Optical apparatus and method for detecting the focusing state and positional accuracy of a light beam directed onto an optical disk tracking guide in an optical read/write system

Claim 2

An optical system for controlling a light beam which is directed onto a light reflecting surface having a tracking guide, comprising: means for generating a light beam; objective lens means for converging said light beam into a converged light beam having a beam waist, and for directing said converged light beam onto said light reflecting surface to produce a beam spot on said tracking guide, said objective lens means being in focus when said beam spot is equal in size to said beam waist and being out of focus when said beam spot is larger than said beam waist, and for directing light reflected from said light reflecting surface, said directed light having a beam spot image and diffraction patterns which result from light reflected from said tracking guide; means for transferring and deflecting said directed light; astigmation lens means for reconverging said directed light received from said transferring and deflecting means; and photodetecting means for receiving the reconverged light and detecting the focus and tracking state of said converged light beam on said tracking guide, said photodetecting means being positioned substantially on a plane where the beam spot image in said reconverged light is in focus, said photodetecting means including an arrangement having first, second, third, and fourth photosensitive regions disposed to cause: (1) the beam spot image in said reconverged light to fall substantially onto the center of said arrangement when said converged light beam is in focus on said tracking guide, (2) said reconverged light beam spot to fall predominantly into at least one of said photosensitive regions when said converged light beam is out of focus, (3) the diffraction patterns in said reconverged light to fall on said photodetecting means substantially in the center of said reconverged light beam spot when said converged light beam is properly tracking said tracking guide, and (4) said reconverged light diffraction patterns to fall off center in said reconverged light beam spot when said converged light beam is not properly tracking said tracking guide.

Claim 3

An optical system according to claim 1, wherein said astigmation lens means includes a cylindrical lens and a convex lens.

Claim 4

An optical system according to claim 2, wherein said cylindrical lens is a convex cylindrical lens.

Claim 5

An optical system according to claim 3, wherein said astigmation lens means has a long and a short focal point, and wherein said photodetecting means is substantially located at said long focal point.

Claim 6

An optical system according to claim 2, wherein said cylindrical lens is a concave cylindrical lens.

Claim 7

An optical system according to claim 5, wherein said astigmation lens means has a long and a short focal point, and wherein said photodecting means is substantially located at said short focal point.

Claim 8

An optical system according to claim 1, wherein said light beam generating means generates laser beams.

Claim 9

An optical system according to claim 1, wherein said objective lens means has an optical axis perpendicular to said light-reflecting surface.

Claim 10

An optical system according to claim 1, wherein said transferring means receives and converts said light beam into a plurality of parallel light beams and transfers the parallel light beams to said objective lens means.

Claim 11

An optical system according to claim 1, wherein said light-reflecting surface includes a light-reflecting layer of an optical disk.

Claim 12

An optical system according to claim 1, wherein said objective lens means has an optical axis and wherein said transferring and deflecting means includes a convex lens having an optical axis which intersects with the optical axis of said objective lens means.

Claim 13

An optical system according to claim 1, wherein said astigmation means includes a cylindrical lens having a base line arranged in parallel with the direction in which said tracking guide extends, and a convex lens located on an optical axis on which said cylindrical lens is located.

Claim 14

An optical system according to claim 12, wherein said astigmation lens means has a long and a short focal point, said cylindrical lens is a convex cylindrical lens and said photodetector means is located at said long focal point.

Claim 15

An optical system according to claim 12, wherein said directed light has a beam path with an optical axis and wherein said transferring and deflecting means includes a light-shielding plate which transmits only part of said directed light passing through said beam path in a region apart from said optical axis.

Claim 16

An optical system according to claim 12, wherein said directed light has a beam path with an optical axis and wherein said cylindrical lens is so located as to converge only part of said directed light passing along said beam path in a region spaced from said optical axis.

Claim 17

An optical system according to claim 1, further including means for moving said beam waist in a direction which traverses said tracking guide so that said diffraction patterns in said reconverged light are made to fall on said center of said reconverged light beam spot on said photodetecting means.

Claim 18

An optical system according to claim 16, wherein the direction in which said beam waist is moved is substantially perpendicular to a direction in which said tracking guide extends.

Claim 19

An optical system according to claim 1, wherein said transferring and deflecting means includes a prism arranged between said astigmation lens means and said photodetecting means.

Claim 20

An optical system according to claim 1, the four photosensitive regions are arranged in a diamond shape, and wherein said photodetecting means produces a track focusing signal corresponding to a difference between a sum of signals produced by mutually adjacent photosensitive regions.

Claim 21

An optical head according to claim 1, wherein said four photosensitive regions are arranged so that when said converged light beam is out of focus, said reconverged light beam spot falls in one of said third and fourth photosensitive regions.

Claim 22

An optical system according to claim 20, wherein said photodetecting means includes a photoinsensitive region which can not substantially detect the presence of light rays and which is formed between adjacent photosensitive regions.

Claim 23

The system according to claim 21, wherein said photoinsensitive region includes a light-shielding layer to shield light rays.

Claim 24

The system according to claim 22, wherein said light-shielding layer is an alumina layer.

Claim 25

The system according to claim 21, wherein said photodetecting means includes a semiconductor photodetector, and wherein said photoinsensitive region includes a recess region formed in said semicondcutor photodetector.

Claim 26

The system according to claim 21, wherein said photodetecting means is formed on a semiconductor substrate, and wherein each photoinsensitive region includes an impurity region having a conductivity type which is the same as the conductivity type of said substrate but has a higher impurity density than that of said substrate.

Claim 27

The system according to claim 21, wherein said reconverged light beam spot has a width and wherein a width of said photoinsensitive region is equal to a quarter or more of the width of said reconverged light beam spot, the width of said reconverged light beam spot being defined as the width of a region on said photodetecting means in which a light intensity of said reconverged light beam spot has a maximum equal to 1/e 2 .

Claim 28

The system according to claim 26, wherein the width of said photoinsensitive region is equal to from 1/3 to 3 times the width of said reconverged light beam spot.

Claim 29

An optical system according to claim 1, wherein said objective lens means and said astigmation lens means have a common axis and said transferring and deflecting means includes a light-shielding plate arranged on said common axis to transmit only that part of said directed light which is spaced apart from said common axis.

Claim 30

An optical system according to claim 28, wherein said light-shielding plate includes an aperture.

Claim 31

An optical system according to claim 28, wherein said light-shielding plate includes a slit.

Claim 32

An optical system according to claim 28, wherein said light-shielding plate includes a knife edge.

Claim 33

An optical system according to claim 1, wherein said transferring and deflecting means includes a mirror arranged between said astigmation lens means and said photodetecting means.

Claim 34

Apparatus for controlling the focusing and positional accuracy of a light beam incident on a light reflecting surface having a tracking guide, comprising: means for (a) converging said light beam; (b) directing the converged light beam onto said light reflecting surface to form a beam spot thereon, and (c) forming a reflected light beam from light reflected from said light reflecting surface, said reflected light beam having an axis and including an image of said beam spot which includes diffraction patterns caused by light reflected from said tracking guide; means for partially blocking said reflected light beam so as to allow passage of only a portion of said reflected light beam which is off of said axis; means for astigmating said portion of said reflected light beam so that said beam spot image becomes elongated; means for (a) receiving the astigmated portion of said reflected light beam on a photosensitive surface which is positioned so that said elongated beam spot image is in focus on said photosensitive surface, (b) detecting the focusing state of said converged light beam, said converged light beam being in focus when said elongated beam spot image is substantially in the center of said photosensitive surface, and (c) determining the positional accuracy of said beam spot on said tracking guide, said beam spot being accurately positioned on said tracking guide when the diffraction patterns are located substantially in the center of said elongated beam spot image on said photosensitive surface; and means for controlling said converging, directing and forming means so as to place said converged light beam in focus and to accurately position said beam spot on said tracking guide.

Claim 35

Apparatus for controlling the focusing and positional accuracy of a light beam incident on a light reflecting surface having a tracking guide, comprising: means for (a) converging said light beam; (b) directing the converged light beam onto said light reflecting surface to form a beam spot thereon, and (c) forming a reflected light beam from light reflected from said light reflecting surface, said reflected light beam having an axis and including an image of said beam spot which includes diffraction patterns caused by light reflected from said tracking guide; means for partially blocking said reflected light beam so as to allow passage of only a portion of said reflected light beam which is off of said axis; means for astigmating said portion of said reflected light beam so that said beam spot image becomes elongated; means for (a) receiving the astigmated portion of said reflected light beam on a photosensitive surface which is positioned so that said elongated beam spot image is in focus on said photosensitive surface, (b) detecting the focusing state of said converged light beam, said converged light beam being in focus when said elongated beam spot image is substantially in the center of said photosensitive surface, and (c) determining the positional accuracy of said beam spot on said tracking guide, said beam spot being accurately positioned on said tracking guide when the diffraction patterns are located substantially in the center of said elongated beam spot image on said photosensitive surface; and means for controlling said converging, directing and forming means so as to place said converged light beam in focus and to accurately position said beam spot on said tracking guide.

Claim 36

Apparatus according to claim 33 wherein said astigmating means includes a cylindrical lens.

Claim 39

An optical system for controlling a light beam which is directed onto a light reflecting surface having a tracking guide, comprising: means for generating a light beam; objective lens means for converging said light beam into a converged light beam having a beam waist, and for directing said converged light beam onto said light reflecting surface to produce a beam spot on said tracking guide, said objective lens means being in focus when said beam spot is equal in size to said beam waist and being out of focus when said beam spot is larger than said beam waist, and for directing light reflected from said light reflecting surface, said directed light having an optical path and containing a beam spot image with diffraction patterns which are caused by light reflected from said tracking guide; astigmation means, positioned in said directed light optical path to cause a first portion of said directed light to pass through said astigmation means while a second portion of said directed light bypasses said astigmation means, for refracting said first portion to produce refracted light; projection lens means for reconverging said refracted light and said second portion of said directed light; and photodetecting means for receiving the reconverged light and detecting the focus and tracking state of said converged light beam on said tracking guide, said photodetecting means including four photosensitive regions disposed in a square and separated by first and second transverse boundaries to cause: (1) said refracted light and said second portion of said directed light to fall substantially on the intersection of said boundaries when said converged beam is in focus on said tracking guide, (2) said refracted light and said second portion to fall predominantly on opposite sides of said first boundary when said converged light beam is out of focus, (3) said diffraction patterns to fall symmetrically with respect to said second boundary when said converged light beam is properly tracking said tracking guide, and (4) said diffraction patterns to fall assymmetrically with respect to said second boundary when said tracking is improper.

Claim 40

An optical system for controlling a light beam which is directed onto a light reflecting surface having a tracking guide, comprising: means for generating a light beam; objective lens means for converging said light beam into a converged light beam having a beam waist, and for directing said converged light beam onto said light reflecting surface to produce a beam spot on said tracking guide, said objective lens means being in focus when said beam spot is equal in size to said beam waist and being out of focus when said beam spot is larger than said beam waist, and for directing light reflected from said light reflecting surface, said directed light having an optical path and containing a beam spot image with diffraction patterns which are caused by light reflected from said tracking guide; astigmation means, positioned in said directed light optical path to cause a first portion of said directed light to pass through said astigmation means while a second portion of said directed light bypasses said astigmation means, for refracting said first portion to produce refracted light; projection lens means for reconverging said refracted light and said second portion of said directed light; and photodetecting means for receiving the reconverged light and detecting the focus and tracking state of said converged light beam on said tracking guide, said photodetecting means including four photosensitive regions disposed in a square and separated by first and second transverse boundaries to cause: (1) said refracted light and said second portion of said directed light to fall substantially on the intersection of said boundaries when said converged beam is in focus on said tracking guide, (2) said refracted light and said second portion to fall predominantly on opposite sides of said first boundary when said converged light beam is out of focus, (3) said diffraction patterns to fall symmetrically with respect to said second boundary when said converged light beam is properly tracking said tracking guide, and (4) said diffraction patterns to fall assymmetrically with respect to said second boundary when said tracking is improper.

Claim 41

An optical system according to claim 36 wherein said astigmation means includes a cylindrical lens.