EP0075192A2
Expired / Lapsed
EP
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An optical head
Assignee: Toshiba Corp
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Filing: 1982-09-08
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Granted: —
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Expires: 2002-09-08
Abstract
Abstract In the optical head, laser beams are converged by the objective lens (42) and projected on the light-receiving surface (14) of the optical disk (2). The diverged laser beam is reflected from the light receiving surface (14) converged by the objective lens into a parallel laser beam, and directed to the light shielding plate (52). Only the laser beam passing through the region spaced in the direction (72) in which the tracking guide (16) is extending from the common optical axis (73) is picked up by the light shielding plate (52), and part of this laser beam is converged by the convex lens (54) and the cylindrical lens (57) whose base line is arranged in the direction parallel with the direction (72) in which the tracking guide is extending, and projected on the light-receiving surface (66) of the photodetector. The light-receiving surface (66) is located at the long focal point (65-2) which is determined by the convex lens (54) and the cylindrical lens (57). When the objective lens (42) is at the just focusing state, an elongated image of beam waist on the light-reflecting surface (14) is formed on the light-receiving surface. When the objective lens (42) is at the defocusing state, part of laser beam is deflected by the light shielding plate (52), and a pattern which is larger than and deformed from the image is formed on the region which is shifted from a region on the light-receiving surface (66) on which said image is formed, in the direction (76) parallel with the direction (72) in which the tracking guide (16) is extending.
Inventors
- 👤 Hideo Ando
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-06 08:25
CPC Classifications
G; G11; G11B; G11B7/00; G11B7/12; G11B7/135; G11B7/1381; G11B7/08; G11B7/09; G11B7/0908; G11B7/0909; G11B7/0916; G11B7/13; G11B7/131; G11B7/1359; G11B7/1372; G11B7/1378; G11B7/22
Claims Analysis
Total Claims: 35
Claim 1
Independent Claim
329 words
An optical head for focusing light beam on a light-reflecting surface comprising: means (30) for generating a light beam; means (32, 34, 36) for transferring the light beam; an objective lens (42) which converts the transferred light beam into a convergent light beam with a beam waist, projects the light beam on the light-reflecting surface (14) and converges the divergent light beams reflected from the light-reflecting surface (14); and an astigmation lens system (54, 57) for converging the light beam incident through the objective lens (42); characterized by means (50, 52, 218, 220, 210) for deflecting the light beam directing from the objective lens (42) to the lens system, depending on the distance between the objective lens (42) and the light-reflecting surface (14); and a photodetector provided with a light-receiving surface (66), when said objective lens (42) being at the just focusing state and the beam waist of the convergent light beam projected from said objective lens (42) being formed on the light-reflecting surface (66), the beam waist image as the first projected pattern being formed on the light-receiving surface (66) located on the image forming plane by the objective lens (42) and the lens system (54, 57), and when the objective lens (42) being at the defocusing state and a beam spot larger in size than the beam waist being formed on the light-reflecting surface (14) by the convergent light beam projected from the objective lens (42), the second projected pattern larger in size than the beam waist image being formed on the light-receiving surface (66), the light-receiving surface (66) having at least first and second photosensitive regions (70-1, 70-3) which are arranged in a direction in which the pattern is shifted, and when the objective lens (42) changing from the just focusing state into the defocusing state, the first projected pattern on the light-receiving surface (66) being shifted in the direction and deformed into the second projected pattern by the deflecting means (50, 52, 218, 220, 210).
Claim 2
Dependent Claim
329 words
An optical head for focusing light beam on a light-reflecting surface comprising: means (30) for generating a light beam; means (32, 34, 36) for transferring the light beam; an objective lens (42) which converts the transferred light beam into a convergent light beam with a beam waist, projects the light beam on the light-reflecting surface (14) and converges the divergent light beams reflected from the light-reflecting surface (14); and an astigmation lens system (54, 57) for converging the light beam incident through the objective lens (42); characterized by means (50, 52, 218, 220, 210) for deflecting the light beam directing from the objective lens (42) to the lens system, depending on the distance between the objective lens (42) and the light-reflecting surface (14); and a photodetector provided with a light-receiving surface (66), when said objective lens (42) being at the just focusing state and the beam waist of the convergent light beam projected from said objective lens (42) being formed on the light-reflecting surface (66), the beam waist image as the first projected pattern being formed on the light-receiving surface (66) located on the image forming plane by the objective lens (42) and the lens system (54, 57), and when the objective lens (42) being at the defocusing state and a beam spot larger in size than the beam waist being formed on the light-reflecting surface (14) by the convergent light beam projected from the objective lens (42), the second projected pattern larger in size than the beam waist image being formed on the light-receiving surface (66), the light-receiving surface (66) having at least first and second photosensitive regions (70-1, 70-3) which are arranged in a direction in which the pattern is shifted, and when the objective lens (42) changing from the just focusing state into the defocusing state, the first projected pattern on the light-receiving surface (66) being shifted in the direction and deformed into the second projected pattern by the deflecting means (50, 52, 218, 220, 210).
Claim 3
Dependent Claim
25 words
An optical head according to claim 1, characterized in that the lens system (54, 57) includes a cylindrical lens (57) and a convex lens (54).
Claim 4
Dependent Claim
19 words
An optical head according to claim 2, characterized in that the cylindrical lens (54) is a convex cylindrical lens.
Claim 5
Dependent Claim
36 words
An optical head according to claim 3, characterized in that the lens system (54, 57) has a long and a short focal point, and the light-receiving surface (66) is substantially located at said long focal point.
Claim 6
Dependent Claim
19 words
An optical head according to claim 2, characterized in that the cylindrical lens (57) is a concave cylindrical lens.
Claim 7
Dependent Claim
35 words
An optical head according to'claim 5, characterized in that the lens system (54, 57) has a long and short focal point, and the light receiving surface (66) is substantially located at said short focal point.
Claim 8
Dependent Claim
19 words
An optical head according to claim 1, characterized in that the light beam generating means (30) generates laser beams.
Claim 9
Dependent Claim
24 words
An optical head according to claim 1, characterized in that the objective lens (42) has an optical axis perpendicular to the light-reflecting surface (66).
Claim 10
Dependent Claim
35 words
An optical head according to claim 1, characterized in that the transferring means (32, 34, 36) converts the light beams to parallel light beams and transfers the parallel light beams to the objective lens (42).
Claim 11
Dependent Claim
23 words
An optical head according to claim 1, characterized in that the light-reflecting surface (14) comprises a light-reflecting layer of the optical disk (2).
Claim 12
Dependent Claim
68 words
An optical head according to claim 1, characterized in that a tracking guide or a row of information pattern (16) is formed on the light-reflecting surface (66) toward which convergent light beams are projected from the objective lens (42), an image of the tracking guide or the information pattern (16) is formed on the light-receiving surface (14) when the objective lens (42) is in the just focusing state.
Claim 13
Dependent Claim
61 words
An optical head according to claim 11, characterized in that the lens system (54, 57) includes the cylindrical lens (52) having a base line arranged in parallel with the direction in which the tracking guide or row of information pattern (16) is extending, and a convex lens (54) located on an optical axis on which the cylindrical lens (57) is located.
Claim 14
Dependent Claim
44 words
An optical head according to claim 12, characterized in that the lens system (54, 57) has a long and a short focal point, the cylindrical lens (57) is a convex cylindrical lens and the light-receiving surface (66) is located at said long focal point.
Claim 15
Dependent Claim
58 words
An optical head according to claim 12, characterized in that the beam deflection means (50, 52, 218, 220, 210) includes a light-shielding plate (50, 52) which transmits only part of the light beam passing through the region apart from the optical axis in the direction in which the tracking guide or row of information pattern (16) is extending.
Claim 16
Dependent Claim
62 words
An optical head according to claim 12, characterized in that the beam deflection means (50, 52, 218, 220, 210) comprises the cylindrical lens (57) which is so located as to converge only part of the light beam passing through the region spaced from the optical axis in the direction in which the tracking guide or row of information pattern (16) is extending.
Claim 17
Dependent Claim
122 words
An optical head according to claim 11, characterized in that said optical system (54, 57) further comprises means (38) for moving the beam waist in a direction to traverse the tracking guide or the row of information pattern (16), so that the image of the tracking guide or the information pattern (16) within the beam waist image formed on said light-receiving surface (66) is moved in a specific direction when the objective lens (42) is in the just focusing state and the beam waist is moved by said moving means (38), the specific direction being different from a direction along which the beam pattern projected onto the light reflecting surface (66) is shifted by said deflecting means (50, 52, 218, 220, 210).
Claim 18
Dependent Claim
41 words
An optical head according to claim 16, characterized in that the direction along which the image of the tracking guide or the information pattern (16) is moved is substantially perpendicular to the direction along which the beam projected pattern is shifted.
Claim 19
Dependent Claim
23 words
An optical head according to claim 16, characterized in that the light-receiving surface (66) further includes third and fourth photosensitive regions (70-2, 70-4).
Claim 20
Dependent Claim
47 words
An optical head according to claim 18, characterized in that the four photosensitive regions (70-1, 70-2, 70-3, 70-4) are arranged on the respective diagonal lines and a track focusing signal produced by taking a difference between a sum of signals of the mutually adjacent regions (70-2, 70-4).
Claim 21
Dependent Claim
76 words
An optical head according to claim 18, characterized in that the four photosensitive regions (70-1, 70-2, 70-3, 70-4) are arranged on the respective diagonal lines, the third and fourth photosensitive regions (70-2, 70-4) are arranged in the direction along which the image of the tracking guide or the information pattern (16) is moved, and a track focusing signal produced by taking a difference between signals produced from the photosensitive regions (70-2, 70-4) on the diagonal lines.
Claim 22
Dependent Claim
46 words
An optical head according to any one of claims 18 to 20, characterized in that the light receiving surface (66) has the photoinsensitive region (102) which can not substantially detect the light rays and which is formed between the mutually adjacent regions (70-1, 70-2, 70-3, 70-4).
Claim 23
Dependent Claim
22 words
The system according to claim 21, characterized in that the photoinsensitive regions (102) is a light-shielding layer (104) to shield light rays.
Claim 24
Dependent Claim
17 words
The system according to claim 22, characterized in that the light-shielding layer (104) is an alumina layer.
Claim 25
Dependent Claim
32 words
The system according to claim 21, charac-. terized in that the photodetector (48) is semiconductor photodetector, and the photoinsensitive region (102) is a recess region (114) formed in the semiconductor photodetector (48).
Claim 26
Dependent Claim
49 words
The system according to claim 21, characterized in that the photodetector (48) is formed on a semiconductor substrate (108), and the photoinsensitive region (102) is an impurity region (116) of the same conductivity type as the substrate (108) having a higher impurity density than that of the substrate (108).
Claim 27
Dependent Claim
62 words
The system according to claim 21, characterized in that the width of said photoinsensitive region (102) is a quarter or more of the width of the beam waist image formed on the light-receiving surface (66), the width of the beam waist image being defined as the width of the region in which the intensity of the beam spot has a maximum, 1/e2.
Claim 28
Dependent Claim
28 words
The system according to claim 26, characterized in that the width of the photoinsensitive region (102) ranges from 1/3 to 3 times the width of the beam spot.
Claim 29
Dependent Claim
66 words
An optical head according to claim 1, characterized in that the objective lens (42) and the lens system (54, 57) have a common axis and the beam deflecting means (50, 52, 218, 220, 210) includes a light-shielding plate (50, 52) being arranged on the common axis to transmit only part of the light beams passing through an area which is spaced apart from the common axis.
Claim 30
Dependent Claim
19 words
An optical head according to claim 28, characterized in that the light-shielding plate (50, 52) has an aperture. -
Claim 31
Dependent Claim
18 words
An optical head according to claim 28, characterized in that the light-shielding plate (50, 52) has a slit.
Claim 32
Dependent Claim
20 words
An optical head according to claim 28, characterized in that the light-shielding plate (50, 52) has a . knife edge.
Claim 33
Dependent Claim
42 words
An optical head according to claim 1, characterized in that the means (50, 52, 218, 220, 210) for deflecting the light beam comprises the convex lens (54) having an optical axis which intersects with the optical axis of the objective lens (42).
Claim 34
Dependent Claim
37 words
An optical head according to claim 1, characterized in that said means (50, 52, 218, 210,_220) for deflecting the light beam comprises a prism (210) arranged between the lens system (54, 57) and the light-receiving surface (66).
Claim 35
Dependent Claim
38 words
An optical head according to claim 1, characterized in that the means (50, 52, 218, 210, 220) for deflecting the light beam comprises a mirror (218) arranged between the lens system (54, 57) and the light-receiving surface (66).
References Cited (Backward Citations)
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