• Current Optics and Photonics
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• 제5권2호
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• pp.101-113
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• 2021

Adaptive optics (AO) systems are becoming more complex to improve their optical performance and enlarge their field of view, so it is a hard and time consuming process to set up and optimize the components of AO systems with actual implementation. However, simulations allow AO scientists and engineers to experiment with different optical layouts and components without needing to obtain and prepare them physically. In this paper, we introduce a new AO simulation named the Korea Adaptive Optics Simulation (KAOS), independently developed by LIG Nex1. We verified the performance of KAOS by comparing with other AO simulation tools. In the comparison simulation, we confirmed the results from KAOS and other AO simulation tools were very similar. Also, we proposed a laser tomography AO system with five Rayleigh laser guide stars (LGSs) optimized by using KAOS to overcome the disadvantages of the AO system with a single sodium LGS for the satellite imaging system. We verified the performance of the proposed AO system using KAOS, and the simulation result showed averaged Strehl ratio of 0.37.

• International journal of advanced smart convergence
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• 제8권1호
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• pp.65-74
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• 2019

3D file formats typically include OBJ (Wavefront file format), STL (STereoLithography), and FBX (Filmbox). Each format has limitations depending on its configuration and usage, and supported formats are different depending on the software application. glTF helps uniform integration of 3D file formats and allows for more efficient transmission of large 3D geometry files by organizing them in a binary format. This paper presents explanation on OBJ, FBX, and STL which are major examples of existing 3D file formats. It also explains the concept and characteristics of glTF and compares its performance with other 3D file formats on the web. The loading time and packets of each 3D file format are measured according to the web browser environment by means of Google Chrome, Firefox and Microsoft Edge. Experimental results show that glTF is the most efficient and that it exhibits the best performance. As to STL, relatively excessive traffic was observed. This study is expected to contribute to reducing rendering time on the web as 3D file formats are used.

• International Journal of Internet, Broadcasting and Communication
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• 제11권2호
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• pp.31-42
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• 2019

As smartphone H/W performance and mobile communication service have been enhanced, large-capacity 3D modeling files are available in smartphones. Common formats of 3D modeling files include STL (STereoLithography), OBJ (Wavefront file format specification), FBX (Filmbox), and glTF (open GL Transmission Format). Each format has different characteristics depending on the configuration and functions, and formats that are supported are varied depending on the applications. Large-size files are commonly used. The 4th generation mobile communication network secures loading of 3D modeling files and transmission of large-size geometric files in order to provide augmented reality services via smartphones. This paper explains the concepts and characteristics of major 3D file formats such as OBJ, FBX, and glTF. In addition, it compares their performance in a wired web with that in the 4th generation mobile communication network. The loading time and packet transmission in each 3D format are also measured by means of different mobile web browsers (Google Chrome and MS Edge). The experiment result shows that glTF demonstrated the most efficient performance while the loading time of OBJ was relatively excessive. Findings of this study can be utilized in selecting specific 3D file formats for rendering time reduction depending on the mobile web environments.

• 한국군사과학기술학회지
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• 제26권3호
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• pp.205-213
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• 2023

An optimal design of a simple beam-shaped flexure hinge mount supporting an optical mirror is presented. An optical mirror assembly is an opto-mechanically coupled system as the optical and mechanical behaviors interact. This side-supporting mount is flexible in the radial direction and rigid for the remaining degrees of freedom to support the mirror without transferring thermal load. Through thermo-elastic, optical and eigenvalue analysis, opto-mechanical performance was predicted to establish the objective functions for optimization. The key design parameters for this flexure are the thickness and length. To find the optimal values of design parameters, response surface analysis was performed using the design of experiment based on nested FCD. Optimal design candidates were derived from the response surface analysis, and the optimal design shape was confirmed through Opto-mechanical performance validation analysis.

• Journal of Astronomy and Space Sciences
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• 제40권4호
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• pp.237-245
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• 2023

Laser communication has been considered as a novel method for earth observation satellites with generation of high data volume. It offers faster data transmission speeds compared to conventional radio frequency (RF) communication due to the short wavelength and narrow beam divergence. However, laser beams are refracted due to atmospheric turbulence between the ground and the satellite. Refracted laser beams, upon reaching the receiver, result in angle-of-arrival (AoA) fluctuation, inducing image dancing and wavefront distortion. These phenomena hinder signal acquisition and lead to signal loss in the course of laser communication. So, precise alignment between the transmitter and receiver is essential to guarantee effective and reliable laser communication, which is achieved by pointing, acquisition, and tracking (PAT) system. In this study, we simulate the effectiveness of tip/tilt compensation for more efficient laser communication in the satellite-ground downlink. By compensating for low-order terms using tip/tilt mirror, we verify the alleviation of AoA fluctuations under both weak and strong atmospheric turbulence conditions. And the performance of tip/tilt correction is analyzed in terms of the AoA fluctuation and collected power on the detector.

• Journal of the Optical Society of Korea
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• 제19권4호
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• pp.403-408
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• 2015

To evaluate the effects of spherical aberration (SA) correction on optical quality in pseudophakic eyes, we simulated the optical quality of the human eye by computation of the modulation transfer function (MTF). We reviewed the medical records of patients who underwent cataract surgery in Asan Medical Center, retrospectively. A Zywave aberrometer was used to measure optical aberrations at 1-12 postoperative months in patients with AR40e intraocular lens implants. The MTF was calculated for a 5 mm pupil from measured wavefront aberrations. The area under the MTF curve (aMTF) was analyzed and the maximal aMTF was calculated while changing the SA ($-0.2{\sim}+0.2{\mu}m$) and the defocus (-2.0 ~ +2.0 D). Sixty-four eyes in 51 patients were examined. The maximal aMTF was $6.61{\pm}2.16$ at a defocus of $-0.25{\pm}0.66D$ with innate SA, and $7.64{\pm}2.63$ at a defocus of $0.08{\pm}0.53D$ when the SA was 0 (full correction of SA). With full SA correction, the aMTF increased in 47 eyes (73.4%; Group 1) and decreased in 17 eyes (26.6%; Group 2). There were statistically significant differences in Z(3, -1) (vertical coma; P = 0.01) and Z(4, 4) (tetrafoil; P = 0.04) between the groups. The maximal aMTF was obtained at an SA of $+0.01{\mu}m$ in Group 1 and an SA of $+0.13{\mu}m$ in Group 2. Optical quality can be improved by full correction of SA in most pseudophakic eyes. However, residual SA might provide benefits in eyes with significant radially asymmetric aberrations.

• 한국광학회지
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• 제17권4호
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• pp.359-365
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• 2006

광학계의 파면오차는 광학계의 성능을 나타내는 주요 지표이며, 광학면의 변형에 의해 발생한다. 광기계의 개발에 있어서 주요 하중조건에서 발생하는 파면오차 양은 중요 규격으로 설정되고 관리되어 진다. 광학면의 변형은 유한요소해석 등의 발달과 더불어 정확한 수준까지 계산할 수 있게 되었다. 유한요소해석 결과로부터 파면오차를 계산하기 위해서는 광학면에서의 변형량을 근사하고 분석해야 한다. 이를 위해 추가적인 격자나 요소망으로 결과를 변화하여 근사하는 방법이 사용되고 있으나, 격자 구성의 번거로움과 변환으로 인한 오차 발생 소지를 가지고 있다. 본 연구에서는 추가적인 격자의 구성없이 절점 정보만으로 효과적인 근사를 할 수 있는 이동 최소제곱 근사법을 사용하여 변형량을 근사하고 파면오차를 계산하는 방법을 제안하였다. 제안된 방법의 효용성을 보이기 위하여 해양탑재체 스캔 미러의 자중에 의한 파면오차를 계산하였고, 기존의 방법과 비교 분석하였다.

• 한국임상보건과학회지
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• 제3권2호
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• pp.372-377
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• 2015

Purpose: The aim of this study is to compare total high order aberrations between surgery which uses TransPRK and general laser assisted sub-epithelial keratomileusis. Methods: The patients who had general laser assisted sub-epithelial and TransPRK laser assisted sub-epithelial by visiting ophthalmic clinic in Ulsan from January 2014 to August 2014 was researched. Results: When comparing total high order aberrations before and after operation, it was found that total high order aberration in general laser assisted sub-epithelial group increased to $0.222{\pm}0.078{\mu}m$ from $0.074{\pm}0.019{\mu}m$ while that in TransPRK assisted sub-epithelial group increased to $0.179{\pm}0.045{\mu}m$ from $0.076{\pm}0.032{\mu}m$. When comparing the increment in total high order aberrations between two groups after surgery, it was found that the increments of TransPRK assisted sub-epithelial group were statistically smaller than that of general laser assisted sub-epithelial group (p<0.05). Conclusions: This study made a comparative analysis of total high order aberrations between general laser assisted sub-epithelial and TransPRK assisted sub-epithelial which was introduced recently and the result showed a significant difference. The findings of this study suggest that TransPRK assisted sub-epithelial can be used widely in simply improving eye sight and quality of vision by reducing an increase in high order aberration caused by orthokeratology surgery. It is expected that TransPRK assisted sub-epithelial will be helpful for improving the understanding quality of eye sight which occurs by several methods of vision correction surgery.

• Journal of Astronomy and Space Sciences
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• 제29권3호
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• pp.321-328
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• 2012

We have designed a 30 cm cryogenic space infrared telescope for astronomical observation. The telescope is designed to observe in the wavelength range of 0.5~2.1 ${\mu}m$, when it is cooled down to 77 K. The result of the preliminary design of the support structure and support method of the mirror of a 30 cm cryogenic space infrared telescope is shown in this paper. As a Cassegrain prescription, the optical system of a 30 cm cryogenic space infrared telescope has a focal ratio of f/3.1 with a 300 mm primary mirror (M-1) and 113 mm secondary mirror (M-2). The material of the whole structure including mirrors is aluminum alloy (Al6061-T6). Flexures that can withstand random vibration were designed, and it was validated through opto-mechanical analysis that both primary and secondary mirrors, which are assembled in the support structure, meet the requirement of root mean square wavefront error < ${\lambda}/8$ for all gravity direction. Additionally, when the M-1 and flexures are assembled by bolts, the effect of thermal stress occurring from a stainless steel bolt when cooled and bolt torque on the M-1 was analyzed.

• 전자통신동향분석
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• 제35권4호
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• pp.65-80
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• 2020

In this article, we review the study trends of three-dimensional (3D) displays that can display stereoscopic images from the perspective of a display device. 3D display technology can be divided into light field, holographic, and volume displays. Light field display is a display that can reproduce the intensity and direction of light or 'ray' in each pixel. It can display stereoscopic images with less information than a holographic display and does not require coherence of the light source. Therefore, it is expected that it will be commercialized before the holographic display. Meanwhile, the holographic display creates a stereoscopic image by completely reproducing the wavefront of an image using diffraction in terms of wave characteristics of light. This technology is considered to be able to obtain the most complete stereoscopic image, and the digital holographic display using a spatial light modulator (SLM) is expected to be the ultimate stereoscopic display. However, the digital holographic display still experiences the problem of a narrow viewing angle due to the finite pixel pitch of the SLM. Therefore, various attempts have been made at solving this problem. Volumetric display is a technology that directly creates a stereoscopic image by forming a spatial pixel, which is known as a volumetric pixel, in a physical space, and has a significant advantage in that it can easily solve the problem of the viewing angle. This technology has already been tested for commercial purposes by several leading companies. In this paper, we will examine recent research trends regarding these 3D displays and near-eye display that is emerging as a significant application field of these technologies.