FOCUSING-ERROR DETECTION USING A MIXED-ABERRATION-GENERATING HOLOGRAPHIC OPTICAL-ELEMENT

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.