• Journal of Sensor Science and Technology
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• v.14 no.5
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• pp.302-307
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• 2005

Precision displacement of less than a few nm resolution was measured in real-time using fiber optic EFPI sensor. The novel method for real-time processing of analyzing EFPI output signal was developed and verified. Linearity in the mean values of interferometric light intensity among adjacent fringes was shown and verified the sinusoidal approximation algorithm that estimates past and coming fringe values. Real-time signal processing program was developed and the intensity signal of the EFPI sensor was transformed to the phase shift with this program. The resolution below $0.36{\sim}8.6$ nm in the displacement range of $0{\sim}300{\mu}m$ was obtained. The nano-positioner with a piezoelectric actuator and the EFPI sensor system was designed and tested. The positioner successfully reached to the desired destination within 1 nm accuracy.

• Korean Journal of Optics and Photonics
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• v.1 no.2
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• pp.204-209
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• 1990

The temperature variation at a laser rod center induced by high repetetion rate pumping was measured by counting the number of inteference frigne shift and found to be consistent with the theoretical value obtained from heat diffusion equation. The spatial homogeneity and energy transfer rate of flashlamp pumping by the single elliptical reflector plated with gold were evaluated by measuring interference fringes oever the cross section of a Nd:YAG laser rod.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.208-211
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• 2005

The volumetric interferometer, which uses the interference of wavefronts emitted from two single mode fibers, measures the target position in 3-D. In this paper, we suggest a new calculation method which doesn't need a non-linear optimization and an initial guess. We find the relationship between the coefficients of the Zernike polynomials for a spherical wavefront and its center and reconstruct a spherical wavefront by using the Zernike polynomials from two interference fringes like a lateral shearing interferometer. The target position can be obtained from the coefficients of the Zernike polynomials of the reconstructed wavefront. We can get the target position in 3-D with $sub-{\mu}m$ errors in a simulation.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.6
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• pp.550-555
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• 2007

Stress intensity factor is one of the most important parameters in fracture mechanics. Both the stress field distribution and the crack propagation are closely related to these parameters. Due to the complexity of actual engineering problems, it is difficult to calculate the stress intensity factor by theoretical formulation, so photoelasticity method is a good choice. In this paper, modified two parameter method is employed to calculate stress intensity factor for opening mode by using data from more than one photoelastic fringe loop. For getting accurate experiment results, the initial fringes are doubled and sharpened by digital image programs from the fringe patterns obtained by a CCD camera. Photoelastic results are compared with those obtained by the use of empirical equation and FEM. Good agreement shows that the methods utilized in experiments are considerably reliable. The photoelastic experiment can be used for bench mark in theoretical study and other experiments.

• Proceedings of the Optical Society of Korea Conference
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• 1989.02a
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• pp.113-118
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• 1989

By using the single mode optical fiber, we fabricated Fiber-optic Fabry-Perot interferometer (FFPI). The change over a wide range in the optical path length of a FFPI is observed. The temporal movement of the interference fringes by external condition to P.Z. T) is converted to circular motion on an oscilloscope display and then recorded with a micro-computer. The two output voltages of the D/A converters are applied to X and Y terminals of oscilloscope to display circular motion on oscilloscope. Thus the direction of phase shift can be determined with observing the direction of circular motion. The variation of the optical length can be measured by calculating the angle of spot of circle with an accuracy of λ/90 wave length due to variation of temperature in this system 2.7x10-4$^{\circ}C$.

• Current Applied Physics
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• v.18 no.11
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• pp.1441-1446
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• 2018

We demonstrate an acousto-optic mode converter based on a tapered optical fiber to efficiently generate orbital angular momentum states of light. In our scheme an acoustic wave is deployed to the waist of tapered optical fiber where two degenerate $HE_{21}$ modes leading to +1 and -1 orbital angular momentum eigen-modes are resonantly excited. The excitation of $TM_{01}$ and $TE_{01}$ modes is suppressed by enlarging the intermodal index difference between near-degenerate spatial modes. Numerical calculation for optimization of the taper diameter is provided. The experimental characterization of generated states is performed by analyzing the output far-field pattern and the spatial interference fringes with a uniform reference beam.

• Corrosion Science and Technology
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• v.4 no.6
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• pp.217-221
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• 2005

In the present investigation, holographic interferometry was utilized for the first time to monitor in situ the thickness of the oxide film of aluminium samples during anodization processes in boric acid solutions. The anodization process (oxidation) of the aluminium samples was carried out by the technique of the electrochemical impedance spectroscopy(EIS), in different concentrations of boric acid (0.5-5.0% $H_3BO_3$) at room temperature. In the mean time, the real-time holographic interferometry was used to measure the thickness of anodized (oxide) film of the aluminium samples in solutions. Consequently, holographic interferometry is found very useful for surface finish industries especially for monitoring the early stage of anodization processes of metals, in which the thickness of the anodized film of the aluminium samples can be determined without any physical contact. In addition, measurements of electrochemical values such as the alternating current (A.C) impedance(Z), the double layer capacitance($C_{dl}$), and the polarization resistance(Rp) of anodized films of aluminium samples in boric acid solutions were made by the electrochemical impedance spectroscopy(EIS). Attempts to measure electrochemical values of Z, Cdl, and Rp were not possible by holographic interferometry in boric acid especially in low concentrations of the acid. This is because of the high rate of evolutions of interferometric fringes during the anodization process of the aluminium samples in boric acid, which made measurements of Z, Cdl, and Rp are difficult.

• Journal of the Korean Society for Nondestructive Testing
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• v.6 no.2
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• pp.37-45
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• 1987

Speckle photography is a very useful method for measuring in-plane surface displacement. In its basic form, the object to be studied is illuminated with a divergent laser beam, and a double exposure photograph of the object is recorded, on a fine-grain film or plate, before and after the object is deformed, The magnitude and the direction of the displacement can then be obtained by measuring the spacing and the direction of the Young's fringe, which is produced by probing the developed negative with an unexpaned laser beam, and consists of a pattern of parallel equi-spaced dark bands. In this paper, a hybrid optical and electronic image processing is described-Young's fringe on the viewing screen is observed by a TV-camera and the 2-D video signal is converted from analog to digital and transfered to the computer where the spacing and direction of the fringes are calculated. Several examples of application show that the displacement magnitude and direction can be determined with an accuracy of $0.1{\mu}m\;and\;0.1^{\circ}$ respectively.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.11
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• pp.1-9
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• 1998

In this paper, an incoherent imaging of a high-contrast cylindrical cavity in a lossy medium illuminated by the time-harmonic cylindrical wave is obtained via the backprojections of the intensity patterns of the forward total electric field in the cross-borehole measurement configuration. The phenomenon that the interference fringes in the intensity pattern, which are caused by the superposition of the incident field and the scattered field with different optical paths, are removed in the backprojection process is interpreted numerically. This imaging method is validated by imaging an air circular cylinder in a lossy medium of $\varepsilon$$_{r}$=9 and $\sigma$ = 0.0005, 0.002 S/m, and the conditions for obtaining better images are investigated.d.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.8
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• pp.739-746
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• 2005

When we design a binary phase holographic optical low-pass filter (HOLF), the phase difference is generally set to be $\pi$ to optimize the diffraction efficiency. However, the phase difference of real HOLF mostly deviate from $\pi$ by the error in the fabrication process. The deviation causes the (0,0)-th order diffracted beam to increase, which results In raising the diffraction efficiency. To study the effects of the phase error on the performance of HOLF, we calculated the MTF of HOLF for various phase differences. The results show that the phase error of 10 $\%$ makes little change in the filtering characteristics of HOLF. Considering the filtering by lens and CCD, the effects of the phase error becomes much smaller. To confirm it experimentally, we fabricated HOLFs for various phase differences. After installing it in a digital camera, we take picture of test targets and observe the Moire fringes and the resolution. The results agree with our prediction.