• Korean Journal of Optics and Photonics
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• v.8 no.1
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• pp.26-30
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• 1997

A wide dynamic range heterodyne interferometer scheme using intermode beat between a stabilized, dual frequency He-Ne laser beam has been applied for a measurement of optical thickness of an optical medium. Resolution of the optical thickness measurement is about $\pm$ 1.74 ${\mu}{\textrm}{m}$. Using this technique, we are able to determine the optical thickness of an organic dye film. We also obtain a map of the optical thickness variations over a surface of the film

• Proceedings of the IEEK Conference
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• 2000.07b
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• pp.919-922
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• 2000

A robust optical security technique using ortho-gonally polarized lights in the interferometer is proposed. We use orthogonally polarized lights in order to minimize the noise generated by the refractive index change due to vibration, flow of air, change of temperature etc. To make orthogonally polarized lights the first beam splitter in the Mach-Zehnder interferometer is substituted by a polarizing beam splitter(PBS). Because of incoherence of orthogonally polarized lights, the noise generated by the change of refractive index is minimized. To encrypt an image we use the random partition and the diffusing of pixel. Finally we make Phase-only-filters of each image which is randomly partitioned and diffused pixel by pixel. Simulation results show the proposed system has the ability of encryption and decryption of an image.

• Proceedings of the Optical Society of Korea Conference
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• 2008.07a
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• pp.187-189
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• 2008

The spatial coherence function of multy-mode beam was measured by using a Sagnac interferometer and self referencing technique. For leaner polarization laser beam passing through a multy-mode fiber, its change value of spatial mode and polarization from stress of faber and input coupling angle. And each spatial mode have each polarizations, when we simulation Wigner distribution function and Spatial Correlation function of spatial multi-mode beam by using Hermit Gaussian modes leaner sum. We measured spatial coherence function of using by multy-mode fiber. One can use this measurement method to study and characterize the property of multy-mode light field coming out of GRIN multy-mode fiber.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.3
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• pp.31-38
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• 2004

The wavelength variation of a scanned fiber laser is analyzed using quadrature sampling technique. By time delayed sampling of a phase modulated Mach-Zender interferometer, the wavelength information can be precisely determined regardless of the nonlinearity in the Fabry-Perot wavelength filter which scanned the fiber laser. A wavelength readout resolution of ～20 pm was obtained at 2 KHz M-Z modulation frequency, and it was shown that the resolution could be improved in case of using an electro-optic phase modulator.

• Journal of the Optical Society of Korea
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• v.11 no.2
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• pp.71-75
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• 2007

The spatial coherence function of a laser beam was measured by using a Sagnac interferometer and self referencing technique. For a laser beam passing through a narrow slit, the absolute value of the measured spatial coherence function becomes more symmetric as the slit size is reduced. For diverging beams, the spatial coherence function shows fast oscillations in its real and imaginary parts. We explain this by using a Gaussian Schell-model. One can use this measurement method to study and characterize the property of the light field coming out of a small sample.

• Current Optics and Photonics
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• v.7 no.2
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• pp.191-199
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• 2023

We propose a dual Fabry-Perot interferometer (DFPI) structure that combines two Fabry-Perot interferometers. The structure is designed to have spectral peaks in the red, green, and blue regions simultaneously, to be applicable to R, G, and B subpixels without any patterning process. The optimized structure has been fabricated on a glass substrate using a thermal evaporation technique. When the DFPI structure was attached to the quantum-dot color-conversion layer, the full width at half maximum values of the green and red spectra decreased by 47.29% and 51.07% respectively. According to CIE 1931 color space, the DFPI showed a 37.66% wider color gamut than the standard RGB color coordinate. Thus it was experimentally proven that the proposed DFPI structure improved color purity. This DFPI structure will be useful in realizing a display with high color purity.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.203-206
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• 2002

One of the ever-increasing demands on the performances of heterodyne interferometers is to improve the measurement resolution, of which current state-of-the-art reaches the region of sub-nanometers. We propose a new scheme of phase-measuring electronics that reduces the measurement resolution without further increase in clock speed. Our scheme adopts a super-heterodyne technique that lowers the original beat frequency to a level of 1 MHz by mixing it with electrically generated reference signal. The technique enables us to measure the phase of Doppler shift with a resolution of 1.58 nanometer at a sampling rate of 1 MHz. To avoid the undesirable decrease in the maximum measurable speed caused by the lowered beat frequency, a special from of frequency up-down counting technique is combined with the super-heterodyning. This alloys performing required phase unwrapping simply by using programmable digital gates without 2$\pi$ ambiguities up to the maximum velocity of 2.35 m/s.

• Journal of Sensor Science and Technology
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• v.9 no.6
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• pp.416-423
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• 2000

A new demodulation technique which can be used for the fiber optic acoustic sensor system using Sagnac interferometer is described. The theoretical limitation in dynamic range of the quadrature demodulation technique can be removed by the proposed BPSK(Binary Phase Shift Keying) demodulation technique. Full demodulation of input acoustic signal is possible with just simple electronics by eliminating the necessity of the high frequency phase modulation. This technique is suitable for digital signal processing of fiber optic sensor systems and can be applicable for other interferometers.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.10a
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• pp.268-271
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• 2004

Non-contact technique should be developed for receiving ultrasonic wave for on-line monitoring of processing defects of fiber reinforced composites, since couplant must be applied on composite materials when conventional ultrasonic testing technique was used. Restriction of conventional ultrasonic testing technique was proven by transmitting and receiving ultrasonic wave on CFRP in various direction of wave propagation with various incident angle of ultrasonic beam. Air-coupled transducer and laser interferometer were applied for non-contacting reception of ultrasonic wave in fiber reinforced composite materials. Air-coupled transducer has optimal sensitivity and frequency band of 300kHz has homogeneous characteristics on direction of wave propagation.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.27-28
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• 2006

This study performs to investigate deformation of wall thinning pipe and to find out the position of the internal thinning defect by shearography. Shearography is one of optical methods those have applied to nondestructive testing (NDT) and the strain/stress analysis. This technique has the merit of the directly measuring the first derivative of displacement, sensitivity of which can be adjusted by the handling of optical component in interferometer. In this paper, we tested carbon steel pipe locally wall thinned and loaded internal pressure and developed the nondestructive out-of-plane deformation analysis technique fur internal thinning defect of elbow by shearography. From the results, it was confirmed that this technique is proper to the practical application on the pipe line system with internal defect.