JP2828751B2 - Recording / reproducing method for optical recording medium - Google Patents

Description

The present invention relates to a recording and / or reproducing method for an optical recording medium for recording and / or reproducing information on / from an optical recording medium.

(B) Conventional technology In recent years, research on using a photochromic material for a recording layer of a medium has been actively promoted. Such a photochromic material has properties such that when irradiated with light of a predetermined wavelength, the structure of a molecule changes due to a photochemical reaction, and the optical characteristics of light having a specific wavelength change according to the change in the structure of the molecule. Have. In addition, when light of another predetermined wavelength is irradiated, the structure of the changed molecule returns to the original structure.

Recently, a study of multiplex recording of information on a medium using such a material has been studied. As this type of wavelength multiplex recording method, for example, a method disclosed in Japanese Patent Application Laid-Open No. 61-203450 (G03C1 / 733) is known. In such a medium, a plurality of recording layers including photochromic materials having different light absorption wavelength regions are formed. When this medium is irradiated with a light beam of a specific wavelength, a photochromic material in the recording layer that absorbs the light of the above-mentioned wavelength among the recording layers causes a photochemical reaction, whereby information is recorded on this recording layer. Will be By irradiating the recording layer with light beams of a plurality of wavelengths absorbed by the photochromic material, wavelength multiplex recording of information is performed on each recording layer. Reading of information in each recording layer is performed by irradiating this medium with light rays of the above-mentioned plural wavelengths having about 1/10 the intensity at the time of recording. This light beam is mainly absorbed in the corresponding recording layer, and the degree of absorption varies depending on whether or not a photochemical reaction has occurred in the photochromic material of the recording layer. Therefore, when the medium is a reflection type, the information on the corresponding recording layer can be read by detecting the difference in the intensity of the reflected light from the medium. When the medium is irradiated with a light beam causing a reverse photochemical reaction, the irradiated portion of the photochromic material returns to the initial state, thereby erasing information.

(C) Problems to be Solved by the Invention However, in the above-described conventional wavelength multiplex recording method, the photochromic material generally does not have a steep absorption spectrum and the spectra of the photochromic materials overlap each other. Some photochromic materials may cause photochemical reactions. As a result, there is a problem that crosstalk occurs when recording and reproducing information. The present invention has been made to solve such a problem, and proposes a recording / reproducing method for an optical recording medium which prevents crosstalk.

(D) Means for Solving the Problems In view of the above problems, the recording / reproducing method of the present invention provides an optical recording medium including first and second photochromic materials having different light absorption wavelength regions, respectively. A recording / reproducing method of an optical recording medium for recording / reproducing information by irradiating light of a first wavelength corresponding to the second wavelength and light of a second wavelength corresponding to the second photochromic material, The light of the second wavelength and the light of the second wavelength are linearly polarized lights whose polarization directions are orthogonal to each other, and the optical recording medium has optical anisotropy by the light of the first wavelength and the light of the second wavelength. It is characterized in that the information is recorded by causing it to occur, and the information is reproduced by the light of the first wavelength and the light of the second wavelength according to the direction of the optical anisotropy.

(E) Function When the molecules of the photochromic material are dispersed in the recording layer in a non-oriented state in the unrecorded state when the recording layer is irradiated with linearly polarized light. ,
Of the molecules dispersed in the recording layer, only specific molecules corresponding to the polarization direction (polarization plane) of the linearly polarized light cause a photochemical reaction, and the molecular structure changes. In this way, among the molecules dispersed in the recording layer, only specific molecules have a different molecular structure from other molecules (the generation of anisotropy),
Recording of information can be performed. As one type of this anisotropy (optical anisotropy), there is one in which the absorbance has an angle dependency. That is, when the recording layer on which information is recorded is irradiated with linearly polarized light, the difference in absorbance depending on the angle formed by the two linearly polarized light directions of the linearly polarized light used for recording and the linearly polarized light used for reproduction. (Dichroism). Therefore, information can be reproduced by irradiating light having a polarization state corresponding to the polarization state of the light for recording and detecting a change in absorbance. The present invention utilizes such a principle for multiplex recording. That is,
When an optical recording medium composed of a plurality of photochromic materials having different light absorption wavelength regions is irradiated with polarized light having a wavelength absorbed by each photochromic material, a photochromic material corresponding to light of each wavelength among the plurality of photochromic materials is obtained. The information is recorded by mainly causing a photochemical reaction according to the polarization state of the material. The recording layer on which recording has been performed has a direction dependency and a wavelength dependency in the difference in absorbance. or,
Reproduction of information is performed by detecting a difference in absorbance caused by irradiating polarized light according to the nature (wavelength and polarization state) of the light at the time of recording. Therefore, in the recording and reproduction of the information, in addition to the wavelength dependency of the conventional method, the difference in absorbance at each wavelength has direction dependency, so that crosstalk can be reduced.

(F) Example Hereinafter, the present invention will be described in detail with reference to the drawings.

 The present invention utilizes the following principle.

As shown in FIG. 1, in a recording layer made of a non-oriented photochromic material, the recording layer irradiated with linearly polarized light for recording (recording state) and the recording layer not irradiated (unrecorded state) Absorbance is different, and, for the recording layer irradiated with the linearly polarized light for recording, the linearly polarized light for reproduction having an angle θ with respect to the polarization direction of the linearly polarized light for recording. This is performed using the fact that the absorbance differs depending on the angle θ. In other words, a large output is obtained with linearly polarized light in a specific direction (optically anisotropic direction) (θ = 0 ° in FIG. 1), and on the other hand, in an unrecorded track and 90 ° different from the above specific direction. The fact that the output decreases when the recording track is reproduced with linearly polarized light in the direction is used. However, the relationship shown in FIG. 1 may be different depending on the photochromic material and the wavelength of the light for recording or reproduction. At this time, the direction of optical anisotropy is defined as a direction in which a large difference in absorbance occurs between generally used light for recording and light for reproduction. However, when a large birefringence occurs in the recording layer, the direction of light for reproduction is defined. It is desirable that the polarization direction of the linearly polarized light be set so that θ = 0 °.

In the present invention, a recording medium containing several types of photochromic materials has a wavelength in a light absorption wavelength region of each photochromic material,
In addition, information is recorded by irradiating linearly polarized light having a specific polarization direction, and the light having the above wavelength has a direction corresponding to the polarization direction of the linearly polarized light at the time of recording (generally, θ = 0 ° is sufficient). Information is reproduced by irradiating weak light of linearly polarized light and changing the absorbance.

Hereinafter, description will be made with reference to the conceptual diagram shown in FIG. For example, the recording layer has a photochromic material (X) having light absorption at a wavelength λ _X (generally, a maximum absorption wavelength) and a photochromic material having light absorption at a wavelength λ _Y (generally, a maximum absorption wavelength). Y), the absorbance curve of the weakly random polarized light or linearly polarized light in the unrecorded state is the second.
The curves shown by the solid lines in FIGS.

Conventional irradiated with light of the randomly polarized light or circularly polarized light of wavelength lambda _X in the recording layer in the same manner, when absorbance is measured at weak light of the randomly polarized light or circularly polarized light of the same polarization state as the Thereafter, the second view ( An absorbance curve (broken line) shown in a) is obtained. As it can be seen from the above results, in the conventional method when the light of wavelength lambda _X in the recording layer is irradiated, greatly changes the absorbance at a wavelength lambda _Y not only the wavelength lambda _X. This is the wavelength λ _X
At the time of recording information, information is also recorded at the wavelength λ _Y ,
Therefore, it means that crosstalk occurs. The occurrence of the crosstalk is caused by the fact that the absorption spectrum of the photochromic material is not steep and the absorption wavelength regions overlap.

In contrast, linearly polarized light of wavelength lambda _X is irradiated to the recording layer, absorbance shown in FIG. 2 when the polarization direction measuring absorbance with light of theta = 0 ° linearly polarized light (b) thereafter A curve (broken line) is obtained. When the absorbance is measured with linearly polarized light having a polarization direction of θ = 90 °, an absorbance curve (dashed line) shown in FIG. 2C is obtained. That is, in the method of the present invention, the wavelength λ
Absorbance with light of theta = 0 ° linearly polarized light by _Y Although the same result as the conventional, almost unchanged absorbance at the wavelength lambda _Y in light of theta = 90 ° linearly polarized light. Although the absorbance at the light even in the same manner as above at the wavelength λ _X θ = 0 ° linearly polarized light in the irradiation of linear polarized light of wavelength lambda _Y is the same result as the conventional, theta
= Hardly changes absorbance at a wavelength lambda _X in the light of 90 ° linearly polarized light. Further, the wavelengths λ _X and λ
Irradiation with linearly polarized light of _Y can similarly detect a difference in absorbance that is hardly affected by irradiation of each wavelength. Therefore, a linearly polarized light perpendicular to each other, by performing recording and reproduction of information in two light with wavelength lambda _X and wavelength lambda _Y, it is possible to perform the reduction of crosstalk.

Hereinafter, the first embodiment will be described in detail with reference to the drawings.

As a photochromic material contained in the recording layer,
Fluchromic, diallylethene, spiropyran-based photochromic materials can be used. As an example, two types of spiropyran-based photochromic materials shown in FIG. 3 (hereinafter, one photochromic material is referred to as material (A) and the other is referred to as material (B)) will be described. The molecular structure of these two materials changes from a spiropyran type to a photomerocyanine type by irradiation with ultraviolet light, and reverts from a photomerocyanine type to a spiropyran type by irradiation with visible light. In order to restore the molecular structure from the photomerocyanine type to the spiropyran type, the material (A) is irradiated with light having a maximum absorption wavelength of about 620 nm, and the material (B) is irradiated with light having a maximum absorption wavelength of about 470 nm. Is irradiated. When the material (A) and the material (B) are of the photomerocyanine type, the absorbance at each of the absorption maximum wavelengths becomes small.

Next, a recording medium in which a recording layer was formed by mixing the two types of photochromic materials and applying the mixture by spin coating on a quartz substrate was manufactured. The recording medium contains a photochromic material in a non-oriented state without uniform molecular orientation. Experiments for recording and reproducing data on and from this recording medium were performed for the conventional method and the method of the present invention, and will be described below.

First, the conventional method will be described. First, the recording medium is irradiated with UV light of random polarization to color the entire surface of the recording layer, that is, an unrecorded state (photomerocyanine state).
After that, the absorbance was measured with light of random polarization. The result is shown in a curve a of FIG. 4 (the curve a shows the absorbance in an unrecorded state). Next, after irradiating the recording medium in a colored state (unrecorded state) with circularly polarized light at a wavelength of 470 nm, that is, after recording, the absorbance was measured with randomly polarized light. The result is shown by curve b in FIG. Further, subsequently, the storage medium has a wavelength 62 different from the recording wavelength.
After irradiation with circularly polarized light at 0 nm, that is, recording, the absorbance was measured with randomly polarized light. The result is shown by curve c in FIG. From FIG. 4, it can be seen that irradiation of light of one wavelength has a large effect on the absorbance of the other wavelength. This means that crosstalk occurs remarkably in recording and reproducing information.

Next, this embodiment will be described. FIG. 5 (a) and FIG.
FIG. 7B shows the absorbance characteristics of linearly polarized light having a polarization direction of θ = 0 ° and θ = 90 ° with respect to the polarization direction of the linearly polarized light during recording according to the curve b. 5 (a) and 5 (b), the curve a shows the state of being colored by irradiating random polarized ultraviolet light, that is, the absorbance of the unrecorded recording medium, and the curve b shows the colored state (unrecorded state). The absorbance after recording by irradiating the recording medium with linearly polarized light having a wavelength of 470 nm, and the curve c indicates that the polarization directions are orthogonal to each other on the colored recording medium.
Polarization state consisting of two linearly polarized light is the same wavelength 470nm and 620nm
And the absorbance after recording by simultaneously irradiating this light. From this result, by orthogonalizing the state of linearly polarized light according to the wavelength 470 nm and the wavelength 620 nm, irradiation of the recording layer with light of linearly polarized light of one wavelength, the linearly polarized light orthogonal to the linearly polarized light of the other wavelength. It can be seen that it hardly affects the absorbance due to light. Although not shown, a recording medium colored by irradiating random polarized ultraviolet light (unrecorded state)
Irradiation with linearly polarized light having a wavelength of 620 nm similarly hardly affected the absorbance at a wavelength of 470 nm with linearly polarized light having a polarization direction θ = 90 °. Therefore, information is recorded by irradiating the recording layer with linearly polarized light having two wavelengths orthogonal to each other, and information is recorded with linearly polarized light having the same polarization direction as the recording direction at the same wavelength as during recording. By performing reproduction, recording and reproduction with almost no crosstalk can be performed.

In the above description, a recording medium having a recording layer containing two types of photochromic materials has been described. However, the present invention can be applied to a recording medium containing three or more types of photochromic materials.
For example, three types of photochromic materials (material a, material b
The case where the material c) has the absorbance characteristic as shown in FIG. 6 will be described. However, at this time, each photochromic material is dispersed non-oriented.

In this case, light of wavelength lambda _a and the wavelength lambda _c is a linear polarized light having the same polarization direction, light of the wavelength lambda _b may be performed recording and reproducing information with linear polarization perpendicular to the light of the two linearly polarized light.
At this time, between the wavelength lambda _a and the wavelength lambda _b, also the wavelength lambda _b and the wavelength lambda _c by the same effect as in the case of using two kinds of photochromic materials described above, it can prevent crosstalk. or,
Since the absorption line wavelength lambda _a and the wavelength lambda _c hardly overlap, the crosstalk is sufficiently small. Therefore, recording and reproduction of information with almost no crosstalk can be performed.

Hereinafter, a second embodiment will be described. The same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

The recording layer of the recording medium is formed on a transparent substrate by spin coating after mixing two types of photochromic materials of the material (A) and the material (B). The photochromic material is dispersed in the recording layer in a non-oriented state. Information is recorded on the recording layer by the wavelength λ _A absorbed by the material (A).
Of linearly polarized light and the material linearly polarized light of wavelength lambda _B is absorbed to (B) is carried out by irradiation. At this time, at the same location on the recording layer, the linearly polarized light of wavelength λ _A and the wavelength λ _B
The information is recorded by irradiating such that the polarization directions of the linearly polarized light are orthogonal to each other, and the directions of the linearly polarized light of each wavelength are orthogonal to each adjacent track. That is, as shown in FIG. 7, linearly polarized light having an absorption wavelength λ _A and an absorption wavelength λ _B (indicated by a solid arrow and a dotted arrow in the figure, respectively) is applied. Further, information is reproduced by irradiating linearly polarized light having the same wavelength as that at the time of recording and corresponding to the polarization direction of each wavelength at the time of recording.

As described above, according to the second embodiment, it is possible to prevent crosstalk based on light of different wavelengths. Further, since the linear polarization directions of the light having the respective absorption wavelengths are orthogonal to each other in the adjacent tracks, the output of the adjacent tracks can be reduced, and the crosstalk from the adjacent tracks can be reduced.

In the first and second embodiments, a recording medium including a plurality of photochromic materials in a single recording layer has been described. However, a stacked recording layer formed by stacking a plurality of recording layers made of photochromic materials having different absorption wavelength regions. Crosstalk can be similarly reduced in a recording medium. Further, the same effect can be obtained also in a laminated recording medium in which a plurality of recording layers made of a plurality of photochromic materials having different absorption wavelength regions are stacked.

FIG. 8 shows an example of an optical system of a recording / reproducing apparatus for implementing the present invention.

The recording medium ( 1 ) comprises a recording layer (23) on a transparent substrate (21).
Is formed, and a reflective layer (22) of Au or the like is further formed on the recording layer (22). In the recording layer (23), three types of photochromic materials having absorbance characteristics as shown in FIG. 6 of the first embodiment are dispersed in a non-oriented manner. First
The light source (301), the second light source (401), and the third light source (501) output linearly polarized light having wavelengths λ _a , λ _b, and λ _c that are absorbed by the three types of photochromic materials, respectively. After being collimated beam while linearly polarized light in the light of the linearly polarized light of wavelength lambda _a outputted from the first light source (301) is a lens (302), by the reflected light returns to the first light source (301) It passes through an isolator (303) that combines a Faraday rotator, a polarizer, and the like for preventing generated noise.
The parallel light passes through the half mirror (304) as a P wave or an S wave, passes through the dichroic mirror (6) and the dichroic mirror (7), and is recorded by the objective lens (2) on the recording layer of the recording medium ( 1 ). The information is condensed on (23) and information is recorded. Similarly, the wavelength λ _b output from the second light source (401)
The linearly polarized light is converted into parallel light by the lens (402) while keeping the linearly polarized light, and then passes through the isolator (403) and the half mirror (404). High dichroic mirror reflectance of the parallel light as described above passed through the wavelength lambda _b of light (6)
Then, the light passes through the dichroic mirror (7).
The passed parallel light is condensed on the recording layer (23) by the objective lens (2) to record information. Also,
After being collimated light in the state of the linearly polarized light of the linearly polarized light of wavelength lambda _c output from the third light source (501) is a lens (502), isolator (503) and the half mirror (5
04). After the parallel light above passage is reflected in high dichroic mirror (7) reflectance of light of wavelength lambda _c,
The information is recorded by focusing the light on the recording layer (23) by the objective lens (2). At this time, the wavelength λ _a condensed on the recording layer
And the polarization direction of the linearly polarized light having the wavelength λ _c is the same, and the wavelength λ
linearly polarized light of _b are adjusted such that the light and the polarization direction of the linearly polarized light of wavelength lambda _a and the wavelength lambda _c is orthogonal (e.g., 1 /
It may be adjusted by appropriately using a two-wavelength plate or the like).

In reproducing information, generally, the output of each light source is weakened, and linear polarization of each wavelength is applied to the recording layer according to the polarization direction of linear polarization of each wavelength applied to the recording layer at the time of recording. The same direction is sufficient) and the reflected light generated by irradiation is detected by sensors corresponding to the respective wavelengths. That is, linearly polarized light of wavelength lambda _a output from the first light source (301) is a lens (302), isolator (30
3) After passing through the half mirror (304), the dichroic mirror (6), and the dichroic mirror (7),
The light is focused on the recording layer (23) by the objective lens (2). At this time, the polarization direction of the linearly polarized light of wavelength lambda _a is in general coincide with the polarization direction of the linearly polarized light at the time of recording wavelength lambda _a. The linearly polarized light condensed on the recording layer (23) passes through the recording layer (23), is reflected on the reflection layer (22), and the reflected light is emitted from the recording medium ( 1 ). After reflected light passes through the dichroic mirror (7) and the dichroic mirror (6), is reflected by the half mirror (304), passes through a filter (305) for passing only the main light of the wavelength lambda _a. Then the lens (3
07), the light is collected and detected by the sensor (306), and the information is reproduced. Further, the linearly polarized light of wavelength lambda _b emitted from the second light source (401) produces a reflected light in the recording medium (1) as well, the reflected light is the objective lens (2) and dichroic mirrors (7) after passing through the light reflectance of the wavelength lambda _b is reflected at a high dichroic mirror (6). Thereafter, the light is reflected by the half mirror (404), and the wavelength λ _b
Through the filter (405), which mainly transmits only the light. The transmitted reflected light is condensed on the sensor (406) by the lens (407) and the information is reproduced. Furthermore, linearly polarized light of the third light source (501) emitted from the wavelength lambda _c produces a reflected light in the recording medium (1) as well, the reflected light is a wavelength lambda dichroic high reflectance of light _c after being reflected by the mirror (7), is reflected by the half mirror (504), a filter (50 mainly transmits only light of the wavelength lambda _c
5) through. The transmitted reflected light is condensed on the sensor (506) by the lens (507) and the information is reproduced.

As a light source, a gas laser such as a He-Ne laser and an Ar laser and a laser such as a semiconductor laser are generally used. When the above-mentioned gas laser is adopted, an AO element or the like for modulating the output light is provided. Further, the optical system corresponding to each wavelength may be arranged in the same optical head, or a configuration of a plurality of optical heads corresponding to each wavelength may be employed. In the above description, one optical system is shown for the reflection type recording medium, but a configuration other than the above may be adopted. Further, a transmission type recording medium can be easily realized using a similar principle. Further, the above-mentioned recording medium is configured to include three types of photochromic materials, but a recording layer including two or more types of photochromic materials can be realized by the same optical system. In the first, second and third embodiments, linearly polarized light is used for recording and reproducing information. However, similar effects can be obtained in other polarization states (elliptically polarized light). The polarization directions of the linearly polarized light and the elliptically polarized light are not limited to those in the above-described embodiment. For example, in the first embodiment, the angle formed by the polarization directions of the linearly polarized light is 90 ° (perpendicular), but the angle formed by the linearly polarized light is such that the effect of preventing the crosstalk is not lost.
It may be different from 90 ゜.

(G) Effects of the Invention In the wavelength multiplex recording method for an optical recording medium, crosstalk based on light of different wavelengths can be sufficiently suppressed.

[Brief description of the drawings]

1 is a conceptual diagram showing the direction dependency of the absorbance, FIG. 2 is a conceptual diagram showing the principle of the present invention, and FIGS. 3 to 6 are related to the first embodiment. 3 (a) and 3 (b) are structural formulas showing molecular structures, FIG. 4 is a diagram showing absorbance characteristics, and FIGS. 5 (a) and 5 (b) are diagrams showing absorbance characteristics. FIG. 6, FIG. 6 is a diagram showing the absorbance characteristics of the photochromic material contained in the recording medium, FIG. 7 is a diagram showing the polarization direction of light irradiated on the recording layer according to the second embodiment, FIG.
FIG. 1 is a diagram showing an example of a recording / reproducing apparatus for implementing the present invention. ( 1 ) Recording medium, (23) Recording layer.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G11B 7/00

Claims (1)

(57) [Claims] An optical recording medium including first and second photochromic materials having different light absorption wavelength regions, wherein light of a first wavelength corresponding to the first photochromic material and light of the second
In the recording / reproducing method of an optical recording medium for recording / reproducing information by irradiating light of a second wavelength corresponding to the photochromic material of (1), the light of the first wavelength and the light of the second wavelength are mutually Linearly polarized light whose polarization directions are orthogonal to each other;
Optical anisotropy is generated in the optical recording medium by the light of the second wavelength and the light of the second wavelength to record information, and the first wavelength corresponding to the direction of the optical anisotropy is recorded. A method for recording / reproducing information on / from an optical recording medium, wherein information is reproduced using light and the light having the second wavelength.