Recent Submissions


High-Speed 650-nm Red Vertical-Cavity Surface-Emitting Lasers for Optical Communications

(2024-08) Almaymoni, Nawal K.; Ooi, Boon S.; Mohammed, Omar F.; Ohkawa, Kazuhiro; Nguyen, Hieu P.; Physical Science and Engineering (PSE) Division

Optical communications, which utilize visible light, have been termed the "next generation" of communication technology because of their potential for reliable, high-speed, and secure broadband connections. Although light-emitting diodes (LEDs) are commonly used as transmitters in optical communications, they suffer from limited modulation bandwidths and low output power density. In contrast, vertical-cavity surface-emitting lasers (VCSELs) can offer a higher modulation bandwidth in the gigahertz range and a higher output power density, making them ideal transmitters. Moreover, VCSELs have circular and symmetric beam profiles with low divergence, facilitating efficient coupling with optical fibers. However, visible VCSELs still require significant progress to meet this technology's demands. This dissertation aims to provide high-quality and high-speed 650-nm red VCSEL arrays with the added potential of integrating orbital angular momentum (OAM) beams as low-cost, low-crosstalk, and compact sources and to design several novel systems to increase the data rate of optical communication channels toward terabit per second (Tb/s) aggregate rates. To that end, we demonstrate 650-nm red VCSEL-based optical communications to achieve Gb/s links. We achieved, for the first time, the highest data rate (up to 4.7 Gbit/s) of a single 650-nm red VCSEL with the lowest energy consumption (2 pJ/bit) through plastic optical fiber communication by using direct current-biased optical orthogonal frequency-division multiplexing (DCO-OFDM). Moreover, we report a novel technique to increase the data rate capacity to 1 Tb/s using a massively parallel interconnected system based on a (14×16) 650-nm red VCSEL array. A single 650-nm red VCSEL also reaches a 2 Gbit/s data rate through underwater wireless optical communication (UWOC) using non-return-to-zero on-off keying (NRZ-OOK). We further propose a novel scheme to increase the data rate of red VCSELs in highly turbid water using the wavelength-division multiplexing (WDM) technique with another 680-nm red VCSEL. In addition, the beam of the VCSEL has been converted from a Gaussian to an OAM beam with a high purity by using 3D two-photon lithography printing of spiral phase plates (SPPs) on top of the aperture of the VCSEL. This novel technique allows design flexibility given its high resolution and fast printing. We achieved 7.6 Gb/s in free-space optical communication based on a 2×2 OAM red VCSEL array through the mode division multiplexing (MDM) technique. All reported techniques are promising for using red VCSELs in optical communication applications to offer the potential for high-speed communications with high data rates and low energy consumption. Their compatibility with existing infrastructure, energy efficiency, miniaturization, spectral efficiency, and reliability make them well-suited for a wide range of applications, including data centers, telecommunications networks, and high-performance computing environments.


Green turtle tracking leads the discovery of seagrass blue carbon resources

(KAUST Research Repository, 2024-07-20) Mann, Hugo; Tarek Ahmed Juffali Research Chair in Red Sea Ecology

Fabrication of Transparent Microfluidic Devices for Advanced Imaging and High-Pressure Applications

(2024-07-10) Hoecherl, Martin; Hoteit, Hussein; Habuchi, Satoshi; Vahrenkamp, Volker; Physical Science and Engineering (PSE) Division

Microfluidics offers unique insights into pore-scale multiphase flow dynamics. Nevertheless, the value and relevance of the observations strongly depend on the utilized microfluidic device. In particular, material, channel geometry, resolution, flow domain pattern, fluid phases, and experimental pressure/ temperature environment must be chosen carefully to ensure representative flow conditions. This study investigates the fabrication of novel microfluidic devices from fused silica and borosilicate glass by state-of-the-art semiconductor processing technology. Dry and wet etching techniques were explored. Four inch wafer scale deep inductively coupled plasma (ICP) reactive ion etching (RIE) of silicon dioxide in C4F8/ Ar/ O2 plasma with chromium hardmasks was optimized. Mechanical failure of evaporated chromium thin films was prevented by introducing a polycrystalline silicon-based stress relief layer. High mask to substrate selectivities (>56), nearly vertical and smooth channel sidewalls (>83 degrees) were achieved at moderate etch rates (0.2 um/min) for lateral channel dimensions down to 2 um in fused silica. Borosilicate glass deep reactive ion etching (DRIE) posed challenges as material impurities induce substantial surface roughness. Post ICP RIE smoothing by atomic layer etching (ALE) is demonstrated for the first time. Next to dry processing, wet patterning of fused silica and borosilicate glass in 50% HF with amorphous silicon masks was carried out successfully. Finally, fusion bonding techniques were developed for both substrates. Ultimately, optimized methodologies for fabricating pressure and temperature-stable, chemically inert, and transparent microfluidic devices are laid out. Thereby, this study contributed to the development of an advanced microfluidic platform, targeting dynamic single-molecule fluorescence microscopy as well as flow experiments with supercritical carbon dioxide and hydrogen.


Green turtle tracking leads the discovery of seagrass blue carbon resources

(2024-07-03) Mann, Hugo; Wildermann, Natalie; Barrios-Garrido, Hector; Duarte, Carlos M.; King Abdullah University of Science and Technology (KAUST); Tarek Ahmed Juffali Research Chair in Red Sea Ecology