![]() ![]() The resolution of in-plane displacement measurement is determined by the pitch of the grating in a planar/surface encoder. In planar/surface encoders, a two-dimensional diffraction grating is employed as the scale for displacement measurement. Figure 1 shows some examples of the surface/planar encoders. In recent years, multi-axis planar/surface encoders capable of measuring multi-axis displacement with a single measurement laser beam are attracting attention. Therefore, a scale grating requires high-precision manufacturing process, as well as the verification/calibration process. The accuracy of the grating pitch, which is the distance between the neighboring pattern structures of the diffraction grating, directly affects the accuracy of displacement measurement in a linear encoder. In the manufacturing industry, the diffraction grating is an important optical element employed as a scale of an optical linear encoder for precision positioning. Its dispersive characteristics have been used for spectroscopic measurement, and nowadays it is widely employed in state-of-the-art scientific applications such as the pulse compression of an ultra-short pulse laser, as well as in industrial products such as optical drives or head-up displays. In this paper, major methods for the evaluation of a grating pitch are also reviewed.Ī diffraction grating is one of the most important optical components employed in many academic and industrial fields. Verification of the pitch of the fabricated pattern structures, whose accuracy strongly affects the performance of planar/surface encoders, is also an important task to be addressed. In this review article, principles of generating interference fringe fields for the fabrication of a scale grating based on the interference lithography are reviewed, while focusing on the fabrication of a two-dimensional scale grating for planar/surface encoders. Furthermore, the optical setup for the non-orthogonal two-axis Lloyd’s mirror interferometer has been optimized for the fabrication of a large-area scale grating. ![]() In addition, the concept of the patterning of the two-dimensional orthogonal pattern structure at a single exposure has been extended to the non-orthogonal two-axis Lloyd’s mirror interferometer. For the fabrication of a two-dimensional scale grating to be used in a planar/surface encoder, an orthogonal two-axis Lloyd’s mirror interferometer, which has been realized through innovation to Lloyd’s mirror interferometer, has been developed. ![]() Especially, optical configurations such as Lloyd’s mirror interferometer based on the division of wavefront method can generate interference fringe fields for the patterning of grating pattern structures at a single exposure in a stable manner. Laser interference lithography is an attractive method for the fabrication of a large-area two-dimensional planar scale grating, which can be employed as a scale for multi-axis optical encoders or a diffractive optical element in many types of optical sensors. ![]()
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