JP2537989B2 - optical disk - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical disc for recording or reproducing information.

2. Description of the Related Art The configuration of a conventional optical disk device will be described below with reference to the drawings. FIG. 6 is a sectional view (a) and a plan view (b) of a conventional optical disk recording surface.

By applying heat on the disc substrate 1, the signal recording medium 2 containing a material whose optical constant changes is formed. Substantially rectangular periodic guide grooves are formed on the surface of the substrate 1.

The thickness of the signal recording medium 2 is substantially equal in the groove 5 (convex toward the base material 1 side) and in the space 6 between the grooves, and the recording dots 4 are formed on the signal recording medium 2 by focusing and heating the laser light. . The recording dots 4 are formed over the groove portions 5 and the inter-groove portions 6, and the difference in reflectance between the recording dots 4 and the outside recording dots 7 is large.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention Generally, the crosstalk of a reproduced signal becomes worse as the recording dots extend to the groove portion, so it is necessary to set the groove pitch with a margin, and there is a limit to achieving high recording density. was there. On the other hand, if the material forming the signal recording medium 2 is reversible with respect to changes in optical constants depending on how heat is applied, the recording dots 4 can be erased by beam spots having different beam powers or beam profiles. At this time, as shown in (c), when the erasing width d _E is small, an unerased portion 4C occurs after erasing the recording dot 4, and the difference in reflectance between the unerased portion 4C and the outside of the recording dot 7 is large enough. However, there was a problem that a high erasing rate (degree of erasing recorded dots) could not be obtained.

Means for Solving the Problems In order to solve the above problems, the present invention provides a material whose optical constant is changed by converging laser light and applying heat on a transparent substrate on which guide grooves are formed. A signal recording medium including the signal recording medium, the film thickness of the signal recording medium is made different on the guide groove and on the guide groove (or on the guide groove), and before and after the change of the optical constant, Reflectance of the signal recording medium above the guide groove (or a part above the guide groove),
Alternatively, the optical disc is characterized in that the change in transmittance is smaller than the change on the guide groove.

Also, the optical depth of the guide groove should be approximately 3/8 wavelength or 5
The optical disc is characterized in that the film formation speed of the signal recording medium is made different between on the guide grooves and on the guide grooves (or on a part between the guide grooves) by setting / 8 wavelength.

Action With the above-described configuration, the area where the reflectance changes (or the transmittance changes) can be limited to the groove portion, and crosstalk does not pose a problem even if the groove pitch is reduced. Even if the erasing width is small, a sufficient erasing rate can be obtained because the difference in reflectance (or the difference in transmittance) between the unerased portion and the outside of the recording dot in the inter-groove portion is small.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 to 5. 1 to 5, the same components as those of the conventional optical disk device (FIG. 6) are designated by the same reference numerals and detailed description thereof will be omitted.

FIG. 1 is a cross-sectional view (a) and a plan view (b) of an optical disk recording surface in a first embodiment of the present invention, showing a signal containing a material whose optical constant is changed by applying heat on the disk substrate 1. The recording medium 2 is deposited in the direction of arrow 3. A substantially rectangular periodic groove (pitch p) having a depth d and a width w is formed as a guide groove on the surface of the base material 1. The thickness of the signal recording medium 2 differs between the groove 5 (convex toward the base material 1 side) and the space 6 between the grooves, and is t _{G at} the groove portion and t _L at the groove portion.

Signal recording medium 2 by condensing and heating laser light
The recording dot 4 is formed at. The recording dot 4 is formed over the groove portion 5 and the inter-groove portion 6, and the reflectance difference between the recording dot 4A and the outside recording dot 7A in the groove portion is large, but the recording dot 4B and the outside recording dot 7B between the grooves are large. The difference in reflectance is small. That is, the region where the optical constant is changed by heating extends over the groove portion 5 and the inter-groove portion 6, but the region where the reflectance is changed is limited to the groove portion 5.

Generally, the crosstalk of the reproduction signal becomes worse as the recording dots extend to the groove portion, so that it is necessary to set the groove pitch p with a margin. However, as in the present invention, the area where the reflectance changes is limited to the groove portion. However, it is possible to reduce the groove pitch and increase the recording density. on the other hand,
When the erase width d _E is small as shown in (c), the recording dot 4
After erasing, there will be an unerased part 4C, but the unerased part 4C
Since the difference in reflectance between the outside of the recording dot 7B and the outside of the recording dot is small, a sufficient erasing rate (degree of erasing the recording dot) can be obtained.

FIG. 2 is an explanatory diagram showing the difference in reflectance with the difference in film thickness of the signal recording medium in the first embodiment. In general,
As shown in (a), the optical disk has a dielectric layer 8 (complex refractive index n ₁ , thickness t ₁ ) on a disk substrate 1 (complex refractive index n ₀ ),
Active layer 9 (the pre-recording complex refractive index n _2, after recording complex refractive index n _'2, the thickness t _2), the dielectric layer 10 (complex refractive index n _3, thickness
t ₃ ), a reflective layer 11 (complex refractive index n ₄ , thickness t ₄ ) is formed on the signal recording medium 2, and an adhesive layer 12 (complex refractive index
n ₅ ) forms a structure in which it is attached to another disk substrate 13.

_{However, n 0 = 1.59 n 1 =} 2.4 t 1 = 60 × α (nm) n 2 = 4.0-i × 1.0 t 2 = 40 × α (nm) (n '2 = 6.0-i × 2.0) n 3 = 2.4 t ₃ = 180 × α (nm) n ₄ = 2.9−i × 3.5 t ₄ = 40 × α (nm) n ₅ = 1.53 At this time, laser light of wavelength λ from the disk substrate 1 side 14
Is plotted and the reflectance is plotted against the film thickness coefficient α in (b). However, λ = 830 nm, the solid line 15 is before recording, and the dotted line 16 is after recording. At the intersection of the solid line 15 and the dotted line 16, for example, near the points A and B, the difference in reflectance before and after recording is small. On the other hand, for example, near points C and C ′ and points D and D ′, the difference in reflectance before and after recording is large. Therefore, the film thickness of the signal recording medium 2 is set to the film thickness of points C and C'or points D and D '(film thickness coefficient α _C or α _D ) in the groove portion, and the film thickness of point A or point B in the groove portion. By setting the film thickness coefficient α _A or α _B , it is possible to make the difference in reflectance between the recording dots and outside the recording dots large in the groove portions and small in the groove portions. If points D and D'are the film thickness of the groove portion and point B is the film thickness of the groove portion, the film thickness of the groove portion is
thickness difference between the land part and the groove with respect to t _G ratio _{(t L -t G) (t} L
-T _G ) / t _G needs to be about 0.1.

FIG. 3 is an explanatory view showing the principle of the difference in film thickness of the signal recording medium between the groove portion and the groove portion in the first embodiment.
(A) shows the direction dependence of the film formation rate with respect to the film formation surface 17, and shows the relationship between the deviation angle θ with respect to the normal line 18 and the film formation rate v. The film forming rate v does not become 0 even if the film forming method such as sputtering is θ90 degrees, for example.
When rectangular grooves (depth d, width w, pitch p) perpendicular to the paper surface are formed on the film forming surface 17 as in (b), the space between the grooves (convex when viewed from the film forming direction 3) The deposition rate at point A is The film formation rate at a point B on the groove (concave when viewed from the film formation direction 3) is proportional to Is proportional to However, tan α = 2d / w. Therefore, the film thickness on the groove is generally smaller than the film thickness on the groove, and the difference is related to the groove shape.

FIG. 4 is an explanatory diagram showing a difference in film thickness of the signal recording medium between the groove portion and the groove portion based on the actual measurement result. The film thickness difference (t _L −t _G ) between the groove part and the groove part increases almost linearly with respect to the film thickness t _G of the groove part, and becomes (t _L −t _G ) / t _G 0.0625. However, this result shows that the depth d = 660 nm (optical groove depth n ₀ d = λ /
8), values obtained by sputtering film formation with a width w = 0.70 μm and a pitch p = 1.6 μm. Assuming that (t _L −t _G ) / t _G is proportional to the groove depth, the groove depth is tripled (that is, the optical groove depth is 3λ / 8, and at this time, the polarity of the tracking output by push-pull is used. Other than the above, other optical characteristics are exactly the same as the groove depth λ / 8.) (T _L −t _G ) / t
_G was about 0.2, which was required in Fig. 2 (t _L −t _G ) / t
_It is much larger than the film thickness difference of about _G 0.1. In general,
It is easy to reduce the film thickness difference by increasing it, and the film thickness difference required in FIG. 2 can be easily achieved by touching other parameters (such as groove width and film forming conditions). . It is also possible to change the film thickness difference itself required in Fig. 2 by touching the film material and its film thickness, and to eliminate the difference in the reflectance between the recording dots on the grooves and outside the recording dots. Is easy. If the groove depth is set to 5λ / 8, a larger film thickness difference can be expected (the optical characteristics at this time are exactly the same as the groove depth λ / 8).

FIG. 5 is a sectional view of the recording surface of the optical disc in the second embodiment of the present invention. That is, the thickness of the signal recording medium 2 does not need to be t _L over the entire groove portion 6 as in the first embodiment, and the portion of the groove portion 6 in contact with the groove portion 5 (width w ₂
If it becomes t _L at a portion smaller than w ₁ but the width w ₂ is larger than the width of the recording dot, the same effect as in the first embodiment can be obtained.

In the above description, the method of using the reflected light amount for the reproduction signal has been discussed, but the same applies to the method of using the transmitted light amount for the reproduction signal. At this time, the difference in the transmittance between the recording dots and the outside of the recording dots in the groove portion is large, but the difference in the film thickness may be made such that the difference in the transmittance between the recording dots and outside the recording dots between the grooves is small. Also,
In the above description, the recording track is grooved (convex when viewed from the base material 1)
However, the recording track is located between the grooves (concave when viewed from the base material 1).
Even in this case, the difference in the reflectance between the recording dots and the outside of the recording dots between the grooves is large, and the difference in the film thickness is set so that the difference in the reflectance between the recording dots and the outside of the recording dots in the groove is small. The same effect can be obtained. Furthermore, the reflectance used in the above description is the ratio of the reflected light (or transmitted light) condensed by the diaphragm lens to the incident light (the amount of light applied to the optical disk), and the formation of recording dots. Changes not only the amplitude component of reflected light (or transmitted light) but also the phase component, and changes in the reflected light amount (or transmitted light amount) (mainly due to change in amplitude component) due to these changes cause the reflected light (or transmitted light) to change. ) (Due to the change in the phase component) of the lens aperture is also taken into account.

Effects of the Invention As described above, according to the optical disc of the present invention, since the area of reflectance change (transmission light change) is limited to the groove portion, crosstalk is small, the groove pitch can be reduced, and the recording density can be increased. Also, since the difference in reflectance (difference in transmittance) between the non-erased portion and the outside of the recorded dots after the recorded dots are erased is small, a sufficient erase rate (degree of erased recorded dots) can be obtained.
It is extremely effective in improving the performance of optical disks.

[Brief description of drawings]

FIG. 1 is a cross-sectional view and a plan view of an optical disk recording surface in an embodiment of the present invention, and FIG. 2 is an explanatory view showing a reflectance difference due to a film thickness difference of a signal recording medium in the embodiment. FIG. 4 is an explanatory view showing the principle of the difference in film thickness of the signal recording medium between the groove portion and the groove portion in the embodiment, and FIG. 4 is a film of the signal recording medium in the groove portion and the groove portion according to the actual measurement result. FIG. 5 is an explanatory view showing a thickness difference, FIG. 5 is a sectional view of an optical disk recording surface in a different embodiment of the present invention, and FIG. 6 is a sectional view and a plan view of an optical disk recording surface of a conventional example. 1 ... Disk substrate, 2 ... Signal recording medium, 4, 4A, 4B ...
… Recording dots, 4C …… Unerased area, 5 …… grooves, 6 …… between grooves, 7A, 7B …… outside the recording dots.

Claims (3)

(57) [Claims] 1. A signal recording medium containing a material whose optical constant is changed by converging a laser beam and applying heat on a transparent substrate having a guide groove formed thereon. Is different between the guide grooves and between the guide grooves, and a change in the reflectance or the transmittance of the signal recording medium between the guide grooves before and after the change in the optical constants causes a change in the guide grooves. An optical disk characterized by being smaller than the conventional one. 2. The optical disk according to claim 1, wherein there is no change in reflectance or transmittance of the signal recording medium before and after the change of the optical constant and between the guide grooves. 3. The film forming speed of the signal recording medium according to claim 1, wherein the optical depth of the guide groove is approximately 3/8 wavelength or 5/8 wavelength so that the film forming speed of the signal recording medium is above the guide groove and above the guide groove. An optical disc characterized in that