• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2001.05a
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• pp.329-332
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• 2001

In this paper, it's shown that the saturable absorber Nd:LSB has a capability as a saturable absorber in Q-switching system. In the passively Q-switched 1.3${\mu}{\textrm}{m}$ Nd:YAG laser with saturable absorber, we theoretically investigated the optimized output mirror, peak power, output power, pulse width and output efficiency. The passively Q-switched Nd:YAG laser with saturable absorber Nd:LSB gives peak power of 30MW and pulse width of 6.23 ps at 30cm resonator length and output mirror reflectivity 98%. Consequently the output energies are 143, 200 and 209 $\mu$J at loss of 2.2%, 2.1% and 1.5%, respectively.

• Korean Journal of Optics and Photonics
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• v.14 no.1
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• pp.92-96
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• 2003

Dielectric apertures in vertical cavity laser have been used for improved device performance. Numerical analysis is used to estimate the optical losses as the aperture diameter is reduced. The optical losses depend on the aperture size, thickness and location. The optical loss strongly depend on the aperture size and thickness when the aperture size is similar or smaller than the emitted wavelength. The optical loss is negligible and not depend on the aperture thickness when the aperture size is larger than 5 times emitted wavelength.

• Proceedings of the Optical Society of Korea Conference
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• 2003.07a
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• pp.226-227
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• 2003

광자 크리스탈 (Photonic Crystals)은 서로 다른 유전체의 주기적인 구조로 이루어져 있으며, 전자기파가 특정한 주파수 범위에서 전파하지 못하고 차단되는 영역인 광자 밴드갭 (Photonic Band Gap)이 존재한다. 이러한 광자 밴드갭의 존재로 인하여 빛의 흐름을 조절할 수 있다는 점 때문에 반사거울, 휘어진 도파로(bent waveguide), 레이저, 채널 드롭핑 필터(channel dropping filter) 등 여러 가지 다양한 분야에 응용될 수 있다. (중략)

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.3
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• pp.2117-2122
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• 2015

Wide FOV(Field-of-View) is required to contain much more visual information in a single image. The wide FOV imaging system has many industrial applications such as surveillance, security, tele-conference, and mobile robots. In order to obtain a wide FOV panorama image, an imaging system with hyperbolic cylinder mirror is proposed in this paper. Because the horizontal FOV is more important than the vertical FOV in general, a hyperbolic cylinder mirror is designed in this paper, that has a hyperbolic curve in the horizontal surface and is the same as a planar mirror in the vertical axis. Imaging model of the proposed imaging system is presented by ray tracing method and the hyperbolic cylinder mirror is implemented. The imaging performance of wide FOV is verified by experiments in this paper. This imaging system is cost-effective and is possible to acquire a wide panorama image having 210 degree horizontal FOV in real-time without an extra image processing.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.6
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• pp.4108-4114
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• 2015

An image acquisition by using an optical mirror is called as a catadioptric method. The catadioptric imaging method is generally used for acquisition of 360-degree all directional visual information in an image. An exemplar omnidirectional optical mirror is the bowl-shaped hyperbolic mirror. In this paper, a single camera omnidirectional stereo imaging method is studied with an additional concave lens. It is possible to obtain 3 dimensional coordinates of environmental objects from the omnidirectional stereo image by matching the stereo image having different view points. The omnidirectional stereo imaging system in this paper is cost-effective and relatively easy for correspondence matching because of consistent camera intrinsic parameters in the stereo image. The parameters of the imaging system are extracted through 3-step calibration and the performance for 3-dimensional coordinates reconstruction is verified through experiments in this paper. Measurable range of the proposed imaging system is also presented by depth-resolution analysis.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.171-174
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• 2004

표적강도는 수중 산란체의 능동 탐지 확률을 좌우하는 중요한 변수중 하나이며 산란체의 기하학적 형상에 의해 결정이 되기 때문에 수치해석을 통한 해석 및 예측이 가능하다. 수치해석 기법은 현재 여러 가지가 알려져 있으며, 그중 Kirchhoff approximation이 다른 해석 기법에 비해 거울면 반사특성의 산란해석에 적합하며, 프로그램으로의 적용이 용이하다는 장점으로 인해 많이 사용되고 있다. 본 연구에서는 이러한 장점에 의거하여 Kirchhoff approximation을 이용하여 표적강도 수치해석 프로그램을 개발 및 검증하였다. 프로그램의 성능 검증은 원통형 산란체에 대한 이론해 검증과 원통형 실험 산란체를 통한 실험 검증을 수행하였다.

• Korean Chemical Engineering Research
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• v.50 no.6
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• pp.952-959
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• 2012

The photocatalytic reactor was designed to have improved efficiency by enhancing a light intensity of photocatalytic reactor using a reflector coated on the surface at the outer radius of annular shaped photocatalytic reactor. The improved photocatalytic reactor performed to treat waste air containing malodor and VOC with the enhanced light intensity, of which the effect on their removal efficiency was investigated. The intensities of illumination of the improved photocatalytic reactor filled with porous silica-based media and nonporous glass bead media carrying photocatalyst were observed to increase by 28.5% and 30.1%, respectively, compared to those of photocatalytic reactor without any reflector. Using the improved photocatalytic reactor filled with porous silica-based media and nonporous glass bead media carrying photocatalyst, the removal efficiencies were enhanced by 2~3% and insignificantly, respectively. The removal efficiencies of the optimized photocatalytic reactor with reflectors, filled with porous silica-based media carrying photocatalyst, were observed to increase by 26% and 60%, compared to those of photocatalytic reactor (i.e., 19% and 53%), without any reflector, filled with nonporous glass bead media carrying photocatalyst, for hydrogen sulfide and toluene, respectively. The roughness of used reflector surface was measured to be ca. four times as big as that of a commercial mirror. However, their removal efficiencies are expected to be enhanced by increasing an light intensity resulting from lowering the roughness of used reflector coated on the improved photocatalytic reactor in the future.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.426.2-426.2
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• 2014

Wavefront control은 렌즈, 거울 등을 포함한 많은 광학소자를 대체할 수 있는 기술이며, 이는 광 직접 소자 개발에 매우 유용하다. 기존의 Distributed bragg reflector (DBR) 구조의 경우 lattice mismatch, 낮은 효율, 작은 굴절률 차이의 물질만을 사용해야 하는 문제 등으로 광 직접 소자에의 적용에는 한계가 있다. 본 연구에서는 이러한 한계점을 극복하고, 더 나아가 광학소자 구조 내에서의 빛의 거동을 조절하기 위해서 High-index contrast grating (HCG), 즉, 큰 굴절률 차이가 나는 물질로 이루어진 격자 구조 내의 빛이 가지는 waveguide 특성에 대한 연구가 수행되었다. 굴절률 차이가 큰 물질을 sub-wavelength의 주기적인 혹은 비주기적인 격자 구조로 만듦으로써 투과된 빛의 투과도와 위상 등을 조절할 수 있고 이를 통해 빛의 초점 거리, 휘어짐을 조절 할 수 있다. HCG 구조 내의 빛의 거동을 Rigorous coupled wave analysis (RCWA) 및 Finite element method (FEM) 계산을 이용하여 시뮬레이션 하였다. RCWA 계산을 통해 주기 격자구조의 투과도 및 반사도, 빛의 위상을 계산하여 비주기를 갖는 전체적인 HCG 구조를 결정하였고, FEM 계산을 통하여 그 구조 내에서 빛의 거동을 시뮬레이션 하였다. 1,300 nm 파장의 빛이 광원으로 사용되었고 시뮬레이션을 위해 낮은 굴절률의 물질로 ITO, 높은 굴절률의 물질로는 Si이 사용되었다. $15{\mu}m$ 포커싱, $7.91^{\circ}$의 휘어짐을 시뮬레이션 하였고, 실제 소자 공정을 하여 제작한 후, 광 측정 결과 포커싱은 $15{\mu}m$, 휘어짐은 $4.5{\sim}6.5^{\circ}$를 확인하였다. 이러한 결과를 바탕으로 HCG구조체를 통하여 빛의 엔지니어링이 가능함을 알 수 있었다. HCG구조체는 빛이 투과하는 광학 소자의 전반에 적용이 가능하며 더 나아가 인위적인 빛의 엔지니어링이 가능함을 시사한다.

• Korean Journal of Optics and Photonics
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• v.23 no.4
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• pp.167-171
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• 2012

This paper reports on the stray light analysis results of a compact imaging spectrometer (COMIS) for a microsatellite STSAT-3. COMIS images Earth's surface and atmosphere with ground sampling distances of 27 m at the 18~62 spectral bands (0.4 ~ 1.05 ${\mu}m$) for the nadir looking at an altitude of 700 km. COMIS has an imaging telescope and an imaging spectrometer box into which three electronics PCBs are embedded. The telescope images a $27m{\times}28km$ area of Earth surface onto a slit of dimensions $11.8{\mu}m{\times}12.1mm$. This corresponds to a ground sampling distance of 27 m and a swath width of 28 km for nadir looking posture at an altitude of 700 km. Then the optics relays and disperses the slit image onto the detector thereby producing a monochrome image of the entrance slit formed on each row of detector elements. The spectrum of each point in the row is imaged along a detector column. The optical mounts and housing structures are designed in order to prevent stray light from arriving onto the image and so deteriorating the signal to noise ratio (SNR). The stray light analysis, performed by a non-sequential ray tracing software (LightTools) with three dimensional housing and lens modeling, confirms that the ghost and stray light arriving at the detector plane has the relative intensity of ${\sim}10^{-5}$ and furthermore it locates outside the concerned image size i.e. the field of view of the optics.

• Korean Journal of Optics and Photonics
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• v.8 no.4
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• pp.283-290
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• 1997

Scattering measurement on high reflection dielectric multilayer mirrors deposited on quartz substrate in a vacuum chamber were performed using a total integrated scattering method. Scattering of (Ta$_2$$O_5$/SiO$_2$) multilayer mirrors deposited at 250-30$0^{\circ}C$ was 0.048-0.050% and did not change with an annealing at 30$0^{\circ}C$ for 4 hours. On the other hand, scattering of (TiO$_2$/SiO$_2$) multilayer mirror at 25$0^{\circ}C$ was 0.029% and it showed the heavy tensile stress after an annealing. The rms roughness of (Ta$_2$$O_5$/SiO$_2$) multilayer mirror was almost the same as that of (TiO$_2$/SiO$_2$)multilayer mirror. The column size of Ta$_2$$O_5$ film was smaller than that of TiO$_2$film and the packing density of (Ta$_2$$O_5$/SiO$_2$) multilayer mirrors was higher than that of (TiO$_2$/SiO$_2$) multilayer mirror. It seems that the higher packing density and smaller column size of Ta$_2$$O_5$ films lead to more scattering.