HK1099401B - Method and apparatus for reproducing information recorded on an information storage medium - Google Patents

Description

Method and apparatus for reproducing information recorded on information recording medium

Technical Field

The present invention relates to an information storage medium configured to use a super-resolution phenomenon and an apparatus and method for reproducing information recorded on the information storage medium, and more particularly, to an information storage medium configured to reduce the influence of defocus or tilt, and a method and apparatus for reproducing information recorded on the information storage medium.

Background

Information storage media are widely used in optical pickup systems for non-contact type recording/reproducing. As the demand for high-density recording has increased, research has been conducted to develop information storage media using a super-resolution phenomenon, the recording marks of which are smaller than the resolution limit (resolution limit) of a laser beam.

An information storage medium using the super-resolution phenomenon includes a mask layer (mask layer) in which surface plasmons are generated by an incident beam. Thus, high-density recording can be achieved using surface plasmon generated in the mask layer.

For example, platinum oxide (PtO) is used_x) In the case of the formed mask layer, PtO of the mask layer is formed when a laser beam is irradiated to the mask layer_xDecomposition into Pt and oxygen (O)₂). A near field is generated when surface plasmon is generated in Pt. Accordingly, a signal can be reproduced from a recording mark having a size below the resolution limit of a laser beam focused onto an information storage medium through an objective lens.

Disclosure of the invention

Technical problem

Meanwhile, intensive research into information storage media using the super-resolution phenomenon is required to obtain a carrier-to-noise ratio (CNR) required to perform signal reproduction and to prevent signal degradation due to repeated reproduction.

Technical solution

The present invention provides a method and apparatus for reproducing information recorded on an information storage medium, which can adjust a read power after comparing a reference signal recorded in the information storage medium with a reproduction signal, thereby reducing the influence of defocus and tilt and increasing a signal margin.

Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

According to an aspect of the present invention, there is provided a method of reproducing a signal from an information storage medium containing recording marks having a size smaller than a resolution limit of an incident light beam emitted from an information reproducing apparatus. The method comprises the following steps: emitting a light beam having a predetermined read power onto the information storage medium; receiving a light beam reflected from the information storage medium, and detecting a reproduction signal of the information storage medium and a reference signal for determining whether a level of the reproduction signal is higher than or equal to a level required to perform reproduction; and determining whether the detected level of the reproduction signal is higher than or equal to a level required to perform reproduction, and adjusting the readout power of the light source in response to a case where the level of the reproduction signal is lower than the level required to perform reproduction.

According to another aspect of the present invention, there is provided an information reproducing apparatus that reproduces a signal from an information storage medium having a recording mark having a size smaller than a resolution limit of an incident beam, and a lead-in area, a data area, and a lead-out area, wherein a reference signal compensating for defocus or tilt is recorded in the lead-in area and/or the lead-out area in the form of data. The apparatus comprises: a pickup and a signal processor, wherein the pickup includes: a light source for emitting a light beam onto the information storage medium; and a photodetector for receiving the light beam reflected from the information storage medium and detecting a reproduction signal and a reference signal; the signal processor is used for determining whether the read-out power level of the light beam emitted from the light source is higher than or equal to the lowest read-out power level required for executing reproduction based on the reference signal detected by the photodetector; wherein the signal processor adjusts the read power of the light source in response to a situation in which the read power level of the light beam is lower than a minimum read power level required to perform reproduction.

Advantageous effects

Further, in the information reproducing apparatus and method according to the present invention, the read power is adjusted after comparing the reference signal recorded in the information storage medium with the reproduction signal, thereby reducing the influence of defocus and tilt and increasing the signal margin.

Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.

Drawings

These and/or other aspects and advantages of the present invention will become apparent from and elucidated with reference to the embodiments described hereinafter, when taken in conjunction with the accompanying drawings.

Fig. 1 is a schematic cross-sectional view of a super-resolution information storage medium that can be used with the present invention;

fig. 2 is a graph showing the change in CNR for 75nm and 300nm recording marks with respect to read power;

FIG. 3 is a graph of a change in a peak value of normalized light intensity for tilt angles in the information storage medium of FIG. 1;

FIG. 4 is a diagram showing a ratio of a beam spot diameter when a tilt occurs to a beam spot diameter when there is no tilt in the information storage medium of FIG. 1;

FIG. 5 is a graph showing a change in peak light intensity for a defocus amount in the information storage medium of FIG. 1;

FIG. 6 is a diagram showing a ratio of a beam spot diameter when defocus occurs to a beam spot diameter when defocus does not occur in the information storage medium of FIG. 1;

FIG. 7 is a schematic cross-sectional view of an information storage medium used to check for variations in optical characteristics for read power, according to an embodiment of the present invention;

fig. 8 is a diagram showing changes in CNR for the defocus amount for recording marks of 75nm and 300 nm;

fig. 9 and 10 are diagrams showing changes in CNR for tangential tilt and radial tilt for 75nm and 300nm recorded marks;

fig. 11 to 13 are graphs showing changes in CNR for an amount of defocus, an amount of tangential tilt, and an amount of radial tilt, respectively, where the CNR values are measured at different read powers for recording marks having a size of 75nm below a resolution limit in the information storage medium of fig. 7;

FIG. 14 illustrates a layout of each area in an information storage medium according to an embodiment of the present invention;

FIG. 15 shows a detailed layout of the disk control test area shown in FIG. 14;

FIG. 16 is a schematic diagram of an apparatus to reproduce information from an information storage medium according to an embodiment of the present invention; and

fig. 17 is a flowchart illustrating a method of reproducing information from an information storage medium according to an embodiment of the present invention.

Detailed Description

Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures.

Before describing some possible embodiments of the present invention, a super-resolution optical recording medium constructed as shown in fig. 1, for which a patent application was filed in 10/2/2003 to the korean intellectual property office under application No. 2003-75635, will be described in detail. Referring to fig. 1, the information storage medium 10 using the super-resolution phenomenon includes a substrate 11, and a first insulating layer (dielectric layer)12, a recording layer 13, a second insulating layer 14, a recording auxiliary layer 15, and a third insulating layer 16 are sequentially formed over a surface of the substrate 11. Here, the recording layer 13 includes a metal oxide such as platinum oxide, and the recording auxiliary layer includes a phase change material.

When a laser beam is irradiated onto the recording layer 13, platinum oxide forming the mask layer is decomposed into oxygen and platinum generating surface plasmon. A near field is generated when surface plasmons are generated in platinum. Accordingly, a signal can be reproduced from a recording mark having a size below the resolution limit of the laser beam focused on the information storage medium through the objective lens OL. For example, if the resolution limit of the optical pickup is 119nm, the recording mark of 75nm smaller than the resolution limit of 119nm can be successfully reproduced.

In order to reproduce recording marks smaller than the resolution limit of the optical pickup in an information storage medium using the super-resolution phenomenon, a read power larger than that in usual use is required. Fig. 2 shows the variation of the carrier-to-noise ratio (CNR) for the readout power for the recording marks of 75nm and 300nm when an optical pickup having a resolution limit of 119nm, which includes a light source emitting a light beam of 405nm wavelength and an objective lens having a Numerical Aperture (NA) of 0.85, is used. Referring to fig. 2, for a recording mark of 300nm, the CNR is 50dB or even higher at a read power of less than 1.0mW, while for a recording mark of 75nm, a stable CNR of 40dB or higher can be obtained only when the read power is about 1.2mW or more. That is, the CNR required for reproduction cannot be obtained at a low read power for a recording mark of 75 nm. This is because the super-resolution effect can be generated only when the amount of the incident beam is greater than a predetermined amount or the temperature within the information storage medium rises above a predetermined value.

Meanwhile, in an apparatus for reproducing information from the information storage medium, when a focus failure occurs or a laser beam incident on the information storage medium is inclined to a recording surface so as not to be perpendicular to the recording surface, the size of a beam spot (beam spot) created on the information storage increases, and thus its energy density decreases. Thus, CNR can be reduced due to the reduction of the amount of light beam. These phenomena will now be described in detail with reference to fig. 3-6.

Fig. 3 shows a variation in peak value of normalized light intensity for tilt angle on the information storage medium of fig. 1, and fig. 4 shows a ratio of a beam spot diameter when tilt occurs to a beam spot diameter when no tilt occurs. Here, a comparison was made between two groups using an optical pickup, one group having a light source emitting a light beam with a wavelength of 400nm and having an objective lens with an NA of 0.6, and the other group having a light source emitting a light beam with a wavelength of 650nm and having an objective lens with an NA of 0.65. In fig. 3, both groups show that the peak light intensity decreases as the tilt angle increases, although the wavelengths of the light beams are different. As is apparent from fig. 4, in the case of a light beam wavelength of 400nm, the beam spot diameter at a tilt angle of 1 degree is 1.76 times that in the case of no tilt. In the case of a light beam wavelength of 650nm, the former is 1.08 times as long as the latter.

Fig. 5 shows a variation in peak light intensity for the defocus amount on the information storage medium shown in fig. 1, and fig. 6 shows a ratio of a beam spot diameter when a light beam is focused in the information storage medium of fig. 1 to a beam spot diameter when the light beam is defocused. Here, a comparison was made between two groups using an optical pickup, one group having a light source emitting a light beam with a wavelength of 400nm and having an objective lens with an NA of 0.6, and the other group having a light source emitting a light beam with a wavelength of 650nm and having an objective lens with an NA of 0.65. In fig. 5, although the wavelengths of the light beams used are different, both groups show that the peak light intensity decreases with increasing defocus. As is apparent from fig. 6, in the case where the beam wavelength is 400nm, the beam spot diameter significantly increases with an increase in the amount of defocus, as compared to when the beam is focused. Therefore, the information storage medium of fig. 1 has a problem in that: even when the same read power is applied for reproduction, the amount of light decreases because the energy density thereof decreases with an increase in the amount of tilt or defocus.

Accordingly, the present invention provides a method of increasing defocus and tilt margins that are not considered in the above-described information storage medium.

One embodiment of the present invention that may achieve this and/or other aspects is an information storage medium constructed as shown in fig. 7. Fig. 8 to 13 show test results obtained using the information storage medium of fig. 7.

Referring to fig. 7, the information storage medium includes: sequentially formed on the surface thereof by a process such as sputteringA dry layer of polycarbonate substrate. The layers are ZnS-SiO with a thickness of about 85nm₂An insulating layer, a Ge-Sb-Te recording auxiliary layer having a thickness of about 15nm, a ZnS-SiO layer having a thickness of about 25nm₂Insulating layer, PtO with thickness of about 3.5nm_xMetal oxide recording layer, ZnS-SiO with thickness of about 25nm₂An insulating layer, a Ge-Sb-Te recording auxiliary layer having a thickness of about 15nm, and a ZnS-SiO having a thickness of about 95nm₂An insulating layer.

In the apparatus having the optical pickup of the embodiment using the information storage medium, the light beam incident on the information storage medium may undergo defocusing, or the optical axis of the incident light beam may be inclined to the recording surface so as not to be perpendicular to the recording surface of the information storage medium. The effect of such defocusing and tilting will now be described.

Fig. 8 to 10 show changes in CNR for the amounts of defocus, tangential tilt, and radial tilt, respectively, on the super-resolution information storage medium of fig. 7. More specifically, when run-length limited (RLL) (1, 7) modulation coding is used, changes in CNR for the defocus amount, the tangential tilt amount, and the radial tilt amount are measured for 2T (mark length is 75nm) and 8T (mark length is 300nm) pulses at a read power of 1.2 mW. Here, the RLL is a modulation technique that limits the number of consecutive 0 s between consecutive 1 s. RLL (d, k) indicates that 0 continuously ranges from d to k.

Referring to fig. 8 to 10, for a mark length of 8T longer than the resolution limit of the optical pickup, the CNR is about 50dB without being affected by the defocus amount and the tilt amount. In contrast, for a mark length of 2T shorter than the resolution limit, the CNR decreases below 40dB when the defocus amount deviates from the range of plus or minus 0.2 μm. When the amount of tilt deviates from the range of plus or minus 0.5 degrees, the CNR decreases to significantly less than 40 dB. This is because the energy density of the incident beam per unit area is reduced due to the occurrence of defocus or tilt, thereby impairing the super-resolution effect. Therefore, in the information storage medium of fig. 7, a signal can be reproduced at a read power of more than 1.2mW in principle. However, since the CNR is sensitive to changes in the defocus amount and the tilt amount, the signal margin is significantly reduced.

Fig. 11 to 13 show changes in CNR for defocus amount, tangential tilt amount, and radial tilt amount, respectively, where the CNR values are measured at different read powers for recording marks having a size of 75nm below the resolution limit in the information storage medium of fig. 7. Here, the information storage medium was rotated at a linear velocity of 5m/sec, and measured at read powers of 1.2, 1.3, and 1.4mW, respectively.

As is apparent from fig. 11, when the defocus amount deviates from the range of plus or minus 0.3 μm, the CNR decreases to less than 40dB at a read power Pr of 1.2mW, while the CNR remains at the same level of about 40dB at a read power Pr between 1.3 and 1.4 mW.

It is apparent from fig. 12 and 13 that, when the tangential and radial tilts deviate ± 0.5 degrees, the CNR drops significantly below 40dB at a readout power Pr of 1.2mW, while at a readout power Pr between 1.3 and 1.4, the CNR remains at a level of about 40dB even when the tangential and radial tilts deviate ± 0.7 degrees. Accordingly, when the CNR is reduced to less than 90% of the CNR range required for reproduction due to the occurrence of defocus or tilt, the reduced energy density per unit area can be compensated for by increasing the readout power based on the reference signal stored on the information storage medium, thereby restoring the required CNR. Accordingly, defocus and tilt tolerance (tolerance) on the information storage medium may be improved.

Accordingly, the information storage medium according to an embodiment of the present invention includes recording marks having a size smaller than a resolution limit of an incident beam to allow information to be recorded/reproduced using a super-resolution phenomenon. In order to improve defocus and tilt tolerance, the information storage medium further includes a reference signal.

Referring to fig. 14, an information storage medium 20 according to an embodiment of the present invention includes: a data area 23 containing user data; a lead-in area 21 located at the inner periphery (inner circumference) of the data area 23; and a lead-out area 25 located at the periphery (outer circumference) of the data area 23. Here, predetermined data (to be described later) is prerecorded in at least a portion of the lead-in area 21, which is used as a prerecorded area 30 on which recorded data is permanently stored. The remaining portion of the lead-in area 21, the data area 23, and the lead-out area 25 serve as a recordable area 40.

When the information storage medium 20 is used as a write-once disc or a rewritable disc, user data is recorded on the recordable area 40. When the information storage medium 20 is used as a read-only disc, the remaining portion of the lead-in area 21, the data area 23, and the lead-out area 25 are used as the read-only area 40' in place of the recordable area 40.

The pre-recorded area 30 comprises a buffer area 31 and a disc control data area 33 containing disc related information and copy protection information. The recordable area 40 includes a disc test area 41, a drive test area 42, a defect management area 43, a reserved area 44, a buffer area 45, and a data area 46.

As shown in fig. 15, the disc control data area 33 contains disc-related information, a reserved area, and a reference level 35. Here, the disc-related information includes, for example, the type (e.g., recordable, write-once, or read-only) and version number of the information storage medium, a disc size (e.g., diameter 120mm), a disc structure (e.g., single layer structure), and a recording speed.

The reference level 35 is an area where a reference signal is recorded in the form of data to compensate for signal degradation due to defocus or tilt of the information storage medium 20. Preferably, although not necessarily, the reference signal may be recorded in the form of recording marks having a size larger than a resolution limit of the incident beam so that the reference signal can also be reproduced by a general optical pickup having a lower readout power than the super-resolution optical pickup. The recording marks may be recorded in the form of wobbles or pre-pits. The reference signal may also be recorded in super-resolution recording marks that can be read at a high readout power (e.g., 1.2mW or more) required for super-resolution reproduction.

The reference signal is used to determine whether the level of a signal detected by an apparatus for reproducing information, which will be described later, is higher than or equal to a level required for reproduction. In other words, the reference signal represents a signal that can be reproduced when the signal is detected by an apparatus for reproducing information, and is prerecorded in the form of data using RLL modulation coding. Here, the reference signal is recorded as the highest level or the lowest level among a plurality of levels required to perform reproduction, a difference in amplitude between a high signal level and a low signal level, or reflectivity. Although in the illustrative embodiment the reference signal has been recorded in the disc control data area 33, the scope of the present invention is not limited thereto. That is, the reference signal may be recorded in another area of the lead-in area 21, or the lead-out area 25, or both.

An information reproducing apparatus and method of reproducing a signal from an information storage medium recorded with a reference signal according to an embodiment of the present invention will now be described in detail.

Fig. 16 schematically shows an information storage medium 20 and an information reproducing apparatus 50 according to an embodiment of the present invention. Referring to fig. 16, the information reproducing apparatus 50 includes: a drive 60 for rotating the information storage medium 20; a pickup 70 for reading a reproduction signal from the information storage medium 20; and a signal processor 80 for processing the read signal. The picker 70 includes: a light source 71 for emitting a light beam having a predetermined power and wavelength; a beam splitter 73 for converting a propagation path of the light beam; an objective lens 75 for focusing the light beam on the information storage medium 20; and a photodetector 77 for receiving the light beam reflected from the information storage medium 20 and detecting a reproduced signal and a reference signal.

The signal processor 80 determines whether the read-out power level of the light beam emitted from the light source 71 is higher than or equal to a power level required to perform reproduction based on the reference signal detected by the photodetector 77, and adjusts the read-out power of the light source 71 if it is lower than the required power level. In addition, the signal processor 80 controls the driver 60 so that it rotates at a predetermined linear velocity, for example, 5 m/sec.

To achieve these functions, the signal processor 80 includes: a reproduction signal detector 81, a central controller 83 and a power controller 85 that adjusts the readout power of the light source 71, wherein the reproduction signal detector 81 detects the level of the actually reproduced signal read by the photodetector 77. The central controller 83 includes a reference signal demodulator 90, a comparator 91, and a memory 92. The reference signal demodulator 90 demodulates the reference signal to obtain information on the range of the signal where reproduction can be performed. The memory 92 stores the information, and the comparator 91 compares the stored information with the reproduction signal detected from the reproduction signal detector 81 to determine whether the level of the detected reproduction signal satisfies a signal range in which reproduction can be performed.

Here, the detected reproduction signal varies according to the defocus amount, the tangential tilt amount, or the radial tilt amount of the information storage medium 20. It is impossible to accurately know whether the level of the reproduction signal is determined due to defocus or tilt. However, regardless of which of these factors determines the level of the reproduction signal, deterioration of the reproduction signal can be solved by increasing the read power. The reference signal is not affected by the position of the information storage medium 20 compared to the reproduced signal.

When the reproduction signal is within the signal range where reproduction is possible, the central controller 83 controls the output power of the light beam emitted from the light source 71 through the power controller 85 to perform reproduction at the initial readout power. In contrast, when the reproduction signal is not within the signal range in which reproduction can be performed, the central controller 83 gradually increases the readout power so that the reproduction signal reaches the range in which reproduction can be performed based on the variation of the CNR for the readout power explained with reference to fig. 11 to 13. An information reproducing method of reproducing a signal from an information storage medium including recording marks having a size smaller than a resolution limit of an incident beam by the information reproducing apparatus 50 will now be described in detail.

Referring to fig. 16 and 17, in operation S10, a light beam having a predetermined read power is emitted onto the rotating information storage medium 20. On the information storage medium 20, the reference signal is recorded in the form of data.

The photodetector 77 receives the light beam reflected from the information storage medium 20 to detect the reference signal and the reproduction signal in operations S21 and S25. Here, the reproduction signal varies with the amount of defocus by which the beam spot is off the focal point or the amount of tilt in the tangential or radial direction. The reference signal is used to determine whether the reproduced signal has a minimum reproduction quality, which may be done by comparing the reference signal with the reproduced signal based on the signal level, the amplitude and the reflectivity of the signal. It is determined whether the level of the detected reproduction signal is higher than or equal to a level required to perform reproduction based on the reference signal in operation S31, and if the level of the reproduction signal is lower than the level of the required signal in operation S30, the level is adjusted by changing or increasing the readout power of the light source 71 in operation S35. After adjusting the level and repeating operations S25-S30, the reproduction signal has a level required to perform reproduction, and then normal reproduction is performed in operation S40.

Claims (6)

1. A method of reproducing a signal from an information storage medium containing recording marks having a size smaller than a resolution limit of an incident light beam emitted from an information reproducing apparatus, the method comprising:

emitting a light beam having a predetermined read power onto the information storage medium;

receiving a light beam reflected from the information storage medium, and detecting a reproduction signal of the information storage medium and a reference signal for determining whether a level of the reproduction signal is higher than or equal to a level required to perform reproduction; and

it is determined whether the detected level of the reproduction signal is higher than or equal to a level required to perform reproduction, and the readout power of the light source is adjusted in response to a case where the level of the reproduction signal is lower than the level required to perform reproduction.

2. The method of claim 1, wherein the information storage medium comprises a lead-in area, a data area, and a lead-out area, and the reference signal is recorded in the form of data in the lead-in area and/or the lead-out area.

3. The method of claim 2, wherein the reference signal is used to compensate for defocus of the emitted light beam or tilt of the information storage medium.

4. The method of claim 1, wherein after comparing the detected reference signal with the reproduction signal, the power of the emitted light beam is increased to make the level of the reproduction signal higher than or equal to a level required to perform reproduction in response to a case where the reproduction signal is lower than the level required to perform reproduction.

5. An information reproducing apparatus for reproducing a signal from an information storage medium having recording marks with a size smaller than a resolution limit of an incident beam, and a lead-in area, a data area, and a lead-out area, wherein a reference signal compensating for defocus or tilt is recorded in the lead-in area and/or the lead-out area in the form of data, the apparatus comprising:

a pickup and a signal processor, wherein the pickup includes:

a light source emitting a light beam onto the information storage medium, and a photodetector receiving the light beam reflected from the information storage medium and detecting a reproduction signal and a reference signal;

the signal processor is used for determining whether the read-out power level of the light beam emitted from the light source is higher than or equal to the lowest read-out power level required for executing reproduction based on the reference signal detected by the photodetector;

wherein the signal processor adjusts the read power of the light source in response to a situation in which the read power level of the light beam is lower than a minimum read power level required to perform reproduction.

6. The information reproducing apparatus of claim 5, wherein the signal processor comprises:

a reference signal demodulator that demodulates the reference signal to determine a minimum read power required to perform reproduction;

a memory storing the lowest read power; and

and a comparator comparing the stored information with the reproduction signal to determine whether the read power of the light source is higher than or equal to a minimum read power required to perform reproduction.