• Journal of the Microelectronics and Packaging Society
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• v.19 no.1
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• pp.81-87
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• 2012

This paper focuses on three-dimensional measurement system of micro balls on micro Ball-Grid-Array(BGA) packages in-line. Most of visual inspection system still suffers from sophisticate reflection characteristics of micro balls. For accurate shape measurement of them, a specially designed visual sensor system is proposed under the sensing principle of phase shifting moire interferometry. The system consists of a pattern projection system with four projection subsystems and an imaging system. In the projection system, four subsystems have spatially different projection directions to make target objects experience the pattern illuminations with different incident directions. For the phase shifting, each grating pattern of subsystem is regularly moved by PZT actuator. To remove specular noise and shadow area of BGA balls efficiently, a compact multiple-pattern projection and imaging system is implemented and tested. Especially, a sensor fusion algorithm to integrate four information sets, acquired from multiple projections, into one is proposed with the basis of Bayesian sensor fusion theory. To see how the proposed system works, a series of experiments is performed and the results are analyzed in detail.

• Korean Journal of Optics and Photonics
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• v.34 no.6
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• pp.261-268
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• 2023

We propose a compact differential interference contrast microscopic module, which enables snapshot measurements for quantitative phase imaging. The proposed module adopts the lateral shearing interferometric principle, which can obtain self-interference without a reference. Due to the absence of the reference, the system is more stable than the typical interferometric systems. It uses a polarization grating to generate two laterally shifted wavefronts based on its birefringence and polarizing beam-splitting characteristics. Furthermore, the use of a polarization camera does not require sequential measurements for the phase extraction. In the experiments, we observe and measure the timely varying changes of various specimens to verify the system performance with the bright field images and phase contrast images. Because the proposed microscopic module also has the merit of being adaptable to typical microscopy instead of using an imaging camera, it can conveniently replace conventional contrast microscopy.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.637-639
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• 2015

The Korean very-long-baseline interferometry (VLBI) network (KVN) and VLBI Exploration of Radio Astrometry (VERA) Array (KaVA) is the first international VLBI array dedicated to high-frequency (23 GHz (K-band) and 43 GHz (Q-band)) observations in East Asia. To evaluate the imagine capability of KaVA, we performed imaging observations of three bright active galactic nuclei (AGNs) known for their complex morphologies: 4C 39.25, 3C 273, and M87 by KaVA at K-/Q-band. Our KaVA images reveal extended outflows with complex substructure such as knots and limb brightening, in agreement with previous observations by other VLBI facilities. Angular resolutions are better than 1.4 and 0.8 milliarcsecond (max) at K-/Q-band, respectively. KaVA achieves a high dynamic range of ~1000, more than three times the value achieved by VERA. We conclude that KaVA is a powerful array with a great potential for the study of AGN outflows, at least comparable to the best existing radio interferometric arrays.

• ETRI Journal
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• v.41 no.1
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• pp.84-92
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• 2019

Recent advances in digital holography in the far-infrared region of the spectrum have demonstrated the potential use of digital holography in homeland security as a tool to observe hostile environments in which smoke, flames, and dust impair vision. However, to make this application practical, it is necessary to simplify the optical setup. Here, we show an off-axis, self-reference scheme that spills the reference beam out from the object beam itself and avoids the need for a complex interferometric arrangement. We demonstrate that this scheme allows the reconstruction of high-quality holograms of objects captured under visible as well as far-infrared light exposure. This could pave the way to the industrialization of holographic systems to enable users to see through fire. Moreover, the quantitative nature of the holographic signal is preserved. Thus, the reported results demonstrate the possibility to use this setup for optical metrology.

• Journal of radiological science and technology
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• v.42 no.1
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• pp.67-75
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• 2019

Grating interferometry based imaging technology is a kind of radiation imaging system, which can acquire not only absorption image but also phase difference and dark field image using the Talbot pattern. However, because of the technological difficulties and high cost of fabricating the gratings that make up the system, much efforts are being made to look for ways to replace them. The is a preliminary study to see how the Talbot pattern transfer through various kinds of scintillators and if the optical grating can be a way to replace the conventional absorption gratings. The geometry of the interferometer, the scintillator model, and the scintillator thickness are the main inputs for our simulation. We have used the concept of modulation for quantitative analysis of the contrast ratio of the Talbot pattern. This research is expected to provide very useful information on the design of optical gratings, which is an alternative way to analyze the Talbot pattern, which we have filed a patent on.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.05a
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• pp.211-214
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• 2001

Electronic Speckle Pattern Interferometry(ESPI) is one of optical technique to measure displacement precisely, uses CCD camera to show result image in real time. General ESPI system measures in-plane or out-of-plane displacement. Shearography is one of electronic speckle pattern interferometric methods which allow full-field observation of surface displacement derivatives and it is robust in vibration. The shearography provides non-contacting technique of evaluating defects nondestructively. In this study, the shearography was used to evaluate defects in Carbon Fiber Reinforced Plastic(CFRP). Various sizes of artificial defects were embedded in various depths of woven CFRP plate. Effects due to the variation of size and depth of defects were evaluated in this study.

• Journal of the Optical Society of Korea
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• v.15 no.3
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• pp.264-271
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• 2011

In this paper we examine and compare the computational speeds of three-dimensional (3D) object recognition by use of digital holography based on central unit processing (CPU) and graphic processing unit (GPU) computing. The holographic fringe pattern of a 3D object is obtained using an in-line interferometry setup. The Fourier matched filters are applied to the complex image reconstructed from the holographic fringe pattern using a GPU chip for real-time 3D object recognition. It is shown that the computational speed of the 3D object recognition using GPU computing is significantly faster than that of the CPU computing. To the best of our knowledge, this is the first report on comparisons of the calculation time of the 3D object recognition based on the digital holography with CPU vs GPU computing.

• Journal of the Optical Society of Korea
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• v.18 no.5
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• pp.495-499
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• 2014

In this paper, a method is proposed for simultaneously measuring the front and back surface profiles of transparent micro-optical components. The proposed method combines a dual-wavelength digital holographic microscope with liquids to record holograms at different wavelengths, and then numerically reconstructs the three-dimensional phase information to image the front and back sides of the sample. A theoretical model is proposed to determine the surface information, and imaging of an achromatic lens is demonstrated experimentally. Unlike conventional interferometry, our proposed method supports nondestructive measurement and direct observation of both front and back profiles of micro-optical elements.

• Transactions of the Korean Society of Automotive Engineers
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• v.1 no.2
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• pp.125-133
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• 1993

Electronic Speckle Pattern Interferometry(ESPI) using a CW laser, a video system and image processor was applied to the rotating displacement of rigid body. ESPI require no special surface preparation or attachments and displacements between any two arbitrary points on the surface can be measured. The characteristic speckle pattern formed when imaging a scattering surface illuminated by laser light retains phase information, which can be used for interferometric measurement of surface displacement. The application of this principle to measuring in-plane displacement resolved in one direction is described, together with the novel use of television equipment to detect and process the information contained in the speckle pattern. This is faster, and more convenient and versatile than customary photographic methods.

• Journal of the Optical Society of Korea
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• v.12 no.4
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• pp.281-287
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• 2008

An acousto-optic tunable filter based 3-D micro surface profile measurement using an equally spaced 5 spectral phase shifting is described. The 5-bucket spectral phase shifting method is compared with a Fourier-transform method in the spectral domain. It can provide a fast measurement capability while maintaining high accuracy since it needs only 5 pieces of spectrally phase shifted imaging data and a simple calculation in comparison with the Fourier transform method that requires full wavelength scanning data and relatively complicated computation. The 3-D profile data of micro objects can be obtained in a few seconds with an accuracy of ${\sim}10nm$. The 3-D profile method also has an inherent benefit in terms of being speckle-free in measuring diffuse micro objects by employing an incoherent light source. Those simplicity and practical applicability is expected to have diverse applications in 3-D micro profilometry such as semiconductors and micro-biology.