Mr. Chao Gao Profile

Chao Gao

at National Univ. of Defense Technology

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Proceedings Article | 20 January 2023 Paper

Accurate optical rotation measurement by using spatial polarization modulation and digital image processing

Xueke Wen, Bing Lei, Chao Gao, Fujei Wang

Proceedings Volume 12560, 125600C (2023) https://doi.org/10.1117/12.2652110

KEYWORDS: Glucose, Modulation, Polarization, Scanning probe microscopy, Polarimetry, Optical testing, Digital image processing, Tissue optics, Polarizers, Image processing

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Polarimetry is an important noninvasive blood glucose measurement method and attracts extensive attention from researchers. However, one of the difficulties associated with polarimetry is the low concentration of blood glucose, which results in weak optical rotation signals. In this paper, we report a fast and accurate spatial polarization modulation system (SPMS) that can measure the low glucose concentration by analyzing a single digital image. In this system, the rotated polarizer gain mechanism (RPGM) is adopted to amplify the weak optical rotation signals. And in order to extract the optical rotation signals from the background more easily, a vortex phase difference retarder (VPDR) is employed to modulate the optical rotation signals, which is a specially designed birefringent crystal with a vortex phase difference along the azimuth angle. We have established the theoretical model of the SPMS by the Jones matrix theory, and both the simulation experiments with noise and without noise have shown that the SPMS has a resolution of 100mg/dl.

Proceedings Article | 18 December 2019 Paper

Novel ellipsometry based on the manipulation of vectorial optical field and digital image processing

Chao Gao, Bing Lei

Proceedings Volume 11338, 1133828 (2019) https://doi.org/10.1117/12.2547432

KEYWORDS: Image processing, Ellipsometry, Wave plates, Jones vectors, Digital image processing, Polarization, Thin films

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Ellipsometry is a kind of measuring techique to research the optical properties of materials by utilizing the polarization characteristics of light. The key of the optical ellipsometry is to utilize the polarization transformation that occurs as a beam of polarized light is reflected or transmitted through the dielectric film, and the characteristic parameters of this film can be obtained by measuring this transformation. In this paper, we present a novel scheme of ellipsometry that can extract the ellipsometric parameters of the reflected light from a single shot, which is achieved by using the vectorial optical field and digital image processing technique. In order to obtain the ellipsometric parameters of the reflected light, a zero-order vortex half-wave retarder is placed after the thin film to transfer the reflected elliptically polarized light to a vectorial optical field. When this vectorial optical field is analyzed by a linear polarizer, the transmitted light pattern with an hourglass-shaped intensity distribution can be obtained, and two gradual dark and bright areas show alternately. The azimuth angles and the intensity values of the central lines of dark and bright areas are related to the ellipsometric parameters, which can be obtained by processing the hourglass-shaped intensity image with our specially designed image processing algorithm. The theoretical model of our presented ellipsometer system is established firstly by using the Jones matrix theory, and the simulating and analyzing formulas are obtained based on the model. Some numerical analyzing studies have been carried out to validate the feasibility of our scheme, and the results of the simulated research indicate that the retrieved values of the ellipsometric parameters are consistent with the preset values.

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