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 plat behind the test sample and using the heterodyne interferometric phash-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 0999993 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 59° × 10 -4 has been obtained for glucose solutions with concentrations ranging form 0 to 12 gdl -1 , with a correlation coefficient value of 099989 between the measured rotation angle and the glucose concentration A standard deviation of rotation angle aroud 15° × 10 -4 is achieved according to the repeatability experiments, and the relative error of rotation angle corresponding to the lowest measurable concentration of 001 gdl -1 has been determined to be 588%

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

Wave plates (WPs) are key components in optical polarization systems whose phase retardations and fast axis azimuths should be determined accurately. At present many measurement methods are based on light intensity detection which is inevitably affected by light intensity fluctuations so that the measurement accuracy is limited. What’s more, quite a few methods cannot measure WPs’ fast axis azimuths simultaneously. In this paper a method of simultaneously measuring the phase retardation and fast axis azimuth of arbitrary WP is proposed, which is based on equivalent component and phase detection. A rotatable half wave plate (HWP) and a retroreflector are used and its effect is equivalent to measuring an equivalent WP whose phase retardation is twice that of the measured wave plate, which is equivalent to doubling the measurement resolution. Phase detection is used to process the signals which means the measurement accuracy is better than that by usual light intensity detection. What’s more, the presented method eliminates the angle positioning errors of birefringent components in principle which exists in many present WP measurement methods. Finally, the measurement system setup is simple as well as the measurement process. The measurement formulae are deduced and corresponding WP measuring system is established. The error analysis shows that the system measurement uncertainty is about 3.9′ for the phase retardation and 5” for the fast axis azimuth. Experiment results and comparisons of quarter WPs and HWPs show that the presented method is in good agreement with other method. The phase retardation measurement repeatability is also good with a standard deviation about 2′.

S.H. Chen

Papers

Heterodyne polariscope for measuring the principal angle and phase retardation of stressed plastic substrates