Focus detection system for an optical disk drive using photo sensor elements in the far field of information pits

Claim 1

An apparatus for reproducing an information signal optically from the track shaped information structure on a record carrier, said apparatus comprising: objective means for reading said information structure on said record carrier; photo sensor means divided to first through fourth elements aligned sequentially in the direction of an image of said track in a far field for converting said light beam diffracted by said information structure to electric signals, said first element and said second element being disposed in a half area of said far field image divided by a plane including an optical axis of said objective means, said third element and said fourth element being disposed in another half area of said far field image; and phase detection means for deriving a focus error signal by detecting phase differences among outputs from said first through fourth elements.

Claim 2

An apparatus for reproducing an information signal optically from the track shaped information structure on a record carrier, said apparatus comprising: objective means for reading said information structure on said record carrier; photo sensor means divided to first through fourth elements aligned sequentially in the direction of an image of said track in a far field for converting said light beam diffracted by said information structure to electric signals, said first element and said second element being disposed in a half area of said far field image divided by a plane including an optical axis of said objective means, said third element and said fourth element being disposed in another half area of said far field image; and phase detection means for deriving a focus error signal by detecting phase differences among outputs from said first through fourth elements.

Claim 3

An apparatus for reproducing an information signal optically from a track shaped information structure on a record carrier, said apparatus comprising: radiation source means for emitting a light beam; objective lens for focusing said light beam on said information structure; photo sensor means divided to first through fourth elements aligned sequentially in the direction of an image of said track in a far field for converting said light beam diffracted by said information structure to electric signals, said first element and said second element being disposed in a half area of said far field image divided by a plane including an optical axis of said objective means, said third element and said fourth element being disposed in another half area of said far field image; first phase detection means for deriving a phase detection signal between outputs of said first element and said second element; second phase defection means for deriving a phase detection signal between outputs of said third element and said fourth element; and adder means for adding outputs from said first and second phase detection means to obtain a focusing error signal.

Claim 4

An apparatus for reproducing an information signal optically from a track shaped information structure on a record carrier, said apparatus comprising: radiation source means for emitting a light beam; objective lens for focusing said light beam on said information structure; photo sensor means divided to first through fourth elements aligned sequentially in the direction of an image of said track in a far field for converting said light beam diffracted by said information structure to electric signals, said first element and said second element being disposed in a half area of said far field image divided by a plane including an optical axis of said objective means, said third element and said fourth element being disposed in another half area of said far field image; first phase detection means for deriving a phase detection signal between outputs of said first element and said second element; second phase defection means for deriving a phase detection signal between outputs of said third element and said fourth element; and adder means for adding outputs from said first and second phase detection means to obtain a focusing error signal.

Claim 6

An apparatus for reproducing an information signal optically from a track shaped information structure on a record carrier, said apparatus comprising: radiation source means for emitting a light beam; objective lens for focusing said light beam on said information structure; photo sensor means divided to first through fourth elements in the direction of a far field image of said track for converting said light beam diffracted by said information structure to electric signals; first phase detection means for deriving a phase difference signal between outputs from said first and fourth photo sensor elements; second phase detection means for deriving a phase difference signal between outputs from said second and third photo sensor elements; first amplifier means for amplifying said phase detection signal from said first phase detection means with a proper gain; second amplifier means for amplifying said phase detection signal from said second phase detection means with a proper gain different from the gain of said first amplifier means; and adder means for adding electrically two electric signals from said first and second amplifier means to obtain a focusing error signal.

Claim 7

An apparatus for reproducing an information signal optically from a track shaped information structure on a record carrier, said apparatus comprising: radiation source means for emitting a light beam; objective lens for focusing said light beam on said information structure; photo sensor means divided to first through fourth elements in the direction of a far field image of said track for converting said light beam diffracted by said information structure to electric signals; first phase detection means for deriving a phase difference signal between outputs from said first and fourth photo sensor elements; second phase detection means for deriving a phase difference signal between outputs from said second and third photo sensor elements; first amplifier means for amplifying said phase detection signal from said first phase detection means with a proper gain; second amplifier means for amplifying said phase detection signal from said second phase detection means with a proper gain different from the gain of said first amplifier means; and adder means for adding electrically two electric signals from said first and second amplifier means to obtain a focusing error signal.

Claim 10

An apparatus for reproducing an information signal optically from a track shaped information structure on a record carrier, said apparatus comprising: radiation source means for emitting a light beam; an objective lens for focusing said light beam on said information structure; photo sensor means divided to first through fourth elements sequentially in the direction of a far field image of said track for converting said light beam diffracted by said information structure to electric signals, an output of said first element and an output of said third element being added substantially, an output of said second element and an output of said fourth element being added substantially; and phase detection means for deriving a phase difference signal between said added outputs from said first and third elements and said added outputs from second and fourth elements to obtain a focus error signal.

Claim 11

An apparatus for reproducing an information signal optically from a track shaped information structure on a record carrier, said apparatus comprising: radiation source means for emitting a light beam; an objective lens for focusing said light beam on said information structure; photo sensor means divided to first through fourth elements sequentially in the direction of a far field image of said track for converting said light beam diffracted by said information structure to electric signals, an output of said first element and an output of said third element being added substantially, an output of said second element and an output of said fourth element being added substantially; and phase detection means for deriving a phase difference signal between said added outputs from said first and third elements and said added outputs from second and fourth elements to obtain a focus error signal.