• International Journal of Advanced Culture Technology
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• v.10 no.4
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• pp.478-486
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• 2022

Holography is a human-friendly technology that can express 3D stereoscopic information without eye fatigue. You can experience the mysterious features of light directly and indirectly, and you can also experience the principles of 3D imaging, which makes it a very good curriculum. As such, although holography is very effective in teaching students optics and 3D imaging technology, it has not yet been systematically established. The reason is the cost burden such as expensive equipment and laboratories, and the lack of easily accessible educational equipment. We implemented a portable holographic recording system to solve this problem. In addition, since silver halides, which use harmful chemicals, are not used in the process of developing the recording medium, and photopolymers are used, it is possible to educate not only the general public but also young students. In order to improve the completeness of the recorded result, the mechanism part, light source, and recording medium part of the production system were newly constructed to complement all the existing problems. The proposed system will make holography easily accessible to many people in a variety of fields, not just education. Through the interesting experience of various features and principles of light and the production of holograms with high satisfaction, we hope to popularize them in various fields such as education.

• Current Optics and Photonics
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• v.7 no.3
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• pp.254-262
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• 2023

Novel thermo-optically focus-switchable Fresnel zone plates based on phase-change metafilms are designed and analyzed at a visible wavelength (660 nm). By virtue of the large thermo-optic response of vanadium dioxide (VO₂) thin film, a phase-change material, four different plasmonic phase-change absorbers are numerically designed as actively tunable Gires-Tournois Al-VO₂ metafilms in two and three dimensions. The designed phase-change metafilm unit cells are used as the building blocks of actively focus-switchable Fresnel zone plates with strong focus switching contrast (40%, 83%) and high numerical apertures (1.52, 1.70). The Fresnel zone plates designed in two and three dimensions work as cylindrical and spherical lenses in reflection type, respectively. The coupling between the thermo-optic effect of VO₂ and localized plasmonic resonances in the Al nanostructures offer a large degree of freedom in design and high-contrast focus-switching performance based on largely tunable absorption resonances. The proposed method may have great potential in photothermal and electrothermal active optical devices for nonlinear optics, microscopy, 3D scanning, optical trapping, and holographic displays over a wide spectral range including the visible and infrared regimes.

• ETRI Journal
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• v.44 no.1
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• pp.85-93
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• 2022

We propose an efficient method for synthesizing mesh-based realistic computer-generated hologram (CGH). In a previous nonanalytic mesh-based CGH synthesis, the angular spectrum of the two-dimensional (2D) plane is calculated using the fast Fourier transform (FFT) with the same size as the resolution of the final hologram. Because FFT increases the computation time as the size of the input matrix increases, the previous method has a problem: The higher the resolution of the hologram, the greater the computational load, thereby delaying synthesis time. In this study, when calculating the angular spectrum of the 2D plane in mesh-based CGH synthesis, we propose a method to calculate the angular spectrum by defining the 2D plane with an arbitrary size smaller than the resolution of the final hologram. The resolution adjustment method reduces the computation time and can be applied to occlusion culling and texturing for the realistic effect of mesh-based CGH. We describe the principle, error analysis, application of realistic effect, and experimental results of the proposed method.

• Smart Structures and Systems
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• v.31 no.6
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• pp.573-583
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• 2023

Although unmanned aerial vehicles have been used to overcome the limited accessibility of human-based visual inspection, unresolved issues still remain. Onsite inspectors face difficulty finding previously detected damage locations and tracking their status onsite. For example, an inspector still marks the damage location on a target structure with chalk or drawings while comparing the current status of existing damages to their previous status, as documented onsite. In this study, an augmented-reality-based structural inspection system with onsite damage information marking was developed to enhance the convenience of inspectors. The developed system detects structural damage, creates a holographic marker with damage information on the actual physical damage, and displays the marker onsite via an augmented reality headset. Because inspectors can view a marker with damage information in real time on the display, they can easily identify where the previous damage has occurred and whether the size of the damage is increasing. The performance of the developed system was validated through a field test, demonstrating that the system can enhance convenience by accelerating the inspector's essential tasks such as detecting damages, measuring their size, manually recording their information, and locating previous damages.

• Journal of the Korean Society of Safety
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• v.14 no.4
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• pp.204-210
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• 1999

We propose an optical fingerprint identification system using volume hologram for database of matched filter. Matched filters in VanderLugt correlator are recorded into a volume hologram that can store data with high density, transfer them with high speed, and select a randomly chosen data element. The multiple reference fingerprint photographs of database are prerecorded in a photorefractive material in the form of Fourier transform images, simply by passing the image displayed in a spatial light modulator through a Fourier transform lens. The angular multiplexing method for multiple holograms of database is achieved by controlling the reference directions with a step motor. Experimental results show that the proposed system can be used for secure entry systems to identify individuals for access to a restricted area, security verification of credit cards, passports, and other IDs.

• Current Optics and Photonics
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• v.7 no.6
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• pp.673-682
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• 2023

In this paper, a three-key triple data encryption algorithm (TDEA) of a digital cryptosystem based on phase-shifting interferometry is proposed. The encryption for plaintext and the decryption for the ciphertext of a complex digital hologram are performed by three independent keys called a wavelength key k₁(λ), a reference distance key k₂(d_r) and a holographic encryption key k₃(x, y), which are represented in the reference beam path of phase-shifting interferometry. The results of numerical simulations show that the minimum wavelength spacing between the neighboring independent wavelength keys is about δλ = 0.007 nm, and the minimum distance between the neighboring reference distance keys is about δd_r = 50 nm. For the proposed three-key TDEA, choosing the deviation of the key k₁(λ) as δλ = 0.4 nm and the deviation of the key k₂(d_r) as δd_r = 500 nm allows the number of independent keys k₁(λ) and k₂(d_r) to be calculated as N(k₁) = 80 for a range of 1,530-1,562 nm and N(d_r) = 20,000 for a range of 35-45 mm, respectively. The proposed method provides the feasibility of independent keys with many degrees of freedom, and then these flexible independent keys can provide the cryptosystem with very high security.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.8
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• pp.816-827
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• 2009

This paper deals with a bearing faults localization technique based on holographic approach by visualizing sound radiated from the faults. The main idea stems from the phenomenon that bearing faults in a moving vehicle generate impulsive sound. To visualize fault signal from the moving vehicle, we can use the moving frame acoustic holography [Kwon, H.-S. and Kim, Y.-H., 1998, "Moving Frame Technique for Planar Acoustic Holography," J. Acoust. Soc. Am. Vol. 103, No. 4, pp. 1734${\sim}$1741]. However, it is not easy to localize faults only by applying the method. This is because the microphone array measures noise(for example, noise from other parts of the vehicle and the wind noise) as well as the fault signal while the vehicle passes by the array. To reduce the effect of noise, we propose two ideas which utilize the characteristics of fault signal. The first one is to average holograms for several frequencies to reduce the random noise. The second one is to apply the partial field decomposition algorithm [Nam, K.-U., Kim, Y.-H., 2004, "A Partial Field Decomposition Algorithm and Its Examples for Near-field Acoustic Holography," J. of Acoust. Soc. Am. Vol. 116, No. 1, pp. 172${\sim}$185] to the moving source, which can separate the fault signal and noise. Basic theory of those methods is introduced and how they can be applied to localize bearing faults is demonstrated. Experimental results via a miniature vehicle showed how well the proposed method finds out the location of source in practice.

• Journal of the Korean Institute of Telematics and Electronics T
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• v.36T no.1
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• pp.25-31
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• 1999

A real-time holography system using LCD with CCD camera is proposed. In this system, the rainbow hologram is used since it can be reconstructed by white light source. And to record on CCD camera, a kind of in-line holography method is used to widen the width of the fringe pattern. The interference fringe pattern by proposed system is detected with CCD camera and transferred to the LCD. A 3-dimensional image is reconstructed when the white light source illuminates the LCD. If the position of the input image is changed, that of the reconstructed image is also changed. So it can represent 3-dimensional moving images at real-time. In this paper, to confirm the usefulness of the proposed method, the reconstructed image by holographic film is compared to the same reconstructed image by LCD. In the recording process, the optimal ratio of the reference and object beam intensity is also investigated.

• Macromolecular Research
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• v.12 no.2
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• pp.156-171
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• 2004

We describe the precision synthesis schemes of siloxane-containing polymers, i.e., the control of their molecular weight, stereoregularity, and higher-order structures. First, we found a new catalytic dehydrocoupling reaction of water with bis(dimethylsilyl)benzene to give poly(phenylene-disiloxane). Together with this reaction, we applied hetero-condensations to the synthesis of thermally stable poly(arylene-siloxane)s. The dehydrocoupling reaction was applied to the synthesis of syndiotactic poly(methylphenylsiloxane) and poly(silsesquioxane)s, which we also prepared by hydrolysis and deaminative condensation reactions. We discuss the tendency for loop formation to occur in the synthesis of poly(silsesquioxane) by hydrolysis, and provide comments on the design of functionality of the polymers produced. By taking advantage of the low energy barrier to rotation in the silicon-oxygen bond, we designed selective oxygen-permeable membrane materials and liquid crystalline materials. The low surface free energy of siloxane-containing systems allows surface modification of a blend film and the design of holographic grating materials.

• Proceedings of the Korean Institute of Interior Design Conference
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• 2004.05a
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• pp.156-160
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• 2004

Our time is called as the era of information-oriented society and up-to-date scientific technology, but it can be also called as the era of image. It is because the image has much influence upon our everyday life. In the deluge of images, the delivery of image Is a better and faster synergic tool than the delivery of language, and this trend is consistent with the phases of the times in which the analog modality of synergy is converted into the digital one. The image is a picture that is formed by a physical process, and is all the figures reflected by electronic equipments that reproduce the image. After the discovery of photograph in 1893, the image has been appeared first with the form of movie, and then with the form of TV. However, the appearance of such unidirectional synergic tools as movies and TV. has provided artists with some creative motives with which they intercommunicate their messages via some experimental bidirectional synergic tools. Among image-media arts, the performance of installation and participation is an important example that causes many changes through conceptional conversion, such as the conception of the time in space and formative characteristics. What satisfy this trend have been videos, lasers, holographic, and etc. Furthermore, the appearance of computer has provided a synesthesia, that is, a virtual reality, and mixed a real image with a visional one. The image-media art will realize better synergy through combining brand new machines, informational technology, and art, and have much influence upon our everyday life formatively and artistically in the future. with this study, through analyzing the meaning of relationship between image equipments and space.