A full-field heterodyne polariscope for using new image signal process

This study develops a heterodyne polariscope for measuring the two-dimensional principal axis and phase retardation in a linear birefnngence material using novel three-frame and two-frame integrating-bucket methods and a Charge Couple Device (CCD). By using a CPLD (Complex Programmable Logic Device) to provide an external trigger to the CCD, integrating buckets with multiple frames are achieved. The advantages of the proposed three-frame and two-frame integrating-bucket methods include a simpler signal processing algorithm based on fewer frames and the elimination of flyback error caused by a saw-tooth modulation signal at higher frequencies. A quartz quarter-wave plate is chosen for demonstration purposes. It is shown that the three-frame integrating-bucket method has an average absolute error of 0.39° in the principal axis measurement and an average error of 0.61° in the phase retardation measurement for measurements at the same pixel. The long-term standard deviations of the phase stability calculated using the novel three-frame method and the conventional four-frame integrating-bucket method are 0.4678° and 0.4733°, respectively. Therefore, it can be surmised that the two methods have similar measurement capabilities. However, the conventional four-frame integrating-bucket method is readily contaminated by flyback error under saw-tooth modulation.