FABRICATION OF OPTICAL MOSAIC TWO-DIMENSIONAL GRATINGS WITH A DUAL LLOYD'S MIRROR INTERFEROMETER

Hengyan Zhou, Lijiang Zeng

Abstract

Planar encoders can be used to measure two-dimensional (2D) displacements. In order to achieve large measuring ranges, planar encoders require large-size 2D gratings, which can be made by optical mosaic technique. We set up a dual Lloyd’s mirror interferometer to make optical mosaic 2D gratings. The key point to obtain good mosaic gratings is to fine tune the attitude and position of the substrate relative to the exposure beams during consecutive exposures, which can be realized by utilizing the interference fringes formed by the diffraction of the exposure beams from the latent gratings (exposed but undeveloped gratings). As the diffraction efficiency of the latent gratings is extremely low (~ 10^-5), we use a high-sensitivity CCD to monitor the interference fringes. The attitude error of the substrate needs to be adjusted only once in order to ensure the groove direction’s parallelism for both dimensions of the grating. Experimentally we made 1 × 2 2D mosaics of 34 × (30+30) mm² area. A Fizeau interferometer is used to measure the mosaics. The Fizeau interferograms are well connected at the joint areas, demonstrating a good mosaic quality.

Keywords

two-dimensional grating, mosaic grating, dual Lloyd’s mirror interferometer, latent grating

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IMEKO TC

TC14 - Measurement of Geometrical Quantities

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