JP2006236570A - Optical recording reproducing method and optical recording reproducing device and optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical recording reproducing method and an optical recording reproducing device and an optical recording medium in which the recording surface of an optical disk is efficiently irradiated with an optical beam small in the diameter of a beam spot. <P>SOLUTION: The device is equipped with an objective lens 4 for condensing light flux from a light source on an optical disk 20, and a hemispherical lens 5 arranged so that it has a flat surface on the side for an optical coupling layer 1. If a refractive index of the hemispherical lens 5 is N1, a radius is r, the refractive index of the optical coupling layer 1 is N2, a thickness is d, a distance D from the apex of the hemisphere face of the hemispherical lens 5 to the flat surface is D=r-d×N1/N2. Light outgoing from the objective lens 4 is obliquely injected on the surface of the hemispherical lens 5. The signal recording surface of the optical disk 20 is irradiated with the light flux by introducing the light flux in the optical coupling layer 1 from the objective lens 4 and the hemispherical lens 5 in a state that the propagating direction of the light flux from the light source at the edge of the outgoing light in the objective lens 4 and the hemispherical lens 5 is approximately maintained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical recording / reproducing method, an optical recording / reproducing apparatus, and an optical recording medium for condensing light from a light source on a signal recording surface of an optical recording medium such as an optical disk.

  Optical discs, magneto-optical discs, and the like are used as computer recording devices and package media for music and image information. In these optical recording / reproducing apparatuses, a light beam emitted from a light source is condensed by an objective lens and irradiated onto a recording surface (hereinafter referred to as Conventional Example 1).

  In such an optical recording / reproducing apparatus, in recent years, a higher density is required. As one method for increasing the density, it is conceivable to reduce the diameter of the light spot irradiated on the optical recording medium surface.

  This is because when the spot diameter is reduced, when an information signal is reproduced from an optical recording medium in which the information signal is recorded with a minute mark at a high density, mixing of signals from marks other than the mark to be reproduced (so-called crosstalk) occurs. This is because even a small recording mark can be correctly reproduced, and even when an information signal is recorded on a recording medium, a minute mark can be accurately placed without affecting adjacent marks. This is because it can be recorded.

  By the way, the spot diameter of the light beam is proportional to λ / NA, where λ is the wavelength and NA is the numerical aperture. Therefore, in order to reduce the spot diameter of the light beam, the numerical aperture of the objective lens that focuses the light beam on the recording medium surface may be increased. However, the numerical aperture of the objective lens is limited (specifically, about 0.6) due to the difficulty in manufacturing the objective lens.

  Accordingly, it has been proposed to reduce the spot diameter by using a lens complex (referred to as an objective lens complex) as the objective lens. The objective lens composite will be specifically described with reference to FIG. In FIG. 5, 200 is an objective lens (numerical aperture NA), and 201 is a hemispherical lens (refractive index N). A parallel light beam P <b> 1 is incident on the objective lens 200. Further, the hemispherical lens 201 has a spherical incident surface facing the objective lens 200, and is arranged so that the light beam P2 whose beam diameter is reduced by the objective lens 200 is incident on the incident surface perpendicularly. Has been. The opposite surface of the hemispherical lens 201 is a flat surface.

  In such an objective lens complex, the light beam P <b> 2 emitted from the objective lens 200 is hardly reflected or diffracted when entering the hemispherical lens 201. Therefore, the light beam P2 enters the hemispherical lens 201 while maintaining the aperture angle of the objective lens 200 having a numerical aperture NA. Here, since the refractive index of the hemispherical lens 201 is N, the wavelength is 1 / N times inside the hemispherical lens 201.

  Then, when emitted from the flat surface of the hemispherical lens 201, the emitted light beam P3 corresponds to a further reduced numerical aperture N × NA due to the refractive index difference between the hemispherical lens 201 and air (the wavelength becomes λ). And return).

  As described above, according to the objective lens composite as shown in FIG. 5, a light beam having a large numerical aperture can be easily produced. Accordingly, several optical disk apparatuses using such an objective lens composite have been proposed.

  FIG. 6 is a schematic diagram showing a configuration of a conventional example (Patent Document 1, Patent Document 2, hereinafter referred to as Conventional Example 2) proposed as an optical disk apparatus using the objective lens composite. In this optical disc apparatus, the light beam emitted from the objective lens complex 210 composed of the objective lens 200 (numerical aperture = NA) and the hemispherical lens 201 (refractive index = N) is applied to the optical disc 211 through a gap 212 of several μm or more. Incident light is applied to the recording surface 213 on which information is recorded. Here, the light beam from the objective lens complex 210 is incident on the optical disk 211 in the gap 212 corresponding to the numerical aperture N × NA as described above.

  As described above, in the optical disc apparatus, a light beam having a large numerical aperture by the refractive index N times that of the hemispherical lens 201, that is, a light beam having a beam spot size of 1 / N times, compared with the case where only the objective lens 200 is used. The light can enter the optical disk 211.

  FIG. 7 is a schematic diagram for explaining another example (Patent Document 3, Non-Patent Document 1, hereinafter referred to as Conventional Example 3) proposed as an optical disk apparatus using an objective lens complex. In this optical disc apparatus, an objective lens complex 210 including an objective lens 200 (numerical aperture = NA) and a hemispherical lens 201 (refractive index = N) is close to the recording surface 213 of the optical disc 211 (˜λ / 4) Arranged.

  When the objective lens complex 210 and the recording surface 213 are arranged close to each other, a near-field effect works, and the light beam that is going to be emitted from the flat surface of the hemispherical lens 201 is in the hemispherical lens 201. The recording surface 213 is irradiated by leaching from the flat surface with the same properties as the state. Here, as described above, since the light beam in the hemispherical lens 201 is a light beam having a numerical aperture NA and a wavelength of 1 / N times, the light beam irradiated on the recording surface 213 is compared with the conventional irradiation light. Thus, the light beam is reduced in wavelength by 1 / N times. Therefore, a light beam having a beam spot size of 1 / N times enters the recording surface 213.

As described above, in the conventional example 3, by using the near field, the light beam whose wavelength is reduced in the hemispherical lens 201 is guided to the recording surface 213 as it is, thereby reducing the beam spot size. Yes.
Japanese Patent Application Laid-Open No. 8-221277 JP-A-8-221790 US Pat. No. 5,121,256 Japanese Patent Laid-Open No. 9-161311 (released on June 20, 1997) JP-A-5-189796 (published July 30, 1993) Nikkei Electronics 1997.6.16, p. 99-p. 108

  As described above, according to the conventional examples 2 and 3, in principle, the size of the beam spot that irradiates the recording surface can be reduced, and thereby the density of the optical disk can be increased.

  However, in the case of Conventional Example 2 shown in FIG. 6, the light beam emitted from the objective lens complex 210 is emitted from the hemispherical lens 201 when the numerical aperture is increased. Near the outside of the light beam, the incident angle is large, causing a total reflection phenomenon, and limiting the numerical aperture.

  For example, the reflectance when light is emitted from the hemispherical lens 201 having a refractive index of 1.5 into air having a refractive index of 1.0 begins to increase from around 33 ° of the so-called Brewster angle. Full reflection at °. An increase in reflectivity means that the amount of light incident on the optical disc 210 eventually decreases, and light does not enter the optical disc 210 in the case of complete reflection. Therefore, in the case of Conventional Example 2, there is a limit to increase the numerical aperture to improve the recording density, and the numerical aperture can only be increased to about 0.85.

  Further, in Conventional Example 3 shown in FIG. 7, in order to guide a light beam focused to 1 / N of the wavelength in the air in the hemispherical lens 201 to the recording surface 213 without changing the wavelength, the recording surface 213 and the hemispherical lens 201 are connected. The recording medium needs to be close to ¼ of the wavelength of light, and there is a problem that an effective protective film cannot be attached to the recording medium. For this reason, even if dust of a wavelength order is greatly affected by dust, not only the operation is affected but also the recording medium itself may be damaged. Further, in order to avoid dust, there is a problem that the medium cannot be exchanged, which is a feature of the optical disk.

Further, in the optical disc device of Conventional Example 3, the light coupling efficiency between the hemispherical lens 201 and the recording surface 213 is as low as about 50%, and there is a problem that sufficient information light cannot be obtained. As inferred by the present inventor, in Conventional Example 3, the light beam is emitted from the flat surface into the atmosphere in a state where the wavelength of light is reduced inside the hemispherical lens 201 (set to 1 / N of the wavelength). Since the light beam diameter (the light beam diameter of the part where the light intensity is 1 / e ^{2 of the} peak intensity) is equal to or smaller than the wavelength in the atmosphere and cannot be present in the atmosphere, This is probably due to some loss.

  The present invention solves the above-described problems, and provides an optical recording / reproducing method, an optical recording / reproducing apparatus, and an optical recording medium capable of efficiently irradiating a recording surface of an optical disc with a light beam having a small beam spot diameter. Objective.

The optical recording / reproducing method of the present invention is an optical recording / reproducing method for recording or reproducing information by irradiating a light beam from a light source onto an optical recording medium having an optical coupling layer on the light incident side of a signal recording surface. Objective lens means for condensing the light beam from the light source is arranged on the optical recording medium, and the objective lens means is arranged in a hemispherical shape having a flat surface on the objective lens and the optical coupling layer. A hemispherical lens having a refractive index N1, a radius of the hemispherical lens r, a refractive index of the optical coupling layer N2, and a thickness of the optical coupling layer d. The distance D from the top of the hemispherical surface of the lens to the flat surface is
D = r−d × N1 / N2
The light emitted from the objective lens is obliquely incident on the surface of the hemispherical lens, and the traveling direction of the light beam from the light source at the light exit end portion in the objective lens means is substantially maintained, By introducing a light beam into the optical coupling layer from the objective lens means, the signal recording surface of the optical recording medium is irradiated with the light beam.

  The optical recording / reproducing method of the present invention is characterized in that, in the optical recording / reproducing method, the thickness d of the optical coupling layer is 0.4 μm or more and 10 μm or less.

  The optical recording / reproducing method of the present invention is characterized in that, in the optical recording / reproducing method, the thickness d of the optical coupling layer is 3 μm to 7 μm.

The optical recording / reproducing apparatus of the present invention has an optical recording medium having a light source and at least one objective lens unit, and having an optical coupling layer on the light incident side with respect to the signal recording surface. An optical recording / reproducing apparatus that records and / or reproduces information by irradiating a light beam from the light source, wherein the objective lens unit is applied to the optical coupling layer at an interval equal to or less than a wavelength of light from the light source. The objective lens means is disposed at a close position, and the objective lens means includes an objective lens and a hemispherical lens arranged to have a flat surface on the optical coupling layer, and the refractive index of the hemispherical lens is N1, When the radius of the hemispherical lens is r, the refractive index of the optical coupling layer is N2, and the thickness of the optical coupling layer is d, the distance D from the top of the hemispherical lens to the flat surface is given by
D = r−d × N1 / N2
The light emitted from the objective lens is obliquely incident on the surface of the hemispherical lens, and the light beam condensed by the objective lens unit is combined with the optical coupling layer.

  The optical recording / reproducing apparatus of the present invention is characterized in that, in the optical recording / reproducing apparatus, the thickness d of the optical coupling layer is 0.4 μm or more and 10 μm or less.

  The optical recording / reproducing apparatus of the present invention is characterized in that, in the optical recording / reproducing apparatus, the thickness d of the optical coupling layer is 3 μm to 7 μm.

  The optical recording medium of the present invention is a light for recording or reproducing information in a state where objective lens means for condensing a light beam from a light source is arranged at an interval equal to or less than a wavelength of light from the light source. A recording medium having a transparent dielectric layer and an optical coupling layer for coupling light emitted from the objective lens unit on a side facing the objective lens unit with respect to a recording surface for recording information It is characterized by that.

  In the optical recording medium of the present invention, the film thickness of the transparent dielectric layer is preferably λ / 4n (n is the refractive index of the transparent dielectric layer).

  The optical recording medium of the present invention is characterized in that in the optical recording medium, the thickness d of the optical coupling layer is 0.4 μm or more and 10 μm or less.

  The optical recording medium of the present invention is characterized in that, in the optical recording medium, the thickness d of the optical coupling layer is 3 μm to 7 μm.

  As described above, according to the optical disk apparatus according to the present invention, since the objective lens means is brought close to the optical recording medium, the loss of light quantity can be suppressed without causing total reflection even when the numerical aperture is increased. A high-density recording / reproducing operation can be realized by reducing the spot diameter of the beam irradiated on the recording surface. Furthermore, since the loss of light quantity can be suppressed, recording / reproduction with low power can be realized, the life of the light source (laser or the like) can be extended, and the reliability can be improved.

  In addition, since an optical coupling layer is provided on the optical recording medium, it can function sufficiently as a protective film, so that it is sufficiently strong against dust and can be improved in reliability.

(Embodiment 1)
Embodiments of an optical recording / reproducing apparatus according to the present invention will be described below with reference to the drawings. Here, an example in which the optical recording / reproducing apparatus of the present invention is applied to an optical disk apparatus will be described. However, the optical recording / reproducing apparatus of the present invention can be applied to an optical card apparatus, an optical tape apparatus, etc. in addition to the optical disk apparatus. Needless to say.

  First, the principle of this embodiment will be described with reference to FIG. In FIG. 1, 4 is an objective lens and 5 is a hemispherical lens, both of which constitute objective lens means. Here, the numerical aperture of the objective lens 4 is NA, and the refractive index of the hemispherical lens 5 is N1. The optical disk 20 is provided with a recording surface 2 on a substrate 3 and an optical coupling film 1 on the recording surface 2.

  In such an optical disc system, the light (wavelength = λ) incident on the objective lens 4 enters the spherical surface of the hemispherical lens 5 perpendicularly. This incident light becomes a luminous flux having a numerical aperture NA and a wavelength of λ / N 1 in the hemispherical lens 5. Then, the light is emitted from the flat surface of the hemispherical lens 5 and once enters the atmosphere, then enters the optical disk 20.

  Here, normally, as in the above-described Conventional Example 2, the light emitted from the hemispherical lens 5 is reflected when the numerical aperture is increased, resulting in a loss of light amount.

  Therefore, in the present invention, as described above, the optical coupling layer 1 having substantially the same refractive index as that of the hemispherical lens 5 is provided on the light incident surface of the optical disk 20, and the optical coupling layer 1 is disposed close to the optical coupling layer 1 (wavelength λ of light Place the hemispherical lens 5 (with the following distance). Thus, by bringing a medium having substantially the same refractive index as that of the hemispherical lens 5 close to the surface where total reflection occurs, the evanescent light of the total reflection surface is transmitted to the approaching medium. That is, the light beam emitted from the flat surface of the hemispherical lens 5 is coupled to the optical coupling layer 1 by the near field effect and travels in substantially the same direction as the traveling direction in the hemispherical lens 5. For this reason, it is possible to guide the light flux to the optical coupling layer 1 without generating a large reflection when the light is emitted from the hemispherical lens 5 into the atmosphere.

  Here, since the light beam guided to the optical coupling layer 1 has the same property as that in the hemispherical lens 5, the light beam has a numerical aperture NA and a wavelength λ / NA. This light beam travels in the optical coupling layer 1 and irradiates the recording surface 2. Therefore, a light flux having a wavelength of λ / NA and a numerical aperture NA is incident on the recording surface 2.

  For this reason, the density which can be recorded on an optical disk can be raised compared with a normal optical disk. Further, unlike the conventional example 2, it is possible to record or reproduce information on the recording surface 2 with a sufficient amount of light without reflection.

  As described above, the present invention uses the near-field effect and suppresses the occurrence of reflection when the light beam is emitted from the hemispherical lens into the atmosphere due to the “property that the light travels in the same direction”. The light beam is guided to the optical coupling layer, and the technical idea is different from that in which the energy of the light collected by the hemispherical lens is propagated to the optical disk using the near-field effect as in Conventional Example 3. is there. For this reason, unlike the conventional example 3, it is not necessary to bring the recording surface and the hemispherical lens close to each other, and the light flux in the atmosphere (the light emitted from the flat surface of the hemispherical lens) exists in a normal state. There is no need to make it unobtainable.

  Therefore, by providing the optical coupling layer 1 with a function of protecting the recording surface 2, it is possible to realize protection against destruction of the recording surface 1 due to running of the hemispherical lens 5 or the like. In addition, the light coupling rate can be increased by setting the diameter of the light beam at the time of emission from the hemispherical lens 5 to a size greater than or equal to a predetermined value. In addition, what is necessary is just to set it as more than the wavelength of light (in air | atmosphere) as a light beam diameter at the time of the emission of hemispherical lens 5.

  In the present invention described above, the near-field effect is used. To obtain this effect, the distance between the flat surface of the hemispherical lens 5 and the optical coupling layer 1 is 1 / wavelength (in the atmosphere). 4 or less is desirable, and if it is 1/8 or less, the near-field effect can be made to function more effectively.

  Here, the objective lens 4 and the hemispherical lens 5 constitute a lens system for obtaining a large numerical aperture. However, the objective lens 4 and the hemispherical lens 5 are not limited to this as long as the numerical aperture is large. There may be.

  The recording surface 2 may be any one that records information by means of uneven pits as long as it can read information by light, or that that records information by phase change recording or magneto-optical recording. Also good.

  In the optical disk system of the present embodiment described above, the information is recorded / reproduced by irradiating the recording surface with light with a smaller beam spot size as compared with the optical disk apparatus shown in the conventional example 1 as described above. However, the recording / reproducing method and the beam spot servo control method can be realized by a method similar to the conventional method. For this reason, the description is omitted here.

Hereinafter, embodiments of the present invention will be described more specifically. In FIG. 1, the objective lens 4 has a numerical aperture of 0.6, and collects incident light having a wavelength of 400 nm. The condensed light is incident on the hemispherical lens 5 having a refractive index of 1.6. The hemispherical lens 5 runs above the surface of the optical disk by about 20 to 100 nm. Here, since the distance between the hemispherical lens 5 and the optical disk is ¼ or less of the wavelength, the light emitted from the hemispherical lens 5 is in the same direction as the traveling direction in the hemispherical lens 5 due to the near-field effect. It goes straight and enters the optical coupling layer 1 of the optical disc 20. Here, the light beam emitted from the flat surface of the hemispherical lens 5 has a spot diameter of 400 nm or more on the flat surface. The optical coupling layer 1 is made of an ultraviolet curable resin having a refractive index of about 1.6 and functions as a protective film for the recording surface 2. In addition, as the optical coupling layer 1, glass, SiO ₂ , acrylic, polycarbonate, polyolefin resin, or the like can be used.

  The light beam incident on the optical coupling layer 1 is condensed on the recording surface 2 and irradiated onto the recording surface 2 with a spot diameter that is 1 / 1.6 times that of the conventional example 1 (effective numerical aperture 0.6 × 1.6 = 0.96). Thus, high-density recording or reproduction from a high-density recording medium is possible.

  Next, the relationship between the optical coupling layer 1 and the hemispherical lens 5 will be described with reference to FIG. In FIG. 2, S is a spherical surface having a hemispherical lens 5 as a partial spherical surface, r is a radius of the spherical surface S, and l is a plane parallel to the flat surface of the hemispherical lens 5 and passing through the center of the spherical surface S. D represents the distance from the upper end to the lower end of the hemispherical lens 5, and d represents the thickness of the optical coupling layer 1 in the optical disc 20 (the refractive indices of the hemispherical lens 5 and the optical coupling layer 1 are the same as the refractive index). If).

  As shown in this figure, when the refractive indices of the hemispherical lens 5 and the optical coupling layer 1 are the same, the hemispherical lens 5 becomes thinner from the geometrical hemisphere by the thickness d of the optical coupling layer 1. Thus, the light is correctly focused on the recording surface 2.

  When the refractive indexes of the hemispherical lens 5 and the optical coupling layer 1 are different, it is necessary to optically correct that much to determine the lens thickness. Specifically, when the refractive index of the hemispherical lens 5 is N1, the radius of the hemispherical lens 5 is r, the refractive index of the optical coupling layer 1 is N2, and the thickness is d, the hemispherical lens 5 has an upper end to a lower end. Is determined to be approximately r−d × N1 / N2. In this way, the light beam can be condensed on the recording surface 2. When the refractive indexes N1 and N2 are substantially equal, a line passing through the center of the hemispherical lens 5 is located on the recording surface 2, and a value obtained by subtracting the thickness of the optical coupling layer 1 from this is required for the hemispherical lens 5. It becomes the thickness to be done.

  If the thickness of the optical coupling layer 1 is not uniform, there is a possibility that the recording / reproducing operation may be hindered. The non-uniform thickness is significant when the thickness is large, so that the optical coupling layer 1 is desirably 10 μm or less. If the thickness of the optical coupling layer 1 becomes too thin, the function as a protective film of the recording surface 2 is lost, and the diameter of the light beam emitted from the flat surface of the hemispherical lens 5 is small (smaller than the wavelength λ in the atmosphere). ) Since it is necessary to set and the optical coupling rate may deteriorate, it should be set to a wavelength λ or more in the atmosphere, that is, 0.4 μm or more in this case. In view of ease of manufacturing, it is desirable to set the thickness to about 3 to 7 μm.

  Further, here, since the hemispherical lens 5 is used that floats and travels on the optical disk 20 (floating head) as described above, either the surface of the optical coupling layer 1 or the slider portion of the flying head is lubricated. It is desirable to apply an agent or the like to suppress the influence of friction with the flying head.

(Embodiment 2)
The present embodiment relates to an optical disc system in which the numerical aperture is improved by the objective lens 4 and the hemispherical lens 10 in order to realize a higher density than in the first embodiment. FIG. 3 is a diagram for explaining this optical disk system. In FIG. 3, the same parts as those of FIG.

  In the first embodiment, the light beam from the objective lens 4 is incident on the hemispherical lens 5 perpendicularly, but here it is incident obliquely on the surface of the hemispherical lens 10. For this reason, light is refracted on the surface of the hemispherical lens 10, and an extremely high numerical aperture (for example, about 2.0) can be obtained.

  In the present embodiment, since the hemispherical lens 10 and the optical coupling layer 1 are placed close to each other as in the first embodiment, the optical coupling layer is not totally reflected even at the high numerical aperture as described above. 1 can be efficiently incident. Therefore, it is possible to achieve both higher density and suppression of light loss.

(Embodiment 3)
In this embodiment, an example in which the optical disk system shown in Embodiment 1 is applied to a magneto-optical recording / reproducing apparatus will be described.

  FIG. 4 is a diagram for explaining the configuration of the magneto-optical recording / reproducing apparatus of the present embodiment. In FIG. 4, reference numeral 4 denotes an objective lens that collects incident light and guides it to the hemispherical lens 5. As described in the first embodiment, the hemispherical lens 5 is arranged so that the surface thereof is perpendicular to the light beam from the objective lens 4. The light beam from the hemispherical lens 5 is incident on the optical coupling layer 1 of the optical disc 20 while maintaining the same traveling direction as the inside of the hemispherical lens 5 due to the near-field effect. For this reason, as shown in the first embodiment, it enters the recording surface 2 of the optical disc 20 as a minute beam spot. Therefore, high-density recording can be realized during recording, and information reproduction operation with high signal quality without crosstalk can be performed during reproduction. The recording operation and the reproducing operation can be performed by the same operation as that of a normal magneto-optical recording / reproducing apparatus.

  In the magneto-optical recording / reproducing apparatus of FIG. 4, since the interval between the hemispherical lens 5 and the optical disk 20 is shortened as described in the first embodiment, the magnetic head 30 and the optical head (the hemispherical lens 5) are moved to the slider. 14 is embedded and integrated. Specifically, in FIG. 4, a yoke 11 and a coil 12 are arranged around the hemispherical lens 5. The slider 14 is supported by the slider suspension 13 and is driven by a drive mechanism (not shown) to move on the optical disk 20 that is rotationally driven, thereby guiding the optical head and the magnetic head 30 to desired positions. Thereby, the recording / reproducing operation at a desired position (address) is executed.

  With such a configuration, the magnetic head 30 can be disposed close to the optical disc 20, thereby enabling high-speed data transfer. In addition, low power consumption, reduction in drive voltage, and suppression of heat generation can be realized.

  Further, since a magnetic field and light can be applied to the optical disc 20 from one side, information is provided on both sides of the disc by arranging heads on both sides of the optical disc 20 and providing recording surfaces (magneto-optical recording layers) on both sides of the substrate. Can be recorded, and further higher density can be realized.

  The slider 14 travels on the optical disc 20 according to the information recording / reproducing operation. The flying height at this time is not more than the wavelength λ of the incident light to the objective lens 4 (preferably λ / 4 or less, more preferably Is designed such that a groove is formed on the lower surface of the slider 14 so as to be λ / 8 or less. In the present embodiment, the hemispherical lens 5 and the optical coupling layer 1 of the optical disk 20 are brought close to each other, so that the slider surface where the slider 14 is in contact with the disk surface and the height of the surface facing the recording medium of the hemispherical lens are set. The distance between the lens surface and the optical coupling layer (protective film) 1 of the recording medium is made as small as possible. Although the objective lens 4 is separated from the slider 14 here, the objective lens 4 and the hemispherical lens 5 need to be in a certain positional relationship, so that they are preferably integrated.

  By the way, the light beam incident on the optical coupling layer 1 enters the magneto-optically recorded recording surface 2 (magneto-optical recording layer: may be composed of a plurality of layers), where the polarization direction is changed, Information is posted. Here, if a transparent dielectric layer having a film thickness of λ / 4n (n is the refractive index of the transparent dielectric layer) is provided between the recording surface 2 and the optical coupling layer 1, the Kerr rotation angle increases and the reproduction signal is increased. Quality can be improved. The transparent dielectric film needs to have a refractive index different from that of the optical coupling layer 1 when it is disposed adjacent to the optical coupling layer 1.

  Further, it is preferable to dispose a transparent dielectric layer and a reflective layer in this order on the opposite side of the optical coupling layer 1 with respect to the recording surface 2 because the Kerr rotation angle is increased due to the light interference effect. Therefore, the optical disc 20 is suitable for use on the substrate 3 in which a heat dissipation layer for heat dissipation, a reflective layer, a transparent dielectric layer, a recording layer, a transparent dielectric layer, and an optical coupling layer are sequentially formed. is there. As the recording layer, a rare earth transition metal thin film such as GdTbFe, TbFeCo, DyFeCo, or TbDyFeCo is used.

  In the case of a medium using magnetic super-resolution, a heat dissipation layer, a protective film such as a dielectric film, a recording auxiliary layer such as GdFeCo, a recording layer such as GdTbFe, TbFeCo, DyFeCo, and TbDyFeCo (from the substrate 3 side). It is suitable to use an AlN, SiN, or intermediate layer such as a low Tc medium, a reproduction auxiliary layer such as GdFe, a reproduction layer such as GdFeCo, a transparent dielectric, and an optical coupling layer. It is.

  Furthermore, when using the magnetic domain expansion reproduction system, a heat dissipation layer, a protective film such as a dielectric film, a recording auxiliary layer such as GdFeCo, a recording medium such as GdTbFe, TbFeCo, DyFeCo, and TbDyFeCo from the substrate side, AlN, SiN, and the like are low. It is appropriate to use a magnetic mask layer made of Tc medium or the like, a reproduction auxiliary layer such as GdFe, a reproduction layer such as GdFeCo, and a transparent dielectric layer in that order.

  Here, an example in which the optical disk system of the present invention is applied to a magneto-optical disk system is shown, but by providing a transparent dielectric film on the optical coupling layer 1 side and / or the opposite side with respect to the recording surface 2. The technique for improving the modulation intensity of the reproduction signal is the same for the phase change recording medium.

It is a figure explaining the optical disk device concerning the present invention. It is a figure which shows the relationship between the hemispherical lens of FIG. 1, and the thickness of an optical coupling layer. FIG. 6 is a diagram for explaining an optical disc device according to a second embodiment. FIG. 10 is a diagram for explaining an optical disc device according to a third embodiment. It is a figure explaining an objective-lens complex. It is a figure explaining the optical disk apparatus of the prior art example 2. FIG. It is a figure explaining the optical disk apparatus of the prior art example 3. FIG.

Explanation of symbols

1 optical coupling layer 2 recording medium 3 substrate 4 objective lens 5 hemispherical lens 10 hemispherical lens 11 magnetic yoke 12 magnetic coil 13 slider suspension 14 slider 20 optical disc D hemispherical lens thickness d optical coupling layer thickness l passes through the center of the spherical surface Plane S Spherical surface

Claims (10)

An optical recording / reproducing method for recording or reproducing information by irradiating a light beam from a light source to an optical recording medium having an optical coupling layer on a light incident side of a signal recording surface,
Objective lens means for condensing the light beam from the light source with respect to the optical recording medium is disposed,
The objective lens means includes an objective lens and a hemispherical lens arranged to have a flat surface on the optical coupling layer, the refractive index of the hemispherical lens is N1, the radius of the hemispherical lens is r, When the refractive index of the optical coupling layer is N2 and the thickness of the optical coupling layer is d, the distance D from the top of the hemispherical surface of the hemispherical lens to the flat surface is:
D = r−d × N1 / N2
And
The light emitted from the objective lens is incident obliquely on the surface of the hemispherical lens,
By introducing a light beam from the objective lens unit into the optical coupling layer in a state where the traveling direction of the light beam from the light source is substantially maintained at the light exit end portion in the objective lens unit, the optical recording medium is An optical recording / reproducing method comprising irradiating a signal recording surface with a light beam.   2. The optical recording / reproducing method according to claim 1, wherein a thickness d of the optical coupling layer is 0.4 μm or more and 10 μm or less.   2. The optical recording / reproducing method according to claim 1, wherein a thickness d of the optical coupling layer is 3 μm to 7 μm. An optical recording medium having a light source and an objective lens unit made of at least one member and having a light coupling layer provided on the light incident side with respect to the signal recording surface is irradiated with a light beam from the light source. An optical recording / reproducing apparatus that performs at least one of recording and reproduction of information,
The objective lens means is disposed at a position close to the optical coupling layer at an interval equal to or smaller than the wavelength of light from the light source,
The objective lens means includes an objective lens and a hemispherical lens arranged to have a flat surface on the optical coupling layer, the refractive index of the hemispherical lens is N1, the radius of the hemispherical lens is r, When the refractive index of the optical coupling layer is N2 and the thickness of the optical coupling layer is d, the distance D from the top of the hemispherical surface to the flat surface of the hemispherical lens is:
D = r−d × N1 / N2
And
The light emitted from the objective lens is incident obliquely on the surface of the hemispherical lens,
An optical recording / reproducing apparatus, wherein a light beam condensed by the objective lens means is coupled to the optical coupling layer.   5. The optical recording / reproducing apparatus according to claim 4, wherein a thickness d of the optical coupling layer is 0.4 μm or more and 10 μm or less.   5. The optical recording / reproducing apparatus according to claim 4, wherein a thickness d of the optical coupling layer is 3 μm to 7 μm. The objective lens means for condensing the light flux from the light source is an optical recording medium on which at least one of information recording or reproduction is performed in a state where the objective lens means is arranged at intervals equal to or less than the wavelength of the light from the light source,
Light having a transparent dielectric layer and an optical coupling layer for coupling light emitted from the objective lens unit on a side facing the objective lens unit with respect to a recording surface for recording information recoding media.   8. The optical recording medium according to claim 7, wherein the film thickness of the transparent dielectric layer is λ / 4n (n is the refractive index of the transparent dielectric layer).   The optical recording medium according to claim 7, wherein the thickness d of the optical coupling layer is 0.4 μm or more and 10 μm or less.   8. The optical recording medium according to claim 7, wherein the thickness d of the optical coupling layer is 3 μm to 7 μm.

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