Browsing by Author "Chang, Wei-Yao"

Now showing 1 - 14 of 14

Alternative method for measuring the full-field refractive index of a gradient-index lens with normal incidence heterodyne interferometry
(2010-12-20)
Chen, Yen-Liang
;
Hsieh, Hung-Chih
;
Wu, Wang-Tsung
;
Chang, Wei-Yao
;
Su, Der-Chin
A linearly/circularly polarized heterodyne light beam coming from a heterodyne light source with an electro-optic modulator in turn enters a modified Twyman-Green interferometer to measure the surface plane of a GRIN lens. Two groups of periodic sinusoidal segments recorded by a fast complementary metal-oxide semiconductor camera are modified, and their associated phases are derived with the unique technique. The data are substituted into the special equations derived from the Fresnel equations, and the refractive index can be obtained. When the processes are applied to other pixels, the full-field refractive-index distribution can be obtained similarly. Its validity is demonstrated. (C) 2010 Optical Society of America
An alternative bend-testing technique for a flexible indium tin oxide film
(2010-12-01)
Chen, Yen-Liang
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Hsieh, Hung-Chih
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Wu, Wang-Tsung
;
Wen, Bor-Jiunn
;
Chang, Wei-Yao
The two-dimensional refractive index distribution of a flexible indium tin oxide film deposited on a PET layer is measured before/after the bend-testing with an alternative technique based on Fresnel equations and the heterodyne interferometry. Their standard deviations are derived and they vary more obviously than the resistance variations measured in the conventional method. Hence the standard deviation of the refractive index can be used as the indicator to justify the durability of a flexible indium tin oxide film. The validity is demonstrated. (C) 2010 Elsevier B.V. All rights reserved.
Collimation testing and calibration using a heterodyne Moire method
(2014-11-01)
Chang, Wei-Yao
;
Hsu, Ken Y.
;
Chen, Kun-Huang
;
Chen, Jing-Heng
;
光電工程學系
This study proposes a simple, rapid, and highly accurate method to achieve the collimation testing and calibration of laser light beams. By applying a relative constant velocity to two gratings, every pixel of a CMOS camera can receive a series of heterodyne moire signals. Based on the least squares sine fitting algorithm, the phase of the optimized sinusoidal wave can be obtained. Consequently, the phase slope along the direction perpendicular to the grating lines can be estimated and then used to judge the degree of collimation. Furthermore, by measuring only two phase slopes at two positions of the collimating lens, the calibration of the light beam collimation can also be achieved. The experiment validated the proposed method, and the positioning error of the light beam collimation was approximately 7 mu m. (C) 2014 Elsevier Ltd. All rights reserved.
Corneal surface reconstruction by using heterodyne moire method
(2013)
Chang, Wei-Yao
;
Chen, Kun-Huang
;
Chen, Der-Chin
;
Tseng, Jung-Kai
;
Chen, Shyan-Tarng
In this paper, we propose a simple method for reconstructing the corneal surface profile by using the Talbot effect, projection moire method, and heterodyne interferometry. A linear grating is obliquely illuminated by an expanding collimated light, and a self-image of this grating can be generated and projected on the corneal surface. The deformed grating fringes are imaged on the second grating to form the moire fringes. If the first grating is moved with a constant velocity along the grating plane, a series of sampling points of the sinusoidal wave which behave like the heterodyne interferometric signal can be recorded by a CMOS camera. The phase distribution of the corneal surface then can be obtained with the IEEE 1241 least-square sine fitting algorithm and 2D phase unwrapping. Finally, the corneal surface profile can be reconstructed by substituting the phase distribution into special derived equation. This method provides the advantages of a simple optical setup, ease of operation, high stability, and high resolution.
Full-field refractive index distribution measurement of a gradient-index lens with heterodyne interferometry
(2010-10-01)
Hsieh, Hung-Chih
;
Chen, Yen-Liang
;
Wu, Wang-Tsung
;
Chang, Wei-Yao
;
Su, Der-Chin
A light beam coming from a circular heterodyne light source with an electro-optic modulator is incident on a gradient-index lens obliquely. The reflected light passes through an analyzer and an imaging lens, and is recorded by a fast CMOS camera. A group of periodic sinusoidal segments recorded by each pixel is modified, and its associated phase is derived with a unique technique. The processes are applied to other pixels; the two-dimensional phase distribution can be obtained similarly. The estimated data are substituted into the special equations derived from Fresnel's equations, and the full-field refractive index distribution of the gradient-index lens can be obtained. This method has the merits of both common-path interferometry and heterodyne interferometry.
Full-field refractive index distribution measurement of a gradient-index lens with heterodyne interferometry
(2010-10-01)
Hsieh, Hung-Chih
;
Chen, Yen-Liang
;
Wu, Wang-Tsung
;
Chang, Wei-Yao
;
Su, Der-Chin
A light beam coming from a circular heterodyne light source with an electro-optic modulator is incident on a gradient-index lens obliquely. The reflected light passes through an analyzer and an imaging lens, and is recorded by a fast CMOS camera. A group of periodic sinusoidal segments recorded by each pixel is modified, and its associated phase is derived with a unique technique. The processes are applied to other pixels; the two-dimensional phase distribution can be obtained similarly. The estimated data are substituted into the special equations derived from Fresnel's equations, and the full-field refractive index distribution of the gradient-index lens can be obtained. This method has the merits of both common-path interferometry and heterodyne interferometry.
Full-field refractive index measurement with simultaneous phase-shift interferometry
(2014)
Chu, Yen-Chang
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Chang, Wei-Yao
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Chen, Kun-Huang
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Chen, Jing-Heng
;
Tsai, Bo-Chung
Using the phenomenon of total internal reflection and a beam splitting device, a technique of simultaneous phase-shift interferometry is proposed for measuring the full-field refractive index. Because this method applies a beam splitting device that mimics the characteristics of beam splitting and phase modulation, four interferemetric images of various phase distributions can be simultaneously captured. Therefore, this setup can avoid errors caused by non-simultaneous capturing of images and offers the benefits of high stability, ease of operation, and real-time measurement. Furthermore, using the phenomenon of total internal reflection, the phase difference between p- and s-polarized light varies considerably with the refractive index of a tested specimen. This can substantially increase the measurement resolution. The feasibility of this method is verified using an experiment, and the measurement resolution can be higher than 3.65 x 10(-4) RIU. (C) 2014 Elsevier GmbH. All rights reserved.
Heterodyne moire interferometry for measuring corneal surface profile
(2014-03-01)
Chang, Wei-Yao
;
Chen, Kun-Huang
;
Chen, Der-Chin
;
Tseng, Jung-Kai
;
Chen, Shyan-Tarng
This study proposes an accurate method for reconstructing the corneal surface profile. By applying a constant velocity to the projection grating along the grating plane, a series of sampling points of the sinusoidal wave, which behaves in the manner of heterodyne interferometric signals, can be recorded using a CMOS camera. The phase distribution of the moire fringes can then be obtained using the IEEE 1241 least-square sine fitting algorithm and two-dimensional (2D) phase unwrapping. Finally, the corneal surface profile can be reconstructed by substituting the phase distribution into a specially derived equation. To validate the proposed method, the corneal surface of a pig eyeball was measured. The measurement resolution was approximately 3.5 mu m. Because of the introduction of the Talbot effect, the projection moire method, and heterodyne interferometry, this approach provides the advantages of a simple optical setup, ease of operation, high stability, and high resolution. (C) 2013 Elsevier Ltd. All rights reserved.
Heterodyne moire surface profilometry
(2014-02-10)
Chang, Wei-Yao
;
Hsu, Fan-Hsi
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Chen, Kun-Huang
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Chen, Jing-Heng
;
Hsu, Ken Y.
In this study, a novel moire fringe analysis technique is proposed for measuring the surface profile of an object. After applying a relative displacement between two gratings at a constant velocity, every pixel of CMOS camera can capture a heterodyne moire signal. The precise phase distribution of the moire fringes can be extracted using a one-dimensional fast Fourier transform (FFT) analysis on every pixel, simultaneously filtering the harmonic noise of the moire fringes. Finally, the surface profile of the tested objected can be generated by substituting the phase distribution into the relevant equation. The findings demonstrate the feasibility of this measuring method, and the measurement error was approximately 4.3 mu m. The proposed method exhibits the merits of the Talbot effect, projection moire method, FFT analysis, and heterodyne interferometry. (C) 2014 Optical Society of America
High-accuracy thickness measurement of a transparent plate with the heterodyne central fringe identification technique
(2011-07-20)
Wu, Wang-Tsung
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Hsieh, Hung-Chih
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Chang, Wei-Yao
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Chen, Yen-Liang
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Su, Der-Chin
In a modified Twyman-Green interferometer, the optical path variation is measured with the heterodyne central fringe identification technique, as the light beam is focused by a displaced microscopic objective on the front/rear surface of the test transparent plate. The optical path length variation is then measured similarly after the test plate is removed. The geometrical thickness of the test plate can be calculated under the consideration of dispersion effect. This method has a wide measurable range and a high accuracy in the measurable range. (c) 2011 Optical Society of America
Method for gauge block measurement with the heterodyne central fringe identification technique
(2010-06-01)
Wu, Wang-Tsung
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Chen, Yen-Liang
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Hsieh, Hung-Chih
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Chang, Wei-Yao
;
Su, Der-Chin
In a modified Michelson interferometer, the top face of the wringing platen is first identified using the heterodyne central fringe identification technique. Then the reference mirror located in the other arm is moved by a precision translation stage until the top face of the tested gauge block is also identified with the same technique. The displacement of the mirror is exactly equivalent to the length of the tested gauge block. The measurable range of the interferometer relates to the maximum travel range of the translation stage and its uncertainty depends on the uncertainty of the heterodyne central fringe identification method and the resolution of the translation stage. (C) 2010 Optical Society of America
Optimal sampling conditions for a commonly used charge-coupled device camera in the full-field heterodyne interferometry
(2011-04-01)
Hsieh, Hung-Chih
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Wu, Wang-Tsung
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Chang, Wei-Yao
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Chen, Yen-Liang
;
Su, Der-Chin
The processes to derive the associated phase of an interference signal from the data of a series of recorded frames are performed, and we find that the sampling frequency being lower than the Nyquist sampling rate can also be applied to the full-field heterodyne interferometry. Two optimal sampling conditions for a commonly used CCD camera are proposed based on the relation between the heterodyne frequency and the contrast of the interference signal under the condition that the phase error is set to be 0.05 deg. (C) 2011 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.356712]
Reconstruction of surface profile by using heterodyne moire method
(2012-11-01)
Chang, Wei-Yao
;
Hsu, Fan-Hsi
;
Chen, Kun-Huang
;
Chen, Jing-Heng
;
Hsieh, Hung-Chih
Based on the projection moire method and heterodyne interferometry, this study proposes an alternative method for reconstructing the surface profile of an object. Obliquely illuminating a linear grating with an expanding collimated light, a self-image of this grating can be generated and projected on the surface of the tested object. The grating fringes distorted by the surface profile are imaged on the reference grating to form the moire fringes. These moire fringes are then captured by a CMOS camera. If the projection grating moves with a constant velocity along the grating plane, each pixel of the CMOS camera records a series of sampling points of the sinusoidal wave. These sinusoidal waves behave like heterodyne interferometric signals. Hence, the accurate and stable phase distribution of the tested object surface can be obtained using the IEEE 1241 least-squares sine fitting algorithm and 20 phase unwrapping. Substituting the phase values into the derived equation, the surface profile of the tested object can be reconstructed. The experiments in this study verified the feasibility of this method, showing a measurement resolution of approximately 1.9 mu m. The proposed measurement method has the merits of both the projection moire method and the heterodyne interferometry. (C) 2012 Elsevier B.V. All rights reserved.
Stress measurement of thin film on flexible substrate by using projection moire method and heterodyne interferometry
(2016-06-01)
Chen, Kun-Huang
;
Chen, Jing-Heng
;
Tseng, Hua-Ken
;
Chang, Wei-Yao
;
光電工程學系
We propose a stress measurement system based on a projection moire method and heterodyne interferometry for thin films on a flexible substrate. In the measurement setup, a CMOS camera in which every pixel can receive a series of heterodyne moire signals by using a continuously relative displacement with a constant velocity is used. Furthermore, the phase of the optimized sinusoidal curve and the surface profile of the flexible substrate are determined using a least-squares sine fitting algorithm. The thin-film stress is obtained by representing the cross-sectional curve of the surface profile by using a polynomial fitting method, estimating the resultant curvature radii of the uncoated and coated substrates, and using these two radii in the corrected Stoney formula. The proposed measurement system has the advantages of high accuracy, high resolution, and high capacity for substrates with high flexibility and a large measurement depth. (C) The Authors.