[OPTICAL REVIEW Vol. 8, No. 6 (2001) 463-468]
Pickup Lens Inspection on the 5th Order Aberration Using Shearing Interference by Grating with Curve Fitting Algorithm
Kazumasa TAKADA1,* and Masahiro NAKAJO2
1Production Engineering Laboratory, Matsushita Electric Industrial Co., Ltd., 2-7, Matsuba-cho, Kadoma, Osaka, 571-8502 Japan, 2Manufacturing Process Engineering Center, Corporate Production Engineering Division, Matsushita Electric Industrial Co., Ltd., 2-7, Matsuba-cho, Kadoma, Osaka, 571-8502 Japan
(Received March 28, 2001; Accepted July 26, 2001)
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.
Key words : digital versatile disc pickup lens inspection, reflective diffraction grating, shearing interference, spherical wavefront, curve fitting algorithm