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  • Prism-based tunable InGaN/GaN self-injection locked blue laser diode system: study of temperature, injection ratio, and stability

    Khan, Mohammed Zahed Mustafa; Mukhtar, Sani; Holguin Lerma, Jorge Alberto; Alkhazragi, Omar; Ashry, Islam; Ng, Tien Khee; Ooi, Boon S. (Journal of Nanophotonics, SPIE-Intl Soc Optical Eng, 2020-07-02) [Article]
    A quasicontinuously wavelength tuned self-injection locked blue laser diode system employing a prism is presented. A rigorous analysis of the injection ratio (IR) in the form of three systems, namely high (HRS, ∼ − 0.7 dB IR), medium (MRS, ∼ − 1.5 dB IR), and low (LRS, ∼ − 3.0 dB IR) reflection systems, showed a direct relationship with the wavelength tunability whereas the usable system power exhibited an inverse correlation. In particular, MRS configuration demonstrated a concurrent optimization of tuning window and system power, thus emerging as a highly attractive candidate for practical realization. Moreover, a comprehensive investigation on two distinct MRS configurations employing different commercially available InGaN/GaN blue lasers, i.e., MRS-1 and MRS-2, displayed a wavelength tunability (system power) of ∼8.2 nm (∼7.6 mW) and ∼6.3 nm (∼11.6 mW), respectively, at a low injection current of 130 mA. In addition, both MRS configurations maintained high-performance characteristic with corresponding average optical linewidths of ∼80 and ∼58 pm and a side-mode-suppression-ratio of ≥12 dB. Lastly, a thorough stability analysis of HRS and MRS configurations, which are more prone to system instabilities due to elevated IRs, is performed at critical operation conditions of a high injection current of ≥260 mA and a temperature of 40°C, showing an extended stable performance of over 120 min, thus further substantiating the promising features of the prism-based systems for practical applications.
  • Sensing within the OTDR dead-zone using a two-mode fiber

    Mao, Yuan; Ashry, Islam; Wang, Biwei; Hveding, Frode; Bukhamseen, Ahmed Y.; Ng, Tien Khee; Ooi, Boon S. (Optics Letters, The Optical Society, 2020-04-20) [Article]
    An optical time-domain reflectometer (OTDR) is incapable of providing sensing or diagnostic information within dead-zones. We use a two-mode fiber (TMF) and a photonic lantern to completely overcome the main OTDR's dead-zone originating from the front facet of optical fiber. This is achieved by injecting the optical pulses of the OTDR in the form of the fundamental LP01 mode and meanwhile collecting the Rayleigh signals associated with the higher-order modes. Using the reported TMF-based OTDR, we accurately sense the position and frequency of a vibration event located within the dead-zone as a proof-of-concept demonstration.
  • Blue laser diode system with an enhanced wavelength tuning range

    Mukhtar, Sani; Shen, Chao; Ashry, Islam; Ng, Tien Khee; Ooi, Boon S.; Khan, Mohammed Zahed Mustafa (IEEE Photonics Journal, IEEE, 2020-03-30) [Article]
    A prism-based self-injection locked seamlessly tunable blue InGaN/GaN laser diode composite cavity system is presented. A rigorous analysis of this external cavity diode laser (ECDL) system is performed at two different optical feedback powers. At 130 mA low injection, the high reflection system (HRS) exhibits a record wideband tuning span of ~12.11 nm with a side-mode-suppression-ratio (SMSR) ≥ 15 dB, measuring as high as 40 dB, linewidth ≤ 110 pm, and a working power of about 3 mW. Whereas, a tuning range of 8 nm with linewidth ≤ 88 pm, SMSR ≥ 13 dB, reaching a maximum of 35 dB with 14.5 mW usable power is achieved from the low reflection system (LRS) at the same injection current. Moreover, an inverse relationship between the optical power and the tunability is observed in both the systems with a value as high as 180 mW exhibited by LRS configuration and attaining a tunability of 4.5 nm. Both systems highlight high stability even at higher injection currents and temperature. Such a robust, simple, and compact system may serve as a crucial light source in a plethora of diverse applications besides visible optical communications. To the best of our knowledge, this is the first report on a continuously tunable self-injection locked tunable laser system.
  • Tunable Violet Laser Diode System for Optical Wireless Communication

    Mukhtar, Sani; Sun, Xiaobin; Ashry, Islam; Ng, Tien Khee; Ooi, Boon S.; Khan, Mohammed Zahed Mustafa (IEEE Photonics Technology Letters, IEEE, 2020-03-26) [Article]
    We report a tunable self-injection locked violet laser diode external cavity system exhibiting a continuous wavelength tunability of 5.15 nm (400.28 - 405.43 nm) with mean side-mode-suppression-ratio (SMSR) and linewidth of ~23 dB and ~190 pm, respectively. The effects of injection current and temperature indicate a robust system besides being cost-effective and straightforward. Moreover, a successful indoor on-off keying transmission at two different locked modes on a 0.4 m free space channel showed ~10 times improvement in the bit-error-rate (BER) with value ~8×10-4 at 2 Gb/s, and better performance on 0.8 m channel length at 1.75 Gb/s compared to the free-running laser case. Our work is a potential step towards the realization of future high data capacity narrow-wavelength-spaced multiplexed optical wireless communication system wherein continuously tunable laser sources are expected to play a crucial role as transmitters.
  • Identifying structured light modes in a desert environment using machine learning algorithms

    Ragheb, Amr; Saif, Waddah; Trichili, Abderrahmen; Ashry, Islam; Esmail, Maged Abdullah; Altamimi, Majid; Almaiman, Ahmed; Altubaishi, Essam; Ooi, Boon S.; Alouini, Mohamed-Slim; Alshebeili, Saleh (Optics Express, The Optical Society, 2020-03-12) [Article]
    The unique orthogonal shapes of structured light beams have attracted researchers to use as information carriers. Structured light-based free space optical communication is subject to atmospheric propagation effects such as rain, fog, and rain, which complicate the mode demultiplexing process using conventional technology. In this context, we experimentally investigate the detection of Laguerre Gaussian and Hermite Gaussian beams under dust storm conditions using machine learning algorithms. Different algorithms are employed to detect various structured light encoding schemes including the use of a convolutional neural network (CNN), support vector machine, and k-nearest neighbor. We report an identification accuracy of 99% under a visibility level of 9 m. The CNN approach is further used to estimate the visibility range of a dusty communication channel.
  • Hybrid distributed acoustic-temperature sensing using a few-mode fiber

    Ashry, Islam; Mao, Yuan; Ng, Tien Khee; Hveding, Frode; Arsalan, Muhammad; Ooi, Boon S. (SPIE, 2020-03-02) [Conference Paper]
    Optical fiber distributed acoustic sensor (DAS) and distributed temperature sensor (DTS) are considerably desirable for many important applications including oil and gas industry. Simultaneous measurements of vibration and temperature will exclude the need for two separate DAS and DTS systems, reduce overall cost, and ensure continuous real-time monitoring of these two important sensing parameters. We here devise a hybrid DAS-DTS system using a few-mode fiber (FMF). Although the system requirements for DAS and DTS are quite different, FMF is considered an ideal compromise to satisfy the requirements of the two systems.
  • Early detection of red palm weevil using distributed optical sensor

    Ashry, Islam; Mao, Yuan; Al-Fehaid, Yousef; Al-Shawaf, Abdulmoneim; Al-Bagshi, Mansour; Al-Brahim, Salman; Ng, Tien Khee; Ooi, Boon S. (Scientific Reports, Springer Science and Business Media LLC, 2020-02-21) [Article]
    Red palm weevil (RPW) poses a serious threat to the cultivation of date palms. It is considered to be the most destructive epidemic pest of palms, responsible for massive economic losses worldwide. Curative methods for RPW are not difficult to apply; however, the early detection of the pest remains a great challenge. Although several detection techniques have been implemented for the early detection of RPW, none of these methods have been proven to be reliable. Here, we use an optical-fiber-distributed acoustic sensor (DAS) as a paradigm shift technology for the early detection of RPW. Our sensitive sensor shows a detection of feeding sound produced by larvae as young as 12 days, in an infested tree. In comparison with existing, commonly-used technologies, this novel sensing technique represents a cost-effective and non-invasive alternative that could provide 24-7, real-time monitoring of 1,000 palm trees or even more. It could also monitor the temperature, an essential feature to control farm fires, another major problem for the cultivation of palm trees around the world.
  • Titanium Carbide MXene Nucleation Layer for Epitaxial Growth of High-Quality GaN Nanowires on Amorphous Substrates

    Prabaswara, Aditya; Kim, Hyunho; Min, Jung-Wook; Subedi, Ram Chandra; Anjum, Dalaver H.; Davaasuren, Bambar; Moore, Kalani; Conroy, Michele; Mitra, Somak; Roqan, Iman S.; Ng, Tien Khee; Alshareef, Husam N.; Ooi, Boon S. (ACS Nano, American Chemical Society (ACS), 2020-02-03) [Article]
    Growing III-nitride nanowires on 2D materials is advantageous, as it effectively decouples the underlying growthsubstrate from the properties of the nanowires. As a relatively new family of 2D materials, MXenes are promising candidates as III-nitride nanowire nucleation layers capable of providing simultaneous transparency and conductivity. In this work, we demonstrate the direct epitaxial growth of GaN nanowires on Ti3C2 MXene films. The MXene films consist of nanoflakes spray coated onto an amorphous silica substrate. We observed an epitaxial relationship between the GaN nanowires and the MXene nanoflakes due to the compatibility between the triangular lattice of Ti3C2 MXene and the hexagonal structure of wurtzite GaN. The GaN nanowires on MXene show good material quality and partial transparency at visible wavelengths. Nanoscale electrical characterization using conductive atomic force microscopy reveals a Schottky barrier height of ∼330 meV between the GaN nanowire and the Ti3C2 MXene film. Our work highlights the potential of using MXene as a transparent and conductive preorienting nucleation layer for high-quality GaN growth on amorphous substrates.
  • Time–Energy Quantum Uncertainty—Quantifying the Effectiveness of Surface Defect Passivation Protocols for Low-Dimensional Semiconductors

    Alfaraj, Nasir; Alghamdi, Wael; Alawein, Meshal; Ajia, Idris A.; Priante, Davide; Janjua, Bilal; Sun, Haiding; Ng, Tien Khee; Ooi, Boon S.; Roqan, Iman S.; Li, Xiaohang (ACS Applied Electronic Materials, American Chemical Society (ACS), 2020-01-22) [Article]
    The degree of enhancement in radiative recombination in ensembles of semiconductor nanowires after chemical treatment is quantified within a derived limit, by correlating the energy released during the photoemission processes of the light–matter reaction and the effective carrier recombination lifetimes. It is argued that the usage of surface recombination velocity or surface saturation current density as passivation metrics that assess the effectiveness of surface passivation does not provide strict and universal theoretical bounds within which the degree of passivation can be confined. In this context, the model developed in this study provides a broadly applicable surface passivation metric for direct energy bandgap semiconductor materials. This is because of its reliance on the dispersion in energy and lifetime of electron–hole recombination emission at room temperature, in lieu of the mere dependence on the ratio of peak emission spectral intensities or temperature- and power-dependent photoluminescence measurements performed prior and subsequent to surface treatment. We show that the proposed quantification method, on the basis of steady-state and transient photoluminescence measurements performed entirely at room temperature, provides information on the effectiveness of surface state passivation through a comparison of the dispersion in carrier lifetimes and photon energy emissions in the nanowire ensemble before and after surface passivation. Our measure of the effectiveness of a surface passivation protocol is in essence the supremum of lower bounds one can derive on the product of Δt and ΔE.
  • Simultaneous Distributed Acoustic and Temperature Sensing Using a Multimode Fiber

    Mao, Yuan; Ashry, Islam; Hveding, Frode; Bukhamsin, Ahmed; Hong, Yuxi; Ng, Tien Khee; Ooi, Boon S. (IEEE Journal of Selected Topics in Quantum Electronics, IEEE, 2020-01-08) [Article]
    Fiber optic distributed acoustic sensor (DAS) and distributed temperature sensor (DTS) are considerably important for many applications. It is challenging to design a hybrid DAS-DTS system using the same optical fiber because the operation principles of the two sensors are different. We here deploy the widespread standard multimode fiber (MMF) for simultaneous distributed acoustic and temperature sensing. In particular, we operate the MMF in a quasi-single-mode (QSM) state to simultaneously fulfill the functionality requirements of the DAS and DTS. The reported design offers simultaneous vibration and temperature monitoring with high accuracy. In particular, the DAS has a 12.98 dB mean signal-to-noise ratio (SNR) and the DTS offers temperature measurements with ±1 °C accuracy. This technique is significant for many industrial applications because it efficiently tackles a long-standing issue in practical implementation.
  • Quasi-single mode operated few-mode fiber for distributed acoustic sensing

    Ashry, Islam; Mao, Yuan; Ng, Tien Khee; Hveding, Frode; Arsalan, Muhammad; Ooi, Boon S. (SPIE, 2019-11-21) [Conference Paper]
    We experimentally report a proof-of-concept demonstration of a few-mode fiber (FMF) based distributed acoustic sensor (DAS) design, aiming at upgrading the capabilities of the typical DAS that employs the standard single mode fiber (SMF). We only excite the fundamental mode at the input port of the FMF, and further, we minimize the impact of intermodal coupling within it such that the FMF operates in a quasi-single mode (QSM) state. The QSM operated FMF keeps the basic operation principle of the DAS valid and, in comparison with the standard SMF, it allows injection of higher pump peak-power before reaching the threshold power of nonlinearity. We validate our design by sensing vibration events produced by a piezoelectric transducer (PZT) cylinder. The FMF based DAS successfully figures out the locations and frequencies of these events. This reported design would enable the realization of a DAS design with longer sensing range and higher spatial resolution, in comparison to the standard SMF based DAS.
  • High-speed colour-converting photodetector with all-inorganic CsPbBr3 perovskite nanocrystals for ultraviolet light communication

    Kang, Chun Hong; Dursun, Ibrahim; Liu, Guangyu; Sinatra, Lutfan; Sun, Xiaobin; Kong, Meiwei; Pan, Jun; Maity, Partha; Ooi, Ee-Ning; Ng, Tien Khee; Mohammed, Omar F.; Bakr, Osman; Ooi, Boon S. (Light: Science & Applications, Springer Science and Business Media LLC, 2019-10-16) [Article]
    Optical wireless communication (OWC) using the ultra-broad spectrum of the visible-to-ultraviolet (UV) wavelength region remains a vital field of research for mitigating the saturated bandwidth of radio-frequency (RF) communication. However, the lack of an efficient UV photodetection methodology hinders the development of UV-based communication. The key technological impediment is related to the low UV-photon absorption in existing silicon photodetectors, which offer low-cost and mature platforms. To address this technology gap, we report a hybrid Si-based photodetection scheme by incorporating CsPbBr3 perovskite nanocrystals (NCs) with a high photoluminescence quantum yield (PLQY) and a fast photoluminescence (PL) decay time as a UV-to-visible colour-converting layer for high-speed solar-blind UV communication. The facile formation of drop-cast CsPbBr3 perovskite NCs leads to a high PLQY of up to ~73% and strong absorption in the UV region. With the addition of the NC layer, a nearly threefold improvement in the responsivity and an increase of ~25% in the external quantum efficiency (EQE) of the solar-blind region compared to a commercial silicon-based photodetector were observed. Moreover, time-resolved photoluminescence measurements demonstrated a decay time of 4.5 ns under a 372-nm UV excitation source, thus elucidating the potential of this layer as a fast colour-converting layer. A high data rate of up to 34 Mbps in solar-blind communication was achieved using the hybrid CsPbBr3–silicon photodetection scheme in conjunction with a 278-nm UVC light-emitting diode (LED). These findings demonstrate the feasibility of an integrated high-speed photoreceiver design of a composition-tuneable perovskite-based phosphor and a low-cost silicon-based photodetector for UV communication.
  • Ultraviolet-to-blue color-converting scintillating-fibers photoreceiver for 375-nm laser-based underwater wireless optical communication

    Kang, Chun Hong; Trichili, Abderrahmen; Alkhazragi, Omar; Zhang, Huafan; Subedi, Ram Chandra; Guo, Yujian; Mitra, Somak; Shen, Chao; Roqan, Iman S.; Ng, Tien Khee; Alouini, Mohamed-Slim; Ooi, Boon S. (Optics Express, The Optical Society, 2019-10-08) [Article]
    Underwater wireless optical communication (UWOC) can offer reliable and secure connectivity for enabling future internet-of-underwater-things (IoUT), owing to its unlicensed spectrum and high transmission speed. However, a critical bottleneck lies in the strict requirement of pointing, acquisition, and tracking (PAT), for effective recovery of modulated optical signals at the receiver end. A large-area, high bandwidth, and wide-angle-of-view photoreceiver is therefore crucial for establishing a high-speed yet reliable communication link under non-directional pointing in a turbulent underwater environment. In this work, we demonstrated a large-area, of up to a few tens of cm2, photoreceiver design based on ultraviolet(UV)-to-blue color-converting plastic scintillating fibers, and yet offering high 3-dB bandwidth of up to 86.13 MHz. Tapping on the large modulation bandwidth, we demonstrated a high data rate of 250 Mbps at bit-error ratio (BER) of 2.2 × 10−3 using non-return-to-zero on-off keying (NRZ-OOK) pseudorandom binary sequence (PRBS) 210-1 data stream, a 375-nm laser-based communication link over the 1.15-m water channel. This proof-of-concept demonstration opens the pathway for revolutionizing the photodetection scheme in UWOC, and for non-line-of-sight (NLOS) free-space optical communication.
  • Investigating the Performance of a Few-Mode Fiber for Distributed Acoustic Sensing

    Mao, Yuan; Ashry, Islam; Alias, Mohd Sharizal; Ng, Tien Khee; Hveding, Frode; Arsalan, Muhammad; Ooi, Boon S. (IEEE Photonics Journal, Institute of Electrical and Electronics Engineers (IEEE), 2019-09-17) [Article]
    We experimentally investigated the performance of a distributed acoustic sensor (DAS) designed using a few-mode fiber (FMF), when launching different spatial modes under intentional index perturbation within the fiber. Our demonstration showed that the quasi-single mode (QSM) operated FMF offers higher signal-to-noise ratio (SNR) for the DAS, compared with the case when launching other degenerate higher order modes. Additionally, we compared the behavior of the single-mode fiber (SMF)- and FMF-based DAS when using optical pulses of varying power levels. The FMF enables the realization of a DAS with longer sensing range and higher spatial resolution. The developed FMF-based DAS is further tested via sensing various vibration events produced by piezoelectric transducer (PZT) cylinder, pencil break, and loudspeaker.
  • Performance enhancement of noisy distributed acoustic sensor using normalized differential method

    Ashry, Islam; Mao, Yuan; Alias, Mohd Sharizal; Ng, Tien Khee; Hveding, Frode; Arsalan, Muhammad; Ooi, Boon S. (SPIE, 2019-09-09) [Conference Paper]
    We experimentally report a normalized differential signal processing technique to improve the signal-To-noise ratio (SNR) of a fiber optic distributed acoustic sensor (DAS), in the time-domain. The introduced method is calibrated through comparing it with the typical differential method when using a noisy DAS system that includes a relatively wide linewidth laser. For this system, the normalized differential method allows measuring the vibration locations, produced by a piezoelectric transducer (PZT) cylinder, with enhanced SNR.
  • Catalyst-Free Vertical ZnO-Nanotube Array Grown on p-GaN for UV-Light-Emitting Devices

    Alwadai, Norah M.; Ajia, Idris A.; Janjua, Bilal; Flemban, Tahani H.; Mitra, Somak; Wehbe, Nimer; Wei, Nini; Lopatin, Sergei; Ooi, Boon S.; Roqan, Iman S. (ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2019-07-25) [Article]
    One-dimensional (1D) structures-based UV-light-emitting diode (LED) has immense potential for next-generation applications. However, several issues related to such devices must be resolved first, such as expensive material and growth methods, complicated fabrication process, efficiency droop, and unavoidable metal contamination due to metal catalyst that reduces device efficiency. To overcome these obstacles, we have developed a novel growth method for obtaining a high-quality hexagonal, well-defined, and vertical 1D Gd-doped n-ZnO nanotube (NT) array deposited on p-GaN films and other substrates by pulsed laser deposition. By adopting this approach, the desired high optical and structural quality is achieved without utilizing metal catalyst. Transmission electron microscopy measurements confirm that gadolinium dopants in the target form a transparent in situ interface layer to assist in vertical NT formation. Microphotoluminescence (PL) measurements of the NTs reveal an intense ZnO band edge emission without a defect band, indicating high quality. Carrier dynamic analysis via time-resolved PL confirms that the emission of n-ZnO NTs/p-GaN LED structure is dominated significantly by the radiative recombination process without efficiency droop when high carrier density is injected optically. We developed an electrically pumped UV Gd-doped ZnO NTs/GaN LED as a proof of concept, demonstrating its high internal quantum efficiency (>65%). The demonstrated performance of this cost-effective UV LED suggests its potential application in large-scale device production.
  • Wideband Self-Injection-Locked Green Tunable Laser Diode

    Shamim, Md. Hosne Mobarok; Ng, Tien Khee; Ooi, Boon S.; Khan, Mohammed Zahed Mustafa (Institute of Electrical and Electronics Engineers (IEEE), 2019-07-01) [Conference Paper]
    A wideband tunability of 6.53 nm with appreciable SMSR (> 10 dB) and linewidth (~0.1 nm) is demonstrated from a simple and low-cost tunable self-injection locked InGaN/GaN green laser based external-cavity system, for the first time.© 2019 The Author(s)
  • All-day radiative cooling using beam-controlled architectures

    Zhou, Lyu; Song, Haomin; Liang, Jian-Wei; Singer, Matthew; Zhou, Ming; Stegenburgs, Edgars; Zhang, Nan; Ng, Tien Khee; Yu, Zongfu; Ooi, Boon S.; Gan, Qiaoqiang (Institute of Electrical and Electronics Engineers (IEEE), 2019-07-01) [Conference Paper]
    We report an inexpensive planar polydimethylsiloxane (PDMS)/metal thermal emitter in a beam-controlled architecture for all-day radiative cooling and realized∽11°C reduction compared with the ambient temperature. © 2019 The Author(s)
  • Electrical Characterization of Solar-Blind Deep-Ultraviolet (Al0.28Ga0.72)2O3Schottky Photodetectors Grown on Silicon by Pulsed Laser Deposition

    Alfaraj, Nasir; Li, Kuang-Hui; Kang, Chun Hong; Priante, Davide; Braic, Laurentiu; Guo, Zaibing; Ng, Tien Khee; Li, Xiaohang; Ooi, Boon S. (Institute of Electrical and Electronics Engineers (IEEE), 2019-07-01) [Conference Paper]
    This study reports on (Al0.28Ga0.72)2O3-based ultraviolet-C Schottky metal-semiconductor-metal and metal-insulator-metal photodetectors with peak responsivities of 1.17 and 0.40 A/W, respectively, for an incident-light wavelength of 230 nm at 2.50 V reverse-bias. © 2019 The Author (s)
  • Producing OAM Information Carriers using Micro-structured Spiral Phase Plates

    Stegenburgs, Edgars; Bertoncini, Andrea; Trichili, Abderrahmen; Alias, Mohd Sharizal; Ng, Tien Khee; Alouini, Mohamed-Slim; Liberale, Carlo; Ooi, Boon S. (Institute of Electrical and Electronics Engineers (IEEE), 2019-07-01) [Conference Paper]
    We report on small foot-print spiral phase plates for orbital angular momentum (OAM) light beam generation used in free space communication. A modal decomposition process confirms high purity of the generated beams at 980-nm wavelength. © 2019 The Author(s)

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