JP4498056B2 - Optical information recording medium and optical information recording / reproducing method - Google Patents

Description

  The present invention relates to an optical recording medium and an optical storage device using an optical signal recording / reproducing system, and is applied to an information processing device, an optical file system, and a storage device of a video system.

In Patent Document 1, in a conventional optical recording medium, a multi-layer optical recording layer having a different light absorption region and causing an optical nonlinear reaction upon irradiation with recording light is laminated by exceeding the number of types of materials. In addition, since the optical recording layers containing the same kind of material are laminated so that the distance between the layers is larger than the focal depth of the recording light beam spot, the crosstalk between the same recording materials is made sufficiently low. It is described that multiple recording exceeding the number of types of materials can be performed.
However, in this prior art, as shown in FIG. 1, a plurality of optical recording layers 11, 12, and 13 made of different photochromic materials that have different light absorption regions and respond nonlinearly to absorbed light irradiation are stacked. Configured. In such an optical recording medium having a multilayer structure, the difference in reflectivity between layers necessary for applying focusing servo is small, and it is difficult to stably apply focus servo at the interface of each layer. In order to increase the difference in reflectance between the layers, the difference in refractive index between the layers must be increased. However, in the case of photochromic dyes, it is generally difficult to increase the difference in refractive index.

Japanese Patent Laid-Open No. 7-114747

An object of the present invention is to propose an optical recording on an optical recording medium having a multilayer structure using a recording material such as a photochromic material, the method which can be stably applied to the focus servo.

The said subject is solved by (1)-(8) of this invention.
(1) “A recording medium for optical recording comprising an optical recording layer formed using a material exhibiting photochromic characteristics and two fluorescent materials having different absorption wavelengths .”
( 2 ) "The optical recording layer according to item (1), wherein the optical recording layer has a stripe structure having a portion including the material exhibiting the photochromic property and a portion including a fluorescent material." Recording media. "
(3) “The optical recording layer according to the item (1) or (2), wherein the optical recording layer has a multilayer structure in which two layers of an intermediate layer made of a transparent material are repeated. Recording media. "
(4) “ The optical recording medium according to item (3), wherein a reflective layer is provided below the multilayer structure. ”
(5) “ Light is irradiated to an optical recording medium having an optical recording layer formed using a material exhibiting photochromic properties and two types of fluorescent materials having different absorption wavelengths, and the photochromic in the optical recording layer A signal is recorded by a change in the material due to light absorption generated in the material portion, a signal is detected by a change in transmitted light due to the change in the material, and fluorescence generated from one of the two types of fluorescent materials having different absorption wavelengths by light irradiation. Detecting and obtaining a focusing signal, irradiating light having a wavelength different from the wavelength of the light to be recorded, erasing the recording signal of the photochromic material, and absorbing the light having the wavelength to be erased from the other fluorescent material emitted An optical signal recording / reproducing system characterized by detecting a generated fluorescence to obtain a focusing signal. "
(6) "the optical recording layer 2 minutes in a portion and a portion of the fluorescent material of the photochromic material track portion was formed at a portion of the fluorescent material, the second (5), characterized in that the obtaining a tracking signal The optical signal recording / reproducing system described. "
(7) “The recording medium for optical recording is composed of a multilayer structure in which two layers of the optical recording layer and an intermediate layer made of a transparent material are repeated, and a reflective layer provided below the multilayer structure, wherein the item (5) or the (6) an optical signal recording and reproducing method according to claim, characterized in that for detecting the reflected return light from the reflective layer. "
(8) The optical signal recording / reproducing system according to any one of ( 5 ) to (8), wherein two-photon recording is performed using a high-power pulse laser as a recording light source.

An optical recording medium comprising an optical recording layer formed using a material exhibiting photochromic properties and a fluorescent material of the present invention is an optical recording for recording and reproducing signals with light in the photochromic material . by detecting fluorescence, is possible to obtain a focusing signal, or a reflective layer of high refractive index between the optical recording layer and the intermediate layer, in order to increase its reflectivity of the two different layers, the recording layer and the intermediate There is an excellent effect that the reflectance between the optical recording layer and the intermediate layer can be lowered without requiring measures such as increasing the refractive index difference of the layers.
In the optical signal recording / reproducing system of the present invention, a layer structure composed of two layers of an optical recording layer containing a material exhibiting photochromic properties and a fluorescent material and an intermediate layer made of a transparent material overlaps each other. In the optical recording method for recording and reproducing a signal to and from a photochromic material with respect to the optical recording medium configured as described above, fluorescence is detected and a focusing signal is obtained. In order to provide a reflective layer having a high refractive index between them or to increase the reflectance between two different layers, there is no need for a method such as increasing the refractive index difference between the recording layer and the intermediate layer. The reflectance can be lowered. Therefore, stray light and flare can be reduced. For this reason, the stability of servo control and signal detection can be enhanced in a multilayer configuration.
In addition to the above structure, the optical recording layer includes two types of fluorescent dyes having different absorption wavelengths, and a focus servo can be applied during erasing. For this reason, in addition to the above-described effects, a servo can be applied at the time of erasing, and a local signal can be erased.
Further, the contents include that the optical recording layer is divided into a photochromic material and a fluorescent dye portion to form a track portion at the fluorescent material portion to obtain a tracking signal. For this reason, in addition to the above-described effects, a tracking of the fluorescent dye can be formed on the recording layer, and a tracking error signal can be obtained from the fluorescence, thus enabling tracking servo.
Furthermore, a reflective layer is provided on the bottom layer of an optical recording medium having a multilayer structure composed of two layers of an optical recording layer containing a material exhibiting photochromic properties and a fluorescent material, and an intermediate layer made of a transparent material. , Including detecting reflected return light. For this reason, since it is possible to reduce stray light and flare while detecting reflected return light, the configuration of the optical system can be made compact.
In addition, two-photon recording is performed using a high-power pulse laser as a recording light source. For this reason, in addition to the effects described above, since absorption in the recording layer can be reduced, there is also an effect that it can be applied even if the number of layers constituting the optical recording medium is increased.

The present invention is described in detail below.
Example 1
A first embodiment of the present invention will be described with reference to FIGS.
FIG. 2 shows the configuration of the optical recording medium of the present invention. An optical recording layer (3) containing a photochromic material and a fluorescent material is formed on the intermediate layer (2). Further, an intermediate layer (2) is formed thereon again, and thereafter, this is repeated to form a multilayer optical recording medium (8). Such an optical recording medium (8) is irradiated with the light beam (1) in the configuration shown in FIG. 4 to record and reproduce information.

  In FIG. 4, the light from the light source (4) is condensed by the condenser lens (5), passes through the dichroic mirror (6), and is condensed on the optical recording medium (8) by the objective lens (7). Here, the wavelength of the light source (4) is selected in accordance with the absorption spectrum of the state A out of the two states A and B of the absorption spectrum of the photochromic material shown in FIG. Next, when the optical recording layer (3) in the optical recording medium (8) is irradiated with the light beam from the light source (4), the structure of the photochromic material changes, and the absorption spectrum is in the state of A in FIG. Changes to the B state. This change corresponds to signal recording.

  Further, in FIG. 3, C represents the absorption spectrum of the fluorescent material, and C ′ represents the emission spectrum of fluorescence when the fluorescent material is excited at the absorption wavelength of the absorption spectrum. Here, it is necessary to select a material whose absorption spectrum of the fluorescent material substantially overlaps with the absorption spectrum of the state A of the photochromic material.

  Next, the light from the light source (4) is absorbed from the fluorescent material that has absorbed the light from the light source (4), converted into fluorescence, and emitted in the optical recording layer (3). This fluorescence passes through the objective lens (7) and the dichroic mirror (6), passes through the condenser lens (12) and the cylindrical lens (13), and is collected on the quadrant photodetector (14). Here, astigmatism is generated by the cylindrical lens (13), and a focus error signal can be obtained by taking a differential signal of each photodetector of the quadrant photodetector (14). Using this, it is possible to apply a focus servo. Here, the dichroic mirror (6) needs to set the separation wavelength of transmission and reflection to be between wavelengths λ1 and λ1 ′ corresponding to the peak wavelengths of C and C ′ in FIG.

  Next, a signal reproduction method will be described. As a result of signal recording, the absorption spectrum of the photochromic material is changed from the state A to a partially different state B. At the time of signal reproduction, light from the light source (4) is irradiated in the optical recording layer (3) in the same manner as at the time of signal recording. The light beam that has passed through the optical recording layer (3) emerges from the opposite surface of the optical recording medium (8), is focused by the condensing lens (9), passes through the filter (10), and the photodetector (11). It reaches the top and is detected electrically. The filter (10) needs to be configured to transmit the light of wavelength λ1 and cut the light of wavelength λ1 '.

  At this time, it is necessary to irradiate with light power much smaller than that at the time of signal recording. In the optical system shown in FIG. 4, when the light from the light source (4) is condensed on an optical recording layer (3) in the optical recording medium (8) and transmitted therethrough, the signal is recorded. 3 is in the state B of FIG. 3, the absorption is relatively small with respect to the light of the wavelength of the light source (4), and the transmitted light has a small attenuation. On the other hand, when the signal passes through an unrecorded place, the state A in FIG. 3 is obtained, and the absorption of the light of the wavelength of the light source (4) is relatively large and the attenuation of the transmitted light is large. Therefore, the signal can be detected by monitoring the output of the photodetector (11). Even during the signal reproduction, by detecting the fluorescence, the focus error signal can be detected as in the signal recording, and the focus servo can be applied.

Next, the configuration of the optical recording medium (8) in FIG. 2 will be described.
The intermediate layer (2) is made of a material transparent to the wavelength of the light source (4). An inorganic material such as PMMA, polycarbonate, or glass that is an organic material is also applicable. For the optical recording layer (3), diarylethene dyes, fulgide dyes, and the like are applicable as photochromic materials.

  As the fluorescent material, stilbene dyes, quinolone dyes, AF-50, and the like are applicable. The photochromic material and the fluorescent material can be manufactured by dispersing in an organic material such as PMMA or PVB. In the case of these material systems, the light source (4) needs to have a wavelength between blue and green. Blue LD, LED and other light sources are applicable.

(Example 2)
FIG. 5 shows another configuration of the optical recording medium (8) of the present invention. In this example, the optical recording layer of the optical recording medium (8) of Example 1 contains a part containing a photochromic material and a fluorescent material instead of the optical recording layer (3) containing a photochromic material and a fluorescent material. The optical recording layer (3) is used which is divided into the parts described above. Furthermore, the part containing the fluorescent material and the part containing the photochromic material are formed in a track shape and an annular shape.

  For such an optical recording medium (8), the optical system shown in FIG. 4 is used, and the entire optical system or only the objective lens is periodically oscillated in a direction crossing the track, so that the fluorescence for the period is obtained. Thus, a tracking error signal can be obtained. Here, with respect to the method of forming the portion containing the fluorescent material and the portion containing the photochromic material in a track shape and an annular shape, a layer containing the photochromic material and the fluorescent material is first formed, and a pattern by photolithography and etching is formed. It is conceivable to remove a part of the layer containing the fluorescent material by etching, removal with an electron beam, an ion beam or the like, etching, etc., and to form a layer containing only the photochromic material thereon. Furthermore, the convex portion can be removed by etching or the like. Other configurations and operations are the same as those in the first embodiment.

(Example 3)
A third embodiment of the present invention will be described with reference to FIGS. This example has almost the same configuration as Examples 1 and 2, but the optical recording layer (3) containing the photochromic material and the fluorescent material in FIG. 2 contains two types of fluorescent materials having different absorption wavelengths. Is different.

  Here, regarding the two types of fluorescent materials, as shown in FIG. 3, the wavelength λ2 obtained by combining the absorption spectrum with the absorption spectrum of the photochromic material in the state A and the state B is absorbed, and fluorescence with the wavelength λ2 ′ is generated. It is necessary to select the material. In this embodiment, when a diarylethene dye is applied to the photochromic material, two kinds of fluorescent materials are combinations of, for example, a stilbene dye, a quinolone dye, AF-50, a coumarin dye, a xanthene dye, and rhodamine B. Etc. are considered.

  In such a configuration of the optical recording medium (8), not only signal recording and reading but also a separate light source corresponding to the absorption spectrum of the state B is prepared and applied to the optical system configured as shown in FIG. Can do. When the light from the light source is irradiated onto the recording layer (3) of the optical recording medium (8), the state changes from the state B where the photochromic material is signal-recorded. As a result, the recording signal can be erased. Furthermore, fluorescence is emitted also to the light source having the wavelength to be erased. Since this fluorescence has a wavelength different from that of the fluorescence generated during recording, the dichroic mirror (6), the filter (10), etc. need to correspond to the wavelengths λ2 and λ2 'in FIG. Other configurations and operations are the same as those in the first and second embodiments.

Example 4
A fourth embodiment of the present invention will be described with reference to FIGS. 2, 3, 5, and 6. FIG. In the present embodiment, optical recording media containing a photochromic material and a fluorescent material on the intermediate layer (2) in the optical recording medium (8) shown in FIGS. Layer (3) is formed. Further, the intermediate layer (2) is again formed thereon, and thereafter, this is repeated to form a multilayer optical recording medium (8). However, the difference is that a reflective layer is provided under the lowest layer of the optical recording layer (3) and the intermediate layer (2) consisting of repetitions of the optical recording medium (8). Therefore, in FIG. 2 and FIG. 5, the light beam (1) is shown to be transmitted, but in this embodiment, the light beam (1) is reflected by the reflecting layer to the incident side of the optical recording medium (8). And then come back.

  FIG. 6 shows the configuration of an optical system applied to such an optical recording medium (8). In FIG. 6, the light from the light source (4) is collected by the condenser lens (5), passes through the polarization beam splitter (15) and the quarter-wave plate (10), passes through the dichroic mirror (6), and enters the objective. The light is condensed on the optical recording medium (8) by the lens (7). Here, the wavelength of the light source (4) is selected in accordance with the absorption spectrum of the state A out of the two absorption spectra of the absorption spectrum of the photochromic material shown in FIG. To do.

  Next, when the optical recording layer (3) in the optical recording medium (8) is irradiated with the light beam from the light source (4), the structure of the photochromic material changes, and the absorption spectrum is in the state of A in FIG. Changes to the B state. This change corresponds to signal recording. Further, in FIG. 3, C represents the absorption spectrum of the fluorescent material, and C ′ represents the emission spectrum of fluorescence when the fluorescent material is excited at the absorption wavelength of the absorption spectrum. Here, it is necessary to select a material whose absorption spectrum of the fluorescent material substantially overlaps with the absorption spectrum of the state A of the photochromic material.

  Next, the light from the light source (4) is absorbed from the fluorescent material that has absorbed the light from the light source (4), converted into fluorescence, and emitted in the optical recording layer (3). This fluorescence passes through the objective lens (7) and the dichroic mirror (6), passes through the condenser lens (12) and the cylindrical lens (13), and is collected on the quadrant photodetector (14). Here, astigmatism is generated by the cylindrical lens (13), and a focus error signal can be obtained by taking a differential signal of each photodetector of the quadrant photodetector (14). Here, the dichroic mirror (6) needs to set the transmission and reflection separation wavelengths to be between wavelengths λ1 and λ1 ′ corresponding to the peak wavelengths of C and C ′ in FIG.

  Next, a signal reproduction method will be described. As a result of signal recording, the absorption spectrum of the photochromic material is changed from the state A to a partially different state B. At the time of signal reproduction, the light from the light source (4) is irradiated to the optical recording layer (3) in the same procedure as at the time of signal recording, and the reflected return light of the transmitted light by the reflection layer in the optical recording medium (8). Are separated from the polarization beam splitter (15), converged by the condenser lens (9), and measured by the photodetector (11). These points are different from the previous embodiments. Other configurations and operations are the same as those in the first, second, and third embodiments.

(Example 5)
A fifth embodiment of the present invention will be described with reference to FIGS. The present embodiment has substantially the same configuration as each of the first to fourth embodiments described above, except that the light source (4) is not a normal light source but a high-power pulse light source (4). This makes it possible to perform signal recording with two photons on the optical recording layer (3) in the optical recording medium (8). Since two-photon recording corresponds to normal one-photon recording at a half wavelength of the recording wavelength, only the light source (4) can be used as a high-power pulse light source without changing other configurations. . Other configurations and operations are the same as those of the first to fourth embodiments.

It is sectional drawing which shows the conventional optical recording medium. 1 shows an example of the configuration of an optical recording medium of the present invention. The absorption spectrum of the fluorescent material represents the emission spectrum of fluorescence when the fluorescent material is excited at the absorption wavelength of the absorption spectrum. 1 shows an example of the configuration of an optical system applied to the optical recording medium of the present invention. 4 shows another configuration of the optical recording medium of the present invention. 2 shows another configuration of an optical system applied to the optical recording medium of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light beam 2 Intermediate | middle layer 3 Optical recording layer 4 Pulse light source 5 Condensing lens 6 Dichroic mirror 7 Objective lens 8 Optical recording medium 9 Condensing lens 10 1/4 wavelength plate 11 Photodetector 12 Condensing lens 13 Cylindrical lens 14 4 Split photodetector 15 Polarizing beam splitter

Claims (8)

An optical recording medium comprising an optical recording layer formed using a material exhibiting photochromic characteristics and two types of fluorescent materials having different absorption wavelengths . 2. The optical recording recording medium according to claim 1, wherein the optical recording layer has a stripe structure having a portion including a material exhibiting the photochromic characteristics and a portion including a fluorescent material. 3. The optical recording recording medium according to claim 1, wherein the optical recording layer has a multilayer structure in which two layers of an intermediate layer made of a transparent material are repeated. The optical recording medium according to claim 3, wherein a reflective layer is provided below the multilayer structure. Light is irradiated to a recording medium for optical recording having an optical recording layer formed using a material exhibiting photochromic properties and two types of fluorescent materials having different absorption wavelengths, and is generated at the photochromic material portion in the optical recording layer A signal is recorded by a change in the material due to light absorption, a signal is detected by a change in the transmitted light due to the change in the material, and a fluorescence generated from one of the two types of fluorescent materials having different absorption wavelengths is detected by the light irradiation to focus. While obtaining a signal, irradiating light of a wavelength different from the wavelength of the recording light, erasing the recording signal of the photochromic material, and detecting the fluorescence generated from the other fluorescent material emitted by absorbing the light of the erasing wavelength And a focusing signal to obtain an optical signal recording and reproducing system. 6. The optical signal recording / reproducing system according to claim 5 , wherein the optical recording layer is divided into a photochromic material portion and a fluorescent material portion, and a track portion is formed by the fluorescent material portion to obtain a tracking signal. . The recording medium for optical recording includes a multilayer structure in which two layers of the optical recording layer and an intermediate layer made of a transparent material are repeated, and a reflective layer provided below the multilayer structure. 7. The optical signal recording / reproducing system according to claim 5 or 6 , wherein the reflected return light is detected. 8. The optical signal recording / reproducing system according to claim 5, wherein two-photon recording is performed using a high-power pulse laser as a recording light source.

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