JPH0954994A - Magneto-optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the crosstalks at the time of signal reproduction with a land-and-groove magneto-optical recording medium for recording information on both of lands and grooves. SOLUTION: The ratio of a land width and groove width is deviated from 1:1. The magnitude of the deviation is set within the range meeting the phase difference tan<-1> (εk /θk ) which occurs on the light with a Kerr effect, where the Kerr ellipticity in the Kerr effect generated by photoirradiation is defined as εk and a Kerr rotating agle as θk . More particularly, the magnitude of the deviation described above is so set as to satisfy [ tan<-1> (εk /θk )}/2π].3.10<2> <=|R-50|<=[ tan<-1> (εk /θk )}/2π.6.10<2> , where [land width/(groove width + land width)].100 is defined as R. The magnitude is also so set as to satisfy |R-50|<=10 more preferably in terms of the level of reproduced signals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording / reproducing technique, and in particular, an optical disc for recording signals in both concave and convex portions of a track guide groove formed in advance with concave and convex portions. The present invention relates to a magnetic recording medium.

[0002]

2. Description of the Related Art In information recording / reproducing using an optical information recording medium, research and development for higher density recording / reproducing have been actively conducted. Conventionally, a signal is recorded only in one of a concave portion (land) and a convex portion (groove) of a track guide groove which is previously formed with unevenness, and only one of the concave portion and the convex portion is used as an information track. Then, in order to perform the high-density recording / reproduction, a land / groove recording medium is used in which information is recorded between conventional information tracks (that is, the other of the concave portion and the convex portion of the track guide groove formed in advance with concave and convex portions). Has attempted to further increase the capacity. In this case, suppression of signal leakage (crosstalk) from an adjacent information track becomes a major issue.

In Japanese Laid-Open Patent Publication No. 5-282705, the depth of a track guide groove (hereinafter simply referred to as “groove”) in an optical disk of a reflectance changing type is set to, for example, λ / 5, where λ is the wavelength of the reproduction light. It has been proposed to reduce the crosstalk by the interference effect by setting the distance to the vicinity.

In addition, SOM, '94 TECHNICA
L DIGEST, pp41-42, "CROSS-T"
ALK ANALYSIS OF LAND / GROO
VEMAGNETO-OPTICAL RECORD
NG "discloses that the method of reducing crosstalk due to the interference effect is applied to a magneto-optical disk.

[0005]

SUMMARY OF THE INVENTION SOM, '94.
TECHNICAL DIGEST, pp41-42,
"CROSS-TALK ANALYSIS OF L
AND / GROOVEMAGENETO-OPTICAL
In the case of a magneto-optical disk, "RECORDING"
It has been pointed out that due to the phase difference caused by the Kerr effect, the dependence of crosstalk on groove depth is different between when a land is traced and when a groove is traced.

In view of the above problems, it is an object of the present invention to reduce crosstalk during signal reproduction on a land / groove magneto-optical recording medium in which information is recorded on both the land and the groove. In particular, it is an object of the present invention to provide a land / groove magneto-optical recording medium with a small crosstalk during signal reproduction.

[0007]

According to the present invention, in order to achieve the above object, there is provided a track guide groove formed in advance with concave and convex portions, and both of the concave and convex portions are tracks for signal recording. A magneto-optical recording medium in which information is recorded along the track by light irradiation and the recorded information on the track is reproduced by light irradiation, and the ratio of the track width of the concave portion to the track width of the convex portion is 1 There is provided a magneto-optical recording medium, which is deviated from 1: 1.

In one aspect of the present invention, the amount of deviation of the ratio of the track width of the concave portion to the track width of the convex portion from 1: 1 is the Kerr ellipticity in the Kerr effect caused by the light irradiation. Letting ε _k and the Kerr rotation angle be θ _k , the phase difference tan generated in the light due to the Kerr effect is described.
It is set within the range according to ^-1 (ε _k / θ _k ).

In one aspect of the present invention, the deviation of the ratio of the track width of the concave portion to the track width of the convex portion from 1: 1 is expressed by [concave track width / (convex track width + concave track width)]. ] · 100 where R is 0 <| R-50 | ≦ [{tan ⁻¹ (ε _k / θ _k )} / 2
π] · 6 · 10 ² is satisfied.

In one aspect of the present invention, the deviation of the ratio of the track width of the concave portion to the track width of the convex portion from 1: 1 is [{tan ⁻¹ (ε _k / θ _k )} / 2π ] ・ 3 ・ 10 ² ≦
| R-50 | is satisfied.

In one aspect of the present invention, the deviation of the ratio of the track width of the concave portion to the track width of the convex portion from 1: 1 satisfies | R-50 | ≦ 10.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

First, the difference in groove depth dependency of crosstalk between land tracing and groove tracing in the land / groove magneto-optical recording medium will be described.

In general, when linearly polarized light is incident on a magneto-optical recording medium, the reflected light becomes an elliptically polarized light in which the direction of the linearly polarized light is slightly inclined with respect to the original incident linearly polarized light, and at the same time the linearly polarized light is slightly deviated. . The minute angle is the Kerr rotation angle, and the arctangent of the ratio of the lengths of the major axis and the minor axis of the elliptically polarized light is the Kerr ellipticity. The Kerr rotation angle is θ _k , and the Kerr ellipticity is ε _k .

Originally, the Kerr effect has left and right circularly polarized light as eigenstates, and when the left and right circularly polarized light is expressed as e ₊ and e ₋ , the following matrix formula is approximately used except for the amplitude reflectance. It can be represented by (Equation 1).

[0016]

[Equation 1] Here, "in" means an input state to the magneto-optical recording medium, and "out" means an output state from the magneto-optical recording medium.

The Kerr effect matrix is converted into a matrix having linearly polarized light as an eigenstate. The matrix T for converting linearly polarized light into circularly polarized light by Jones's Matrix can be expressed as follows (Equation 2).

[0018]

[Equation 2] Therefore, the matrix of the Kerr effect is sandwiched between this matrix T and its inverse matrix, and the linearly polarized light is converted into a matrix having an eigenstate. As a result, the following matrix (Equation 3) is obtained.

[0019]

(Equation 3) The following linearly polarized light P (Equation 4) is applied to this.

[0020]

(Equation 4) Then, due to the Kerr effect, the linearly polarized light becomes as shown below (as in Expression 5).

[0021]

(Equation 5) Here, φ = tan ⁻¹ (ε _k / θ _k ).

From the above, the polarized light generated by the Kerr effect
The component (Kerr component) is (θ_k ² + Ε _k ² )^1/2 exp (i
φ). Therefore, focusing on the Kerr component, the Kerr effect
It can be seen that a phase shift of φ occurs with.

That is, at the time of land trace,
Looking at the groove carefully, the reflected light from the groove is
Phase difference 2θ_g Will have -φ, groove trace
Sometimes, looking at the land focusing on the car component,
The reflected light from is phase difference -2θ _g Will have −φ.
That is, the adjacent track of the trace track that is reproducing information is
The groove is θ_g Φ equivalent to the reference value
It looks low and the land is θ_g Equivalent to φ than equivalent reference value
It looks deep. Where θ_g Is the groove depth of the medium
It is a phase conversion value, and the groove depth is h in terms of air and the wavelength of light is
If λ, θ _g = (2π / λ) h.

Thus, in the medium where φ = 0 is not satisfied, the dependence of crosstalk on groove depth between land trace and groove trace is shown in FIG. With φ = 0 as a reference, the groove trace shifts to a depth corresponding to α / 2, and the land trace shifts to α / 2.
Shift to a fairly shallow side. Here, α is the air-equivalent groove depth of φ, and α = (λ / 2π) φ. Therefore, when the magneto-optical recording medium is manufactured with the air-equivalent groove depth being h0, h0 is not the optimum groove depth and the crosstalk is large. Depending on the polarity of φ, with respect to φ = 0, the groove trace shifts to a depth corresponding to α / 2 corresponding to the groove depth, and the land trace shifts to a depth corresponding to α / 2 corresponding to the deep depth. It shifts (that is, the groove depth dependence of the crosstalk between the groove trace and the land trace is opposite to that shown in FIG. 6).

Therefore, in the present invention, by shifting the ratio of the land width to the groove width from 1: 1, the difference in crosstalk groove depth dependency between land tracing and groove tracing caused by the above phase difference. To reduce. That is,
The dependency is shifted in a direction in which the difference in the dependency of the crosstalk between the land trace and the groove trace on the groove depth is canceled.

In FIG. 3, wavelength 785 nm, objective lens numerical aperture (NA) = 0.55, land-land pitch = 1.
6 μm, groove depth λ / 10 to λ / 5 (near λ / 6)
Within the range, when the ratio of the land width to the groove width (Duty ratio) is deviated from 1: 1, the ratio of the land width to the groove width and the groove depth that minimizes the crosstalk (minimum crosstalk groove depth) ) Shows the relationship with. Here, the duty ratio (duty ratio) means land width / (land width + groove width), that is, the above R. The uneven shape of the medium is as shown in FIG. When the duty ratio is 50%, land width = groove width = 0.7 μm.

FIG. 5 shows Dut at the time of land trace.
The groove depth dependence of crosstalk at y ratios of 40%, 50%, and 60% is shown. From FIGS. 3 and 5, in the vicinity of λ / 6, (1) when the width of the trace track becomes narrow (for example, D
When the duty ratio is 40%), the minimum crosstalk groove depth moves to the deeper side (however, the crosstalk at that time becomes slightly larger). (2) When the trace track becomes wide (for example, Dut
When the y ratio is 60%), the crosstalk minimum groove depth is hardly changed, but the crosstalk is improved. I understand that.

FIG. 5 shows the case where the trace track is a land, but as can be seen from FIG. 3, the above (1) and (2) also apply when the trace track is a groove. I can say.

As a result, the groove depth dependency of crosstalk shifts to the shallow side based on the phase difference φ (φ in FIG. 6).
≠ 0 land trace), the duty ratio is appropriately controlled to shift the groove depth dependency of crosstalk to the deep side by approximately α, so that the minimum crosstalk groove depth during land trace and the cross trace during groove trace can be obtained. It is possible to make the talk minimum groove depth coincide or be close to each other. Crosstalk reduction is realized by adopting a groove depth in which the crosstalk is smaller than that when the duty ratio is 50% both in the land trace and the groove trace.

As described above, since the crosstalk is reduced by the above (1) during the land trace, the groove depth dependency of the crosstalk shifts to the deep side based on the phase difference φ during the groove trace. (Φ ≠ in FIG. 6
In contrast to the 0 groove trace), the crosstalk in the vicinity can be improved by the above (2), so that the crosstalk can be reduced even in the groove trace.

Next, the above three expressions in the present invention 0 <| R-50 | ≦ [{tan ⁻¹ (ε _k / θ _k )} / 2
π] · 6 · 10 ² [{tan ⁻¹ (ε _k / θ _k )} / 2π] · 3 · 10 ² ≦
| R-50 | | R-50 | ≦ 10 will be described.

For simplification, in FIG. 3, the side where the minimum crosstalk groove depth changes greatly (that is, the duty ratio is 40 to 50% in the land trace, and D is the groove trace).
Linear approximation is performed at a duty ratio of 50 to 60%. Then, the shift of the minimum crosstalk groove depth is approximately | R-50 | · 1.6 · 10 ⁻³ · λ. If the magnitude of this shift is made equal to the groove depth conversion value α = (λ / 2π) φ of the phase difference φ due to the Kerr effect, the minimum crosstalk groove depth and groove trace at the time of the land trace described above. The minimum groove depth of crosstalk can be matched. That is, α = (λ / 2π) φ = (λ / 2π) tan ⁻¹ (ε _k / θ _k ) = | R-50 | · 1.6 · 10 ⁻³ · λ Therefore, | R-50 | = [{Tan ^-1 (ε _k / θ _k )} / 2π]
By setting to 6 · 10 ² , it is possible to match the minimum crosstalk groove depth at the time of land tracing and the minimum crosstalk groove depth at the time of groove tracing.

However, as can be seen from FIG. 6, the cross toe
Crosstalk due to groove depth change near the minimum groove depth
Changes rapidly, so | R-50 | becomes [{tan
^-1(Ε_k/ Θ_k )} / 2π] ・ 6 ・ 10² Is consistent with
Land trace and groove
The effect of reducing crosstalk is sufficient for both traces.
There is fruit. Therefore, in the present invention, the range of | R-50 |
Then, for example, [{tan ^-1(Ε_k / Θ_k )} / 2π]
・ 6 ・ 10² Centered on, the upper limit is doubled, and the lower limit
Can be 0 (but not including 0). Preferred
As a range of | R-50 |, [{tan^-1(Ε_k 
/ Θ_k )} / 2π] ・ 6 ・ 10² Centered on
1.5 times that and the lower limit can be 0.5 times
You. In reality, | R-50 | is, for example, 0 <| R-
50 | ≦ [{tan^-1(Ε_k / Θ_k )} / 2π] ・ 6 ・
10² And preferably [{tan^-1(Ε_k / Θ
_k )} / 2π] ・ 3 ・ 10² ≦ | R-50 | ≦ [{ta
n^-1(Ε_k / Θ_k )} / 2π] ・ 6 ・ 10² It is.

Considering the level of the trace signal,
In the signal reproduction of the track on the side where the width becomes narrower when the duty ratio R is deviated from 50%, the level of the signal being traced relatively decreases due to the narrow track width.
That is, when | R-50 |> 10, for example, as shown in FIG. 7, the level reduction of the traced signal becomes large. In FIG. 7, when the solid line indicates the groove depth λ / 7, the broken line indicates the groove depth λ.
The relative signal level with respect to the trace signal level when R = 50% at / 6 is shown.
A value of 10 indicates that the signal level difference between the land and the groove exceeds 3 to 4 dB. Therefore, considering the level of the trace signal, | Duty ratio −50 |
It is preferable that ≦ 10.

[0035]

Embodiments are described below.

FIG. 2 shows a wavelength of 785 nm and an objective lens NA.
= 0.55, objective lens focal length 3.0 mm, collimator focal length 7.71 mm, beam shaping ratio 2 optical head, land-land pitch 1.6 μm, Duty ratio 5
The groove depth dependence of crosstalk when reproducing a magneto-optical disk with 0% and a phase difference φ = 5.35 ° is shown. Land width =
Groove width = about 0.7 μm.

Phase difference 5.35 ° (0.093 radian)
, The above three equations 0 <| R-50 | ≦ [{tan ⁻¹ (ε _k / θ _k )} / 2
π] · 6 · 10 ² {[tan ⁻¹ (ε _k / θ _k )} / 2π] · 3 · 10 ² ≦
| R-50 | | R-50 | ≦ 10 is 0 <| R-50 | ≦ 8.8 4.4 ≦ | R-50 | | R-50 | ≦ 10, respectively.

Further, as shown in FIG. 2, the groove depth dependency of crosstalk at the time of groove tracing is shifted to the shallow side. Therefore, according to the above (1), the groove depth of crosstalk at the time of groove tracing. R-50> 0 in order to shift the dependency to the deep side. Therefore, 50 <R ≦ 5
It is 8.8.

Therefore, in this embodiment, the duty ratio R = 55% is set so as to satisfy the above conditions. The dependency of the crosstalk groove depth of the magneto-optical disk in this case is as shown in FIG.

In the case of FIG. 2, the optimum groove depth at which the crosstalk is most reduced at both the land trace and the groove trace is about 130 nm, and the crosstalk value at this time is about -23 dB. On the other hand, in the case of FIG. 1, the optimum groove depth at which the crosstalk is most reduced at both the land trace and the groove trace is about 1
The crosstalk value at 30 nm is about -30 dB. That is, in the present embodiment, the crosstalk is improved from the state of FIG. 2 to the state of FIG. 1, the crosstalk value is halved (reduction of 6 dB or more), and a good crosstalk reduction effect is obtained by controlling the duty ratio. I understand that it was done.

[0041]

As described above, according to the present invention, the ratio between the track width of the land and the track width of the groove is deviated from 1: 1 so that the cross caused by the phase difference between the land trace and the groove trace. The difference in dependence on the depth of the talk groove is reduced, and the crosstalk from the adjacent track during signal reproduction is sufficiently reduced.

[Brief description of drawings]

FIG. 1 is a graph showing groove depth dependence of crosstalk.

FIG. 2 is a graph showing groove depth dependence of crosstalk.

FIG. 3 is a graph showing the duty ratio dependency of the minimum crosstalk groove depth.

FIG. 4 is a diagram showing the shapes of lands and grooves of a magneto-optical disk.

FIG. 5 is a graph showing groove depth dependence of crosstalk.

FIG. 6 is a graph showing groove depth dependence of crosstalk.

FIG. 7 is a graph showing a duty ratio dependency of a reproduction signal level.

Claims (5)

[Claims] 1. A track guide groove formed in advance with concavities and convexities, and both of the concave and convex portions are used as tracks for signal recording, and information is recorded along the track by light irradiation, and the track is recorded. The magneto-optical recording medium for reproducing the recorded information as set forth in claim 1, wherein the ratio of the track width of the concave portion to the track width of the convex portion is deviated from 1: 1. 2. The amount of deviation of the ratio of the track width of the concave portion to the track width of the convex portion from 1: 1 is Kerr ellipticity ε _k in the Kerr effect caused by the light irradiation and Kerr rotation. 2. The light according to claim 1, wherein the angle is θ _k , and the angle is set within a range according to a phase difference tan ⁻¹ (ε _k / θ _k ) generated in the light due to the Kerr effect. Magnetic recording medium. 3. The deviation of the ratio of the track width of the concave portion to the track width of the convex portion from 1: 1 is defined as R of [concave track width / (convex track width + concave track width)] · 100. , 0 <| R-50 | ≦ [{tan ⁻¹ (ε _k / θ _k )} / 2
The magneto-optical recording medium according to claim ^2, which satisfies [π] · 6 · 10 ² . 4. The deviation of the ratio of the track width of the concave portion to the track width of the convex portion from 1: 1 is [{tan ⁻¹ (ε _k / θ _k )} / 2π] · 3 · 10 ² ≤
The magneto-optical recording medium according to claim 3, which satisfies | R-50 |. 5. The deviation of the ratio of the track width of the concave portion to the track width of the convex portion from 1: 1 satisfies: | R-50 | ≦ 10. The magneto-optical recording medium described.