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
  • G11B7/14—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
• • 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
• • 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
  • G11B7/1362—Mirrors

Definitions

• the present invention relates to a method and system of reading/writing data on an optical disc, and more particularly, to a method and system of reading/writing data on an optical disc by a plurality of spots.
• optical discs have become a data carrier widely used for storage of multi-media audio/video information considering its relatively low cost and large data storage capacity.
• increasing the data rate has become an important factor of improvement, since data stored on the optical disc can be read faster, or data be stored on the optical disc can be written faster.
• a way to increase the data rate of an optical drive is using multiple spots that read or write multiple tracks of an optical disc in parallel.
• spots will encounter a part of the track that already has been read or written by another spot, as illustrated by Fig. IA and Fig. IB.
• Fig. IA is a schematic diagram showing the situation where data are recorded/read on the optical disc by spot A from start of block 1, and by spot B from start of block 5. This parallel process of recording/reading by spot A and B goes on until spot A arrives at start of block 5, as illustrated by Fig. IB. In other words, spot A arrives at a block previously recorded/read by spot B. To avoid spot A record new data on the previously recorded/read area by spot B, a displacement of the spots is needed at this point.
• the displacement comprises moving all spots over an equal distance.
• the advantage of this spot displacement strategy is that it is very easy to implement because only a radial displacement of the objective lens is required.
• European Patent Application No. EP 0 840 294 A2 discloses a multiple track scanning method for optical pickup using multiple spots, in which this spot displacement strategy is employed.
• the displacement must be (Nb-I)Ng-I tracks (for a system with Nb spots, with a distance of Ng tracks between the spots) in order to read or write all data.
• the data rate of this method is limited to a factor Nb-l/Ng times the data rate for one spot.
• Ng is often 1, so the data rate gain will be limited to Nb-I.
• a method of reading/writing data on an optical disc by a plurality of spots positioned along inner tracks to outer tracks of the optical disc comprises the steps of detecting successively that each spot has reached a data area previously read/written; and moving the spot to a position adjacent to the current outermost spot if the reading/writing is done from inner to outer tracks, or to a position adjacent to the current innermost spot if the reading/writing is done from outer to inner tracks.
• a system of reading/writing data on an optical disc by a plurality of spots positioned along inner tracks to outer tracks of the optical disc comprises a detection device for detecting successively that each spot has reached a data area previously read/written, and generating a detection signal; and an actuation device, triggered by the detection signal, for moving the spot to a position adjacent to the current outermost spot if the reading/writing is done from inner to outer tracks, or to a position adjacent to the current innermost spot if the reading/writing is done from outer to inner tracks.
• the displacement strategy according to the present invention allows a data rate increase of a factor Nb.
• the displacement strategy of moving the spots individually allows to increase the data rate of reading and writing on an optical disc.
• the strategy of moving the spots can be implemented in an easy way since not all spots have to be moved over an equal distance simultaneously, resulting in a cost- effective solution.
• FIG. IA and FIG. IB illustrate schematic diagrams showing the situation of a spot encountering a region that has been read or written by another spot.
• FIGs. 2A-2D illustrate different stages of multi-spot readout of an optical disc using the spot displacement strategy according to one embodiment of the present invention.
• FIG.3 illustrates a schematic diagram showing that a mirror array is used to displace individual spots from a laser array.
• FIG.4 illustrates a schematic diagram showing the spot arrangement on an optical disc.
• FIG.5 shows angular displacements of the mirrors which follow a saw tooth pattern over time.
• FIG.6 illustrates a schematic block diagram showing the structure of a closed loop control system for controlling the spots on an optical disc.
• FIG.7 illustrates a schematic flowchart showing a method of reading data on an optical disc in an open-loop control according to one embodiment of the present invention.
• Fig.2A to Fig.2D illustrates different stages of multi-spot readout of an optical disc using the spot displacement strategy according to one embodiment of the present invention.
• This strategy is illustrated by the use of three spots A, B and C being distant by one track from each other.
• Three spots, Spot A, Spot B and Spot C are positioned along inner tracks to outer tracks of the optical disc, such as at Tracks Tl, T2 and T3 respectively, and read tracks in parallel with the orientation of the arrow in Fig.2A (the regions which have been read are marked with shadow in Figs. 2B-2D), wherein the distance between all spots are kept constant by at least one track and along the radial direction.
• a detection device detects successively the position of each spot and generates a detection signal.
• Spot A As soon as Spot A reaches a part of the track that has been read before by another spot, as illustrated by Fig.2A, Spot A becomes useless and a detection signal is generated indicating that Spot A has to be moved to continue reading data.
• Spot A is moved by an actuation device in response to the detection signal to a position adjacent to (i.e. next to) the current outermost spot if the reading/writing is done from inner to outer tracks, or to a position adjacent to (i.e. next to) the current innermost spot if the reading/writing is done from outer to inner tracks.
• Spot A is moved to Track T4, next to Spot C.
• adjacent means that the spot which is moved will be positioned next to the current outermost/innermost spot, and will be distant by one track (as in the example given by Fig.2) or by a plurality of tracks from said current outermost/innermost spot (for example in the case where the spots are distant by more than one track from each other).
• Spot B also encounters a part of the track that has been read before. Similarly as Spot A, Spot B is also moved to Track T5, as shown in Fig.2D.
• Fig.3 is a schematic diagram illustrating realization of the jump strategy by means of a mirror array to displace individual spots in a dual laser system for improving the data rate of the drive.
• the system comprises a laser array with two laser sources 4 and 5.
• laser beams see dashed lines in Fig.3
• the mirror array comprises two mirrors 1 and 2.
• Mirror 1 deflects laser beam A from the laser source 5
• mirror 2 deflects laser beam B from the laser source 4.
• Each of mirrors 1 and 2 can be rotated over a small angle ⁇ l, ⁇ 2 and the rotation axis 3 approximately lies in the plane going through the optical axis of the laser beams.
• the laser beam after deflection by the mirror is changed so that the corresponding spot on optical disc is controlled.
• the spot will be moved toward the edge of the optical disc.
• the spot will be moved toward the centre.
• a preferred embodiment of the present invention is to position the spots in an almost tangential orientation. This is advantageous because it minimizes the mechanical movement of components during displacement of the spots and therefore simplifies the actuation.
• the mirrors In order to deflect only the laser beam from one laser source per mirror, the mirrors have to be placed closely to the laser array at a distance where the beams do not overlap yet. As a result, small mirrors, for example with width and height around 50-100 micron, are preferred due to the advantage that the mirrors can be displaced very quickly and can be integrated with the laser array in the same housing to form one component. Thus, a simpler application in an optical light path is provided to carry out the present invention.
• the mirror array may also be placed elsewhere in the light path. For example, in order to create beams which do not overlap, a telescope that creates focal points is needed. The mirror array is then placed near these focal points.
• a mirror array is used to displace each spot.
• the displacement of each spot may be implemented by other means, such as a group of lens which is used to change the orientations of the laser beams.
• displacement of individual spot is managed by controlling the deflection angle of each of different parallel non-overlapping beams with a liquid crystal module in a plane perpendicular to the optical axis.
• the liquid crystal module has a constant index of refraction gradient.
• the light source corresponds to a laser array.
• Other light sources for example a single- beam laser source split by a grating or collimated by a lens, can also be used in the embodiments of the present invention.
• a mirror array used to deflect the collimated laser beams is suitable for a read only system.
• the light source can be formed by using an acousto-optic modulator that can both split an incoming beam into modulated beam at different (and variable) angles, or discrete lasers of which the beams are combined into the same light path.
• each mirror it is preferable to let each mirror slowly go back to its starting position after each jump because if the spot encounters another region which has been read, another jump may be needed. Repetitive displacement of a spot would otherwise lead to an over-increasing displacement of the mirror.
• the normal radial tracking system including an objective lens actuator will make that all spots stay on their respective tracks while the mirrors return to their initial position.
• Fig.4 shows the typical arrangement of the spots on the disc, in view of explaining the result of choosing the rotation axis approximately in the plane of laser beams.
• the spots are distant by lO ⁇ m, and the track pitch is 320 nm (e.g. according to Blu-ray Discs standard).
• the spots are therefore on a line with only a small angle with respect to the tracks.
• the displacement of a spot after rotation of one mirror with its rotation axis in the plane of the laser array's optical axes is perpendicular to this line (as indicated with the arrow).
• Fig.5 shows angular displacements of the mirrors which follow a saw tooth pattern over time, wherein, ⁇ l, ⁇ 2 represent angles of rotation of the mirrors, as indicated by the solid line and the dash line.
• the mirrors are controlled individually as shown in Fig.5.
• the decreasing lines represent the duration of the mirror going back to its starting point and the steep increasing lines represent the duration of displacement.
• the mirrors return to their initial position more quickly, and then stay constant for a short time.
• either of the two methods might be easier to implement.
• the objective lens actuator which is generally one part of a typical radial feedback loop control system is used to focus the spot on its track.
• Fig.6 is a schematic block diagram showing the structure of a closed loop control system for controlling the spots on an optical disc.
• the system comprises an optics 601 which includes an light path, a disc, and a returning light path with a photo-detector and some other electronics.
• the optics 601 transmits the measured results to a radial tracking error generator 602 for generating an electrical signal, called radial error signal, which is more or less proportional to the distance of the spot on the disc to the center of the data track.
• This distance can be adjusted by the radial actuator 603, which moves the objective lens in radial direction (i.e. the objective lens actuator).
• the force (amplitude and sign) with which the radial actuator 603 has to be moved to keep the spot on the center of the track and thus reduce the radial error to zero defined by a controller module, radial controllers 604.
• the radial controller 604 takes the radial error signal as input and calculates an output signal such that it will reduce its input to zero.
• the radial controller 604 is an electronic filter that has different characteristics in different frequency regions.
• a typical, and often applied example of such a controller is a
• PID controller which has an integrator function dominating the controller output at low frequencies, a proportional gain dominating the output at middle frequencies and a differentiator dominating the output at high frequencies.
• the average tracking error of all spots can be fed back.
• the feedback loop contains a Low Pass Filter (LPF) 605 of the top part, such that the movement of the spots is only controlled up to a certain bandwidth.
• LPF Low Pass Filter
• the portions of the tracking errors above that bandwidth are removed by the other feedback loops (bottom part) controlling the rotatable mirrors. Because the mirrors are small and light, a very high bandwidth can be achieved.
• the wide arrows indicate a collection of signals, one for each spot.
• the signal starts from the optics and then the radial tracking errors are generated for all spots.
• These radial tracking errors are filtered by High Pass Filters (HPF) 606, such that only higher frequency components are addressed.
• HPF High Pass Filters
• the cut off frequencies of the LPF 605 and HPF 606 have similar values.
• the jump signals from jump signal generator 607 as shown in Fig.6 are added to signal mixer 608.
• N controllers 609 for example of the PID-type, each controller being in charge of controlling a spot or mirror, the signals are fed to the actuated mirrors 610, which in turn deflect the individual beams to the correct positions on the tracks of disc.
• the displacement of the spots on the disc also causes a displacement of the spots in the photo-detector plane in charge of generating electrical signals from which the data signal (High Frequency - HF - signal), the focus error and the radial tracking error signals can be derived from.
• an open-loop or closed-loop control can be chosen to implement the displacement of the spots.
• One difference between open-loop and closed- loop control is that in an open loop scheme the rotation is done by feeding a predefined electric signal into an actuator, while for a closed loop reversing jump, the electric signal going into the actuator depends on the measured radial error signal from one of the non- static spots.
• Fig.7 is a schematic flowchart showing a method of reading/writing data on an optical disc by a plurality of spots positioned along inner tracks to outer tracks of the optical disc in an open-loop control according to one embodiment of the present invention. At step S710, whether each spot has reached a data area previously read/written is successively detected.
• step S720 the spot which has been detected is moved to a position adjacent to the current outermost spot if the reading/writing is done from inner to outer tracks, or to a position adjacent to the current innermost spot if the reading/writing is done from outer to inner tracks. Therefore, the spot displacement is finished.
• a method in open-loop control is in general simpler to be carried out. In a closed-loop control, the position of the moving spots is measured during displacement and the movement of each spot is controlled on the basis of the measured signal.
• the data rate improvement is a factor 1.9, whereas with the typical method the data rate factor would drop below 1.
• the present invention can be applied in almost all optical storage systems with multiple spots, such as CD, DVD and Blu-Ray drives.

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

Applications Claiming Priority (2)

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• 2005
  • 2005-11-29 CN CNA2005101285930A patent/CN1979647A/zh active Pending
• 2006
  • 2006-04-20 TW TW095114170A patent/TW200741689A/zh unknown
  • 2006-11-23 CN CNA2006800447447A patent/CN101317223A/zh active Pending
  • 2006-11-23 WO PCT/IB2006/054398 patent/WO2007063458A1/en active Application Filing
  • 2006-11-23 KR KR1020087015658A patent/KR20080078020A/ko not_active Application Discontinuation
  • 2006-11-23 JP JP2008541889A patent/JP2009517793A/ja not_active Withdrawn
  • 2006-11-23 EP EP06831905A patent/EP1958192A1/de not_active Withdrawn
  • 2006-11-23 BR BRPI0619048A patent/BRPI0619048A2/pt not_active IP Right Cessation

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