Patent Application
20090310473
The present invention is in the field of optical data carriers, and relates to a multi-layered optical data carrier and a method of recording/reproducing data therein. More particularly, the invention relates to an optical data carrier including recording and reference layers, where information is recorded on a plurality of recording planes in the recording layer.
The existing approach for optical data carriers is based on the use of reflective media. Accordingly, commercially available optical data carriers have one or two data layers, where in the latter case; the two layers are separated by a distance of about 50 microns.
Various techniques have been developed in the field of optical recording media to provide fine-patterned pit length and track pitch, to shorten the laser wavelength, and to increase the recording density by using the increased numerical aperture (NA) of an objective lens.
In recent years, for the purpose of a further increase in the recording density, recording media have been proposed that include multi-layered recording planes. When a recording light beam is focused on a position at a higher optical intensity, the optical interaction property (e.g. reflectivity) of the recording layer varies only on the focused position, resulting in data recording.
Data recording in such multi-layered optical recording medium requires precise control of the beam spot of a recording/reproducing beam to a desired position in the thickness direction of the medium, or the focus direction. For example, U.S. Pat. Nos. 5,408,453 and 6,538,978 disclose an optical information storage system having a multi-recording-layer record carrier and a scanner device for the carrier. The scanner produces a radiation beam which is compensated for spherical aberration for a single height of the scanning spot with the stack of layers. The height of the stack is determined by the maximum spherical aberration permissible for the system. The number of layers in the stack is determined by the minimum distance between layers, which depends on the crosstalk in the error signals due to currently unscanned layers.
Another recently developed technique for a multi-layered recording scheme employs a recording medium having a fluorescent property variable on occurrence of single- or multi-photon absorption (see for example WO 2004/032134 assigned to the assignee of the present application). In this scheme, recorded data is in the form of a three-dimensional pattern of spaced-apart data spots, such that the recording plane is not physically formed. Therefore, the conventional scheme cannot be used for precise recording in a recording plane on a desired position.
The present invention is aimed at providing a novel optical data carrier configured to enable recording data in and reproducing (reading) data from multiple recording planes, which are located within at least one recording layer (recording medium). To this end, the data carrier of the present invention utilizes one or more reference layers presenting reflective surface(s), and one or more non-recording layers. The present invention also provides a method for recording/reproducing data in/from such a data carrier.
According to one broad aspect of the invention, there is provided an optical data carrier, comprising:
at least one recording layer comprised of a material having a fluorescent property variable on occurrence of multi-photon absorption resulted from an optical beam, said recording layer having a thickness for recording therein data in the form of a three-dimensional pattern of spaced-apart recording regions arranged in a plurality of recording planes;
at least one non-recording layer interfacing with said recording layer on, respectively, at least one of upper and lower surfaces of said recording layer, said at least one non-recording layer having a fluorescent property different from that of said recording layer, said non-recording layer having a predetermined thickness selected to be equal or larger than a focal depth of an optical system producing said optical beam incidence onto the data carrier; and
at least one reflective interface comprising at least one reference layer having a reflecting property, said at least reflective layer being formed on the other surface of said at least one non-recording layer, such that the non-recording layer in sandwiched between the reference layer and said recording layer.
It should be understood that different fluorescent properties of the recording and non-recording layers can be achieved for example by providing the recording layer which in non-recorded state is fluorescent while the non-recording layer is a non-fluorescent layer; or by providing the recording layer, which in its non-recorded state is non-fluorescent, while the non-recording is fluorescent.
Preferably, the non-recording layer is made of an adhesive material to enable adhering of the recording layer to the reference layer. For example, the thickness of the non-recording layer may be in the range of 3 μm to 80 μm.
The reflective interfaces may be constituted by the reflective reference layer spaced from the recording layer by the non-recording layer, or may be an interface between the non-recording layer and the recording layer formed by a difference in refractive indices of the recording and non-recording layers' materials.
The reference layer has a pattern configured to enable tracking of the optical reference beam, based on reflections of the optical beam from this pattern. The pattern may comprise a plurality of discrete pits; or may comprise a plurality of concentric circular grooves or a spiral groove; or a combination of the above, namely groove(s) with discrete pits therein.
The pattern in the reference layer may be configured to enable tracking of the optical beams of different wavelengths, based on reflections of the optical beam from the pattern. These optical beams of different wavelengths are recording/reproducing and reference beams.
In those embodiments of the invention, where the pattern in the reference layer is in the form of the plurality of concentric grooves or a spiral groove, the groove depth may be of about λ1/8n1. Here, n1 is a refractive index of the non-recording layer interfacing with the reference layer upstream thereof in a direction of propagation of the optical beam towards the reference layer, at wavelength λ1 of the reference beam.
In those embodiments of the invention, where the pattern in the reference layer is formed by the plurality of pits, arranged either along a plurality of concentric circular arrays or along spiral paths, the plurality of pits may include pits of a depth of about λ1/4n1; or of a depth of about λ1/6n1.
As indicated above, the pattern in the reference layer may be configured to enable tracking of the recording/reproducing beam based on reflection of this beam from said pattern in the reference layer. In these embodiments, considering the pattern in the reference layer formed by a plurality of concentric grooves or a spiral groove, the groove depth may be of about (λ1/16n2+λ1/16n2). Here, n1 and n2 are refractive indices at wavelengths λ1 and λ2 of the reference beam and the recording/reproducing beam, respectively, of the non-recording layer interfacing with said reference layer upstream thereof. In case of the pattern formed by a plurality of discrete pits (arranged either in concentric circular arrays or along spiral paths), the plurality of pits may include pits of a depth of about (λ1/8n2+λ2/8n2); or may include pits of a depth of about (λ1/2n2+λ2/12n2). In some other examples, the plurality of pits may include pits of a depth d1=λ1/4n2 and d2=λ2/4n2; or pits of a depth d1=λ1/6n2 and d2=λ2/6n2.
The reference layer may comprise position information of radial direction and tangential direction. The reference layer may also comprise information about the thickness of the recording layer.
Preferably, the data carrier configuration is such that the recording layer is enclosed between the first and second non-recording layers, where one of these non-recording layers or both of them at its opposite surface interface with the reflective reference layer.
According to another aspect of the invention, there is provided a method for use in recording/reproducing data in the above-described optical data carrier, said method comprising controlling focusing of the recording/reproducing optical beam on each of multiple recording planes in the recording layer, by detecting at least one of the following: reflection of the recording/reproducing and reference optical beams from the at least one reflective interface, and a change of a fluorescent response from the data carrier at interface between the recording and non-recording layers, to thereby enable at least one of the following: aligning the recording/reproducing beam propagation relative to the reference beam propagation and identifying two opposite interfaces of the recording layer with its surroundings.
In some embodiments of the invention, the above is implemented by controlling an axis of propagation of the recording/reproducing beam towards and inside the data carrier by aligning the axis of propagation of the recording/reproducing beam so as to substantially coincide or be in a desired relation with an axis of propagation of a reference beam. This can be achieved by focusing the reference beam onto a desired track in the reference layer and focusing the recording/reproducing beam at either the same track or a track at a desired relative position with said track onto which the reference beam is being focused.
Preferably, the method utilizes calibration of a moving distance of a focused position of the recording/reproducing beam along a focus direction. This may include locating first and second interfaces of the recording layer at opposite sides thereof, thereby determining a thickness of said recording layer. Generally, the calibration is based on detecting and analyzing light coming from the data carrier in response to the data carrier irradiation by the recording/reproducing beam. This light from the data carrier includes a fluorescent response from the data carrier and/or reflection of the recording/reproducing beam from the data carrier, and is indicative of a distance between the first and second interfaces and therefore the thickness of the recording layer
Thus, in some embodiments of the invention, the calibration includes detecting the fluorescent response from the data carrier, analyzing the detected fluorescent response to detect the change therein, which is indicative of a distance between the first and second interfaces of the recording layer at opposite sides thereof, thereby determining a thickness of the recording layer. In some other embodiments of the invention, the calibration includes determining reflection of the recording/reproducing beam from the at least one reflective reference layer. As indicated above, the optical data carrier may include said recording layer interfacing at opposite sides thereof with respectively first and second non-recording layers, which in turn interface with first and second reflective reference layers.
In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting examples only, with reference to the accompanying drawings, in which:
Some embodiments of the present invention will now be exemplified with reference to the accompanying drawings.
Reference is made to
The recording layer 4 serves to record data therein and reproduce the recorded data therefrom, where the data is in the form a three-dimensional pattern of spaced-apart recorded regions arranged in multiple recording planes. The reference layer 2 serves as a reference surface to focus a recording/reproducing light beam on a desired position in the recording layer 4. The substrate 1 serves as a base layer for the reflective reference surface 2 to thereby provide patterns for tracking. The substrate 1 is made of at least one transparent material such as polycarbonate, methacrylic resin, or polyolefin. The non-recording layer 3 and the recording layer 4 material compositions are selected to have different fluorescent properties (as will be described below). The non-recording layer 3 serves for positioning of the recording/reproducing beam by detecting the interface D1 between the recording and non-recording layers from a change in a fluorescent response.
The recording layer 4 is composed of non-linear medium having a fluorescent property variable on occurrence of multi-photon (two-photon) absorption. Such a recording medium is disclosed in various patent applications and patents assigned to the assignee of the present application. For example Patent Convention Treaty (PCT) publication WO 01/73779 discloses a non-linear three dimensional memory for storing information in a volume comprising an active medium. The active medium is capable of changing from a first to a second isomeric form as a response to radiation of a light beam having energy substantially equal to first threshold energy. The concentration ratio between a first and a second isomeric form in any given volume portion represents a data unit. This PCT publication discloses an optical storage medium that comprises diarylalkene derivatives, triene derivatives, polyene derivatives or a mixture thereof. An optical storage medium with photoactive groups has been disclosed in various PCT publications assigned to the assignee of the present application, for example WO 2006/0117791, WO 2006/075326, WO 2001/073779, WO 2006/075328, WO 2003/070689, WO 2006/111973, WO 2006/075327, WO 2006/075329. As disclosed for example in WO 03/070689, assigned to the assignee of the present application, such material may be a copolymer of 4-methoxy-4′-(8-acryloxyoctyloxy)-trans-α,β-dicyanostylbene (hereinafter referred to as a compound trans-A) and methyl methacrylate, as well as other materials. Plural recording planes, for example, in tens of layers, can be formed in one recording layer 4. The recording layer 4 itself is a bulk substrate, monolithic with respect to the wavelength resolution as discussed in WO 06/075327 assigned to the assignee of the present application. Such a bulk substrate may be composed of a single material having a fluorescent property variable on occurrence of two-photon absorption, and may be a material having a fluorescent property variable on occurrence of two-photon absorption and uniformly dissolved or substantially uniformly organized or dispersed in a substrate material.
The recording layer 4 need not contain any dedicated positional information about either the radial direction (tracking direction) or the data carrier thickness direction (focus direction). Positional information is given from the reference layer 2, as will be described further below, such that data can be recorded with the aid of the tracking direction position signal in the reference layer 2 and the data for setting the focus direction distance from the interface between the recording layer 4 and non-recording layer 3 to the recording plane. As indicated above, the reference layer 2 has a reflecting surface. This can be formed by a film with low reflectance (about 2-50%) evaporated on a pitted/protruded surface, which is pre-formatted in the top surface of the substrate 1 using the well-known stamper. Alternatively, the reflective surface 2 may be formed by an appropriate difference in refractive indices of the substrate 1 and the non-recording layer 3 materials.
The reflecting surface 2 has a certain pattern. In some embodiments of the invention, the pattern may be in the form of a plurality of pits arranged in a spaced-apart relationship either in concentric circular arrays or along a zoned spiral track. In some other embodiments of the invention, the pattern is in the form of either an array of concentric circular grooves or a spiral groove. In yet further embodiments of the invention, the pattern is in the form of a combination of pits and grooves, namely includes a concentric circular array of grooves or a spiral groove, and a plurality of pits arranged in a spaced-apart relationship either inside the groove(s) or in a “land” segments in between the groove segments.
The recording layer 4 is given a thickness in accordance with the pre-designed number of the recording planes for multi-layered recording. The number of the recording planes is determined from the non-linear media response, the optics (e.g. interrogation wavelength or numerical aperture), the accuracy of the recording/reproducing optical system and the dimensional precision of the data carrier itself. For example, to form about 50 recording planes in the recording layer 4, the thickness of the recording layer 4 can be about 300-600 cm.
The non-recording layer 3 serves for adhering the recording layer 4 with the reference layers 2 while keeping these layers substantially parallel to one another. The thickness of the non-recording layer 3 is selected so as to be equal to or preferably larger than the focal depth of an objective lens system used in data recording/reproducing processes (as will be described below). The focal depth of objective lens system is expressed as λ/(NA)2, where λ is the wavelength of an optical beam and NA is a numerical aperture of the lens system. For example, the thickness of the non-recording layer 3 is in a range of 3-80 μm. If the thickness of the non-recording layer 3 is smaller than the focal depth, the detection of the interface D1 between the recording and non-recording layers 4 and 3 might become somewhat inaccurate. The non-recording layer 3 is typically a bonding layer which may be made by spin coating. In order to make the non-recording layer substantially parallel to the recording planes in the recording layer, the thickness of the non-recording layer 3 is preferably from about 5 μm to about 100 μm, and more preferably from about 10 μm to about 50 μm.
The non-recording layer 3 is highly transmitting for wavelength(s) of reference and recording/reproducing beams, while its material composition differs in a fluorescent property from the material of the recording layer 4 used in the data carrier. For example, epoxy resin, a photo-cured acrylic photo-polymerizing adhesive may be employed as the material of the non-recording layer 3. The use of these materials in the non-recording layer will also satisfy a requirement for different fluorescent properties of the recording and non-recording layers. The non-recording layer 3 may be composed of a material having no fluorescent property at all or a material differing in fluorescence emission efficiency or emission wavelength from the recording layer 4. Yet another option is that the recording layer 4 itself is composed of a material which, in its initial non-recording state, has a weak fluorescent property while the non-recording layer 3 is composed of a material having a relatively strong fluorescent property. A copolymer of methyl methacrylate and the 4-methoxy-4′-(8-acryloxyoctyloxy)-cis-α,β-dicyanostylbene (hereinafter referred to as a compound cis-A) may be used in the recording layer 4, while a copolymer of the above compound trans-A and acrylic photo-curing adhesive may be used in the non-recording layer 3. This provides for different fluorescent properties for layers 4 and 3. According to yet other possible option, both the recording layer 4 and the non-recording layer 3 are produced of the isomeric copolymer of the same material, such as the copolymer of the compound A, with one of these layers being made mainly of the compound trans A (trans-rich) and the other being made mainly of the compound cis-A (cis-rich). This also satisfies the requirement for different fluorescent properties in layers 4 and 3. The non-recording layer may be formed of air. As the air layer has no fluorescent property, it is possible to achieve the same effect as the above configuration has.
As will be described further below, focusing of the recording/reproducing beam is controlled by detection of at least one of the following: reflection of the reference beam from the reflective interface(s) in the data carrier, and a fluorescent response from the data carrier. The reflective interface may be constituted by the reflective layer 2 (or two reflective layers 2 and 2′ at opposite sides of the recording layer as will be described below with reference to
More specifically, during recording, focusing of the recording/reproducing beam is controlled by detection of reflection of the reference beam, and during reading, focusing of the recording/reproducing beam is controlled by detection of the fluorescent response and preferably also reflection of the reference beam. It should be noted that when speaking about detection of the fluorescent response for the purposes of controlling the focusing, this fluorescent response may be from the recording layer or from the non-recording layer in accordance with the selected change in the fluorescent property of these layers.
As also will be described more specifically further below, a calibration of the recording/reproducing beam focusing is preferably conducted. In some embodiments of the invention, this calibration is aimed at determining a thickness of the recording layer. This can be implemented by detecting a change in the fluorescent response at the interface between the recording and non-recording layers, and/or by detecting reflection of the reference beam and/or recording/reproducing beam from the reflective interface(s) in the data carrier, based on the known (typically with a high precision) thickness of the non-recording layer(s).
Reference is made
The system 1000A includes a light source system formed by a first light source unit (laser) 11 operative to emit a recording/reproducing light beam L1, and a second reference light source (laser) 21 operative to emit a reference light beam L2. The system 1000A further includes a light detection system, which in the present example is formed by two detection units 16 and 27; and a light directing system, generally at 17, configured for directing and focusing the recording/reproducing beam L1 onto a desired location in the medium 10 and for directing light returned from the medium towards the detection system. The detection unit 16 is associated with its collection optics 15 (formed by two lenses in the present example) and serves for detecting a light response LR of the medium to the reading beam. The detection unit 27 is also associated with its imaging optics 26 (e.g. two lenses) and serves for detecting reflection Rref of the reference beam from the reference layer 2. Also provided in the system 1000A is a control unit 30, connectable to the light source system and the detection system (via wires or wireless signal transmission as the case may be), and operating to adjust the operational mode of the light source system and receive and analyze the output of the detection system. Further optionally provided in system 1000A is a controllably movable reflector unit 28 (e.g. mirror driven for movement by a piezo-element) accommodated in the optical path of the recording/reproducing beam L1, for the beam wobbling purposes and/or for co-aligning the beams, as will be described further below.
The recording/reproducing laser source unit 11 includes a light source capable of emitting light of a wavelength range suitable to cause the multi-photon interaction (e.g. two-photon interaction) for the data recording/reproducing in the data carrier 10, for example a wavelength λ1 of about 671 nm. The laser source 11 is configured for controllably varying the output thereof such that it selectively emits a light pattern suitable for recording and reading processes, for example light of an average output of 1 W and a pulse(s) width of about tens to hundreds of pico-seconds for recording and light of an average output of 0.1 W and pulse(s) width of about tens of pico-seconds for reading.
The reference laser source unit 21 includes a light source operable for tracking servo and focusing servo of the data carrier 10. This light source emits the reference light beam (laser beam) L2 of a suitable wavelength range (which may be different or not from that of the recording/reproducing beam), for example having a wavelength 2 of about 780 μm. The reference light source unit preferably also includes a polarized beam splitter 22 and a polarization rotator (e.g. ¼-wavelength plate) 23 in the optical path of the emitted reference beam L2.
The light directing and focusing system 17 includes a beam splitter/combiner 12 in the optical path of the recording/reproducing and reference beams L1 and L2; a focusing optics 24 (formed by one or more lenses for example—two such lenses being shown in the present example) at the output of the reference light system configured for focusing the reference light beam L2 (of the appropriate polarization) onto the beam splitter/combiner 12; and a focusing/collecting optics 14 (formed by one or more lenses—two such lenses being shown in the present example) for focusing the incident light (optical beam) onto a desired location in the medium and collecting light returned from the medium. Further provided is a mirror 13 accommodated in the optical path of the incident light propagating from the beam splitter/combiner 12 to direct it to the optical data carrier 10 and to direct light returned from the data carrier to the beam splitter/combiner 12. The focal depth of optics 14 defines the thickness of the non-recording layer 3: the thickness of this layer is equal to or larger than the focal depth of optics 14.
The system 1000A operates as follows: The reference beam L2 is directed towards the medium as described above, i.e. its polarization is preferably appropriately adjusted; and then it is focused by optics 24 onto the beam combiner 12, reflected by the mirror 13, and further focusing by the optics 14 onto the reference layer 2. This reference light is reflected from the reference layer 2 and the reflection Rref returns back through the same optical path, i.e. optics 14, mirror 13, beam splitter/combiner 12, optics 24 and polarized beam splitter 22. The latter reflects the beam Rref to pass through the imaging lens 26 to the detector 27. Based on the output signal from the detector 27 (being analyzed by the controller 30), the operation of the focusing optical systems 14 is controlled such that the focused position of the reference beam L2 is always substantially coincident with the reference layer 2. Considering for example a four-part split detector is used in the detection unit 27, tracking control can be executed using a well-known push-pull method.
The recording/reproducing beam L1 in turn passes the beam splitter/combiner 12, is reflected by the mirror 13, and focused in the data carrier 10. In this example, optical axes of the recording/reproducing beam L1 and the reference beam L2 are coincided mechanically in advance and are kept coincided throughout the operation (e.g. using the piezo mirror 28).
A focusing position of the recording/reproducing beam L1 in the disk thickness direction can be controlled by driving the collimator lens pair 24, while a focused position of the reference beam L2 is kept on the reference track (pattern) in the reference layer 2 through the action of the controller 30 and the focusing optical system 14. Focused position is determined based on the first interface D1, that is the interface between the recording layer 4 and the non-recording layer 3 (bonding layer). Position of the first interface D1 can be detected by moving the focused position of the recording/reproducing beam L1 by the action of the collimator lens pair 24 and detecting an inflexion point of the fluorescent light intensity detected at the detector 16. Further moving the focused position of the recording/reproducing beam L1 by the action of the collimator lens pair 24, the second surface D2 that is an upper surface of the recording layer 4 in the present example (or an interface between the recording layer 4 and top substrate 1 in the example of
The thicknesses of the non-recording layer and the recording layer are preferably substantially uniform in the data carrier. Practically, however, some deviation might exist. In such case, the position should be determined under a predetermined rule. It should be understood that measuring the thickness of recording layer does not signify measurement of a correct value, but rather getting a scale for measuring the distances between the recording planes. So it is important to carry out such measure under the same rule, predetermined as the standard, during data recording and reproducing procedures. One such method consists in getting the minimum thickness, such that the recording plane does not go out from the recording layer. This can be implemented by defining the interface D1 as the furthest point at some radius in the interface to the reference layer and the interface D2 as the nearest point at the same radius with respect to the reference layer. Generally, other definitions, such as an average, etc., can be used, but the use of the abovementioned definition is preferred because by such a method the calculated position of the recording/reproducing beam in between those interfaces will always be within the recording layer 4. By using such a scale, the distance between the recording layer interfaces can be measured in a reproducible way even if different optical devices are used in the recording and reproducing process and/or the recording and reproducing device(s) is/are replaced or their parameters are changed from time to time, or if the thickness of the data carrier is changed for some reason, for example as a result of absorption of humid. The reason for the robustness is associated with that the scale is contained in the optical data carrier itself.
By controlling the intensity of the recording/reproducing beam L1 to be of the intensity suitable for recording, the fluorescent property of the recording layer 4 (constituting the medium excitation by multi-photon interaction) varies on the focused position, resulting in execution of data recording. During the data reading process, when the recording/reproducing beam L1 is focused on the recorded position, fluorescent light LR (constituting the light response of the data carrier) is emitted in accordance with the condition on the interrogated (recorded mark or space) position. The fluorescent light LR is then guided through the lens system 15 to the detector 16, and, based on the detected signal, the recorded data pattern can be reproduced. To form the beam spot of the recording/reproducing beam L1 precisely on a desired recording plane in the recording layer 4, the optical system 14 is preferably configured as a spherical aberration-corrected optical system. This actually means that the focusing optical system 14 is designed such as not to cause any spherical aberration higher than a predetermined tolerance. As for the reference beam L2, small spherical aberration is generally allowed.
In the example of
According to the invention, alignment of the propagation axes of the recording/reproducing beam L1 and the reference beam L2 can be achieved using, for example, reference tracks in the data carrier detectable for both beams. The reference track is formed as a pattern in the reference layer 2, where the pattern may be in the form of an array of spaced-apart pits and/or grooves as described above (the array may be arranged in a concentric or spiral form).
Examples of the optical data carriers with the patterned reference layer are shown, in a self-explanatory manner, in
As indicated above, in some embodiments, the spaced-apart discrete pits are formed in a planar surface of the reference layer. In some other embodiments, a single spiral groove or a plurality of concentric closed-loop (e.g. circular) grooves spaced from one another by land regions are formed in a planar surface of reference layer. In yet other embodiments, both of the spaced-apart discrete pits and grooves are formed in a planar surface of the reference layer.
In order to use the optical data carrier for aligning the optical axis of the system exemplified in
It should be understood that, generally, the structure of the reference layer is selected such as to enable guiding of the reference beam and indicating the position information. In order to achieve this, reference layer has a pattern in the form of pits and/or grooves.
In the above-described example of
It should also be noted that in the case of a groove structure, for the purpose of detecting the tracking error signal by the use of push/pull method, the groove of a substantially rectangular cross section and a depth d of about (λ1/16n1+λ2/16n2) is preferably used, where n1 and n2 are refractive indices of the non-recording material interfacing with the reference layer upstream thereof (in a direction of propagation of the optical beam towards the reference layer) at, respectively, the wavelength λ1 of the reference beam L2 and the wavelength λ2 of the recording/reproducing beam L1. This is exemplified in
In the case of pits array structure is used for sampled servo method, it is preferred to use the pits of a substantially rectangular cross section and a depth d of about (λ1/8n1+λ2/8n2). This is exemplified in
A “mixed” array of pits with different depths d1 and d2 of, respectively, λ1/4n1 and λ2/4n2 may also be used in the sampled servo system. This is exemplified in
Turning back to
Then, the focus of the recording/reproducing beam L1 is tracked on the reference track (pattern in the reflective reference layer 2) by operating the piezo mirror 28. Typically the recording/reproducing beam L1 is tracked on the same track as the reference beam L2 and tangential position is also coincided to the same position as the reference beam L2, but different tangential position may be possible. In order to keep two beams substantially coinciding, the track number and position information included in the reference layer are used (similar to synchronization information for the tangential position information).
By the operation described above, even if the propagation axes of both the recording/reproducing and reference beams are not mechanically coincided in advance as in the first embodiment of
Focusing the recording/reproducing beam L1 onto a certain recording plane in the recording layer 4 is set by moving the collimator lens pair 24a distance calculated from the information described above. When the collimator lens pair 24 is moved, the focusing optical system 14 is controlled to move such that the reference beam L2 is kept focused on the reference layer 2 and the focusing point of the recording/reproducing beam L1 changes accordingly.
As indicated above, in some embodiment of the invention, a calibration procedure is carried out for controlling the moving distance, based on the determination of the fluorescent response from the data carrier to identify interfaces of the recording layer, namely the at least one interface between the recording layer and the at least one non-recording layer, respectively. In some other embodiments of the invention, a calibration procedure utilizes determination of the reflection of the recording/reproducing beam from the reflective interfaces 2 and 2′ (see
Thus, one possible method of calibration of the above described moving distance of the collimator lens pair 24 consists of comparing a certain predetermined value (chosen to be a standard), for example the thickness of the data carrier 10, with the actually measured moving distance between the upper and lower interfaces D1 and D2 (see
Tracking and controlling the position of the recording/reproducing beam L1 can be realized by keeping a constant relative position of the recording/reproducing beam L1 based on the reflection of the reference beam L2 from the reference layer 2 and following the reference beam L2 along the reference track in the reference layer 2. It should be understood that mainly the focused position of the recording/reproducing beam is fixed apart to the reference beam and moves with the reference beam. Even in the case of wobbling, the reference beam is wobbled and the recording/reproducing beam wobbles accordingly, and optimization is done as offset of the wobbling center. Another possible procedure consists of independently wobbling the recording/reproducing beam, while the recording/reproducing beam follows a movement of the reference beam (with a certain controlled relation between them). So, the relative position is determined with respect to the reference layer which is always tracked by the reference beam.
The pits in the reference layer are used in tracking of the reference beam L2 and the recording/reproducing beam L1 in the tracking and focus directions and for indicating the radial and tangential position. Therefore, the pits are formed to detect focusing of the reference beam L2 on the reference layer 2 and in some embodiments to detect recording/reproducing beam L1 on the reference layer 2 as will be described in more details further below.
The principle of detecting the interface between the recording layer and the non-recording layer or the surface of the recording layer, by recording/reproducing beam L1 will now be described with reference to
As described above, the recording layer 4 and the non-recording adhesive layer 3 have different fluorescent properties. It is assumed herein that the recording layer 4 in its initial non-recording state has a fluorescent property (e.g. is excitable by two-photon interaction to fluoresce) and the non-recording adhesive layer 3 has no fluorescent property. In this case, as shown in
Turning back to
As described above with reference to
Reference is now made to
Subsequently, focusing optics (24 in
A distance b of the movement of focus position of the recording/reproducing beam L1 (a distance between the interfaces D1 and D2) is then determined by the control unit. Based on this moved distance b, when N recording planes are formed in one recording layer, a distance δ to be moved between the adjacent recording planes can be determined as δ=b/(N+1) (step S4).
A calibration of the focusing servomechanism is performed as described above. After the completion of this calibration procedure, actual data recording by the recording/reproducing beam L1 can be started. During the recording procedure, the focus position of the reference beam L2 is kept on a reference track in the reference layer 2 (via the operation of the servomechanism), and the piezo mirror 28 is kept in a fixed state. Accordingly, the optical axis of the recording/reproducing beam L1 propagation is kept such that it coincides or is in a constant relative position with the optical axis of the reference beam L2 propagation. In this situation, by increasing the intensity of the recording/reproducing beam L1, data recording may be conducted.
A procedure for determining a distance between the recording planes in the data carrier exemplified in
It should be noted that as to the distance b between the interfaces D1 and D2 and the number N of the recording planes, a value provided by a standard can be used as is, i.e. as specified by the standard. Alternatively, when various types of standards exist, specific information about the standard to be used may be recorded in the reference layer 2 of the data carrier, and this information may then be read from the reference layer when the medium is used to set the desired distances between the recorded layers in the medium and between the recorded layers and the corresponding layer(s).
On data reproducing, the position of data layer can be detected roughly by above mentioned method. It should be noted that sometimes, for example when the data carrier is tilted or the setting is decentered, the actual position of data layer might differ from the calculated position. In order to get an optimal signal, adjustment of the tracking by fine servo might be necessary.
Preferably, on data reproducing from the data carrier 10, the recording/reproducing beam is driven at a certain cycle (wobbling frequency f1) while setting, as a reference, a constant relative focused position of the reproducing beam L1 relative to the focused position of the reference beam L2 on the reference track in the reference layer, to vary the focused position of the reference beam L2 in the data carrier thickness direction. In other words, in this specific example, the reproducing process proceeds while scanning within a nominal plane (ideally, the so-called “flat spiral” movement of the recording/reproducing beam) with a small wobble perturbation. Turning back to
Thus, as a result, as shown in
Reference is made to
As shown in
Reference is now made to
where the index i refers to the specific error signal (FES or TES), mi is the derived phase locked internal signal, and I(t) is the detected fluorescent signal from the medium.
The beam position approximately on track can be achieved by using the controlled distance from the reference layer, by a slow motion in either one of the radial and axial directions and by the fact that a spiral shape of a track helps to be approximately on track in a ‘once around’ fashion.
As noted above, using two frequencies is also a method for separating between the signal components for the FES and TES.
Those skilled in the art will readily appreciate that various modifications and changes can be applied to the embodiments of the invention as hereinbefore described, without departing form its scope defined in and by the appended claims.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IL07/00069 | 1/18/2007 | WO | 00 | 4/3/2009 |
| Number | Date | Country | |
|---|---|---|---|
| 60759580 | Jan 2006 | US |
