JPH0677338B2 - Light disk - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to an optical disc for recording / reproducing by light irradiation.

(Prior Art and its Problems) As a method of forming recording pits on a predetermined track of an optical disc, a method of previously providing a concave or convex groove on a substrate is used.

FIG. 1a is a diagram showing a track position detecting method. Incident light passes through the substrate 2 by the condenser lens 1 to form a spot on the recording medium 3. When the center of the spot coincides with the center of the track 7, the distribution of the reflectance from the spot becomes symmetrical as shown by the curve 4 shown by the solid line in FIG. 1b. On the other hand, if the spot center deviates from the track center, the diffraction due to the groove becomes non-uniform, so that the reflected light distribution is biased as shown by a broken line 5. Therefore, if the reflected light is received by the two-divided photodetector 6 as shown in FIG. 1C and the difference between the left and right detection outputs is taken, the deviation of the spot from the track can be known. The relationship between the difference between the track center and the spot center and the difference output is as shown in FIG.

The inclination of the differential output before and after the track center gives the detection sensitivity of the track error signal. This detection sensitivity depends on the depth of the groove. The depth of the groove gives a phase difference to the reflected light. Assuming that the groove depth is d, the substrate refractive index is n, and the wavelength is λ, the track top 7 and the track gap 8 are formed, that is, the convex portion and the concave portion (groove portion). The phase difference between the reflected light and is: = 2π · 2dn / λ (In the figure, for convenience, the convex portion is the track groove portion between the tracks, but the reverse is also true.) The track detection sensitivity with respect to is approximately a sine wave function as shown in FIG. The inversion of the sign indicates that the gradient of the difference output is inverted.

Since the track detection sensitivity becomes maximum when the phase difference is 90 ° from FIG. 2, the groove depth of this value is used in the conventional optical disc.

This is true for a medium without uniform recording pits, but in reality, the phase difference is 90 ° due to the formation of pits.
It will be off.

For example, in the medium in which the recording layer 3 made of a low melting point medium (Bi, Te, phthalocyanine, etc.) is formed on the substrate 2 as shown in FIG. 3, the difference in the phase change amount of the reflected light between the pit position 9 and the outside of the pit 10 △ indicates reflection at the changing surface from the high refractive index material to the low refractive index material at the pit position and reflection at the changing surface from the low refractive index material to the high refractive index material outside the pit.
° get closer. Therefore, if the groove depth is set to 90 °, + △ = 270 at the pit formation part.
And the track detection sensitivity is reversed, making stable tracking servo operation difficult.

Even in a recording medium which exhibits a phase change upon light irradiation, there is a phase difference Δ because the complex refractive index of the recording layer changes.

Actually, the pits are partially formed on the track, and the track detection sensitivity is an average value when the beam moves on the track. It has been confirmed by the inventor's experiment that the value may decrease to 50% or less compared to before the formation of pits.

(Object of the Invention) It is an object of the present invention to provide an optical recording disk capable of stable tracking operation without deterioration of sensitivity even after formation of recording pits.

(Structure of the Invention) In the optical recording disk of the present invention, a recording layer in which complex pits are changed by irradiation of energy rays such as light to form recording pits is provided on a substrate having concave or convex tracks. In the optical disc, the difference Δ of the phase change amount of the reflectance between the area where the recording pit is formed and the area where the recording pit is not formed is −90 ° <△
It is characterized by being processed so that it becomes <90 °.

(Detailed description of configuration) The decrease in track detection sensitivity due to the formation of the recording pit is due to the difference Δ of the phase change amount of the reflected light before and after the formation of the recording pit is 180.
° It has already been pointed out that it occurs because it is near.

As shown in FIG. 2, even if the phase difference is 90 ° which is the optimum value before pit formation, if the difference in phase change amount of reflected light before and after pit formation | Δ | It can be seen that no inversion occurs. The same can be said whether the groove track is convex or concave.

A method of setting | Δ | to 90 ° or less can be realized by providing an underlayer 11 having a dielectric constant higher than that of the substrate 2 to an appropriate thickness, as shown in FIG.

In addition, the phase difference of the groove is shifted from the optimum value, and sin
By selecting a structure in which and sin (+ Δ) have the same value, it is possible to realize a recording medium with little change in track detection sensitivity due to pit formation.

For example, if = 45 ° and △ = 90 °, sin and sin (＋
△) has the same value. Actually, the absolute value of the reflectance also changes in the pit part, so the track detection sensitivity does not always match before and after pit formation, but the amount of change is 90 °.
It can be significantly reduced compared to.

By adjusting not only the phase difference but also the track width,
It is possible to reduce changes in track detection sensitivity due to pit formation.

The track detection sensitivity becomes maximum when the track width W becomes half the track interval P W = P / 2, but if the track width is shifted from W = P / 2, the change in track detection sensitivity due to pit formation can be reduced. You can However, this width is different for each recording medium, and is different between recording on the convex portion and recording on the concave portion, so it is difficult to show a general tendency.
Generally, W <P / 2.

(Example 1) In the structure shown in FIG. 4, vanadyl phthalocyanine (VoPc) [n = 2.9, k = -0.8] was used as the recording layer 3, and SnO ₂ was used as the underlayer 11.
[N = 2.2], PMMA [n = 1.5] is used for the substrate 2, and if the recording layer thickness is 30 nm and the underlayer thickness is 30 nm, the difference Δ in the phase change amount of the reflected light before and after the pit formation is about 90 °. Becomes Therefore, if the phase difference of the groove is set to about 50 °, the change in track detection sensitivity is small.

(Embodiment 2) As shown in FIG. 5, the reflection layer 12 is formed under the underlayer 11 in a front-face incident structure.
And the recording layer has Te [n = 4, k = −
2], PMMA [n = 1.5] for the underlayer 11 and Al [n = for the reflective layer
2, k = -7], the recording layer thickness is 10 nm, and the underlayer thickness is 150 nm.
And The pit is formed by removing the recording layer 3, the reflectance in the pit increases, and the difference Δ in the phase change amount becomes about 80 °. Therefore, a suitable phase difference of the groove is 50 to 60 °.

(Effect of the Invention) As described above, according to the present invention, it is possible to realize an optical disc in which the track detection sensitivity is hardly changed by forming pits in the recording layer.

In each of the above examples, an example of a recording layer in which recording pits are formed by forming holes is shown. However, the complex reflectance changes from a transparent state to an opaque state (black in the case of tellurium oxide) due to a phase change of tellurium oxide. A material that changes, or a material such as a shape memory alloy whose surface state changes concavely or convexly and as a result the complex reflectance of the surface changes may be used for the recording layer.

[Brief description of drawings]

1A to 1D are views showing the principle of track error detection, FIG. 2 is a view showing changes in track detection sensitivity with respect to a phase difference of a groove, and FIGS. 3 to 5 are views showing configuration examples of recording layers. Is. In the figure, 1 ... condenser lens, 2 ... substrate, 3 ... recording layer, 4, 5
...... Reflected light distribution, 6 …… 2-division photodetector, 9 …… Pit position, 10 …… Outside pit recording medium surface, 11 …… Underlayer, 12 …… Reflective layer.

Claims (1)

[Claims] 1. An optical disc having a recording layer, on which a recording pit having a complex reflectance on the surface thereof is changed by a phase change or hole formation due to irradiation of energy rays such as light, formed on a substrate having concave or convex tracks. In, the difference Δ between the phase change of the reflected light at the recording pit formation position of the optical disk and the phase change of the reflected light at the portion where the recording pit is not formed Δ
However, the optical disc is characterized in that it is processed so that −90 ° <Δ <90 °.