• Korean Journal of Optics and Photonics
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• v.33 no.1
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• pp.22-27
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• 2022

We fabricate a polarization-independent dielectric multilayer thin-film diffraction grating for a spectral-beam-combining (SBC) system with a simple grating structure and low aspect ratio. Due to the refractive index and thickness error of the manufactured thin films, the diffraction efficiency of the fabricated diffraction grating was lower than that of the design. The causes of the errors were analyzed, and it was confirmed through simulation that diffraction efficiency could be compensated through an additional coating on the manufactured diffraction grating. As a result of sputtering an additional Ta₂O₅ layer on a fabricated diffraction grating, the diffraction efficiency was corrected and a maximum 91.7% of polarization-independent diffraction efficiency was obtained.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.8
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• pp.76-85
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• 2000

Effects of the random fluctuation in grating half-period have been studied by an effective index transfer matrix method in DFB lasers. The laser facets are assumed to be perfectly antireflection coated, and the period fluctuation is modeled as a Gaussian random variable. The random fluctuation breaks spectral symmetry in both uniform-grating and quarter-wavelength -shifted(QWS) DFB lasers, and decreases the effective coupling coefficient. This leads to increased average mirror loss of ${\pm}$1 modes and reduced stopband width in uniform grating DFB lasers, and degradation in the wavelength accuracy and the single mode stability in QWS-DFB lasers. Threshold gain difference decreases with increasing period fluctuation irrespective of grating coupling coefficient in QWS-DFB lasers, while spatial hole-burning effect is exacerbated or alleviated when the normalized coupling coefficient is lower and higher than 1.5, respectively.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.434-438
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• 2003

XeCl 엑시머 레이저로 펌핑되는 쌍공진기형 색소레이저와 2단 증폭시스템을 개발하여 원격계측 시스템에 적합한 두 개의 파장을 동시 또는 순차적으로 출력하였다. 개발된 쌍공진기는 1200 g/mm의 회절격자를 갖는 grazing-incidence 방법에서 제 1차 및 제 2차 회절차수를 이용하여 구성되었다. 출력특성은 스펙트럼 선폭이 10 pm이하이고, 펌프 에너지에 대하 전체효율은 6% 이상이다. 또한, 파장가변 영역은 제 1차 및 제 2차의 회절차수에 대해 각각 434-470 nm, 436-468 nm 이며, 2단의 증폭기의 증폭이득은 37dB, 추출효율은 9%이다. 개발된 레이저 증폭시스템에서 Coumarine-450의 색소로 발진하고, 이의 출력 6 mJ을 원격계측시스템에 적용하여 수원상공의 NO$_2$의 가스농도분포를 측정하였다. 이 결과 개발된 색소레이저 시스템은 원격계측 시스템의 광원으로 매우 적합함을 확인하였다.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.4
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• pp.713-722
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• 2000

This study analysed error of measurement and reproducibility for particle size analysis by the laser diffraction spectrometer. Laser diffraction spectrometers has become a very important method of particle size analysis. This measuring method has the advantage of simple operation, good reproducibility and rapid analysis. A feeding and dispersing system have been developed, which allows mass throughputs between 0.1~23 g/min in flowing air and 1.4~35% in flowing liquid. It has been used as a feeder unit for wet and dry particle size analysis from diffraction patterns. Relevant parameters, such as particle shape, particle size, dispersion, flow rate, concentration were analysed for measuring error. And system parameters of instruments for measurement of dynamic processes, eg, measuring time, focal plane, injection pressure drop and dispersion effect by the ultrasonic and mixing of preliminary treatment, were also discussed.

• Laser Solutions
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• v.15 no.2
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• pp.6-10
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• 2012

We fabricated the diffraction grating on the surface of fused silica glass using a femtosecond laser. The grooves of diffraction grating has a lot of micro crack and debris result in reduced diffraction efficiency. So, we polished the diffraction grating with $CO_2$ laser beam. With different scan number of $CO_2$ laser beam, we observed the image of diffraction grating and measured the diffraction efficiency.

• Korean Journal of Optics and Photonics
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• v.12 no.6
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• pp.496-502
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• 2001

We generated a nondiffracting beam and investigated its intensity profile on propagation. We first obtained an annular output beam from Nd:YAG laser with a negative branch unstable ring resonator and, using a 1m focal length lens, we generated a Bessel- Gauss beam. The inner radius of the annular output beam was 2.57 mm and the ring width was 0.145 mm. The intensity profile of the nondiffracting beam did not show any appreciable diffraction up to 33 m distance from the focal lens. This result was compared with the theory.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.8
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• pp.48-56
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• 2000

Effects of the correlated random fluctuation in each grating half-period have been studied by an effective index transfer matrix method in quarter wavelength shifted DFB lasers. As the correlation coefficient changes from 0 to -1, single mode stability and wavelength accuracy are less degraded by the reduced error in the grating period. This fact shows that holographic grating fabrication is better than electron-beam lithography in discrete device fabrication provided that the magnitude of the random fluctuation is the same.

• Korean Journal of Optics and Photonics
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• v.5 no.1
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• pp.100-105
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• 1994

We have reduced the oscillating linewidth of the commercial single mode InGaAsP visible laser diodes which emits in the 657 nm region of the spectrum down to 10 MHz by making a extended cavity employing the Littrow-type grating. The wavelength tuning characteristics of the commercial visible laser diode (CQL820D, Philips Co.) for the grating angle, laser temperature, and injection currents were measured by using the wavemeter. The proportional coefficients of the laser were found to be 1 THzlmrad, 32.4 GHz/K, and 6.14 GHz/mA, respectively.tively.

• Proceedings of the Korean Society of Laser Processing Conference
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• 1998.11a
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• pp.20-23
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• 1998

• Proceedings of the KSEEG Conference
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• 2007.04a
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• pp.492-492
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• 2007