• Transactions of the Society of Information Storage Systems
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• v.1 no.1
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• pp.58-66
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• 2005

Pseudo-Near Field Recording (Pseudo-NFR) system is proposed to prevent contamination and oxidation of media surface occurred in conventional NFR systems. To solve these critical problems of the NFR systems, we investigate the optimal thickness of cover layer for Pseudo NFR. This paper presents the theoretical analysis for cover layer thickness based on the measured length of dust particle and numerical simulation for the temperature distribution using Finite Difference Time Domain (FDTD) method and heat conduction equation. To verify the simulation results, we conduct and compare simulation results in case of far field MO recording and near field MO recording. A measured dust particle length in general environment was mostly less than $20{\mu}m$, and the optimal thickness of cover layer is $30{\mu}m$ in this case. Based on the designed optimal cover layer thickness, temperature distribution is simulated to have $800{\~}850^{\circ}C$.

• Korean Journal of Optics and Photonics
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• v.10 no.4
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• pp.267-272
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• 1999

We attached a fiber tip on the branch of a quartz crystal oscillator in order to make a feedback control system for near field optical microscope. The electrical impedance of the quartz crystal oscillator depends on the distance between the surface of the sample and the tip caused by the surface damping. Using this method, we can directly monitor the distance between the sample and the tip without inserting extra beam which might give extra optical noise. We characterize the XY scanning resolution and the amplitude of the vibrating tip and the Z-dependent decay of the evanescent wave.

• Journal of Korea Water Resources Association
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• v.40 no.11
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• pp.899-908
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• 2007

In this study, wave reflection due to depression of seabed is calculated by using eigenfunction expansion method. The proper numbers of steps and evanescent modes needed for analysis are suggested by applying the eigenfunction expansion method to bottom topography of which slope or curvature varies. While satisfying shallow or intermediate water depth condition, the optimal figure of depression of seabed is obtained by calculating reflection coefficient for various depressions of seabed. The reflection coefficient with distance between the depression of seabeds is then calculated after arraying the optimal geometry in two and three rows.

• Current Optics and Photonics
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• v.1 no.1
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• pp.65-72
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• 2017

We propose a nearly lossless, compact, electrically modulated vertical directional coupler, which is based on the controllable evanescent coupling in a previously proposed graphene-assisted total internal reflection (GA-FTIR) scheme. In the proposed device, two single-mode waveguides are separate by graphene-$SiO_2$-graphene layers. By changing the chemical potential of the graphene layers with a gate voltage, the coupling strength between the waveguides, and hence the coupling length of the directional coupler, is controlled. Therefore, for a properly chosen, fixed device length, when an input wave is launched into one of the waveguides, the ratio of their output powers can be controlled electrically. The operation of the proposed device is analyzed, with the dispersion relations calculated using a model of a one-dimensional slab waveguide. The supermodes in the coupled waveguide are calculated using the finite-element method to estimate the coupling length, realistic devices are designed, and their performance was confirmed using the finite-difference time-domain method. The designed $3{\mu}m$ by $1{\mu}m$ device achieves an insertion loss of less than 0.11 dB, and a 24-dB extinction ratio between bar and cross states. The proposed low-loss device could enable integrated modulation of a strong optical signal, without thermal buildup.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.22 no.5
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• pp.123-128
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• 2022

Applying rigorous modal transmission-line theory (MTLT), the properties of resonant diffraction gratings under conical light incidence is investigated. The mode vectors pertinent to resonant diffraction under conical mounting vary less with incident angle than those associated with diffraction gratings in classical mounting. Furthermore, as the evanescent diffracted waves drive the leaky modes responsible for the resonance effects, the conical mounting imbues diffraction gratings with larger angular tolerance than their classical counterparts. Based on these concepts, the angular-spectral and wavelength-spectral performance of resonant diffraction gratings in conical and classical mounts by numerical calculations with spectra found for conical incidence are quantified. These results will be useful in various applications demanding resonant diffraction gratings that are efficient and physically sparse.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2000.11a
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• pp.125-129
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• 2000

In this paper, We designed and fabricated C-band bandpass filter using dielectric resonators. From waveguide cutoff frequency which applied the region between adjacent dielectric resonators, the height of cavity is determined. The cavity's diameter is determined to the twice of dielectric resonator's diameter considering the conductor loss. The resonant frequency of the DR-cavity is calculated with travelling wave mode analysis. Conventionally, circular cylindrical dielectric resonator is analysed by Cohn's model which use the evanescent mode in the region between dielectric resonator wall and circular cavity wall, which is an approximated method. The external quality factor, Q$_{ex}$ has found with simulation result using Ansoft's Maxwell simulation tool. The designed filter using dielectric resonators with dielectric constant of 45 has the passband center at 5.065GHz. The bandpass filter using dielectric resonators have about 1dB insertion loss. 20MHz bandwidth and more than 30dB attenuation at f$_{0}$$\pm$15MHz.z.z.

• Journal of Korea Water Resources Association
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• v.53 no.10
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• pp.871-876
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• 2020

Understanding the wave characteristics near the outlet of coastal power plants for cooling water in the vicinity of the dredged areas is critically important for the construction and operation of the plants. By Employing the eigenfunction expansion method, in this study, we analyzed the reflection of monochromatic water waves over (1) shear currents near the outlet and (2) multi-arrayed trenches representing dredged areas. We firstly optimized the number of grids expressing shear currents and the number of evanescent modes based on a convergence test. We then analyzed the sensitivity of the reflection coefficients depending on (1) magnitude of shear currents, (2) width of shear currents, (3) a distance between adjacent trenches, and (4) a number of trenches. The results showed that the reflection coefficient was more sensitive to the number of trenches and the distance between trenches than the velocity of shear currents and the width of shear currents. We also found that even the effect of shear currents is relatively small, the effect is not negligible in a relative water depth from shallow to near shallow water waves (0.01 < kh ≦ 0.70).