Classifications

• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
  • G11B7/125—Optical beam sources therefor, e.g. laser control circuitry specially adapted for optical storage devices; Modulators, e.g. means for controlling the size or intensity of optical spots or optical traces
  • G11B7/127—Lasers; Multiple laser arrays
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
  • G11B7/0055—Erasing
  • G11B7/00557—Erasing involving phase-change media
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
  • G11B7/125—Optical beam sources therefor, e.g. laser control circuitry specially adapted for optical storage devices; Modulators, e.g. means for controlling the size or intensity of optical spots or optical traces
  • G11B7/126—Circuits, methods or arrangements for laser control or stabilisation
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
  • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
  • G11B7/1353—Diffractive elements, e.g. holograms or gratings
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
  • G11B7/26—Apparatus or processes specially adapted for the manufacture of record carriers

Definitions

• the present invention relates to the field of optical discs, and more generally to recording media comprising a phase change medium, as well as to the methods and equipment for initializing such optical discs and recording media.
• a phase change is any reversible state change requiring initialization, that is to say an action consisting in bringing the entire recording medium into a given state.
• An actual phase change optical recording medium is based on the change of the reflection coefficient of certain materials between their amorphous state and their crystalline state.
• a recording medium in the form of a disc such as a rewritable CD or DVD
• it is necessary that the recording medium carried by the disc is entirely in the crystalline state ( deleted) so that it can be formatted by the user.
• a step in the manufacture of the disc is the initialization aimed at putting the recording medium in the same state - crystalline in this case.
• the invention consists of a new device for shaping the initialization laser beam from a power laser diode, a device for which the lifetime is not limited to the lifetime of the source. Such a device decreases thus the cost per unit linked to the initialization of the recording medium.
• phase-change optical recording media (CD-RW, DVD-RAM, DVD-RW, etc.) goes through an initialization step aimed at crystallizing the entire disc. .
• This initialization is done by heating the recording medium to a temperature at which the material can reorganize (crystallization) without melting (ar ⁇ orphization). A significant part of the cost of a disc is then due to this step
• the heating device is optical: a laser source produces a beam, which beam is shaped by an optical system
• the recording medium absorbs the incident light power which is converted into heat.
• the power of the laser is adjusted so that the temperature of the layer is within a range called crystallization temperature.
• a second device at a different wavelength allows the control in focusing.
• Each of the discontinuous crystal phase areas at a width which is wider than the width of the amorphous stripe, so that said data is recorded as registration marks in the form of the remaining amorphous phase area of the stripe amorphous phase other than discontinuous crystal phase zones.
• the laser source is generally a multimode semiconductor laser, for example in the form of a strip of discrete diodes.
• the major drawback of sources of this type is the possible failure of an emitter, or more generally of an area of the source, which results in the "spot" of heating by an inhomogeneity which can cause a failure of initialization of the media. This phenomenon reduces the life of the optical heads since a defect local transmitter induces a prohibitive problem with the disc.
• the lifetime of an emitter is only a statistical specification, and some manufacturers may consider their sources to be correct if only one emitter on a strip is faulty. This means that a sorting phase must take place to select the right sources for initialization, thereby increasing the price of the sources.
• the object of the invention is to remedy these drawbacks by proposing a method and a device implementing an extended light source, in particular in the form of a plurality of discrete laser sources, the possible failures of which do not cause any anomaly. major, because their beams converge by an optical element in a common heating zone.
• the geometrically extended light source can be constituted by a source composed of an assembly of discrete sources, for example a strip of laser diodes, or also by a continuous source having an emission zone capable of exhibiting local failures, for example a laser diode having a large junction.
• Patent EP318200 describes for example an optical information recording method comprising the steps of erasing and recording during the irradiation of said support by two spots of laser beam which are spaced along the same recording track .
• the two spots are spaced along of the same recording track of the support while maintaining the spacing between adjacent points of intensity half of said two spots between 0 and 100 ⁇ m and are focused on said track.
• One of the spots first radiates each position of said track with a circular or elliptical shape.
• the second spot irradiates a position of the track previously irradiated by the first spot with a circular shape.
• US patent US5321707 also describes an apparatus forming two laser beams for erasing data. The two beams coming from a single erasing head so that their focal points are located on the same track of the optical disc. This document proposes to use a semiconductor laser with two beams or to divide in two a beam emitted by a semiconductor laser.
• phase change media in two ways: on the one hand allowing an increase in the life of the optical illumination assembly, on the other hand by bringing a reduction in the cost of the optical components used.
• the invention relates, in its most general sense, to a method for initializing a phase change recording medium consisting in heating the phase change medium to be initialized by scanning the surface.
• said medium using a light source characterized in that the laser source consists of an extended light source, in particular in the form of a plurality of discrete laser sources emitting at least one beam directed towards an optical element ensuring convergence into a single heating zone.
• heating zone will be understood to mean a geometrically extended zone in the form of a spot
• single heating zone means that the heating zones generated by each of the beams cover the surface to be initialized. , after convergence, uniformly.
• Each beam produces a bidirectional intensity profile. All the profiles are identical, so that the failure of one of the beams does not affect the shape of the intensity profile, but only the level of energy received by the surface to be initialized.
• the method according to the invention makes it possible to increase the life of the illuminators intended for heating the phase-change optical recording media with a view to their initialization, by allowing the source to fail at one or more points without this either prohibitive for a correct initialization of the recording medium.
• said optical element ensuring the convergence of all of said beams in a single heating zone consists of a diffractive optical element.
• the use of a diffractive optical element makes it possible to facilitate the development of the homogenization of the optical task on the disc.
• the laser source consists of an array of laser diodes.
• the supply current of the laser source is adjusted as a function of the failures of the discrete sources.
• the discrete sources are identical and are supplied in a uniform manner.
• the invention also relates to a device for initializing a phase change recording medium comprising a laser source and means for relative displacement of the laser source with respect to the phase change medium to be initialized, characterized in that the laser source consists of a plurality of discrete laser sources (1 to 9) emitting beams directed towards an optical element ensuring the convergence of all of said beams in a single heating zone.
• FIG. 1 represents a schematic view of the mechanisms for initialization of a phase change medium ;
• FIG. 2 represents a front view of a device according to the invention;
• Figure 3 shows a sectional view of a device according to the invention;
• Figures 4 and 5 show the intensity profiles in two perpendicular directions.
• Figure 1 describes the operation of an optical phase change recording medium.
• the upper part shows the temperature profile in the phase change medium at a given instant, in the case of initialization or erasure, and of writing.
• the central part shows the state of the material before and after passing the laser in both cases.
• the material considered reflects more light in the crystalline state than in the amorphous state.
• the invention aims to increase the life of the illumination devices, and thereby reduce the cost associated with the initialization of phase change optical disks. For this, it is necessary to ensure that a local fault of the source does not induce a fault homogeneity of the illumination at the focal point of the beam.
• the device comprises a strip of laser diodes (1 to 9).
• a diffractive optical element (10) mixes the beams coming from each of the individual emitters (1 to 9), or from the whole extent of the source if the latter is continuous, so that the failure of one of the emitters or a local fault of the extended source does not cause an inhomogeneity of illumination of the recording medium, but a uniform drop in the power received by it.
• the useful power required is then adjusted by the supply current from the source.
• the configuration described in Figures 2 and 3 refers to the case of a bar of discrete transmitters.
• the diffractive optical element combines for each part of the transmitter a focusing function (spot shaping) and a deflection function (lens off-axis function superimposing the contributions of the different zones of the transmitter).
• the invention is not limited to the case of a transmitter made up of juxtaposed discrete sources, but can also take into account a continuous emission line.
• a diffractive optical element makes it possible to shape the beam (s) in order to ensure good homogeneity of the intensity profile of the task according to its large dimension.
• each transmitter or each point of the source giving rise to the same intensity profile on the recording medium a local fault of the source ideally results in a decrease in the power available in the spot without altering the intensity profile.
• adjusting the source supply current increases the available power to the desired value.
• Such a diffractive device can have an overall efficiency of 25 to 50% with binary or quaternary technologies. If we allow 10% variation in intensity, we can reach a depth of field of 20 ⁇ m. The following description relates to a particular embodiment of a device according to the invention.
• each diode is an ultimode power adjustable source by servo control current, capable of emitting a power of 800 mW each.
• the emission diagram forms an angle of 10 ° in the plane of the bar and 40 ° in the direction orthogonal to the plane of the bar.
• the wavelength is 830 nm, and the source has 9 transmitters.
• the final task in the recording medium plane must have dimensions of 200 ⁇ m in the direction of the strip, and 5 ⁇ m in the other direction. In this example, we choose to individually treat the beams from each of the transmitters.
• the distance d2 and the diameter of the microlenses are linked.
• the transverse useful diameter is of the order of 1.2 ⁇ m, whence a maximum frontal distance of 6 mm. We therefore take a distance of 3 mm between the diffractive optical element and the entry of the disc substrate (1.2 mm, index 1.59).
• the minimum pitch of the network is around 2.4 ⁇ m.
• holographic optical elements recorded on photopolymers may also be suitable. This method poses more the problem of recording.

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• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Optical Recording Or Reproduction (AREA)
• Manufacturing Optical Record Carriers (AREA)
• Optical Head (AREA)

Applications Claiming Priority (3)

Publications (1)

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Family Applications (1)

Country Status (4)

Family Cites Families (4)

• 2000
  • 2000-09-05 FR FR0011306A patent/FR2813695B1/fr not_active Expired - Fee Related
• 2001
  • 2001-09-05 WO PCT/FR2001/002756 patent/WO2002021521A1/fr not_active Application Discontinuation
  • 2001-09-05 EP EP01965384A patent/EP1316089A1/de not_active Withdrawn
  • 2001-09-05 AU AU2001286029A patent/AU2001286029A1/en not_active Abandoned

Non-Patent Citations (1)

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