• 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

• Journal of the Korean Society for Precision Engineering
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• v.19 no.4
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• pp.195-201
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• 2002

We propose a new scheme of high-resolution heterodyne interferometer that employs the two-axial mode He-Ne laser with an inter-mode beat frequency of 600~1000 MHz. An electronic RF-heterodyne circuit lowers the beat frequency down to 5 MHz, so that the phase change of the interferometer output is precisely measured with a displacement resolution of 0.1 nanometer without significant loss of dynamic bandwidth. A thermal control scheme is adopted to stabilize the cavity length with ainus to suppress frequency drifts caused by the phenomena of frequency pulling and polarization anisotropy of the two-axial made laser to a stability level of 2 parts in $10^9$. The two-axial mode HeNe laser yields a high output power of 2.0 mW, which allows us to perform multiple measurements of up to 10 machine axes simultaneously.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.5 no.2
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• pp.22-26
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• 2006

This paper addresses the development of a laser interferometer to measure micro displacement for a micro system. The laser interferometer is able to measure micro displacement during a few micro seconds with non-contact. In order to employ the interferometer, the displacement calibration experiment should be required. For the experiment, a laser probe installed on the optical table with optical devices and a micro stage. The velocity decoding board is also added to calculate doppler shift frequency directly. The output signal is processed by LabView. Finally experiments are found out the relation between displacement and output signal.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1195-1198
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• 2003

Micro former has been known as a useful tool for machining micro parts. It makes micro holes automatically with punches, a hole-shape die and material by rotation of crank shaft synchronously. Micro displacement in micro forming affects on the performance of machining because micro forming size is similar with its mechanical displacement. Therefore, the measurement of this micro displacement is essential to be guaranteed to obtain high forming precision in the whole machine as well as its devices. This paper addresses the development of a laser interferometer to measure micro displacement for a micro former. The laser interferometer is able to measure micro displacement during a few micro seconds with non-contact. For the experiment, a laser probe is installed on the optical table with optical devices and a micro displacement generating device. The velocity decoding board is also added to calculate doppler shift frequency directly. Finally simple experiments are conducted to confirm its functional operation.

• Proceedings of the IEEK Conference
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• 2009.05a
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• pp.310-312
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• 2009

The heterodyne laser interferometer has been widely used in precise measurement field. However, the accuracy is limited by the nonlinearity error caused from incomplete laser sources and nonideal optical components. In this paper, we propose the Dual-EKF which estimates states and weights simultaneously to improve the resolution of heterodyne laser interferometer. As a proof, we demonstrate the effectiveness of our proposed method through experimental results.

• Proceedings of the KIEE Conference
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• 2007.10a
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• pp.283-284
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• 2007

In this paper we introduce a compensation of nonlinearity Heterodyne laser interferometer. The Laser Interferometer is used for length measurement in various industries. However, it has nonlinearity error caused by the imperfect optical equipment. This acts as an obstacle in the measurement improvement. We propose an adaptive error compensation using least mean square(LMS) to improve precision.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.195-198
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• 2002

Demand for high precision measurement of large area is increasing in many industrial fields. White-light Scanning Interferometer(WSI) is a well-known method for 3D profile measurement. However WSI has some limitations in a measurement range because of the sensing mechanism. Therefore, in this paper we use a heterodyne laser interferometer to get over the limitations of a short measurement range in WSI, We suggest a new WSI system combined with heterodyne laser interferometer. This system is aimed at eliminating Abbe error with measuring the focus point directly. With the use of triggering functionality of WSI, we can use this system as a probe of a precision stage such as a probe of CMM. The suggested system gives a repeatability of 87 nm in the absolute distance measurement test under the laboratory environment.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.6
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• pp.1042-1047
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• 2008

As an ultra-precision measurement system the heterodyne laser interferometer plays an important role in semiconductor industry. However the errors of environment and nonlinearity which are caused by air refraction and frequency-mixing separately reduce the accuracy of displacement measurement. In this paper we propose a DFNN(data fusion and neural network) method for error compensation. As a hybrid method of data fusion and neural network, DFNN method reduces the environmental and nonlinear error simultaneously. The effectiveness of the proposed error compensation method is proved through experimental results.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1751-1752
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• 2008

The heterodyne laser interferometer has a nano-meter scale resolution. However, the unwanted nonlinearity error caused from frequency-mixing limits the ultra-precise resolution. In this paper, we propose a recursive WLS algorithm to improve the resolution of heterodyne laser interferometer. Some experimental results show an effectiveness of the recursive WLS algorithm in nano-meter scale resolution.

• Proceedings of the KIEE Conference
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• 2007.10a
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• pp.225-226
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• 2007

In the semiconductor manufacturing industry, the heterodyne laser interferometer plays as an ultra-precise measurement system. However, the heterodyne laser interferometer has some unwanted environmental error which is caused from refraction in the air. This is an obstacle to improve the measurement accuracy in nanometer scale. In this paper we propose a compensation algorithm based on Data Fusion method which reduces the environmental error in the heterodyne laser interferometer. Through some experiments, we demonstrate the effectiveness of the proposed algorithm in measurement accuracy.