Hsien Cheng 程志賢 (JSPS Research Fellow with the University of Tokyo) on the ultrafast 2 × 2 green micro-light-emitting-diode (micro-LED) array has broken a new world record on data transmission speed via visible-light (optical) wireless communication in free space: 5-Gbit/s and beyond.

This latest ultrafast green micro-LED array has followed in the footsteps of high-speed blue and red micro-LED devices to complete the last research mile that enables free-space optical wireless communication using smart display devices. The research paper resulting from the three researchers’ collaboration has been accepted for publication by Optica (formerly the Optical Society of America), subsequently reviewed and recommended by Prof. Harald Haas of the University of Edinburgh in Scotland, and selected to be included in Optica’s Spotlight on Optics, which publishes the top 1% articles from the nearly 10,000 papers published by Optica annually. Spotlight on Optics has been published electronically for over a decade and is known to be extremely selective. Prof. Lin, Prof. Kuo and Dr. Cheng’s article is one of only two with correspondence addresses of Taiwanese academic institutions this year.

Prof. Haas is a world-renowned scholar in the fields of lighting fidelity (LiFi) and visible light communication (VLC). As recommended in his summary report to this research in Spotlight on Optics, Prof. Haas pointed out that data rates as high as 5 Gbps, as delivered by Dr. Lin and Dr. Kuo’s teams using high-bandwidth, spectrally stable micro-LEDs in the visible light spectrum, will usher in a new era of intelligent displays and metaverse-related applications. Currently the communication data rates of video data streaming require up to 1 terabit per second (Tbps) or at least 4 gigabit per second (Gbps) after distortion-free compression, especially for enabling head-mounted augmented reality (AR) devices to display fluent images that meet the perceived visual quality of humans. To satisfy this demand, it is therefore crucial to develop the ideal candidate for a projecting light source in the visible spectrum that enables such high data rates to realize distortion-free AR vision. For efficient utilization of the spectral frequency band available in the visible spectrum, however, the development of LED devices with ultra-high electrical modulation bandwidth and near-ideal optoelectronic conversion efficiency remains a fundamental challenge in the academic community.

This world-leading 2 × 2 green micro-LED array with ultrafast electrooptical modulation bandwidth originates from Prof. Kuo’s novel structural design for green LED that overcomes the limitation set by the quantum-confined Stark effect, thus effectively solving the bottleneck that reduces emission efficiency under high injected current densities. The device's elegant and unique design essentially solves the problem left for future wave-division multiplexing applications: the spectral broadening and offset under high injection currents that persistently affected modulation speed and efficiency in past component designs. Another significant improvement came from Prof. Lin's proposal for packaging and integrating this array into a specially designed microwave adapter, which effectively improves the 3-dB electrooptical modulation bandwidth to 800-MHz for performing high-speed data encoding assembly. It is envisaged that this component can achieve data transmission rates close to 10 Gbps through enhanced compensated digital driving and modulation circuit technology. The release of the 2 × 2 green micro-LED array device became immediately valued by metaverse-related industry players such as Meta, Foxconn Technology and Brogent Technologies. With its superior performance parameters, the device is expected to lead to explosive growth in the demand for applications in intelligent displays, AR and lighting communications.

Captions:
Upper left: Device structure of a semi-polarized green micro LED (G-μLED)
Upper right: Semi-cylindrical grating design for the semi-polarized G-μLED
Middle right: Bird’s-eye view of the semi-polarized G-μLED surface
Lower left: Microscopic image of the G-μLED
Lower Middle: Light spot of the G-μLED
Lower right: Microscopic view of surface grating of the G-μLED

The researchers’ work has been published in Spotlight on Optics:
https://opg.optica.org/prj/fulltext.cfm?uri=prj-9-10-2077&id=460138