TW202125505A - Optical disc and manufacturing method thereof - Google Patents

Abstract

Provided is an optical disc having, at least on one side thereof, at least a cover layer, a first information recording surface, a first intermediate layer, a second information recording surface, a second intermediate layer, a third information recording surface, a third intermediate layer, a fourth information recording surface, and a substrate, which are sequentially arranged from the surface to be irradiated with a light beam. When the thickness of the cover layer is t1, the thickness of the first intermediate layer is t2, the thickness of the second intermediate layer is t3, and the thickness of the third intermediate layer is t4, |t2-t3| ≥ 1 [mu]m, |t3-t4| ≥ 1 [mu]m, |t4-t2| ≥ 1 [mu]m, (t2+t3+t4)-t1 ≥ 1 [mu]m, t1-(t2+t3) ≥ 1 [mu]m, and t1-(t3+t4) ≥ 1 [mu]m are satisfied, and the minimum value among t2, t3, and t4 is 12.5 [mu]m or more.

Description

Optical disc and its manufacturing method

The present invention relates to an optical recording medium (especially an optical disc) that is irradiated with light to record or play information, and particularly relates to an optical recording medium with 4 sides (sometimes called 4 layers), or 8 sides (sometimes Also known as 8-layer) the information recording surface of the optical disc surface arrangement structure.

As a high-density, large-capacity optical information recording medium that has been commercially available, there is an optical disc called DVD or Blu-ray (registered trademark) disc (hereinafter referred to as BD). Such optical discs are rapidly spreading recently as recording media for recording images, music, and computer data. In order to further increase the recording capacity, an optical disc having a plurality of recording surfaces as shown in Patent Documents 1 to 3 has also been proposed.

FIG. 10 is a diagram showing the structure of a conventional optical disc and a schematic structure of an optical pickup (optical pickup).

The optical disc 401 is composed of a first recording surface 401a, a second recording surface 401b, a third recording surface 401c, and a fourth recording surface 401d in order from the surface 401z on the side irradiated by the light beam 701. In addition, between the respective recording surfaces Form the middle layer.

The optical pickup uses an objective lens 561 to convert the light beam 701 into a convergent light beam. The converted convergent light beam penetrates the transparent substrate of the optical disc 401 and is focused on the first recording surface 401a, the second recording surface 401b, the third recording surface 401c, and the fourth recording surface 401d formed inside the optical disc 401 On either side.

Here, when the thickness of each recording surface is all the same length, various problems such as the following will occur. Specifically, when the light beam 701 is condensed on the fourth recording surface 401d in order to perform recording and playback on the fourth recording surface 401d, a part of the light beam 701 is reflected on the third recording surface 401c. Since the distance from the third recording surface 401c to the fourth recording surface 401d is the same as the distance from the third recording surface 401c to the second recording surface 401b, a part of the light beam 70 reflected on the third recording surface 401c will be on the second recording surface 401c. The back side of the recording surface 401b is imaged, and the reflected light is again reflected on the third recording surface 401c, and is superimposed and mixed with the reflected light from the fourth recording surface 401d that should be read out. In addition, since the distance from the second recording surface 401b to the fourth recording surface 401d is the same as the distance from the second recording surface 401b to the surface 401z of the optical disc 401, part of the light beam 70 reflected on the second recording surface 401b is An image is formed on the back side of the surface 401z of the optical disc 401, and the reflected light is again reflected on the second recording surface 401b, and is superimposed and mixed with the reflected light from the fourth recording surface 401d that should be read. In this way, there will be the following problem: the reflected light that has been imaged on the back side of the other layer is overlapped multiple times and mixed into the reflected light from the fourth recording surface 401d that should be read out, which hinders recording/playback. Light like this has high interference, and forms a light-dark distribution caused by interference. In addition, because this light-dark distribution changes in response to the change in the phase difference between the reflected light from other layers caused by the deviation of the thickness of the tiny intermediate layer formed in the surface of the optical disc, the quality of the signal that should be obtained from the optical disc is significant. To lower. Hereinafter, in this specification, this subject is referred to as a back focus subject.

Patent Documents 1 to 3 disclose configurations in which the inter-surface thickness between the respective recording surfaces is different from each other in order to solve this back focus problem. Prior art literature

Patent literature Patent Document 1: International Publication No. 2010/044245 Patent Document 2: Japanese Patent Application Publication No. 2007-149210 Patent Document 3: Japanese Patent Application Publication No. 2007-257759

However, in order to realize a 4-sided disc with a higher recording density than BDXL (registered trademark), it is necessary to consider a configuration different from the conventional example in order to increase the recording density.

In recent years, with the Internet environment and the improvement of computer capabilities, both the amount of information produced in the world and the amount of information that should be recorded have been increasing rapidly. Therefore, in data centers, etc., as a medium for storing information in a safe, low-cost, and low-energy manner, the need for high-density and large-capacity optical discs is gradually increasing. In such applications, it is less likely to be concerned about contamination due to human hands touching the surface of the optical disc and getting fingerprints, as in the past consumer-oriented markets, but on the other hand, the requirements for high recording density and low cost will change. Get higher.

In Patent Document 1, in the four-sided structure specifically disclosed, taking into account the tolerance of 1.5 μm, the shortest value of the thickness between the respective recording surfaces is 10 μm. The tolerance of the thickness between the respective recording surfaces must be 1.5 μm or more in order to reduce the cost of the optical disc, and this has been considered. In addition, the shortest value of the thickness between the surfaces of 10μm is the following value: Even if there is a difference in reflectivity with the adjacent information recording surface, the influence of cross talk from the adjacent recording surface can be relatively small. Range. BDXL (registered trademark) means that the period (pitch) of the signal track is 0.32μm. As long as the recording density is this level, even if the shortest (thinest) surface is 10μm and there is a relatively small crosstalk, it can still be sufficient To ensure the recording and playback quality of the signal. However, in order to achieve higher-density recording and playback, the crosstalk from adjacent recording surfaces must be set smaller. For this reason, there is a problem that the shortest inter-surface thickness must be set larger.

In addition, in Patent Documents 2 and 3, the tolerance of the inter-surface thickness between the respective recording surfaces is narrow, and the tolerance of 1.5 μm cannot be ensured. Therefore, there are the following problems: there is a concern that the yield of optical discs is lowered and it is difficult to low-cost. Production.

The present disclosure was painstakingly devised in view of the above-mentioned past situation, and aims to provide a higher density optical disc than the conventional ones.

In the present invention, in order to solve the above-mentioned problems, the following optical disc is constructed. (Composition 1)

An optical disc, at least on one side, having at least a cover layer, a first information recording surface, a first intermediate layer, a second information recording surface, a second intermediate layer, and a third information recording surface in order from the surface of the irradiated light beam. The third intermediate layer, the fourth information recording surface, and the base material. The optical disc is characterized in that the thickness of the cover layer is set to t1, the thickness of the first intermediate layer is set to t2, and the thickness of the second intermediate layer is set to t2. When the thickness is set to t3 and the thickness of the aforementioned third intermediate layer is set to t4, |t2-t3|≧1μm, |t3-t4|≧1μm, and |t4-t2|≧1μm, and (t2＋t3＋t4)－t1≧ 1μm, and t1-(t2+t3)≧1μm, and t1-(t3+t4)≧1μm, and the minimum value among t2, t3, and t4 is 12.5μm or more. (Composition 2)

Such as the optical disc of composition 1, the characteristics of the aforementioned optical disc are: the standard values are: t1=46(μm), t2=14(μm), t3=22(μm), t4=18(μm), thickness t1, thickness t2, The tolerances of the thickness t3 and the thickness t4 to the standard value are ±1.5μm, respectively. (Composition 3)

Such as the optical disc of composition 1, the characteristics of the aforementioned optical disc are: the standard values are: t1=45.7(μm), t2=14.1(μm), t3=22.1(μm), t4=18.1(μm), thickness t1, thickness t2, The tolerances of the thickness t3 and the thickness t4 to the standard value are ±1.5μm, respectively. (Composition 4)

Such as the optical disc of composition 1, the characteristics of the aforementioned optical disc are: the standard values are: t1=46(μm), t2=18(μm), t3=22(μm), t4=14(μm), thickness t1, thickness t2, The tolerances of the thickness t3 and the thickness t4 to the standard value are ±1.5μm, respectively. (Composition 5)

Such as the optical disc of composition 1, the characteristics of the aforementioned optical disc are: the standard values are: t1=45.7(μm), t2=18.1(μm), t3=22.1(μm), t4=14.1(μm), thickness t1, thickness t2, The tolerances of the thickness t3 and the thickness t4 to the standard value are ±1.5μm, respectively. (Composition 6)

Such as the optical disc of composition 1, the characteristics of the aforementioned optical disc are: the standard values are: t1=43(μm), t2=19(μm), t3=15(μm), t4=23(μm), thickness t1, thickness t2, The tolerances of the thickness t3 and the thickness t4 to the standard value are ±1.5μm, respectively. (Composition 7)

Such as the optical disc of composition 1, the characteristics of the aforementioned optical disc are: the standard values are: t1=44.5(μm), t2=18.5(μm), t3=14.5(μm), t4=22.5(μm), thickness t1, thickness t2, The tolerances of the thickness t3 and the thickness t4 to the standard value are ±1.5μm, respectively. (Composition 8)

Such as the optical disc of any one of compositions 1 to 7, the aforementioned optical disc is characterized in that: each information recording surface is provided with concave-convex grooves, and information is recorded on both the concave and convex portions. The pitch p of the aforementioned concave-convex grooves is: p< 0.6μm. (Composition 9)

Such as the optical disc of any one of compositions 1 to 8, the aforementioned optical disc is characterized in that the lower limit of the distance from the surface of the optical disc to the first information recording surface is smaller than the standard value of thickness t1 by 1.5 μm. (Composition 10)

A method of manufacturing an optical disc is a method of manufacturing an optical disc of any one of compositions 1-9, characterized in that the thickness t1 to the thickness t4 are made in such a way that the tolerance of each standard value is ±1.5 μm. Invention effect

According to the present disclosure, it is possible to improve the quality of the servo signal and the playback signal by preventing the back focus problem in the four-sided structure and reducing the interference of the reflected light on each recording surface. And, in particular, the influence of crosstalk from adjacent recording surfaces can be reduced, and the quality of the playback signal can be improved, and a higher-density optical disc can be realized.

The form used to implement the invention

Hereinafter, the embodiments will be described in detail with reference to appropriate drawings. However, detailed explanations beyond necessary are sometimes omitted. For example, detailed descriptions of items that have been fully understood or repeated descriptions of substantially the same constitution are sometimes omitted. This is because it is necessary to avoid the situation in which the following description becomes unnecessarily lengthy, so as to be easily understood by those skilled in the art.

Furthermore, the additional drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the scope of the patent application by these. (Embodiment 1)

Hereinafter, an embodiment of the present invention will be described using FIG. 1 and FIG. 2. FIG.

FIG. 1 is a diagram showing a schematic configuration of an optical disc 40 and an optical pickup 201 according to Embodiment 1 of the present invention, and FIG. 2 is a diagram showing a layer configuration of an optical disc according to Embodiment 1 of the present invention.

The optical pickup 201 irradiates the optical disc 40 with laser light with a wavelength λ of about 405 nm to play the signal recorded on the optical disc 40.

Four information recording surfaces are formed on the optical disc 40. As shown in FIG. 2, the optical disc 40 has a first information recording surface 40a, a second information recording surface 40b, a third information recording surface 40c, and a fourth information recording surface 40d in this order from the side close to the surface 40z.

The optical disc 40 further has a cover layer 42, a first intermediate layer 43, a second intermediate layer 44, and a third intermediate layer 45. The thickness t1 of the cover layer 42 represents the thickness of the substrate from the surface 40z to the first information recording surface 40a, and the thickness t2 of the first intermediate layer 43 represents the thickness from the first information recording surface 40a to the second information recording surface 40b The thickness t3 of the second intermediate layer 44 represents the thickness of the substrate from the second information recording surface 40b to the third information recording surface 40c, and the thickness t4 of the third intermediate layer 45 represents The thickness of the substrate from the third information recording surface 40c to the fourth information recording surface 40d.

Also, the distance from the surface 40z to the first information recording surface 40a is set to d1 (≒t1), and the distance from the surface 40z to the second information recording surface 40b is set to d2 (≒t1+t2). The distance to the third information recording surface 40c is set to d3 (≒t1+t2+t3), and the distance from the surface 40z to the fourth information recording surface 40d is set to d4 (≒t1+t2+t3+t4).

In FIG. 1, the divergent and substantially linearly polarized light beam 70 emitted from the light source 1 is incident on the polarization beam splitter 52 and reflected. In addition, it is converted into substantially parallel light by a collimator lens 53 provided with a spherical aberration correction mechanism (moving mechanism) 93. In addition, after passing through the quarter-wavelength plate 54 to be converted into circularly polarized light, the contact lens 56 is converted into a convergent light beam, which penetrates the transparent substrate of the optical disc 40, and the first information formed inside the optical disc 40 Light is collected on any one of the recording surface 40a, the second information recording surface 40b, the third information recording surface 40c, and the fourth information recording surface 40d. Spherical aberrations (spherical aberrations) generated when light is focused on each information recording surface can be removed by moving the collimator lens 53 along the optical axis 60 by the spherical aberration correction mechanism 93.

The opening of the objective lens 56 is restricted by the diaphragm 55, and the numerical aperture NA is set to a desired value of 0.85 or more. The light beam 70 reflected on the fourth information recording surface 40 d penetrates the objective lens 56 and the quarter wave plate 54 to be converted into linearly polarized light that is 90 degrees different from the forward path, and then passes through the polarization beam splitter 52. The light beam 70 that has passed through the polarization beam splitter 52 passes through the cylindrical lens 57 and enters the photodetector 320. The light beam 70 will be given astigmatism when it penetrates the cylindrical lens 57.

The photodetector 320 has four light-receiving parts (not shown), and respectively output current signals corresponding to the amount of light received. From these current signals, the following signals can be generated: the focus error (hereinafter referred to as FE) signal formed by the astigmatism method, and the tracking error (hereinafter referred to as TE) signal formed by the push-pull method, which is recorded in Information (hereinafter referred to as RF) signal of the optical disc 40. After the FE signal and TE signal are amplified to a desired level and phase compensation is performed, they are supplied to actuators 91 and 92 for focusing and tracking control.

Here, the points to be noted when there are a plurality of information recording surfaces are explained.

As the first point of attention, use Figures 3 to 7 to illustrate the interference caused by multi-faceted reflected light.

As shown in FIG. 3, the light beams condensed for playback or recording are divided into the following plural light beams due to the semi-transmitting properties of each information recording surface. (1) The beam 70 focused on the recording surface (Figure 3) (2) The light beam 71 reflected on the third information recording surface 40c, focused and reflected on the second information recording surface 40b, and again reflected on the third information recording surface 40c is the back focus light on the information recording surface (Figure 4) (3) The light beam 72 reflected on the second information recording surface 40b, focused and reflected on the surface, and again reflected on the second information recording surface 40b, is the back focus light to the surface (Figure 5) (4) Although not focused on the information recording surface, the light beam 73 reflected in the order of the third information recording surface 40c, the first information recording surface 40a, and the second information recording surface 40b (FIG. 6) (5) Although not focused on the information recording surface, the light beam 74 reflected in the order of the second information recording surface 40b, the surface 40z, and the first information recording surface 40a (FIG. 7)

For example, in the case of t4=t3, the light beam 70 and the light beam 71 are incident on the photodetector 320 with the same optical path length and beam diameter. Similarly, in the case of t4+t3=t2+t1, the light beam 70 and the light beam 72 are incident on the photodetector 320 with the same optical path length and beam diameter. Furthermore, in the case of t2=t4, the light beam 70 and the light beam 73 are incident on the photodetector 320 with the same optical path length and beam diameter. In addition, in the case of t4+t3=t1, the light beam 70 and the light beam 74 are incident on the photodetector 320 with the same optical path length and beam diameter.

Although the light quantity of the light beams 71 to 74 that are multi-faceted reflected light with respect to the light beam 70 will be smaller, because the same optical path length and beam diameter are incident on the photodetector 320, the influence caused by the interference of each beam will be affected. If it is larger, the amount of light received by the photodetector 320 will vary greatly due to a slight change in the thickness between the surfaces or the tilt of the optical disc 40, and it will be difficult to detect a stable signal.

Fig. 8 is a graph showing the relationship between the difference in thickness between surfaces and the amplitude of the FS signal. Furthermore, in FIG. 8, it is shown that the light quantity ratio of the light beam 70 to the light beam 71, the light beam 72, the light beam 73 or the light beam 74 is set to 100:1, and the refractive index of the cover layer 42 and the first intermediate layer 43 are both 1.57 In the case of FS signal amplitude versus the difference in thickness between surfaces. In Figure 8, the horizontal axis is the difference in thickness between the display surfaces, and the vertical axis is the amplitude of the display FS signal. The FS signal amplitude is a value normalized to the amount of DC light when the photodetector 320 receives only the reflected light of the light beam 70. Also, as shown in FIG. 8, it can be seen that if the difference in thickness between the surfaces becomes 1 μm or less, the FS signal changes abruptly.

Furthermore, as with the light beam 72 in FIG. 5, even if the thickness t1 of the cover layer 42 and the thickness t2 of the first intermediate layer 43, the thickness t3 of the second intermediate layer 44, and the thickness t4 of the third intermediate layer 45 are the sum total ( That is, if the difference of (t2+t3+t4)) becomes 1 μm or less, problems such as fluctuations in the FS signal may also occur.

As a second point of attention, if the thickness between adjacent information recording surfaces is too small, it will be affected by crosstalk from adjacent information recording surfaces, so the thickness between the surfaces must be greater than a predetermined value. Therefore, the thickness between the faces is reviewed and the minimum thickness between the faces is determined. Fig. 9 is a graph showing the relationship between the thickness between the surfaces of the optical disc and the jitter. In FIG. 9, the horizontal axis is the thickness between the display surfaces, and the vertical axis is the display jitter value. The reflectance of each information recording surface of the optical disc is set to be almost the same. As the thickness between the surfaces becomes thinner, the jitter will deteriorate. The inflection point is formed to be about 8 μm, and a sudden jitter deterioration is caused in the thickness between the surfaces below this value. In addition, the jitter degradation becomes sufficiently small in the vicinity of 10 to 11 μm.

Also, generally speaking, in the production of discs, the difference in reflectance of each recording surface may appear about 1.5 times. For example, when the reflectance of the other layer is 1.5 times the reflectance of the playback or recording surface, the light amplitude ratio will be √1.5 times the effect of interference on the playback layer, so it is The jitter of the thickness between the surfaces will be shifted by about 2 μm to the right as shown by the dashed line in Fig. 8. Therefore, as long as the minimum value of the thickness between the surfaces is increased by 2 μm from 10 to 11 μm and set to 12 to 13 μm or more, it is possible to offset the increase in the reflection efficiency of other layers. In other words, it can be considered that the minimum thickness between the surfaces is 12 to 13 μm as the most suitable.

2 is used to describe in more detail the structure of the optical disc 40 in the embodiment of the present invention. In the first embodiment, in order to solve the adverse effects of reflected light from each information recording surface or surface, after considering the thickness variation in production, the structure of the four-sided disc is set to ensure the following conditions.

Condition (1): The thickness t1 of the cover layer 42 can be set as thick as possible to suppress the degradation of the information playback signal when the surface of the optical disc is damaged or dirty. It is desirable that t1 be set to about 50 μm so as not to be extremely thinner than BDXL (registered trademark) discs. However, when a data center is used as a medium for storing information, it is less likely to worry about contamination due to human hands touching the surface of the disc and getting fingerprints on the surface of the disc as in the conventional consumer-oriented market, so t1 It is sufficient as long as it is 40 μm or more, and desirably 45 μm or more.

Condition (2): Ensure the total of the thickness t1 of the covering layer 42 and the thickness t2 of the first intermediate layer 43, the thickness t3 of the second intermediate layer 44, and the thickness t4 of the third intermediate layer 45 (ie (t2+t3+t4) )) The difference is 1 μm or more. Since it is expected that the standard value of d4 is set to 100μm, which is the same as the BD in the market, and the minimum thickness between the surfaces is set to 12~13μm, if we consider the case of increasing all t2, t3, and t4 by 2~3μm , Must be set as (t2+t3+t4)－t1≧1μm.

Condition (3): Ensure the sum of the thickness t1 of the cover layer 42 and the thickness t2 of the first intermediate layer 43 (t1+t2), and the sum of the thickness t3 of the second intermediate layer 44 and the thickness t4 of the third intermediate layer 45 ( The difference of t3+t4) is 1 μm or more. However, this condition is automatically satisfied as long as t1 is set to about 50 μm and the standard value of d4 is set to about 100 μm, which is the same as the BDXL (registered trademark) disc.

Condition (4): Ensure that the difference between the thickness t1 of the cover layer 42 and the sum (t2+t3) of the thickness t2 of the first intermediate layer 43 and the thickness t3 of the second intermediate layer 44 is 1 μm or more.

Condition (5): Ensure that the difference between the thickness t1 of the cover layer 42 and the sum (t3+t4) of the thickness t3 of the second intermediate layer 44 and the thickness t4 of the third intermediate layer 45 is 1 μm or more.

Condition (6): The mutual difference between any two values of t1, t2, t3, and t4 is 1 μm or more.

Condition (7): Since the minimum value of the inter-plane thickness (thickness of the intermediate layer) must be 12 to 13 μm or more as described earlier, any of t2, t3, and t4 is 12 to 13 μm or more.

Condition (8): Set the thickness t3 to be greater than the thickness t4, and the thickness t4 to be greater than the thickness t2. Since either of the second information recording surface 40b and the third information recording surface 40c will be affected by the crosstalk signals from the two adjacent surfaces on both sides, it is necessary to try to reduce the crosstalk. When the information on the second information recording surface 40b and the third information recording surface 40c is played back, the crosstalk from other information recording surfaces can be reduced by making the thickness t3 of the second intermediate layer 44 thicker. Therefore, it is desirable to set t3 to be the thickest. In addition, the thinner the distance between each information recording surface and the surface, the greater the tilt margin. Based on this point, it is preferable that the thickness t2 of the first intermediate layer 43 is thinner, and the third intermediate layer The thickness t4 of 45 is relatively thick. From the above consideration, it becomes t3>t4>t2.

Condition (9): By setting the fourth information recording surface 40d farthest from the surface 40z to approximately 100 μm from the surface, the following advantages can be obtained: interchangeability with BDXL (registered trademark) discs and sufficient guarantee System margin such as tilt margin.

Condition (10): For the thickness of the cover layer or the thickness of the intermediate layer, in order to ensure the production yield of the optical disc, the allowable error or deviation in the manufacturing is respectively ensured to be 1.5 μm.

Based on the conditions of (1) to (10) above, consider the following structure: set the thickness of the cover layer as thick as possible to suppress the degradation of the information playback signal when the surface of the disc is damaged or dirty To be lower.

The production variation of the cover layer 42, the first intermediate layer 43, the second intermediate layer 44, and the third intermediate layer 45 is uniformly ±eμm, and the lower limit of t2 is set to sμm.

If the upper limit, lower limit and condition (6) are considered, the central value of the thickness t2~t4 between each surface will become: t2=s+e, t4=(t2+e)+1+e=s+3e+1, t3=(t4+e)+1+e=s+5e+2. As from condition (9), the sum of t1~t4 is 100μm, so condition (10) is also taken into consideration, and it is: 100(μm)=t1+t2+t3+t4 =t1+(s+e)+(s+3e+1)+(s+5e+2) =t1+3s+16.5, Thus, it becomes: t1=83.5-3s.

According to condition (8), as long as condition (5) is secured, condition (4) can also be secured. According to condition (5), t3+t4+2e+1=2s+10e+4≦t1-e, According to condition (10), set e=1.5, and 2s+20.5≦t1=83.5－3s, Therefore, s≦12.6.

In order to satisfy condition (2), the upper limit of t1 must be set to be 1μm thinner than the sum of the lower limit of t2~t4, so it is: t1+e≦(t2+t3+t4－3e)－1 =(s+e)+(s+3e+1)+(s+5e+2)－3e－1 =3s+6e+2, According to this, it becomes: t1=83.5-3s≦3s+5e+2=3s+9.5.

Therefore, 12.333...<s, if described in a unit of 0.1 μm, it becomes 12.4≦s.

From the above, it is 12.4≦s≦12.6, and the standard value is as follows. t1=83.5－3s(μm) t2=s+1.5(μm) t3=s+9.5(μm) t4=s+5.5(μm) d1=t1(μm) d2=d1+t2(μm) d3=d2+t3(μm) d4=100(μm)

In addition, the distance (thickness) from the surface to each information recording surface is d1, d2, d3, and d4 in the order of being closer from the surface, and naturally becomes d1<d2<d3<d4. The difference in the thickness from the surface to the respective information recording surfaces will be the difference in spherical aberration imparted to the light beams converging on the respective information recording surfaces depending on the thickness. In order to reduce this difference and converge the light beam to the diffraction limit, the spherical aberration correction mechanism 93 moves the position of the collimator lens 53 along the optical axis 60. Since the distance that the spherical aberration correction mechanism 93 uses to move the collimator lens 53 is necessary information in the design of the optical pickup 201, it is expected that the maximum and minimum thicknesses from the surface to the recording surface are also The boundaries are clear. d1 is approximately equal to t1, and the maximum value d4 is approximately equal to the sum from t1 to t4. Since the tolerances of d1 and t1 are the same, the tolerance is 1.5μm, and the lower limit should be set to the standard value -1.5μm. In addition, since the tolerance of d4 is 6 μm as the sum of the tolerances of t1 to t4, it is only necessary to set the upper limit to the standard value of (t1+t2+t3+t4) + 6 μm.

The optical disc of the first embodiment of the present invention has a higher recording density than BDXL (registered trademark) discs. It is expected that the track pitch of the arrangement of the information signal is also narrower than the 0.32 μm of the BDXL (registered trademark) disc. However, with a wavelength of λ=0.405μm and a numerical aperture (NA)=0.85, the analytical limit of the optical system that forms a condensing spot on the disc surface is λ/(2xNA)=0.238μm. Even if the NA is expanded to 0.91, the analytical limit is still 0.222μm. In order to make the condensing light spot move along the center of the track (information row), there must be a TE signal showing the deviation of the condensing light spot from the center of the track. However, if the track pitch is set to be narrower than 0.3μm, it will be close to the resolution limit. Therefore, the TE signal will be weakened, and the signal/noise ratio (S/N) will be lowered, and the condensing spot accuracy will not be good. The ground moves along the center of the track (information row).

Therefore, in the optical disc according to the first embodiment of the present invention, grooves formed by concavities and convexities are formed on the recording surface in advance, and information is recorded on both the concavities and convexities. The track pitch of the concave-convex groove is double the track pitch of the information row. For example, if the pitch of the information track is set to 0.3 μm, the pitch of the concave-convex grooves is 0.6 μm. In addition, if the pitch of the concave-convex grooves is set to 0.4 μm, the track pitch of the information row can be narrowed to 0.2 μm. In addition, since the pitch of the concave-convex groove can be narrowed to 0.3μm by setting NA to 0.91, etc., even if the track pitch of the information row is narrowed to 0.15μm, a TE signal with sufficient strength can be obtained, and the The condensing spot moves along the center of the track (information row) with high accuracy.

In this way, in the optical disc of the first embodiment of the present invention, concave and convex grooves are formed on the recording surface, and information is recorded on both the concave and convex portions. The pitch of the concave and convex grooves is set to 0.6 μm or less. It is 0.4 μm or less, and more narrowly, it is preferably 0.3 μm or more. With such a configuration, the following effects can be obtained: the track density can be set higher to achieve high density, and stable tracking servo (tracking servo) can be achieved.

In addition, in the above description, although the refractive index of the cover layer 42, the first intermediate layer 43, the second intermediate layer 44, and the third intermediate layer 45 are set to a uniform refractive index such as 1.6, for example, the description has been made. There may also be different refractive indices. In this case, as disclosed in Patent Publication No. 5281115, NA is used as the numerical aperture when light is condensed on the aforementioned optical disc by an objective lens, and θr and θo are used as the material at refractive index nr and no respectively. The convergence angle of the light in, arcsin and tan are respectively as inverse sine function and tangent function, and the relationship is as follows: θr=arcsin(NA/nr) θo=arcsin(NA/no) do=dr・tan(θr)/tan(θo) As long as the thickness dr of the part of the refractive index nr is converted to the thickness do of the refractive index no (for example, 1.6) according to the above relational expression, and the converted do is used as the value of t1, t2, t3, and t4. Just judge whether it is within the range of the target value. In addition, in order to obtain the actual size target of the intermediate layer made of the material with the refractive index nr, the thickness do under the standard refractive index no can be determined by the relational expression of dr=do·tan(θo)/tan(θr) It can be converted into the actual size and thickness dr of the refractive index nr.

In addition, regarding the lower limit value of d1 and the upper limit value of d4, when the refractive index is different from the standard value, it is desirable that the spherical aberration generated is converted into the same thickness for judgment.

Furthermore, although the above description is directed to one side of the optical disc (the surface on the lower side of the optical disc 40 in FIG. 1), the four-sided recording surface may be 40a, 40a from the upper side of the optical disc 40 in FIG. 40b, 40c, and 40d are produced in the order, and the intermediate layer is produced in the order of t1, t2, t3, and t4. It is also possible to apply a total of 8-sided optical discs by making recording layers on both sides in this way, doubling the capacity of one sheet with 4 sides on both sides.

In this way, the optical disc in this case is at least on one side and has at least a cover layer, a first information recording surface, a first intermediate layer, a second information recording surface, a second intermediate layer, and a third information in order from the surface of the irradiated beam. The recording surface, the third intermediate layer, the fourth information recording surface, and the base material. For the optical disc, the thickness of the cover layer is set to t1, the thickness of the first intermediate layer is set to t2, and the thickness of the second intermediate layer is set Set as t3 and the thickness of the aforementioned third intermediate layer as t4, |t2-t3|≧1μm, |t3-t4|≧1μm, and |t4-t2|≧1μm, and (t2+t3+t4) －T1≧1μm, and t1－(t2＋t3)≧1μm, and t1－(t3＋t4)≧1μm, and the minimum value of t2, t3, and t4 is 12.5μm or more, and it is by including manufacturing deviation Satisfy the aforementioned conditions, and achieve the following effects: avoid back focus issues and reduce crosstalk of information between surfaces, even at high density where the pitch of the information tracks recorded on both the concave and convex portions of the concave-convex groove is 0.3μm or less It can still record and play with good quality. [Example]

The specific embodiments of the present invention will be described in further detail using examples. Specific numerical examples are shown below. (Example 1)

When the value of every 0.5μm is used to make the standard value easy to understand, it becomes s=12.5μm. The standard value is: t1=46(μm), t2=14(μm), t3=22(μm), t4= 18(μm), d1=46(μm), d2=60(μm), d3=82(μm), d4=100(μm), and the lower limit of d1 is 44.5(μm), the upper limit of d4 It is 106 (μm). (Example 2)

In addition, although the numerical values become more complicated, the standard values of the configuration that set s to the maximum are: t1=45.7 (μm), t2=14.1 (μm), t3=22.1 (μm), t4=18.1 (μm), d1=45.7(μm), d2=59.8(μm), d3=81.9(μm), d4=100(μm), and the lower limit of d1 is 44.2(μm), the upper limit of d4 is 106(μm) .

The above two examples satisfy all the conditions (1) to (10). (Example 3)

Regarding the second information recording surface 40b and the third information recording surface 40c, in the case where the resistance of the surface 40z to dust or scratches is more important than the disc tilt margin, the t3>t4> of the condition (8) can also be replaced. t2, and the composition of t3>t2>t4. In this case, the standard values are t1=46(μm), t2=18(μm), t3=22(μm), t4=14(μm), d1=46(μm), d2=64(μm), d3=86 (μm), d4=100 (μm), the lower limit of d1 is 44.5 (μm), and the upper limit of d4 is 106 (μm). (Example 4)

Compared with Example 3, increase s by 0.1μm. The standard values are: t1=45.7(μm), t2=18.1(μm), t3=22.1(μm), t4=14.1(μm), d1=45.7(μm) , D2=63.8(μm), d3=85.9(μm), d4=100(μm), and the lower limit of d1 is 44.2(μm), and the upper limit of d4 is 106(μm).

In the above two cases, condition (8) is excluded to satisfy conditions (1) to (10). (Example 5)

The inter-plane crosstalk under the thickness of the interlayer of about 18μm is smaller than the amount of interplane crosstalk that can be reduced by estimating the manufacturing tolerance of 1.5μm and increasing the thickness of the thinnest interlayer from 12.5μm. , Can also form the following structure: Considering condition (8) as unnecessary, set the standard value as: t1=44.5(μm), t2=18.5(μm), t3=14.5(μm), t4=22.5(μm) , D1=44.5(μm), d2=63(μm), d3=77.5(μm), d4=100(μm), and the lower limit of d1 is 43(μm), the upper limit of d4 is 106(μm) ).

Although this configuration has the effect of estimating the manufacturing tolerance of 1.5μm and enlarging the thickness of the thinnest intermediate layer to 13μm, on the other hand, it has the following disadvantages: the standard value of t1 becomes thinner and becomes larger than 45μm The thin or L1 layer is affected by both the crosstalk from the L2 layer through the thinnest intermediate layer and the crosstalk from the L0 layer. In this embodiment, the condition (8) is excluded to satisfy the conditions (1) to (10). (Example 6)

Compared with Example 5, the configuration in which the thickness of the thinnest intermediate layer is increased to estimate the manufacturing tolerance of 1.5 μm can also be configured as follows: Set the standard values to: t1=43(μm), t2=19( μm), t3=15(μm), t4=23(μm), d1=43(μm), d2=62(μm), d3=77(μm), d4=100(μm), and the lower limit of d1 The value is 41.5 (μm), and the upper limit of d4 is 106 (μm).

Although this structure has the effect of estimating the manufacturing tolerance of 1.5μm and expanding the thickness of the thinnest intermediate layer to 13.5μm, it has the following disadvantages: the standard value of t1 becomes extremely thinner than 45μm. The thin or L1 layer is affected by both the crosstalk from the L2 layer through the thinnest intermediate layer and the crosstalk from the L0 layer.

In addition, it is also a disadvantage that this configuration cannot fully balance condition (5) and condition (10). The following situation can be imagined: even if the tolerance of 1.5μm can be complied with, the condition (5) cannot be complied with. In order to balance condition (5) and condition (10) at any time, it must be t3+t4+2e+1≧t1-e. If the form of the inequality is changed, it is: t1-(t3+t4)≧3e+1=5.5(μm), but since it is 5μm in this configuration, it is less than 0.5μm. Therefore, there are also the following disadvantages: In addition to the 1.5 μm tolerance, it must be confirmed that the thickness t1 of the cover layer 42 can be combined with the thickness t3 of the second intermediate layer 44 and the thickness t4 of the third intermediate layer 45 (t3 The difference of +t4) is ensured to be 1μm or more in the finished value. This embodiment will satisfy the conditions (1) to (4) and (6) to (9). (Example 7)

With respect to Example 6, as a configuration in which the standard value of the thickness of the thinnest intermediate layer is expanded to 15 μm, the following configuration can be considered. In this case, it is the following composition: set the standard values as: t1=47.5(μm), t2=15(μm), t3=23(μm), t4=19(μm), d1=47.5(μm) , D2=62.5(μm), d3=85.5(μm), d4=104.5(μm), and the lower limit of d1 is 46(μm), and the upper limit of d4 is 110.5(μm).

This configuration satisfies all conditions (1) to (10) except for condition (9). However, condition (9) is not satisfied. Since the thickness d4 from the surface of the L0 layer is relatively thick, the disadvantage is that the tilt margin is significantly reduced.

In addition, although the upper limit of d4 is shown on the premise of complying with the tolerance of 1.5 μm in the above-mentioned embodiment, the upper limit of d4 may be increased if it is, for example, about 0.5 to 1.0 μm. The reason is that as long as the errors of t1 to t4 are all on the + side, conditions other than condition (9) can be satisfied, and the inclination margin of the fourth information recording surface 40d is used as one of the deviation requirements, and the situation is a certain This degree can be tolerated. Industrial availability

The multilayer optical disc of the present invention can minimize the influence of reflected light on other information recording surfaces when playing on any information recording surface, thereby reducing the influence of the optical reading head on the servo signal and the playback signal. In this way, it is possible to provide a large-capacity optical disc that can obtain a good-quality playback signal.

1: light source 201: Optical reading head 320: light detector 40,401: optical disc 40a: The first information recording surface 40b: The second information recording surface 40c: The third information recording surface 40d: 4th information recording surface 401a: The first record surface 401b: 2nd record surface 401c: 3rd record surface 401d: 4th record surface 40z, 401z: surface 42: cover layer 43: 1st middle layer 44: 2nd middle layer 45: 3rd middle layer 52: Polarizing beam splitter 53: collimating lens 54: 1/4 wavelength plate 55: Aperture 56,561: contact lens 57: Cylindrical lens 60: Optical axis 70, 71, 72, 73, 74, 701: beam 91, 92: Actuator 93: Spherical aberration correction mechanism (moving mechanism) p: spacing d1, d2, d3, d4, dr, do, t1, t2, t3, t4: thickness NA: Numerical Aperture λ: wavelength nr,no: refractive index

Fig. 1 is a diagram showing a schematic configuration of an optical disc and an optical pickup according to Embodiment 1 of the present invention.

Fig. 2 is a diagram showing the layer structure of the optical disc according to the first embodiment of the present invention.

Fig. 3 is a diagram showing reflected light on an information recording surface for recording and playback.

FIG. 4 is a diagram showing the reflected light of the information recording surface other than the information recording surface for recording and playing.

Fig. 5 is a diagram showing reflected light on an information recording surface other than the information recording surface for recording and playback.

Fig. 6 is a diagram showing reflected light on an information recording surface other than the information recording surface for recording and playback.

FIG. 7 is a diagram showing the reflected light of the information recording surface other than the information recording surface for recording and playing.

FIG. 8 is a graph showing the relationship between the amplitude of the FS signal of the optical disc and the thickness difference between the two surfaces.

FIG. 9 is a graph showing the relationship between the thickness of the base material of the optical disc and the jitter.

Fig. 10 is a diagram showing a schematic configuration of a conventional optical disc and an optical pickup.

40: Disc

40a: The first information recording surface

40b: The second information recording surface

40c: The third information recording surface

40d: 4th information recording surface

40z: surface

42: cover layer

43: 1st middle layer

44: 2nd middle layer

45: 3rd middle layer

d1, d2, d3, d4, t1, t2, t3, t4: thickness

Claims (10)

An optical disc, at least on one side, having at least a cover layer, a first information recording surface, a first intermediate layer, a second information recording surface, a second intermediate layer, and a third information recording surface in order from the surface of the irradiated light beam. The third intermediate layer, the fourth information recording surface, the base material, the aforementioned optical disc is characterized by: When the thickness of the covering layer is set to t1, the thickness of the first intermediate layer is set to t2, the thickness of the second intermediate layer is set to t3, and the thickness of the third intermediate layer is set to t4, t2 －T3|≧1μm, |t3－t4|≧1μm, and |t4－t2|≧1μm, and (t2+t3+t4)－t1≧1μm, and t1－(t2＋t3)≧1μm, and t1－(t3＋t4 )≧1μm, and the minimum of t2, t3, and t4 is 12.5μm or more. Such as the optical disc of claim 1, where the standard values are: t1=46(μm), t2=14(μm), t3=22(μm), t4=18(μm), The tolerances of the aforementioned thickness t1, the aforementioned thickness t2, the aforementioned thickness t3, and the aforementioned thickness t4 to the aforementioned standard value are ±1.5 μm, respectively. Such as the optical disc of claim 1, where the standard values are: t1=45.7(μm), t2=14.1(μm), t3=22.1(μm), t4=18.1(μm), The tolerances of the aforementioned thickness t1, the aforementioned thickness t2, the aforementioned thickness t3, and the aforementioned thickness t4 to the aforementioned standard value are ±1.5 μm, respectively. Such as the optical disc of claim 1, where the standard values are: t1=46(μm), t2=18(μm), t3=22(μm), t4=14(μm), The tolerances of the aforementioned thickness t1, the aforementioned thickness t2, the aforementioned thickness t3, and the aforementioned thickness t4 to the aforementioned standard value are ±1.5 μm, respectively. Such as the optical disc of claim 1, where the standard values are: t1=45.7(μm), t2=18.1(μm), t3=22.1(μm), t4=14.1(μm), The tolerances of the aforementioned thickness t1, the aforementioned thickness t2, the aforementioned thickness t3, and the aforementioned thickness t4 to the aforementioned standard value are ±1.5 μm, respectively. Such as the optical disc of claim 1, where the standard values are: t1=43(μm), t2=19(μm), t3=15(μm), t4=23(μm), The tolerances of the aforementioned thickness t1, the aforementioned thickness t2, the aforementioned thickness t3, and the aforementioned thickness t4 to the aforementioned standard value are ±1.5 μm, respectively. Such as the optical disc of request 1, where the standard values are: t1=44.5(μm), t2=18.5(μm), t3=14.5(μm), t4=22.5(μm), The tolerances of the aforementioned thickness t1, the aforementioned thickness t2, the aforementioned thickness t3, and the aforementioned thickness t4 to the aforementioned standard value are ±1.5 μm, respectively. Such as the optical disc of any one of claims 1 to 7, which is provided with grooves in the shape of concavities and convexities on each recording surface, And record information on both the concave and convex parts, The pitch p of the aforementioned concave-convex-shaped grooves is: p<0.6 μm. An optical disc according to any one of claims 1 to 8, wherein the lower limit of the distance from the surface of the optical disc to the first information recording surface is smaller than the standard value of thickness t1 by 1.5 μm. A method for manufacturing an optical disc is the method for manufacturing an optical disc according to any one of claims 1 to 9, characterized in that: It is produced in such a way that the thickness t1 to the thickness t4 are within a tolerance of ±1.5 μm to their respective standard values.

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