Method for reproducing information data from magneto-optical recording medium using linear polarized beam

• US 6,584,046 B2
• Filed: 04/12/2001
• Issued: 06/24/2003
• Est. Priority Date: 12/19/1996
• Status: Expired due to Term

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Oshima, Mitsuaki, Gotoh, Yoshiho, Tanaka, Shin-ichi, Koishi, Kenji, Moriya, Mitsurou, Murakami, Motoyoshi, Takemura, Yoshinari, Miyatake, Norio, Konishi, Shinichi
• Primary Examiner(s): DINH, TAN X
• Application Number:
  US09/833,995
• Publication Number:
  US 20010021144A1
• Time in Patent Office: 803 Days
• Field of Search: 369/13.31, 369/13.29, 369/13.3, 369/110.01, 369/110.02, 369/110.03, 369/110.04, 369/13.05
• US Class Current: 369/13.31
• CPC Class Codes: G06T 1/0021 Image watermarking
• CPC Class Codes: G06T 2201/0064 for copy protection or copy management, e.g. CGMS, copy only once, one-time copy
• CPC Class Codes: G11B 11/10506 by modulating only the light beam of the transducer
• CPC Class Codes: G11B 11/10515 Reproducing compensating pit shift G11B11/1053
• CPC Class Codes: G11B 11/10584 characterised by the form, e.g. comprising mechanical protection elements
• CPC Class Codes: G11B 11/10595 Control of operating function
• CPC Class Codes: G11B 20/00086 Circuits for prevention of unauthorised reproduction or copying, e.g. piracy indicating unauthorised use of record carriers in general G11B23/28; scrambling for television signal recording H04N5/913; network architectures or network protocols for network security H04L63/00; cryptographic mechanisms or cryptographic arrangements for secret or secure communication H04L9/00
• CPC Class Codes: G11B 20/00123 the record carrier being identified by recognising some of its unique characteristics, e.g. a unique defect pattern serving as a physical signature of the record carrier
• CPC Class Codes: G11B 20/00166 involving measures which result in a restriction to authorised contents recorded on or reproduced from a record carrier, e.g. music or software
• CPC Class Codes: G11B 20/00181 using a content identifier, e.g. an international standard recording code [ISRC] or a digital object identifier [DOI]
• CPC Class Codes: G11B 20/0021 involving encryption or decryption of contents recorded on or reproduced from a record carrier
• CPC Class Codes: G11B 20/00231 wherein the key is obtained from a local external medium, e.g. a card
• CPC Class Codes: G11B 20/0026 the key being stored as a barcode
• CPC Class Codes: G11B 20/00268 said barcode being recorded in a burst cutting area [BCA]
• CPC Class Codes: G11B 20/00347 wherein the medium identifier is used as a key
• CPC Class Codes: G11B 20/00876 wherein physical copy protection means are attached to the medium, e.g. holograms, sensors, or additional semiconductor circuitry
• CPC Class Codes: G11B 20/00884 involving a watermark, i.e. a barely perceptible transformation of the original data which can nevertheless be recognised by an algorithm
• CPC Class Codes: G11B 20/10 Digital recording or reproducing
• CPC Class Codes: G11B 20/1217 on discs
• CPC Class Codes: G11B 20/1258 where blocks are arranged within multiple radial zones, e.g. Zone Bit Recording or Constant Density Recording discs, MCAV discs, MCLV discs
• CPC Class Codes: G11B 2020/122 : Burst cutting area [BCA]
• CPC Class Codes: G11B 2020/1244 : CAV zone, in which a constant angular velocity is used
• CPC Class Codes: G11B 2020/1245 : CLV zone, in which a constant linear velocity is used
• CPC Class Codes: G11B 23/281 : by changing the physical properties of the record carrier
• CPC Class Codes: G11B 23/288 : Protecting disks from being written or overwritten
• CPC Class Codes: G11B 23/40 : Identifying or analogous means applied to or incorporated in the record carrier and not intended for visual display simultaneously with the playing-back of the record carrier, e.g. label, leader, photograph
• CPC Class Codes: G11B 7/0037 : with discs
• CPC Class Codes: G11B 7/0045 : Recording G11B7/006, G11B7/0065 take precedence
• CPC Class Codes: G11B 7/00736 : Auxiliary data, e.g. lead-in, lead-out, Power Calibration Area [PCA], Burst Cutting Area [BCA], control information sector headers or adresses in prepits G11B7/00745; address data in track wobble G11B7/24082
• 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

Abstract

A method for reproducing write-once information from an optical disk. The disk includes a disk substrate and a recording layer on the disk substrate, the recording layer including a magnetic film with a magnetic anisotropy in a direction perpendicular to a surface of the magnetic film. Write-once information formed by first recording areas and second recording areas is stored in a pre-determined portion of said recording layer, the first and second recording areas having different magnetic anisotropies in a direction perpendicular to a surface of the magnetic film. The method includes irradiating linearly polarized laser light onto said pre-determined portion, and detecting a rotational change in a polarization orientation of light reflected from the optical disk or light transmitted through the optical disk, the rotational change being caused depending on which of the first recording area and the second recording area is irradiated with the linearly polarized laser light.

Claims

1. A method for reproducing write-once information from an optical disk (a) comprising a disk substrate, and a recording layer on the disk substrate, the recording layer including a magnetic film with a magnetic anisotropy in a direction perpendicular to a surface of the magnetic film;

and (b) storing write-once information formed by first recording areas and second recording areas in a pre-determined portion of said recording layer, the first and second recording areas having different magnetic anisotropies in a direction perpendicular to a surface of the magnetic film;

the method comprising;

irradiating linearly polarized laser light onto said pre-determined portion; and

detecting a rotational change in a polarization orientation of light reflected from the optical disk or light transmitted through the optical disk, the rotational change being caused depending on which of the first recording area and the second recording area is irradiated with the linearly polarized laser light, the rotational change occurring between +θ

k and approximately 0.

2. The reproducing method according to claim 1, wherein the linearly polarized laser light is irradiated onto said pre-determined portion after magnetizing the recording layer of said pre-determined portion in one step by applying a magnetic field that is larger than a coercive force of the recording layer in said pre-determined portion.

3. The reproducing method according to claim 1, wherein the linearly polarized laser light is irradiated onto said pre-determined portion after aligning a magnetization of said recording layer of said pre-determined portion by applying a unidirectional magnetic field to said pre-determined portion while increasing the temperature of said recording layer in said pre-determined portion above the Curie temperature by irradiating laser light of constant luminous energy.

4. A method for reproducing write-once information from an optical disk (a) comprising a disk substrate, and a recording layer on the disk substrate, the recording layer including a magnetic film with a magnetic anisotropy in a direction perpendicular to a surface of the magnetic film;

and (b) capable of storing write-once information formed by first recording areas and second recording areas in a pre-determined portion of said recording layer, the first and second recording areas having different magnetic anisotropies in a direction perpendicular to a surface of the magnetic film;

the method comprising;

irradiating linearly polarized laser light onto said pre-determined portion; and

detecting a rotational change in a polarization orientation of light reflected from the optical disk or light transmitted through the optical disk, the rotational change being caused depending on which of the first recording area and the second recording area is irradiated with the linearly polarized laser light, the rotational change occurring between +θ

k and approximately 0.

5. The reproducing method according to claim 4, wherein the linearly polarized laser light is irradiated onto said pre-determined portion after magnetizing the recoding layer of said pre-determined portion in one step by applying a magnetic field that is larger than a coercive force of the recording layer in said pre-determined portion.

6. The reproducing method according to claim 4, wherein the linearly polarized laser light is irradiated onto said pre-determined portion after aligning a magnetization of said recording layer of said pre-determined portion by applying a unidirectional magnetic field to said pre-determined portion while increasing a temperature of said recording layer in said pre-determined portion above a Curie temperature by irradiating laser light of constant luminous energy.