• Journal of the Korean Society for Precision Engineering
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• v.18 no.8
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• pp.40-47
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• 2001

Optical measurement methods make it possible to detect object displacements with high resolution and noncontact measurements. Also, they are very robust against EMI noises and have long operation range. An optical triangulation sensor is one of widely used displacement measurement sensors for its sub-micron resolution, fast response, simple structure, and low cost. However. there are several errors caused by inclinations of a surface. speckle effects, power fluctuations of light sources, and noises of detectors. In this paper, in order to minimize error effects, we performed error analysis and proposed a new structure. Then, we setup a new modeling method and verify it through simulations and experiments. Based on the new model. we propose a new sensor structure and establish design criteria. Finally, we design a signal processing system to overcome a resolution-limited problem of light detectors. The resolution of the proposed system is 0.2${\mu}{\textrm}{m}$ in 5mm operating range.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.04a
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• pp.208-212
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• 1993

Third order correlation function is to be advantageous to detect unique features embedded in various random signals that are undtectable with second order correlation or power spectrum. In order paper, we will introduce a real time third order correlator which consists of a laser light source, an acousto-optical modulator with signal controlling circuitry, and a CCD camera connected to computer for image processing. With this correlator, the third order correlation pattern of a signal can be immediately obtained at the camera due to parallelnature of optical computing.

• The KIPS Transactions:PartC
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• v.10C no.3
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• pp.317-324
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• 2003

In this paper, we propose the ATM based Passive Optical Network (PON) using the optical CDMA scheme with optical switches and PN codes in time domain. We also propose the bipolar optical receiving correlator for PN codes. As optical CDMA is performed by driving directly an optical switch on-off switching with PN codes, the number of distinct code sequences can be increased and the flexibility in assigning PN codes can be improved. Finally we theoretically analyze the signal-to-interference -plus-noise ratio and the bit error probability of regenerated signal and compare the performance of proposed scheme compared with ATM based PON using conventional optical CDMA with optical delay lines.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.182-182
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• 2012

Plasma etching is used in various semiconductor processing steps. In plasma etcher, optical- emission spectroscopy (OES) is widely used for in-situ endpoint detection. However, the sensitivity of OES is decreased if polymer is deposited on viewport or the proportion of exposed area on the wafer is too small. Because of these problems, the object is to investigate the suitability of using plasma impedance monitoring (PIM) and self plasma optical emission spectrocopy (SPOES) with statistical approach for in-situ endpoint detection. The endpoint was determined by impedance signal variation from I-V monitor (VI probe) and optical emission signal from SPOES. However, the signal variation at the endpoint is too weak to determine endpoint when $SiO_2$ and SiNx layers are etched by fluorocarbon on inductive coupled plasma (ICP) etcher, if the proportion of $SiO_2$ and SiNx area on Si wafer are small. Therefore, modified principal component analysis (mPCA) is applied to them for increasing sensitivity. For verifying this method, detected endpoint from impedance monitoring is compared with optical emission spectroscopy.

• Journal of the Optical Society of Korea
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• v.2 no.2
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• pp.74-79
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• 1998

The use of a fiber Fabry-Perot interferometer (FFPI) as an optical current transducer is demonstrated. A conventional inductive pickup coil converts the time-varying current I(t) being measured to a voltage waveform V(t) applied across a piezeolectric strip to which the FFPI is bonded. The strip experiences a longitudinal expansion and contraction, resulting in an optical phase shift ${\phi}(t)$ in the fiber proportional to V(t). This phase shift is measured using a frequency-modulated semiconductor light source, photodiodes to monitor the reflected light from the FFPI and the laser power, and a digital signal processor. Calibration routines compute V(t) and I(t) from the measured phase shift at a l KHz rate. Response to 60 Hz ac over the design range 0-1300A rms is characterized Transient response of the FFPI transducer is also measured.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.15 no.4
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• pp.286-294
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• 1990

The objective of this paper lies in presenting in theory an interpretation of how signals are detected from the real-time A/O correlator, and scrutinize by experimental processes, thereby to devise a method by which correlation function can be detected in a favorable way in time. An A/O system for real-time correlation function of two signals has been constructed. This optical correlator when at work in intensity modulation mode by acousto- optic device renders higher output signal to noise ration, as compared with the traditional optical signal detection, has simple system as compared with existing optical correlator in amplitude modulation mode.

• Journal of the Institute of Convergence Signal Processing
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• v.2 no.3
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• pp.86-92
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• 2001

Position controls are very important in semiconductor manufacturing devices, machine tools, precision measuring instruments, etc. to measure the distance of movement of moving objects in minute units and the accuracy of measurement for the moving distance in these devices affect the performance of the whole devices. Therefore, in those precision instruments, a sensing device that can measure the distance of movement with high-precision resolution is required. Thus an optical encoder that has such advantages as easy digital interface, economical price, and a resolution similar to that of laser interferometers can be used. In this paper, a interferometer-type linear scale with easy digital interface and high-resolution has been set up and measured the distance of movement based on the diffraction principle. Interference signals produced in this optical setup of the linear scale have beers digitalized through fabricated photodetectors and designed signal processing circuits. A resolution of 0.5${\mu}{\textrm}{m}$ is acquired from the experimental interferometer-type linear scale without for the movement of scales any additional dividing circuits. It is shown that from this experiment a high-resolution distance measurement device can be designed by a simple optical setup.

• Journal of the Optical Society of Korea
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• v.14 no.4
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• pp.290-297
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• 2010

The paper reviews progress and future prospects of two kinds of planar waveguide devices; they are (a) silica and silicon photonics multi/demultiplexers for communications and signal processing applications, and (b) a novel waveguide spectrometer based on Fourier transform spectroscopy for sensing applications.

• Proceedings of the Optical Society of Korea Conference
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• 2006.07a
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• pp.463-464
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• 2006

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 1991.10a
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• pp.33-37
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• 1991

A now signal precessing system for real time displacement measurement in sinusoidal phase modulating interferometry is described. Although sinusoidal phase modulating interferometry is effective in measuring with high accuracy the displacement of an object, conventional signal processing takes along time. In this method, detection of the object's displacement is easily achieved by sampling the interference signal at those times that satisfy certain conditions and by processing the sampled signals with electric circuits in real time. the delay time of this signal processing system is < 45 $\mu$s. Specially in this paper we describe all electronic circuit and optical system design