JP3024692B2 - Recording mark forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for determining the size and position of a recording mark when forming the recording mark in optical recording.

[0002]

2. Description of the Related Art FIG. 2 is a view showing an example of recording mark formation in conventional optical recording (see, for example, Japanese Patent Application Laid-Open No. Hei 3-178038). In the figure, reference numeral 1 denotes information at each repetition position of an information detection point (hereinafter, referred to as a clock position); 2, a recording mark recorded on an optical disk; 3, a reproduction signal obtained by reproducing the recording mark 2 with an optical head; Indicates a slice level for extracting information from the reproduction signal 3.

First, at the time of recording, a recording mark 2 is formed on an optical disc such that the end of the recording mark coincides with the information point by adjusting the recording current and controlling the amount of light emitted from the optical head. This is performed in substantially the same manner in the formation of pre-pits performed in factories and the like and the accumulation of information performed by users of optical disks. Further, recording marks are recorded on the optical disk in accordance with a change in reflectivity or a direction of magnetization.

At the time of reproduction, a beam spot from the optical head is applied to the recording mark 2 on the optical disk, and the reflected light is reproduced by a detector as a change in the amount of reproduced light or a change in the Kerr rotation angle. , The information is detected by discriminating the reproduction signal 3.

[0005]

As described above, since the recording mark 2 is formed so that the end of the recording mark coincides with the information point at each clock position, the end of the recording mark 2 is formed in an arc shape. You. For this reason, in the conventional recording method, when trying to reproduce a signal, the edge position and the information point of the reproduced waveform are shifted. In addition, this was shifted regardless of which of the 50% slice level and the zero-cross point of the second differentiation was taken as the edge position of the reproduced waveform. Therefore,
At the time of reproduction, phase fluctuation occurs due to the formation of the end of the recording mark in an arc shape, and there is a problem that high-density recording cannot be performed because this phase margin needs to be considered.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a recording mark forming method capable of forming a recording mark optimally so as to suppress phase fluctuation and improving recording density. It is in.

[0007]

In order to achieve the above object, the present invention provides a method for forming a recording mark for optical recording in which information is recorded by changing the length of the recording mark. When a recording mark having a length b and a trailing-edge curved portion having a length c is formed, when the reproducing beam spot radius is W and the constant is α, the average value of the leading edge position of each recording mark With respect to the repetition position of the information detection point
p (-α a ² / w ² ) and shifted forward in proportion to p (-α a ² / w ² ), and the average value of the trailing edge tip position of each recording mark is calculated as c exp (-α a ² / w ² ), and shifted backward or forward in proportion to ² / w ² ).

[0008]

According to the present invention, the information points of the reproduced waveform can be reproduced with an accurate phase, and no phase fluctuation occurs due to the shape of the recording mark. Therefore, it is not necessary to consider the phase margin, so that high-density recording can be performed.

[0009]

FIG. 1 is a diagram for explaining the principle of the method of the present invention. In the figure, 5 is a recording mark formed on an optical disk (not shown), 6 is a reproducing beam spot formed by condensing output light from an optical head on the optical disk, 7 is an equivalent reproducing beam spot, and 8 is an equivalent. Recording marks are shown respectively.

The principle of the method of the present invention will be described below. The light intensity P (Xx, Yy) of the reproducing beam spot 5 is shown in FIG.
(A) and the following equation (1) can be approximated by a Gaussian distribution. P (Xx, Yy) = A exp {-2 [(Xx) ² + (Yy) ² ] / (W / 2) ² } (1) where A is the peak value of the light intensity, and W is the reproduction. This is the diameter at which the light intensity of the beam becomes 1 / e ² . In addition, recording mark width 2
a, a recording mark with a curvature b / a at the leading edge and a curvature c / a at the trailing edge (here, the case of c / a = b / a is shown as an example), and a length d in the track direction that changes depending on information to be recorded. Shape can be approximated. By changing the length d, edge recording in which information is put on the recording mark edge can be realized. Further, since the amount of reflected light from the area other than the recording mark in information reproduction only gives a DC offset in information reproduction, the reflectance R (X, Y) on the optical disk is equivalently set in the recording mark area. 1 and 0 outside the region.

Under these conditions, the reproduced output V (x, y)
Is given by the following equation. Because the shape of the recording mark is elliptical (oval),
In (2), a reproduced waveform cannot be obtained unless integral calculation is performed over the X axis and the Y axis. Therefore, as shown in FIG. 1B, it is approximated that a rectangular equivalent recording mark 8 is recorded by the equivalent reproducing beam spot 7. Here, the influence of the semicircular end of the recording mark is taken as a change in the edge position of the reproduced waveform, and the end of the equivalent recording mark 8 is shortened. The approximation is made by enlarging the X-axis direction of the equivalent reproduction beam spot 7.
The width of the equivalent recording mark 8 is a delta function, and the effect of off-track is approximated by enlarging the equivalent reproduction beam spot 7 in the Y-axis direction. In the approximate calculation, the recording mark width 2a is equal to the diameter W of the reproduction beam spot 6.
, And the convergence value when the recording mark width 2a becomes infinite is not shifted.

When the above approximation is analytically calculated theoretically with respect to equation (2) and arranged, the following equation is obtained. V (x, y) = (π / 4) Aw ² ｛φ [4a / w] -1/2} exp (-8cy / w ² ) {φ [4 (x + x ₀ ) / w _x ]-φ [4 (xx ₀ -d) / w _x ]}… (3) where x ₀ = b [1-0.215exp (-2.44a ² ) / w2)], w _x = w exp {(0.40 b ² / w ² ) g}, c = exp (=-5.33a ² / w ² ) , G = exp (-2.24a ² / w ² ). Wy shown in FIG. 1 is represented by Wy = Wc- ^{1 / 2} .

FIG. 3 shows the result of calculating the reproduction output using the equation (3). As shown in FIG. 3, as the curvature of the leading edge and the trailing edge of the recording mark increases, the edge position of the reproduction output moves to the center of the recording mark, and the inclination of the edge becomes gentle. Thus, equation (3) expresses the characteristics of the elliptical recording mark, and FIG.
Can be approximated to (b) of FIG.

Next, an embodiment of the formation of a recording mark by the method of the present invention will be described with reference to FIG. 4, the same components as those in FIG. 2 showing the conventional example are denoted by the same reference numerals. That is, 1 is recording information, 3 is a reproduction signal when a recording mark is reproduced by an optical head, 4 is a slice level for extracting information from the reproduction signal, 5 is a recording mark recorded on an optical disk (not shown), Reference numeral 51 denotes a portion of the recording mark 5 proportional to the length of the information 1, 52 denotes a leading edge correction portion of the recording mark 5, and 53 denotes a trailing edge correction portion of the recording mark 5.

First, at the time of recording, the front end of the recording mark 5 is shifted from the information point to the front edge correction portion of the recording mark 5 by adjusting the recording current to control the light emission amount and the light emission time from the optical head. The recording mark 5 is formed such that the rear end of the recording mark 5 is shifted rearward from the information point by the trailing edge correction portion 53 of the recording mark 5 so as to be shifted forward by 52.

Here, as described above, the average value of the length of the leading edge correction portion 52 of the recording mark 5 is calculated with respect to the clock position.
x ₁ = b−x0 (= 0.215b exp (−2.44a ² / w ² )) is formed shifted forward. Further, since c = b in this example, the average value of the length of the trailing edge correction portion 53 of the recording mark 5 is calculated as x ₂ = c−x0 (= 0.215b exp (−2.44a ² / w ² )) Formed shifted backward.

That is, when the constant is α, the average value of the leading edge position 52 of each recording mark 5 is calculated in front of the clock position in proportion to b exp (−α a ² / w ² ). And the average value of the trailing edge tip position 53 of each recording mark 5 is calculated as c exp (-α a
² / w ² ) may be formed to shift backward in proportion to ² / w ² ).

The correction amount shown here is 0 in the leading edge correction portion.
At least 2 times x ₁ at the trailing edge correction part, at least 0 times 2 times x ₂
Valid up to. In particular, the leading edge correction part correction amount is 0.5 times
x ₁ or more to 1.5 times x _1, 0.5 at the trailing edge correction portion correcting amount
If multiple of x ₂ or more to 1.5 times the x ₂ can be improved greatly reproduction characteristics less than half the phase shift of the reproduced waveform. The variation of λ / NA that defines the beam spot is usually 5%.
Since it is allowed to the leading edge correction portion correcting amount up to x ₁ of 1.05 times 0.95 times x ₁ or more, 0 in the trailing edge correction portion correcting amount.
If until x ₂ of 1.05 times 95 times x ₂ or more can be almost completely suppressed the phase shift of the reproduced waveform.

Such recording mark formation can be applied not only to the information storage performed by the user of the optical disk, but also to the formation of prepits such as the manufacture of a master disk, the manufacture of a replica, and the manufacture of a ROM performed in a factory or the like. Further, the recording mark may be recorded on the optical disk in accordance with a change in reflectance or a direction of magnetization.

On the other hand, at the time of reproduction, the beam spot from the optical head is applied to the recording mark 5 on the optical disk, and the reflected light is reproduced at the detector as a change in the reproduction light amount or a change in the Kerr rotation angle, and the slice signal is reproduced. Level 4
, The information 1 is detected by discriminating the reproduction signal 3.

As described above, according to the present embodiment, the recording mark 5 is formed so that the edge of the recording mark is shifted from the information point so as to correct the elliptical end of the recording mark. Therefore, the edge of the reproduction signal and the information point coincide,
High-density recording becomes possible. Further, it goes without saying that the information point may be a zero-cross point of the second differentiation in addition to the slice level shown in FIG.

FIG. 5 shows the relationship between the edge curvature and the edge position shift using 2a / w (recording mark width / beam spot diameter) as a parameter. As can be seen from FIG. 5, increasing the edge curvature requires increasing the edge position shift amount. Also, when the recording mark width is increased, the tendency becomes remarkable. As shown by the expression of x0 in FIG. 3, although not shown, when the recording mark width further increases, the edge position shift amount needs to be reduced.

As described above, if the recording mark shape and the reproducing beam spot diameter are given, the correction amount from the clock position can be uniquely given to the bit length 2b + d, and stable high-density recording can be performed. Become like

The recording laser irradiation time for recording includes a time T1 (n) for forming a recording mark having a length of n clock bits, a leading edge time T2 for applying the correction, and a trailing edge time. It can be expressed as follows using T3. T = T1 (n) + T2 + T3 (4) In the equation (4), when the recording laser power is changed or the recording is equalized by applying a pulse, the effective time is calculated as follows. It represents.

In the above description, the case where the leading edge and the trailing edge of the recording mark have the same shape has been described. It is needless to say that different values may be set, for example, b and trailing edge b may be set to c).

Also, since an equalizer is inserted in the reproduction system to eliminate the fluctuation due to the waveform interference, the suppression correction of the influence due to the waveform interference is not considered. However, by using equation (3) and adding the influence from adjacent bits, it is possible to suppress the influence due to waveform interference in addition to the above-described correction. In the slice level detection shown in FIG. 4, the adjacent edge (the leading edge of the recording mark, the trailing edge of the mark itself and the trailing edge of the previous mark, and the trailing edge of the recording mark, the trailing edge of the mark itself, If the leading edge and the leading edge of the subsequent mark are located close to each other, they are shifted away from each other. If both sides are similarly close, do not move. On the other hand, when the detection is performed at the zero-cross point of the second differentiation, on the contrary, the adjacent edge (the leading edge of the recording mark, the trailing edge of the mark itself, the trailing edge of the previous mark, the recording mark If the trailing edge of the mark is the leading edge of the mark itself and the leading edge of the succeeding mark), the shift is made in the approaching direction. Again, do not move if both sides are similarly close. In this way, the waveform interference can also be corrected.

Although the recording mark formed by light modulation has been described here, the average position of the leading edge of the trailing edge of the recording mark is also forward (toward the leading edge position) for so-called chevron-shaped recording marks recorded by magnetic field modulation. Can be similarly explained. Further, the method of forming the recording marks has been described using an optical disk as an example, but the same effect can be obtained in other optical recording and narrow track magnetic recording.

[0028]

As described above, according to the present invention,
Since the recording mark is formed by shifting the recording mark end from the information point so as to suppress the influence of the elliptical end of the recording mark, the information point of the reproduction signal edge point and the clock position (repetition position of the information detection point) is formed. Matches. Accordingly, phase fluctuation due to the arc-shaped end of the recording mark during reproduction does not occur, and high-density recording can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of the method of the present invention.

FIG. 2 is an explanatory diagram of a conventional method.

FIG. 3 is a diagram showing a calculation result of a reproduction output.

FIG. 4 is an explanatory view of one embodiment of the method of the present invention.

FIG. 5 is a diagram illustrating a relationship between an edge curvature and an edge position shift.

[Explanation of symbols]

1 information, 3 reproduction signal, 4 slice level, 5 recording mark, 5 reproduction beam spot, 7 equivalent reproduction beam spot, 8 equivalent recording mark.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-48617 (JP, A) Yasuaki Tanaka, et al., “Analysis of Oval Record Mark Reproduction Characteristics in Optical Recording”, IEICE National Convention Lecture Papers, (1991, Spring), PAGE. 4.393 Yasuaki Tanaka, et al., “Reproduction characteristics analysis of mark long optical recording”, IEICE Technical Report, 91, 42 (MR91, 5- 7), PAGE. 17-23 Yasuki, Tanaka, and 2 others, "Redout Waveform Equalization in Pulse-Width-Modulated Optical Recording", Japan Journal of Japan. Regular Papers, Short Notes & Review Papers (1992), 31, 2B, PAGE. 590− 595 (58) Field surveyed (Int. Cl. ⁷ , DB name) G11B ^7/ 004-7/0045

Claims (1)

(57) [Claims] 1. A recording mark forming method for optical recording in which information is recorded by changing the length of a recording mark, wherein a track width is 2a, a length of a leading edge curved portion is b, and a length of a trailing edge curved portion is c. In the case of forming a recording mark of, when the reproducing beam spot radius is W and the constant is α, the average value of the leading edge position of each recording mark is calculated as b exp (- α a ² / w ² ), and is formed to be shifted forward in proportion to c exp (-α a ² / w ^{2) with} respect to the repetition position of the information detection point. ² ) A recording mark forming method characterized in that the recording mark is formed to be shifted rearward or forward in proportion to ( ² ).