• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.123-126
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• 2004

We have demonstrated the fabrication of patterned 3D photonic crystals by holographic lithography in conjunction with soft lithography. Holographic lithography created 3D ordered macroporous structures and soft lithography made tailored defects. Because the hard baked photoresist pattern possessed high resistance against the uncured photoresist solution and the refractive index did not change appreciably by hard baking, a crosslinked photoresist was used as a relief pattern for the holographic fabrication of patterned 3D photonic crystals. More complicated defect geometries might be easily obtained with more complicated patterns on PDMS stamps. Moreover, the present results might be used as templates for 3D PCs of highindex defects that can be exploited as optical waveguides and optical circuits.

• Journal of the Optical Society of Korea
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• 제14권4호
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• pp.305-309
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• 2010

Photopolymer films containing fluorescent anthracene polymer, polymethyleneanthracene (PMAn), were prepared with different concentrations of PMAn for holographic recording useful for security documents. The fluorescent photopolymer film showed enhanced fluorescent intensity due to the micro-separation which arose from grating formation and diffusion during photopolymerization. Experimental values of diffraction efficiency were well matched to the simulated values for photopolymers having different PMAn concentrations. Holography patterning was carried out using the fluorescent photopolymer under a photo-mask. A grating was confirmed using microscope techniques in the recorded area under the pattern. Importantly the recorded area showed enhanced fluorescence compared to the unrecorded part, allowing fluorescence patterns at micro scale along with the submicron grating pattern. The fluorescence pattern recorded on the photopolymer film provides additional readability of holographic reading and thus is useful for secure recording and reading of information.

• 대한치과보철학회지
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• 제33권1호
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• pp.48-74
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• 1995

Since heat curing acrylic resins undergo unavoidable dimensional changes following polymerization, adaptation can be altered. Until recently, although numerous studies on the dimensional changes of denture base were based on a microscopic technic that measures the relative displacement of a limited reference points on the denture base, but there have been few studies on the distortions of resins using holographic interferometry. Purpose of this study was to determine and compare the dimensional changes and fringe patterns of 4 heat curing acrylic resins, and observe the distortions of acrylic resin denture base by temperature change with the aid of the holographic interferometry. Holographic interferograms were taken on the resin specimens and acrylic resin denture base with the 10mW He-Ne laser and double exposure method. Comparison and analysis of fringe pattern on the recorded object surface was performed. The following results were obtained. 1. The dimensional changes for the high impact resin Lucitone 199 were statistically the greatest of all resins, and the rapid heat curing resin Premium super 20 were the least. 2. The most polymerization shrinkage of all materials occured in initial period of measurements, at this time the difference of polymerization shrinkage properties between resins was founded. 3. The stress distribution of specimens was seen by various type of fringe pattern which had directionality. 4. The polymerization shrinkage of resins was greatly influenced by temperature change. 5. The partial deformations of resin denture base were observed in 70 C and 90 C water.

• 한국광학회:학술대회논문집
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• 한국광학회 1991년도 제6회 파동 및 레이저 학술발표회 Prodeedings of 6th Conference on Waves and Lasers
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• pp.23-28
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• 1991

A single-layer neural network with 4$\times$4 input neurons and 4 output neurons is optically implemented. Holographic lenslet arrays are used for the e optical interconnection topology, a liquid crystal light valve(LCLV) is used for controlling optical interconection weights. Using a Perceptron learning rule, it classifics input patterns into 4 different categories. It is shown that the performance of the adaptive neural network depends on the learning rate, the correlation of input patterns, and the nonlinear characteristic properties of the liquid crystal light valve.

• 대한치과교정학회지
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• 제22권3호
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• pp.531-556
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• 1992

The majority of the commonly used protraction headgears for the protraction of small and/or retropositioned maxilla not allow a change in the point of force application or direction of the force delivery to attain predictable results because of the position of the upper and lower lips to avoid discomfort to the patient. The purpose of this study was to investigate the initial reaction of maxillofacial complex according to the change of force variables such as direction and point of force application with designing an antenna type-modified protraction head gear. A macerated human skull with well aligned upper teeth was used to experimental model and the investigation was done by double exposure holographic interferometry. Fringe patterns of each protraction conditions were compared and analized. The results were as follows. (Frontal view) 1. The Counterclockwise rotation of the maxilla was showed by parallel protraction to occlusal plane and the fringe was decreased in number as higher point of force application. 2. Generally, the number of fringe was increased in 500gm of protraction force than in 300gm. 3. When apply the protraction force to the maxilla with rapid palatal expansion, the direction of fringe patterns was differed from the protraction without expansion. 4. In most of cases, the counterclockwise rotation was decreased in case of the direction of the force is $20^{\circ}$ downward to occlusal plane compared to the parallel direction. 5. At the point of force application is 15mm above and the direction of force is 20 downward to occlusal plane , the translation of the maxillary complex was showed. (Lateral view) 6. The direction of fringe patterns of the facial bones were differed each other by the sutures, and showed almost parallel when apply the 300gm and 500gm of protraction force. 7. In case of rapid palatal expansion with protraction of the maxilla, the fringe patterns between the maxillary area and the area from the posterior of the maxillary first molar to the pterygomaxillary fissure were differed. In case without rapid palatal expansion, the changes of direction and point of the force application did not affect to the direction and the number of the fringe patterns.

• Macromolecular Research
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• 제14권2호
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• pp.155-165
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• 2006

The present article describes the experimental and theoretical observations on the formation of holographic, polymer-dispersed, liquid crystals and electrically switchable, photonic crystals. A phase diagram of the starting mixture of nematic liquid crystal and photo-reactive triacrylate monomer was established by means of differential scanning calorimetry (DSC) and cloud point measurement. Photolithographic patterns were imprinted on the starting mixture of LC/triacrylate via multi-beam interference. A similar study was extended to a dendrimer/photocurative mixture as well as to a single component system (tetra-acrylate). Theoretical modeling and numerical simulation were carried out based on the combination of Flory-Huggins free energy of mixing and Maier-Saupe free energy of nematic ordering. The combined free energy densities were incorporated into the time-dependent Ginzburg-Landau (Model C) equations coupled with the photopolymerization rate equation to elucidate the spatio-temporal structure growth. The 2-D photonic structures thus simulated were consistent with the experimental observations. Furthermore, 3-D simulation was performed to guide the fabrication of assorted photonic crystals under various beam-geometries. Electro-optical performance such as diffraction efficiency was evaluated during the pattern photopolymerization process and also as a function of driving voltage.

• 한국통신학회논문지
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• 제34권2C호
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• pp.163-168
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• 2009

본 논문에서는 홀로그래픽 저장 장치에서 가장 큰 문제점인 고립 픽셀을 허용하지 않는 2차원 변조 부호를 제안한다. 제안하는 2차원 변조 부호는 기존에 사용하던 6/8 변조 부호보다 부호화와 복호화가 간단하며 데이터 검출을 어렵게 하는 1 비트의 고립된 형태를 완벽하게 제거한다. 기존에 사용하던 6/8 변조 부호는 약간의 고립 픽셀을 허용한다. 결과를 보면 blur가 1.4일 때 제안한 변조 부호가 6/8 변조 부호보다 전체적으로 성능이 좋다. 제안한 변조 부호는 수신된 값을 4비트로 양자화 하였을 때 최적의 성능을 낸다.

• 한국광학회지
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• 제1권1호
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• pp.12-15
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• 1990

홀로그래피 간섭법과 스펙클 사진법을 결합한 홀로스펙클 간섭법을 이용하여 3차원 변형을 측정하였다. 이 방법은 이중노출된 하나의 사진건판으로부터 종변위와 횡변위를 모두 알아낼 수 있어 3차원 변형측정에 매우 유용하게 사용되고 있다. 본 연구에서는 물체의 일부분에 밀집되어 일어나는 변형을 측정하기 위하여 image holography에 기초를 둔 광학시스템을 구성하였다. 시스템의 배율을 적절히 증가시키고 기준파의 세기를 감소시킴으로써 보통의 홀로그램에 비해 스펙클의 효과를 증대시켰다. 이로써 가시도가 높은 Young의 무늬 뿐만 아니라 확대되고 명확한 홀로 그래피 간섭무늬를 얻을 수 있어 indentor에 의한 3차원 접촉변형을 측정하였다.

• 한국통신학회논문지
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• 제16권10호
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• pp.934-940
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• 1991

본 논문에서는 새로운 양자화 방법을 도입하여 학습을 수행하는 단층 신경망을 광학적으로 구현하였다 본 논문의 시스템은 입력 마스크 위상형 홀로그램 회절격자. LCD, CCD 카메라 등으로 구성된다. 입력단의 뉴런과 출력단의 뉴런간의 연결은 홀로그램 회절격자를 이용하여 2차원 연결을 이루었으며, 회절광들의 세기를 같게 하기 위하여 진폭형 회절격자를 위상형 회절격자로 변환시켰다. 뉴런간의 가중치는 2진 양자화되어 LCD를 이용하여 나타내었고, 출력값은 CCD를 통하여 컴퓨터에 입력되어 가중치를 보정하며, 이 과정은 학습이 완료될 때가지 반복 수행된다. 실험은 학습도 (learning rate) 0.5, 0.9에 대하여 실행하였으며, 제안된 방식으로 학습을 무리없이 수행할 수 있음을 확인할 수 있었다.

• 한국전기전자재료학회논문지
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• 제20권10호
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• pp.852-858
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• 2007

The dependence of substrate on the Ag photodoping phenomenon into amonhous $({\alpha}-)$ GeSe thin film has been investigated using holographic method. A 442 nm HeCd laser was utilized as a light source for the holographic exposure and a 632.8 nm HeNe laser to measure the variation of diffraction efficiency $(\eta)$ in real time. The films (Ag and ${\alpha}-GeSe$) were thermally deposited on the substrates, i.e. p-type Si(100), n-type Si(100) and slide glass. The sample structures prepared were two types: type I (Ag/${\alpha}$-SeGe/substrate) and type II (${\alpha}$-SeGe/Ag/substrate). The $\eta$ kinetics comprised to be three steps in which $\eta$ initially increases, is saturated to be maximized $(\eta_M)$, and then decreases relatively gradually. For the same substrate, the $\eta_M$ values of the type II were higher than those of type I. In addition, the type II exhibited the highest $\eta_M$ for p-type Si substrate, while that in type I was observed for n-type Si substrate. These tendency is explained by the diffusion of minority carrier in the films and the change of magnitude and direction in internal fields generated at the film interfaces. Atomic-force-microscope (AFM) was used to observe relief-type grating patterns.