• Current Optics and Photonics
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• 제7권3호
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• pp.237-247
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• 2023

In middle- and long-distance imaging systems, due to the atmospheric turbulence caused by temperature, wind speed, humidity, and so on, light waves propagating in the air are distorted, resulting in image-quality degradation such as geometric deformation and fuzziness. In remote sensing, astronomical observation, and traffic monitoring, image information loss due to degradation causes huge losses, so effective restoration of degraded images is very important. To restore images degraded by atmospheric turbulence, an image-restoration method based on improved compound multibranch feature fusion (CMFNetPro) was proposed. Based on the CMFNet network, an efficient channel-attention mechanism was used to replace the channel-attention mechanism to improve image quality and network efficiency. In the experiment, two-dimensional random distortion vector fields were used to construct two turbulent datasets with different degrees of distortion, based on the Google Landmarks Dataset v2 dataset. The experimental results showed that compared to the CMFNet, DeblurGAN-v2, and MIMO-UNet models, the proposed CMFNetPro network achieves better performance in both quality and training cost of turbulent-image restoration. In the mixed training, CMFNetPro was 1.2391 dB (weak turbulence), 0.8602 dB (strong turbulence) respectively higher in terms of peak signal-to-noise ratio and 0.0015 (weak turbulence), 0.0136 (strong turbulence) respectively higher in terms of structure similarity compared to CMFNet. CMFNetPro was 14.4 hours faster compared to the CMFNet. This provides a feasible scheme for turbulent-image restoration based on deep learning.

• 대한기계학회논문집A
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• 제26권6호
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• pp.1194-1202
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• 2002

A study on the topology optimization of a multi-spectral camera for space-use is presented. The optimization is carried out under self-weight and polishing pressure loading. A multi-spectral camera for space-use experiences degradation of optical image in the space, which can not be detected on the optical test bench on the earth. An optical surface deformation of a primary mirror, which is a principal component of the camera system, is an important factor affecting the optical performance of the whole camera system. In this study, topology optimization of the primary mirror of the camera is presented. As an objective function, a measure of Strehl ratio is used. Total mass of the primary mirror is given as a constraint to the optimization problem. The sensitivities of the objective function and constraint are calculated by direct differentiation method. Optimization procedure is carried out by an optimality criteria method. For the light-weight primary mirror design, a three dimensional model is treated. As a preliminary example, topology optimization considering a self-weight loading is treated. In the second example, the polishing pressure is also included as a loading in the topology optimization of the mirror. Results of the optimized design topology for the mirror with various mass constraints are presented.

• 전기전자학회논문지
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• 제2권2호
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• pp.173-177
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• 1998

실내환경에서의 광무선 LAN은 송수신기 사이의 시정선이 성립되지 않는 경우 넓은 수광각을 얻기 위해 반구형 렌즈나 반사체를 사용해야 하며, 실내환경에서 반구형 렌즈를 사용했을 때, 교란대기를 통과하는 광신호는 진폭과 위상이 불규칙하게 변화하고, 빔을 편향시킬 수 있다. 이 페이딩은 비트오류율을 증가시켜 결국 광무선통신의 성능을 저하시키게 된다. 본 논문에서는 시정선이 성립되지 않는 광무선채널을 고려하여 수신기에 반구형 렌즈를 장착한 경우, 천정각에 따른 신호대잡음비를 고찰하고, 또한 실내온도에 기인한 교란효과가 통신성능에 미치는 영향를 살펴 본다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.920-925
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• 2001

A study on the topology optimization of a multi-spectral camera for space-use is presented. A multi-spectral camera for space-use experiences degradation of optical image in the space, which can not be detected on the optical test bench on the earth. An optical surface deformation of a primary mirror, which is a principal component of the camera system, under the self-weight loading is an important factor affecting the optical performance of the whole camera system. In this study, topology optimization of the primary mirror of the camera is presented. Total mass of the primary mirror is given as a constraint to the optimization problem. The sensitivities of the objective function and constraint are calculated by direct differentiation method. Optimization procedure is carried out by an optimality criterion method using the sensitivities of the objective function and the constraint. As a preliminary example, topology optimization considering a self-weight loading is treated. For practical use, the polishing pressure is included as a loading in the topology optimization of the primary mirror. Results of the optimized design topology for the primary mirror with varying mass ratios are presented.

• 접착 및 계면
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• 제4권1호
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• pp.18-27
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• 2003

Micromechanical 시험법과 표면 젖음성 측정을 이용하여 플라즈마 처리된 생분해성 poly(p-dioxanone) (PPDO) 섬유강화 poly(L-lactide) (PLLA) 복합재료의 계면물성과 미세파괴 분해메카니즘을 연구하였다. PPDO 섬유강화 PLLA 복합재료는 장기간의 사용기간 동안 우수한 기계적 물성을 제공할 수 있다. PPDO 섬유와 PLLA 기지재료의 분해정도는 열분석과 광학적인 관찰을 통해서 확인하였다. PPDO 섬유와 PLLA 기지재료 사이의 계면전단강도와 접착일은 플라즈마 처리 시간이 60초 일때 가장 컸으며, 접착일과 polar 표면자유에너지는 계면전단강도와 비례하였다. 초기상태의 PPDO 섬유는 연성파단 형상이 나타났으나, 분해시간이 진행됨에 따라 분자량 감소로 인해 점차적으로 취성 파단 형상으로 변하였다. 계면물성과 미세파괴 분해메카니즘은 분해가 진행됨에 따라 변하기 때문에 섬유강화 생분해성 복합재료의 성능을 조절하는데 중요한 요인들이다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2003년도 춘계종합학술대회
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• pp.218-221
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• 2003

가입자선로 환경이 ADSL 전송성능에 미치는 요인을 조사하기 위해서 본 논문에서는 의사선로를 구성하여 실험, 분석하였다. ADSL 전송성능 저해요인중 선로의 거리, 케이블의 접속 방법, 브리지 탭, 인입선의 종류에 따르는 비교분석과 AM 방송 잡음의 영향에 대하여 관찰하였다. ADSL의 전송성능을 유지하기 위하여는 현재의 동선 선로를 사용하는 경우 환경조건에 적합하도록 개선하여 활용해야 할 것이며, 점차적으로는 전송특성이 우수한 광 케이블로 대체하여 나가야 할 것으로 판단된다.

• Journal of Communications and Networks
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• 제9권4호
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• pp.394-401
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• 2007

High speed all optical network is a viable option to satisfy the exponential growth of internet usage in the recent years. Optical networks offer very high bit rates and, by employing technologies like internet protocol over wavelength division multiplexing(IP-over-WDM), these high bit rates can be effectively utilized. However, failure of a network component, carrying such high speed data traffic can result in enormous loss of data in a few seconds and persistence of a failure can severely degrade the performance of the entire network. Designing IP-over-WDM networks, which can withstand failures, has been subject of considerable interest in the research community recently. Most of the research is focused on the failure of optical links in the network. This paper addresses the problem of designing IP-over-WDM networks that do not suffer service degradation in case of a single link failure. The paper proposes an approach based on the framework provided by a recent paper by M. Kurant and P. Thiran. The proposed approach can be used to design large survivable IP-over-WDM networks.

• ETRI Journal
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• 제38권1호
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• pp.1-8
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• 2016

A large incoherent crosstalk (IC) caused by amplified spontaneous emission (ASE) noise power from Tx-disabled optical network units and a differential path loss has been shown to degrade upstream transmission performance in time-division multiplexing passive optical networks. This paper considers the IC-induced power penalty of an upstream signal both in an XG-PON and in a TWDM-PON. We investigate the degradation of the extinction ratio and relative intensity noise through a simulation and experiments. For the XG-PON case, we observe a 9.6 dB difference in the level of ASE noise power from Tx-disabled ONUs (hereafter known simply as ASE noise) between our result and the ITU-T XG-PON PMD recommendation. We propose an optical filtering method to mitigate an IC-induced power penalty. In the TWDM-PON case, the IC-induced power penalty is naturally negligible because the ASE noise is filtered by a wavelength multiplexer at the optical line terminal. The results provide design guidelines for the level of ASE noise in both XG-PONs and TWDM-PONs.

• 한국광학회지
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• 제29권6호
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• pp.233-240
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• 2018

본 논문에서는 불꽃감지기용 테스트램프의 반사경 형상에 대해 제작 시 오차를 줄일 수 있는 설계 방법 연구를 진행하였다. 테스트램프는 높은 광량의 빛을 평행하게 진행시켜야 하지만, 제작 시 중앙 빛을 제어하는 소형 반사경의 고정이 어렵다는 단점으로 인해 광량 저하가 발생하여 목표 광량을 만족하지 못하는 경우가 많다. 이러한 문제점 해결을 위해 틸트 및 디센터 시에도 성능 저하 현상을 최소화하는 방향으로 광 손실률 5% 미만의 구 소형 반사경 설계를 진행하였고, 설계 분석 결과에 따라 광학계 제작 시에도 오차 영향이 적은 소형 반사경으로 구체 형상을 제시하였다.

• 대한전자공학회논문지SD
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• 제38권5호
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• pp.347-356
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• 2001

광대역 초고속 광변조기소자 패키지와 연계되는 주요 문제점인 die feature, pigtailing, suppression of RF package resonance, RF launcher approach, termination approach의 5가지 특성을 차례로 분석한 후 우수한 특성이 나올 수 있도록 소자를 패키징하였다. Microcoax에 의해 패키징된 변조기의 전기적 특성인 S21은 10㎓ 이상까지 -3㏈ 이상의 파워를 유지하였고, S11은 18㎓까지 -l5㏈를 유지하였다. 10㎓까지 광파워는 최대값으로부터 3㏈ 이상 떨어지지 않았고 50km 전송실험 후 소광비는 약 10.6㏈, 지터 값은 3.2ps로 양호한 값을 나타내어 패키징을 원만히 해결해야만 변조기의 변조 능력은 10㎓ 이상이 됨을 알 수 있다.