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Abstract
This paper develops an electro-optically modulated circular polariscope based on a phase-lock technique for measuring the optical rotation angle of a glucose solution such that its concentration can be proportionally extracted. The validity of the proposed design is demonstrated by measuring the optical rotation angle of a half-wave plate as its principal axis angle is rotated through in increments of
. The corresponding correlation coefficient is found to be 0.999996. Hence, it is inferred that the measurement system has a good linear response. When applied to the measurement of glucose samples with concentrations ranging from 0–1.2 g dl−1, the correlation coefficient between the measured rotation angle and the glucose concentration is determined to be 0.998599, while the corresponding standard deviation is
. The current system is capable of measuring glucose concentration as low as 0.2 g dl−1. Furthermore, the dynamic measurement range of the polarization rotation angle extends from
to
. Compared to other optical measurement systems presented in the literature, the current system has the advantages of a simpler structure, fewer optical elements, a tunable heterodyne frequency and a simple signal processing scheme. Overall, the proposed system provides a highly-precise, straightforward, non-invasive means of obtaining glucose concentration measurements.
Acknowledgements
This research was partially supported by the National Science Council of Taiwan, Republic of China through Contract number 95-2221-E-269-010.