Quasi-common-optical-path heterodyne grating interferometer for displacement measurement

Abstract

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.

6-DOF displacement and angle measurements using heterodyne laser encoder

“…1, the in-plane detection configuration is framed by the blue dashed line. The measurement principle is based on the QCOP configuration [9]. According to the optical arrangement and Jones calculation, the amplitudes of part A and B are given as:…”

“…In our previous research, a heterodyne laser encoder based on the quasi-common optical path (QCOP) design was proposed for 1-DOF displacement measurement [9]. However, the technique was only for 1-DOF displacement measurement.…”

Heterodyne common-path grating interferometer with Littrow configuration

“…However, it used a single photodetector to measure the fringe movement which stems from the grating movement, so it cannot distinguish the direction of displacements. Based on the shearing interference principle, Hsieh et al proposed quasi-common-path grating interferometer (QCOP) with a heterodyne laser source [7]. The QCOP combined the shearing interference technique and the polarization interferometry.…”

Measurement of in-plane displacement by wavelength-modulated heterodyne speckle interferometry

“…The optical interferometer is widely used for length or displacement measurement, because it offers an effective, nocontact alternative to traditional contacting transducers, such as the capacitance sensor and the strain gauge [3,4]. In addition, the optical interferometer not only has high resolution and wide dynamic measurement range, but it also allows for a flexible optical path arrangement [5].…”