JP2013178858A - Optical recording and reproducing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a recording and reproducing method, by which upon reproducing an optical recording medium having a planar recording/reproducing layer, even in a medium subjected to a recording operation while a defect including deformation of a disk surface is present, tracking on a continuing mark line before and after a defect can be maintained.SOLUTION: In a method for operating tracking on the whole defect or a part of the defect, tracking is controlled by using a signal computed by adding or subtracting a focus control signal component to or from a tracking control signal obtained from a mark line by a reproducing operation. Thus, a reproducing operation is performed under the corrected condition of tracking positions before and after the defect.

Description

  The present invention relates to an optical recording / reproducing method for recording / reproducing information on / from an optical recording medium having a planar recording / reproducing layer without an unevenness for tracking control, and recording on an optical recording medium having local deformation on the surface. The present invention relates to an optical recording / reproducing method for realizing stable reading of recorded data.

  Conventionally, for viewing digital moving image contents and recording digital data, CD-DA, CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-R, DVD +/- RW, DVD-RAM, Optical recording media such as Blu-ray Disc (BD) are widely used. Among them, BD, which is one of the next-generation DVD standards, has a wavelength of laser light used for recording and reproduction as short as 405 nm, and a numerical aperture of the objective lens is set to 0.85. On the optical recording medium side corresponding to the BD standard, tracks are formed at a pitch of 0.32 μm. In this way, recording / reproducing of 25 GB or more is possible with respect to one recording / reproducing layer of the optical recording medium.

  By the way, the capacity of moving images and data is expected to increase more and more in the future. Therefore, a method for increasing the capacity of the optical recording medium by increasing the number of recording / reproducing layers in the optical recording medium has been studied. In the BD standard optical recording medium, a technology that realizes a super-large capacity of 200 GB by providing six to eight recording / reproducing layers has also been reported.

  On the other hand, when the recording / reproducing layer is multilayered in the optical recording medium, if the recording / reproducing layer is formed with irregularities for tracking control such as grooves / lands, the medium configuration becomes complicated, and work such as eccentricity adjustment is performed. There is concern that it will be difficult. Further, each time a recording / reproducing layer is provided, a stamper serving as a mother mold for forming irregularities is required. The more the layers are formed, the more times the stamper is used and the higher the manufacturing cost.

  Therefore, in recent years, in an optical recording medium, a servo layer for tracking control having irregularities and grooves and a recording / reproducing layer (hereinafter referred to as a planar recording / reproducing layer) having no irregularities and grooves are provided at least in the information recording area. Thus, there is proposed a technique for recording information on a recording / reproducing layer with a recording / reproducing beam while obtaining a tracking signal from the servo layer using a beam dedicated for tracking control (Patent Documents 1 and 2). ).

JP 2008-97693 A JP 2008-97694 A

M. Ogasawara et. Al., Jpn. J. Appl. Phys., 50 (2011) 09MF01.

One of the issues with optical recording media with a flat recording / reproducing layer is a series of recordings that are performed at least by tracking servo using a servo layer with irregularities and grooves provided separately from this planar recording / reproducing layer. Even when the recording is completed, tracking control is performed using a recording mark array formed on the flat recording / reproducing layer during reproduction, so that the surface is caused by bubbles or the like present in the cover layer formed on the light incident surface. If the reading accuracy of the record mark row deteriorates, such as when the uniformity of the shape deteriorates, not only the reproduction signal quality but also the tracking accuracy deteriorates. There are problems peculiar to optical recording media having layers.

  The above-mentioned object can be achieved by the following means by the inventors' extensive research.

That is, the present invention that achieves the above object includes a servo layer having unevenness or grooves for tracking control, and a recording / reproducing layer that is previously laminated or has no unevenness for tracking control that is formed afterwards. A focus control signal obtained by a tracking control signal obtained by a phase difference detection method (DPD method) using a mark row or a push-pull method (PP method) using a mark row. Is an optical recording / reproducing method characterized in that tracking control is performed by adding and subtracting.

In the optical recording / reproducing method that achieves the object, the focus control signal is multiplied by a coefficient corresponding to the amplitude of the focus control signal or the tracking control signal, and is added to or subtracted from the tracking control signal.

In the optical recording / reproducing method for achieving the object, the focus control signal is added to or subtracted from the tracking control signal only when the amplitude value of the focus control signal or the tracking control signal exceeds a certain threshold value.

In the optical recording / reproducing method that achieves the object, the focus control signal is added to or subtracted from the tracking control signal only immediately before the missing portion of the reproduction signal.

  According to the present invention, in the optical recording medium that performs at least tracking servo and performs a series of recordings using a servo layer having unevenness and grooves provided separately from the planar recording / reproducing layer, bubbles present in the cover layer Tracking control at an appropriate position using the recording mark row formed on the flat recording / reproducing layer even if the reading accuracy of the recording mark deteriorates during reproduction, such as when the uniformity of the surface shape deteriorates due to Therefore, stable tracking can be continued.

1 is a block diagram showing the structure of an optical recording / reproducing apparatus and an optical pickup that perform recording / reproducing of an optical recording medium according to an embodiment of the present invention. It is sectional drawing which shows the laminated structure of the optical recording medium which concerns on embodiment of this invention. FIG. 4 is a cross-sectional view and a plan view showing structures of a recording / reproducing layer and a cover layer of a recorded optical recording medium according to an embodiment of the present invention. FIG. 4 is a cross-sectional view and a plan view showing structures of a recording / reproducing layer and a cover layer of a recorded optical recording medium according to an embodiment of the present invention. It is an error signal, a control signal, and a reproduction signal obtained when the medium of FIG. 3 is reproduced. FIG. 4 is a schematic diagram of a reproduction beam trajectory when the medium of FIG. 3 is reproduced. FIG. 5 shows an error signal, a control signal, and a reproduction signal obtained when the medium of FIG. 4 is reproduced. It is a control signal and an error signal obtained by this recording / reproducing method. FIG. 5 is a schematic diagram of a reproduction beam trajectory when the medium in FIG. 4 is reproduced by a normal method. FIG. 5 is a schematic diagram of a reproduction beam trajectory when the medium of FIG. 4 is reproduced by the method of the present invention. It is a schematic diagram of a control signal processing circuit in the present recording / reproducing method. It is an example of the application procedure of the process of the control signal in this recording / reproducing method.

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows the configuration of an optical recording medium 10 and an optical pickup 90 that realize the present invention. The optical pickup 90 includes a first optical system 100 and a second optical system 200. The first optical system 100 is an optical system that performs recording / reproduction with respect to the recording / reproducing layer group 14 of the optical recording medium 10. The second optical system 200 is an optical system that performs tracking control using a servo layer 18 described later when information is recorded on the recording / reproducing layer group 14 using the first optical system 100.

  A divergent recording / reproducing beam 170 having a blue wavelength of 380 to 450 nm (here, 405 nm) emitted from the light source 101 of the first optical system 100 is transmitted through a collimator lens 153 provided with a spherical aberration correction unit 193. , And enters the polarization beam splitter 152. The beam 170 incident on the polarization beam splitter 152 is transmitted through the polarization beam splitter 152, further converted into circularly polarized light by transmission through the quarter-wave plate 154, and then incident on the beam splitter 260 of the second optical system 200. To do. The beam splitter 260 is set to have a high transmittance and a low reflectance. Specifically, the ratio of the transmittance to the reflectance is set to 10 times or more. Accordingly, the beam 170 passes through the beam splitter 260 and is converted into a convergent beam by the objective lens 156. The beam 170 is focused on either the recording / reproducing layer group 14 or the servo layer 18 to be recorded / reproduced, which is formed inside the optical recording medium 10.

  The aperture of the objective lens 156 is limited by the aperture 155, and the numerical aperture NA is 0.70 to 0.90 (here, 0.85). For example, the beam 170 reflected by the recording / reproducing layer group 14 passes through the objective lens 156, the beam splitter 260, and the quarter-wave plate 154 and is converted into linearly polarized light that is 90 degrees different from the forward path, and then the polarized beam. Reflected by the splitter 152.

  The beam 170 reflected by the polarization beam splitter 152 passes through the condenser lens 159 and is converted into convergent light, and enters the photodetector 132 through the cylindrical lens 157. Astigmatism is imparted to the beam 170 when passing through the cylindrical lens 157.

  The photodetector 132 has four light receiving units (not shown), and outputs an electrical signal corresponding to the amount of light received. From these electrical signals, a focus control signal based on the astigmatism method, a signal based on a phase difference detection method (hereinafter referred to as DPD method) or a push-pull method (hereinafter referred to as PP method) limited during reproduction, and information recorded on the optical recording medium 10 Reproduction signals and the like are generated. The focus control signal and tracking control signal are amplified and phase compensated to the desired level, and the tracking control signal is processed by the focus control signal, the DPD or PP method, and the playback signal, then the actuator Feedback is supplied to 191 and 192 for tracking control.

The divergent beam 270 emitted from the light source 201 of the second optical system 200 and having a red wavelength of 630 to 680 nm (here, 650 nm) is transmitted through the collimator lens 253 provided with the spherical aberration correcting means 293, and the polarization beam splitter 252. Is incident on. The beam 270 incident on the polarization beam splitter 252 passes through the polarization beam splitter 252, further passes through the quarter-wave plate 254 for the second optical system and is converted into circularly polarized light, and then the wavelength selection filter 260. And is transmitted through the polarization beam splitter 152 shared with the first optical system 100. The beam 270 is further converted into a convergent beam by the objective lens 156 and condensed on the servo layer 18 formed inside the optical recording medium 10. The beam 270 reflected by the servo layer 18 is transmitted through the objective lens 156 and the polarization beam splitter 152, reflected by the wavelength selection filter 260 of the second optical system 200, and the forward path of the quarter-wave plate 254 is 90. After being converted into linearly polarized light of different degrees, it is reflected by the polarizing beam splitter 252. The beam 270 reflected by the polarization beam splitter 252 passes through the condensing lens 259 and is converted into convergent light, and enters the photodetector 232 via the cylindrical lens 257. Astigmatism is given to the beam 270 when passing through the cylindrical lens 257.

  The photodetector 232 has four light receiving units (not shown), and outputs an electrical signal corresponding to the amount of light received. From these electrical signals, a focus error (FE) signal by the astigmatism method and a tracking error (TE) signal by the push-pull method are generated. When information is also recorded on the servo layer 18, a reproduction signal is also generated.

  When information is recorded on the recording / reproducing layer group 14 by the first optical system 100, the TE signal of the second optical system 200 is amplified to a desired level and phase compensated, and then fed back to the actuators 191 and 192. Tracking control is performed. As a result, the first optical system 100 records information on the recording / reproducing layer group 14 based on the tracking control of the second optical system 200. In the present embodiment, when information recorded on the recording / reproducing layer group 14 is reproduced, the first optical system 100 independently performs tracking control using the recording mark 19 on the recording / reproducing layer group 14. ing.

  FIG. 2 shows an enlarged cross-sectional structure of the optical recording medium 10 of the present embodiment.

  The optical recording medium 10 has a disk shape with an outer diameter of about 120 mm and a thickness of about 1.2 mm. The optical recording medium 10 includes a cover layer 11, a recording / reproducing layer group 14, an intermediate layer group 16, a buffer layer 17, a servo layer 18, and a support substrate 12 from the light incident surface 10A side.

  Here, the recording / reproducing layer group 14 includes the first to sixth recording / reproducing layers 14A to 14F, and has a structure in which information can be recorded on each of them. It is composed of the same recording / reproducing layer. The first to sixth recording / reproducing layers 14 </ b> A to 14 </ b> F have a planar structure that does not have unevenness and grooves for tracking control, and the first optical system 100 irradiates a recording beam 170 with high energy. As a result, a recording mark is formed. The types of the recording / reproducing layer group 14 include a write-once recording / reproducing layer in which information can be additionally written but cannot be rewritten, and a rewritable recording / reproducing layer in which information can be rewritten.

  The support substrate 12 is a disk-shaped substrate having a thickness of 1.0 mm and a diameter of 120 mm in order to ensure the thickness (about 1.2 mm) required for the optical recording medium. A servo layer 18 is formed on the side surface. Specifically, on the light incident surface 10A side of the support substrate 12, lands 18A and grooves 18B are formed in a spiral shape from the vicinity of the center toward the outer edge. The land 18A and the groove 18B become unevenness for tracking control, and the beam 270 of the second optical system 200 is guided.

  Note that various materials can be used as the material of the support substrate 12, and for example, glass, ceramics, and resins can be used. Of these, a resin is preferred from the viewpoint of ease of molding. Examples of the resin include polycarbonate resin, olefin resin, acrylic resin, epoxy resin, polystyrene resin, polyethylene resin, polypropylene resin, silicone resin, fluorine resin, ABS resin, and urethane resin. Among these, polycarbonate resin and olefin resin are particularly preferable from the viewpoint of processability. In addition, since the support substrate 12 does not become an optical path of the beam 270, it does not need to have high light transmittance.

  The servo layer 18 formed on the support substrate 12 is configured by forming a recording layer on the surface of the support substrate 12. Therefore, the servo layer 18 becomes a recording layer having unevenness for tracking control. When the high-energy beam 270 is irradiated by the second optical system 200, the light reflectance is changed due to a change in chemical or physical characteristics. Changes and information is recorded. Of course, the servo layer 18 also functions as a light reflecting film for tracking control. The type of the recording layer is not particularly limited, and for example, a recording film using an inorganic material or an organic dye material can be employed. In addition, as a recording method in the recording layer, a write-once type or a rewritable type can be appropriately employed. If the servo layer 18 does not require an information recording function, a metal layer such as Ag may be formed to function as a simple light reflecting film. On the support substrate 12, the optimum recording power, recording power range, transmittance, etc. of the near layer are recorded in the form of irregularities such as prepits and grooves.

Here, the track pitch P of the unevenness for tracking control in the servo layer 18 is set to twice the track pitch of the recording marks scheduled to be recorded on the recording / reproducing layers 14A to 14F. Specifically, since the track pitch scheduled to be recorded in the recording / reproducing layers 14A to 14F is set to about 0.32 μm for compatibility with the BD standard, the groove / land track pitch P of the servo layer 18 is It is set to around 0.64 μm. If the track pitch P is around 0.64 μm, sufficient tracking is possible even with a relatively long beam 270 in the red wavelength region. In particular, in the present embodiment, since tracking control is performed using both the groove and the land, as a result, the uneven pitch is about 0.64 μm, but is recorded in the recording / reproducing layers 14A to 14F. The track pitch of the recording marks can be about 0.32 μm, which is half of the track pitch. Therefore, the track pitch of the recording marks of the recording / reproducing layer group 14 can be doubled without reducing the track pitch of the servo layer 18, so that the recording capacity can be increased.

  The buffer layer 17 is made of a light-transmitting acrylic ultraviolet curable resin, and has a thickness of 90 μm here.

  The first to sixth recording / reproducing layers 14A to 14F stacked on the light incident surface 10A side of the buffer layer 17 have substantially the same material composition and film thickness, and are provided on both outer sides of the write-once recording film. It has a three-layer structure in which dielectric films are stacked (not shown). It should be noted that the first to sixth recording / reproducing layers 14A to 14F are optimized in terms of light reflectance, absorptivity, transmittance and the like for the beam 170 in the blue wavelength region (short wavelength) in the first optical system 100. On the other hand, the beam 270 in the red wavelength region (long wavelength) of the second optical system 200 is sufficiently transmitted.

  In addition to the basic function of protecting the write-once recording film, the dielectric film of each recording / reproducing layer also plays a role of expanding the difference in optical characteristics before and after the formation of the recording mark 19.

  When the beam 170 is irradiated, if the energy absorbed by the dielectric film is large, the recording sensitivity tends to be lowered. Therefore, in order to prevent this, it is preferable to select a material having a low absorption coefficient (k) in the wavelength region of 380 nm to 450 nm (particularly 405 nm) as the material of these dielectric films. In the present embodiment, TiO 2 is used as the material for the dielectric film.

  The write-once recording film sandwiched between the dielectric films is a film on which an irreversible recording mark 19 is formed, and the portion where the recording mark 19 is formed and the other portion (blank region) have a reflectivity with respect to the beam 170. to differ greatly. As a result, data can be recorded / reproduced. This write-once recording film also has high transparency in the red wavelength region of the beam 270 of the second optical system 200 for tracking control.

  The write-once recording film is formed mainly of a material containing Bi and O. This write-once recording film functions as an inorganic reaction film, and the reflectance is greatly different due to a chemical or physical change caused by the heat of laser light. Specific materials include Bi-O as the main component, or Bi-MO (where M is Mg, Ca, Y, Dy, Ce, Tb, Ti, Zr, V, Nb, Ta). , Mo, W, Mn, Fe, Zn, Al, In, Si, Ge, Sn, Sb, Li, Na, K, Sr, Ba, Sc, La, Nd, Sm, Gd, Ho, Cr, Co, Ni And at least one element selected from Cu, Ga, and Pb). In this embodiment, Bi—Ge—O is used as the material of the write-once recording film.

  Although the case where the write-once recording film is employed in the first to sixth recording / reproducing layers 14A to 14F is shown here, it is also possible to employ a phase change recording film capable of repetitive recording. In this case, the phase change recording film preferably contains SbTeGe as a main component.

  The intermediate layer group 16 has first to fifth intermediate layers 16A to 16E in order from the side closer to the light incident surface 10A, and is laminated between the first to sixth recording / reproducing layers 14A to 14F. Each of the intermediate layers 16A to 16E is made of an acrylic or epoxy ultraviolet curable resin. The film thicknesses of the intermediate layers 16A to 16E are preferably set to 20 μm or less in order to increase the number of stacked layers. The first intermediate layer 16A is 16 μm, the second intermediate layer 16B is 12 μm, and the third intermediate layer 16C is 16 μm, the fourth intermediate layer 16D is 12 μm, and the fifth intermediate layer 16E is 16 μm. That is, intermediate layers having two kinds of film thicknesses (16 μm and 12 μm) are alternately stacked. As a result, as the interlayer distance between the first to sixth recording / reproducing layers 14A to 14F, the first distance (16 μm) and the second distance (12 μm) different from the first distance are alternately set in order from the light incident surface side. Will be. The difference between the first distance and the second distance is set to 4 μm. In this way, interlayer crosstalk is reduced. Of course, all the intermediate layer groups 16 may have the same film thickness.

  The cover layer 11 is made of a light-transmitting acrylic ultraviolet curable resin, like the intermediate layer group 16, and has a thickness of 100 μm.

  As a result of the optical recording medium 10 being configured as described above, the servo layer 18 is located at a distance of 262 μm from the light incident surface 10A, and the most from the light incident surface 10A in the recording / reproducing layer group 14. The distant sixth recording / reproducing layer 14F is located at a distance of 172 μm from the light incident surface 10A, the fifth recording / reproducing layer 14E is 156 μm from the light incident surface 10A, and the fourth recording / reproducing layer 14D is 164 μm from the light incident surface 10A. The third recording / reproducing layer 14C is 128 μm from the light incident surface 10A, the second recording / reproducing layer 14B is 116 μm from the light incident surface 10A, and the first recording / reproducing layer 14A closest to the light incident surface 10A is the light incident surface 10A. Is located at a distance of 100 μm. The overall thickness of the recording / reproducing layer group 14 (distance between the first recording / reproducing layer 14A to the sixth recording / reproducing layer 14F) is 72 μm.

  In the optical recording medium 10 of the present embodiment, the servo layer 18 is disposed at a position farther from the light incident surface 10A than the recording / reproducing layer group 14. In this way, it can be reduced that the tracking land 18A and the groove 18B adversely affect the recording / reproducing beam 170 irradiated to the recording / reproducing layer group 14.

  Next, a method for manufacturing the optical recording medium 10 of this embodiment will be described.

  First, the support substrate 12 on which grooves and lands are formed is manufactured by injection molding of polycarbonate resin using a metal stamper. By using an injection mold, the support substrate 12 is provided with a recording condition including recording / playback layer group 14 address information, recording / playback power, and the like, and the position or interlayer distance of the recording / playback layers 14A to 14F. Basic information to be held in advance is preformatted. Specifically, basic information, optimum recording power information of the front layer, and the like are preformed using the wobble of the land 18A or the groove 18B. The form to be preformed is not limited to a land groove but may be a pit. Further, basic information, optimum recording power information of the front layer, and the like may be recorded in a pre-write form on the servo layer 18 formed on the support substrate 12. Further, the production of the support substrate 12 is not limited to the injection molding method, and may be produced by the 2P method or other methods.

  Thereafter, the servo layer 18 is formed on the surface of the support substrate 12 on the side where the grooves and lands are provided. The servo layer 18 is formed in the order of a dielectric film, a write-once recording film, and a dielectric film using a vapor phase growth method, and functions as a recording film. Further, the buffer layer 17 is formed on the servo layer 18. The buffer layer 17 is formed, for example, by coating a viscosity-adjusted acrylic or epoxy ultraviolet curable resin by a spin coating method or the like, and irradiating it with ultraviolet rays and curing it. In addition, it can also form by sticking the light transmissive sheet | seat which consists of light transmissive resin on the servo layer 18 using an adhesive agent, an adhesive, etc. instead of an ultraviolet curable resin.

  Next, the sixth recording / reproducing layer 14F is formed. Specifically, a dielectric film, a write-once recording film, and a dielectric film are formed in this order using a vapor phase growth method. Among these, it is preferable to use a sputtering method. Thereafter, a fifth intermediate layer 16E is formed on the sixth recording / reproducing layer 14F. The fifth intermediate layer 16E is formed, for example, by coating an ultraviolet curable resin whose viscosity is adjusted by a spin coating method or the like, and then irradiating the ultraviolet curable resin with ultraviolet rays and curing. By repeating this procedure, the fifth recording / reproducing layer 14E, the fourth intermediate layer 16D, the fourth recording layer reproducing layer 14D, the third intermediate layer 16C,.

  When the first recording / reproducing layer 14A is completed, the cover layer 11 is formed thereon, and the optical recording medium 10 is completed. The cover layer 11 is formed, for example, by coating a viscosity-adjusted acrylic or epoxy ultraviolet curable resin by a spin coating method or the like and irradiating it with ultraviolet rays to cure. In addition, although the said manufacturing method was demonstrated in this embodiment, this invention is not specifically limited to the said manufacturing method, Another manufacturing technique can also be employ | adopted.

Next, an optical recording / reproducing method for recording / reproducing information on / from the optical recording medium 10 of the present embodiment will be described.

3A shows a cross-sectional view after recording a recording mark row on the recording medium 10 of the present embodiment, and FIG. 3B shows a plan view. 4A shows a case where the resin forming the cover layer 11 includes a defect 300 in the resin layer forming the cover layer 11 when the recording medium 10 of the present embodiment is manufactured, and a film thickness variation portion 301 is generated around the defect 300. FIG. 4B shows a plan view.

As shown in this figure, a region 302 in which a recording mark row is not formed is generated in the vicinity immediately below the defect 300. This is because, when information is recorded on the recording / reproducing layer group 14 using the first optical system 100, even if the thickness variation portion 301 is controlled to focus on the recording surface, the thickness around the wide thickness variation distribution 301 due to the defect 300 is increased. This is because when the range is recorded, the original recording mark cannot be formed by changing the incident angle of the recording light and the thickness of the cover layer.

FIG. 5 shows a focus error signal, a tracking error signal, a focus control signal generated based on the reproduction signal and the focus error signal, and a tracking control signal obtained from the reproduction beam subjected to tracking control in FIG. ing.

Since the recording medium 10 is normally manufactured and the recording mark train is normally formed, various error signals and various control signals at the time of reproduction are not particularly noised, and only the reproduction signal indicating the recording mark train is modulated. Voltage is shown.

FIG. 6 shows the trajectory of the reproduction beam when tracking control is performed using the recording mark row of FIG. This indicates that the recording mark row is normally recorded, so that tracking is performed right above the mark row.

FIG. 7 shows a focus error signal, a tracking error signal, a focus control signal generated based on the reproduction signal and the focus error signal obtained from the reproduction beam subjected to the tracking control in FIG. 4, and a tracking control signal. ing.

In order to perform focus control in spite of the presence of the defect 300 in the recording medium 10, the film thickness variation portion 301, and the film thickness variation portion 301, the focus control signal cancels the film thickness variation 301. Need to be generated. FIG. 7B shows the focus control signal generated so that the focus control signal cancels the film thickness variation 301. It can be seen that the focus control signal has a voltage profile corresponding to the film thickness variation 301. Focus error signal A in FIG. 7 is approximately flat because focus control is performed.

In addition, tracking error signal C in FIG. 7 is approximately flat (zero voltage) because tracking is performed in the range where the mark row exists, but the tracking error signal is generated in a place where the mark is missing. Since it cannot be obtained from the mark row, it is flat (zero voltage), and as a result, it is flat despite the presence of the film thickness variation portion 300.

Here, the film thickness fluctuation part 301 is large with respect to the size of the beam condensing part, is asymmetric in shape with respect to the recording mark row, and has a lens effect due to the film thickness fluctuation part. Are recorded as if they had an offset with respect to the track direction.

Therefore, in order to make the tracking error signal flat even though the tracking error signal has a film thickness variation portion as described above, in the region of the film thickness variation portion 301, a voltage profile is applied to the tracking control signal so as to cancel this offset. Will have. Further, in the region 302 where no mark row exists, the tracking error signal has a zero voltage, so that the tracking control signal has a profile with a zero voltage. FIG. 7D shows a tracking control signal that has been tracking-controlled in this way.

  The reproduction signal E in FIG. 7 has a modulation amplitude corresponding to the mark string in the portion reproducing the mark string, and has a constant voltage profile in the region 302 where no mark string exists.

When tracking control is performed as described above, as shown in FIG. 9, when the reproduction beam reaches the film thickness variation portion 300, it proceeds with an offset with respect to the mark row, and after passing through a portion where the recording mark row does not exist, the offset is obtained. As shown in FIG. 9, there is a situation in which tracking cannot be performed on continuous mark rows and tracking is continued on adjacent mark rows.

In the present invention, focus control on the information recording surface 14 is performed using the first optical system 100, and tracking control is performed on the recorded mark row using an arithmetic circuit as shown in FIG.

In tracking control in the conventional reproduction, when tracking control is performed so as to reduce the tracking error of the mark row across the film thickness variation 301, a tracking offset occurs due to the lens effect of the film thickness variation 301 and the asymmetry of the shape. .

Therefore, in order to perform tracking without causing this offset, it is only necessary to cancel the lens effect and the asymmetry of the shape due to the film thickness variation 301. This lens effect and asymmetry are controlled by the focus control indicated by B in FIG. Since it appears in the signal, the tracking offset can be reduced by appropriately adding and subtracting the focus control signal to the tracking control signal.

A new tracking control signal calculated by multiplying the focus control signal indicated by B in FIG. 7 by an appropriate coefficient and subtracted from the tracking control signal indicated by D in FIG. 7 is indicated by A in FIG.

When tracking control is performed by the tracking control signal shown by A in FIG. 8, the tracking error signal has an offset before and after the defect as shown by B in FIG. 8, but the actual reproduction beam locus is shown in FIG. As shown in the figure, it is possible to track a continuous mark row before and after the missing portion of the recording mark.

As a more preferable method, the focus control signal is multiplied by a coefficient corresponding to the amplitude of the focus control signal or the tracking control signal and added to or subtracted from the tracking control signal.

For example, in order to generate a focus control signal and tracking control signal, it is calculated based on the focus error signal and tracking error signal, but after sensitivity variations of individual photodetectors, frequency filter processing, voltage level adjustment, etc. Therefore, there is a case where an optimum tracking control signal cannot be generated around the defect only by simple addition and subtraction of the focus control signal. Therefore, the focus control signal generated around the defect or the coefficient corresponding to the amplitude voltage due to the defect of the tracking control signal is multiplied by the focus control signal, and this is added to or subtracted from the tracking control signal, thereby reducing the tracking deviation due to the defect. I can do it.

As a more preferable method, addition / subtraction of the focus control signal to / from the tracking control signal is performed only when the value of the focus control signal or the value of the tracking control signal exceeds a certain threshold value.

For example, a minute film thickness distribution or a surface shake of a rotating medium affects the amplitude of the focus control signal, but these amplitudes are smaller than those that greatly affect the tracking. Furthermore, the tracking control is not substantially affected. Therefore, by adding / subtracting the focus control signal to / from the tracking control signal only when a certain threshold value is exceeded, it is possible to prevent the reproduction signal from deteriorating due to an unnecessary offset.

As a preferred method, addition / subtraction of the focus control signal to / from the tracking control signal is performed only at a stage until the reproduction signal is lost.

As shown in FIG. 8B, the addition / subtraction of the focus control signal to the tracking control signal gives an unnecessary tracking offset after the missing part and after the missing part, and there is an offset state that leads to an increase in the tracking error signal after the missing part. Means the possibility to do. However, when tracking is performed with the correct mark train after the missing part, the subsequent tracking control is performed under the optimum conditions of the tracking operation for the mark that is read without adding or subtracting the focus control signal to further improve the tracking accuracy. In addition, the reproduction signal can be obtained quickly and satisfactorily.

Note that the stage where the reproduced signal is missing can be regarded as a missing reproduced signal when the reproduced signal is continuously blanked longer than the longest signal in the modulated signal to be reproduced.

[Example 1]
A medium produced by the above-described manufacturing method and having a 50 μm bubble in 11 has a wavelength of 405 nm as the first optical system and a numerical aperture of 0.85, and a wavelength of 650 nm as the second optical system and a numerical aperture of 0.60. In the optical disk evaluation machine having a recording medium, the servo layer having a groove pitch of 0.64 .mu.m is recorded while the second optical system performs land / groove tracking by the PP method and the first optical system performs focus control on the recording / reproducing layer 14A. Recording was performed on the reproduction layer 14A at a density of 25 GB / Layer in a circumferential shape in the range of about 500 μm around the bubble.

Subsequently, the recording mark row was reproduced while performing tracking and focusing using the DPD method on the recording mark row recorded on the recording / reproducing layer 14A using the first optical system.

As a result, when tracking was performed with a new tracking control signal obtained by subtracting the focus control signal from the tracking control signal generated from the DPD signal as in the present embodiment, reproduction was performed with continuous addresses.

The average Jitter value in the mark row immediately after the defect was 9%, and the average Jitter value in the mark row having no defect around it was 7.5%.

[Example 2]
When the medium recorded in the first embodiment is tracked until just before the reproduction signal is lost by the new tracking control signal obtained by subtracting the focus control signal from the tracking control signal generated from the DPD signal as in the present embodiment. , Played with consecutive addresses.

The average Jitter value in the mark row immediately after the defect was 7.6%, and the average Jitter value in the mark row having no defect in the periphery was 7.5%.

[Comparative example]
When the medium recorded in Example 1 was tracked only with the tracking control signal made from the DPD method, reproduction was not performed at continuous addresses around the defect.

  In the optical recording medium 10 of the present embodiment, the servo layer 18 is shown only when disposed on the side farther from the recording / reproducing layer group 14 with respect to the light incident surface 10A, but the present invention is not limited to this. . Also. Although only the case where six recording / reproducing layers are provided as the recording / reproducing layer group 14 is shown, the present invention is not limited to this.

  In the present embodiment, two types of interlayer distances (16 μm, 12 μm) are alternately set in the recording / reproducing layer group. However, the present invention is not limited to this, and three or more types of interlayer distances are set. You may combine. Of course, all may be set to the same film thickness.

Furthermore, in the present embodiment, the support substrate 12 or the servo layer 18 is a recording layer having grooves and lands for tracking control, but the present invention is not limited to this, and is a servo layer using pits or recording marks. It is also possible to perform tracking control.

The reproducing method of the optical recording medium of the present invention can be applied to an optical disc apparatus that records information such as video, audio, or computer data on an optical disc and further reproduces information from the disc.

DESCRIPTION OF SYMBOLS 10 Optical recording medium 11 Cover layer 12 Support substrate 14 Recording / reproducing layer group 16 Intermediate layer group 17 Buffer layer 18 Servo layer 70 Optical recording / reproducing apparatus 90 Optical pickup 101 Light source 132 of the first optical system Photo detector 170 of the first optical system Beams 191 and 192 for recording / reproducing in the first optical system Actuator 201 Light source 232 in the second optical system Photodetector 270 in the second optical system 300 Beam for reproducing in the second optical system 300 Defect 301 Film thickness variation portion 302 Recording mark Area where no columns are formed

Claims (4)

A method for reproducing an optical recording medium, comprising: a servo layer having an unevenness or groove for tracking control; and a recording / reproducing layer that is previously laminated or formed without an unevenness for tracking control. An optical recording / reproducing method, wherein tracking control is performed by adding / subtracting a focus control signal to / from a tracking control signal obtained by a phase difference detection method using a mark row or a push-pull method using a mark row. 2. The optical recording / reproducing method according to claim 1, wherein the focus control signal is multiplied by a coefficient corresponding to the amplitude of the focus control signal or the tracking control signal and added to or subtracted from the tracking control signal. 3. The optical recording / reproducing method according to claim 1, wherein the focus control signal is added to or subtracted from the tracking control signal only when the amplitude value of the focus control signal or the tracking control signal exceeds a certain threshold value. 4. The optical recording / reproducing method according to claim 1, wherein the focus control signal is added to or subtracted from the tracking control signal only immediately before the missing part of the reproduction signal.

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