Gigabit per second visible light communication based on AlGaInP red micro-LED micro-transfer printed onto diamond and glass

Multi-Gb/s visible light communication based on AlGaInP amber micro-LED

Light-emitting diodes (LEDs), pivotal for solid-state illumination (SSL) and highly regarded as potential candidates in visible light communication (VLC) systems, have garnered significant interest as a solution to alleviate the congested radio frequency spectrum in next-generation communications. Addressing the challenge of extremely limited bandwidth due to the low response of phosphor in conventional illumination, our research focuses on an AlGaInP-based amber LED. This LED represents a promising avenue for phosphor-free, high-speed VLC applications when used in conjunction with the prevalent blue LED technology based on nitride materials. The fabricated AlGaInP amber LED, with a mesa diameter of 100 µm2, has undergone comprehensive optoelectronic property and transmission performance characterization. We have successfully demonstrated a proof-of-concept for VLC using the amber LED, achieving a data transmission rate of 2.94 Gb/s that complies with the forward-error-correction (FEC) standard of 3.8 × 10-3, utilizing adaptive bit and power loading with discrete multitone (BPL-DMT) modulation.

Recent Advances in Micro-LEDs Having Yellow-Green to Red Emission Wavelengths for Visible Light Communications

Visible light communication (VLC), which will primarily support high-speed internet connectivity in the contemporary world, has progressively come to be recognized as a significant alternative and reinforcement in the wireless communication area. VLC has become more popular recently because of its many advantages over conventional radio frequencies, including a higher transmission rate, high bandwidth, low power consumption, fewer health risks, and reduced interference. Due to its high-bandwidth characteristics and potential to be used for both illumination and communications, micro-light-emitting diodes (micro-LEDs) have drawn a lot of attention for their use in VLC applications. In this review, a detailed overview of micro-LEDs that have long emission wavelengths for VLC is presented, along with their related challenges and future prospects. The VLC performance of micro-LEDs is influenced by a number of factors, including the quantum-confined Stark effect (QCSE), size-dependent effect, and droop effect, which are discussed in the following sections. When these elements are combined, it has a major impact on the performance of micro-LEDs in terms of their modulation bandwidth, wavelength shift, full-width at half maximum (FWHM), light output power, and efficiency. The possible challenges faced in the use of micro-LEDs were analyzed through a simulation conducted using Crosslight Apsys software and the results were compared with the previous reported results. We also provide a brief overview of the phenomena, underlying theories, and potential possible solutions to these issues. Furthermore, we provide a brief discussion regarding micro-LEDs that have emission wavelengths ranging from yellow-green to red colors. We highlight the notable bandwidth enhancement for this paradigm and anticipate some exciting new research directions. Overall, this review paper provides a brief overview of the performance of VLC-based systems based on micro-LEDs and some of their possible applications.

Hundred-meter Gb/s deep ultraviolet wireless communications using AlGaN micro-LEDs

We demonstrate the use of deep ultraviolet (DUV) micro-light-emitting diodes (LEDs) for long-distance line-of-sight optical wireless communications. With a single 285 nm-emitting micro-LED, we have respectively achieved data rates greater than 6.5 Gb/s at a distance of 10 m and 4 Gb/s at 60 m. Moreover, we obtained >1 Gb/s data rates at a distance of 116 m. To our knowledge, these results are the highest data rates at such distances thus far reported using DUV micro-LEDs and the first demonstration of Gb/s communication at >100 m using any micro-LED-based transmitter.

4-bit DAC based 6.9Gb/s PAM-8 UOWC system using single-pixel mini-LED and digital pre-compensation

Low-cost underwater wireless optical communication (UOWC) systems are attractive for high-speed connections among unmanned vehicles or devices in various underwater applications. Here we demonstrate a high-speed and low-cost UOWC system using a low-resolution digital to analog converter (DAC), a single-pixel mini-sized light-emitting diode (mini-LED), and digital pre-compensation (DPC). The enabled DPC scheme comprises digital pre-distortion (DPD), digital pre-emphasis (DPE), and digital resolution enhancer (DRE), which pre-compensate for mini-LED nonlinearity, the bandwidth limitation of the mini-LED and avalanche photodiode detector, and DAC resolution limitation, respectively. The simulation results show that the in-band signal-to-quantization noise ratio can be increased by 6.8 dB using DRE based on a 4-bit DAC. To further improve the system capacity, we tune the level of DPE in order to optimize the trade-off between the residual inter-symbol interference and signal-to-noise ratio. With the combination of optimized DPE and DRE, we obtain a 21.1% higher data rate compared with full DPE only and demonstrate the transmission of 6.9 Gb/s PAM-8 signal over a 2-m distance underwater based on a single-pixel mini-LED and 4-bit DAC. This paper reports a cost-effective UOWC system first using a low-resolution DAC and DPC, which offers a promising path toward low-cost underwater optical wireless networks.

Micro-LED with red-green-blue super-pixel integration for simultaneous display and optical near field communication

This work presents a novel all-in-one Micro-LED pixel (µLEDP) technology by integrating red-green-blue super-pixels (RGBSP) in a single unit cell. Measurement results show that the proposed µLEDP delivers excellent optical and electrical characteristics, including wide color gamut (109% NTSC), wide correlated color temperature range (2831.7-10016.8 K), and high modulation system bandwidth (58-62 MHz). To the best of our knowledge, the proposed integrated µLEDP achieves the highest data rate compared to published results based on other multi-color low-capacitance high-bandwidth LEDs. The maximum simulated non-return-to-zero (NRZ) and 4-level pulse-amplitude-modulation (PAM-4) data rates of 0.3-Gb/s and 1.1-Gb/s, respectively.

Responsibility optimization of a high-speed InP/InGaAs photodetector with a back reflector structure

Top-illuminated PIN photodetectors (PDs) are widely utilized in telecommunication systems, and more efforts have been focused on optimizing the optical responsibility and bandwidth for high-speed and capacity applications. In this work, we develop an integrated top-illuminated InP/InGaAs PIN PD with a back reflector by using a microtransfer printing (µ-TP) process. An improved µ-TP process, where the tether of silicon nitride instead of photoresist, is selected to support an underetched III-V device on an InP substrate before transfer. According to theoretical simulations and experimental measurements, the seamless integration of the PD with a back reflector through µ-TP process makes full use of the 2^nd or even multiple reflecting light in the absorption layer to optimize the maximum responsibility. The integrated device with a 5 µm square p-mesa possesses a high optical responsibility of 0.78 A/W and 3 dB bandwidth of 54 GHz using a 500 nm i-InGaAs absorption layer. The present approach for top-illuminated PIN PDs demonstrates an advanced route in which a thin intrinsic layer is available for application in high-performance systems.

2000 PPI silicon-based AlGaInP red micro-LED arrays fabricated via wafer bonding and epilayer lift-off

In this article, 2000 PPI red silicon-based AlGaInP micro-LED arrays were fabricated and investigated. The AlGaInP epilayer was transferred onto the silicon substrate via the In-Ag bonding technique and an epilayer lift-off process. The silicon substrate with a high thermal conductivity could provide satisfactory heat dissipation, leading to micro-LED arrays that had a stable emission spectrum with increasing current density from 20 to 420 A/cm² along with a red-shift of the peak position from 624.69 to 627.12 nm (Δλ = 2.43 nm). Additionally, increasing the injection current density had little effect on the CIE (x, y) of the micro-LED arrays. Further, the I-V characteristics and light output power of micro-LED arrays with different pixel sizes demonstrated that the AlGaInP red micro-LED array on a silicon substrate had excellent electrical stability and optical output.

White-lighting and WDM-VLC system using transmission gratings and an engineered diffuser

A white-lighting and wavelength-division-multiplexing (WDM)-visible light communication (VLC) system with over 20 m of free-space distance and 3 m of lighting distance is demonstrated via a red/green/blue (R/G/B) triple-source polarization-multiplexing scheme, transmission gratings, and an engineered diffuser with a double-convex lens. Integrating four-level pulse amplitude modulation (PAM4) with a triple-source polarization-multiplexing scheme, the aggregate transmission rate is noticeably enhanced to 300 Gb/s [50Gb/sPAM4/source×3sources×2polarizations (p- and s-polarizations)]. White-light is produced by multiplexing the R/G/B lights with two transmission gratings and separated by demultiplexing them using the other two transmission gratings. By adopting an engineered diffuser with a double-convex lens, the white-light is diffused over 3 m of free-space distance to provide general white-light illumination (>100lux). This demonstrated white-lighting and WDM-VLC system meets a high aggregate transmission rate with a qualified indoor lighting target. It opens up a new category for lighting and communication.