Focus error signal generation using a birefringent plate with confocal detection

A method for generating a focus error signal from a read light beam returning from an optical storage media comprising the steps of:

• focussing said read light beam;
• providing a birefringent plate through which said read light beam passes to create a first focal plane of a first polarization and a second focal of a second polarization;
• providing a pinhole in the path of said read light beam after said birefringent plate and in close proximity to said first and second focal planes;
• providing a polarizing beam splitter disposed in said path of said read light beam after said second focal plane, said polarizing beam splitter creating a first polarization beam and a second polarization beam from said read beam;
• providing a first optical detector in the path of said first polarization beam;
• providing a second optical detector in the path of said second polarization beam;
• and
• generating a focus error signal related to the difference between an output from said first optical detector and an output from said second optical detector.

A system for optical delivery and detection comprising:

• a laser source that emits a first light beam;
• an optical head that receives said first light beam;
• an optical lens within said optical head that focuses said first light beam on a location within a storage media;
• a data detector that receives said first light beam returning from said storage media and provides data signals;
• a tracking error detector that receives said first light beam returning from said storage media and provides a tracking error signal to said optical head;
• and
• a focus error signal generator that receives said first light beam returning from said optical storage media and provides a focus error signal to said optical head, said focus error signal generator including:
• a first optical lens disposed in the path of said first light beam;
• a birefringent plate disposed in the path of said first light beam after said first optical lens, said birefringent plate creating a first focal plane of a first polarization and a second focal plane of a second polarization from said first light beam;
• a pinhole disposed in the path of said first light beam after said birefringent plate and in close proximity to said first and second focal planes;
• a polarizing beam splitter disposed in the path of said first light beam after said second focal plane, said polarizing beam splitter creating a second light beam of first polarization and a third light beam of second polarization from said first light beam;
• a first optical detector disposed in the path of said second light beam;
• a second optical detector disposed in the path of said third light beam;
• and
• an electrical differencing circuit having a first input coupled to said first optical detector, a second input coupled to said second optical detector and an output.