• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.149-149
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• 2010

The double-layer antireflection (DLAR) coatings have significant advantages over single-layer antireflection (SLAR) coatings. This is because they will be able to cover a broad range of the solar spectrum which would enhance the overall performance of solar cells. Moreover films deposited at high frequency are expected to show excellent and UV-stable passivation in the refractive index that we adopted. In this work, we present a novel DLAR coating using SiNx:H thin films with refractive indices 1.9 and 2.3 as the top and bottom layers. This approach is cost effective when compared to earlier DLAR coatings with two different materials. SiNx:H films were deposited by Plasma enhanced chemical vapor deposition (PECVD) technique using $SiH_4$, $NH_3$ and $N_2$ gases with flow rates 20~80sccm, 200sccm and 85 sccm respectively. The RF power, plasma frequency and substrate temperature for the deposition were 300W, 13.56 MHz and $450^{\circ}C$, respectively. The optimum thickness and refractive indices values for DLAR coatings were estimated theoretically using Macleod simulation software as 82.24 nm for 1.9 and 68.58 nm for 2.3 respectively. Solar cells were fabricated with SLAR and DLAR coatings of SiNx:H films and compared the cell efficacy. SiNx:H> films deposited at a substrate temperature of $450^{\circ}C$ and that at 300 W power showed best effective minority carrier lifetime around $50.8\;{\mu}s$. Average reflectance values of SLAR coatings with refractive indices 1.9, 2.05 and 2.3 were 10.1%, 9.66% and 9.33% respectively. In contrast, optimized DLAR coating showed a reflectance value as low as 8.98% in the wavelength range 300nm - 1100nm.

• ETRI Journal
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• v.27 no.4
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• pp.377-384
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• 2005

We investigate near-infrared light (NIR) propagation in a model of an adult head using an extensive Monte Carlo (MC) simulation. The adult head model is a four-layered slab which consists of a surface layer, a cerebrospinal fluid layer, a gray-matter layer, and a white-matter layer. We study the effects of a refractive index mismatch on the model, calculating the intensity of detected light, mean flight time, and partial mean flight time of each layer for various refractive indices of the cerebrospinal fluid layer as functions of source-detector spacing. The Monte Carlo simulation shows that the refractive index mismatch presents very rich results including rapidly decaying intensity of detected light and a peak and cross-over in the partial mean flight time with source-detector spacing. We also investigate spatial sensitivity profiles at various source-detector spacings, discussing the index mismatch effect on the model.

• Current Optics and Photonics
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• v.3 no.5
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• pp.423-428
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• 2019

Visibility of road-surface markings is one of the critical issues that should be secured for self-driving cars as well as human drivers. Glass beads are taking on the role of retroreflectors, and therefore are considered a necessity in modern pavements. In this context, retroreflectance is sensitively dependent not only on the refractive index of glass beads but also on that of the surrounding medium. This implies that the optimum refractive index of glass beads immersed in water, i.e. under wet conditions, is different from that of glass beads surrounded by air, i.e. under dry conditions. A refractive index of approximately 1.9, which is known to maximize retroreflectance under dry conditions, actually exhibits much poorer retroreflectance under wet conditions. This suggests that glass beads with optimal refractive index for wet conditions need to be installed together with those for dry conditions. We propose a facile but practical model capable of calculating retroreflectance of glass beads surrounded by an arbitrary medium, here water in particular, and experimentally verify its capability of assessing the refractive index of commercial glass beads. Changes in retroreflectance according to the mixing ratio of glass beads with different refractive indices are also discussed, in an effort to propose the proper use of glass beads produced for dry and wet conditions.

• Journal of Korean Ophthalmic Optics Society
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• v.19 no.1
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• pp.1-8
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• 2014

Purpose: To observe changes of coatings and lens materials with varying temperature to understand effect of temperature on plastic lens. Methods: In this study, three lenses of different refractive indices (2 of thiourethane oriented lenses, an allyl diglycol carbonate oriented lens) were exposed to high temperature (50, 80, and 100 degree) for 5 hours and changes of individual coating (anti-refractive coating, hard coating, and water repellent coating) were measured. Results: As a result, high-refractive index lenses did not exhibit significant variation of hardness. However, hardness of mid-refractive index lens were decreased when exposed to high temperature and destructions of hard coating layer was inferred. Surface contact angles of lens were decreased with increasing temperature and water repellent coating layer were damaged at higher than 80 degree. Conclusions: Multi including water repellent coatings on all three lenses with different refractive indices were damaged when exposed to at or higher than 80 degree. The degree of changes in mechanical and physical properties were depended on polymer material type.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.9
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• pp.643-651
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• 2001

Fused vertical directional coupler switches (FVCSs) with switching operation induced section (SOIS) and extinction ratio enhanced section (ERES) are proposed. In these FVCSs, switching operation is achieved by changing the refractive indices of both cores in SOIS and improvement of extinction ratios larger than 30dB for both cross and bar states is achieved by controlling the asymmetry of refractive indices between both cores in ERES. In addition, the design guidelines to have high extinction ratios larger than 30dB with large tolerances of the refractive index of cores are presented.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.10
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• pp.42-50
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• 2000

We show that both cross and bar states with high extinction ratios larger than 30dB can be achieved at eh same ends of ultra-short fused vertical directional coupler switches with two sections by changing the refractive indices of cores and inner cladding layers less than 1%. Based on the calculation of extinction ratios of cross state and bar state for various refractive index and thickness of inner cladding layer and core using the improved coupled mode theory and beam propagation method, the guidelines for design to achieve large tolerances in refractive indices of core and inner cladding layer in fused vertical directional coupler switches are presented.

• Korean Journal of Crystallography
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• v.5 no.1
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• pp.7-13
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• 1994

Light propagation in an anisotropic crystal in the presence of strains and temperature change is investigated. This phenomenon appears in an embedded optical films sensor inside the structure or in an optical on the substrate for optical devices. The refractive indices which represent the light propagation in an anisotopic crystal are calculated and the changes of these refractive indices in the presence of strains and tepmerature change are also calculated. The calculations for the light propagation. In an isotropic medium with the simplified model are performed and the results are compared with devious investigators.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.291-292
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• 2005

Comparing with conventional STN-LCD, a good electro-optical characteristics were observed on the STN-LCDs of low cell gap using liquid crystals that have large refractive indices. Especially, A stable voltage-transmittance(V-T) curve of the plastic STN-LCD was measured and fast response time characteristics were obtained. We suggested that fast response STN-LCD is promising technique in the flexible display of small size because it has lots of advantages such as low cost, simple manufacture process comparing with other modes.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2406-2409
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• 2008

The concept of optical mobility in the optical particle separation was derived. To verify the concept of the optical mobility, three particles were chosen to test the effects of optical mobility, namely, PSL, PMMA and silica particles. Three different experiments were performed. Firstly, retention distances of the different sized particles were measured and predicted. Secondly, retention distances of particles, having same size but different refractive indices, were measured and predicted. Finally, retention distances of the particles, which had the same optical mobility but very different sized and refractive indices, were measured and predicted.

• Journal of the Korean institute of surface engineering
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• v.29 no.5
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• pp.556-562
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• 1996

Carbon nitride (CN) films were synthesized on silicon substrates by a combined ion-beam and laser-ablation method under various conditions; ion-beam energy and ion-beam current were varied. Raman spectroscopy and spectroscopic ellipsometry (SE) were employed to characterize respectively the structural and the optical properties of the CN films. Raman spectra show that all the CN films are amorphous independent of the ion-beam current and the ion-beam energy. Refractive indices, extinction coefficients and optical band gaps which were determined from the measured SE spectra exhibit a significant dependence on the synthesis conditions. Especially, the decrease of the refractive indices and the shrinkage of the optical band gap is noticeable as the ion-beam current and/or the ion-beam energy increase.