Apparatus and method for compensating coma aberration

Claim 2

An optical pick-up apparatus comprising: a light source; an objective lens for converging a light beam emitted from said light source onto a spot on an optical disc; a beam splitter for separating said light beam emitted from said light source from a returning light reflected back from said optical disc; a detector for detecting said returning light separated from said light beam emitted from said light source; an optical compensating device for compensating coma aberration, said optical compensating device comprising a first optical compensating device having a convex aspherical surface represented by -αR 4 and a second optical compensating device having a concave aspherical surface represented by +αR 4 , wherein α is a fourth-order aspherical coefficient which represents a magnitude of the curve of said aspherical surfaces and R is a pupil radius of said aspherical surfaces, said optical compensating device being located on an optical path of said light beam emitted from said light source; and, a driver for moving at least one of said first and second optical compensating devices in a direction perpendicular to an optical axis of said light beam emitted from said light source so as to offset said coma aberration.

Claim 3

The optical pick-up apparatus according to claim 1, said first optical compensating device and said second optical compensating device are located at said optical path between said light source and said beam splitter.

Claim 4

The optical pick-up apparatus according to claim 2, said convex aspherical surface of said first optical compensating device is located at the side to which said light beam is emitted from said light source and said concave aspherical surface of said second optical compensating device is located at the side to which said light beam is emitted from said light source.

Claim 5

The optical pick-up apparatus according to claim 3, said first optical compensating device is located closer to said light source than said second optical compensating device.

Claim 6

An optical disc recording and/or reproducing apparatus comprising: a light source; an objective lens for converging a light beam emitted from said light source at one spot on an optical disc on an optical axis; a beam splitter for separating said light beam emitted from said light source from a returning light reflected back from said optical disc; a first detector for detecting said returning light separated from said light beam emitted from said light source; an optical compensating device for compensating coma aberration, said optical compensating device having a convex aspherical surface and a concave aspherical surface, said optical compensating device being located on an optical path of said light beam emitted from said light source, wherein each surface is described by an expression including a term having a pupil radius of the surface raised to the fourth power; a second detector for optically detecting a tilt of said optical disc and producing an output representative thereof; and a driver for moving said optical compensating device in a direction perpendicular to the optical axis of said light beam emitted from said light source in response to said output.

Claim 7

An optical disc recording and/or reproducing apparatus comprising: a light source; an objective lens for converging a light beam emitted from said light source at one spot on an optical disc on an optical axis; a beam splitter for separating said light beam emitted from said light source from a returning light reflected back from said optical disc; a first detector for detecting said returning light separated from said light beam emitted from said light source; an optical compensating device for compensating coma aberration, said optical compensating device having a convex aspherical surface and a concave aspherical surface, said optical compensating device being located on an optical path of said light beam emitted from said light source, wherein each surface is described by an expression including a term having a pupil radius of the surface raised to the fourth power; a second detector for optically detecting a tilt of said optical disc and producing an output representative thereof; and a driver for moving said optical compensating device in a direction perpendicular to the optical axis of said light beam emitted from said light source in response to said output.

Claim 8

The optical pick-up apparatus according to claim 5, further comprising a position detector for detecting a position of said optical compensating device in the direction perpendicular to the optical axis of said light beam emitted from said light source and producing a second output representative thereof, wherein said driver moves said optical compensating device in response to said second output.

Claim 9

An optical disc recording and/or reproducing apparatus comprising: a light source; an objective lens for converging a light beam emitted from said light source at one spot on an optical disc on an optical axis; a beam splitter for separating said light beam emitted from said light source from a returning light reflected back from the optical disc; a first detector for detecting said returning light separated from said light beam emitted from said light source; an optical compensating device for compensating coma aberration, said optical compensating device being located on an optical path of said light beam emitted from said light source, said optical compensating device comprising a first optical compensating device having a convex aspherical surface described by an expression including a term having a pupil radius of the convex aspherical surface raised to the fourth power and a second optical compensating device having a concave aspherical surface described by an expression including a term having a pupil radius of the concave aspherical surface raised to the fourth power; a second detector for optically detecting a tilt of said optical disc; and a driver for moving at least one of said optical compensating devices in a direction perpendicular to the optical axis of said light beam emitted from said light source based on an output signal of said second detector so as to offset said coma aberration generated by said tilt of said optical disc.

Claim 10

An optical disc recording and/or reproducing apparatus comprising: a light source; an objective lens for converging a light beam emitted from said light source at one spot on an optical disc on an optical axis; a beam splitter for separating said light beam emitted from said light source from a returning light reflected back from the optical disc; a first detector for detecting said returning light separated from said light beam emitted from said light source; an optical compensating device for compensating coma aberration, said optical compensating device being located on an optical path of said light beam emitted from said light source, said optical compensating device comprising a first optical compensating device having a convex aspherical surface described by an expression including a term having a pupil radius of the convex aspherical surface raised to the fourth power and a second optical compensating device having a concave aspherical surface described by an expression including a term having a pupil radius of the concave aspherical surface raised to the fourth power; a second detector for optically detecting a tilt of said optical disc; and a driver for moving at least one of said optical compensating devices in a direction perpendicular to the optical axis of said light beam emitted from said light source based on an output signal of said second detector so as to offset said coma aberration generated by said tilt of said optical disc.

Claim 11

The optical pick-up apparatus according to claim 7, said first optical compensating device and said second optical compensating device are located at said optical path between said light source and said beam splitter.

Claim 12

The optical pick-up apparatus according to claim 8, said convex aspherical surface of said first optical compensating device is located between said light source and a beam splitter for separating said light beam emitted from said light source from a returning light reflected back from said optical disc and said concave aspherical surface of said second optical compensating device is located between said light source and a beam splitter for separating said light beam emitted from said light source from a returning light reflected back from said optical disc.

Claim 13

The optical pick-up apparatus according to claim 7, further comprising a position detector for detecting a position of said optical compensating device in the direction perpendicular to the optical axis of said light beam emitted from said light source, wherein said driver moves said optical compensating device based on said output signal from said second detector and on an output signal from said position detector.

Claim 16

The method for compensating coma aberration according to claim 11, wherein said first and second optical compensating devices are located between said light source and a beam splitter for separating said light beam emitted from said light source from a returning light reflected back from said optical disc.

Claim 17

An optical pick-up apparatus comprising: a light source; an objective lens for converging a light beam emitted from said light source onto a spot on an optical disc; a beam splitter for separating said light beam emitted from said light source from a returning light reflected back from the optical disc; a detector for detecting said returning light separated from said light beam emitted from said light source; and an optical compensating device for compensating coma aberration, said optical compensating device being located on optical path of said light beam emitted from said light source, said optical compensating device comprising a first optical compensating device having a convex aspherical surface described by an expression including a term having a pupil radius of the convex aspherical surface raised to the fourth power and a second optical compensating device having a concave aspherical surface described by an expression including a term having a pupil radius of the concave aspherical surface raised to the fourth power; and, a driver for moving at least one of said first and second optical compensating devices in a direction perpendicular to an optical axis of said light beam emitted from said light source so as to offset said coma aberration.

Claim 18

An optical pick-up apparatus comprising: a light source; an objective lens for converging a light beam emitted from said light source onto a spot on an optical disc; a beam splitter for separating said light beam emitted from said light source from a returning light reflected back from the optical disc; a detector for detecting said returning light separated from said light beam emitted from said light source; and an optical compensating device for compensating coma aberration, said optical compensating device being located on optical path of said light beam emitted from said light source, said optical compensating device comprising a first optical compensating device having a convex aspherical surface described by an expression including a term having a pupil radius of the convex aspherical surface raised to the fourth power and a second optical compensating device having a concave aspherical surface described by an expression including a term having a pupil radius of the concave aspherical surface raised to the fourth power; and, a driver for moving at least one of said first and second optical compensating devices in a direction perpendicular to an optical axis of said light beam emitted from said light source so as to offset said coma aberration.

Claim 19

The optical pick-up apparatus according to claim 13, wherein said driver move said first and second optical compensating device in opposite directions.