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.

Abstract: The present invention provides a system for causing an optical beam to impinge on a spot on an optical medium, while keeping an optical head apparatus in an essentially stationary position, such that it eliminates the need for a tracking function to move an optical head apparatus in order to direct an optical beam between tracks or to an location on the optical medium.

Abstract: The present invention is a numerical aperture device and method. According to an embodiment of the present invention, a beam from a light source is caused to contact a numerical aperture (NA) plate. The NA plate has a first and second surface. The first surface splits the beam into two twin rays and directs the twin beams into adjacent and oppositely oriented re-direction elements within the first surface of the NA plate. The two twin rays are directed in opposite directions from each other (and 90 degrees apart from each other) such that as they traverse a specific distance through an internal area of the NA plate before striking the second surface of the plate. As the twin beams leave the NA plate's second surface they converge together and meet at the location of the medium to produce a spot.