Method and apparatus for differing focus between at least two dimensions
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United States of America Patent
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Mar 11, 2008
Grant Date -
Aug 17, 2006
app pub date -
Feb 16, 2005
filing date -
Feb 16, 2005
priority date (Note) -
Expired
status (Latency Note)
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Abstract
The present invention obtains a more optimal focus in at least two dimensions (such as axial and radial dimensions) by setting or keeping a focus in at least a first dimension (such as both axial and radial dimensions) and detecting and adjusting the focus in a second dimension (such as radial dimension) so that it can be brought to the same focal plane as the focus for the at least first dimension (such as both axial and radial dimension). An actuator lens assembly is used to continually adjust the focus for either primarily the first dimension or primarily the second dimension, using a feedback loop. In one embodiment of the present invention, certain photocell(s), (such as photocells E and F that are normally used for tracking) are compared to certain photocell(s), (such as photocells A and B and C and D) in order to derive a Radial Focus Error (RFE) signal, by observing radial spot size.
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