WO2006064426A1 - Optical device wit multi-spot scanning - Google Patents

Optical device wit multi-spot scanning Download PDF

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Publication number
WO2006064426A1
WO2006064426A1 PCT/IB2005/054129 IB2005054129W WO2006064426A1 WO 2006064426 A1 WO2006064426 A1 WO 2006064426A1 IB 2005054129 W IB2005054129 W IB 2005054129W WO 2006064426 A1 WO2006064426 A1 WO 2006064426A1
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WO
WIPO (PCT)
Prior art keywords
satellite
central
sub light
light beam
detecting
Prior art date
Application number
PCT/IB2005/054129
Other languages
French (fr)
Inventor
Joris Vrehen
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Arima Devices Corporation
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Publication date
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Publication of WO2006064426A1 publication Critical patent/WO2006064426A1/en

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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
    • G11B7/13—Optical detectors therefor
    • G11B7/131—Arrangement of detectors in a multiple array
    • 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
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers 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
    • G11B7/0908—Disposition or mounting of heads or light sources relatively to record carriers 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 for focusing only
    • 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
    • G11B7/14—Heads, e.g. forming of the optical beam spot or modulation of the optical beam specially adapted to record on, or to reproduce from, more than one track simultaneously

Definitions

  • the present invention relates to an optical device for scanning an information carrier with a plurality of spots.
  • the present invention is particularly relevant for an optical disc apparatus capable of multi spots readout, such as a CD, DVD or TwoDOS player.
  • Multi spots scanning of an information carrier has several advantages.
  • multi spots readout can be used in order to increase the data rate. Instead of one spot scanning one track, several tracks are scanned simultaneously by means of several spots, which increases the data rate.
  • multi spots readout is used to increase the density of data on the disc.
  • Fig. 1 illustrates an optical scanning device for multi spots scanning.
  • This optical scanning device comprises a polarized radiation source 101, a grating 102, a polarizing beam splitter 103, a collimator 104, a folding mirror 105, an objective lens 106, a quarter wave plate 107 and a multi-spots detector module 108.
  • This optical scanning device is intended for scanning an information carrier 100.
  • the radiation source 101 generates a radiation beam, from which a plurality of spots is generated by means of the grating 102.
  • the spots pass through the polarizing beam splitter 103 and through the collimator 104 before being reflected towards the information carrier 100 by means of the folding mirror 105. They are then focused on the information carrier 100 by means of the objective lens 106.
  • the spots are reflected by the beam splitter 103 towards the multi spots detector module 108, because they have a polarization orthogonal to the polarization of the radiation beam generated by the radiation source 101, due to the presence of the quarter wave plate 107 in the optical path.
  • the multi-spots detector module 108 comprises at least as many detectors as the number of spots.
  • the distance between spots should be as small as possible.
  • a large distance between spots causes coma in the system, because the used field of view of the objective lens 106 is large.
  • the distance between spots is large, the system is critical for so-called Y-errors.
  • a so-called Y-error misalignment occurs.
  • the movement of the objective lens 106 during tracking is not always perpendicular to the tracks, because of a misalignment of the axis along which the objective lens 106 is moved with respect to a direction perpendicular to the tracks. This results in a so-called static Y-error misalignment.
  • a dynamic Y- error misalignment also occurs during rotation of the information carrier, due to eccentricity and ellipticity of the tracks.
  • a focusing method is needed in order to ensure that the spots are focused on the information layer to be scanned.
  • a conventional focusing method is the so-called astigmatic method. In this method, an astigmatic lens is placed before the multi-spots detector module 108, which lens has the effect of enlarging the spots. As a consequence, if the distance between spots is too small, the spots will overlap on the detectors, which makes the focusing method impossible to use.
  • an optical scanning device comprising means for generating at least two scanning beams, means for focusing said at least two scanning beams on an information carrier so as to produce a first and a second information beam, means for generating at least a first central sub light beam and a first satellite first sub light beam from the first information beam and at least a second central sub light beam from the second information beam, a detecting module comprising a first central detector for detecting the first central sub light beam and a second central detector for detecting the second central sub light beam, the first and second central detectors being arranged along a detecting direction, the detecting module further comprising at least a first satellite detector array for detecting the first satellite first sub light beam, said first satellite detector array comprising a first set of at least three adjacent satellite detectors located side by side in a direction perpendicular to the detecting direction, the generating means and the detecting module being arranged in such a way that when the first and second central sub light beams are focused on the first and second central detectors, the first
  • the focusing method is based on a spot size detection.
  • Central detectors are used for detecting the readout signals, whereas at least one satellite detector array is used for measuring a focusing signal.
  • the satellite detector array is arranged in such a way that the satellite spots may overlap on said satellite detector array, without perturbing the focusing method, as will be explained in detailed later on. As a consequence, the distance between spots can be made as small as possible.
  • the generating means are arranged in such a way that the first central sub light beam and the first satellite first sub light beam have different focal planes. In this case, the central and satellite detectors may be in a same plane, which simplifies the detecting module.
  • the first central detector and the first satellite detector array are in different planes. This simplifies the generating means, because a simple grating may be use as generating means in this case.
  • the generating means are arranged to generate a second satellite first sub light beam from the first information beam, the detecting module further comprising a second satellite detector array for detecting the second satellite first sub light beam. This makes the focusing method more robust.
  • the generating means are arranged to generate a first satellite second sub light beam from the second information beam, the generating means and the detecting module being arranged in such a way that when the first and second central sub light beams are focused on the first and second central detectors, the first satellite first sub light beam and the first satellite second sub light beam overlap on the first satellite detector array.
  • the generating means comprise a holographic element.
  • Use of such a holographic element reduces the bulkiness of the system.
  • the generating means comprise a prismatic element comprising a first, semi-reflective surface and a second, at least semi-reflective surface, said prismatic element being arranged in such a way that a first portion of the first information beam passes through the first surface and a second portion is reflected by the first surface and by the second surface before exiting the prismatic element.
  • At least one central detector comprises two sub-detectors located side by side in a direction parallel to the detecting direction. This further allows to center the spots on the central detectors.
  • the first satellite detector array further comprises a second set of at least three adjacent satellite detectors located side by side in a direction perpendicular to the detecting direction, the first and second set of satellite detectors being arranged along the detecting direction. This further improves focusing of the spots on the scanned information layer.
  • - Fig. 1 shows an optical scanning device in accordance with the prior art
  • - Fig. 2a shows a detection branch of an optical scanning device in accordance with the invention
  • Fig. 2b shows a detecting module of the detection branch of Fig. 2a
  • Fig. 2c shows a focus signal obtained with the detecting module of Fig. 2b;
  • - Fig. 3 shows a detection branch of an optical scanning device in accordance with a preferred embodiment of the invention
  • - Fig. 4a shows a detection branch of an optical scanning device in accordance with an advantageous embodiment of the invention
  • Fig. 4b shows a detecting module of the detection branch of Fig. 4a
  • Fig. 4c shows a focus signal obtained with the detecting module of Fig. 4b;
  • Fig. 5 shows another detecting module that can be used in the detection branches of Figs. 2 to 4;
  • FIG. 6 shows a detecting module in accordance with another advantageous embodiment of the invention.
  • FIG. 7 shows a detecting module in accordance with another preferred embodiment of the invention.
  • a detection branch in accordance with the invention is depicted in Figs. 2a and 2b.
  • the information beams reach generating means 201.
  • the generating means 201 generate four central sub light beams and at least one satellite sub light beam.
  • the generating means 201 generate one satellite sub light beam from a second information beam, but the generating means 201 may generate, for example, one satellite sub light beam per information beam.
  • the detection branch further comprises a detecting module comprising a central detector array 202 for detecting the central sub light beams and a satellite detector array 203 for detecting the satellite sub light beam.
  • the central detector array 202 comprises a first central detector 202a, a second central detector 202b, a third central detector 202c and a fourth central detector 202d.
  • the central detectors 202a to 202d are arranged along a detecting direction, which is shown by the arrow DD in Fig. 2b.
  • the satellite detector array 203 comprises a set of at least three adjacent satellite detectors 203a, 203b and 203c located side by side in a direction perpendicular to the detecting direction DD.
  • the generating means 201 comprise a prismatic element comprising a first, semi-reflective surface 201a and a second, at least semi-reflective surface 201b.
  • the second, at least semi-reflective surface 201b may also be completely reflective.
  • the prismatic element 201 is arranged in such a way that a first portion of the second information beam passes through the first surface and a second portion is reflected by the first surface and by the second surface before exiting the prismatic element.
  • the second central sub light beam and the satellite beam have different focal plane.
  • Such a prismatic element 201 is known, for example, from patent US 6,278,681.
  • the central detector array 202 and the satellite detector array 203 are placed in a same plane. As a consequence, when the central sub light beams are focused on the central detector array 202, the satellite sub light beam is defocused on the satellite detector array 203. This is illustrated in Fig. 2b, where the central sub light beams are focused on the central detector array 202, whereas the satellite sub light beam is defocused on the satellite detector array 203 and thus has a greater size than the central sub light beams.
  • the central detectors 202a to 202d measure the HF signal corresponding to each information beam, i.e. the signal encoded on adjacent tracks of the scanned information layer.
  • the satellite detector array 203 is used in order to derive a focus signal, as explained hereinafter.
  • the satellite detector array 203 is designed in such a way that, when the central sub light beams are focused on the central detector array 202, the quantity a + c - b is null, where a, b and c represents the intensity of the signals detected by satellite detectors 203 a, 203b and 203 c respectively.
  • Fig. 2c shows the quantity a + c - b as a function of the focus of the scanning beams on the scanned information layer. This quantity is null only when the scanning beams are focused on the scanned information layer, i.e. when the central sub light beams are focused on the central detectors 202a to 202d. This property can be used in order to adjust the position of the objective lens 106 of Fig.
  • a servo control may be used.
  • Servo control is well known to those skilled in the art and will thus not be described further.
  • a servo control similar to the servo control used in conventional CD players may be used, which is based on the so-called focus s-curve signal.
  • the generating means may comprise, for example, means for blocking the other satellite sub light beams generated by the second, at least semi-reflective surface 201b, before they exist the generating means 201.
  • the invention is not limited to the use of only one satellite sub light beam, and the generating means preferably generate as many satellite sub light beams as the number of information beams.
  • the shape of the focus signal represented in Fig. 2c is not modified, even if the satellite sub light beams overlap on the satellite detector array 203. This is explained in further details in Figs. 4 and 5.
  • the central sub light beams may be as close together as desired, because this has no influence on the focus signal.
  • the scanning beams may be as close together as desired on the information carrier, the minimum distance being of course one track pitch.
  • other generating means may be used.
  • a holographic element such as described in patent US 6,014,359 may be used.
  • this patent describes an optical device in which central spots and satellite spots are generated.
  • the optical device comprises central detectors and a satellite detector array.
  • the satellite detector array comprises adjacent satellite detectors which are located side by side in a direction that is parallel to the direction of the central detectors. As a consequence, it is not possible to generate a reliable focus signal from this satellite detector array, especially when the satellite sub light beams overlap. Hence, this optical device is not suitable for multi spots scanning.
  • the generating means comprise a grating 301, which generate first and second orders light beams form each information beam.
  • the first order light beams corresponds to the central sub- light beams
  • the second order light beams corresponds to the satellite sub-light beams.
  • the central and satellite sub light beams have the same focal plane.
  • the detection branch comprises a central detector array 302, which is identical to the central detector array of Fig. 2a, and a satellite detector array 303, which is identical to the satellite detector array of Fig. 2a.
  • the central detector array 302 and the satellite detector array 303 are in different planes. As a consequence, when the central sub light beams are focused on the central detector array 302, the satellite sub light beams are defocused on the satellite detector array
  • the sub light beams on the detecting module are identical to the sub light beams represented in Fig. 2b, and the focus signal is identical to the focus signal represented in Fig. 2c.
  • a detection branch in accordance with an advantageous embodiment of the invention is shown in Figs. 4a and 4b.
  • the generating means 401 generate four central sub light beams, four first satellite sub light beams and four second satellite sub light beams.
  • the detection branch further comprises a detecting module comprising a central detector array 402 for detecting the central sub light beams, a first satellite detector array 403 for detecting the first satellite sub light beams and a second satellite detector array 404 for detecting the second satellite sub light beams.
  • the central detector array 402 comprises a first central detector 402a, a second central detector 402b, a third central detector 402c and a fourth central detector 402d.
  • the first satellite detector array 403 comprises a set of three adjacent satellite detectors 403 a, 403b and 403 c located side by side in a direction perpendicular to the detecting direction DD and the second satellite detector array 404 comprises a set of three adjacent satellite detectors 404d, 404e and 404f located side by side in a direction perpendicular to the detecting direction DD.
  • the generating means 401 comprise a prismatic element comprising a first, semi-reflective surface 401a, a second, semi-reflective surface 401b and a third, at least semi-reflective surface 401c.
  • the third, at least semi-reflective surface 401c may also be completely reflective.
  • the prismatic element 401 is arranged in such a way that a first portion of the information beam passes through the first surface 401a, a second portion is reflected by the first surface 401a and by the second surface 401b before exiting the prismatic element 401 and a third portion is transmitted towards the third surface 401c and reflected by said third surface 401c before exiting the generating means 401.
  • the central sub light beams, the first satellite sub light beams and the second satellite sub light beams have different focal planes.
  • the central detector array 402, the first satellite detector array 403 and the second satellite detector array 404 are placed in a same plane.
  • the first satellite detector array 403 is designed in such a way that, when the central sub light beams are focused on the central detector array 402, the quantity a + c - b is null, and the quantity d + f - e is also null.
  • Fig. 2c shows the quantity a + c - b - (d + f - e) as a function of the focus of the scanning beams on the scanned information layer. This quantity is null only when the scanning beams are focused on the scanned information layer, i.e. when the central sub light beams are focused on the central detectors 402a to 402d. This property is used in order to adjust the position of the objective lens 106 of Fig. 1 until this quantity is null.
  • Fig. 5 shows another detecting module that can be used in the detection branches of Figs. 2 to 4.
  • This detecting module comprises four central detectors 502a to 502d and a satellite detector array 503 comprising three satellite detectors 503a, 503b and 503c located side by side in a direction perpendicular to the detecting direction DD.
  • the size of the detector array 503 in the detecting direction DD is at least as large as the size of the central detector array 502 in the detecting direction.
  • the focus signal takes into account the intensities of all the satellite sub light beams, which makes the focusing method more robust.
  • a detecting module in accordance with another advantageous embodiment of the invention is depicted in Fig. 6.
  • This detecting module comprises a satellite detector array 603, which is identical to the satellite detector array 503 of Fig. 5. It also comprises a central detector array 602, which comprises four central detectors 602a to 602d.
  • Each central detector comprises two sub-detectors located side by side in a direction parallel to the detecting direction.
  • the first central detector 602a comprises a first central sub detector 602al and a second central sub detector 602a2. This makes it possible to center the central sub light beams on the central detectors. For example, by calculating the difference in intensities of the first central sub detector 602al and the second central sub detector 602a2, the first central sub light beam may be centered.
  • the second central detector 602b also comprises two sub detectors, it is further possible to align the spots in the detecting direction, in that the second central spot is centered on the second central detector 602b.
  • a detecting module in accordance with another preferred embodiment of the invention is depicted in Fig. 7.
  • This detecting module comprises a central detector array 702, which is identical to the central detector array 502 of Fig. 5. It also comprises a satellite detector array 703, which comprises a first set of three adjacent satellite detectors 703a to 703c and a second set of satellite detectors 703g to 703i. This makes the focusing more robust. Actually, if in Fig.
  • the quantity a + c - b will be null, although the focus could be improved.
  • This problem is solved by means of the satellite detector array of Fig. 7. Actually, in the situation described hereinbefore, the quantity a + c - b will not be null, and the quantity g + i - h will not be null, but the quantity (a + g) + (c + i) - (b + h) will be null.
  • This property can be used to modify the optical scanning device, for example in that the objective lens 106 is rotated until the three abovementioned quantities are null, which means that the four information beams are well focused on the scanned information layer.

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Recording Or Reproduction (AREA)
  • Mechanical Optical Scanning Systems (AREA)

Abstract

An optical scanning device comprises means (101, 102) for generating two scanning beams, means (104, 105, 106) for focusing the two scanning beams on an information carrier (100) so as to produce a first and a second information beam, means (201, 301, 401) for generating at least a first central sub light beam and a first satellite first sub light beam from the first information beam and at least a second central sub light beam from the second information beam, a detecting module comprising a first central detector (202a, 402a, 502a, 602a, 702a) for detecting the first central sub light beam and a second central detector (202b, 402b, 502b, 602b, 702b) for detecting the second central sub light beam, the first and second central detectors being arranged along a detecting direction (DD). The detecting module further comprises at least a first satellite detector array (203, 303, 403, 503, 603, 703) for detecting the first satellite first sub light beam. The first satellite detector array comprises a first set of at least three adjacent satellite detectors (203a-203c, 3O3a-3O3c, 403a-403c, 503a- 503c, 603a-603c, 703a-703c) located side by side in a direction perpendicular to the detecting direction. The generating means and the detecting module are arranged in such a way that when the first and second central sub light beams are focused on the first and second central detectors, the first satellite first sub light beam is defocused on the first satellite detector array.

Description

Optical device wit multi-spot scanning
FIELD OF THE INVENTION
The present invention relates to an optical device for scanning an information carrier with a plurality of spots.
The present invention is particularly relevant for an optical disc apparatus capable of multi spots readout, such as a CD, DVD or TwoDOS player.
BACKGROUND OF THE INVENTION Multi spots scanning of an information carrier has several advantages. In case of a conventional optical disc such as CD or DVD, multi spots readout can be used in order to increase the data rate. Instead of one spot scanning one track, several tracks are scanned simultaneously by means of several spots, which increases the data rate. In case of future systems were data are stored in two dimensions, such as TwoDOS, multi spots readout is used to increase the density of data on the disc.
Fig. 1 illustrates an optical scanning device for multi spots scanning. This optical scanning device comprises a polarized radiation source 101, a grating 102, a polarizing beam splitter 103, a collimator 104, a folding mirror 105, an objective lens 106, a quarter wave plate 107 and a multi-spots detector module 108. This optical scanning device is intended for scanning an information carrier 100. The radiation source 101 generates a radiation beam, from which a plurality of spots is generated by means of the grating 102. The spots pass through the polarizing beam splitter 103 and through the collimator 104 before being reflected towards the information carrier 100 by means of the folding mirror 105. They are then focused on the information carrier 100 by means of the objective lens 106. On reflection from the disc, the spots are reflected by the beam splitter 103 towards the multi spots detector module 108, because they have a polarization orthogonal to the polarization of the radiation beam generated by the radiation source 101, due to the presence of the quarter wave plate 107 in the optical path. The multi-spots detector module 108 comprises at least as many detectors as the number of spots. In such a multi- spots system, the distance between spots should be as small as possible. Actually, a large distance between spots causes coma in the system, because the used field of view of the objective lens 106 is large. Moreover, if the distance between spots is large, the system is critical for so-called Y-errors. In a typical optical scanning device, a so-called Y-error misalignment occurs. Actually, the movement of the objective lens 106 during tracking is not always perpendicular to the tracks, because of a misalignment of the axis along which the objective lens 106 is moved with respect to a direction perpendicular to the tracks. This results in a so-called static Y-error misalignment. Moreover, a dynamic Y- error misalignment also occurs during rotation of the information carrier, due to eccentricity and ellipticity of the tracks.
However, reducing the distance between spots makes it difficult to use conventional focusing methods. A focusing method is needed in order to ensure that the spots are focused on the information layer to be scanned. A conventional focusing method is the so-called astigmatic method. In this method, an astigmatic lens is placed before the multi-spots detector module 108, which lens has the effect of enlarging the spots. As a consequence, if the distance between spots is too small, the spots will overlap on the detectors, which makes the focusing method impossible to use.
SUMMARY OF THE INVENTION It is an object of the invention to provide an optical scanning device capable of multi spots scanning, in which the distance between spots is reduced while a robust focusing method is implemented.
To this end, the invention proposes an optical scanning device comprising means for generating at least two scanning beams, means for focusing said at least two scanning beams on an information carrier so as to produce a first and a second information beam, means for generating at least a first central sub light beam and a first satellite first sub light beam from the first information beam and at least a second central sub light beam from the second information beam, a detecting module comprising a first central detector for detecting the first central sub light beam and a second central detector for detecting the second central sub light beam, the first and second central detectors being arranged along a detecting direction, the detecting module further comprising at least a first satellite detector array for detecting the first satellite first sub light beam, said first satellite detector array comprising a first set of at least three adjacent satellite detectors located side by side in a direction perpendicular to the detecting direction, the generating means and the detecting module being arranged in such a way that when the first and second central sub light beams are focused on the first and second central detectors, the first satellite first sub light beam is defocused on the first satellite detector array.
According to the invention, the focusing method is based on a spot size detection. Central detectors are used for detecting the readout signals, whereas at least one satellite detector array is used for measuring a focusing signal. The satellite detector array is arranged in such a way that the satellite spots may overlap on said satellite detector array, without perturbing the focusing method, as will be explained in detailed later on. As a consequence, the distance between spots can be made as small as possible. Advantageously, the generating means are arranged in such a way that the first central sub light beam and the first satellite first sub light beam have different focal planes. In this case, the central and satellite detectors may be in a same plane, which simplifies the detecting module.
Preferably, the first central detector and the first satellite detector array are in different planes. This simplifies the generating means, because a simple grating may be use as generating means in this case.
Advantageously, the generating means are arranged to generate a second satellite first sub light beam from the first information beam, the detecting module further comprising a second satellite detector array for detecting the second satellite first sub light beam. This makes the focusing method more robust.
Preferably, the generating means are arranged to generate a first satellite second sub light beam from the second information beam, the generating means and the detecting module being arranged in such a way that when the first and second central sub light beams are focused on the first and second central detectors, the first satellite first sub light beam and the first satellite second sub light beam overlap on the first satellite detector array.
Advantageously, the generating means comprise a holographic element. Use of such a holographic element reduces the bulkiness of the system.
Preferably, the generating means comprise a prismatic element comprising a first, semi-reflective surface and a second, at least semi-reflective surface, said prismatic element being arranged in such a way that a first portion of the first information beam passes through the first surface and a second portion is reflected by the first surface and by the second surface before exiting the prismatic element.
Advantageously, at least one central detector comprises two sub-detectors located side by side in a direction parallel to the detecting direction. This further allows to center the spots on the central detectors.
Preferably, the first satellite detector array further comprises a second set of at least three adjacent satellite detectors located side by side in a direction perpendicular to the detecting direction, the first and second set of satellite detectors being arranged along the detecting direction. This further improves focusing of the spots on the scanned information layer.
These and other aspects of the invention will be apparent from and will be elucidated with reference to the embodiments described hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in more detail by way of example with reference to the accompanying drawings, in which :
- Fig. 1 shows an optical scanning device in accordance with the prior art; - Fig. 2a shows a detection branch of an optical scanning device in accordance with the invention, Fig. 2b shows a detecting module of the detection branch of Fig. 2a and Fig. 2c shows a focus signal obtained with the detecting module of Fig. 2b;
- Fig. 3 shows a detection branch of an optical scanning device in accordance with a preferred embodiment of the invention; - Fig. 4a shows a detection branch of an optical scanning device in accordance with an advantageous embodiment of the invention, Fig. 4b shows a detecting module of the detection branch of Fig. 4a and Fig. 4c shows a focus signal obtained with the detecting module of Fig. 4b;
- Fig. 5 shows another detecting module that can be used in the detection branches of Figs. 2 to 4;
- Fig. 6 shows a detecting module in accordance with another advantageous embodiment of the invention;
- Fig. 7 shows a detecting module in accordance with another preferred embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
A detection branch in accordance with the invention is depicted in Figs. 2a and 2b. After the beam splitter 103 of Fig. 1, the information beams reach generating means 201. In the example of Figs. 2a and 2b, four information beams are generated. However, the invention applies to any number of information beams, as soon as there is to at least two information beams. The generating means 201 generate four central sub light beams and at least one satellite sub light beam. In the example of Figs. 2a and 2b, the generating means 201 generate one satellite sub light beam from a second information beam, but the generating means 201 may generate, for example, one satellite sub light beam per information beam. The detection branch further comprises a detecting module comprising a central detector array 202 for detecting the central sub light beams and a satellite detector array 203 for detecting the satellite sub light beam. The central detector array 202 comprises a first central detector 202a, a second central detector 202b, a third central detector 202c and a fourth central detector 202d. The central detectors 202a to 202d are arranged along a detecting direction, which is shown by the arrow DD in Fig. 2b. The satellite detector array 203 comprises a set of at least three adjacent satellite detectors 203a, 203b and 203c located side by side in a direction perpendicular to the detecting direction DD.
In the example of Fig. 2a, the generating means 201 comprise a prismatic element comprising a first, semi-reflective surface 201a and a second, at least semi-reflective surface 201b. The second, at least semi-reflective surface 201b, may also be completely reflective. In this example, the prismatic element 201 is arranged in such a way that a first portion of the second information beam passes through the first surface and a second portion is reflected by the first surface and by the second surface before exiting the prismatic element. As can be shown from Fig. 2b, the second central sub light beam and the satellite beam have different focal plane. Such a prismatic element 201 is known, for example, from patent US 6,278,681.
The central detector array 202 and the satellite detector array 203 are placed in a same plane. As a consequence, when the central sub light beams are focused on the central detector array 202, the satellite sub light beam is defocused on the satellite detector array 203. This is illustrated in Fig. 2b, where the central sub light beams are focused on the central detector array 202, whereas the satellite sub light beam is defocused on the satellite detector array 203 and thus has a greater size than the central sub light beams. The central detectors 202a to 202d measure the HF signal corresponding to each information beam, i.e. the signal encoded on adjacent tracks of the scanned information layer. The satellite detector array 203 is used in order to derive a focus signal, as explained hereinafter.
In this example, the satellite detector array 203 is designed in such a way that, when the central sub light beams are focused on the central detector array 202, the quantity a + c - b is null, where a, b and c represents the intensity of the signals detected by satellite detectors 203 a, 203b and 203 c respectively. Fig. 2c shows the quantity a + c - b as a function of the focus of the scanning beams on the scanned information layer. This quantity is null only when the scanning beams are focused on the scanned information layer, i.e. when the central sub light beams are focused on the central detectors 202a to 202d. This property can be used in order to adjust the position of the objective lens 106 of Fig. 1 until this quantity is null, i.e. until the scanning beams are focused on the scanned information layer. To this end, a servo control may be used. Servo control is well known to those skilled in the art and will thus not be described further. For example, a servo control similar to the servo control used in conventional CD players may be used, which is based on the so-called focus s-curve signal.
In order to generate only one satellite sub light beam, the generating means may comprise, for example, means for blocking the other satellite sub light beams generated by the second, at least semi-reflective surface 201b, before they exist the generating means 201. However, the invention is not limited to the use of only one satellite sub light beam, and the generating means preferably generate as many satellite sub light beams as the number of information beams. In this case, the shape of the focus signal represented in Fig. 2c is not modified, even if the satellite sub light beams overlap on the satellite detector array 203. This is explained in further details in Figs. 4 and 5. As a consequence, the central sub light beams may be as close together as desired, because this has no influence on the focus signal. Hence, the scanning beams may be as close together as desired on the information carrier, the minimum distance being of course one track pitch. Instead of the prismatic element 201, other generating means may be used. For example, a holographic element such as described in patent US 6,014,359 may be used. It should be noted that this patent describes an optical device in which central spots and satellite spots are generated. The optical device comprises central detectors and a satellite detector array. The satellite detector array comprises adjacent satellite detectors which are located side by side in a direction that is parallel to the direction of the central detectors. As a consequence, it is not possible to generate a reliable focus signal from this satellite detector array, especially when the satellite sub light beams overlap. Hence, this optical device is not suitable for multi spots scanning.
A detection branch in accordance with a preferred embodiment of the invention is depicted in Fig. 3. In this embodiment, the generating means comprise a grating 301, which generate first and second orders light beams form each information beam. The first order light beams corresponds to the central sub- light beams, whereas the second order light beams corresponds to the satellite sub-light beams. According to this embodiment, the central and satellite sub light beams have the same focal plane. The detection branch comprises a central detector array 302, which is identical to the central detector array of Fig. 2a, and a satellite detector array 303, which is identical to the satellite detector array of Fig. 2a. The central detector array 302 and the satellite detector array 303 are in different planes. As a consequence, when the central sub light beams are focused on the central detector array 302, the satellite sub light beams are defocused on the satellite detector array
303. Hence the sub light beams on the detecting module are identical to the sub light beams represented in Fig. 2b, and the focus signal is identical to the focus signal represented in Fig. 2c.
A detection branch in accordance with an advantageous embodiment of the invention is shown in Figs. 4a and 4b. The generating means 401 generate four central sub light beams, four first satellite sub light beams and four second satellite sub light beams. The detection branch further comprises a detecting module comprising a central detector array 402 for detecting the central sub light beams, a first satellite detector array 403 for detecting the first satellite sub light beams and a second satellite detector array 404 for detecting the second satellite sub light beams. The central detector array 402 comprises a first central detector 402a, a second central detector 402b, a third central detector 402c and a fourth central detector 402d. The first satellite detector array 403 comprises a set of three adjacent satellite detectors 403 a, 403b and 403 c located side by side in a direction perpendicular to the detecting direction DD and the second satellite detector array 404 comprises a set of three adjacent satellite detectors 404d, 404e and 404f located side by side in a direction perpendicular to the detecting direction DD. In the example of Fig. 4a, the generating means 401 comprise a prismatic element comprising a first, semi-reflective surface 401a, a second, semi-reflective surface 401b and a third, at least semi-reflective surface 401c. The third, at least semi-reflective surface 401c, may also be completely reflective. In this example, the prismatic element 401 is arranged in such a way that a first portion of the information beam passes through the first surface 401a, a second portion is reflected by the first surface 401a and by the second surface 401b before exiting the prismatic element 401 and a third portion is transmitted towards the third surface 401c and reflected by said third surface 401c before exiting the generating means 401. The central sub light beams, the first satellite sub light beams and the second satellite sub light beams have different focal planes. The central detector array 402, the first satellite detector array 403 and the second satellite detector array 404 are placed in a same plane. As a consequence, when the central sub light beams are focused on the central detector array 402, the first satellite sub light beams are defocused on the first satellite detector array 403 and the second satellite sub light beams are defocused on the second satellite detector array 404. This is illustrated in Fig. 4b, where the central sub light beams are focused on the central detector array 402, whereas the first satellite sub light beams are defocused on the first satellite detector array 403 and the second satellite sub light beams are defocused on the second satellite detector array 404 and thus have a greater size than the central sub light beams. In this example, the first satellite detector array 403 is designed in such a way that, when the central sub light beams are focused on the central detector array 402, the quantity a + c - b is null, and the quantity d + f - e is also null. Fig. 2c shows the quantity a + c - b - (d + f - e) as a function of the focus of the scanning beams on the scanned information layer. This quantity is null only when the scanning beams are focused on the scanned information layer, i.e. when the central sub light beams are focused on the central detectors 402a to 402d. This property is used in order to adjust the position of the objective lens 106 of Fig. 1 until this quantity is null.
Fig. 5 shows another detecting module that can be used in the detection branches of Figs. 2 to 4. This detecting module comprises four central detectors 502a to 502d and a satellite detector array 503 comprising three satellite detectors 503a, 503b and 503c located side by side in a direction perpendicular to the detecting direction DD. The size of the detector array 503 in the detecting direction DD is at least as large as the size of the central detector array 502 in the detecting direction. As a consequence, the focus signal takes into account the intensities of all the satellite sub light beams, which makes the focusing method more robust.
A detecting module in accordance with another advantageous embodiment of the invention is depicted in Fig. 6. This detecting module comprises a satellite detector array 603, which is identical to the satellite detector array 503 of Fig. 5. It also comprises a central detector array 602, which comprises four central detectors 602a to 602d. Each central detector comprises two sub-detectors located side by side in a direction parallel to the detecting direction. For example, the first central detector 602a comprises a first central sub detector 602al and a second central sub detector 602a2. This makes it possible to center the central sub light beams on the central detectors. For example, by calculating the difference in intensities of the first central sub detector 602al and the second central sub detector 602a2, the first central sub light beam may be centered. If the second central detector 602b also comprises two sub detectors, it is further possible to align the spots in the detecting direction, in that the second central spot is centered on the second central detector 602b. A detecting module in accordance with another preferred embodiment of the invention is depicted in Fig. 7. This detecting module comprises a central detector array 702, which is identical to the central detector array 502 of Fig. 5. It also comprises a satellite detector array 703, which comprises a first set of three adjacent satellite detectors 703a to 703c and a second set of satellite detectors 703g to 703i. This makes the focusing more robust. Actually, if in Fig. 5 the first and second information beams are slightly after focus and the third and fourth information beams are slightly before focus, the quantity a + c - b will be null, although the focus could be improved. This problem is solved by means of the satellite detector array of Fig. 7. Actually, in the situation described hereinbefore, the quantity a + c - b will not be null, and the quantity g + i - h will not be null, but the quantity (a + g) + (c + i) - (b + h) will be null. This property can be used to modify the optical scanning device, for example in that the objective lens 106 is rotated until the three abovementioned quantities are null, which means that the four information beams are well focused on the scanned information layer.
Any reference sign in the following claims should not be construed as limiting the claim. It will be obvious that the use of the verb "to comprise" and its conjugations does not exclude the presence of any other elements besides those defined in any claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

Claims

1 An optical scanning device comprising means (101, 102) for generating at least two scanning beams, means (104, 105, 106) for focusing said at least two scanning beams on an information carrier (100) so as to produce a first and a second information beam, means (201, 301, 401) for generating at least a first central sub light beam and a first satellite first sub light beam from the first information beam and at least a second central sub light beam from the second information beam, a detecting module comprising a first central detector (202a, 402a, 502a, 602a, 702a) for detecting the first central sub light beam and a second central detector (202b, 402b, 502b, 602b, 702b) for detecting the second central sub light beam, the first and second central detectors being arranged along a detecting direction (DD), the detecting module further comprising at least a first satellite detector array (203, 303, 403, 503, 603, 703) for detecting the first satellite first sub light beam, said first satellite detector array comprising a first set of at least three adjacent satellite detectors (203a-203c, 303a- 303c, 403a-403c, 503a-503c, 603a-603c, 703a-703c) located side by side in a direction perpendicular to the detecting direction, the generating means and the detecting module being arranged in such a way that when the first and second central sub light beams are focused on the first and second central detectors, the first satellite first sub light beam is defocused on the first satellite detector array. 2 An optical scanning device as claimed in claim 1, wherein the generating means are arranged in such a way that the first central sub light beam and the first satellite first sub light beam have different focal planes.
3 An optical scanning device as claimed in claim 1, wherein the first central detector and the first satellite detector array are in different planes. A An optical scanning device as claimed in claim 1, wherein the generating means are arranged to generate a second satellite first sub light beam from the first information beam, the detecting module further comprising a second satellite detector array (404) for detecting the second satellite first sub light beam. 5 An optical scanning device as claimed in claim 1, wherein the generating means are arranged to generate a first satellite second sub light beam from the second information beam, the generating means and the detecting module being arranged in such a way that when the first and second central sub light beams are focused on the first and second central detectors, the first satellite first sub light beam and the first satellite second sub light beam overlap on the first satellite detector array. 6 An optical scanning device as claimed in claim 2, wherein the generating means comprise a holographic element.
7 An optical scanning device as claimed in claim 2, wherein the generating means (201, 401) comprise a prismatic element comprising a first, semi-reflective surface and a second, at least semi- reflective surface, said prismatic element being arranged in such a way that a first portion of the first information beam passes through the first surface and a second portion is reflected by the first surface and by the second surface before exiting the prismatic element.
8 An optical scanning device as claimed in claim 1, wherein at least one central detector comprises two sub-detectors (602al, 602a2) located side by side in a direction parallel to the detecting direction.
9 An optical scanning device as claimed in claim 1, wherein the first satellite detector array further comprises a second set of at least three adjacent satellite detectors (703g, 703h, 703i) located side by side in a direction perpendicular to the detecting direction, the first and second set of satellite detectors being arranged along the detecting direction.
PCT/IB2005/054129 2004-12-15 2005-12-08 Optical device wit multi-spot scanning WO2006064426A1 (en)

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8154975B1 (en) 2010-11-18 2012-04-10 General Electric Company Servoing system for multiple spot registration for holographic replication system
US8248905B2 (en) 2010-10-15 2012-08-21 General Electric Company Method of parallel bit-wise holographic data storage source using a parallel light source
US8254224B2 (en) 2010-11-18 2012-08-28 General Electric Company Servoing system for master with parallel tracks in a holographic replication system

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5526330A (en) * 1992-12-24 1996-06-11 Matsushita Electric Industrial Co., Ltd. Optical head assembly for optical information player
EP1005031A2 (en) * 1998-11-26 2000-05-31 Sharp Kabushiki Kaisha Multi-beam optical pickup apparatus appropriately controlling distance between objective lens and optical information recording medium.
US6229771B1 (en) * 1998-10-09 2001-05-08 Zen Research (Ireland), Ltd. Method and apparatus for generating focus error signals in a multi-beam optical disk drive

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5526330A (en) * 1992-12-24 1996-06-11 Matsushita Electric Industrial Co., Ltd. Optical head assembly for optical information player
US6229771B1 (en) * 1998-10-09 2001-05-08 Zen Research (Ireland), Ltd. Method and apparatus for generating focus error signals in a multi-beam optical disk drive
EP1005031A2 (en) * 1998-11-26 2000-05-31 Sharp Kabushiki Kaisha Multi-beam optical pickup apparatus appropriately controlling distance between objective lens and optical information recording medium.

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8248905B2 (en) 2010-10-15 2012-08-21 General Electric Company Method of parallel bit-wise holographic data storage source using a parallel light source
US8154975B1 (en) 2010-11-18 2012-04-10 General Electric Company Servoing system for multiple spot registration for holographic replication system
US8254224B2 (en) 2010-11-18 2012-08-28 General Electric Company Servoing system for master with parallel tracks in a holographic replication system

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