JP2810466B2 - Optical recording medium and reproducing method thereof - Google Patents

Description

The present invention relates to an optical recording medium capable of high-density recording and a reproducing method thereof.

(B) Conventional technology Recently, research on optical recording media using a photon-mode organic photochromic material as a recording layer has been advanced. Such a photochromic material changes its molecular structure by a photochemical reaction when irradiated with light of a predetermined wavelength, and further, when irradiated with light of another wavelength, the changed molecular structure returns to its original structure. It has the property of returning.
In addition, when the molecular structure changes in this way, there is such a property that the light absorption characteristics with respect to a beam of a predetermined wavelength largely change accordingly.

Therefore, when a photochromic material having such properties is used as a recording layer of a medium, information can be recorded by using a beam having the above-mentioned wavelength for recording, and a beam having a later wavelength can be achieved. By using for reproduction, information can be reproduced.

However, when such a reproducing method is used, there is a disadvantage that the recorded portion of the recording layer absorbs the reproducing beam, and the recorded portion changes to an unrecorded molecular structure.

On the other hand, as one of methods for solving such inconvenience, a reproducing method utilizing the optical rotation of a photochromic material is disclosed in Japanese Patent Application Laid-Open No. 63-259850 (G11B7 / 24). Optical rotation is a phenomenon in which, when a linearly polarized beam is incident on a predetermined material, the plane of polarization of this beam gradually rotates as it passes through the material. In the above photochromic material, since the presence or absence of optical rotation exists depending on the above-mentioned recorded / unrecorded state, information can be read if the reading device is provided with means for detecting the rotation of the polarization plane. Becomes Also, in this method, since the rotation of the polarization plane exists even in a wavelength region where there is no absorption, as a reproduction beam,
A beam having a wavelength that is not absorbed at all by the recording layer can be selected, thereby preventing erasure of information by the reproduction beam as described above.

By the way, in recent years, studies have been made on multiplex recording and reproduction in which a recording layer is arranged on a medium and data is recorded and reproduced on each layer. At this time, a dedicated beam is used for each recording layer as a recording / reproducing beam, and each layer performs recording in response to only the dedicated beam, and at the time of reproduction, the dedicated beam is a data of the corresponding recording layer. Is modulated only by

However, when the above-mentioned optical rotation is used, an arbitrary linearly polarized beam is subjected to an optical rotation by each layer at the time of reproduction regardless of recording, and therefore, a dedicated beam corresponding to each layer cannot be used as a reproduction beam. For this reason, the conventional multiplex recording / reproducing method cannot perform beam recording / reproducing.

(C) Problems to be Solved by the Invention Therefore, an object of the present invention is to provide an optical recording medium capable of multiplex recording and reproduction of data even in a medium utilizing optical rotation, and a reproduction method thereof.

(D) Means for Solving the Problems In view of the above problems, the present invention provides an optical recording medium including a recording layer containing a plurality of types of recording materials whose optical rotation changes according to predetermined physical conditions. It is characterized in that the optical rotation by any one type or the sum of the optical rotations by any number of types have unique values different from each other.

In a reproducing method for reproducing such a medium, a linearly polarized beam is used as a light source, and the rotation angle of the plane of polarization of a transmitted beam or a reflected beam from the medium of the beam is detected to be carried by each material. Data is identified in parallel.

As still another invention, a recording layer containing a plurality of types of photochromic materials whose optical rotation changes by a photochemical reaction is provided, and the optical rotation of any one of the photochromic materials or the sum of the optical rotations of any of the several types is determined. A method of reproducing an optical recording medium, each of which has a unique value different from each other, wherein a linearly polarized light beam having a zero or relatively small wavelength absorbance for each photochromic material is used as a light source; The rotation angle of the plane of polarization of the transmitted beam or the reflected beam from the detector is detected, and the data carried on each photochromic material is identified in parallel.

(E) Operation When a linear beam is incident on a medium, the plane of polarization of the beam is rotated according to the state of each material. The rotation angle at this time corresponds one-to-one with the combination of the recording state of each material.
Therefore, depending on the rotation angle of the plane of polarization of the transmitted beam from the medium (the reflected beam if the medium has a reflective layer),
The recording state of each layer can be identified.

When a photochromic material is used as the material contained in the recording layer, a beam having a wavelength that is not easily absorbed by each photochromic material is used as a reproducing beam, so that the photochemical in the data erasing direction of the recorded portion by the reproducing beam is used. Reaction can be prevented.

(F) Example Hereinafter, an example of the present invention will be described. FIG. 1 shows the configuration of a medium according to the present embodiment. In the figure, (4) is a transparent substrate, and (1), (2) and (3) are recording layers. The substrate (4) is formed of quartz glass, and the recording layers (1), (2), and (3) contain the following materials as optical rotation materials.

Each of the materials is a spiropyran-based photochromic material, and when colored by a photochromic reaction, the materials A, B, and C preferentially absorb beams having wavelengths of 550 nm, 600 nm, and 650 nm, respectively. In addition, each material has optical rotation only when colored by a photochromic reaction.

Each layer is formed by dissolving these materials in a predetermined solvent and then applying the same on a substrate (4) by spin coating. Each layer has a ratio of optical rotation of θ _A :
θ _B : θ _C = 1: 2: 4 (θ _A , θ _B , and θ _C are the optical rotations of the recording layers (1), (2), and (3), respectively). Here, the optical rotation is determined by the concentration of the optical rotation material contained in each layer and the film thickness of each layer.

An experiment on data recording and reproduction was performed using a medium having such a configuration. The following table shows numerical values for each recording layer of the medium used in this experiment.

Each layer was prepared by dissolving the materials shown in Table 1 at a concentration shown in Table 2 in a solution obtained by adding 10 mt% of polyvinyl butyral (PVB) as a binder to methyl ethyl ketone (MEK) from quartz glass of 20 mm square. It is formed by sequentially coating the substrate by spin coating.
The optical rotation shown in Table 2 was obtained by measuring only the rotation angle of the polarization plane of the transmitted beam when irradiating a laser beam with a wavelength of 830 nm to this layer after forming each layer on the substrate and then irradiating this layer with a laser beam having a wavelength of 830 nm. The following values are shown.

Next, the medium is irradiated with ultraviolet light having a wavelength of 300 nm to 400 nm over the entire surface to cause a photochemical reaction in each layer, and each layer is brought into a colored state. Eight identical media in such a state are prepared, and the absorption wavelengths (550 nm, 600 nm,
(0 nm) with different combination patterns of irradiation and non-irradiation. On this occasion,
The intensity of each beam is 200 mw, and the irradiation time is 20 seconds each. Further, each beam is sequentially applied to the same portion of each medium so that the spot diameter on the substrate becomes 5 mm. Each beam is absorbed by the corresponding recording layer and causes a photochemical reaction in the recording layer in a direction opposite to the coloring direction. A change in the colored state of the medium after each beam irradiation was confirmed.

Next, the optical rotation of the transmitted beam was measured for each medium using the optical system shown in FIG. In the figure, (5)
Is a semiconductor laser that outputs a linearly polarized beam with a wavelength of 830 nm,
(6) is a collimator lens for converting a laser beam into a parallel beam, (M) is a medium, (7) is a polarizing beam splitter,
(8) and (9) are photo sensors. Here, the semiconductor laser (5) and the polarizing beam splitter (7) are connected to the medium (M).
When there is no laser beam, polarizing beam splitter (7)
Are positioned so that the light is totally transmitted. The output intensity of the semiconductor laser is set to 3 mw.

When the beam undergoes a rotation of the plane of polarization through the medium (M), an output appears at the sensor (8). Here, assuming that the rotation angle of the polarization plane is θ, the amplitude intensity of the S wave reflected by the polarization beam splitter (7) is proportional to sin θ.
Output appearing at the sensor (8) is proportional to sin ² theta. The following relationship holds between the output P of the sensor (8) and the rotation angle θ when the output intensity of the semiconductor laser (1) is 3 mw.

P = 3 sin ² θ [mw] (1) Therefore, the rotation angle of the beam polarization plane can be confirmed from the output of the sensor (8).

 The results of the above measurements are shown in the table below.

In Table 3, ○ indicates that the beam of the wavelength was irradiated on the medium, and-indicates that the beam of the wavelength was not irradiated on the medium. For example, the medium 7 is irradiated with only a beam having a wavelength of 550 nm. The optical rotation A is a value obtained by predicting the optical rotation of each medium after each beam is applied to the medium based on the optical rotation shown in Table 1 above. For example, in the medium 3, since the medium is irradiated with a beam having a wavelength of 550 nm and a beam wavelength of 650 nm, the states of the recording layers (1) and (3) become uncolored and have no optical rotation. The optical rotation of 3 can be predicted to be 2 ° only for the recording device (2). Further, the optical rotation B is obtained by calculating the optical rotation of each medium from the first equation using the output of the sensor (8).

When the optical rotation A and the optical rotation B shown in Table 3 are compared, they are substantially the same. From these results, it can be confirmed that the irradiation of the beam of each wavelength causes a photochemical reaction in the anti-coloring direction in the recording layer absorbing each beam, and the optical rotation of the layer is lost. Therefore, at the time of recording, data can be recorded on each layer by scanning the medium with a beam of each wavelength, and at the time of reproduction, by scanning the medium with a beam of a wavelength of 830 nm using the optical system of FIG. ,
Data can be read from each layer. At this time, the data of each layer is created in parallel according to the identification of the recording state of each layer from the sensor output. Therefore, in the reproduction circuit,
A converter that creates data of each layer in parallel from the sensor output is required. Incidentally, when the level of the beam toward the sensor (8) is small and the output of the sensor (8) does not show a sufficient output to discriminate a difference corresponding to the difference in the recording state, The ratio of the output of the sensor (9) to the output of the sensor (8) is used to clarify the difference corresponding to the difference in the recording state.

As described above, according to the present embodiment, the recording state of each layer can be identified by the sensor output, so that the data of each recording layer can be created from the sensor output when scanning the multiplex-recorded data track.

Note that the present invention is not limited to such an embodiment, and various other modifications are possible. For example, in the above-described embodiment, a configuration in which a large number of recording layers are independently formed for multiplex recording of data is used, but instead of such a configuration, a single recording layer contains a plurality of types of optically active materials. You may make it so. In such a case, each material causes a photochemical reaction independently in the same recording layer, and when the reproducing beam passes through the recording layer, it is simultaneously subjected to optical rotation by each optical rotation material. Similarly, a change in the optical rotation angle according to the data carried by each material occurs in the reproduction beam. However, in this case, since the thicknesses of the recording layers are common, in order to set the optical rotation ratio of each material to a desired value, means for mainly changing the content of each material in the recording layer is used.

Further, in the above embodiment, the medium is of the transmission type, but the medium may be of the reflection type using a reflection layer. However, in this case,
If a reflective layer is simply formed on the upper surface of the recording layer farthest from the substrate, the plane of polarization rotates in the opposite direction to the direction of incidence while the reflected beam passes through each recording layer again, and the optical rotation generated at the time of incidence Disappears, so that the reflected beam from the medium does not rotate the deflecting surface regardless of the presence or absence of data. Such a disadvantage is solved by interposing a birefringent layer between the recording layer and the reflective layer.
The principle, details, and the like are described in Japanese Patent Application No. 1-26693 filed earlier by the applicant. Therefore, it is necessary to take measures such as using the medium as a reflection type.

Furthermore, the ratio of the optical rotation by each layer or material may be set so that the optical rotation by any one of the recording materials or the optical rotation by any of several types of the recording material has an independent value. or,
As the optical rotatory material, those other than those in the above embodiment can be used. The number of recording layers is not limited to three, but may be two or four or more.

In the case of the above embodiment, the polarizing beam splitter (7)
The output of the sensor (8) monotonically increases in accordance with the rotation angle of the beam polarization plane due to the characteristic of (1) when the rotation angle is between 0 ° and 90 °, and when the rotation angle exceeds 90 °, the sensor (8) increases. ) Output decreases. Therefore, when the maximum value of the rotation angle of the beam polarization plane by all the recording layers exceeds 90 °, the sensor output corresponding to this maximum value and the sensor output up to a rotation angle of 90 ° match, and the sensor output Therefore, it is preferable to set the optical rotation of each recording layer so that the maximum rotation angle is 90 ° or less.

(G) Effects of the Invention As described above, according to the present invention, it is possible to provide a recording medium capable of multiplex recording / reproduction utilizing optical rotation and a reproduction method thereof.
When a photochromic material is used for the recording layer,
Since the wavelength of the reproducing beam is set to zero or a relatively small value for the absorbance of each recording layer, there is no fear that the reproducing layer absorbs the reproducing beam and causes a photochemical reaction at the time of reproducing. Erasure of the recorded data due to this can be prevented.

[Brief description of the drawings]

1 and 2 relate to an embodiment of the present invention.
The figure is a sectional view of the medium, and FIG. 2 is a view showing an optical system. (1) (2) (3) ... recording layer, (5) ... semiconductor laser, (7) ... polarization beam splitter, (8) (9) ...
... Sensor, (M) ... Medium.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G11B 7/24 G11B 7/00 G03C 1/73

Claims (3)

(57) [Claims] 1. An optical recording medium comprising a recording layer containing a plurality of types of recording materials whose optical rotation changes according to predetermined physical conditions, wherein the degree of optical rotation by any one of the recording materials or an arbitrary number of types thereof is provided. An optical recording medium characterized in that the sum of optical rotations of the optical recording media has unique values different from each other. 2. A recording layer containing a plurality of types of recording materials whose optical rotation changes according to predetermined physical conditions, and wherein the optical rotation by any one of the recording materials or the sum of the optical rotations by any of several types is determined. A method of reproducing an optical recording medium, each having a unique value different from each other, wherein a linearly polarized beam is used as a light source, and a rotation angle of a polarization plane of a transmitted beam or a reflected beam from the medium of the beam is determined. A method for reproducing an optical recording medium, comprising detecting and identifying data carried by each material in parallel. 3. A recording layer comprising a plurality of photochromic materials whose optical rotation changes due to a photochemical reaction, wherein the optical rotation of any one of the photochromic materials or the sum of the optical rotations of any of the plurality of photochromic materials is different. What is claimed is: 1. A method for reproducing an optical recording medium having unique values different from each other, wherein a linearly polarized light beam having a zero or relatively small wavelength absorbance for each of said photochromic materials is used as a light source, and said beam is transmitted from said medium. A method for reproducing an optical recording medium, comprising detecting a rotation angle of a polarization plane of a transmitted beam or a reflected beam and identifying data carried by each photochromic material in parallel.