• Korean Journal of Optics and Photonics
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• v.15 no.5
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• pp.469-474
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• 2004

We have fabricated and designed wavelength-tunable sampled grating distributed Bragg reflector laser diodes(SGDBR-LD) by using, for the first time, planar buried heterostructures(PBH). The diodes have low threshold current values and high-performance of laser operation. Growth condition using metal organic chemical vapor deposition(MOCVD) was optimized for the formation of a good butt-coupling at the interface. A maximum output power of the fabricated device was 20 mW under 200 mA continuous wave(CW) operation at $25^{\circ}C$. Average threshold current and voltage were 12 mA and 0.8 V, approximately. This output power is higher than those of ridge waveguide(RWG) and buried ridge stripe(BRS) structures by amounts of 9 mW and 13 mW, respectively. We obtained a tuning range of 44.4nm which is well matched with the target value of our design. The side mode suppression ratio of more than 35 dB was obtained for the whole tuning range. Optical output power variation was less than 5 dB, which is 4 dB smaller than that of RWG structures.

• Korean Journal of Optics and Photonics
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• v.31 no.3
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• pp.142-147
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• 2020

In this paper, we report highly efficient second harmonic generation of continuous-wave Yb fiber lasers incorporating a periodically poled LiTaO₃ device (MgO:PPSLT) as a frequency converter. The seed laser output from a Yb fiber master oscillator using a Fabry-Perot feedback cavity was amplified in a Yb fiber amplifier stage, yielding 28.5 W of linearly polarized output at 1064 nm in a beam with beam quality, M², of ~1.07. Second harmonic generation was achieved by passing the laser beam through MgO:PPSLT. Under optimized conditions, we obtained 11.1 W of green laser output at 532 nm for an incident signal power of 25.0 W at 1064 nm, corresponding to a conversion efficiency of 44.4%. The detailed investigation to find the optimized operating conditions and prospects for further improvement are discussed.

• Restorative Dentistry and Endodontics
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• v.27 no.3
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• pp.290-298
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• 2002

3차원적으로 잘 충전된 근관은 치근단 누출과 재감염을 방지하며, 조직이 잘 치유될 수 있는 생물학적 환경을 제공해준다. 이 때문에 근관계의 완전한 충전은 근관치료의 중요한 목표 중의 하나이다. 본 연구의 목적은 4가지 방법으로 근관충전 후 디지털 방사선 사진을 촬영하여 근관충전의 질을 평가하고 투명표본을 제작하여 색소침투범위를 측정함으로써, 근관충전방법에 따른 치근단부 폐쇄능을 비교 평가하고자 하는 것이다. 직선형의 단근관을 갖는 80개의 전치를 선택하여 ProFile$^{\circledR}$ 니켈-티타늄 회전식 기구를 사용하여 근관을 성형한 후 무작위로 20개씩 4군으로 나누었다. 사용된 근관충전법은 다음과 같다：MicroSeal$^{\circledR}$(Group A), Thermafil$^{\circledR}$(Group B), Continuous wave 충전법(Group C), 측방가압충전법(Group D), 각 군에서 10개 치아는 Sealapex를, 나머지 10개 치아는 AH26$^{\circledR}$을 충전용 시멘트로 사용하였다. 근관충전이 끝난 치아는 충전의 질과 길이를 평가하기 위해, 근원심과 협설방향으로 디지털 방사선 사진을 이용하여 촬영하였다. 각 치아의 치근단부 2mm를 제외한 나머지 부위는 두겹의 nail varnish를 바르고, 2% methlylene blue용액에 48시간동안 침잠시켰다. 흐르는 물에 깨끗이 세척한 후, 투명치아를 만들었다. 선상의 색소침투를 관찰하고 치관측 최대깊이를 입체현미경하에서 40배율로 평가하여 다음과 같은 결과를 얻었다. 1. 충전방법에 따른 근단부 폐쇄효과를 비교시, 실험군 모두 비교적 양호한 근단부 폐쇄효과를 보였고 통계학적으로 유의성이 없었다. 2. 충전용 시멘트에 따른 근단부 폐쇄효과를 비교시, AH26$^{\circledR}$을 사용한 군에서 Sealapex를 사용한 군보다 더 적은 색소침 투를 나타냈다(p<0.05). MicroSeal$^{\circledR}$을 이용한 실험 1군내에서 AH26$^{\circledR}$을 사용하였을 때 미세누출이 더 적었고(p<0.05), 다른 군내에서는 통계학적으로 유의성이 없었다. 3. 근단부 충전상태에 따른 미세누출 비교시, 저충전, 과충전과 색소침투간에는 상관관계가 없었다. 4.충전방법에 따른 근단부 충전상태 평가시, Thermafil$^{\circledR}$을 이용한 실험 2군에서 과충전이 많이 나타났다(p<0.05). 이상의 결과로, 기존의 측방가압법 및 여러 열가소성 충전법이 유사한 근단부 폐쇄효과를 나타낸 바, 방법에 따른 술자의 숙련도, 충전시간, 재근관치료의 편이성 등을 고려하여 근관충전방법을 선택하는 것이 합리적일 것이라고 사료된다.

• Child Health Nursing Research
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• v.6 no.1
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• pp.32-50
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• 2000

A descriptive exploratory design was used in this study to evaluate the effects of sponge bathing on physiological(heart rate, heart period, vagal tone, oxygen saturation, respiration) and behavioral responses in newly born 40 preterm infants from intensive care unit of S University Hospital in Seoul. Data has been collected from October, 1997 to March, 1999. The infants were between 27-33 weeks gestational age at birth, and were free of congenital defects. The subjects entered the protocol when they were medically stable (determined by initiation of feeding and discontinuation of all respiratory support) but still receiving neonatal intensive care. The infants' physiologic parameters were recorded a 10 - minute before, during, and after bathing. Continuous heart rate data were recorded on a notebook computer from the infant's EKG monitor. The data were digitized off-line on software(developed by Lee and Chang in Wavelet program) which detected the peak of the R wave for each heart beat and quantified sequential R-R intervals in msec(i.e. heart periods). Heart period data were edited to remove movement artifact. Heart period data were quantified as : 1) mean heart period; 2) vagal tone. Vagal tone was quantitfied with a noninvasive measure developed by Porges(1985) in Mxedit software. To determine behavioral status, tools were developed by Scafidi et al(1990) were used. Collected data were analyzed with the SPSS program using paried t-test, ANOVA, and Pearson correlation. The result were as follow. 1. The results of the ANOVAs indicated that vagal tone were signifcantly lower during bathing than baseline and post-bathing. There were significant differences in heart period and heart rate levels across the bathing. But the mean oxygen saturations and respirations were no differences. Also, there were no significant differences on behavioral sign, motor activity, behavioral distress, weight changes, morbidity, and hospitalization period. 2. To evaluate the relation between vagal tone and subsequent parameters, the two groups (the high group had 19 subjects and low group had 21subjects) were divided by the mean baseline vagal tone. Vagal tone measured prior to bathing were significantly associated with respiration before bathing, vagal tone during bathing, and the magnitude of change in both vagal tone. But, other subsequent reactivities were no differences in two groups. 3. Correlations were also calculated between vagal tone and the subsequent physiological reactivities from baseline through after- bathing. Correlations were significant between baseline vagal tone and baseline heart rate, between baseline vagal tone and baseline heart period, between baseline vagal tone and oxygen saturation after bathing. In summary, the bathing in this study showed a stressful stimulus on premature infants through there was significance in the physiological parameters. In addition, our study represents the documentation that vagal tone reactivity in response to clearly defined external stimulation provides an index of infant's status.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.12
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• pp.1047-1053
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• 2016

In this study, welding of pure titanium was carried out by using a continuous wave fiber laser with a maximum output of 6.3 kW. Because brittle regions form easily in titanium as a result of oxidation or nitriding, the weld must be protected from the atmosphere by using an appropriate shielding gas. Experiments were performed by changing the type and the flow rate of shielding gases to obtain the optimal shielding condition, and the weldability was then evaluated. The degree of oxidation and nitriding was distinguished by observing the color of beads, and weld microstructure was observed by using an optical microscope and a scanning electron microscope. The mechanical properties of the weld were examined by measuring hardness. When the weld was oxidized or nitrified, the bead color was gray or yellow, and the oxygen or nitrogen content in the bead surface and overall weld tended to be high, as a result of which the hardness of the weld was thrice that of the base metal. A sound silvery white bead was obtained by using Ar as the shielding gas.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.4
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• pp.906-911
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• 2004

In this paper, a VCDRO(Voltage Control Dielectric Resonator Oscillator) applied to FMCW(Frequency Modulated Continuous Wave)Radar as stable source is implemented and constructed with a MESFET(Metal-semiconductor Field-Effect Transistor) for low noise, a dielectric resonate. of high frequency selectivity, and high Q varator diode to obtain a good phase noise performance and stable sweep characteristics. The designed circuits is simulated thrash harmonic balance simulation technique to provide the optimum performance. The measured result of a fabricated VCDRO shows that output is 2.22㏈m at 12.05GHz, harmonic suppression -30㏈c, phase noise -130㏈c at 100KHz offset, and sweep range of varator diode $\pm$18.7MHz, respectively. This oscillator will be available to FMCW Radar.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.12
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• pp.2511-2517
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• 2009

Recently, a FMCW radar is used for the various purposes in the short range detection and tracking of targets. The main advantages of a FMCWradar are the comparative simplicity of implementation and the low peak power transmission characterizing the very low probability of signal interception. Since it uses the frequency modulated continuous wave for transmission and demodulation, the received beat frequency represents the range and Doppler information of targets. Detection and extraction of useful information from targets are performed in this beat frequency domain. Therefore, the resolution and accuracy in the estimation of a beat spectrum are very important. However, using the conventional FFT estimation method, the high resolution spectrum estimation with a low sidelobe level is not possible if the acquisition time is very short in receiving target echoes. This kind of problems deteriorates the detection performance of adjacent targets having the large magnitude differences in return echoes and also degrades the reliability of the extracted information. Therefore, in this paper, the model parameter estimation methods such as autoregressive and eigenvector spectrum estimation are applied to mitigate these problems. Also, simulation results are compared and analyzed for further improvement.

• Journal of Biomedical Engineering Research
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• v.24 no.4
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• pp.319-328
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• 2003

The purpose of this paper is to develop a medical laser system using the semiconductor diode laser in order to photodynamic cancel therapy as a light source. The ideal light source for photodynamic therapy would be a homogeneous nondiverging light with variable spot size and specific wavelength with stability. After due consideration in this point, in this paper, we used a diode laser resonator of 635nm wavelength. The development laser system have a statistical laser out beam with accuracy control using the constant current control of method and clinic-friendly with compact. In order to protect the diode resonator from the over-current, the rush-current and electrical fault, we specially designed. The most importance therapeutic factor are the radiation mode for cancer therapy. So we developed the radiation mode of CW(Continuous Wave), long pulse, short pulse, and burst pulse and can adjust the exposure time from several milli-second to several minute. The experimental result shows that laser beam power was increased linear from 10mW to 300mW according to the increasing input current and the increasing exposure time. The developed new compact diode laser system have a stability of output power and specific wavelength with easy control and transportable for many applications of PDT.

• Journal of Advanced Navigation Technology
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• v.17 no.5
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• pp.516-523
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• 2013

In this paper, The path loss model of Air Traffic Control(ATC) telecommunication radio channel has been studied at the Incheon International Airport(IIA) with the terminal with two antlers. We measured two frequencies among VHF/UHF channel bands. The transmitting site radiated the Continuous Wave(CW). The propagation measurement was taken using the moving vehicle equipped with receiver and antenna. The transmitting power, frequency and antenna height are the same as the current operating condition. The path loss exponent and intercept parameters were extracted by the basic path loss model and hata model. The path loss exponents at passager terminal areas were 3.32 and 3.10 respectively in 128.2 MHz and 269.1 MHz. The deviation of prediction error is 9.69 and 9.65. The new path loss equation at the terminal area was also developed using the derived path loss parameters. The new path loss was compared with other models. This result will be helpful for the ATC site selection and service quality evaluation.

• Korean Journal of Optics and Photonics
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• v.30 no.4
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• pp.154-158
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• 2019

We have used a mid-IR (mid-infrared) continuous-wave (cw) optical parametric oscillator (OPO), developed previously and described in Ref. 12, to build a performance-evaluation setup for a mid-IR spectrometer. The used CW OPO had a wavelength tuning range of $ 2.5-3.6{\mu}m$ using a pump laser with a wavelength of 1064 nm and a fan-out MgO-doped periodically poled lithium niobate (MgO:PPLN) nonlinear crystal in a concentric cavity design. The OPO was combined with a near-IR integrating sphere and a Fourier-transform IR optical spectrum analyzer to build a performance-evaluation setup for mid-IR spectrometers. We applied this performance-evaluation setup to evaluating a mid-IR spectrometer developed domestically, and demonstrated the capability of evaluating the performance, such as spectral resolution, signal-to-noise ratio, spectral stray light, and so on, based on this setup.