Pickup lens inspection on the 5th order aberration using shearing interference by grating with curve fitting algorithm |
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Authors: | Kazumasa Takada Masahiro Nakajo |
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Institution: | (1) Production Engineering Laboratory, Matsushita Electric Industrial Co., Ltd., 2-7, Matsuba-cho, 571-8502 Kadoma, Osaka, Japan;(2) Manufacturing Process Engineering Center, Corporate Production Engineering Division, Matsushita Electric Industrial Co., Ltd., 2-7, Matsuba-cho, 571-8502 Kadoma, Osaka, Japan |
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Abstract: | An optical system based on shearing interference using diffraction grating was applied, to carry out the aberration inspection
process of the pickup lens of a digital versatile disc (DVD) at high speed. An algorithm was devised that processes points
allocated on certain lines on a fringe and fits relations between the distance from basis point to the measurement points,
and phase data of the fringe at these points to an equation of higher degree as curve fitting. Aberration was numerically
estimated as the size of a certain coefficient. Simulation showed that this algorithm could detect all 5th order aberrations
independently. An inspection system developed based on this optical system and algorithm detected aberration as accurately
as a conventional interferometer that has been used as the standard, attaining an inspection time of 1/10-1/20. In comparison
with the spot method, this system has 5th order aberration detecting ability and 1/3 the inspection time. |
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Keywords: | digital versatile disc pickup lens inspection reflective diffraction grating shearing interference spherical wavefront curve fitting algorithm |
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