PROCEEDINGS ARTICLE | June 26, 2017
Proc. SPIE. 10329, Optical Measurement Systems for Industrial Inspection X
KEYWORDS: Mathematical modeling, Optical imaging, Light sources, Metrology, Data modeling, Imaging systems, Interferometers, Calibration, Error analysis, Geometrical optics, Freeform optics, Spherical lenses, Systems modeling
Smaller and lighter optical systems with better performance can be built by the use of freeform optics.
However, most optical systems were constrained to traditional surfaces for the accurate metrology of
freeform surface is a challenge so far unsolved. One high-precision approach to measure freeform
surface with less time and expense is using tilted wave interferometer. A lens array is placed in the test
path of the interferometer, which can generate light source array that locally compensate the gradient of
test surface. But each source generated by lens array is not ideal spherical wave which contains
aberrations. In addition, the sources cannot be activated individually during the measurement, so that it
is impossible to perform an irregular source array according to the gradient variation of each test
surface. Thus, a novel technique based on fiber array is proposed for generating irregular source array.
Whereas, the position deviation of each fiber and phase difference produced by the length of each fiber
affect the measurement result. In this paper, the consequences of above errors are analyzed. A
calibration method can obtain the exact spatial coordinates of each fiber is suggested to calculate the
position deviation of each fiber. Meanwhile, a method based on Mach-Zehnder interference system is
presented, which can get phase difference produced by the length of each fiber accurately. Afterwards,
the data obtained by the two calibration methods are introduced into the mathematical model of system
error for eliminating the measurement error introduced by the use of fiber array. An elliptical mirror is
measured by our tilted wave interferometer based on fiber array showing the feasibility of the proposed
methods.
