• Current Optics and Photonics
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• v.1 no.2
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• pp.150-156
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• 2017

A diffraction limited optical system for head mounted displays (HMDs) was designed. This optical system consists of four modules, including 1:5 mm and 5:30 mm beam expanders, polarization grating-polarization conversion system (PG-PCS) and refractive/diffractive projection optical module. The PG-PCS module transforms the unpolarized Gaussian beam to a linearly polarized beam and it simultaneously homogenizes the spatial intensity profile. The optical projector module has a $30^{\circ}$ field of view, a 22 mm eye relief, and a 10 mm exit pupil diameter with a compact structure. Common acrylic materials were utilized in the optical design process; therefore, the final optical system was lightweight. The whole optical system is suitable for a 0.7 inch liquid crystal on silicon microdisplay (LCOS) with HDTV resolution ($1920{\times}1080$) and $8.0{\mu}m$ pixel pitch.

• Broadcasting and Media Magazine
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• v.11 no.1
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• pp.78-85
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• 2006

Cognitive radio is a paradigm for wireless communication in which either network of wireless node itself changes particular transmission or reception parameters to execute its tasks efficiently without interfering with the licensed users. This paper represents a performance of the cognitive radio technology on dual polarized MIMO system using six-port receiver. Six-port technology is well known direct conversion receiver. In this paper, a six-port phase discriminator based polarization signal separation is shown. That is, the SER(Symbol Error Rate) performance is improved using polarization separator and simple receiver architecture is proposed applying six-port receiver. The six-port technology has priority to adapt changeable frequency system and variable environments for cognitive radio. In general, dual polarized MIMO system has good capacity and quality using polarization separator [1].

• ETRI Journal
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• v.36 no.2
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• pp.206-213
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• 2014

This paper presents a novel 90 GHz band 16-quadrature amplitude modulation (16-QAM) orthogonal frequency-division multiplexing (OFDM) communication system. The system can deliver 6 Gbps through six channels with a bandwidth of 3 GHz. Each channel occupies 500 MHz and delivers 1 Gbps using 16-QAM OFDM. To implement the system, a low-noise amplifier and an RF up/down conversion fourth-harmonically pumped mixer are implemented using a $0.1-{\mu}m$ gallium arsenide pseudomorphic high-electron-mobility transistor process. A polarization-division duplex architecture is used for full-duplex communication. In a digital modem, OFDM with 256-point fast Fourier transform and (255, 239) Reed-Solomon forward error correction codecs are used. The modem can compensate for a carrier-frequency offset of up to 50 ppm and a symbol rate offset of up to 1 ppm. Experiment results show that the system can achieve a bit error rate of $10^{-5}$ at a signal-to-noise ratio of about 19.8 dB.

• Current Optics and Photonics
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• v.3 no.4
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• pp.275-284
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• 2019

Chirality is ubiquitous in physics and biology from microscopic to macroscopic phenomena, such as fermionic interactions and DNA duplication. In photonics, chirality has traditionally represented differentiated optical responses for right and left circular polarizations. This definition of optical chirality in the polarization domain includes handedness-dependent phase velocities or optical absorption inside chiral media, which enable polarimetry for measuring the material concentration and circular dichroism spectroscopy for sensing biological or chemical enantiomers. Recently, the emerging field of non-Hermitian photonics, which explores exotic phenomena in gain or loss media, has provided a new viewpoint on chirality in photonics that is not restricted to the traditional polarization domain but is extended to other physical quantities such as the orbital angular momentum, propagation direction, and system parameter space. Here, we introduce recent milestones in chiral light-matter interactions in non-Hermitian photonics and show an enhanced degree of design freedom in photonic devices for spin and orbital angular momenta, directionality, and asymmetric modal conversion.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.5
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• pp.745-752
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• 2016

The parameters of Debye's equation were applied to analyze the frequency-dependent ground impedance of horizontally-buried wires. We present a new method, based on Debye's equation, of analyzing the effect of polarization on frequency-dependent ground impedance. The frequency-dependent ground impedances of a horizontally-buried wire are directly measured and calculated by applying sinusoidal current in the frequency range of 100 Hz to 10 MHz. Also, the results obtained in this work were compared with the data calculated from empirical equations and commercial programs. A new methodology using the delta-gap source model is proposed in order to calculate frequency-dependent ground impedance when the ground current is injected at the middle-point of the horizontal ground electrode. The high frequency ground impedance of horizontal electrodes longer than 30 m is larger or equal to its low frequency ground resistance. Consequently, the frequency-dependent ground impedance simulated with the proposed method is in agreement with the experimental data, and the validity of the computational simulation approach is confirmed.

• Journal of the Optical Society of Korea
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• v.13 no.1
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• pp.15-21
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• 2009

High-order harmonic generation from a solid surface affected by the contrast of a laser pulse was studied using an oscillating mirror model. High-order harmonics generated from solid surfaces have unusual properties such as spectral redshift, and an intensity difference between even- and odd-order harmonics which is not reported for high-order harmonics generated by a gas medium. We confirmed that high-order harmonics from solid surfaces have selectivity of polarization as well as cut-off extension and the enhancement of conversion efficiency proportional to laser intensity. And the principle of operation and the characteristics of a plasma mirror system developed for achieving high contrast laser pulses to pursue the experimental realization of high-harmonic generation from solid surfaces are reported. Energy fluence on the plasma mirrors is tunable between $10\;J/cm^2$ and $1000\;J/cm^2$ and around 1000 shots are available before the plasma mirrors require replacement.

• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.13-16
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• 2008

Solid oxide fuel cell(SOFC) is an electrochemical energy conversion system with high efficiency and low-emission of pollution. In order to reduce the operating temperature of SOFC system under $800^{\circ}C$, the thickness reduction of YSZ electrolyte to be as thin as possible, e.g., less than 10 ${\mu}m$ are considered with the microstructure control and optimum design of unit cell. Methods for reducing the thickness of YSZ electrolyte have been investigated in coin cell. Moreover, a large unit cell($8cm{\times}8cm$) for SOFC was fabricated using an anode-supported electrolyte assembly with a thinner electrolyte layer, which was prepared by a tape casting method with a co-sintering technique. we studied the design factors such as active layer, electrolyte thickness, cathode composition, etc,. by the coin type of unit cell ahead of the fabrication process of a large unit cell and also reviewed about the evaluation technique of a large size unit cell such as interconnect design, sealing materials and current collector and so forth. Electrochemical evaluations of the unit cells, including measurements such as power density and impedance, were performed and analyzed. Maximum power density and polarization impedance of coin cell were 0.34W/$cm^2$ and $0.45{\Omega}cm^2$ at $800^{\circ}C$, respectively. However, Maxium power density of a large unit cell($5cm{\times}5cm$) decreased to 0.21W/$cm^2$ at $800^{\circ}C$ due to the increase of ohmic resistance. However, It was found that the potential value of a large unit cell loaded by 0.22A/$cm^2$ showed 0.76V at 100hrs without the degradation of unit cell.

• Journal of the Korean Ceramic Society
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• v.39 no.1
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• pp.86-91
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• 2002

Solid Oxide Fuel Cells (SOFC) are of great interest of next generation energy conversion system due to their high energy efficiency and environmental friendliness. The basic SOFC unit consists of anode, cathode and solid electrolyte. Among these components, anode plays the most important role for the oxidation of fuel to generate electricity and also behaves as a substrate of the whole cell. It is normally requested that the anode materials should have the high electrical conductivity and gas permeability to reduce the polarization loss of the cell. In this study, the effect of pore former on the microstructure of anode substrate was investigated and thus on the electrical conductivity and the gas permeability. According to the results, microstructure and electrical conductivity of anode substrate were greatly influenced by the shape of pore former and especially by the anisotrpy of the pore former. The use of anisotropic pore former is supposed to deteriorate the cell performance by which the electrical conduction path is disconnected but also the effective gas diffusion path for the fuel is reduced.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.12
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• pp.1308-1315
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• 2009

A full-polarimetric scatterometer(HPS: Hongik Polarimetric Scatterometer) for X-band is designed, fabricated, and verified using the theoretically well-known point-targets in this paper. The X-band full-polarimetric scatterometer consists of an OMT(Orthogonal-Mode Transducer)+horn antenna, the angle control part for the OMT+horn antenna, a transmitter/receiver with a network analyzer and a frequency-conversion circuitry, and a movable support of these parts. We use an inclinometer sensor to control the vertical and horizontal incidence angles. The full polarimetric data can be obtained because of the polarization switches and the OMT. The accuracy of the scatterometer system is verified by measuring the polarimetric RCS(Radar Cross Section) of one of the theoretically well-known point-targets, i.e., a corner reflector.

• Journal of the Microelectronics and Packaging Society
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• v.27 no.2
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• pp.33-38
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• 2020

In the photoelectrochemical (PEC) water splitting, GaN is one of the most promising photoanode materials due to high stability in electrolytes and adjustable energy band position. However, the application of GaN is limited because of low efficiency. To improve solar to hydrogen conversion efficiency, we introduce a Cobalt Phosphate (Co-pi) catalyst by photo-electrodeposition. The Co-pi deposition GaN were characterized by SEM, EDS, and XPS, respectively, which illustrated that Co-pi was successfully decorated on the surface of GaN. PEC measurement showed that photocurrent density of GaN was 0.5 mA/㎠ and that of Co-pi deposited GaN was 0.75 mA/㎠. Impedance and Mott-Schottky measurements were performed, and as a result of the measurement, polarization resistance (R_p) and increased donor concentration (N_D) values decreased from 50.35 Ω to 34.16 Ω were confirmed. As a result of analyzing the surface components before and after the water decomposition, it was confirmed that the Co-pi catalyst is stable because Co-pi remains even after the water decomposition. Through this, it was confirmed that Co-pi is effective as a catalyst for improving GaN efficiency, and when applied as a catalyst to other photoelectrodes, it is considered that the efficiency of the PEC system can be improved.