JP2771656B2 - Recording / reproducing method for optical recording medium - Google Patents

Description

The present invention relates to a recording / reproducing method for an optical recording medium in which a recording layer contains a photochromic material.

(B) Conventional technology Recently, research using a photon-mode organic photochromic material as a recording layer has been advanced. In such a photochromic material, when light of a predetermined wavelength is irradiated, the molecular structure is changed by a photochemical reaction, and when light of another wavelength is irradiated, the changed molecular structure is changed to the original structure. It has the property of returning to. Further, when the molecular structure is changed in this manner, there is also a property that the light absorption characteristic for a beam of a predetermined wavelength is greatly changed.

Therefore, when a photochromic material having such properties is used for 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 obtained. Reproduction of information can be achieved by using it for reproduction.

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.

(C) Problems to be Solved by the Invention The present invention is to provide a novel recording / reproducing method for an optical recording medium which solves the above-mentioned disadvantages.

(D) Means for Solving the Problems According to the recording / reproducing method for an optical recording medium of the present invention, a recording having a wavelength which is absorbed by the photochromic material in an unrecorded state on a recording layer of the optical recording medium containing the photochromic material. Irradiating a linearly polarized light beam for recording, and among the molecules dispersed in the recording layer, a molecule parallel to the beam polarization plane of the linearly polarized light beam causes a photochemical reaction to change the molecular structure, thereby recording information. Irradiating a linearly or circularly polarized reproducing beam having a predetermined angle with respect to the linearly polarized light beam for recording, the light having a wavelength that is absorbed by the recording layer and having a small polarization plane; Receiving a transmitted beam or a reflected beam of the application beam from the optical recording medium, detecting a change in the polarization state of the beam, and reading information recorded on the recording layer. And a reproducing step.

(E) Function The photochromic material molecules in the recording layer are dispersed in the recording layer in a non-oriented state when the recording layer is in an unrecorded state. When such a recording layer is irradiated with a linearly polarized light beam, of the molecules dispersed in the recording layer, only molecules whose molecular orientation is parallel to the beam polarization plane cause a photochemical reaction, and the molecular structure changes. . For this purpose, if only molecules having a specific molecular orientation among the molecules arranged in the recording layer have a different molecular structure from other molecules (generation of anisotropy), Has birefringence with the neutral axis in the direction of the specific molecular orientation.

It is known that such birefringence causes a change in polarization state with respect to a laser beam having an arbitrary wavelength, for example, in “Proceedings of the Spring Meeting of the Chemical Society of Japan in 1989, p429”.

For example, in the recording method of the medium, a birefringence is introduced into the recording layer by irradiating the recording layer with a linearly polarized beam according to the above-described principle, and the portion where the birefringence is introduced is recorded as a recording portion of the recording layer. Data is recorded for the layer.

In the reproducing method of the present invention, the data in the recording layer is read by detecting a change in the polarization state of the beam when passing through the recording layer. At this time, the reproducing beam is hardly absorbed by the recording layer, so that an undesired photochemical reaction does not occur in the recording layer.

(F) Example Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows the structure of a spiropyran-based photochromic material that can be used as an example of the photochromic material contained in the recording layer in this embodiment. Such a material changes its molecular structure from a spiropyran type to a merocyanine type by irradiation with ultraviolet light, and returns from a merocyanine type to a spiropyran type by irradiation or heating with visible light. FIG. 2 shows the wavelength vs. absorbance characteristics of this material when in each type of molecular structure. The recording medium was prepared by applying a solution obtained by dissolving the photochromic material to a solvent obtained by adding PVB (polyvinyl butyral) as a binder to MEK (methyl ethyl ketone) on a substrate made of quartz glass by a spin coating method. It is produced by forming a recording layer.

FIG. 3 is a diagram illustrating an optical system of the recording / reproducing apparatus according to the present embodiment. The ultraviolet beam emitted from the Ar ion laser (1) is converted into a pulse beam by a beam modulator (2), and then a wavelength of 360 nm is applied by a wavelength selection filter (3).
Beams other than m are removed, and further converted into a linearly polarized beam by the analyzer (4). After being converted into a uniform beam by the beam expander (5), the beam is incident on the objective lens (8) via the tie-lock mirror (6) and the Faraday rotation element (7), and the objective lens (8) Converges on the recording layer (10) of the medium (9). Like this
When the Ar ion laser (1) is driven,
A beam modulator (2) modulates a beam according to data while relatively moving the medium (9) in a predetermined direction, thereby forming a row of birefringent portions (recording portions) on the recording layer (10). As an information track is formed.

On the other hand, a linearly polarized beam having a wavelength of 780 nm is emitted from the semiconductor laser (11), and this beam is converted into a parallel beam by a collimator lens (12). It is converged on the recording layer (10) of the medium (9) via the objective lens (8). Here, when the Faraday rotator (7) is driven and controlled by the control circuit (13), the polarization plane of the beam is 45 ° with respect to the polarization plane of the beam from the Ar ion laser (1). Recording layer (1
0). As described in the above section, the neutral axis of the birefringence of the recording portion formed on the recording layer (10) by the Ar ion laser (1) is formed parallel to the polarization plane of the ion laser (1). Therefore, such a semiconductor laser (1
When the linearly polarized beam from 1) is applied to the recording part of the recording layer (10), its plane of polarization will have an angle of 45 ° to the neutral axis.

When a linearly polarized beam is incident on a birefringent material such that the plane of polarization is at a predetermined angle (excluding 90 °) with respect to the neutral axis, the beam transmitted through this material is converted to an elliptically polarized beam. The birefringent material has the property of changing the phase of a component parallel to the neutral axis of a beam transmitted therethrough with respect to the phase of a component perpendicular to the neutral axis. The principle that the above-mentioned linearly polarized beam changes to an elliptically polarized beam is as follows.
It is based on such properties.

In the case of the present embodiment, when the linearly polarized beam from the semiconductor laser (11) is applied to the recording portion of the recording layer (10), its polarization plane has an angle of 45 ° with respect to the neutral axis. When transmitted through the recording layer (10), the polarization state of the beam is converted from linearly polarized light to elliptically polarized light. If the angle of the linearly polarized beam with respect to the neutral axis of the polarization plane is set to 45 ° in this way, the parallel component and the vertical component with respect to the neutral axis of the linearly polarized beam become equal. Can be the largest.

However, the beam transmitted through the recording layer (10) is incident on the polarizing beam splitter (15) via the converging lens (14), and the transmitted beam and the reflected beam are respectively transmitted to the sensor (16).
And (17). Here, the polarizing beam splitter (15) is arranged so as to completely transmit the linearly polarized light beam from the semiconductor laser (11) when the medium (9) is not present. For this reason, in the state of FIG.
When the beam is applied to an unrecorded portion (a portion having no birefringence) of the recording layer (10), the beam transmitted through the medium (9) does not change its polarization state. (15) is completely transmitted, so that only the sensor (16) produces an output. Meanwhile, the semiconductor laser (11)
Is irradiated on the recording portion of the recording layer (10), the beam transmitted through the medium (9) is converted into circularly polarized light as described above, and this beam is converted by the polarizing beam splitter (15). Partially reflected, in this case an output is produced at both sensors (16) and (17).

Therefore, when the objective lens (8) is displaced while the medium (9) is relatively moved and the track on the recording layer (10) is scanned with the beam from the semiconductor laser (11), the sensors (16) and (17) An output corresponding to the data on the track is generated, and the data on the track can be converted into an electric signal by comparing the outputs of the sensors (16) and (17).

An experiment of data recording and reproduction was performed using the optical system according to the present embodiment and the medium described above.
6) Changes were recorded in the output of (17) according to whether the data was recorded or not recorded. In this experiment, the laser power from the Ar ion laser (1) and the semiconductor laser (11) were set to 6 nw and 0.5 mw, respectively, and the beam from the Ar ion laser (1) was set to 10 μs
By irradiating the medium (9) in the form of a pulse to form a spot-shaped recording portion on the recording layer (10), this recording portion and other unrecorded portions are irradiated with a beam from the semiconductor laser (11). In this case, the outputs of the sensors (16) and (17) are compared.

As described above, according to the present embodiment, the Ar ion laser (1)
The medium (9) is controlled by controlling the Faraday rotation element (7) and the beam scanning mechanism (not shown) while selectively driving the semiconductor laser (11) according to recording and reproduction.
Can be recorded and reproduced. The semiconductor laser (11) used as a reproducing beam has a wavelength of 780 nm, and according to the characteristic diagram shown in FIG. 2, it is not absorbed at all by the photochromic material in the recording layer (10). The reproducing beam does not act on the photochromic material to change the molecular structure of the photochromic material. Therefore, at the time of reproducing, the reproducing beam may cause an undesired change in the recording layer (10). There is no.

It should be noted that the present invention is not limited to the above embodiment, and various other modifications are possible. For example, in the above embodiment, the polarization plane of the beam from the semiconductor laser (11) is changed to the recording layer (10) using the Faraday rotator (7) and the control circuit (13).
The recording portion above was inclined with respect to the neutral axis, but instead of disposing the Faraday rotator (7) and the control circuit (13), the arrangement of the semiconductor laser (11) was adjusted (the emission optical axis). May be set so that the polarization plane of the laser beam is inclined with respect to the neutral axis on the recording layer (10).

In the above embodiment, a linearly polarized beam is used as the reproducing beam, but a circularly polarized beam can be used instead. FIG. 4 shows the optical system in this case. In this embodiment, two λ / 4 plates (18) and (19) are arranged by omitting the Faraday rotator (7) and the control circuit (13), as compared with the embodiment shown in FIG. Is different.
The λ / 4 plate (18) is shifted out of the beam optical path during recording.

In the case of the present embodiment, the linearly polarized light beam from the semiconductor laser (11) is converted into a circularly polarized light beam by the λ / 4 plate (18), and then is incident on the recording layer (10) of the medium (9). At this time, when the beam is incident on the unrecorded portion of the recording layer (10), the beam does not change its polarization state due to transmission through the recording layer (10). Then, it is incident on the λ / 4 plate (19) and is converted again into a linearly polarized beam. Polarizing beam splitter (15)
Has been pre-positioned so as to completely transmit the linearly polarized beam thus converted. Therefore, when the beam is incident on the recording portion of the recording layer (10),
The beam from the medium (9) is incident only on the sensor (16) and an output appears only on the sensor (16).

On the other hand, when the beam is incident on the recording portion of the recording layer (10), while the beam passes through the recording portion, the polarization state is changed from circular polarization to elliptical polarization due to the birefringence of the recording portion. Therefore, in this case, even if the beam passes through the λ / 4 plate (19), it is not converted into linearly polarized light. Therefore, when the beam passes through the recording portion of the recording layer (10), a part of the beam is reflected by the polarizing beam splitter (15), and an output also appears on the sensor (17).

Thus, even when a circularly polarized beam is used as a reproducing beam as in the present embodiment, data can be read on the recording layer (10).

Furthermore, even when an elliptical polarized beam is used as the reproducing beam, the polarization state changes after transmitting through the recording portion. Therefore, by providing an appropriate means for detecting this change, the recording layer (10) Data can be read.

In the above embodiment, the medium is formed as a transmission type.
The recording / reproducing operation similar to that described above can be achieved by slightly changing the optical system of the reflection type.

Further, it goes without saying that various other changes such as the photochromic material and the wavelength of the laser beam are possible.

(G) Effects of the Invention According to the present invention, in a medium containing a photochromic material in a recording layer, information is recorded by introducing birefringence into the photochromic material, and the introduced birefringence is detected. Thus, it is possible to provide a completely new recording / reproducing method for reproducing information, and in this case, there is an effect that an undesired change of the recording layer due to the reproducing beam can be prevented. be able to.

[Brief description of the drawings]

1 are diagrams showing the composition of the photochromic material contained in the recording layer, FIG. 2 is a diagram showing the light absorption characteristics of this material, FIG. FIG. 4 is a diagram showing an optical system according to the first embodiment, and FIG. 4 is a diagram showing an optical system according to the second embodiment. (10) Recording layer, (1) Ar ion laser, (11)
…… Semiconductor laser, (15) …… Polarization beam splitter,
(16) (17) ... Sensor.

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

Claims (1)

(57) [Claims] A recording layer of an optical recording medium containing a photochromic material is irradiated with a recording linearly polarized beam having a wavelength that is absorbed by the photochromic material in an unrecorded state, and is dispersed in the recording layer. A recording step of recording information by causing a photochemical reaction to a molecule parallel to the beam polarization plane of the linearly polarized beam among the molecules to change the molecular structure, and having a small wavelength whose absorption by the recording layer is small, and The surface is irradiated with a linearly or circularly polarized reproducing beam having a predetermined angle with respect to the recording linearly polarized beam to receive a transmitted beam or a reflected beam of the reproducing beam from the optical recording medium. Reading the information recorded on the recording layer by detecting a change in the polarization state of the beam by reading the optical recording medium. Raw way.