JP2006048807A - Optical memory device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical memory device capable of information recording with higher density than in the conventional practice without damaging portability being a merit of a conventional optical disk. <P>SOLUTION: This optical memory device is provided with a semiconductor layer 101 in which a beam cross section intensity distribution is an annular intensity distribution and which generates an axial symmetrical polarized doughnut beam of radial polarization having a radial electric field intensity distribution with respect to a center axis, a collimating lens 102, a polarization sensing element 103, a light shielding element 104, an objective lens 106 for converging axial symmetrical polarized doughnut beams of the radial polarization on a recording surface of a recording medium 20 to emit the beams, and a beam splitter 105 for guiding beams obtained by allowing the axial symmetrical polarized doughnut beams of radial polarization to be reflected at the recording surface of the recording medium 20 to a photodetector 108. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical memory device that uses light to record information on an information recording medium and reproduce or erase information recorded on the information recording medium.

  In an optical memory device (CD-ROM drive or DVD-ROM drive) currently in practical use, information is recorded by irradiating an information recording medium with a laser beam condensed by an objective lens, and from the irradiated area. Information is reproduced by detecting reflected light. In such a recording / reproducing system, the condensing spot size on the recording surface affects the recording density (the amount of information recorded per unit area).

  In the method of condensing a Gaussian beam with an objective lens as in the current optical memory device, the size of the focused spot is limited to about the wavelength due to the limitation of light diffraction.

  Currently, a blue-violet semiconductor laser (wavelength of about 405 nm) is used as a light source. An optical memory device that condenses this light using an objective lens with an A (numerical aperture) of 0.85 has already been realized, and a method following a conventional recording / reproducing method of condensing a Gaussian beam with an objective lens is as follows: It is considered that the limit is almost reached in high density recording.

  In order to solve such a problem, techniques aiming at higher density recording of an optical memory have been studied conventionally.

  For example, in the old days, an optical memory device using a phenomenon called a super-resolution effect has been proposed in Patent Document 1 and the like.

An optical memory device using the super-resolution effect will be described using FIG. 19 as an example.
Laser light emitted from the semiconductor laser 1 is collimated by the collimating lens 2 and enters the light shielding element 3. In the light shielding element 3, the central portion of the parallel light is attenuated, and the transmitted light becomes a beam having an annular intensity distribution. Thereafter, the light passes through the polarization beam splitter 4 and the quarter wavelength plate 5 for polarization separation, and is focused on the recording medium 20 by the objective lens 6. At this time, the light intensity distribution on the recording surface of the recording medium 20 is slightly smaller than that in the case where a normal Gaussian beam is condensed while accompanied by side lobes.

  Reflected light from the recording medium having an information signal is reflected by the polarization beam splitter 4 through the objective lens 6 and the quarter wavelength plate 5, and is reproduced in the signal detection system including the lens 7 and the photodetector 8. Servo signals are detected.

  Although such an optical memory device using the super-resolution effect can be configured by a simple method such as inserting a light-shielding element in a conventional optical system, it reduces the light utilization efficiency, the appearance of side lobes, the optical axis On the other hand, there are many disadvantages in exchange for reducing the spot diameter by 20-30%, such as asymmetric spot intensity distribution, and it is difficult to dramatically increase the density.

  On the other hand, as an optical memory not limited by the diffraction limit itself, a method called a near-field optical memory has been proposed in Patent Document 2 and the like.

The near-field optical memory device will be described with reference to FIG.
The laser light emitted from the semiconductor laser 11 passes through the lens 12 and is then focused and incident on the fiber probe 13 (an element for generating near-field light). At the tip of the fiber lobe 13, a minute opening (for example, a circular opening having a diameter of 50 nm) covered with a metal light-shielding film is formed, and near-field light having a spread about the opening diameter is generated in the vicinity of the opening. To do.

  The tip of the fiber lobe 13 is disposed close to the surface of the recording medium 20 up to a distance of several tens of nanometers. At this time, the near-field light generated in the fiber lobe is scattered and transmitted according to the recording information on the surface of the recording medium 20, so that the light is collected by the lens 14 and is located on the opposite side of the fiber lobe. Information can be reproduced by detecting with.

  Such a method using near-field light can be expected as a means for realizing a high-density optical memory independent of the wavelength of the light source. However, the method using a recording medium that has been an advantage of a conventional optical disk (CD, DVD, etc.). It is difficult to realize portability (removability).

There is also a method of obtaining a minute spot using a hemispherical lens called SIL (solid immersion lens), but this also uses the near-field light, and the problem of portability similarly occurs.
Japanese Patent Laid-Open No. 9-231607 JP 2004-178640 A

  As described above, it is difficult to achieve a recording density sufficiently superior to the current optical memory device using the blue-violet semiconductor laser while following the conventional method represented by CD and DVD. Moreover, it is difficult to realize the portability, which is an advantage of the conventional optical disc, by the method for achieving high density recording by using near-field light.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide an optical memory device capable of recording information at a higher density than before without impairing the portability, which is an advantage of the conventional optical disk.

  To achieve the above object, the present invention provides, as a first aspect, an axially symmetric polarization donut of radial polarization having a circular cross-sectional intensity distribution and a radial electric field vibration distribution with respect to the central axis. A light emitting optical system for generating a beam, a condensing optical system for condensing and irradiating an axially symmetric polarized donut beam on a recording medium, and an axially symmetric polarized donut beam of the recording medium The present invention provides an optical memory device comprising a detection optical system that guides light reflected from a recording surface to a photodetector.

In the first aspect of the present invention, the light-shielding unit included in the light-emitting optical system and converts light emitted from the laser light source into a donut beam having an annular cross section, and the detection optical system includes an axially symmetric polarized donut. It is preferable to include a beam splitter in which a beam is integrated with a reflection unit that reflects light reflected by the recording surface of the recording medium toward the detector.
Alternatively, the light emitting optical system preferably converts light emitted from the laser light source into a donut beam using an axicon.
Alternatively, the light-emitting optical system preferably includes a configuration in which an axicon is disposed between a laser light source and a collimating lens that converts diffused light emitted from the laser light source into parallel light. More preferably, the light source is housed in a case, and an axicon is disposed in an opening that guides diffused light emitted from the laser light source to the outside of the case.

  In order to achieve the above object, as a second aspect, the present invention provides a light-emitting optical system that generates a radially polarized axially symmetric polarized beam having a radial electric field vibration distribution with respect to the central axis, and a radial polarization axis. Converts a symmetric polarized beam into an axially symmetric axially symmetric donut beam with an annular cross section, and converts and condenses the light onto the recording surface of the recording medium, and records a radial polarized axisymmetric polarized donut beam. The present invention provides an optical memory device comprising a detection optical system that guides light reflected from a recording surface of a medium to a photodetector.

  In the second aspect of the present invention, it is preferable that the conversion condensing optical system is configured using a reflection type objective lens.

  In any of the configurations of the first aspect and the second aspect of the present invention, the recording medium is preferably a surface recording type recording medium.

  In both configurations of the first aspect and the second aspect of the present invention, it is preferable to have means for holding the recording medium in a detachable manner. Alternatively, the recording medium is preferably incorporated in the apparatus.

  According to the present invention, it is possible to provide an optical memory device capable of recording information at a higher density than before without impairing the portability which is an advantage of the conventional optical disk.

[Principle of the Invention]
In the present invention, information is recorded and reproduced using an axially symmetric polarized donut beam instead of a conventional Gaussian beam.
As shown in FIG. 1 (a diagram showing a polarization distribution on a cross section perpendicular to the beam propagation direction), the axially symmetric polarized beam has a radial polarization that is distributed so that the oscillation direction of the electric field of the light is in the radial direction. (Polarized light having a radial electric field vibration distribution with respect to the central axis) and azimuth polarized light distributed in the azimuth direction (polarized light whose magnetic field vibration direction is radial), and in the present invention, the former radial polarized light is axially symmetric. A radially polarized axially symmetric donut beam based on a polarized beam is used. Here, an axially symmetric polarized donut beam in the present invention is described as an axially symmetric polarized beam (TEM _{01 *} or R-TEM _{01 *)} obtained by solving the Maxwell equation on cylindrical coordinates. In the beam cross-sectional intensity distribution, the intensity in the vicinity of the center is attenuated or the area where the intensity is weak is wide.
When such a radially polarized axially symmetric polarized donut beam (hereinafter abbreviated as a radially polarized donut beam) is condensed with a lens, a condensing spot diameter much smaller than when a Gaussian beam is condensed can be obtained. (S. Quabis, R. Dron, M. Eberier, O. Glocki, G. Leuchs: Optics Communications 179 (2000)). According to this report, radial polarized donut beams are When condensing with a condensing lens with a large A (numerical aperture), the full width at half maximum of the intensity distribution can be reduced to half or less compared to the case where a Gaussian beam is condensed with the same objective lens. Yes.

  The present invention realizes a high-density optical memory using a micro spot obtained by condensing such a radially polarized donut beam.

  A preferred embodiment of the present invention based on the above principle will be described below.

[First Embodiment]
A first embodiment in which the present invention is suitably implemented will be described. The configuration of the optical memory device according to the present embodiment is shown in FIG. The optical memory device according to the present embodiment includes a semiconductor laser 101, a collimator lens 102, a polarization conversion element 103, a light shielding element 104, a beam splitter 105, an objective lens 106, a lens 107, and a photodetector 108. This optical memory device includes a semiconductor laser 101 (for example, a blue-violet semiconductor laser having an emission wavelength of about 405 nm) as a light source, and the laser light emitted therefrom is converted into parallel light by a collimator lens 102 and then converted into polarized light. In this configuration, the light is incident on the element 103. The linearly polarized Gaussian beam incident on the polarization conversion element 103 is converted into a radial polarization axially symmetric polarization beam and emitted, and further converted into a radial polarization donut beam by the light shielding element 104.

  There are various configurations of the polarization conversion element 103, but the configuration is not limited to a specific configuration. If an example of a structure is given, the polarization conversion element using the liquid crystal introduced in literature (Miyaji Goyo et al .: Laser Research, Vol. 32, No. 4, p. 259-) can be used.

  As the light shielding element 104, a structure in which a metal 1042 (aluminum, silver, chromium, or the like) is provided at the center of a transparent substrate 1041 (glass, resin, or the like) as shown in FIG. 3 can be applied.

  The beam that has passed through the light-shielding element 104 passes through a beam splitter 105 (for example, having no polarization dependency such that the ratio of transmitted light to reflected light is 7: 3) for optical path branching with the signal detection optical system. After passing, the light is condensed on the recording medium 20 by the objective lens 106.

  The reflected light from the recording medium 20 passes through the objective lens 106, is guided to the photodetector 108 (for example, photodiode) side by the beam splitter 105, and enters the photodetector 108 through the lens 107. The photodetector 108 detects a signal for performing reproduction signal detection and focus servo (control to always move the focused spot on the recording surface).

  As for the focus servo and tracking operation, for example, the same method as introduced in the literature (Morio Oshiage et al. “Optical Disc Technology” Radio Technology Co., Ltd.) can be used.

  N. of the objective lens 106. The higher A is, the smaller the focused spot diameter becomes. In this embodiment, N.I. An objective lens of A0.85 or higher is used.

  The recording medium 20 has a disk-shaped transparent substrate 21 (for example, one using polycarbonate or glass material) on one side thereof with a metal film 22 (gold, silver, aluminum, etc.), and further a protective film 23 (dielectric material, etc.) thereon. ) Is provided. As shown in FIGS. 4 and 5, irregularities (recording pits 24 representing recording information) reflecting the recording information are formed at the interface between the transparent substrate 21 and the metal film 22. The recording pits 24 are arranged concentrically or spirally with respect to the center of the disk.

  The thickness of the transparent substrate 21 is not particularly limited, but it is necessary to increase the diameter of the objective lens 106 as the thickness increases. This is because the focal length of the objective lens 106 increases as the thickness of the transparent substrate 21 increases. In order to obtain the same spot diameter at a long focal length, the lens diameter must be increased. As in the case of a conventional optical disk, if a recording medium having a diameter of 12 cm using polycarbonate as a substrate is used, a thickness of at least 0.5 mm is necessary in consideration of the rigidity of the recording medium.

  As an example of the arrangement configuration of the recording pit 24 and a data track in which a series of continuous data are arranged, for example, the distance between the data tracks (track pitch) is about 200 nm, and the length of the recording pit 24 (the vertical direction in FIG. 5). (Length) is the shortest of about 100 nm.

  The entire recording medium 20 is attached to the motor 10 through a hole formed in the center and rotates when the information is reproduced, and the laser beam is rotated on the recording surface (transparent substrate 21). When the light is applied to the interface between the metal film 22 and the metal film 22, a change in the optical signal intensity according to the continuous recording data is detected by the photodetector 108. The recording medium 20 is detachably attached to the motor 10, and when reproducing information from other recording media, the recording medium is replaced and the above operation is performed.

  In this example, the recording medium 20 on which the recording information expressed by the projections and depressions is recorded in advance is used as an example of reproducing the information. However, the present invention is not limited to this, and a conventional recordable optical disc (CD) is used. -R, CD-RW, DVD-R, DVD-RW, MO, etc.) Information can be recorded by a guide groove called a land groove instead of the above-described irregularities and light alone or a combination of light and magnetism. It is also possible to configure an optical memory device capable of recording information by providing a possible layer structure (a film of a recordable material provided on a transparent substrate and a dielectric film or a metal film necessary for the film). It is.

In this embodiment, the laser is incident from the transparent substrate 21 side and the information on the recording surface on the opposite side is read. However, a recording surface for recording information between the two transparent substrates is used. A transparent protective film is provided on the recording surface on the transparent substrate as in the configuration to be provided and Blue-ray Disk (standard of an optical disk combining a blue-violet semiconductor laser and an NA 0.85 objective lens). A configuration in which laser is irradiated from above the transparent protective film, or a surface recording type configuration in which the recording surface is irradiated from the side opposite to the substrate may be employed.
Further, the recording medium may be a rectangular or cylindrical recording medium without being constrained by a disk shape like a conventional optical disk.

  Further, the polarization conversion element 103 and the light shielding element 104 for generating the radial polarization donut beam are not necessarily separate elements, and an element in which these elements are integrated may be used alone. Further, the beam splitter 105 may have a part or all of the functions of these elements.

  With regard to the arrangement of the light shielding element 104 and the polarization conversion element 103, it is sufficient that the light shielding element 104 and the polarization conversion element 103 are disposed between the laser light source (semiconductor laser 101) and the objective lens 106, and these elements are disposed between the beam splitter 105 and the objective lens 106. It is also possible to configure. Further, it may be configured such that the laser light first passes through the light shielding element 104 and then passes through the polarization conversion element 103.

  The optical memory device according to the present embodiment is capable of recording and reproducing at high density using a minute spot obtained by condensing a radially polarized donut beam.

[Second Embodiment]
A second embodiment in which the present invention is suitably implemented will be described. FIG. 6 shows a configuration of the optical memory device according to the present embodiment. The optical memory device according to this embodiment has substantially the same configuration as that of the first embodiment, but is different in that a light shielding element is integrated with the beam splitter 201. In addition, about the component similar to 1st Embodiment, the same code | symbol is attached | subjected and it represents, and the overlapping description is abbreviate | omitted.

In the first embodiment, the beam splitter 201 has a film configuration in which the entire surface is a half mirror made of a dielectric multilayer film 2011, as shown in FIG. 7, such as a metal material (aluminum, silver, chromium, etc.) at the center. ) Is changed to a configuration in which the light shielding / reflecting film 2012 is provided.
The portion of the light shielding / reflecting film 2012 operates so as to shield the vicinity of its center and convert it into a radially polarized donut beam when a radially polarized axially symmetric polarized beam that has passed through the polarization conversion element 103 is incident. On the other hand, when light that is reflected by the recording medium 20 and returns from the objective lens 106 side is incident, it operates as a reflective film that reflects this light to the photodetector 108 side. In the configuration of the first embodiment, the amount of light is reduced because the central portion of the beam is completely concealed. However, in the configuration of the present embodiment, although the reflectance is low in the central portion of the beam. Since it is not completely concealed, it has a feature that the amount of light when detecting reflected light is increased as compared with the configuration of the first embodiment.

  Since the operation for reproducing information and other configurations are the same as those in the first embodiment, a duplicate description is omitted.

[Third Embodiment]
A third embodiment in which the present invention is preferably implemented will be described. FIG. 8 shows the configuration of the optical memory device according to the present embodiment. This optical memory device has substantially the same configuration as that of the first embodiment, but it uses two axicons (optical elements having a frustoconical surface made of a transparent material such as glass) (301, 302). The point which produces | generates a beam is different from 1st Embodiment. In addition, about the component similar to 1st Embodiment, the same code | symbol is attached | subjected and the overlapping description is abbreviate | omitted.
The light that has been collimated by the collimator lens 102 is converted by the first axicon 301 into annular divergent light (a donut beam in which the ring expands as it propagates), and is incident on the second axicon 302. The second axicon 302 converts the divergent light, which is a donut beam, into parallel light, and then is converted into radial polarized light by the polarization conversion element 103.

  Unlike the method using a light shielding element, part of the light from the light source is not excluded, so that the light use efficiency can be improved.

  Since it is the same as that of the first embodiment except that two axicons are used to generate a donut beam, a duplicate description is omitted.

  Although a configuration using two axicons has been described here as an example, as shown in FIG. 9, a donut beam can be formed even if axicons 303 having two truncated cone portions are used alone. The donut beam generated in this case is the same as when two axicons are used.

[Fourth Embodiment]
A fourth embodiment in which the present invention is preferably implemented will be described. FIG. 10 shows the configuration of the optical memory device according to the present embodiment. This optical memory device has substantially the same configuration as that of the first embodiment, but uses an axicon 401 having one conical surface and is disposed between a semiconductor laser 101 serving as a light source and a collimator lens 102 to form a donut beam. Is different. In addition, about the component similar to 1st Embodiment, the same code | symbol is attached | subjected and the overlapping description is abbreviate | omitted.
The donut beam converted into linearly polarized parallel light by the collimator lens 102 is converted into a radially polarized donut beam by the polarization conversion element 103 and condensed on the recording medium 20 by the objective lens 106.

  Similar to the first embodiment, the optical memory device according to the present embodiment can use a recording medium capable of recording information or a surface recording type recording medium, and is limited to a specific recording medium. It is applicable without.

[Fifth Embodiment]
A fifth embodiment in which the present invention is preferably implemented will be described. 11 and 12 show the configuration of the optical memory device according to the present embodiment. In the present embodiment, the axicon 401 in the fourth embodiment is integrated with the semiconductor laser 101. As shown in FIG. 12, a donut beam that diverges is generated by using a transparent window 1011 for taking out laser light emitted from the chip (laser light emitting part) of the semiconductor laser 101 to the outside as a conical glass window. is doing.

  The donut beam is converted into parallel light by the collimator lens 102, and is converted into a radially polarized donut beam by the polarization conversion element 103.

  Similar to the first embodiment, the optical memory device according to the present embodiment can use a recording medium capable of recording information or a surface recording type recording medium, and is limited to a specific recording medium. It is applicable without.

[Sixth Embodiment]
A sixth embodiment in which the present invention is preferably implemented will be described. FIG. 13 shows the configuration of the optical memory device according to the present embodiment. This optical memory device is different from the first embodiment in that a radially polarized axially symmetric donut beam is formed using a reflective objective lens. In addition, about the component similar to 1st Embodiment, the same code | symbol is attached | subjected and it represents, and the overlapping description is abbreviate | omitted. In this optical memory device, a semiconductor laser 101 (for example, a blue-violet semiconductor laser having an emission wavelength of about 405 nm) is used as a light source, and a linearly polarized Gaussian beam emitted therefrom is converted into parallel light by a collimator lens 102. , And input to the polarization conversion element 103. The linearly-polarized Gaussian beam incident on the polarization conversion element 103 is converted into a radial-polarized axially symmetric polarized beam and emitted.

  There are various configurations of the polarization conversion element 103, but the configuration is not limited to a specific configuration. If an example of a structural example is given, the polarization conversion element using a liquid crystal can be used similarly to 1st Embodiment.

  The beam that has passed through the polarization conversion element 103 is a beam splitter 105 for branching an optical path with the signal detection optical system (for example, a beam having no polarization dependency such that the ratio of transmitted light to reflected light is 7: 3). After passing, the light is condensed on a recording medium by a reflective objective lens 601.

  14 and 15 show the configuration of a reflective objective lens 601. FIG. As shown in the figure, the reflective objective lens 601 includes one refractive surface 6012 and two reflective surfaces 6013 and 6014 (a metal film such as aluminum or silver) made by processing a transparent member 6011 (glass or resin). Or a dielectric multilayer reflective film).

  The beam incident on the reflective objective lens 601 is condensed toward the first reflecting surface 6013 by the refracting surface 6012, and is reflected radially toward the second reflecting surface 6014 at the first reflecting surface 6013, Further, the light is reflected by the second reflecting surface 6014 and condensed on the recording surface of the recording medium 20. That is, the radially polarized axially symmetric polarized beam incident on the reflective objective lens 601 is converted into a donut beam and condensed in the reflective objective lens 601.

  Even when the objective lens having such a configuration is used, as in the first embodiment, N.I. The larger A is, the smaller the focused spot becomes. For this reason, the reflection type objective lens includes N.I. A 0.85 or more is applied.

The light condensed by the reflective objective lens 601 is reflected by the recording medium 20, and again passes through the reflective objective lens 601 and is guided to the photodetector 108 (for example, photodiode) side by the beam splitter 105.
The photodetector 108 detects a reproduction signal, performs focus servo (control to always form a focused spot on the recording surface) and tracking (forms a focused spot along a data track in which a series of recorded data is arranged). A signal for performing control) is detected.

As shown in FIGS. 16 and 17, the recording medium 30 of the present embodiment is a surface recording type recording medium that irradiates laser light from the opposite side of the substrate to the recording surface on which information is recorded. That is, a metal film 32 (gold, silver, aluminum, etc.) is provided on one side of a disk-shaped substrate 31 (for example, using polycarbonate or glass as a material), and a transparent protective film 33 (dielectric material) is provided thereon. It has been.
Concavities and convexities (recording pits 34 representing recording information) reflecting the recording information are arranged concentrically or spirally with respect to the center of the disk.

  The thickness of the substrate 31 is not particularly limited, but a substrate having a thickness of about 1 mm can be used. As an example of the arrangement structure of the recording pit 34 and the data track in which a series of continuous data is arranged, for example, the distance between the data tracks (track pitch) is about 200 nm, and the length of the recording pit 34 (in the vertical direction of the drawing in FIG. 17). The length is the shortest size of 100 nm.

The transparent protective film 33 is for protecting irregularities on the recording surface, and is formed by bonding a film on which a dielectric material is deposited, a transparent resin film, or the like. The thickness of the protective film 33 is the same as that of the reflective objective lens 601. The optimum value is selected according to conditions such as A, the mechanical accuracy of the apparatus, and the uniformity of the protective film 33. For example, a recording medium 30 having a diameter of 12 cm using polycarbonate as the substrate 31 and N.I. A configuration in which a protective layer of several hundred nm is provided for the combination with the reflective objective lens 601 of A0.9 is applied. The entire recording medium 30 is attached to the motor 10 through a hole formed in the center and rotates when reproducing information. When laser light is incident from the side of the protective film 33 in the rotating state and irradiated onto the recording surface, a change in optical signal intensity according to continuous recording data is detected by the photodetector 108 (for example, a photodiode).
The recording medium 30 is detachably attached to the motor 10, and when reproducing another recording medium, the recording medium may be replaced and the same operation as described above may be performed.

  Here, the configuration using the reflective objective lens 601 is taken as an example. However, when the light emission intensity of the light source is sufficient, the objective lens 106 is used instead of the reflective objective lens 601 as shown in FIG. Alternatively, a circular light shielding film 1061 made of a metal material (aluminum, silver, chromium, or the like) may be provided at the center to generate a donut beam.

  Further, here, the recording medium 30 on which the recording information expressed by the projections and depressions is recorded in advance is used as an example of reproducing the information. However, the present invention is not limited to this, and a conventional recordable optical disc is used. Similar to (CD-R, CD-RW, DVD-R, DVD-RW, MO, etc.), a guide groove called a land groove instead of the above-described irregularities and light alone or a combination of light and magnetism An optical memory device capable of recording information is provided by providing a layer structure capable of recording (a film of a recordable material provided on a transparent substrate and a dielectric film or a metal film necessary for the film). Is also possible.

Further, here, a configuration in which laser light is incident from the protective film 33 side and information on the recording surface on the opposite side is read has been described as an example. However, a configuration in which laser light is incident from the substrate 31 side or between two transparent substrates is described. It may be configured to provide a recording surface for recording information.
Further, the recording medium may be a rectangular or cylindrical recording medium without being constrained by a disk shape like a conventional optical disk.

  The polarization conversion element 103 only needs to be between the laser light source (semiconductor laser 101) and the objective lens 106, and can be arranged between the beam splitter 105 and the reflective objective lens 601.

Each of the above embodiments is an example of a preferred embodiment of the present invention, and the present invention is not limited to these.
For example, in each of the above-described embodiments, the configuration in which the recording medium is detachable has been described as an example. However, the recording medium may be provided in the apparatus like a hard disk drive that is a kind of magnetic recording apparatus.
As described above, the present invention can be variously modified.

It is a figure which shows the polarization direction of radial polarization. 1 is a diagram illustrating a configuration of an optical memory device according to a first embodiment in which the present invention is preferably implemented; It is a figure which shows the structure of a light shielding element. It is a figure which shows the structure of a recording medium. It is a figure which shows the shape of a recording pit. It is a figure which shows the structure of the optical memory device concerning 2nd Embodiment which implemented this invention suitably. It is a figure which shows the structure of the reflecting plate with which the beam splitter of the optical memory device concerning 2nd Embodiment is provided. It is a figure which shows the structure of the optical memory device concerning 3rd Embodiment which implemented this invention suitably. It is a figure which shows the modification structural example of the optical memory device concerning 3rd Embodiment. It is a figure which shows the structure of the optical memory device concerning 4th Embodiment which implemented this invention suitably. It is a figure which shows the structure of the optical memory device concerning 5th Embodiment which implemented this invention suitably. It is a figure which shows the structure of the semiconductor laser with which the optical memory device concerning 5th Embodiment is provided. It is a figure which shows the structure of the optical memory device concerning 6th Embodiment which implemented this invention suitably. It is a figure which shows the structure of the reflection type objective lens with which the optical memory device concerning 6th Embodiment is provided. It is a figure which shows the structure of the reflection type objective lens with which the optical memory device concerning 6th Embodiment is provided. It is a figure which shows the structure of the recording medium used for the optical memory device concerning 6th Embodiment. It is a figure which shows the shape of a recording pit. It is a figure which shows the structure of the objective lens used when the optical memory device concerning 6th Embodiment is comprised using a transmissive | pervious objective lens. It is a figure which shows the structure of the optical memory device by a prior art. It is a figure which shows the structure of the optical memory device by a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Motor 20, 30 Recording medium 21, 31 Transparent substrate 22, 32 Recording layer 23, 33 Protective layer 24, 34 Recording pit 101 Semiconductor laser 102 Collimating lens 103 Polarization conversion element 104 Light shielding element 105, 201 Beam splitter 106 Objective lens 107 Lens 108 Photodetectors 301, 302, 401 Axicon 601 Reflective objective lens 1011 Transparent window 1061 Light shielding film 2011 Dielectric multilayer film 2012 Reflective film 6011 Transparent resin 6012 Refractive surface 6013 First reflective surface 6014 Second reflective surface

Claims (10)

A light emitting optical system for generating a radially polarized axially symmetric donut beam having a circular cross-sectional intensity distribution and a radial electric field oscillation distribution with respect to the central axis;
A condensing optical system for condensing and irradiating the recording surface of the recording medium with the axially symmetric polarized donut beam of radial polarization;
An optical memory device comprising: a detection optical system that guides light reflected by the recording surface of the recording medium to the radial-polarized axially symmetric polarized donut beam to a photodetector. A light-shielding part that is included in the light-emitting optical system and converts light emitted from a laser light source into a donut beam having an annular cross section;
A beam splitter that is included in the detection optical system and that is integrated with a reflecting portion that reflects the light reflected by the recording surface of the recording medium toward the detector, with respect to the radial-polarized axially symmetric polarized donut beam; The optical memory device according to claim 1.   2. The optical memory device according to claim 1, wherein the light emitting optical system converts light emitted from a laser light source into a donut beam using an axicon.   2. The optical memory according to claim 1, wherein the light-emitting optical system includes a configuration in which an axicon is disposed between a laser light source and a collimating lens that converts diffused light emitted from the laser light source into parallel light. apparatus.   5. The optical memory device according to claim 4, wherein the laser light source is housed in a case, and the axicon is disposed in an opening that guides diffused light emitted from the laser light source to the outside of the case. A light emitting optical system for generating a radially polarized axially symmetric polarized beam having a radial electric field vibration distribution with respect to the central axis;
A conversion condensing optical system for converting the radially polarized axially symmetric polarized beam into a radially polarized axially symmetric donut beam having a circular cross section and condensing and irradiating the recording surface of the recording medium;
An optical memory device comprising: a detection optical system that guides light reflected by the recording surface of the recording medium to the radial-polarized axially symmetric polarized donut beam to a photodetector.   7. The optical memory device according to claim 6, wherein the conversion condensing optical system is configured using a reflection type objective lens.   The optical memory device according to claim 1, wherein the recording medium is a surface recording type recording medium.   9. The optical memory device according to claim 1, further comprising means for detachably holding the recording medium.   9. The optical memory device according to claim 1, wherein the recording medium is incorporated in the device.

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