Apparatus and method for a modified half-aperture focus/tracking/data sensor system

A method for detecting a resulting radiation beam from a data track of a storage medium of an optical information storage and retrieval systems to provide tracking signals, focusing signals, and data signals;

• said method including the steps of:
• dividing said resulting radiation beam into a first and a second resulting radiation beam components with a prism, a division between said first and said second resulting radiation beam components being perpendicular to a projection of said data track on said prism;
• focusing said first resulting radiation beam component on a first four-quadrant sensor;
• focusing said second resulting radiation beam component on a second four-quadrant sensor;
• providing an astigmatism for defocusing said first and second radiation beam components in a direction perpendicular to said projection of said data track;
• and
• coupling output signals from elements of said first and said second four-quadrant sensors to provide a tracking signal, a focusing signal, and a data signal.

A radiation sensor system responsive to a resulting radiation beam which has interacted with a data track in an optical storage and retrieval systems for providing tracking signals, focusing signals and data signals, said sensor system comprising:

• optical means responsive to said resulting radiation beam for providing a first and a second resulting radiation beam components, said first and said second resulting radiation beam components being separated by a division perpendicular to a projection of said data track of said optical storage and retrieval systems on said optical means;
• a focusing element for receiving said first and second resulting radiation beam components transmitted by said optical means;
• a first four-quadrant sensor, wherein said focusing element focuses said first resulting radiation beam component thereon;
• a second four-quadrant sensor, wherein said focusing element focuses said second resulting radiation beam component thereon, first selected sensor elements of said first and said second four-quadrant sensors being coupled to provide a tracking signal, second selected sensor elements of said first and said second four-quadrant sensors being coupled to provide a focusing signal, third selected sensor elements of said first and said second four-quadrant sensors being coupled to provide a data signal;
• and
• astigmatic means for defocusing said first and said second resulting radiation beam components in a direction perpendicular to said projection of said data track.