• Bulletin of the Korean Chemical Society
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• 제35권3호
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• pp.705-708
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• 2014

We demonstrate the blue InGaN/GaN multiple quantum wells light-emitting diodes (LEDs) with an embedded air-gap photonic crystal (PC) which was fabricated by the lateral epitaxial overgrowth of GaN layer on the tungsten (W) nano-masks. The periodic air-gap PC was formed by the chemical reaction of hydrogen with GaN on the W nano-mask. The optical output power of LEDs with an air-gap PC was increased by 26% compared to LEDs without an air-gap PC. The enhanced optical output power was attributed to the improvement in internal quantum efficiency and light extraction efficiency by the air-gap PC embedded in GaN layer.

• The Transactions of The Korean Institute of Electrical Engineers
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• 제58권8호
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• pp.1580-1584
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• 2009

We have theoretically analyzed the monolithic integration of vertical cavity lasers with depleted optical thyristor (VCL-DOT) structure and experimentally demonstrated optical logic gates such as AND-gate, OR-gate, and INVERTER implemented by VCL-DOT for an optical programmable gate array. The optical AND and OR gates have been realized by changing a input bias of the single VCL-DOTs and all kinds of optical logic functions are also implemented by adjusting an intensity of the reference input beams into the differential VCL-DOTs. To achieve the high sensitivity, high slope efficiency and low threshold current, a small active region of lasing part and a wide detecting area are simultaneously designed by using a selective oxidation process. The fabricated devices clearly show nonlinear s-shaped current-voltage characteristics and lasing characteristics of a low threshold current with 0.65 mA and output spectrum at 854 nm.

• Journal of the Institute of Electronics Engineers of Korea SD
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• 제41권7호
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• pp.13-20
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• 2004

In order to set up the design of micro optical bench, optical coupling efficiencies of two sets of test benches are calculated. Simple linear connections of incoming and outgoing optical fibers with and without ball lenses are designed. Positional errors that are possible in actual fabrication processes we considered in the calculations and their tolerances are determined from -3 ㏈ conditions. For a simple fiber-to-fiber connection, the lateral misalignment should be limited to 2.7 um and tilt error 5.8o. In case of the fiber-to-fiber with ball lens, the working distance between fibers can be extended over 60 um. The optical coupling efficiency depends strongly on the positional errors of ball lenses along the optical axis, and it is also found that the lateral and vertical positional errors should be considered simultaneously in order to keep the high coupling efficiency.

• Korean Journal of Optics and Photonics
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• 제31권2호
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• pp.81-87
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• 2020

This study examines the design technology of searchlight optics featuring narrow beam angles and high luminous intensities. Halogen and xenon lamps, which are conventional searchlight sources, are vulnerable to vibration and shock, and are large and heavy, making them difficult to transport. In addition, the parabolic mirror located at the rear of the searchlight has the disadvantages of poor performance and low light efficiency, due to the assembly error produced during manufacturing. To solve this problem, a 1-kW halogen lamp is replaced by a 150-W high-power COB LED, and a high-efficiency TIR lens is designed to meet the target performance. Afterward, the TIR lens array is proposed to solve the surface error generated during optical injection. After a prototype is manufactured based on the designed optical system, the optical performance is confirmed to be excellent, by comparing it to that of a commercial halogen-lamp searchlight.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• 제23권8호
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• pp.638-644
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• 2010

We have carry out numerical simulation of the electric-optical characteristics of organic light emitting diodes with gradient-doped emitting layer which were reported to be effective in improving luminous efficiency and lifetime. In this paper, the basic structure is comprised of ITO/NPB/$Alq_3$:C545T[%]/$Alq_3$/LiF/Al, six devices by separating the emitting layer of $Alq_3$:C545T[%] were studied. As the result, the uniformly-doped devices exhibited superior luminous efficiency-current density characteristics over conventional undoped device. In the case of gradient-doped devices, electric-optical characteristics were improved similar to uniformed-doped devices, unusually the distribution of traped-charge density in the OLED devices was shown as the staircase.

• Journal of Integrative Natural Science
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• 제2권1호
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• pp.32-36
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• 2009

The purpose of this project is the synthesis of dihydrosilole and its optical characterization for their applications. Dihydrosilole was synthesized from the reduction reaction of either dichlorosilole or chlorohydrosilole with lithium aluminium hydride. The reaction yield for the dihydrosilole through the latter method was higher. The optical characteristics and AIEE effect of dihydrosilole nanoaggregates was investigated for the purpose of increasing the photoluminescence efficiency. Photoluminescence efficiency of dihydrosilole nanoaggregates increased about 100 times compared to that of molecular state.

• Proceedings of the Materials Research Society of Korea Conference
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• 한국재료학회 2011년도 춘계학술발표대회
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• pp.7.2-7.2
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• 2011

Photoelectrochemical solar cells such as dye-sensitized cells (DSSCs), which exhibit high performance and are cost-effective, provide an alternative to conventional p-n junction photovoltaic devices. However, the efficiency of such cells plateaus at 11~12%, in contrast to their theoretical value of 33%. The majority of research has focused on improving energy conversion efficiency of DSSC by controlling nanostructure and exploiting new materials in photoelectrode consisting of semiconducting oxide nanoparticles and a transparent conducting oxide electrode (TCO). In this presentation, we introduce monodisperesed TiO2 nanoparticles prepared by forced hydrolysis method and their superiority as photoelectrode materials was characterized with aids of optical and electrochemical analysis. Inverse opal-based scattering layers containing highly crystalline anatase nanoparticles are also introduced and their feasibility for use as bi-functional light scattering layer is discussed in terms of optical reflectance and charge generation properties as a function of optical wavelength.

• Journal of the Optical Society of Korea
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• 제20권1호
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• pp.169-173
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• 2016

Terahertz (THz) generation by a GaP ridge waveguide with a collinear modal phase-matching scheme based on cascaded difference frequency generation (DFG) processes is theoretically analyzed. The cascaded Stokes interaction processes and the cascaded anti-Stokes interaction processes are investigated from coupled wave equations. THz intensities and quantum conversion efficiency are calculated. Compared with non-cascaded DFG processes, THz intensities from 11-order cascaded DFG processes are increased to 5.48. The quantum conversion efficiency of 177.9% in cascaded processes can be realized, exceeding the Manley-Rowe limit.

• ETRI Journal
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• 제24권3호
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• pp.255-258
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• 2002

We created a new design for an Nd-doped clad-pumped silica fiber laser to enhance the pump absorption and lasing efficiency for a butt-coupled, end-pumped scheme. Two concatenated adiabatic tapers formed within the laser cavity simultaneously removed higher order modes and were spliced to conventional single mode fibers. We theoretically analyzed mode propagation along the composite cavity and experimentally achieved continuous wave oscillation in the $LP_{01}$ mode at $1.06\;{\mu}m$ and a laser output power of over 820 mW with a slope efficiency of 27%.

• Journal of the Korean Institute of Telematics and Electronics A
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• 제33A권3호
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• pp.152-162
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• 1996

Diffraction gratings were designed to generate multiple beams for the real-time optical interconnection in free-space using a liquid crsytal television. Multi-level phase gratings consisted of stepped phase value, 0 to 2$\pi$, and generate a 5$\times$5 spot array, and V-shaped spot patterns which have a maximum diffraction efficiency of 78.84%. Simulated annealing technique was used to determine phase states of each pixel having uniform intensity and high diffraction efficiency. Through the optical interconnection experiments, we compared the diffraction characteristics of beam paterns obtained by binary-level, four-level, and eight-level phase gratings.