Glucose concentration measurement using an electro-optically modulated circular polariscope

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 180 degrees in increments of 5 degrees. 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 0.00654 degrees. 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 -90 degrees to +90 degrees. 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.