WO2009040821A1

WO2009040821A1 - Optical data carrier and method and system for recording/reading data therein

Info

Publication number: WO2009040821A1
Application number: PCT/IL2008/001299
Authority: WO
Inventors: Yair Salomon; Masanobu Arise; Ortal Alpert; Kozo Nakao
Original assignee: Mempile Inc.
Priority date: 2007-09-25
Filing date: 2008-09-25
Publication date: 2009-04-02

Abstract

The present invention discloses an optical data carrier comprising an optical recording medium in which data is recordable and readable as a result of one-or multi-photon interaction. The data carrier comprises one or more recording layers, each comprising spaced-apart recording regions arranged in multiple planes. The spaced-apart recording regions are arranged in a composite data pattern comprising a first main data and second tone data of different spatial frequencies to thereby respond to a reading one- or multi-photon signal by a first data signal and second tone signals, respectively. There is also disclosed a method for recording the data in the optical carrier, an optical system for use in recording/reading the data in the optical data carrier, and a control system for use with an optical head system for recording/reading the data in the optical data carrier.

Description

OPTICAL DATA CARRIER AND METHOD AND SYSTEM FOR RECORDING/READING DATA THEREIN

FIELD OF THE INVENTION

This invention is generally in the field of optical storage, and relates to methods of data recording and reading, and to an optical data carrier. More specifically, the present invention relates to the recording/reading technique utilizing tones recorded in the optical data carrier.

BACKGROUND OF THE INVENTION

In the conventional optical storage media, such as optical disks in general and DVDs in particular, data is stored along tracks in a recording layer and is read by focusing a laser beam produced by light sources (typically semiconductor diodes) on to the tracks, while spinning the disk on its axis. The tracks are typically segments of a spiral track on which data is written and from which the data is read. The conventional CDs and DVDs utilize reflective recording media, and therefore are limited to a single data layer configuration.

An alternative to a reflective-type medium is a medium based on one- or multi-photon interaction (e.g., Ramman scattering photo-refractive effects, fluorescence phenomena or various χ(3) processes). In such memory storage, the data is presented as local variations of one- or multi-photon interaction with one or more light beams. The variations may be recorded by non-linear interaction with a linearly or non-linearly absorbed light, as disclosed for example in PCT IL2008/000725 assigned to the assignee of the present application. The substance is illuminated with radiation at excitation wavelength(s) during data recording and reading processes, and the non-linear response signal emitted in response to the reading radiation is registered at a different wavelength. An example of utilizing these principles in the optical storage is the implementation of a 3-D storage enabling creation of a three-dimensional data pattern in the form of spaced-apart recording regions arranged in multiple layers (e.g. virtual layers). This approach utilizes a non-linear (e.g. fluorescent) medium containing photochromic molecules capable of existing in two forms. For example, the first form A has absorption bands for UV radiation, and is capable of being transferred into the second isomeric form B upon the simultaneous absorption of two long wavelength photons. The second form B has a different fluorescent property as compared to the form A, and thus may be capable of exhibiting fluorescence response different from fluorescence response of form A upon simultaneous two- photon absorption of a reading light in the infrared range. Some examples of non-linear recording media and techniques of data recording/reading therein are disclosed in WO 2006/075327, WO 2007/060674, WO 07/010519, WO 06/117791, US 7,011,925, WO 06/075328, WO 04/032134, and WO 03/070689, all assigned to the assignee of the present application.

GENERAL DESCRIPTION

The present invention takes an advantage of recording/reading beam tracking methods disclosed in the following patent publications US 20030174594 and WO 03/077240, both assigned to the assignee of the present application. These techniques are aimed at correcting tracking errors while reading/recording in an optical storage medium formed of multiple tracks arranged in different layers (virtual), the so-called "3-D recording medium". A light spot (recording/reading spot) that is nominally focused onto a track, while being directed into the optical storage medium, is continually moved in axial and radial directions. A signal having amplitude, which varies according to respective offsets from the track in radial and/or axial directions is received and used to determine a direction of a respective offset from the track in radial and axial directions, and thus adjust a location of the recording/reading spot accordingly.

An optical data carrier of the present invention utilizes a medium in which data is recordable and readable as a result of one- or multi-photon interaction. Such media is disclosed for example in WO 07/010519, WO 06/117791, US 7,011,925, WO 06/075328, WO 04/032134, and WO 03/070689, all assigned to the assignee of the present application. Such carriers represent an optically monolithic disk-like structure formed by one or more plates each made of a photochromic material (active plate). Multiple plates may be adhered to each other. In the depth of each plate data is recorded/read in/from being in the form of a three-dimensional pattern of spaced-apart recorded regions (sometime termed "data marks"). Typically, the marks are organized to form nominally, almost planar, patterns. This approach allows for constructing a data carrier having multiple recording layers for recording data in the form of a three- dimensional pattern of spaced-apart recorded regions arranged in multiple planes which are actually virtual strata and are termed herein as recording planes or planes or layers (where the context is clear).

According to the present invention, the data carrier comprises a plurality of spaced-apart recorded regions (marks) arranged according to a certain composite data code or pattern comprising data and tones, where the tones related signals are of spatial frequencies different from that of the data signals.

It should be understood that the term "recorded region" used herein signifies a region of an optical property different from that of its surroundings (spaces between the recorded regions) and refers to both the data and the tone, as the data and tone form together the composite pattern of spaced-apart recorded regions.

In other words, data as well as tones is/are represented by a plurality of region including recorded regions and spaces between them. The arrangement of spaced-apart recorded regions (marks) in each recording plane corresponds to a certain composite code or pattern.

The data and the tone respond to a reading beam by the respectively data and tone signals of the same wavelength but at different spatial frequency ranges, where the spatial frequencies of the tone signal corresponding to a specific recording plane is different from at least some of other recording planes. This enables identification of a focal location of the reading beam and thus controlling the reading beam scan, and optionally filtering out the tone signal to extract the data signal.

The spaced-apart recorded regions may be arranged in the recording plane in concentric tracks, zoned spiral tracks, or a single spiral track. The tones in adjacent tracks (being for example segments of the spiral tracks) in both the radial and thickness (focus) directions (i.e. in the same recording plane and in different recording planes) have different spatial frequencies. The tones of different spatial frequencies can be embedded in the composite data pattern in, all the concentric tracks (or all the segments of the spiral track) of the same recording plane and/or of different recording planes. Alternatively, by using groups of concentric tracks (or segments of spiral tracks), within the same recording plane and/or in different recording planes, tones of different spatial frequencies having a certain set of frequencies can be embedded in tracks/segments of each group while all the groups have the same set of frequencies (e.g. even and odd tracks/segments have different first and second frequencies, respectively).

In some embodiments of the invention, the optical data carrier includes one or more reference layers. The use of a reference layer in an optical data carrier for controlling a beam spot of a reading beam to a desired position in the thickness direction of the carrier or the focus direction is generally known. These techniques are described for example in U.S. Patents Nos. 5,408,453, 6,538,978 and 6,738,322; U.S. Patent Application Publication US 2005/0036421; Japanese Patent Publication No. 2001-283448; and International Publication No. WO 98/53448. Various configurations of the reference layer suitable to be used in the recording medium in which data is recordable/readable by one- or multi-photon interaction allowing data recording in multiple planes, are disclosed for example, in WO 06/111972 and WO 06/111973, both assigned to the assignee of the present application. In the embodiments of optical data carrier of the present invention utilizing reference layer(s), the recording layer are at least partially transparent for recording, reading and reference wavelength(s), and the reference layer(s) is/are at least partially transparent to the recording/reading wavelength and at least partially reflective to the reference wavelength.

Generally speaking, recording/reading and reference wavelengths may or may not be different; the reference beam has parameters (intensity, pulse duration, wavelength) such that interaction thereof with the recording medium causes neither recording nor reading event. The reference layer may be used for controlling the procedures of focusing and/or tracking the recording/reading beam movement while scanning during the recording/reading procedure. Generally, in order to use the reference layer for controlling the focusing, the reference layer may be of a flat surface. Preferably however, the reference layer has a certain pattern in the form of an array of spaced-apart pits and/or grooves, or in the form of a spiral groove. This allows using the reference layer for both focusing and tracking.

In some embodiments of the invention, the reference layer is coded (e.g. by sector partitioning) to allow for controlling the tones' recording process.

Also, in some embodiments of the invention, the tones are embedded in the reference layer(s), e.g. during the manufacture of the data carrier. In this case, additional tones may be embedded in a composite data pattern recorded in the recording layer.

Detection of reflection of the reference beam from the reference layer serves for controlling a process of recording the three-dimensional composite pattern in the recording layer interfacing with said reference layer. As for the detection of the tone signals, embedded in the composite data pattern and recorded during the data recording process, it serves for controlling a process of reading the recorded data. More specifically, signal indicative of cross-talk between the tones of the adjacent tracks/segments (which are of different spatial frequencies) is used for identifying the reading beam moving off the track, enabling appropriately correction of the reading beam propagation path in the carrier.

According to the invention, a method for recording data in the above- described optical data carrier comprises scanning the reference layer with the reference beam and detecting reflection of the reference beam from the reference layer, while scanning the optical recording layer/plate with a recording beam, thereby controlling the scan of the recording beam to create a three dimensional composite data pattern of spaced-apart recorded regions arranged in multiple planes. This composite data pattern includes data and tones and thus responds to a reading beam by a first data signal and second tone signals of different spatial frequencies.

Alternatively to scanning the reference layer, a second reading beam spaced from the first reading/recording beam may scan a group of recorded tracks such that the first reading/recording beam is positioned on a determined track and the second reading beam is between the recorded tracks tracking a reference path at determined (axial and radial) offset from the first reading beam focus.

The data carrier in its recorded state thus contains an arrangement of the spaced-apart recorded marks or regions corresponding to a composite data pattern which include data (recorded regions and spaces) and predetermined tones. Accordingly, when a certain track/segment of the data carrier is scanned by a reading beam, it responds by a main data signal of a certain spatial frequency range and by a tone signal of a different spatial frequency range. These signals are of the same wavelength (e.g. fluorescent response) but vary during a scan by different spatial frequencies and can thus be detected and distinguished by using appropriate band filters.

When the reading beam focus moves off the track (in radial direction or axial/focus direction, or both), the detected tone signals are prominently a result of a cross-talk between the tone signal from the track that is to be read and that from the adjacent track(s). For example, when the beam moves away from the track, the amplitude of a respective detected component (tone signal from a first adjacent track) decreases while the amplitude of the other (tone signal from a second adjacent track) increases. The difference in the two amplitudes constitutes an error signal which is then used for redirecting the recording beam accordingly to maintain its focus position on the desired track/segment. In other words, by detecting the difference between the tone amplitudes of adjacent tracks/segments, the direction of the beam movement from the desired track can be determined. Thus, the reading beam is driven based on a tracking error signal (in radial direction) and a focusing error signal (in axial direction) obtained from cross-talk of the tone signals in the recorded marks of the adjacent tracks/segments. The error signal can be based on a combination of any detectable tones. Once the error in the focus position of the reading/recording beam with respect to the addressed (being created) track (in the currently recorded/read plane) is identified, the recording/reading beam propagation is adjusted accordingly

The recording technique of the present invention is particularly useful for the so-called Run Length Limited (RLL) data encoding; a pattern formed by the marks and spaces of varying lengths that is indicative of the stored information. In order to distinguish between the data and tone signals and thereby enable the data reading, the data is encoded such that the power spectral density function of the encoded stream is significantly attenuated at the tone frequencies.

As indicated above, the tones (tone spatial frequencies) in successive tracks/segments and successive planes may be different from one another, either for all the tracks/segments and planes or for a group of tracks/segments and planes.

The tone signal may be in the form of a frequency modulation or amplitude modulation of the main data signal or may be superimposed (e.g. digitally) on the main data signal. The error signal may be produced from the intensity difference between the tone signals of each opposite adjacent tracks in each of the two directions (axial and radial directions). Layers may be recorded in correlated or uncorrelated arrangement, and the signal comparison may take into account more than one tone in each layer. Based on the detected error signal, the reading beam is driven such that the read signal (response) is maximized while continuously varying offset values based on said error signals produced from the intensity difference between said tone signals.

Methods of encoding data with tones are generally known in the art; "guided scrambling" (see for example Immink, "Codes for Mass Data Storage Systems", chap. 12, pages 247-255) may be used to incorporate tones into a composite data. Alternatively, an appropriate encoding scheme that digitally enables tones may be used by targeting a tone constraint instead of a DC free constraint. An example of DC free RLL encoded data digitally embedding a tone is provided in PCT/IL2008/000877 assigned to the same assignee of the present patent application incorporated herein by reference.

According to the invention, the tones are created in the data carrier during the data recording process, and present a part of the composite data pattern. The tone signal is identifiable upon detecting an optical response of the data carrier to a reading beam.

There is also provided an optical system for use in recording/reading data in the optical data carrier comprising an optical head system including a light source unit configured for generating recording, reading and reference beams, the reference beam being separable from the reading and recording beams may be of a different wavelength or polarization; and a detection unit comprising a first detector for detecting reflection of the reference beam from the reference layer, a second detector for detecting an optical response of the recording regions to the reading beam to thereby identify the tone signals, and a third detector for detecting an optical response of the medium to the reading beam to thereby identify the recorded data and the tone signals, The detection of the tone signals and the recorded data may be separated into two tasks that may be performed by two detectors located at opposite sides of the medium. Tones have a typically relative low frequency and the tone detection signal-to-noise ratio may be improved by using an appropriate low bandwidth detector.

The optical system is associated with a control system. The control system may be a computer system configured (preprogrammed) for analyzing data to be recorded and using predetermined tone signals to generate data indicative of a composite data pattern (comprising a first main data and second tone data of different spatial frequencies) and operate the optical head accordingly to record said composite data pattern.

Thus, according to one broad aspect of the invention, there is provided an optical data carrier comprising an optical recording medium in which data is recordable and readable as a result of one- or multi-photon interaction, the data carrier comprising one or more recording layers each comprising spaced-apart recording regions arranged in multiple planes {virtual strata), said spaced-apart recording regions being arranged in a composite data pattern comprising a first main data and second tone data of different spatial frequencies to thereby respond to a reading one- or multi-photon signal by a first data signal and second tone signals, respectively.

According to another broad aspect of the invention, there is provided an optical data carrier comprising an optical recording medium in which data is recordable and readable as a result of one- or multi-photon interaction, the data carrier comprising: one or more recording layers transparent for reading and reference wavelengths and each comprising spaced-apart recording regions arranged in multiple planes, said spaced-apart recording regions being arranged in a composite data pattern comprising a first main data and second tone data of different spatial frequencies to thereby respond to a reading one- or multi-photon signal by a first data signal and second tone signals, respectively; one or more reference layers at least partially transparent to the recording/reading wavelength and at least partially reflective to the reference wavelength.

According to yet another broad aspect of the invention, there is provided an optical data carrier comprising: one or more recording layers each comprising an optical recording medium in which data is recordable and readable as a result of one- or multi- photon interaction, the recording layer being at least partially transparent for recording, reading and reference wavelengths; one or more reference layers at least partially transparent to the recording/reading wavelength and at least partially reflective to the reference wavelengths, the reference layer comprising tones embedded therein; thereby enabling creation of a composite data pattern while recording main data in the form of spaced-apart recording regions arranged in multiple planes in said one or more recording layers, said composite data pattern comprising first main data and second tone data of different spatial frequencies to thereby respond to a reading one- or multi-photon signal by a first data signal and second tone signals, respectively.

According to yet another broad aspect of the invention, there is provided a method for recording data in the above described optical data carrier, the method comprising: while scanning the optical recording layer with a recording beam, scanning the reference layer with the reference beam and detecting reflection of the reference beam from the reference layer, thereby controlling the scan of the recording beam to create a composite three dimensional pattern of spaced-apart recording regions arranged in multiple planes, said composite pattern including a first main data and second tone data of different spatial frequencies, thereby enabling reading of a data signal corresponding to the first main data by detection of tone signals corresponding to the second tone data. According to yet further aspect of the invention, there is provided an optical system for use in recording/reading data in an optical data carrier, the system comprising: an optical head system including a light source system configured for generating recording, reading and reference beams; and a light directing optics for focusing each of the recording and reading beams onto a desired recording plane in the data carrier and scan this plane along a predetermined path, and for focusing and scanning the reference beam in a desired reference plane; and comprising a detection system comprising a first detector unit for detecting reflection of the reference beam from the data carrier and generating data indicative thereof, and a second detector unit for detecting an optical response of the data carrier to the reading beam and generate data indicative thereof; and a control system configured for operating the optical head system for creating a composite pattern of spaced-apart recording regions in said recording plane including a first main data and second tone data such that the tone signal have different spatial frequencies in the adjacent tracks/segment within the recording plane and/or adjacent recording planes, and for receiving and analyzing the data generated by the second detector unit during the reading beam scan to thereby identify a tone signal corresponding to the tone data and control the reading beam to maintain it on the recording plane and to identify data recorded in said plane corresponding to said main data.

According to yet another broad aspect of the present invention, there is provided a control system for use with an optical head system for recording/reading data in an optical data carrier, the control system being configured for analyzing input data to be recorded and using predetermined tone signals to generate data indicative of a composite data pattern comprising a first main data and second tone data of different spatial frequencies and to operate the optical head system to record said composite data pattern. BRIEF DESCRIPTION OF THE FIGURES

In order to understand the invention and to see how it may be implemented in practice, preferred embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawing, in which:

Fig. 1 schematically illustrates an example of an optical data carrier according to the teachings of the present invention;

Figs. 2A and 2B illustrates respectively, a cross-sectional side view and a tangential view (which are not at scale) of tracks in the data carrier of Fig. 1;

Fig. 3 schematically illustrates an optical data carrier structure in which a pattern of spaced-apart recording regions is recorded by time separated recording events;

Fig. 4 schematically illustrates a detailed view of the structure of Fig. 3;

Fig. 5 illustrates an optical carrier in which only two layers are recorded in a recording session;

Fig. 6 schematically illustrates an example of an optical system for use in recording and reading data in an optical data carrier; and;

Fig. 7 A schematically illustrates an example of an optical carrier structure in which a main beam focus and an additional beam focus of the reading beam are provided; and;

Fig. 7B schematically illustrates an example of an optical carrier structure in which a main beam focus and more than one additional beam foci of the reading beam are provided.

DETAILED DESCRIPTION OF EMBODIMENTS

Referring to Fig. 1, there is illustrated an example of an optical data carrier 10 according to the present invention. The data carrier 10 comprises one or more recording plates or media represented in the present example by two such recording plates Ia and Ib, and one or more reference layers, represented in the present example by the single reference layer 2 arranged between the recording plates Ia and Ib. The reference layer 2 is used for detecting reflection of a reference beam from the reference layer, and may have a pattern (not shown) of spaced-apart pits and/or grooves defining two, three or more interfaces with the recording layer at different distances (depth) from the recording layer. Each of the recording plates is configured for recording/reading data in/from multiple layers or planes. As exemplified with respect to plate Ia, three recorded planes 4a, 4b and 4c are schematically shown in the recording plate Ia. Each of the recording planes comprises a composite data pattern with tones embedded therein and having a different set of spatial frequencies, thus differently responding to a reading beam.

It should be noted that in some embodiments of the invention, the reference layer may be formed with tones (during the data carrier manufacture).

Thus, in the recorded state of the data carrier, the composite data pattern is constituted by a main data pattern recorded in the recording layer, by tones which are embedded in the reference layer(s) associated with a respective recording layer, and optionally by tones recorded, together with the main data pattern, in the recording layer.

Figs. 2A and 2B show, respectively, a cross-sectional side view and a tangential view (which are not at scale) of a track in the data carrier 10. In the present example, the composite data pattern in each recording plane is in the form of spaced-apart recording regions arranged along a spiral track. Fig. 2A shows an example of a track recorded in virtual plane P₁ in which the composite data pattern regions (not shown) extends along a spiral track Ti. This composite data pattern comprises track segments T\, Υ'\, T'"_I and T""_! along the spiral track Ti, and includes data and tones signals formed together by spaced-apart recorded regions arranged in different spiral track segments TV T""i with different spatial frequencies /; to /'";, respectively, such that the spatial frequency of a data signal produced by the data pattern in response to a reading beam minimally overlaps with that of the tone signals. The tone frequencies may be indicated by specific contents located in the respective track segments (e.g. headers or specific fields) or encoded in the data.

It should be noted that tones in sequential track segments may overlap to allow smooth tone detection transition between different sequentially scanned track segments. In such embodiment, more than three tones are required to enable correct tracking. Fig. 2B shows four recording virtual planes P₁-P₄ of the recording layer

Ia, and a reference layer structure 2 interfacing with the recording layer Ia. The recording planes P₁-P₄ include spiral tracks T₁-T₄ respectively, each configured as described above regarding the spiral track T_x. Tones in vertically aligned spiral track segments TVT'₄ (as well as T'^-T'^ and so on) have different spatial frequencies /V /V

Using the tone embedding technique disclosed for example in PCT/IL2008/000877 incorporated herein by reference, different tones may be implemented by selecting different block numbers and lengths within each segment. Thus, tones included in adjacent spiral track segments are different in their spatial frequencies in subsequent four tracks in both the tracking direction (radial direction) and the focus direction, and are different from that of the data.

It should be noted that the tracking tone signals are combined with the main data signal during recording. Reference is made to Fig. 3 schematically illustrating an optical data carrier structure in which a pattern of spaced-apart recording regions is recorded by time separated recording events. Each ellipse schematically represents a track in tangential view (as viewed when looking in parallel to the optical carrier rotation). In this schematic drawing, five recording planes (virtual layers) L₁-L₅ are shown, wherein the lower trio of recording layers L₃-L₅ as a first group Gi and the upper pair of recording layers L₁-L₂ as a second group G₂ are strongly correlated, each group forming a grid.

The first and the second groups may be weakly correlated, e.g. due to recording the marks in these groups at different sessions (time separated events), where in between the sessions the optical system might have been subjected to changes, e.g. the optical carrier might have been subjected to deformations, or the optical carrier might have been removed and reassembled. The recorded regions recorded in a first session and the recorded tracks recorded in a second session are therefore weakly correlated leading to the use of safety margins to prevent overriding previously first recorded data group with second recorded data group.

The recording virtual layers in each group may be vertically separated by a distance d, while a distance dj between the groups may be of different value, d and dj being in a specific predetermined range (in this illustration dj<d). Vertical grid lines in the first and second groups are shown to facilitate understanding.

When a light beam 502 is focused onto a certain position in the recording layer L₄, it illuminates an approximately Gaussian beam volume (cone) and profile schematically defined by lines A, and when a light beam 504 is focused onto a certain position within the recording layer L₂, it illuminates a beam

(spatio-temporal) profile schematically defined by lines B.

When layers are correlated within a group having a tightly tolerance grid, a response signal from an adjacent layer above the data plane onto which the beam is focused is similar to the signal from a layer below this data plane. More specifically, when the beam is focused at the center of a track (as shown in Fig. 3) the tone signals from the adjacent layers/planes are similar in amplitude, and tracking can thus be performed by comparison of the respective tone amplitudes. However, there are many cases that result in dynamically offset between the track positions at different layers, and most prominently in layers recorded at different sessions. Thus, in one turn of the optical carrier, the relative position of the tracks in adjacent layers might offset by several track pitches (track pitch being a distance between consecutive track coils) and may vary in the inter-plane distance. Reference is made to Fig. 4 illustrating a method of recording and tone tracking to overcome dynamic offset between the layers of the data carrier. This figure is a detailed view of the structure of Fig. 3. Letters a - i designate different tones recorded in tracks of layers that are dynamically and arbitrary offset. An integrated signal reaching a detector is predominantly coming from the beam focus position, and includes a signal part from adjacent layers that may be 20 dB, 30 dB and even more weaker than the signal part from the focus point. However, a very narrow bandwidth of the tone signal allows for filtering of the tone signal and enables comparison of weak tone signals. In this example, tone signals d and f are used to derive an error control signal for the radial direction, but the offset between layers prevents such straight forward comparison.

As illustrated by cone 504, the width of the beam at a distance from the focus point is significantly large. Accordingly, the interaction at adjacent layers provides tone signals from more than one track or more than one segment of the spiral track. In some embodiments, the tone signals from each layer are dynamically detected. At each moment, the strongest tone from the adjacent track is selected as the central focus tone, and ratios between the detected tone signals from each of the adjacent layers are used to determine the relative weight that is to be given to the respective central tone signals. In the present not-limiting example, a ratio b/a ' is close to one and a ratio g/i is smaller than one, and the exact ratios can be used to estimate the relative positions between track segments c and h and determine the target ratio for c/h. It should be noted that additional ratios and weights may be used as well. For the above described technique, every recorded layer should preferably be surrounded by other recorded data layers. This may be possible if at the end of a recording session, an additional dummy recorded layer is recorded (i.e. a layer comprising dummy data). Similarly, the data track may be finalized by an additional dummy track spiral segment.

In an alternative embodiment, only one adjacent layer is used to derive tone tracking for the focus direction. This enables treatment of recording session block edges in almost the same way as the layer in the middle of the recording session.

Fig. 5 illustrates an optical carrier in which only two layers are recorded in a recording session. A tone signal f is derived from the detected signal from the target data track pattern, and a ratio between tone signals f and c may be derived to indicate a distance between the respective tracks. Ratios between the signals, corresponding to tones c, a' and b', may be used to determine the offset between the layers. If tone b is to be tracked, tones e, f and d' will be used for tone tracking on the other layer. The present configuration of the optical data carrier and the method of tracking avoid the need to record more than two layers in one session.

Encoding (embedding) of tones in an optical data carrier may be performed by digitally combining a tone with a data stream, whose active bandwidth is selected to avoid the frequency region in which tones are recorded.

Methods for tone embedding include modification of direct DC free encoding, guided scrambling and addition of tone to a notch filtered code.

Encoding (embedding) of many relatively close tones in an optical data carrier may be performed in a simplified way by using a family of very close encoding schemes that differ from one another by the length of the recorded sector which is coupled to the tone frequency.

Reference is made to Fig. 6 schematically illustrating an optical system 100 for use in recording and reading data in an optical data carrier 10. The optical data carrier 10 is configured as described above, namely including recording layer(s) 1 and reference layer(s) 2 interfacing with the recording layer 1. The system 100 includes an optical head system including a light source system 102 and an appropriate light directing arrangement 106, and includes a light detection system 104. Connected to the optical system 100 (via wires or wireless signal transmission) is a control system 108.

The light source system 102 includes a first light source unit 102a for producing recording and/or reading beams R_rec/read which may be of the same wavelength, and a second light source unit 102b for producing a reference beam R_ref. The detection system 104 includes a first detector unit for detecting a response beam (e.g. fluorescence) R_FL, and a second detector unit 104b for detecting reflection of the reference beam R_ref from the data carrier (from the reference layer 2). The first detector unit may include a single detector located at either side of the data carrier, or as shown in the present example may include two detectors 104a and 104a' located at opposite sides of the data carrier, one detector 104a serving for detecting the response signal to identify the tone signals therein, and the other detector 104a^f serving for detecting the response signal to identify and register the data signal.

The control system 108 is a computer system including inter alia a memory utility, a data processing and analyzing utility, and data input and output utilities. The control system 108 is configured and preprogrammed to be responsive to input data, indicative of information to be recorded, for analyzing this data and using predetermined tones' data (pre-stored in the memory utility) to generate data indicative of a composite data pattern (comprising a first main data and tones). This data generated by the control system 108 is used for operating the optical head system to create (record) the composite data pattern in the data carrier. The control system 108 is also configured for receiving output of all the detectors and operating the light directing optics accordingly to correct the scan path of the recording and reading beams. The light directing arrangement 106 includes a beam splitter/combiner

106a for directing reference and recording/reading beams coming from different light sources towards a wavelength selective filter 106d (e.g. dichroic mirror) accommodated in the optical path of light passing towards and from the data carrier so as to pass these beams towards an objective lens unit 106g and reflects the reference beam coming from the data carrier towards the reference detector

104b and transmit the data signal towards detector 104a. Also provided in the light directing arrangement 106 are quarter waveplate 106e and 106f to isolate

102b and 102a from reflected light and beam splitter 106b to separate between the reference input light and its reflection.

During the data recording process, the control system 108 operates the light source unit 102a according to the data pattern combined with tone patterns (different in adjacent spiral track segment or concentric tracks) to create the corresponding composite pattern of spaced-part recording regions, and operates the light source unit 102b to produce the reference beam. While scanning the recording plane by the recording beam R_rec and scanning the reference layer by the reference beam R_ref, the control system operates to analyze data indicative of the reflections of the reference beam from the patterned reference layer structure and to operate the light directing optics accordingly to focus the recording beam onto the targeted recording plane and scan the track therein. During the data reading process, the control system analyzes data indicative of the response signal detected by tracking detector 104a and operates the light directing optics accordingly to maintain the reading beam on the targeted track. During the data reading process, the tracking of the data pattern may be additionally supported by the tracking of the reference layer by the reference beam.

In additional embodiments of the method of tone tracking, the tone tracking in the vertical dimension may be achieved by using an additional focus point(s) of the reading beam, providing a reading signal from additional adjacent layers. Fig. 7 A illustrates an embodiment in which a main beam focus 1502 and an additional beam focus 1504 of the reading beam are provided. The additional beam focus 1504 may be of significantly lower reading power and is located at a plane corresponding to (n+l/2)*D layer vertical offset from the main beam focus 1502 towards the direction in which layers are already recorded, n being a small integer (typically 0 to 10 ) and D being the distance between the recording planes. As a result, the tracking in the vertical direction follows the tone tracking of layers adjacent to the data layer of interest.

The reading beam splitting can be achieved by one or more methods known in the art; diffractive or holographic beam splitting, controlling of divergence angle of incoming light beam, e.g. by an electro-optic modulator, different wavelength or others. It should be emphasized that the signal from differently located beam foci may be still collected and used in combination with a non position-sensitive signal collector. Fig. 7B illustrates another embodiment in which, in addition to a main beam focus 1512, more than one additional beam foci 1514 and 1516 of the reading beam are provided, where the additional beam foci are located at integer n (n = 0,1..) layer pitch distances one from the other and from the data layer of interest. Thus the additional beam foci are nominally located on a track, providing a stronger tone signal by each of the tone tracking beam foci.

The reference layer may comprise information concerning a servo method. According to a progress of technology, servo method or parameters used for the method may be changed. This optical data carrier has very flexible structure and so various types of data structure and recording/reading methods can be applied on the same type of data carrier. By using advanced data structure or method, advanced performance will be achieved. Even if the method is the same, the parameter, for example the spatial frequency of a tone signal or the repetition rate of main data signal and tone signal, may be changed according to the advance in the recording medium. In those cases, a drive machine can change recording/reading method or the parameter by reading information recorded in the reference layer. The recorded information may be a code representing the method.

It should be noted that detection of signal across the data carrier requires careful correlation of the positioning of the interrogating source optical unit with the detection unit positioned across the data carrier. The use of tone tracking and additional auxiliary information such as track or layer identification allows for correlation in two dimensions (axial and radial). However (track) tangential positioning is also required and may be achieved by the use of at least one of phase locking onto an appropriate tones pattern, synchronizing words or headers and rigid assembly of the two optical units (with fine degrees of tuning for the

(dynamical) calibrations).

Claims

CLAIMS:

1. An optical data carrier comprising an optical recording medium in which data is recordable and readable as a result of one- or multi-photon interaction, the data carrier comprising one or more recording layers each comprising spaced- apart recording regions arranged in multiple planes, said spaced-apart recording regions being arranged in a composite data pattern comprising a first main data and second tone data of different spatial frequencies to thereby respond to a reading one- or multi-photon signal by a first data signal and second tone signals, respectively.

2. An optical data carrier comprising an optical recording medium in which data is recordable and readable as a result of one- or multi-photon interaction, the data carrier comprising: one or more recording layers transparent for reading and reference wavelengths and each comprising spaced-apart recording regions arranged in multiple planes, said spaced-apart recording regions being arranged in a composite data pattern comprising a first main data and second tone data of different spatial frequencies to thereby respond to a reading one- or multi-photon signal by a first data signal and second tone signals, respectively; one or more reference layers at least partially transparent to the recording/reading wavelength and at least partially reflective to the reference wavelength.

3. An optical data carrier comprising: one or more recording layers each comprising an optical recording medium in which data is recordable and readable as a result of one- or multi- photon interaction, the recording layer being at least partially transparent for recording, reading and reference wavelengths; one or more reference layers at least partially transparent to the recording/reading wavelength and at least partially reflective to the reference wavelength, the reference layer comprising tones embedded therein; thereby enabling creation of a composite data pattern while recording main data in the form of spaced-apart recording regions arranged in multiple planes in said one or more recording layers, said composite data pattern comprising first main data and second tone data of different spatial frequencies to thereby respond to a reading one- or multi-photon signal by a first data signal and second tone signals, respectively.

4. A method for recording data in an optical data carrier, which comprises one or more optical recording layers in which data is recordable and readable as a result of one- or multi-photon interaction, and one or more reference layers, configured such that said one or more recording layers are at least partially transparent for recording, reading and reference wavelengths and said one or more reference layers are at least partially transparent to the recording/reading wavelengths(s) and at least partially reflective to the reference wavelength, the method comprising: while scanning the optical recording layer with a recording beam, scanning the reference layer with the reference beam and detecting reflection of the reference beam from the reference layer, thereby controlling the scan .of the recording beam to create a composite three dimensional pattern of spaced-apart recording regions arranged in multiple planes, said composite pattern including a first main data and second tone data of different spatial frequencies, thereby enabling reading of a data signal corresponding to the first main data by detection of tone signals corresponding to the second tone data.

5. An optical system for use in recording/reading data in an optical data carrier, the system comprising: - an optical head system including a light source system configured for generating recording, reading and reference beams, the reference beam being separable from the recording and reading beams, and a light directing optics for focusing each of the recording and reading beams onto a desired recording plane in the data carrier and scan this plane along a predetermined path, and for focusing and scanning the reference beam in a desired reference plane;

- a detection system comprising: a first detector unit for detecting reflection of the reference beam from the data carrier and generating data indicative thereof, and a second detector unit for detecting an optical response of the data carrier to the reading beam and generate data indicative thereof; and

- a control system configured for operating the optical head system for creating a composite pattern of spaced-apart recording regions in said recording plane including a first main data and second tone data of different spatial frequencies in at least one recording plane, and for receiving and analyzing the data generated by the second detector unit during the reading beam scan to thereby identify a tone signal corresponding to the tone pattern and control the reading beam to maintain it on the recording plane and to identify data recorded in said plane corresponding to said main data pattern.

6. The optical system of Claim 5, wherein said second detector unit comprises two detectors for detecting said tone signal and said data respectively.

7. The optical system of Claim 6, wherein said two detectors are accommodated at opposite sides of said optical data carrier.

8. The optical system of Claim 6, wherein the detector for detecting tone signal is a low bandwidth detector.

9. A control system for use with an optical head system for recording/reading data in an optical data carrier, the control system being configured for analyzing input data to be recorded and using predetermined tone signals to generate data indicative of a composite data pattern comprising a first main data and second tone data of different spatial frequencies and to operate the optical head system to record said composite data pattern.