JPH05266514A - Optical recording medium and its tracking method - Google Patents

Abstract

PURPOSE:To enhance a reflected beam at the boundary between the substrate and the recording layer of an optical recording medium. CONSTITUTION:A groove is not formed on the substrate 11 and the high refractive index layer 13 of a concentric circular shape or a spiral shape is provided, or the groove of the concentric circular shape or the spiral shape is formed on the substrate and the high refractive index layer 13 is held between with the recording layer 12, or the groove of the concentric circular shape or the spiral shape is formed on the recording layer and the high refractive index layer is formed on the surface of the recording layer, or the reiteration pattern of a colored state and a uncolored state is formed on the recording layer by the pattern of the concentric circular shape or the spiral shape and the high refractive index layer is formed on the surface of the pattern. Thus, the difference of the refractive index between the substrate and the recording layer is enhanced and the detection of a tracking error signal is facilitated.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an optical recording medium containing a photochromic compound in a recording layer.

[0002]

2. Description of the Related Art In recent years, research on optical recording media using photochromic compounds has been actively pursued.

When such a photochromic compound is irradiated with light of a predetermined wavelength, the structure of the molecule changes due to a photochemical reaction, and the optical characteristics such as absorbance, optical rotation and refractive index change in accordance with the structural change of the molecule. have.

Further, when the light of a specific wavelength is irradiated, the changed molecular structure has a property of returning to the original structure.

Therefore, it is possible to record and reproduce information by utilizing the difference in the optical characteristics, and it is also possible to erase information by converting the molecular structure to the original state.

As described above, the optical recording medium using the photochromic compound is a recording / reproducing system using a photochemical reaction. For example, a recording method such as wavelength multiplex recording or polarization multiplex recording achieves a density higher than that of a conventional optical disk. Is believed to be possible.

When the photochromic compound is used as a medium, various medium structures have been studied.

On the other hand, a typical spiropyran compound is LB
Evaluation by various film forming methods such as a film, a vapor deposition film, and a polymer composite film has been carried out, and evaluation of the vapor deposition film and the polymer composite film in a disk state is being studied.

Also for fulgide, the recording / reproducing characteristics have been evaluated with a polymer composite film dispersed in PMMA.

However, in general, when the concentration of the above-mentioned photochromic compound in the polymer increases, the interaction between the compounds increases, which induces the deterioration of the characteristics, and in some cases, the vapor-deposited film does not react at all.

Therefore, the method of dispersing a suitable amount of photochromic compound in a polymer to form a thin film is the simplest film forming method and is considered to be excellent in mass productivity.

On the other hand, since the recording layer thus obtained basically has a high polymer content, the refractive index of the recording layer is very close to that of the substrate material such as PC, PMMA, glass and the like. It becomes a value.

This means that the reflectance at the substrate-recording layer interface is lowered, and the tracking error signal cannot be detected.

Usually, write-once discs, MD discs and the like are disclosed in JP-A 1-189042, JP-A 2-101647 and JP-A
As disclosed in Japanese Patent Laid-Open No. 2-101648, a substrate is preliminarily formed into a concentric circle or spiral called a groove.
The tracking error signal is detected by using a guide groove having a circular shape and utilizing the fact that when the light beam is diffracted by the track, an asymmetric light amount distribution of the light beam is generated in proportion to the deviation between the light beam and the track. There is.

The so-called push-pull method and wobbling method are basically one of the methods of detecting by the above-mentioned method.

By the way, the organic dye (single film) and the metal material which are write-once recording materials are PC and PM which are substrate materials.
The refractive index is larger than that of MA, glass, etc., the reflected light at the interface between the substrate and the recording layer is very high, and the tracking error signal can be easily detected by the above method.

In the photochromic compound-polymer composite system, since the reflection at the interface between the substrate and the recording layer is extremely small, a tracking error signal cannot be detected, and recording must be performed relying on mechanical accuracy. There is.

On the other hand, an optical recording medium using a photochromic compound usually uses a laser light source having three different wavelengths for recording-erasing-reproducing or at least two wavelengths for recording and erasing-reproducing and recording-reproducing and erasing. It is a wavelength region where the photochromic compound in the recording layer has absorption at any wavelength.

That is, as described above, a sufficient reflectance can be obtained even at the substrate-recording layer interface, and even if tracking is performed using any one of recording, reproducing, and erasing laser beams, the recording layer is There is a problem that the photochromic compound of (1) causes photoreaction.

FIG. 17 is a diagram showing an absorption spectrum of the compound shown in FIG. 14 in a benzene solution (1.0 × 10 ^-4 mol / l). In the figure, the solid line shows the spectrum in the 100% ring-opened state, and the broken line shows the spectrum in the 100% ring-closed state. The dotted line is an absorption spectrum when light with a wavelength of 405 nm is irradiated to a photo-steady state.

Now, assuming that the ring-opened state is the unrecorded state and the photo-steady state is the recorded state, λ ₁ (near 405 nm) is the recording light source, and λ ₂ (near 546 nm) is the erasing and reproducing light source.

When the light of λ ₁ or λ ₂ is continuously or pulsed for tracking, even if the light is weak enough, the same spot is repeatedly irradiated (still state). If so, a photoreaction will occur and the recorded information will be erased.

Therefore, when tracking is performed with the light of λ ₁ , the unrecorded state (open ring state) is converted to the recorded state (optical steady state), while the recording state (optical steady state) is obtained with λ _2.
However, there is a problem that the state changes to an unrecorded state (open ring state).

[0024]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, the problem to be solved by the present invention is that the refractive index of the recording layer is small and the refractive index of the substrate material such as PC, PMMA, or glass. It is an object of the present invention to develop a medium structure that enables good tracking even in a medium close to the above, that is, a medium in which the reflected light at the recording layer-substrate interface is small and the tracking error signal is insufficient.

[0025]

The first invention of the present invention is as follows:
Using a substrate having a substantially flat surface, a recording layer having a substantially flat surface laminated on the substrate surface using a material having a relatively low refractive index, and a material having a relatively high refractive index An optical recording medium comprising a high refractive index layer laminated on the surface of the recording layer spirally or concentrically.

A second aspect of the invention is a substrate having a groove formed on the surface thereof, and a recording layer which is formed by using a material having a relatively low refractive index so as to fill the groove on the surface of the substrate. An optical recording medium comprising a high refractive index layer formed at the interface between the substrate and the recording layer using a material having a relatively high refractive index.

In the second aspect of the invention, it is desirable that the high refractive index layer is a metal reflective layer.

A third invention is a substrate having a substantially flat surface, and a recording layer formed by laminating a material having a relatively low refractive index on the surface of the substrate and forming grooves on the surface. An optical recording medium comprising a high-refractive index layer which is formed by using a material having a relatively high refractive index so as to fill the groove on the surface of the recording layer.

Further, in the fourth invention, a substrate having a substantially flat surface and a material having a relatively low refractive index are used to spirally or concentrically alternate the recording state and the erasing state on the substrate surface. An optical recording medium comprising a recording layer laminated in a repeating pattern and a high refractive index layer laminated on the surface of the recording layer using a material having a relatively high refractive index.

Then, in the optical recording medium according to the second aspect of the present invention, tracking is performed using a light source in a wavelength region where the recording layer does not have absorption.

[0031]

By the function of the substrate-recording layer interface or the high refractive index layer laminated on the recording layer surface, even if a material having a small refractive index is selected for the recording layer, sufficient reflected light can be obtained at the substrate-recording layer interface. It becomes possible to easily obtain the tracking error signal.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The four inventions of the present invention will be described in detail below with reference to an embodiment of the drawings.

[First Invention] FIG. 5 is a sectional view showing the structure of a conventional optical disk. The structure of the conventional optical disk will be described first with reference to this drawing.

In the figure, 101 is a substrate, 102 is a recording layer (reflection layer), and a concentric or spiral groove 103 is formed on the surface (lower surface in the figure) of the substrate 101. The recording layers 102 are laminated so as to fill up the recording layers 102.
The surface (lower surface in the figure) of is substantially flat.

Laser light for reproduction enters from the side of the substrate 101 and is reflected on the groove of the recording layer 102.
The tracking error signal is detected by utilizing the interference phenomenon caused by the laser light 105 reflected on the land of 04 and the recording layer 102.

The reflectance R at the interface between the substrate 101 and the recording layer 102 is calculated by the following equation.

[0037]

[Equation 1]

Therefore, for example, when the recording layer 102 has the same refractive index as that of the substrate 101, the reflectance R at the interface between the substrate 101 and the recording layer 102 becomes small based on the above equation 1, and a sufficient tracking error occurs. No signal can be obtained and accurate tracking cannot be performed during playback.

On the other hand, in the first aspect of the invention, as shown in the sectional view of the structure of the optical disk shown in FIG. 1, a substrate having a substantially flat surface (lower surface in the figure) and having no groove found in the prior art.
A recording layer 12 having a relatively low refractive index having a substantially flat surface is formed on the surface of 11, and a high refractive index layer 13 having a relatively high refractive index is concentrically or spirally formed on the surface. is there.

A method of forming such an optical recording medium will be described. As shown in FIGS. 2 and 3, the recording layer 12 is formed on the substrate 11.
After laminating, a spiral or concentric high-refractive index layer 13 is formed by using a vacuum deposition method or a sputtering method through a mask 14 in which slits are spirally or concentrically formed. Of course, if necessary, a protective layer may be provided on the surface of the high refractive index layer 13.

A substrate is attached to the optical recording medium thus obtained.
A laser beam 15 having a predetermined wavelength is irradiated from the 11 side to perform recording / reproduction / erasing of the optical disc.

Next, the method of tracking the laser beam with respect to the medium associated with the recording-reproducing-erasing will be described with reference to FIGS.
A description will be given along with (c).

To the optical recording medium formed as described above, the conventional push-pull method, the heterodyne method, the three-beam method, the wobbling method, and the like can be applied. Here, the push-pull method is applied. Will be described.

The left half of FIGS. 4A to 4C is a substrate.
The top view of the 1st invention seen from the 11 side is shown. Here, the shaded portion 16 is a portion where the high refractive index layer 13 is provided, and the blank portion 17 is a portion where the high refractive index layer is not provided.

The right half of FIGS. 4 (a) to 4 (c) show distribution charts of the amount of reflected light on the detector surface where the laser light 15 reflected by the medium is detected.

Therefore, even if the blank portion 17 is irradiated with the laser light 15, almost no light is reflected.

FIG. 4A shows the on-track state, and the light spot 18 is exactly operating on the high refractive index layer 13. At this time, the detector surface 19 is bright in the center and dark on both sides (the shaded areas are bright and the blank areas are dark).

Next, when the spot 18 is displaced to the left as shown in FIG. 4B, the left side of the detector surface 19 becomes bright and the right side becomes dark.

On the contrary, when the spot 18 is displaced to the right as shown in FIG. 4C, the right side of the detector surface 19 is bright and the left side is dark.

Since the deviation of the spot 18 can be easily detected in this manner, it can be corrected quickly and accurate tracking can be performed.

Therefore, DRAW (write-once type), E-DRA
In an optical recording medium having a recording layer such as W (rewritable type), a good tracking error signal is obtained even when the refractive index of the recording layer is small and reflected light at the substrate-recording layer interface cannot be obtained. Can be obtained.

Further, it is not necessary to form a groove on the substrate in advance, and the manufacturing process is simple.

The laminated concentric or high refractive index layer may be formed by using ZnS, ZrO2, TiO2 or the like by a vapor deposition method or a sputtering method, but in order to obtain a higher reflectance, Cu is used. Good reflectance can be obtained even when a metal such as Al, Ag, Au, or an alloy thereof is formed by a vapor deposition method or a sputtering method.

In the medium of the first aspect of the present invention, there is no problem even if a protective layer or the like is formed on the high refractive index layer.

[Second Invention] FIG. 6 is a sectional view showing the structure of the second invention, in which 21 is a substrate having grooves 22 formed on its surface, and 23 is a substrate.
Is a recording layer laminated so as to fill the groove 22 with a thin film of the high refractive index layer 24 interposed therebetween.

The groove 22 is formed in a concentric circle shape or a spiral shape, and the laser light 25 (reflected on the groove in FIG. 6) is irradiated from the substrate 21 side.

The medium having the above-mentioned structure was used to prepare samples of some examples by variously changing the material forming the high refractive index layer 24, and as shown in FIG.
As a comparative example, a medium without the above was prepared, each sample and the comparative example were irradiated from the side of the substrate 21 using a semiconductor laser of 780 nm, and the reflected light was measured while focusing on the interface between the substrate 21 and the recording layer 23.

In the comparative example, the grooved P
On C substrate 21 (refractive index 1.58), 100% by weight of methylocerosolve, 10% by weight of polymethacrylic acid, 2,3-bis (2-methylbenzo [b] thiophen-3-yl) maleic anhydride as a diarylethene derivative. A 0.1% by weight solution of the product is uniformly mixed and then applied and dried to form a recording layer 223 of about 1 μm.

Further, each measurement was made to be 10 points, and on the groove 26,
And 27 of each land were measured.

The following were prepared as samples.

Sample 1: Substrate on which groove 22 is formed (material P
ZnS was deposited as a high refractive index layer 24 on C) by a vacuum vapor deposition method to form a high refractive index layer 24 having a thickness of about 800Å.

Next, the recording layer 23 is formed on the ZnS high refractive index layer 24.
Were laminated to obtain a sample 1 of the optical recording medium.

[0063] Sample 2: to obtain a sample 2 to create a medium in the same manner as Sample 1, except that the high refractive index layer 24 was formed using the ZnO _2.

Sample 3: High refractive index layer 24 having a thickness of 300Å
A medium was prepared in the same manner as in sample 1 except that a film was formed using about ₂ % of TiO ₂ to obtain sample 3.

Sample 4: A medium was prepared in the same manner as in Sample 1 except that the high refractive index layer 24 was formed using Cu to obtain Sample 4.

The measurement results are shown in Table 1 below.

[0067]

[Table 1]

The medium of Samples 1 to 4 is 1800 rpm.
When the tracking error signal was detected using a 780 nm semiconductor laser while rotating at, a good error signal was obtained. In one comparative example, the error signal could not be detected.

As described above, in the optical recording medium having the substrate-recording layer, a good tracking error signal can be obtained even in the medium in which the refractive index of the recording layer is small and the reflected light at the interface between the substrate and the recording layer is small.

Although the tracking method of this embodiment is the push-pull method, it goes without saying that other tracking methods are also possible.

For example, the heterodyne method, the three-beam method,
The wobbling method and the like are possible, and all of these tracking methods detect the light amount distribution due to phase interference due to diffracted light, and if the reflected light at the interface between the substrate and the recording layer is insufficient, it cannot be detected. As in the example, the reflected light at the interface between the substrate and the recording layer is sufficient, and detection is possible.

Furthermore, even if a reflective layer or a protective layer is present on the recording layer, no trouble will occur.

On the other hand, with respect to the sample 3, an experiment was conducted by changing the kind of laser used for tracking.

That is, a semiconductor laser having a wavelength of 780 nm which does not absorb the sample 3 was emitted to the same track for 1 hour to measure the absorption spectrum before and after the laser scanning.

For comparison, an absorption spectrum before and after laser scanning was measured under the same conditions using a He—Ne laser having a wavelength of 633 nm, which has an absorption in a colored state for Sample 3. In both of these cases, the laser output was 1 mW / φ1 μm on the film surface. The recording layers were all colored. The results are shown in Table 2 below.

[0076]

[Table 2]

However, E _(t) is the absorbance after 1 hour tracking, and E ₀ is the initial absorbance. From this result, if light of a wavelength that does not have absorption in the medium is used for tracking, the high refractive index layer laminated at the interface between the substrate and the recording layer allows the substrate-recording layer to be selected even if a material having a small refractive index is selected for the recording layer. It can be seen that the reflected light at the interface can be sufficiently obtained and the tracking can be performed without deteriorating the recorded information.

[Third Embodiment] FIG. 8 is a sectional view showing the structure of the optical recording medium of the third embodiment.

In the figure, 31 is a substrate, 32 is a recording layer formed on the substrate 31 (lower surface in the figure), 33 is a high refractive index layer formed on the recording layer 32, and the recording layer A groove 34 is formed at the interface between the 32 and the high refractive index layer 33.

Then, as shown in FIG. 8, the laser light 35 enters from the substrate 31 side, almost no reflected light is generated at the interface between the substrate 31 and the recording layer 32, and is reflected by the recording layer 32-the high refractive index layer 33.

At this time, since the groove 34 is formed at the interface between the recording layer 32 and the high refractive index layer 33, the normal tracking method as described in the second embodiment can be performed by adjusting the depth of the groove 34. It is applicable as it is.

Next, a method of manufacturing the optical recording medium of FIG. 8 will be described with reference to FIGS.

First, a recording layer 32 is formed on the substrate 31 of FIG. 9 (a) by the spin coating method, and spiral or concentric concavo-convex shapes similar to those used in injection molding of a CD or MD substrate are formed. Using the stamper 36 (the convex portion is indicated by 37) having
By pressing on the surface of the recording layer 32, the recording layer
A groove 34 is formed on the surface of 32.

At this time, the surface of the recording layer 32 or the stamper 36 itself is heated to perform molding at a temperature not lower than the Tg temperature peculiar to the recording layer 32.

This process is the same method as the injection generation of PC and PMMA substrates.

In this way, the stamper 36 is removed, the temperature is lowered to fix the shape of the groove 34, and then the high refractive index layer 33 (or the reflection layer) is formed on the recording layer 32 by the vapor deposition method or the sputtering method. Are formed so as to fill up.

At this time, a protective layer may be formed on the surface of the high refractive index layer 33, if necessary.

The interval between the convex portions 37 of the stamper 36 is about
The pitch is 1.6 μm.

As described above, in the medium structure of the present embodiment, since the refractive index of the recording layer is small, even a medium in which it is difficult to obtain sufficient reflected light at the interface between the substrate and the recording layer is equivalent to the conventional medium such as CD and MD. The above error signals can be easily detected, and good tracking can be enabled.

The material of the substrate and the material of the recording layer can be arbitrarily selected as a matter of course, and good conditions can be found by appropriately changing the height of the convex portion of the stamper.

[Embodiment 4] FIG. 11 is a diagram showing the structure of an optical recording medium of Embodiment 4.

In the figure, 41 is a substrate, 42 is a recording layer formed on the substrate 41 (lower surface in the figure), and 43 is the recording layer 42.
The high refractive index layer (reflection layer) formed above, 44 is the substrate 41
Laser light emitted from the side, and 45 is an objective lens that focuses the laser light 44.

In the recording layer 42 of FIG. 11, the shaded portion shows the coloring state (recording state) of the photochromic compound used as the recording layer 42, and the blank portion shows the decoloring state (erasing state).

Next, a method of manufacturing the above optical recording medium will be described.
It will be described with reference to FIGS.

First, after the recording layer 42 is laminated on the surface of the substrate 41, a laser beam 47 is formed on the surface of the recording layer 42 through a mask 46 provided with concentric or spiral slits as shown in FIG. Irradiation.

The laser beam 47 at this time is for recording (recording layer 42
(The photochromic compound used for coloring is colored), and the recording layer 42 and the mask 46 are brought into close contact with each other until the optical density of the portion irradiated with the laser beam 47 and the other portion have sufficient contrast. The entire surface of the recording layer 42 is irradiated with the laser light 47.

At this time, when the initial state of the recording layer 42 is the colored state, it is necessary to use the laser light 47 having a wavelength for erasing, and conversely, when the initial state is the decoloring state, the wavelength for coloring is changed. Must be used.

In this way, the recording layer 42 is provided with a contrast between the colored state and the decolored state (see FIG. 13A).

Next, on the 42 recording layers thus obtained, Al,
A metal reflective layer 43 of Au, Ag, Cu or the like is formed (FIG. 13B).
), And if necessary, the surface of the reflective layer 43 is covered with a protective layer.

FIG. 14 shows the molecular structure of 2-3-bis (2-methyl-benzo [b] thiophen-3-yl) maleic anhydride as a typical photochromic compound used in the recording layer 42. Similarly, FIG. 15 is an absorption spectrum diagram. In FIG. 14, A on the left side shows the molecular structure in the ring-opened state, and the absorption spectrum at this time is shown by the solid line in FIG. The right side B in FIG. 14 shows the molecular structure in the closed ring state, and the absorption spectrum at this time is shown by the broken line in FIG.

Now, let A in FIG. 14 be the unrecorded state and B be the recorded state.

When the recording layer 42 in the state A is irradiated with the laser beam λ1 having a wavelength near 400 nm, the state becomes close to the state B and the recording state is set.

On the other hand, when the recording layer 42 in the state B is irradiated with the laser beam λ2 having a wavelength near 550 nm, the state returns to the state A,
Erase state.

Reproduction can be performed by scanning with weak power using the wavelength of the laser light λ1 or λ2 and detecting the difference in the absorption rate or the reflection rate with respect to the medium.

FIGS. 16 (a) to 16 (c) show a tracking method using the above optical recording medium.
It is the top view seen from the side.

Here, the shaded portion 48 in the left half of the drawing shows the decolored state of the recording layer 42, the blank portion 49 shows the colored state, and the center circle 50 shows the spot of the laser beam 44.

On the other hand, the drawing on the right half shows the light quantity distribution of the laser light on the detector surface, the shaded area 51 indicates the dark area where the light quantity is small on the detector surface, and the blank area 52 indicates the bright area where the light quantity is large. There is.

First, a tracking method for irradiating the laser beam λ1 during recording will be described.

FIG. 16A is a diagram showing an on-track state. Since the central portion of the spot 50 scans over the decolored state 48, the reflected light is smaller than both sides of the spot 50 in the colored state 49. Become. Therefore, the central part of the detector surface is dark,
Both sides are bright.

Further, FIG. 16B shows the case where the spot 50 is displaced to the left, where the left side of the detector surface is dark and the right side is bright.

Further, FIG. 16C shows the case where the spot 50 is displaced to the right, where the right side of the detector surface is dark and the left side is bright.

In this way, it becomes possible to judge whether the spot is scanning at the correct position or the state of right shift or left shift depending on the lightness and darkness of the detector surface.

On the other hand, in the case of irradiating the laser beam λ2 at the time of erasing, unlike the case of the above laser beam λ1, FIG.
In the on-track state of the detector surface, the light amount distribution on the detector surface is bright at the center and dark on both sides, and the brightness is reversed in FIGS. 16 (b) and 16 (c).

When reproducing, the laser beam λ1 or λ2
Tracking may be performed using the same as in the case of recording or erasing.

In the above description, the erased state is described as the initial state. However, when the erased state is used as the initial state, the laser beam λ2 is used as the recording beam and the laser beam λ1 is used as the erased beam. Is possible.

As described above, it is possible to provide a medium capable of tracking even a medium having a small reflectance at the recording layer-substrate interface and in which sufficient reflected light cannot be obtained.

Further, it goes without saying that the substrate material and the composition of the recording layer can be arbitrarily selected in this embodiment, and the photochromic compound is not limited to this embodiment.

[0118]

EFFECTS OF THE INVENTION When the optical recording media disclosed in the first to fourth embodiments of the present invention are used, the reflectance at the recording layer-substrate interface is small due to the relationship between the material used for the substrate and the material used for the recording layer. Even if it is one, a sufficient reflectance can be obtained, a tracking error signal can be detected easily and accurately, and good tracking can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of an optical recording medium of Example 1 of the present invention.

FIG. 2 is an external perspective view showing the manufacturing method of the first embodiment.

FIG. 3 is an external perspective view showing the tracking method of the first embodiment.

FIGS. 4A to 4C are plan views showing an on-track state of laser light and a state of left / right deviation of the laser light according to the first embodiment.

FIG. 5 is a cross-sectional view showing the structure of a conventional optical recording medium.

FIG. 6 is a sectional view showing a structure of an optical recording medium of Example 2 of the present invention.

FIG. 7 is a cross-sectional view showing a configuration of an optical recording medium of a comparative example with respect to the second example.

FIG. 8 is a sectional view showing the structure of an optical recording medium of Example 3 of the present invention.

9A and 9B are cross-sectional views showing the manufacturing method of the third embodiment.

FIG. 10 is an external perspective view showing the manufacturing method of the third embodiment.

FIG. 11 is a sectional view showing the structure of the fourth embodiment of the present invention (when laser light is irradiated).

FIG. 12 is an external perspective view showing the manufacturing method of the fourth embodiment.

13A and 13B are cross-sectional views showing the manufacturing method of the fourth embodiment.

FIG. 14 is a diagram showing a structural formula and a reaction formula of a photochromic compound used in a recording layer of a fourth example.

FIG. 15 is a diagram showing absorption spectra in the two states shown in FIG.

16A to 16C are plan views showing an on-track state and a lateral shift state of the laser light according to the fourth embodiment.

FIG. 17 is an absorbance characteristic diagram in the benzene solution of the second example.

[Explanation of symbols]

 11, 21, 31, 41 Substrate 12, 23, 32, 42 Recording layer 13, 24, 33, 43 High refractive index layer 22, 34 Groove 15, 25, 35, 44, 47 Laser light

Claims (6)

[Claims] 1. A substrate having a substantially flat surface, a recording layer having a substantially flat surface laminated on the substrate surface using a material having a relatively low refractive index, and a relatively high refractive index. An optical recording medium comprising a high refractive index layer which is laminated spirally or concentrically on the surface of the recording layer using the material having the above. 2. A substrate having a groove formed on the surface thereof, a recording layer formed by using a material having a relatively low refractive index so as to fill the groove on the surface of the substrate, and a relatively high refractive index. An optical recording medium comprising a high refractive index layer formed at the interface between the substrate and the recording layer using a material having 3. The optical recording medium according to claim 2, wherein the high refractive index layer is a metal reflective layer. 4. A substrate having a substantially flat surface, a recording layer formed by laminating a material having a relatively low refractive index on the surface of the substrate and forming grooves on the surface, and a relatively high refractive index. An optical recording medium, comprising: 5. A substrate having a substantially flat surface and a material having a relatively low refractive index are laminated on the surface of the substrate in a spiral or concentric pattern in which a recorded state and an erased state are alternately repeated. And a high refractive index layer laminated on the surface of the recording layer using a material having a relatively high refractive index. 6. The tracking method for an optical recording medium according to claim 2, wherein the tracking is performed using a light source in a wavelength region where the recording layer does not absorb.