JP2012226809A - Optical recording medium and drive unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical recording medium capable of improving recording density in a radial direction even if it has a separated guide layer.SOLUTION: An optical recording medium 4A includes: an information recording layer L1 that is exposed to a light beam B2 of a wavelength λ2 collected by a light collection optical system 38; and a guide layer Lg that is exposed to a light beam B1 of a wavelength λ1(λ1>λ2) collected by the light collection optical system 38. The guide layer Lg has a guide track including a pit array. The pit length is equal to or greater than a half of a diffraction limit that is determined based on the wavelength λ1 and the number of apertures of the light collection optical system 38.

Description

  The present invention relates to an optical recording medium such as an optical disk, and a drive device that performs one or both of recording and reproducing information on the optical recording medium.

  Optical discs such as CD (Compact Disc), DVD (Digital Versatile Disc: Digital Versatile Disc) and BD (Blu-ray Disc: Blu-ray Disc; registered trademark) receive information on video data, music data, etc. when irradiated with laser light. Is an information recording medium used for recording or reproducing recorded information. Optical discs continue to develop large capacities as generations increase. For example, in a CD, the thickness of a disk substrate that is a light transmitting layer is about 1.2 mm, the wavelength of a laser beam is about 780 nm, the numerical aperture NA (Numerical Aperture) of an objective lens is 0.45, and a capacity of 650 MB is realized. ing. Moreover, in DVDs of generations later than CD, the thickness of the disk substrate, which is a light transmission layer, is about 0.6 mm, the laser light wavelength is about 650 nm, and the NA is 0.6, and a capacity of 4.7 GB is realized. ing. For example, a DVD having a thickness of about 1.2 mm can be manufactured by bonding two disk substrates having a thickness of about 0.6 mm. Further, in a BD having a high recording density, the thickness of the protective layer (light transmission layer) covering the information recording surface is about 0.1 mm, the laser beam wavelength is about 405 nm, and the NA is 0.85. When the BD is a single-layer disc, a large capacity of about 25 GB is realized, and when the BD is a double-layer disc, a large capacity of about 50 GB is realized. A high-definition high-definition video is recorded on the BD for a long time. can do.

  With regard to next-generation high-definition video and stereoscopic video that exceed high-definition video, it is expected that the amount of data handled by general users will continue to increase, so large volumes of data that exceed the capacity of BD can be stored. Optical discs are desired.

  As described above, the capacity of the optical disk is increased by reducing the size of the focused spot on the focal plane of the objective lens by shortening the wavelength of the laser beam and increasing the NA of the objective lens. This has been achieved by reducing the size of the recording mark on the track. However, the miniaturization of the focused spot size has a physical limit determined by the optical performance of the objective lens and the laser beam wavelength.

  Therefore, in recent years, a multilayer optical disc having a multilayer structure in which a plurality of information recording layers are laminated at a predetermined interval in the thickness direction has been developed and marketed. For example, a two-layer optical disc (DL disc: Dual-Layer disc) having a recording capacity of about 25 GB per layer, a three-layer optical disc (TL disc: Triple Layer disc) having an improved recording capacity per layer to about 33 GB, A four-layer optical disk (QL disc: Quadruple Layer disc) with a recording capacity per layer of about 32 GB is commercially available.

  However, in such a multilayer optical disc, when the number of information recording layers is increased, it becomes difficult to perform optical design in consideration of transmittance, reflectance, and light absorption characteristics for light used for recording or reproduction. For example, when trying to access the information recording layer on the far side of the information recording layer of a multilayer optical disc that is far from the light incident surface by irradiating it with light, it is interposed between the information recording layer to be accessed and the light incident surface. A light amount loss occurs due to the reflectance and light absorption rate of the information recording layer, and it may be difficult to secure the light amount necessary for recording or reproducing information.

  In particular, in a conventional multilayer (DL, TL, or QL) optical disc, a guide groove or pit row for tracking (tracking servo) is provided in each information recording layer. As a result, there is a problem that the loss of light amount increases. Further, such diffracted light becomes unnecessary stray light in an optical system used for recording and reproducing information on an optical disk, and may cause a problem of adversely affecting recording characteristics and reproduction characteristics. Therefore, techniques for suppressing the effects of light loss and stray light due to the guide grooves and pit rows for tracking servo of such multilayer optical discs are disclosed in, for example, Non-Patent Document 1 and Patent Documents 1 to 4 below. Yes.

  Non-Patent Document 1 discloses a multilayer optical disc including a plurality of information recording layers (Recording Layers) and a guide layer (Guide Layer) having a guide track for tracking servo. The guide layer is formed as a separate layer from the information recording layer. In addition, the recording apparatus disclosed in Non-Patent Document 1 condenses the first light beam (wavelength: 655 nm) on the guide layer via the objective lens to cause the objective lens to follow the guide track, and at the same time. The second light beam (wavelength: 405 nm) is condensed on the information recording layer through the same objective lens, and information is recorded or reproduced. The effective numerical aperture NA of the objective lens for the first light beam is set to a value smaller than the effective numerical aperture NA for the second light beam. In this multilayer optical disc, since the guide track is separated from the information recording layer, the information recording layer is not provided with a guide groove or a pit row for tracking servo. For this reason, it is possible to suppress the loss of light quantity and stray light of the second light beam used for recording or reproducing information.

  Patent Documents 2 to 4 cited in Patent Document 1 also disclose optical discs having a structure similar to the guide layer separation type structure disclosed in Non-Patent Document 1.

Masaharu Nakano, et al. "Recording System for Multilayer Disk with a Separated Guide Layer", Tech. Dig of ISOM 2009, Th-I-03, pp. 230-231.

International Publication No. 2008/120354 (paragraphs 0003-0005) Japanese Patent No. 2835074 (FIGS. 1 to 3 etc.) JP 2001-307344 A (FIGS. 3 and 4, paragraphs 0033 to 0040 and paragraphs 0045 to 0049, etc.) JP 2004-241088 A (FIGS. 1 and 2, paragraphs 0016 to 0020 and paragraphs 0021 to 0024, etc.)

  In the case of the guide layer separation type optical disc structure, the first optical beam for tracking servo and the second optical beam for recording or reproducing information are simultaneously irradiated onto the multilayer optical disc. In order to detect the reflected light of the first and second light beams separately from each other by the optical system, the wavelengths of the two need to be different from each other. The wavelength of the first light beam for tracking servo is 2 longer than the wavelength of the light beam. For this reason, it is not easy to reduce the track pitch of the guide layer.

  For example, according to Non-Patent Document 1, the wavelength of the first light beam is 655 nm, the effective numerical aperture of the objective lens with respect to the wavelength of the first light beam is 0.6, and the wavelength of the second light beam is 405 nm. The effective numerical aperture of the objective lens with respect to the wavelength of the second light beam is 0.85. The track pitch of the guide track is 740 nm, which is larger than the track pitch of 320 nm for BD. For this reason, the guide layer separation type structure disclosed in Non-Patent Document 1 has a problem in that the recording density in the radial direction is low, which hinders the increase in the capacity of the optical disk.

  In view of the above, an object of the present invention is to provide an optical recording medium and a driving device that can improve the recording density in the radial direction even if it has a guide layer separation type structure.

  The optical recording medium according to the first aspect of the present invention includes a first light beam having a first wavelength and a second light beam having a second wavelength shorter than the first wavelength at different positions in the optical axis direction. An optical recording medium on which information is recorded or reproduced using a condensing optical system for condensing, and information of at least one layer that is irradiated with the second light beam condensed by the condensing optical system A recording layer; and a guide layer that is spaced apart from the information recording layer in the thickness direction of the information recording layer and receives the irradiation of the first light beam condensed by the condensing optical system, and the guide The layer has a guide track including a pit row composed of a plurality of pits, and the length of the pit in the extending direction of the guide track is determined by the first wavelength and the aperture of the condensing optical system with respect to the first wavelength. 1/2 or less of the diffraction limit determined by the number And characterized in that.

  The optical recording medium according to the second aspect of the present invention includes a first light beam having a first wavelength and a second light beam having a second wavelength shorter than the first wavelength at different positions in the optical axis direction. An optical recording medium on which information is recorded or reproduced using a condensing optical system for condensing, and information of at least one layer that is irradiated with the second light beam condensed by the condensing optical system A recording layer, and a guide layer having a guide track that is spaced apart from the information recording layer in the thickness direction of the information recording layer and receives the irradiation of the first light beam condensed by the condensing optical system; A superposition that is disposed adjacent to the guide layer in the thickness direction and generates localized light in a local region in which optical characteristics have changed due to irradiation of the first light beam condensed by the condensing optical system. And a resolution function layer.

  A driving device according to a third aspect of the present invention is a driving device that records or reproduces information on the optical recording medium, and outputs a rotation driving unit that rotates the optical recording medium and the first light beam. A first light source for emitting information, a second light source for emitting a light beam for recording or reproducing information as the second light beam, and condensing the first light beam on the guide layer. And a first optical signal for receiving a return light of the first light beam reflected by the guide layer and outputting a first detection signal. A light-receiving element; a second light-receiving element that receives the return light of the second light beam reflected by the information recording layer and outputs a second detection signal; and a tracking error based on the first detection signal A tracking controller that generates the signal and Characterized in that it comprises an actuator to follow the guide track by driving the focusing optical system in response to the tracking error signal.

  A drive device according to a fourth aspect of the present invention is a drive device for recording or reproducing information with respect to the optical recording medium, wherein the driving device rotates the optical recording medium, and emits the first light beam. A first light source for emitting information, a second light source for emitting a light beam for recording or reproducing information as the second light beam, and condensing the first light beam on the guide layer. And a first optical signal for receiving a return light of the first light beam reflected by the guide layer and outputting a first detection signal. A light-receiving element; a second light-receiving element that receives the return light of the second light beam reflected by the information recording layer and outputs a second detection signal; and a tracking error based on the first detection signal A tracking controller that generates the signal and An actuator that drives the condensing optical system according to the tracking error signal to follow the guide track, and embedded information including address information that represents a position on the guide track based on the first detection signal. Each of the pits constituting the pit row has a length corresponding to a code length according to a predetermined modulation method, and the address detection unit corresponds to the length of the pit. The embedded information is detected based on a signal waveform of the first detection signal.

  A drive device according to a fifth aspect of the present invention is a drive device for recording or reproducing information with respect to the optical recording medium, wherein the driving device rotates the optical recording medium, and emits the first light beam. A first light source for emitting information, a second light source for emitting a light beam for recording or reproducing information as the second light beam, and condensing the first light beam on the guide layer. And a first optical signal for receiving a return light of the first light beam reflected by the guide layer and outputting a first detection signal. A light-receiving element; a second light-receiving element that receives the return light of the second light beam reflected by the information recording layer and outputs a second detection signal; and a tracking error based on the first detection signal A tracking controller that generates the signal and An actuator for driving the condensing optical system in accordance with the tracking error signal to follow the guide track; and an address detecting unit for detecting embedded information based on the first detection signal; , Each of which forms a series of wobble patterns meandering at a predetermined spatial frequency, and the first light receiving element has a pair of light receiving surfaces facing each other in a direction corresponding to a direction orthogonal to the guide track. The address detection unit detects the embedded information based on a difference between detection signals respectively output from the pair of light receiving surfaces.

  According to the present invention, the recording density in the radial direction of the information recording layer can be increased even if it has a guide layer separation type structure.

It is a functional block diagram which shows roughly the main structures of the drive device of Embodiment 1 of this invention. FIG. 2A is a plan view schematically showing an example of concentric guide tracks formed on the guide layer of the multilayer optical disc according to the first embodiment, and FIG. 2B is a diagram according to the first embodiment. It is a top view which shows roughly the example of the spiral guide track formed in the guide layer of a multilayer optical disk. 1 is a cross-sectional view schematically showing the structure of a multilayer optical disc according to Embodiment 1. FIG. 2 is a perspective view schematically showing a pit row of a guide layer of the multilayer optical disc according to Embodiment 1. FIG. It is a figure which shows roughly an example of the 4-part light-receiving surface of the light receiving element which receives the reflected light from a guide layer. It is a figure which shows an example of the 4-part light-receiving surface of the light receiving element which receives the reflected light from an information recording layer. (A) is a figure which shows an example of the pit row | line | column in a guide layer in case address information is recorded by modulation of pit length. (B) is a figure which shows roughly the waveform of the reproduction signal corresponding to the pit row | line | column of (A). (A), (B) is a figure which shows an example of the pit row | line | column in the guide layer Lg when embedding information is recorded by meandering of a pit row | line. It is sectional drawing which shows roughly the structure of the multilayer optical disk based on Embodiment 2 of this invention. It is a figure which shows roughly the structural example of the light-receiving surface of the light receiving element used for a push pull method. It is sectional drawing which shows roughly the structure of the multilayer optical disk based on Embodiment 3 of this invention. 6 is a perspective view schematically showing a groove structure of a guide layer of a multilayer optical disc according to Embodiment 3. FIG. It is a figure which shows the structure of the stray light removal means which has a Kepler type optical system. It is a figure which shows an example of a spatial filter.

  Hereinafter, various embodiments of the present invention will be described with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 is a functional block diagram schematically showing a main configuration of a drive device 1 which is an optical disk system according to Embodiment 1 of the present invention. The drive device 1 has a function of recording or reproducing information on a multilayer optical disc 4A having an information recording layer group ML composed of a plurality of stacked information recording layers.

  As shown in FIG. 1, the multilayer optical disc 4A includes an information recording layer group ML and a guide layer Lg. The guide layer Lg is spaced apart from the information recording layer group ML in the thickness direction, and the information recording layer group ML. It is formed as a separate layer completely separated from. The information recording layer group ML is not provided with guide tracks such as guide grooves and pit rows for tracking servo, and the guide tracks are formed concentrically or spirally on the guide layer Lg. FIG. 2A is a plan view schematically showing concentric guide tracks TR, TR, TR,... Formed on the guide layer Lg of the multilayer optical disc 4A, and FIG. FIG. 2 is a plan view schematically showing a spiral guide track TR formed in the above.

FIG. 3 is a cross-sectional view schematically showing a part of the structure of the multilayer optical disc 4A according to the first embodiment. 3, reference numeral X _R indicates the radial direction of the multilayer optical disc 4A, the code Y _theta, shows a tangential direction of the multilayer optical disc 4A perpendicular to the radial direction X _R.

  As shown in FIG. 3, the multilayer optical disc 4A includes information recording layers L0 to L6 laminated together, a guide layer Lg, and a translucent protective layer that covers the information recording layers L0 to L6 and the guide layer Lg ( Cover layer) 401. Further, the back surface of the guide layer Lg is covered with a back surface protective layer 409. The information recording layers L0 to L6 are separated from each other by translucent intermediate layers 402 to 407, and the information recording layer L0 and the guide layer Lg are separated from each other by the translucent intermediate layer 408. In the example of FIG. 3, the information recording layers L0 to L6 are seven layers, but the number of layers is not limited.

  In the guide layer Lg, pits Pt constituting a guide track are formed. The guide layer Lg can be formed, for example, by forming a concavo-convex pattern on the surface of the substrate by embossing and forming a reflective film (not shown) such as aluminum on the concavo-convex pattern.

FIG. 4 is a perspective view schematically showing a pit row of the guide layer Lg. As shown in FIG. 4, the guide layer Lg has a plurality of pits Pt constituting each of the guide tracks TR _k−1 , TR _k , TR _{k + 1} , TR _{k + 2} ,. Each of these guide tracks TR _k−1 , TR _k , TR _{k + 1} , TR _{k + 2} ,... Extends in the tangential direction Y _θ of the multilayer optical disc 4A. As shown in FIG. 4, the guide track _{TR k-1, TR k,} TR k + 1, TR k + 2, ... are arranged at regular intervals (track pitch) lambda in the radial direction _{X R,} each pit Pt is The guide track has a length α in the extending direction. In FIG. 4, the pits Pt are illustrated as having a convex shape from the base material, but may be formed in a concave shape instead of the convex shape.

Each of the information recording layers L0 to L6 has a recording track corresponding to each of the guide tracks TR _k−1 , TR _k , TR _{k + 1} , TR _{k + 2} ,. An uneven pattern such as an information pit or an information mark of a phase change material may be formed on each recording track.

  Referring to FIG. 1, the driving device 1 includes an optical head (optical pickup) 2, a collimator lens control circuit (CL1 control circuit) 52, a tracking control circuit 53, an address detection unit 54, a rotation control unit 55, and a reproduction / recording control circuit 61. A laser driver 62, a data processing circuit 65, a collimator lens control circuit (CL2 control circuit) 66, and a focus control circuit 67. Operations of these components 2, 52 to 55, 61, 62, 65 to 67 are controlled by an MPU (Micro Processing Unit) (not shown). The MPU executes various control processes in accordance with commands received from an external host device (not shown).

  The multilayer optical disk 4A is detachably mounted on a turntable (not shown) fixed to a drive shaft (spindle) 3a of the disk rotation motor 3. The disk rotation motor 3 is driven to rotate the multilayer optical disk 4A under the control of the rotation control unit 55. The rotation controller 55 extracts a rotation pulse detection circuit 552 that extracts a pulse signal waveform representing the actual rotation speed of the multilayer optical disc 4A, and the disk rotation motor 3 so that the actual rotation speed matches the target rotation speed based on the pulse signal. A motor control circuit 551 for controlling the operation of The motor control circuit 551 can control the operation of the disk rotation motor 3 so that the scanning linear velocity of the light beam B1 with respect to the guide track is constant.

  The optical head 2 simultaneously collects and irradiates two types of light beams B1 and B2 having different wavelengths on the multilayer optical disc 4A, and returns light reflected by the guide layer Lg and the information recording layer of the multilayer optical disc 4A, respectively. It has a function to detect. The drive device 1 includes an optical head drive mechanism for positioning the optical head 2 by moving the optical head 2 in the radial direction of the multilayer optical disc 4A and its control circuit. The optical head drive mechanism and the control circuit are shown in FIG. Not shown.

  Specifically, as shown in FIG. 1, the optical head 2 is driven by a laser driver (not shown) to emit a light beam B1 having a wavelength λ1 and a laser driver 62 to drive a wavelength λ2 ( and a laser light source 29 that emits a light beam B2 of λ1> λ2). The light beam B1 is focused on the guide layer Lg of the multilayer optical disc 4A, and the light beam B2 is focused on the information recording layer to be accessed among the plurality of information recording layers of the multilayer optical disc 4A. In FIG. 1, the effective light beams of the light beams B1 and B2 are schematically shown by broken lines and solid lines, respectively.

  Further, as shown in FIG. 1, the optical head 2 has a configuration in which the light beam B1 emitted from the laser light source 21 is guided to the multilayer optical disk 4A and condensed on the guide layer Lg, as shown in FIG. CL1) 23, a wavelength selective prism 27, a polarizing beam splitter 30, a collimator lens (CL2) 34, a reflection mirror (rise mirror) 36, a quarter wavelength plate 37, and an objective lens 38.

  The light beam B 1 emitted from the laser light source 21 passes through the polarization beam splitter 22 and the collimator lens 23 in order and enters the wavelength selective prism 27. Here, the lens driving unit 24 operates under the control of the collimator lens control circuit 52, and shifts the collimator lens 23 along the optical axis direction by using, for example, a pulse motor, so that optical aberration (for example, the multilayer optical disc 4A). Correction of the focal point of the light beam B1 in the multilayer optical disc 4A can be performed. The collimator lens control circuit 52 can shift the collimator lens 23 to an appropriate position using the detection signal supplied from the light receiving element 26.

The wavelength selective prism 27 reflects the light beam B 1 having the wavelength λ 1 incident from the collimator lens 23 in the direction of the polarization beam splitter 30. The light beam B1 that has entered the polarization beam splitter 30 from the wavelength selective prism 27 passes through the polarization beam splitter 30 and the collimator lens 34 in order, is reflected by the reflection mirror 36, and enters the quarter wavelength plate 37. The light beam B1 reflected by the reflection mirror 36 is converted into circularly polarized light by the quarter-wave plate 37 and then condensed on the guide layer Lg of the multilayer optical disk 4A by the objective lens 38. At this time, as shown in FIGS. 3 and 4, the focusing spot of the light beam B1 is formed on the guide track TR _k. As shown in FIG. 4, the focused spot SP1 has a light intensity distribution D1 that forms a peak at the center.

  The return light including the diffraction component of the light beam B1 reflected by the guide layer Lg is converged by the objective lens 38, converted into linearly polarized light by the quarter wavelength plate 37, and then reflected by the reflection mirror 36 toward the collimator lens 34. reflect. Note that the magnitude relationship of the effective diameter of the objective lens 38 with respect to the light beams B1 and B2 varies depending on the design of the objective lens 38.

  The return light of the light beam B1 reflected by the reflection mirror 36 is sequentially transmitted through the collimator lens 34 and the polarization beam splitter 30, and then reflected by the wavelength selective prism 27 in the direction of the collimator lens 23. Then, the return light of the light beam B 1 is transmitted through the collimator lens 23 and then reflected by the polarization beam splitter 22 toward the condenser lens 25. The light receiving element 26 receives the return light of the light beam B1 that has passed through the condenser lens 25.

The light receiving element 26 has a four-divided light receiving surface suitable for tracking error detection by a phase difference detection (DPD: Differential Phase Detection) method. FIG. 5 is a diagram schematically illustrating an example of a four-divided light receiving surface of the light receiving element 26. A spot (light receiving spot) RS1 of the return light of the light beam B1 is formed on the four-divided light receiving surface 260. 4-split light receiving surface 260 in FIG. 5, closed the dividing line (optical dead zone) 261 in a direction X1 corresponding to the radial direction _{X R} of the multilayer optical disk 4A, a dividing line (optical dead zone) 262 orthogonal to the division line 261 In addition, there are four light receiving regions 260A to 260D defined by the dividing lines 261 and 262. These light receiving areas 260A, 260B, 260C, and 260D photoelectrically convert incident light to generate detection signals I _A , I _B , I _C , and _ID , respectively.

  The tracking control circuit 53 generates a tracking error signal TE based on the DPD method based on the detection result of the return light by the light receiving element 26, and supplies a driving signal corresponding to the tracking error signal TE to the actuator 40. The actuator 40 can shift (displace) the objective lens 38 in the radial direction of the multilayer optical disc 4A according to the drive signal. Thereby, when the detrack (track deviation) of the objective lens 38 with respect to the guide track occurs, the tracking control circuit 53 can cause the objective lens 38 to follow the guide track.

When the quadrant light receiving surface 260 of FIG. 5 is used, the tracking error signal TE by the DPD method is given by one of the following arithmetic expressions (1A) and (1B).
TE = φ (I _A + I _C ) −φ (I _B + I _D ) (1A),
TE = {φ (I _A ) −φ (I _B )} + {φ (I _C ) −φ (I _D )} (1B)

Here, φ (I) is a symbol representing the phase of the signal I. When the above formula (1A) is adopted, the addition result of the detection signals I _A and I _C output from the light receiving areas 260A and 260C diagonally opposed to the four-divided light receiving surface 260 and the light receiving areas 260B and 260 diagonally opposed to each other. A temporal phase difference between the addition result of the detection signals I _B and _ID output from 260D is generated as the tracking error signal TE. On the other hand, when the above equation (1B) is adopted, the temporal phase difference between the detection signals I _A and I _B output from the light receiving regions 260A and 260B facing the X1 direction of the four-divided light receiving surface 260, and X1 An addition result with the temporal phase difference between the detection signals I _C and _ID output from the light receiving areas 260C and 260D facing in the direction is generated as the tracking error signal TE. Regardless of which of the above formulas (1A) and (1B) is employed, when the center of the focused spot SP1 of the light beam B1 scans the center line of the pit row, the signal level of the tracking error signal TE becomes zero. Meanwhile, when the center of the focused spot SP1 scans the position shifted in the radial direction X _R from the center line of a row of pits, the signal level of the tracking error signal TE shows the signal level in accordance with the deviation.

The tracking error detection sensitivity according to the DPD method depends on the external dimensions of the pits Pt in the tangential direction Y _θ (substantially the guide track extending direction). In general, the detection sensitivity of the tracking error by the push-pull method depends on the resolution of the radial X _R of the focused spot with respect to the track pitch. Therefore, if the track pitch in the radial direction is small and the diffracted light reflected by the guide track propagates off the opening of the objective lens 38, tracking error detection by the push-pull method cannot be performed. In contrast, in the DPD method, as long as more than a predetermined SN ratio for the signal crosstalk amount between the adjacent guide tracks is obtained, it is possible to ensure high detection sensitivity without depending on the resolution of the radial X _R .

  Therefore, one of the features of the multilayer optical disc 4A in the present embodiment is that the length α of all the pits Pt of the guide layer Lg is set to ½ or more of the diffraction limit. If the effective numerical aperture of the objective lens 38 for the wavelength λ1 is NA1, it is theoretically said that the diffraction limit is given by λ1 / (2 × NA1). This diffraction limit λ1 / (2 × NA1) substantially coincides with the resolution limit of the periodic pattern in which pits and spaces of the same length are repeatedly arranged in the tangential direction of the optical disk. It is considered to be about half of the limit λ1 / (2 × NA1), that is, about λ1 / (4 × NA1).

  Therefore, by setting all the pit lengths α to be equal to or larger than the pit resolution limit λ1 / (4 × NA1), even if the track pitch Λ is reduced to near the diffraction limit λ1 / (2 × NA1), the tracking error is reduced. The recording density in the radial direction XR of the information recording layers L0 to L6 can be increased while ensuring the detection sensitivity. Therefore, even if the multilayer optical disc 4A according to the present embodiment has a guide layer separation type structure, the capacity can be further increased as compared with the conventional multilayer optical disc.

  For example, in the case where the wavelength λ1 = 655 nm for DVD and NA1 = about 0.6 as described in Non-Patent Document 1, the track pitch Λ is 640 nm or less and the diffraction limit is used. In a range larger than λ1 / (2 × NA1), the DPD method can secure a larger detection sensitivity than the push-pull method, and therefore it is desirable to apply the DPD method. Here, the amplitude of the tracking error signal obtained by the push-pull method when the track pitch Λ is 640 nm is about 3 dB lower than the amplitude of the tracking error signal obtained by the push-pull method when the track pitch Λ is 740 nm. The upper limit of the pit length α may be set to about 5 to 10 times the diffraction limit, for example.

  On the other hand, the laser driver 62 drives the laser light source 29 under the control of the reproduction / recording control circuit 61. The laser light source 29 emits a light beam B2 having a reproduction power or a recording power corresponding to the drive signal supplied from the laser driver 62. The light beam B 2 emitted from the laser light source 29 is reflected by the polarization beam splitter 30 in the direction of the lens driving unit 35, then passes through the collimator lens 34 and is reflected by the reflection mirror 36, and is reflected on the quarter wavelength plate 37. Incident.

  Here, the lens driving unit 35 operates under the control of the collimator lens control circuit 66, and shifts the collimator lens 34 along the optical axis direction by using, for example, a pulse motor, so that optical aberration (for example, the multilayer optical disc 4A) is obtained. Correction of the spherical aberration due to the thickness of the cover layer and manufacturing error), and focus control of the light beams B2 and B1 in the multilayer optical disc 4A can be performed. The collimator lens control circuit 66 can shift the collimator lens 35 to an appropriate position using the detection signal supplied from the light receiving element 32.

  The light beam B2 reflected by the reflection mirror 36 is converted into circularly polarized light by the quarter wavelength plate 37, and then is accessed by the objective lens 38 as an information recording layer Lm (m is any one of 1 to 7) of the multilayer optical disc 4A. ). The information recording layer (access layer) to be accessed is a specific information recording layer that is a target (target) of information recording or reproduction among the plurality of information recording layers L0 to L6.

  The return light of the light beam B2 reflected by the information recording layer Lm is converged by the objective lens 38, converted into linearly polarized light by the quarter wavelength plate 37, and then reflected by the reflecting mirror 36 in the direction of the collimator lens 34. The return light of the light beam B2 reflected by the reflection mirror 36 sequentially passes through the polarization beam splitter 30, the wavelength selective prism 27, and the condenser lens 31, and is then detected by the light receiving element 32.

The light receiving element 32 has a light receiving surface suitable for RF signal generation and focus error detection. As for the focus error, for example, focus error detection by a known astigmatism method can be performed. FIG. 6 is a diagram illustrating an example of a four-divided light receiving surface of the light receiving element 32. 6 has cross-shaped dividing lines 321 and 322, and has four light receiving areas 320A to 320D defined by the dividing lines 321 and 322. The light receiving areas 320A, 320B, 320C, and 320D photoelectrically convert incident light to generate detection signals K _A , K _B , K _C , and K _D , respectively. On the four-divided light receiving surface 320, a spot (light receiving spot) RS2 of the return light of the light beam B2 is formed as shown in FIG.

The data processing circuit 65 generates a reproduction RF signal based on the detection result by the light receiving element 32. Further, the data processing circuit 65 generates reproduction data by performing amplification, binarization, and demodulation processing on the reproduction RF signal using the address information detected by the address detection unit 54. When the quadrant light receiving surface 320 of FIG. 6 is used, the reproduction RF signal can be generated by adding the detection signals K _A , K _B , K _C , and K _D. That is, the reproduction RF signal can be generated according to the equation: reproduction RF signal = K _A + K _B + K _C + K _D.

The focus control circuit 67 generates a focus error signal FE based on the detection result by the light receiving element 32 and supplies a drive signal corresponding to the focus error signal FE to the actuator 40. The actuator 40 can shift the objective lens 38 in the focus direction according to the drive signal. When the quadrant light receiving surface 320 of FIG. 6 is used, the focus control circuit 67 can generate the focus error signal FE according to the following equation (2) by the astigmatism method, for example.
FE = (K _A + K _C ) − (K _B + K _D ) (2)

  On the other hand, the rotation pulse detection circuit 552 has a function of extracting a pulse signal waveform representing the actual rotation speed of the multilayer optical disc 4A based on the detection result by the light receiving element 26. Specifically, the rotation pulse detection circuit 552 can extract the pulse signal waveform based on the reflected light amount change signal (guide track reproduction signal) detected from the pit group of the guide layer Lg. The motor control circuit 551 performs, for example, PLL (Phase Locked Loop) control that uses the extracted pulse signal as an input clock and makes the phase difference between the input clock and the reference clock corresponding to the target rotation speed constant or zero. The rotational speed of the disk rotation motor 3 can be controlled. Alternatively, the motor control circuit 551 uses the extracted pulse signal as an input clock, and the phase difference between the input clock and the conversion clock generated by multiplying or dividing the reference clock corresponding to the target rotation speed is constant or zero. The rotational speed of the disk rotation motor 3 may be controlled by performing PLL control.

  Here, by adopting a simple pit row configuration in which the length α of all the pits Pt of the guide layer Lg is a fixed length, the pits of the guide layer Lg can be easily formed. Since the reproduction RF signal obtained from the column becomes a single frequency signal, there is an advantage that the circuit configuration for performing the PLL control in the motor control circuit 551 can be simplified.

  In parallel with the tracking error detection, the address detection unit 54, based on the change in the amount of return light from the guide layer Lg, previously stores address information, control information, and the like recorded on the guide track of the guide layer Lg. It has a function of detecting embedded information. The address information is information recorded in advance on the guide layer Lg in order to specify the position in the information recording layers L0 to L6. The data processing circuit 65 can perform data processing using the detected address information and control information. The reproduction / recording control circuit 61 can also perform reproduction control or recording control of information using the detected address information and control information.

  In the multilayer optical disc 4A according to the present embodiment, the embedded information is guided by modulating the pit length (pit length) of the guide layer Lg or by meandering the pit row at a predetermined spatial frequency (period). It can be recorded on the layer Lg. Since the embedded information is recorded on the guide layer Lg different from the information recording layers L0 to L6, the data recording area and the embedded information recording area can be separated from each other. Therefore, there is an advantage that the restriction on the design of the guide track and the information pit (or information mark) that carries data can be removed.

  Hereinafter, the structure of the guide layer Lg for taking advantage of such advantages will be described.

FIG. 7A is a diagram illustrating an example of a pit row in the guide layer Lg when the embedded information is recorded by modulation of the pit length. FIG. 7B is a diagram schematically showing the waveform of the reproduction signal corresponding to the pit string in FIG. The reproduction signal in FIG. 7B may be an optical intensity signal of the return light of the light beam B2. 5 is used, for example, the address detection unit 54 adds all the detection signals I _A , I _B , I _C , and I _D , and the addition result (= I _A + I _B + I). The reproduction signal shown in FIG. 7B can be generated by correcting the signal amplitude of ( _C + I _D ) with a filter.

In the pit row of FIG. 7 (A), the interval T _A, comprises three pits having a constant length a0 to produce a periodic fundamental component as a reproduction signal, the interval T _B is different from the predetermined length a0 It includes four pits having lengths a1, a2, a3, a4, respectively, the interval T _C includes three pits having a constant length a0 to produce a periodic fundamental component. Pits having a length a1, a2, a3, a4 in the section T _B is to generate a signal waveform cycle and phase of the fundamental wave component is changed. Each pit has a pit length corresponding to a code length defined by a modulation method such as MSK (Minimum-Shift-Keying) adopted in BD, for example. Further, it is possible to obtain a reproduction signal corresponding to the MSK signal by changing the signal cycle according to the pit length. Note that the modulation scheme is not limited to MSK.

  Here, if a pit length that can secure a sufficient modulation component is selected, it is not necessary to adjust the gain characteristics in a wide frequency band, and a simple equalizer circuit that gives gain only to the frequency component corresponding to the pit row is adopted. be able to. Further, if the pit length is set to be larger than λ1 / (2 × NA1), which is approximately a half of the spot diameter of the focused spot, the modulation amplitude can be ensured without employing the equalizer circuit.

  Further, if the pit length of the pit row in FIG. 7A is defined by MSK, this pit row is configured as a simple pit row with the pit length limited to, for example, three types. Thus, the pits of the guide layer Lg can be easily formed. Furthermore, when the reproduction signal obtained from the guide layer Lg is also used for the rotation speed control of the disk rotation motor 3, in order to stabilize the frequency of the reference clock used for the PLL control with respect to the rotation speed of the disk rotation motor 3. It is desirable that the difference between the lengths of the three pits is set to a fixed multiple of the physical length of the pit corresponding to the frequency of the reference clock. Thereby, a stable clock can be obtained.

Next, FIGS. 8A and 8B are diagrams illustrating an example of a pit row in the guide layer Lg when embedded information is recorded by meandering of the pit row. FIG. 8A is a diagram showing an embedding unit 80 composed of a series of wobble patterns 81 _{1 to} 81 _N (N is an integer of several tens to several hundreds) formed in the guide track TR _k of the guide layer Lg. FIG. 8B is a diagram showing a meandering state of a pit row including a part of a series of wobble patterns 81 _{1 to} 81 _N. As shown in FIG. 8 (B), a row of pits, tangential along the tangential direction Y _theta is meandering at a predetermined spatial frequency (wobble), the guide track _{TR k-1, TR k,} TR k + 1, ... Is composed of these meandering pit rows.

When the quadrant light receiving surface 260 of FIG. 5 is used, the address detection unit 54 performs filtering (waveform shaping) by filtering the push-pull signal PP (= (I _A + I _D ) − (I _B + I _C )). A wobble signal having a waveform corresponding to the wobble pattern of 8 (B) can be generated.

  8A and 8B, a configuration corresponding to an ADIP (Address In Pregroove) unit employed in BD can be realized. ADIP employs a wobble track structure in which guide grooves of a certain depth meander, and each ADIP unit has two MSK (Minimum-Shift-Keying) elements and 37 STWs (Saw-Tooth-Wobble). ) Element. On the other hand, in this embodiment, since the meandering structure of the pit row is adopted, the embedding unit 80 in FIG. 8A is called an AIWP (Address In Wobbling Pit) unit. By changing the spatial frequency (cycle) and phase of each wobble pattern, it is possible to generate a wobble signal corresponding to an MSK signal or STW signal.

  Although all the pits Pt in FIG. 8B have a fixed length, the length of the pits Pt may be modulated instead or may be a random length. Good. Further, the embedded information may be recorded in advance in the guide layer Lg by combining the above-described meandering of the pit row and modulation of the pit length.

  FIG. 8B shows only the state of the meandering of the pit row, but in reality, the longitudinal direction of each pit coincides with the tangential direction of the locus where the pit row meanders. It may be formed as follows. Further, in FIG. 8B, all the meandering phases of adjacent pit rows are illustrated, but in actuality, the phase may be shifted for each guide track.

As described above, the multilayer optical disc 4A according to the first embodiment has the guide layer separation type structure, but all the pits Pt formed on the guide track of the guide layer Lg have the wavelength of the light beam B1. It is formed so as to have a pit length equal to or greater than the resolution limit (1/2 of the diffraction limit) determined by λ1 and the effective numerical aperture NA1 of the objective lens 38 for this wavelength λ1. Therefore, it is possible to sufficiently secure the detection sensitivity of a tracking error when applying the DPD method, moreover, it is possible to increase the recording density in the radial direction X _R of the information recording layer L0 to L6. Therefore, even if the multilayer optical disc 4A according to the present embodiment has a guide layer separation type structure, the capacity can be further increased as compared with the conventional multilayer optical disc.

  In a conventional optical disc such as a BD, a short pit length is employed so that data can be recorded with high density, and the amplitude of a reproduction signal is generally very small. Therefore, there is a limitation that the pit cannot be set long so that the detection sensitivity of the DPD method is prioritized at the expense of data reproduction performance and recording density. On the other hand, the multilayer optical disc 4A according to the present embodiment has an advantage that, as described above, a design optimized for tracking error detection by the DPD method is possible regardless of the reproduction signal.

  Further, the guide layer Lg is separated from the information recording layers L0 to L6, and a pit Pt having a length α not less than the resolution limit may be formed on the guide layer Lg. For this reason, the fine processing for forming a short pit according to the fine structure of the information recording layers L0 to L6 is not required. In addition, the pit length of the guide layer Lg can be made larger than the length of the information marks or information pits formed on the information recording layers L0 to L6. Therefore, compared with a conventional optical disc such as BD, the processing accuracy or molding accuracy related to the guide layer Lg can be relaxed. Therefore, the multilayer optical disc 4A can be manufactured at low cost.

  In the present embodiment, the rotation control unit 55 can accurately perform the rotation control of the multilayer optical disc 4A based on the reflected light amount change signal (guide track reproduction signal) detected from the pit row of the guide layer Lg. .

  Further, in the multilayer optical disc 4A of the present embodiment, address information, control information, etc. are obtained by modulating the pit length of the guide layer Lg or by meandering the pit row at a predetermined spatial frequency (period). The embedded information can be recorded in the guide layer Lg. For this reason, the address detection unit 54 of the driving device 1 can detect the embedded information. The data processing circuit 65 can perform data processing using the detected embedded information, and the reproduction / recording control circuit 61 can perform reproduction control and recording control using the detected embedded information.

  Since the embedded information is recorded in a guide layer Lg different from the information recording layers L0 to L6, the signal amplitude detected by the light receiving element 26 can be increased by setting the pit length to a large value. Therefore, even when the radial track pitch Λ is set to a small value, the tracking error detection sensitivity by the DPD method can be increased.

Embodiment 2. FIG.
Next, a second embodiment according to the present invention will be described. Since the configuration of the drive device of the present embodiment is almost the same as the configuration of the drive device 1 of the first embodiment, the second embodiment will be described below with reference to FIG. The drive device 1 of the present embodiment can reproduce or record information on a multilayer optical disc having a super-resolution function layer.

  FIG. 9 is a diagram schematically showing a cross-sectional structure of a multilayer optical disc 4B having the super-resolution functional layer Ls according to the second embodiment. As shown in FIG. 9, the multilayer optical disc 4B includes the laminated information recording layers L0 to L6, the guide layer Lgp, the super-resolution functional layer Ls adjacent to the guide layer Lgp, and the information recording layers L0 to L0. It has a translucent protective layer (cover layer) 401 that covers L6, the guide layer Lgp, and the super-resolution functional layer Ls. The back surface of the guide layer Lgp is covered with a back surface protective layer 409. The information recording layers L0 to L6 are separated from each other by translucent intermediate layers 402 to 407, and the super-resolution functional layer Ls is interposed between the guide layer Lgp and the information recording layers L0 to L6. In the example of FIG. 9, the information recording layers L0 to L6 are seven layers, but the number of layers is not limited to this.

  The multilayer optical disc 4B has the same structure as the guide layer Lg of the first embodiment except for the dimensions of the super-resolution functional layer Ls and the guide layer Lgp. However, for the pits formed in the guide layer Lgp, the lengths of all the pits do not have to be greater than or equal to the resolution limit (1/2 of the diffraction limit) due to the presence of the super-resolution function layer Ls.

  When the super-resolution functional layer Ls is irradiated with the light beam B1, the optical characteristics of the super-resolution functional layer Ls are temporarily changed in a local region having a high light intensity or a high temperature at the focused spot of the light beam B1. Change. The super-resolution functional layer Ls generates localized light such as near-field light and localized plasmon light in the local region. This localized light is converted into propagating light (returned light) by interacting with the fine structure (pit array or the like) of the guide track of the guide layer Lgp.

  The super-resolution functional layer Ls is made of a material whose optical characteristics (light absorption characteristics, light transmission / reflection characteristics, and light scattering characteristics) change nonlinearly according to the light intensity of the light beam B1, and the condensing spot of the light beam B1. It has a non-linear light absorption characteristic or a non-linear light characteristic in which an optical characteristic such as a refractive index changes during irradiation. The super-resolution functional layer Ls can be formed of, for example, a semiconductor material, a phase transition material, or a metal oxide material. For example, when the laser beam is condensed and irradiated, the super-resolution functional layer Ls changes its optical characteristics in a local region smaller than the diffraction limit to form an optical minute aperture. Light (near field light) leaks out. As a result, the reproduction resolution by the focused spot is increased, and a guide track having a track pitch smaller than the diffraction limit λ1 / (2 × NA1) determined by the numerical aperture NA1 of the objective lens 38 and the wavelength λ1 can be detected. Become.

  For the light absorption characteristics, light transmission reflection characteristics, and light scattering characteristics given as an example of the optical characteristics of the super-resolution functional layer material that gives high resolution to the condensing spot of the light beam B1, the super-resolution functional layer Ls Changes in transmittance, reflectance, and absorptance may be increased or decreased depending on the intensity of the laser beam. Any change in the optical characteristics of light absorption characteristics, light transmission reflection characteristics, and light scattering characteristics may occur in a region smaller than the focused spot.

  The super-resolution functional layer material can be formed of, for example, a Ge—Sb—Te, Ag—In—Sb—Te, Sb—Te, or In—Sb material. Alternatively, a metal oxide material such as ZnO may be used. In addition to the material layer having the super-resolution function, in order to adjust the amount of reflected light from the heat dissipation function layer or the heat absorption function layer or the guide layer Lgp, An interference layer or a dielectric layer for preventing flow and enhancing durability may be provided. The interference layer has both a function of causing multiple interference of light and a function of preventing thermal diffusion. The interference layer can be formed of, for example, AlN, GeN, or ZrO2. By providing the dielectric layer and the interference layer, it is possible to improve the reproduction durability of the super-resolution functional layer. The laminated structure including the super-resolution functional layer Ls, the interference layer, and the dielectric layer is not particularly limited, and the number of films, constituent materials, and the like are not particularly limited. If these interference layers and dielectric layers are laminated on the front side closer to the incident surface of the light beam B1 than the super-resolution functional layer Ls and / or the opposite side (back side) of the incident surface, Good.

  When the super-resolution functional layer Ls is provided, the effective resolution of the condensing spot of the light beam B1 can be increased. Therefore, the wavelength λ1 is longer than the wavelength λ2 of the information recording or reproducing light beam B2. Even when the light beam B1 is used, the track pitch Λ can be set to a small value. Thereby, the recording density in the radial direction of the multilayer optical disc 4B can be increased.

  At the same time, the resolution of the super-resolution functional layer Ls is improved in the tangential direction, so that the modulation signal amplitude of the guide track reproduction signal is further increased. In the case of detecting a signal, there is an advantage that the detection sensitivity is further improved.

  For example, the diffraction limit λ1 / (2 × NA1) when the wavelength λ1 of the light beam B1 irradiated to the guide layer Lgp is 655 nm and the effective numerical aperture NA1 of the objective lens 38 with respect to the wavelength λ1 of the light beam B1 is 0.60. ) Is about 564 nm. Further, the diffraction limit when the wavelength λ2 of the light beam B2 irradiated to any one of the information recording layers L0 to L6 is 405 nm and the effective numerical aperture NA2 of the objective lens 38 with respect to the wavelength λ2 of the light beam B2 is 0.85. λ2 / (2 × NA2) is about 238 nm. In Non-Patent Document 1, even if a light beam with a short wavelength of 405 nm irradiated on the information recording layer is used, the guide is limited by the diffraction limit determined by the light beam with a wavelength of 655 nm irradiated on the guide layer and the numerical aperture of the objective lens. The track pitch of the layer is limited, and the track pitch of the guide track is set to 740 nm. Since the track pitch in BD is 320 nm, the recording density in the radial direction of the guide layer separation type structure of Non-Patent Document 1 is low.

  On the other hand, in the multilayer optical disc 4B of the present embodiment, the effective resolution of the light beam B1 can be improved and the recording density in the radial direction can be increased. For example, when the super-resolution functional layer Ls is configured using a phase change material such as InSb, GeSbTe, or AgInSbTe, the track pitch Λ can be reduced to about 370 nm if the resolution can be increased by about twice. it can.

  The super-resolution functional layer Ls in FIG. 9 is formed on the near side closer to the incident surface of the light beam B1 than the guide layer Lgp, but is not limited to this and is opposite to the incident surface. A super-resolution functional layer may be formed on the side (back side), or a super-resolution functional layer may be formed on both the near side and the opposite side.

  Further, a super-resolution function layer adjacent to all of the information recording layers L0 to L6 or any one of the information recording layers L0 to L6 may be provided to increase the data recording density.

  The multilayer optical disc 4B according to the present embodiment has substantially the same structure as the guide layer Lg of the first embodiment except for the dimensions of the super-resolution functional layer Ls and the guide layer Lgp. The same effects as those of the multilayer optical disc 4A of the first embodiment can be obtained. Further, since the multilayer optical disk 4B of the present embodiment has the super-resolution functional layer Ls, the reproduction resolution is improved, so that the modulation can be obtained with the reproduction resolution of the super-resolution functional layer Ls. A part of pits having a length less than the diffraction limit may be included, and the same effect as the multilayer optical disc 4A of the first embodiment can be obtained. Furthermore, since the multilayer optical disc 4B of the present embodiment has the super-resolution functional layer Ls, the recording density in the radial direction can be further increased.

Although tracking error detection for the multilayer optical disc 4B of the present embodiment is preferably performed by the DPD method, the tracking error signal may be detected by using a push-pull method instead of the DPD method. As the push-pull method, a three-beam type push-pull method or a one-beam type push-pull method can be used. The three-beam type push-pull method (DPP method) uses one main beam (for example, zero-order transmitted diffracted light beam) and two sub beams (for example, from the light beam B1 to be irradiated to the guide layer Lg of the optical disc. This is a system that uses a light separation element (not shown) such as a diffraction grating that separates the first-order transmitted diffraction light beam. For example, the irradiation positions of the two sub beams on the guide layer Lg are symmetrical with respect to the irradiation position of the main beam, are separated from each other in the tangential direction Y _θ of the multilayer optical disc 4A, and are radial. It is adjusted so as to be separated from one another by about 1/2 track pitch in the direction X _R. For example, a light separation element can be disposed in the optical path between the laser light source 21 and the polarization beam splitter 22. On the other hand, the one-beam push-pull method uses, for example, a light beam B1 reflected by the guide layer Lg using a light separation element such as a hologram element disposed in the optical path between the polarization beam splitter 22 and the light receiving element 26. In this system, the 0th-order diffracted light beam and the ± 1st-order diffracted light beam are separated from the return light and received by the light receiving element 26. Regardless of whether the 3-beam type or the 1-beam type push-pull method is used, the DC component (direct current) of the tracking error signal caused by the offset component generated when the objective lens 38 is displaced with respect to the light receiving element 26 (objective lens shift). Component) variation can be suppressed.

FIG. 10 is a diagram schematically showing a configuration example of the light receiving surface of the light receiving element 26 used in the three-beam push-pull method. The light receiving surface of FIG. 10 includes a main light receiving surface 260 that receives the spot RS1m of the return light of the main beam, a sub light receiving surface 263 that receives the spot RS1a of one of the two sub beams, and two light receiving surfaces. And a sub light receiving surface 265 for receiving the other return light spot RS1b of the sub beams. From these main receiving surface 260 and the auxiliary light-receiving surface 263, 265 are arranged in a direction X1 corresponding to the radial direction _{X R} of the multilayer optical disc 4A. The main light receiving surface 260 in FIG. 10 is the same as the four-part light receiving surface 260 in FIG. 5 and can be applied to the DPD method and the astigmatism method. One sub light receiving surface 263 is divided into two light receiving regions 263E and 263F with a dividing line 264 as a boundary, and the other sub light receiving surface 265 has two light receiving regions 265G and 265H with a dividing line 266 as a boundary. It is divided into These light receiving regions 263E, 263F, 265G, and 265H photoelectrically convert incident light to generate detection signals I _E , I _F , I _G , and I _H , respectively.

The tracking error signal TE by the push-pull method is given by the following equations (3), (3a), (3b).
TE = MPP-k × SPP (3)
MPP = (I _A + I _D ) − (I _B + I _C ) (3a)
_{SPP = (I E -I F)} + (I G -I H) ··· (3b)

  Here, k is a gain coefficient. MPP represents a main push-pull signal, and SPP represents a sub push-pull signal. The main push-pull signal MPP and the sub push-pull signal SPP have the same phase with respect to the objective lens shift. That is, when the MPP signal level increases, the SPP signal level also increases, and when the MPP signal level decreases, the SPP signal level also decreases. For this reason, the offset component resulting from the objective lens shift is obtained as a signal component k × SPP. Therefore, the tracking error signal TE in which the offset component due to the objective lens shift is canceled can be generated by appropriately adjusting the gain coefficient k and amplifying the sub push-pull signal SPP.

Embodiment 3 FIG.
Next, a third embodiment according to the present invention will be described. The multilayer optical disc 4B according to the second embodiment is an example in which the guide track of the guide layer Lgp is constituted by a pit row, but the guide track may be constituted by a groove structure instead of the pit row. The multilayer optical disc according to Embodiment 3 has a guide track having a groove structure.

  FIG. 11 is a diagram schematically showing a cross-sectional structure of a multilayer optical disc 4C according to the third embodiment. The configuration of the drive device of the present embodiment is substantially the same as the configuration of the drive device 1 of the first embodiment, and therefore the third embodiment will be described below with reference to FIG. The drive device according to the present embodiment can reproduce or record information on the multilayer optical disc 4C.

  As shown in FIG. 11, the multilayer optical disc 4C includes the laminated information recording layers L0 to L6, the guide layer Lgg, the super-resolution functional layer Ls adjacent to the guide layer Lgg, and the information recording layers L0 to L0. It has a translucent protective layer (cover layer) 401 that covers L6, the guide layer Lgg, and the super-resolution functional layer Ls. Further, the back surface of the guide layer Lgg is covered with a back surface protective layer 409. The information recording layers L0 to L6 are separated from each other by translucent intermediate layers 402 to 407, and the super-resolution functional layer Ls is interposed between the guide layer Lgg and the information recording layers L0 to L6. In the example of FIG. 11, the information recording layers L0 to L6 are seven layers, but the number of layers is not limited.

  This multilayer optical disc 4C has the same structure as the multilayer optical disc 4B of the second embodiment except for the guide layer Lgg. Further, the function and constituent material of the super-resolution functional layer Ls of the multilayer optical disc 4C are the same as the function and constituent material of the super-resolution functional layer Ls of the multilayer optical disc 4B according to the second embodiment. Therefore, the super-resolution functional layer Ls of the multilayer optical disc 4C is made of a material whose optical characteristics (light absorption characteristics, light transmission / reflection characteristics, and light scattering characteristics) change nonlinearly in accordance with the light intensity of the light beam B1. While receiving the focused spot of the beam B1, it has a non-linear light absorption characteristic or a non-linear light characteristic in which an optical characteristic such as a refractive index changes.

  When the super-resolution functional layer Ls of the multilayer optical disc 4C is irradiated with the light beam B1, the optical characteristics of the super-resolution functional layer Ls in a local region where the light intensity of the condensed spot of the light beam B1 is high or the temperature is high. Changes temporarily. The super-resolution functional layer Ls generates localized light such as near-field light and localized plasmon light in the local region. This localized light is converted into propagating light (returned light) by interacting with the fine structure (such as a pit row) of the guide track of the guide layer Lgg. As a result, the reproduction resolution by the focused spot is increased, and a guide track having a track pitch smaller than the diffraction limit λ1 / (2 × NA1) determined by the numerical aperture NA1 of the objective lens 38 and the wavelength λ1 can be detected. Become.

FIG. 12 is a perspective view schematically showing a groove structure constituting a guide track of the guide layer Lgg of the multilayer optical disc 4C according to the third embodiment. As shown in FIG. 12, the guide layer Lgg, a guide track _{GT k-1, GT k,} GT k + 1, GT k + 2, chromatic and groove 410G and lands 410L extending ... configured in the tangential direction Y _theta and doing. Guide track _{GT k-1, GT k,} GT k + 1, GT k + 2, ... are arranged at regular intervals (track pitch) lambda in the radial direction _{X R.} Such a guide layer Lgg is irradiated with the light spot LS1 of the localized light LB1 having the light intensity distribution LD1 generated in the super-resolution functional layer Ls.

  In the present embodiment, the tracking control circuit 53 uses the groove 410G as a guide track and causes the light spot LS1 to follow the approximate center line of the groove 410G. Instead, the land 410L is used as a guide track. The light spot LS1 may be made to follow the target with the approximate center line of the land 410L.

  Further, as in the case of the second embodiment, the super-resolution functional layer Ls in FIG. 11 is formed on the near side closer to the incident surface of the light beam B1 than the guide layer Lgg, but is limited to this. The super-resolution functional layer may be formed on the opposite side (back side) to the incident surface, or the super-resolution functional layer may be formed on both the near side and the opposite side. . Furthermore, a super-resolution functional layer adjacent to all of the information recording layers L0 to L6 or any one of the information recording layers L0 to L6 may be provided to increase the data recording density.

Based on the change in the amount of return light from the guide layer Lgg, the address detection unit 54 stores address information or the like recorded in advance on the guide tracks GT _k−1 , GT _k , GT _{k + 1} , GT _{k + 2} ,. It has a function of detecting embedded information such as control information. The address information is information recorded in advance on the guide layer Lgg in order to specify the position in the information recording layers L0 to L6. The data processing circuit 65 can perform data processing using the detected address information and control information. The reproduction / recording control circuit 61 can also perform reproduction control or recording control of information using the detected address information and control information.

  As shown in FIG. 12, the groove 410G wobbles at a spatial frequency defined by a modulation method such as MSK or STW. Therefore, the address detection unit 54 generates a push-pull signal based on the detection signal supplied from the light receiving element 26, and filters (waveform shaping) the push-pull signal, thereby corresponding to the spatial frequency of the groove 410G. A wobble signal having a waveform can be generated. The address detection unit 54 can detect embedded information such as address information and control information from the wobble signal. For example, a groove structure can be formed by adopting an address management method by pre-groove wobbling adopted in DVD + R and BD. Alternatively, a land structure with land pre-pits may be formed by using an address management method using land pre-pits as used in DVD-R.

In the present embodiment, tracking error detection may be performed using either the DPD method or the push-pull method described above. For example, tracking error detection can be performed by the DPD method using the light receiving surface of FIG. 5 or the three-beam push-pull method using the light receiving surface of FIG. In this case, the address detection unit 54 push-pull signal (= I _A + I _D ) − (I _B + I _C ) corresponding to the difference between the received light amounts in the light receiving regions 260A and 260D and the received light amounts in the light receiving regions 260B and 260C. )) Can be obtained as a wobble signal.

  As described above, in the third embodiment, the super-resolution functional layer Ls can increase the effective resolution of the focused spot of the light beam B1, so that the light beam B2 for recording or reproducing information is used. Even when the light beam B1 having the wavelength λ1 longer than the wavelength λ2 is used, the track pitch Λ can be set to a small value. Thereby, the recording density in the radial direction of the multilayer optical disc 4C can be increased.

  For example, when the resolution in the radial direction is set to about 2.32 times or more due to the super-resolution effect, the condensing optical system equivalent to that of DVD (the wavelength λ1 of the light beam B1 is 655 nm, and the effective numerical aperture of the objective lens 38 is While using NA1 of 0.60), the track pitch can be reduced to 320 nm, which is the same as that of the conventional BD disc, or less. For example, when the super-resolution functional layer Ls is configured using a phase change material such as InSb, GeSbTe, or AgInSbTe, the track pitch Λ can be reduced to about 370 nm if the resolution can be increased by about twice. it can.

Modifications of the first to third embodiments.
Although various embodiments according to the present invention have been described above with reference to the drawings, these are examples of the present invention, and various forms other than the above can be adopted. For example, the optical system that propagates the light beams B1 and B2 in the driving apparatus 1 of FIG. 1 shows an example thereof, and the present invention is not limited to this. Furthermore, although only the main components of the drive device 1 are shown in FIG. 1, the drive device 1 may have other components.

  The driving device 1 preferably has stray light removing means for removing light (stray light) reflected from the information recording layers L0 to L6 other than the information recording layer to be accessed. Such stray light is unnecessary for servo error detection (such as tracking error detection and focus error detection) and reproduction signal detection. FIG. 13 is a diagram showing a configuration of stray light removing means having a Kepler type optical system. The stray light removing unit in FIG. 13 includes two lenses 42 and 43 and a spatial filter 44 disposed at the condensing point of these lenses 42 and 43. As the spatial filter 44, for example, one having a pinhole 44p as shown in FIG. 14 can be used, but a diffraction grating may be used instead. Such stray light removing means may be inserted between the collimator lens 34 and the reflection mirror 36, for example.

  The drive device 1 can also be incorporated in electronic equipment such as a personal computer, a workstation, an audio device, or a digital broadcast recording device.

  DESCRIPTION OF SYMBOLS 1 Drive apparatus, 2 Optical head (optical pick-up), 3 Disc rotation motor, 4A, 4B, 4C Multilayer optical disk (optical recording medium), L0-L6 information recording layer, Lg, Lgp, Lgg guide layer, Ls super-resolution function Layer, 401 protective layer (cover layer), 402 to 408 intermediate layer, 409 back surface protective layer, 21 laser light source, 22 polarization beam splitter, 23 collimator lens (CL1), 24 lens driving unit, 25 condensing lens, 26 light receiving element , 260 four-divided light receiving surface, 260A to 260D light receiving region, 263, 265 sub light receiving surface (two-divided light receiving surface), 263E, 263F, 265G, 265H light receiving region, 27 wavelength selective prism, 29 laser light source, 30 polarization beam splitter , 31 condenser lens, 32 light receiving element, 34 collimator lens (CL2), 35 lens drive unit, 36 reflecting mirror, 37 1/4 wavelength plate, 38 objective lens, 39 lens holder, 40 actuator, 52 collimator lens control circuit (CL1 control circuit), 53 tracking control circuit, 54 address detection unit, 55 rotation control unit, 551 motor control circuit, 552 rotation pulse detection circuit, 61 reproduction / recording control circuit, 62 laser driver, 65 data processing circuit, 66 collimator lens control circuit (CL2 control circuit), 67 focus control circuit.

Claims (18)

Information recording using a condensing optical system that condenses a first light beam having a first wavelength and a second light beam having a second wavelength shorter than the first wavelength at different positions in the optical axis direction. Or an optical recording medium to be reproduced,
At least one information recording layer that is irradiated with the second light beam condensed by the condensing optical system;
A guide layer that is spaced apart from the information recording layer in the thickness direction of the information recording layer and receives the irradiation of the first light beam condensed by the condensing optical system,
The guide layer has a guide track including a pit row composed of a plurality of pits,
The length of the pit in the extending direction of the guide track is ½ or more of a diffraction limit determined by the first wavelength and the numerical aperture of the condensing optical system with respect to the first wavelength.
An optical recording medium characterized by the above.   2. The optical recording medium according to claim 1, wherein an optical characteristic is changed by irradiation of the first light beam disposed adjacent to the guide layer in the thickness direction and condensed by the condensing optical system. An optical recording medium, further comprising a super-resolution functional layer that generates localized light in a localized region.   3. The optical recording medium according to claim 1, wherein when the first wavelength is λ and the numerical aperture of the condensing optical system with respect to the first wavelength is NA, the diffraction limit is λ / ( 2NA), an optical recording medium characterized by   4. The optical recording medium according to claim 1, wherein the guide track has a track pitch of 640 nm or less and larger than the diffraction limit. 5. Information recording using a condensing optical system that condenses a first light beam having a first wavelength and a second light beam having a second wavelength shorter than the first wavelength at different positions in the optical axis direction. Or an optical recording medium to be reproduced,
At least one information recording layer that is irradiated with the second light beam condensed by the condensing optical system;
A guide layer having a guide track that is spaced apart from the information recording layer in the thickness direction of the information recording layer and receives the irradiation of the first light beam condensed by the condensing optical system;
A superposition that is disposed adjacent to the guide layer in the thickness direction and generates localized light in a local region in which optical characteristics have changed due to irradiation of the first light beam condensed by the condensing optical system. An optical recording medium comprising a resolution functional layer.   6. The optical recording medium according to claim 5, wherein the guide track is composed of a pit row composed of a plurality of pits.   6. The optical recording medium according to claim 5, wherein the guide track has a groove structure having a groove and a land. An optical recording medium according to any one of claims 1 to 4 and claim 6,
Each of the pits has a length corresponding to a code length according to a predetermined modulation method,
The pit row has embedded information corresponding to the length of the pit.
An optical recording medium characterized by the above.   7. The optical recording medium according to claim 1, wherein each of the pit rows forms a series of wobble patterns each meandering at a predetermined spatial frequency. An optical recording medium having embedded information corresponding to a pattern.   10. The optical recording medium according to claim 1, wherein the guide track is formed concentrically or spirally in the guide layer. 11. The optical recording medium according to any one of claims 1 to 10,
A protective layer covering the information recording layer and having incident surfaces for the first light beam and the second light beam collected by the condensing optical system;
The guide layer is disposed on the side opposite to the incident surface with respect to the information recording layer.
An optical recording medium characterized by the above.   12. The optical recording medium according to claim 1, wherein the information recording layer is composed of two or more layers. A drive device for recording or reproducing information with respect to the optical recording medium according to any one of claims 1 to 12,
A rotation drive unit for rotating the optical recording medium;
A first light source that emits the first light beam;
A second light source for emitting a light beam for recording or reproducing information as the second light beam;
The condensing optical system for condensing the first light beam on the guide layer and condensing the second light beam on the information recording layer;
A first light receiving element that receives the return light of the first light beam reflected by the guide layer and outputs a first detection signal;
A second light receiving element for receiving a return light of the second light beam reflected by the information recording layer and outputting a second detection signal;
A tracking control unit that generates a tracking error signal based on the first detection signal;
An actuator for driving the condensing optical system in accordance with the tracking error signal so as to follow the guide track; The drive device according to claim 13,
The first light receiving element has a four-divided light receiving surface;
The tracking control unit generates the tracking error signal by a phase difference detection method;
A drive device characterized by that. A drive device for recording or reproducing information on an optical recording medium according to any one of claims 1 to 4 and claim 6,
A rotation drive unit for rotating the optical recording medium;
A first light source that emits the first light beam;
A second light source for emitting a light beam for recording or reproducing information as the second light beam;
The condensing optical system for condensing the first light beam on the guide layer and condensing the second light beam on the information recording layer;
A first light receiving element that receives the return light of the first light beam reflected by the guide layer and outputs a first detection signal;
A second light receiving element for receiving a return light of the second light beam reflected by the information recording layer and outputting a second detection signal;
A tracking control unit that generates a tracking error signal based on the first detection signal;
An actuator that drives the condensing optical system according to the tracking error signal to follow the guide track;
An address detection unit for detecting embedded information including address information indicating a position on the guide track based on the first detection signal;
Each of the pits constituting the pit row has a length corresponding to a code length by a predetermined modulation method,
The address detection unit detects the embedding information based on a signal waveform of the first detection signal corresponding to the length of the pit;
A drive device characterized by that. A drive device for recording or reproducing information on an optical recording medium according to any one of claims 1 to 4 and claim 6,
A rotation drive unit for rotating the optical recording medium;
A first light source that emits the first light beam;
A second light source for emitting a light beam for recording or reproducing information as the second light beam;
The condensing optical system for condensing the first light beam on the guide layer and condensing the second light beam on the information recording layer;
A first light receiving element that receives the return light of the first light beam reflected by the guide layer and outputs a first detection signal;
A second light receiving element for receiving a return light of the second light beam reflected by the information recording layer and outputting a second detection signal;
A tracking control unit that generates a tracking error signal based on the first detection signal;
An actuator that drives the condensing optical system according to the tracking error signal to follow the guide track;
An address detector for detecting embedded information based on the first detection signal,
The pit row forms a series of wobble patterns each meandering at a predetermined spatial frequency,
The first light receiving element has a pair of light receiving surfaces facing each other in a direction corresponding to a direction orthogonal to the guide track,
The address detection unit detects the embedded information based on a difference between detection signals output from the pair of light receiving surfaces, respectively.
A drive device characterized by that.   17. The drive device according to claim 13, wherein a rotation control signal is generated based on the first detection signal, and the optical recording medium is rotated based on the rotation control signal. A drive device further comprising a rotation control unit for controlling speed.   18. The driving apparatus according to claim 17, wherein the rotation control unit controls a rotation speed of the optical recording medium so that a linear velocity of the first light beam with respect to the guide track is constant. A drive device.

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