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
• • 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
  • G11B7/0904—Dithered tracking systems
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
  • G11B7/005—Reproducing
• • 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
  • G11B7/085—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam into, or out of, its operative position or across tracks, otherwise than during the transducing operation, e.g. for adjustment or preliminary positioning or track change or selection
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
  • G11B7/2403—Layers; Shape, structure or physical properties thereof
  • G11B7/24035—Recording layers
  • G11B7/24038—Multiple laminated recording layers
• • 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
• • 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
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
  • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
  • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
  • G11B7/244—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising organic materials only
  • G11B7/245—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising organic materials only containing a polymeric component
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
  • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
  • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
  • G11B7/244—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising organic materials only
  • G11B7/246—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising organic materials only containing dyes
  • G11B7/2467—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising organic materials only containing dyes azo-dyes

Definitions

• the invention relates to methods and apparatus for reading information from a 3D optical storage medium.
• the storage medium should be transparent to light having a frequency v ls and also to light having the frequency v 2 .
• WO 01/73779 it is suggested in WO 01/73779 to use a matrix carrying stilbene derivatives, having one characteristic absorption in a given frequency when in the cis isomer and another, when in the trans.
• data is stored along tracks formed in the bulk of the optical disk and is read by focusing a laser beam produced by semiconductor diodes on to the tracks, while spinning the disk on its axis.
• the tracks generally comprise spiral tracks on which data is written and from which the data is read.
• the data storage medium includes a number of concentric shells each of which has a curvilinear data storage surface for storing data in a number of substantially parallel data tracks.
• the data storage medium includes a number of data storage surfaces, which are rotatable about a common axis, each data storage surface for storing data in a number of substantially circular data tracks and having an optically transparent window, which transects each of the data tracks.
• each shell or data storage surface is rotated about a common axis and tracking is achieved by directing the reading beam through the optically transparent windows on to a data track of interest.
• this reference is not applicable to retrieving data from a solid optical storage medium wherein the data is stored in multiple layers.
• CD and DVD reading head track a destination track is based on focusing the reading spot on to the track and measuring the intensity of a reflected spot by position sensitive detectors. This allows calculation of the position of the reading spot and subsequent adjustment of the reading head's location based on the measured error.
• Optical drive error tracking method and apparatus discloses a method and apparatus for obtaining a tracking error signal for an optical disk player which is general across the various data formats found in CD audio disks and DVDs.
• a photodetector having at least four active areas is used to sense the reflected laser beam.
• a differential amplitude tracking error signal is generated by comparing the signal strength in the different active areas.
• a method for retrieving information from a three dimensional storage medium comprising: using a three dimensional storage medium comprising an active medium capable of being in two states, wherein a data unit is represented by the ratio between the concentration of the first and second of said two states in a given volume portion of said medium and a data sequence is represented by a sequence of such data units; irradiating said active medium with light as to concentrate light flux through a volume portion of said storage medium so as to generate in said volume portion a detectable non-linear optical response characteristic of said concentration ratio; detecting said non-linear optical response to retrieve information stored in said volume portion; and tracking a data sequence for retrieving said data sequence in a reproducible manner.
• the term "data unit” refers to a bit or symbol of a finite alphabet.
• the data sequence is tracked via a tracking feedback signal for positioning the light at a predetermined volume portion of the storage medium.
• a method for correcting tracking errors in an optical storage medium having multiple tracks arranged in different layers of the optical storage medium comprising: (a) directing a reading spot that is nominally focused on to a track in the optical storage medium,
• any active medium known in the art is suitable for use according to the present invention.
• Some non-limiting examples to active media are those described in WO 01/73779 and in US 5,268,862, both of which are incorporated herein by reference, stillbene derivatives, and azobenzene derivatives.
• the active medium is preferably embedded in a supporting matrix, for instance, as a dopant or, when the supporting matrix is a polymer, as a monomer co-polymerized with the supporting matrix.
• the supportive matrix should be transparent for the light irradiated on it by the method of the invention and to the light generated by the non-linear optical process.
• supportive matrices suitable for use according to the present invention are polyethylene, polypropylene, polycarbonate, and polymethylmetacrilate (PMMA).
• the data is stored in a binary mode, so that the concentration ratio representing one digit is 1 :0 and the concentration ratio representing the other digit is 0:1.
• 1 and 0 are not absolute values but rather should be interpreted as the highest and lowest concentrations that may be achieved during the writing process, which is not discussed herein.
• the size of the volume portion from which a data unit is retrieved according to the invention is the size of the light spot wherein the flux is large enough to generate a detectable non-linear reaction.
• smaller spot sizes may compensate for weaker light intensities. Therefore, working with spots having a radius of less than 30 ⁇ m is advisable, and spots having a radius equal to or smaller than the wavelength of the irradiated light is preferable.
• Detection of the signal requires its separation from other light signals that may exist in the environment. Such separation may be achieved by any method known for this purpose in the art, such as directing the non-linearly generated signal into a direction where it is the only source for light of its frequency by satisfying phase matching conditions; filtering the light through a filter, prism, grating, polarizers, etc.; using phase sensitive detection, lock-in amplifier, a boxcars, and/or gated averaging method. All the available methods may be applied whether the beams irradiating the active medium are collinear or not. Non-linear optical processes are very sensitive to the flux of light.
• One family of non-linear optical responses suitable for use according to the present invention is a multi-photon fluorescence, such as, but not limited to, two-photon fluorescence.
• Non-limiting examples of non-linear optical responses related to a ⁇ (n>2) process are four wave mixing processes such as Stimulated Raman Scattering,
• CARS Coherent Anti-Stokes Raman Scattering
• Raman induced Kerr effect Raman induced Kerr effect
• degenerate four-wave mixing Similar ⁇ 5 processes and higher are also known in the art and may be used according to the present invention.
• an apparatus for retrieving information from a three dimensional storage medium by generating a non-linear optical response of said storage medium, detecting said non-linear optical response and analyzing and processing it includes, in order to generate and detect a non-linear optical response, at least one light source, which in some cases (such as CARS) must be coherent; a detector for detecting light, which is different in at least one characteristic from the light provided by said light sources.
• a light source which in some cases (such as CARS) must be coherent
• a detector for detecting light which is different in at least one characteristic from the light provided by said light sources.
• examples of light characteristics are the light wavelength, polarization, and propagation direction.
• means for tracking i.e. process the signals received from the medium to get a tracking feedback signal and correct the location of the read spot accordingly.
• the apparatus may also include means, known per se in the art for analyzing and processing detected signals and retrieving information therefrom. These may comprise means for digitizing the detected signal, such as an A/D converter, and an algorithmic error detection means, such as error detector code running on a computer or on an electronic chip.
• means for digitizing the detected signal such as an A/D converter
• algorithmic error detection means such as error detector code running on a computer or on an electronic chip.
• a light source according to the present invention may be an active light source like a laser, or a passive light source like a mirror.
• a beam splitter for example, may be considered as two (passive) light sources.
• the data sequences are arranged as layers within the medium, each layer consisting of a spiral track of the respective data sequences, where the medium is shaped as a disk, and rotated around its axis by the apparatus.
• the purpose of the invention is to track the spiral track corresponding to a required data sequence in r and z coordinates when the disk rotates. It is assumed that the track suffers limited amount of run-out both in r (radial run-out) and z (axial run-out) coordinates. Such distortions can occur in the event that the axis of rotation is slightly off the disk center and slightly non- parallel to the disk plane normal, such that the data spiral moves relative to the reading spot while the disk rotates.
• the invention enables tracking the data spirals by calculating a tracking error signal that is used as feedback for the servo- mechanisms that control the r and z position.
• the basic tracking principle is to perpetually move (modulate) the reading spot in a periodical path around its nominal current position (traveling the r-z plane by two orthogonal functions of time). This modulation causes a modulation in amplitude and phase of the read signal that depends on the position of the reading spot relative to the data spiral. This dependence is used to determine the tracking error.
• the tracking algorithm calculates an error signal
• the spot's radial position is modulated in the radial direction so that the spot is half the time in (towards the center of the disk) and half the time out relative to the track (i.e. r ⁇ r 0 half of the time and r>r 0 half of the time).
• the offset relative to track center has to be small to ensure that signal is still detected with a signal to noise ratio that is high enough for other functions such as symbol detection or synchronization to be accomplished.
• the signal has a fixed average and the tracking is perfect, than the average of the 'in' signal (signal detected when spot is 'in' relative to the track) is equal to the 'out' signal. If the spot's position begins to diverge from the track's position e.g. because of eccentricity of the disk, the expansion of the spiral or some other reason, then the difference between the 'in' and 'out' parts of the modulated signal, out - in, is negative if there were a small 'run-out' or positive if there was 'run-in'. Two main factors determine the frequency of the modulation.
• the averaging of the data can be accomplished by window integration or other appropriate low pass techniques. To ensure that in each integration window the signal is data-independent, DC free encoding techniques are used.
• the error signal calculation is accomplished by multiplying (inner product) the time variation of the data envelope (the read signal) with the reading spot modulation function.
• the error signal is weighted by the strength of the modulation, i.e. signal measured when the amplitude of the modulation is high contribute more to the error signal.
• Further refinement of the invention is to include delay compensation before the multiplication between the signal and the modulation.
• the tracking errors are used as feedback signals for the servo machine controlling the nominal spot position.
• Fig. 1 is a graph showing CARS spectra of solid solutions having two different concentration ratios between cis and trans isomers of a given compound
• Fig. 2 is a schematic illustration of an apparatus according to the present invention.
• Fig. 3 is a block diagram showing functionally a read/write system for use with the invention.
• Figs. 4a and 4b are pictorial representations showing the effect of sinu- soidally modulating the position of the reading head in the system of Fig. 2;
• Figs. 5 and 6 are block diagrams showing details of a tracking system for use with the system shown in Fig. 2.
• a solid solution of 10% cis-4,4'-dimethoxy- ⁇ , ⁇ -diciano stillbene (hereinafter compound A) in PMMA was irradiated with collinear laser beams of 844 and 1037 nm that were focused through a lens to a spot smaller than lO ⁇ m.
• CARS signal at a wavelength of 711nm was detected.
• the spectra of the signal detected from a solid solution of the cis isomer and of a cis-trans mixture is given in Fig. 1.
• Fig. 2 is an illustration of an apparatus 100 according to the present invention for retrieving information from a three dimensional storage medium (hereinafter referred to as "disk") 102 having an information carrying volume (not shown).
• the apparatus 100 includes two lasers 104 and 106, each being a source for a beam of coherent light (110 and 112 respectively), and a detector 120 for detecting a beam of coherent light 116 which is of different wavelength to the light provided by the lasers 104 and 106.
• the detector 120 transfers an electric signal, created therein due to the detection of an optical signal produced by the beam of coherent light 116, to a low noise amplifier 123, which can be a lock in amplifier to a tracking unit 125, so that the data sequence may be faithfully followed, and to an A/D converter 126, whose output is fed to a decoder and error detection and correction (ECC) unit 128 (constituting an algoritlimic error detector), so that information encoded in the data sequence may be retrieved.
• ECC error detection and correction
• a disk mount 202 for mounting thereon the disk 102, so that the disk, when mounted, may be rotated around its center by a motor 205.
• the two light sources 104 and 106 are connected to two optical fibers 104' and 106' arranged to direct the light signals 110 and 112 to a dichroic mirror, 220.
• the signal 112 is transferred through the mirror and the signal 110 is reflected thereby.
• the light may irradiate the disk 102, in such a manner that the beams common focus 222 is located within the information carrying volume of the disk 102.
• the optical unit 101 is mounted on an arm 210, which may rotate around an arm axis 230.
• a lens 240 of the kind used in CD players, is positioned between the dichroic mirror 220 and the disk 102. Its position in the direction parallel to the disk's surface 102' is controlled by the combination of the rotations of the arm 210 around the arm axis 230 and the disk 102 around the disk mount 202. Its position in the direction perpendicular to the disk's surface 102' is controlled by a magnetic coil 242, which is also used to control small radial motions of the lens and thus the position of the common focus 222 within the disk 102 may be fully controlled. To achieve tracking, the location of the common focus is modulated by moving the lens 240 by applying a periodical electric signal to the magnetic coil 242.
• the coherent light sources 110 and 112 in combination with the dichroic mirror 220, the lens 240 and the magnetic coil 242 constitute an optical system 245.
• a collecting mirror 250 is positioned to collect the non- linearly generated signal 116 and directs it to the detector 120, positioned near the arm axis 230, through a filter 152.
• the laser drivers are not shown in Fig. 2.
• the large ratios between the radius of the motion of the optical unit 101 around its axis 230 and track radius on the one hand and the size of the spot and the distance between adjacent tracks and layers on the other hand allow the approximation that the motion controlled by the rotation of the optical unit 101 around its axis is essentially orthogonal to the track of the data sequence.
• the system is provided with a tracking servo system shown generally as 125, which feeds a correction signal to the magnetic coil 242 for moving the lens 240 under control of the tracking error signal to nominally position the beam spots at the center of the track so that the tracking error signal is zero.
• Coarse motion of spot is achieved by motion of the optical unit as a whole.
• Fine motion is achieved by the motion of the lens using the magnetic coil 242.
• the tracking system 125 shown in Fig. 2 serves to track the data sequence recorded on the specific disk 102 as described above, it is to be noted that the invention encompasses a novel tracking system, which is well-suited for use in the apparatus 100 described above with reference to Fig. 2 although it is also suitable for use in other optical data retrieval systems. Likewise, it is to be noted that other tracking systems may be employed in the apparatus 100.
• the improved tracking system according to the invention is described below with particular reference to Figs. 4a, 4b and 5 of the drawings. However, by way of general introduction there will first be described functionally with reference to Fig. 3 a read/write system 300 for a 3-D optical storage medium 102 having a tracking system. To the extent that the read/write system 300 includes components that are common to the apparatus 100 shown in Fig. 2, identical reference numerals will be employed.
• the read/write system 300 comprises a rotary shaft 302 driven by an appropriate driving motor 205 for rotating the optical storage medium 102 set thereon, and an optical unit 101 for reading information from one of the tracks in the optical storage medium 102.
• the optical unit 101 comprises semiconductor lasers 104 and 106 for radiating a pair of intersecting light beams having a volume of intersection that forms a "spot". Also included within the optical unit 101 is an optical system 245 for creating a focused spot whose location is controlled by an actuator 306, which in the particular embodiment shown in Fig. 2 is constituted by the magnetic coil 242. The optical unit 101 is driven by a motor 307 so as to produce the required coarse and fine motion of spot described above.
• the system further comprises a laser driving circuit 308 for energizing the semiconductor lasers 104, and 106 to emit the respective laser beams.
• the optical focus 222 In order to retrieve information from a desired track on the optical storage medium 102, the optical focus 222 must be kept on the desired track.
• the system is provided with a tracking servo system shown generally as 125, which feeds a correction signal to the lens actuator 306 for moving the optical system 245 under control of the tracking error signal to nominally position the beam spots at the center of the track so that the tracking error signal is zero.
• Figs. 4a and 4b shows pictorially the effect of sinusoidally modulating the position of the optical focus 222 in the system of Figs. 2 and 3.
• the reading spot tracks data written into a continuous linear data track 321 while being subjected to spatial modulation that shifts its position continually from one side of the track to the other.
• the invention relies on the principle that even if the optical focus 222 is slightly off- center, data signal will still be read, albeit at reduced intensity. Thus, the further off-center the optical focus 222 is moved, the lower will be the magnitude of the data signal.
• the tracking operates on the principle that by continually reading the data and, at the same, continually modulating the position of the reading head, the resulting moving average signal intensity that is read may be used to indicate to which side, both axially and radially, the reading head is located. This having been detemiined, the reading head may then be moved in an opposite direction until it is found to be disposed symmetrically relative to the track in both axial and radial directions.
• Figs. 5 and 6 are block diagrams showing functionally details of a tracking system 125 that is described in polar coordinates (r, ⁇ , z) defining a position of the beams' intersection in the optical recording medium.
• the tracking system behaves substantially identically for both radial and axial tracking.
• a modulator 332 spatially modulates the location of the optical focus 222 by a (r, z) modulation signal and feeds the resulting modulated data signal to the optical storage medium 102.
• the modulation signal itself is fed together with the measured data signal to an error determination unit 333, whose output is an error signal that is fed back to the optical unit 101 to correct the axial and radial offsets thereof.
• the modulator 332 in conjunction with the error determination unit 333 constitutes a tracking error correction unit.
• a rotation unit 334 provides a continuous change of ⁇ .
• Fig. 6 shows in simplified form the principal functionality of the error determination unit 333 comprising a first 2-input multiplier 340 to whose first input the (r, z) modulation signal is fed and to whose second input is fed the data signal read by optical unit 101 at the position (r, ⁇ , z) in the optical storage medium 102.
• An output of the multiplier 340 is fed to a window integrator 341 which integrates the product of the data signal with the modulation signal so as to generate at its output a composite (r, z) error signal in the radial and axial directions.
• the intensity I(t) is inversely proportional in a non linear fashion to the distance from the center of the track.
• T represents the length of the time window of the integrator during which the modulated intensity is averaged.
• T should not be so large that it impacts negatively on the reaction time and creates distortions; but neither should it be too low since it is very difficult to construct a mechanical scanning system.
• the modulation signal can be any suitable cyclic function which serves to move the optical focus 222 on either side, in both axial and radial directions, of the reading spot.
• it can be a square wave function or any other suitable cycle function. It is assumed that the frequency of the modulation signal is much lower than the frequency at which data is read.
• the window integrator 341 thus operates as a low pass filter.
• the tracking operates on the principle that by continually reading the data and, at the same, continually modulating the position of the reading head, the resulting moving average signal intensity that is read may be used to indicate to which side, both axially and radially, the reading head is located. This having been determined, the optical focus may then be moved in an opposite direction until it is found to be disposed symmetrically relative to the track in both axial and radial directions. Whilst the tracking method has been described with particular regard to a tracking system for use with a 3-D optical storage retrieval system wherein data is stored at voxels written in the bulk of the material, it will be understood that the principles of the invention are equally applicable to other kinds of optical storage media where data is stored as a quasi-linear data sequence.
• FIG. 2 is only one of many embodiments available to the artisan when designing an apparatus according to the present invention.
• Some non-limiting examples for variations from this embodiment include: the lens and the mirror may be replaced by any other optical means which is known to bring to the same result, the optical fibers may be omitted or replaced by any other wave-guide, the combination of a disk mount and an arm axis may be replaced by any other means for controlling the location of the common focus in the plains parallel to the disk's surface 102', etc.

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• 2003
  • 2003-03-11 AU AU2003209660A patent/AU2003209660A1/en not_active Abandoned
  • 2003-03-11 US US10/507,101 patent/US7269118B2/en not_active Expired - Fee Related
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  • 2003-03-11 EP EP03743973A patent/EP1488415B1/en not_active Expired - Lifetime
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  • 2003-03-11 EP EP08018792A patent/EP2045804A1/en not_active Withdrawn
  • 2003-03-11 JP JP2003575375A patent/JP2005520272A/ja active Pending
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