Study Of Zone Plate Interferometer For Testing Optical Hyperboloid

Aspheric surface testing technology is a difficult problem, which restricts it to obtain the widespread development. In this paper, conventional testing methods were summarized. An interferometer was designed based on the schematic of zone-plate with a total optical path for testing aspheric surfaces. The zone-plate was Designed and manufactured. By testing a hyperboloid, of which radius of curvature R is 103.26mm and caliber D is 40mm, gathering the interference fringe by CCD and writing program based on Coordinate transformation stripe center method. The interference fringe was process testing.Compared with results of identical hyperboloid tested by Taylor-Hobson, the method is confirmed feasible and advanced.Aiming at the closed fringe patterns gathered by CCD, image pretreatment technology, Coordinate transformation stripe center method and Zernike interferogram fitting technology were investigated. Image pretreatment technology mainly includes image graying, image binarization, image subtraction, geometric correction, median filter, and morphological filter, etc. Through the pretreatment technology, a high accuracy two value image was obtained. Closed fringe patterns can be converted to open fringe patterns by transforming the interferogram from the Cartesian coordinate system to a polar coordinate system. The fringe center can be located by means of fringe thinning. The phase distribution for the original closed fringe pattern was obtained by Zernike fitting and coordinate transformation inversing from the polar coordinate system to the Cartesian coordinate system. According to the algorithms mentioned above, the computer program was written and the simulation analysis was performed. To the actual interferogram, measurements showed that the value of PV is 0.4036λand the value of the RMS is 0.06243λ. As well as the algorithm error of PV is approximatelyλ/50 and RMS is approximatelyλ/230.As the test light and reference light in the same optical path, the interference fringes cannot be affected from vibration and air effects, therefore, the zone plate interference method can be used in online testing. In the actual process of detection, for the same type of measured components, optical path and zone plate are fixed. Only need to put the measured object on the test position, the CCD will receive signal and computer will process. Test work is easy and it can attain the required test accuracy. As the zone plate was designed with a low cost,light path achieved simple and interferogram measured surface can be well reflected in the aspheric surface, so this method is applicable to the actual processing and detection. For production of aspheric surface components in mass, it has a high practical significance.