JP2001319376A - Optical recording medium and optical reproducing device for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently deviate the peak position of temperature distribution from the center of a spot of laser beam for reproduction in the case of adopting a reproducing manner in which the recorded information of the information recording layer of an optical recording medium is detected in such a condition as to deviate the peak position of temperature distribution from the center of the spot on the medium toward the backside of the spot in its scanning direction in the spot and to moderate sensitivity and to improve input power margin in the case of adopting a similar reproducing manner by making temperature distribution gentle in a spot of laser beam for reproduction. SOLUTION: The objective optical recording medium with an information recording layer 3 has a heat controlling film having a heat conductivity nearly equal to or lower than that of the layer 3 or an isometric specific heat nearly equal to or larger than that of the layer 3 on one side of the layer 3 opposite to the side on which laser bema L for reproduction is incident.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the use of a temperature distribution of an optical recording medium in a laser beam irradiation spot.
The present invention relates to an optical recording medium adapted to improve super-resolution reproduction, an improvement in reproduction S / N characteristics, and the like, and an optical recording medium and an optical reproduction apparatus suitable for use in the optical reproduction apparatus.

[0002]

2. Description of the Related Art A medium capable of recording a large amount of digital data has been strongly demanded by the market due to digitization of information in recent years, and a phase change optical disk or a magneto-optical disk is a medium that can meet such a demand. .

In general, a phase change optical disk or a magneto-optical disk has a light-transmitting dielectric film,
The information recording layer and the like are sequentially laminated.

A phase change optical disk is reproduced by detecting a recorded information signal as a change in the reflectance of an optical characteristic with respect to a predetermined light. In other words, the phase change material layer is generally in an amorphous state in the recording area of the phase change optical disk, and is in a polycrystalline state in the unrecorded area. Are different. For this reason, the recorded information is detected as the intensity of the reflected light because the reflectivity for the laser beam of a predetermined wavelength at the time of reproduction differs between the recorded area and the unrecorded area.

On the other hand, detection of recorded information on a magneto-optical disk is performed by a magneto-optical effect on a laser beam having a predetermined wavelength,
That is, reproduction is performed by detecting a change in the polarization state due to the Kerr effect. That is, the information recording layer of the magneto-optical disk, that is, the magnetic recording information layer has a magnetic film having an easy magnetization direction upward or downward in the direction perpendicular to the film surface, and the magneto-optical recording film is formed in accordance with the recording information signal. A recording signal sequence is formed by upward or downward magnetization, that is, a recording magnetic domain. The reproduction is based on the principle of detection of a change in light wave due to magneto-optical interaction between the magnetization of the recording magnetic domain and the laser beam, that is, the magnetic Kerr effect. It irradiates the magnetic domain and detects the angle of application of the polarization of the reflected light, that is, the change in the Kerr rotation angle. At that time, the playback output is
Since it is proportional to the figure of merit, that is, the product of the reflectance R and the Kerr rotation angle θ _K , the larger the values of R and θ _K , the higher the reproduction output.

As described above, in the optical reproducing method of irradiating the information recording layer with the laser beam and detecting the optical change of the reflected light, the detectable limit period length of the recording signal is determined by setting the wavelength of the reproducing laser beam to λ. , The numerical aperture of the objective lens A.
Λ / N. A. Is proportional to Therefore, in order to detect a signal sequence having a shorter period, λ may be reduced or N.N. A. Should be increased.

In recent years, in order to achieve a high recording density, a so-called super-resolution reproduction method, a magnetic domain expansion detection method, and a wavelength reduction of a reproduction laser beam and a high numerical aperture (NA) of an objective lens have been proposed. A reproduction method called a domain wall movement detection method and the like, and an optical recording medium structure suitable for this reproduction method have been proposed. Most of them use the temperature distribution of the optical recording medium obtained by the increase in the medium temperature induced by the laser light irradiated on the optical recording medium, and the wavelength λ of the laser light of the optical system, N.P. of the objective lens of the reproducing optical system A. Thus, it is possible to obtain a detection ability exceeding the optical limit of the light spot diameter determined by the above.

For example, in a so-called DWDD (Domain Wall Displacement Detection) method (for example, see Japanese Patent Application Laid-Open No. 6-290496) using a domain wall displacement detection method, a high-density minute recording magnetic domain is moved by a domain wall during reproduction to enlarge the magnetic domain. To increase the detection capability, that is, the reproduction output. In this case, the amount of movement of the magnetic domain wall generated by the temperature distribution in the laser beam spot due to the irradiation of the reproduction laser beam on the optical recording medium is strongly related to its detection ability. As the distance is longer, that is, the maximum temperature position of the medium, that is, the peak position is more eccentric with respect to the center of the laser spot, the reproduction magnetic domain is expanded, and further this reproduction domain is located at the center of the laser spot where the light intensity is the highest. Since the image can be enlarged over the entire area, a large reproduction output can be obtained.

An optical recording medium based on a D-RAD (double mask RAD (Rear Aperture Detection)) method used for a high-density magnetic recording medium known as GIGAMO (trade name) has a front and a rear in a laser spot. Then, a magneto-optical mask is formed by a low-temperature region and a high-temperature region according to the medium temperature distribution, and the recording information magnetic domain of the recording layer is transferred to the reproducing layer in a limited region between these masks. , The super-resolution reproduction effect is effectively obtained (for example, see Japanese Patent Application Laid-Open No. 4-2710).
No. 39). That is, also in this case, the high-temperature region, that is, the highest temperature position in the spot of the reproduction laser beam is decentered with respect to the center of the laser spot. Can be detected, so that the reproduction output can be increased.

On the other hand, in recent years, the wavelength of a laser beam has been reduced and the objective lens has a high N.I. A. With this, the laser beam spot diameter is reduced. As described above, as the spot of the laser beam is reduced, the light intensity distribution becomes steep near the center of the light spot, and a high density of light energy is concentrated at the center of the spot. For this reason, the temperature rise induced on the medium is also concentrated in a local range near the center of the light spot, and the spatial temperature distribution becomes steep and has a sharp peak.

As described above, by miniaturizing the light spot diameter,
The sharpness of the temperature distribution significantly increases the thermal sensitivity of the optical recording medium to the input optical power.
That is, the fluctuation of the temperature with respect to the input power is large, and the input power margin becomes extremely small.

[0012]

In the present invention, as described above, in the reproduction laser beam spot on the optical recording medium, the peak position of the temperature distribution is shifted from the center of the spot toward the rear side in the scanning direction of the spot. In a state where the recording information is detected in the information recording layer of the optical recording medium in a generated state, the peak position of the temperature distribution is effectively reduced even when the spot size of the reproduction laser beam is reduced as described above. The position can be shifted sufficiently from the center of the spot of the laser beam.

Further, in the present invention, when a similar reproduction mode is adopted, an increase in the temperature of the optical recording medium with respect to an increase in the unit power of the reproduction laser light is suppressed to a small value.
Sensitivity is relaxed so that the input power margin can be improved.

[0014]

The optical recording medium according to the present invention is a single layer such as a ROM (Read Only Memory) type information recording layer, a writable type information recording layer, a rewritable type information recording layer, or the like. A state in which the information recording layer has a multi-layer structure, and the reproduction laser beam scans the information recording layer, thereby causing a peak position of the temperature distribution to be shifted from the center of the reproduction laser beam spot to the rear side in the scanning direction of the spot. In this configuration, the recording information recorded on the information recording layer is detected. Then, from the information recording layer of the optical recording medium, on the opposite side to the incident side of the reproduction laser beam, the thermal conductivity of the information recording layer is substantially the same,
The configuration is such that a thermal control film having a smaller thermal conductivity is provided.

The optical recording medium according to the present invention has a single-layer structure such as a ROM-type information recording layer, a writable-type information recording layer, and a rewritable-type information recording layer, as in the optical recording medium described above. Alternatively, the information recording layer has an information recording layer having a multilayer structure, and the reproduction laser beam scans the information recording layer, so that the peak position of the temperature distribution is shifted from the center of the reproduction laser beam spot to the rear side in the scanning direction of the spot. In this state, the recording information recorded on the information recording layer is detected. In this optical recording medium, a heat control film having a volume specific heat substantially equal to or larger than the volume specific heat of the information recording layer is provided on the side opposite to the side where the reproduction laser beam is incident from the information recording layer. This is the configuration provided.

An optical reproducing apparatus according to the present invention is an optical reproducing apparatus using each of the optical recording media described above, wherein at least a reproducing laser light source unit, an objective lens, and a reproducing laser light from the reproducing laser light source unit are transmitted. A drive unit for scanning on an optical recording medium, wherein the reproducing laser light source unit is constituted by a laser light source having a wavelength of 415 nm or less, or the objective lens is constituted by an objective lens having a numerical aperture (NA) of 0.7 or more. Constitute. Alternatively, the reproducing laser light source section is constituted by a laser light source having a wavelength of 415 nm or less, and the objective lens is constituted by an objective lens having a numerical aperture (NA) of 0.7 or more.

The above-described optical recording medium according to the present invention has a thermal conductivity substantially equal to or smaller than the thermal conductivity of the information recording layer on the opposite side of the information recording layer of the optical recording medium from the side where the reproducing laser beam is incident. The thermal control film having a conductivity is provided, and this is used to set the peak position of the temperature distribution due to the irradiation of the reproducing laser light in the spot of the reproducing laser light for scanning the optical recording medium. It has been found that the position can be greatly shifted to the rear side in the scanning direction from the center of the spot, thereby ensuring super-resolution reproduction, ensuring reproduction output, and thus improving S / N characteristics. .

In the optical recording medium according to the present invention, the volume specific heat of the information recording layer of the optical recording medium is substantially equal to or greater than the volume specific heat of the information recording layer on the side opposite to the side on which the reproducing laser beam is incident. This is to increase the apparent heat capacity of the optical recording medium and to suppress the increase in the temperature of the optical recording medium due to an increase in the unit power of the reproducing laser power. Can be
As a result, the sensitivity due to the reproduction laser power can be reduced, and the margin of the reproduction power can be improved.

Incidentally, in the conventional optical recording medium, in order to lower the thermal sensitivity of the medium, it is necessary to add a material layer, such as Al or AlTi, having a higher thermal conductivity than the optical recording medium. Is commonly done. However, with this configuration, the spatial temperature distribution on the medium changes in addition to the apparent thermal sensitivity of the medium. Therefore,
In the application of the reproducing method utilizing the temperature distribution of the medium in the spot of the reproducing laser light as described above, the reproducing characteristics are deteriorated, and it has been difficult to achieve both the thermal sensitivity control and the maintenance of the reproducing performance.

Further, in the optical recording medium according to the present invention, by increasing the volume specific heat of the heat control layer, the thickness for obtaining a required heat capacity can be reduced, and the film can be easily formed. As a result, it is possible to improve the workability in manufacturing the optical recording medium, the reliability, and the yield.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION An optical recording medium according to the present invention records information on an information recording layer in a state where a peak position of a temperature distribution is shifted from the center of a reproducing laser beam spot to a rear side in the scanning direction of the spot. This is an optical recording medium used for, for example, a magnetic domain expansion detection method, a domain wall movement detection method, a super-resolution reproduction method (MSR), and the like, in which the recorded information is detected. For example, DWD by the domain wall movement detection method described above
D, double-mask type D-RAD by super-resolution reproduction method (MSR), or R-MSR (inverse MSR) disclosed in, for example, JP-A-7-262541, for example, JP-A-3-292632 PS disclosed in
R (Premastered Optical Disc by Super Resolusion)
It is an optical recording medium used for etc.

Embodiments and examples of the optical recording medium and the optical reproducing apparatus according to the present invention will be described, but the present invention is not limited to these embodiments and examples. FIG. 1 is a sectional view showing a basic configuration of an embodiment of an optical recording medium 25 according to the present invention. In this configuration, for example, S
A similar light-transmitting dielectric film 2 made of iN, an information recording layer 3, a heat control film 4, and a protective film 5 made of an ultraviolet curable resin or the like are adhered. Between the information recording layer 3 and the heat control film 4, as shown in FIG.
May be arranged. 2, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and redundant description is omitted.

In the configuration shown in FIGS. 1 and 2, irradiation of recording laser light or reproduction laser light, particularly irradiation of reproduction laser light L, is focused and irradiated by the objective lens 20 from the light-transmitting substrate 1 side. Also in this case, the heat control film 4
Are arranged on the opposite side of the information recording layer 3 from the incident side of the laser beam L.

In the embodiment shown in FIGS. 1 and 2, the laser beam, in particular, the reproduction laser beam L is irradiated from the substrate 1 side. FIG. 3 shows an example of another embodiment. FIG. 3 shows a schematic cross-sectional view of the optical recording medium 25, in which a laser beam, in particular, a reproduction laser beam L is irradiated from the side opposite to the substrate 1. In this case, the base 1 has a structure in which at least the heat control film 4, the information recording layer 3, and the light-transmitting layer 7 are formed on the base 1 regardless of whether or not it is light-transmitting. That is, also in this case, the heat control film 4 is disposed on the side of the information recording layer 3 opposite to the side on which the laser beam L is irradiated (incident).

In the configuration shown in FIGS. 1 to 3, the dielectric film 2,
The information recording layer 3, the heat control film 4, and the heat conductive film 6 can be formed by sputtering or the like. Dielectric film
The protective film 5 and the light transmitting layer 7 can be formed of a resin film, an ultraviolet curable resin film, or the like. The thermal control layer 4 has a film composition having a thermal conductivity substantially equal to or lower than the thermal conductivity of the information recording layer 3. Alternatively, the film composition has a volume specific heat substantially equal to or larger than the volume specific heat of the information recording layer 3.

The reproducing laser beam for the optical recording medium according to the present invention is 415 nm or less, for example, 350 nm to 415 n.
m, and the objective lens 20 has a numerical aperture N. A. Is 0.
7 or more. As shown in FIG. 3, when the reproduction laser beam is irradiated from the light transmission layer 7 side, the light transmission layer 7 is formed of a thin film having a thickness of about 10 μm to 177 μm so that the information recording layer 3 and the objective The lens 20 can be brought close to the lens 20 and can have a high numerical aperture. And
By setting the thickness to 10 μm to 177 μm, the skew margin of the optical recording medium can be increased.

As described above, in the optical recording medium according to the present invention, a film composition having a thermal conductivity substantially equal to or smaller than the thermal conductivity of the information recording layer 3 or a volume specific heat of the information recording layer 3 By providing the thermal control film 4 having a film composition having a volume specific heat almost equal to or larger than that of the laser beam L, the spot is located on the rear side of the spot of the laser beam L in the scanning direction with respect to the optical recording medium with respect to the optical recording medium. ,
The peak position of the temperature rise in the optical recording medium due to the irradiation of the laser beam can be offset, the apparent heat capacity of the optical recording medium is increased, and the increase in the temperature of the medium due to the increase in the unit power of the reproduction laser power is suppressed. Therefore, the reproduction sensitivity can be reduced and the margin (allowable amount) of the reproduction power can be improved.

With respect to the optical recording medium having the structure of the present invention and the optical recording medium having the conventional structure, the spatial distribution of the temperature rise induced on the surface of the information recording layer of the optical recording medium when irradiating a laser beam was examined by thermal simulation.

In this case, the wavelength of the laser light is 400 nm,
N. of objective lens A. Is set to 0.60, and the relative speed between the laser light spot and the optical recording medium due to the rotation of the optical recording medium is set to 4.0 m / sec. The temperature rise induced on the recording medium surface was determined by thermal simulation.

As a conventional structure, as shown in FIG. 2, a transparent substrate 1 has a light-transmitting dielectric film 2 made of silicon nitride, an information recording layer 3 and a heat conductive film 6. The optical recording medium having no heat control layer 4 was designated as Conventional Structure A. Further, in the configuration of the above-described conventional configuration A, the heat control layer 4 is provided on the heat conductive film 6, but the heat control layer 4 has a heat conductivity larger than that of the information recording layer. Constructed by material. The optical recording medium having this configuration is referred to as a conventional configuration B.

In these conventional structures A and B, the light-transmitting dielectric film 2 and the heat conductive layer 6 were made of silicon nitride having a thickness of 35 nm and 12 nm, respectively (thermal conductivity 0.03 J / cm · s · K). , Volume specific heat 1.924 J / c
m ³ · K), and the information recording layer 3 has a thickness of 30
nm TbFeCo (thermal conductivity 0.07 J / cm · s ·
K, volume specific heat 3.0 J / cm ³ · K). The heat control layer 4 in the conventional configuration B has a thickness of 60 mm.
nm of Al (thermal conductivity 2.4 J / cm · s · K, 2.5
92 J / cm ³ · K).

On the other hand, an optical recording medium according to the present invention has the same structure as that of the conventional structure B. However, the heat control layer 4 has a thickness of 60 nm, 55 atomic% of Al and 33% of Fe.
Al alloy containing 12 atomic% of Tb and 12 atomic% of Tb (having a thermal conductivity of 0.1%).
05J / cm · s · K, volume specific heat 3.3J / cm ³ ·
K).

FIG. 4 shows the results of a thermal simulation of the temperature rise for these optical recording media. In this case,
The laser beam power was adjusted so that the maximum temperature of the medium rise was the same. The horizontal axis in FIG. 4 passes through the center of the laser light spot and indicates the direction in which the light spot moves with respect to the optical recording medium. The 0 position indicates the center position of the laser light spot, and the + direction indicates the position of the spot. Means the direction of travel.
In FIG. 4, a curve 40 shows the case according to the configuration of the present invention, and curves 41 and 42 show the cases according to the conventional configurations A and B, respectively.

As a result of this simulation, the laser beam power at each peak of the temperature distribution is
Was 1.15 mW, the conventional configuration B was 3.9 mW, and the configuration of the present invention was 1.50 mW.

In the medium configuration of the present invention, the temperature rise distribution of the medium is almost the same as that of the conventional configuration A, and the required optical power is about 1.4 times. That is, the sensitivity to the increase in the laser power can be appropriately reduced. In the conventional configuration B, the required optical power is about 3.5 times that in the conventional configuration A, and the sensitivity can be reduced.
The temperature peak position moved to the center position of the spot, and the temperature rise distribution of the optical recording medium became steep.

That is, according to the configuration of the present invention, the sensitivity can be reduced as compared with the case where the heat control layer of the conventional configuration A is not provided, and the center position of the spot is set at the center position of the spot as compared with the conventional configuration A. Similarly, the spot is shifted backward in the moving direction of the spot by about 100 nm.

As described above, in the optical recording medium according to the present invention, the peak position of the temperature distribution can be brought to a position spaced apart from the center of the spot of the reproducing laser beam, and the unit of the reproducing laser power can be changed. There is an effect that the increase in the temperature of the medium with respect to the increase in the laser power can be suppressed.

Next, an embodiment according to the present invention will be described, but the present invention is not limited to this embodiment. [Embodiment 1] This embodiment is an optical recording medium applied to DWDD where it is desired that the peak position of the temperature distribution in the optical recording medium by the reproduction laser beam is located behind the center position of the spot in the scanning direction. . In this case, the structure shown in FIG. 2 is adopted, and a light transmitting dielectric film 2, an information recording layer 3, a heat conductive film 6, a heat control film 4, and a protective film 5 are formed on a polycarbonate substrate 1. Transparent dielectric film 2
And thermal conductive layer 6 were formed of silicon nitride (thermal conductivity 0.03 J / cm) having thicknesses of 35 nm and 12 nm, respectively.
S · K, specific volume heat 1.924 J / cm ³ · K), and the information recording layer 3 is made of TbFeC having a thickness of 30 nm.
o (thermal conductivity 0.07 J / cm · s · K, volume specific heat 3.
0 J / cm ³ · K). The thermal control layer 4 is 60 nm thick, with 55 atomic% Al and 3 Fe.
Al alloy with 3 atomic% and Tb of 12 atomic% (thermal conductivity: 0.05 J / cm · s · K, volume specific heat: 3.3 J / cm
³ · K).

As shown in a schematic sectional view of FIG. 5, the information recording layer 3 is composed of a reproducing layer 3R made of GdFeCoAl having a thickness of 30 nm, a cutting layer 3C made of TbFeCoAl having a thickness of 15 nm, and a TbFeCo film having a thickness of 60 nm. The recording layer 3M has a three-layer structure. A reproduction laser beam is focused and irradiated on the optical recording medium having this configuration from the reproduction layer 3R side. In this case, the laser beam scans the optical recording medium from left to right in FIG. 5 in the direction indicated by the arrow b, and the magnetization direction is schematically indicated by a white arrow on the recording layer 3M. The indicated information record is made. At room temperature, the recording layer 3M, the cutting layer 3C, and the reproducing layer 3R are exchange-coupled with each other, and their magnetization directions are the same, as schematically shown by white arrows. . The information recording layer 3 has a temperature distribution shown by a curve 51 due to the irradiation of the reproduction laser beam L, and the temperature is, for example, the Curie temperature T _{1 of the} cutting layer 3C.
As described above, the exchange coupling between the recording layer 3M and the reproducing layer 3R is eliminated, and at the same time, the domain wall of the reproducing layer 3R moves toward a higher temperature direction, that is, up to the temperature peak position, as shown by an arrow a. The reproducing layer 3 is moved by the domain wall movement.
The magnetic domain of R expands. Therefore, in the reproducible area in the reproducing laser beam spot, the polarization plane is rotated by the Kerr effect due to the expanded magnetic domain. Therefore, only the enlarged single magnetic domain of the reproducing layer can be detected by detecting the return light (reflected light) in which the polarization plane of the reproducing laser light is rotated. A large detection output (reproduction output) can be obtained by the expansion of the magnetic domains, and a high reproduction S / N is achieved. Therefore, in this case, the temperature peak position P is
As the distance from the center position O of the laser beam spot increases, the amount of movement of the domain wall can be increased, and the magnetic domain can be expanded, the reproduction output can be improved, and the recording density of the recording layer 3M can be improved.

[Comparative Example 1] In this comparative example, the information recording layer 3 of the above-described conventional configuration A had the same configuration as the information recording layer 3 of the first embodiment.

COMPARATIVE EXAMPLE 2 In this comparative example, the information recording layer 3 of the conventional configuration B described above has the same configuration as the information recording layer 3 of the first embodiment, and the heat control layer 4
Is converted to a 60 nm thick Al (thermal conductivity 2.4 J / cm · s).
.K, 2.592 J / cm ³ · K).

For each of the optical recording media of Example 1, Comparative Example 1, and Comparative Example 2 according to the present invention, a tone signal of 0.2 μm was subjected to magnetic field modulation recording, and DWDD reproduction was performed by the above-described laser beam irradiation. FIG. 6 shows the result of measuring the reproduction power dependency of the carrier-to-noise ratio (C / N) obtained at this time. In FIG. 6, when the curve 60 is Example 1 of the present invention, the curves 61 and 62 are Comparative Example 1 respectively.
And 2. In FIG. 6, the value of the reproduction light power is normalized by the light power at which DWDD is obtained.

From the comparison between Example 1 and Comparative Example 1 and Comparative Example, the configuration of the present invention shows that the decrease in C / N (CNR) due to the increase in the reproducing power is smaller than that of the conventional configuration A. I understand. This is because the thermal sensitivity is reduced, and the change in the DWDD operation characteristic with respect to the change in the reproduction power becomes slow. In addition, the decrease in the car rotation angle θk due to the temperature rise is suppressed, and the reproduction in the DWDD operation is performed. Because the power can be increased, the reflectivity R
X This is because the carrier level proportional to the car rotation angle θk can be effectively increased.

In the conventional configuration B, when the information recording layer 3 had the same configuration as that of the first embodiment and the first comparative example, good signal characteristics could not be obtained. This is because the position of the highest temperature of the medium approaches the center of the light spot, the moving distance of the domain wall, that is, the effective reproduction output is reduced compared to the noise level at the time of reproduction, and the temperature gradient behind the light spot is reduced. This is due to the fact that the ghost signal becomes steeper and the ghost signal is easily generated.

Further, in the optical recording medium according to the present invention and the conventional structure B, thermal simulation was attempted by changing only the film thickness without changing the thermal conductivity and the specific heat of each heat control layer 4. When the optical power was adjusted so that the maximum temperature became the same, the change in the shape of the spatial distribution of the temperature rise of the medium with respect to the change in the film thickness was small, and only the necessary optical power changed. Therefore, it was found that the shape of the temperature rise distribution of the medium was less affected by the film thickness.

In the first embodiment, a DWDD optical recording medium is formed. Needless to say, the optical recording medium according to the present invention is not limited to this DWDD. In the state where the peak position of the temperature distribution is shifted to the rear side in the scanning direction of the spot, detection of the recorded information recorded on the information recording layer is performed, and a magnetic domain expansion detection method, a super-resolution reproduction method, and the like. The optical recording medium to be used can be constituted.

The formation of the information magnetic domain on the optical recording medium according to the present invention, that is, the recording of information, is performed by various known recording methods, for example, by applying a magnetic field and / or irradiating a recording laser modulated in accordance with recording information. Is made.

Next, an embodiment in which the present invention is applied to an optical recording medium used for PSR will be described. That is, in this case, the information recording layer is configured to have a reproducing layer that changes the optical constant with respect to the reproducing laser light in the spot of the reproducing laser light due to the temperature distribution due to the irradiation of the reproducing laser light.

[Embodiment 2] In this embodiment, FIG.
As shown in the schematic sectional view of FIG. 1, a heat control film 4 is formed on a substrate 1, and an information recording layer 3 serving as a reproduction layer by a phase change layer is formed thereon. The light transmitting layer 7 is provided. At the same time as the molding,
The information recording layer 3 has information pits, that is, an uneven surface 14 for forming the ROM type recording surface 13. Base 1
Is formed by injection molding of polycarbonate, and at the same time as this molding, the uneven surface 14 corresponding to the recorded information is formed.

That is, in the information recording layer 3 of the phase change layer, a recording surface 13 of recording pits corresponding to the uneven surface 14 of the base 1 is formed. The phase change layer constituting the information recording layer 3 is in a crystalline state at a temperature lower than a required temperature Ts and exhibits a high reflectance, and melts at a temperature equal to or higher than the temperature Ts to have optical constants (refractive index n and absorption coefficient k). Changes and the laser light L
Is made of a phase change material having a low reflectance.

For this optical recording medium, the light transmitting layer 7
The reproduction laser beam L is focused and irradiated from the side. In this case, FIG.
Shows a state in which the reproduction laser beam scans in the direction shown by the arrow b. Also in this case, as described above, by providing the thermal control film 4 having at least one of a small thermal conductivity and a large volume ratio as compared with the information recording layer 3, the temperature distribution due to the irradiation of the laser beam is increased. Is the curve 71
As shown in the figure, the peak P can be located behind the center position O of the laser beam spot.

As described above, the information recording layer 3 formed of the phase change layer is melted at a temperature equal to or higher than the required temperature Ts, and the optical constants (refractive index n and absorption coefficient k) change, so that the reflectivity of the laser beam L decreases. Therefore, in a region where the temperature becomes equal to or higher than the temperature Ts due to the irradiation of the reproducing laser beam, the reflected light of the reproducing laser beam from the recording surface 13 hardly occurs, and a so-called mask portion is formed here. You. And
In a region where the temperature is lower than the temperature Ts, a crystalline state is exhibited and a high reflectance is exhibited. Therefore, recording pits in this region can be selectively detected as reflected light of the reproduction laser beam L, that is, return light.

In this case as well, the peak position P of the temperature can be located on the rear side of the laser beam spot, and therefore, near the center of this spot,
In addition, information can be reproduced at a limited position in front of the spot.

Incidentally, the optical recording medium according to the present invention is not limited to the above-described example, and various configurations can be adopted in the film configuration of the information recording layer. Is formed by a phase change layer, but the information recording layer 3 in the PSR may be formed by an organic dye layer. The substrate 1 is not limited to one formed by injection molding.
Various modifications and changes can be made, for example, a configuration based on the ation method can be used.

Next, an optical reproducing apparatus for reproducing information from an optical recording medium according to the present invention will be described. An optical reproducing apparatus for an optical recording medium according to the present invention includes at least a reproducing laser light source unit, an objective lens, and a driving unit that scans the optical recording medium with laser light from the reproducing laser light source unit.

FIG. 8 is a schematic structural view of an example of the optical reproducing apparatus according to the present invention. In this example, for example, the first embodiment
This is a case where an optical disk using an optical recording medium having a configuration in which information is reproduced by the magneto-optical effect described above is used. In this example, for example, a GaN-based laser light source 21 that generates a laser beam L having a wavelength of 415 nm or less, for example, 400 nm, a mirror 22, a polarization beam splitter 23, and a numerical aperture N. A. Objective lens 2 with 0.7 or more
0, an optical recording medium 25 according to the present invention is mounted thereon, and a driving device 26 for driving the optical recording medium 25 to rotate the laser recording medium 25, and a laser beam L can be moved in the radial direction of the optical recording medium 25, though not shown. And a moving device for the optical system such as the objective lens 20, that is, a moving stage.

The laser light L of linearly polarized light from the laser light source 21 is introduced into the objective lens 20 through the mirror 22 and the polarization beam splitter 23, and is condensed on the optical recording medium 25. The reflected laser light whose polarization plane has been rotated by the information recorded on the optical recording medium 25, for example, due to the magneto-optical effect, is separated by the polarization beam splitter 22 and detected by the unit 27.

The optical reproducing apparatus according to the present invention employs a reproducing laser beam L having a short wavelength and an objective lens 20 having a high numerical aperture.
Although the spot diameter in the optical recording medium 25 is reduced, the density of the optical recording medium can be increased. However, since the optical recording medium 25 according to the present invention is used, the spot diameter can be reduced. It is possible to solve a problem caused by an increase in laser light density due to miniaturization, that is, a problem of a peak position of a temperature distribution of an optical recording medium in a spot and a steepening thereof. That is, since the peak position of the temperature distribution can be sufficiently deviated backward from the center position of the spot, the expanded magnetic domain is detected at or near the center position of the reproduction laser spot, for example, in reproduction by the domain wall moving method. As a result, the reproduction output can be further improved, that is, the reproduction characteristics can be improved. Further, since the change in the medium temperature with respect to the increase in the reproduction laser power can be made gentle, the sensitivity to the laser power can be appropriately reduced, and the power margin can be improved.

The optical reproducing apparatus according to the present invention is not limited to the above-described example, and various modifications and changes can be made according to the form of the optical recording medium according to the present invention. Similarly, in an optical reproducing apparatus using an optical recording medium based on a super-resolution reproducing method, the spot diameter is similarly reduced, so that the density of the optical recording medium can be increased. It is possible to solve the problem caused by the increase in the laser beam density due to the miniaturization of the diameter, that is, the problem of the peak position of the temperature distribution of the optical recording medium in the spot and the steepening thereof. That is, even in this case, the peak position of the temperature distribution can be sufficiently deviated backward from the center position of the spot, so that the limited position within the spot is at or near the center position of the reproduction laser spot. Since the recorded information can be detected in a limited manner, the reproduction output, that is, the reproduction characteristics can be further improved. Further, since the temperature change with respect to the power of the reproduction laser beam of the optical recording medium can be made gentle, the sensitivity to the laser power can be appropriately reduced, and the power margin can be improved.

[0060]

As described above, in the optical recording medium according to the present invention, the problem of the peak position of the temperature distribution of the optical recording medium in this spot and the steepening thereof can be solved even when the spot diameter of the reproducing laser is reduced. By solving the problem, the recorded information can be limitedly detected at or near the center position of the reproduction laser spot, so that the reproduction output, that is, the reproduction characteristics can be improved.
In addition, since the temperature change of the optical medium with respect to the reproduction laser beam power can be reduced, the sensitivity to the reproduction laser beam power can be appropriately reduced, and the power margin can be improved.

The optical reproducing apparatus according to the present invention uses the optical recording medium according to the present invention and reduces the spot diameter by shortening the wavelength of the reproducing laser and / or increasing the numerical aperture of the objective lens. Thus, reproduction of high-density recording and reproduction characteristics can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an example of an optical recording medium according to the present invention.

FIG. 2 is a schematic sectional view of an example of an optical recording medium according to the present invention.

FIG. 3 is a schematic sectional view of an example of an optical recording medium according to the present invention.

FIG. 4 is a diagram showing a relationship between a medium temperature and a spot of an optical recording medium according to the present invention and an optical recording medium having a conventional configuration.

FIG. 5 is a schematic sectional view of an information recording layer of an example of an optical recording medium according to the present invention.

FIG. 6 is a diagram showing reproduction characteristics of an optical recording medium according to the present invention and an optical recording medium having a conventional configuration.

FIG. 7 is a schematic sectional view of an example of an optical recording medium according to the present invention.

FIG. 8 is a configuration diagram of an example of an optical reproducing apparatus according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Base, 2 ... Light transmissive dielectric film, 3 ... Information recording layer, 3M ... Recording layer, 3C ... Cutting layer, 3R
... Reproduction layer, 4 ... Thermal control film, 5 ... Protective film, 6
... heat conductive film, 20 ... objective lens, 21 ... laser light source, 22 ... mirror, 23 ... polarization beam splitter, 25 ... optical recording medium, 26 ... drive unit,
27: detection unit, L: laser beam

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G11B 11/105 516 G11B 11/105 516K 516F 531 531W 551 551A 551L 586 586M F term (reference) 5D029 JC03 JC06 MA28 5D075 AA03 CD06 CD17 EE03 FF12 FG02 5D090 AA01 BB05 BB10 CC04 DD01 FF41 5D119 AA09 BA01 FA02 JA43 JB02

Claims (10)

[Claims] 1. An information recording layer, wherein a scanning position of a reproducing laser beam on the information recording layer causes a peak position of a temperature distribution to be shifted from the center of the reproducing laser beam spot to a rear side in the scanning direction. An optical recording medium in which recording information recorded on the information recording layer is detected in a state, wherein the heat conduction of the information recording layer is opposite to the incident side of the reproduction laser light from the information recording layer. An optical recording medium comprising a thermal control film having a thermal conductivity substantially equal to or lower than the thermal conductivity. 2. A peak position of a temperature distribution, which has an information recording layer and is shifted from the center of the reproduction laser beam spot to the rear side in the scanning direction by scanning the reproduction laser beam on the information recording layer. An optical recording medium in which the recording information recorded on the information recording layer is detected in the state, wherein the volume specific heat of the information recording layer is on the opposite side of the information recording layer from the incident side of the reproduction laser beam. An optical recording medium comprising a heat control film having a volume specific heat substantially equal to or larger than that of the optical recording medium. 3. The information recording layer forms an information magnetic domain according to recorded information, and detects, within a spot of the reproduction laser light, a detection area based on a change in a magneto-optical effect with respect to the reproduction laser light based on the information magnetic domain. 2. The optical recording medium according to claim 1, wherein the optical recording medium is selected or changed according to a temperature distribution by laser beam irradiation. 4. The information recording layer forms an information magnetic domain according to recorded information, and detects, within a spot of the reproduction laser light, a detection area based on a change in a magneto-optical effect with respect to the reproduction laser light based on the information magnetic domain. 3. The optical recording medium according to claim 2, wherein the optical recording medium is selected or changed according to a temperature distribution by laser light irradiation. 5. The information recording layer moves a magnetic domain wall of an information magnetic domain according to recording information in a spot of the reproduction laser light by a temperature distribution due to the reproduction laser light irradiation, and based on the magnetic domain, a magnetic field against the reproduction laser light. 2. The optical recording medium according to claim 1, wherein a recording magnetic domain is detected by changing an optical effect. 6. The information recording layer moves a magnetic domain wall of an information magnetic domain according to recording information in a spot of the reproduction laser light by a temperature distribution due to the reproduction laser light irradiation, and based on the magnetic domain, magnetically reacts with the reproduction laser light. 3. The optical recording medium according to claim 2, wherein a recording magnetic domain is detected by changing an optical effect. 7. The information recording layer according to claim 1, further comprising: a reproducing layer which changes an optical constant with respect to the reproduction laser light in a spot of the reproduction laser light by a temperature distribution due to the irradiation of the reproduction laser light. 2. The optical recording medium according to 1. 8. The information recording layer according to claim 1, further comprising: a reproducing layer in which a change in an optical constant with respect to the reproducing laser light occurs in a spot of the reproducing laser light by a temperature distribution due to the irradiation of the reproducing laser light. 3. The optical recording medium according to 2. 9. An information recording layer having a temperature distribution peak position offset from the center of the reproduction laser beam spot toward the rear side in the scanning direction by scanning the reproduction laser beam on the information recording layer. In this state, the recording information recorded on the information recording layer is detected, and the thermal conductivity of the information recording layer is substantially equal to or less than the thermal conductivity of the information recording layer on the side opposite to the incident side of the reproduction laser light from the information recording layer. An optical recording medium provided with a thermal control film having a smaller thermal conductivity is used, and at least a reproducing laser light source unit, an objective lens, and laser light from the reproducing laser light source unit are scanned on the optical recording medium. The reproducing laser light source unit is a laser light source unit having a wavelength of 415 nm or less, or the objective lens is a numerical aperture N.
A. An optical reproducing apparatus characterized in that the objective lens has at least one of an objective lens of 0.7 or more. 10. An information recording layer, wherein a scanning position of a reproducing laser beam on the information recording layer causes a peak position of a temperature distribution to be shifted from a center of the reproducing laser beam spot to a rear side in the scanning direction. In this state, the recording information recorded on the information recording layer is detected, and the volume specific heat of the information recording layer is substantially equal to or less than the volume specific heat of the information recording layer on the side opposite to the incident side of the reproduction laser light from the information recording layer. An optical recording medium provided with a heat control film having a large volume specific heat is used. At least a reproducing laser light source unit, an objective lens, and a drive for scanning laser light from the reproducing laser light source unit on the optical recording medium. Or the reproducing laser light source unit is a laser light source unit having a wavelength of 415 nm or less, or the objective lens is a numerical aperture N.
A. An optical reproducing apparatus characterized in that the objective lens has at least one of an objective lens of 0.7 or more.