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• 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]

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]

Heterojunction bipolar light-emitting transistors (HBLETs) with a cleaved facet in the lateral direction for light emission are proposed for real-time optical wireless transmission. To prevent light shielding by the top metal electrodes, the light output power of the edge-emitting HBLETs exceeds that of those emitting from the top surface. Although the proposed HBLETs can generate spontaneous light emissions at λ ~965 nm, a reduced common-emitter current gain (β ~ 0.41) was found due to some of the minority carriers (electron) from the emitter being radiatively recombined within the In 0.15 Ga 0.85 As/GaAs multiple-quantum-well containing base layer. Results also show that a 300 Mbit/s optical link can be constructed using the proposed HBLET transmitter with a lateral emission geometry but its modulation bandwidth is as high as 237.5 MHz. The paper also describes the use of HBLET-based optical wireless communications to achieve real-time transmissions of digital TV signals over a distance of 100 cm in free space. • HBLETs are used as optical transmitter for optical wireless communications.. • The lateral emission geometry of HBLETs is useful to increase the light output power.. • Proposed HBLETs not only exhibit a high modulation bandwidth of 237.5 MHz but also enable 300 Mbit/s optical transmission.. • Real-time transmission of digital TV signals over a 1 m optical link is shown to be feasible using proposed HBLETs. [ABSTRACT FROM AUTHOR]