JP2006147128A - Optical disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk of a land-and-groove recording system capable of narrowizing a track pitch while suppressing the drop of an S/N ratio of reproduction signals. <P>SOLUTION: In the optical disk which includes guide groove portions G and space portions L between the groove portions and is loaded to an optical disk recording/reproduction apparatus having a mechanism for removing or reducing leakage signals from adjacent tracks by using three or more light beam spots and wherein signals are recorded to the groove portions G and the space portions L between the groove portions, depth d of the groove portions G is specified to be ≥λ/12n and <λ/6n, when a wavelength of reproduction light emitted from the optical disk recording/reproduction apparatus and a refractive index of a cover layer 16 on an incidence side of reproduction light or a substrate 11 are defined as λ and n, respectively. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical disk, and more particularly to an optical disk that is mounted on an optical disk recording / reproducing apparatus having a crosstalk reduction mechanism and that records a signal in both the guide groove and the guide groove.

  As optical discs capable of recording information signals, phase change type optical discs that cause changes in the optical constants in the recording layer by laser light irradiation, and changes in the physical shape in the recording layer due to laser light irradiation. Further, there are known shape-changing type optical discs and magneto-optical discs using a material layer having a magneto-optical effect as a recording layer, such as a rare earth transition metal-based amorphous alloy thin film.

  The recording of information signals on such a recordable optical disk is usually performed along guide grooves formed as continuous spiral or concentric grooves on one main surface of the transparent substrate.

  That is, the transparent substrate is formed with an area corresponding to the guide groove (hereinafter referred to as a groove part) and an area corresponding to a hill between the guide grooves (hereinafter referred to as a land part). One of these grooves and lands is a recording track, and the other is a guard band that separates adjacent tracks.

  Such an increase in the recording capacity of the optical disc is achieved by improving the recording density in the linear direction and the recording density in the track direction. Among these, the improvement of the recording density in the linear direction is achieved by reducing the spot diameter of the recording light and shortening the pit length. On the other hand, improvement in recording density in the track direction is achieved by narrowing the track pitch.

  Separately, a land-and-groove recording type optical disc that records information signals in both the groove portion and the land portion has been proposed (see, for example, Patent Document 1). The optical disk of this system is more advantageous in improving the recording density in the track direction than the optical disk of the system that records information signals only in one of the groove part and the land part. However, even in this method, if the track pitch is narrowed in order to increase the recording density, both the groove and land recording tracks overlap in the signal reproduction light spot, and the signal from the adjacent track is reproduced during signal reproduction. This causes a problem that signal leakage (crosstalk) occurs and the SN ratio of the reproduction signal deteriorates.

  As a technique for suppressing the crosstalk in the land-and-groove recording type optical disk, the depth d of the groove portion is set to λ / 6n (where λ is a value so that the amount of crosstalk is minimized in consideration of the optical phase). Conventionally, a technique for setting the laser wavelength and n near the refractive index of the transparent substrate has been proposed (see, for example, Patent Document 2). In an optical disc in which the phase depth d of the groove portion is set so as to satisfy the above condition, the amount of crosstalk from the adjacent track becomes a minimum value. For example, when the groove portion is being reproduced, the laser beam is applied to the land portion adjacent to the groove portion. The amount of light returning from the land portion can be suppressed to a small value even when. This is the same even when the relationship between the groove portion and the land portion is reversed.

  However, even if the depth d of the groove portion is set in the vicinity of λ / 6n, the amount of crosstalk cannot be made completely zero, and the amount of crosstalk varies depending on the spot diameter of the reproduction light and the track pitch. Then, in order to increase the recording density, the track pitch is set to 0.7 of the spot diameter φ of reproduction light (0 · 84 × λ / NA, where λ is the wavelength of the reproduction light and NA is the numerical aperture of the objective lens). If it is narrowed to less than double, crosstalk during signal reproduction becomes a practical problem.

On the other hand, as a technique for suppressing crosstalk in the optical disc recording / reproducing apparatus, three light beams of a main light beam and two sub light beams positioned on both sides of the main light beam are used, and the reflected light signal of each sub light beam is used. Based on this, a so-called crosstalk cancellation technique for removing the signal component of the adjacent track included in the reflected light signal of the main light beam has been proposed (see, for example, Patent Document 3).
JP 57-50330 A Japanese Patent Laid-Open No. 5-282705 JP-A-9-171620

  By the way, in an optical disc, it is ideal that the step portion between the land portion and the groove portion is formed with a vertical surface, but it is practically difficult to form the step portion vertically, and the inclination angle is about 50 degrees. In general, it has a slanted surface. The width of the stepped portion formed with this inclined surface is determined by the depth of the groove portion. Therefore, when the track pitch is narrowed while keeping the depth constant, the ratio of the width of the stepped portion is relatively widened. The flat part of the minute groove part and the land part becomes narrow. Even if the track pitch is the same, the width of the stepped portion becomes relatively wide as the depth of the groove portion becomes deeper, and the flat portions of the groove portion and the land portion become narrower. In this way, when the track pitch is narrowed for higher density, the flat part of the groove part and the land part becomes narrower, and the amount of return light to the photodetector decreases, so that the reproduction signal intensity decreases. As a result, the S / N ratio of the reproduction signal is lowered.

  In a land-and-groove recording type optical disk, even when the track pitch is 0.6 times or less of the spot diameter φ of the reproduction light, if the optical disk recording / reproduction apparatus having the crosstalk cancellation mechanism is used, the adjacent track However, it is not possible to compensate for the decrease in the S / N ratio of the reproduction signal due to the narrow flat portions of the groove portion and the land portion.

  The present invention has been made to solve the problems of the prior art, and an object of the present invention is to provide a land-and-groove recording type optical disc capable of narrowing a track pitch while suppressing a decrease in the SN ratio of a reproduction signal. In offer.

  In order to solve the above-mentioned problems, the present invention is an optical disc having a guide groove and a space between the guide grooves, and includes a mechanism for removing or reducing a leakage signal from an adjacent track using three or more light spots. Mounted on the optical disk recording / reproducing apparatus, and a signal is recorded in both the guide groove and the guide groove, the depth of the guide groove determines the wavelength of the reproduction light emitted from the optical disk recording / reproducing apparatus. λ, where the refractive index of the cover layer or the substrate existing on the reproduction light incident side is n, λ / 12n or more and less than λ / 6n.

  If the depth of the guide groove is regulated within the above range, the groove depth becomes shallower than λ / 6n, which is the groove depth at which crosstalk is minimized, so the ratio of the stepped portion to the flat portion of the groove portion and the land portion The signal-to-noise ratio of the reproduction signal when the track pitch is narrowed can be suppressed. Crosstalk, which becomes larger by reducing the groove depth, can be suppressed to a level with no problem by the crosstalk cancellation mechanism, so that the recording density can be improved by narrowing the track of the optical disk. That is, when the track pitch is narrowed to a predetermined value or less, the noise reduction effect caused by the crosstalk due to the crosstalk cancellation mechanism is fully utilized, so that the margin obtained by this effect is increased to increase the signal component As a means, the flat part of the groove part and the land part can be widened. As a result, the error rate is the best in the part shallower than the conventional optimum groove depth.

  If the groove depth is set to λ / 6n, which is a groove depth at which crosstalk is minimized, or a groove depth deeper than that, it is not possible to sufficiently secure the flat portions of the groove portion and the land portion. Even if the crosstalk component removal by the mechanism is effective, the signal component itself cannot be increased.

  In particular, when the track pitch is narrowed, specifically, when the spot diameter φ of the main light beam is expressed as φ = 0.84 × λ / NA (NA is the numerical aperture of the objective lens), and the track pitch is Tp. When Tp / φ ≦ 0.70, the effect appears remarkably, and the effect appears effectively in the range where the track pitch is narrowed to Tp / φ ≧ 0.50.

  The optical disc of the present invention is an optical disc having a guide groove and a space between the guide grooves, and is an optical disc recording / reproducing apparatus provided with a mechanism for removing or reducing a leakage signal from an adjacent track using three or more light spots. When a signal is recorded in both the guide groove and the guide groove, the depth of the guide groove is set to λ, the wavelength of the reproduction light emitted from the optical disk recording / reproduction device, and the reproduction light incident side. When the refractive index of the existing cover layer or substrate is n, the ratio is set to λ / 12n or more and less than λ / 6n, so that the ratio of the step portion to the flat portion of the groove portion and the land portion can be reduced, and the track pitch It is possible to suppress a decrease in the S / N ratio of the reproduction signal when the signal is narrowed. Therefore, combined with the crosstalk suppression effect by the crosstalk cancellation mechanism, it is possible to improve the recording density by narrowing the track of the optical disk.

  Embodiments of an optical disk according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view of an optical disc according to an embodiment, and shows a single-plate structure film-illuminated optical disc having a recording layer made of a phase change material. As is clear from this figure, the optical disk of this example has a substrate 11 on which guide grooves (grooves) G and guide grooves (lands) L are formed, and a reflection film sequentially formed on the substrate 11 by a sputtering method. A layer 12, a first dielectric layer 13, a recording layer 14 made of a phase change material, a second dielectric layer 15, and a transparent made of an ultraviolet curable resin formed on the second dielectric layer 15 by spin coating. And a cover layer 16. As the substrate 11, a polycarbonate injection-molded product formed so that the widths of the groove G and the land L are substantially the same is used. An AgAu alloy was used for the reflective layer 12 and the film thickness was about 50 nm. ZnS—SiO ₂ was used for the first dielectric layer 13 and the second dielectric layer 15 and the film thicknesses were about 20 nm and about 55 nm, respectively. The recording layer 14 was made of a phase change recording material having a Ge ₅ Sb ₂ Te ₈ composition and had a thickness of about 20 nm. The thickness of the cover layer 16 was about 0.1 mm.

  In addition, each above-mentioned material and film thickness show an example of implementation, and the summary of this invention is not limited to this. These can be appropriately selected depending on the recording / reproducing system (reflectance modulation system, magneto-optical recording system) and capacity of the optical disk.

  As a material of the substrate 11, in addition to polycarbonate, acrylic resin, methacrylic resin, polycarbonate resin, polyolefin resin (particularly amorphous polyolefin), polyester resin, polystyrene resin, epoxy resin and other resin materials, glass, or What provided the resin layer which consists of radiation curable resins, such as photocurable resin, on glass etc. can be used. In view of high productivity, low cost, hygroscopicity, and the like, polycarbonate injection-molded products are preferred.

  The reflection layer 12 is formed of a metal layer or an alloy layer having a high light reflectance, such as an AgAu alloy. Specifically, the main component is at least one metal selected from a metal selected from Au, Al, Ag, Cu, Ti, Cr, Ni, Pt, Ta, Cr and Pd, or a group of these metals. Alloys can be used. For example, Mg, Se, Hf, V, Nb, Ru, W, Mn, Re, Fe, Co, Rh, Ir, Cu, Zn, Cd, Ga are used as the metal layer or alloy layer constituting the reflective layer 12. , In, Si, Ge, Te, Pb, Po, Sn, Bi, and other metals and metalloids can be included as additive elements.

The first dielectric layer 13 and the second dielectric layer 15 are provided on both sides of the recording layer 14. As a material for forming the first dielectric layer 13 and second dielectric layer 15, in addition to the mixture of ZnS and _{SiO 2, SiO 2, Al 2} O 3, Cr 2 0 3, SnO 2, Ta 2 O 5 And oxides such as SiN, GeN, TaN, and AlN.

  The recording layer 14 can be formed of any known heat mode recording material or photon mode recording material in addition to the phase change material. Among these, the recording layer 14 made of a phase change material is excellent in that it hardly deforms. The recording layer made of a phase change material records data by a phase change from a crystalline phase to an amorphous phase or vice versa. Specific examples of the phase change recording material include Sb—Te, Ge—Te, Ge—Sb—Te, In—Sb—Te, Ag—In—Sb—Te, and MA—Ge—Sb—. Te-based (MA is Au, Cu, Pd, Ta, W, Ir, Sc, Y, Ti, Zr, V, Nb, Cr, Mo, Mn, Fe, Ru, Co, Rh, Ni, Ag, Tl, S , Se and Pt), Sn—Sb—Te system, In—Se—Tl system, In—Se—Tl—MB system (MB is Au, Cu, Pd, Ta, W, Ir, Sc) Y, Ti, Zr, V, Nb, Cr, Mo, Mn, Fe, Ru, Co, Rh, Ni, Ag, Tl, S, Se, and Pt), Sn—Sb—Se system And so on.

  As a material for the cover layer 16, an ultraviolet curable resin obtained by curing a prepolymer component and a monomer component using a photopolymerization initiator such as benzophenone or benzoin ether is usually used. Examples of the prepolymer component include polyester acrylate, polyurethane acrylate, epoxy acrylate, polyether acrylate, and the like. Examples of the monomer component include dicyclopentanyl diacrylate, ethylene oxide (EO) -modified bisphenol A acrylate, trimethylpropane triacrylate, and EO-modified trimethylolpropane triacrylate dipentaerythritol hexaacrylate. In addition, a transparent thin sheet such as polycarbonate can be attached via a pressure-sensitive curable resin to form a cover layer.

  Next, with respect to the optical disk having the disk structure of FIG. 1, the track pitch and groove depth are changed variously, and the change in the crosstalk amount from the adjacent track and the change in the error rate of the reproduced signal when the signal is recorded and reproduced. Will be described. However, signal recording / reproduction is performed by using three light beams composed of a main light beam and two sub light beams located on both sides of the main light beam, with the wavelength of the recording / reproducing light being 405 nm and the NA of the objective lens being 0.85. Using an optical disk recording / reproducing apparatus equipped with a crosstalk cancellation mechanism that irradiates the optical disk and removes the signal component of the adjacent track contained in the reflected light signal of the main light beam based on the reflected light signal of each sub light beam It was.

  Signal recording was performed with the groove track as the central track. In measuring the error rate, a recording signal modulated by the PR (1, 7) method was recorded at a minimum mark length of 140 nm and a linear velocity of 4.55 m / s. The PRML system was used for the reproduction system. On the other hand, in the measurement of the amount of crosstalk, a repetitive pattern of 560 nm marks / spaces is recorded, and the amount of crosstalk is the average of the carrier level of the recording track leaked into the C_center and both side tracks adjacent to the recording track. When the value was C_side, the amount of crosstalk was calculated as (C_Side) − (C_center).

FIG. 2 shows the measurement results of the crosstalk amount and the error rate when the groove depth is fixed to λ / 6n and the track pitch is variously changed. The error rate shown in FIG. 2 is the value at which the error rate was the lowest among the cases where the recording power was changed and measured. As apparent from FIG. 2, the crosstalk amount increases as the track pitch is reduced. Further, the error rate when the crosstalk canceller mechanism is not used also increases as the track pitch becomes narrower. That is, even if the groove depth d is set to the phase depth at which the crosstalk is minimized, the crosstalk amount increases as the track pitch decreases. Since the error rate at the practical level is 4 × 10 ⁻⁴ , when recording up to both side tracks, the track pitch up to about 0.28 μm is the practical level limit when the crosstalk canceller mechanism is not used. I understand. The track pitch in this case is expressed as Tp / φ = 0.70 when the spot diameter φ of the main light beam is expressed as φ = 0.84 × λ / NA, and the track pitch is Tp.

  On the other hand, when the crosstalk canceller mechanism is used, the error rate is suppressed to a lower value than when not used, and the error rate is suppressed to a value close to the error rate of the isolated track recorded only on the groove track. That is, the crosstalk can be eliminated to a level where there is no influence of the recording of the adjacent track. However, when the track pitch is narrowed to 0.20 μm, the error rate is just below the practical level. The track pitch in this case is Tp / φ = 0.50 under the same conditions as described above.

  On the other hand, the error rate of an isolated track is a sufficiently low value, but increases as the track pitch becomes narrower. The error rate of the isolated track is not recorded in the adjacent land or groove, i.e., there is no influence of crosstalk. This is due to a decrease in reproduction SN due to narrowing.

  The error rate when the crosstalk canceller mechanism is used cannot be improved beyond the error rate of an isolated track, which is a model without the influence of crosstalk. It can be seen that it is necessary to reduce the error rate of the isolated track in order to further reduce the error rate while effectively acting. That is, it is necessary to secure as much as possible the flat portion of the groove portion that decreases as the track pitch becomes narrower, and to suppress the decrease in reproduction SN.

  FIG. 3 shows the measurement results of the crosstalk amount and error rate when the track pitch is 0.20 μm and the groove depth d is variously changed. As is clear from this figure, when the groove depth becomes shallower, the optical phase condition shifts and the amount of crosstalk increases.

When recording is also performed on both side tracks, if the crosstalk canceller mechanism is not used, the error rate of 4 × 10 ⁻⁴ that is a practical level is cleared regardless of the group depth because the amount of crosstalk is large. I can't. On the other hand, when the crosstalk canceller mechanism is used, the error rate decreases by at least an order of magnitude even though the crosstalk amount increases. Note that the decrease in error rate when the crosstalk canceller mechanism is used corresponds to the decrease in the error rate of isolated track recording when the groove depth d is shallow.

  The error rate of isolated track recording decreases when the groove depth d is decreased. Even when the track pitch is narrowed to 0.2 .mu.m, the inclination generated at the step portion between the groove portion and the land portion by decreasing the groove search. This is because the flat part of the groove part and the land part can be easily secured and the reduction of the reproduction SN due to the narrow track pitch can be suppressed. That is, it is shown that by making the groove depth shallower, the effect of the crosstalk canceller mechanism can be effectively used, and the margin obtained by the effect can contribute to the increase of the reproduction signal.

  In FIG. 3, the error rate when the crosstalk canceller mechanism is used is minimized at the groove depth λ / 10, and when the groove depth is further decreased, the error rate starts to increase. This is because if the groove depth becomes too shallow, the heat at the time of recording is easily diffused to the adjacent track, and signal deterioration due to cross-write starts to occur.

Therefore, considering that the error rate at a practical level is 4 × 10 ⁻⁴ , when using the crosstalk canceller mechanism, the wavelength of the reproduction light emitted from the optical disk recording / reproduction apparatus is λ, It can be seen that the group depth d may be set so that the refractive index of the cover layer 16 existing on the incident side is n and not less than λ / 12n and less than λ / 6n.

  FIG. 4 shows the measurement results of the crosstalk amount and the error rate when the track pitch is 0.28 μm wider than that in FIG. 3 and the groove depth d is variously changed. As is clear from this figure, even when the track pitch is 0.28 μm, the crosstalk amount increases as the groove depth d becomes shallower. When the crosstalk canceller mechanism is not used, the crosstalk amount is increased. The error rate has increased with the increase of. However, when the side of the crosstalk canceller is used, the error rate is decreased. Therefore, when the crosstalk canceller mechanism is used, the error rate margin is widened by reducing the groove depth regardless of the track pitch, that is, the effect of the crosstalk canceller mechanism is effectively utilized. However, it can be seen that the margin obtained by the effect can contribute to the increase of the reproduction signal.

  In the above measurement example, the result when the groove track is the center is shown, but the same result is obtained when the land track is the center.

  Further, in the above-described embodiment, the film surface incident type optical disc in which recording / reproducing light (laser light) is incident from the cover layer 16 side has been described as an example, but the second dielectric layer 15 and the phase change material are formed on the substrate 11. The same effect was obtained even when the recording layer 14, the first dielectric layer 13, and the reflective layer 12 were laminated in this order, and the substrate surface incident type optical disc in which the recording / reproducing light was incident from the substrate 11 side.

It is sectional drawing of the optical disk which concerns on the example of embodiment. It is a table | surface figure which shows the measurement result of the crosstalk amount and error rate at the time of fixing a groove depth to (lambda) / 6n and changing a track pitch variously. It is a table | surface figure which shows the measurement result of the crosstalk amount and error rate when a track pitch is 0.20 micrometer and groove depth d is variously changed. It is a table | surface figure which shows the measurement result of the crosstalk amount and error rate when a track pitch is 0.28 micrometers and the groove depth d is variously changed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Board | substrate 12 Reflective layer 13 1st dielectric material layer 14 Recording layer 15 2nd dielectric material layer 16 Cover layer

Claims (3)

  An optical disk having a guide groove and a space between the guide grooves, which is mounted on an optical disk recording / reproducing apparatus having a mechanism for removing or reducing a leakage signal from an adjacent track using three or more light spots, and the guide groove In the case where a signal is recorded both between the guide groove and the guide groove, the depth of the guide groove is λ the wavelength of the reproduction light emitted from the optical disk recording / reproduction device, and the cover exists on the reproduction light incident side. An optical disc, wherein a refractive index of a layer or a substrate is n and is λ / 12n or more and less than λ / 6n.   The optical disk according to claim 1, wherein the spot diameter φ of the main light beam is expressed as φ = 0.84 × λ / NA (NA is the numerical aperture of the objective lens), and the track pitch is Tp, Tp / φ ≦ An optical disc characterized by being 0.70.   2. The optical disk according to claim 1, wherein when the spot diameter φ of the main light beam is expressed as φ = 0.84 × λ / NA (NA is the numerical aperture of the objective lens) and the track pitch is Tp, 0.50 ≦ An optical disc characterized by Tp / φ ≦ 0.70.

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