JPH03201227A - Optical recording medium and its reproducing method - Google Patents

Abstract

PURPOSE:To enable multiple recording and reproducing of data by forming magnetic layers so that any material in the magnetic layer has different intrinsic value of the angle of optical rotation from others or any combination of materials has different intrinsic values of the angle of optical rotation. CONSTITUTION:Recording layers 1 - 3 having different angle of optical rotation are formed on a transparent substrate 4. The angle of optical rotation of each layer is determined by the concn. of optical rotating material incorporated into the layer and by the thickness thereof. When a light beam irradiates the medium, the polarization plane of the beam is rotated according to the state of each material, each corresponding to the combination of recording state of the materials. Therefore, by detecting the angle of optical rotation of the polarization plane of transmitted light (or reflected light if the medium has a reflecting layer) from the medium, the recording state of each layer can be identified. Thereby, multiple recording/reproducing is possible with this medium by making use of optical rotatory power.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to an optical recording medium that enables high-density recording and a method for reproducing the optical recording medium.

(b) Prior Art Recently, research has been progressing on optical recording media that use a 7-oton mode organic photochromic material as a recording layer.

When such a photochromic material is irradiated with light of a predetermined wavelength, its molecular structure changes through a photochemical reaction, and when it is irradiated with light of another wavelength, this changed molecular structure returns to its original structure. It has the property of returning to . or,
When the molecular structure changes in this way, it also has the property that the light absorption characteristics for a beam of a predetermined wavelength change greatly.

Therefore, when a photochromic material having such properties is used in the recording layer of a medium, information can be recorded in a distant manner by using a beam having the above-mentioned wavelength for recording, and by using a beam having a later wavelength. By using for reproduction, it is possible to reproduce information in a distant manner.

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

On the other hand, as one method for solving this problem, a regeneration method using the optical rotation of photochromic materials is disclosed in Japanese Patent Application Laid-Open No. 63-259850 (G11B7/24).
has been disclosed. Optical rotation is a phenomenon in which when a linearly polarized beam is incident on a given material, the plane of polarization of this beam gradually rotates as it passes through the material. The above-mentioned photochromic materials have optical rotation depending on the recorded/unrecorded state mentioned above, so if the reading device is equipped with a means to detect the rotation of the plane of polarization, it is possible to read the information. becomes. In addition, in this method, since the rotation of the plane of polarization does not depend on the wavelength of the beam, it is possible to select a beam with a wavelength that is not absorbed at all by the recording layer as the reproduction beam. It is possible to prevent information from being erased by the reproduction beam.

Incidentally, in recent years, research has been conducted on multiple recording/reproduction in which a medium has multiple recording layers and data is recorded/reproduced in each layer. At this time, a dedicated beam for each recording layer is used as the recording/reproducing beam, and each layer is recorded in response only to this dedicated beam, and during playback, this dedicated beam is used to read data from the corresponding recording layer. It is designed to be modulated only by.

However, when the above-mentioned optical rotation is utilized, any linearly polarized beam is subjected to optical rotation by each layer during recording as well as during reproduction, so a dedicated beam corresponding to each layer cannot be used as a reproduction beam. For this reason, it has been impossible to record and reproduce data using conventional multiplex recording and reproduction methods.

(c) Problems to be Solved by the Invention Therefore, the present invention aims to provide an optical recording medium that allows multiple recording and reproduction of data even in a medium that utilizes optical rotation, and a method for reproducing the optical recording medium.

(d) Means for Solving the Problems In view of the above problems, this optical recording medium is an optical recording medium equipped with a recording layer containing multiple types of recording materials whose optical rotation changes depending on predetermined physical conditions. It is characterized in that the optical rotation of any one kind or the sum of the optical rotations of several arbitrary kinds have unique values that are different from each other.

In addition, there is a reproduction method for reproducing such media, which uses a linearly polarized beam as a light source, detects the rotation angle of the polarization plane of the transmitted beam or reflected beam from the medium, and detects the rotation angle of the polarization plane of the transmitted beam or reflected beam from the medium. It is characterized by identifying data in parallel.

Still another invention is provided with a recording layer containing a plurality of types of photochromic materials whose optical rotations change due to photochemical reactions, and the optical rotation of any one kind of the photochromic materials or the sum of the optical rotations of any several kinds of the photochromic materials is A method for reproducing optical recording media having different peripheral values, wherein a linearly polarized beam having a wavelength with zero or relatively small absorbance for each of the photochromic materials is used as a light source, and the medium of the beam is It is characterized in that data carried on each photochromic material is identified in parallel by detecting the rotation angle of the polarization plane of the transmitted beam or reflected beam from the photochromic material.

(e) When a straight beam is made incident on the working 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 to the combination of recording states of each material. Therefore, the recording state of each layer can be identified by the rotation angle of the polarization plane of the transmitted beam from the medium (or the reflected beam if the medium has a reflective layer).

In addition, when a photochromic material is used as the material contained in the recording layer, by using a beam with a wavelength that is difficult to be absorbed by each photochromic material as the reproduction beam, the direction in which data is erased in the green area by the reproduction beam can be changed. can prevent photochemical reactions.

(f) Examples Examples of the present invention will be described below. FIG. 1 shows the configuration of a medium according to this embodiment. In the figure, (4) is a transparent substrate, and (1), (2), and (3) are recording layers. substrate(
4) is made of quartz glass, and the recording layer (
1), (2), and (3) each contain the materials listed in the table below as optically active materials.

Margin table below 1 Each material is a spiropyran-based photochromic material, and when colored by causing a photochromic reaction,
Materials A, B, and C are 550 nm, 600 nm, and 650 nm, respectively.
It preferentially absorbs beams with wavelengths of nm. Further, each material becomes optically active only when a photochromic reaction occurs and the material becomes colored.

Each layer is formed by dissolving these materials in a predetermined solvent and then applying this onto the substrate (4) using a spin coating method. In addition, each layer has a ratio of optical rotations θA:
θB: θ. =1:2:4 (θ8, θ3, and θ are the optical rotation angles of the recording layers (1), (2), and (3), respectively). Here, the optical rotation is determined by the concentration of the optically active material contained in each layer and the thickness of each layer.

Experiments regarding data recording and reproduction were conducted using a medium having such a configuration. The table below shows numerical values for each recording layer of the medium used in this experiment.

Table 2 Each layer contains 10 mt of polyvinyl butyral (PVB) as an inder in addition to methyl ethyl ketone (MEK)! The material shown in Table 1 is dissolved in the added solution at the concentration shown in Table 2, and the material is sequentially applied onto a substrate made of quartz glass with a diameter of 20 mm by a spin code method. . In addition, the optical rotation shown in Table 2 is obtained by forming only each layer on the substrate and then coloring this layer.
The actual measured value of the rotation angle of the polarization plane of the transmitted beam when irradiated with a 0 nm laser beam is shown.

Next, the entire surface of the medium is irradiated with ultraviolet light having a wavelength of 300 nm to 400 nm to cause a photochemical reaction in each layer, thereby making each layer colored. Eight types of media in such a state were prepared, and each medium was given the above-mentioned absorption wavelength (550 nm,
Three types of laser beams having wavelengths of 600 nm and 650 nm are irradiated with different combination patterns of irradiation and non-irradiation. At this time, the intensity of each beam is 200m
w, and the irradiation time was 20 seconds. Furthermore, each beam is sequentially irradiated onto the same location on each medium so that the spot diameter on the substrate is 5 mm. Each beam is
It is absorbed into the corresponding recording layer, causing a photochemical reaction in this recording layer in the opposite direction to the coloring direction. Changes in the coloring state of the medium after each beam irradiation were 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 that converts the laser beam into a parallel beam, (M) is a medium, (7) is a polarizing beam splitter, and (8) is a collimator lens that converts the laser beam into a parallel beam. (9) is a 7-oto sensor. Here, the semiconductor laser (5) and the polarizing beam splitter (7) are connected to the medium (M
), the laser beam will pass through the polarizing beam splitter (7
) is positioned so that it is completely transparent. Further, the output intensity of the semiconductor laser is set to 3 mW.

When the beam undergoes rotation of the plane of polarization through the medium (M),
An output appears on the sensor (8). Here, if the rotation angle of the polarization plane is θ, the amplitude intensity of the S wave reflected by the polarizing beam splitter (7) is proportional to sin θ, so the output appearing at the sensor (8) is proportional to sin” θ. A semiconductor laser (
When the output intensity of 1) is 3 mW, the following relationship holds true.

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

The above measurement results are shown in the table below.

In Margin Table 3 below, ◯ indicates that the medium was irradiated with a beam of that wavelength, and - indicates that the medium was not irradiated with a beam of that wavelength. For example, the medium 7 is irradiated with only a beam having a wavelength of 550 nm. The optical rotation A is a predicted value of the optical rotation of each medium after the medium is irradiated with each beam, based on the optical rotation shown on the cloth 1. For example, in medium 3, a beam with a wavelength of 550 nm and a beam with a wavelength of 6
Since the beam of 50 nm is irradiated, the recording layer (1)
State (3) becomes an uncolored state and no longer has optical rotation, so the optical rotation of medium 3 is 2 of only recording layer (2).
It can be predicted that . Moreover, the optical rotation B is the sensor (
The optical rotation of each medium was calculated from the first equation of Jingji using the output of 8).

Comparing the optical rotation A and the optical rotation B shown in Table 3, they are substantially the same. From these results, it can be confirmed that irradiation with beams of each wavelength causes a photochemical reaction in the opposite coloring direction in the recording layer that absorbs each beam, and the optical rotation of that layer is eliminated. Therefore, during recording, data can be recorded in each layer by scanning the medium with a beam of each wavelength, and during reproduction, by scanning the medium with a beam of wavelength 830 nm using the optical system shown in FIG.
Data can be read from each layer. At this time, data for each layer is created in parallel according to the identification by identifying the recording state of each layer from the sensor output.

Therefore, the reproduction circuit requires a converter that creates data for each layer in parallel from the sensor output.

Incidentally, when the level of the beam directed toward the sensor (8) is small and the output of the sensor (8) does not have enough output to distinguish between the differences in the recording state, The ratio between the output of the sensor (9) and the output of the sensor (8) is calculated to clarify the difference depending on the recording state.

As described above, according to this embodiment, since the recording state of each layer can be identified based on the sensor output, data for each recording layer can be created from the sensor output when scanning multiple recorded data tracks.

Note that the present invention is not limited to such examples,
Various other changes are possible. For example, in the above embodiment, a groove bottom in which many recording layers are formed independently for multiple recording of data is used. It may be made to contain a material. In such a case, each material causes a photochemical reaction independently within the same recording layer, and the reproducing beam is simultaneously subjected to optical rotation by each optically active material when passing through the recording layer. Similarly, a change in the optical rotation angle occurs in the reproducing beam depending on the data carried by each material. However, in this case, since the thickness of the recording layer is the same, in order to set the ratio of the optical rotations of each material to a desired value, means are mainly used to change the content of each material in the recording layer.

Further, in the above embodiments, the medium is of a transmission type, but it can also be made of a reflection type by using a reflective layer. However, in this case, if a reflective layer is simply formed on the upper surface of the recording layer that is farthest from the substrate, the plane of polarization will rotate in the opposite direction to that at the time of incidence while the reflected beam passes through each recording layer again. The optical rotation generated in the medium disappears, and therefore, no rotation of the plane of deflection occurs in the reflected beam from the medium, regardless of the presence or absence of data. Such disadvantages can be solved by interposing a birefringent layer between the recording layer and the reflective layer. still,
The principle and details thereof are explained in Japanese Patent Application No. 1-246693 previously filed by the applicant. Therefore,
In order to use the medium as a reflective type, it is necessary to take such measures.

Further, the ratio of the optical rotations of each layer or material may be set so that the optical rotations of any one type of recording material or the optical rotations of any number of recording materials have independent values. Furthermore, optically active materials other than those used in the above embodiments can also be used. Furthermore, the number of recording layers is not limited to three, but can also be two, four or more.

In the case of the above embodiment, due to the characteristics of the polarizing beam splitter (7), the output of the sensor (8) increases monotonically according to the rotation angle of the beam polarization plane when the rotation angle is between 0° and 90°.
If it exceeds 90", the output of the sensor (8) will decrease. Therefore, if the maximum rotation angle of the beam polarization plane by all recording layers exceeds 90", this maximum The sensor output according to the value and the sensor output when the rotation angle is up to 90° are the same, and we are used to not being able to distinguish each rotation angle based on the sensor output. It is better to set the optical rotation of each recording layer so that

(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 and reproduction using optical rotation, and a reproduction method thereof. or,
When a photochromic material is used as the recording layer, the wavelength of the reproduction beam is set to a value such that the absorption by each recording layer is zero or relatively small, so the recording layer absorbs the reproduction beam during reproduction and causes a photochemical reaction. This prevents the recorded data from being erased by the reproduction beam.

[Brief explanation of drawings]

Both FIG. 1 and FIG. 2 relate to embodiments of the present invention.
The figure is a cross-sectional view of the medium, and FIG. 2 is a diagram showing the optical system. Fig. 1 (1) (2) (3”)... Recording layer, (5)... Semiconductor laser, (7)... Polarizing beam splitter, (8) (9)... Sensor, ( M)...Medium.

Claims (3)

[Claims] (1) An optical recording medium comprising a recording layer containing multiple types of recording materials whose optical rotation changes depending on predetermined physical conditions, wherein the optical rotation is determined by any one type of recording material or by any number of types of recording materials. An optical recording medium characterized in that the sum of degrees has a unique value that is different from each other. (2) A recording layer containing a plurality of types of recording materials whose optical rotations change depending on predetermined physical conditions, and the optical rotation of any one type of recording material or the sum of the optical rotations of any number of types of recording materials is A method for reproducing optical recording media having different unique values, which uses a linearly polarized beam as a light source and detects the rotation angle of the polarization plane of the transmitted beam or reflected beam from the medium. A method for reproducing an optical recording medium, characterized in that data carried by each material is identified in parallel. (3) A recording layer containing a plurality of types of photochromic materials whose optical rotations change due to photochemical reactions, and the optical rotation of any one kind of the photochromic materials or the sum of the optical rotations of any several kinds of the photochromic materials are different from each other. A method for reproducing an optical recording medium having a specific value of 0 or 1, wherein a linearly polarized beam having a wavelength of zero or relatively small absorbance for each of the photochromic materials is used as a light source, and a beam transmitted from the medium of the beam is used as a light source. Alternatively, a method for reproducing an optical recording medium, characterized in that data carried by each photochromic material is identified in parallel by detecting a rotation angle of a polarization plane of a reflected beam.