High-Accuracy Wave Plate Measurement Based on Dual- Frequency Laser Interferometry and Phase Detection

Objective The accuracy of wave plates has a significant influence on the performance of polarized optical systems, and thus the high-accuracy measurement of their phase retardation and fast axis azimuths is required. Many wave plate measurement methods at present are based on the principle of light intensity measurement. The measurement accuracy is easily affected by light intensity fluctuations, and the requirements for light source and stability of light path are high. Quite a few methods among them cannot measure the fast axis azimuth of the wave plate at the same time. Therefore, many researchers have also studied other measurement methods, such as laser feedback method, to improve the performance of wave plate measurement. In this study, a high-accuracy wave plate measurement method based on dual frequency laser interferometry and phase detection is proposed. It has good advantages of wave plate measurement. Methods A dual-frequency laser heterodyne interference optical path is constructed by using a rotatable half-wave plate and a corner prism in this study (Fig. 1). The relationship between the phase retardation of the wave plate to be measured and the phase difference between the measured signal and the reference signal is obtained by Jones matrix method. During the measurement, the phase retardation and the fast axis azimuth of the measured wave plate can be obtained by rotating the half wave plate, monitoring the change of phase difference between the measured signal and the reference signal through a phase meter, and recording the maximum value and minimum value as well as the corresponding fast axis azimuth of the half wave plate. Results and Discussions Error analysis shows that the measurement uncertainty of the phase retardation is about 3.9', and that of the fast axis azimuth is about 5'' under the experimental conditions. The experimental comparison results indicate that the result of the proposed method is in good agreement with that of other methods. The repeated experiments show that the measurement standard deviation is about 2'. The measurement is not affected by the azimuth accuracy of birefringent devices such as wave plates and polarizers in principle. The common optical path structure is one of the advantages of the proposed measurement system, so the measurement is highly stable. The signal processing adopts the phase detection means which has higher accuracy than intensity detection means. In addition, the proposed method has the advantages of few components, a simple structure and a quick measurement process. Conclusions Wave plates are important optical components, whose accuracy has a significant influence on the performance of polarized optical systems. Therefore, the high-precision measurement of the phase retardation and fast axis azimuth of the wave plate is required. A high-accuracy wave plate measurement method based on dual-frequency laser interferometry and phase detection is proposed in this paper. A dual-frequency laser heterodyne interference optical path is constructed by using a rotatable half- wave plate and a corner prism. It can accurately measure the phase retardation and the fast axis azimuth of an arbitrary wave plate. The measurement is not affected by the azimuth accuracy of birefringent devices such as wave plates and polarizers in principle. The common optical path structure is one of the advantages of the measurement system, so the measurement stability is good. The signal processing adopts the phase detection means which has higher accuracy than intensity detection means. The measurement formulae are deduced and the measurement system is built. Error analysis reveals that the measurement uncertainty of the phase retardation is about 3.9', and that of the fast axis azimuth is about 5'' under the experimental conditions. The experimental comparison results indicate that the result of the proposed method is in good agreement with that of other methods. The repeated experiments demonstrate that the measurement standard deviation is about 2'. In addition, the presented method has the advantages of few components, a simple structure and a quick measurement process.