Visible light communication (VLC) is an advanced, highly developed optical wireless communication (OWC) technology that can simultaneously provide lighting and high-speed wireless data transmission. A VLC system has several key advantages: ultra-high data rate, secure communication channels, and a lack of interference from electromagnetic (EM) waves, which enable a wide range of applications. Light-emitting diodes (LEDs) have been considered the optimal choice for VLC systems since they can provide excellent illumination performance. However, the quantum confinement Stark effect (QCSE), crystal orientation, carrier lifetime, and recombination factor will influence the modulation bandwidth, and the transmission performance is severely limited. To solve the insufficient modulation bandwidth, micro-LEDs (μ-LEDs) and laser diodes (LDs) are considered as new ideal light sources. Additionally, the development of modulation technology has dramatically increased the transmission capacity of the system. The performance of the VLC system is briefly discussed in this review article, as well as some of its prospective applications in the realms of the industrial Internet of Things (IoT), vehicle communications, and underwater wireless network applications.

Visible light communication system technology review: Devices, architectures, and applications

In this study, we present a high-efficiency InGaN red micro-LED fabricated by the incorporation of superlattice structure, atomic layer deposition passivation, and a distributed Bragg reflector, exhibiting maximum external quantum efficiency of 5.02% with a low efficiency droop corresponding to an injection current density of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m1"> <mml:mrow> <mml:mn>112</mml:mn> <mml:mtext> </mml:mtext> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">A</mml:mi> <mml:mo>/</mml:mo> <mml:mi>cm</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> . The fast carrier dynamics in the InGaN is characterized by using time-resolved photoluminescence, which is correlated to a high modulation bandwidth of 271 MHz achieved by a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m2"> <mml:mrow> <mml:mn>6</mml:mn> <mml:mo form="postfix">×</mml:mo> </mml:mrow> </mml:math> 25-μm-sized micro-LED array with a data transmission rate of 350 Mbit/s at a high injection current density of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m3"> <mml:mrow> <mml:mn>2000</mml:mn> <mml:mtext> </mml:mtext> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">A</mml:mi> <mml:mo>/</mml:mo> <mml:mi>cm</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> . It holds great promise for full-color micro-displays as well as high-speed visible light communication applications based on monolithic InGaN micro-LED technologies. 

High-Efficiency InGaN Red Micro-LEDs for Visible Light Communication

In this Perspective, we will introduce possible future developments on group III-nitride nano-LEDs, which are based on current achievements in this rapidly arising research-technological field. First, the challenges facing their fabrication and their characteristics will be reported. These developments will be set in a broader context with primary applications in lighting, display technology, biology, and sensing. In the following, we will center on advanced applications in microscopy, lithography, communication, and optical computing. We will discuss unconventional device applications and prospects for emerging photon source-based technologies. Beyond conventional and current achievements in optoelectronics, we will present hybrid nano-LED architectures. Novel device concepts potentially could play an essential role in future photon source developments and serve as a key component for optical computing. Therefore, forefront fully photon operated logic circuits, photon-based computational processors, and photon driving memories will be discussed. All these developments will play a significant role in a future highly secure, low energy consuming green IT. Besides today's environmentally friendly terrestrial industrial and information technologies, an enormous potential of nano-LED technology for a large range of applications especially in the next stage of space research is envisaged.

Cutting-edge nano-LED technology

Multigigabit Visible Light Communication Based on High-Bandwidth InGaN Quantum Dot Green Micro-LED

Deep ultraviolet (DUV) optical wireless communications have seen increased interest in recent years due to the unique properties of light in this spectral region. However, the reported DUV data rates remain significantly lower than comparable demonstrations at visible wavelengths due to lower modulation bandwidths and/or output power of the sources. Here, we present a wavelength division multiplexing demonstration using three UV micro-light-emitting diodes emitting at nominal peak wavelengths of 285, 317, and 375 nm, respectively, each with an emitting area of approximately <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m1"> <mml:mrow> <mml:mn>1369</mml:mn> <mml:mtext> </mml:mtext> <mml:msup> <mml:mrow> <mml:mi>μm</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msup> </mml:mrow> </mml:math> (equivalent to circular device pixels of diameter <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m2"> <mml:mrow> <mml:mo form="prefix">∼</mml:mo> <mml:mn>40</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>μm</mml:mi> </mml:mrow> </mml:math> ). Using orthogonal frequency division multiplexing, data rates of 4.17, 3.02, and 3.13 Gbps were achieved from the 285, 317, and 375 nm devices, respectively, for a combined data rate of 10.32 Gbps transmitted over a distance of 0.5 m. 

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10 Gbps wavelength division multiplexing using UV-A, UV-B, and UV-C micro-LEDs

A green 2×2 micro light-emitting diode (μ-LED) array with nanostructured grating patterns grown on a semipolar (20-21)-oriented gallium nitride (GaN) buffered layer on (22-43)-oriented sapphire substrate is specially transistor-outline can (TO-can) packaged with a sub-miniature-A (SMA) connector for high-speed data communication beyond 5 Gbit/s. Through a specific design for suppressing the quantum-confined Stark effect (QCSE) in the green 2×2 μ-LED array with a low polarization-related electric field and flat quantum well band diagram, the green 2×2 μ-LED array exhibits a turn-on voltage of 2.5 V and output power of 0.3 mW at 1  A/cm2. The green 2×2 μ-LED array also reveals a wavelength shift from 543 nm to 537 nm smaller than that of conventional devices grown on c-plane buffered GaN substrate due to the inhibited QCSE. The 50 µm emission aperture of the green 2×2 μ-LED array ensures a lower capacitance for a larger −3  dB modulation bandwidth, which exhibits −1  dB power compression at a larger bias under high-speed operation, as it is less affected by the high resistance of the single μ-LED element. With a specific TO-can+SMA package, the green 2×2 μ-LED array exhibits maximal data rates exceeding 1.5 Gbit/s for the non-return-to-zero on–off keying format and beyond 5.02 Gbit/s for the bit-loaded discrete multitone (BL-DMT) format, which is very promising for optical wireless communication. As the sampling rate increases from 4 GSa/s to 16 GSa/s, the μ-LED array’s received signal-to-noise ratio (SNR) improves dramatically from 15.4 dB to 12.2 dB. The SNR remains about 15.4 dB, with a matching bit-error ratio (BER) of 2.7×10−3, whereas the 10-fold oversampling of the eight-ray quadrature amplitude modulation orthogonal frequency-division multiplexing (8-QAM OFDM) data stream with 16 GSa/s appears to reduce the SNR by −3  dB, resulting in a decoded BER of 3.3×10−3. The green 2×2 μ-LED array has demonstrated greater potential in data transmission beyond 5 Gbit/s using the BL-DMT algorithm for future applications in domains of visible light communication or optical wireless communication when packaged with handed mobile devices.

Yi Che Lee

Papers

Ultrafast 2 × 2 green micro-LED array for optical wireless communication beyond 5 Gbit/s