Improvements of the modulation bandwidth and data rate of green-emitting CsPbBr3 perovskite quantum dots for Gbps visible light communication.

CsPbBr3 perovskite quantum dots (PQDs) as promising color conversion materials have been widely used in display and visible light communication (VLC), but most CsPbBr3 PQDs for VLC are randomly selected without optimization. Thereby the exploration of fundamental experimental parameters of QDs is essential to better employ their performance advantages. Herein, we investigated the concentration and solvent effects on photoluminescence (PL) properties and communication performance of CsPbBr3 PQDs. The PL, time-resolved PL characterization and communication measurements of CsPbBr3 PQDs all exhibit concentration dependence, suggesting that there exists an optimum concentration to take advantages of performance merits. CsPbBr3 PQDs with a concentration of 0.5 mg/ml show the shortest carrier lifetime and achieve the highest -3 dB bandwidth (168.03 MHz) as well as the highest data rate (660 Mbps) comparing to other concentrations. And in terms of the optimal concentration, we further explored the approach to improve the communication performance, investigating the effect of polarity solvent on the communication performance of CsPbBr3 PQDs. Original 0.5 mg/ml CsPbBr3 PQDs (1 ml) with 55 µL ethanol added in obtain a higher -3 dB bandwidth of 363.68 MHz improved by ∼116.4% and a record data rate of 1.25 Gbps improved by ∼89.4% but weaker PL emission due to energy transfer. The energy transfer assisted improvement may open up a promising avenue to improve the communication performance of QDs, but more feasible energy transfer path needs to be explored to ensure the stability of QDs.

Red, green and blue InGaN micro-LEDs for display application: temperature and current density effects.

Micro-LED has attracted tremendous attention as next-generation display, but InGaN red-green-blue (RGB) based high-efficiency micro-LEDs, especially red InGaN micro-LED, face significant challenges and the optoelectronic performance is inevitably affected by environmental factors such as varying temperature and operating current density. Here, we demonstrated the RGB InGaN micro-LEDs, and investigated the effects of temperature and current density for the InGaN RGB micro-LED display. We found that temperature increase can lead to the changes of electrical characteristics, the shifts in electroluminescence spectra, the increase of full width at half maximum and the decreases of light output power, external quantum efficiency, power efficiency, and ambient contrast ratios, while current density increase can also give rise to different changing trends of the varieties of parameters mentioned just above for the RGB micro-LED display, creating great challenges for its application in practical scenarios. Despite of the varying electrical and optical charateristics, relatively high and stable colour gamut of the RGB display can be maintained under changing temperature and current density. Based on the results above, mechanisms on the temperature and current density effects were analyzed in detail, which would be helpful to predict the parameters change of micro-LED display caused by temperature and current density, and provided guidance for improving the performance of InGaN micro-LED display in the future.

4.0 Gbps visible light communication in a foggy environment based on a blue laser diode.

Fog has a strong attenuation effect on the optical channel, which will greatly degrade the performance of visible light communication (VLC). Studying the effect of the fog on communication performance is crucial to realize outdoor VLC for next generation networks, but there is little research on this topic. In this work, the transmission characteristics of visible light band in the foggy channel were measured and a high-speed VLC system based on a 450 nm blue laser diode (LD) and 16-ary quadrature amplitude modulation orthogonal frequency division multiplexing (16-QAM-OFDM) in the artificial fog environment was demonstrated experimentally. Through a foggy channel of 60 cm, a maximum data rate of up to 4 Gbps was achieved at the pass loss of 13.06 dB with a bit error rate (BER) of 3.5 × 10-3 below the forward error correction (FEC) limit (3.8 × 10-3), which was the highest data rate ever reported for VLC in the foggy channel. Even at a higher pass loss of 17.32 dB, the proposed system still could achieve a data rate of 2.84 Gbps with a BER of 2.8 × 10-3. Further extending the distance to 16.9 m for a more practical application, a data rate of 2.0 Gbps was also demonstrated successfully.

2 Gbps free-space ultraviolet-C communication based on a high-bandwidth micro-LED achieved with pre-equalization.

In this Letter, we experimentally achieve high-speed ultraviolet-C (UVC) communication based on a 276.8 nm UVC micro-LED. A record ${-}{{3}}\;{\rm{dB}}$ optical bandwidth of 452.53 MHz and light output power of 0.854 mW at a current density of ${{400}}\;{\rm{A/c}}{{\rm{m}}^2}$ are obtained with a chip size of 100 µm. A UVC link over 0.5 m with a data rate of 2 Gbps is achieved using 16-ary quadrature amplitude modulation orthogonal frequency division multiplexing and pre-equalization, and an extended distance over 3 m with a data rate of 0.82 Gbps is also presented. The demonstrated high-speed performance shows that micro-LEDs have great potential in the field of UVC communication.

Deep-Ultraviolet Micro-LEDs Exhibiting High Output Power and High Modulation Bandwidth Simultaneously.

Deep-ultraviolet (DUV) solar-blind communication (SBC) shows distinct advantages of non-line-of-sight propagation and background noise negligibility over conventional visible-light communication. AlGaN-based DUV micro-light-emitting diodes (µ-LEDs) are an excellent candidate for a DUV-SBC light source due to their small size, low power consumption, and high modulation bandwidth. A long-haul DUV-SBC system requires the light source exhibiting high output power, high modulation bandwidth, and high rate, simultaneously. Such a device is rarely reported. A parallel-arrayed planar (PAP) approach is here proposed to satisfy those requirements. By reducing the dimensions of the active emission mesa to micrometer scale, DUV µ-LEDs with ultrahigh power density are created due to their homogeneous injection current and enhanced planar isotropic light emission. Interconnected PAP µ-LEDs with a diameter of 25 µm are produced. This device has an output power of 83.5 mW with a density of 405 W cm-2 at 230 mA, a wall-plug efficiency (WPE) of 4.7% at 155 mA, and a high -3 dB modulation bandwidth of 380 MHz. The remarkable high output power and efficiency make those devices a reliable platform to develop high-modulation-bandwidth wireless communication and to meet the requirements for bio-elimination.