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The feasibility of using InGaN/GaN multiple-quantum-well light-emitting diode arrays (LED arrays) as photodiodes (PDs) is investigated experimentally in addition to their light emitting function. Two discrete LED arrays are produced from one 4 × 4 LED array with a parallel-connected pixel configuration. Such compact designs are useful for light emission or detection at the transmitting/receiving terminals of optical wireless communication systems. Despite 4 × 2 LED arrays achieving a light output power of 67.4 mW at 250 mA, they exhibit an optical responsivity (detectivity) of 0.183 A/W (1.61 × 1012 cm Hz1/2W−1) under ultraviolet light illumination (λ = 380 nm) at zero bias. For 4 × 2 LED arrays, the presence of an appreciable ultraviolet light response, together with a high 3-dB bandwidth (∼8 MHz) for modulated light detection, allowed us to build a 15 Mbit/s directed optical link with these LEDs functioning as both the optical transmitter and the receiver. Finally, the unitary LED array-based optical link is capable of real-time transmission of digital audio signals (data rate = 6 Mbit/s) at a propagation distance of 100 cm in free space even though some of the constituent pixels are inactive for light detection. [ABSTRACT FROM AUTHOR]

• InGaN LED arrays are used as optical transmitters in underwater optical communications. • The parallel-connected design of the constituent pixels is useful to avoid LED failure. • With increasing inactive pixel number, improved LED emission efficiency and the transmission performance were found. • Real-time transmissions of digital TV signals over a 100 cm water channel is shown to be feasible using proposed LED arrays. SU-8 planarized InGaN LED arrays are proposed for use as optical transmitters in underwater optical communications. In addition to alleviating current crowding effects, the parallel-connected design of the constituent pixels is useful to avoid LED failure. Experiments are conducted to investigate the impact of different numbers of emitting pixels on LED performance and system bandwidth of a data communication link passing through a water tank. Although a maximum light output power of 56.7 mW was obtained for LED arrays with all pixels available for light emission, LED arrays with 2 emitting pixels exhibit a high external quantum efficiency at a lower current (i.e., η ext = 8.9% @ 9 mA). In addition, the maximum 3-dB modulation bandwidth of optical links in the water tank increased from 18 to 30.3 MHz with the use of LED arrays, but the number of emitting pixels is reduced from 16 to 2. Such improvement also reflects an increased data transmission rate of 200 Mbit/s through the use of a 2-emitting-pixel LED array. Finally, real-time transmission of digital TV signals over a moderate distance (∼100 cm) in tap water is shown to be feasible even when modifying the number of the emitting pixels within the LED arrays. [ABSTRACT FROM AUTHOR]

InGaN light-emitting diodes (LEDs) grown with a thin GaN barrier and a gradually reduced well width in the multiple-quantum-well (MQW) regions close to n-GaN are proposed for use in underwater optical wireless communications. Experimentally, LED epiwafers grown by metal–organic vapor phase epitaxy were found to have comparable crystalline quality despite using a different epistructure design from InGaN MQWs. The modified MQWs facilitated hole transport to the deep quantum wells while preventing energetic electrons from accumulating at the topmost quantum wells close to p-GaN, thus improving the current-light output performance at high currents. In addition, relatively strong carrier localization in the proposed LEDs indicates more injected carriers within the modified MQWs can participate in radiative recombinations to contribute to light output. On the other hand, the available bandwidth of a line-of-sight LED-based optical link passing through a 100-cm-long water tank was found to be around 148.7 MHz using the proposed LED, which is $1.3\times $ higher than that obtained using normal LED. This type of optical link produces data transmission at rates in tap water exceeding 300 Mbit/s and enables real-time transmission of digital TV signals. [ABSTRACT FROM AUTHOR]

Visible light communications with InGaN-based light-emitting diodes (LEDs) grown on large-diameter (6-inch) and cost-effective Si (111) substrates are investigated experimentally. During epitaxial growth, the transition layers consisted of the step-graded AlGaN buffers incorporated with three low-temperature-grown (∼900 °C) AlN interlayers on AlN/Si substrates that are used to compensate for thermally induced tensile stress and to maintain a reasonable crystalline quality of GaN-on-Si LEDs. Strong light absorption from Si can be prevented by fabricating a Si substrate-free InGaN LED with a composite metal coating of Al/Ag/Al multilayer, providing improved adhesive strength and reflectivity comparable to the unitary Ag film. In comparison with GaN-on-Si LEDs, stripping Si substrates combined with the use of a highly reflective bottom mirror (Al/Ag/Al multilayer) reflected a more intense emission pattern corresponding to a 2.2 times (@ 190 mA) increase in light output power in thin-film LEDs. In addition, a 1.8 times (@ 160 mA) increase in optical channel bandwidth is achieved by using thin-film LEDs as optical transmitters. A direct line-of-sight optical link using the proposed thin-film LEDs achieved data transmission rates of up to 100 Mb/s over a distance of 100 cm, indicating that the proposed LEDs have potential for use as optical transmitters in indoor visible light communications. [ABSTRACT FROM PUBLISHER]

An experimental evaluation of a directed line-of-sight visible light communication system based on phosphor-converted white resonant-cavity light-emitting diodes (RCLEDs) is presented. With a simple dielectric coating of the transistor outline-can-packaged InGaN LEDs, a $\lambda $ /4-thick Ta2O5/SiO2 distributed Bragg reflector functioning as the top mirror of near-UV RCLEDs can be formed automatically without inducing a registration misalignment as in conventional photolithography. In addition, a passivation coating can also be created over the entire LED structure. As a result of the optical cavity effect, the completed RCLEDs exhibit improved output performance in terms of light output power, external quantum efficiency, and directionality. The resulting RCLEDs are more suitable for building a 200 Mb/s ON–OFF keying nonreturn-to-zero optical link for data transmission over a distance of 100 cm in free space. Finally, we show that real-time transmissions of digital TV signals can be accomplished using the proposed short-range ( $\sim 100$ cm) optical wireless link (data rate $\sim 150$ Mb/s) mainly consisting of a field-programmable gate array-based video encoder/decoder, an optical bandpass filter, and the phosphorescent white RCLEDs made by a simple process. [ABSTRACT FROM PUBLISHER]

A constant stress accelerated life testing has been implemented to obtain the useful lifetime of white organic light emitting displays (OLEDs) based on the lognormal distribution. However, other distributions such as Weibull and log-logistic may offer a better fit for failure time data at each stress level. The mean time to failure (MTTF) of a white OLED at each stress level will be estimated by the best fit statistical model. A response model based on an inverse power (exponential) law for all MTTFs under different stress levels is then used to predict the useful lifetime of a white OLED under normal conditions. In addition, the confidence interval of MTTF for a white OLED is provided. The results show that the MTTF of a white OLED is about 15,912 h. [ABSTRACT FROM AUTHOR]

Highlights: [•] The degradation-data-driven method is used to analyze the lifetime of HPWLEDs. [•] We present a bi-exponential model to improve the fit accuracy for the data. [•] The two-stage method provides the highest ability to explain variation. [•] A response model was used to predict the useful lifetime. [Copyright &y& Elsevier]