Error detecting device for optical head

• US 5,195,072 A
• Filed: 03/23/1989
• Issued: 03/16/1993
• Est. Priority Date: 03/25/1988
• Status: Expired due to Fees

• Current Assignee: Tosoh Corporation
• Original Assignee: Tosoh Corporation
• Inventors: Kawai, Akira, Fukui, Kenji
• Primary Examiner(s): Envall, Jr., Roy N.
• Assistant Examiner(s): Dang, Hung
• Application Number:
  US07/327,820
• Time in Patent Office: 1,454 Days
• Field of Search: 369/44.24, 369/44.11, 369/44.23, 369/44.25, 369/44.32, 369/44.14, 369/59, 369/44.12, 369/44.37, 369/44.38, 369/44.41, 369/112, 369/109, 369/110, 250/201.5
• US Class Current: 369/44.23
• CPC Class Codes: G11B 2007/13722 Fresnel lenses
• CPC Class Codes: G11B 7/0909 by astigmatic methods
• CPC Class Codes: G11B 7/1378 Separate aberration correction lenses; Cylindrical lenses to generate astigmatism; Beam expanders

Abstract

An error detecting device for an optical head detects a focussing error and a tracking error. The error detection device includes an optical structure for converting a reflected light of a light irradiating a surface to be irradiated into an astigmatic pencil of rays having a first focal point and a second focal point, the optical structure having a first focussing member for focussing the reflected light on the first focal point of the astigmatic pencil of rays, and a second focussing member for focussing the reflected light on the second focal point of the astigmatic pencil of rays, the first and the second focussing members being made integral, and a device for detecting errors of the light irradiating the surface to be irradiated, based on a detecting signal of a spot of the reflected light formed by the first focussing member, and a detecting signal of a spot of said reflected light formed by the second focussing member. The error detecting device can be small-sized and light, have a small astigmatic difference, easily to align optical elements.

Claims

1. An error detecting device for an optical head, comprising:

optical means for converting a reflected light of a light irradiating a surface to be irradiated into an astigmatic pencil of rays having a first focal point and a second focal point, said optical means having a first focusing means for focusing said reflected light on said first focal point of said astigmatic pencil of rays, and a second focusing member for focusing said reflected light on said second focal point of said astigmatic pencil of rays, said first and second focusing members being made integral; and

means for detecting errors of said light irradiating the surface to be irradiated, based on a detecting signal of a spot of said reflected light formed by said first focusing member, and a detecting signal of a spot of said reflected formed by said second focusing member, wherein said optical means is provided by a Fresnel zone plate, said zone plate including;

a first, second, third and a fourth Fresnel zone plate member divided in four by two parting lines passing the center of said Fresnel zone plate,

said first and said third Fresnel zone plate members opposed to each other across said center has said first focal point, and

said second and said fourth Fresnel zone plate members opposed to each other across said center has said second focal point; and

said detecting means having;

a first, a second, a third and a fourth detecting section for respectively detecting a spot of said reflected light formed by said first, said second, said third and said fourth Fresnel zone plate members,

a focusing error computing unit for computing a focusing error signal, based on detecting signals from said first, said second, said third and said fourth detecting sections, and

a tracking error computing unit for computing a tracking error signal, based on detecting signals from at least said second and said fourth detecting sections.

2. An error detecting device for an optical head according to claim 1, wherein said Fresnel zone plate is provided by a phase reversal type Fresnel zone plate.

3. An error detecting device for an optical head according to claim 1, wherein said Fresnel zone plate is provided by a binary transmitted type Fresnel zone plate.

4. An error detecting device for an optical head according to claim 3, wherein said binary transmitted type Fresnel zone plate has a primary phase of about 30 to 60 degrees.

5. An error detecting device for an optical head, comprising:

optical means for converting a reflected light of a light irradiating a surface to be irradiated into an astigmatic pencil of rays having a first focal point and a second focal point, said optical means having a first focusing means for focusing said reflected light on said first focal point of said astigmatic pencil of rays, and a second focusing member for focusing said reflected light on said second focal point of said astigmatic pencil of rays, said first and second focusing members being made integral; and

means for detecting errors of said light irradiating the surface to be irradiated, based on a detecting signal of a spot of said reflected light formed by said first focusing member, and a detecting signal of a spot of said reflected formed by said second focusing member, wherein said optical means is provided by a Fresnel zone plate, wherein said Fresnel zone plate is provided by a binary transmitted type Fresnel zone plate.

6. An error detecting device for an optical head according to claim 5 wherein said binary transmitted type Fresnel zone plate has a primary phase of about 30 to 60 degrees.

7. An error detecting device for an optical head, comprising:

optical means for converting a reflected light of a light irradiating a surface to be irradiated into an astigmatic pencil of rays having a first focal point and a second focal point, said optical means having a first focusing means for focusing said reflected light on said first focal point of said astigmatic pencil of rays, and a second focusing member for focusing said reflected light on said second focal point of said astigmatic pencil of rays, said first and second focusing members being made integral; and

means for detecting errors of said light irradiating the surface to be irradiated, based on a detecting signal of a spot of said reflected light formed by said first focusing member, and a detecting signal of a spot of said reflected formed by said second focusing member, wherein said optical means is provided by a Fresnel lens, said lens including;

a first, second, third and a fourth Fresnel lens member divided in four by two parting lines passing the center of said Fresnel lens,

said first and said third Fresnel lens members opposed to each other across said center has said first focal point, and

said second and said fourth Fresnel lens members opposed to each other across said center has said second focal point; and

said detecting means having;

a first, a second, a third and a fourth detecting section for respectively detecting a spot of said reflected light formed by said first, said second, said third and said fourth Fresnel lens members,

a focusing error computing unit for computing a focusing error signal, based on detecting signals from said first, said second, said third and said fourth detecting sections, and

a tracking error computing unit for computing a tracking error signal, based on detecting signals from at least said second and said fourth detecting sections.

8. An error detecting device for an optical head, comprising:

optical means for converting a reflected light of a light irradiating a surface to be irradiated into an astigmatic pencil of rays having a first focal point and a second focal point, said optical means having a first focusing means for focusing said reflected light on said first focal point of said astigmatic pencil of rays, and a second focusing member for focusing said reflected light on said second focal point of said astigmatic pencil of rays, said first and second focusing members being made integral; and

means for detecting errors of said light irradiating the surface to be irradiated, based on a detecting signal of a spot of said reflected light formed by said first focusing member, and a detecting signal of a spot of said reflected formed by said second focusing member, wherein said optical means is provided by a convex lens, said zone plate including;

a first, second, third and a fourth convex lens member divided in four by two parting lines passing the center of said convex lens,

said first and said third convex lens members opposed to each other across said center has said first focal point, and

said second and said fourth convex lens members opposed to each other across said center has said second focal point; and

said detecting means having;

a first, a second, a third and a fourth detecting section for respectively detecting a spot of said reflected light formed by said first, said second, said third and said fourth convex lens members,

a focusing error computing unit for computing a focusing error signal, based on detecting signals from said first, said second, said third and said fourth detecting sections, and

a tracking error computing unit for computing a tracking error signal, based on detecting signals from at least said second and said fourth detecting sections.