Y. Honguh et I. Hoshino, FOCUSING-ERROR DETECTION USING A MIXED-ABERRATION-GENERATING HOLOGRAPHIC OPTICAL-ELEMENT, JPN J A P 1, 31(2B), 1992, pp. 544-547
A new focus error detecting method for an optical disk drive has been
developed using a holographic optical element (HOE). The groove patter
n on the HOE was designed using the ray-tracing and least-squares-fitt
ing methods to attain a symmetric beam profile. It has been proven suc
cessfully that this method of focus error detection is insensitive to
wavelength fluctuations, objective lens shifts, and tracking grooves.