• Journal of the Korean Ceramic Society
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• v.42 no.6 s.277
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• pp.399-404
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• 2005

Anti-reflection film was coated by using spherical silica nano colloidal particles and fumed silica particles. Silica colloid sol was reserved between two inclined slide glasses by capillary force, and particles were stacked to form a film onto the substrate as the upper glass was sliding. The deposition processes were studied to enhance the wavelength dependency of the light transmittance and to control the effective refractive index of the film. Both of the spherical and fumed silica particles showed an enhancement of $4.0-4.4\%$ in light transmittance by one step coating. The dependence of the transmittance on wavelength was largely improved at the longer wavelength by partial coating of fumed particles on the film of spherical particles. The effective refractive index of the film was controlled by removing latex particles that were co-deposited with silica particles. Using this process the light reflectance from one side of the glass substrate could be reduced from $4.2\%$ to $0.6\%$ although zero reflectance was not achieved due to the agglomeration of the latex particles.

• Journal of the Optical Society of Korea
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• v.18 no.6
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• pp.691-697
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• 2014

Optical measurements of the morphological and biochemical imaging of phytoplankton are presented. Employing quantitative phase imaging techniques, 3-D refractive index maps and high-resolution 2-D quantitative phase images of individual live phytoplankton are simultaneously obtained without exogenous labeling agents. In addition, biochemical information of individual phytoplankton including volume, mass, and density of individual phytoplankton are also quantitatively obtained from the measured refractive index distributions. We expect the present method to become a powerful tool for the study of phytoplankton.

• Journal of IKEEE
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• v.14 no.4
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• pp.263-269
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• 2010

In this paper, we present high temperature characteristics of a tunable all-optical filter using fiber Bragg grating(FBG) filter in Ge doped and Ge & B co-doped fiber, including peak reflectivity, bandwidth and various normalized refractive index change with temperature variation. The reflection spectrum of a FBG filter with refractive index change is affected by its thermal stability. Consequently Ge doped FBG tunable filter has a better thermal stability than Ge & B co-doped FBG tunable filter. Also, both FBG tunable filters show good thermal stability up to about $500^{\circ}C$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.1
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• pp.61-66
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• 2002

A method for designing antireflection (AR) and antistatic (AS) coating layer by the use of conducting polymer as an electrically conductive transparent layer is proposed. The conducting AR coating is composed of four-layer with alternating high and low refractive index layer: silicon dioxide (n=1.44) and titanium dioxide (n=2.02) prepared at low temperature by sol-gel method are used as the low and high refractive index layer, respectively. The poly(3,4-ethylenedioxythiophene) which has the surface resistivity of 10$^4$Ω/$\square$ is used as a conductive layer. Optical constant of each ARAS coating layers such as refractive index and optical thickness were measured by 7he spectroscopic ellipsometer and from the measured optical constants the spectral properties such as reflectance and transmittance were simulated in the risible region. The reflectance of ARAS films on glass substrate was below 1 %R and the transmittance was higher than 95 % in the visible wavelength (400-700 nm). The measured AR spectral properties was very similar to its simulated results.

• Journal of Sensor Science and Technology
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• v.30 no.6
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• pp.415-419
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• 2021

We developed a highly accurate, yet inexpensive, refractive index (RI)-based soil moisture sensor. To detect the RI, a light guide was set with a light-emitting diode and photodiode. When the air fills the space between the soil particles, most of the incident light is reflected at the interface between the waveguide and the air because of the large RI difference. As the moisture of the soil increases, the macroscopic soil RI increases. This allows incident light to pass through the interface. The intensity of the light reaching the photodiode was simulated according to the change in the soil RI. Using the simulation results, we designed and manufactured a curved glass waveguide. We evaluated the performance of the RI-based soil sensor by comparing it with a commercially available, high-cost and high-performance time-domain reflectometer (TDR). Our sensor was 96% accurate, surpassing the costly TDR sensor.

• Journal of the Korean Ceramic Society
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• v.42 no.1
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• pp.28-32
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• 2005

The optical properties and intrinsic stress of $Ta_{2}O_{5}$ thin films deposited by Dual ion-Beam Sputtering: (DIBS) and Single ion-Beam Sputtering (SIBS) were studied as a function of the substrate temperature and assist ion beam voltage. The refractive index showed the maximum value (n = 2.144) at $150^{circ}C$ in the SIBS process. When the substrate temperature has above $150^{circ}C$ in the SIBS process the refractive index decreased. In the DIBS process, the increase of the substrate temperature affected the increase of the refractive index at a maximum value (n = 2.1117, at $200^{circ}C$). The low temperature process $(<100^{circ}C)$ can greatly reduce residual stress with the assist ion gun, but the high temperature process was unaffected. As the assist ion beam voltage increase from 250 to 350 V the refractive index increased to 2.185. However, the refractive index was decreased at the range of 350-650 V, As the assist ion beam voltage increased, the stress of the deposited film decreased to 0.1834 GPa at 650 V.

• Korean Journal of Remote Sensing
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• v.27 no.2
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• pp.163-170
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• 2011

In this paper, we analyzed the phase change of 5-triangular trihedral comer reflectors by using X-band Ground-Based Synthetic Aperture Radar (GB-SAR) system. Each reflector was set as a stationary target at a different distance from the system. We obtained total 123 full-polarization images during 40 hours continuously at 20 minute interval. Results of SAR interferometric analysis showed phase changes of maximum 2 radians and followed similar pattern with atmospheric data. Through a GB-SAR phase formula that includes refractive index in the air, we performed regression analysis for refractive index as a function of atmospheric humidity, temperature and pressure. As a result, refractive index of air in X-band showed relatively high coefficient of determination with humidity and temperature (0.72 and 0.76 on average, respectively) but not so with pressure (0.34). The refractive index of air in X -band changed by 3.14\;{\times}\;10^{-5}$ during the measuring time with a humidity range of 50% ~ 90% and a temperature range of $-1^{\circ}C$ ~ $9^{\circ}C$. We expect that a total expression of refractive index of air including humidity, temperature and pressure can be calculated when more extensive data would be collected at various atmospheric conditions.

• Korean Journal of Optics and Photonics
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• v.18 no.6
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• pp.395-400
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• 2007

We propose a design and analysis of an optical system using a prism with a high enough refractive index for wet fingerprint identification. Important parameters including the tilting angle($\beta$) of the $1^{st}$ image plane, an anamorphic distortion, and a tilt of image plane are considered in terms of the apex angle of the prism($\alpha$) and refractive index of the prism material. Our suggestion on refractive index and apex angle of the prism corroborates well with experimental results.

• Journal of the Korean Chemical Society
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• v.53 no.6
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• pp.755-760
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• 2009

Styrene is broadly used as a polymer and a copolymer and is useful in manufacturing contact lenses due to its high refractive index. This study used styrene with the cross-linker EGDMA (ethylene glycol dimethacrylate), HEMA (2-hydroxyethyl methacrylate) and the initiator AIBN (azobisisobutyronitrile) for copolymerization. Measurement of the physical characteristics of the copolymerized material showed that the refractive index is 1.4412 - 1.4628, water content 20 - 35%, visible transmittance 82.6 - 87% and the tensile strength 0.143 - 0.344 Kgf. Also, measurements showed that the refractive index and tensile strength increased while the water content decreased as the ratio of styrene increased. Based on the results of this study, the produced copolymer can be estimated to be suitable for use as a material for high performance functional contact lenses.

• Current Optics and Photonics
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• v.2 no.5
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• pp.460-467
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• 2018

Three-dimensional (3D) refractive-index (RI) imaging and quantitative analyses of angiosperm pollen grains are presented. Using optical diffraction tomography, the 3D RI structures of individual angiosperm pollen grains were measured without using labeling or other preparation techniques. Various physical quantities including volume, surface area, exine volume, and sphericity were determined from the measured RI tomograms of pollen grains. Exine skeletons, the distinct internal structures of angiosperm pollen grains, were identified and systematically analyzed.