A method based on a specific quasi-common-optical-path (QCOP) configuration for two-dimensional displacement measurement is presented. The measurement system consists of a heterodyne light source, two-dimensional holographic grating, specially designed set of half wave plates, and lock-in amplifiers. Two measurement configurations, for single and differential detection, are designed. The sensitivity, resolution and nonlinear phase error of the differential detection type are better than those of the single detection type. The experimental results demonstrate that the QCOP interferometer has the ability to measure two-dimensional displacement while maintaining high system stability.

No abstract

We present a heterodyne grating interferometer based on a quasi-common-optical-path (QCOP) design for a two-degrees-of-freedom (DOF) straightness measurement. Two half-wave plates are utilized to rotate the polarizations of two orthogonally polarized beams. The grating movement can be calculated by measuring the phase difference variation in each axis. The experimental results demonstrate that our method has the ability to measure two-DOF straightness and still maintain high system stability. The proposed and demonstrated method, which relies on heterodyne interferometric phase measurement combined with the QCOP configuration, has the advantages of high measurement resolution, relatively straightforward operation, and high system stability.

A novel heterodyne grating interferometer based on a quasi-common-optical-path design is proposed for displacement measurement. The quasi-common-optical-path design relies on the phase shift between the zeroth and first diffraction grating orders which have been rotated in polarization using a half-wave plate. We achieved a measurement resolution better than 3 nm with a system stability of less than 14 nm over 1 h. We discussed the performances of the system addressing the effect of dominant errors, namely grating pitch, frequency mixing, polarization mixing and polarization-frequency mixing. While the theoretically quasi-common-optical-path heterodyne grating system allows for sub-nanometer resolution, we found that the measurement resolution here is limited by the displacement stage. Relying on heterodyne interferometric phase measurement combined with quasi-common-optical configuration, the proposed and demonstrated method has the advantages of high measurement resolution, relatively straightforward operation and high stability.

An angular displacement measurement sensor with high resolution for large range measurement is presented. The design concept of the proposed method is based on the birefringence effect and phase detection of heterodyne interferometry. High system symmetry and simple operation can be easily achieved by employing an innovative sandwich optical design for the angular sensor. To evaluate the feasibility and performance of the proposed method, several experiments were performed. The experimental results demonstrate that our angular displacement measurement sensor can achieve a measurement range greater than 26°. Considering the high-frequency noise, the measurement resolution of the system is approximately 1.2° × 10^-4. Because of the common-path arrangement, our proposed method can provide superior immunity against environmental disturbances.