Optimal design of a reflective diffraction grating scale with sine-trapezoidal groove for interferential optical encoders

Interferential optical encoders are promising nano-positioning sensors in precision manufacturing and metrology instrumentation. As measuring standard, the quality of diffraction grating scales primarily determines the performance of the interferential optical encoders. In this work, the optimal design and fabrication of a reflective diffraction grating scale with sine-trapezoidal groove is performed. Firstly, the requirement for diffraction characteristics of diffraction grating scales is specified by introducing the basic principle of interferential optical encoders. Sequentially, the critical requirements of the diffraction grating scales are further specified by theoretically investigating the influence of groove-profile parameters (i.e. line height, groove and ridge widths) and micro-defect parameters (i.e. surface roughness and line roughness) on the diffraction characteristics of diffraction grating scales. Finally, morphological parameter optimization of a diffraction grating scale with a pitch of 4 μm is performed, and the diffraction grating scale is fabricated and characterized. The characterization results indicate that the fabricated diffraction grating scale conforms well to the optimal design, and is ideal for application in interferential optical encoders.