JP4516125B2 - Information recording medium - Google Patents

Description

  The present invention relates to an optical disc such as a CD, a DVD, and a Blu-Ray loaded in an optical disc apparatus, and an information recording medium such as an optical card.

In general, in an optical disk, a CD has a structure of one 1.2 mm thick light transmissive substrate, and a DVD has a structure of two 0.6 mm thick light transmissive substrates bonded together. In a bonded double-sided type such as a DVD, a pair of disk substrates having an information recording area on a transparent substrate are bonded to each other on the recording layer side. This DVD includes a multi-layer disc having a plurality of recording layers that can be read from one side of the disc, and a two-layer disc having two recording layers on one side is put into practical use for reproduction only or for recording.
In recent years, optical disks have been widely used as means for recording and reproducing data such as video data, audio data, and computer data. ROM-type optical disks include CDs and DVDs, and types that allow the user to write data include CD-R, CD-RW, DVD-R, DVD-RW, DVD + R, and DVD + RW.
There is a need to record data on an optical disc of a type that can be written by an optical disc recording apparatus, then take out the optical disc, set a so-called label surface on the back side of the data recording layer in a printer, and print the recorded contents. Therefore, a system has been proposed in which desired information can be printed on the label surface by laser light on the remaining data recording layer of the optical disc or by turning the optical disc upside down without using a printer.
For example, LightScribe (registered trademark) is known as a method of recording and reproducing data by irradiating a data recording layer from one side and writing a visible image, recorded content, and the like on a label surface. With this technology, in a specific optical disk recording apparatus, a specific optical disk having a visible information recording layer formed on the label surface side can be set face down, and image information can be recorded using a data recording laser. In this method, a CD laser is used for recording visible information. As shown in FIG. 1, since the CD has the data recording layer 3 at a position where the substrate thickness is 1.2 mm on which the optical disk 10 is mounted, the CD laser is used for the reference surface 11 (the optical disk 10 is contacted) during normal recording. The position of the objective lens OB of the pickup is adjusted so that the data recording layer 3 is in focus over a substrate thickness of 1.2 mm from a virtual plane including the contact surface 13 to the turntable 12 to be placed in contact. The working distance WD is set. Further, when recording visible information (when the visible information recording layer 4 is recorded by irradiating a laser beam), the optical disk is turned over, so that the substrate thickness is displaced by 1.2 mm from the setting (the same position as the reference surface 11). However, it is necessary to largely move the objective lens OB in the focus direction so that the focus is achieved.
In addition to this conventional technique, a visible information recording layer is formed on the label surface side of the optical disc, and the visible information recording layer is irradiated with laser light modulated in accordance with image data such as characters and pictures. There is a technique for forming an image on a visible information recording layer by changing characteristics (see Japanese Patent Application Laid-Open Nos. 2002-203321, 2004-55076, and 2003-203348).

In these prior arts, the CD data recording layer and the visible information recording layer are located at a height different by 1.2 mm from the reference plane. As shown in FIG. The stroke St in the focus direction of the lens OB (the movement distance from the working distance WD in the direction away from the optical disk) needs to be larger than in the case of CD data recording. For this reason, the recording apparatus itself needs to be changed significantly, such as a setting change of the objective lens driving actuator. In particular, in a thin optical disk device for a notebook personal computer, the product height is greatly limited, so that it is not easy to increase the stroke of the objective lens.
If a specific DVD having a visible information recording layer is used instead of a laser for CD and a specific DVD having a visible information recording layer is used, both recording layers are located at a position 0.6 mm from the reference surface even if the optical disk is turned over. It is not necessary to change the position of the objective lens when recording visible information on the screen. However, when visual information is recorded on the visible information recording layer of a CD with this DVD system, it is necessary to move the focal position of the laser by 0.6 mm (difference between the DVD bonding surface and the reference surface height) from the set value. Therefore, it is difficult to move the focal position by 0.6 mm when setting the stroke of the objective lens of the current recording apparatus.
In the techniques disclosed in JP-A-2002-203321, JP-A-2004-55076, and JP-A-2003-203348, the configuration of the optical disk is not mentioned from the viewpoint of the stroke of the objective lens of the pickup. In the technique disclosed in Japanese Patent Laid-Open No. 2003-203348, the use of a 1.2 mm-thick adapter (relative position adjusting means) that can be mounted on the chucking portion at the center of the optical disk is shown. In the device, it is impossible to chuck the disk itself.
The present invention has been made in view of such a situation, and an object thereof is to provide an information recording medium capable of recording information on a visible information recording layer without increasing the stroke of an objective lens.
The information recording medium of the present invention is an information recording medium having a light-transmitting substrate, a reflective layer, and a data recording layer disposed between the substrate and the reflective layer,
A visible information recording layer provided on the opposite side of the data recording layer via the reflective layer; a reference surface including a contact surface for placing the visible information recording layer so as to contact; And an optical distance adjusting unit that defines a distance from the information recording layer.

FIG. 1 is a schematic partial cross-sectional view showing an objective lens and an optical disk for explaining the prior art.
FIG. 2 is a schematic partial cross-sectional view in the thickness direction of the recording optical disc according to the embodiment of the present invention.
FIG. 3 is a schematic partial cross-sectional view showing the objective lens and the optical disc for explaining the operation of the recordable optical disc according to the embodiment of the present invention.
FIG. 4 is a schematic partial sectional view showing an optical disc according to an embodiment of the present invention.
5 to 10 are schematic partial sectional views showing optical disks according to other embodiments of the present invention.
11 and 12 are schematic partial cross-sectional views showing the objective lens and the optical disc for explaining the operation of the recordable optical disc according to the embodiment of the present invention.
Detailed Description of the Invention
Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 2 shows a cross section in the thickness direction of a recordable optical disc 1 such as a CD-R as an embodiment.
As shown in FIG. 2, in the optical disc 1, a data recording layer 3, a reflective layer 3a, and a visible information recording layer 4 are sequentially laminated on a light transmissive substrate 2, and a light transmissive cover substrate 5 is formed thereon. It is composed by pasting together. Although not shown, the optical disc 1 may have a configuration in which a transparent layer or the like is provided between the reflective layer 3 a and the visible information recording layer 4. The data recording layer 3, the reflective layer 3a, the visible information recording layer 4 and the like are collectively referred to as a recording function layer 34.
The data recording layer 3 is a layer for recording data by irradiating a laser beam from the substrate 2 side. The reflective layer 3a reflects the laser light irradiated from the visible information recording layer 4 side and the data recording layer 3 side. The visible information recording layer 4 is a translucent layer whose reflectance changes, for example, when irradiated with laser light from the visible information recording layer 4 side of the optical disc 1. The cover substrate 5 is a member that reverses the optical disc 1 to define the distance between the reference surface 11 and the visible information recording layer 4 and protects the visible information recording layer 4 from the outside.
As shown in FIG. 3, the optical disc 1 is provided with a center hole CH penetrating the base 2 and the cover substrate 5 sandwiching the recording function layer 34, and the cover substrate 5 includes the periphery of the center hole CH and the visible information recording layer 4. It is provided with a uniform thickness so as to cover. The optical disk 1 is loaded on the turntable 12 of the spindle motor through the center hole CH. By irradiating the laser beam for CD onto the data recording layer 3 side of the optical disc 1, the laser beam incident from the objective lens OB via the substrate 2 is reflected by the data recording layer 3 and the reflection layer 3a, and the objective lens OB. Return to normal recording operation. By turning the optical disk 1 over and irradiating the visible information recording layer 4 side with laser light, the laser light incident from the objective lens OB via the cover substrate 5 is reflected by the visible information recording layer 4 and the reflective layer 3a. Returning to the objective lens OB, the user can arbitrarily record image information such as characters and pictures in the visible information recording layer 4. Further, the same effect can be obtained by using DVD laser light.
As an example of the embodiment, as shown in FIG. 4, a polycarbonate disc having a radius of 60 mm is used as the base 2, and a center hole CH having a radius of 7.5 mm is formed at the center. Further, on the visible information recording layer 4 side of the optical disc 1, a clamp area CZ is set between a radius 13 mm and a radius 16.5 mm, and an image area IZ is set between a radius 22 mm and a radius 59 mm, for example.
The optical disk 1 has a structure in which a base 2 having a thickness of 1.2 mm and a cover substrate 5 having a thickness of 0.3 mm are bonded together. Therefore, the thickness of the entire optical disk 1 is 1.5 mm, which is the upper limit of the CD standard.
According to the present embodiment, visible information recording on the visible information recording layer 4 of the optical disc 1 can be realized at low cost without any significant structural change in any recording apparatus for DVD CD. As shown in FIG. 3, in this embodiment, by providing a cover substrate 5 having a thickness of, for example, 0.3 mm on the visible information recording layer 4 of the CD, the visible information is recorded on the visible information recording layer 4 by turning the optical disc 1 upside down. At this time, the visible information recording layer 4 has a thickness of the cover substrate 5 of, for example, 0.3 mm from the reference surface 11 (a plane including the contact surface 13 to the turntable 12 for placing the optical disk 1 so as to contact). It will be located at a position that is far away. Accordingly, when a DVD laser is used to record visible information, the focal position needs to be moved by 0.3 mm, and there is no problem even with the stroke setting of the objective lens OB of the current machine. Even when the CD laser is used, the movement amount of the focal position is reduced from 1.2 mm to 0.9 mm. That is, the cover substrate 5 as an optical distance adjusting unit is an optical element from the reference surface 11 to the objective lens OB in the laser light incident from the objective lens OB via the reference surface 11 when recording on the visible information recording layer 4. It has a thickness that reduces the distance.
As a second embodiment, as shown in FIG. 5, a cylindrical projection PT projecting from the surface of the visible information recording layer 4 is provided around the center hole CH, and the cover substrate 5 is pasted over the entire surface of the optical disc 1. The same effect can be obtained by adopting a bonding configuration only for the data area such as the recording function layer 34 instead of matching. When two substrates are bonded together over the entire surface, the bonded portion of the substrates is exposed on the inner surface of the center hole CH. For this reason, there is a risk that an incomplete chuck is generated in which the ball chuck enters the bonded portion of the optical disc 1 with respect to a spindle motor of a self-chucking type as employed in the thin optical disc 1 device. In the second embodiment, the bonding is not exposed on the inner surface of the center hole CH, which is advantageous for an incomplete chuck.
The thicknesses of the base 2 and the cover substrate 5 of the optical disc 1 are not limited to the set of thicknesses of 1.2 mm and 0.3 mm as long as they are within the CD thickness standard range. The base 2 of the 1.1 mm-thick optical disc 1 and the cover substrate 5 having a thickness of 0.4 mm, or the base 2 of the 1.2 mm-thick optical disc 1 and the set of the cover substrate 5 having a thickness of 0.2 mm may be used. The thickness of the cover substrate 5 can be selected from 0.1 to 0.4 mm, and the thickness of the substrate 2 can be selected from 1.1 to 1.4 mm. The thicker the cover substrate 5, the greater the effect. However, the thickness on the CD data recording layer 3 side needs to be at least 1.1 mm. In addition, when the total thickness exceeds 1.5 mm, there is an increased possibility of occurrence of malfunctions in the conventional optical disk device (such as the optical disk 1 cannot be clamped, the optical disk 1 is scratched, and the optical disk 1 cannot be ejected). Therefore, the upper limit of the thickness of the cover substrate 5 is up to 0.4 mm. In the case where the thickness of the bonded substrate is “1.1 mm + 0.4 mm”, the visible information recording layer 4 is positioned 0.4 mm from the reference surface 11 when the optical disk 1 is turned over. Then, the focal distance is 0.2 mm, which is more advantageous for the movement of the objective lens OB.
The material of the cover substrate 5 is not limited to polycarbonate which is a CD substrate material. The cover substrate 5 as the optical distance adjusting unit may be made of a material such as acrylic, glass material, or translucent ceramic as long as an appropriate refractive index is obtained. At this time, the lower the refractive index material, the greater the effect of reducing the stroke of the objective lens OB. Bonding the two substrates of the base 2 and the cover substrate 5 easily suppresses the warp of the optical disc 1. The standard of surface blur caused by warpage or the like is ± 0.5 mm for a CD (one substrate) and ± 0.3 mm for a DVD (two substrates bonded together). If the objective lens OB is made to follow the optical disc 1 with large surface blurring, the required stroke becomes large and cannot be handled by the current pickup, but this can be avoided by the substrate bonding structure.
In the third embodiment, as shown in FIG. 6, air having a value of 1 is ideal as the refractive index of light without providing the actual cover substrate 5 that transmits light to the visible information recording layer 4. Therefore, in order to play a role as an optical distance adjusting unit that causes an air layer to exist between the reference surface 11 and the visible information recording layer 4, it protrudes from the surface of the visible information recording layer 4 around the center hole. Thus, only the cylindrical protrusion PT is provided. Even in this case, an effect similar to that of the above-described embodiment can be obtained. Furthermore, in terms of refractive index, it is more advantageous than the cover substrate 5 as a substance having a value of 1 or more. That is, the optical distance adjusting unit may be a member having a thickness that reduces the optical distance from the reference surface 11 to the objective lens OB. For example, when the thickness of the substrate 2 and the thickness of the air layer on the image area IZ defined by the projecting portion PT (clamp area CZ) is “1.1 mm + 0.4 mm”, it is visible when the optical disk 1 is turned over. Since the position of the information recording layer 4 is 0.4 mm from the reference plane 11, the focal distance of the DVD laser is 0.2 mm, which is more advantageous for the movement of the objective lens OB.
The thickness of the base 2 of the optical disc 1 and the height (step) of the protrusion PT are not limited to 1.2 mm + 0.3 mm = 1.5 mm as long as they are within the CD thickness standard range. A structure such as a set of 1.1 mm-thick optical disc 1 base 2 and a height of 0.4 mm protrusion PT, or a set of 1.2 mm-thick optical disc 1 base 2 and a height of 0.2 mm protrusion PT may be used. . The height of the protrusion PT can be selected from 0.1 to 0.4 mm, and the thickness of the base 2 can be selected from 1.1 to 1.4 mm. In the case of taking this form, a layer for protecting the visible information recording layer 4 (not shown) (for example, a layer to which an ultraviolet curable resin is applied by spin coating) is formed on the visible information recording layer 4. In this embodiment, the step of attaching the optical disc 1 is not necessary, and the optical disc 1 can be produced at a low cost.
In the third embodiment, as shown in FIG. 6, first, a method <D-1> in which a shape having a step (protrusion PT) in the clamp region CZ is integrally formed with the same material, and as shown in FIG. A method <D-2> is conceivable in which a shape having no step (protrusion PT) is formed as in the normal recording optical disc 1 and a step (protrusion PT) is added in a later process. That is, the base 2 and the projecting part PT can be formed separately and bonded to each other.
When the projecting portion PT is integrally formed as in <D1>, the current CD production process can be used as it is only by correcting the mold. Moreover, the danger of the said incomplete chuck | zipper resulting from a center hole bonding part can also be prevented. In addition, if a concave portion DP having an inner diameter larger than the outer shape of the projecting portion PT is provided on the opposite side of the projecting portion PT, it becomes more stable when the plurality of optical discs 1 are placed on top of each other. In FIG. 8, when the height d2 of the projecting portion PT is smaller than the depth d1 of the recessed portion DP, the optical discs 1 are loosely fitted to each other, so that they can be stacked more stably. That is, the concave portion is provided on the surface of the base 2 on the opposite side to the protruding portion PT of the optical distance adjusting portion protruding from the surface of the visible information recording layer 4.
If the method of adding the protrusion PT later is used as in <D2>, a step-shaped optical disk can be created without correcting the current mold, so the mold of the injection molding machine can be used for conventional optical disks. There is an advantage that can be shared with.
Further, the method of adding the projecting portion PT later as shown in <D2> can be easily handled technically if, for example, a bonding method of the DVD optical disk 1 is employed. In this case, for example, as shown in FIG. 9, if the inner diameter d3 of the projecting portion PT is larger than the inner diameter d4 of the center hole CH, the clamping error in the self-chucking method due to the increase in the thickness of the optical disk 1 or the like. A malfunction can be prevented. That is, the projecting portion PT projecting from the surface of the visible information recording layer 4 is provided with a through-opening that is concentric with the center hole CH and has a large diameter. This can be applied even when the projecting portion PT of <D1> is integrally formed.
Furthermore, in the method of adding the projecting portion PT later as in <D2>, a recess for fitting the spacer that forms the projecting portion PT of the optical distance adjusting portion is provided in the base 2 in advance, and the spacer is adhered later. You can also As shown in FIG. 10, the thickness d5 of the spacer forming the protrusion PT and the thickness d6 of the bottom of the recess of the base 2 do not have to be 0.3 mm + 1.2 mm. For example, when it is difficult to mold a 0.3 mm polycarbonate, the thickness may be, for example, 0.6 mm + 0.9 mm.
Further, in the case of the slim drawer type optical disc 1 apparatus, the same effect can be obtained by sandwiching a protrusion PT having a thickness of 0.3 mm between the optical disc 1 and the reference surface 11 instead of changing the shape of the optical disc 1. The slim drawer type optical disc apparatus is configured such that the chucking portion of the optical disc 1 is exposed to a user's reach. In the case of such a self-chucking type apparatus, the protrusion PT can be sandwiched between the turntable 12 and the optical disc 1 when the optical disc 1 is turned over.
In the above embodiment, the recording function to the visible information recording layer 4 can be realized only by the change on the recording medium side without mechanical change of the apparatus. As a result, the recording function to the visible information recording layer 4 can be easily added to an existing apparatus on the market. Considering only the amount of movement of the objective lens OB, when the CD laser is used, the protrusion PT having a thickness of 0.77 mm is most advantageous. However, if the protrusion PT having a thickness of 0.77 mm is attached to the optical disc 1 (thickness 1.2 mm), the total thickness of the optical disc 1 greatly exceeds 1.5 mm. In this case, the current apparatus cannot chuck the optical disk 1. Further, when a DVD laser is used, the protrusion PT having a thickness of 0.39 mm is ideal, but in this case too, the thickness standard (1.5 mm) is exceeded. (Thickness 1.2 + 0.3 = thickness is within 1.5) is desirable.
Embodiments and effects thereof will be specifically described below.
Conventionally, the objective lens OB of a device that records / reproduces a CD or DVD has to satisfy the following conditions at a minimum as a stroke in a direction away from the optical disc 1.
In the case of a CD, the amount of fluctuation in which the focal position is changed from 1.2 mm to 1.1 mm due to the influence of the surface blur amount of the CD disk of 0.5 mm and the influence when the thickness of the disk substrate 2 is minimum (thickness 1.1 mm) is 0. 0.05 mm, 0.03 mm of tilt when the pickup inner and outer peripheries are moved (radius 59.5 mm to 22 mm) due to 0.05 ° of adjustment variation of turntable and shaft, and objective lens OB position adjustment amount 0.08 mm Therefore, the stroke amount of the objective lens OB when using the CD laser needs to be approximately 0.675 mm.
In the case of DVD, the fluctuation amount of the focal position from 0.6 mm to 0.57 mm is 0 due to the surface blur amount of the DVD disk of 0.3 mm and the influence when the thickness of the disk substrate 2 is minimum (thickness 1.14). 0.02 mm, 0.03 mm of tilt when the pickup inner and outer periphery moves (radius 59.5 mm to 22 mm) due to the adjustment variation of 0.05 ° for the turntable and shaft, and the objective lens OB position adjustment amount 0.08 mm Therefore, the stroke amount of the objective lens OB when using the DVD laser needs to be approximately 0.43 mm.
The current pickup is set based on the above dimensions. With the pickup set in this manner, when focusing on the lower surface of the optical disc 1 for recording on the visible information recording layer 4, the stroke necessary for dealing with surface blurring of the optical disc 1 becomes insufficient.
FIG. 11 is a cross-sectional view for explaining the stroke of the objective lens OB (working distance 0.85 mm) when the CD laser is used for various optical discs 1.
As shown in FIG. 11A, recording / reproduction of a CD is usually performed at the position of the objective lens OB at the working distance WD. In the pickup described here as an example, the objective lens OB is set to be movable 0.80 mm as the stroke lower limit LL from the position of the working distance WD. When the refractive index of polycarbonate (PC), which is the material of the optical disc 1 substrate 2, is about 1.55 (strictly, the refractive index varies slightly depending on the laser wavelength), the recording is performed on the visible information recording layer 4 by flipping over the conventional technique. When performing, as shown in FIG.11 (b), the objective lens OB needs to be 1.2 / 1.55 = 0.77 mm lower than the working distance WD position (position b). In this state, if surface blurring (CD: ± 0.5, DVD: ± 0.3) occurs during rotation of the optical disc 1, the stroke of the objective lens OB is insufficient.
Here, as shown in FIG. 11 (c), the optical disk 1 of the first embodiment (the bonding of the 1.2mm-thick optical disk 1 substrate 2 and the 0.3mm-thick cover substrate 5) is turned over and used. Here, the visible information recording layer 4 is 0.3 mm higher than the reference surface 11. Therefore, the focal position of the objective lens OB can be raised, and when the cover substrate 5 is made of the same material (for example, polycarbonate) as the optical disk 1 substrate 2, the objective lens OB is higher than the position b as shown in FIG. The position c can be set. At this time, a margin of 0.22 mm is generated in the direction away from the optical disc 1 with respect to the stroke of the objective lens OB, so that even if surface blurring of the optical disc 1 occurs, the current pickup can cope with it. Thus, the cover substrate 5 adjusts the optical distance to reduce the optical distance from the reference surface 11 to the objective lens OB. Here, it is desirable to set the surface blurring standard of the bonded optical disc 1 of the embodiment to about ± 0.2 mm.
FIG. 11D shows a third embodiment. In this case, since the 0.3 mm cover substrate 5 is replaced with air, and air is considered to have a refractive index of 1, the lens position in this case is a position d that is 0.47 mm lower than the working distance WD.
FIG. 11E shows a modification of the first embodiment. In this case, the thickness of the cover substrate 5 is 0.4 mm. As a result, the objective lens OB is at a position e that is more advantageous by 0.06 mm than in the embodiment of FIG.
In order to reduce the stroke of the objective lens OB, in addition to the method of increasing the thickness of the cover substrate 5 as the optical distance adjusting portion as described above, the material of the cover substrate 5 is changed to adopt a material having a lower refractive index. However, the same effect can be obtained. For example, when the cover substrate 5 material having a thickness of 0.4 mm is replaced with a low refractive index material (fluorine polymer coating or the like) from polycarbonate, the stroke of the objective lens OB is further reduced by 0.036 mm (refractive index 1.55 to 1.36). If you can).
FIG. 12 is a cross-sectional view similar to FIG. 11 for explaining the stroke of the objective lens OB when a DVD laser is used for various optical disks 1.
The objective lens OB position (working distance 1.22 mm) when the DVD laser is used is a position that is further lower than the position when the CD laser is used. When the DVD in FIG. 12G is turned upside down, the lens position becomes a position d that is 0.39 mm lower than the working distance WD. In FIGS. 12H, 12I, and 12J, the lens position is 0 from the working distance WD. The position d is lowered by 19 mm, 0.09 mm, and 0.13 mm. Even in these cases, the moving stroke of the objective lens OB can be suppressed by applying the present embodiment.
If the surface blur of the optical disk 1 is set to ± 0.15 mm which is half of the DVD standard under the conditions shown in FIG. 12, the thickness of the cover substrate 5 (material is polycarbonate) is 0. In the case of using a 2 mm DVD laser, the same effect can be obtained even if the thickness is as thin as about 0.15 mm.
The substrate bonding technique has been put to practical use with DVDs, and can be produced at low cost without significantly modifying existing production equipment. In addition, since the visible information recording layer 4 is exposed to the outside of the optical disc 1 (visible information recording layer 4 side) in the optical disc 1 used in the prior art, there is a risk that the recording layer may be damaged by external scratches. However, the visible information recording layer 4 is also protected against damage from the outside by bonding the cover substrate 5 as in the present embodiment.
According to the above embodiment, the substrate bonding technique is applied not only to the CD family, but also to the DVD family and the Blu-Ray family, or the optical disk 1 projects around the center hole. By providing the section, the recording function to the visible information recording layer 4 can be realized without making a significant change to the current recording apparatus. Although the optical disk having one data recording layer 3 has been described in the embodiment, the present invention can also be applied to a multilayer disk such as a double-layer disk having two recording layers on one side.

Claims (8)

An information recording medium having a light-transmitting substrate, a reflective layer, and a data recording layer disposed between the substrate and the reflective layer,
A visible information recording layer provided on the opposite side of the data recording layer via the reflective layer; a reference surface including a contact surface for placing the visible information recording layer so as to contact; An optical distance adjusting unit for defining a distance between the information recording layer, a center hole penetrating the light-transmitting substrate and the optical distance adjusting unit, and surrounding the center hole An information recording medium, wherein an optical distance adjusting unit is provided so as to protrude from the surface of the visible information recording layer.   The information recording medium according to claim 1, wherein the optical distance adjusting unit has a thickness of 0.1 to 0.4 mm.   The information recording medium according to claim 1, wherein the light-transmitting substrate has a thickness of 1.1 to 1.4 mm. The information recording medium according to claim 1, wherein the light-transmitting substrate and the optical distance adjustment unit protruding from the surface of the visible information recording layer are integrally formed of the same material. The information recording medium according to claim 1, wherein the light-transmitting substrate and the optical distance adjusting unit protruding from the surface of the visible information recording layer are separately formed and bonded to each other. The information recording medium according to claim 5 , wherein a concave portion that fits into the optical distance adjustment portion that protrudes from the surface of the visible information recording layer is provided . 6. The information recording medium according to claim 5 , wherein the optical distance adjusting portion protruding from the surface of the visible information recording layer is provided with a through-opening having a concentric and large diameter in the center hole . To any one of claims 4-7, characterized in that recesses in the optical path length adjusting unit opposite the light transmittance of the substrate surface opposite the projecting from the surface of the visible information recording layer is provided The information recording medium described.

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