An electro-optic modulated heterodyne interferometer for measuring low glucose concentration

Abstract

An electro-optic modulated heterodyne interferometer using the phase-lock technique for measuring the optical rotation angle corresponding to glucose concentration is presented. By inserting a half-wave plate behind the test sample and using the heterodyne interferometric phase-lock technique, it demonstrates a high sensitivity and is capable of measuring low glucose concentration. The validity of the proposed design is demonstrated by the measurements of rotation angles in a half-wave plate sample and the glucose sample, respectively. A correlation coefficient value of 0.999993 indicates a high linear response between the reference rotation angle and the measured rotation angle in a half-wave plate. Moreover, a standard deviation in rotation angle level of 5.9^○ × 10⁻⁴ has been obtained for glucose solutions with concentrations ranging from 0 to 1.2 g dl⁻¹, with a correlation coefficient value of 0.99989 between the measured rotation angle and the glucose concentration. A standard deviation of rotation angle around 1.5^○ × 10⁻⁴ is achieved according to the repeatability experiments, and the relative error of rotation angle corresponding to the lowest measurable concentration of 0.01 g dl⁻¹ has been determined to be 5.88%.

Keywords:

• chiral medium
• circular birefringence
• heterodyne interferometer
• optical rotation
• phase-lock

Acknowledgements

This research was supported by National Science Council of Taiwan Republic of China through contract number NSC-96-2622-E-269-026-CC3.