Browsing by Author "Chang, W. Y."

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An alternative method for measuring the index profile of a gradient-index lens
(2011)
Hsieh, H. C.
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Wu, W. C.
;
Chang, W. Y.
;
Hsu, F. S.
;
Su, D. C.
An alternative method for measuring the index profile of the GRIN lens is proposed based on Fresnel's equations and the common-path phase-shifting interfermetry. A light beam composing of the right- nd the left- ircularly polarized components is obliquely incident on the tested GRIN lens and the reflected light passes through an analyzer. The light is collected and imaged by an imaging lens to a CMOS camera. Four interferograms under different additional phases are taken and Carre's phase-shifting method is used to calculate the full-field phase distribution. Next, the estimated data are substituted into the special equations derived from the Fresnel's equations, and the index profile of the GRIN lens can be obtained. Its validity has been demonstrated. It has both merits of the common-path interferemetry and the phase-shifting interferemetry.
Step Height Measurement by Using Heterodyne Central Fringe Identification Technique
(2010)
Wu, W. T.
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Hsieh, H. C.
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Chen, Y. L.
;
Chang, W. Y.
;
Su, D. C.
A simple method for measuring a step-height sample is presented with the heterodyne central fringe identification technique and a precision translation stage. This method can accurately point out the zero optical path difference position such that the optical path lengths of two arms of the interferometer are absolutely equivalent. Thus, the two surfaces of the step-height sample can be identified sequentially with the translation stage. The displacement of the translation stage is equal to the step-height of the test sample. The feasibility of the technique is demonstrated. The measurable range is not limited by the coherence length of the light source. The measurement accuracy depends on the uncertainties of the heterodyne central fringe identification method and the translation stage. In our setup, we have a 100 mm measurable range and a 4 nm uncertainty. The wavelength stability of the light source has a minor effect on the measurement.
Two-dimensional refractive index distribution measurement of a GRIN lens
(2010)
Hsieh, H. C.
;
Chen, Y. L.
;
Wu, W. T.
;
Chang, W. Y.
;
Su, D. C.
Based on the Fresnel's equations and the phase-shifting method, an alternative method for measuring the refractive index distribution of a GRIN lens is presented. A linearly/circularly polarized light in order enters a modified Twyman-Green interferometer, in which an electro-optical modulator is used as a phase shifter. In the interferometer, the light beam is divided by a beam-splitter into two beams, a reference beam and a test beam. After they are reflected by a plane mirror and the tested GRIN lens, respectively, they are combined together and pass through an analyzer. The analyzer extracts the same polarized components to interfere each other, and the full-field interference signals produced by the components of the s- and the p-polarizations can be obtained. The full-field interference signals are taken by a CMOS camera. The phase differences can be obtained by using the four-step phase-shifting interferometric method. Substituting these two groups of data into special equations derived from Fresnel equations, and the two-dimensional refractive index distribution of the GRIN lens can be calculated. Its validity is demonstrated and has some merits such as simple optical configuration, easy operation and high resolution.