Article

Enhanced Light Extraction by Photonic Quasi-Crystals in GaN Blue LEDs

Univ. of Bath, Bath, UK
IEEE Journal of Selected Topics in Quantum Electronics (Impact Factor: 3.47). 09/2009; 15(4):1269 - 1274. DOI: 10.1109/JSTQE.2009.2016674
Source: IEEE Xplore

ABSTRACT The far-field profile of photonic quasi-crystal patterned and unpatterned LEDs, fabricated from commercial epitaxial substrates by electron beam lithography, has been measured prior to lapping and dicing. Emission enhancements reach a maximum of 62%, and are strongly dependent on the filling factor. Qualitative agreement is achieved between 2-D finite-difference time-domain calculations and the experimental data.

Full-text

Available from: Wang Nang Wang, Mar 31, 2015
0 Bookmarks
 · 
122 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We design an ytterbium-doped large pitch photonic quasi-crystal fiber (PQF) for amplifying high-energy ultrashort laser pulses. The proposed fiber exhibits unique properties such as very large mode area (4660 $\mu\hbox{m}^{2}$), less attenuation (0.42 dB/km), high overlapping factor (0.55 for the fundamental mode), and low bending loss. These properties help amplify with high-average power ultrashort pulses with less distortion and high efficiency. To meet these requirements, we design a fiber with optimum gain filtering as well as loss filtering. From the numerical simulation of the analytical model, we confirm that the large pitch PQF plays an indispensable role in amplifying high-energy ultrashort pulses.
    IEEE Photonics Journal 06/2012; 4(3):943-951. DOI:10.1109/JPHOT.2012.2201147 · 2.33 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper we investigate the use of a patterned layer placed at the substrate / GaN interface region of a p-side up LED to improve light extraction and investigate the optimization of performance geometry by adjustment of geometrical parameters associated with the shaped structures including: side wall angle, side wall curvature, height and lattice constant. Performance is in each case evaluated in terms of angular extraction efficiency and far field angular beam profile. Comparisons are made between conventional large pitch patterned substrate (PSS) designs which have multiple wavelength length scales, and photonic crystal lattices which have a (sub) wavelength length scale. Physical mechanisms giving rise to the improvements are identified and discussed in each case. Overall a maximum improvement in extraction efficiency of 66% was obtained for a 4500nm pitch lattice of truncated cones.
    Proceedings of SPIE - The International Society for Optical Engineering 02/2011; DOI:10.1117/12.874187 · 0.20 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We show that arrays of emissive nanorod structures can exhibit strong photonic crystal behavior, via observations of the far-field luminescence from core-shell and quantum disc InGaN/GaN nanorods. The conditions needed for the formation of directional Bloch modes characteristic of strong photonic behavior are found to depend critically upon the vertical shape of the nanorod sidewalls. Index guiding by a region of lower volume-averaged refractive index near the base of the nanorods creates a quasi-suspended photonic crystal slab at the top of the nanorods which supports Bloch modes. Only diffractive behavior could be observed without this region. Slab waveguide modelling of the vertical structure shows that the behavioral regime of the emissive nanorod arrays depends strongly upon the optical coupling between the nanorod region and the planar layers below. The controlled crossover between the two regimes of photonic crystal operation enables the design of photonic nanorod structures formed on planar substrates that exploit either behavior depending on device requirements.
    Journal of Applied Physics 07/2014; 116(4):044305-044305-7. DOI:10.1063/1.4891236 · 2.19 Impact Factor