JP2011044190A - Optical disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that a reproducer based on a first standard cannot reproduce information from an optical disk, from which more information is reproduced by a reproducer based on a second standard for an optical disk having higher information recording density than that of an optical disk based on the first standard. <P>SOLUTION: The optical disk 1 includes: a first substrate 2; a first information recording layer 4 disposed on the first substrate 2 and reflecting first light; a second substrate 6 disposed on the first information recording layer 4 and transmitting the first light; a second information recording layer 8 disposed on the second substrate 6, transmitting the first light, and reflecting second light; an intermediate layer 9 disposed on the second information recording layer 8 and transmitting the first light and the second light; and a third information recording layer 11 disposed on the intermediate layer 9, transmitting the first light and a part of the second light, reflecting the remaining part of the second light, and formed of dielectric. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical disc having a plurality of information recording layers.

  With the spread of thin large-screen TVs and the rise of multimedia, the handling of large volumes of information such as digital moving images is increasing, and the demand for larger capacity of optical disks is increasing. Currently, in addition to a CD (Compact Disc) having a capacity of about 650 MB (megabytes) and a DVD (Digital Versatile Disc) having a capacity of about 4.7 GB (gigabytes), a BD-ROM having a capacity of about 25 GB ( Blu-ray-Disc Read Only Memory) has been commercialized.

  A DVD is an optical disc that supports red light, is suitable for recording standard-definition (SD) digital moving images, and is reproduced by a DVD player. A BD-ROM is an optical disc that supports blue light, is suitable for recording high-definition (HD) digital moving images, and is reproduced by a BD player. Hereinafter, the DVD-ROM and the BD-ROM will be described in order with reference to the drawings.

  First, the configuration of the DVD-ROM will be described with reference to FIG. FIG. 29 is a cross-sectional view of the DVD-ROM 190. As shown in FIG. 29, the DVD-ROM 190 includes a dummy substrate 191, an adhesive layer 192, an information recording layer 193, and a substrate 194. A pit row 194a including tracks having a pitch of 0.74 μm is formed on the upper surface of the substrate 194, and the information recording layer 193 is provided on the substrate 194 on which the pit row 194a is formed. The DVD-ROM 190 is formed by bonding a substrate 194 provided with an information recording layer 193 and a dummy substrate 191 with an adhesive layer 192. Information recorded on the DVD-ROM 190 is reproduced by using a DVD player to collect the red DVD laser light Lr on the information recording layer 193 by the DVD objective lens 39r and processing the reflected light. .

  Next, a single-layer BD-ROM having one information recording layer will be described with reference to FIG. FIG. 30 is a cross-sectional view of a single-layer BD-ROM 200 having one information recording layer. As illustrated in FIG. 30, the single-layer BD-ROM 200 includes a substrate 201, an information recording layer 202 provided on the substrate 201, and a protective layer 203 provided on the information recording layer 202. . On the upper surface of the substrate 201, pit rows 201a including tracks having a pitch of 0.32 μm are formed. Information recorded in the single-layer BD-ROM 200 is reproduced by collecting the blue BD laser light Lb on the information recording layer 202 by the BD objective lens 39b and processing the reflected light using a BD reproduction machine. Is done.

  A two-layer BD-ROM having a capacity (about 50 GB) twice that of the one-layer BD-ROM is also commercialized. FIG. 31 is a cross-sectional view of a two-layer BD-ROM 210 having two stacked information recording layers. As shown in FIG. 31, the two-layer BD-ROM 210 includes a substrate 211, a first information recording layer 212 provided on the substrate 211, and an intermediate layer provided on the first information recording layer 212. 213, a second information recording layer 214 provided on the intermediate layer 213, and a protective layer 215 provided on the second information recording layer 214.

  A pit row 211a including tracks having a pitch of 0.32 μm is formed on the upper surface of the substrate 211, and a second layer pit row 213a including tracks having a pitch of 0.32 μm is formed on the upper surface of the intermediate layer 213. Is formed. The first information recording layer 212 and the second information recording layer 214 are equivalent to the information recording layer 202 of the one-layer BD-ROM 200 shown in FIG. The information recorded in the two-layer BD-ROM 210 is reflected by using a BD reproduction machine and collecting the BD laser light Lb on the first information recording layer 212 and the second information recording layer 214 by the BD objective lens 39b. Regenerated by processing the light.

  A BD / DVD hybrid disc is disclosed in Patent Document 1. The BD / DVD hybrid disc is an optical disc in which a relatively low-density DVD-ROM information recording layer and a relatively high-density BD-ROM information recording layer are stacked. FIG. 32 is a cross-sectional view of the BD / DVD hybrid disc 220. As shown in FIG. 32, the BD / DVD hybrid disc 220 includes a first information recording substrate 221 corresponding to a DVD-ROM and a second BD-ROM corresponding to a BD-ROM provided on the first information recording substrate 221. It has an information recording substrate 222 and a protective layer 223 provided on the second information recording substrate 222. The first information recording substrate 221 and the second information recording substrate 222 are bonded together by an adhesive layer 224.

  The first information recording substrate 221 includes a substrate 221a on the surface of which DVD information recording pits 221c having a pitch of 0.74 μm are formed, and a DVD information recording layer 221b provided on the substrate 221a. The second information recording substrate 222 has a substrate 222a on the surface of which BD information recording pits 222c having a pitch of 0.32 μm are formed, and a BD information recording layer 222b provided on the substrate 222a. The second information recording substrate 222 transmits the laser beam Lr for DVD.

  Information recorded on the first information recording substrate 221 of the BD / DVD hybrid disc 220 is obtained by collecting the DVD laser light Lr on the DVD information recording layer 221b by the DVD objective lens 39r using a DVD player and reflecting the information. Regenerated by processing the light. The information recorded on the second information recording substrate 222 of the BD / DVD hybrid disc 220 is reflected on the BD laser beam Lb collected by the BD objective lens 39b on the BD information recording layer 222b using a BD player. Regenerated by processing the light.

  If an SD moving image is recorded on the first information recording substrate 221, an HD moving image having the same content is recorded on the second information recording substrate 222, and the BD / DVD hybrid disc 220 is distributed, the HD on one optical disc Video and SD video can be provided.

JP 2008-97755 A

  The two-layer BD-ROM can record a higher quality digital moving image corresponding to a large screen monitor or projector that is rapidly spreading, but can be played back by a DVD player that is widely spread now. Can not.

  Since the BD / DVD hybrid disc has a DVD-ROM information recording layer and a BD-ROM information recording layer, it can be reproduced by a DVD player, but the recording capacity of the information recording layer of the BD-ROM is small. It is not possible to record a higher quality digital moving image.

  The present invention can be reproduced by a reproducing apparatus corresponding to the first standard, and more information can be reproduced by a reproducing apparatus corresponding to the second standard related to the optical disc having a higher recording density of information than the optical disc of the first standard. It is an object of the present invention to provide an optical disc capable of reproducing the image.

  In order to solve the above problems and achieve the above object, an optical disc according to the present invention includes a first substrate having a first pit row corresponding to a first standard formed on an upper surface thereof, and the first substrate. Provided on the first information recording layer reflecting the first light corresponding to the first standard, and provided on the first information recording layer. A second substrate that transmits the first light, on which a second pit row corresponding to a second standard relating to a disk having a higher information recording density than that of the first standard disk is formed; A second information recording layer which is provided on the substrate and transmits the first light and reflects the second light corresponding to the second standard; and The third pit row corresponding to the second standard is formed on the upper surface. An intermediate layer that transmits the first light and the second light, and an intermediate layer that is provided on the intermediate layer, transmits the first light and transmits a part of the second light. And a third information recording layer formed of a dielectric that reflects the remainder.

  The present invention can be reproduced by a reproducing apparatus corresponding to the first standard, and more information can be reproduced by a reproducing apparatus corresponding to the second standard related to the optical disc having a higher recording density of information than the optical disc of the first standard. Can be provided.

It is sectional drawing of the optical disk of this Embodiment. It is a block diagram of the optical disk drive device for DVD. It is a block diagram of a multi-segment light receiving detector. It is a block diagram of a quadrant detector for focus control. It is a figure which shows an example of the relationship between the distance of an objective lens and an optical disk, and RF signal (reflectance) obtained during execution of a focus search. It is a figure which shows an example of the relationship between the distance of an objective lens and an optical disk, and RF signal (reflectance) obtained during execution of a focus search. It is a figure which shows the mode of condensing in the quadrant detector for focus control in case spherical aberration is small, the focus error signal FE, and RF signal. It is a figure which shows the mode of condensing in the 4 division detector for focus control in case spherical aberration is large, the focus error signal FE, and RF signal. It is a figure which shows the relationship between the thickness and the reflectance with respect to the light of wavelength 405nm, and the relationship between the thickness and the reflectance with respect to the light of wavelength 650nm about the compound of Si and H. It is a figure which shows the relationship between the thickness and the transmittance | permeability with respect to the light of wavelength 405nm, and the relationship between the thickness and the transmittance | permeability with respect to the light of wavelength 650nm about the compound of Si and H. For ZnS-SiO _2, a thickness of 56 nm, 111 nm, 135 nm, 167 nm, and 195 in each case, it is a diagram showing the relationship between the wavelength and the reflectance. For ZnS-SiO _2, a thickness of 56 nm, 111 nm, 135 nm, 167 nm, and 195 in each case, it is a graph showing the relationship between the wavelength and transmittance. It is a figure which shows the relationship between the wavelength and reflectance in the case where the thickness of the material whose refractive index is 2.2 obtained by optical thin film simulation is 10 nm. It is a figure which shows the relationship between the wavelength and reflectance in the case where the thickness of the material whose refractive index is 2.2 obtained by optical thin film simulation is 30 nm. It is a figure which shows the relationship between the wavelength and reflectance in the case where the thickness of the material whose refractive index is 2.2 obtained by optical thin film simulation is 60 nm. It is a figure which shows the relationship between the wavelength and reflectance in the case where the thickness of the material whose refractive index is 2.2 obtained by optical thin film simulation is 90 nm. It is a figure which shows the relationship between the wavelength and reflectance in the case where the thickness of the material whose refractive index is 2.2 obtained by optical thin film simulation is 110 nm. It is a figure which shows the relationship between the wavelength and reflectance in the case where the thickness of the material whose refractive index is 2.2 obtained by optical thin film simulation is 124 nm. It is a figure which shows the relationship between the wavelength and reflectance in the case where the thickness of the material whose refractive index is 2.2 obtained by optical thin film simulation is 152 nm. It is a figure which shows the relationship between the wavelength and reflectance in the case where the thickness of the material whose refractive index is 2.2 obtained by optical thin film simulation is 160 nm. It is a figure which shows the relationship between the wavelength and reflectance in the case where the thickness of the material whose refractive index is 2.2 obtained by optical thin film simulation is 200 nm. It is a figure which shows the relationship between the wavelength and reflectance in the case where the thickness of the material whose refractive index is 2.2 obtained by optical thin film simulation is 230 nm. It is the 1st figure which shows the relationship between the wavelength and reflectance when the wavelength of the light with the maximum reflectance obtained by the optical thin film simulation is about 405 nm. It is a 2nd figure which shows the relationship between the wavelength and reflectance in case the wavelength of the light with the maximum reflectance obtained by optical thin film simulation becomes the vicinity of 405 nm. It is the 3rd figure which shows the relationship between the wavelength and reflectance when the wavelength of the light with the maximum reflectance obtained by the optical thin film simulation is near 405 nm. It is the 4th figure which shows the relationship between the wavelength and reflectance when the wavelength of the light with the maximum reflectance obtained by the optical thin film simulation is near 405 nm. It is a 5th figure which shows the relationship between the wavelength and reflectance when the wavelength of the light with the maximum reflectance obtained by the optical thin film simulation is near 405 nm. It is a figure for demonstrating the manufacturing method of the optical disk of this Embodiment. It is sectional drawing of DVD-ROM. It is sectional drawing of 1 layer BD-ROM which has one information recording layer. It is sectional drawing of 2 layer BD-ROM which has two information recording layers laminated | stacked. It is sectional drawing of a BD / DVD hybrid disc.

  EMBODIMENT OF THE INVENTION Below, the form for implementing this invention is demonstrated with reference to drawings.

  First, the configuration of the optical disc 1 of the present embodiment will be described with reference to FIG. FIG. 1 is a cross-sectional view of an optical disc 1 according to the present embodiment. As shown in FIG. 1, the optical disc 1 of the present embodiment includes a first substrate 2, a first information recording layer 4 provided on the first substrate 2, and a first information recording layer. 4, the second substrate 6 provided on the second substrate 6, the second information recording layer 8 provided on the second substrate 6, and the second information recording layer 8. It has an intermediate layer 9, a third information recording layer 11 provided on the intermediate layer 9, and a protective layer 12 provided on the third information recording layer 11.

  The first substrate 2 and the first information recording layer 4 correspond to a conventional DVD-ROM. The second substrate 6 and the second information recording layer 8, the intermediate layer 9 and the third information recording layer 11 correspond to a conventional BD-ROM.

  The first substrate 2 is made of polycarbonate and has a diameter of 120 mm and a thickness of 0.6 mm. On the upper surface of the first substrate 2, concave first information recording pits 3 having a pitch of 0.74 μm are formed from the inner periphery toward the outer periphery. The first information recording pit 3 conforms to the DVD-ROM standard. In order to maintain compatibility with a conventional DVD-ROM and perform so-called reverse reading, the spiral direction of the first information recording pit 3 is from the inner periphery to the outer periphery.

  The first information recording layer 4 is a reflective film formed by sputtering a metal such as Ag, Al, Au, or an alloy containing them as a main component on the upper surface of the first substrate 2, and is a DVD. The laser beam Lr for use is reflected. The thickness of the first information recording layer 4 is designed so that the reflectance with respect to the laser beam Lr for DVD is 45% or more.

  The second substrate 6 is a substrate conforming to the BD-ROM standard, and has a diameter of 120 mm and a thickness of 0.4 mm to 0.5 mm. On the upper surface of the second substrate 6, concave second information recording pits 7 having a pitch of 0.32 μm are formed from the inner periphery toward the outer periphery. The second information recording pit 7 conforms to the BD-ROM standard. Note that the first information recording layer 4 and the second substrate 6 are bonded together by the adhesive sheet 5.

  The second information recording layer 8 is a layer that transmits the laser beam Lr for DVD and reflects the laser beam Lb for BD. For example, on the upper surface of the second substrate 6, silicon (Si), It is formed by sputtering a compound composed of all or part of aluminum (Al), germanium (Ge), and titanium (Ti) and all or part of nitrogen, oxygen, and hydrogen. The thickness of the second information recording layer 8 is designed so that the transmittance with respect to the laser beam Lr for DVD is 50% or more, and the laser beam Lb for BD is sufficiently reflected.

  The intermediate layer 9 is a layer that transmits the laser beam Lr for DVD and the laser beam Lb for BD, and an ultraviolet curable resin or the like is applied to the upper surface of the second information recording layer 8 by spin coating. It is formed. The thickness of the intermediate layer 9 is designed so that the transmittance with respect to the laser beam Lr for DVD and the transmittance with respect to the laser beam Lb for BD are 80% or more, for example, 25 μm. On the upper surface of the intermediate layer 9, concave third information recording pits 10 having a pitch of 0.32 μm are formed. The third information recording pit 10 conforms to the BD-ROM standard. The third information recording pit 10 is formed by curing the ultraviolet curable resin forming the intermediate layer 9 with ultraviolet rays using a transparent polycarbonate resin or polyolefin resin stamper in the process of forming the intermediate layer 9. .

  The third information recording layer 11 is a layer that transmits the laser beam Lr for DVD and reflects part of the laser beam Lb for BD and transmits the remaining part. For example, on the upper surface of the intermediate layer 9, Sputtering or vapor deposition of a compound composed of all or part of Si, ZnS, Zr, Y, W, Ta, Nb, Cr, Hf, Ce and Ti and all or part of oxygen and nitrogen, etc. It is formed by. The thickness of the third information recording layer 11 is designed to transmit 80% or more of the DVD laser beam Lr, to transmit 70% or more of the BD laser beam Lb, and to reflect 12% or more.

  The protective layer 12 is a layer of an ultraviolet curable resin or a polycarbonate sheet, and the thickness thereof is designed to transmit 80% or more of the laser beam Lr for DVD and the laser beam Lb for BD, for example, 75 μm. is there. Further, a hard coat layer having a thickness of about 1 μm may be applied to the surface of the protective layer 12 in order to make it difficult to get scratches and dirt.

  As described above, the optical disc 1 according to the present embodiment has the first information recording layer 4 that is a DVD signal surface corresponding to a DVD-ROM and the second information recording layer 4 that is a BD signal surface corresponding to a BD-ROM. It has an information recording layer 8 and a third information recording layer 11. Therefore, the optical disk 1 of the present embodiment can be reproduced by either a DVD player or a BD player. Further, more information (for example, higher quality moving images) corresponding to the BD standard can be recorded on the second information recording layer 8 and the third information recording layer 11 corresponding to the BD-ROM.

  The information recorded in the first information recording layer 4 is obtained by applying the laser beam Lr for DVD to the first information recording layer 4 by the DVD objective lens 39r having NA (numerical aperture) 0.6 or 0.65. It is reproduced by collecting and processing the reflected light. The information recorded in the second information recording layer 8 and the third information recording layer 11 is obtained by using the BD laser light Lb by the BD objective lens 39b with NA of 0.85 for the second information recording layer 8 and the third information recording layer 11. It is reproduced by collecting in the information recording layer 11 and processing the reflected light.

  By the way, the reproduction of the optical disc 1 of the present embodiment having the first information recording layer 4 corresponding to the DVD-ROM, and the second information recording layer 8 and the third information recording layer 11 corresponding to the BD-ROM. May not be played properly when trying to play a DVD with a DVD player. Therefore, the configuration of the optical disc 1 that is normally played back by a DVD player will be described below.

  For the explanation, prior to the explanation, the operation of the DVD optical disc drive device 20 for reproducing the optical disc 1 of the present embodiment will be explained with reference to FIG. FIG. 2 is a configuration diagram of the DVD optical disk drive apparatus 20.

  When the optical disk 1 is loaded into the DVD optical disk drive device 20, the optical disk 1 is rotated by a spindle motor (not shown). An optical pickup 30 is disposed below the laser beam incident surface 1a of the optical disc 1. The laser beam incident surface 1 a is the surface of the protective layer 12 constituting the optical disc 1.

  The optical pickup 30 is provided so as to be movable in the radial direction of the rotatable optical disc 1. The optical pickup 30 includes a semiconductor laser light source 31, a collimator lens 32, a polarization beam splitter 34, a monitor condenser lens 35, a monitor photodetector 36, a rising mirror 37, and a ¼ wavelength plate 38. A DVD objective lens 39r, a lens holder 40, a tracking coil 41, a focus coil 42, a half prism 43, a detection lens 44, a multi-segment light receiving detector 45, a cylindrical lens 46, and a focus control. A quadrant detector 47.

  In the optical pickup 30, the red DVD laser light Lr emitted from the semiconductor laser light source 31 is converted into parallel light by the collimator lens 32.

  The laser beam Lr for DVD converted into parallel light by the collimator lens 32 enters the polarization beam splitter 34, and is a polarization selective dielectric multilayer film 34a (p-polarized light: provided inside the polarization beam splitter 34). 95% transmission, 5% reflection, s-polarized light: reflection) is transmitted about 95%. About 5% of the light incident on the polarization beam splitter 34, that is, the light reflected by the polarization-selective dielectric multilayer film 34a, is monitored as a monitoring laser beam through the monitoring condenser lens 35. Incident light enters the optical detector 36. The monitoring photodetector 36 monitors the output of the DVD laser light Lr emitted from the semiconductor laser light source 31.

  The DVD laser light Lr that has passed through the polarization beam splitter 34 is bent upward by 90 ° by the rising mirror 37 and directed upward, giving a phase difference of ¼ wavelength to the DVD laser light Lr. The light is incident on a DVD objective lens 39r having an NA of about 0.6 to 0.65 through a quarter-wave plate 38 that converts it into circularly polarized light. A tracking coil 41 and a focus coil 42 are attached to the outside of the lens holder 40 to which the DVD objective lens 39r is attached.

  The DVD laser beam Lr narrowed down by the DVD objective lens 39r is incident on the laser beam incident surface 1a of the optical disc 1. The DVD laser light Lr incident on the laser beam incident surface 1a is transmitted through the second information recording layer 8 and the third information recording layer 11 as the BD signal surface, and the first laser signal Lr as the DVD signal surface. The information recording layer 4 is collected in a spot shape.

  The return light reflected by the first information recording layer 4 is incident on the DVD objective lens 39r again, passes through the quarter wavelength plate 38, and is linearly polarized light (s-polarized light) whose polarization direction is orthogonal to the forward path. ) And head to the startup mirror 37. Then, the return light is reflected by the polarization-selective dielectric multilayer film 34 a of the polarization beam splitter 34 via the rising mirror 37 and travels toward the half prism 43.

  The half prism 43 divides the light from the polarization beam splitter 34 into light (RF signal light) traveling toward the detection lens 44 and light traveling toward the cylindrical lens 46. The light of the RF signal system is collected on the multi-segment light receiving detector 45 by the detection lens 44. The light traveling toward the cylindrical lens 46 is given astigmatism by the cylindrical lens 46 and travels toward the focus control quadrant detector 47.

  FIG. 3 is a configuration diagram of the multi-segment light receiving detector 45. As shown in FIG. 3, the multi-segment light receiving detector 45 includes four detection areas A to 4 which are divided into four by orthogonally intersecting a straight line along the track direction of the optical disc 1 and a straight line along the radial direction of the optical disc. D. In FIG. 3, reference signs A to D indicate the respective detection areas of the multi-segment light reception detector 45, and in the following description, reference signs “a” to “d” indicate received light amounts in the respective detection areas.

  The multi-segment light receiving detector 45 outputs the amount of light received in each detection region to the RF signal processing circuit 50 and the tracking control circuit 60 provided in the optical disk drive device 20 for DVD.

  The RF signal processing circuit 50 adds the respective received light amounts of the detection areas A to D in the multi-segment light receiving detector 45 that has received the RF signal light, as shown in the following equation (1). Calculate the signal. The RF signal is a main data signal recorded on the first information recording layer 4 of the optical disc 1.

RF signal = (a + b + c + d) (1)
“A” is the amount of light received in the detection region A, “b” is the amount of light received in the detection region B, “c” is the amount of light received in the detection region C, and “d” is in the detection region D. This is the amount of light received.

  The tracking control circuit 60 obtains a diagonal difference signal by using a well-known differential phase detection method (DPD method).

  Specifically, the tracking control circuit 60 has two diagonal lines in one of the four detection areas A to D of the multi-segment light receiving detector 45 as shown in the following equation (2). A diagonal difference signal is obtained by calculating a difference between the sum of the received light amounts in the detection region and the sum of the received light amounts in the two detection regions on the other diagonal line. That is, the tracking control circuit 60 calculates the difference between the total received light amount (a + c) of the detection region A and the detection region C and the total received light amount (b + d) of the detection region B and the detection region D, and obtains a diagonal difference signal. .

Diagonal difference signal = {(a + c) − (b + d)} (2)
The tracking control circuit 60 uses the diagonal difference signal (differential phase detection signal DPD) obtained by the equation (2) as the tracking error signal TE, and uses the diagonal difference signal (differential phase detection signal DPD) inside the optical pickup 30. Is supplied to the tracking coil 41 and the DVD objective lens 39r is moved to perform tracking control.

  Next, light traveling from the half prism 43 toward the cylindrical lens 46 will be described. As described above, the light traveling toward the cylindrical lens 46 is provided with astigmatism by the cylindrical lens 46 and collected on the focus control quadrant detector 47.

  FIG. 4 is a configuration diagram of the focus control quadrant detector 47. The focus control quadrant detector 47 is the same means as the multi-segment light receiving detector 45, and as shown in FIG. 4, a straight line along the track direction of the optical disc 1 and a straight line along the radial direction of the optical disc are obtained. It has four detection areas E to H divided into four orthogonally. 4 and 8, reference symbols E to H indicate detection areas of the focus control quadrant detector 47, and in the following description, reference symbols e to h indicate received light amounts in the detection areas. Further, the detection region E corresponds to the detection region A of the multi-segment light reception detector 45, the detection region F corresponds to the detection region B of the multi-segment light reception detector 45, and the detection region G is detected by the multi-segment light reception detector 45. Corresponding to the region C, the detection region H corresponds to the detection region D of the multi-segment light receiving detector 45.

  The focus control quadrant detector 47 outputs the amount of light received in each detection region to a focus control circuit 70 provided in the DVD optical disk drive device 20.

  The focus control circuit 70 obtains the focus error signal FE using a known astigmatism method. Specifically, the focus control circuit 70 is positioned at one diagonal of the four detection areas E to H of the focus control quadrant detector 47 as shown in the following equation (3). The difference between the sum of the received light amounts in the two detection regions and the sum of the received light amounts in the two other detection regions located on the other diagonal is calculated to obtain a focus error signal FE. That is, the focus control circuit 70 calculates the difference between the total received light amount (e + g) of the detection region E and the detection region G and the total received light amount (f + h) of the detection region F and the detection region H, and generates the focus error signal FE. obtain.

Focus error signal FE = {(e + g) − (f + h)} (3)
“E” is the amount of light received in the detection region E, “f” is the amount of light received in the detection region F, “g” is the amount of light received in the detection region G, and “h” is in the detection region H. This is the amount of light received.

  Then, the focus control circuit 70 supplies the focus error signal FE to the focus coil 42 inside the optical pickup 30 and moves the DVD objective lens 39r to perform focus control. That is, the focus control circuit 70 performs a focus search by moving the DVD objective lens 39r closer to or away from the optical disc 1 based on the focus error signal FE, so that the DVD laser light Lr is the first information recording. Control is performed so that the layer 4 is just focused.

  Incidentally, the DVD objective lens 39r for just focusing the laser beam Lr for DVD on the first information recording layer 4 is at one position, and the laser beam Lr for DVD is used for the first information at other positions. Do not just focus on the recording layer 4. During the execution of the focus search, the focus control circuit 70 changes the distance between the DVD objective lens 39r and the optical disc 1 to check the amount of reflected light from the optical disc 1, and at the position where the amount of reflected light is maximized, the DVD objective. The lens 39r is moved. At this time, data indicating the value of the RF signal with respect to the distance between the DVD objective lens 39r and the optical disc 1 is obtained.

  5 and 6 are diagrams showing the relationship between the distance between the DVD objective lens 39r and the optical disc 1 and the RF signal obtained during execution of the focus search. The RF signal indicates the amount of reflected light from each part of the optical disc 1, but is proportional to the reflectance of each part because the amount of incident light is constant. In FIGS. 5 and 6, the symbol “X” indicates the reflection of the laser beam incident surface 1a with respect to the DVD laser beam Lr, and the symbol “Y” indicates the second information recording with respect to the DVD laser beam Lr. The reflection of the layer 8 and the third information recording layer 11 is shown, and the symbol “Z” shows the reflection of the first information recording layer 4 with respect to the laser beam Lr for DVD.

  In the following, in order to investigate the conditions under which the optical disc 1 is normally played back by a DVD player, the value of the RF signal for the optical disc 1 is used, and the second information recording of the optical disc 1 with respect to the laser beam Lr for DVD is performed. The relationship between the reflectance of the layer 8 and the third information recording layer 11 and the reflectance of the laser beam incident surface 1a was examined, and the result will be described.

  The reason for measuring the reflectance using the RF signal is as follows. That is, if it is attempted to optically accurately measure the reflectances of the laser beam incident surface 1a, the third information recording layer 11, and the second information recording layer 8, an accurate reflectance measuring optical device is required. In addition, there are many measurement steps. Also, when the focus error signal FE is used, a problem occurs as will be described later. On the other hand, when an RF signal is used, the reflectance can be measured easily and relatively accurately. Therefore, the reflectance is measured using the RF signal.

  The occurrence of a problem when the focus error signal FE is used to obtain the reflectance will be described with reference to FIGS.

  FIG. 7 is a diagram showing a state of focusing in the focus control quadrant detector 47 when the spherical aberration is small, a focus error signal FE, and an RF signal. Specifically, FIG. 7A shows a state of condensing in the focus control quadrant detector 47 when the spherical aberration is small, and FIG. 7B shows a focus when the spherical aberration is small. An error signal FE is shown, and FIG. 7C shows an RF signal when the spherical aberration is small. 7A, 7B, and 7C, the drawings overlapping in the vertical direction are related to each other.

  FIG. 8 is a diagram illustrating a state of light collection in the focus control quadrant detector 47 when the spherical aberration is large, a focus error signal FE, and an RF signal. Specifically, FIG. 8A shows a state of condensing in the focus control quadrant detector 47 when the spherical aberration is large, and FIG. 8B shows a focus when the spherical aberration is large. An error signal FE is shown, and FIG. 8C shows an RF signal when the spherical aberration is large. 8A, 8B, and 8C, the drawings that overlap in the vertical direction are related to each other.

  When the spherical aberration is small, as shown in the center diagram of FIG. 7A, the reflected light from each information recording layer of the optical disc 1 collected by the cylindrical lens 46 is used for focus control when the information recording layer is focused. A small circle is collected at the center of the quadrant detector 47. However, if the information recording layer is nearer or farther from the focus, the light in the quadrant detector 47 for focus control is an ellipse inclined by 45 degrees as shown in the second two figures from both ends of FIG. It becomes. When the information recording layer is further closer to or farther from the focal point, the amount of light in the focus control quadrant detector 47 decreases as shown in the two diagrams at both ends of FIG.

  When the spherical aberration is large, as shown in the center diagram of FIG. 8A, the reflected light from each information recording layer of the optical disc 1 collected by the cylindrical lens 46 is used for focus control when the information recording layer is focused. A small circle is collected at the center of the quadrant detector 47. However, as is clear from a comparison between the center diagram of FIG. 7A and the center diagram of FIG. 8A, the size of the light circle collected at the center of the focus control quadrant detector 47 is as follows. The spherical aberration is large compared to the small case. If the information recording layer is closer or farther than the focal point, the light in the focus control quadrant detector 47 becomes an ellipse inclined by 45 degrees as shown in the second two figures from both ends of FIG. When the information recording layer is further closer to or farther from the focal point, the amount of light in the focus control quadrant detector 47 decreases as shown in the two diagrams at both ends of FIG.

  Usually, an optical pickup for DVD is designed so that reflected light having a low quality can be obtained from the first information recording layer 4 of 0.6 mm from the laser beam incident surface 1 a of the optical disc 1. On the other hand, the second information recording layer 8 and the third information recording layer 11 of the optical disc 1 have large aberrations because spherical aberration is not considered. That is, the reflected light from the second information recording layer 8 and the third information recording layer 11 is collected on the focus control quadrant detector 47 as shown in FIG.

  When the spherical aberration is large as is apparent from comparing the focus error signal FE when the spherical aberration shown in FIG. 7B is small and the focus error signal FE when the spherical aberration shown in FIG. 8B is large. The focus error signal FE has a smaller amplitude than the focus error signal FE when the spherical aberration is small. For this reason, if the focus error signal FE in the case where the spherical aberration is large is used to obtain the reflectance, an accurate reflectance cannot be obtained. On the other hand, the amplitude of the RF signal when the spherical aberration shown in FIG. 8C is large is similar to the amplitude of the RF signal when the spherical aberration shown in FIG. Accurate reflectance can be obtained.

  Therefore, in order to obtain the reflectance, a problem occurs when the focus error signal FE is used. Therefore, the RF signal is used without using the focus error signal FE.

  Next, the second information recording of the optical disc 1 with respect to the laser beam Lr for DVD is performed using the value of the RF signal for the optical disc 1 in order to examine the conditions when the optical disc 1 is normally reproduced by the DVD player. The relationship between the reflectance of the layer 8 and the third information recording layer 11 and the reflectance of the laser beam incident surface 1a will be described with reference to FIGS.

The second information recording layer 8 which is the BD signal surface of the optical disc 1 of the present embodiment is formed of a compound of Si and H (hereinafter, a compound of Si and H is referred to as “Si—H”). The third information recording layer 11 is made of ZnS—SiO ₂ , the thickness of the second information recording layer 8 is 7.5 nm, and the thickness of the third information recording layer 11 is 135 nm. In this case, the data shown in FIG. 5 was obtained. That is, the reflectivity of the second information recording layer 8 and the third information recording layer 11 which are BD signal surfaces with respect to the DVD laser light Lr is lower than the reflectivity of the laser beam incident surface 1a.

  When the reflectance of the second information recording layer 8 and the third information recording layer 11 is lower than the reflectance of the laser beam incident surface 1a, the DVD player uses the second information recording layer 8 and the third information recording layer. It is determined that there should be an information recording layer to be reproduced having a reflectance higher than the reflectance of the laser beam incident surface 1a behind (lower) than 11, and the first information recording layer 4 is searched. Therefore, the DVD player uses the first information of the optical disc 1 in which the reflectivity of the second information recording layer 8 and the third information recording layer 11 with respect to the DVD laser beam Lr is lower than the reflectivity of the laser beam incident surface 1a. The information recorded on the recording layer 4 is normally reproduced.

  The optical disk 1 that is normally played back by a DVD player is played back normally when it is loaded into a BD optical disk drive device (not shown). This is because the second information recording layer 8 and the third information recording layer 11 which are signal surfaces for BD exist near the surface, and the BD optical disc drive device searches the information recording layer at the back (lower side). Because there is no need to do.

  On the other hand, the relationship between the distance between the DVD objective lens 39r and the optical disk 1 and the RF signal (reflectance) for the optical disk 1 that is not normally reproduced by a DVD player is expressed as shown in FIG. That is, the reflectivity of the second information recording layer 8 and the third information recording layer 11 which are BD signal surfaces with respect to the DVD laser light Lr is higher than the reflectivity of the laser beam incident surface 1a. Therefore, the DVD player mistakenly recognizes that the second information recording layer 8 and the third information recording layer 11 are information recording layers to be reproduced, and the second information recording layer 8 and the second information recording layer 8 for the DVD laser beam Lr The optical disk 1 in which the reflectance of the third information recording layer 11 is higher than the reflectance of the laser beam incident surface 1a is not normally reproduced.

  Therefore, in order for the optical disc 1 to be normally reproduced by a DVD player, the reflectivity of the second information recording layer 8 and the third information recording layer 11 of the optical disc 1 with respect to the laser beam Lr for DVD is Each layer must be designed so as to be less than the reflectance of the laser beam incident surface 1a (the surface of the protective layer 12) with respect to the laser light Lr.

  Next, the reflectance of the second information recording layer 8 and the third information recording layer 11 of the optical disc 1 of the present embodiment with respect to the BD laser beam Lb will be considered. Since the second information recording layer 8 and the third information recording layer 11 are BD signal surfaces, the reflectance “which is a standard for the reflectance of the two-layer BD-ROM with respect to the BD laser light Lb” It is desirable to satisfy 12% to 28% ".

  Therefore, the thickness and reflection when Si-H, which is one of the candidate materials for forming the second information recording layer 8 and the third information recording layer 11, is provided on the substrate to form a disk shape. The relationship between the rate and the relationship between the thickness and the transmittance will be described with reference to FIGS. FIG. 9 shows the relationship between the thickness and the reflectance with respect to light having a wavelength of 405 nm, and the reflectance with respect to light having a thickness and wavelength of 650 nm, for a sample obtained by sputtering a Si—H film on a flat and transparent polycarbonate substrate. FIG. FIG. 10 shows the relationship between the thickness and the transmittance for light having a wavelength of 405 nm, and the transmittance for the light having a thickness and wavelength of 650 nm, for a sample formed by sputtering on a flat and transparent polycarbonate substrate of Si—H. FIG. The wavelength of incident light on each sample was confirmed using a spectrophotometer UV-3100 manufactured by Shimadzu Corporation.

  As shown in FIG. 9, it can be seen that the reflectance with respect to light with a wavelength of 405 nm is higher than the reflectance with respect to light with a wavelength of 650 nm when the thickness of Si—H is less than 30 nm. In addition, it can be seen that the reflectance with respect to light having a wavelength of 405 nm is maximum at about 35% when the thickness is about 20 nm, and decreases when the thickness is more than that. Further, as shown in FIG. 10, it can be seen that Si—H has a higher transmittance with respect to light with a wavelength of 650 nm than that with respect to light with a wavelength of 405 nm.

  When the third information recording layer 11 is formed of Si—H, in order to make the reflectance of the third information recording layer 11 with respect to light having a wavelength of 405 nm 12% or more of the two-layer BD-ROM standard, FIG. As shown, the thickness of the third information recording layer 11 needs to be 5.5 nm or more. Considering the transmittance shown in FIG. 10, the third information recording layer 11 is preferably as thin as possible. If the thickness of the third information recording layer 11 is 5.5 nm, the transmittance for light with a wavelength of 405 nm is 53% as shown in FIG.

  In the case where the second information recording layer 8 is also formed of Si-H, in order to make the reflectance with respect to light having a wavelength of 405 nm transmitted through the third information recording layer 11 12% or more of the two-layer BD-ROM standard Since the light passes through the third information recording layer 11 twice in the forward path and the return path, assuming that the reflectance of the second information recording layer 8 alone is R2 (%), R2 is expressed by the following formula ( 4) must be satisfied.

0.53 × 0.53 × R2 ≧ 12 (4)
That is, R2 must be 43% or more. However, as described with reference to FIG. 9, the maximum reflectivity for light with a wavelength of 405 nm of Si—H is about 35%. Therefore, when the second information recording layer 8 and the third information recording layer 11 are formed of Si—H, the reflectance of the second information recording layer 8 with respect to light having a wavelength of 405 nm is 12% of the two-layer BD-ROM standard. I can't do more.

  Therefore, the third information recording layer 11 is formed so that the reflectance of the second information recording layer 8 and the third information recording layer 11 with respect to light having a wavelength of 405 nm is 12% or more of the two-layer BD-ROM standard. As a material to be used, a dielectric material having a small light absorption and a high translucency, a so-called small extinction coefficient was considered to be appropriate. The examination results are shown below.

FIG. 11 shows thicknesses of 56 nm, 111 nm, 135 nm, and 167 nm for samples in which ZnS—SiO ₂ , which is one of so-called dielectrics having a small extinction coefficient, is formed on a flat and transparent polycarbonate substrate by sputtering. It is a figure which shows the relationship between a wavelength and a reflectance in each case of 195 nm and 195 nm. As shown in FIG. 11, when the thickness is 135 nm, the reflectance for light having a wavelength near 400 nm is high, and the reflectance for light having a wavelength near 600 nm is low.

FIG. 12 shows the wavelength and transmittance of a sample in which ZnS—SiO ₂ is formed on a flat and transparent polycarbonate substrate by sputtering, with thicknesses of 56 nm, 111 nm, 135 nm, 167 nm, and 195 nm, respectively. It is a figure which shows the relationship. As shown in FIG. 12, regardless of the thickness, the transmittance for light having a wavelength of 650 nm is 80% or more, and the transmittance for light having a wavelength of 405 nm is 70% or more.

  13 to 22 are diagrams showing the relationship between the wavelength and the reflectance at each thickness of a material having a refractive index of 2.2, obtained by optical thin film simulation. In FIG. 13, the thickness is 10 nm, in FIG. 14, the thickness is 30 nm, in FIG. 15, the thickness is 60 nm, in FIG. 16, the thickness is 90 nm, in FIG. 17, the thickness is 110 nm, and in FIG. In FIG. 19, the thickness is 152 nm, in FIG. 20, the thickness is 160 nm, in FIG. 21, the thickness is 200 nm, and in FIG. 22, the thickness is 230 nm.

  As is apparent from comparison between FIGS. 13 to 22, it can be seen that the reflectance with respect to light having a wavelength of 405 nm is lowest when the thickness is 90 nm (see FIG. 16). The round-trip optical path length in the film is a length obtained by multiplying the thickness of the film by twice the refractive index. Therefore, if the thickness is 90 nm, the round-trip optical path length is 90 × 2 × 2.2 = 396 nm. . The phase of light that has entered a large medium from a medium having a low refractive index is inverted with respect to the light before entering. Therefore, it is considered that the light having a wavelength near 396 nm has a phase that is canceled and has a low reflectance.

  Similarly, when the thickness is 110 nm (see FIG. 17), the phase is canceled and the reflectance is low for light having a wavelength near 110 × 2 × 2.2 = 484 nm. When the thickness is 124 nm (see FIG. 18), the phase of the light having a wavelength near 124 × 2 × 2.2 = 546 nm is canceled and the reflectance becomes low. When the thickness is 152 nm (see FIG. 19), the phase is canceled and the reflectance is low for light having a wavelength in the vicinity of 152 × 2 × 2.2 = 669 nm. The concept described with reference to FIGS. 16 to 19 also in the case where the thickness is 160 nm (see FIG. 20), the thickness is 200 nm (see FIG. 21), and the thickness is 230 nm (see FIG. 22). Applies.

  On the other hand, when the thickness is 152 nm (see FIG. 19), the wavelength with high reflectivity is less than 450 nm. As described above, the phase of light incident on a medium having a small refractive index from a medium having a low refractive index is inverted with respect to the light before being incident. Therefore, for light having a wavelength corresponding to the length obtained by multiplying the refractive index by (2 / (1.0 + 0.5)) times the thickness of the film, the light reflected on the surface of the film and the back surface of the film The phase with the reflected light is aligned and enhanced to enhance the reflectance.

  FIG. 23 to FIG. 27 are diagrams showing the relationship between the wavelength and the reflectance when the wavelength of light having the maximum reflectance is about 405 nm, which is obtained by optical thin film simulation. In FIG. 23, the refractive index n of the film is 1.8 and the thickness is 170 nm. In FIG. 24, the refractive index n of the film is 2.0 and the thickness is 152 nm. The refractive index n of the film is 2.2 and the thickness is 135 nm. In FIG. 26, the refractive index n of the film is 2.3 and the thickness is 135 nm. In FIG. 27, the refractive index n of the film is 2.5 and the thickness is 120 nm. It can be seen that FIG. 27 substantially matches FIG. 11 obtained by experiments.

  As shown in FIGS. 23 to 27, the reflectance of light near 405 nm is less than 10% when the refractive index is 2.0 or less (FIGS. 23 and 24), but the refractive index is 2.2. In the case of the above (FIGS. 25 to 27), it is 12% or more. When the refractive index is 2.2, as shown in FIGS. 13 to 22 and 25, the maximum value of the reflectance of light in the vicinity of 405 nm is when the film thickness is 138 nm. When the refractive index is 2.2 and the film thickness is 0.9 times 138 nm, that is, when the film thickness is 124 nm, the reflectance of light near 405 nm is 12 as shown in FIG. % Or more. Also, when the refractive index is 2.2 and the film thickness is 1.1 times 138 nm, that is, when the film thickness is 152 nm, the reflectance of light in the vicinity of 405 nm as shown in FIG. Is 12% or more.

  On the other hand, when the refractive index is 2.2 and the film thickness is 0.8 times of 138 nm, that is, when the film thickness is 110 nm, as shown in FIG. Is 10% or less. When the refractive index is 2.2 and the film thickness is 1.2 times 138 nm, that is, when the film thickness is 160 nm, the reflectance of light in the vicinity of 405 nm is as shown in FIG. 10% or less.

  Therefore, when the refractive index is 2.2, the thickness of the third information recording layer 11 is from −10% to + 10% with respect to the thickness at which the reflectance with respect to light having a wavelength of 405 nm is maximized. The reflectance for light having a wavelength of 405 nm is 12% or more.

As described above, the phase of light incident on a medium having a small refractive index from a medium having a low refractive index is inverted with respect to the light before being incident. Therefore, the thickness of the third information recording layer 11 that maximizes the reflectance with respect to light having a wavelength of 405 nm has a refractive index of 2.2.
405 × (1 + 0.5) / (2 × 2.2) = 607.5 / (2 × 2.2) = 138 (nm)
It becomes.

When the refractive index is x (2.2 ≦ x ≦ 2.5), the thickness of the third information recording layer 11 at which the reflectance with respect to light with a wavelength of 405 nm is 12% or more is:
It is 0.9 times to 1.1 times of “405 × (1 + 0.5) / (2 × x) = 607.5 / (2 × x)”.

  Hereinafter, with respect to the optical disc 1 of the present embodiment when the configuration of each layer is changed, the reflectance of each layer with respect to the laser beam Lr for DVD, the reflectance of each layer with respect to the laser beam Lb for BD, and a commercially available reproduction machine Thus, the reproduction results of BD and DVD when the reproduction was attempted were examined.

  First, the optical disk of Example 1 will be described together with its manufacturing method.

  The optical disc of Example 1 has a first information recording layer 4, a second information recording layer 8, and a third information recording layer 11. These manufacturing processes will be described in order, and thereby the optical disk of Example 1 and the manufacturing method thereof will be described.

  First, the manufacturing process of the first information recording layer 4 will be described.

  First, a disk-shaped glass master having a thickness of 5 mm and a diameter of 200 mm was polished with ultrapure water and cerium oxide, and then washed. Then, a photoresist containing a cresol novolac resin and a benzophenone ester is uniformly applied on the glass master with a thickness of about 1/5 of the wavelength of the laser beam Lr for DVD by an spin coat method through an adhesive. did. The photoresist may be either a positive type or a negative type, but a positive type photoresist was used in Example 1.

  Thereafter, the glass master coated with the photoresist was baked by a hot plate at a temperature of 60 ° C. to 80 ° C. to evaporate the organic solvent adhering to the glass master. Baking may be performed in a thermostatic bath.

  Next, in order to obtain information determined by the DVD standard later, a laser beam recorder is formed so that concave pits are formed in a spiral shape at a pitch of 0.74 μm on the photoresist on the baked glass master. The photoresist was exposed to light with light having a wavelength in the UV region from.

  Then, the exposed portion is removed with an alkaline developer, and a first glass master having concave pits having information modulated by the DVD standard such as an SD moving image to which information such as address and error correction is added is formed. Got.

  Next, a conductive film such as nickel was formed on the first glass master photoresist by sputtering, and nickel was plated using the conductive film as an electrode. As a result, convex pits having information modulated by the DVD standard such as SD moving images, which are reverse patterns of concave pits formed in the photoresist, were copied onto the plated nickel layer.

  Next, the nickel layer was peeled from the first glass master to form a first master stamper. Then, the first master stamper is subjected to electrolytic treatment or the like to peel off the oxide, and then plated with nickel, so that a concave pit having a shape opposite to the pit formed in the first master stamper is formed. Obtained one mother stamper.

  Then, electrolytic treatment was performed on the first mother stamper, and then nickel was plated to obtain a first baby stamper having convex pits having the same shape as the pits of the first master stamper.

  Next, the first baby stamper was attached to a mold, and polycarbonate resin was injection-molded to obtain a first substrate 2 having a thickness of 0.6 mm. When the first substrate 2 was obtained, first information recording pits 3 which were pits conforming to the DVD-ROM standard were formed on the surface of the first substrate 2. Note that the first substrate 2 can also be obtained by using the first master stamper instead of the first baby stamper.

  Next, the first information recording layer 4 was formed by laminating a reflective film on the first information recording pit 3 formed on the surface of the first substrate 2. As the reflective film used for the first information recording layer 4, Al, Ag, Au, or the like, or a reflective film containing them as a main component is suitable. In Example 1, Ag was used as the material of the first information recording layer 4 so that the first information recording layer 4 alone can obtain a reflectivity as high as possible with respect to the laser beam Lr for DVD. The first information recording layer 4 was formed by performing magnetron sputtering, and its thickness was set to 70 nm.

  Subsequently, a manufacturing process of the second information recording layer 8 will be described.

  First, a disk-shaped glass master having a thickness of 5 mm and a diameter of 200 mm was polished with ultrapure water and cerium oxide, and then washed. Then, a photoresist containing a cresol novolac resin and a benzophenone ester is uniformly applied to the glass master with a thickness of about 1/5 of the wavelength of the laser beam Lb for BD by an spin coat method through an adhesive. did. The photoresist may be either a positive type or a negative type, but a positive type photoresist was used in Example 1.

  Thereafter, the glass master coated with the photoresist was baked by a hot plate at a temperature of 60 ° C. to 80 ° C. to evaporate the organic solvent adhering to the glass master. Baking may be performed in a thermostatic bath.

  Next, in order to later obtain 1-7PP modulated information determined by the BD-ROM standard, a pit having a minimum pit length of 0.15 μm is 0.32 μm on the photoresist on the baked glass master. The photoresist was exposed and exposed to light having a wavelength below the UV region from a laser beam recorder so as to be formed in a spiral shape with a pitch of.

  Then, the exposed portion was removed with an alkali developer to obtain a second glass master in which concave pits were formed.

  Next, a conductive film such as nickel was formed on the second glass master photoresist by sputtering, and nickel was plated using the conductive film as an electrode. As a result, convex pits, which are the reverse pattern of the concave pits formed in the photoresist, were copied onto the plated nickel layer.

  Next, the nickel layer was peeled from the second glass master to form a second master stamper. Then, the second master stamper was subjected to electrolytic treatment or the like to peel off the oxide, and then plated with nickel to form a concave pit opposite to the pit formed in the second master stamper. A second mother stamper was obtained.

  Then, nickel was plated on the second mother stamper to obtain a second baby stamper having convex pits having the same shape as the pits of the second master stamper.

  Next, a second baby stamper was attached to the mold, and polycarbonate resin was injection molded to obtain a second substrate 6 having a thickness of 0.48 mm. When the second substrate 6 was obtained, second information recording pits 7 which were pits conforming to the BD-ROM standard were formed on the surface of the second substrate 6. Note that the second substrate 6 can also be obtained by using the second master stamper instead of the second baby stamper.

  Next, a manufacturing process of a soft stamper for manufacturing the third information recording layer 11 will be described before the description of the manufacturing process of the second information recording layer 8 is finished.

  First, a disk-shaped glass master having a thickness of 5 mm and a diameter of 200 mm was polished with ultrapure water and cerium oxide, and then washed. Then, a photoresist containing a cresol novolac resin and a benzophenone ester is uniformly applied to the glass master with a thickness of about 1/5 of the wavelength of the laser beam Lb for BD by an spin coat method through an adhesive. did. The photoresist may be either a positive type or a negative type, but a positive type photoresist was used in Example 1.

  Thereafter, the glass master coated with the photoresist was baked by a hot plate at a temperature of 60 ° C. to 80 ° C. to evaporate the organic solvent adhering to the glass master. Baking may be performed in a thermostatic bath.

  Next, in order to later obtain 1-7PP modulated information determined by the BD-ROM standard, a pit having a minimum pit length of 0.15 μm is 0.32 μm on the photoresist on the baked glass master. The photoresist was exposed and exposed to light having a wavelength below the UV region from a laser beam recorder so as to be formed in a spiral shape having a pitch of.

  Then, the exposed portion was removed with an alkali developer to obtain a third glass master in which concave pits were formed.

  Next, a conductive film such as nickel was formed on the photoresist of the third glass master by sputtering, and nickel was plated using the conductive film as an electrode. As a result, convex pits, which are the reverse pattern of the concave pits formed in the photoresist, were copied onto the plated nickel layer.

  Next, the nickel layer was peeled from the third glass master to form a third master stamper. Then, the third master stamper was subjected to electrolytic treatment or the like to peel off the oxide, and then plated with nickel to form a concave pit reverse to the pit formed in the third master stamper. A third mother stamper was obtained.

  Then, a polycarbonate resin was injection molded on the third mother stamper to obtain a soft stamper for manufacturing the third information recording layer 11. The soft stamper may be formed of a material such as a polyolefin resin.

  After the soft stamper was obtained, the second information recording layer 8 was formed on the second information recording pits 7 formed on the surface of the second substrate 6. Specifically, the second substrate 6 is put in a chamber and the inside of the chamber is evacuated, and then hydrogen gas is introduced into the chamber together with argon gas to perform sputtering, thereby depositing Si—H, and the thickness is 7 A second information recording layer 8 having a thickness of 5 nm was formed.

  Next, an ultraviolet curable resin having a transmittance of 85% or more with respect to the laser beam Lr for DVD and the laser beam Lb for BD is applied on the second information recording layer 8, and the intermediate layer 9 has a thickness of 25 μm. Formed with. When the intermediate layer 9 is formed, the surface on which the pits of the soft stamper for manufacturing the third information recording layer 11 described above are pressed against the applied ultraviolet curable resin to form the pits of the soft stamper. Ultraviolet rays were irradiated from the surface that was not. Then, the soft stamper was removed, and third information recording pits 10 were formed on the upper surface of the intermediate layer 9. Note that the upper surface of the intermediate layer 9 is a surface not in contact with the second information recording layer 8 of the intermediate layer 9. In addition, it is desirable that the ultraviolet curable resin for forming the intermediate layer 9 has a transmittance of 90% or more for the DVD laser beam Lr and the BD laser beam Lb.

Next, on the third information recording pit 10 formed on the upper surface of the intermediate layer 9, ZnS—SiO ₂ , which is one of dielectric materials, is formed to a thickness of 135 nm by RF sputtering, thereby forming the first information recording pit 10. 3 information recording layers 11 were formed.

  Then, a protective layer 12 having a thickness of 0.1 mm was pressure-bonded on the third information recording layer 11, and the production of the BD signal surface of the optical disc of Example 1 was completed. The protective layer 12 is a layer composed of a polycarbonate resin sheet having a transmittance of 85% or more for the DVD laser beam Lr and the BD laser beam Lb and an adhesive material. Further, the transmittance of the protective layer 12 with respect to the laser beam Lr for DVD and the laser beam Lb for BD is desirably 90% or more.

  Finally, the first substrate 2 on which the first information recording layer 4 is formed and the second substrate 6 on which the second information recording layer 8 and the third information recording layer 11 are formed are shown in FIG. As shown, the surface of the first substrate 2 on which the first information recording layer 4 is formed and the surface of the second substrate 6 on which the protective layer 12 is not attached are opposed to each other. The adhesive sheet 5 was used for bonding. Thereby, the manufacture of the optical disk of Example 1 was completed.

  The total thickness of the second substrate 6, the pressure-sensitive adhesive sheet 5, and the protective layer 12 is desirably 0.6 mm. This is because the thickness of the conventional DVD and BD is 1.2 mm, the thickness of the optical disk of Example 1 is preferably 1.2 mm, and the thickness of the first substrate 2 is 0.6 mm. Because. In Example 1, since the thickness of the 2nd board | substrate 6 is 0.48 mm and the thickness of the protective layer 12 is 0.1 mm, the thickness of the adhesive sheet 5 was 0.02 mm.

  Pulse tech which has an objective lens which emits light having a wavelength of 650 nm which is the same as the wavelength of the laser beam Lr for DVD, and has reflectivity of the second information recording layer 8 and the third information recording layer 11. It measured by the method shown below using ODU-1000 by a company. That is, the focus control is performed to change the distance between the objective lens and the optical disc by moving the objective lens closer to or away from the optical disc, and the second information recording layer 8 and the third information with respect to the distance between the objective lens and the optical disc. The reflectance of the recording layer 11 was measured. FIG. 5 is a diagram schematically showing the measurement results of the reflectivity of the second information recording layer 8 and the third information recording layer 11 with respect to the distance between the objective lens and the optical disc in the optical disc of Example 1.

  As shown in FIG. 5, the reflected light from the second information recording layer 8 and the reflected light from the third information recording layer 11 cannot be clearly distinguished, and the second information with respect to the laser beam Lr for DVD is used. The reflectance of the recording layer 8 and the third information recording layer 11 was 1.0%. The reflectance 1.0% is lower than the reflectance 5% of the laser beam incident surface 1a formed of polycarbonate resin.

  The reflectance of the second information recording layer 8 with respect to the BD laser light Lb was 14%, and the reflectance of the third information recording layer 11 with respect to the BD laser light Lb was 12%.

  Further, the reflectance of the first information recording layer 4 with respect to the laser beam Lr for DVD was 49%, which satisfied 45% to 85% of the specified reflectance of the DVD standard.

  When the reproduction of the optical disk of Example 1 was attempted by using any seven commercially available BD / DVD players, the second information recording layer 8 and the third information recording layer 11 were used in all seven devices. A certain BD signal surface could be reproduced. Further, reproduction of the optical disk of Example 1 was attempted by using any 20 commercially available DVD players, and the signal surface for DVD, which is the first information recording layer 4, was reproduced in all 20 devices. I was able to.

In addition, when ZnS-SiO ₂ used for the third information recording layer 11 was measured with an ellipsometer, the extinction coefficient for light with a wavelength of 405 nm was 0.1 or less and almost 0, and the refractive index was About 2.2. The reciprocating optical path length of the third information recording layer 11 is 135 × 2 × 2.2 = 594 (nm) because it is a length obtained by multiplying the refractive index by twice the thickness. The phases of the reflected light at the incident surface of the film and the reflected light at the inner surface of the film are inverted, so that the phase is canceled and the reflectance is lowered in the light near the wavelength of 594 nm. Considering the shift of half wavelength, the reflectance of light having a wavelength in the vicinity of 135 × 2 × 2.2 / (1.0 + 0.5) = 396 nm is increased. Therefore, it is considered that the reflectance of the third information recording layer 11 with respect to the BD laser beam Lb having a wavelength of 405 nm is 12%. Further, since the extinction coefficient of the third information recording layer 11 is almost 0, most of the light other than the reflected light is transmitted to the second information recording layer 8 which is the back information recording layer.

The thickness d ₆₅₀ of ZnS—SiO ₂ for reducing the reflectance of the laser beam Lr for DVD having a wavelength of 650 nm as much as possible is because the refractive index of ZnS—SiO ₂ is 2.2.
d ₆₅₀ = 650 / (2 × 2.2) = 147 (nm). The thickness 135 nm of the third information recording layer 11 of Example 1 is about 9% thinner than 147 nm. For this reason, it is considered that the DVD laser light Lr having a wavelength of 650 nm is sufficiently transmitted through the third information recording layer 11 and the reflectance of the first information recording layer 4 with respect to the DVD laser light Lr is increased. In addition, the thickness d ₄₀₅ of ZnS—SiO ₂ for increasing the reflectance of light having a wavelength of 405 nm is:
d ₄₀₅ = 405 × 1.5 / (2 × 2.2) = 607.5 / (2 × 2.2) = 138 (nm).

  Next, the optical disk of Example 2 will be described.

  The basic configuration of the optical disc of the second embodiment is the same as that of the optical disc of the first embodiment, but the thickness of the second information recording layer 8 and the third information recording layer 11 is the same as that of the optical disc of the second embodiment. It differs from the optical disc of Example 1.

In the optical disc of Example 2, the second information recording layer 8 is formed of Si—H, the thickness thereof is 8 nm, and the third information recording layer 11 is formed of ZnS—SiO ₂ . Its thickness is 138 nm.

  For the optical disk of Example 2, the reflectances of the second information recording layer 8 and the third information recording layer 11 with respect to the laser beam Lr for DVD were measured in the same manner as in Example 1. FIG. 5 is also a diagram schematically showing the measurement results of the reflectance of the second information recording layer 8 and the third information recording layer 11 with respect to the distance between the objective lens and the optical disc in the optical disc of Example 2.

  As shown in FIG. 5, the reflected light from the second information recording layer 8 and the reflected light from the third information recording layer 11 cannot be clearly distinguished, and the second information with respect to the laser beam Lr for DVD is used. The reflectance of the recording layer 8 and the third information recording layer 11 was 1.3%. The reflectance 1.3% is lower than the reflectance 5% of the laser beam incident surface 1a.

  The reflectance of the second information recording layer 8 with respect to the BD laser light Lb is 13.4%, and the reflectance of the third information recording layer 11 with respect to the BD laser light Lb is 12.2%. there were.

  Further, the reflectance of the first information recording layer 4 with respect to the laser beam Lr for DVD was 46%, which satisfied 45% to 85% of the prescribed reflectance of the DVD standard.

As described above, the thickness d ₆₅₀ of ZnS—SiO ₂ for reducing the reflectance of the laser beam Lr for DVD having a wavelength of 650 nm as much as possible is 147 (nm). The thickness 138 nm of the third information recording layer 11 of Example 2 is about 6% thinner than 147 nm. For this reason, it is considered that the DVD laser light Lr having a wavelength of 650 nm is sufficiently transmitted through the third information recording layer 11 and the reflectance of the first information recording layer 4 with respect to the DVD laser light Lr is increased.

  When reproduction of the optical disk of Example 2 was attempted with any seven commercially available BD / DVD players, the second information recording layer 8 and the third information recording layer 11 were used in all seven devices. A certain BD signal surface could be reproduced. Further, reproduction of the optical disk of Example 2 was attempted by using any 20 commercially available DVD players, and the DVD signal surface as the first information recording layer 4 was reproduced in all 20 devices. I was able to.

  Next, the optical disk of Example 3 will be described.

  The basic configuration of the optical disc of the third embodiment is the same as that of the optical disc of the first embodiment, but the thickness of the second information recording layer 8 and the third information recording layer 11 is the same as that of the optical disc of the third embodiment. It differs from the optical disc of Example 1.

In the optical disk of Example 3, the second information recording layer 8 is formed of Si—H, the thickness thereof is 8 nm, and the third information recording layer 11 is formed of ZnS—SiO ₂ . Its thickness is 111 nm.

  For the optical disk of Example 3, the reflectances of the second information recording layer 8 and the third information recording layer 11 with respect to the laser beam Lr for DVD were measured in the same manner as in Example 1. FIG. 6 is a diagram schematically showing the measurement results of the reflectivity of the second information recording layer 8 and the third information recording layer 11 with respect to the distance between the objective lens and the optical disc in the optical disc of Example 3.

  As shown in FIG. 6, the reflected light from the second information recording layer 8 and the reflected light from the third information recording layer 11 cannot be clearly distinguished, and the second information with respect to the laser beam Lr for DVD is used. The reflectance of the recording layer 8 and the third information recording layer 11 was 5.5%. The reflectance 5.5% is higher than the reflectance 5% of the laser beam incident surface 1a.

  The reflectance of the second information recording layer 8 with respect to the BD laser light Lb was 9.5%, and the reflectance of the third information recording layer 11 with respect to the BD laser light Lb was 6%. .

  Further, the reflectance of the first information recording layer 4 with respect to the laser beam Lr for DVD was 43%, which did not satisfy 45% to 85% of the specified reflectance of the DVD standard.

As described above, the thickness d ₆₅₀ of ZnS—SiO ₂ for reducing the reflectivity of the DVD laser beam Lr having a wavelength of 650 nm as much as possible is 147 nm. The thickness 111 nm of the third information recording layer 11 of Example 3 is about 24% thinner than 147 nm. Therefore, the DVD laser light Lr having a wavelength of 650 nm cannot sufficiently pass through the third information recording layer 11, and the reflectivity of the first information recording layer 4 with respect to the DVD laser light Lr becomes low. It is thought.

  The reproduction of the optical disk of Example 3 was attempted with any seven commercially available BD / DVD players, and the second information recording layer 8 and the third information recording layer 11 were obtained in six devices. The signal surface for BD could be reproduced normally, but it took about twice as long to reproduce one signal. Further, when reproduction of the optical disk of Example 3 was attempted with any 20 commercially available DVD players, the DVD signal surface, which is the first information recording layer 4, could be reproduced with 19 devices. Although it was possible, it was not possible to reproduce with one.

  Next, an optical disk of Example 4 will be described.

  In the optical disc of Example 4, the second information recording layer 8 is formed of Si—H, the thickness thereof is 8 nm, and the third information recording layer 11 is formed of ZrO, and the thickness thereof is 130 nm.

  For the optical disk of Example 4, the reflectivities of the second information recording layer 8 and the third information recording layer 11 with respect to the laser beam Lr for DVD were measured in the same manner as in Example 1. FIG. 5 is also a diagram schematically showing the measurement results of the reflectance of the second information recording layer 8 and the third information recording layer 11 with respect to the distance between the objective lens and the optical disc in the optical disc of Example 4.

  As shown in FIG. 5, the reflected light from the second information recording layer 8 and the reflected light from the third information recording layer 11 cannot be clearly distinguished, and the second information with respect to the laser beam Lr for DVD is used. The reflectance of the recording layer 8 and the third information recording layer 11 was 4.8%. The reflectance 4.8% is lower than the reflectance 5% of the laser beam incident surface 1a.

  The reflectance of the second information recording layer 8 with respect to the BD laser light Lb is 13.6%, and the reflectance of the third information recording layer 11 with respect to the BD laser light Lb is 12.3%. there were.

  Further, the reflectance of the first information recording layer 4 with respect to the laser beam Lr for DVD is 43%, which is lower than 45% to 85% of the prescribed reflectance of the DVD standard.

  When the reproduction of the optical disk of Example 4 was attempted by using any six commercially available BD / DVD players, the second information recording layer 8 and the third information recording layer 11 were used in all six devices. A certain BD signal surface could be reproduced. Further, when reproduction of the optical disk of Example 4 was attempted with any 20 commercially available DVD players, it was possible to reproduce the DVD signal surface as the first information recording layer 4 in 18 devices. However, there were cases where it took a long time to play back with two devices, or the disc could not be recognized.

  In addition, when ZrO used for the third information recording layer 11 was measured by an ellipsometer, the extinction coefficient for light having a wavelength of 405 nm was 0.1 or less and almost 0, and the refractive index was about 2. 33. The reciprocating optical path length of the third information recording layer 11 is 130 × 2 × 2.33 = 606 (nm) because it is a length obtained by multiplying the refractive index by twice the thickness. The phase is inverted between the reflected light on the incident surface of the film and the reflected light on the back surface of the film. For this reason, the phase of the light in the vicinity of the wavelength of 606 nm is canceled and the reflectance is lowered. Considering the shift of half wavelength, the reflectance of light having a wavelength in the vicinity of 130 × 2 × 2.33 / (1.0 + 0.5) = 404 nm is increased. Therefore, it is considered that the reflectance of the third information recording layer 11 with respect to the BD laser beam Lb having a wavelength of 405 nm is 12%. Further, since the extinction coefficient of the third information recording layer 11 is almost 0, most of the light other than the reflected light is transmitted to the second information recording layer 8 which is the back information recording layer.

The ZrO thickness d ₆₅₀ ′ for reducing the reflectivity of the DVD laser beam Lr having a wavelength of 650 nm as much as possible is ZnO having a refractive index of 2.33.
d ₆₅₀ ′ = 650 / (2 × 2.33) = 139 (nm). The thickness 130 nm of the third information recording layer 11 of Example 4 is about 7% thinner than 139 nm. For this reason, it is considered that the DVD laser light Lr having a wavelength of 650 nm is sufficiently transmitted through the third information recording layer 11 and the reflectance of the first information recording layer 4 with respect to the DVD laser light Lr is increased. Further, the ZnO thickness d ₄₀₅ ′ for increasing the reflectance of light having a wavelength of 405 nm is:
d ₄₀₅ ′ = 405 × 1.5 / (2 × 2.33) = 607.5 / (2 × 2.33) = 130 (nm).

  Next, an optical disk of Example 5 will be described.

  The basic configuration of the optical disc of the fifth embodiment is the same as that of the optical disc of the first embodiment. However, in the optical disc of the fifth embodiment, the second information recording layer 8 is formed of Si—H and has a thickness. Is 8 nm, and the third information recording layer 11 is made of TiO and has a thickness of 122 nm.

  For the optical disk of Example 5, the reflectivities of the second information recording layer 8 and the third information recording layer 11 with respect to the laser beam Lr for DVD were measured in the same manner as in Example 1. FIG. 5 is also a diagram schematically showing the measurement results of the reflectivity of the second information recording layer 8 and the third information recording layer 11 with respect to the distance between the objective lens and the optical disc in the optical disc of Example 5.

  As shown in FIG. 5, the reflected light from the second information recording layer 8 and the reflected light from the third information recording layer 11 cannot be clearly distinguished, and the second information with respect to the laser beam Lr for DVD is used. The reflectance of the recording layer 8 and the third information recording layer 11 was 4.8%. The reflectance 4.8% is lower than the reflectance 5% of the laser beam incident surface 1a.

  The reflectance of the second information recording layer 8 with respect to the BD laser light Lb is 12.7%, and the reflectance of the third information recording layer 11 with respect to the BD laser light Lb is 12.9%. there were.

  Further, the reflectance of the first information recording layer 4 with respect to the laser beam Lr for DVD was 43%, which was lower than 45% to 85% of the prescribed reflectance of the DVD standard.

  When the reproduction of the optical disk of Example 5 was attempted with any six commercially available BD / DVD players, the second information recording layer 8 and the third information recording layer 11 were used in all six devices. A certain BD signal surface could be reproduced. Further, reproduction of the optical disk of Example 5 was attempted with any 20 commercially available DVD players, and the DVD signal surface as the first information recording layer 4 was reproduced in all 20 devices. I was able to.

  Further, when TiO used in the third information recording layer 11 was measured by an ellipsometer, the extinction coefficient was 0.1 or less and almost 0 with respect to light having a wavelength of 405 nm, and the refractive index was about 2. It was 5. The reciprocating optical path length of the third information recording layer 11 is 122 × 2 × 2.5 = 610 (nm) because it is the length obtained by multiplying the refractive index by twice the thickness. The phase is inverted between the reflected light on the incident surface of the film and the reflected light on the back surface of the film. For this reason, the phase of the light in the vicinity of the wavelength of 610 nm is canceled and the reflectance is lowered. Considering the shift of half wavelength, the reflectance of light having a wavelength in the vicinity of 122 × 2 × 2.5 / (1.0 + 0.5) = 407 nm is increased. Therefore, it is considered that the reflectance of the third information recording layer 11 with respect to the BD laser beam Lb having a wavelength of 405 nm is 12%. Further, since the extinction coefficient of the third information recording layer 11 is almost 0, most of the light other than the reflected light is transmitted to the second information recording layer 8 which is the back information recording layer.

The TiO thickness d ₆₅₀ ″ for reducing the reflectivity of the DVD laser beam Lr having a wavelength of 650 nm as much as possible is 2.5 because the refractive index of TiO is 2.5.
d ₆₅₀ ″ = 650 / (2 × 2.5) = 130 (nm). The thickness 122 nm of the third information recording layer 11 of Example 5 is about 6% thinner than 130 nm. For this reason, it is considered that the DVD laser light Lr having a wavelength of 650 nm is sufficiently transmitted through the third information recording layer 11 and the reflectance of the first information recording layer 4 with respect to the DVD laser light Lr is increased. Also, the TiO thickness d ₄₀₅ ″ for increasing the reflectance of light having a wavelength of 405 nm is:
d ₄₀₅ ″ = 405 × 1.5 / (2 × 2.5) = 607.5 / (2 × 2.5) = 122 (nm).

  Here, when the refractive index of the material of the third information recording layer 11 is x (2.2 ≦ x ≦ 2.5) and the thickness of the third information recording layer 11 is t (nm), the wavelength of 405 nm T for maximizing the reflectance of the third information recording layer 11 with respect to the BD laser beam Lb is specified by the following equation (5).

t = 405 × 1.5 / (2 × x) = 607.5 / (2 × x) (5)
That is, when the wavelength of the BD laser beam Lb is “λ”, t for maximizing the reflectance of the third information recording layer 11 with respect to the BD laser beam Lb is expressed by the following equation (6). Identified.

t = λ × 1.5 / (2 × x) (6)
Therefore, generally, when the refractive index of the third information recording layer 11 is x and the wavelength of the light (reproducing light) for reproducing the information recorded on the third information recording layer 11 is λ, If the thickness of the third information recording layer 11 is {λ × 1.5 / (2 × x)}, the reflectance of the third information recording layer 11 with respect to the reproduction light is maximized.

  That is, the thickness of the third information recording layer 11 is such that the phase of the reproduction light reflected by the surface of the third information recording layer 11 and the phase of the reproduction light reflected by the back surface of the third information recording layer 11 If the thicknesses are equal, the reflectance of the third information recording layer 11 with respect to the reproduction light is maximized.

  In the above-described embodiment, the reflectance of the second information recording layer 8 and the third information recording layer 11 with respect to the BD laser light Lb is a reflectance standard of the two-layer BD-ROM. The case where “12% to 28%” is satisfied has been described. The reflectivity of the second information recording layer 8 and the third information recording layer 11 with respect to the laser beam Lb for BD preferably satisfies “12% to 28%”. The reflectivity of the two-layer BD-RE or the two-layer BD-R may be 3.5% or more. In that case, the second information recording layer 8 and the third information recording layer 11 may be formed of Si—H. Si-H is also one of dielectrics.

  Further, as described with reference to FIG. 1, the optical disc 1 according to the embodiment described above includes the first substrate 2, the first information recording layer 4 provided on the first substrate 2, A second substrate 6 provided on the first information recording layer 4, a second information recording layer 8 provided on the second substrate 6, and a second information recording layer 8. It has an intermediate layer 9 provided thereon, a third information recording layer 11 provided on the intermediate layer 9, and a protective layer 12 provided on the third information recording layer 11. . That is, the optical disc 1 of the above-described embodiment has two BD signal surfaces on the DVD signal surface.

  However, the second substrate 6 having the second information recording layer 8 and the third information recording layer 11 and the first substrate 2 having the first information recording layer 4 may be replaced. That is, the optical disc may have one DVD signal surface on the front surface side and two BD signal surfaces stacked on the back surface side. The optical disk 1 can also be reproduced by a DVD player or a BD player. Also, more information corresponding to the BD standard can be recorded on the two BD signal surfaces.

  The optical disk in that case is expressed as follows. That is, the optical disc is provided on the first substrate having the first pit row corresponding to the first standard formed on the upper surface and the first substrate corresponding to the first standard. A first information recording layer reflecting one light and a first information recording layer, and a second pit row corresponding to the first standard is formed on the upper surface. A second information recording layer formed of a dielectric material that is provided on the intermediate layer and transmits a part of the first light and reflects the remaining part; A third pit row corresponding to a second standard relating to a disk having a recording density of information lower than that of the first standard disk is formed on the upper surface. A second substrate that transmits one light, and a second substrate that is provided on the second substrate and that corresponds to the second standard. As well as reflecting light, and a third information recording layer which transmits first light.

  DESCRIPTION OF SYMBOLS 1 Optical disk, 1a Laser beam incident surface, 2 1st board | substrate, 3 1st information recording pit, 4 1st information recording layer, 5 Adhesive sheet, 6 2nd board | substrate, 7 2nd information recording pit, 8 2nd information recording layer, 9 intermediate layer, 10 3rd information recording pit, 11 3rd information recording layer, 12 protective layer, laser beam for Lr DVD, laser beam for Lb BD, 39r DVD objective lens 39b BD objective lens.

Claims (6)

A first substrate on the upper surface of which a first pit row corresponding to the first standard is formed;
A first information recording layer provided on the first substrate and reflecting a first light corresponding to the first standard;
A second pit row corresponding to a second standard relating to a disc having a higher information recording density than the first standard disc is formed on the upper surface of the first information recording layer. A second substrate that transmits the first light;
A second information recording layer which is provided on the second substrate and transmits the first light and reflects the second light corresponding to the second standard;
Provided on the second information recording layer, and formed with a third pit row corresponding to the second standard on the upper surface, and transmits the first light and the second light. The middle layer,
A third information recording layer provided on the intermediate layer, which is formed of a dielectric material that transmits the first light and transmits a part of the second light and reflects the remaining light. An optical disc comprising: And a protective layer that is provided on the third information recording layer and transmits the first light and the second light.
The optical disc according to claim 1, wherein reflectances of the second information recording layer and the third information recording layer with respect to the first light are lower than reflectances of the protective layer with respect to the first light. The first standard is a DVD standard, and the second standard is a BD standard,
The thickness of the third information recording layer is
When the refractive index of the third information recording layer is x (2.2 ≦ x ≦ 2.5)
The optical disk according to claim 1, wherein {607.5 / (2 × x)} × 0.9 nm or more and {607.5 / (2 × x)} × 1.1 nm or less. The optical disc according to claim 3, wherein an extinction coefficient of the dielectric with respect to the second light is substantially zero. The thickness of the third information recording layer is {λ × 1.5 / (2 ×) when the refractive index of the third information recording layer is x and the wavelength of the second light is λ. x)}. The optical disc according to claim 1. The thickness of the third information recording layer is such that the phase of the second light reflected on the surface of the third information recording layer and the second information reflected on the back surface of the third information recording layer are The optical disc according to claim 1, wherein the thickness is equal to the phase of light.

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