• Journal of the Optical Society of Korea
• /
• v.12 no.3
• /
• pp.200-204
• /
• 2008

Coherent tunable terahertz generation was demonstrated in periodically poled stoichiometric lithium tantalate crystal via difference frequency generation of femtosecond laser pulses. Simultaneous forward and backward terahertz radiations were obtained around 1.35 and 0.63 THz, respectively at low temperature. By cooling the crystal to reduce losses caused by phonon absorptions, the generated THz bandwidth was as narrow as 23GHz at the center frequency of 0.63 THz. The measurement result of temperature-dependent showed gradual intensity increase of the generated terahertz pulse and red shift of the center frequency as the temperature decrease from 291 to 143 K, but insignificant reduction of the spectral bandwidth. Furthermore, the stoichiometric crystal was very suitable for the suppression of THz loss at low temperature compared to the congruent $LiNbO_3$ crystal.

• Korean Journal of Optics and Photonics
• /
• v.16 no.1
• /
• pp.79-84
• /
• 2005

To increase the tolerance for passive fiber alignment, a single mode polymer waveguide with a large core structure is demonstrated. The large core waveguide is designed to have a mode profile comparable to that of a thermally expanded core (TEC) fiber, and it can be connected to a high-contrast waveguide through an adiabatic transition taper structure. From a waveguide with a rectangular core of 25 ${\times}$ 25 ${\mu}{\textrm}{m}$$^2$, a single mode propagation is observed when the index contrast is as low as 0.0005. A UV-cured injection molding method is used to fabricate the thick core structure. Due to the large mode size, the insertion loss of the device is below 0.5 dB until the lateral displacement of the TEC fiber is 4.5 ${\mu}{\textrm}{m}$. The low insertion loss is important for reproducible passive alignment.

• Bulletin of the Korean Chemical Society
• /
• v.32 no.9
• /
• pp.3311-3316
• /
• 2011

New poly(arylene ether)s (PAEs) with both transparency and heat-resistance were prepared by a polycondensation of FBPODS, an ordered-sequence aromatic dihalide, and cardo typed aromatic diols containing fluorene and/or adamantane moiety and also non-cardo typed 1,5-naphthalene diol. The resulting polymers had their glass transition temperatures ranged from 202 to $247^{\circ}C$. Based on TGA data, they exhibited excellent thermal stabilities, showing 5% weight loss at $434-487^{\circ}C$. They had low thermal expansion coefficients of 58-59 ppm at temperature range of $50-200^{\circ}C$ as well as good mechanical properties with moduli of 1757-2143 MPa. The optical transmittance for the PAE films was over 70% at 550 nm, except for the PAE that contains naphthalene moiety (30% at 550 nm). They also showed water uptake of about 0.68% regardless of their chemical compositions. Therefore, the newly developed PAEs show strong potential as plastic substrates for flexible devices for display, solar cell and e-paper.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
• /
• 2006.06a
• /
• pp.129-136
• /
• 2006

Although cleaner and cheaper deinking of ONP could be performed at the neutral or low alkaline condition excessive loss from froth-flotation is unavoidable and so reduction of alkali or caustic soda dosage sacrifices recycling yield. Now the new trade-off regarding alkali dosage versus flotation yield is urgently required in order to set the optimized neutral or low alkaline deinking process of ONP. Lipase from Thermomyces Lanuginosus has an effect on desizing and deacetylation reaction and it could be applied to the stock of pre flotation secondary stage in order to reduce the flotation reject without the sacrifice of optical properties of flotation accepts. Instead of inorganic base, lipase could be applied as a biochemical catalyst for the selective modification of valuable hydrophobic particles in deinking stock, for example cellulose fines and inorganic fillers covered by hydrophobic additives or contaminants. When the enzymatic hydrolysis of ester bond could be made on the surface of hydrophobic particulates, unwanted float of fine particles could be prevented. Now the enhancement of flotation selectivity or the modification of the hydrophobicity of deinking stock is expected to be promoted by the enzymatic pre treatment. And the reduction of recycling cost with the saves of raw material, recovered paper would be possible as a result.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.27 no.12
• /
• pp.871-876
• /
• 2014

Efficiency of crystalline Si solar cell can be maximized as minimizing optical loss through antireflection texturing with inverted pyramids. Even if cost-competitive, soft lithography can be employed instead of photolithography for the purpose, some limitations still remain to apply the soft lithography directly to as-received solar grade wafer with a bunch of micro trenches on surface. Therefore, it is needed to develop a low-cost, effective planarization process and evaluate its output to be applicable to patterning process with PDMS stamp. In this study new surface planarization process is proposed and the change of micro scale trenches on the surface as a function of etching time is observed. Also, the effect of trenches on pattern quality by soft lithography is investigated using FEM structural analysis. In conclusion it is clear that the geometry and shape of trenches would be basic considerations for soft lithography application to low quality wafer.

• Journal of Astronomy and Space Sciences
• /
• v.40 no.4
• /
• pp.237-245
• /
• 2023

Laser communication has been considered as a novel method for earth observation satellites with generation of high data volume. It offers faster data transmission speeds compared to conventional radio frequency (RF) communication due to the short wavelength and narrow beam divergence. However, laser beams are refracted due to atmospheric turbulence between the ground and the satellite. Refracted laser beams, upon reaching the receiver, result in angle-of-arrival (AoA) fluctuation, inducing image dancing and wavefront distortion. These phenomena hinder signal acquisition and lead to signal loss in the course of laser communication. So, precise alignment between the transmitter and receiver is essential to guarantee effective and reliable laser communication, which is achieved by pointing, acquisition, and tracking (PAT) system. In this study, we simulate the effectiveness of tip/tilt compensation for more efficient laser communication in the satellite-ground downlink. By compensating for low-order terms using tip/tilt mirror, we verify the alleviation of AoA fluctuations under both weak and strong atmospheric turbulence conditions. And the performance of tip/tilt correction is analyzed in terms of the AoA fluctuation and collected power on the detector.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.42 no.12
• /
• pp.31-36
• /
• 2005

In this paper, we propose a new optical switching system as a infrastructure of the BcN, in which the high traffic volume will be expected due to the multimedia service, like P2P services. Because the JET protocol, the most popular protocol in OBS (Optical Burst Switching) research area, has high blocking probability for burst, it prevents commercialization in real network for its low throughput in TCP layer. To improve high blocking rate in OBS network, we segment large network into small network and perform burst scheduling to avoid burst loss. By using proposed scheme, Internet provider can reduce network deployment cost in Metro network as well as large mesh core networks

• Journal of the Korean institute of surface engineering
• /
• v.51 no.4
• /
• pp.249-255
• /
• 2018

High temperature and low temperature gaseous nitriding was performed in order to study of the surface hardening and wear properties of the nitrided AISI 410 Martensitic stainless steels. High temperature gaseous nitiridng (HTGN) was carried out using partial pressure $N_2$ gas at $1,100^{\circ}C$ for 10 hour, and Low temperature gaseous nitiridng (LTGN) was conducted in a gas mixture of NH3 and N2 at $470^{\circ}C$ for 10 hour. The nitrided samples were characterized by microhardness measurements, optical microscopy and scanning electron microscopy. The phases were identified by X-ray diffraction and nitrogen concentration was analyzed by GD-OES. The HTGN specimen had a surface hardness of about $700HV_{0.1}$, $350{\mu}m$ of case depth. A ${\sim}50{\mu}m$ thick, $1,250HV_{0.1}$ hard nitrided case formed at the surface of the AISI 410 steel by LTGN, composed nitrogen supersaturated expanded martensite and ${\varepsilon}-Fe_{24}N_{10}$ iron nitrides. Additionally, the results of the wear tests, carried out LTGN specimen was low friction coefficient and high worn mass loss of ball. The increase in wear resistance can be mainly attributed to the increase in hardness and to the lattice distortion caused by higher nitrogen concentration.

• Journal of the Institute of Electronics and Information Engineers
• /
• v.51 no.1
• /
• pp.152-157
• /
• 2014

Digital still camera generally uses optical low-pass filter(OLPF) to enhance its image quality because it removes high spatial frequencies causing aliasing. However, the use of OLPF causes some loss of detail. On the other hand, when image are captured by using no OLPF, the moir$\acute{e}$ is generally existed in high spatial frequency region of an image. Therefore, in this paper, moir$\acute{e}$ reduction method in case of using no OLPF is suggested. To detect the moir$\acute{e}$, spatial frequency response(SFR) of camera was firstly analyzed by using ISO 12233 resolution chart. Then, moir$\acute{e}$ region is detected by using the patterns that are related to the SFR of camera. next, this region is analysed in the frequency domain. Then, the moir$\acute{e}$ is reduced by removing its frequency component, which represents inflection point between high frequency and DC components. Through the experimental results, it is shown that the proposed method can achieve moir$\acute{e}$ reduction with preserving the detail.

• Korean Journal of Optics and Photonics
• /
• v.13 no.4
• /
• pp.336-339
• /
• 2002

For the improvement of the lock-in frequency of a ring laser gyro, a low-scattering mirror was employed in the laser resonator. A super-polishing technique produced fine mirror substrates of less than 1-A-rms-roughness. The mirror coating using an ionbeam sputtering technique reduced the scattering loss to less than 30 ppm. As a result of the mirror scattering enhancement of the ring laser, the lock-in frequency of the gyro was improved up to about 0.1 deg/sec.