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Patent US6917454 - Holographic optical element, position shift detecting apparatus, optical ... - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsIn a holographic pattern provided in a holographic optical element, a pattern 1 a twists a diffracted light beam in a clockwise direction, to form a semi-circular light spot Sa on photodetection parts A and B so as to extend over a dividing line LX in a four-segment photodetection part. A pattern 1 b...http://www.google.com/patents/US6917454?utm_source=gb-gplus-sharePatent US6917454 - Holographic optical element, position shift detecting apparatus, optical pickup apparatus, optical recording medium drive and method of fabricating holographic optical elementAdvanced Patent SearchPublication numberUS6917454 B2Publication typeGrantApplication numberUS 10/237,170Publication dateJul 12, 2005Filing dateSep 9, 2002Priority dateSep 7, 2001Fee statusPaidAlso published asUS7113316, US20030067640, US20050174619Publication number10237170, 237170, US 6917454 B2, US 6917454B2, US-B2-6917454, US6917454 B2, US6917454B2InventorsKazushi Mori, Mitsuaki Matsumoto, Koji Tominaga, Atsushi Tajiri, Minoru SawadaOriginal AssigneeSanyo Electric Co., Ltd.Export CitationBiBTeX, EndNote, RefManPatent Citations (10), Non-Patent Citations (6), Referenced by (1), Classifications (24), Legal Events (3) External Links: USPTO, USPTO Assignment, EspacenetHolographic optical element, position shift detecting apparatus, optical pickup apparatus, optical recording medium drive and method of fabricating holographic optical elementUS 6917454 B2Abstract In a holographic pattern provided in a holographic optical element, a pattern 1 a twists a diffracted light beam in a clockwise direction, to form a semi-circular light spot Sa on photodetection parts A and B so as to extend over a dividing line LX in a four-segment photodetection part. A pattern 1 b similarly twists the diffracted light beam in a clockwise direction, to form a semi-circular light spot Sb on photodetection parts C and D so as to extend over a dividing line LX in the four-segment photodetection part.
a diffraction surface that diffracts an incident light beam, said diffraction surface having in at least its part a holographic pattern having a function of twisting said diffracted light beam using an optical axis of the diffracted light beam as an axis of rotation; wherein said diffraction surface is divided into a first region and a second region, at least one of said first and second regions having said holographic pattern; wherein said first region has a first holographic pattern having the function of twisting said diffracted light beam in a clockwise direction using the optical axis of the diffracted light beam as an axis of rotation, and said second region has a second holographic pattern having the function of twisting said diffracted light beam in a counterclockwise direction using the optical axis of the diffracted light beam as an axis of rotation. 2. The holographic optical element according to claim 1, wherein
when said diffraction surface is defined by XY-coordinates comprising the X-axis and the Y-axis which are orthogonal to each other, and letting (X0, Y0) be a point to be a basis on said diffraction surface, (X, Y) be an arbitrary point on said diffraction surface, f (X, Y) be an X-direction component of a grating vector for performing predetermined diffraction at the point (X, Y) on said diffraction surface, and g (X, Y) be a Y-direction component of said grating vector, said holographic pattern is represented by a set of points (X′, Y′) satisfying the following equation: ∫ X 0 X ′ ⁢ f ⁡ ( X , Y 0 ) ⁢ ⅆ X + ∫ Y 0 Y ′ ⁢ g ⁡ ( X ′ , Y ) ⁢ ⅆ Y = 2 ⁢ ⁢ π ⁢ ⁢ M + C ⁢ ⁢ or ( 19 ) ∫ Y 0 Y ′ ⁢ g ⁡ ( X 0 , Y ) ⁢ ⅆ Y + ∫ X 0 X ′ ⁢ f ⁡ ( X , Y ′ ) ⁢ ⅆ X = 2 ⁢ ⁢ π ⁢ ⁢ M + C , ( 20 ) where M is an integer and C is a constant; when a Z-axis coordinate perpendicular to said diffraction surface is defined at the origin of said XY-coordinates, and letting (X, Y, 0) be an arbitrary point on said diffraction surface, (Xp(X, Y), Yp(X, Y), Zp) be a point on a predetermined detection surface on which a diffracted light beam diffracted by said diffraction surface impinges, (Xr, Yr, Zr) be the coordinates of a light emitting point of a light source for emitting a light beam to said diffraction surface, λ be the wavelength of the light beam, and n be the refractive index of a substrate including said holographic pattern, the X-direction component f (X, Y) and the Y-direction component g (X, Y) of the grating vector for performing predetermined diffraction at the point (X, Y, 0) on said diffraction surface are respectively set so as to satisfy the following equations: f ⁡ ( X , Y ) = ⁢ - ( 2 ⁢ π / λ ) � [ ( X - Xp ⁡ ( X , Y ) ) � ⁢ { ( X - Xp ⁡ ( X , Y ) ) 2 + ( Y - Yp ⁡ ( X , Y ) ) 2 + Zp 2 } - 1 / 2 - ⁢ n ⁢ ( X - Xr ) � { ( X - Xr ) 2 + ( Y - Yr ) 2 + Zr 2 } - 1 / 2 ] ( 16 ) g ⁡ ( X , Y ) = ⁢ - ( 2 ⁢ π / λ ) � [ ( Y - Yp ⁡ ( X , Y ) ) � { ( X - Xp ⁡ ( X , Y ) ) 2 + ⁢ ( Y - Yp ⁡ ( X , Y ) ) 2 + Zp 2 } - 1 / 2 - ⁢ n ⁢ ( Y - Yr ) � { ( X - Xr ) 2 + ( Y - Yr ) 2 + Zr 2 } - 1 / 2 ] when the ratio of the size of a light spot on said detection surface to the size of a light spot on said diffraction surface is taken as a reduction ratio R, a point (Xp, Yp) on said detection surface obtained by moving the light beam impinging on the arbitraiy point (X, Y) on said diffraction surface by x1 in the X-axis direction and moving the light beam by y1 in the Y-axis direction, and rotating the light beam by an angle of β centered at a point (x1, y1) is set so as to satisfy the following equations: Xp(X,Y)=R(X 2 +Y 2)1/2 cos[arctan(Y/X)+β]+x 1 (21) Yp(X,Y)=R(X 2 +Y 2)1/2 sin[arctan(Y/X)+β]+y 1 (22). 3. A method of fabricating a holographic optical element comprising a diffraction surface having in at least its part a holographic pattern for diffracting an incident light beam, comprising:
the step of representing, when said diffraction surface is defined by XY-coordinates comprising the X-axis and the Y-axis which are orthogonal to each other, and letting (X0, Y0) be a point to be a basis on said diffraction surface, (X, Y) be an arbitrary point on said diffraction surface, f(X, Y) be an X-direction component of a grating vector for performing predetermined diffraction at the point (X, Y) on said diffraction surface, and g (X, Y) be a Y-direction component of said grating vector, said holographic pattern by a set of points (X′, Y′) satisfying the following equation: ∫ X 0 X ′ ⁢ f ⁡ ( X , Y 0 ) ⁢ ⅆ X + ∫ Y 0 Y ′ ⁢ g ⁡ ( X ′ , Y ) ⁢ ⅆ Y = 2 ⁢ ⁢ π ⁢ ⁢ M + C ⁢ ⁢ or ( 19 ) ∫ Y 0 Y ′ ⁢ g ⁡ ( X 0 , Y ) ⁢ ⅆ Y + ∫ X 0 X ′ ⁢ f ⁡ ( X , Y ′ ) ⁢ ⅆ X = 2 ⁢ ⁢ π ⁢ ⁢ M + C , ( 20 ) where M is an integer and C is a constant; setting, when a Z-axis coordinate perpendicular to said diffraction surface is defined at the origin of said XY-coordinates, and letting (X, Y, 0) be an arbitrary point on said diffraction surface, (Xp(X, Y), Yp(X, Y), Zp) be a point on a predetermined detection surface on which a diffracted light beam diffracted by said diffraction surface impinges, (Xr, Yr, Zr) be the coordinates of a luminescent point of a light source for emitting a light beam to said diffraction surface, λ be the wavelength of the light beam, and n be the refractive index of a substrate including said holographic pattern, the X-direction component f(X, Y) and the Y-direction component g (X, Y) of the grating vector for performing predetermined diffraction at the point (X, Y, 0) on said diffraction surface, respectively, so as to satisfy the following equations: f ⁡ ( X , Y ) = ⁢ - ( 2 ⁢ π / λ ) � [ ( X - Xp ⁡ ( X , Y ) ) � ⁢ { ( X - Xp ⁡ ( X , Y ) ) 2 + ( Y - Yp ⁡ ( X , Y ) ) 2 + Zp 2 } - 1 / 2 - ⁢ n ⁢ ( X - Xr ) � { ( X - Xr ) 2 + ( Y - Yr ) 2 + Zr 2 } - 1 / 2 ] ( 16 ) g ⁡ ( X , Y ) = ⁢ - ( 2 ⁢ π / λ ) � [ ( Y - Yp ⁡ ( X , Y ) ) � { ( X - Xp ⁡ ( X , Y ) ) 2 + ⁢ ( Y - Yp ⁡ ( X , Y ) ) 2 + Zp 2 } - 1 / 2 - ⁢ n ⁢ ( Y - Yr ) � { ( X - Xr ) 2 + ( Y - Yr ) 2 + Zr 2 } - 1 / 2 ] ; ( 17 ) and
the step of forming said holographic pattern set by said equations (16), (17), (19), and (20) on said diffraction surface by a photolithographic process and an etching process. 4. The method according to claim 3, comprising the step of
setting, when the ratio of the size of a light spot on said detection surface to the size of a light spot on said diffraction surface is taken as a reduction ratio R, and such diffraction that the light beam impinging on the arbitrary point (X, Y) on said diffraction surface is moved by x1 in the X-axis direction and by y1 in the Y-axis direction, and is rotated through an angle of β centered at a point (x1, y1) is performed, said holographic pattern such that a point (Xp, Yp) on said detection surface obtained by the diffraction satisfies the following equations: Xp(X,Y)=R(X 2 +Y 2)1/2 cos[arctan(Y/X)+β]+x 1 (21) Yp(X,Y)=R(X 2 +Y 2)1/2 sin[arctan(Y/X)+β]+y 1 (22). 5. The method according to claim 3, comprising the step of
setting, when the ratio of the size of a light spot on said detection surface to the size of a light spot on said diffraction surface is taken as a reduction ratio R, and such diffraction that the light beam impinging on the arbitrary point (X, Y) on said diffraction surface is moved by x1 in the X-axis direction and by y1 in the Y-axis direction, is inverted with respect to a straight line parallel to the X-axis passing through the point (x1, y1), and is further rotated through an angle of 2α. centered at the point (x1, y1) is performed, said holographic pattern such that a point (Xp, Yp) on said detection surface obtained by the diffraction satisfies the following equations: Xp(X,Y)=R(X cos 2α+Y sin 2α)+x 1 (23) Yp(X,Y)=R(X sin 2α−Y cos 2α)+y1 (24). 6. The method according to claim 3, comprising the step of
setting, when the ratio of the size of a light spot on said detection surface to the size of a light spot on said diffraction surface is taken as a reduction ratio R, and an angle which a straight line connecting the arbitrary point (X, Y) and the origin on said diffraction surface makes with the X-axis is taken as θ, and such diffraction that the light beam impinging on the arbitrary point (X, Y) on said diffraction surface is moved by x1 in the X-axis direction and by y1 in the Y-axis direction, and is moved, on a straight line connecting a point (X+x1, Y+y1) and the point (x1, y1), to a position spaced r1 apart from the point (x1, y1) is performed, said holographic pattern such that a point (Xp, Yp) on said detection surface obtained by the diffraction satisfies the following equations: Xp(X,Y)=r 1 cos θ+x 1 (25) Yp(X,Y)=r 1 sin θ+y 1 (26). 7. A holographic optical element comprising:
a diffraction surface that diffracts an incident light beam, said diffraction surface having in at least its part a holographic pattern having a function of twisting said diffracted light beam using an optical axis of the diffracted light beam as an axis of rotation; wherein when said diffraction surface is defined by XY-coordinates comprising the X-axis and the Y-axis which are orthogonal to each other, and letting (X0, Y0) be a point to be a basis on said diffraction surface, (X, Y) be an arbitrary point on said diffraction surface, f(X, Y) be an X-direction component of a grating vector for performing predetermined diffraction at the point (X, Y) on said diffraction surface, and g (X, Y) be a Y-direction component of said grating vector, said holographic pattern is represented by a set of points (X′, Y′) satisfying the following equation: ∫ X 0 X ′ ⁢ f ⁡ ( X , Y 0 ) ⁢ ⅆ X + ∫ Y 0 Y ′ ⁢ g ⁡ ( X ′ , Y ) ⁢ ⅆ Y = 2 ⁢ ⁢ π ⁢ ⁢ M + C ⁢ ⁢ or ( 19 ) ∫ Y 0 Y ′ ⁢ g ⁡ ( X 0 , Y ) ⁢ ⅆ Y + ∫ X 0 X ′ ⁢ f ⁡ ( X , Y ′ ) ⁢ ⅆ X = 2 ⁢ ⁢ π ⁢ ⁢ M + C , ( 20 ) where M is an integer and C is a constant; when a Z-axis coordinate perpendicular to said diffraction surface is defined at the origin of said XY-coordinates, and letting (X, Y, 0) be an arbitrary point on said diffraction surface, (Xp(X, Y), Yp(X, Y), Zp) be a point on a predetermined detection surface on which a diffracted light beam diffracted by said diffraction surface impinges, (Xr, Yr, Zr) be the coordinates of a light emitting point of a light source for emitting a light beam to said diffraction surface, λ be the wavelength of the light beam, and n be the refractive index of a substrate including said holographic pattern, the X-direction component f (X, Y) and the Y-direction component g (X, Y) of the grating vector for performing predetermined diffraction at the point (X, Y, 0) on said diffraction surface are respectively set so as to satisfy the following equations: f ⁡ ( X , Y ) = ⁢ - ( 2 ⁢ π / λ ) � [ ( X - Xp ⁡ ( X , Y ) ) � ⁢ { ( X - Xp ⁡ ( X , Y ) ) 2 + ( Y - Yp ⁡ ( X , Y ) ) 2 + Zp 2 } - 1 / 2 - ⁢ n ⁢ ( X - Xr ) � { ( X - Xr ) 2 + ( Y - Yr ) 2 + Zr 2 } - 1 / 2 ] ( 16 ) g ⁡ ( X , Y ) = ⁢ - ( 2 ⁢ π / λ ) � [ ( Y - Yp ⁡ ( X , Y ) ) � { ( X - Xp ⁡ ( X , Y ) ) 2 + ⁢ ( Y - Yp ⁡ ( X , Y ) ) 2 + Zp 2 } - 1 / 2 - ⁢ n ⁢ ( Y - Yr ) � { ( X - Xr ) 2 + ( Y - Yr ) 2 + Zr 2 } - 1 / 2 ] when the ratio of the size of a light spot on said detection surface to the size of a light spot on said diffraction surface is taken as a reduction ratio R, a point (Xp, Yp) on said detection surface obtained by moving the light beam impinging on the arbitrary point (X, Y) on said diffraction surface by x1 in the X-axis direction and moving the light beam by y1 in the Y-axis direction, and rotating the light beam by an angle of β centered at a point (x1, y1) is set so as to satisfy the following equations: Xp(X,Y)=R(X 2 +Y 2)1/2 cos[arctan(Y/X)+β]+x 1 (21) Yp(X,Y)=R(X 2 +Y 2)1/2 sin[arctan(Y/X)+β]+y 1 (22). Description
FIG. 36 is a diagram showing how the intensity distribution of a reflected light beam on a recording medium surface. The intensity distribution of the reflected light beam changes depending on the relative position among a pre-groove 881 b formed on the recording medium surface, a raised land part 881 a, and a light spot. In a recordable optical disk such as a CD-R (Compact Disc Recordable), a pre-groove 881 b is formed on a recording medium surface, and information is recorded on a land part 881 a. The intensity distribution F of the reflected light beam is determined due to the diffracting effect by an edge of the land part 881 a (or the pre-groove 881 b). When a light spot of a laser is positioned at the center of the land part 881 a (or the pre-groove 881 b), a symmetrical, double-humped intensity distribution F shown in FIG. 36(b) is obtained. At this time, the laser is in focus on a surface of an optical disk.
In FIG. 37(a), a light beam 901 is converged by a lens 900 into a focal point 902. Herein, a shielding plate 903 is arranged for the half of a region of the light beam 901, as shown in FIG. 37(b). In this case, only the half of the light beam 901 is shielded by the shielding plate 903. The state of a light beam partly shielded by an object is referred to as �shading�. The �shading� causes only the half of the light beam 901 to converge into the focal point 902.
SUMMARY OF THE INVENTION An object of the present invention is to provide a holographic optical element having a complicated function of diffracting an incident light beam.
∫ X 0 X ′ ⁢ f ⁡ ( X , Y 0 ) ⁢ ⅆ X + ∫ Y 0 Y ′ ⁢ g ⁡ ( X ′ , Y ) ⁢ ⅆ Y = 2 ⁢ ⁢ π ⁢ ⁢ M + C ⁢ ⁢ or ( 19 ) ∫ Y 0 Y ′ ⁢ g ⁡ ( X 0 , Y ) ⁢ ⅆ Y + ∫ X 0 X ′ ⁢ f ⁡ ( X , Y ′ ) ⁢ ⅆ X = 2 ⁢ ⁢ π ⁢ ⁢ M + C ( 20 ) When a Z-axis coordinate perpendicular to the diffraction surface is defined at the origin of the XY-coordinates, and letting (X, Y, 0) be an arbitrary point on the diffraction surface, (Xp (X, Y), Yp (X, Y), Zp) be a point on a predetermined detection surface on which a diffracted light beam diffracted by the diffraction surface impinges, (Xr, Yr, Zr) be the coordinates of a light emitting point of a light source for emitting a light beam to the diffraction surface, λ be the wavelength of the light beam, and n be the refractive index of a substrate including the holographic pattern, the X-direction component f (X, Y) and the Y-direction component g (X, Y) of the grating vector for performing predetermined diffraction at the point (X, Y, 0) on the diffraction surface may be respectively set so as to satisfy the following equations: f ⁡ ( X , Y ) = ⁢ - ( 2 ⁢ π / λ ) � [ ( X - Xp ⁡ ( X , Y ) ) � ⁢ { ( X - Xp ⁡ ( X , Y ) ) 2 + ( Y - Yp ⁡ ( X , Y ) ) 2 + Zp 2 } - 1 / 2 - ⁢ n ⁢ ( X - Xr ) � { ( X - Xr ) 2 + ( Y - Yr ) 2 + Zr 2 } - 1 / 2 ] ( 16 ) g ⁡ ( X , Y ) = ⁢ - ( 2 ⁢ π / λ ) � [ ( Y - Yp ⁡ ( X , Y ) ) � { ( X - Xp ⁡ ( X , Y ) ) 2 + ⁢ ( Y - Yp ⁡ ( X , Y ) ) 2 + Zp 2 } - 1 / 2 - ⁢ n ⁢ ( Y - Yr ) � { ( X - Xr ) 2 + ( Y - Yr ) 2 + Zr 2 } - 1 / 2 ] ( 17 ) When the ratio of the size of a light spot on the detection surface to the size of a light spot on the diffraction surface is taken as a reduction ratio R, a point (Xp, Yp) on the detection surface obtained by moving the light beam impinging on the arbitrary point (X, Y) on the diffraction surface by x1 in the X-axis direction and moving the light beam by y1 in the Y-axis direction, and rotating the light beam by an angle of β centered at a point (x1, y1) may be set so as to satisfy the following equations:
Xp(X,Y)=R(X 2 +Y 2)1/2 cos[arctan(Y/X)+β]+x 1 (21) Yp(X,Y)=R(X 2 +Y 2)1/2 sin[arctan(Y/X)+β]+y 1 (22)
The diffraction surface has the holographic pattern designed on the basis of the foregoing equations, whereby diffracting functions �twisting�, �condensing�, and �translating� are added to the diffracted light beam.
∫ X 0 X ′ ⁢ f ⁡ ( X , Y 0 ) ⁢ ⅆ X + ∫ Y 0 Y ′ ⁢ g ⁡ ( X ′ , Y ) ⁢ ⅆ Y = 2 ⁢ ⁢ π ⁢ ⁢ M + C ⁢ ⁢ or ( 19 ) ∫ Y 0 Y ′ ⁢ g ⁡ ( X 0 , Y ) ⁢ ⅆ Y + ∫ X 0 X ′ ⁢ f ⁡ ( X , Y ′ ) ⁢ ⅆ X = 2 ⁢ ⁢ π ⁢ ⁢ M + C , ( 20 ) setting, when a Z-axis coordinate perpendicular to the diffraction surface is defined by the origin of the XY-coordinates, and letting (X, Y, 0) be an arbitrary point on the diffraction surface, (Xp(X, Y), Yp(X, Y), Zp) be a point on a predetermined detection surface on which a diffracted light beam diffracted by the diffraction surface impinges, (Xr, Yr, Zr) be the coordinates of a luminescent point of a light source for emitting a light beam to the diffraction surface, λ be the wavelength of the light beam, and n be the refractive index of a substrate including the holographic pattern, the X-direction component f (X, Y) and the Y-direction component g (X, Y) of the grating vector for performing predetermined diffraction at the point (X, Y, 0) on the diffraction surface, respectively, so as to satisfy the following equations: f ⁡ ( X , Y ) = ⁢ - ( 2 ⁢ π / λ ) � [ ( X - Xp ⁡ ( X , Y ) ) � ⁢ { ( X - Xp ⁡ ( X , Y ) ) 2 + ( Y - Yp ⁡ ( X , Y ) ) 2 + Zp 2 } - 1 / 2 - ⁢ n ⁢ ( X - Xr ) � { ( X - Xr ) 2 + ( Y - Yr ) 2 + Zr 2 } - 1 / 2 ] ( 16 ) g ⁡ ( X , Y ) = ⁢ - ( 2 ⁢ π / λ ) � [ ( Y - Yp ⁡ ( X , Y ) ) � { ( X - Xp ⁡ ( X , Y ) ) 2 + ⁢ ( Y - Yp ⁡ ( X , Y ) ) 2 + Zp 2 } - 1 / 2 - ⁢ n ⁢ ( Y - Yr ) � { ( X - Xr ) 2 + ( Y - Yr ) 2 + Zr 2 } - 1 / 2 ] ; ( 17 ) and the step of forming the holographic pattern set by the equations (16), (17), (19), and (20) on the diffraction surface by a photolithographic process and an etching process.
The holographic pattern is designed on the basis of the foregoing equations, thereby making it possible to easily form on the diffraction surface a holographic pattern for providing the diffracted light beam with complicated diffraction including �twisting�, �condensing�, and �translating�.
Xp(X,Y)=R(X cos 2α+Y sin 2α)+x 1 (23) Yp(X,Y)=R(X sin 2α−Y cos 2α)+y 1 (24)
Xp(Y,X)=r 1 cos θ+x 1 (25) Yp(X,Y)=r 1 sin θ+y 1 (26)
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of an optical pickup apparatus according to a first embodiment of the present invention;
DESCRIPTION OF THE PREFERRED EMBODIMENTS In first to seventh embodiments, description is now made of an optical pickup apparatus which is an example of a position shift detecting apparatus according to the present invention. In an eighth embodiment, a position shift sensor which is an example of the position shift detecting apparatus according to the present invention.
When the light beam condensed by the objective lens 5 is in focus on the optical disk 1, the diffracted light beam forms the light spots Sa and Sb in a state where it is twisted by 90�, as shown in FIG. 4(b). In this case, the respective quantities of light received in the photodetection parts A and B by the light spot Sa become equal, and the respective quantities of light received in the photodetection parts C and D by the light spot Sb become equal.
On the other hand, when the light beam condensed by the objective lens 5 is out of focus on the optical disk 1, the diffracted light beam forms the light spots Sa and Sb in a state where it is twisted by an angle different from 90�, as shown in FIGS. 4(a) and 4(c).
When the optical disk 1 is too near the objective lens 5 to exceed the focal point of the light beam, the light spots Sa and Sb are formed in a state where they are rotated through an angle smaller than 90� to the dividing line LX on the four-segment photodetection part 60, as shown in FIG. 4(a).
When the optical disk 1 is farther from the focal point of the light beam, the light spots Sa and Sb are formed in a state where they are rotated through an angle larger than 90� to the dividing line LX on the four-segment photodetection part 60, as shown in FIG. 4(c).
A reflected light beam from an optical disk 1 is diffracted in the X-direction by the holographic pattern 40, and impinges on the four-segment photodetection part 60 while being twisted in a clockwise direction in the pattern 1 a and twisted in a counterclockwise direction in the pattern 1 b. When the light beam condensed by an objective lens 5 is in focus on an optical disk 1, the diffracted light beam by the pattern 1 a and the diffracted light beam by the pattern 1 b respectively form light spots Sa and Sb in a state where it is twisted by 90� in a clockwise direction and in a state where it is twisted by 90� in a counterclockwise direction, as shown in FIG. 6(b). In this case, the respective quantities of light received in photodetection parts A and B by the light spot Sa become equal, and the respective quantities of light received in photodetection parts C and D by the light spot Sb become equal.
On the other hand, when the light beam condensed by the objective lens 5 is out of focus on the optical disk 1, the diffracted light beam forms the light spots Sa and Sb in a state where it is twisted by an angle different from 90� irrespective of the direction of rotation, as shown in FIGS. 6(a) and 6(c).
When the optical disk 1 is too near the objective lens 5 to exceed the focal point of the light beam, the light spot Sa is formed in a state where it is rotated in a clockwise direction through an angle smaller than 90� to a dividing line LX, and the light spot Sb is formed in a state where it is rotated in a counterclockwise direction through an angle smaller than 90� to the dividing line LX, on the four-segment photodetection part 60, as shown in FIG. 6(a).
When the optical disk 1 is farther from the focal point of the light beam, the light spot Sa is formed in a state where it is rotated in a clockwise direction through an angle larger than 90� to the dividing line LX, and the light spot Sb is formed in a state where it is rotated in a counterclockwise direction through an angle larger than 90� to the dividing line LX, on the four-segment photodetection part 60, as shown in FIG. 6(c).
The method of diffracting according to one of the two types of patterns 1 a and 1 b is the same as that in the first embodiment, and the knife edge method is used as a method of diffracting according to the other pattern 1 b. FIG. 7 is a schematic view showing respective changes in the shapes of light spots condensed on a four-segment photodetection part 60 in the third embodiment.
When the light beam condensed by an objective lens 5 is in focus on the optical disk 1, the diffracted light beam by the pattern 1 a forms a light spot Sa on photodetection parts A and B so as to extend over a dividing line LX in the four-segment photodetection part 60 in a state where it is twisted by 90�, and the diffracted light beam by the pattern 1 b forms a dot-shaped light spot Sb on the dividing line LX in the four-segment photodetection part 60. In this case, the respective quantities of light received in the photodetection parts A and B by the light spot Sa become equal, and the respective quantities of light received in photodetection parts C and D by the light spot Sb become equal.
On the other hand, when the optical disk 1 is too near the objecitive lens 5 to exceed the focal point of the light beam, the diffracted light beam by the pattern 1 a forms the light spot Sa on the photodetection parts A and B in a state where it is rotated through an angle smaller by 90� to the dividing line LX in the four-segment photodetection part 60, and the diffracted light beam by the pattern 1 b forms the light spot Sb on the photodetection part C in the four-segment photodetection part 60, as shown in FIG. 7(a).
When the optical disk 1 is farther from the focal point of the light beam, the diffracted light beam by the pattern 1 a forms the light spot Sa on the photodetection parts A and B in a state where it is rotated through an angle larger than 90� to the dividing line LX in the four-segment photodetection part 60, and the diffracted light beam by the pattern 1 b forms the light spot Sb on the photodetection part D in the four-segment photodetection part 60, as shown in FIG. 7(c).
In this case, a focus error signal having high sensitivity is obtained by the pattern 1 b. Furthermore, the focus error signal FE is detected using the rotation (twisting) of the diffracted light beam by the pattern 1 a, thereby making it possible to set the size of the light spot on the photodetector 6 to a large value. Consequently, it is possible to obtain a focus error signal FE and a reproduction signal HF which are sufficiently stable and are high in intensity.
When the light beam condensed by an objective lens 5 is in focus on the optical disk 1, the diffracted light beam forms a light spot Sa in a state where it is twisted by 90� in a counterclockwise direction in the two-segment photodetection part 60 a, and forms a light spot Sb in a state where it is twisted by 90� in a counterclockwise direction in the two-segment photodetection part 60 b, as shown in FIG. 8(b). In this case, the respective quantities of light received in the photodetection parts A and B in the two-segment photodetection part 60 a by the light spot Sa become equal. Further, the respective quantities of light received in the photodetection parts C and D in the two-segment photodetection part 60 b by the light spot Sb become equal.
On the other hand, when the light beam condensed by the objective lens 5 is out of focus on the optical disk 1, the diffracted light beam forms the light spots Sa and Sb in a state where it is twisted by an angle different from 90�, as shown in FIGS. 8(a) and 8(c).
When the optical disk 1 is too near the objective lens 5 to exceed the focal point of the light beam, the light spots Sa and Sb are respectively formed in a state where they are rotated in a counterclockwise direction through an angle smaller than 90� to the X-direction on the two-segment photodetection parts 60 a and 60 b, as shown in FIG. 8(a).
When the optical disk 1 is farther from the focal point of the light beam, the light spots Sa and Sb are respectively formed in a state where they are rotated in a counterclockwise direction through an angle larger than 90� to the X-direction on the two-segment photodetection parts 60 a and 60 b, as shown in FIG. 8(C).
A reflected light beam from an optical disk 1 is diffracted in the X-direction by the holographic pattern 40, and impinges on the two-segment photodetection parts 60 a and 60 b while being twisted in a clockwise direction in the pattern 1 a and twisted in a counterclockwise direction in the pattern 1 b. The two-segment photodetection part 60 a is divided into two photodetection parts A and B by a dividing line LX1 slightly inclined from the diffraction direction (X-direction). The two-segment photodetection part 60 b is divided into two photodetection parts C and D by a dividing line LX2 slightly inclined from the diffraction direction (X-direction). The dividing line LX1 and the dividing line LX2 are line-symmetric with respect to the X-direction.
The reflected light beam from the optical disk 1 is diffracted in the X-direction by the holographic pattern 40, and impinges on the two-segment photodetection parts 60 a and 60 b while being twisted in a clockwise direction in the pattern 1 a and twisted in a counterclockwise direction in the pattern 1 b. When the light beam condensed by an objective lens 5 is in focus on the optical disk 1, the diffracted light beam forms a light spot Sa in a state where it is twisted by 90� in a clockwise direction in the two-segment photodetection part 60 a, and forms a light spot Sb in a state where it is twisted by 90� in a counterclockwise direction in the two-segment photodetection part 60 b, as shown in FIG. 9(b). In this case, the quantity of light received in the photodetection part A in the two-segment photodetection part 60 a by the light spot Sa and the quantity of light received in the photodetection part B in the two-segment photodetection part 60 a by the light spot Sa become equal.
On the other hand, when the light beam condensed by the objective lens 5 is out of focus on the optical disk 1, the diffracted light beam forms the light spots Sa and Sb in a state where it is twisted by an angle different from 90�, as shown in FIGS. 9(a) and 9(c).
When the optical disk 1 is too near the objective lens 5 to exceed the focal point of the light beam, the light spot Sa is formed in a state where it is rotated in a clockwise direction through an angle smaller than 90� to the X-direction, and the light spot Sb is formed in a state where it is rotated in a counterclockwise direction through an angle smaller than 90� to the X-direction, respectively, on the two-division photodetection parts 60 a and 60 b, as shown in FIG. 9(a).
When the optical disk 1 is farther from the focal point of the light beam, the light spot Sa is formed in a state where it is rotated in a clockwise direction through an angle larger than 90� to the X-direction, and the light spot Sb is rotated in a counterclockwise direction through an angle larger than 90� to the X-direction, respectively, on the two-segment photodetection parts 60 a and 60 b, as shown in FIG. 9(C).
When the light beam condensed by an objective lens 5 is in focus on the optical disk 1, the diffracted light beam forms light spots Sa and Sb in a state where it is twisted by 90� in a counterclockwise direction using the X-direction as a basis in the three-segment photodetection part 60 c, as shown in FIG. 10(b). In this case, the sum of the quantity of light received in the photodetection part A in the three-segment photodetection part 60 c by the light spot Sa and the quantity of light received in the photodetection part C in the three-segment photodetection part 60 c by the light spot Sb is equal to the quantity of light received in the photodetection part B in the three-segment photodetection part 60 c by the light spots Sa and Sb.
On the other hand, when the light beam condensed by the objective lens 5 is out of focus on the optical disk 1, the diffracted light beam forms the light spots Sa and Sb in a state where it is twisted by an angle different from 90�, as shown in FIGS. 10(a) and 10(c).
When the optical disk 1 is too near the objective lens 5 to exceed the focal point of the light beam, the light spots Sa and Sb are respectively formed in a state where they are rotated in a counterclockwise direction through an angle smaller than 90� to the X-direction on the three-segment photodetection part 60 c, as shown in FIG. 10(a).
When the optical disk 1 is farther from the focal point of the light beam, the light spots Sa and Sb are respectively formed in a state where they are rotated in a counterclockwise direction through an angle larger than 90� to the X-direction on the three-segment photodetection part 60 c, as shown in FIG. 10(C).
Herein, when the X-direction component of a grating vector K, described later, for performing predetermined diffraction is denoted by f (X, Y), and the Y-direction component thereof is denoted by g (X, Y), the X-direction component f (X, Y) and the Y-direction component g (X, Y) of the grating vector K for performing predetermined diffraction in the above-mentioned circumstances are expressed by the following equations, which are derived by geometrical consideration: f ⁡ ( X , Y ) = ⁢ - k 0 ⁢ [ ( X - Xp ⁡ ( X , Y ) ) � ⁢ { ( X - Xp ⁡ ( X , Y ) ) 2 + ( Y - Yp ⁡ ( X , Y ) ) 2 + Zp 2 } - 1 / 2 - ⁢ n ⁢ ( X - Xr ) � { ( X - Xr ) 2 + ( Y - Yr ) 2 + Zr 2 } - 1 / 2 ] ( 16 ) g ⁡ ( X , Y ) = ⁢ - k 0 [ ( Y - Yp ⁡ ( X , Y ) ) � { ( X - Xp ⁡ ( X , Y ) ) 2 + ⁢ ( Y - Yp ⁡ ( X , Y ) ) 2 + Zp 2 } - 1 / 2 - ⁢ n ⁢ ( Y - Yr ) � { ( X - Xr ) 2 + ( Y - Yr ) 2 + Zr 2 } - 1 / 2 ] ( 17 ) In the foregoing equations (16) and (17), k0 denotes the wave number of a light beam. Herein, when k0 is expressed by an equation, k0=2π/λ. λ denotes the wavelength of the light beam.
In the foregoing equations (16) and (17), suppose that converged light beam is incident on the transmission-type holographic optical element 4. When it is assumed that parallel light beam is incident on the transmission-type holographic optical element 4, the second term on the right side �−n(X−Xr)�{(X−Xr)2+(Y−Yr)2+Zr2}−1/2� is not required in the foregoing equation (16), and the second term on the right side �−n(Y−Yr)�{(X−Xr)2+(Y−Yr)2+Zr2}1/2� is not similarly required in the foregoing equation (17).
When the holographic pattern 40 is formed on a surface, on the side of the optical disk, of the transmission-type holographic optical element 4, the first term on the right side �(X−Xp(X−Y))�{(X−Xp(X−Y))2+(Y−Yp(X,Y))2+Zp2}−1/2� of the equation (16) and the first term on the right side �(Y−Yp(X,Y))�{(X−Xp(X,Y))2+(Y−Yp(X,Y))2+Zp2}−1/2� of the equation (17) must be multiplied by the refractive index n of the substrate, and the refractive index n by which the second term on the right side of the equation (16) and the second term on the right side of the equation (17) are multiplied must be eliminated. Further, in this case, the effective positions of the converging point of the reflected light beam from the optical disk and of the light receiving surface of the photodetector in the Z-axis direction are changed due to the effect of the substrate, so that �Z0� and �Zp� must be corrected.
At an arbitrary point (X, Y) on the holographic surface, the X-direction component Kx of the grating vector K for performing desired diffraction, as described above, is taken as f (X, Y), and the Y-direction component Ky is taken as g (X, Y). In this case, a holographic pattern is derived as a set of points (X′, Y′) satisfying the following equations (19) and (20), described below, on the basis of a constant point (X0, Y0) on the holographic surface. Herein, a set of points (X′, Y′) denotes the grating line of the holographic pattern: ∫ X 0 X ′ ⁢ f ⁡ ( X , Y 0 ) ⁢ ⅆ X + ∫ Y 0 Y ′ ⁢ g ⁡ ( X ′ , Y ) ⁢ ⅆ Y = 2 ⁢ ⁢ π ⁢ ⁢ M + C ( 19 ) ∫ Y 0 Y ′ ⁢ g ⁡ ( X 0 , Y ) ⁢ ⅆ Y + ∫ X 0 X ′ ⁢ f ⁡ ( X , Y ′ ) ⁢ ⅆ X = 2 ⁢ ⁢ π ⁢ ⁢ M + C ( 20 ) In both the equations (19) and (20), M is an integer, and C is a constant.
In the equation (19), in the following first term on the left side indicates a phase difference in the X-direction of a grating period from the constant point (X0, Y0) in the XY plane which is the holographic surface to a point (X′, Y0): ∫ X 0 X ′ ⁢ f ⁡ ( X , Y 0 ) ⁢ ⅆ X Further, the following second term on the left side indicates a phase difference in the Y-direction of the grating period from the point (X′, Y0) to the point (X′, Y′): ∫ Y 0 Y ′ ⁢ g ⁡ ( X ′ , Y ) ⁢ ⅆ Y With respect to the left side of the equation (20), the first term indicates a phase difference in the Y-direction of a grating period from the constant point (X0, Y0) in the XY plane which is the holographic surface to a point (X0, Y′), and the second term indicates a phase difference in the X-direction of a grating period from the point (X0, Y′) to the point (X′, Y′), as in the equation (19).
In this case, an arbitrary point on the holographic surface is caused to correspond to a desired point on the light receiving surface of the photodetector in accordance with a predetermined rule, thereby making it possible to easily and accurately design holographic patterns in various holographic optical elements having not only an astigmatism adding function in the conventional example but also complicated functions such as the function of �twisting a light beam�.
Suppose a case where the holographic pattern has the function of twisting the incident light beam by 90� and converging the twisted incident light beam to a predetermined size.
As shown in FIG. 24(b), light impinging on a holographic pattern 40 in a direction indicated by an arrow G is twisted by90� at a position Fb which is its focal point and is converged to a predetermined size. At a position Fa nearer from the focal point shown in FIG. 23, light impinging on the holographic pattern 40 in the direction indicated by the arrow G is twisted by an angle which is less than 90�, as shown in FIG. 24(a). Further, at a position Fc farther from the focal point shown in FIG. 23, light impinging on the holographic pattern 40 in the direction indicated by the arrow G is twisted by an angle exceeding 90�, as shown in FIG. 24(c). As shown in FIGS. 24(a) and 24(c), the incident light beam is not converged to a predetermined size at the positions Fa and Fc which are shifted from the focal point position.
The point P1, is then rotated through an angle of β centered at the point Pn (step S2). This operation corresponds to the function of �rotating (twisting)� a light beam. When a point after the movement is taken as a point P2, the coordinates of the point P2 are represented by (r cos(α+β)+x1, r sin(α+β)+y1).
Herein, r denotes a distance �(X2+Y2)1/2� from the origin to the point P0. On the other hand, α denotes an angle formed between a straight line connecting the point P0 and the origin and the X-axis direction which is the diffraction direction, and is represented by �arctan(Y/X)�.
Furthermore, the distance between the point (x1, y1) and the point P2 is shortened (step S3). This operation is work for adjusting the size of a spot on the light receiving surface of the photodetector. That is, letting R be a reduction ratio, the coordinates of a point P3 after the reduction are represented by (Rr cos(α+β)+x1, Rr sin(α+β)+y1). Herein, R denotes the reduction ratio, and is a value obtained by dividing �the distance from the point Pn to the point P3� by �the distance from the point Pn to the point P2�.
In the above-mentioned embodiment, y1=0, and β=90�
The point P11 is then moved so as to approach the point Pn in order to converge a light beam on a straight line connecting the point P11 and the point Pn (step S12). When a point after the movement in the step S12 is taken as a point P12, the coordinates of the point P12 are represented by (Rr cos(θ)+x1, Rr sin(θ)+y1). Herein, R denotes a reduction ratio, and is a value obtained by dividing �the distance from the point Pn to the point P12� by �the distance from the point Pn to the point P11�. r denotes a distance �(X2+Y2)1/2� from the origin to the point P0. On the other hand, θ denotes an angle formed between a straight line connecting the point P0 and the origin and the X-axis direction which is the diffraction direction, and is represented by �arctan(Y/X)�.
Thereafter, the point P12 determined in the step S12 is inverted with respect to a line parallel to the X-axis after passing through the point Pn. This operation corresponds to the function of �providing astigmatism� for a light beam. Consequently, the coordinates of a point P13 after the inversion are (Rr cos(−θ)+x1, Rr sin(−θ)+y1).
Xp(X,Y)=r 1 cos θ+x 1 (25) Yp(X,Y)=r 1 sin θ+y 1 (26)
Patent CitationsCited PatentFiling datePublication dateApplicantTitleUS4731772May 6, 1986Mar 15, 1988Lee Wai HonOptical head using hologram lens for both beam splitting and focus error detection functionsUS4794585Dec 4, 1986Dec 27, 1988Lee Wai HonOptical head having a hologram lens and polarizers for use with magneto-optic mediumUS4945529 *Dec 10, 1986Jul 31, 1990Nec CorporationOptical head comprising a diffraction grating for directing two or more diffracted beams to optical detectorsUS6490088 *Jan 26, 1996Dec 3, 2002California Institute Of TechnologyOptical system using a radial harmonic pupil filter for generating collimated beamsUS20040160998 *Feb 13, 2003Aug 19, 2004Gruhlke Russell W.Method and apparatus for modifying the spread of a laser beamJPH059821A Title not availableJPH059851A Title not availableJPH0376035A Title not availableJPH0538374A Title not availableJPS6332743A Title not available* Cited by examinerNon-Patent CitationsReference1J. Kedmi et al. "Optimized Holographic Optical Elements", Journal Optical Society of America, vol. 3, No. 12, pp. 2011-2018 (1986).2K. Tatsumi et al., "A Multi-Functional Reflection Type Grating Lens for the CD Optical Head", Proc. Int. Symp. On Optical Memory (Tokyo, Japan, 1987), Japanese Journal of Applied Physics, vol. 26, Suppl. 26-4 (1987).3Patent Abstracts of Japan dated No. 01151022 dated Dec. 26, 1983/Corresponds to AG.4Patent Abstracts of Japan dated No. 58223866 dated Dec. 26, 1983/Corresponds to AF.5Patent Abstracts of Japan No. 63013134 dated Jan. 20, 1988/Corresponds to AE.6V. Soifer, ed., Methods for Computing Design of Diffractive Optical Elements (John Wiley & Sons, Inc., New York, 2002), pp. 27-35.Referenced byCiting PatentFiling datePublication dateApplicantTitleUS7522484 *Nov 15, 2005Apr 21, 2009Panaosnic CorporationOptical information processor* Cited by examinerClassifications U.S. Classification359/15, 369/112.12, 359/566, G9B/7.138, G9B/7.113, 369/112.07International ClassificationG11B7/13, G11B7/135, G11B7/22, G11B7/09, G03H1/04, G02B5/32Cooperative ClassificationG11B7/0916, G11B7/131, G11B7/133, G11B7/22, G11B7/1353, G11B7/0909, G02B5/32European ClassificationG11B7/133, G11B7/131, G11B7/1353, G02B5/32, G11B7/22Legal EventsDateCodeEventDescriptionOct 2, 2012FPAYFee paymentYear of fee payment: 8Dec 11, 2008FPAYFee paymentYear of fee payment: 4Dec 9, 2002ASAssignmentOwner name: SANYO ELECTRIC CO., LTD., JAPANFree format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:MORI, KAZUSHI;MATSUMOTO, MITSUAKI;TOMINAGA, KOJI;AND OTHERS;REEL/FRAME:013556/0056;SIGNING DATES FROM 20021126 TO 20021129Owner name: SANYO ELECTRIC CO., LTD. 2-5-5 KEIHANHONDORI MORIGFree format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:MORI, KAZUSHI /AR;REEL/FRAME:013556/0056;SIGNING DATES FROM 20021126 TO 20021129RotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services©2012 Google