WO2008117228A1 - Procédé pour détecter la piste de données d'un disque optique - Google Patents

Procédé pour détecter la piste de données d'un disque optique Download PDF

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Publication number
WO2008117228A1
WO2008117228A1 PCT/IB2008/051087 IB2008051087W WO2008117228A1 WO 2008117228 A1 WO2008117228 A1 WO 2008117228A1 IB 2008051087 W IB2008051087 W IB 2008051087W WO 2008117228 A1 WO2008117228 A1 WO 2008117228A1
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WO
WIPO (PCT)
Prior art keywords
spot
radiation beam
main
signal
push
Prior art date
Application number
PCT/IB2008/051087
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English (en)
Inventor
Alexander Marc Lee
Erwin Altewischer
Emile Johannes Karel Verstegen
Original Assignee
Koninklijke Philips Electronics N.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips Electronics N.V. filed Critical Koninklijke Philips Electronics N.V.
Publication of WO2008117228A1 publication Critical patent/WO2008117228A1/fr

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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
    • G11B7/08—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
    • G11B7/0901—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 track following only
    • G11B7/0903—Multi-beam tracking systems
    • 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
    • G11B2007/0003—Recording, reproducing or erasing systems characterised by the structure or type of the carrier
    • G11B2007/0009—Recording, reproducing or erasing systems characterised by the structure or type of the carrier for carriers having data stored in three dimensions, e.g. volume storage
    • G11B2007/0013—Recording, reproducing or erasing systems characterised by the structure or type of the carrier for carriers having data stored in three dimensions, e.g. volume storage for carriers having multiple discrete layers

Definitions

  • the subject matter relates to a method for tracking the information track of an optical disc, and more specifically, to tracking the information tracks in multi-layer optical discs.
  • US Patent 5923632 discloses an optical pick-up device for a multi-layer optical disc wherein a light beam generated by a light source is separated into a main beam, a first side beam and a second side beam.
  • the main beam is focused onto the main spot; the first side beam and the second side beam are focused on to the first and second side spots respectively on the multi-layer optical discs.
  • Reflected light beams from the main spot, the first and the second side spots are photo-electrically converted by the main beam receiving means, the first side beam receiving means and the second side beam receiving means to obtain push-pull tracking signals.
  • the first side beam receiving means and the second side beam receiving means are spaced a distance apart from the main beam receiving means so that no interference with the first and the second side beam receiving means results from the main beam reflected from an unfocused information layer of the multi-layer optical disc.
  • This solution may be technically challenging because positioning the first side beam receiving means and the second side beam receiving means with a high degree of precision may be difficult to achieve. There may be some amount of interference from the main beam reflected from an unfocussed information layer of the multi-layer optical disc. This may result in inaccurate push-pull tracking signal affecting the recording/reproducing of the data.
  • a method of radially tracking the information track of a multi- layer optical record carrier comprises generating a push-pull tracking signal derived from the light of a main spot, a first side spot and a second side spot falling on an optical detector, wherein the main spot, the first side spot and the second side spot are formed by focusing a main radiation beam, a first side radiation beam and a second side radiation beam, respectively, taking into consideration the effect of a background spot resulting from reflections of the main spot from out-of- focus layers of the multi-layer optical record carrier.
  • the optical pick-up unit comprises a control unit arranged to generate a push-pull tracking signal derived from the light of a main spot, a first side spot and a second side spot falling on an optical detector, wherein the main spot, the first side spot and the second side spot are formed by focusing a main radiation beam, a first side radiation beam and a second side radiation beam, respectively, taking into consideration the effect of a background spot resulting from reflections of the main spot from out-of- focus layers of the multi-layer optical record carrier.
  • the method of obtaining accurate push-pull tracking signal for a multi-layer optical record carrier could be implemented with a computer program.
  • Fig. 1 schematically illustrates an exemplary optical pick-up unit
  • Fig. 2 schematically illustrates an exemplary optical detector used for obtaining radial push-pull tracking signals
  • Fig. 3 schematically illustrates the positional relationship between the main spot, the first side spot and the second side spot in an exemplary differential push-pull method
  • Fig. 4 schematically illustrates the distribution of the light intensity on the optical detector plane showing a background spot along with the main spot, the first side spot and the second side spot, the background spot resulting from reflections from out-of-focus layer of an exemplary multi-layer Blu-ray disc;
  • Fig. 5A and Fig. 5B graphically illustrates the magnitude of distortion of the push-pull tracking signal with the side spots (i.e. with the first side spot and the second side spot) and without the side spots (i.e. without the first side spot and the second side spot);
  • Fig. 6 shows the method of generating the push-pull tracking signal according to an embodiment of the present subject matter;
  • Fig. 7 shows schematically an exemplary liquid crystal grating
  • Fig. 8 shows schematically an exemplary acousto-optic modulator
  • Optical record carrier 2 can be a multi-layer Recordable (R) or Rewritable (RW) type, where information may be stored or recorded on information tracks, such as DVD+RW, DVD-RW, DVD+R, HD-DVD and BD+RW.
  • R Recordable
  • RW Rewritable
  • the optical pick-up unit 30 has a radiation generator 31 (e.g. laser diode), arranged to generate a radiation beam 32a.
  • the radiation beam 32a passes a beam splitter 33 and an objective lens 34.
  • the objective lens 34 focuses the radiation beam 32b in a focal spot F on the optical record carrier 2.
  • the radiation beam 32b reflects from the optical record carrier 2 (reflected radiation beam 32c) and passes the collimator lens 34a and the objective lens 34b and the beam splitter 33 (beam 32d) and passes through an astigmatic lens 36 (for focusing error signal generation) to reach an optical detector 35.
  • the objective lens 34 is mounted axially displaceable.
  • the optical detector 35 comprises a plurality of detector segments, in this case four detector segments, 35a, 35b, 35c and 35d, capable of providing individual detector signals A, B, C, and D, respectively, indicating the amount of radiation incident on each of the four detector quadrants.
  • a centerline 37 separates the first and fourth segments 35a and 35d from the second and third segments 35b and 35c.
  • the optical detector 35 comprises two detector segments 35e and 35f capable of providing detector signals E and F, indicating the amount of light incident on each of the detector segments (i.e. 35e and 35f).
  • the optical detector 35 comprises two detector segments 35g and 35h capable of providing individual detector signals G and H, indicating the amount of light incident on each of the detector segments (i.e. 35g and 35h).
  • Push-pull methods and three beam methods have generally been employed as tracking servo methods for recording/reproducing the data on/from an optical record carrier.
  • typical one is a differential push-pull method.
  • the principle of differential push-pull method is schematically illustrated in Fig. 3.
  • the radiation beam generated by the radiation generator 31 is passed through the optical means 39 (Cf. Fig. 1) and is separated into a main radiation beam, a first side radiation beam and a second side radiation beam.
  • the main radiation beam results in the main spot M
  • the first side radiation beam results in the first side spot Si
  • the second side radiation beam results in the second side spot S 2 on the optical record carrier 2.
  • the three radiation beam spots (a main spot M and the side spots Si and S 2 ) formed by the optical pick up 31 are positioned so that the side spots Si and S 2 are shifted with respect to the main spot M by half of a track pitch P.
  • Reflected radiation beams from the main spot M and both side spots Si and S 2 are photo-electrically converted by the optical-detector 35 so that push-pull tracking signals can be obtained for the spots M, Si and S 2 .
  • the photo-electrically converted signals are used to obtain data and servo signals such as radial, focus and tilt control signals that are required by the disc drive.
  • main spot here refers to central spot or primary spot and the side spot refers to satellite spots or sub-spot or secondary spot.
  • the optical system 30 can be suitably modified to form the main spot M and the side spots Si and S 2 .
  • the inventors have found that for dual layer or multi-layer optical record carriers, distortions appear in the three spots push-pull tracking signal used for radial tracking.
  • the inventors have also found that the cause of these distortions is not only the coherent cross talk (i.e. interference of the first side spot and the second side spot with the out-of-focus layer spot), but for a large part variation present in the out-of- focus spots itself.
  • Fig. 4 the reflected radiation beam from the main spot M and the first side spot Si and the second side spot S 2 fall on the optical detector 35. It is to be noted that a background spot is also formed resulting from the reflections from out-of-focus layers of the optical record carrier 2.
  • the reflected radiation beams from the background spot is incident on all the detector segments (namely 35a, 35b, 35c, 35d, 35e, 35f, 35 g, and 35 h).
  • the measurements without the side spots i.e. without Si and S 2 ), showed variation in the signals detected at the position of the side spots Si and S 2 . This is shown in Fig. 5 A and 5B.
  • the horizontal axis represents the push-pull tracking signal values and the vertical axis represents the magnitude of the push-pull tracking signal with the first side spot and the second side spot.
  • the horizontal axis represents the push-pull tracking signal values and the vertical axis represents the magnitude of the push-pull tracking signal without the first side spot and the second side spot. It can be observed from Fig. 5A and Fig. 5B that the magnitude of distortion of the push-pull tracking signal is very similar to the distortion where no side spots are present. Referring to Fig. 5B, the fluctuations in the magnitude of the push-pull tracking signal values is caused by the fluctuation in the spot on the optical detector 35 reflected by the out-of- focus layer.
  • a method of radially tracking the information track of a multilayer optical record carrier comprises generating a push-pull tracking signal derived from the light of a main spot, a first side spot and a second side spot falling on an optical detector, wherein the main spot, the first side spot and the second side spot are formed by focusing a main radiation beam, a first side radiation beam and a second side radiation beam, respectively, taking into consideration the effect of a background spot resulting from reflections of the main spot from out-of- focus layers of the multi-layer optical record carrier.
  • the push-pull tracking signals are generated taking into account the fluctuations in the background spot and hence results in accurate push-pull tracking signal values.
  • the method disclosed here separates the cause of the distortion in the three spots push-pull tracking signal, namely the variation in the background spot, from the signal with the side spots on from which the beam landing can be deduced.
  • the method 600 of generating the push-pull tracking signal for the main spot, the first side spot and the second side spot comprises the steps illustrated in Fig. 6.
  • step 602 the first side radiation beam and the second side radiation beam resulting in the first side spot Si (Cf. Fig. 3) and the second side spot S 2 (Cf. Fig. 3) is switched off.
  • step 604 a first signal associated with the background spot is measured by photo-electrically converting reflected radiation beams coming from the background spot.
  • the first side radiation beam and the second side radiation beam resulting in the first side spot Si (Cf. Fig. 3) and the second side spot S 2 (Cf. Fig. 3) is switched on.
  • a second signal associated with the background spot, the first side radiation beam, and the second side radiation beam is measured by photo-electrically converting reflected radiation beams coming from the background spot, the first side radiation beam and the second side radiation beam.
  • a corrected signal is computed based on a difference of the first signal and the second signal.
  • the push-pull tracking signal for the main spot, the first side spot and the second side spot is generated by using the corrected signal on the photo-electrically converted (i.e. photo-electric signals) reflected radiation beams coming from the main spot, the first side spot and the second side spot. Switching on and switching off the first side spot and the second side spot is advantageous since the signal without the side spots (i.e.
  • the signal with the side spots i.e. with the first side spot and the second side spot
  • the push-pull tracking signals are obtained considering the fluctuations in the background spot and hence the push-pull tracking signals are accurate. This improves the recording/reproducing of the data from the optical record carrier.
  • switching on and switching off of the first side radiation beam and the second side radiation beam includes transmitting the main radiation beam through a switchable grating having an ON state that generates, besides the main radiation beam, the first side radiation beam and the second side radiation beam and an OFF state that transmits only the main radiation beam. In other words, in the OFF state the first side radiation beam and the second side radiation beam is not transmitted.
  • the switchable grating comprises one of a liquid crystal material and an acousto-optic modulator.
  • the grating is made switchable by liquid crystal material as shown in Fig. 7.
  • the grating is made via a cell in which a transparent structure is present, e.g. created by photo-polymerization or by photolithography.
  • the structure has the shape of the desired grating, given the optical constants of the materials used.
  • the cell substrates consist of a transparent electrode necessary to enable the liquid crystal to be addressed.
  • Fig. 7 shows an extra parallel layer of liquid crystal material on top of the structures. It is to be noted that the extra parallel layer is for manufacturing purposes only and does not influence the function of the optical pick up unit 31. It is also possible to omit this layer. Referring to Fig.
  • one of the refractive indices of the switchable liquid crystal material should be matched to the non-switchable part of the grating.
  • the ON or OFF state then corresponds to diffraction or no diffraction depending on whether a liquid crystal with positive or negative dielectric anisotropy is used.
  • a voltage to the grating it starts or stops to diffract.
  • the signal of the background spots without the side spots i.e. without the first side spot and the second side spot
  • the signal of the background spots including the side spots i.e. with the first side spot and the second side spot
  • m is an integer number and T is the time period it takes to complete a cycle of switching the granting off and on.
  • the new three spots signal (i.e. the main spot, the first side spot and the second side spot) is constructed by sampling the side spot push-pull tracking signal in phase with on/off switching of the spots that results in the samples a m and b m , from which c m is calculated.
  • c m consists of the side spot push-pull value without the background spot. The signal is then subtracted from the push-pull tracking signal of main spot to arrive at the three spots signal.
  • the discreteness of the sampling influences the radial tracking performance.
  • the bandwidth of the side spot push-pull tracking signal will be reduced.
  • the side spot signal is used to compensate for beam landing, which is also a slow varying signal (the roundtrip frequency or the second, third harmonic of this). So, as long as the switching time is well above the frequency needed to compensate for beam landing, this solution will work adequately.
  • the idea is that by switching the liquid crystal material the light will only encounter a phase shift and not a polarization rotation; this should be accomplished by the right design of the liquid crystal cells and their orientation with respect to the incoming polarization direction.
  • a grating could be made in which the entire cell would be filled with liquid crystal, but now with a patterned electrode conformation.
  • the conformation should be chosen such as to enable the proper phase shift to be realized.
  • the pattern to be created is in the form of a binary grating with a duty cycle of 50 %.
  • the intensity of the side spots should typically be in the order of l/10 th to l/15 th of the intensity of the main spot.
  • I 1n is the intensity of the radiation beam and ⁇ (phi) is the phase depth of the binary grating.
  • the phase depth difference is 0.15 of a wavelength.
  • the phase depth difference is 0.12 of a wavelength.
  • the switchable grating can also be an acousto-optic modulator as shown in Fig. 8. Referring to Fig. 8, switching ON/OFF the acoustic wave generates the grating profile and will induce the switching ON and switching OFF of the grating. Basically, by switching on and off the sound wave, the grating can be switched on and off. The processing of the side spots can be carried out as described in the previous paragraph with regard to liquid crystal grating. The only difference is that the switching time of an acousto-optic modulator can be very short, in the order of 1 - 5 micro seconds.
  • the liquid crystal material comprises ferro- electric liquid crystalline material.
  • ferro- electric liquid crystalline material Several gratings can be made utilizing different types of liquid crystals such as the ones using nematic liquid crystal materials and others using ferroelectric liquid crystalline materials.
  • the advantage of using the ferro-electric liquid crystalline materials as compared to nematic liquid crystals is their large difference in switching time approximately 20 ⁇ s switching time v/s 5 - 0.1ms, for nematic liquid crystals. The actual switching time depends on cell gap and applied field strength.
  • the optical pick up unit 30 is adapted to perform the method of generating the push-pull tracking signal for the main spot, the first side spot and the second side spot taking into consideration the background spot (Cf. Fig. 4) formed on the multi-layer optical record carrier.
  • the optical pick-up unit 30 has a control unit 38 arranged to generate a push-pull tracking signal derived from the light of a main spot, a first side spot and a second side spot falling on an optical detector, wherein the main spot, the first side spot and the second side spot are formed by focusing a main radiation beam, a first side radiation beam and a second side radiation beam, respectively, taking into consideration the effect of a background spot resulting from reflections of the main spot from out-of- focus layers of the multi- layer optical record carrier.
  • the optical means 39 (Cf. Fig. 1) comprises a switchable grating arranged to switch off and on the focusing of the first side radiation beam and the second side radiation beam on to the first side spot and the second side spot respectively.
  • the control unit 38 further comprises: i) a measurement unit 38a arranged to measure a first signal associated with the background spot when the switchable grating is in ON state and to measure a second signal associated with the background spot when the switchable grating is in OFF state, by photo-electrically converting reflected radiation beams coming from the background spot; ii) a computing unit 38b arranged to compute a corrected signal based on a difference of the first signal and the second signal; and iii) a logic unit 38c arranged to generate the push-pull tracking signal for the main spot, the first side spot and the second side spot by applying the corrected signal on photo-electrically converted (i.e. photo-electric signals) reflected radiation beams coming from the main spot, the first side spot and the second side spot.
  • a measurement unit 38a arranged to measure a first signal associated with the background spot when the switchable grating is in ON state and to measure a second signal associated with the background spot when the switchable grating is in OFF state, by photo
  • a drive such as Blu-ray disc drive or a DVD drive or a HD-DVD drive having the optical pick- up unit 30 can obtain accurate push-pull tracking signals and thereby improve recording/reproducing of data.
  • the technique is applicable to all types of multi-layer record carriers, e.g. write-once media and write-many recordable types (DVD-RW, DVD+RW, HD-DVD). Further, the above technique is not limited to a two-layer one sided record carrier, i.e. a dual layer record carrier, or to a two-layer double sided record carrier, i.e. a dual layer double sided record carrier.

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

Abstract

L'invention concerne un procédé de détection radiale de la piste de données d'un support d'enregistrement optique multicouche. Le procédé comporte les étapes consistant à : produire un signal de détection symétrique obtenu à partir de la lumière d'un point principal, d'un premier point latéral et d'un second point latéral tombant sur un détecteur optique, le point principal, le premier point latéral et le second point latéral étant formés par la concentration d'un faisceau de rayonnement principal, d'un premier faisceau de rayonnement latéral et d'un second faisceau de rayonnement latéral, respectivement, compte tenu de l'effet d'un point d'arrière-plan résultant des réflexions du point principal provenant des couches hors foyer du support d'enregistrement optique multicouche. Ce procédé est utile pour des unités de lecture optique s'utilisant avec des disques multicouche tels que des disques Blu-ray, HD-DVD et DVD.
PCT/IB2008/051087 2007-03-23 2008-03-24 Procédé pour détecter la piste de données d'un disque optique WO2008117228A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP07104755.9 2007-03-23
EP07104755 2007-03-23

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WO2008117228A1 true WO2008117228A1 (fr) 2008-10-02

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8520483B2 (en) 2010-07-29 2013-08-27 General Electric Company Method and system for processing information from optical disk layers

Citations (6)

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Publication number Priority date Publication date Assignee Title
US5764606A (en) * 1995-12-12 1998-06-09 Sony Corporation Tracking control apparatus for a multi-layer optical disc and method therefor
US20020027840A1 (en) * 2000-09-01 2002-03-07 Ichiro Morishita Dynamic control diffraction grating, information read/write apparatus and information read apparatus
US20050100061A1 (en) * 2003-09-30 2005-05-12 Katsushige Masui Optical pickup and hologram laser
WO2005106862A1 (fr) * 2004-04-30 2005-11-10 Sharp Kabushiki Kaisha Unite de lecture optique et dispositif de lecture optique et dispositif d’enregistrement/de reproduction d’informations pourvu de l’unite de lecture optique
EP1605448A2 (fr) * 2004-06-07 2005-12-14 Sony Corporation Tête et appareil de lecture optique et procédé a générer un signal d'erreur de suivi de piste
WO2006013879A1 (fr) * 2004-08-06 2006-02-09 Pioneer Corporation Reconnaisseur de l'état optique, traitement de l'information, et méthode de reconnaissance de l'état optique

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5764606A (en) * 1995-12-12 1998-06-09 Sony Corporation Tracking control apparatus for a multi-layer optical disc and method therefor
US20020027840A1 (en) * 2000-09-01 2002-03-07 Ichiro Morishita Dynamic control diffraction grating, information read/write apparatus and information read apparatus
US20050100061A1 (en) * 2003-09-30 2005-05-12 Katsushige Masui Optical pickup and hologram laser
WO2005106862A1 (fr) * 2004-04-30 2005-11-10 Sharp Kabushiki Kaisha Unite de lecture optique et dispositif de lecture optique et dispositif d’enregistrement/de reproduction d’informations pourvu de l’unite de lecture optique
US20080062826A1 (en) * 2004-04-30 2008-03-13 Sharp Kabushiki Kaisha Optical Pickup Unit and Optical Pickup Device Having Same and Information Writing/Reading Device Having Same
EP1605448A2 (fr) * 2004-06-07 2005-12-14 Sony Corporation Tête et appareil de lecture optique et procédé a générer un signal d'erreur de suivi de piste
WO2006013879A1 (fr) * 2004-08-06 2006-02-09 Pioneer Corporation Reconnaisseur de l'état optique, traitement de l'information, et méthode de reconnaissance de l'état optique
US20080084804A1 (en) * 2004-08-06 2008-04-10 Pioneer Corporation Optical State Recognizer, Information Processor, And Optical State Recognizing Method

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8520483B2 (en) 2010-07-29 2013-08-27 General Electric Company Method and system for processing information from optical disk layers

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