• Composites Research
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• v.19 no.1
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• pp.29-35
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• 2006

The avoidance of enemy's radar detection is very important issue in the modem electronic weapon system. Researchers have studied to minimize reflected signals of radar. In this research, two types of radar absorbing structure (RAS), 'C'-type shell and 'U'-type shell, were fabricated using fiber-reinforced composite materials and their radar cross section (RCS) were evaluated. The absorption layer was composed of glass fiber reinforced epoxy and nano size carbon-black, and the reflection layer was fabricated with carbon fiber reinforced epoxy. During their manufacturing process, undesired thermal deformation (so called spring-back) was observed. In order to reduce spring-back, the bending angle of mold was controlled by a series of experiments. The spring-back of parts fabricated by using compensated mold was predicted by finite element analysis (ANSYS). The RCS of RAS shells were measured by compact range and predicted by physical optics method. The measured RCS data was well matched with the predicted data.

• Korean Journal of Optics and Photonics
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• v.17 no.1
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• pp.81-88
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• 2006

Delayed luminescence from human hands after illumination by light at different wavelength bands was studied. A delayed luminescence measurement system equipped with photomultiplier tube (PMT), fiber optics and automatic mechanical shutter system was developed. Three spectrum band-pass filters, fer which transmissions are on 350${\~}$450 nm, 450${\~}$550 nm and 550${\~}$650 nm, were used to select irradiation wavelength, and 150W metal-halide lamp was used as an illumination source. Six volunteers put their palms (dorsa) onto the measurement system, and after light illumination, delayed luminescence were measured for 10 minutes. The results show that delayed luminescence after shorter wavelength illumination was higher than that a(ter longer wavelength one. These results indicate the existence of accepters in human skin which can be excited at short wavelengths. Furthermore, each subjects showed different delayed luminescence curve patterns. Reactive oxygen species (ROS) are known to have important roles on delayed luminescence, and this research suggests that ROS concentration can be measured noninvasively with optical methods.

• Journal of Korean Ophthalmic Optics Society
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• v.18 no.3
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• pp.329-339
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• 2013

Purpose: In this study, nutrient intake during the adolescent period is a critical time for the development of the vision. Therefore we analyzed the relationship between the obesity index and the refractive power. Methods: We used the Korean National Health and Nutrition Examination Survey 2010 document. The obesity index is classified as Broca index (less than 80.0% is low weight, 80 to 89.9% is underweight, 90.0 to 109.9% is normal, overweight is from 110.0 to 119.9%, 120.0% or more is obesity) and body mass index (BMI)(less than 18.5 is underweight, 18.6~22.9 is normal, 23.0 to 24.9 is overweight, and obesity is higher than 25.0). We analyzed correlation with the body mass index and refractive error in adolescent. Results: As shown in the statistics, according to Broca index and body mass index (BMI), the refractive power and the obesity index showed a statistically significant correlation in the ages 15 to 18. Under weight subjects are ingested 43.84% dietary fiber, vitamin C 56.55%, 35.20% iron, 31.84% of, and 38.03% potassium less than the average food intake by the standard group. Conclusions: Moderate weight with a broad variety of taking nutrition and good eating habits seems to have an effect to the good growth and the good vision.

• Journal of the korean academy of Pediatric Dentistry
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• v.28 no.3
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• pp.363-368
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• 2001

It is well known that numerous factors influence the light output of curing units, but many dentists are un aware that the output of their curing lights are inadequate. This study was conducted to evaluate the light in tensity of visible-light curing units in some private dental clinics and hospital dental clinics. In order to determine the maximum light intensity of the curing units, lamps, filters and fiber optic bundles, they were replaced with new ones and light intensity was remeasured. Light intensity was measured by employing a digital radiometer (EFOS model #8000, USA). Light intensity ranged in $29\sim866mW/cm^2$ (below $150mW/cm^2$ ; 17.8%, $150\sim300mW/cm^2$ : 46.6%, above $300mW/cm^2$ ; 35.6%). The replacement of the components increased the light intensity, with maximum increases of 94.8% for lamps, 82.3% for filters, 200.8% for fiber optics and 361.5% for all three parts. According to the manufacturer of radiometer, curing light is considered as unsuitable for use with a reading of above $300mW/cm^2$ by the radiometer. Applying these criteria to the present study, 64.4% of the curing units required repair or replacement. The results of this study indicated that the light intensities of the curing units used in dental practice were lower than optimum level.

• Korean Journal of Optics and Photonics
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• v.16 no.3
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• pp.287-294
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• 2005

In this paper, an optical true time-delay (TTD) for two-dimensional (2-D) phased array antennas (PAAs), composed of a multi-wavelength optical source and a fiber optic delay line matrix consisting of $2\times2$ optical switches with optical fiber connected between cross ports, has been proposed. A 2-bit $\times4-bit$ optical TTD for 10-GHz 2-D PAAs has been implemented by cascading a wavelength dependent TTD (WD-TTD) and a wavelength independent TTD (WI-TTD). The unit time delay for WD-TTD and WI-TTD have been chosen as ${\Delta}T=12ps$ and $\Delta\tau=6ps$, respectively. Time delay have been measured at all radiation angles. The maximum delay error for WD-TTD was measured to be 3 ps due to jitter incurred from gain switching. For the case of WI-TTD, error was within ${\pm}\;1\;ps$. The proposed optical TTD for a 2-D PAA has the following advantages: 1) higher gain compared to one-dimensional linear PAAs, 2) stabilization of optical power and wavelength by using a multi-wavelength optical source, and 3) fast beam scan and simple operation due to electronic control of the $2\times2$ optical switches matrix on a column-by-column basis.

• Korean Journal of Optics and Photonics
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• v.28 no.1
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• pp.22-27
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• 2017

Time-encoded near-infrared spectroscopy (NIRS) system is proposed, based on a near-infrared (NIR) swept laser source, for comparison to the conventional NIRS method using a detector-type spectrometer. The cavity of the NIR swept laser source consists of a semiconductor optical amplifier (SOA) with a gain region around 800 nm, and several fiber-optic components. To change the output wavelength in time using an applied electric radio-frequency signal, an acousto-optic tunable filter (AOTF) is introduced in the fiber ring cavity configuration. To demonstrate the feasibility of an NIR swept laser source for NIRS imaging, the spectroscopic comparison of two kinds of absorbance-measuring systems a detector-type spectrometer using a white light source, and a source-type spectrometer using an NIR swept laser is successfully performed with an NIR-absorbing dye.

• Korean Journal of Optics and Photonics
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• v.24 no.4
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• pp.196-200
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• 2013

Heretofore, it was enough that most of optical transceiver modules for automotive networks have the performance of data rate from 10 Mbps to 150 Mbps. As the required data rate in automotive infotainment systems has recently been increasing, the development of a new optical transceiver having high speed data rate over 1Gbps is now required. Therefore, we suggested a next-generation bi-directional optical transceiver module using vertical cavity surface emitting laser technology and plastic clad fiber technology, for the next-generation automotive optical network, MOST1000. We fabricated the high-speed and compact optical transceiver having 1 Gbps data rate and -22 dBm sensitivity satisfying bit error rate $10^{-12}$.

• Korean Journal of Optics and Photonics
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• v.23 no.6
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• pp.274-280
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• 2012

A normal incidence ellipsometer is fabricated to measure the optical anisotropy of a small spot whose diameter is less than $8.0{\mu}m$, by adding a beam splitter and a prism to the conventional rotating analyzer type ellipsometer. The polarizing actions of the added optical components are calibrated to improve the accuracy of the anisotropy measurement. The standard deviation of the optical anisotropy factor decreased to 0.00083, and the variation of the optical anisotropy factor of rutile versus sample azimuth angle variation also decreased to 0.015, after adoption of a non-polarizing beam splitter and a quarter wavelength phase retarder, followed by removal of the optical fiber and a careful choice of measurement wavelength.

• Korean Journal of Optics and Photonics
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• v.10 no.1
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• pp.73-79
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• 1999

Semiconductor optical switch modules of 1$\times$2, 1$\times$4, and 4$\times$4 types for 1550 nm optical communication systems were fabricated by using laser welding technique, embodying in 30-pin butterfly package. For better coupling efficiency between switch chip and optical fiber, tapered fibers of 10~15mm lens radii were used, which provided up to 60% optical coupling efficiency. With the help of new laser hammering process, we could recover the lost optical power almost completely up to average 82% of initially obtained power. The fabricated optical switch modules showed good thermal stability of less than 5% degradation even after 200 times thermal cycling test. The 2.5 Gbps optical transmission characteristics of the 4$\times$4 switch module showed low sensitivities of less than -30dB for all possible switching paths. The transmission penalties of 1$\times$2 switch module at $10^{-10}$ BER were 0.6dB and 0.7dB for 50Xm and 90 Km optical fibers, respectively.

• The Transactions of the Korea Information Processing Society
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• v.4 no.6
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• pp.1589-1600
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• 1997

The construction of optical access network costs upper 40% in total installation cost of total optical network. Optimization of access network therefore is core in optical network. Advanced countries include EU, Japan and USA already have researched access network. This paper presents analysis of three broad-band fiber-optics subscriber loop architectures(HFC, ATM-PON, Super PON). The analyses focus on the specific demonstrated architectures and use component cost projections to estimate future network costs on a per-subscriber basis. We use TITAN(Tool for Introduction Scenarios and Techno-Economic Evaluation of The Access Network) model. We find that ATM-PON can deliver voice and ISDN data at installed first costs than the other architectures. This is due to the sharing bandwidth among a cluster of subscribers within Curb. This work intends to support establishing guidelines for strategic decisions regarding the development of the access network alternatives of different operators.