Spatial Filtering Theory Of Diffraction Grating And Experimental Research On Design And Fabrication Of Diffraction Grating

Photoelectric encoder, which integrates the advantages from Optics, Electricity and Machinery together, is designed for precision measurement. Due to multiple merits such as high precision, high distinguishability, good stability, long-service life and easy to operate, photoelectric encoder is widely applied in various kinds of fields, including aviation, military, transportation and scientific research, etc. The quality of the Moire fringe of gratings is the key indicator that determinates encoder’s performance, while the precision of gratings has the most important influence to the quality of the fringes. We started from researching on the gratings and then extended to the spatial filtering theory of gratings and the experimental study of designing and fabricating optical gratings. Our work is of great significance to the improvement of the precision of encoder’s measurement.After studying of the previous work from at home and abroad, and careful analysis of the research progress of the photoelectric signal compensation technology based on Moiré Fringe, we did theoretical study of the interference light field, diffraction light field, and the spatial filtering imaging of the diffraction gratings respectively. This has laid the theoretical foundation of this paper. Also, we proposed a design scheme of improving the quality of grating’s signal using optical methods. Moreover, we used sinusoidal gratings and rectangular gratings as an example, and the optical system for fabricating the sinusoidal gratings as well as the detection system for detecting the quality of sinusoidal gratings were designed and established in this experiment. Specifically, we designed the multiple beam interference gratings using Mach-Zehnder interference method, operated spatial filtering imaging processing to the rectangular gratings and the multiple beam interference gratings. Then the grating constant of each grating was examined before and after implementing the image processing of spatial filter. Besides, we selected the parallel light source and the point light source to irradiate the diffraction gratings vertically. By using the plane array CCD and liner array CCD, we did grating detection from three aspects: the image of fringe collected, the transmittance function and the spectrum.After studying of the diffraction gratings’ spatial filtering image processing experiment, we finally came to the conclusion: Firstly, the spatial filtering image processing method can effectively suppress the content of high harmonic and greatly enhance the sinusoidal property of gratings, due to which the quality of gratings’ signal is well improved. Secondly, the sinusoidal property of gratings has been improved as the frequency of the diffraction gratings increased gradually. This has proved that high grating frequency gratings can be fully responsible for the improvement of the precision of photoelectric encoder. Our research has laid a foundation for the experimental study of improving the precision of the encoders from the perspective of diffraction gratings.