Abstract

Most focus sensing schemes rely on an array of optical detector elements placed in a beam of light reflected from the recording medium so that redistribution of optical power on the detector elements should sensitively and accurately indicate the state of focus of the spot. However, small changes in the spatial distribution of optical power on these detectors, caused for example by beam motion, diffraction, or partial obscuration, may cause relatively large inaccuracies in the focus error signal. I will refer to these effects collectively as "pattern noise", by which I mean all spurious local redistributions in optical power in a light beam used to generate optical error signals.

© 1991 Optical Society of America