JP2014179139A - Optical recording medium and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multi-layered optical recording medium capable of recording and reproducing information by using any recording layer while ensuring amount of light beam which reaches the deepest layer.SOLUTION: The optical recording medium includes: a substrate; a first recording area disposed over the substrate including a recording layer and an optically transparent spacer layer, which are alternately laminated in plural layers; a reference layer disposed over the recording area formed with recesses and protrusions which are used as a reference for tracking; a second recording area further disposed over the reference layer including a recording layer and an optically transparent spacer layer, which are laminated in plural layers; an optically transparent cover layer disposed over the second recording area; and plural sets of marks corresponding to the recesses and protrusions disposed on every recording layers of the first and second recording areas.

Description

  The present invention relates to an optical recording medium and the like, and more particularly to an optical recording medium capable of super multi-layer recording with 10 or more recording layers.

  As a large-capacity optical recording medium, a multilayer optical disc having a plurality of information recording layers stacked with a light-transmitting spacer layer interposed therebetween is known (see, for example, Patent Document 1).

  FIG. 18 shows an optical disc structure having six recording layers. This is done by preparing a polycarbonate (PC) substrate 1000 having a thickness of 1.1 mm with irregularities to be track grooves formed on the surface, and sputtering the L0 recording layer 1001 on the surface having the irregularities to be track grooves. To form. The L0 recording layer 1001 includes a recording film and dielectric layers arranged on both sides thereof as shown in the drawing of the detailed portion, and a metal reflective layer is provided between the dielectric layer on one side and the substrate 1000. It has been. A spacer layer 1002 is formed on the L0 recording layer 1001, and an L1 recording layer 1003 is further formed thereon. Similarly, the spacer layers (1004, 1006, 1008, 1010) and the recording layers (1005, 1007, 1009, 1011) are alternately formed to constitute the L2 to L5 recording layers. A cover layer 1012 is formed on the L5 recording layer 1011. Each spacer layer has a thickness of about 10 to 30 μm and is formed of an ultraviolet curable resin. Each spacer layer is formed using a 2P method and / or a sheet-like nanoprint method, and a track groove similar to the track groove formed on the PC substrate 1000 is formed on each surface.

  By irradiating the cover layer 1012 side with the laser beam 1013 from the optical pickup and writing / reading information to / from the necessary recording layer, information is written / reproduced on / from the optical disc. For this tracking, track grooves in which irregularities are formed in each recording layer are used (see, for example, Patent Document 2).

JP 2004-213720 A JP 2009-110557 A

  However, the conventional configuration requires a track groove for controlling the tracking of the optical pick for each recording layer. When the recording layer is made multilayer, the light beam from the optical pick is diffracted by the influence of the track groove. However, the loss due to this diffraction increases each time it passes through the layer. For this reason, when the number of recording layers is increased to, for example, four or more layers, the amount of light beam reaching the deepest layer is greatly reduced, and information recording and reproduction cannot be performed as the recording layer becomes closer to the deepest layer. .

  The present invention solves the above-described conventional problems, and provides an optical recording medium capable of recording / reproducing information in any recording layer without greatly reducing the amount of light beam reaching the deepest layer even when the number of layers is increased. The purpose is to do.

  In order to solve the conventional problems, an optical recording medium of the present invention includes a substrate and a first recording region in which a plurality of recording layers and optically transparent spacer layers are alternately stacked on the substrate. A reference layer provided with a concavo-convex portion serving as a reference for tracking on the recording region, and a plurality of recording layers and optically transparent spacer layers alternately stacked on the reference layer; A recording layer, an optically transparent cover layer is disposed on the second recording area, and a set of marks corresponding to the concavo-convex portions on all the recording layers of the first and second recording areas. It is characterized by having a plurality.

  The method for producing an optical recording medium of the present invention includes a substrate, a first recording area in which a plurality of recording layers and optically transparent spacer layers are alternately stacked on the substrate, and the recording area. Arranged is a reference layer provided with a concavo-convex portion serving as a reference for tracking, and a second recording region in which a plurality of recording layers and optically transparent spacer layers are alternately stacked on the reference layer. In the method for manufacturing an optical recording medium, a mark corresponding to the concavo-convex portion is recorded on each recording layer in the first and second recording regions with a blue wavelength laser while tracking the concavo-convex portion with a red wavelength laser. It is characterized by recording a set of.

  According to the optical recording medium of the present invention, no matter how the number of recording layers is increased, the amount of light beam reaching the deepest layer is not greatly reduced, and information can be recorded / reproduced in any recording layer.

Diagram showing diffraction loss due to tracking groove Graph showing the relationship between the number of recording layers and diffraction loss External view of the optical disk of the present invention Sectional view of the optical disk of the present invention The perspective view which shows the structure of the reference layer of the optical disk of this invention The figure which shows the other structure of the optical disk of this invention Sectional drawing for demonstrating the manufacturing method of the single-sided disk of this invention Sectional drawing for demonstrating the manufacturing method of the double-sided disc of this invention Block diagram of the optical disk formatter of the present invention The figure which shows the principal part of AO modulator vicinity of the optical disk of this invention The figure which shows the 1st form of the servo mark of this invention The figure explaining the function of the 1st form of the servo mark of this invention The figure which shows the 2nd form of the servo mark of this invention The block diagram for recording the 2nd form of the servo mark of this invention The figure which shows the 3rd form of the servo mark of this invention Block diagram for recording and reproducing the optical disk of the present invention The figure which shows the relationship between the servo mark reproduced | regenerated from the optical disk of this invention, and a sample hold pulse Sectional view of a conventional multilayer optical disk

  FIG. 1 shows a conceptual diagram of diffraction loss due to the tracking groove. As shown in the figure, when the recording layers having tracking grooves are stacked on the optical disc, the reduction of transmitted light increases. This is because, when a recording layer is irradiated with a light beam, diffraction by this tracking groove occurs, and the amount of the light beam transmitted to the next recording layer is reduced (this is called diffraction loss).

  This diffraction loss occurs according to the phase difference between the optical path length that passes through the portion of the tracking groove and the optical path length that passes through the land portion adjacent to the groove. For example, the diffraction loss when the phase difference is 90 degrees is about 40%, and the diffraction loss when the phase difference is 180 degrees is 100%. Further, the light hitting the edge of the tracking groove is scattered and becomes a diffraction loss. The diffraction loss due to this scattering increases as the groove depth increases and the edge of the groove curves due to variations in the recording film deposited on the groove.

  As a general method, a push-pull tracking method is used to obtain a tracking signal. In this push-pull tracking method, when the phase difference is 90 degrees, that is, the phase difference is a quarter wavelength, the far-field diffraction is the most asymmetric and the S / N of the tracking signal is improved. Normally, the tracking signal is obtained by reflected light. At this time, since the phase difference is determined by reciprocation, the best tracking signal can be obtained when the phase difference of the track groove becomes 1/8 wavelength. . However, if the phase difference is 1/8 wavelength, the diffraction loss due to the groove shape is too large as described above, so the phase difference needs to be 1/8 wavelength or less.

  FIG. 2 shows the diffraction loss of each of the optical discs in which a plurality of recording layers having tracking grooves are stacked and the optical disc in which a plurality of recording layers without tracking grooves are stacked. Here, the loss due to the absorption of the recording film was calculated as 3% and the diffraction loss as 7%. The reduction in the amount of light due to this diffraction loss becomes more prominent as the layers are stacked. As shown in the figure, in the case of an optical disc in which a plurality of recording layers having tracking grooves are stacked, if the number of recording layers is about 4 to 5 or more, the recording light amount limit is not reached, so that information recording / reproduction becomes extremely difficult. On the other hand, since there is no diffraction loss in an optical disc in which a plurality of recording layers having no tracking groove are stacked, up to 17 layers may be practically used. As a result of intensive studies on a method for reducing this diffraction loss, the present inventors have come up with a very effective method.

  Embodiments of an information recording / reproducing disk and its apparatus according to the present invention will be described below in detail with reference to the drawings.

(Embodiment)
(Configuration of optical disc of the present invention)
FIG. 3A is a perspective view of the optical disc 100 of the present invention, as seen from the optically transparent cover layer side. Although details will be described later, a first recording region in which a flat recording layer 101 without a groove is laminated on a substrate is formed, and a reference layer 106 is formed on the first recording region. A second recording area in which the recording layer 101 is further laminated is formed on the reference layer 106. An optically transparent cover layer is formed on the surface of the second recording area. Each recording layer of the optical disc 100 includes a recording area 104, a lead-in 102 which is an inner peripheral area where recording is not performed, and an outer peripheral area lead-out 103 where recording is not performed. Since the lead-out 103 does not record information, the recording film may be omitted. However, as will be described later, it is desirable that the same recording film as the recording layer is formed on the lead-out 103. Therefore, in the following embodiment, it is assumed that the same recording film as the recording layer is formed on the lead-out 103.

  FIG. 3B is a perspective view in which the reference layer 106 is taken out from the optical disc 100. A reference track 108 is provided in the reference layer 106. In the drawing, a reference track including a spiral groove is shown as an example, but the present invention is not limited to this. The reference track shape may be any shape in which information that can be tracked is formed, such as spirals, concentric circles, or discretely arranged pits.

  FIG. 3C is a perspective view in which one recording layer 101 is taken out from the optical disc 100. The portion indicated by the arrow is an enlarged view of the recording layer. Reference numeral 111 denotes a virtual track that is freely set corresponding to the reference track, such as the center or edge of the reference track 108 provided in the reference layer 106. 110 is a servo mark which is a feature of the present invention, and is formed along the reference track corresponding to the reference track. Details of the servo mark shape and the like will be described later.

  FIG. 4 shows a cross section 200 of the optical disc taken along the line AA ′ of FIG. As shown in FIG. 4, a first recording region is formed on a substrate 201 by alternately laminating a flat recording layer 203 without a groove and a transparent spacer layer 205. A reference layer 206 is disposed on the first recording area, and a second recording area is formed by alternately laminating a flat recording layer 203 without a groove and a transparent spacer layer 205 on the surface of the reference layer 206. Has been. An optically transparent cover layer 202 is formed on the surface of the second recording area. In this figure, the lead-in area is 204, and all the lead-out areas are recording layers.

  The number of recording layers 203 in the first recording area is arranged to be larger than the number of recording layers 203 in the second recording area. This is because the arrangement of the recording layer 203 in the second recording area and the arrangement of the existing Blu-ray DISC (registered trademark) recording layer can be partially matched, so that it can be a compatible layer. . By disposing the recording layer 203 in the second recording area in this way, it is easy to be partially compatible with conventional disc manufacturing apparatuses and backward compatible with Blu-ray DISC (registered trademark) recorders and players. There is an advantage to become. Therefore, it is possible to reduce hardware and optical disc costs, and for example, the application can cope with recording management areas and thumbnails in this compatible layer, or sequentially recording only file entries in this compatible layer. For example, the contents can be confirmed on a conventional machine, and usability is improved.

  FIG. 5 shows an enlarged perspective view of the basic reference layer 206 of the present invention. In the reference layer 206, a reference track 208 and unique information pits 207 are formed, and clock pits are provided as necessary. This reference layer 206 is manufactured by applying an optically transparent material, for example, UV resin, as a spinner, curing it using a transparent resin or glass stamper, and forming an appropriate reflective film thereon by vapor deposition or sputtering. To do.

  There are two types of information recording methods for optical discs: a concentric land groove track method and a spiral land groove method. Both methods change the shape of the reference track 208 formed in the reference layer 206 of the present invention. Can be realized. The shapes of various reference tracks 208 are shown in FIGS. The reference track 208 corresponding to these information recording methods is provided on the first recording area side of the reference layer 206 and is formed in an area corresponding to the adjacent flat recording layer 203 as described above. . The reference track 208 is used as a reference track for forming servo marks, which is a feature of the present invention, in all the recording layers 203 in the first and second recording areas.

  FIG. 5A shows a concentric land / groove track. In the concentric land / groove track system, the track land portion and the groove portion can be switched for every round of the optical disk, and tracking with a half track pitch can be performed. In order to make the track pitch of the sample servo mark the same, it is preferable that the track width of the reference track 208 and the width of the inter-track groove 209 are equal. Therefore, in the present embodiment, the track width of the reference track 208 and the width of the inter-track groove 209 are set to 0.32 μm. Therefore, the track pitch is 0.64 μm. This increases the degree of modulation of the push-pull signal, so that tracking can be performed easily. The phase difference of the reference track groove is preferably set to 1/8 or less of the wavelength for tracking in order to obtain a good tracking signal and reduce the diffraction loss as much as possible.

  FIG. 5B shows a spiral land / groove method, in which a land portion and a groove portion of a track are alternately formed by a switching unit 210 for each round of the optical disk. At this time, as in FIG. 5A, the track width of the reference track 208 and the width of the inter-track groove 209 were set to 0.32 μm. In this method, it is necessary to switch the polarity of the tracking servo by the switching unit 210, but for example, tracking can be easily performed using a tracking technique of DVD-RAM.

  FIG. 5C shows an example in which clock pits 220 and 221 are arranged inside the reference track 208. By using these clock pits, it is possible to improve the accuracy of generation of sample servo marks described later. Various other uses such as optical disk rotation control can also be used. A required number of clock pits may be arranged on the reference track 208 according to the form to be used.

  If the reference track 208 formed on the reference layer 206 is used, servo marks can be formed on each recording layer as will be described later.

  In a region (ROM region) corresponding to the lead-in region 204, a plurality of unique information pits 207 are provided. The unique information pits 207 are recorded in the shape of uneven embossed pits, that is, ROM shapes, and their positions are uniquely determined. The unique information pit 207 can be used for the purpose of pre-recording unique information unique to the optical disc. This unique information includes, for example, an individual ID of the optical disc, the number of recording layers, the position of the reference layer, the manufacturer, and the lot number. If such unique information is recorded in the unique information pit 207 in advance, it is effective for shortening the startup time of the optical disk and managing the traceability of each optical disk.

  As described above, since the position of the unique information pit 207 is uniquely determined, a use method other than storing the unique information of the optical disk described above is also conceivable. For example, it can be used as a starting position for performing individual learning or the like by turning on the focus and tracking after loading the disk.

  In addition, when the optical disk of the present invention is inserted into the drive, if it starts with the flat recording layer 203, it may be erroneously recorded on the adjacent flat recording layer when the linear velocity is slow or when laser learning is inappropriate. There is sex. Therefore, erroneous recording can be prevented by setting the starting position as the inner peripheral ROM area. Note that this ROM can also be arranged on the outer peripheral side of the recording layer 203.

  As described above, in the configuration of the optical disc of the present invention described above, the reference layer is disposed in the middle of the two recording areas. However, the configuration is not limited to this. FIG. 6 shows another form.

  As shown in FIG. 6, a reference track 208 constituting a reference layer and a unique information pit 207 are formed in advance on a substrate. This portion is referred to as a reference portion 206 for convenience, but has the same function as the reference layer 206 described with reference to FIG. On the reference portion 206, the recording layer 203 and the spacer layer 205 are alternately stacked to form a recording area. Thereafter, the cover layer 202 is formed on the surface of the recording area. If the thickness of the optical disk at this time is 1.2 mm and the thickness of the reference unit 206 is 0.6 mm or 0.1 mm, compatibility with a conventional DVD or Blu-ray (registered trademark) can be achieved. For this purpose, the thickness of the substrate 201 or the cover layer 202 may be adjusted as appropriate according to the number of recording layers.

(Method for producing optical disk of the present invention)
Next, a method for producing an optical disk of the present invention will be described based on FIG. FIG. 7A shows a first laminated substrate composed of a reference layer, a first recording region, and a substrate, and a second laminated substrate composed of a cover layer and a second recording region.

  A method for manufacturing the first multilayer substrate will be described. First, a recording layer 902 made of, for example, a phase change material, a metal oxide material, a dye material, an organic material, or the like is formed on a recording / reproducing area on a 1 mm thick substrate 901 made of a resin material such as polycarbonate or a glass material. It is formed with a thickness of ˜20 nm. For this formation, a known vapor deposition or spin coating method may be used. After the formation of the recording layer, for example, a UV curable material is applied by spin coating and is cured with ultraviolet rays to form a spacer layer 903 having a thickness of about 15 μm. As the UV curable material, an optically transparent material after UV curing is used. A recording layer 904 is further formed on the spacer layer 903. The material and the formation method are the same as those of the recording layer 902 described above. In this way, the spacer layer made of the UV curable material and the recording layer made of the phase change material are alternately repeated to produce the required number of recording layers.

  Thereafter, a UV curable material is applied by spin coating, and the optically transparent stamper 923 having the reference track, the unique information pit, and the clock pit formed thereon is pressed in the direction of the drawing to be cured by ultraviolet rays. An appropriate reflective film is formed by vapor deposition or sputtering. In this way, a reference layer is formed.

  Next, a method for manufacturing the second multilayer substrate will be described. On the cover layer 932 made of an optically transparent material, a recording layer 931 having a thickness of 10 to 20 nm made of, for example, a phase change material, a metal oxide material, a dye material, an organic material, or the like is formed. Thereafter, these forming methods are the same as the manufacturing method of the first laminated substrate. By repeating these operations, the required number of recording layers is formed to produce the second laminated substrate.

  The adhesive 924 that becomes transparent after curing is applied to the reference layer 923 side of the first multilayer substrate manufactured as described above, and the recording layer side of the second multilayer substrate is bonded to the reference layer 923 side. The positioning at the time of bonding may be based on the center of the reference layer of the first laminated substrate. Since tracking information (servo marks) for each recording layer is created with reference layer 923 as a reference as will be described later, positioning accuracy of 10 or more super multi-layer recording layers can be easily achieved. Further, since it is not necessary to align the lead-out, it is more preferable that the recording layer is formed to the outer periphery without providing the lead-out in the recording layer.

  The optical disk of the present invention produced as described above is shown in FIG. By adjusting the coating amount of the spacer layer, the total of the first and second recording areas sandwiching the reference layer from the cover layer can be easily formed to about 200 μm. Since the thickness of the substrate 901 is 1 mm, the thickness of the optical disk of the present invention is 1.2 mm. Therefore, an optical disk having the same thickness as a commercially available CD, DVD, and BD can be realized. In the present embodiment, the number of recording layers in the first laminated substrate is 10, but the number is not limited thereto.

  In the above description, the bonded portion is the reference layer. However, as another manufacturing method, there is a method in which a cover layer is finally attached. That is, on the reference layer 923 side of the first laminated substrate, a UV curable adhesive is applied by spin coating and cured with ultraviolet rays, and a spacer layer is formed so that the surface becomes flat. An optical disk of the present invention can be produced by alternately forming a required number of recording layers and spacer layers on this and then bonding the cover layer with an adhesive.

  Next, a method for producing a double-sided recording / reproducing optical disk using the optical disk of the present invention will be described. FIG. 8A is a cross-sectional view of one side of a double-sided recording / reproducing optical disc. The materials for the substrate, recording layer, spacer layer, and the like are the same as those of the optical disk described above with reference to FIG. 7, but the thickness of the substrate 801 is as thin as 400 μm. The total of layers other than the substrate 801 is 200 μm as in the optical disk described in FIG. With such a thickness, as shown in FIG. 8B, a single-sided optical disk may be bonded to each other via an adhesive 833 to produce a double-sided recording / reproducing optical disk. Since the total thickness of a single-sided optical disk is 600 μm, the total thickness becomes 1.2 mm when pasted together, and an optical disk having the same thickness as that of a commercially available CD, DVD, and BD can be realized. Thus, by adjusting the substrate thickness of the single-sided disk, the thickness compatibility with the conventional optical disk can be achieved. In this embodiment, the substrate thicknesses of both single-sided disks are set to the same value, but both substrate thicknesses may be adjusted to 1.2 mm. In this way, if the recording layer of a single-sided optical disk is 16 layers and the recording capacity is 512 GB, an optical disk with a recording capacity of 1024 GB can be realized by performing double-side bonding. In this way, the recording capacity can be easily doubled by adjusting the thickness of the substrates and performing bonding.

(Servo mark production method)
FIG. 9 is a configuration diagram of an optical system of a formatter apparatus for writing servo marks (hereinafter referred to as a format) on each recording layer of the optical disc 200 according to the present invention. The formatter device 300 includes a red laser light source 331 (wavelength 650 nm) for tracking control and a blue laser light source 311 (wavelength 405 nm) for servo mark recording. Hereinafter, for convenience, an optical system using the red laser light source 331 is a red optical system, and an optical system using the blue laser light source 311 is a blue optical system.

  The wavelength characteristics of these laser light sources are preferable as long as they satisfy the specifications of laser light sources used for Blu-ray (registered trademark) and DVD. The outline of the format is as follows. First, after the tracking of the objective lens 318 is controlled by the red laser using the reference track on the reference layer 206, the objective lens 318 is controlled and servo marks are sequentially written on the recording layer by the blue laser.

  Details will be described below. The light beam emitted from the red laser 331 is transmitted through the polarization beam splitter 332, converted into a substantially parallel light beam by the collimator lens 333, reflected by the quarter-wave plate 334 and the wavelength separation beam splitter 317, and incident on the objective lens 318. To do. The objective lens 318 is designed so that the spherical aberration in the red laser beam and the blue laser beam is minimized in the reference layer 206. In this embodiment, the NA of the objective lens 318 by the red laser beam is set to 0.60. An aperture (not shown) is required to limit the NA, and can be formed on, for example, a quarter wave plate 334. The objective lens 318 is provided with a tracking coil 339 and a focusing coil 322 as actuators in the tracking direction and the focusing direction, respectively. The focusing coil 322 is controlled in advance so that the light beam emitted from the red laser 331 is focused on the surface of the reference layer 206.

  Now, the red light beam emitted from the objective lens 318 is incident on the reference layer 206 of the optical disc 200 (outward path) and reflected on the surface thereof. The optical path of the reflected light beam follows the forward path in the reverse direction, becomes a polarization plane orthogonal to the polarization plane of the forward path by the quarter wavelength plate 334, is reflected by the polarization beam splitter 332, passes through the detection lens 335, The light enters the photodetector 336. The focus of the red light beam controls the focusing coil 338 based on the focus signal Fo from the photodetector. The photodetector 336 controls the tracking coil 339 based on the tracking signal Tr formed by diffraction from the reference track 208 formed in the reference layer 206. The tracking control using the tracking signal may use a known tracking method such as a push-pull tracking method or a phase method according to the shape of the reference track.

  In the state where the tracking control is performed with the red laser light as described above, servo marks are written on the recording layer with the blue laser light. The blue light beam emitted from the blue laser light source 311 is collected by a relay lens 312, passes through an AO modulator (Acousto-Optic Modulator) 313 and a polarization beam splitter 314, and becomes a substantially parallel light beam by a collimator lens 315. The parallel light beam further passes through the quarter-wave plate 316 and the wavelength separation beam splitter 317 and enters the objective lens 318. At this time, the focusing coil 322 is controlled so that the light beam emitted from the objective lens 318 can enter the recording layer for recording (outward path). Further, since the spherical aberration of the objective lens 318 due to the blue light is designed to be minimal in the vicinity of the reference layer 206, it is necessary to correct the spherical aberration with the blue laser light in accordance with the target recording layer. is there. For this purpose, an actuator 324 may be provided on the collimating lens 315 and adjustment may be performed using a stepping motor or the like.

  Next, the blue laser light reflected by the recording layer traces the optical path in the reverse direction, becomes a polarization plane orthogonal to the polarization plane of the forward path by the quarter-wave plate 316, is reflected by the polarization beam splitter 314, and is detected by the detection lens. The light passes through 319 and enters the photodetector 320. By combining the detection lens 319 and the photodetector 320, the focus error signal 321 between the objective lens 318 and the recording surface 203 of the optical disc 100 can be detected. Since the focus error signal 321 can be detected by a known method such as an astigmatism method, a detailed description is omitted. Using the focus error signal 321, the focusing coil 322 is controlled to perform focusing with blue laser light. Servo marks can be written only after focus control is completed. This focusing control may be performed prior to the focusing control by the red laser beam.

  When the objective lens 318 is focused with blue laser light in this way, a focus error occurs with the red laser light. This is because the distance between the recording layer to which the servo mark is written and the reference layer 206 is different for each recording layer, so that all the recording layers do not fit within the focus depth of the objective lens 318. Therefore, it is necessary to correct the focus error according to the recording layer in which the servo mark is written. Therefore, a focus correction coil 338 is provided in the collimator lens 333, the focus correction coil 338 is controlled based on the focus error signal from the photodetector 336, and the collimator lens 333 is moved in the optical axis direction to correct the focus error.

  Next, the optical disk 200 is formatted by this formatter device, that is, the servo marks for sample servo are formed on the recording layer with the blue laser light while following the reference track of the reference layer 206 with the red laser light. The format operation will be described.

  The servo mark is written at the position of each recording layer corresponding to the reference track 208 of the reference layer 206. Here, the track of the recording layer corresponding to the reference track 208 is called a virtual track, and the servo mark is offset from the center to the inner and outer peripheral sides in the direction perpendicular to the virtual track. It is necessary to write in the position. For this purpose, an AO modulator 313 is used.

  FIG. 10 shows an enlarged optical configuration around the blue laser 311. The blue laser light emitted from the blue laser light source 311 is collected by the relay lens 312 and is incident on the AO modulator 313. In accordance with this modulation, the blue laser light is diffracted and converted into a parallel light beam by the collimating lens 315 via the polarization beam splitter 314. Here, when a signal is given to the AO modulator when recording the servo mark, the diffraction angle of the AO slightly changes according to the modulation frequency as shown in FIG. Assuming that the diffraction angle θ changes and the focal length fo of the objective lens, the displacement δ of the servo mark on the recording layer is δ = θ · fo from the center of the virtual track. If the track pitch is the same as that of a Blu-ray (registered trademark) disc, the modulation frequency may be set so that the displacement δ is about 0.08 μm.

  The blue laser light source 311 performs the focus error signal 321 with the reproduction level power, and sets the recording power when recording the servo mark. The focus servo is not affected because the laser output becomes the recording power for only a short time. However, if the drive signal is saturated and adversely affected, the focus error signal is gated for the recording interval and held or no signal is output. And it is sufficient.

  As described above, by using the formatter apparatus described above, it is possible to freely form a servo mark in accordance with the reference track on a desired recording layer. By combining these servo marks, sample servo information in the form described below can be freely created.

(First form of sample servo information)
FIG. 11 shows a first form of sample servo information according to the present invention. The sample servo information in this embodiment is composed of a set of three types of servo marks. In other words, it is composed of a timing mark 412 located on the center 411 of the recording track, a first track king mark 413 and a second track king mark 414 located on both sides of the recording track center 411. The center 411 of the recording track coincides with the center of the reference track of the reference layer. This set of servo information is provided at predetermined intervals along the center of the recording track. For convenience of explanation, the outer peripheral direction and the inner peripheral direction are indicated by arrows in the drawing. Reversing this orientation does not interfere with the practice of the invention.

  The interval Ts between timing marks is set based on the repetition frequency Fs of the sample servo of the tracking servo control system. That is, the interval Ts between the adjacent timing marks 412 is Ts = 1 / Fs. It is practical to set Fs to 10 times or more the servo band frequency of the servo control system.

  For example, applying the BD standard (linear speed: 4.917 m / s, data pit length: 111.75 nm, channel clock: 66 MHz), the track has an inner circumference (radius position: 24 mm), and the rotation speed is about 2000 rpm, that is, 30 rpm per rotation. Become. Assuming that the servo band is 10 kHz and Fs of 100 KHz is secured at the radial position, Ts = 10 μs, and 3000 servo marks are required for one revolution. The interval between the timing mark and the pair of tracking marks is preferably matched to the data bit length. Basically, the intervals are Tsv = 111.75 nm and Tse = 2Tsv = 223.5 nm.

  Further, the interval Tsv between the timing mark 412 and the first track king mark 413 can be changed for each layer to indicate the layer number, and can also indicate the virtual track number. decide. This technique is disclosed in, for example, Japanese Patent Application Laid-Open Nos. 1-2232539 and 1-222334, and detailed description thereof is omitted.

  FIG. 12 is a timing chart showing the waveform of the signal output obtained when the light beam crosses each servo mark shown in FIG. As shown in the drawing, when the light beam spot from the optical pickup passes over the center 411 of the recording track (on-track state), the timing mark 412 constituting the servo information is the largest compared to the other marks. Playback at signal level. At that time, the first track king mark 413 and the second track king mark 414 have the same signal level and are lower than the signal level of the timing mark. When the light beam from the optical pickup moves to the inner circumference side from the center 411 of the recording track, the light beam passes near the first track king mark 413. At this time, the reproduction of the first track king mark 413 is performed. The signal is reproduced with a signal level larger than that of the timing mark 412. Further, the level of the reproduction signal of the second track king mark is lower than the signal level of the timing mark 412. On the other hand, when the light beam from the optical pickup moves to the outer peripheral side, the magnitude of the reproduction signal becomes second track king mark 414> timing mark 42> first track king mark 413. By using this relationship, the moving direction and moving amount of the optical pickup for making the on-track state can be known. Therefore, tracking control can be performed by using a known sample servo using the servo mark of this embodiment.

(Second form of sample servo information)
FIG. 13 shows a second form of sample servo information suitable for the optical disc of the present invention. The difference from the first form of the sample servo information is that all servo marks represented by 1602 are recorded on the center 1601 of the recording track. With this arrangement, all the servo marks are on the center 1601 of the recording track, so that the servo marks can be formed without using the AO modulator that was necessary in the previous example.

  The sample servo information in the second form is composed of mark rows in which servo marks having the same shape are arranged at equal intervals. In the figure, a mark row 1810 composed of four servo marks is shown. The tracking information can be easily detected by using a known DPD (Differential Phase Detection) method. In principle, even a single mark can be used. In order to reduce the influence of error, the timing of the center of the third and subsequent marks is calculated from the center of the first mark and the center of the second mark as shown in FIG. If the diffraction signal and the diffraction signal for the latter half are binarized and the phases are compared, the detection accuracy can be improved.

  FIG. 14 is a block diagram for recording the sample servo information of this embodiment on a disk. In the red optical system of the formatter described with reference to FIG. 9, the clock signal 390 reproduced from the track of the reference layer 206 by the red beam spot is input to the reproduction amplifier 391. The signal is converted into a pulse train by the binarization device 392, and the PLL 393 synchronized with the pulse train is driven. Since the PLL includes a programmable frequency division ratio setting unit 394, the frequency division ratio can be set by an external command. A mark row for sample servo information is output to the recording amplifier 396 as a servo mark row 397 generated by the servo mark generator 395, and is supplied to the recording layer of the optical disc via the blue optical system described in FIG. The Then, in synchronization with the reference track reproduction signal, servo marks are recorded on the recording layer at positions corresponding to the reference track of the reference layer.

  By performing such recording, mark rows 1810 and 1820 are sequentially recorded on the center 1601 of the recording track. Similar to the first form of sample servo information, the interval Ts between mark rows is set with reference to the repetition frequency Fs of the sample servo of the tracking servo control system. That is, the interval Ts between the adjacent timing marks 412 is Ts = 1 / Fs. It is practical to set Fs to 10 times or more the servo band frequency of the servo control system.

  In order to perform tracking with such a mark row, a well-known DPD (Differential Phase Detection) method can be used. A quadrant photodetector is used to detect the tracking signal. The diagonals of the four-divided photodetectors are added to each other, and the obtained two added signals are subtracted to obtain a tracking signal. At this time, a good tracking signal can be obtained by switching the polarity of the tracking signal at the cycle of Fsv at the center of each mark with the leading pit as the clock timing signal.

  This method is already used for DVD, Blu-ray (registered trademark), etc., and can perform stable tracking servo. As a method for improving the S / N ratio of the DPD tracking signal, the center of the quadrant photodetector is masked or attenuated. By doing so, the influence of low-order diffracted light received around the center of the quadrant photodetector can be avoided, so that the influence of the distortion of the light beam generated in the low-order part due to, for example, tilt can be eliminated. Further, since the servo mark of the first embodiment is displaced from the recording track, the diffraction in the radial direction of the light spot received by this displacement is detected, whereas the servo mark of the second embodiment is A good tracking signal can be obtained by using the principle that the light spot is diffracted in the 45-degree direction by the mark.

(Third form of sample servo information)
FIG. 15 shows the shape of the third embodiment of the sample servo information of the present invention. Similar to the second form of sample servo information, this can be formed by the recording method shown in FIG. The difference from the second embodiment is in the generation of a pulse train in the servo mark generator 395. In the servo mark of the present embodiment, a pulse train whose servo mark cycle is delayed by T1 every round is supplied to the recording amplifier by the servo mark generator 395 via the blue optical system of the formatter described in FIG. Then, in synchronization with the reference track reproduction signal, a servo mark row that records the servo mark period T1 between adjacent tracks is recorded on the recording disk layer. In this case, it is necessary to control the rotational speed of the disk to be CAV (constant angular velocity) or MCAV (modified constant angular velocity).

The signal format of the reference track 208 formed on the reference layer 206 is optimized for the period and delay amount of the servo mark, and is optimized according to the form of the servo mark.
The period of the servo mark can be synchronized with, for example, the period of the synchronization signal of the signal to be recorded. In this case, it is possible to reduce the interference of the servo mark with the reproduction of the recorded signal.

  In this way, the first track king servo mark 512 and the second track king servo mark 513 are formed repeatedly on both sides of the center 511 of the recording track. The period between servo marks is indicated by T0.

  The servo mark is determined so that, for example, the servo mark whose timing precedes is positioned on the inner peripheral side with respect to the scanning direction of the light beam. In the embodiment, a pulse train whose servo mark cycle is delayed by T1 for each round is supplied to the recording amplifier by the servo mark generator via the blue laser optical system of the formatter described in FIG. Then, in synchronization with the reference track reproduction signal, a servo mark row in which the servo mark located on the outer peripheral side adjacent on the flat recording disk layer maintains the constant value T1 in the period of the adjacent servo mark located on the inner peripheral side is recorded. . As shown in FIG. 15, these servo marks are offset from the virtual center of the track by a certain value in the inner or outer circumferential direction.

  As described above, three types of servo marks can be formed on the recording layer of the optical disc of the present invention using the formatter device of FIG.

(Information recording / reproducing method for optical recording medium of the present invention)
FIG. 16 is a block diagram of a recording / reproducing apparatus for recording / reproducing information on / from the optical recording medium of the present invention. A blue laser is used as a laser for recording and reproduction. In the figure, the blue light beam emitted from the blue laser 311 is converted into a substantially parallel light beam by the collimator lens 315, passes through the beam splitter 317, and enters the objective lens 318. The light beam emitted from the objective lens 318 enters the optical disc 200. At this time, the spherical aberration for the blue light of the objective lens 318 is designed to be minimum in the vicinity of the reference layer 206. The spherical aberration is adjusted by moving the collimating lens 315 in the optical axis direction. The blue light beam incident on the optical disc 200 is applied to the reference layer 206 or the recording layer. The light beam reflected by the reference layer 206 follows the optical path in reverse, passes through the beam splitter 317, passes through the detection lens 333, is reflected by the beam splitter 332, and enters the photodetector 336.

  Focusing is performed by moving the objective lens 318. The distance between the recording layer on which the blue light beam is collected and the reference layer 206 is not within the focus depth of the objective lens 318 because the position of each recording layer differs and the distance is not constant. Therefore, it is necessary to correct the focus position error. In this case, the collimator lens 315 may be moved in the optical axis direction to correct the position, obtain a focus error signal from the photodetector 336, and correct the focus error by the focusing actuator 322.

  Next, a tracking operation when information signals are recorded and reproduced on the optical disc 200 using the servo mark information of the formatted recording layer will be described. In order to explain the operation of the servo system, the servo mark information shown in FIG. 15 will be described as an example. The servo marks are recorded on the recording layer with reference to the reference track of the reference layer 206 at the time of the formatter, and each servo mark constituting the servo mark information is recorded at a position offset to the left and right from the center of the virtual track. ing. A block diagram of a servo system for tracking servo marks with a blue light beam is shown in the lower part of FIG.

  In FIG. 16, reference numeral 520 denotes a regenerative amplifier that amplifies the tracking output Tr of the photodetector 336. The servo mark signal is regenerated and converted into a binary signal by a binarizer 521. Reference numeral 522 denotes a delay unit that delays by the period T1 shown in FIG. 15, and outputs a pulse when the output of the binarizer 521 and the pulse signal delayed by T1 input to the gate of 523A are synchronized. The gate 523B operates so as not to output when the output of the binarizer 521 and the output of the gate 523A are synchronized. Reference numerals 524 and 525 denote sample and hold devices which sample and hold the output of the regenerative amplifier 520 by the output pulse of the gate 523 and the output pulse of the binarizer 521. These two sample hold values are sent to the differential amplifier 526 to output the difference between them.

  FIG. 17 shows the relationship between the reproduced servo mark and the sample hold pulse. Here, for convenience, the larger the servo mark output, the closer to the center of the servo mark, and the smaller the output, the farther from the servo mark center. Therefore, this difference (the output of the differential amplifier 526) indicates the amount of deviation from the track center. Therefore, if the deviation approaches 0, the blue light beam follows the center of the track.

  As described above, a differential signal (deviation amount) is output by the differential amplifier 526, and after the response characteristic is made appropriate by the tracking servo equalizer 527, the tracking actuator 339 is controlled by the drive amplifier 528. Thus, tracking control using servo marks can be performed.

  By configuring the servo system as described above, a servo mark can be additionally recorded on a flat recording layer without a groove, and a tracking servo for recording an information signal can be operated by the additionally recorded servo mark.

  The focusing control and tracking control methods for the optical recording medium of the present invention have been described above. Thus, the method for recording information on the optical recording medium of the present invention can be performed by a known technique. Therefore, description of the information recording method is omitted here. When designing the recording circuit, it is necessary to consider that the amount of light reproducing the servo mark when switching from the reproduction state to the recording state varies. In addition, since the light for reading the servo mark is modulated by the information signal, the light modulation waveform may be corrected in advance so as not to cause disturbance in the servo system in synchronization with the servo mark reading cycle.

  As described above, since the optical recording medium of the present invention is not provided with tracking grooves or bits in each recording layer, diffraction loss does not occur. Therefore, even if the recording layers are stacked to 10 layers or more, there is no increase in diffraction loss between the recording layers, and a large-capacity optical disk can be easily realized.

  In addition, there are many advantages compared to a method of recording / reproducing data directly on each recording layer while tracking by one reference layer. In the above method, since tracking is performed with only one reference layer, the recording / reproducing apparatus requires a tracking optical system and a recording / reproducing optical system. Since the laser beam of the recording / reproducing optical system has an aberration every time it passes through the recording layer, it is necessary to correct the aberration for each recording layer based on the spherical aberration value of the reference layer. However, a correction error occurs in the aberration correction. For this reason, as the recording layer is overlapped with the reference layer, aberration correction errors accumulate, the accuracy deteriorates with respect to the focus position and tracking position, and good recording and reproduction cannot be performed. Further, these two optical systems cannot make the laser wavelength the same, and the optical system of the recording / reproducing apparatus cannot be simplified. In the present application, such a drawback can be solved in principle, and since sample servo information is formed in each recording layer, the disc compatibility in the recording apparatus is good. In addition, the optical system of the recording / reproducing apparatus can be simplified, and conventional Blu-ray (registered trademark) and DVD parts can be easily shared and data can be easily interchanged.

  The optical recording medium according to the present invention can record and reproduce information in any recording layer without greatly reducing the amount of light beam reaching the deepest layer, no matter how many recording layers are formed. It is useful as an optical recording medium having more than one recording layer. Further, if the optical recording medium according to the present invention is used, it can be easily applied to a super-large capacity recording / reproducing apparatus.

DESCRIPTION OF SYMBOLS 100 Substrate 101 Recording layer 106 Reference layer 108 Reference track 110 Servo mark 111 Virtual track 200 Cross section of optical disc 201 Substrate 202 Cover layer 203 Recording layer 204 Lead-in area 205 Spacer layer 206 Reference layer 207 Unique information pit 208 Reference track 210 Switching unit 220 Clock pit 221 Clock pit 311 Blue laser light source 312 Relay lens 313 AO modulator 314 Polarization beam splitter 315 Collimator lens 316 Quarter wave plate 317 Wavelength separation beam splitter 318 Objective lens 319 Detection lens 320 Photo detector 321 Focus error signal 322 Focusing coil 324 Actuator 331 Red laser light source 332 Polarizing beam splitter 33 Collimator lens 334 quarter wave plate 335 the detection lens 336 optical detectors 338 focusing coil 339 tracking coil 390 clock signal 391 reproduced amplifier 392 binarizing circuit 393 PLL
394 Programmable division ratio setting device 395 Servo mark generator 396 Recording amplifier 397 Servo mark 412 Timing mark 413 First track king mark 414 Second track king mark 511 Recording track center 512 First track king servo Mark 513 Servo mark for second tracking 520 Reproducing amplifier 521 Binarizer 522 Delay device 523A, 523B Gate 524, 525 Sample hold device 526 Differential amplifier 527 Equalizer 528 Drive amplifier 1601 Recording track center 1602 Servo mark 1810, 1820 Mark row

Claims (14)

A substrate,
A first recording region in which a plurality of recording layers and optically transparent spacer layers are alternately stacked on the substrate;
A reference layer provided with a concavo-convex portion serving as a reference at the time of tracking is disposed on the first recording area,
Furthermore, a second recording area in which a plurality of recording layers and optically transparent spacer layers are alternately stacked is disposed on the reference layer,
An optically transparent cover layer is disposed on the second recording area;
An optical recording medium having a plurality of sets of marks corresponding to the concavo-convex portions in all the recording layers of the first and second recording areas. The optical recording medium according to claim 1, wherein the recording layer is flat without unevenness. The optical recording medium according to claim 1, wherein the reference layer has a plurality of pits on an inner peripheral side of the uneven portion. The optical recording medium according to claim 1, wherein the uneven portion is a continuous groove, a pit, or a combination of a continuous groove and a pit. The optical recording medium according to claim 1, wherein the set of marks includes only information for tracking control. A substrate on which a reference portion provided with a concavo-convex portion serving as a reference for tracking is formed on the surface;
A recording area in which a plurality of recording layers and optically transparent spacer layers are alternately stacked on the reference portion is disposed,
An optically transparent cover layer is disposed on the recording area,
An optical recording medium in which a plurality of sets of marks consisting only of information for tracking control are arranged on all the recording layers in the recording area so as to correspond to the concave and convex portions. The optical recording medium according to claim 6, wherein the substrate has a plurality of pits on an inner peripheral side of the uneven portion. The optical recording medium according to claim 6, wherein the recording layer is flat without unevenness. The optical recording medium according to claim 6, wherein the uneven portion is a continuous groove or a pit, or a combination of a continuous groove and a pit. The set of marks is
A first servo mark indicating the center to be tracked;
A second servo mark located on the inner circumference side from the first servo mark;
The optical recording medium according to claim 1, further comprising a third servo mark positioned on an outer peripheral side of the first servo mark. The set of marks is
A first servo mark indicating the center to be tracked;
The optical recording medium according to claim 1, comprising a servo mark row including a plurality of servo marks adjacent to the first servo mark. The set of marks is
A first servo mark indicating an intermediate position between adjacent centers to be tracked;
The optical recording medium according to claim 1, comprising a servo mark row including a plurality of servo marks adjacent to the first servo mark. A substrate, a first recording region in which a plurality of recording layers and optically transparent spacer layers are alternately stacked on the substrate, and an uneven portion serving as a reference in tracking disposed on the recording region. In the method of manufacturing an optical recording medium, in which a provided reference layer and a second recording region in which a plurality of recording layers and optically transparent spacer layers are alternately stacked are disposed on the reference layer,
While tracking the irregularities with a red wavelength laser,
A method of manufacturing an optical recording medium, wherein a set of marks corresponding to the concavo-convex portion is recorded on each recording layer in the first and second recording areas with a blue wavelength laser. A substrate having a reference portion provided with a concavo-convex portion serving as a reference for tracking on the surface, and a recording region in which a plurality of recording layers and optically transparent spacer layers are alternately stacked on the reference portion; In the method of manufacturing an optical recording medium in which
While tracking the irregularities with a red wavelength laser,
A method of manufacturing an optical recording medium, wherein a set of marks corresponding to the concavo-convex portions is recorded on each recording layer in the recording region with a blue wavelength laser.