KR19990081513A - Reproduction-only optical recording medium - Google Patents

Abstract

A plurality of lands formed in a spiral structure on at least one surface of a substrate which is transparent to laser light of an optical pickup having a wavelength of?, A plurality of lands formed at the surface height of the substrate, a plurality of lands formed at a predetermined depth with respect to the lands, There is disclosed a read-only optical recording medium including a plurality of grooves arranged alternately and a track having a plurality of pits formed in the lands and / or grooves.

In the disclosed read-only optical recording medium, when the refractive index of the substrate is n and λ _e = λ / n and the focus size variable ξ = λ / (the numerical aperture of the objective lens of the optical pickup)

And the height difference between the lands and grooves _e 0.15λ or more, characterized in that the distance of the track pitch (TP) between the center line between the width (PW) of the pit, adjacent the land and the groove satisfy the following condition equation .

[Conditional expression]

Description

Reproduction-only optical recording medium

The present invention relates to a read-only optical recording medium capable of optically reproducing information, and more particularly to a read-only optical recording medium in which the structure of tracks and pits is improved so as to reduce crosstalk between adjacent tracks .

In general, a read-only optical recording medium such as a compact disc (CD) or a digital video disc (DVD) is converted into a change of the distance between the pit and the pit according to a predetermined data coding scheme, have. Here, the pits are arranged in a circumferential spiral shape on the recording surface to form a plurality of tracks.

The above-mentioned tracks are spaced apart from each other by a predetermined pitch, that is, at a track pitch. In order to record a larger amount of information in the same area, it is preferable to narrow the track pitch as much as possible. However, when the track pitch is narrower than the diameter of the light spot formed on the recording surface by the objective lens of the optical pickup as the reproducing apparatus, optical interference due to the adjacent tracks occurs and crosstalk, that is, Deterioration) occurs. Therefore, there is a limit in reducing the track pitch.

For example, when the wavelength of the light irradiated from the light source for the optical pickup is λ And the numerical aperture of the objective lens for the optical pickup is NA, the diameter? Of the light spot formed on the optical disk by the optical pickup is given by Equation (1).

Here, in order for the pits formed in adjacent tracks to be divided without crosstalk, the distance between the two tracks, that is, the track pitch, should be at least 1/2 of the diameter? Of the light spot. For example, in the optical pickup of DVD, since the wavelength? Of the light source is 650 nm and the numerical aperture NA of the objective lens is 0.6, the diameter? Of the light spot becomes 1.3 占 퐉 based on the expression (1). Therefore, the theoretical track pitch should be 0.65 탆 or more, which is half of the light spot diameter (actually, the track pitch in DVD is 0.74 탆).

In order to overcome the limit of the track pitch as described above and to increase the recording density within the limited recording area, an intersection land and a groove are formed between the track and the track so that a difference in depth occurs between adjacent tracks, A write-once optical recording medium has been proposed.

1 is a schematic cross-sectional view showing a conventional read-only optical recording medium. As shown in the figure, the optical recording medium 1 has a substrate 2 on which a track having a spiral structure is formed and transmits incident light, a reflective film 6 formed on the substrate 2, and a reflective film 6 And a protective layer 7 formed on the protective layer 7. The track is provided with a plurality of lands 3 having a height of the surface 1a of the substrate 2 and a plurality of grooves 4 provided adjacent to the lands 3 and drawn into a predetermined depth, ) And / or the groove (4) are formed as information signals.

Here, the land 3 and the groove 4 have a height difference of? _E / 8 and the pit 5 is formed at a depth of? _E / 4 with respect to the land 3 and the groove 4, respectively. Here, when the wavelength of the optical pickup is? And the refractive index of the substrate 2 itself is n,? _E is defined as? / N.

Although not only the depth of the grooves 4 and the pits 5 but also the width of the pits 5 and the width of the lands 3 and the grooves 4 are variables influencing the crosstalk, Since a conventional read-only optical recording medium 1 does not consider the widths of the pits 5, the lands 3 and the grooves 4, the cross talk can be extremely large at the depth of the grooves 4 There is a problem that a good reproduction signal can not be obtained.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in order to solve the above-mentioned problems, and it is an object of the present invention to provide an optical recording medium having a groove width of a new standard, a track pitch, And an optical disc having a predetermined depth.

1 is a schematic perspective view showing a part of a conventional read-only optical recording medium.

2 is a schematic perspective view showing a part of a read-only optical recording medium according to the first embodiment of the present invention;

FIG. 3 is a schematic view showing that a light spot is formed on the optical recording medium of FIG. 2; FIG.

4 is a schematic perspective view showing a part of a read-only optical recording medium according to a second embodiment of the present invention;

5 is a schematic view for explaining the principle of diffraction of a read-only optical recording medium according to the embodiments of the present invention.

Figs. 6 and 7 are schematic views for explaining a change in signal level according to a pit position when a light spot follows a groove; Fig.

8 is a graph showing signal amplitude, noise, and crosstalk according to the groove depth when the track pitch is 0.9λ, the pit width is 0.4λ, and the pit depth is 0.25λ _e .

9 is a track pitch when the 0.9λ, 0.4λ pit width, pit depth 0.20λ _{e, e} 0.25λ, 0.30λ _e graphic diagram showing the signal amplitude of the respective groove depths.

Each of Figures 10 to 21 is a track pitch, a graph showing the signal amplitude, noise and cross-talk in accordance with the groove depth for the change in track width and pit depth 0.25λ _e.

22 is a schematic partial cross-sectional view of a read-only optical recording medium according to the third embodiment of the present invention.

23 to 25 are graphs showing the signal amplitude and noise according to the groove depth, for each groove ratio of the optical recording medium of FIG. 22;

26 is a schematic partial cross-sectional view of a read-only optical recording medium according to the fourth embodiment of the present invention.

Each of Figs. 27 and 28 shows, with respect to the optical recording medium of Fig. 26, a pit having a pit width of 0.4? And a pit ratio of 0.6 when the track pitch is 0.85 lambda and the groove depth is 0.16 lambda _e , (V ₂ ) according to the pit depth of the pit having the pit depth.

29 and 30, respectively, when the grooves and the pits have a trapezoidal or triangular shape as shown in Figs. 22 and 26, when the track pitch is 0.9λ, the groove ratio is 0.64, and the groove depth is 0.17λ _e , and a signal level (V ₂ ) according to a pit depth of a pit having a pit width of 0.5? and a pit ratio of 0.6.

Description of the Related Art

10 ... optical recording medium 11 ... substrate

12 ... Land 13 ... Groove

14 ... feet 15 ... reflective film

17 ... protective layer

According to an aspect of the present invention, there is provided an optical pickup apparatus including: a plurality of lands formed in a spiral structure on at least one surface of a substrate transparent to laser light of an optical pickup having a wavelength of? And a track having a plurality of pits formed in the lands and / or the grooves, the tracks being alternately arranged with the lands,

N as the refractive index of the substrate, λ _e = λ / n referred to, and a variable focal spot size ξ = λ / d when (numerical aperture of the objective lens of the optical pick-up), the height difference between the lands and grooves 0.15λ _e And a track pitch (TP), which is a distance between the pit width (PW) and a center line between the land adjacent to the groove and the groove, satisfies the following expression.

[Conditional expression]

Hereinafter, preferred embodiments of a read-only optical recording medium according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a schematic perspective view showing a part of a read-only optical recording medium according to an embodiment of the present invention, and FIG. 3 is a schematic view showing that a light spot is formed on the optical recording medium of FIG.

As shown in the figure, the read-only optical recording medium 10 is transparent to the laser light of an optical pickup (not shown) having a wavelength of lambda, and has a substrate 11 on which a light spot focused by the objective lens 21 is formed A reflection film 15 formed on the substrate 11 to reflect the incident light and a protection layer 17 for protecting the reflection film 15. [ On at least one surface of the substrate 11, a track having a spiral structure is formed to form an information recording surface.

The track includes a plurality of lands 12 formed at a height of the surface of the substrate 11 and a plurality of grooves 13 formed at a predetermined depth with respect to the lands 12 and alternately arranged with the lands 12, And a plurality of pits 14 which are formed at predetermined depths in the lands 12 and the grooves 13 and are downwardly convex.

4 is a schematic perspective view showing a part of a read-only optical recording medium according to another embodiment of the present invention.

In the structure of the read-only optical recording medium 10 according to the present embodiment, the remaining components except the shape of the pits are substantially the same as those of the optical recording medium shown in FIG. 2, and thus a detailed description thereof will be omitted.

The pit 14 'is protruded from the land 12 and the groove 13 by a predetermined height. Here, the projecting height of the pit 14 'corresponds substantially to the depth of the pit 14 disclosed in an embodiment. That is, when the other conditions are the same, if the height of the protruding pit 14 'is equal to the depth of the led pit 14, I have. Therefore, the result of the protruded pit 14 'can apply the result of the playback signal, noise, and crosstalk to the pit 14 that has been brought in, and thus a detailed description thereof will be omitted.

In the read-only optical recording medium 10 having the configuration as shown in Figs. 2 and 4, the present invention is characterized in that the track pitch TP (TP) defined as the distance between the radial center of one track and the radial center of a neighboring track The track pitch TP, the pit width PW, and the pit depth dp are newly defined so that the above-mentioned crosstalk can be minimized by designing the laser beam with a laser wavelength? There are features.

In order to design such an optical recording medium having a structure, a signal must be calculated with respect to the same optical configuration as that in the information reproduction state of the optical recording medium by the actual optical pickup. In the optical system thus constructed, the principle of signal detection will be described with reference to Fig.

5, substantially the incident light 31 and the light 35 (36, 37) reflected from the hyperplane 33 of the optical recording medium are located in the same direction. That is, the incident light 31 is focused on the optical recording medium 33 by the objective lens 21, and then reflected by the optical recording medium 33 (shown in the figure as being transmitted). The reflected light is diffracted by the zeroth-order light 35 and the ± first-order light 36 and 37 due to the influence of the pit. After passing through the objective lens 21 again, the reflected light is received by the photodetector 23.

Since the incident beam 31 of the objective lens 21 has a Gaussian distribution around the Z axis for the characteristic of the laser beam, when the beam is converged by the ideal objective lens 21, And becomes a spherical wave centered on the focus O. Therefore, since the characteristics of the incident laser beam and the characteristics of the incident light can be well known, the amplitude and phase at an arbitrary point P on the incident wavefront SI can be calculated, and the light energy at the point P can be calculated from the hyperplane surface 33 ), The amplitude and phase of the light wave at point T can be obtained by superimposing the waves transmitted at point T on all points on the incident wave surface SI. Therefore, the amplitude and phase at an arbitrary point T on the hyperplane 33 can be calculated.

As described above, the phase characteristics of the light wave at the calculated point T are changed by the land 12, the groove 13 and the pit 14, ΔΦ Is given by Equation (2) when the land height of the point T is d.

Here, n is a refractive index of the substrate 11, and? _E is a wavelength of a substantial laser beam in the substrate 11, and is defined as? _E =? / N. The reason that the right side of the equation (2) is multiplied by 2 is because the effect of the optical path difference due to the depth difference in the reflection type optical recording medium 10 is doubled. As described above, the phase-shifted laser beam proceeds in the form of diverging toward the objective lens 21 again. Here, the outgoing wavefront SO of the laser beam forms a spherical surface centering on the focus O in the same manner as the incident wavefront SI, and the characteristic of the light wave at an arbitrary point Q on the outgoing wavefront SO is a wave The amplitude and phase of the light wave at point Q can be calculated. It is also possible to calculate the amount of light reaching the photodetector 23 by summing only the amount of light of the region converged by the objective lens 21 out of the total amount of light on the outgoing wavefront SO. Such a calculation method is based on the diffraction theory of light, precisely the vector diffraction theory of electromagnetic waves. Particularly, diffraction theory related to optical recording medium is called "Principles of Optical Disc Systems" [G Bouwhuis et al. , Adam Hilger Ltd, Bristiol (1985), pp. 88-124, and " Distribution of light at and near the focus of high numerical-aperture objectives " Mansuripur, J. Opt. Soc. Am, Vol. 3, No. 12 / December 1986, pp2086-2093].

The present invention has determined the parameters of the optical recording medium using the above-described method.

Figs. 6 and 7 are schematic views showing a change in signal level according to the pit position when the light spot S follows the one groove 13. Fig.

6, S1 denotes a light spot formed in a portion where no pit is formed in both the land 12 and the groove 13, S2 denotes a pit 14a formed in the groove 13, A light spot in the case where a pit is not formed in the groove 13 and a pit 14b is formed in the land 12 in the vicinity of the groove 13 is shown as a light spot .

When the light spots follow the groove and are sequentially placed in the states of the light spots S1, S2, S1, and S3 while following the groove, the signal level of the reproduction signal, i.e., the electric signal, detected and output by the photodetector 23, As shown in FIG. That is, in the case of the state of S1, when the detected signal level is V ₀ , in the state of S2, the signal level differs by V ₁ by the signal amplitude A [= (V ₀ - V ₁ )]. On the other hand, in the case of S3, the signal level should theoretically be V ₀ but has a signal level of V ₂ lower than V ₀ due to noise. Here, as the smaller the signal amplitude of the noise is less good, the quality of the reproduced signal traffic pitch (TP), the groove depth (d _g) having the smallest cross-talk by calculating the value of the crosstalk defined by the equation (3) , The pit width (TW) and the pit depth (d _p ).

In order to minimize the track pitch TP in consideration of the crosstalk and noise characteristics as described above, each of the pit width and the track pitch satisfies the following expression (4), and the height difference between the land and the groove And is preferably 0.15 lambda _e or more.

Here,? Is defined as? / (Numerical aperture of the objective lens of the optical pickup) as a focus magnitude variable, n is the refractive index of the substrate, and? _E =? / N.

Fig. 8 is a graph showing the signal amplitude, noise, and crosstalk according to the groove depth when the light spot passes through the groove when the track pitch is 0.9 lambda, the pit width is 0.4 lambda, and the pit depth is 0.25 lambda _e .

In the case where there is a pit in the groove, as shown in the figure, it can be seen that the crosstalk is approximately -47 dB when the groove depth is 0.155? _E , which is sufficiently smaller than -28 dB which is the crosstalk of the conventional DVD. On the other hand, the groove depth 0.155λ _e in the optical recording medium, known as cross-talk in the case where the feet of the chair near the land the groove depth look at -0.155λ _e, at which point, the cross-talk at that point substantially -47dB .

6, the symmetry of the reproduction signal, noise, and crosstalk in the (+) direction and the (-) direction with respect to the groove depth 0 is as follows: the lands on the left and right sides of the light spot are symmetrical, This is due to the fact that the depth of the quadrangular pit is approximately 0.25 lambda _e .

9 is to examine the depth of the pit is approximately 0.25λ _e necessity under the conditions for maintaining the symmetry as described above, when the track pitch is 0.9λ, 0.4λ pit width, pit depth _e 0.20λ, 0.25λ _e , And 0.30? _E, respectively.

If the groove depth ± 0.2λ _e Looking at the reproduction signal level in a range, the pit depth is large, the pit depth than the signal amplitude in the case of 0.2λ _e, the signal amplitude of a land-groove pits feet of 0.3λ _e is opposed to the land The signal amplitude of the pit is greater than the signal amplitude of the groove pit. Therefore, asymmetry occurs in which the amplitudes of the reproduction signals in the groove and land are changed. The depth of the pit in order to prevent such asymmetry can be seen that by default, be 0.25λ _e.

Hereinafter, with reference to FIGS. 10 to 21, the signal amplitude, noise, and crosstalk when different parameters are changed while the pit depth is set to 0.25? _E will be examined. Here, the numerical aperture of the objective lens was set to 0.6.

10 to 12 are graphs showing the signal amplitude, noise, and crosstalk according to the groove depth when the pit width is set to 0.3λ, 0.4λ, and 0.5λ for a track pitch of 0.8λ, respectively.

13 to 15 are graphs showing the signal amplitude, noise, and crosstalk according to the groove depth when the pit width is set to 0.3λ, 0.4λ, and 0.5λ for the track pitch of 0.85λ, respectively.

16 to 18 are graphs showing the signal amplitude, noise, and crosstalk according to the groove depth when the pit width is set to 0.3λ, 0.4λ, and 0.5λ for the track pitch of 0.9λ, respectively.

19 to 21 are graphs showing the signal amplitude, noise, and crosstalk according to the groove depth when the pit width is set to 0.3?, 0.4? And 0.5?, Respectively, for a track pitch of 1.0?.

Referring to FIGS. 10 to 21, the pit width and the groove depth at which the crosstalk is minimized at each track pitch are summarized in Table 1.

Track pitch [?] Feet width [λ] Groove depth [lambda _e ] The amplitude of the reproduction signal 0.80 0.3 0.175 0.28 0.4 0.16 0.30 0.5 0.15 0.25 0.85 0.3 0.17 0.34 0.4 0.16 0.36 0.5 0.15 0.32 0.90 0.3 0.17 0.39 0.4 0.16 0.42 0.5 0.16 0.35 1.00 0.3 0.17 0.43 0.4 0.155 0.48 0.5 0.15 0.45

Referring to Table 1, it can be seen that the amplitude of the reproduced signal decreases as the track pitch decreases with respect to the same pit width. This is because the diffraction angle of the diffracted light caused by the land and groove becomes large as the track pitch is reduced and the amount of light captured by the objective lens is reduced. When the track pitch is reduced below the track pitch, the reproduced signal becomes too small Signal regeneration becomes difficult.

On the other hand, if the track pitch, the pit width 0.8λ to 0.4λ, so that the increase in the groove depth, the amplitude of the reproduction signal when the 0.30 0.16λ _e, the pit width and the groove depth is optimum optical recording medium standard Can be presented. From above 10 to 21 and Table 1, wherein a track pitch and, pit width 0.3λ to about 0.5λ, the groove depth _e 0.15λ to 0.5λ _e in the range of crosstalk is seen that the present point is the cheapest The track pitch of the optical recording medium according to the present invention preferably satisfies the range of 0.8? To 1.0? With respect to the numerical aperture 0.6 as described above.

The range of the track pitch can be changed from 0.48? To 0.60? From Equation (4) by using the focus size variable?.

22 is a schematic partial cross-sectional view of a read-only optical recording medium according to the third embodiment of the present invention.

The cross-sectional shape of the groove 13 of the read-only optical recording medium according to the present embodiment may have a trapezoidal shape or a triangular shape in addition to the rectangular shape as described above. In this case, the optical effect due to the depths of the grooves 13 and the pits 14 is weaker than in the case of having a rectangular shape. Therefore, it is necessary to reset the groove depth, the pit depth, and the pit width for the same track pitch. 22, the shape of the groove is determined by the groove ratio (= P / Q) and the groove depth Gd, which are defined by the ratio of the width Q of the bottom surface to the width P of the top surface.

Each of Figs. 23 to 25 shows the relationship between the signal amplitude according to the groove depth and the groove width, for the optical recording medium of Fig. 22, with a track pitch of 0.9 lambda, a pit width of 0.4 lambda, a pit depth of 0.25 lambda _e and groove ratios of 0.80, 0.38 and 0.0, Fig. Here, assuming that the cross-sectional shape of the pit is a rectangular shape, the signal amplitude and noise are calculated. Here, when the groove ratio is 0.0, the cross-sectional shape means a triangular shape, and it can be seen that the groove changes from 0.16? _E to 0.24? _E as the distance from the trapezoidal shape to the triangular shape increases.

26 is a schematic partial cross-sectional view of a read-only optical recording medium according to the fourth embodiment of the present invention. Here, when the pits 14 are formed in the lands 12 and the grooves 13, the shape of the pits must be precisely determined in order to minimize the interference due to the phase difference between the pits 14. 26 shows a model in the case where the cross-sectional shape of a pit is a trapezoid, in which the height of the pit is h, the width of the pit in the reflection plane is Ps, and the width in the incident plane is Pl, The determined pit ratio is defined as Ps / Pl. Here, the pit parameter with the minimum noise is as follows.

Fig. 27 is a graph showing the relationship between a pit width of 0.4? And a pit width of 0.4? When a track pitch is 0.85? And a groove depth is 0.16? _E when a light spot is formed in a groove and a noise pit is present on a land around the optical recording medium of Fig. And a signal level (V ₂ ) according to a pit depth of a pit having a pit width of 0.5? And a pit ratio of 0.6.

In Figure 27, to the noise can be zero that is, V ₂ = V ₀ to be a, and the pit width (PW) when the approximately 0.4λ, the pit depth is approximately 0.32λ _e formed in the groove, the feet When the width PW is approximately 0.5, the depth of the pits formed in the grooves is approximately 0.30 lambda _e .

28 is a graph showing the relationship between a pit width of 0.4? And a pitch of 0.4? When the track pitch is 0.85? And the groove depth is 0.16? _E in the case where a light spot is formed on a land and a noise pit is formed on a groove around the optical spot, And a signal level (V ₂ ) according to a pit depth of a pit having a pit width of 0.5? And a pit ratio of 0.6.

In this case, in order for the noise to become 0, that is, V ₂ = V ₀ , when the pit width PW is approximately 0.4 ?, the depth of the pit formed in the groove is approximately 0.33? _E , The depth of the pits formed is approximately 0.30 lambda _e .

FIG. 29 is a graph showing the relationship between the groove pitch and the groove pitch when the grooves and the pits have a trapezoidal or triangular shape as shown in FIGS. 22 and 26, light spots are formed in the grooves, 0.64, a groove depth of 0.17? _E , and a signal level (V ₂ ) according to a pit depth of a pit having a pit width of 0.4? And a pit ratio of 0.6 and a pit having a pit width of 0.5? And a pit ratio of 0.6.

In this case, in order for the noise due to the noise pits of the left and right lands in the groove to be zero, the depth of the pit formed in the groove is approximately 0.3? _E when the pit width PW is approximately 0.4? The depth of the pit formed in the groove is approximately 0.36 lambda e.

Fig. 30 is a graph showing the relationship between the track pitch and the groove pitch when the grooves and the pits have a trapezoidal or triangular shape as shown in Figs. 22 and 26, light spots are formed on the lands, 0.64, a groove depth of 0.17? _E , and a signal level (V ₂ ) according to a pit depth of a pit having a pit width of 0.4? And a pit ratio of 0.6 and a pit having a pit width of 0.5? And a pit ratio of 0.6.

In this case, in order for the noise due to the noise pits of the left and right grooves to become 0 in the land, the depth of the pit formed in the groove is approximately 0.315? _E when the pit width PW is approximately 0.4? The depth of the pit formed in the groove is approximately 0.3 lambda e.

Therefore, in the case where the structure of the optical recording medium is as shown in Figs. 22 and 26, the depth and height of the pit must be independently determined so that crosstalk is minimized in each groove and land. It can also be seen that the cross-sectional shape of the pit should be made deeper than 0.25? _E , which is the depth when it is rectangular.

As described above, in the read-only optical recording medium according to the present invention, the height difference between the groove and the land, the width of the pit, and the depth range of the pit determine the interval between adjacent tracks, that is, the track pitch is 0.48? there is an effect that the crosstalk can be reduced while keeping it short by?. That is, when the track pitch is set to 0.8? (= 0.48?) Instead of the standard digital video disk standard of 1.14 ?, the recording capacity is increased to 1.4 times (= 1.14 / 0.8) , The information storage capacity can be greatly increased.

Claims (12)

A spiral structure is formed on at least one surface of a substrate transparent to laser light of an optical pickup having a wavelength of? A plurality of lands formed at a height of the surface of the substrate, a plurality of grooves alternately arranged with the lands formed at a predetermined depth with respect to the lands, and a track having a plurality of pits formed in the lands and / or grooves In the read-only optical recording medium, When the refractive index of the substrate is n and? _E =? / N and the focus size variable? =? / (The numerical aperture of the objective lens of the optical pickup) The height difference between the land and the groove is 0.15? _E or more, Wherein a track pitch (TP), which is a distance between the pit width (PW) and a center line between the land adjacent to the groove and the groove, satisfies the following conditional expression. [Conditional expression] The optical recording medium according to claim 1, wherein the groove has a groove ratio (= P / Q) defined by a ratio of a width Q of a bottom surface to a width P of an upper surface of the groove in a trapezoidal shape of 0.8 or less, a read-only optical recording medium, it characterized in that the depth of the groove is approximately 0.16λ _e. The read-only optical recording medium according to claim 1 or 2, wherein the pit is formed at a predetermined depth with respect to the reference plane of each of the land and the groove. The read-only optical recording medium according to claim 3, wherein the depth of the pit is 0.25? _E or more. The optical recording medium according to claim 3, wherein the pits formed in the land and the pits formed in the groove are formed at different depths from each other, Wherein noises due to the pits existing in the land are minimized when the groove is reproduced and noise caused by the pits existing in the groove is minimized when the land is reproduced. The method as claimed in claim 5, wherein, when the pit width (PW) is approximately 0.4 lambda, The depth of the pit formed in the groove is approximately 0.3 lambda _e , and the depth of the pit formed in the land is approximately 0.315 lambda _e . The method according to claim 5, wherein when the pit width (PW) is approximately 0.5, The depth of the pit formed in the groove is approximately 0.36 lambda _e , and the depth of the pit formed in the land is approximately 0.3 lambda _e . The read-only optical recording medium according to claim 1 or 2, wherein the pit is formed so as to protrude a predetermined height from a reference plane of each of the land and the groove. The read-only optical recording medium according to claim 8, wherein the height of the pit is 0.25 lambda _e or more. The optical recording medium according to claim 8, wherein the pits protruding from the land and the pits protruding from the groove are formed at mutually different heights, Wherein noises due to the pits existing in the land are minimized when the groove is reproduced and noise caused by the pits existing in the groove is minimized when the land is reproduced. 11. The method according to claim 10, wherein when the pit width (PW) is approximately 0.4 lambda, The height of the pit formed in the groove is approximately 0.3 lambda _e , and the height of the pit formed in the land is approximately 0.315 lambda _e . 11. The method according to claim 10, wherein when the pit width (PW) is approximately 0.5 lambda, The height of the pit formed in the groove is approximately 0.36 lambda _e , and the height of the pit formed in the land is approximately 0.3 lambda _e .