JP2006228359A - Recording medium, information recording and reproducing apparatus, and information recording and reproducing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reproduce a signal with a high S/N ratio as compared with a conventional one. <P>SOLUTION: Information is recorded in a recording medium 2 by irradiating a desired storage region 13 with a laser beam to transfer the state of the desired recording region 13 into a second state. The power Pw of the laser beam during recording generates intense two-photon absorption in the recording region 13 and is large to the extent that photochromism from a first state to the second state is generated. Information is reproduced from the recording medium 2 by irradiating the recording region 13 with a laser beam having a wavelength λ and detecting the transmission beam intensity by a light receiving part 6. When the laser beam is made incident in the recording region 13 in the first state, a weak transmission beam is detected by the two-photon absorption of the laser beam. When the laser beam is made incident in the recording region 13 in the second state, an intense transmission beam is detected since the laser beam is not two-photon absorbed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a recording medium for recording information using light, an information recording / reproducing apparatus and an information recording / reproducing method for recording information on the recording medium.

  Various forms such as CD, DVD, and MO are known as recording media for recording information using light. In recent years, it has been required to store a larger amount of information such as video in a smaller area, and efforts have been made to increase the density of the recording area two-dimensionally or expand the recording area three-dimensionally on these recording media. Yes. However, the conventional method of recording information by forming pits such as CD and DVD has a limit in increasing the density, so a new method is required.

  Patent Document 1 uses a photorefractive material in which a refractive index is changed by an electric field due to a distribution of charges generated by spatially separating charges by irradiation of electromagnetic waves as a recording material of an optical recording disk. As a change, a method for recording information on an optical recording disk has been proposed.

  In Patent Document 1, information is reproduced by modulating reproduction light according to a change in the refractive index of the recording material. Therefore, even when the difference in refractive index is large, the transmittance is 0.1 or less and is on the order of 0.01. In addition, the amount of change in reflectance is reduced, and the modulation degree of the reproduction light cannot be increased.

JP 2000-228014 A

  An object of the present invention is to provide a recording medium, an information recording / reproducing apparatus, and an information recording / reproducing method capable of obtaining a modulation degree of reproducing light larger than that of the prior art.

  The first recording medium of the present invention includes a first state in which multiphoton absorption is dominant for light of a specific wavelength, and a second state in which the multiphoton absorption amount for light of a specific wavelength is smaller than the first state. A recording area is provided.

  In the second recording medium of the present invention, in the first recording medium, when the recording area is irradiated with light of a specific wavelength at a predetermined intensity, the first state may be changed to the second state. In the third recording medium of the present invention, the recording area may be formed of a photochromic material in the first or second recording medium. In the fourth recording medium of the present invention, in any one of the first to third recording media, the second state may be formed by holes. According to a fifth recording medium of the present invention, in any one of the first to fourth recording media, the recording area is formed smaller than the spot diameter of the light irradiated during reproduction, and the multiphoton absorption amount for light of a specific wavelength is small. It is better to be surrounded by a medium.

  According to a sixth recording medium of the present invention, in the first to fourth recording media, a recording layer including a recording area and a non-recording layer having a multiphoton absorption amount smaller than that of the recording area may be laminated. . According to a seventh recording medium of the present invention, in the sixth recording medium, the thickness of the recording layer is preferably made thinner than the thickness at which light during recording can form the second state in the vicinity of the spot. According to an eighth recording medium of the present invention, in the sixth recording medium, the difference between the refractive index of the recording layer and the refractive index of the non-recording layer may be reduced.

  According to a ninth recording medium of the present invention, in any of the sixth to eighth recording media, a land-shaped track may be provided. The tenth recording medium of the present invention is preferably provided with a groove-shaped track in any of the sixth to eighth recording media. According to an eleventh recording medium of the present invention, in any one of the sixth to tenth recording media, the recording medium may include a reflective layer on a side opposite to a direction in which the recording layer emits light. In a twelfth recording medium of the present invention, the reflective layer may be formed in a track shape in the eleventh recording medium.

  A first information recording / reproducing apparatus of the present invention comprises any one of the above recording media and a laser light source that irradiates the recording medium with a laser beam having a specific wavelength, and applies the laser beam to the recording medium while controlling a condensing position. Irradiation causes the recording area to transition from the first state to the second state to record information.

  A second information recording / reproducing apparatus of the present invention is emitted from the recording medium according to any one of claims 1 to 12, a laser light source for irradiating the recording medium with a laser beam having a specific wavelength, and the recording medium. A light receiving means for receiving light, irradiating the recording medium with laser light at a lower intensity than during recording while controlling the focusing position, and discriminating between the first state and the second state based on the intensity of the received light Thus, the information recorded on the recording medium is reproduced.

  According to a first information recording / reproducing method of the present invention, the recording area of the recording medium according to any one of the above is irradiated with a laser beam having a specific wavelength to change the recording area from the first state to the second state. Record.

  According to a second information recording / reproducing method of the present invention, the recording region of any one of the above recording media is irradiated with a laser beam having a specific wavelength at a lower intensity than that during recording, and the amount of absorption of the irradiated light at the specific wavelength is determined. The information recorded on the recording medium is reproduced while identifying the first state and the second state based on the difference in the amount of absorption.

  According to the recording medium, information recording / reproducing apparatus, and information recording / reproducing method of the present invention, information can be reproduced by detecting a difference in absorption due to multiphoton absorption in storage areas in different states. The signal can be reproduced with a higher S / N ratio.

  As shown in the block diagram of FIG. 1, the information recording / reproducing apparatus 1 of the first embodiment includes a recording medium 2, a spindle motor 3, a coarse movement mechanism 4, a head 5, a light receiving unit 6, a signal processing unit 7, and drive control. Unit 8, controller 9, and interface 10 are connected to host computer 11.

  As shown in the perspective view of FIG. 2 (a) and the a1-a2 cross-sectional view of FIG. 2 (b), the recording medium 2 has a three-dimensional regular recording area 13 in a base 12 of a disk-shaped optical disk. It has a structure dispersed in. The recording region 13 is a non-linear material that causes two-photon absorption corresponding to a wavelength 2λ when irradiated with a high-power laser beam 14 having a wavelength λ, and has different absorption spectra as shown in the graph of FIG. It is made of a material capable of transitioning between the first state and the second state. When the recording area 13 is in the first state, the one-photon absorption at the wavelength λ is small, while the absorption at the double wavelength 2λ is relatively large. When the recording area 13 is in the second state, the absorption is small at both the wavelength λ and the wavelength 2λ. When the recording region 13 in the first state is irradiated with laser light having a wavelength λ at a high output, two-photon absorption occurs and the state transitions to the second state. As a material constituting the recording region 13, a photochromic material such as fulgide or a diarylethene-based material, or a material in which a photochromic material is dispersed in a material such as PMMA can be used. The recording medium 2 is not limited to a disc shape, and may have a plate shape, a rectangular parallelepiped shape, or other various shapes.

  The spindle motor 3 rotates the recording medium 2. The coarse movement mechanism 4 moves the head 5 in the radial direction of the recording medium 2. The head 5 condenses the laser light having the wavelength λ emitted from the laser light source on the recording medium 2 while moving the beam waist by the objective lens that is slightly moved by the actuator. The light receiving unit 6 converts the light transmitted through the recording medium 2 into an electric signal by a photoelectric conversion element and outputs the electric signal. The signal processing unit 7 creates an error signal of the position of the head 5 and a read signal from the recording medium 2 based on the electric signal output from the light receiving unit 6, sends the error signal to the drive control unit 8, and reads the read signal. Is sent to the host computer 11 via the interface 10. The drive control unit 8 controls the spindle motor 3, the coarse movement mechanism 4, and the head 5 while performing fine adjustment based on the error signal, thereby emitting laser light at a desired position on the recording medium 2. Collect light. The controller 9 controls the operation of the entire information recording / reproducing apparatus 1 by controlling the signal processing unit 7 and the drive control unit 8 in accordance with a command from the host computer 11 connected via the interface 10.

  When recording information on the recording medium 2, all the recording areas 13 are formed in the first state in the initial state, the desired storage area 13 is irradiated with the laser beam, and the desired recording area 13 is set in the second state. This is done by making a transition. The power Pw of the laser beam at the time of recording is large enough to cause strong two-photon absorption in the recording area 13 and to generate photochromism from the first state to the second state.

  Information is reproduced from the recording medium 2 by irradiating the recording region 13 with a laser beam having a wavelength λ and detecting the transmitted light intensity by the light receiving unit 6. When laser light is incident on the recording area 13 in the first state, weak transmitted light is detected by two-photon absorption of the laser light. When laser light is incident on the recording area 13 in the second state, strong transmitted light is detected because the laser light is not absorbed by two photons. The power Pr of the laser beam during reproduction is large enough to cause two-photon absorption in the recording area 13 and smaller than the power Pw during recording to prevent the recording area 13 from being altered. For example, if the power Pr during reproduction is 1/3 to 1/4 or less of the power Pw during recording, two-photon absorption can be caused and the power absorbed in the recording area 13 during reproduction can be recorded. 1/9 to 1/16 of the quality can be prevented.

  The recording area 13 is not limited to two-photon absorption, and may be a material that changes state by multiphoton absorption. By using multiphoton absorption that absorbs more photons, the difference in power absorbed in the recording area 13 during recording and during reproduction can be further increased. The information recording / reproducing apparatus 1 may reproduce information by detecting reflected light.

  According to the information recording / reproducing apparatus 1 of the first embodiment, since the state of the recording region 13 is detected by the difference in the two-photon absorption amount with respect to the wavelength λ to be irradiated, the state is compared between the cases where a change in refractive index is used. The S / N ratio at the time of reproduction can be improved by increasing the difference in the amount of reflected light or transmitted light.

  As shown in the configuration diagram of FIG. 2, the information recording / reproducing apparatus 15 of the second embodiment includes a recording medium 16, a spindle motor 17, a coarse movement mechanism 18, a head 19, a light receiving unit 20, a signal processing unit 21, and drive control. A unit 22, a controller 23, and an interface 24 are provided, and are connected to a host computer 25.

As shown in the plan view of FIG. 5A and the b1-b2 cross-sectional view of FIG. 5B, the recording medium 16 has a three-dimensional regular recording area 27 in the base material 26 of the disk-shaped optical disk. It has a structure dispersed in. The recording area 27 transitions between the first state and the second state. In the first state, as shown in the graph of FIG. 6, while the absorption at the wavelength λ is weak, the recording region 27 is irradiated with high-power light with the wavelength λ. It is filled with a non-linear material that causes two-photon absorption corresponding to the wavelength 2λ, and in the second state, holes 28 are formed. As a material for filling the recording region 27, various dyes such as rhodamine B which is an organic material and absorbs at a specific wavelength, those dyes dispersed in an organic material such as PMMA, PC, SiO ₂ , Al ₂ O _{3 and} others Crystals of various inorganic materials, those in which metal ions are dispersed in various glass materials, and the like can be used.

  The spindle motor 17 drives the recording medium 16 to rotate. The coarse movement mechanism 18 moves the head 19 in the radial direction of the recording medium 16. The head 19 condenses the laser light having the wavelength λ emitted from the laser light source on the recording medium 16 while moving the beam waist by the objective lens that is slightly moved by the actuator. The light receiving unit 20 receives the light reflected by the recording medium 16 and separated by the splitter of the head, converts the light into an electric signal by the photoelectric conversion element, and outputs it. The signal processing unit 21 creates an error signal of the position of the head 19 and a read signal from the recording medium 16 based on the electrical signal output from the light receiving unit 20, sends the error signal to the drive control unit 22, and reads the read signal. Is sent to the host computer 25 via the interface 24. The drive control unit 22 controls the spindle motor 17, the coarse movement mechanism 18, and the head 19 while performing fine adjustment based on the error signal, so that the laser beam is emitted at a desired position on the recording medium 16 with a desired intensity. Collect light. The controller 23 controls the overall operation of the information recording / reproducing apparatus 15 by controlling the signal processing unit 21 and the drive control unit 22 in accordance with a command from the host computer 25 connected via the interface 24.

  When recording information on the recording medium 16, all the recording areas 27 are formed in the first state in the initial state, and the desired recording area 27 is irradiated with a high-power laser beam 29 to absorb heat by two-photon absorption. This is done by evaporating the nonlinear material by the action to form the holes 28. The information recording / reproducing apparatus 15 may record information on the recording medium 16 by reducing the multiphoton absorption rate of the recording area 27 by oxidation or the like.

  Information is reproduced from the recording medium 16 by irradiating the recording region 27 with laser light having a wavelength λ and detecting the reflected light intensity by the light receiving unit 20. When laser light is incident on the filled recording area 27 in the first state, weak reflected light is detected by two-photon absorption of the laser light. When laser light is incident on the recording area 27 in the second state with holes formed, strong reflected light is detected because the laser light is not absorbed by two photons. Furthermore, strong reflected light is detected due to the large difference in refractive index between the holes in the second state and the surrounding base material 26. The power Pr of the laser beam during reproduction is large enough to cause two-photon absorption in the recording area 27 and smaller than the power Pw during recording so as to prevent the recording area 27 from being altered.

  According to the information recording / reproducing apparatus 2 of the second embodiment, since the state of the recording area 27 is detected based on the presence or absence of two-photon absorption with respect to the wavelength λ to be irradiated, the state between the two states is smaller than when using a change in refractive index. The difference in the amount of reflected light and transmitted light can be increased to improve the S / N ratio during reproduction, and the refractive index difference between the recording area 27 in which holes are formed and the substrate 26 is large. The S / N ratio during reproduction can be further improved.

  The recording region 27 is not limited to two-photon absorption, and may be a material that changes state by multiphoton absorption. By using multi-photon absorption that absorbs more photons, the difference in power absorbed in the recording area 27 during recording and during reproduction can be further increased.

  The information recording / reproducing apparatus of the third embodiment is similar to the information recording / reproducing apparatus 1 of the first embodiment. The recording medium 16, spindle motor 17, coarse movement mechanism 18, head 19, light receiving unit 20, and signal processing unit 21 are the same. A drive control unit 22, a controller 23, and an interface 24, and a recording medium 30 that is different from the recording medium 16 of the first embodiment.

  As shown in the plan view of FIG. 7A and the c1-c2 cross-sectional view of FIG. 7B, the recording medium 30 has a disk shape in which recording layers 31 and non-recording layers 32 are alternately stacked in the thickness direction. It is formed as an optical disc. The recording layer 31 has a structure in which the recording areas 33 are two-dimensionally dispersed at predetermined intervals, and is formed by overlapping the recording areas 33 of the respective layers. The recording area 33 is formed of the same material as that of the recording area 13 of the first embodiment. The non-recording layer 32 is formed of a nonlinear material having a small two-photon absorption corresponding to the wavelength 2λ.

  The recording medium 30 is formed by, for example, pressure-bonding two kinds of film-like materials of the recording layer 31 and the non-recording layer 32, by applying two kinds of materials, or by sputtering, vapor deposition, or other methods. Overlapped. The refractive index difference between the recording layer 31 and the non-recording layer 32 is small.

  As shown in the schematic enlarged view in the thickness direction of the recording region 33 in FIG. 8A, when the laser beam 34 is condensed on the recording layer 31 formed to be sufficiently thick, the thickness d1 near the spot is When the second state is formed in the region 35, it is preferable to form the actual thickness d2 of the recording layer 31 smaller than d1 as shown in FIG. 8B. By forming the thickness d2 of the recording layer 31 thinner than d1, it is possible to reduce the area unrelated to the state change and increase the recording density in the thickness direction of the recording medium 30.

  The information recording / reproducing method for the recording medium 30 is the same as in the first embodiment. Note that the recording region 33 is not limited to two-photon absorption but may be a material that changes state by multiphoton absorption. By using multiphoton absorption that absorbs more photons, the difference in power absorbed in the recording area 33 during recording and during reproduction can be further increased. Note that the information recording / reproducing apparatus of the third embodiment may reproduce information by detecting reflected light. The information recording / reproducing apparatus of the third embodiment may form holes as in the second embodiment.

  According to the information recording / reproducing apparatus of the third embodiment, since the state of the recording region 33 is detected by the difference in the two-photon absorption amount with respect to the wavelength λ to be irradiated, the state between the two states is compared with the case where the refractive index change is used. The S / N ratio at the time of reproduction can be improved by increasing the light amount difference between the reflected light and the transmitted light, and by disposing a material having a small two-photon absorption near the recording layer 31, Only two-photon absorption can be detected with a high S / N ratio.

  Further, by reducing the difference in refractive index between the recording layer 31 and the non-recording layer 32, reflection between the layers can be suppressed, and reflected light or transmitted light can be reduced at a high S / N ratio by reducing stray light especially during reproduction. Can be detected.

  The information recording / reproducing apparatus of the fourth embodiment is similar to the information recording / reproducing apparatus 1 of the first embodiment. The recording medium 16, spindle motor 17, coarse movement mechanism 18, head 19, light receiving unit 20, and signal processing unit 21 are the same. A drive control unit 22, a controller 23, and an interface 24, and a recording medium 40 different from the recording medium 16 of the first embodiment.

  As shown in the plan view of FIG. 9 (a) and the e1-e2 cross-sectional view of FIG. 9 (b), the recording medium 40 has a three-dimensional regular recording area 42 in a base 41 of a disk-shaped optical disc. It has a structure dispersed in. The size of the recording area 42 is formed to be smaller than the beam spot diameter of the laser beam 43 collected during recording / reproduction. The recording area 42 is formed of the same material as the recording area 13 of the first embodiment.

  The recording medium 40 is formed by dispersing particles in the recording area 42 in the base material 41, forming the recording area 42 from the base material 41 by phase separation, and laminating the base material 41 and the recording area 42 in layers. It is created by a method of patterning by etching or the like while forming the film.

  The information recording / reproducing method for the recording medium 40 is the same as in the first embodiment. Note that the recording region 42 is not limited to two-photon absorption but may be a material that changes state by multiphoton absorption. By using multiphoton absorption that absorbs more photons, the difference in power absorbed in the recording area 42 during recording and during reproduction can be further increased. Note that the information recording / reproducing apparatus of the fourth embodiment may reproduce information by detecting reflected light. The information recording / reproducing apparatus of the fourth embodiment may form holes as in the second embodiment.

  According to the information recording / reproducing apparatus of the fourth embodiment, since the state of the recording area 42 is detected by the difference in the two-photon absorption amount with respect to the wavelength λ to be irradiated, the state between the two states is compared with the case where the refractive index change is used. The difference in the amount of reflected light and transmitted light can be increased to improve the S / N ratio during reproduction, and the recording area 42 can be reduced to increase the recording density.

  The information recording / reproducing apparatus according to the fifth embodiment is the same as the information recording / reproducing apparatus according to the third embodiment, except that a land-shaped or groove-shaped track 50 as shown in the perspective sectional view of FIG. Is provided. By recording while changing the state of the recording area 33 along the land or groove of the track 50, the land or groove is also formed in the recording area 33. Therefore, tracking servo can be performed by a push-pull method or the like. Signal recording and reproduction can be performed more stably.

  The information recording / reproducing apparatus according to the sixth embodiment is the same as the information recording / reproducing apparatus according to the third embodiment except that it is superimposed on the recording layer 31 of the recording medium 30 as shown in the perspective sectional view of FIG. The rate of reflection layer 60 is provided. By providing the reflective layer 60, the reflected light increases, the intensity of the return light at the time of signal detection can be increased, the S / N ratio can be improved, and the reflected servo is controlled to easily perform the focus servo. be able to.

It is a block diagram of the information recording / reproducing apparatus of 1st Embodiment. 1A and 1B are a perspective view and a cross-sectional view of a recording medium according to a first embodiment. It is an absorption spectrum of the recording area of the first embodiment. It is a block diagram of the information recording / reproducing apparatus of 2nd Embodiment. It is the perspective view and sectional drawing of the recording medium of 2nd Embodiment. It is an absorption spectrum of the recording area of the second embodiment. It is the perspective view and sectional drawing of the recording medium of 3rd Embodiment. It is a cross-sectional enlarged view of a recording area of the third embodiment. It is the perspective view and sectional drawing of the recording medium of 4th Embodiment. It is a perspective sectional view of a recording layer of a recording medium of a 5th embodiment. It is a perspective sectional view of a recording layer and a reflective layer of a recording medium of a 6th embodiment.

Explanation of symbols

1; information recording / reproducing apparatus, 2; recording medium, 3; spindle motor, 4; coarse movement mechanism,
5; head, 6; light receiving unit, 7; signal processing unit, 8; drive control unit, 9; controller,
10; interface, 11; host computer, 12; substrate, 13; recording area,
14; laser beam, 15; information recording / reproducing apparatus, 16; recording medium, 17; spindle motor,
18; Coarse movement mechanism, 19; Head, 20; Light receiving unit, 21; Signal processing unit,
22; drive control unit, 23; controller, 24; interface,
25; Host computer, 26; Base material, 27; Recording area, 28;
29; laser beam, 30; recording medium, 31; recording layer, 32; non-recording layer, 33;
34; laser beam, 35; area, 40; recording medium, 41; substrate, 42; recording area,
43; Laser light, 50; Track, 60; Reflective layer.

Claims (16)

  A recording medium comprising a recording region that takes a first state in which multiphoton absorption is dominant for light of a specific wavelength and a second state in which the amount of multiphoton absorption for light of the specific wavelength is smaller than the first state .   The recording medium according to claim 1, wherein the recording area transitions from the first state to the second state when irradiated with light of the specific wavelength at a predetermined intensity.   The recording medium according to claim 1, wherein the recording area is formed of a photochromic material.   The recording medium according to claim 1, wherein the second state is formed of holes.   5. The recording area according to claim 1, wherein the recording area is formed smaller than a spot diameter of light irradiated during reproduction, and is surrounded by a medium having a small amount of multiphoton absorption with respect to the light of the specific wavelength. The recording medium described.   The recording medium according to any one of claims 1 to 4, wherein a recording layer including the recording area and a non-recording layer having a multiphoton absorption amount smaller than that of the recording area are stacked.   The recording medium according to claim 6, wherein a thickness of the recording layer is thinner than a thickness at which light during recording can form the second state in the vicinity of the spot.   The recording medium according to claim 6, wherein a difference between a refractive index of the recording layer and a refractive index of the non-recording layer is small.   The recording medium according to claim 6, comprising a land-shaped track.   The recording medium according to claim 6, comprising a groove-shaped track. The recording medium according to claim 6, wherein the recording medium includes a reflective layer on a side opposite to a direction in which the recording layer is irradiated with light.   The recording medium according to claim 11, wherein the reflective layer is formed in a track shape. A recording medium according to any one of claims 1 to 12,
A laser light source for irradiating the recording medium with laser light of the specific wavelength;
An information recording / reproducing apparatus for recording information by changing the recording area from the first state to the second state by irradiating the recording medium with the laser beam while controlling a condensing position. A recording medium according to any one of claims 1 to 12,
A laser light source for irradiating the recording medium with laser light of the specific wavelength;
A light receiving means for receiving light emitted from the recording medium,
The recording medium is irradiated with the laser beam with a weaker intensity than that during recording while controlling the condensing position, and the first state and the second state are identified based on the intensity of the received light, and the recording medium is applied to the recording medium. An information recording / reproducing apparatus for reproducing recorded information.   13. The information on the recording area is changed from the first state to the second state by irradiating the recording area of the recording medium according to claim 1 with the laser beam having the specific wavelength. An information recording / reproducing method comprising: Irradiating the recording area of the recording medium according to any one of claims 1 to 12 with a laser beam having the specific wavelength at a weaker intensity than that during recording,
Detect the amount of absorption of the irradiated light at the specific wavelength,
An information recording / reproducing method for reproducing information recorded on the recording medium while discriminating between the first state and the second state based on the difference in the amount of absorption.

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