• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.10a
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• pp.665-666
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• 2009

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.12
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• pp.691-697
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• 2000

A fiberoptic sensor using a low-coherence SLD as a light source has been studied. The sensor system employing an intrinsic fiber Fabry-Peort interferometer as a sensing tip and a fiber Mach-Zehnder interferometer as a processing one, overcomes the ambiguous reading caused by the highly periodic natrue of conventional high-precision interferometric sensors and provides unambiguous identification of the desired phase among several candidates on the transfer function of an interferometric signal. A tentative application to the temperature sensor shows the potential that the fiberoptic sensor has a side-dynamic range of $0-900^{\circ}C$ as well as reasonable resolution higher than $0.1^{\circ}C$ without ambiguity. Due to the inherent property of the optical fiber itself and the intrinsic fiber Fabry-Perot interferometer, the proposed fiberoptic sensor will give obvious benefits when it is applied to harsh environments to monitor some physical parameters such as temperature, strain, pressure and vibration.

• Proceedings of the Optical Society of Korea Conference
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• 2009.02a
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• pp.389-390
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• 2009

• Korean Journal of Remote Sensing
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• v.40 no.2
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• pp.141-150
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• 2024

Ground subsidence in urban areas is mainly caused by anthropogenic factors such as excessive groundwater extraction and underground infrastructure development in the subsurface composed of soft materials. Global Navigation Satellite System data with high temporal resolution have been widely used to measure surface displacements accurately. However, these point-based terrestrial measurements with the low spatial resolution are somewhat limited in observing two-dimensional continuous surface displacements over large areas. The synthetic aperture radar interferometry (InSAR) technique can construct relatively high spatial resolution surface displacement information with accuracy ranging from millimeters to centimeters. Although constellation operations of SAR satellites have improved the revisit cycle, the temporal resolution of space-based observations is still low compared to in-situ observations. In this study, we evaluate the extraction of a time-series of surface displacement in Incheon Metropolitan City, South Korea, using the small baseline subset technique implemented using the commercial software, Gamma. For this purpose, 24 COSMO-SkyMed X-band SAR observations were collected from July 12, 2011, to August 27, 2012. The time-series surface displacement results were improved by reducing random phase noise, correcting residual phase due to satellite orbit errors, and mitigating nonlinear atmospheric phase artifacts. The perpendicular baseline of the collected COSMO-SkyMed SAR images was set to approximately 2-300 m. The surface displacement related to the ground subsidence was detected approximately 1 cm annually around a few Incheon Subway Line 2 route stations. The sufficient coherence indicates that the satellite orbit has been precisely managed for the interferometric processing.

• Korean Journal of Optics and Photonics
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• v.20 no.1
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• pp.29-33
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• 2009

We propose a new measuring technique based on optical low-coherence reflectometry that enables us to determine the refractive index and the geometrical thickness of a transparent sample by one-time scanning only. By passing a collimated beam having a finite size through the edge of the sample, the refractive index and the geometrical thickness can be determined simultaneously from the comparison of interferograms generated by two kinds of reflected beams. In this study, a refractive index could be determined with the accuracy of $10^{-3}$, and its accuracy would be enhanced by using a more precise translator and a thicker sample.

• Korean Journal of Remote Sensing
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• v.23 no.6
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• pp.559-566
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• 2007

The generation of precise digital elevation model (DEM) is very important in coastal area where time series are especially required. Although a LIDAR system is useful in coastal regions, it is not yet popular in Korea mainly because of its high surveying cost and national security reasons. Recently, precise DEM has been made using radar interferometry and waterline methods. One of these methods, spaceborne imaging radar interferometry has been widely used to measure the topography and deformation of the Earth. We acquired ALOS PALSAR FBD mode (Fine Beam Dual) data for evaluating the quality of interferograms and their coherency. We attempted to construct DEM using ALOS PALSAR pairs - One pair is 2007/05/22 and 2007/08/22, another pair is 2007/08/22 and 2007/10/22 with respective perpendicular baseline of 820 m, 312m and respective height sensitivity of 75 m and 185m at southern of Ganghwa tidal flat, Siwha- and Hwaong-lake over west coastal of Korea peninsula. Ganghwa tidal flat has low coherence between 0.3 and 0.5 of 2007/05/22 and 2007/08/22 pair. However, Siwha-lake and Hwaong-lake areas have a higher coherence value (From 0.7 and 0.9) than Ganghwa tidal area. The reason of difference coherence value is tidal condition between tidal flat area (Ganghwa) and reclaimed zone (Siwha-lake and Hwaong-lake). Therefore, DEM was constructed by ALOS PALSAR pair over Siwha-lake and Hwaong-lake. If the temporal baseline is enough short to maintain the coherent phases and height sensitivity is enough small, we will be able to successfully construct a precise DEM over coastal area. From now on, more ALOS PALSAR data will be needed to construct precise DEM of West Coast of Korea peninsular.

• Restorative Dentistry and Endodontics
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• v.36 no.5
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• pp.367-376
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• 2011

Early detection of carious lesions increases the possibility of treatment without the need for surgical intervention. Optical coherence tomography (OCT) is an emerging three-dimensional imaging technique that has been successfully used in other medical fields, such as ophthalmology for optical biopsy, and is a prospective candidate for early caries detection. The technique is based on low coherence interferometry and is advantageous in that it is non-invasive, does not use ionizing radiation, and can render threedimensional images. A brief history of the development of this technique and its principles are discussed in this paper. There have been numerous studies on caries detection, which were mostly in vitro or ex vivo experiments. Through these studies, the feasibility of OCT for caries detection was confirmed. However, further research should be performed, including in vivo studies of OCT applications, in order to prove the clinical usefulness of this technique. In addition, some technological problems must be resolved in the near future to allow for the use of OCT in everyday practice.

• Journal of the Optical Society of Korea
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• v.20 no.6
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• pp.784-793
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• 2016

We present a single shot low coherence white light Hilbert phase microscopy (WL-HPM) for quantitative phase imaging of Si optoelectronic devices, i.e., Si integrated circuits (Si-ICs) and Si solar cells. White light interferograms were recorded by a color CCD camera and the interferogram is decomposed into the three colors red, green and blue. Spatial carrier frequency of the WL interferogram was increased sufficiently by means of introducing a tilt in the interferometer. Hilbert transform fringe analysis was used to reconstruct the phase map for red, green and blue colors from the single interferogram. 3D step height map of Si-ICs and Si solar cells was reconstructed at multiple wavelengths from a single interferogram. Experimental results were compared with Atomic Force Microscopy and they were found to be close to each other. The present technique is non-contact, full-field and fast for the determination of surface roughness variation and morphological features of the objects at multiple wavelengths.