JPH06290486A - Optical recording medium - Google Patents

Abstract

(57) [Summary] [Object] To provide an optical disk used for recording and reproducing at high density by making the spot light substantially small by utilizing the change of the optical characteristics of the auxiliary layer. [Structure] An optical disc is formed by laminating an information layer and an auxiliary layer made of a light transmittance changing material. The diameter of the irradiated spot light is x, the diameter of the spot light reduced by the auxiliary layer is y, and the ratio of the diameter of the spot light reduced by the auxiliary layer is α (α = y / x). Z is the final diameter of the spot light, p is the shortest pit length of the pit row read using the spot light, S is the moving speed of the relatively moving spot light and the pits, and When the required time (reaction rise time) for the desired change in optical characteristics of the auxiliary layer (light transmittance changing material) is ta, {x (1 + α) -2z} / 2S ≦ ta <x (1 + α) / Two
S. Alternatively, if y ≦ p, ta ≦ x (1-α) / 2S, and if y> p, x (1-α) / 2S <ta <x (1 + α) /
2S.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an optical disc, an optical card,
The present invention relates to an optical recording medium such as an optical tape in which information reproduction or recording / reproduction is performed optically by using spot light, and in particular, the spot light is practically utilized by utilizing a change in optical characteristics in the auxiliary layer. The present invention relates to an optical recording medium in which a suitable material is selected as an auxiliary layer when recording and reproducing at high density by reducing the value.

[0002]

2. Description of the Related Art As an optical recording medium, for example, a CD (Compact Disc) is generally used, but recently, attempts have been actively made to record information at a higher density. Japanese Patent Application No. 2-96926 discloses a technique that attempts such a high density. According to this, a non-linear optical layer (hereinafter, also referred to as an auxiliary layer) is provided on the light incident side of the record carrier. The action of this nonlinear optical layer reduces the beam spot diameter of incident light (sometimes referred to as spot light), and as a result, high density information recording and reproduction can be performed.

As the non-linear optical layer, a light transmittance changing material such as gallium arsenide whose light transmittance is increased by light irradiation and is substantially restored when light irradiation is stopped or other light irradiation is performed. And indium antimony are used.
The light transmittance changing material has a nonlinear light transmittance characteristic with respect to the incident light intensity, for example, as shown by a solid line GA in FIG. Such a light transmittance characteristic has a function of substantially reducing the spot diameter of the incident light beam. For example, when the incident light intensity and the light transmittance are proportional to each other as shown by the dotted line GB in the figure, the light spot diameter is approximately 3
It is reduced to about / 4. In the case of the solid line GA graph in the figure, the light spot diameter is further reduced to about 3/5.

According to the above-mentioned conventional technique, as shown in FIG. 5A, a pit row (or unevenness corresponding to a guide groove).
First, an auxiliary layer 102 made of a light transmittance changing material is formed on the main surface of the substrate 100 on which is formed. Then, the reflective layer 104 and the protective layer 106 are respectively formed on the auxiliary layer 102. When a light beam having a spot diameter SA as shown in FIG. 1B is incident on such an optical disc, the spot diameter SA (x described later) is changed by the action of the auxiliary layer (light transmittance changing material) 102. Substantially reduced to SB (y to be described later), which is incident on the pit.
Therefore, even if the track interval is narrowed due to the high density of information recording, the information can be read out satisfactorily.

[0005]

Conventionally, as a light transmittance changing material which is an auxiliary layer, a material having a good change reaction (a material having a large non-linear light transmittance change and a fast reaction rate) is used. ) Was required. However, in the case of constructing an optical recording medium using a light transmittance changing material, obtaining a material having a better change reaction than necessary causes a delay in its practical use, and its improvement has been demanded.

Therefore, according to the present invention, when an optical recording medium is constructed, the characteristics of an appropriate auxiliary layer (for example, a light transmittance changing material) are clarified so that it can be easily realized and effective optical recording. It provides a medium.

[0007]

In order to solve the above-mentioned problems, the present invention firstly provides an information layer having a pit row which is read and written by using relatively moving spot light, and an irradiated spot. An optical recording medium comprising an auxiliary layer whose optical characteristics change according to the intensity of light, wherein the auxiliary layer reduces the substantial light diameter of the spot light in the information layer, The auxiliary layer moves relatively with x being the light diameter of the irradiated spot light, α being the ratio of the light diameter of the spot light smaller by the auxiliary layer, and z being the final light diameter of the spot light at the information layer. The moving speed of the spot light and the pit is S, and the time required for the desired optical characteristics to change in the auxiliary layer by the irradiation of the spot light (reaction rising time) is
When ta, {x (1 + α) -2z} / 2S ≦ ta <x (1 + α) / 2
An optical recording medium is provided which is a material satisfying the condition of S 2, and

Secondly, it is composed of an information layer having a pit string which is read and written by using the relatively moving spot light, and an auxiliary layer whose optical characteristics change according to the intensity of the irradiated spot light. In the optical recording medium configured to reduce the substantial light diameter of the spot light on the information layer by the auxiliary layer, the auxiliary layer has an optical diameter of the irradiated spot light of x, and an auxiliary layer. The light diameter of the spot light that has become smaller by y, the ratio of the light diameter of the spot light that becomes smaller by the auxiliary layer is α (α = y / x), and the shortest pit length of the pit row read using the spot light is p. , S is the moving speed of the relatively moving spot light and pit, and ta is the time required for the desired optical characteristics to change in the auxiliary layer by irradiation of the spot light (reaction rising time), y ≦ p Then ta ≦ x ( -Α) / 2S y> p provides an optical recording medium characterized by being a material satisfying the condition of x (1-α) / 2S <ta <x (1 + α) / 2S. is there.

When the optical recording medium configured as described above is read / written (reproduced or recorded / reproduced) using spot light, the light transmittance changes according to the intensity of the spot light. At this time, various conditions (the light diameter x of the spot light, the ratio α of the light diameter of the spot light smaller by the auxiliary layer, the final light diameter z of the spot light in the information layer, the relatively moving spot light and the pit) According to the moving speed S of and the shortest pit length p) of the pit row read using the spot light,
Within the required and properly set reaction rise time ta,
The irradiation of the spot light causes a change in the optical characteristics of the auxiliary layer, and the diameter of the spot light is substantially reduced. That is,
In the first optical recording medium, the delay of the reaction rise time ta is allowed within an appropriate range, and the material forming the auxiliary layer (for example,
The condition of the light transmittance changing material) becomes lenient. In the second optical recording medium, the final spot diameter z becomes smaller than the diameter y reduced by the auxiliary layer due to the delay of the reaction rise time ta.

[0010]

An embodiment of an optical recording medium according to the present invention will be described in detail below with reference to the drawings. <Basic Structure> FIGS. 2A and 2B are a side view and a plan view of an optical recording medium (hereinafter referred to as an optical disc). As shown in FIG. 1, the optical disc 1 is a rotary disc-shaped optical recording medium including a substrate (information layer) 10 in which pit rows (or irregularities corresponding to guide grooves) are formed in an arc shape or a spiral shape. (Note that this basic structure is
It is the same as the configuration of FIG. 5 described above). Substrate (information layer) 1
An auxiliary layer 12 made of a light transmittance changing material is formed on the main surface 0. The auxiliary layer 12 is, for example, a light transmittance changing material whose light transmittance changes according to the intensity of the irradiated spot light. In other words, it is a material that has low light transmittance when light irradiation is not performed or weak light irradiation, increases light transmittance when strong light irradiation is performed, and returns light transmittance to almost the original value when light irradiation is stopped. Then, the reflective layer 14 and the protective layer 16 are formed on the auxiliary layer 12, respectively. The pit train is read and written using spot light that moves relatively.

The optical disc 1 configured as described above is reproduced or recorded / reproduced by utilizing spot light from a spot light irradiating means (not shown). That is, the light spot emitted from the spot light irradiating means is incident from the information layer 10 to the side of the auxiliary layer 12 which is the light transmittance changing material, and reproduction and recording / reproducing operations are performed. The reflected light (or transmitted light) of the light incident on the information layer 10 is read and reproduced. Also,
The recording layer 10 is fixedly (irreversibly) changed by the light spot to record information.

When the spot light is irradiated, the auxiliary layer 12, which is a light transmittance changing material, has the same optical characteristics of light intensity and light transmittance as in FIG. 4 described above, and is therefore used for reproduction / recording. The light spot diameter will be substantially reduced.
That is, the spot light X similar to that shown in FIG.
When the (light diameter x) is incident on the auxiliary layer 12 that is the light transmittance changing material, as shown in FIGS. 1A to 1F described later, the central portion with high intensity is compared with the peripheral portion with low intensity. And since the light transmittance is large, more light passes through,
In the peripheral portion having a low intensity, the light transmittance is smaller than that in the central portion having a high intensity, so that the light is less transmitted and transmitted, and the auxiliary layer 12 has a sharp light spot Y (light diameter y) having a small light spot diameter. Becomes As a result, high-density reading / writing (reproduction, recording / reproduction) is performed by the light spot Y having a substantially small diameter y (see FIG. 5 described above).
(See (B)), the spot light finally contributing to reading and writing is a portion z where the spot light X and the diameter y reduced by the light transmittance changing material of the auxiliary layer 12 overlap. This point will be described later in detail with reference to FIG.

<Auxiliary Layer as Light Transmittance Change Material> Next, the reaction rise time ta and the reaction fall time tb of the light transmittance change material constituting the auxiliary layer 12 which is the main part of the present invention will be described. FIGS. 1A to 1F are diagrams for explaining the transition of the read state in the information layer 10 depending on the magnitude of the reaction rise time ta of the light transmittance changing material. In the figure,
x to tb are as follows. x: the diameter of the irradiated spot light X, y: the diameter of the spot light Y in which the spot light is reduced by the auxiliary layer (diameter in a virtual range), α: the proportion of the spot light reduced by the auxiliary layer ( α = y / x, 0 <α <1), z: the diameter of the final spot light Z on the information layer, p: the shortest pit length of the pit train reproduced using the spot light, S: relative Moving speed of the spot light and the pits that move dynamically, ta: time required for reaction (reaction rise time) in which the optical characteristics of the auxiliary layer change due to irradiation of the spot light, tb: irradiation of the spot light disappears, and the auxiliary layer The time required for the reaction to return to the original value (reaction fall time) even if the optical characteristics of the are no longer changed.

FIG. 3A shows the state when the reaction rise time ta is zero. (B) to (E) in the figure have a reaction rise time (there is a delay in the reaction), and due to the relationship between the relatively moving spot and pit, the spot light X irradiated and the auxiliary layer 12 are smaller. It shows a state where the center position of the spot light Y is deviated. The reaction rise time ta increases in the order of (B), ..., (E). Further, in FIGS. 7A to 7C, the diameter y of the portion Y that is smaller due to the auxiliary layer 12 and the final spot light Z on the information layer 10 are shown.
Is substantially equal to the light diameter z. On the other hand, in FIG. 6D, the light diameter z of the final spot light (portion indicated by a dot in the figure) is smaller due to the delay of the reaction rise time ta. This is because the spot light that finally contributes to reading and writing is a portion where the spot light X and the diameter y reduced by the light transmittance changing material of the auxiliary layer 12 overlap. On the other hand, FIGS. 7E and 7F show a state in which the final spot light does not exist on the information layer 10 and the reading and writing is impossible. Based on the above premise, a specific configuration of the optical recording medium will be described in detail.

(Embodiment 1) In this embodiment, the reaction rise necessary from the surface of the final spot light diameter z of the information layer 10, that is, to obtain the final spot light Z light diameter z. The time ta is defined as the reaction ratio of the light transmittance changing material (the ratio α of the light diameter x of the irradiated spot light X and the light diameter y of the spot light reduced by the auxiliary layer) and the relative movement of the spot light. The light transmittance changing material required for the auxiliary layer 12 is limited by clarifying the relationship between the pit and the moving speed S.

First, as is apparent from FIG. 1E, ta <(x + y) / 2S must be satisfied in order to obtain the final spot light Z. If it is slower than this, the final spot light Z is not generated. However, as is clear from the relationship between (x + y) / 2 and z shown in FIGS. 1 (D) and (E),
In order to obtain the final light diameter z of the spot light Z, (x + y−2z) / 2S ≦ ta is sufficient, and a reaction rising faster than necessary is not necessary. Particularly, when y = z (in FIG. 1C), it is sufficient that (x−y) / 2S ≦ ta <(x + y) / 2S.

Further, since α = y / x, {x (1 + α) -2z} / 2S ≦ ta <x (1 + α) / 2
If the auxiliary layer 12 is made of a light transmittance changing material that satisfies the reaction rising time ta, which is S 2, to form an optical recording medium, the final spot light diameter is reduced to z. Therefore, the light diameter x of the spot light X to be irradiated, the proportion α of the spot light reduced by the auxiliary layer (light transmittance changing material) 12 and the moving speed of the relatively moving spot and pit so as to satisfy the above conditions. It suffices to set S appropriately, and it is not necessary to use a light transmittance changing material whose reaction rise time is fast.

(Embodiment 2) In this embodiment, in terms of the light diameter y of the spot light reduced by the auxiliary layer 12 and the shortest pit p of the pits reproduced by using the spot light, that is, the auxiliary layer The reaction rise time ta required when the shortest pit p of the pits is smaller than the light diameter y of the spot light reduced by the (light transmittance changing material), the light diameter x of the irradiated spot light X, and the light transmittance. The reaction ratio of the changing material (ratio α between the light diameter x of the irradiated spot light and the diameter y of the portion that becomes smaller due to the auxiliary layer) and the relationship between the moving speed S of the relatively moving spot and pit are clarified. The light transmittance changing material (reaction rising time ta) required for the auxiliary layer 12 is limited.

FIGS. 3A and 3B show the light diameter (or the diameter of the smaller portion) y of the spot light reduced by the auxiliary layer 12 and the pit train reproduced by using the spot light (FIG. 3). Shortest pit p (p, p) of middle and diagonal lines Pa, Pb)
It is a figure which shows the relationship with a, pb). In contrast to FIG. 7A, FIG. 8B targets smaller pits for reading (pa> pb).

First, as shown in FIG. 3A, when y ≦ p, the spot light Y reduced by the auxiliary layer 12 is obtained.
You can read and write with. Then, as is clear from FIGS. 1A to 1C, when the entire spot diameter Y of the spot light Y is the final spot light, the light amount is larger and the SN ratio of the signal is better. That is, when y ≦ p, ta ≦ (x−y) / 2S On the other hand, as shown in FIG. 3B, when y> p, the light diameter of the spot light reduced by the auxiliary layer 12 is obtained. (To be precise, the diameter of the smaller part) y
I need to read and write. That is, as shown in FIGS. 1D and 3B, the light diameter z of the final spot light Z on the information layer 10 needs to be smaller than the shortest pit p. That is, when y> p, (x−y) / 2S ≦ ta <(x + y) / 2S The right side is the same as the limitation of the first embodiment.

Further, α = y / x, so that y ≦ p, ta ≦ x (1-α) / 2S y> p, x (1-α) / 2S ≦ ta <x (1 + α) If the auxiliary layer is made of a light transmittance changing material satisfying the condition of / 2S and used as an optical recording medium, the pit string having the shortest pit length p can be efficiently read according to the shortest pit length. become.

(Embodiment 3) In this embodiment, particularly in a rotary disk-shaped optical recording medium (optical disk in which the pit rows of the information layer are formed in an arc shape or a spiral shape), a read position R and a radius in the radial direction are used. The required reaction fall time tb is clarified in terms of the track pitch in the direction, and the light transmittance changing material required for the auxiliary layer 12 is limited.

As described above, FIG. 2B is a plan view of an optical recording medium formed in a rotary disc shape, and an optical disc in which the pit rows of the information layer 10 are formed in an arc shape or a spiral shape. It is 1. In such an optical disc 1,
Adjacent tracks are sequentially read every one rotation. In this case, if the change in the optical characteristics of the auxiliary layer 12 is not eliminated during one rotation, the pit of the adjacent track will be read.

Therefore, for the reaction fall time tb, the auxiliary layer may be made of a light transmittance changing material satisfying the condition of tb ≦ 2πR / S. If r is the radius to the track next to the track defined by R and the track pitch is T, then T = R−r, so tb ≦ π (R−r) (R + r) / TS Can be represented.

In the third embodiment, the reaction fall time tb is limited by focusing on the radial direction of the optical recording medium formed in the rotary disk shape. It is necessary to limit the reaction rise time ta as in 2.

Further, as the auxiliary layer whose optical characteristics change according to the intensity of the irradiated spot light, the light transmittance changing material is taken as an example, but a material whose refractive index and reflectance are changed may be used.

[0027]

As described above in detail, according to the optical recording medium of the present invention, the delay of the reaction rise time is allowed within an appropriate range, and the material forming the auxiliary layer (for example, the change in the light transmittance). Material) conditions become mild. Further, by utilizing the delay of the reaction rise time, the final spot diameter can be made smaller than the diameter reduced by the auxiliary layer. Further, an optical recording medium having an appropriate reaction fall time is provided and can be used as a rotary disc-shaped optical recording medium.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of an optical recording medium according to the present invention, and is a diagram for explaining a transition of a read state in an information layer depending on a reaction rise time of a light transmittance changing material.

FIG. 2 is a structural diagram of an optical recording medium according to the present invention.

FIG. 3 is a relationship between a light diameter of a spot light (or a diameter of a smaller portion) which is reduced by an auxiliary layer of an optical recording medium according to the present invention and a shortest pit of a pit string reproduced by using the spot light. FIG.

FIG. 4 is a diagram showing characteristics of an auxiliary layer (light transmittance changing material) in a general optical recording medium.

5A is a diagram showing a general optical recording medium having an auxiliary layer, and FIG. 5B is an example of a light spot intensity distribution on the surface of the optical recording medium.

[Explanation of symbols]

1 optical disk (optical recording medium), 10 information layer, 12 auxiliary layer (light transmittance changing material) 14 reflective layer 16 protective layer x light diameter of irradiated spot light X, y spot where spot light is reduced by auxiliary layer Light diameter of light Y (diameter of virtual range to be reduced), ratio of light diameter of spot light smaller by α auxiliary layer z Final light diameter of spot light Z in information layer, p Spot light is used The shortest pit length of the pit row to be reproduced, X is the spot light that is irradiated, Y is the spot light that is reduced by the auxiliary layer (the virtual range that becomes small), Z is the final spot light, S is the spot that moves relatively and the pit. Movement speed, P pit (row) ta The reaction time required for the optical properties of the auxiliary layer to change due to spot light irradiation (reaction rise time), tb spot light irradiation stopped, The reaction time required for the sex change disappears (time falling reaction elevation).

Claims (3)

[Claims] 1. An information layer having a pit train that is read and written by using relatively moving spot light, and an auxiliary layer having optical characteristics that change according to the intensity of the irradiated spot light. In an optical recording medium configured such that the substantial light diameter of the spot light on the information layer is reduced by the auxiliary layer, the auxiliary layer reduces the light diameter of the irradiated spot light by x, and reduces it by the auxiliary layer. The ratio of the light diameter of the spot light is α, the final light diameter of the spot light on the information layer is z, the moving speed of the relatively moving spot light and the pit is S, and the auxiliary layer is irradiated by the spot light to form an auxiliary layer. Assuming that the required time (reaction rise time) at which a desired change in optical characteristics occurs is ta, {x (1 + α) -2z} / 2S ≦ ta <x (1 + α) / 2
An optical recording medium characterized by being a material satisfying a condition of S 2. 2. An information layer having a pit row that is read and written by using spot light that moves relatively, and an auxiliary layer whose optical characteristics change according to the intensity of the spot light irradiated, In an optical recording medium configured such that the auxiliary layer reduces the substantial light diameter of the spot light on the information layer, the auxiliary layer reduces the light diameter of the irradiated spot light to x, and reduces the light diameter of the spot light to the auxiliary layer. The light diameter of the spot light that has become smaller is y, the proportion of the light diameter of the spot light that becomes smaller due to the auxiliary layer is α (α = y / x), and the shortest pit length of the pit row read using the spot light is p, relative S is the moving speed of the spot light and the pits that are moving dynamically, and ta is the time required for the desired optical characteristics to change in the auxiliary layer by irradiation of the spot light (reaction rise time).
Then, for y ≦ p, ta ≦ x (1-α) / 2S For y> p, a material that satisfies the condition x (1-α) / 2S <ta <x (1 + α) / 2S An optical recording medium characterized by being present. 3. An information layer in which a pit row read and written by using a relatively moving spot light is formed in an arc shape or a spiral shape, and optical characteristics change according to the intensity of the irradiated spot light. Which is a rotary disc-shaped optical recording medium constituted by an auxiliary layer, which is configured such that the substantial light diameter of the spot light on the information layer is reduced by the auxiliary layer, wherein the auxiliary layer is The radius from the center of rotation to an arbitrary pit row is R, the moving speed of the relatively moving spot light and the pit is S, and there is no change in the desired optical characteristics in the auxiliary layer after the irradiation of the spot light is stopped. Time required (reaction fall time)
3. The optical recording medium according to claim 1, wherein the material is a material that satisfies the condition of tb ≦ 2πR / S, where tb is tb.