• Current Optics and Photonics
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• v.6 no.1
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• pp.60-68
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• 2022

We report on the design of the secondary and the tertiary mirrors used in lightweight assemblies made entirely of silicon carbide (SiC). The essential design points are weight reduction within the acceptable deformation of the mirror surface by gravity release, temperature change, and vibration during or after space launch. To find a design that achieves the target requirements, we established finite element models for various candidate designs and subjected each one to wave front error analyses along gravity directions and in operation temperatures. We also calculated the natural frequencies of the candidate assemblies. Our study suggested that a triangular cell with bipod flexure support can satisfy the target weight within the requirements.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.7
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• pp.682-687
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• 2011

Calibration mirror mechanism has been widely used for on-board calibration with black body. The calibration mirror is deployed to reflect the radiation energy from the black body to the image sensor for calibrating the sensor system. After the calibration, the calibration mirror is stowed not to hide a main optical path. It also has a fail-safe function which can stow the mirror by just removing the input power of motor when the calibration mirror is stopped at certain position during the calibration. In the present work, the operation concept, design, torque analysis and functional test results of the calibration mirror mechanism with the aforementioned function have been introduced and investigated.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.177-178
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• 2014

This work proposes a two-dimensional (2-D) laser scanning mirror actuator with a simple structure composed of one magnet and four coils. The mirror-actuating device generates 2-D scanning motions about two orthogonal axes by combining electromagnetic actuators of the conventional moving-magnet types. The magnet is attached to back side of the mirror placed inside of the moving frame. The four coils is placed on the base frame in a cross shape. We implement a finite element analysis to calculate magnetic flux in the electromagnetic system with the overall size of $20mm(W){\times}20mm(D){\times}13mm(H)$ for the mirror size of $8mm{\times}8mm$. The each moving-magnet type electromagnetic actuator has the motor constant 3.41 mNm/A and the restoring constant 1.75 mNm/rad and the resonance frequency of 58 Hz and the bandwidth of 80 Hz. The proposed compact and simple 2-D scanning mirror predicted advantages of large 2-D angular deflections, wide frequency bandwidth and low manufacturing cost.

• Journal of the Optical Society of Korea
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• v.16 no.3
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• pp.243-246
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• 2012

An off-axis four-mirror-anastigmatic telescope is presented here which is composed of two aspheric surfaces and two spherical surfaces. The entrance pupil diameter is 290 mm and the stop is located at the primary mirror. The effective focal length is 900 mm. The strip field of view for the telescope is $15^{\circ}{\times}0.2^{\circ}$ and if the telescope is launched into an orbit about 400 km altitude, the observed range width will be more than 105 km within a scene without any other auxiliary scanning instrument. The spectral range can be as wide as from visual wave band to infrared wave band in the mirror system. This telescope can be used for environmental monitoring with different detectors whose pixel is adapted to the optical resolution. In this paper, the spectral range is chosen as 3.0 -5.0 ${\mu}m$, and center distance of the pixel is 30 ${\mu}m$. And the image quality is near the diffraction limit.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.2
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• pp.55.4-56
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• 2018

Linear Astigmatism Free - Three Mirror System (LAF-TMS) is the linear astigmatism free off-axis wide field telescope with D = 150 mm, F/3.3, and $FOV=5.51^{\circ}{\times}4.13^{\circ}$. We report the design and analysis results of its mirrors and optomechanical structures. Tolerance allowance has been analyzed to the minimum mechanical tolerance of ${\pm}0.05mm$ that is reasonable tolerance for fabrication and optical alignment. The aluminum mirrors are designed with mounting flexure features for the strain-free mounting. From Finite Element Analysis (FEA) results of mounting torque and self-weight, we expect 33 - 80 nm RMS mirror surface deformations. Shims and the L-bracket are mounted between mirrors and the mirror mount for optical alignment. The mirror mount is designed with four light-weighted mechanical parts. It can stably and accurately fix mirrors, and it also suppresses some of stray light.

• Publications of The Korean Astronomical Society
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• v.30 no.1
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• pp.17-29
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• 2015

The IGRINS is a near infrared high resolution spectrograph jointly developed by the Korea Astronomy and Space Science Institute and the University of Texas at Austin. We present design and fabrication of the optomechanical mount for the five mirrors, i.e., an input fold mirror, a slit mirror, a dichroic, and two camera fold mirrors. Based on the structure analysis and the thermal analysis of finite element methods, the optomechanical mount scheme satisfies the mechanical and the thermal design requirements given by the optical tolerance analysis. The performance of the fabricated mirror mounts has been verified through three IGRINS commissioning runs.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.91.2-91.2
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• 2014

A near infrared wide-band high resolution spectrograph, immersion grating infrared spectrometer (IGRINS) has been jointly developed by the Korea Astronomy and Space Science Institute and the University of Texas at Austin. The compact white-pupil design of the instrument optics includes five cryogenic flat mirrors including a slit mirror, an input fold mirror, a dichroic mirror, and H&K camera fold mirrors. In this study, we introduce the optomechanical mount designs of the five cryogenic mirrors. In order to meet the structural stability and thermal requirements of the mount models, we conducted the design work with the aid of 3-dimensional computer modeling and the finite element analysis (FEA) method. We also present the actual fabricated parts and assemblies of the mounts and mirrors as well as their CAD models.

• Korean Journal of Optics and Photonics
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• v.28 no.6
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• pp.263-272
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• 2017

To design a wide-field optical system, the inverted telephoto configuration, which has a negative front group and a positive rear group, is popular. For a two-mirror system, the inverse Cassegrain system has the inverted telephoto configuration, but the inverse Cassegrain system with the conventional, axially symmetric configuration shows severe field screening and ray obstruction. To avoid these problems, we put the aperture stop on the secondary mirror of an inverse Cassegrain system to increase field of view, and designed a wide-field off-axis two-mirror system which only uses the off-axis field, without ray obstruction.

• Journal of the Korean Solar Energy Society
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• v.31 no.2
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• pp.53-62
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• 2011

Heliostat in the tower type solar thermal power plant is a sun tracking mirror system to reflect the solar energy to the receiver and the optical performance of it affects to the efficiency of whole power plant most significantly. Thus a proper design of structure of the heliostat reflective surface could be the most important step in the construction of such power plant. The work presented here is a design of structure of optical surface of heliostat, which will be used in 200kW solar thermal power plant. The receiver located at 43(m) high from ground in tower has $2{\times}2$(m) rectangular shape. We first developed the software tool to simulate the energy concentration characteristics of heliostat using the ray tracing technique. Then, the shape of heliostat reflective surface is designed with the consideration of heliostat's energy concentration characteristics, production cost and productivity. The designed heliostat's reflective surface has a structure formed by canting four of $1{\times}1$(m) rectangular flat plate mirror facet and the center of each mirror facet is located on the spherical surface, where the spherical surface is formulated by the mirror facet mounting frame.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.3
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• pp.578-585
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• 2009

In this paper, we present the design of an electromagnetic scanning mirror with torsional springs. The scanning mirror consisting of torsional springs and electromagnetic coils was designed for the applications of laser animation systems. We analyzed and optimized three types of torsional springs, namely, straight beam springs (SBS), classic serpentine springs (CSS), and rotated serpentine springs (RSS). The torsional springs were analyzed in terms of electrical resistance, fabrication error tolerance, and resonance mode separation of each type using analytical formula or numerical analysis. The RSS has advantages over the others as follows: 1) A low resistance of conductors, 2) wide resonance mode separation, 3) strong fabrication error tolerance, 4) a small footprint. The double-layer coils were chosen instead of single-layer coils with respect to electromagnetic forces. It resulted in lower power consumption. The geometry of the scanning mirror was optimized by calculations; RSS turn was 12 and the width of double-layer coil was $100{\mu}m$, respectively. When the static rotational angle is 5 degrees, the power consumption of the mirror plate was calculated to be 9.35 mW since the resistance of the coil part and a current is $122{\Omega}$ and 8.75 mA, respectively. The power consumption of full device including the mirror plate and torsional springs was calculated to be 9.63 mW.