Multi-layer information storage system with improved aberration correction

• US 5,677,903 A
• Filed: 09/01/1994
• Issued: 10/14/1997
• Est. Priority Date: 03/25/1991
• Status: Expired due to Term

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: Visser, Derk, Holtslag, Antonius H. M., Coops, Peter, Heemskerk, Jacobus P. J.
• Primary Examiner(s): Edun, Muhammad N.
• Application Number:
  US08/299,861
• Time in Patent Office: 1,139 Days
• Field of Search: 369/112, 369/118, 369/103, 369/44.21, 369/44.25, 369/44.23, 369/94, 369/95, 369/13, 369/44.14, 369/93
• US Class Current: 369/112.28
• CPC Class Codes: G11B 2007/0013 for carriers having multiple discrete layers
• CPC Class Codes: G11B 2007/13727 Compound lenses, i.e. two or more lenses co-operating to perform a function, e.g. compound objective lens including a solid immersion lens, positive and negative lenses either bonded together or with adjustable spacing
• CPC Class Codes: G11B 7/004 Recording, reproducing or erasing methods; Read, write or erase circuits therefor magneto-optical systems G11B11/105
• CPC Class Codes: G11B 7/005 Reproducing G11B7/0065 takes precedence
• CPC Class Codes: G11B 7/08511 with focus pull-in only
• CPC Class Codes: G11B 7/09 with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
• CPC Class Codes: G11B 7/0903 Multi-beam tracking systems
• CPC Class Codes: G11B 7/0909 by astigmatic methods
• CPC Class Codes: G11B 7/0948 specially adapted for detection and avoidance or compensation of imperfections on the carrier, e.g. dust, scratches, dropouts G11B7/095 takes precedence
• CPC Class Codes: G11B 7/13 Optical detectors therefor
• CPC Class Codes: G11B 7/1353 Diffractive elements, e.g. holograms or gratings diffraction gratings per se G02B5/18; holograms per se G02B5/32; grating systems G02B27/44
• CPC Class Codes: G11B 7/1365 Separate or integrated refractive elements, e.g. wave plates
• CPC Class Codes: G11B 7/1369 Active plates, e.g. liquid crystal panels or electrostrictive elements
• CPC Class Codes: G11B 7/1378 Separate aberration correction lenses; Cylindrical lenses to generate astigmatism; Beam expanders
• CPC Class Codes: G11B 7/13925 active, e.g. controlled by electrical or mechanical means
• CPC Class Codes: G11B 7/14 specially adapted to record on, or to reproduce from, more than one track simultaneously
• CPC Class Codes: G11B 7/24 Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the arrangement of information on the carrier G11B7/007
• CPC Class Codes: G11B 7/24038 Multiple laminated recording layers

Abstract

An optical information storage system has a multi-recording layer record carrier and a scanner device for the carrier. The scanner produces a radiation beam which is compensated for spherical aberration for a single height of the scanning spot with the stack of layers. The height of the stack is determined by the maximum spherical aberration permissible for the system. The number of layers in the stack is determined by the minimum distance between layers, which depends on the crosstalk in the error signals due to currently unscanned layers.

Claims

1. An information storage system comprising an optical record carrier having a stack of information layers alternating with spacer layers,

and a device for scanning the information layers, which device is provided with a radiation source and focusing means for selectively focusing a radiation beam from the radiation source on the separate information layers,

characterized in that the focusing means introduce such a fixed, stack-associated spherical aberration in the radiation beam that this aberration compensates the spherical aberration incurred by the radiation beam when it is focused at approximately half the height of the stack of information layers.

2. An information storage system as claimed in claim 1, characterized in that said stack of information layers has a height no greater than approximately 100 μ

m, and said focusing means comprises an objective system having a numerical aperture of approximately 0.52.

3. An information storage system as claimed in claim 1, characterized in that said focusing means comprises a single corrector plate only, placed in an uncollimated part of the radiation beam, for compensating spherical aberration.

4. An information storage system as claimed in claim 1, characterized in that the thickness of the stack is smaller than 2d which is a function of the refractive index of the material of the stack and of the numerical aperture of the focusing means.

5. An information storage system as claimed in claim 4, characterized in that 2d is also a function of the maximally admissible decrease of the Strehl intensity of the radiation beam due to spherical aberration.

6. An information storage system comprising an optical record carrier having a stack of information layers alternating with spacer layers,

and a device for scanning the information layers, which device is provided with a radiation source and focusing means for selectively focusing a radiation beam from the radiation source on the separate information layers,

characterized in that during reading the focusing means continuously introduces such a fixed, stack-associated spherical aberration in the radiation beam that this aberration compensates the spherical aberration incurred by the radiation beam when it is focused at approximately half the height of the stack of information layers.

7. An information system as claimed in claim 6, characterized in that said stack of information layers has a height no greater than approximately 100 μ

m, and said focusing means comprises an objective system having a numerical aperture of approximately 0.52.

8. An information system as claimed in claim 6, characterized in that said focusing means comprises a single corrector plate only, placed in an uncollimated part of the radiation beam, for compensating spherical aberration.

9. An information system as claimed in claim 6, characterized in that the thickness of the stack is smaller than 2d which is a function of the refractive index of the material of the stack and of the numerical aperture of the focusing means.

10. An information system as claimed in claim 9, characterized in that 2d is also a function of the maximally admissible decrease of the Strehl intensity of the radiation beam due to spherical aberration.

11. An information storage system comprising an optical record carrier having a stack of information layers alternating with spacer layers,

and a device for scanning the information layers, which device is provided with a radiation source and focusing means for selectively focusing a radiation beam from the radiation source on the separate information layers,

characterized in that:

the thickness of the stack is smaller than 2d which is a function of the refractive index of the material of the stack, of the numerical aperture of the focusing means, and of the maximally admissible decrease of the Strehl intensity of the radiation beam due to spherical aberration,

the value 2d is defined by the equation ##EQU4## in which n is the refractive index of the spacer layers, λ

is the vacuum wavelength of the radiation beam, NA is the numerical aperture of the focusing means, and r is the maximally admissible decrease of the Strehl intensity due to spherical aberration, and

the focusing means introduces such a fixed, stack-associated spherical aberration in the radiation beam that this aberration compensates the spherical aberration incurred by the radiation beam when it is focused at approximately half the height of the stack of information layers.

12. An information storage system as claimed in claim 11, in which the record carrier comprises a transparent substrate having an entrance face for the radiation beam at one side and said stack at the other side, characterized in that the thickness of the stack is smaller than 2d minus the thickness tolerance of the substrate.

13. An information storage system as claimed in claim 11, wherein r is equal to 0.05.

14. An information storage system as claimed in claim 11, wherein r is equal to 0.01.