Patent Application
20090010145
The present invention relates to an optical record carrier comprising a substrate and a plurality of tracks disposed substantially spirally and substantially concentrically on the carrier. The invention also relates to a method for manufacturing such a carrier.
The invention further relates to a corresponding optical apparatus adapted for reproducing and/or recording information from/to an optical record carrier according to the invention. In order to meet the demand of increasing information storage capacity the available optical media, i.e. compact disc (CD), digital versatile disc (DVD) and the Blu-ray Disc (BD), show a constant improvement in storage capacity. In these optical media, the reproduction resolution has hitherto been mostly dominated by the wavelength, λ, of the reproduction light and the numerical aperture (NA) of the optical reproduction apparatus. However, since it is not easy to shorten the wavelength of the reproduction light or to increase the numerical aperture of the corresponding lens system, attempts to increase the recording density has pre-dominantly been focused at improving the recording media and/or the recording/reproduction method.
In particular, for optical media adapted for recording information two different approaches have been suggested: The land-groove format wherein information is recorded both in the groove of the track and next to the groove, and the groove-only format wherein the information is only recorded in the groove, e.g. the BD disc format. Both of these formats have advantages and disadvantages, in particular with respect to radial tracking and inter-track/symbol cross-write/erase issues.
Presently, the density limit reached by combining a track pitch of 240 nm with a channel bit length of 50 nm has shown that the capacity of the BD-type disc can potentially be increased from the current 23-25-27 GB up to 50 GB per layer of information on the media. However, an inherent conflict between further downscaling of the track pitch versus the need for stabile radial tracking and limited cross-write/erase problems is encountered in present state of the art discs. In particular, a disc format with both the advantages of the land-groove format with respect to stable radial tracking and the advantages of the groove-only format with respect to limited cross-write/erase problems is therefore desirable.
Hence, an improved optical record carrier would be advantageous, and in particular a more efficient and/or reliable optical record carrier would be advantageous.
Accordingly, the invention preferably seeks to mitigate, alleviate or eliminate one or more of the above-mentioned disadvantages singly or in any combination. In particular, it may be seen as an object of the present invention to provide an optical record carrier that solves the above mentioned problems of the prior art with obtaining an increased information storage density on the optical record carrier.
This object and several other objects are obtained in a first aspect of the invention by providing an optical record carrier comprising a substrate, a plurality of tracks disposed substantially spirally and substantially concentrically, each track being adapted for recording and/or reproducing optically readable effects positioned substantially in a groove, wherein the plurality of tracks are arranged adjacently in a multi-track spiral on the optical record carrier, and wherein a tracking area between the windings of the multi-track spiral is adapted for providing a radial tracking error signal from the optical record carrier.
The invention according to the first aspect is particularly but not exclusively advantageous for obtaining a lower track pitch, i.e. track width, of the tracks in the spiral due to the tracking area positioned between the windings of the multi-track spiral. In addition, the possibility of a lowered track pitch does not jeopardize the radial tracking as the radial tracking is to be performed in the dedicated tracking area also known as guard band. The commonly used single spiral format has an inherent conflict between the radial tracking provided by the groove and the wish to minimize the track pitch, a conflict that is solved by the present invention. The optical record carrier, and in particular the track and groove format, according to the present invention thereby provides several advantages for obtaining more efficient and reliable optical record carrier.
In a second aspect, the invention relates to an optical record carrier that comprises a substrate, a plurality of tracks disposed substantially spirally and substantially concentrically, each track being adapted for recording and/or reproducing optically readable effects positioned substantially in a groove, wherein the plurality of spirals are arranged in concentric consecutive layers on the optical record carrier with one spiral in each layer, and wherein tracking areas between the said layers of the plurality of spirals are adapted for providing a radial tracking error signal from the optical record carrier.
The invention according to the second aspect is particularly but not exclusively advantageous for obtaining a lower track pitch of the tracks in the spirals due to the tracking areas positioned between the consecutive spirals. Moreover, the possibility of a lowered track pitch does not jeopardize the radial tracking as the radial tracking is to be performed in the dedicated tracking areas also known as guard bands. It is a particular advantage of the invention according to the second aspect that the media manufacturing may be performed on manufacturing equipment adapted for producing media with a single spiral as the guard bands can be made by just skipping mastering a groove at regular intervals. Thus, already present manufacturing equipment may relatively simple be adapted to produce the optical record carrier according to the second aspect of the invention.
The tracking areas or the guard bands have a certain width. The width of the guard band should be chosen such that proper radial tracking signals are ensured. This means in practice that the guard band should be around 280-300 nm (or wider) for the case of BD optics. In this case the well-known push-pull signal, as used for radial tracking on the empty discs in all the current write-once and rewritable systems, can be generated robustly. The push-pull signal is advantageous because the effective track spacing as seen by the optical spot placed on the guard band is much larger (locally under the spot) than the actual track spacing within the tracks in the multi-spiral according to the first aspect of the invention or within the tracks of a single spiral according to the second aspect of the invention. The optical record carrier according to the first or the second aspect may have at least one of the one or more guard bands or tracking area(s) having a width that is at least equal to a track width of a track positioned adjacently to the tracking area. The said lower limit may also be set as two, three or fours times an adjacent track width. Advantageous lower limits on the width of the tracking area(s) are approximate values of: 50, 100, 150, 200, 250, 300, 350, and 400 nm.
The width of the tracking area(s) may also be limited from above in order to minimize the carrier area used for radial tracking. Thus, the optical record carrier may have at least one of the one or more tracking area(s) of a width that is maximum equal to four times the track width of a track positioned adjacently to the tracking area, alternatively two, three, five or six times an adjacent track width. Advantageous upper limits on the width of the tracking area(s) are approximate values of: 200, 250, 300, 350, 400, 450, and 500 nm.
The track width or track pitch may also calculated as an average value of the nearest neighboring tracks, i.e. up till two, three, four or more tracks next to the tracking area(s).
The optical record carrier according to the first or the second aspect of the invention is particularly advantageous in that there is at least one of the one or more trucking area(s) that does not comprise a groove or any other pre-embossed marks like pre-pits or similar intended and/or adapted for radial tracking. This makes the manufacturing of a carrier according to the present invention easier to manufacture relative to prior art carriers with dedicated tracking pits in guard bands, see for example US 2004/0076110. In the context of the present application, by “tracking area” is meant a continuous area having substantially uniform optical properties in the radial servo frequency band such that a reliable radial tracking error signal can be generated there for controlling the tracking closed loop. This servo-frequency requirement allows writing DC-free data in the guard band. In many write-once and rewritable disc formats known at present (like CD-R/RW, DVD±R/RW or BD-R/RE), a wobble is embedded in the grooves for carrying the timing and/or the address information. The channel bit size at a certain position on the disc is directly related to the wobble period at that position. The optical record carrier according to the first and second aspect of the invention may similarly have wobbling grooves, i.e. a groove with a physical parameter varying in a longitudinal direction of the groove, said variation being indicative of timing and/or address information related to said groove on the optical record carrier.
In particular, the varying physical parameter of a first groove within a spiral varies substantially in phase with the same physical parameter of a second groove within the same spiral; thus the first and second groove may be synchronous wobbling. This is advantageous to minimize the effective track pitch if the first and second grooves are adjacent on the carrier. Even with some out-of-phase deviation it would still provide advantages; e.g. up till a quarter of a period phase difference may be acceptable.
The varying physical parameter of a first groove within a spiral may vary, at least locally, with an substantially constant angular frequency (CAF) relative to a central position of the optical record carrier. In this case, the inter-groove spacing is constant (which is nice from the cross-write performance point of view), but the linear wobble frequency decreases towards the outer radius of the disc. In order to obtain sufficiently uniform storage density across the carrier and to maintain simultaneously the constant ratio between the wobble and the data frequencies, zoned or locally CAF wobble can be used. However, this solution is somewhat cumbersome from the carrier mastering and the drive implementation points of view.
Alternatively, the optical record carrier may have the varying physical parameter of a first groove within a spiral to vary, at least locally, with a substantially constant frequency in the longitudinal direction of the first groove. This is known as a constant linear frequency (CLF) wobbling. This ensures an equal tangential storage density across the whole disc and it is normally used in case of the regular single-spiral systems like CD, DVD and BD. However, the inter-groove spacing (land width) is not constant in this case. This should be taken into account when targeting very small track pitches, since the cross-write performance can be compromised at the positions where the grooves come too close with respect to each other. This makes the CLF format less suitable for the case of very small track pitches. However, if the CLF format is applied locally the storage density may be kept substantially constant in this locally constant linear frequency format (LCLF).
Recently, the advent of Two Dimensional Optical Storage (TwoDOS) has been demonstrated. In TwoDOS, information is written as a number of data rows in parallel along a broad spiral on and carrier, and the data is read-out in parallel from the spiral using an array of laser spots. The TwoDOS system is particularly well adapted for applying an optical record carrier according to the first of aspect of the present invention as the optical record carrier may adapted for having the optical readable effects of a plurality of tracks within said spiral being simultaneously reproduced. This is so because the TwoDOS-like systems with joint multi-row detection become advantageous with respect to the one-dimensional ones in terms of cross-talk performance only when the track pitch is very small, typically in the order of 220 nm for the case of BD optics, and such a low track pitch may be obtainable with the present invention.
If the first aspect of the present invention is applied in connection with a TwoDOS-like system, the plurality of tracks may each have at least a portion of a groove having a physical parameter varying in a longitudinal direction of the groove, e.g. wobbling of the groove, said variation being indicative of timing and/or address information related to said groove on the optical record carrier, and wherein the said variation provides information related to synchronizing the said simultaneous reproduction as synchronizing is an important parameter to control for a TwoDOS-like system. In particular, the information provided for synchronizing may be the channel bit clock.
For an optical record carrier according to the second aspect of the invention, the plurality of spirals may have a starting point for each track and an end point for each track, and each end point of a track may be positioned with a relative angular separation in relation to the start point of the adjacent consecutive spiral, the relative angular separation between adjacently positioned spirals may be, at least locally, substantially constant on the optical record carrier. Thus, a constant angular frequency (CAF) shift may be implemented between the consecutive spirals. This is advantageous in order to perform radial tracking “jumps”, i.e. changes between spirals, at a substantially constant carrier rotation speed at a specific time of operation. The angular separation between the different “rounds” of the spirals may be substantially constant, possibly just a local level, e.g. when averaged over a portion of the carrier by e.g. introducing a number of carrier zones in which the rounds are substantially constant. The number of zones may vary from 2 to, say, 10.000.
For an optical record carrier according to the second aspect of the invention, the plurality of spirals may have a starting point for each track and an end point for each track, and each end point of a track may be positioned with a tangential linear separation in relation to the start point of the adjacent consecutive spiral, the tangential linear separation between adjacently positioned spirals being, at least locally, substantially constant on the optical record carrier. Such a constant linear frequency (CLF) shift is advantageous as the radial tracking “jumps”, i.e. changes between spirals, may be performed at a substantially constant linear carrier speed at a specific time of operation.
An optical record carrier according to the first or the second aspect of the invention may additionally be further adapted for recording and/or reproducing optically readable effects substantially outside a groove so as to increase the storage density of the carrier. This is similar to the land-groove format applied in the DVD-RAM format. Additionally or alternatively, the optical record carrier may be further adapted for recording and/or reproducing optically readable effects in a tracking area under due consideration of the cross-write effects. Normally, the presence of data is not disturbing the radial tracking. Hence, data or information in the form of optically readable effects may be recorded outside the grooves because the influence of data outside the grooves on the tracking signals does not dependent on data density but rather on the average reflectivity level of the written track. Hence, there is effectively no limit with respect to the data density in connection with tracking. However, the data density in the guard bands may be limited by the laser power used for writing the data, as the power should avoid too much thermal influence on the adjacent tracks e.g. data marks there may not be erased or otherwise damaged. Earlier it was stated that the tracking area(s) has substantially uniform optical properties, at least locally, but any data in the tracking area(s) may be considered an exception to such a uniformity. This is so because DC-free data in the guard band may then allowed since they are invisible in the servo frequency band if the DC-notch of the data is made sufficiently wide.
In a third aspect, the invention also relates to method for manufacturing an optical record carrier comprising the steps of providing a substrate, providing in or on said substrate a plurality of tracks disposed substantially spirally and substantially concentrically, each track being adapted for recording and/or reproducing optically readable effects positioned substantially in a groove, wherein the plurality of spirals are arranged in concentric consecutive layers on the optical record carrier with one spiral in each layer, and wherein tracking areas between the said layers of the plurality of spirals are adapted for providing a radial tracking error signal from the optical record carrier.
The invention according to the third aspect is particularly but not exclusively advantageous for obtaining a method that may easily be implemented by applying already known manufacturing equipment for conventional single-spiral groove format carriers. In a particular embodiment, the tracking areas between the said layers of the plurality of spirals is obtained by simply not mastering one or more tracks, i.e. during the manufacturing of the optical record carrier the track mastering equipment simply “jumps” one or more grooves, preferably just one groove.
In a fourth aspect, the invention relates to an optical apparatus adapted for reproducing and/or recording information from/to an optical record carrier according to the first or the second aspect of the invention, the optical apparatus comprising holding means to fixate and rotate the optical record carrier, a light source capable of emitting a light beam for reading information as readable effects and/or recording information as readable effects, photodetection means capable of detecting reflected light from the optical record carrier and transform it into electrical signals, and processing means adapted to process said electric signals and generate control signals in response thereto for controlling the holding means and the light source, by at least one control mechanism, said at least one control mechanism comprising at least a radial tracking error control mechanism adapted for performing radial tracking on a carrier according to the first or the second aspect of the invention.
The invention according to the fourth aspect is particularly but not exclusively advantageous for obtaining an optical apparatus that may reproduce and/or record information from/to an optical record carrier according to the first or the second aspect of the invention. In particular, some standard optical drives may only require relatively few modifications, especially with respect to the radial tracking, to be able to reproduce/record from/to optical record carrier according to the first or the second aspect. Accordingly, the optical apparatus according to the fourth aspect of the invention is readily implemented.
The first, second, third and fourth aspect of the present invention may each be combined with any of the other aspects.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. The present invention will now be explained with reference to the accompanying Figs., where
The plurality of tracks 2 are arranged adjacently in a multi-track spiral 1 on the optical record carrier and the number of tracks in
The tracking area 5 between the windings of the multi-track spiral 1 is adapted for providing a radial tracking error signal from the optical record carrier. Several methods are available for obtaining the error in a radial direction, i.e. the deviation from the actual radial position relative to the intended or ideal radial position, one such method being the push-pull (PP) method where a tracking error signal is generated on the basis of the level difference between optical signals detected in an optical sensor of an optical reproducing apparatus. Another option is the differential time (or phase) detection (DTD) method, where a phase difference between the optical signals detected in the optical sensors of the optical reproducing apparatus is applied for generating a radial tracking error signal. State-of-the-art differential PP methods apply the 3-spot method where a main light beam follows the track of information and two auxiliary light beams are shifted in opposite directions relative to the track, but any suitable method for performing radial tracking so as to keep the focused light on the intended radial position on the carrier by a closed loop control mechanism may be adapted within the context of the present invention.
The grooves are grouped in either a multi-spiral 1 with tracks 2 or consecutive spirals 12 in the carrier format 10 according to the aspect of the invention. Both are 10-track-wide, and the inter-spiral separation, i.e. the tracking area(s) or guard band 5 or 15, is achieved by not mastering every 11-th groove. Since the optical spot resolution is finite leading essentially to a low-pass characteristic of the channel response, the very high frequency of tracks within the broad groups 2 or 12 is not getting captured. In the given embodiment the following data applies: numerical aperture (NA)=0.85, wave length of light=405 nm and track pitch of 220 nm with a duty circle of 50%.
As it is visible in
In the following Figs., particular embodiments of the first and second aspect will be explained.
Although the present invention has been described in connection with the specified embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. In the claims, the term comprising does not exclude the presence of other elements or steps. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. In addition, singular references do not exclude a plurality. Thus, references to “a”, “an”, “first”, “second” etc. do not preclude a plurality. Furthermore, reference signs in the claims shall not be construed as limiting the scope.
| Number | Date | Country | Kind |
|---|---|---|---|
| 04104922.2 | Oct 2004 | EP | regional |
| 05100149.3 | Jan 2005 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB05/53178 | 9/26/2005 | WO | 00 | 4/5/2007 |
