JP2006048825A - Reproducing method of optical information medium, and optical information medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for easily determining optimum reproduction power by which thermal damage to a mask layer and a function layer bearing super resolution reproduction can be reduced in an optical information medium wherein the reproduction of a super resolution exceeding a diffraction limit is performed, and to provide the optical information medium. <P>SOLUTION: When the wavelength of reproduction light and a numerical aperture of an objective lens of a reproducing optical system are defined as λ and NA, respectively, a short mark having a length LS or shorter and a long mark having a length LL or shorter (wherein LL>LS) are previously formed, the reproducing output of the short mark and the reproducing output of the long mark changed by changing reproducing power are obtained and the optimum power of the reproducing light is determined based on the output values, keeping relations of λ/NA≥LS≥λ/4NA and LL>LS. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for reproducing an optical information medium having a minute recording mark exceeding the diffraction limit, and an optical information medium used for this method.

  Optical information media include read-only optical discs such as compact discs, rewritable optical recording discs such as magneto-optical recording discs and phase change optical recording discs, and write-once optical recording discs using organic dyes as recording materials. .

  An optical information medium can generally have an information density higher than that of a magnetic recording medium, but in recent years, it has been required to further increase the information density in order to process enormous information such as images. In order to increase the information density per unit area, there are a method of narrowing the track pitch and a method of increasing the linear density by reducing the interval between recording marks and phase pits. However, if the track density or linear density is too high with respect to the beam spot of the reproduction light, the carrier to noise ratio (CNR) becomes low, and eventually signal reproduction becomes impossible. The resolution at the time of signal reproduction is determined by the beam spot diameter. Specifically, when the wavelength of the reproduction light is λ and the numerical aperture of the optical system of the reproduction apparatus is NA, generally the spatial frequency 2NA / λ is the reproduction limit. . Therefore, it is effective to shorten the wavelength of the reproduction light and increase the NA in order to improve the CNR and the resolution during reproduction, and many technical studies have been made. Need to be resolved.

  Under these circumstances, various methods for exceeding the reproduction limit determined by light diffraction, that is, so-called super-resolution reproduction methods have been proposed.

  The most common super-resolution reproduction method is a method in which a so-called mask layer is provided on a recording layer. In this method, utilizing the fact that the intensity distribution of the laser beam spot is a Gaussian distribution, an optical aperture smaller than the beam spot is formed in the mask layer, thereby narrowing the beam spot smaller than the diffraction limit. This method is roughly divided into a heat mode method and a photon mode method depending on the difference in the mechanism of optical opening formation.

  In the heat mode method, the optical characteristics change in a region where the temperature becomes a certain value or more in the beam spot irradiation part of the mask layer. The heat mode method is used, for example, in an optical disc described in Patent Document 1. This optical disc has a material layer whose reflectivity varies with temperature on a transparent substrate on which recording pits that can be optically read in accordance with an information signal are formed. That is, this material layer functions as a mask layer. The element specifically mentioned as the material constituting the material layer in the publication is a lanthanoid. In the optical disc described in the publication, when the reading light is irradiated, the reflectance of the material layer changes depending on the temperature distribution in the scanning spot of the reading light, and after reading, the reflectance is in an initial state when the temperature is lowered. Returning to the above, the material layer does not melt at the time of reproduction. As a heat mode method, for example, as described in Patent Document 2, an amorphous-crystal transition material is used for a mask layer, and a high temperature region in a beam spot is crystallized to improve reflectance. A medium for performing super-resolution reproduction is also known.

  In the heat mode method, the size of the optical aperture is uniquely determined by the temperature distribution of the mask layer. Therefore, the reproduction light takes into consideration all of the linear velocity of the medium, the power of the reproduction light, and the ambient temperature of the medium during reproduction. It is necessary to set the optimum power.

  On the other hand, in the photon mode method, the optical characteristics change in a region where the photon amount is a certain value or more in the beam spot irradiation part of the mask layer. The photon mode method is used in, for example, the information recording medium described in Patent Document 3, the optical recording medium described in Patent Document 4, and the optical information recording medium described in Patent Document 5. Patent Document 3 discloses a mask layer in which phthalocyanine or a derivative thereof is dispersed in a resin or an inorganic dielectric, and a mask layer made of chalcogenide. Further, in Patent Document 4, a super-resolution reproduction film containing a semiconductor material having a forbidden band in which light absorption characteristics are changed by electron excitation to the energy level of excitons by irradiation of the reproduction light is used as a mask layer. As a specific example of the mask layer, a material in which CdSe fine particles are dispersed in a SiO2 base material is cited. Moreover, in the said patent document 5, the glass layer from which the intensity distribution of the irradiated light and the intensity distribution of the transmitted light changes nonlinearly is used as a mask layer.

  Unlike the heat mode super-resolution reproduction medium, the photon mode super-resolution reproduction medium is not affected by the ambient temperature of the medium during reproduction, and deterioration due to repeated reproduction is relatively less likely to occur.

  The region where the optical characteristics change in the photon mode method is determined by the number of incident photons. The number of incident photons depends on the linear velocity of the medium with respect to the beam spot. Even in the photon mode method, the size of the optical aperture depends on the power of the reproduction light. If an excessive power is applied, the optical aperture becomes excessive, and super-resolution reproduction becomes impossible. Therefore, also in the photon mode method, it is necessary to set the optimum power of the reproduction light according to the linear velocity and according to the dimensions of the pit and recording mark to be read.

  Super-resolution reproduction media include super-resolution reproduction media having a mask layer and super-resolution reproduction media not using a mask layer. An example of a super-resolution reproduction medium that does not use a mask layer is an optical information medium disclosed in Patent Document 6. This optical information medium has a functional layer made of a specific material and having a specific thickness corresponding to each of the specific materials. This functional layer is a layer that enables super-resolution reproduction by a mechanism completely different from that of a conventional super-resolution reproduction medium having a mask layer. Examples of the specific material include Nb, Mo, W, Mn, Pt, C, Si, Ge, Ti, Zr, V, Cr, Fe, Co, Ni, Pd, Sb, Ta, Al, In, Cu, and Sn. , Te, Zn, Ag, Au, and Bi, or a simple substance or an alloy containing at least one element selected from Bi, or a compound thereof is used. In a conventional super-resolution reproduction medium using a mask layer, the intensity of light reflected or transmitted through the mask layer changes corresponding to the formation of an optical aperture in the mask layer. That is, when the reproduction power is increased, the reflectance or transmittance of the mask layer changes when the specific reproduction power is reached. On the other hand, in the super-resolution reproduction medium having the functional layer, the reflectance or transmittance of the functional layer does not change even when the reproduction light power is increased.

  As described above, when performing super-resolution reproduction, it is necessary to set an optimum reproduction power in both the heat mode method and the photon mode method.

  Conventionally, in order to determine the optimum playback conditions for an optical information medium, proposals have been made to provide a test area for performing trial reading on the optical information medium. For example, Patent Document 7 describes a method in which a plurality of test areas are provided at different radial positions, and an optimum reproduction power that varies depending on a change in operating environment temperature or a radial position. In this patent document, trial reading is performed by changing the reproduction power in each test area, and the optimum reproduction power is obtained from the error rate of the reproduction signal. Also, the patent document describes that the superiority or inferiority of the reproduction signal may be determined based on the amplitude of the reproduction signal. In the example of the specific procedure described in the patent document, a magneto-optical disk using MSR (Magnetically induced Super Resolution) technology is used. The optimum reproduction power is determined by reproducing the test pattern of a single signal alternately arranged. However, this publication does not describe whether a recording mark having a length of 0.38 μm exceeds the diffraction limit.

  However, it is not practical to incorporate an error rate detection circuit into a commercially available optical disk drive device from the viewpoint of cost, for example. Further, the signal processing system of the optical disk drive device incorporates an AGC (automatic gain control) function for controlling the level of the reproduction signal. Therefore, the optimum reproduction power is obtained using the absolute value of the amplitude of the reproduction signal. It is difficult.

  Patent Document 8 describes a method of setting the reproduction power based on a reproduction signal of a mark having a length shorter than the diffraction limit and a mark having a length longer than the diffraction limit.

However, if the reproduction power is as low as possible, it is suitable when considering the life of the laser. Therefore, when determining the optimum reproduction power, the method of increasing the power as needed from the low power can reduce the load on the laser as much as possible.
When this method is adopted, if the power is low, it is difficult to properly track and reproduce the mark below the diffraction limit, and in the worst case, reproduction may not be possible.
In addition, it is technically difficult to stably form a minute mark below the diffraction limit on the disk. In order to form a mark stably by the injection molding method, a mark having a length longer than the diffraction limit is required. Can be formed more stably.

JP-A-5-205314 Japanese Patent No. 2844824 JP-A-8-96412 Japanese Patent Laid-Open No. 11-86342 Japanese Patent Laid-Open No. 10-340482 Japanese Patent Laid-Open No. 10-327048 JP-A-11-126340 JP 2001-222820 A

  Accordingly, an object of the present invention is to easily determine the optimum reproduction power that can reduce the thermal damage of the mask layer and the functional layer that are responsible for super-resolution reproduction, for an optical information medium in which high-resolution reproduction exceeding the diffraction limit is performed. It is to provide a method and to provide an optical information medium used in this method.

Such an object of the present invention is achieved by the following configurations (1) to (12).
(1) When the wavelength of the reproduction light is λ and the numerical aperture of the objective lens of the reproduction optical system is NA, a short mark having a length LS or less and a long mark having a length LL or less (where LL> LS) Obtain the short mark reproduction output and the long mark reproduction output, which are formed in advance on the optical information medium and change by changing the reproduction power, and set the optimum power of the reproduction light based on these outputs A method for reproducing an optical information medium.
(2) The method for reproducing an optical information medium according to the above (1), wherein the relationship of λ / NA ≧ LS ≧ λ / 4NA and LL> LS is satisfied with respect to the LS and LL.
(3) The optical information medium has a data recording area and a test reproduction area, and the short mark and the long mark are previously formed in the test reproduction area. 2) A method for reproducing an optical information medium as described above.
(4) When the difference in light quantity caused by the presence or absence of a short mark having a length LS or less is Ils and the difference in light quantity caused by the presence or absence of a long mark having a length LL or less is Ill, the minimum reproduction power that enables detection of Ils. The above-mentioned (1) is characterized in that, with the obtained Ils / Ill as an initial value, the reproduction power at which the value of Ils / Ill is larger by 10% or more relative to the initial value is the optimum power of the reproduction light. A method for reproducing an optical information medium according to any one of to (3).
(5) With respect to the Ils and Ill, the reproduction power in a range where Ils / Ill ≦ 0.95 is obtained is the optimum power of the reproduction light. Method for reproducing optical information media.
(6) When Ils is a light amount difference caused by the presence or absence of a short mark having a length of LS or less, Ils obtained with the lowest reproduction power at which Ils can be detected is defined as an initial value Ilsf, and a relative value of 1.05 < The reproducing method for an optical information medium according to any one of the above (1) to (5), wherein the reproducing power for obtaining a range of Ilsf / Itop ≦ 5 is the optimum power of the reproducing light. Here, Itop represents unrecorded state signal intensity.
(7) When the wavelength of the reproduction light is λ, the numerical aperture of the objective lens of the reproduction optical system is NA, and the maximum length of the shortest mark among the marks constituting the information pattern is Lm,
An optical information medium that is reproduced under the condition that Lm <λ / 4NA is satisfied,
An optical information medium, wherein a short mark having a length LS or less and a long mark having a length LL or less (where LL> LS) are formed in advance.
(8) The optical information medium as described in (7) above, wherein the relationship of λ / NA ≧ LS ≧ λ / 4NA and LL> LS is satisfied with respect to the LS and LL.
(9) The optical information medium has a data recording area and a test reproduction area, and the short mark and the long mark are previously formed in the test reproduction area. The optical information medium according to 8).
(10) When the difference in light quantity caused by the presence or absence of a short mark having a length LS or less is Ils and the difference in light quantity caused by the presence or absence of a long mark having a length LL or less is Ill, the minimum reproduction power that makes it possible to detect Ils. The above-mentioned (7) to (7), wherein the obtained Ils / Ill is used as an initial value, and the reproduction power is irradiated with reproduction power that makes the value of Ils / Ill 10% or more relative to the initial value. The optical information medium according to any one of 9).
(11) The light according to any one of (7) to (10) above, wherein the reproduction power is irradiated and reproduced in a range where Ils / Ill ≦ 0.95 is obtained with respect to the Ils and Ill. Information medium.
(12) When Ils is a light amount difference caused by the presence or absence of a short mark having a length of LS or less, Ils obtained at the lowest reproduction power at which Ils can be detected is defined as an initial value Ilsf, and a relative value of 1.05 < The reproducing method for an optical information medium according to any one of the above (7) to (11), wherein the reproducing power for obtaining a range of Ilsf / Itop ≦ 5 is the optimum power of the reproducing light. Here, Itop represents the unrecorded state signal intensity.

  According to the present invention, when performing super-resolution reproduction on an optical information medium, it is possible to easily set an optimum reproduction power that can reduce thermal damage to a mask layer and a functional layer that are responsible for super-resolution reproduction.

  An optical information medium to which the present invention is applied has a data recording area and a test reproduction area. This optical information medium may be a read-only type or a recordable type (write-once type or rewritable type). In the case of a read-only medium, marks (usually concave or convex phase pits) forming an information pattern are formed in advance in the data recording area. On the other hand, in the case of a recordable medium, the data recording area is an area in which marks (recording marks) constituting an information pattern are written. The test reproduction area is an area in which marks used for test reproduction are formed in advance. The mark provided in this area is not limited to the read-only type or the recordable type, and may be either a phase pit or a recording mark.

The optical information medium used when carrying out the reproducing method of the present invention is a medium capable of reproducing at a high resolution exceeding the diffraction limit, that is, a super-resolution reproducing medium. Assuming that the wavelength of the reproduction light is λ and the numerical aperture of the objective lens of the reproduction optical system is NA, a mark row in which the space between the mark and the adjacent mark has the same length has a spatial frequency of 2 NA / λ or less. It is readable. That is, the readable mark length is λ / 4NA or more. Accordingly, the medium on which super-resolution reproduction is performed is that when the length of the shortest mark constituting the information pattern is Lm,
Lm <λ / 4NA
It is an optical information medium that is reproduced under the condition that

In the optical information medium of the present invention, a short mark having a length LS or less and a long mark having a length LL or less are formed in advance in the test reproduction area.
λ / NA ≧ LS ≧ λ / 4NA
LL> LS
It is.
That is, the short mark has a length substantially equal to the spot diameter and can be read out under normal conditions. The long mark has a longer length than the short mark. The lengths of the short and long marks may be determined regardless of the mark length in the data recording area. Here, the longer the long mark, the smaller the deterioration of MTF (Modulation Transfer Function) due to the influence of disturbances and aberrations of the optical system. As a result, it becomes easy to obtain the optimum reproduction power stably.

  Next, a method for obtaining the optimum reproduction power using the optical information medium of the present invention will be described. In the following description, a medium having a mask layer in which an optical aperture is formed in a heat mode or a photon mode will be described as an example of the super-resolution reproduction medium.

  When the mask layer used for super-resolution reproduction is irradiated with a laser beam with a predetermined intensity or higher, the optical characteristics of the irradiated area of the mask layer change, which increases the reflectance or transmittance. An optical aperture is formed.

When a super-resolution film is further provided on the medium on which the short and long marks are formed, an optical aperture is formed in the short mark, and the amplitude Ils of the short mark increases.
Next, the amplitude Ill of the long mark will be described. In a super-resolution reproduction medium having a mask layer, the reflectance or transmittance of the mask layer is not zero even in the state where the optical aperture is not formed. Therefore, the reproduction output of the long mark can be obtained even when the reproduction light having a power that does not form an optical aperture is irradiated. Further, when the reproduction light power is increased, the amplitude Ill of the long mark decreases.

  In the present invention, the optimum reproduction power is determined by utilizing the behavior of reproduction output for each of the short mark and the long mark or independently. Further, it is preferable to use the reproduction output itself without going through the gain control circuit.

  In the present invention, the optimum reproduction power is such that if a sufficient reproduction output can be obtained with a short mark, the lower the reproduction power, the less damage to the mask layer and the longer the life of the reproduction light irradiation laser element.

  The procedure for obtaining the optimum reproduction power is not particularly limited, but the following method is preferably used. In this method, first, the optical head is moved to the test reproduction area, then the short mark and the long mark are reproduced, and then the reproduction of the short mark and the long mark is repeated while gradually increasing the reproduction power. The ratio of the short mark reproduction output to the long mark reproduction output is equal to or greater than a specific value, the ratio of the long mark reproduction output to the short mark reproduction output is equal to or less than a specific value, or the rate of change of this ratio is The optimum reproduction power is determined when the value falls below a specific value or from the ratio or intensity ratio of the reproduction output of the short mark. The specific values relating to the ratio and change rate at this time may be set in advance in accordance with the standard of the optical information medium to be reproduced, or experimentally.

A specific procedure of this method will be described.
First, an optical disc to be played is loaded into a playback device. After the apparatus side confirms that the optical head of the reproducing apparatus is at a position opposite to the test reproducing area, a test reproduction is performed with a relatively low initial power Pr1, and the value at reproduction power Pr1; Ils / Ill is obtained from the reproduction output. Ask. At the same time, Ils is obtained and set as Ilsf.

  Next, reproduction is performed in the same manner with a reproduction power pr2 that is slightly higher than Pr1, and similarly the value; Ils / Ill is obtained. This operation is repeated, and the reproduction power at which the value of Ils / Ill is greater than the initial value by 10% or more is set as the optimum power of the reproduction light. Alternatively, when Ils / Ill ≦ 0.95 or the difference in light quantity caused by the presence or absence of a short mark of length LS or less is Ils, Ils obtained with the lowest reproduction power at which Ils can be detected is set as the initial value Ilsf. The reproduction power that provides a relative value of 1.05 <Ilsf / Itop ≦ 5 is set as the optimum power of the reproduction light. Here, Itop represents the unrecorded state signal intensity. The optical disk is played back with this power.

Desirably, as a reproduction power that makes the optical aperture clearer,
Ils / Ill is more than 1.25 times the initial value,
That is, Ils / Ill ≧ 1.25 * Ils / Ill initial value.

Alternatively, if the laser power is too high, noise is easily detected or the influence of sub-refraction of the substrate is likely to occur. Therefore, reproduction power that satisfies the condition of Ils / Ill ≦ 0.8 is preferable.
Further, when only Ils can be perceived by the sensitivity of the detector, it is preferable to pay attention to Ils and to select a reproduction power that satisfies 1.05 <Ilsf / Itop ≦ 2.

  The optimum power can also be obtained from the rate of change. The rate of change rIls / Ill = (Ils2 / Ill2-Ils1 / Ill1) / (Ils2 / Ill2) can be obtained from Ils1 / Ill1 at the reproducing power Pr1 and Ils2 / Ill2 at the reproducing power Pr2.

This operation is repeated, and the rate of change in the nth reproduction is obtained by the following equation.
Rate of change r (n) Ils / Ill = (Ilsn / Illn-Ils (n-1) / Ill (n-1)) / (Ilsn / Illn)
If this value falls below the set value, then Prn at that time is set as the optimum power.

  Normally, the increase in reproduction power (Prn−Prn−1) is a constant value. In consideration of the time required for setting the optimum reproduction power and the setting accuracy, it is desirable to select this increment from the range of 0.1 to 2 mW.

  The present invention can be applied to a super-resolution reproduction medium having no mask layer as well as a super-resolution reproduction medium having a mask layer. In a conventional super-resolution reproduction medium using a mask layer, the intensity of light reflected or transmitted through the mask layer changes corresponding to the formation of an optical aperture in the mask layer. That is, when the reproduction power is increased, the reflectance or transmittance of the mask layer changes when the specific reproduction power is reached. In contrast, in a super-resolution reproduction medium having a functional layer, the reflectance or transmittance of the functional layer does not change even when the power of the reproduction light is increased. For example, in the super-resolution reproduction medium having the functional layer disclosed in Patent Document 6 described above, the reproduction output usually increases as the reproduction power increases, and the reproduction output increases at a power lower than the power at which the functional layer is destroyed. Becomes a peak.

  When the present invention is applied to a super-resolution reproduction medium having the functional layer, if the reproduction power that maximizes the reproduction output is set to the optimum reproduction power, thermal damage to the functional layer becomes extremely large. For this reason, the method of the present invention in which the reproduction power at which the change rate of the super-resolution is not more than a specific value is not the reproduction power at which the short mark reproduction output is maximized but the optimum reproduction power is particularly effective.

  The position where the test reproduction area is provided is not particularly limited. For example, when the present invention is applied to a disk-shaped medium, the test reproduction area may be provided on the inner periphery or the outer periphery of the medium. Further, the arrangement pattern of the short marks and the long marks in the test reproduction area is not particularly limited. In the present invention, at least a short mark and a long mark may be provided in the test reproduction area, but other marks may be provided.

A method for forming a mark in the test reproduction area is not particularly limited. For example, in a read-only medium and a recordable medium, phase pits can be integrally formed on a substrate to form marks when the substrate is manufactured. In addition, phase pits or pits having different reflectivities can be formed using patterning means such as screen printing. On the other hand, in a recordable medium, a test reproduction area can be formed by writing a short mark and a long mark after the medium is manufactured.
In the present invention, it is not necessary that a long mark exists in the data recording area. That is, all the marks that hold the recording information may be short marks.

  The present invention is characterized in that the short mark and the long mark are tested and reproduced, and the optimum power of the reproduction light is set based on the reproduction output of both, so that the short mark and the long mark can be easily reproduced alternately. It is preferable that the mark and the long mark are provided together in the test reproduction area. However, in the present invention, since it is only necessary to obtain a short mark reproduction output and a long mark reproduction output, the test reproduction area is not provided independently, but the short mark and the long mark provided in advance in the data recording area are used. It is good also as a structure. As a short mark and a long mark provided in advance in the data recording area, a mark itself for holding recording information can be used. However, when there is no long mark in the mark for holding the recording information, it is necessary to provide a test reproduction long mark in the data recording area.

  The super-resolution reproduction medium to which the present invention is applicable is not limited to a medium using a mask layer and a medium using the functional layer. That is, the present invention is based on the mechanism of super-resolution reproduction as long as the short mark reproduction output is greatly affected by reproduction power and the long mark reproduction output is hardly affected by reproduction power. It can be applied.

[Example 1]
A functional layer was provided on a substrate having pits. As the substrate, a disk-shaped polycarbonate having a diameter of 120 mm and a thickness of 0.6 mm in which phase pits were simultaneously formed by injection molding was used. The pit was provided within a radius of 23.5 to 24.0 mm from the center of the substrate, and this was used as a test reproduction area. This pit is based on the 1-7 modulation method, the length of the pit corresponding to the shortest signal (used as the short mark) is 400 nm, and the length of the pit corresponding to the longest signal (used as the long mark). Is 1800 nm. Since an address signal indicating the position of the test reproduction area is recorded at a predetermined position of the sample, the optical head can be moved to the test reproduction area. The functional layer is an Ag layer having a thickness of 90 nm formed by sputtering.

  This sample was subjected to test reproduction using an optical disk evaluation apparatus DDU1000 manufactured by Pulstec Corporation (laser wavelength 650 nm, numerical aperture 0.65) at a linear velocity of 3.5 m / s. The results are shown in Table 1 (reproduction power intensity, Ils / Ill, and C / N relationship of fine marks).

As can be seen from Table 1, Ils / Ill increases as the reproduction power is increased. In particular, when the reproduction was performed at 1.7 mW, in which Ils / Ill increased by 10% or more from the initial value, the super-resolution CN increased to 38 dB.
Here, super-resolution C / N represents C / N when a signal having a mark length of 200 nm is reproduced through the functional layer.
In the medium having the configuration of the present embodiment, fine marks can be reproduced satisfactorily by selecting reproduction power at which Ils / Ill increases by 10% or more.

[Example 2]
A material represented by the following chemical formula was formed on a substrate having pits by spin coating to provide a functional layer. Further, a silver reflective film was formed on the functional layer by sputtering, and a UV protective layer was further laminated.

In Chemical Formula, M = VO, 4 pieces of R is _{C 6 H 5 - (CF 3} ) 2 is C-O-.

  As the substrate, a disk-shaped polycarbonate having a diameter of 120 mm and a thickness of 0.6 mm in which phase pits were simultaneously formed by injection molding was used. The pit was provided within a radius of 23.5 to 24.0 mm from the center of the substrate, and this was used as a test reproduction area. This pit is based on the 1-7 modulation method, the length of the pit corresponding to the shortest signal (used as the short mark) is 400 nm, and the length of the pit corresponding to the longest signal (used as the long mark). Is 1800 nm. Since an address signal indicating the position of the test reproduction area is recorded at a predetermined position of the sample, the optical head can be moved to the test reproduction area.

  This sample was subjected to test reproduction using an optical disk evaluation apparatus DDU1000 manufactured by Pulstec Corporation (laser wavelength 650 nm, numerical aperture 0.65) at a linear velocity of 3.5 m / s. The results are shown in Table 2 (relation power intensity, Ils / Ill, and C / N relationship of fine marks).

As can be seen from Table 2, Ils / Ill increases as the reproduction power is increased. In particular, when the value of Ils / Ill exceeds 0.80, the value of the super-resolution CN is lowered, and further 0.94 is 40 dB or less.
Here, super-resolution C / N represents C / N when a signal having a mark length of 200 nm is reproduced through the functional layer.
In the medium having the configuration of the present embodiment, it is possible to select a reproducing power with little damage to the functional layer by setting Ils / Ill to 90% or less. With this power, fine marks can be reproduced satisfactorily.

Example 3
In Example 1, everything was the same except that the functional layer was changed to a 15 nm thick Si layer. The results of the test reproduction are shown in Table 3 (reproduction power intensity, Ils, and relationship between fine mark C / N).

  In the medium of this configuration, fine marks can be reproduced satisfactorily by selecting a reproduction power that satisfies the relationship of 1.05 <Ilsf / Itop ≦ 5 with respect to the initial value of Ils / Itop. .

Example 4
In Example 1, when paying attention to the rate of change, as shown in Table 4 (relationship between reproduction power intensity and rate of change, and C / N of fine marks), the rate of change increases as the reproduction power increases. . Here, the rate of change was derived from the following equation.
The rate of change rIls / Ill = (Ils2 / Ill2-Ils1 / Ill1) / (Ils2 / Ill2) can be obtained from Ils1 / Ill1 at the reproducing power Pr1 and Ils2 / Ill2 at the reproducing power Pr2.
This operation is repeated, and the rate of change in the nth reproduction is obtained by the following equation.
Rate of change r (n) Ils / Ill = (Ilsn / Illn-Ils (n-1) / Ill (n-1)) / (Ilsn / Illn)

  As shown in Table 4, the change rate of the super-resolution phenomenon decreases as the reproduction power increases. The change rate when the reproduction power is 3.7 mW is 0.014%. Therefore, in the optical disc having a functional layer composed of an Ag layer having a thickness of 100 nm used in the present embodiment, when the optimum reproduction power is obtained based on the super resolution and the rate of change thereof, the lower limit corresponding to the required CNR is exceeded. It can be seen that it is sufficient to set the lowest reproduction power indicating the super-resolution and the change rate of the super-resolution, for example, smaller than 0.1 to the optimum reproduction power.

As described above, according to the present invention, when performing super-resolution reproduction on an optical information medium, it is possible to easily set an optimum reproduction power that can reduce thermal damage to the mask layer and functional layer responsible for super-resolution reproduction.

Claims (12)

  When the wavelength of the reproduction light is λ and the numerical aperture of the objective lens of the reproduction optical system is NA, a short mark having a length LS or less and a long mark having a length LL or less (however, LL> LS) are represented by an optical information medium. The reproduction power of the short mark and the reproduction output of the long mark are obtained by changing the reproduction power, and the optimum power of the reproduction light is set based on these outputs. A method for reproducing an optical information medium.   2. The method of reproducing an optical information medium according to claim 1, wherein the relations λ / NA ≧ LS ≧ λ / 4NA and LL> LS are satisfied with respect to the LS and LL.   3. The optical information according to claim 1, wherein the optical information medium has a data recording area and a test reproduction area, and the short mark and the long mark are previously formed in the test reproduction area. Media playback method.   Ils is obtained with the lowest reproduction power that enables detection of Ils, where Ils is the light amount difference caused by the presence or absence of a short mark of length LS or less and Ill is the light amount difference produced by the presence or absence of a long mark of length LL or less. The reproduction power at which / Ill is an initial value and the value of Ils / Ill is 10% or more relative to the initial value is set as the optimum power of the reproduction light. A method for reproducing an optical information medium according to claim 1.   5. The optical information medium according to claim 1, wherein the reproduction power in a range in which Ils / Ill ≦ 0.95 is obtained for the Ils and Ill is the optimum power of the reproduction light. How to play.   When the light amount difference caused by the presence or absence of a short mark of length LS or less is Ils, the initial value Ilsf is Ils obtained with the lowest reproduction power that can detect Ils, and the relative value is 1.05 <Ilsf / Itop. 6. The method of reproducing an optical information medium according to claim 1, wherein the reproduction power that can obtain a range of ≦ 5 is the optimum power of the reproduction light. Here, Itop represents unrecorded state signal intensity. When the wavelength of the reproduction light is λ, the numerical aperture of the objective lens of the reproduction optical system is NA, and the maximum length of the shortest mark among the marks constituting the information pattern is Lm,
An optical information medium that is reproduced under the condition that Lm <λ / 4NA is satisfied,
An optical information medium, wherein a short mark having a length LS or less and a long mark having a length LL or less (where LL> LS) are formed in advance.   8. The optical information medium according to claim 7, wherein the relation of λ / NA ≧ LS ≧ λ / 4NA and LL> LS is satisfied with respect to the LS and LL.   The optical information medium according to claim 7 or 8, wherein the optical information medium has a data recording area and a test reproduction area, and the short mark and the long mark are formed in advance in the test reproduction area. Information medium.   Ils is obtained with the lowest reproduction power that enables detection of Ils, where Ils is the light amount difference caused by the presence or absence of a short mark of length LS or less and Ill is the light amount difference produced by the presence or absence of a long mark of length LL or less. 10. The reproduction is performed by irradiating with reproduction power that makes / Ill an initial value and the value of Ils / Ill is 10% or more relative to the initial value. An optical information medium according to Item.   11. The optical information medium according to claim 7, wherein the reproduction information is irradiated and reproduced with a reproduction power in a range in which Ils / Ill ≦ 0.95 is obtained with respect to the Ils and Ill. When the light amount difference caused by the presence or absence of a short mark of length LS or less is Ils, the initial value Ilsf is Ils obtained with the lowest reproduction power that can detect Ils, and the relative value is 1.05 <Ilsf / Itop. 12. The method for reproducing an optical information medium according to any one of claims 7 to 11, wherein the reproduction power for obtaining a range of ≦ 5 is the optimum power of the reproduction light. Here, Itop represents the unrecorded state signal intensity.