JP2009104718A - Optical recording medium and recording/reproducing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical recording medium which can inexpensively be manufactured in a small number of manufacturing processes with a simpler structure while securing a storage capacitance nearly equal to conventional one, to provide its recording and reproducing method, to provide an optical recording medium having a novel structure which has recording density matching that of land-groove recording and also eliminates defects that land-groove recording, and to provide a recording/reproducing method thereof. <P>SOLUTION: In the recording/reproducing method by which the optical recording medium 10 is irradiated with an optical beam 21 to record or reproduce information in/from recording layers 18, 16 and 14 of the optical recording medium 10, the recording layers 18, 16 and 14 have first recording regions S5, S4 and S3, respectively, and second recording regions S0, S1 and S2, respectively, and the beam 21 is condensed from one side (an upper side) of the recording layers 18, 16 and 14 to the first recording regions S5, S4 and S3 and condensed from the other side (a lower side) of the recording layers 18, 16 and 14 to the second recording regions S0, S1 and S2. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical recording medium and a recording / reproducing method.

  2. Description of the Related Art In recent years, optical recording media (such as optical discs) as information recording media that record a large amount of data at a high density and reproduce quickly have been attracting attention in response to the development of multimedia. As such a next-generation optical recording medium, a write-once Blu-ray disc (BD-R (BD-R (BD) (BD-R)) can be obtained by setting the wavelength of the laser light source to about 405 nm and the aperture ratio NA to 0.85. Blu-ray Disc Recordable)). This write-once Blu-ray disc can record about 25 GB of data on one layer.

  In order to further increase the capacity of such an optical recording medium, it is conceivable to increase the recording layer. A multilayer optical recording medium such as a BD-R has been commercialized having two recording layers. In addition, as a multilayer optical recording medium, a dual-layer read-only disk (double-layer DVD-ROM (Digital Versatile Disk Read Only Memory)), a dual-layer write-once disk (double-layer DVD-R (Digital Versatile) Disk Recordable)) has already been commercialized.

  Non-Patent Document 1 and Non-Patent Document 2 disclose that a recording-type Blu-ray disc in which six recording layers are stacked can be used as a six-layer Blu-ray disc.

“Six-layer write-once media using the Blu-ray Disc system” (Laser Society of Miyazaki Symposium Reference Documents S19-S20, published on January 18, 2007, Yasuko Mishima et al.) “150 GB, 6-Layer Write Once Disk for Blu-ray Disk System” (IEEE (The Institute of Electrical and Electronics Engineers, Inc.)), 2006 publication, literature number “0-7803-9494-1 / 06” p123 -125, Koji Mishima and others)

  However, when the recording layer is multi-layered, the manufacturing process becomes more complicated than in the case of a single layer. As a result, the price of the multi-layer optical recording medium becomes higher than that of the single layer, or the mass production of the optical recording medium cannot be expected. Although six layers of optical recording media can be manufactured at the laboratory level, the current manufacturing technique has a limit of about two layers at the mass production level.

  In other words, at the manufacturing site of optical recording media, manufacturing is performed with an expectation of margin in each manufacturing process. In many cases, various parameters do not meet the required specifications on the finished disc. The required specifications that are difficult to maintain when the recording layer is multilayered include, for example, the optical characteristics and recording / reproducing characteristics of each recording layer, the absolute film thickness and uniformity of the spacer layer and the cover layer, and the optical recording medium. There is an amount of eccentricity of each recording layer in the radial direction with respect to the rotation center.

As a result, even if it is possible to manufacture a multilayer optical recording medium in which each parameter value falls within the required specifications, the yield is lowered. Specifically, with the current manufacturing technology, the yield of the two-layer optical recording medium is about 70 to 80%, and the yield of the six-layer optical recording medium is about 17 (= 0 even if simply estimated). .7 ⁵ ) to 33 (= 0.8 ⁵ )%. With such a low yield, the unit price of the disk when the disk is mass-produced becomes high, and the product cannot be realized.

  Here, the two-layer BD-R disc will be described in detail. FIG. 8 shows a partial cross-sectional view of the dual-layer BD-R disc 100 in the radial direction. In the two-layer BD-R disc 100, an L0 recording layer 102 is formed on a 1.1 mm thick polycarbonate (PC) substrate 101 having concave and convex grooves. The L0 recording layer 102 has a layer structure in which both sides of a recording film whose internal structure can be changed are sandwiched between dielectric layers, and further has a metal reflective film on the side in contact with the PC substrate 101. An L1 recording layer 104 is formed on the L0 recording layer 102 via a first spacer layer 103. Although not shown, the L1 recording layer 104 has a layer structure in which both sides of the recording film are sandwiched between dielectric layers. The L1 recording layer 104 does not have a metal reflection film in order to transmit the beam 110. The first spacer layer 103 is formed with a uniform film thickness of about 25 μm by a 2P method using an ultraviolet curable resin or a nanoprint method using a sheet-like member. On the L1 recording layer 104, a cover layer 105 having a thickness of about 75 μm is formed.

  The dual-layer BD-R disc 100 is irradiated with a beam 110 for recording or reproduction from the cover layer 105 side. The beam 110 is irradiated onto the two-layer BD-R disc 100 from the upper side in FIG. Then, the beam 110 is focused on a portion (convex portion 107) that is convex in the incident direction of the beam 110 for each of the recording layers 102 and 104. For example, in FIG. 8, the beam 110 is focused on the six convex portions 107 of the recording layers 102 and 104. In the Blu-ray system, on-groove recording is performed only on the convex portions 107 of the recording layers 102 and 104. As a result, in the Blu-ray system, the recording surfaces S1 and S0 on which recording is actually performed are the same two as the number of recording layers 102 and 104. In addition, the names of S0 and S1 are assigned to the recording surfaces S1 and S0 of the Blu-ray system so that the numbers sequentially increase from the recording layer on the back side in the incident direction of the beam 110.

  In the two-layer BD-R disc 100 of FIG. 8, in order to increase the recording surface, for example, it is conceivable to execute both on-groove recording and in-groove recording for each of the recording layers 102 and 104, for example. That is, it is conceivable to perform so-called land / groove recording on the two-layer BD-R disc 100 of FIG. In this specification, when the recording layers 101 and 103 are uneven as shown in FIG. 8, the recording surface (surface constituted by the convex portions 107) on the near side with respect to the beam 110 in the incident direction of the beam 110. Recording is called on-groove recording, and recording on a recording surface (surface constituted by the concave portions 108) on the back side with respect to the beam 110 in the incident direction of the beam 110 is called in-groove recording. Thereby, it can be expected that the number of recording surfaces becomes twice the number of recording layers 102 and 104 and the storage capacity of the two-layer BD-R disc 100 of FIG. 8 becomes about twice.

  However, in the Blu-ray method, as described above, the wavelength of the laser light source is 405 nm (blue laser) and an objective lens having an aperture ratio NA of 0.85 is used. Therefore, the beam 110 is collected at a steep angle. Shine. Moreover, the pitch of the convex portions 106 and the pitch of the concave portions 107 are as narrow as 0.32 micrometers. Therefore, although the beam 110 can be stably focused on the on-groove (convex portion 107), even if the beam 110 is focused on the in-groove (recessed portion 108), the beam 110 becomes the groove (recessed portion 108). It is difficult to reliably collect the beam 110 into the groove (recess 108). Even if both on-groove (convex portion 107) recording and in-groove (recessed portion) recording are realized in the Blu-ray system, the concentrations of the beams 110 are different from each other. This is also supported by numerical simulations.

  For this reason, in the Blu-ray system, recording of both on-groove (convex portion 107) and in-groove (concave portion 108), that is, land-groove recording has not been adopted.

  The present invention solves such problems in the prior art, and provides an optical recording medium and a recording / reproducing method thereof with a simpler structure and a smaller number of manufacturing processes while ensuring the same storage capacity as that of the conventional one. The purpose is to provide. It is another object of the present invention to provide an optical recording medium having a large storage capacity and a recording / reproducing method thereof that can secure a manufacturing margin by reducing the number of manufacturing processes and thereby can be manufactured at low cost. Furthermore, another object of the present invention is to provide an optical recording medium having a novel structure which has a recording density comparable to that of land / groove recording and which eliminates the disadvantages of land / groove recording, and a recording / reproducing method thereof.

  According to a first aspect of the present invention, in a recording / reproducing method for irradiating a beam onto an optical recording medium and recording or reproducing information on a recording layer of the optical recording medium, the recording layer includes a first recording area and a first recording area. Two recording areas, and the beam is focused from one side of the recording layer to the first recording area, and focused from the other side of the recording layer to the second recording area. A characteristic recording / reproducing method is provided.

  In this recording / reproducing method, the beam is condensed from one side and the other side with respect to the recording layer of the optical recording medium. Even in a single recording layer, there are two recording areas: a first recording area when the beam is condensed from one side and a second recording area when the beam is condensed from the other side. Can function. By doing so, it is possible to eliminate the problem of crosstalk and the disadvantage of the land / groove recording that can occur when high-density recording is performed by irradiating the recording layer with a beam from only one side. Therefore, according to the recording / reproducing method of the present invention, high-density recording can be realized without excessively multilayering the recording layers. Thereby, since the storage capacity of each recording layer is increased, the storage capacity of the entire optical recording medium can be increased while suppressing an increase in the number of manufacturing processes of the optical recording medium.

  Further, in the recording / reproducing method of the first aspect, the recording layer further includes a concave portion and a convex portion that form irregularities on a surface substantially perpendicular to the beam traveling direction, and the first recording area is formed on the convex portion. In addition, the second recording area may be formed in the concave portion, and the beam condensing direction with respect to the recording layer may be reversed in the concave portion and the convex portion.

  With this configuration, the first recording area and the second recording area are realized by the concave portions and the convex portions formed in the storage layer. The first recording area and the second recording area are separated in the beam traveling direction by the unevenness and are formed on separate planes substantially parallel to each other.

  Further, in the recording / reproducing method of the first aspect, the beam may be on-groove recording or on-groove reproduction for both the first recording area by the convex part and the second recording area by the concave part. .

  By configuring in this way, for example, during on-groove recording and reproduction on the convex portion, a pair of concave portions exist on both sides thereof, so that the beam is condensed with a beam diameter that fits within the width of the convex portion and the pair of concave portions. do it. In addition, during on-groove recording and reproduction in the concave portion, a pair of convex portions exist on both sides thereof, so that the beam may be condensed with a beam diameter that fits within the width of the concave portion and the pair of convex portions. The condensing state of the beam on the convex portion and the condensing state of the beam on the concave portion are substantially the same, and only one kind of beam is collected on these. On the other hand, when performing in-groove recording or reproduction in the concave portion, the beam must be focused so as to be within the interval between the pair of convex portions. It is different from the focused state of the beam.

  Further, in the recording / reproducing method of the first aspect, the beam is further applied to the optical recording medium from one side of the recording layer, passes through the recording layer, and is reflected by the reflecting surface existing on the other side of the recording layer. Thus, the light may be condensed from the other side of the recording layer with respect to the second recording area.

  With this configuration, by irradiating the optical recording medium with a beam from one side of the recording layer, the first recording area is condensed from one side of the recording layer, and the second recording layer Light can be condensed from the other side of the recording layer with respect to the recording area. The first recording area and the second recording area, which are formed in the same recording layer and have opposite beam condensing directions, function as a so-called single-sided double layer.

  In the recording / reproducing method of the first aspect, the optical recording medium further has a reflecting surface formed on the other side of the recording layer, and the beam is irradiated from one side of the recording layer to the optical recording medium. The light may be condensed from the other side of the recording layer with respect to the second recording area by being transmitted through the recording layer and reflected by the reflecting surface.

  With this configuration, by irradiating the optical recording medium with a beam from one side of the recording layer, on-groove recording and reproduction can be performed on the first recording area (convex portion), and On-groove recording and reproduction can be performed on the second recording area (concave portion). Both on-groove recording and reproduction can be performed on two recording areas of a single-sided two-layer with opposite condensing directions.

  When the on-groove recording and reproduction are performed on two recording areas of one side and two layers by reflecting the beam by the reflecting surface in this way, the first recording area for the same recording layer is used. The optical path difference between the beam focused on and the beam focused on the second recording area is larger than the depth of the projections and depressions formed by the projections and the recesses.

  In addition, in the case where on-groove recording and reproduction are performed on two recording areas of a single-sided two-layer by reflecting the beam on the reflecting surface, the beam is further generated by a blue laser and has a numerical aperture. The light is collected by a 0.85 condenser lens, and the pitch of the concave portions and the pitch of the convex portions may be 0.32 micrometers.

  By adopting this configuration, it is possible to perform on-groove recording and reproduction using the blue laser for each of the concave portions and the convex portions formed in high density for the blue laser in one recording layer. On-groove recording and reproduction can be performed using a blue laser for two recording areas of a single-sided two-layer with opposite condensing directions.

  According to a second aspect of the present invention, there is provided an optical recording medium capable of recording or reproducing information by being irradiated with a beam, the recording layer on which the beam is condensed, and the first recording A recording layer having a region and a second recording region, the beam being condensable from one side of the recording layer to the first recording region, and the beam from the other side of the recording layer to the second recording region An optical recording medium having a structure capable of condensing light is provided.

  In the optical recording medium of the present invention, the beam can be condensed from one side and the other side with respect to the recording layer of the optical recording medium. Even in a single recording layer, there are two recording areas: a first recording area when the beam is condensed from one side and a second recording area when the beam is condensed from the other side. Function. By doing so, it is possible to eliminate the problem of crosstalk and the disadvantage of the land / groove recording that can occur when high-density recording is performed by irradiating the recording layer with a beam only from one side. Therefore, the recording medium of the present invention can realize high-density recording while suppressing the number of recording layers. Thereby, the storage capacity of each recording layer is increased, so that the storage capacity of the entire optical recording medium can be increased while suppressing an increase in the number of manufacturing processes of the optical recording medium. Also, this optical recording medium can store or reproduce more information than other optical recording media manufactured with the same number of processes.

  The optical recording medium according to the second aspect of the present invention further includes a reflective surface at a position spaced from the recording layer on the other side of the recording layer, and the first recording area of the recording layer. The beam irradiated to the optical recording medium from one side of the recording layer is condensed, and the second recording area is irradiated to the optical recording medium from one side of the recording layer and transmitted through the recording layer. The beam may be reflected from the reflecting surface and condensed from the other side of the recording layer.

  By configuring in this way, by irradiating the optical recording medium with a beam from one side of the recording layer, the first recording area can be recorded and recorded with the beam condensed from one side of the recording layer. The second recording area can be recorded and reproduced by the beam that is reproduced and condensed from the other side of the recording layer. The first recording area and the second recording area of the recording layer function as a so-called single-sided dual layer.

  In the optical recording medium of the second aspect of the present invention, the recording layer and the reflecting surface may be further separated by an interval of 5 μm or more.

  With this configuration, the optical path length of the beam condensed on the first recording area from one side of the recording layer and the light reflected by the reflecting surface are collected on the second recording area from the other side of the recording layer. The optical path length of the beam is an interval more than twice the interval between the recording layer and the flat reflecting surface, that is, an interval of 10 μm or more. Therefore, interlayer crosstalk is unlikely to occur between the first recording area and the second recording area.

  The optical recording medium according to the second aspect of the present invention further includes three recording layers, the reflection surface is disposed on the other side of the three recording layers, and the beam is 90 It may have a reflectance of percent or more.

  With this configuration, since the optical recording medium has a reflective surface on the other side of the three recording layers, the optical recording medium is irradiated with a beam from one side of the recording layer. A beam can be condensed from one side and the other side of each of the recording layers. In addition, since the reflectance of the reflecting surface is 90% or more, one side of the first recording area and the second recording area of the three recording layers, that is, the recording area corresponding to six layers. On-groove recording and reproduction can be performed under the irradiation of the beam from. With three recording layers, a large storage capacity optical recording medium having a recording area corresponding to six surfaces on one side can be realized.

  In the optical recording medium according to the second aspect of the present invention, the reflecting surface may be formed for the information recording area and the address area of the optical recording medium.

  With this configuration, the information on the recording area and the address area can be read using the reflecting surface.

  According to the present invention, it is possible to provide an optical recording medium having a larger storage capacity than the other manufactured by the same number of processes and a recording / reproducing method thereof, while suppressing an increase in the number of manufacturing processes due to multilayering. As a result, the present invention can provide an optical recording medium having a large storage capacity that can be manufactured at a low cost with a manufacturing margin secured, and a recording / reproducing method thereof. Furthermore, the present invention can provide an optical recording medium having a novel structure which has a recording density comparable to that of land / groove recording and which eliminates the disadvantages of land / groove recording, and a recording / reproducing method thereof.

  Embodiments of an optical recording medium and a recording / reproducing method according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a front view of a multilayer BD-R disc 1 according to the first embodiment. FIG. 2 is a cross-sectional view of the multilayer BD-R disc 1 of FIG. The multilayer BD-R disc 1 is a kind of optical recording medium, and has a disc shape (disc shape) similar to a CD (Compact Disc), a DVD (Digital Versatile Disc), and a BD (Blu-ray Disc). A chuck hole 1a is formed at the center. In the following description, the upper and lower sides are used on the basis of the illustrated posture of FIG.

  In the multilayer BD-R disc 1 of Example 1, a highly reflective metal layer 3, a first spacer layer 4, an L0 recording layer 5, and a cover sheet layer 6 are formed on a substantially disc-shaped polycarbonate (PC) substrate 2. , They are stacked in that order.

  The L0 recording layer 5 has a spiral convex portion 7 with the rotation center of the multilayer BD-R disc 1 as a reference. Concave portions 8 are formed between the convex portions 7 formed by forming the convex portions 7 into a spiral shape. For this reason, the concave portion 8 also has a spiral shape in the same winding direction as the convex portion 7 with the rotation center of the multilayer BD-R disc 1 as a reference. In the multilayer BD-R disc 1, the recording surface S0 is formed by the concave portion 8 of the L0 recording layer 5, and another recording surface S1 is formed by the convex portion 7. That is, two recording surfaces are formed on one recording layer. The pitch of the concave portions 8 and the pitch of the convex portions 7 are each 0.32 micrometers.

  In this embodiment, the name of the recording surface is defined as follows. That is, the names of S0 and S1 are given in order from the back side with reference to the incident direction of the beam 21 from the cover sheet layer 6 side. Since the direction from the upper side to the lower side in FIG. 2 is the incident direction of the laser light, the recording surface on the lower side (substrate 2 side) in FIG. 2 is S0, and the recording surface on the upper side (cover sheet layer 6 side) is S1. It becomes.

  As shown in FIG. 2, the multilayer BD-R disc 1 is irradiated with a laser beam 21 from the cover sheet layer 6 side using a known Blu-ray recording / reproducing apparatus as shown in FIG. As a result, information can be recorded on the L0 recording layer 5 and information recorded on the L0 recording layer 5 can be reproduced. In the Blu-ray method, laser light is condensed on the L0 recording layer 5 using a laser light source that outputs a beam 21 having a wavelength of 405 nm (blue laser) and a lens having an aperture ratio NA of 0.85. Note that a Blu-ray recording / reproducing apparatus is a known device and is not particularly illustrated.

  The polycarbonate (PC) substrate 2 is formed by forming a polycarbonate resin into a substantially disc shape having a thickness of 1.1 mm. The upper surface (front surface) of the substrate 2 is a flat mirror surface (a mirror surface or a flat surface), and is a flat surface on which uneven grooves and pit rows are not formed.

  A high reflectivity metal layer 3 is formed on the flat mirror surface of the polycarbonate (PC) substrate 2. The high reflectivity metal layer 3 has a thickness of about 100 nanometers, and is formed over the entire mirror surface of the substrate 2. The upper surface of the high reflectivity metal layer 3 is a flat reflecting surface 3a having no irregularities. The high reflectivity metal layer 3 is formed using a metal such as silver or aluminum or an alloy containing them, for example. For this reason, the reflectance of the upper surface 3 a of the high reflectance metal layer 3 can reflect 90% or more of the incident beam 21 at the wavelength of the beam 21.

  The high reflectivity metal layer 3 only needs to be formed in the multilayer BD-R disc 1 at least in an area where information is recorded or reproduced. The information recording or reproducing area includes an information recording area, an address area, and the like on the disk surface of the multilayer BD-R disk 1.

  A first spacer layer 4 is formed on the high reflectivity metal layer 3. Irregularities are formed on the upper surface of the first spacer layer 4. The unevenness has a spiral shape and corresponds to the unevenness of the L0 recording layer 5.

  An L0 recording layer 5 is formed on the uneven surface of the first spacer layer 4. Although not shown, the L0 recording layer 5 includes a recording film and a dielectric layer sandwiching both sides thereof. The L0 recording layer 5 has a characteristic of absorbing a part of the beam 21 and reflecting or transmitting the rest. In this embodiment, the distance between the high reflectance metal layer 3 and the L0 recording layer 5, that is, the thickness of the first spacer layer 4 is 5 micrometers or more, and is separated by the focal depth of the incident beam 21. Yes.

The material of the recording film 4 may be a conventionally used phase change type recording film material, but in order to obtain a high transmittance, a nitride-based or oxide-based material should be properly used as necessary. Is good. In this example, an oxide-based material (germanium oxide) was used. In addition, the film thickness of the recording film and the dielectric layer (ZnS—SiO ₂ or the like) was adjusted to optimize the reflectance and the absorptance at each recording surface S0 and S1.

  On the L0 recording layer 5, a polycarbonate cover sheet layer 6 is formed. The cover sheet layer 6 has concave and convex grooves formed by a nanoprint method and has a thickness of 90 to 95 micrometers.

  Next, a manufacturing method of the multilayer BD-R disc 1 shown in FIG. 1 will be described. FIG. 3 is a process diagram showing an example of a procedure for manufacturing the multilayer BD-R disc 1 of FIG. 1 by the nanoprint method.

  When the multilayer BD-R disc 1 shown in FIG. 1 is formed by the nanoprint method, first, the unevenness of a stamper (not shown) is transferred to the surface of the transparent cover sheet layer 6 (the lower surface in FIGS. 2 and 3). The L0 recording layer 5 was formed on the uneven surface. For the L0 recording layer 5, germanium oxide was formed on the concavo-convex surface by sputtering.

  Further, as shown in FIG. 3A, a high reflectivity metal layer 3 was formed on the surface of the substrate 2 in which at least a region where information is recorded or reproduced is a mirror surface. The high reflectivity metal layer 3 was formed by depositing silver on the entire mirror surface of the substrate 2 by sputtering. Further, an ultraviolet curable resin 4a to be the first spacer layer 4 was applied on the high reflectance metal layer 3 having a flat surface by a spin coating method. Thereafter, the cover sheet layer 6 on which the L0 recording layer 5 was formed was pressed from above the ultraviolet curable resin 4a.

  Next, as shown in FIG. 3B, ultraviolet rays were appropriately exposed from the transparent cover sheet layer 6 to the ultraviolet curable resin 4a by the ultraviolet exposure light source 22. Thereby, the ultraviolet curable resin 4a is cured, and the cover sheet layer 6 on which the L0 recording layer 5 is formed and the substrate 2 on which the high reflectivity metal layer 3 is formed adhere to each other. A first spacer layer 4 is formed between the high reflectivity metal layer 3 and the L0 recording layer 5. Through these processes, the multilayer BD-R disc 1 of the present embodiment as shown in FIG. 3C is completed.

  In this embodiment, the unevenness of the L0 recording layer 5 is formed by using the cover sheet layer 6 on which the unevenness is formed by the nanoprint method. However, the unevenness may be formed by the 2P method. . In this case, the L0 recording layer 5 may be formed on the uneven surface of the first spacer layer 4 by, for example, sputtering.

  FIG. 4 is an explanatory diagram showing a beam 21 irradiation method at the time of recording / reproduction of the multilayer BD-R disc 1 shown in FIGS. FIG. 4A is an explanatory diagram showing a focused state of the beam 21 with respect to the near-side S1 surface with reference to the incident direction of the beam 21. FIG. FIG. 4B shows a state where the beam 21 is focused on the S0 surface on the back side in the incident direction of the beam 21.

  As shown in FIG. 4A, on the recording surface S1, which is the recording surface on the near side of the recording layer 5 with respect to the beam 21, the beam 21 is directly applied to the recording surface S1 (the convex portion 7 of the recording layer 5). Focused. At this time, the condensing direction of the beam 21 on the recording surface S <b> 1 is a direction from the cover sheet layer 6 toward the substrate 2.

  On the other hand, as shown in FIG. 4B, the beam 21 passes through the recording surface S0 and then reaches the recording surface S0 which is the recording surface on the back side of the recording layer 5 with respect to the beam 21. The light is reflected by the reflectance metal layer 3 and collected on the recording surface S0 (the concave portion 8 of the recording layer 5). Since the traveling direction of the beam 21 is reversed by being reflected by the metal layer 3, the condensing direction of the beam 21 on the recording surface S0 is opposite to the direction from the substrate 2 toward the cover sheet layer 6, that is, the recording surface S1. This is in the direction opposite to the direction in which the beam 21 is focused. If the traveling direction of the beam 21 is taken as a reference, the beam 21 is condensed on the convex portion (land) when entering the recording surface S0, and on-groove recording or reproduction is performed.

  As described above, the multilayer BD-R disc 1 according to FIGS. 1 and 2 can perform on-groove recording and reproduction on all the recording surfaces S0 and S1 during recording and reproduction.

  Note that either of the writing order and the reading order with respect to the two recording surfaces S0 and S1 may be first. In the above description, it is described first that the beam 21 is focused on the recording surface S1 as shown in FIG. 4A, and then the beam 21 is focused on the recording surface S0 as shown in FIG. 4B. On the contrary, first, the beam 21 may be condensed on the recording surface S1 in order from the recording surface S0 as shown in FIG. 4B.

  As described above, in the multilayer BD-R disc 1 of this embodiment, two recording surfaces S0 and S1 are formed by forming one L0 recording layer 5. Therefore, as compared with a conventional disk having two recording layers 5 for each recording surface (on-groove recording disk), a simple structure may be used while ensuring the same storage capacity. As a result, the number of manufacturing processes is small. This makes it easy to secure a final manufacturing margin. Therefore, an inexpensive recording medium can be manufactured. Also, as shown in FIG. 2, the same recording surface as the conventional one has two surfaces (S0 and S1). However, since only one recording layer 5 is required, the total thickness of the spacer layer can be reduced. Furthermore, since there is only one recording layer 5 in this embodiment, there is no need to make an eccentric alignment between the two recording layers 5, which makes it easier to manufacture the multilayer BD-R disc 1 than in the prior art. This makes it possible to reduce the price.

  That is, in the multilayer BD-R disc 1 of this embodiment, the L0 recording layer 5 has two recording surfaces (first recording region and second recording region) S0 and S1, and the beam is directed to the recording surface S1. 21 has a structure capable of condensing light from the incident direction side (one side) 21 and condensing light from the opposite side (the other side) of the incident direction of the beam 21 with respect to the recording surface S1. Therefore, the storage capacity of the L0 recording layer 5 can be made larger than that of an on-groove type disk that can collect the beam 21 from only one side of the recording layer 5. By increasing the storage capacity of the L0 recording layer 5, it is possible to increase the storage capacity while suppressing an increase in the number of manufacturing processes of the multilayer BD-R disc 1. Further, more information can be recorded or reproduced as compared with other multilayer BD-R discs 1 manufactured by the same number of processes. In addition, it is possible to eliminate the problem of crosstalk and the disadvantage of the land / groove recording that can occur when the L0 recording layer 5 is irradiated with the beam 21 from only one side to perform high density recording.

  In particular, the multilayer BD-R disc 1 of this embodiment has a characteristic that the L0 recording layer 5 transmits a part of the beam 21, and the multilayer BD-R disc 1 is the other side of the L0 recording layer 5. , At a position separated from the L0 recording layer 5, a flat reflecting surface (surface of the high reflectivity metal layer 3) 3 a for reflecting the beam 21 transmitted through the L0 recording layer 5 to the L0 recording layer 5 is provided. Then, the reflected light from the flat reflecting surface 3 a is collected from the other side of the L0 recording layer 5. In this embodiment, the multi-layer BD-R disc 1 is irradiated with a beam 21 from one side of the L0 recording layer 5 so that the beam 21 focused from one side of the L0 recording layer 5 is applied to the recording surface S1. Thus, recording and reproduction can be performed on the recording surface S0 by the beam 21 condensed from the other side of the L0 recording layer 5. The two recording surfaces S1 and S0 are comparable to a so-called single-sided dual-layer disc.

  In the multilayer BD-R disc 1 of this embodiment, the L0 recording layer 5 and the flat reflecting surface 3a are separated by an interval of 5 μm or more. Therefore, the optical path length (optical distance) of the beam 21 condensed on the recording surface S1 from one side of the L0 recording layer 5, and the optical path length of the beam 21 reflected by the reflecting surface 3a and condensed on the recording surface S0. Even if simply estimated, an optical path difference of 10 μm or more occurs. Since this optical path difference is sufficiently larger than the depth of focus of the beam 21, the generation of interlayer crosstalk between the two recording surfaces S1 and S0 is prevented.

  Therefore, in the multilayer BD-R disc 1 of this embodiment, the storage capacity can be increased as compared with other discs manufactured with the same number of processes while suppressing an increase in the number of manufacturing processes accompanying the multilayering. As a result, a large-capacity multilayer BD-R disc 1 can be manufactured at a low cost with a manufacturing margin secured.

  Further, in the recording / reproducing method of this embodiment, the beam 21 is focused from one side of the L0 recording layer 5 with respect to the recording surface S1 of the L0 recording layer 5 and also to the recording surface S0 of the L0 recording layer 5. Light is collected from the other side of the L0 recording layer 5. Therefore, in this recording / reproducing method, the beam 21 is condensed from one side and the other side with respect to one L0 recording layer 5 of the multilayer BD-R disc 1 so as to function as two recording surfaces S0 and S1. Can do. Therefore, the storage capacity of the L0 recording layer 5 can be doubled compared to the case of on-groove recording in which the beam 21 is condensed from only one of the L0 recording layer 5. As a result, the storage capacity can be increased while suppressing an increase in the number of manufacturing processes of the multilayer BD-R disc 1. Further, more information can be recorded or reproduced as compared with other multilayer BD-R discs 1 manufactured by the same number of processes. In addition, the optical recording medium of the present invention is also superior in that it can prevent a decrease in yield due to multilayering.

  Further, for example, during on-groove recording and reproduction on the convex portion 7, since there is a pair of concave portions 8 on both sides thereof, the beam 21 can be condensed with a beam diameter that fits within the width of the convex portion 7 and the pair of concave portions 8. That's fine. Moreover, at the time of on-groove recording and reproduction in the concave portion 8, there are a pair of convex portions 7 on both sides of the concave portion 8. Good. The condensing state of the beam 21 on the convex portion 7 and the condensing state of the beam on the concave portion 8 are substantially the same, and only one kind of beam 21 is collected on these. On the other hand, when performing the land / groove recording method, that is, in-groove recording or reproduction in the concave portion 8, the beam 21 must be condensed so as to fit between the pair of convex portions 7. The condensing state of the beam 21 and the condensing state of the beam 21 on the recess 8 are different from each other. In this case, complicated control of the beam diameter or two types of beams must be used.

  In particular, in the recording / reproducing method of this embodiment, the multilayer BD-R disc 1 has a flat reflection formed on the other side of the L0 recording layer 5 together with the L0 recording layer 5 having a characteristic of transmitting part of the beam 21. The beam 21 is irradiated to the multilayer BD-R disc 1 from one side of the recording layer and reflected by the reflecting surface 3a, so that the other side of the L0 recording layer 5 with respect to the recording surface S0. Condensed from the side. Therefore, by irradiating the multilayer BD-R disc 1 with the beam 21 from one side of the L0 recording layer 5, on-groove recording and reproduction are performed on the recording surface S1, and on the recording surface S0. Groove recording and playback can be performed. On-groove recording and reproduction can both be performed on two recording surfaces S0 and S1 of a single-sided double-layer in which the condensing direction is opposite. As in the conventional Blu-ray system, one laser light source can be used.

  In addition, by reflecting the beam 21 by the reflecting surface 3a in this way, when both on-groove recording and reproduction are performed on the two recording surfaces S1 and S0 of the single-sided two layers, the light is condensed on the recording surface S1. The optical path difference between the beam 21 and the beam 21 focused on the recording surface S0 is characterized in that it is larger than the depth of the irregularities formed by the convex portions 7 and the concave portions 8 of the L0 recording layer 5. For example, in this embodiment, the optical path difference between the beam 21 focused on the recording surface S1 and the beam 21 focused on the recording surface S0 is 10 micrometers or more (twice the thickness of the first spacer layer 4 × first The refractive index of the spacer layer 4), and the depth of the irregularities formed by the convex portions 7 and the concave portions 8 of the L0 recording layer 5 is several tens to several hundreds of nanometers. Therefore, the occurrence of crosstalk between the recording surfaces S0 and S1 can be prevented.

  In this embodiment, the blue laser is condensed by a lens having a numerical aperture of 0.85, and is condensed on the concave portion 8 and the convex portion 7 having a pitch of 0.32 micrometers. Information can be recorded and reproduced (land-groove type recording and reproduction) in the recess 8 which cannot be realized by the conventional Blu-ray standard. That is, in this embodiment, on-groove recording and reproduction can be performed using the blue laser for each of the concave portions 8 and the convex portions 7 formed at high density for the blue laser in one recording layer 5. . On-groove recording and reproduction using a blue laser as a one-sided two-layer recording area for two recording areas formed in one recording layer 5 in which the converging direction of the beam 21 is opposite Can do.

  FIG. 5 is a cross-sectional view of the multilayer BD-R disc 10 of the second embodiment. The multilayer BD-R disc 10 of this embodiment is a kind of optical recording medium and has a structure in which recording layers are stacked in three layers. Each recording layer has two recording surfaces, and there are six recording surfaces for actual recording and reproduction.

  Specifically, the multilayer BD-R disc 10 has a polycarbonate (PC) substrate 11 having a thickness of 1.1 mm. On this polycarbonate (PC) substrate 11, a high-reflectance metal layer 12 having a flat surface, a first spacer layer 13, an L0 recording layer 14, a second spacer layer 15, and an L1 recording layer 16 whose surface is an uneven groove. The third spacer layer 17, the L2 recording layer 18, and the cover sheet layer 19 are formed by being stacked in that order. The material of each component is the same as the corresponding component in the first embodiment. The high reflectivity metal layer 12 has a thickness of about 100 nanometers, and is formed over the entire mirror surface of the substrate 11. The upper surface 12a of the high reflectivity metal layer 12 is a flat reflecting surface 12a having no irregularities.

  Each of the L0 recording layer 14, the L1 recording layer 16, and the L2 recording layer 18 has a recording film and a dielectric layer sandwiching both sides thereof, and has a characteristic of absorbing part of the beam and reflecting or transmitting the rest. . All of the plurality of recording layers 14, 16, 18 including the recording layer 14 closest to the reflecting surface 12a has a characteristic of transmitting a part of the beam. Since the recording film requires high transmittance, a nitride-based or oxide-based (germanium oxide) material is properly used as necessary. Further, in order to optimize the reflectance and the absorptance on each recording surface, the film thickness of the recording film and the dielectric layer (ZnS—SiO 2 or the like) is optimized. The L0 recording layer 14 is separated from the high reflectivity metal layer 2 by 10 μm. Thereby, the L0 recording layer 14 and the high reflectivity metal layer 2 are separated by a distance equal to or greater than the focal depth of the incident beam.

  Each of the first spacer layer 13, the second spacer layer 15, and the third spacer layer 17 was formed to have a thickness of about 5 to 30 μm by using a 2P method using an ultraviolet curable resin or a sheet-like nanoprint method. .

  In this embodiment, the name of the recording surface is defined as follows. That is, the names of S0, S1, S2, S3, S4, and S5 were given in order from the back side with reference to the incident direction of the beam 21 from the cover sheet layer 19 side. Since the direction from the upper side to the lower side in FIG. 5 is the incident direction of the laser beam 21, the on-groove recording surface by the convex portion on the upper side (the cover sheet layer 19 side) of the L2 recording layer 18 is S5, and the lower side (substrate) The recording surface formed by the concave portion on the (11 side) is S0. For the middle L1 recording layer 16, the on-groove recording surface by the upper convex portion of the L1 recording layer 16 is S4, and the recording surface by the lower concave portion is S1. For the lower L0 recording layer 14, the on-groove recording surface by the upper convex portion of the L0 recording layer 14 is S3, and the recording surface by the lower concave portion is S2.

  As shown in FIG. 5, the multilayer BD-R disc 10 is irradiated with a beam 21 having a wavelength of 405 nm from the cover sheet layer 19 side using a known Blu-ray recording / reproducing apparatus, as shown in FIG. As a result, information can be recorded on the L0 recording layer 14, L1 recording layer 16 or L2 recording layer 18, and information recorded on the L0 recording layer 14, L1 recording layer 16 or L2 recording layer 18 can be reproduced. Is possible. In the Blu-ray method, a laser light source that outputs a beam having a wavelength of 405 nm (blue laser) and a lens having an aperture ratio NA of 0.85 are used to record laser light in the L0 recording layer 14, the L1 recording layer 16, or the L2 recording. Concentrate on layer 18.

  Next, a manufacturing method of the multilayer BD-R disc 10 shown in FIG. 5 will be described. FIG. 6 is a process diagram showing an example of a procedure for manufacturing the multilayer BD-R disc 10 of FIG. As shown in FIG. 6A, a high reflectance metal layer 12 was deposited by sputtering on the surface of a substrate 11 where at least a region where information is recorded or reproduced is a mirror surface. The high reflectivity metal layer 12 is formed, for example, of silver to a thickness of about 100 nanometers. Next, an ultraviolet curable resin is applied onto the high reflectance metal layer 12 by a spin coating method, and a transparent stamper 23 having a predetermined uneven groove is pressed.

  Next, as shown in FIG. 6B, ultraviolet rays were appropriately exposed to the ultraviolet curable resin using an ultraviolet exposure light source 22. The ultraviolet rays reach the ultraviolet curable resin through the transparent stamper 23. Thereby, the ultraviolet curable resin is cured and the first spacer layer 13 is formed. The unevenness of the transparent stamper 23 is transferred to the upper surface of the first spacer layer 13.

  Next, after the transparent stamper 23 was peeled off, the L0 recording layer 14 was formed on the first spacer layer 13 as shown in FIG. For the L0 recording layer 14, for example, germanium oxide was formed on the uneven surface by sputtering. The transparent stamper 23 is a soft stamper and is discarded.

  Subsequently, as shown in FIG. 6D, an ultraviolet curable resin was applied onto the L0 recording layer 14, and a transparent stamper 24 having a predetermined uneven groove was pressed. Next, as shown in FIG. 6E, ultraviolet rays are appropriately exposed to the ultraviolet curable resin using an ultraviolet exposure light source 22. The ultraviolet rays reach the ultraviolet curable resin through the transparent stamper 24. Thereby, the ultraviolet curable resin is cured and the second spacer layer 15 is formed. The unevenness of the transparent stamper 24 is transferred to the upper surface of the second spacer layer 15.

  Next, after the transparent stamper 24 was peeled off, the L1 recording layer 16 was formed on the second spacer layer 15 as shown in FIG. The L1 recording layer 16 is formed on the uneven surface by, for example, sputtering. The transparent stamper 24 is a soft stamper and is discarded.

  Subsequently, as shown in FIG. 6G, an ultraviolet curable resin was applied on the L1 recording layer 16. Further, instead of the transparent stamper, a transparent cover sheet layer 19 having the L2 recording layer 18 formed on the lower surface in FIG. 5 was pressed. The transparent cover sheet layer 19 may be formed by transferring the unevenness of the stamper by the nanoprint method and forming the L2 recording layer 18 on the uneven surface by the sputtering method.

  Next, as shown in FIG. 6 (H), ultraviolet rays were appropriately exposed to the ultraviolet curable resin using an ultraviolet exposure light source 22. The ultraviolet rays reach the ultraviolet curable resin through the cover sheet layer 19 and the L2 recording layer 18. Thereby, the ultraviolet curable resin is cured and the third spacer layer 17 is formed.

  Through these processes, as shown in FIG. 6I, the three-layered BD-R disc 10 used in this embodiment is completed. In this embodiment, the unevenness is formed on the cover sheet layer 19 by the nanoprint method, but the unevenness may be formed by the 2P method. Thus, when the 2P method is used to form each spacer layer, the number of transparent stampers used is half that of the conventional method, which is advantageous for cost reduction.

  FIG. 7 is an explanatory diagram showing a beam 21 irradiation method at the time of recording / reproducing of the multilayer BD-R disc 10 shown in FIG. FIG. 7A is an explanatory diagram showing a condensing state of the beam 21 with respect to the nearest S5 surface with the incident direction of the beam 21 as a reference. FIG. 7B shows a state where the beam 21 is focused on the S4 surface. FIG. 7C shows a state where the beam 21 is focused on the S3 surface. FIG. 7D shows a state where the beam 21 is focused on the S2 surface. FIG. 7E shows a state where the beam 21 is focused on the S1 surface. FIG. 7F shows a state in which the beam 21 is focused on the deepest S0 surface in the incident direction of the beam 21.

  As shown in FIG. 7A, when recording or reproduction is performed on the recording surface S5, which is the recording surface closest to the beam 21, the beam 21 passes through the cover sheet layer 19 to the recording surface. The light is directly condensed on S5 (the convex portion 7 of the L2 recording layer 18).

  When recording or reproducing the recording surface S4, the focal position of the beam 21 is moved to the back side as shown in FIG. 7B, and recording is performed via the cover sheet layer 19 and the third spacer layer 17. The beam 21 is condensed on the surface S4. When recording or reproducing the recording surface S3, as shown in FIG. 7C, the focal position of the beam 21 is moved to the back side, and the cover sheet layer 19, the third spacer layer 17, and the second spacer are moved. The beam 21 is condensed on the recording surface S3 through the layer 15. On the recording surface (S5 to S3) on the near side of each of the recording layers 14, 16, and 18 thus far, all are on-groove recording with respect to the convex portion. Further, the condensing direction of the beam 21 on each recording surface S <b> 5 to S <b> 3 is a direction from the cover sheet layer 6 toward the substrate 2.

  On the other hand, as shown in FIG. 7D, when recording or reproduction is performed on the recording surface S2, which is the recording surface on the back side of the L0 recording layer 14, with respect to the beam 21, the focal position is further set to the back. Move to the side. After passing through the recording surfaces S5, S4 and S3, the beam 21 is reflected by the high reflectivity metal layer 3 with a reflectance of 90% or more and condensed on the recording surface S2 (the concave portion 8 of the L0 recording layer 14). . Since the traveling direction of the beam 21 is reversed by being reflected by the metal layer 3, when the traveling direction of the beam 21 is taken as a reference, the beam 21 is collected on the convex portion (land) when entering the recording surface S 2. The light is illuminated and on-groove recording or reproduction is performed.

  When recording or reproducing the recording surface S1, as shown in FIG. 7E, the focal position of the beam 21 is moved further back. The beam 21 passes through the recording surfaces S5, S4, S3, is reflected with a reflectance of 90% or more by the high reflectivity metal layer 3, and further passes through the recording surface S2, and then the recording surface S1 (of the L1 recording layer 16). Condensed in the recess 8). Since the traveling direction of the beam 21 is reversed by being reflected by the metal layer 3, when the traveling direction of the beam 21 is taken as a reference, the beam 21 is collected on the convex portion (land) when entering the recording surface S <b> 1. The light is illuminated and on-groove recording or reproduction is performed.

  Further, when recording or reproducing the recording surface S0, the focal position of the beam 21 is further moved to the far side as shown in FIG. The beam 21 passes through the recording surfaces S5, S4, and S3, is reflected with a reflectance of 90% or more by the high reflectance metal layer 3, and further passes through the recording surfaces S2 and S1, and then the recording surface S0 (L2 recording layer). 18 is condensed in the recess 8). Since the traveling direction of the beam 21 is reversed by being reflected by the metal layer 3, when the traveling direction of the beam 21 is taken as a reference, the beam 21 is collected on the convex portion (land) when entering the recording surface S 0. The light is illuminated and on-groove recording or reproduction is performed.

  Thus, on the recording surface (S2 to S0) on the back side of each recording layer 14, 16, 18 is all on-groove recording with respect to the recess 8. In-groove recording is not performed for the concave portion 8. That is, in the recording / reproducing method of FIG. 7, on-groove recording and reproduction can be performed on all the recording surfaces S5 to S0.

  Although FIG. 7 shows an example in which the beam is focused from the recording surface S5 to the recording surface S0 in order, the actual recording or reproduction is performed from the recording surface S0 to the recording surface S5 in the reverse order. May be. When the high reflectivity metal layer 2 is used as a reference, recording or reproducing is performed on both surfaces in the order of the recording surface S3 to the recording surface S5, the recording surface S2 to the recording surface S0, or the L0 recording layer 4 to the L2 recording layer 4. Is preferable. Of course, the order of the plurality of recording surfaces S5 to S0 may be determined as necessary, such as recording or reproduction in random order.

  In the multilayer BD-R disc 10 of this embodiment, as shown in FIG. 5, there are six recording surfaces (S0 to S5) which are the same as the conventional one, and the recording capacity is almost the same as the conventional six-layer optical recording medium. Although the same, the number of recording layer formation processes is three, the number of spacer layer formation processes is three, and the number of cover sheet layer formation processes is one. Compared to a conventional on-groove recording disk in which six recording layers are formed on each recording surface, the same storage capacity is ensured, but a simple structure is required. As a result, the number of recording layer forming processes is 0.5 times, The formation process of the spacer layer is 0.6 times, and the number of processes can be reduced. That is, the final manufacturing margin is widened by significantly reducing the number of processes as compared with the conventional case, and further, the total thickness from the cover sheet layer 19 to the substrate 11 is reduced, so that the material cost can be suppressed. As a result, the price of the multilayer BD-R disc 10 can be reduced.

  As described above, by using the recording / reproducing method of the present invention and the recording / reproducing method suitable for the same, it is possible to provide an inexpensive optical recording medium as compared with the optical recording medium of the prior art.

  In particular, in this embodiment, the multi-layer BD-R disc 10 has three recording layers 14, 16, and 18, and the flat reflective surface 12 a has three recording layers 14, 16, and 18. Arranged on the other side. Moreover, the reflecting surface 12a reflects the beam 21 with a reflectance of 90% or more. Therefore, on-groove recording and reproduction can be performed on the six recording surfaces S5 to S0 by the three recording layers 14, 16, and 18 under irradiation of the beam 21 from one side. With the recording layers 14, 16, and 18 for three layers, it is possible to realize a large-capacity multilayer BD-R disc 10 having recording areas corresponding to six surfaces on one side.

  Although the two-layer BD-R disc has not been described as an example, the manufacturing method, recording / reproducing method, and the light collection state during recording or reproduction are the same as those in the above-described example. . In a two-layer BD-R disc, four recording surfaces are formed in two recording layers, and the recording capacity is almost the same as that of a conventional four-layer optical recording medium. In addition, a two-layer BD-R disc can be formed by a total of five processes: two recording layer formation processes, two spacer layer formation processes, and one cover sheet layer formation process. Therefore, compared to a four-layer on-groove recording disk having a recording layer for each recording surface, the number of processes for forming the recording layer is 0.5 times and the number of processes for forming the spacer layer is 0.67 times, so that the number of processes is reduced. Can do. In this way, compared to conventional on-groove recording disks, the same storage capacity can be ensured and a simple structure is required. As a result, the number of processes is greatly reduced, so that the final manufacturing margin is widened. By reducing the thickness from the sheet layer to the substrate (thickness of the optical recording medium), the material cost can be suppressed, and as a result, the price of the optical recording medium can be reduced. The same applies to an on-groove recording disk having four or more layers.

  Each of the above embodiments is a preferred embodiment of the present invention, but the present invention is not limited to this, and various modifications and changes can be made without departing from the scope of the invention.

  In each of the above embodiments, the L0 recording layers 5, 14, the L1 recording layer 16, and the L2 recording layer 18 have a recording film and a dielectric layer sandwiching both sides in order to transmit the beam 21. In addition, when there are few recording layers, such as two to three layers, in order to improve the characteristics (for example, absorption power) of each recording layer while ensuring the transmission capability of the beam 21, each recording layer is recorded. A semitransparent film or a metal film may be provided on the layers 5, 14, 16, and 18. Further, the transmission characteristics of the plurality of recording layers 14, 16, and 18 of the single multilayer BD-R disc 10 may be the same or different.

  In each of the above embodiments, the on-groove beam 21 is focused on each of the L0 recording layers 5 and 14, the L1 recording layer 16, and the L2 recording layer 18. In addition, for example, the beam 21 may be condensed on each recording layer by an in-groove. In this case, it is expected that the uneven pitch in each recording layer will be widened compared to the case of on-groove, but recording on one recording layer from both sides may result in storage per layer depending on conditions. You can expect to increase capacity.

  In each of the above embodiments, the recording layers of the L0 recording layers 5 and 14, the L1 recording layer 16, and the L2 recording layer 18 are provided with unevenness, and separate recording surfaces (for example, S5 and S0) is formed. In addition, for example, the recording layer may be formed in a planar manner, and the two recording surfaces may be formed on the same surface. However, since the recording layer has projections and depressions as in the above embodiments, the two recording surfaces are separated into separate surfaces that are substantially parallel to each other in the traveling direction of the beam 21, so that the two recording surfaces are formed on the planar recording layer. Heat transfer between the recording surfaces is less likely to occur than when the recording surfaces are provided, that is, when the two recording surfaces are in the same plane.

  In the above embodiments, the multilayer BD-R discs 1 and 10 have the reflecting surfaces 3a and 12a. In addition, for example, the multi-layer BD-R discs 1 and 10 may have a structure that does not have the reflecting surfaces 3a and 12a but can receive the beam 21 from both surfaces. In this case, in order to make the beam 21 incident from one side, a reflecting member that overlaps the multilayer BD-R discs 1 and 10 may be provided on the opposite side of the multilayer BD-R discs 1 and 10.

FIG. 1 is a front view of the optical recording medium of Example 1. FIG. FIG. 2 is a cross-sectional view of the optical recording medium of FIG. 3A to 3C are process diagrams showing an example of a procedure for manufacturing the optical recording medium of FIG. 1 by the nanoprint method. 4A and 4B are explanatory views showing a beam irradiation method during recording and reproduction of the optical recording medium according to FIGS. FIG. 5 is a cross-sectional view of the optical recording medium of Example 2. 6A to 6I are process diagrams showing an example of a procedure for manufacturing the optical recording medium of FIG. 7A to 7F are explanatory views showing a beam irradiation method at the time of recording / reproducing of the optical recording medium according to FIG. FIG. 8 is a cross-sectional view of a conventional optical recording medium.

Explanation of symbols

1, 10: Multilayer BD-R disc (optical recording medium)
2, 11: Polycarbonate substrate 3, 12: High reflectivity metal layer 3a, 12a: Upper surface 4, 13: First spacer layer 5, 14: L0 recording layer 6, 19: Cover sheet layer 7: Convex part 8: Concave part 15 : Second spacer layer 16: L1 recording layer 17: third spacer layer 18: L2 recording layer 21: beam 22: ultraviolet light source 23, 24: transparent stampers S 0, S 1, S 2, S 3, S 4, S 5: recording surface

Claims (12)

In a recording / reproducing method of irradiating a beam to an optical recording medium and recording or reproducing information on a recording layer of the optical recording medium,
The recording layer has a first recording area and a second recording area,
The beam is condensed from one side of the recording layer with respect to the first recording area, and is condensed from the other side of the recording layer with respect to the second recording area. Recording and playback method. The recording / reproducing method according to claim 1,
The recording layer has a concave portion and a convex portion that form irregularities on a surface substantially perpendicular to the traveling direction of the beam,
The first recording area is formed on the convex portion, and the second recording area is formed on the concave portion, and the beam condensing direction with respect to the recording layer is reversed in the concave portion and the convex portion. There is provided a recording / reproducing method. The recording / reproducing method according to claim 2,
The recording / reproducing method according to claim 1, wherein the beam is subjected to on-groove recording or on-groove reproduction for both the first recording area by the convex portion and the second recording area by the concave portion. The recording / reproducing method according to claim 1,
The beam is irradiated onto the optical recording medium from the one side of the recording layer, passes through the recording layer, and is reflected by the reflecting surface existing on the other side of the recording layer, whereby the first A recording / reproducing method, wherein the light is condensed from the other side of the recording layer with respect to a second recording area. The recording / reproducing method according to claim 3,
The optical recording medium has a reflective surface formed on the other side of the recording layer,
The beam is irradiated onto the optical recording medium from the one side of the recording layer, passes through the recording layer, and is reflected by the reflecting surface, so that the recording layer A recording / reproducing method, wherein the light is condensed from the other side. The recording / reproducing method according to claim 5,
For the same recording layer, the optical path difference between the beam focused on the first recording area and the beam focused on the second recording area is an unevenness caused by the convex part and the concave part. A recording / reproducing method characterized by being larger than the depth. The recording / reproducing method according to claim 5,
The beam is focused by a lens with a blue laser and a numerical aperture of 0.85,
The pitch of the concave portions and the pitch of the convex portions are 0.32 micrometers. An optical recording medium capable of recording or reproducing information by being irradiated with a beam,
A recording layer on which the beam is condensed, the recording layer having a first recording area and a second recording area;
The beam can be condensed from one side of the recording layer to the first recording area, and the beam can be condensed from the other side of the recording layer to the second recording area. An optical recording medium characterized by the above. The optical recording medium according to claim 8, wherein
The optical recording medium has a reflective surface at a position separated from the recording layer on the other side of the recording layer,
The beam irradiated to the optical recording medium from the one side of the recording layer is condensed on the first recording area of the recording layer, and the second recording area is An optical recording medium, wherein the beam irradiated to the optical recording medium from one side and transmitted through the recording layer is reflected by the reflecting surface and condensed from the other side. An optical recording medium according to claim 9, wherein
The optical recording medium, wherein the recording layer and the reflecting surface are separated by an interval of 5 μm or more. The optical recording medium according to claim 9 or 10,
Having three recording layers, and
The optical recording medium, wherein the reflective surface is disposed on the other side of the three recording layers and has a reflectance of 90% or more with respect to the beam. The optical recording medium according to any one of claims 9 to 11,
The optical recording medium, wherein the reflection surface is formed for an information recording area and an address area of the optical recording medium.

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