Ultraviolet micro light-emitting diode and color-conversion for white-light communication
AdvisorsOoi, Boon S.
Embargo End Date2023-11-29
Permanent link to this recordhttp://hdl.handle.net/10754/686010
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Access RestrictionsAt the time of archiving, the student author of this thesis opted to temporarily restrict access to it. The full text of this thesis will become available to the public after the expiration of the embargo on 2023-11-29.
AbstractVisible-light communication (VLC) has several advantages over the commonly used radio frequency (RF) spectrum, including high bandwidth and low crosstalk. These features have become of more significance, especially as the proliferation of wireless devices increases and causes spectrum crowding. The white light in VLC systems is typically obtained from blue/violet light-emitting diodes (LEDs) and phosphors partially converting blue light into longer wavelength colors spanning the visible-light band. One phosphor that is frequently used is cerium-doped yttrium aluminum garnet (YAG). However, YAG suffers from a low color-rendering index (CRI) and high correlated color temperature (CCT). Lead halide perovskites provide an alternative to YAG and have been extensively utilized for optoelectronic devices owing to their tunable bandgap and high photoluminescence quantum yield (PLQY). However, their drawbacks, e.g., lead toxicity and instability, hinder their widespread application. Herein, in order to take advantage of a high-performance lead-free tin-based halide perovskite phosphor that has a high absolute PLQY of near unity and a wide spectral emission ranging from 500 to 700 nm, we fabricated ultraviolet (UV) micro light-emitting diodes (micro-LEDs) with a peak wavelength at 365 nm to match the peak of the photoluminescence excitation (PLE) spectra of the material to obtain strong yellow-spectrum emission. Together with a blue LED, white light was obtained with a CRI of 84.9 and 4115-K CCT. Despite the long PL lifetime of the perovskite material, which is in the order of μs, a net data rate of 1.5 Mb/s was achieved using orthogonal frequency-division multiplexing (OFDM) with adaptive bit and power loading to take advantage of the exceptionally high PLQY of the phosphor to improve the data throughput of the VLC system using higher modulation orders. Furthermore, through improvements to the nanostructure of lead-free tin-based halide perovskite phosphor and the use of excitation sources with a higher power, the data rate is expected to be even higher. The lead-free nature of this material, along with its wide spectrum and high conversion efficiency, makes it a promising alternative to conventional toxic perovskite-based phosphors. As the first demonstration of VLC links using lead-free perovskite, this study paves the way for safer, more sustainable VLC systems.
CitationLu, H. (2022). Ultraviolet micro light-emitting diode and color-conversion for white-light communication [KAUST Research Repository]. https://doi.org/10.25781/KAUST-8JTKC
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Gigabit-per-second white light-based visible light communication using near-ultraviolet laser diode and red-, green-, and blue-emitting phosphorsLee, Changmin; Shen, Chao; Cozzan, Clayton; Farrell, Robert M.; Speck, James S.; Nakamura, Shuji; Ooi, Boon S.; DenBaars, Steven P. (Optics Express, The Optical Society, 2017-07-12) [Article]Data communication based on white light generated using a near-ultraviolet (NUV) laser diode (LD) pumping red-, green-, and blue-emitting (RGB) phosphors was demonstrated for the first time. A III-nitride laser diode (LD) on a semipolar (2021) substrate emitting at 410 nm was used for the transmitter. The measured modulation bandwidth of the LD was 1 GHz, which was limited by the avalanche photodetector. The emission from the NUV LD and the RGB phosphor combination measured a color rendering index (CRI) of 79 and correlated color temperature (CCT) of 4050 K, indicating promise of this approach for creating high quality white lighting. Using this configuration, data was successfully transmitted at a rate of more than 1 Gbps. This NUV laser-based system is expected to have lower background noise from sunlight at the LD emission wavelength than a system that uses a blue LD due to the rapid fall off in intensity of the solar spectrum in the NUV spectral region.
Spectrally Selective Smart Window with High Near-Infrared Light Shielding and Controllable Visible Light TransmittanceWu, Mengchun; Shi, Yusuf; Li, Renyuan; Wang, Peng (ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2018-10-26) [Article]Smart windows with high near-infrared (NIR) light shielding and controllable visible light transmittance are highly sought after for cooling energy saving in buildings. Herein we present a rationally designed spectrally selective smart window which is capable of shielding 96.2% of the NIR irradiation from 800 nm to 2500 nm and at the same time permitting acceptable visible light (78.2% before and 45.3% after its optical switching) for indoor daylighting. The smart window synergistically integrates the highly selective and effective NIR absorption based photothermal conversion of cesium tungsten bronze (CsxWO3) with the transparent thermo-responsive poly(N-isopropyl acrylamide) microgel-polyacrylamide (PAM-PNIPAM) hydrogel. The optical switching of the smart window is a direct result of the phase transition of PAM-PNIPAM hydrogel which in turn is induced by the photothermal effect of CsxWO3 under sunlight irradiation. The smart window exhibits fast optical switching, shows a long-term operational stability, and can be made highly flexible. Under the experimental conditions in this work, the indoor temperature with the smart window is ~21 °C lower than that with regular single-layered glass window under one sun irradiation. The smart window design in this work is meaningful for further development of effective smart windows for energy saving in the build environment.
Fabrication and Characterization of GaN-Based Superluminescent Diode for Solid-State Lighting and Visible Light CommunicationAlatawi, Abdullah (2020-04) [Dissertation]
Advisor: Ooi, Boon S.
Committee members: Ohkawa, Kazuhiro; Mohammed, Omar F.; Zhao, HongPingTo date, group-III-nitride has undergone continuous improvements to provide a broader range of industrial applications, such as solid-state lighting (SSL), visible light communications (VLC), and light projection. Recently, VLC has attained substantial attention in the field of wireless communication because it offers ~ 370 THz of bandwidth of unregulated visible spectrum, which makes it a critical factor in the evolution of the 5G networks and beyond. GaN-based light-emitting diode (LED) and laser diode (LD) have become increasingly appealing in energy-sufficient SSL replacing conventional light sources. However, III- nitride LEDs suffer from efficiency-droop in their external quantum efficiency associated with high current densities, and their modulation bandwidth is limited to 10 ~ 100 MHz. Although LDs have shown gigabit-modulation bandwidth, unfavorable artifacts, such as speckles are observed, which may raise a concern about eye safety. This dissertation is devoted to the fabrication and electrical and optical characterization of a new class of III-nitride light-emitter known as superluminescent diode (SLD). SLD works in an amplified spontaneous emission (ASE) regime, and it combines several advantages from both LD and LED, such as droop-free, speckle-free, low-spatial coherence, broader emission, high-optical power, and directional beam. Here, SLDs were fabricated by a focused ion beam by tilting the front facet of the waveguide to suppress the lasing mode. They showed a high-power of 474 mW on c-plane GaN-substrate with a large spectral bandwidth of 6.5 nm at an optical power of 105 mW. To generate SLD- based white light, a YAG-phosphor-plate was integrated, and a CRI of 85.1 and CCT of 3392 K were measured. For the VLC link, SLD showed record high-data rates of 1.45 Gbps and 3.4 Gbps by OOK and DMT modulation schemes, respectively. Additionally, a widely single- and dual-wavelength tunability were designed using SLD-based external cavity (SLD-EC) configuration for a tunable blue laser source. These results underscore the practicality of c-plane SLDs in realizing high-power, high data rate, speckle-free, and droop-free SSL-VLC apparatus. Additionally, the SLD-EC configuration allows a wide range of applications, including biomedical applications, optical communication, and high-resolution spectroscopy.