Double-Resolution Wave Plate Measurement Based on Equivalent Components and Phase Compensation

Objective Wave plates are a key component of optical polarization systems. The study of methods to measure wave plates precisely is becoming increasingly important with continuous improvements in the performance of polarization systems. Currently,most techniques are based on detecting the intensity of light passing through a wave plate. These methods are generally susceptible to fluctuations in the intensity of the light. In contrast, other methods that measure the phase of the light instead typically exhibit greater accuracy and stability. However, relatively few such methods have been described in the relevant literatures for phase measurement. In this study, a high-precision method based on equivalent components and phase compensation is proposed to simultaneously measure the phase retardation and azimuth of arbitrary wave plates. Methods We insert a rotatable half wave plate in front of a measured wave plate and use a reflector to allow the measurement light to pass through both twice. This effect is equivalent to measuring an equivalent wave plate with a phase retardation twice that of the measured wave plate, and double-resolution detection is thus obtained. The proposed system includes a dual-frequency laser source and a phase detector. Simultaneously, the fast-axis azimuth is also determined according to the azimuth of the half wave plate when the maximum or minimum phase difference occurs. Results and Discussions An analysis of error values under the experimental conditions indicated that the measurement uncertainty of the phase retardation was about 3.3', and that of the fast-axis azimuth was better than 5.4''. The results of an experimental comparison show good agreement with the measurement results obtained using other methods. The proposed approach theoretically avoids the influence of fluctuations in the intensity of measurement light that affect conventional methods as well as the typical issue of the influence of the positioning accuracy of birefringent devices azimuth. The proposed optical system adopts a dual-frequency heterodyne interference optical path with common optical path properties to obtain good measurement stability. This system also has a simple structure, requires relatively few components, and can take measurements quickly. In addition, because the measurement beam passes through the position of the measured wave plate twice, birefringent devices with wedge-shaped structures can also be measured. Conclusions The study of high-performance methods to measure wave plates has significant practical significance owing to their applications in optical polarization systems. In this study, a high-precision method for simultaneously measuring the phase retardation and azimuth of arbitrary wave plates based on equivalent components and phase compensation is proposed. By inserting a rotatable half wave plate in front of a measured wave plate and using a reflector to allow the measurement light to pass through the half wave plateand the measured wave plate twice, the proposed method is equivalent to measuring an equivalent wave plate with a phase retardation twice that of the measured wave plate, which allows the system to achieve double-resolution detection. The system uses a dual-frequency laser source and a phase detection sensor. By rotating the half wave plate to compensate for the phase of the measurement light and adjusting the change in the phase difference of the measurement light relative to the reference light to the maximum or minimum value, the phase retardation of an arbitrary wave plate can be obtained. Simultaneously, the fast-axis azimuth is also determined according to the azimuth of the half wave plate when the maximum or minimum phase difference occurs. This method theoretically avoids the influence of fluctuations of the intensity of the measurement light that affect methods based on light intensity in general, as well as the influence of the positioning accuracy of the azimuth of birefringent devices, which affects many different methods. The optical system owns a dual-frequency heterodyne interference optical path, so it has common optical path property and good measurement stability. The proposed approach also has the advantages of a simple structure, relatively few components, and a quick measurement process. In addition, birefringent devices with wedge-shaped structures can also be measured by the proposed method. As noted above, the results of an error analysis under the experimental conditions showed that the measurement uncertainty of the phase retardation was about 3.3', and that of the fast-axis azimuth was better than 5.4''. The results of an experimental comparison also showed good agreement with the results of measurements obtained using other methods.