Simple and compact grating-based heterodyne interferometer with the Littrow configuration for high-accuracy and long-range measurement of two-dimensional displacement

In interferential linear displacement sensors, accurate information about the position of the reading head is calculated out of a pair of quadrature (sine and cosine) signals. In double grating interference schemes, diffraction gratings combine the function of beam splitters and phase retardation devices. Specifically, the reference diffraction grating is located in the reading head and regulates the phase shifts in diffraction orders. Measurement diffraction grating moves along with the object and provides correspondence to the displacement coordinate. To stabilize the phase imbalance in the output quadrature signals of the sensor, we propose to calculate and optimize the parameters of these gratings, based not only on the energetic analysis, but along with phase relationships in diffraction orders. The optimization method is based on rigorous coupled-wave analysis simulation of the phase shifts of light in diffraction orders in the optical system. The phase properties of the reference diffraction grating in the interferential sensor are studied. It is confirmed that the possibility of quadrature modulation depends on parameters of static reference scale. The implemented optimization criteria are formulated in accordance with the signal generation process in the optical branch. Phase imbalance and amplification coefficients are derived from Heydemann elliptic correction and expressed through the diffraction efficiencies and phase retardations of the reference scale. The phase imbalance of the obtained quadrature signals is estimated in ellipticity correction terms depending on the uncertainties of influencing parameters.

Section: Methodsmentioning

confidence: 99%

Phase Imbalance Optimization in Interference Linear Displacement Sensor with Surface Gratings

Одиноков

Shishova

Kovalev

et al. 2020

“…Instead of lengthening the optical path as in a laser interferometer, a grating interferometer increases the measurement range of the grating vector direction using large grating sizes without changing the optical path [ 6 , 7 , 8 ]. In addition to size, the dimension of the grating (one-dimensional line (1-D) or two-dimensional grid (2-D)) is critical to the measurement range of a reading head [ 9 ].…”

Section: Introductionmentioning

confidence: 99%

Grating Interferometer with Redundant Design for Performing Wide-Range Displacement Measurements

Cheng

Zhang

et al. 2022

Grating interferometers that use large two-dimensional grating splice modules for performing wide-range measurements have significant advantages for identifying the position of the wafer stage. However, the manufacturing process of large two-dimensional grating splice modules is very difficult. In contrast to existing redundant designs in the grating line dimension, we propose a novel interferometric reading head with a redundant design for obtaining wide-range displacement measurements. This interferometric reading head uses a one-dimensional grating splice module, and it was observed to be compatible with two orthogonal gratings. We designed a grating interferometer system composed of four reading heads to achieve a wide range of measurements and verified it using ZEMAX simulation. By conducting experiments, we were able to verify the compatibility of the reading head with gratings possessing different grating line directions; the measurement noise was found to be less than 0.3 nm.

“…Although it is difficult to assure high accuracy because there are some critical issues such as a periodic error, a distortion error, and a thermal error, optical linear encoders are often employed in precision positioning systems in machine tools and measuring instruments due to their high resolutions and easy-to-use designs. Many efforts have been made so far to improve the resolution of optical linear encoders [28,32,33,34,35,36,37,38,39,40,41,42], and nowadays state-of-the-art optical linear encoders can realize a sub-nanometer resolution comparable to that of the laser interferometers [4,6,7]. Furthermore, absolute linear encoders enable machine tools, measuring instruments and fabrication equipment to be operated without the initialization of their positioning systems [43], which is mandatory when the incremental laser interferometers and/or linear encoders are employed.…”

Section: Introductionmentioning

confidence: 99%

Optical Sensors for Multi-Axis Angle and Displacement Measurement Using Grating Reflectors

Shimizu

Matsukuma

Gao

2019

In dimensional metrology it is necessary to carry out multi-axis angle and displacement measurement for high-precision positioning. Although the state-of-the-art linear displacement sensors have sub-nanometric measurement resolution, it is not easy to suppress the increase of measurement uncertainty when being applied for multi-axis angle and displacement measurement due to the Abbe errors and the influences of sensor misalignment. In this review article, the state-of-the-art multi-axis optical sensors, such as the three-axis autocollimator, the three-axis planar encoder, and the six-degree-of-freedom planar encoder based on a planar scale grating are introduced. With the employment of grating reflectors, measurement of multi-axis translational and angular displacement can be carried out while employing a single laser beam. Fabrication methods of a large-area planar scale grating based on a single-point diamond cutting with the fast tool servo technique and the interference lithography are also presented, followed by the description of the evaluation method of the large-area planar scale grating based on the Fizeau interferometer.