• Journal of the Optical Society of Korea
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• v.19 no.1
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• pp.88-94
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• 2015

This paper reports the fabrication of a lenticular liquid crystal (LC) lens array with thermally tunable focus and with the function of a convertible lens type, using the surface structure of a UV-curable polymer and a twisted-nematic (TN) LC cell. The TN LC cell makes the LC lenticular lens function as a converging or diverging lens by controlling electrically the polarization of input light. Therefore, the focal lengths for both the converging and diverging lenses, which can be switched from the TN cell, can be tuned by changing the effective refractive index of the LC by Joule heating of the transparent electrode. As a result, the focal length of the lens with the E7 LC was changed continuously from 8.7 to 31.2 mm for the converging lens type and from -9.8 to -14.2 mm for the diverging lens when the temperature was increased from 25 to $56^{\circ}C$.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.5
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• pp.709-715
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• 1990

SiO2 films were nitrided by tungsten-halogen heated rapid thermal annealing in ammonia gas at temperatures of 900-1100\ulcorner for 15-180sec. The nitroxide films were analyzed using Auger electron spectroscopy. MIS caapcitors were fabricated using these films as gate insulators. I-V and C-V characteristics of MIS capacitors were investigated. The AES depth profiles of nitroxide film show that the nitrogen rich layer is, at the early stage of nitridation, formed at the surface of nitroxide film and near the interface between nitroxide and silicon. Nitridation of SiO2 makes the film have a larger effective average refractive index. The thermal nitridation of SiO2 on silicon causes the flatband voltage shift due to the change of the fixed charge density. It is found that the dominant conduction mechanism in nitroxide is Fowler-Nordheim tunneling. Rapid thermal nitridation of 200\ulcornerSiO2 on silicon results in an improvement in the dielectric breakdown electric field.

• 한국정보디스플레이학회:학술대회논문집
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• 2003.07a
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• pp.1034-1037
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• 2003

In this work, Integral photography with variable focusing lens arrays is proposed. We fabricate two-dimensional liquid crystal lens arrays using cohesion of UV curable polymer and lithography. Applied voltage to the cell alters the effective refractive index of the liquid crystal layer and results in a change of the focal length. By adjusting the focal length, synchronized elemental image array for real or virtual mode is integrated in front of or behind the lens array.

• Journal of the Korean Vacuum Society
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• v.12 no.S1
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• pp.15-16
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• 2003

3-D photonic band-gap structures are fabricated from dielectric colloidal polystyrene beads through a centrifuge method. The fabricated photonic crystals exhibit opalescent colors under white light and show a clear diffraction peak dependent on the incident angle of the light beam. Also the scanning electron microscope image was taken to verify the face-centered cubic crystal structure. Bragg's law and Snell's law are employed to describe the position of angle resolved diffraction peaks. It was shown that the optically deduced effective refractive index and lattice constants were in good agreement with the crystal structure identified by scanning electron microscope.

• Bulletin of the Korean Chemical Society
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• v.26 no.6
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• pp.947-951
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• 2005

Rotating compensator multichannel spectroscopic ellipsometry has been employed to determine the optical functions of various liquids used in chemistry. We attempted three different measurement configurations: (1) air-liquid interface, (2) prism-liquid interface, and (3) liquid-sample interface. In prism-liquid interface, we found that the prism surface had roughness and it should be considered in analysis for accurate results. In liquidsample interface, we had much higher reflection, better sensitivity, and less limitation compared to the other two configurations when crystalline silicon was used as reference sample. We discuss the merit of each configuration and present the optical functions of various liquids. Also we demonstrate Bruggeman effective medium theory to determine the optical properties of mixed liquid.

• Korean Journal of Optics and Photonics
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• v.11 no.1
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• pp.33-36
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• 2000

KrF excimer laser, which is useful for fabrication of fiber gratings, was irradiated on the PLC-type WDM directional coupler and the transmission wavelength shift was observed as a function of UV exposure time. The effective refractive index change of rectangular silica waveguide was calculated from the wavelength shift measurement and the coupled mode theory. heory.

• Journal of the Korean Applied Science and Technology
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• v.27 no.3
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• pp.378-384
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• 2010

Regenerated cellulose was prepared from Buckeye wood pulp V60 via dissolution in N-methylmorpholin N-oxide (NMMO) solvent system. The effect of antioxidants such as, n-propylgallate (PG), tris(nonylphenyl) phosphite (TRIS), ethylenediamine tetraacetic acid disodium salt (EDTA), and magnesium sulfate on the properties of regenerated cellulose was studied using X-ray diffraction, copper index calculation, and viscometry. Only addition of more than 0.01% of PG into NMMO solvent was effective to avoid the reduction of the degree of polymerization(DP) of regenerated cellulose during dissolution at $110^{\circ}C$. However, the early stage(within 0.5h of dissolution process) degradation of cellulose was not prevented eventhough up to 0.5% PG was appled to hot NMMO system. In addition, to recover the expensive NMMO after cellulose regenerating process, the washing filtrate was studied using simple techniques, such as refractive index, pH, and conductivity measurements. Through conductivity measurement result, 4-time of washing was enough to remove the NMMO completely from regenerated cellulose.

• Journal of the Korea Convergence Society
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• v.12 no.2
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• pp.29-34
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• 2021

In this paper, a cylindrical photonic crystal waveguide with a low-index core is first proposed. The core can be filled with air, liquid, or arbitrary dielectric materials. Exact analyses for the electromagnetic field characteristics of guided modes, by using appropriate Bessel functions and applying the boundary conditions, are performed to find out the guiding characteristics of the proposed waveguide. For verification and usage in design and manufacturing process, the computer-calculation of the waveguide transmission characteristics is also performed by applying the rigorous full-vectorial finite difference method. Providing variations of the effective area for the fundamental mode of the designed waveguide with different numbers of cladding layers, ranging from 2.6056 ㎛2 to 5.9673 ㎛2 over the operation wavelength, generally as the core refractive index n1 is higher, the mode area becomes smaller and the result leads to more optimistic effect for nonlinear device applications.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.16 no.4
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• pp.133-140
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• 2006

The growth characteristics and properties of large size $SrAlF_5$ single crystals are described and compared with those of $BaMgF_4$. Transmission spectra in the vacuum ultraviolet wavelength region indicate a high transparency of $SrAlF_5$ (about 90% without considering surface reflection loses) down to 150 nm, on contrast to the optical loses observed for $BaMgF_4$. The ferroelectric character of $SrAlF_5$ is evidenced by the reversal of the spontaneous polarization in a hysteresis loop. The higher potential of $SrAlF_5$ in comparison with $BaMgF_4$ for the realization of all-solid-state lasers in the ultraviolet wavelength region by the quasi-phase matching (QPM) technique is pointed out. $SrAlF_5$, besides a higher grade of transparency, shows a nonlinear effective coefficient similar to that of quartz and uniaxial nature, on contrast to the one order smaller nonlinear coefficient and biaxial character of $BaMgF_4$. The refractive index of $SrAlF_5$ from the ultraviolet to the near-infrared wavelength region is measured by the minimum deviation method. The Sellmeier and Cauchy coefficients are obtained from the fits to the curves of the ordinary and extraordinary refractive indices, and the grating period for the first order QPM is estimated as a function of the wavelength. The poling periodicity for 193 nm SHG from 386 nm is $4{\mu}m$.

• Bulletin of the Korean Chemical Society
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• v.27 no.5
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• pp.718-724
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• 2006

The heterogeneous association behaviour of various concentration binary mixtures of mono alkyl ethers of ethylene glycol with ethyl alcohol were investigated by dielectric measurement in benzene solutions over the entire concentration range at 25 ${^{\circ}C}$. The values of static dielectric constant $\epsilon_0$ of the mixtures were measured at 1 MHz using a four terminal dielectric liquid test fixture and precision LCR meter. The high frequency limiting dielectric constant $\epsilon_\infty$ values were determined by measurement of refractive index $n_D$ ($\epsilon_\infty\;=\;n_D\;^2$). The measured values of $\epsilon_0$ and $\epsilon_\infty$ were used to evaluate the values of excess dielectric constant $\epsilon^E$, effective Kirkwood correlation factor $g^{eff}$ and corrective correlation factor $g_f$ of the binary polar mixtures to obtain qualitative and quantitative information about the H-bond complex formation. The non-linear behaviour of the observed $\epsilon_0$ values of the polar molecules and their mixtures in benzene solvent confirms the variation in the associated structures with change in polar mixture constituents concentration and also by dilution in non-polar solvents. Appearance of the maximum in $\epsilon^E$ values at different concentration of the polar mixtures suggest the formation of stable adduct complex, which depends on the molecular size of the mono alkyl ethers of ethylene glycol. Further, the observed $\epsilon^E$ < 0 also confirms the heterogeneous H-bond complex formation reduces the effective number of dipoles in these polar binary mixtures. In benzene solutions these polar molecules shows the maximum reduce in effective number of dipoles at 50 percent dilutions. But ethyl alcohol rich binary polar mixtures in benzene solvent show the maximum reduce in effective number of dipoles in benzene rich solutions.