Shen, Chao; Ng, Tien Khee; Lee, Changmin; Nakamura, Shuji; Speck, James S.; DenBaars, Steven P.; Alyamani, Ahmed Y.; El-Desouki, Munir M.; Ooi, Boon S.(Optics Express, The Optical Society, 2018-02-14)[Article]
GaN-based semiconductor optical amplifier (SOA) and its integration with laser diode (LD) is an essential building block yet to be demonstrated for III-nitride photonic integrated circuits (PICs) at visible wavelength. This paper presents the InGaN/GaN quantum well (QW) based dual-section LD consisting of integrated amplifier and laser gain regions fabricated on a semipolar GaN substrate. The threshold current in the laser gain region was favorably reduced from 229mA to 135mA at SOA driving voltages, VSOA, of 0V and 6.25V, respectively. The amplification effect was measured based on a large gain of 5.7 dB at VSOA = 6.25V from the increased optical output power of 8.2 mW to 30.5 mW. Such integrated amplifier can be modulated to achieve Gbps data communication using on-off keying technique. The monolithically integrated amplifier-LD paves the way towards the III-nitride on-chip photonic system, providing a compact, low-cost, and multi-functional solution for applications such as smart lighting and visible light communications.
Sun, Xiaobin; Cai, Wenqi; Alkhazragi, Omar; Ooi, Ee-Ning; He, Hongsen; Chaaban, Anas; Shen, Chao; Oubei, Hassan M.; Khan, Mohammed Zahed Mustafa; Ng, Tien Khee; Alouini, Mohamed-Slim; Ooi, Boon S.(Optics Express, The Optical Society, 2018-05-04)[Article]
For circumventing the alignment requirement of line-of-sight (LOS) underwater wireless optical communication (UWOC), we demonstrated a non-line-of-sight (NLOS) UWOC link adequately enhanced using ultraviolet (UV) 375-nm laser. Path loss was chosen as a figure-of-merit for link performance in this investigation, which considers the effects of geometries, water turbidity, and transmission wavelength. The experiments suggest that path loss decreases with smaller azimuth angles, higher water turbidity, and shorter wavelength due in part to enhanced scattering utilizing 375-nm radiation. We highlighted that it is feasible to extend the current findings for long distance NLOS UWOC link in turbid water, such as harbor water.
We reported on the design, demonstration, and analysis of white lighting systems based on GaN laser diodes. Compared to light-emitting-diodes (LEDs), lasers have been proposed for the development of high-power light sources for many potential advantages, including circumventing efficiency droop, reduced light emitting surface, directional beam characteristics. Laser-based white light sources are also attractive for visible light communication (VLC) applications that enabling lighting and communication dual functionalities. In this work, we detailed the color-rendering index (CRI), correlated color temperature (CCT), and luminous flux analysis of laser white light sources by using the GaN laser diode exciting color converters at various driving conditions. By using a blue-emitting laser exciting a yellow YAG phosphor crystal, a luminous flux greater than 600 lm has been achieved with a moderate CRI of 67.2. By constructing a white lighting system using phosphor crystal array based on a reflection configuration, an improved CRI of 74.4 and a luminous flux of ~400 lm with a CCT of 6425 K was obtained at 3A. Using a novel ceramic phosphor plate as color converter, the CRI for the white light source has been further improved to ~ 84.1 with a CCT of ~ 4981 K, which suggests that the laser-based white light source is capable of high-quality illumination applications. The CCT of the white laser sources can be engineered from 5000 K to 6500 K and a potential approach to use laser array for high power white lighting is discussed.
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