• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.12
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• pp.1383-1389
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• 2011

The current study focuses on the consistent analysis of heat transfer in multichannel volumetric solar receivers used for concentrating solar power. Changes in the properties of the absorbing material and channel dimensions are considered in an optical model based on the Monte Carlo ray-tracing method and in a one-dimensional heat transfer model that includes conduction, convection, and radiation. The optical model results show that most of the solar radiation energy is absorbed within a very small channel length of around 15 mm because of the large length-to-radius ratio. Classification of radiation losses reveals that at low absorptivity, increased reflection losses cause reduction of the receiver efficiency, notwithstanding the decrease in the emission loss. As the average temperature increases because of the large channel radius or small mass flow rate, both emission and reflection losses increase but the effect of emission losses prevails.

• Transactions of Materials Processing
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• v.13 no.3
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• pp.211-215
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• 2004

Recently, one of remarkable tends in the development of optical communication industry is the miniaturization and integration of products. The alignment system of micro optical module is a key apparatus for the miniaturization of optical module and the development of optical communication parts with high functionality. In this research, we have developed a system capable of automatic alignment of a $30\mu\textrm{m}$-thick film filter and a lensed fiber in order to improve the speed and losses in the optical fiber-to-filter alignment of optical modules. Using the developed automatic alignment system and silicon optical bench, we have measured optical loss and characteristics of the assembled optical add/drop module before packaging $1{\times}1$ OADM optical module. Whole size of add/drop module was less than $5mm{\times}5mm{\times}1mm$. The measured maximum insertion loss was 0.294㏈ that is below 0.3㏈ which is a standard loss of optical module.

• Journal of Power System Engineering
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• v.19 no.3
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• pp.5-10
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• 2015

Femtosecond laser machining has been applied for creating a sensor function in silica glass optical fibers. Femtosecond laser pulses make it possible to fabricate micro structures in processed regions of a very thin glass fiber line because femtosecond laser pulses can extremely minimize thermal effects. With the laser machining to optical fiber using a single shot of 210-fs laser at a wavelength of 800 nm, it was observed that a processed region surrounded a thin layer which seemed to be a hollow cavity monitored by scanning electron microscopy (SEM). This study aims at a theoretical investigation for the processed region by using a numerical analysis in order to embed sensing function to optical fibers. Numerical methods based finite element method (FEM) has been used for an optical waveguide modeling. This report suggests two types modeling and describes a comparative study on optical losses obtained by the experiment and the numerical analysis.

• Proceedings of the Optical Society of Korea Conference
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• 1990.02a
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• pp.257-259
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• 1990

In the design of waveguide E-plane bandpass filter, it is very important to characterize the K-inverters. In the analytical method. losses arising from the metal and the dielectric are ignored for the simplicity of design process. In this paper, based on the new measurement method, characteristics of inverters are measured and compared with those calculated based on mode-matching analysis.

• Current Optics and Photonics
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• v.3 no.4
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• pp.298-303
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• 2019

We propose a photonic quasi-crystal fiber (PQF) for supporting up to 14 orbital angular momentum (OAM) modes with low and ultra-flat dispersion characteristics over the C+L bands. The designed PQF which consists of a large hollow center and quasi structural small air holes in the clad region exhibits low confinement losses and a large effective index separation (>$10^{-4}$) between the vector modes. This proposed fiber could potentially be exploited for mode division multiplexing and other OAM mode applications in fibers.

• Korean Journal of Optics and Photonics
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• v.24 no.1
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• pp.17-22
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• 2013

High performance plastic optical fiber (POF) $N{\times}N$ star couplers are implemented based on fusing and combining technology. A set of cladding-removed POFs are fused into a solid body by heating and pressing them together to form the transition region between the input and output sides. The operation principle of the proposed star coupler is explained based on ray optics. To demonstrate the performance of the device, $2{\times}2$, $4{\times}4$ and $6{\times}6$ type POF couplers were fabricated and characterized. Performances of the POF star couplers were evaluated in terms of the flatness of the coupling ratios and excess losses.

• Solar Energy
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• v.20 no.1
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• pp.73-80
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• 2000

Considering the optical performance of the reflector and analyzing heat losses from the receiver, the optimal diameter of the absorber for a PTC(Parabolic Trough Concentrator) system was numerically determined. The results of this study were compared with the results of the IST (Industrial Solar Technology)-PTC test to verify the validity of the model. Good agreement was obtained with the deviation range from 0.4 to 7.7%. Generally, the net energy gained by the receiver shows the maximum at the particular absorber diameter and the specific gap size between the absorber and the glass envelop because the heat losses from the receiver becomes the minimum. The results showed that the conductive and convective heat losses became the minimum when the gap size was 7 to 10mm. Finally, it was known that the optimal absorber diameter was 62mm at $100^{\circ}C$, 57mm at $150^{\circ}C$, and 53mm at $200^{\circ}C$ of the absorber surface temperature, respectively.

• Korean Journal of Optics and Photonics
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• v.27 no.5
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• pp.181-187
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• 2016

We report on the parameter-dependent optical characteristics of the unidirectional single-mode lasing square ring cavities. Using the taper-step section in the square cavities, the resonant direction can be selected and we characterize the optical losses by changing the taper lengths. Various kinds of square ring cavities are fabricated, based on InGaAsP/InGaAs multiple quantum well semiconductor materials. From the experimental results we obtain the optimized taper length for a given device structure, while maintaining unidirectional single-mode lasing.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.644-647
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• 2004

Optical add/drop multiplexers (OADMs), one of the new network elements, will play a key role enabling greater connectivity and flexibility in the dense wavelength-division multiplexing (DWDM) networks. The importance of OADMs is that they allow the optical network to be local transmitting/extraction on a wavelength-by-wavelength basis to optimize traffic, efficient network utilization, network growth, and to enhance network flexibility. Also, the automatic assembly system of micro optical filters and fibers is a key technology in the development of optical modules with high functionality. Recently, one of remarkable tends in the development of optical communication industry is the miniaturization and integration of products. In this research, we have developed a system capable of automatic alignment of a film filter and a lensed fiber in order to improve the speed and losses in the optical fiber to filter alignment of optical modules. Using the developed automatic alignment system and silicon optical benches, we have fabricated the micro OADM and measured the insertion loss and aging effect.

• Korean Journal of Optics and Photonics
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• v.29 no.2
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• pp.77-84
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• 2018

We analyze the link availability of terrestrial free-space optical (FSO) communication systems in Korea. For this purpose, we utilize several theoretical models to calculate the power losses induced by absorption and scattering in the atmospheric channel, using five-year meteorological data for three major cities in Korea (Seoul, Busan, and Daejeon). Also, we estimate the power variations at the receiver caused by scintillation in the data. Those power losses and variations are used to estimate the availability of FSO links in the three cities. The results show that link availability is estimated to be over 95% in Daejeon for a 3.5-km FSO link, when the transmitter power and receiver diameter are greater than 10 dBm and 7 cm respectively. Slightly worse link availabilities are obtained for Busan and Seoul.