• Journal of the Optical Society of Korea
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• v.12 no.4
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• pp.249-254
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• 2008

In this paper we present an electronic domain solution for chromatic dispersion (CD) monitoring algorithm based on the estimated time domain channel in electronic domain using channel estimation methods. The proposed scheme utilizes kurtosis as a CD measurement, directly computed from the estimated inter-symbol-interference (ISI) channel due to the CD distortion. Hence, the proposed scheme exhibits robust performance under OSNR variation, in contrast to the existing electronic domain approach based on minimum mean squared error (MMSE) fractionally-spaced equalizer taps [1]. The simulation results verify the CD monitoring ability of the proposed scheme.

• Journal of the Optical Society of Korea
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• v.17 no.1
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• pp.81-85
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• 2013

A miniaturized fluorescence detection system based on total internal reflection (TIR) configuration, which is applicable to detecting the presence of biological materials labeled with fluorescence dye in micro total analysis systems (${\mu}TAS$), is proposed. In conventional fluorescence testing and analysis devices, interference between the excitation light beam and the emitted light from dyes is unavoidable. This paper presents a fluorescence detection system based on TIR configuration that allows the excitation light beam and the emitted light to be spatially perpendicular to each other so as to minimize the interference where fluorescence emission is detected at the orthogonal angle to the excitation beam. We achieved the limit of detection of about 5 nmol/L with a high linearity of 0.994 over a wide range of 6-FAM mol concentration, being comparable to that in earlier studies.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.10
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• pp.151-156
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• 1997

A laser measurement system, a modified Michelson interferometer, which can accurately measure high speed length and displacement of servomechanisms by detecting a phase shift in the measurement beam using an optical interference was developed. A frequency stabilized laser source and a 20 fold frequency interpolation and digitizing circuit were applied to the system. The refra- ctive index of the ambient air was calibrated through the Edlens formula. The system achieved a resolution of /40, 16nm, a maximum allow-able measurement speed of 600nm/sec, and a length measure- ment range of 1500 mm. Performance of the system was evaluated on the machining center in short and long length measurements.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2005.11a
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• pp.179-182
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• 2005

In this paper, optical noise is reduced using a differential detector in an 1.3$\mu$m optical wireless system which is more safe for human eye than 0.8$\mu$m optical wireless systems. The differential detector is composed of a InGaAs photodiode and a Si photodiode. This is a very simple and cost effective method to reduce the noise interference from incandescent lamps.

• Journal of the Optical Society of Korea
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• v.16 no.3
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• pp.203-209
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• 2012

Visible light communications (VLC) use modern solid-state light-emitting diodes (LEDs) to broadcast information. Emerging white-light LEDs allow the combination of lighting and optical wireless communication in one optical source. In this paper, a new LED lighting design using one-chip-type white LEDs is proposed for efficient illumination and optical wireless communications under the existence of several obstacles. Lighting and communication performance are analyzed to show the effectiveness of the proposed LED lighting. Specifically, the signal-to-noise ratio considering intersymbol interference and the bit-error rate of variable pulse position modulation (VPPM) with dimming control are considered.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.1
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• pp.129-135
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• 2003

Optical fiber has many advantages, such as high reliability, long lifetime, immunity to the electromagnetic interference, high speed response and low cost. In this study, we proposed and developed an optical fiber impact and pressure sensor for prevention of accident which occurs in the automatic system or auto door. The principle of the sensor is to detect different optical intensity caused by variation of a speckle pattern due to the external perturbation. Speckle pattern appears at the end of a multimode fiber in which coherent beam propagates. The fabricated sensor in this study was tested. As a result of experiments, amplitude of the output signal isn't linear, but it has sufficient sensitivity for a sensor. Moreover, we can control sensitivity of the sensor by an amplifier at receiver. It has several advantages which are ability of detection at all point on the multimode fiber, large sensitive area, and many application areas for a sensing impact and pressure.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.556-560
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• 2005

The measurement method by Laser Speckle Interferometry which uses the interference law which will grow precedes and with it explains a resolution measurement ability and together the change of place arrowhead and general measurement, at real-time measurement sensitivity it has application boat song from candle precise measurement field it is increasing. But, currently the domestic application technique to sleeps and optical science military merit by optical science interferometer and directness it composes purchases to the level which it applies the expensive commercial business equipment the outside and in spite of the technical ripple effect is deficient even in many strong point. The hazard which complements like this problem point form technical development it leads from the research which it sees and an application degree and to sleep as the measurement equipment which tries to develop the small-sized optical science interference sensor and an interpretation program it raises it does.

• Journal of the Optical Society of Korea
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• v.10 no.1
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• pp.16-22
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• 2006

Wavefront sensing using a Shack-Hartmann sensor has been widely used for estimating wavefront errors or distortions. The sensor combines the local slopes, which are estimated from the centroids of each lenslet image, to give the overall wavefront reconstruction. It was previously shown that the pupil-plane irradiance profile effects the centroid estimation. Furthermore, a previous study reported that the reconstructed wavefront from a planar wavefront with a Gaussian pupil irradiance profile contains large focus and spherical aberration terms when there is a focus error. However, it has not been reported yet how seriously the pupil irradiance profiles, which can occur in practical applications, effect the sensing errors. This paper considered two cases when the irradiance profiles are not uniform: 1) when the light source is Gaussian and 2) when there is a partial interference due to a double reflection by a beam splitting element. The images formed by a Shack-Hartmann sensor were simulated through fast Fourier transform and were then supposed to be detected by a noiseless CCD camera. The simulations found that sensing errors, due to the Gaussian irradiance profile and the partial interference, were found to be smaller than RMS ${\lambda}/50$ when ${\lambda}$ is $0.6328\;{\mu}m$, which can be ignored in most practical cases where the reference and test beams have the same irradiance profiles.

• Journal of the Optical Society of Korea
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• v.6 no.4
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• pp.156-160
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• 2002

In this paper, we propose an improved optical security system using three phase-encoded images and the principle of interference. This optical system based on a Mach-Zehnder interferometer consists of one phase-encoded virtual image to be encrypted and two phase-encoded images, en-crypting image and decrypting image, where every pixel in the three images has a phase value of '0'and'$\pi$'. The proposed encryption is performed by the multiplication of an encrypting image and a phase-encoded virtual image which dose not contain any information from the decrypted im-age. Therefore, even if the unauthorized users steal and analyze the encrypted image, they cannot reconstruct the required image. This virtual image protects the original image from counterfeiting and unauthorized access. The decryption of the original image is simply performed by interfering between a reference wave and a direct pixel-to-pixel mapping image of the en crypted image with a decrypting image. Computer simulations confirmed the effectiveness of the proposed optical technique for optical security applications.

• ETRI Journal
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• v.25 no.2
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• pp.81-88
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• 2003

We designed a multimode interference (MMI) coupler to use in vertical coupling of double layered polymeric waveguides and analyzed the coupling characteristics by comparing our experimental and simulation results. We found that our proposed new structure, a stepped MMI coupler, is effective in vertical coupling between waveguide layers with a short length of MMI and has a high tolerance for the variation in the structure of an MMI coupler that can be induced as errors in the fabrication process.