• Title/Summary/Keyword: optical interferometer

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Self-calibration Algorithm of Systematic Errors For Interferometer (간섭계에 있어서의 계통 오차의 자율 교정 알고리즘)

  • Ikumatsu Fujimoto;Lee Taeyong
    • Journal of the Korean Society for Precision Engineering
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    • v.22 no.5 s.170
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    • pp.63-71
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    • 2005

  • When an almost flat surface under test is measured by an interferometer, the measurement result is largely influenced by systematic errors that include geometrical errors of a reference flat surface. To determine the systematic errors of the interferometer by the conventional method that is called the three flat method, we must take the reference flat surface out from the interferometer and measure it. Because of difficulties to set the reference flat surface to the interferometer exactly and quickly, this method is not practical. On the other hand, the method that measures a surface under test with some shifts in the direction being perpendicular to the optical axis of the interferometer is studied. However, the parasitic pitching, rolling and up-down movement caused by the above shifts brings serious error to the measurement result, and the algorithm by which the influences can be eliminated is not still established. In this paper, we propose the self-calibration algorithm for determining the systematic errors that include geometrical errors of a reference flat surface by several rotation shifts and a linear shift of general surface under test, and verify by a numerical experiment that this algorithm is useful for determining the systematic errors.

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Accurate Roughness Measurement Using a Method for Evaluation and Interpolation of the Validity of Height Data from a Scanning White-light Interferometer

  • Kim, Namyoon;Lee, Seung Woo;I, Yongjun;Pahk, Heui-Jae
    • Current Optics and Photonics
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    • v.1 no.6
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    • pp.604-612
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    • 2017

  • An effective and precise method using a scanning white-light interferometer (SWLI) for three-dimensional surface measurements, in particular for roughness measurements, has been proposed. The measurement of a microscopically sloped area using an interferometer has limitations, due to the numerical aperture of the lens. In particular, for roughness measurements, it is challenging to obtain accurate height data for a sloped area using the interferometer, due to diffraction of the light. Owing to these optical limitations of the interferometer for roughness measurements, the Ra measurements performed using an interferometer contain errors. To overcome the limitations, we propose a method consisting of the following two steps. First, we evaluate the height data and set the invalid height area to be blank, using the characteristics of the modulus peak, which has a low peak value for signals that have low reliability in the interferogram. Next, we interpolate the blank area using the adjacent reliable area. Rubert roughness standards are used to verify the proposed method. The results obtained by the proposed method are compared to those obtained with a stylus profilometer. For the considered sinusoidal samples, Ra ranges from $0.053{\mu}m$ to $6.303{\mu}m$, and we show that the interpolation method is effective. In addition, the method can be applied to a random surface where Ra ranges from $0.011{\mu}m$ to $0.164{\mu}m$. We show that the roughness results obtained using the proposed method agree well with profilometer results. The $R^2$ values for both sinusoidal and random samples are greater than 0.995.

  • https://doi.org/10.3807/COPP.2017.1.6.604 인용 PDF KSCI

Low Coherence Interferometer for Measurement of Path Length Errors in Arrayed-Waveguide Grating (Arrayed-Waveguide Grating의 경로 오차 측정을 위한 저 간섭 광원 간섭계)

  • Song, Young-Ki;Heo, Nam-Chun;Chung, Young-Chul
    • Korean Journal of Optics and Photonics
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    • v.15 no.6
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    • pp.539-546
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    • 2004

  • An improved low coherence interferometer system and a new analysis method for the accurate measurement of the optical path difference error of an AWG (Arrayed-Waveguide Grating) are described. The use of software simplifies the experimental setup by eliminating the hardware (clock generator). In addition, the actual distances between the peak positions of the adjacent interference signals are calculated using interpolation methods. The wavelength transmission characteristics of the AWG are calculated assuming the measured phase errors. The calculated AWG characteristic is quite similar to the actual measurement result, confirming accuracy of the proposed measurement setup.

  • https://doi.org/10.3807/KJOP.2004.15.6.539 인용 PDF KSCI