We experimentally investigated the density effect of Ag/SiO2 core–shell nanoparticles (CSNPs) on the carrier recombination rate and photoluminescence (PL) of the InGaN/GaN light-emitting diodes (LEDs). For the high-efficiency InGaN/GaN blue LEDs, there was an optimum Ag/SiO2 CSNP density of about 15 μm−2. From the numerical simulations, the fast carrier recombination rate and the enhanced PL intensity are related to the enhancement of the Purcell factor and the light extraction efficiency due to the localized surface plasmon (LSP) mode. However, this plasmonic enhancement was limited at high Ag/SiO2 CSNP densities by the LSP resonance shift and ohmic loss. We expect that these results could be useful for the practical design of LSP-assisted optoelectronic devices such as LEDs, organic light-emitting diodes, and photovoltaics.
We investigate the terahertz (THz) transmission characteristics of complex slot arrays with various order of rotation symmetry. Our experimental results reveal that an asterisk-shaped aperture with sixfold rotational symmetry is the most appropriate shape for realizing polarization-independent, highly efficient, and frequency-selective transmission of THz radiation. A systematic understanding of the THz transmission characteristics is useful for achieving versatile platforms and custom-designed metallic devices with specific electromagnetic responses.
We investigate subwavelength confinement of terahertz electromagnetic surface modes in a three-dimensional
region with coupled slot structures. Two-dimensional resonance focusing on a subwavelength slot converts to
three-dimensional subwavelength confinement, due to sharp edge confinement effect on asymmetric
plasmonic structure, at the center position of the slot structures which consists of two or more slots. We also
report on the polarization independent confinement of terahertz electromagnetic surface modes beyond
diffraction limit. The structure which consists of radially arranged subwavelength slots located at a same
center position shows the polarization-independent terahertz three-dimensional subwavelength confinement.
We demonstrated lasing in localized optical resonances of deterministic aperiodic structures
with pseudo-random morphologies. The localized lasing modes in the Rudin-Shapiro arrays of air
nanoholes in GaAs membranes occur at reproducible spatial locations and their frequencies are
only slightly affected by the structural fluctuations in different samples. Numerical study on the
resonances of the passive systems and optical imaging of lasing modes enabled us to interpret the
observed lasing behavior in terms of distinctive localized resonances in the two-dimensional Rudin-
Shapiro structures. The deterministic aperiodic media with controllable structural and optical
properties provide a novel platform, alternative to random lasers and different from photonic crystals
lasers, for the engineering of multi-frequency coherent light sources suitable for technological
integration.
We propose and demonstrate a metal-dielectric thin film that delivers low reflection and high absorption over the entire
visible spectrum. This thin black film consists of SiO2/Cr/SiO2/Al layers deposited on glass substrate. Measured
reflectance and absorptance of the black film are 0.7% and 99.3%, respectively, when averaged over the range 380-780
nm. The total thickness of the black film is only about 220 nm. This thin black film can be used as a thin absorbing layer
for displays that require both broadband anti-reflection and high contrast characteristics.
The influence of etching slope on cavity Q-factors in two-dimensional (2D) photonic crystal (PhC) slab is studied. Through FDTD simulation, it is confirmed that the Q-factor decreases with etching slope. The main loss comes from the horizontal coupling into propagating TM-modes. We designed three-lattice-long modified linear cavities having high Q-factors. However, the measured Q-factor was about 250. This small Q-factor is attributed to the non-vertical (13°) side wall.
We fabricated the standing metallic nano-stripe array structure on the thin ITO layer with a very narrow width and a relative high height of the stripe by using the electron-beam lithography and Ar ion milling process. The polarization properties were investigated as the period and the incident angle are varied. In transmission spectra of the TE polarization, the resonance with Fano-like resonance was observed. In case of TM polarization, there's no resonance near normal incidence because the electric field is perpendicular to the very thin metallic grating.
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