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Disorder-mediated enhancement of fiber numerical aperture.
Choi, Youngwoon,Yoon, Changhyeong,Kim, Moonseok,Yang, Juhee,Choi, Wonshik Optical Society of America 2013 Optics letters Vol.38 No.13
<P>The numerical aperture (NA) of a multimode optical fiber sets the limit of the information transport capacity along the spatial degree of freedom. In this Letter, we report that the application of a highly disordered medium can overcome the capacity limit set by the fiber NA. Specifically, we coated the input surface of a multimode fiber with a disordered medium made of ZnO nanoparticles and transported a wide-field image through the fiber with a spatial resolution beyond the diffraction limit given by the fiber NA. This was made possible because multiple scatterings induced by the disordered medium physically increased the NA of the entire system. Our study will lead to enhancing the spatial resolution of fiber-based endoscopic imaging and also improving the information transport capacity in optical communications.</P>
Acute Appendicitis: A Rare But Probable Manifestation of Kawasaki Disease
Choi Wonshik,Yun Sin Weon,Hong Mineui,Suh Suk-Won,Yi Dae Yong,Park Ji Young 대한소아감염학회 2023 Pediatric Infection and Vaccine Vol.30 No.2
Kawasaki disease (KD) is an acute, systemic inflammatory disorder that often targets coronary arteries. Being the common cause of acquired heart disease in children, timely diagnosis and intravenous immunoglobulin treatment are crucial. However, it is challenging for physicians to diagnose KD if it presents with atypical manifestations. We report the case of a 5-year-old boy who initially presented with appendicitis; after an appendectomy, he had a prolonged fever. He was finally diagnosed with atypical KD and successfully recovered after intravenous immunoglobulin treatment. Through a literature review, we found 21 cases of appendicitis associated with KD. In most cases, the patients were male with a mean age of 5.3 years. Most had higher proportions of incomplete KD and coronary artery complications than expected for typical KD. In conclusion, appendicitis could be a rare complication of KD; therefore, multidisciplinary cooperation and early recognition of atypical KD are essential for timely diagnosis.
Perfect transmission through Anderson localized systems mediated by a cluster of localized modes.
Choi, Wonjun,Park, Q-Han,Choi, Wonshik Optical Society of America 2012 Optics express Vol.20 No.18
<P>In a strongly scattering medium where Anderson localization takes place, constructive interference of local non-propagating waves dominate over the incoherent addition of propagating waves. This results in the disappearance of propagating waves within the medium, which significantly attenuates energy transmission. In this numerical study performed in the optical regime, we systematically found resonance modes, called eigenchannels, of a 2-D Anderson localized system that allow for the near-perfect energy transmission. We observed that the internal field distribution of these eigenchannels exhibit dense clustering of localized modes. This strongly suggests that the clustered resonance modes facilitate long-range energy flow of local waves. Our study explicitly elucidates the interplay between wave localization and transmission enhancement in the Anderson localization regime.</P>
Overcoming the Diffraction Limit Using Multiple Light Scattering in a Highly Disordered Medium
Choi, Youngwoon,Yang, Taeseok Daniel,Fang-Yen, Christopher,Kang, Pilsung,Lee, Kyoung Jin,Dasari, Ramachandra R.,Feld, Michael S.,Choi, Wonshik American Physical Society 2011 Physical review letters Vol.107 No.2
Observation of sub-Poisson Photon Statistics in the Cavity-QED Microlaser
Choi, Wonshik,Lee, Jai-Hyung,An, Kyungwon,Fang-Yen, C.,Dasari, R. R.,Feld, M. S. American Physical Society 2006 Physical review letters Vol.96 No.9
<P>We have measured the second-order correlation function of the cavity-QED microlaser output and observed a transition from photon bunching to antibunching with increasing average number of intracavity atoms. The observed correlation times and the transition from super- to sub-Poisson photon statistics can be well described by gain-loss feedback or enhanced-reduced restoring action against fluctuations in photon number in the context of a quantum microlaser theory and a photon rate equation picture. However, the theory predicts a degree of antibunching several times larger than that observed, which may indicate the inadequacy of its treatment of atomic velocity distributions.</P>
Dynamic speckle illumination wide-field reflection phase microscopy
Choi, Youngwoon,Hosseini, Poorya,Choi, Wonshik,Dasari, Ramachandra R.,So, Peter T. C.,Yaqoob, Zahid The Optical Society 2014 Optics letters Vol.39 No.20
<P>We demonstrate a quantitative reflection-phase microscope based on time-varying speckle-field illumination. Due to the short spatial coherence length of the speckle field, the proposed imaging system features superior lateral resolution, 520 nm, as well as high-depth selectivity, 1.03 관m. Off-axis interferometric detection enables wide-field and single-shot imaging appropriate for high-speed measurements. In addition, the measured phase sensitivity of this method, which is the smallest measurable axial motion, is more than 40 times higher than that available using a transmission system. We demonstrate the utility of our method by successfully distinguishing the motion of the top surface from that of the bottom in red blood cells. The proposed method will be useful for studying membrane dynamics in complex eukaryotic cells.</P>
3kW 영구 자석형 동기발전기를 이용한 풍력 터빈 시뮬레이터 개발
최원식(Choi, Wonshik),오중기(Oh, Joongki),박기현(Park, Kihyun),박현철(Park, Hyunchul) 한국신재생에너지학회 2010 한국신재생에너지학회 학술대회논문집 Vol.2010 No.11
본 논문에서는 3kW 영구 자석형 동기발전기(PMSG)를 이용한 풍력 터빈 시뮬레이터 개발에 대해 기술하였다. 풍력발전 시스템은 블레이드를 포함한 회전부, 동력 전달부, 발전기, 전력변환기로 크게 나눌 수 있으며, 시뮬레이터는 유도 모터와 PMSG, 인버터-컨버터와 제어 시스템으로 이루어진다. 시뮬레이터를 운전하기 위해서는 특정 속도의 바람 모델을 적용하여 풍력 발전기의 회전부에 걸리게 되는 토크와 회전 속도 값이 요구된다. 풍력 터빈 모델로부터 계산값을 시뮬레이터에 맞게 스케일링하여 유도 모터를 구동 한다. 발전기측 컨버터는 MPPT(Maximum Power Point Tracking) 알고리즘을 통해 제어하고 계통측 인버터는 유효 전력과 무효 전력을 제어하도록 한다. PSIM과 MATLAB/SIMULINK를 이용하여 컴퓨터 시뮬레이션으로 그 결과를 증명하였다.
Optical Imaging With the Use of a Scattering Lens
Youngwoon Choi,Changhyeong Yoon,Moonseok Kim,Wonjun Choi,Wonshik Choi IEEE 2014 IEEE journal of selected topics in quantum electro Vol.20 No.2
<P>“Turbidity” caused by multiple light scattering distorts the propagation of waves, and thus undermines optical imaging. For example, translucent biological tissues exhibiting optical turbidity have posed limitations on the imaging depth and energy transmission. Here, we introduce a novel method called turbid lens imaging (TLI) that records a transmission matrix of a scattering medium charactering the input-output response of the medium. The knowledge of this transmission matrix allows one to find an incident wave out of the distorted transmitted wave. Therefore, it converts the highly complex medium into a useful imaging optics. We demonstrate that the image distortion by a scattering medium can be eliminated by the use of the transmission matrix and a clean object image can be retrieved as a result. We extend TLI for imaging through a multimode optical fiber, which is also a scattering medium, and demonstrate an endoscopic imaging by using a single multimode optical fiber itself as a lens. In addition, we show that TLI removes the pixelation artifact in using an image fiber bundle and improve spatial resolution. Our method of making use of multiple light scattering will lay a foundation for advance optical bioimaging methods.</P>