WO2009119608A1 - Optical unit, optical information recording/reproducing device and optical information recording/reproducing method - Google Patents

Abstract

A light quantity of a beam can be increased by using a single beam as a focal point controlling beam. At the time of receiving by an optical detector a beam which has been collected on a focal point controlling reference surface, other unnecessary beams received by the optical detector are eliminated.

Description

Optical unit, optical information recording / reproducing apparatus, and optical information recording / reproducing method

The present invention relates to an optical unit for recording and reproducing information three-dimensionally with respect to an optical recording medium, an optical information recording and reproducing apparatus using the optical unit, and an optical information recording and reproducing method.

As one of the technologies for increasing the capacity of optical recording media, information is recorded and reproduced three-dimensionally with respect to the optical recording medium by utilizing not only the in-plane dimension of the optical recording medium but also the dimension in the thickness direction. There is a three-dimensional recording / reproducing technique. As one of the three-dimensional recording / reproducing techniques, there is a multilayer recording technique using an optical recording medium having a plurality of recording layers. Such an optical unit for multilayer recording is disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-51129.

FIG. 1 is a block diagram for explaining an optical unit described in Japanese Patent Application Laid-Open No. 2003-51129. This optical unit includes a laser 52, a convex lens 53a, a convex lens 53b, a diffraction lens 54, a polarizing beam splitter 55, a quarter wavelength plate 56, a mirror 57, an objective lens 58, and a photodetector 59. It comprises. A disk 51 used in this optical unit includes a substrate 60 and a plurality of recording layers 61a to 61d.

The positional relationship of each component of this optical unit will be described. The laser 52, the convex lens 53a, the diffractive lens 54, the polarization beam splitter 55, and the quarter wavelength plate 56 are arranged in this order so as to share the same first optical axis. The polarizing beam splitter 55, the convex lens 53b, and the photodetector 59 are arranged in this order, sharing a second optical axis that intersects the first optical axis at a right angle in the polarizing beam splitter 55. A mirror 57 is disposed on the extended line of the first optical axis at an angle of 45 degrees with respect to the first optical axis. The objective lens 58 and the disk 51 are arranged in this order while sharing a third optical axis that intersects the first optical axis at a right angle in the mirror 57.

The operation of this optical unit will be described. The beam emitted from the laser 52 passes through the convex lens 53a and is converted from divergent light into parallel light, and is divided by the diffraction lens 54 into five beams 63a to 63e. Here, the beam 63a is a recording / reproducing beam, and the beams 63b to 63e are focus control beams. These beams are incident on the polarization beam splitter 55 as P-polarized light, and almost 100% are transmitted, transmitted through the quarter-wave plate 56, converted from linearly polarized light to circularly polarized light, reflected by the mirror 57, and objective lens. The light is condensed in the disk 51 by 58. The five beams reflected in the disk 51 pass through the objective lens 58 in the reverse direction, are reflected by the mirror 57, pass through the quarter wavelength plate 56, and are converted from circularly polarized light to linearly polarized light. The light converted into the linearly polarized light is incident on the polarization beam splitter 55 as S-polarized light, and almost 100% is reflected, passes through the convex lens 53b, is converted from parallel light into convergent light, and is received by the photodetector 59. . Based on the output from the photodetector 59, a focus error signal for controlling the condensing position of the beam 63a in the optical axis direction is generated.

In the disk 51, a reference surface 62 having a groove is formed on a substrate 60, and four recording layers 61a to 61d are formed thereon. By driving the objective lens 58 so that the beams 63e, 63d, 63c, and 63b are condensed on the reference surface 62, the beam 63a is condensed in the recording layers 61a, 61b, 61c, and 61d, respectively. Therefore, information can be recorded / reproduced with respect to each of the recording layers 61a to 61d using the beam 63a.

2A to 2B are cross-sectional views for explaining the configuration of the diffractive lens 54. FIG. FIG. 2A shows a configuration in which a diffractive lens 54a, which is a volume type diffractive lens, is used. FIG. 2B shows a configuration in which a diffractive lens 54b, which is a Fresnel type diffractive lens, is used.

For example, zero-order light from the diffractive lens 54a or 54b is used as the beam 63a, and first-order to fourth-order diffracted light from the diffractive lens 54a or 54b is used as the beams 63b to 63e, respectively.

In this optical unit, the diffraction lens 54 always generates four beams 63b to 63e, which are focus control beams. For this reason, the diffraction efficiency for each beam in the diffractive lens 54 cannot be increased, and the light quantity of each beam cannot be increased. Of the four beams, when the light focused on the reference plane 62 is received by the photodetector 59, unnecessary beams that are not focused on the reference plane 62 are also received by the photodetector 59. As a result, noise and crosstalk are mixed in the focus error signal, and the focusing position of the beam 63a, which is a recording / reproducing beam, cannot be correctly controlled in the optical axis direction.

Also, as one of the three-dimensional recording / reproducing technologies, there is a bit-type hologram recording technology. The two beams facing each other are focused and interfered at the same position in the recording layer of the optical recording medium to form a minute diffraction grating at the focused position. Thereby, information is recorded. Information is reproduced by condensing one of the two beams in the recording layer of the optical recording medium and detecting the reflected light from the diffraction grating. As an optical unit for recording such a bit-type hologram, “Drive System for Micro-Reflector Recording Employing Blue Laser Diode” (Internal Symposium on Optical Memory. is there. However, this optical unit does not have a function of correctly controlling the focusing position of the recording / reproducing beam in the optical axis direction.

In relation to the above, Japanese Patent Application Laid-Open No. 2000-292755 discloses a technique relating to an aberration correction element. In this aberration correction element, a plurality of transparent conductive layers and a plurality of electro-optical material layers are alternately laminated so as to include at least three transparent conductive layers and two or more electro-optical material layers. This aberration correction element corrects aberrations as follows. That is, an arbitrary transparent conductive layer among the plurality of transparent conductive layers is divided. At least some of the divided transparent conductive layers function as a plurality of electrodes. By using these plural electrodes to electrically control the refractive index of the electro-optic material layer, the optical path difference is changed depending on the location, the phase of the incident light is controlled, and the aberration is corrected.

Japanese Patent Application Laid-Open No. 2002-74731 discloses a technique related to an optical pickup device. This optical pickup device includes a recording medium, a semiconductor laser light source, an objective lens, an actuator, an optical axis direction changer, and a change detection means. Here, the recording medium has a recording layer. The semiconductor laser light source emits laser light. The objective lens focuses the laser light in the recording layer of the recording medium. The actuator drives the objective lens at least in the focus direction. The optical axis direction shifter is provided between the objective lens and the light source. The shift detection means detects the shift of the optical axis direction shifter. The optical pickup device has the following characteristics. That is, in an information recording / reproducing apparatus that records and reproduces a signal by moving an optical axis direction shifter and focusing on a recording medium having a different disc thickness, a pupil diameter of the objective lens is set to a and the laser entering the objective lens The maximum movable range of the optical axis direction changer is set to a range where a / w is 0.8 or less, where w is the capturing range of the intensity that is 1 / e ^{2 of} light.

Also, Japanese Patent Laid-Open No. 2002-334476 discloses a technique related to an optical pickup device. This optical pickup device includes a light source, an objective lens, a condensing optical system, a detecting unit, and a driving unit. Here, the objective lens condenses the light beam from the light source on the information recording surface of the optical information recording medium. The condensing optical system includes a spherical aberration correcting unit that is disposed in an optical path between the light source and the objective lens and corrects a variation in spherical aberration. The detecting means detects a change in spherical aberration by detecting reflected light from the information recording surface. The driving unit drives the spherical aberration correcting unit to correct the variation of the spherical aberration according to the detection result of the detecting unit. In this optical pickup device, the spherical aberration correcting means has a movable element that can be displaced along at least one optical axis, and the drive means is at least a first actuator having a different response frequency band for moving the movable element. And a second actuator.

Japanese Patent Laid-Open No. 2003-77142 discloses a technique related to a focusing control device. The focusing control device includes an objective lens, an aberration correction unit, and a photodetector. Here, the objective lens focuses the light beam on the recording layer of the multilayer recording medium having a plurality of recording layers. The aberration correction unit corrects the aberration of the reflected light beam from the recording layer. The photodetector receives the reflected light beam. The optical pickup focusing control device includes a first generator, a second generator, and a controller. Here, the first generator generates a focus error value of the light beam from the detection signal of the photodetector. The second generator generates an aberration amount of the reflected light beam from the detection signal of the photodetector. The controller controls the focus position of the objective lens based on the focus error value, and controls the aberration correction amount of the aberration correction unit based on the aberration amount. Note that the controller executes the focus jump after adjusting the aberration correction unit to the aberration correction value for the other recording layer at the time of the focus jump from one recording layer to the other recording layer.

Also, Japanese Patent Application Laid-Open No. 2005-284081 discloses a technique related to an optical element. This optical element is disposed in the optical path of linearly polarized light emitted from a point light source. This optical element includes a birefringent substrate and switching means. Here, the birefringent substrate has an axis having a high refractive index directed in a direction parallel or perpendicular to the polarization direction. The switching means switches the angle formed between the polarization direction of the linearly polarized light and the high refractive index axis of the birefringent substrate to a direction perpendicular or parallel within a plane orthogonal to the optical path.

Japanese Patent Application Laid-Open No. 2005-317120 discloses recording / reproduction with respect to an optical recording medium in which a plurality of recording layers are laminated, or recording / reproduction with respect to a plurality of optical recording media having different protective substrate thicknesses for protecting the recording surface. A technique related to an optical pickup performed by a light beam having a wavelength and a numerical aperture is disclosed. The optical pickup includes a first light source, a second light source, a third light source, an objective lens, a diffraction unit, a liquid crystal diffraction unit, a light receiving unit, an optical recording medium detection unit, and a liquid crystal control unit. And. Here, the first light source emits a first light beam having a first wavelength. The second light source emits a second light beam having a second wavelength. The third light source emits a third light beam having a third wavelength. The objective lens collects the first, second and third light beams on the individual optical recording media. The diffracting means condenses the first light beam on the first optical recording medium having the first protective substrate thickness through the objective lens, and the second light beam has the second protective substrate thickness. The second optical recording medium is condensed, and the third light beam is condensed on the third optical recording medium having the third protective substrate thickness. Therefore, the diffractive means is disposed immediately before the light source side of the objective lens. The liquid crystal diffractive means is disposed immediately before the light source side of the diffractive means, and changes the refractive index distribution in the cross section perpendicular to the traveling direction of the light beam passing therethrough. The light receiving means receives the reflected beam reflected by each optical recording medium and converts it into an electrical signal. The optical recording medium detection means detects the type of an optical recording medium in which a plurality of recording layers are laminated or an optical recording medium having a different protective substrate thickness for protecting the recording surface. The liquid crystal control means controls the liquid crystal alignment pattern of the liquid crystal diffraction means according to the type of the recording layer or the optical recording medium detected by the optical recording medium detection means. The objective lens, the diffraction unit, and the liquid crystal diffraction unit are fixed to each other, and the first light beam, the second light beam, and the third light beam are incident on the liquid crystal diffraction unit in an infinite system.

Japanese Patent Laid-Open No. 2006-258838 discloses a technique related to an optical scanning device. The optical scanning device includes a light source, a focal length varying unit, an optical deflecting unit, an optical scanning unit, a beam spot diameter detecting unit, and a beam spot position detecting unit. Here, the focal length changing means can change the focal length. The light deflecting means can deflect the light beam at least in the sub-scanning direction. The optical scanning unit scans the light beam. The imaging lens forms an image on the image plane of the light beam scanned by the optical scanning unit. The beam spot diameter detecting means detects, converts, or predicts the beam spot diameter. The beam spot position detecting means detects, converts, or predicts at least the beam spot position in the sub-scanning direction. This optical scanning device controls both the beam spot diameter and the beam spot position based on the detection results of the beam spot diameter detecting means and the beam spot position detecting means.

Also, Japanese Patent Application Laid-Open No. 2006-302367 discloses a technique related to an optical pickup. This optical pickup includes a light source, a collimating lens, an objective lens, and a light receiving element. Here, the collimating lens converts divergent light emitted from the light source into parallel light. The objective lens focuses the light beam on the optical recording medium. The light receiving element detects reflected light from the optical recording medium. In this optical pickup, at least one of a collimator lens and an objective lens has a plurality of electrodes, an insulating layer, and an ultraviolet curable or thermosetting conductive liquid on one surface of a solid lens formed of resin or glass. It is comprised by the liquid lens laminated | stacked in order.

An object of the present invention is to solve the above-described problems in an optical unit and an optical information recording / reproducing apparatus for three-dimensional information recording / reproducing with respect to an optical recording medium, and to collect a recording / reproducing beam. An object of the present invention is to provide an optical unit capable of correctly controlling the position in the optical axis direction, an optical information recording / reproducing apparatus using the optical unit, and an optical information recording / reproducing method.

The optical unit of the present invention, for an optical recording medium having a recording layer and a focus control reference surface, condenses a recording / reproducing beam in the recording layer and a focus control beam on the focus control reference surface, Information is recorded and reproduced by a recording / reproducing beam. The optical unit includes a light source, an objective lens system, a photodetector, variable focus means, and focus movement means. Here, the light source emits a recording / reproducing beam and a focus control beam. The objective lens system is for condensing a recording / reproducing beam and a focus control beam on an optical recording medium. The photodetector receives the reflected light of the recording / reproducing beam and the reflected light of the focus control beam from the optical recording medium. The variable focus means is for changing the interval between the focus position of the recording / reproducing beam and the focus position of the focus control beam. The focus moving means is for enabling the focusing positions of the recording / reproducing beam and the focus control beam to be moved in the optical axis direction.

An optical information recording / reproducing method according to the present invention includes a step of emitting a recording / reproducing beam and a focus control beam from a light source, a step of condensing the recording / reproducing beam in a recording layer of an optical recording medium, and a focus control. The step of condensing the beam for focusing on the reference surface for focus control of the optical recording medium, and the reflected light of the recording / reproducing beam and the reflected light of the focus controlling beam from the optical recording medium are received by the photodetector A step of changing the distance between the condensing position of the recording / reproducing beam and the converging position of the focus control beam using the variable focus means, and the recording / reproducing beam and the focus control beam using the focus moving means. Moving the light collecting position in the direction of the optical axis.

According to the present invention, an optical unit, an optical information recording / reproducing apparatus, an optical unit capable of correctly controlling the focusing position of a recording / reproducing beam in the optical axis direction without mixing noise and crosstalk into the focus error signal. An information recording / reproducing method can be provided.

The objects, effects, and features of the present invention will become more apparent from the description of the embodiments in conjunction with the accompanying drawings.
FIG. 1 is a block diagram for explaining an optical unit in the related art. 2A to 2B are cross-sectional views for explaining the configuration of a diffractive lens in the related art. FIG. 2A shows a configuration in which a diffractive lens 54a, which is a volume type diffractive lens, is used. FIG. 2B shows a configuration in which a diffractive lens 54b, which is a Fresnel type diffractive lens, is used. FIG. 3 is a block diagram showing a schematic configuration of the optical unit according to the first embodiment of the present invention. 4A to 4B are diagrams showing optical paths of an incident beam to the disk 2a and a reflected beam from the disk 2a when information is recorded on the disk 2a. FIG. 4A is a diagram when the beam 25a is selectively generated. FIG. 4B is a diagram when the beam 25i is selectively generated. 5A to 5B are diagrams showing optical paths of an incident beam to the disk 2a and a reflected beam from the disk 2a when information is reproduced from the disk 2a. FIG. 5A is a diagram when the beam 25a is selectively generated. FIG. 5B is a diagram when the beam 25i is selectively generated. FIG. 6 is a cross-sectional view of the active diffractive lens 14. FIG. 7 is a table showing the relationship between the voltage applied to the liquid crystal layer in the active diffractive lens 14 and the focal length of the diffractive lens. FIG. 8 is a block diagram showing a schematic configuration of the optical information recording / reproducing apparatus according to the first embodiment of the present invention. FIG. 9 is a block diagram showing a schematic configuration of an optical unit according to the second embodiment of the present invention. 10A to 10B are diagrams showing optical paths of an incident beam to the disk 2b and a reflected beam from the disk 2b when information is recorded on the disk 2b. FIG. 10A is a diagram when the beam 26a is selectively generated. FIG. 10B is a diagram when the beam 26i is selectively generated. 11A to 11B are diagrams showing optical paths of an incident beam to the disk 2b and a reflected beam from the disk 2b when information is reproduced from the disk 2b. FIG. 11A is a diagram when the beam 26a is selectively generated. FIG. 11B is a diagram when the beam 26i is selectively generated. FIG. 12 is a block diagram showing a schematic configuration of an optical information recording / reproducing apparatus according to the second embodiment of the present invention.

DETAILED DESCRIPTION Embodiments for carrying out the present invention will be described below with reference to the accompanying drawings.

(First embodiment)
FIG. 3 is a block diagram showing a schematic configuration of the optical unit according to the first embodiment of the present invention. This optical unit includes a laser 3a, a convex lens 4a, an active wavelength plate 5, a polarization beam splitter 7a, a mirror 8a, an interference filter 9, a quarter wavelength plate 11a, and an objective lens 12a. This optical unit further includes a mirror 8b, a mirror 8c, a mirror 10a, a quarter-wave plate 11b, and an objective lens 12b. The optical unit further includes a convex lens 4f, a photodetector 13a, a laser 3b, a convex lens 4g, a polarizing beam splitter 7d, an active diffraction lens 14, a convex lens 4h, a cylindrical lens 15, and a photodetector 13b. It comprises.

Lasers 3a and 3b, which are light sources, are semiconductor lasers that emit a recording / reproducing beam having a wavelength of 405 nm and a focus controlling beam having a wavelength of 650 nm, respectively. The interference filter 9 reflects a beam having a wavelength of 405 nm and transmits a beam having a wavelength of 650 nm. The active diffractive lens 14 which is a variable focus unit selectively generates one of a plurality of diffracted beams having different orders from the incident beam. The objective lenses 12a and 12b correspond to focal point moving means and are mounted on an actuator (not shown).

The beam emitted from the laser 3a passes through the convex lens 4a, is converted from divergent light into parallel light, and enters the active wave plate 5. The active wave plate 5 has an effect of a quarter wave plate with respect to incident light when information is recorded on the disk 2a which is an optical recording medium. Further, when reproducing information from the disk 2a, the active wave plate 5 has the effect of a half wave plate with respect to the incident light. Therefore, when recording information on the disk 2a, the beam incident on the active wave plate 5 is transmitted through the active wave plate 5 and converted from linearly polarized light to circularly polarized light, and about 50% of the light is polarized by the polarizing beam splitter 7a. About 50% of the light is transmitted through the polarization beam splitter 7a as a P-polarized component. On the other hand, when information is reproduced from the disk 2a, the beam incident on the active wave plate 5 is transmitted through the active wave plate 5 and the polarization direction is changed by 90 °, and is incident on the polarization beam splitter 7a as S-polarized light. % Is reflected. Here, the active wavelength plate 5 and the polarization beam splitter 7a correspond to beam switching means.

The active wave plate 5 is configured to sandwich a liquid crystal layer between two substrates. Transparent electrodes for applying an alternating voltage to the liquid crystal layer are formed on the surface of the two substrates on the liquid crystal layer side. The liquid crystal layer has uniaxial refractive index anisotropy. The thickness of the liquid crystal layer is determined so that the phase difference between the polarization component in the direction parallel to the optical axis and the polarization component in the direction perpendicular to the optical axis generated in the beam transmitted through the liquid crystal layer is π. . When an AC voltage having an effective value of 2.5 volts is applied to the liquid crystal layer, the direction of the optical axis of the liquid crystal layer is an intermediate direction between the direction perpendicular to the optical axis of the incident light and the direction parallel to the optical axis. At this time, the active wave plate 5 has the effect of a quarter wave plate. On the other hand, when no AC voltage is applied to the liquid crystal layer, the direction of the optical axis of the liquid crystal layer is a direction perpendicular to the optical axis of the incident light. At this time, the active wave plate 5 has the effect of a half wave plate.

When recording information on the disk 2a, the beam reflected by the polarization beam splitter 7a is reflected by the mirror 8a and the interference filter 9, passes through the quarter wavelength plate 11a, and is converted from linearly polarized light to circularly polarized light. The light is condensed in the disk 2a by the lens 12a. The beam that has passed through the polarizing beam splitter 7a is reflected by the mirror 8b, the mirror 8c, and the mirror 10a, passes through the quarter-wave plate 11b, is converted from linearly polarized light to circularly polarized light, and is converted into linearly polarized light by the objective lens 12b. It is focused on.

On the other hand, when information is reproduced from the disk 2a, the beam reflected by the polarization beam splitter 7a is reflected by the mirror 8a and the interference filter 9, passes through the quarter wavelength plate 11a, and is converted from linearly polarized light to circularly polarized light. The light is condensed in the disk 2a by the objective lens 12a. The beam reflected in the disk 2a passes through the objective lens 12a in the reverse direction, passes through the quarter-wave plate 11a, is converted from circularly polarized light to linearly polarized light, is reflected by the interference filter 9 and the mirror 8a, and is polarized. The light enters the splitter 7a as P-polarized light. Almost 100% of the light incident on the polarization beam splitter 7a is transmitted, passes through the convex lens 4f, is converted from parallel light into convergent light, and is received by the photodetector 13a. Based on the output from the photodetector 13a, a reproduction signal indicating information recorded on the disc 2a is generated.

The beam emitted from the laser 3b passes through the convex lens 4g and is converted from divergent light to weak convergent light, and enters the polarization beam splitter 7d as P-polarized light, and almost 100% is transmitted. The light that has passed through the polarization beam splitter 7d is diffracted by the active diffraction lens 14, passes through the interference filter 9, passes through the quarter wavelength plate 11a, and is converted from linearly polarized light to circularly polarized light. It is condensed inside. The beam reflected in the disk 2a passes through the objective lens 12a in the reverse direction, passes through the quarter-wave plate 11a, is converted from circularly polarized light to linearly polarized light, and passes through the interference filter 9. The light transmitted through the interference filter 9 is diffracted by the active diffractive lens 14, enters the polarization beam splitter 7 d as S-polarized light, and is reflected almost 100%. The light reflected by the polarizing beam splitter 7d is transmitted from the convex lens 4h to be converted from weak divergent light to convergent light, transmitted through the cylindrical lens 15 and given astigmatism, and received by the photodetector 13b. Based on the output from the photodetector 13b, a focus error signal for controlling the condensing position of the recording / reproducing beam in the optical axis direction is generated by a known astigmatism method.

4A to 4B are diagrams showing optical paths of an incident beam to the disk 2a and a reflected beam from the disk 2a when information is recorded on the disk 2a. FIG. 4A is a diagram when the beam 25a is selectively generated. FIG. 4B is a diagram when the beam 25i is selectively generated.

FIG. 5 is a diagram showing optical paths of an incident beam to the disk 2a and a reflected beam from the disk 2a when information is reproduced from the disk 2a. FIG. 5A is a diagram when the beam 25a is selectively generated. FIG. 5B is a diagram when the beam 25i is selectively generated.

The disk 2a is configured to sandwich the recording layer 17a between the substrates 16a and 16b. Wavelength selection layers 18a and 18b are formed on the surfaces of the substrates 16a and 16b on the recording layer 17a side, respectively. The wavelength selection layers 18a and 18b transmit a beam having a wavelength of 405 nm and reflect the beam having a wavelength of 650 nm. Here, the wavelength selection layer 18a corresponds to a focus control reference plane. For example, glass is used as the material of the substrates 16a and 16b. As a material of the recording layer 17a, for example, a photopolymer is used. For example, silicon dioxide and titanium dioxide are used as the material of the wavelength selection layers 18a and 18b.

4A to 4B represent beams 23a and 23b emitted from the laser 3a, the beam reflected by the polarization beam splitter 7a and the beam transmitted through the polarization beam splitter 7a, respectively. A beam 23a shown in FIGS. 5A to 5B represents a beam emitted from the laser 3a and reflected by the polarization beam splitter 7a. The beams 25a to 25i shown in FIGS. 4A to 4B or 5A to 5B represent beams that can be selectively generated by the active diffraction lens 14 from the beam emitted from the laser 3b. A solid line and a dotted line in the figure respectively indicate a beam that is actually generated and a beam that is not actually generated. 4A and 5A, and FIGS. 4B and 5B show the optical paths of the beams when the beams 25a and 25i are selectively generated, respectively.

In FIG. 4A, the objective lens 12a is driven in the optical axis direction by an actuator (not shown) so that the beam 25a is condensed on the wavelength selection layer 18a. The beam 25a is reflected by the wavelength selection layer 18a and received by the photodetector 13b. At this time, the interval between the condensing position of the beam 23a and the condensing position of the beam 25a is narrow. Therefore, the beam 23a is condensed on the condensing point 21a in the recording layer 17a, which is a position close to the wavelength selection layer 18a. Further, the objective lens 12b is driven in the optical axis direction by an actuator (not shown) so that the beam 23b is similarly focused on the focusing point 21a. The beam 23a and the beam 23b interfere at the condensing point 21a, and a minute diffraction grating is formed at the condensing point 21a.

In FIG. 4B, the objective lens 12a is driven in the optical axis direction by an actuator (not shown) so that the beam 25i is condensed on the wavelength selection layer 18a. The beam 25i is reflected by the wavelength selection layer 18a and received by the photodetector 13b. At this time, the distance between the condensing position of the beam 23a and the condensing position of the beam 25i is wide. Therefore, the beam 23a is condensed on the condensing point 21b in the recording layer 17a that is far from the wavelength selection layer 18a. Further, the objective lens 12b is driven in the optical axis direction by an actuator (not shown) so that the beam 23b is similarly focused on the focusing point 21b. The beam 23a and the beam 23b interfere at the condensing point 21b, and a minute diffraction grating is formed at the condensing point 21b.

In FIG. 5A, the objective lens 12a is driven in the optical axis direction by an actuator (not shown) so that the beam 25a is condensed on the wavelength selection layer 18a. The beam 25a is reflected by the wavelength selection layer 18a and received by the photodetector 13b. At this time, the interval between the condensing position of the beam 23a and the condensing position of the beam 25a is narrow. Therefore, the beam 23a is focused on the diffraction grating 22a in the recording layer 17a that is close to the wavelength selection layer 18a. The diffraction grating 22a is formed at the condensing point 21a in FIG. 4A. The beam 23a is reflected by the diffraction grating 22a and received by the photodetector 13a.

In FIG. 5B, the objective lens 12a is driven in the optical axis direction by an actuator (not shown) so that the beam 25i is condensed on the wavelength selection layer 18a. The beam 25i is reflected by the wavelength selection layer 18a and received by the photodetector 13b. At this time, the distance between the condensing position of the beam 23a and the condensing position of the beam 25i is wide. Therefore, the beam 23a is focused on the diffraction grating 22b in the recording layer 17a that is far from the wavelength selection layer 18a. The diffraction grating 22b is formed at the condensing point 21b in FIG. 4B. The beam 23a is reflected by the diffraction grating 22b and received by the photodetector 13a.

Here, the diffraction grating formed at the condensing position has bit data information. The active diffractive lens 14 selectively generates one of the beams 25a to 25i. The interval between the condensing position of the beam 23a and the condensing position of the selectively generated beam is controlled to change in nine steps. The objective lens 12a is driven so that the selectively generated beam is condensed on the wavelength selection layer 18a, and the condensing position of the beam 23a is changed in nine steps in the optical axis direction in the recording layer 17a. be able to. Therefore, information can be recorded / reproduced in nine layers in the thickness direction of the recording layer 17a using the beams 23a and 23b.

In the present embodiment, a single beam selectively generated by the active diffraction lens 14 among the beams 25a to 25i is used as the focus control beam. For this reason, the light quantity of the selectively generated beam can be increased. In addition, when the beam focused on the wavelength selection layer 18a is received by the photodetector 13b, there is no unnecessary beam received by the photodetector 13b. As a result, noise and crosstalk are not mixed in the focus error signal, and the condensing position of the beam 23a can be correctly controlled in the optical axis direction.

FIG. 6 is a cross-sectional view of the active diffractive lens 14. In the active diffractive lens 14, the liquid crystal layer 28a and the filler 29a are sandwiched between the substrates 27a and 27b, the liquid crystal layer 28b and the filler 29b are sandwiched between the substrates 27b and 27c, and the liquid crystal is interposed between the substrates 27c and 27d. The layer 28c and the filler 29c are sandwiched, and the liquid crystal layer 28d and the filler 29d are sandwiched between the substrates 27d and 27e. Fresnel type diffractive lenses 30a to 30d are formed on the boundary surfaces between the liquid crystal layers 28a to 28d and the fillers 29a to 29d facing each other. Transparent electrodes 31a and 31b for applying an alternating voltage to the liquid crystal layer 28a are formed on the surfaces of the substrates 27a and 27b on the liquid crystal layer 28a side, respectively. Transparent electrodes 31c and 31d for applying an AC voltage to the liquid crystal layer 28b are formed on the surfaces of the substrates 27b and 27c on the liquid crystal layer 28b side, respectively. Transparent electrodes 31e and 31f for applying an AC voltage to the liquid crystal layer 28c are formed on the surfaces of the substrates 27c and 27d on the liquid crystal layer 28c side, respectively. Transparent electrodes 31g and 31h for applying an alternating voltage to the liquid crystal layer 28d are formed on the surfaces of the substrates 27d and 27e on the liquid crystal layer 28d side, respectively. For example, glass is used as the material of the substrates 27a to 27e. As a material for the liquid crystal layers 28a to 28d, for example, nematic liquid crystal is used. As a material for the fillers 29a to 29d, for example, silicon oxynitride is used. As a material of the transparent electrodes 31a to 31h, for example, ITO (Indium Tin Oxide) is used.

The liquid crystal layers 28a to 28d have uniaxial refractive index anisotropy. When the refractive indexes for the polarization components in the directions parallel to and perpendicular to the optical axes of the liquid crystal layers 28a to 28d are ne and no, and the refractive indexes of the fillers 29a to 29d are nf, nf = (ne + no) / 2. Suppose there is. Further, when the wavelength of the incident light 32a and 32b is λ, the grating pitch of the diffraction lenses 30a to 30d is p, the distance from the optical axis is r, the thickness is t, and the focal length is f, p = fλ / r, Assume that t = 2λ / (ne−no). However, the focal length f of the diffractive lenses 30a and 30b is different from the focal length f of the diffractive lenses 30c and 30d. Here, assuming that the refractive index of the liquid crystal layers 28a to 28d with respect to the incident light 32a and 32b is n and the phase depth of the diffraction lenses 30a to 30d is φ, φ = 2πt (nf−n) / λ. If φ = −2π, the diffractive lenses 30a to 30d have a −1st order diffraction efficiency of 1 and operate as concave lenses with a focal length of −f. If φ = 0, the diffractive lenses 30a to 30d have a transmittance (0th-order light efficiency) of 1, and do not operate as lenses. If φ = + 2π, the diffractive lenses 30a to 30d operate as convex lenses having a + 1st order diffraction efficiency of 1 and a focal length of + f.

The optical axes of the liquid crystal layers 28a and 28c are in a plane parallel to the plane of the paper including the optical axes of the incident lights 32a and 32b, and the optical axes of the liquid crystal layers 28b and 28d are the plane of the paper including the optical axes of the incident lights 32a and 32b. Is in a plane perpendicular to. Further, it is assumed that the polarization direction of the incident light 32a which is a beam emitted from the laser 3b is parallel to the paper surface, and the polarization direction of the incident light 32b which is a beam reflected by the disk 2a is perpendicular to the paper surface. At this time, the diffraction lenses 30a and 30c act on the incident light 32a, but the diffraction lenses 30b and 30d do not act. The diffraction lenses 30b and 30d act on the incident light 32b, but the diffraction lenses 30a and 30c do not act.

When no AC voltage is applied to the liquid crystal layers 28a to 28d, the optical axes of the liquid crystal layers 28a and 28c are perpendicular to the optical axis of the incident light 32a, and the optical axes of the liquid crystal layers 28b and 28d are aligned with the optical axis of the incident light 32b. The vertical direction. At this time, the refractive index of the liquid crystal layers 28a and 28c with respect to the incident light 32a is n = ne, and the phase depth of the diffraction lenses 30a and 30c is φ = −2π. Further, the refractive index of the liquid crystal layers 28b and 28d with respect to the incident light 32b is n = ne, and the phase depth of the diffraction lenses 30b and 30d is φ = −2π. Accordingly, the diffractive lenses 30a and 30c act as concave lenses having a focal length of −f with respect to the incident light 32a, and the diffractive lenses 30b and 30d act as concave lenses with a focal length of −f with respect to the incident light 32b.

When an AC voltage having an effective value of 2.5 volts is applied to the liquid crystal layers 28a to 28d, the optical axes of the liquid crystal layers 28a and 28c are intermediate between the direction perpendicular to the optical axis of the incident light 32a and the direction parallel to the optical axis. Thus, the optical axes of the liquid crystal layers 28b and 28d are intermediate between the direction perpendicular to the optical axis of the incident light 32b and the direction parallel to the optical axis. At this time, if the refractive index of the liquid crystal layers 28a and 28c with respect to the incident light 32a is n = (ne + no) / 2, the phase depth of the diffraction lenses 30a and 30c is φ = 0. If the refractive index of the liquid crystal layers 28b and 28d with respect to the incident light 32b is n = (ne + no) / 2, the phase depth of the diffraction lenses 30b and 30d is φ = 0. Accordingly, the diffractive lenses 30a and 30c do not act as lenses for the incident light 32a, and the diffractive lenses 30b and 30d do not act as lenses for the incident light 32b.

When an AC voltage having an effective value of 5 volts is applied to the liquid crystal layers 28a to 28d, the optical axes of the liquid crystal layers 28a and 28c are parallel to the optical axis of the incident light 32a, and the optical axes of the liquid crystal layers 28b and 28d are The direction is parallel to the optical axis of the incident light 32b. At this time, the refractive index of the liquid crystal layers 28a and 28c with respect to the incident light 32a is n = no, and the phase depth of the diffraction lenses 30a and 30c is φ = + 2π. The refractive index of the liquid crystal layers 28b and 28d with respect to the incident light 32b is n = no, and the phase depth of the diffraction lenses 30b and 30d is φ = + 2π. Accordingly, the diffractive lenses 30a and 30c act as a convex lens with a focal length of + f with respect to the incident light 32a, and the diffractive lenses 30b and 30d act as a convex lens with a focal length of + f with respect to the incident light 32b.

FIG. 7 is a table showing the relationship between the voltage applied to the liquid crystal layer in the active diffractive lens 14 and the focal length of the diffractive lens. The first liquid crystal layer shown in the figure refers to the liquid crystal layer 28a for the incident light 32a and the liquid crystal layer 28b for the incident light 32b. Similarly, the second liquid crystal layer refers to the liquid crystal layer 28c for the incident light 32a and the liquid crystal layer 28d for the incident light 32b. The first diffractive lens refers to the diffractive lens 30a for the incident light 32a and the diffractive lens 30b for the incident light 32b. Similarly, the second diffractive lens refers to a diffractive lens 30c for incident light 32a and a diffractive lens 30d for incident light 32b.

The first and second diffractive lenses are respectively selected from the three diffracted lights of the −1st order diffracted light, the 0th order light, and the + 1st order diffracted light from the incident light 32a and 32b according to the applied voltages to the first and second liquid crystal layers Is selectively generated. Here, the focal lengths f in the first and second diffractive lenses are expressed as fd1 and fd2, and the values are Fd and Fd, respectively. At this time, the focal length fd1 of the first diffractive lens changes in three stages of −Fd, ∞, and + Fd according to the voltage applied to the first liquid crystal layer, and the focal length fd2 of the second diffractive lens changes to the second liquid crystal. Depending on the voltage applied to the layer, it changes in three stages of -3Fd, ∞, and + 3Fd.

As a result, the active diffractive lens 14 selectively generates one of nine diffracted lights having different orders from the incident lights 32a and 32b in accordance with the voltage applied to the first and second liquid crystal layers. At this time, when the focal length of the active diffractive lens 14 that is the combined focal length of the two diffractive lenses is expressed as fd, when the value Fd is sufficiently larger than the interval between the two diffractive lenses, 1 / fd = 1 / fd1 + 1. / Fd2 holds. The focal length fd of the active diffractive lens 14 changes in nine steps as shown in FIGS. 7A to 7I according to the voltage applied to the first and second liquid crystal layers.

If the thickness of the active diffractive lens 14 is ignored and the object point position and the image point position with respect to the active diffractive lens 14 are ad and bd, respectively, 1 / ad + 1 / bd = 1 / fd is established. Further, ignoring the thickness of the objective lens 12a, assuming that the focal length of the objective lens 12a is fo, the object point position with respect to the objective lens 12a, and the image point position are ao and bo, respectively, 1 / ao + 1 / bo = 1 / fo. It holds.

(A) to (i) shown in FIG. 7 correspond to the state in which the beams 25a to 25i in FIGS. 4A to 4B or 5A to 5B are selectively generated by the active diffraction lens 14, respectively. In order from (a) to (i), 1 / fd changes in nine steps from -4/3 Fd to +4/3 Fd at 1/3 Fd intervals. Assuming that ad = −fo ² / ΔF, 1 / bd changes in nine steps at intervals of 1/3 Fd from −4/3 Fd + ΔF / fo ² to +4/3 Fd + ΔF / fo ² . When Fd, fo ² / ΔF is sufficiently larger than the distance between the active diffractive lens 14 and the objective lens 12a, ao = −bd, so 1 / ao is + 4 / 3Fd−ΔF / fo ² to −4 / until 3Fd-ΔF / fo ² varies 9 stage -1 / 3FD intervals. When Fd and fo ² / ΔF are sufficiently larger than fo, bo changes in nine steps from −fo + 4fo ² / 3Fd−ΔF to fo−4fo ² / 3Fd−ΔF at −fo ² / 3Fd intervals.

On the other hand, regarding the beam 23a in FIGS. 4A to 4B or FIGS. 5A to 5B, if ao = ∞, bo = fo. Assuming that the condensing position of the beam 23a with reference to the condensing positions of the beams 25a to 25i is Δf, Δf changes in nine steps from -4fo ² / 3Fd + ΔF to + 4fo ² / 3Fd + ΔF at an interval of fo ² / 3Fd. For example, if ΔF = 5fo ² / 3Fd, Fd = 300 mm, and fo = 3 mm, Δf changes from 10 μm to 90 μm in 9 steps at 10 μm intervals. Here, even if the voltage applied to the first and second liquid crystal layers varies slightly, the diffraction efficiency of the first and second diffractive lenses varies only slightly, and the focal length does not vary. Therefore, Δf does not vary.

In the present embodiment, the active diffractive lens 14 is a first and second diffractive lens that selectively generates one of three diffracted lights of −1st order diffracted light, 0th order light, and + 1st order diffracted light from incident light. It is comprised by. By changing the focal length of the first diffractive lens in three steps of -Fd, ∞, and + Fd and changing the focal length of the second diffractive lens in three steps of -3Fd, ∞, and + 3Fd, Δf becomes -4fo ² From / 3Fd + ΔF to + 4fo ² / 3Fd + ΔF, it changes in 9 steps at an interval of fo ² / 3Fd. As a result, information is recorded / reproduced on nine layers.

In addition, an active diffractive lens is configured by first, second, and third diffractive lenses that selectively generate one of three diffracted lights of −1st order diffracted light, 0th order light, and + 1st order diffracted light from incident light. It is also possible. The focal length of the first diffractive lens is changed in three steps of -Fd, ∞, + Fd, the focal length of the second diffractive lens is changed in three steps of -3Fd, ∞, + 3Fd, and the focal length of the third diffractive lens is changed. Change to 3 levels of -9Fd, ∞, and + 9Fd. In this case, Δf changes in 27 steps from -13fo ² / 9Fd + ΔF to + 13fo ² / 9Fd + ΔF at an interval of fo ² / 9Fd. As a result, information can be recorded and reproduced on the 27th layer.

In addition, the first and second diffractive lenses that selectively generate one of five diffracted lights of -2nd order diffracted light, -1st order diffracted light, 0th order light, + 1st order diffracted light, and + 2nd order diffracted light from the incident light. It is also possible to construct an active diffractive lens. The focal length of the first diffractive lens is changed in five steps: -Fd / 2, -Fd, ∞, + Fd, + Fd / 2, and the focal length of the second diffractive lens is -5Fd / 2, -5Fd, ∞, + 5Fd, Change to 5 levels of + 5Fd / 2. In this case, Δf changes in 25 steps from -12fo ² / 5Fd + ΔF to + 12fo ² / 5Fd + ΔF at intervals of fo ² / 5Fd. As a result, it is possible to record and reproduce information on 25 layers.

FIG. 8 is a block diagram showing the configuration of the optical information recording / reproducing apparatus according to the first embodiment of the present invention. This optical information recording / reproducing apparatus includes an optical unit 1a, a positioner 33a, a spindle 34a, a controller 35, an active wavelength plate driving circuit 36, a modulation circuit 37, a recording signal generating circuit 38, and a laser driving circuit 39. The amplification circuit 40, the reproduction signal processing circuit 41, the demodulation circuit 42, the laser drive circuit 43, the active diffraction lens drive circuit 44, the amplification circuit 45, the error signal generation circuit 46, and the objective lens drive circuit 47, A positioner driving circuit 49 and a spindle driving circuit 50.

The optical unit 1a corresponds to the above-described optical unit and is mounted on the positioner 33a. The disk 2a is mounted on the spindle 34a. The controller 35 includes an active wave plate driving circuit 36, a circuit from the modulation circuit 37 to the laser driving circuit 39, a circuit from the amplification circuit 40 to the demodulation circuit 42, a laser driving circuit 43, and an active diffractive lens driving circuit 44. The circuit from the amplifier circuit 45 to the objective lens driving circuit 47, the positioner driving circuit 49, and the spindle driving circuit 50 are controlled.

The active wave plate driving circuit 36, which is a beam switching means driving circuit, records the active wave plate 5 so that the active wave plate 5 in the optical unit 1a has the effect of a quarter wave plate when recording information on the disk 2a. An AC voltage having an effective value of 2.5 volts is applied to the liquid crystal layer included in. When reproducing information from the disc 2a, the active wave plate driving circuit 36 applies the liquid crystal layer of the active wave plate 5 so that the active wave plate 5 in the optical unit 1a has the effect of a half wave plate. Do not apply AC voltage.

The modulation circuit 37 modulates a signal input from the outside as recording data according to a modulation rule when recording information on the disk 2a. The recording signal generation circuit 38 generates a recording signal for driving the laser 3a in the optical unit 1a based on the signal modulated by the modulation circuit 37. When recording information on the disk 2a, the laser drive circuit 39 supplies the current corresponding to the recording signal to the laser 3a based on the recording signal generated by the recording signal generation circuit 38 to drive the laser 3a. When reproducing information from the disk 2a, the laser driving circuit 39 supplies a constant current to the laser 3a so as to drive the laser 3a so that the power of the emitted light from the laser 3a becomes constant.

The amplification circuit 40 amplifies the voltage signal output from the photodetector 13a in the optical unit 1a when reproducing the information recorded in the form of a diffraction grating on the disk 2a. The reproduction signal processing circuit 41 generates a reproduction signal, equalizes the waveform, and binarizes it based on the voltage signal amplified by the amplifier circuit 40. The demodulation circuit 42 demodulates the signal binarized by the reproduction signal processing circuit 41 according to a demodulation rule, and outputs it as reproduction data to the outside.

When recording information on the disk 2a and reproducing information from the disk 2a, the laser drive circuit 43 applies to the laser 3b so that the power of the laser light emitted from the laser 3b in the optical unit 1a is constant. A constant current is supplied to drive the laser 3b.

The active diffractive lens driving circuit 44, which is a variable focus means driving circuit, has an effective value of 0 in the liquid crystal layers 28a to 28d of the active diffractive lens 14 when recording information on the disk 2a and reproducing information from the disk 2a. An AC voltage of any one of volts, 2.5 volts, and 5 volts is applied. The active diffractive lens 14 in the optical unit 1a selectively generates one of the beams 25a to 25i according to the applied voltage.

The amplification circuit 45 amplifies a voltage signal output from the photodetector 13b in the optical unit 1a when recording information on the disk 2a and reproducing information from the disk 2a. The error signal generation circuit 46 generates a focus error signal for driving the objective lenses 12a and 12b in the optical unit 1a based on the voltage signal amplified by the amplification circuit 45. The objective lens drive circuit 47 is a focus moving means drive circuit that corrects a deviation in the optical axis direction of the light collection position of the selectively generated beam of the beams 25a to 25i with respect to the wavelength selection layer 18a. The objective lens drive circuit 47 supplies current corresponding to the focus error signal to an actuator (not shown) based on the focus error signal generated by the error signal generation circuit 46 to drive the objective lenses 12a and 12b in the optical axis direction. .

Positioner drive circuit 49 supplies current to a motor (not shown) to move the positioner 33a in the radial direction of the disk 2a. Thus, when information is recorded on the disk 2a, the condensing positions of the beams 23a and 23b move in the radial direction of the disk 2a. When information is reproduced from the disk 2a, the condensing position of the beam 23a is the radius of the disk 2a. Move in the direction.

The spindle drive circuit 50 supplies a current to a motor (not shown) to rotate the spindle 34a. Thus, when information is recorded on the disk 2a, the condensing positions of the beams 23a and 23b move in the tangential direction of the disk 2a. When information is reproduced from the disk 2a, the condensing position of the beam 23a is tangent to the disk 2a. Move in the direction.

In the first embodiment, the optical unit forms tracks parallel to the tangential direction of the disk 2a on the wavelength selection layer 18a, and tracks that can move the condensing positions of the beams 23a and 23b in the radial direction of the disk 2a. A moving means may be provided. The optical information recording / reproducing apparatus includes an error signal generation circuit that generates a track error signal for controlling the condensing positions of the beams 23a and 23b in the radial direction of the disk 2a based on the output from the photodetector 13b. And a track moving means driving circuit for driving the track moving means based on the track error signal.

At this time, the objective lenses 12a and 12b correspond to not only the focus moving means but also the track moving means, and are mounted on an actuator (not shown). Based on the voltage signal amplified by the amplifier circuit 45, the error signal generation circuit 46 generates not only a focus error signal for driving the objective lenses 12a and 12b in the optical unit 1a but also a track error signal. The objective lens driving circuit 47 is not only a focus moving means driving circuit but also a track moving means driving circuit. The objective lens driving circuit 47 corrects the deviation in the radial direction of the disk 2a with respect to the track formed on the wavelength selection layer 18a at the condensing position of the beam selectively generated from the beams 25a to 25i. For this purpose, the objective lens driving circuit 47 supplies a current corresponding to the track error signal to an actuator (not shown) based on the track error signal generated by the error signal generation circuit 46, so that the objective lenses 12a and 12b are connected to the disk 2a. Drive in the radial direction.

Further, in the first embodiment, the optical unit has another optical detector for receiving the recording / reproducing beam transmitted through the disk 2a when information is recorded on the disk 2a, and the condensing position of the beam 23a. Beam condensing position of the beam 23b may be provided with beam moving means capable of moving in the optical axis direction, the radial direction of the disk 2a, and the tangential direction. Further, the optical information recording / reproducing apparatus sets the condensing position of the beam 23b with respect to the condensing position of the beam 23a based on the output from another amplifier circuit and another optical detector in the optical axis direction and the radial direction of the disk 2a. A position shift signal generating circuit that generates a position shift signal for controlling in the tangential direction and a beam moving means driving circuit that drives the beam moving means based on the position shift signal may be provided.

At this time, the objective lens 12b corresponds to a beam moving means and is mounted on an actuator (not shown). Another amplifier circuit amplifies a voltage signal output from another photodetector in the optical unit 1a when recording information on the disk 2a. The position shift signal generation circuit generates a position shift signal for driving the objective lens 12b in the optical unit 1a based on the voltage signal amplified by another amplifier circuit. Another objective lens driving circuit, which is a beam moving means driving circuit, corrects deviations in the optical axis direction, the radial direction, and the tangential direction of the disc 2a with respect to the condensing position of the beam 23b. For this purpose, another objective lens driving circuit supplies an electric current corresponding to the position shift signal to an actuator (not shown) based on the position shift signal generated by the position shift signal generation circuit, thereby moving the objective lens 12b in the optical axis direction. Drive in the radial direction and tangential direction of the disk 2a.

(Second Embodiment)
FIG. 9 is a block diagram showing a configuration of an optical unit according to the second embodiment of the present invention. This optical unit includes a laser 3a, a convex lens 4a, an active wavelength plate 5, a half mirror 6, a polarizing beam splitter 7b, an interference filter 9, convex lenses 4b and 4c, a polarizing beam splitter 7c, and an objective lens 12c. And a mirror 10b and convex lenses 4d and 4e. The optical unit further includes a convex lens 4f, a photodetector 13a, a laser 3b, a convex lens 4g, a polarization beam splitter 7d, an active diffraction lens 14, a convex lens 4h, a cylindrical lens 15, and a photodetector 13b. It comprises.

Lasers 3a and 3b, which are light sources, are semiconductor lasers that emit a recording / reproducing beam having a wavelength of 405 nm and a focus controlling beam having a wavelength of 650 nm, respectively. The interference filter 9 reflects a beam having a wavelength of 405 nm and transmits a beam having a wavelength of 650 nm. The polarization beam splitter 7c transmits a P-polarized component for a beam with a wavelength of 405 nm and reflects an S-polarized component, and transmits a P-polarized component and an S-polarized component for a beam with a wavelength of 650 nm. The active diffractive lens 14 which is a variable focus unit selectively generates one of a plurality of diffracted beams having different orders from the incident beam. The relay lens system including the convex lenses 4b and 4c and the relay lens system including the convex lenses 4d and 4e correspond to a focus moving unit. One of the convex lenses 4b and 4c and one of the convex lenses 4d and 4e are mounted on an actuator (not shown).

The beam emitted from the laser 3a passes through the convex lens 4a, is converted from divergent light into parallel light, and enters the active wave plate 5. The active wave plate 5 has the effect of a quarter wave plate for incident light when information is recorded on the disk 2b as an optical recording medium, and the full wave plate for incident light when information is reproduced from the disk 2b. With the effect. Therefore, when recording information on the disk 2b, the beam incident on the active wavelength plate 5 is transmitted from the active wavelength plate 5 to be converted from linearly polarized light to circularly polarized light, and after about 50% is transmitted through the half mirror 6, About 50% passes through the polarization beam splitter 7b as a P polarization component, and about 50% is reflected as an S polarization component by the polarization beam splitter 7b. On the other hand, when reproducing information from the disk 2b, the beam incident on the active wave plate 5 is transmitted through the active wave plate 5 without changing the polarization state, and after about 50% is transmitted through the half mirror 6, the polarized beam is transmitted. Nearly 100% is transmitted as P-polarized light to the splitter 7b. Here, the active wavelength plate 5 and the polarization beam splitter 7b correspond to beam switching means.

The active wave plate 5 is configured to sandwich a liquid crystal layer between two substrates. Transparent electrodes for applying an alternating voltage to the liquid crystal layer are formed on the surface of the two substrates on the liquid crystal layer side. The liquid crystal layer has uniaxial refractive index anisotropy. The thickness of the liquid crystal layer is determined so that the phase difference between the polarization component in the direction parallel to the optical axis and the polarization component in the direction perpendicular to the optical axis generated in the beam transmitted through the liquid crystal layer is π. . When an AC voltage having an effective value of 2.5 volts is applied to the liquid crystal layer, the direction of the optical axis of the liquid crystal layer is an intermediate direction between the direction perpendicular to the optical axis of the incident light and the parallel direction. At this time, the active wave plate 5 has the effect of a quarter wave plate. On the other hand, when an AC voltage having an effective value of 5 volts is applied to the liquid crystal layer, the direction of the optical axis of the liquid crystal layer is parallel to the optical axis of the incident light. At this time, the active wave plate 5 has the effect of a full wave plate.

When recording information on the disk 2b, the beam transmitted through the polarization beam splitter 7b is reflected by the interference filter 9 and is transmitted through the relay lens system including the convex lenses 4b and 4c to be converted from parallel light into weak convergent light. The converted weak convergent light is incident on the polarization beam splitter 7c as P-polarized light and is almost 100% transmitted, and is condensed in the disk 2b by the objective lens 12c. The beam reflected by the polarization beam splitter 7b is reflected by the mirror 10b, passes through a relay lens system including the convex lenses 4d and 4e, is converted from parallel light to weak divergent light, and is converted into S-polarized light to the polarization beam splitter 7c. The incident light is reflected almost 100% and is collected in the disk 2b by the objective lens 12c.

On the other hand, when information is reproduced from the disk 2b, the beam transmitted through the polarization beam splitter 7b is reflected by the interference filter 9 and passes through the relay lens system constituted by the convex lenses 4b and 4c to change from parallel light to weakly convergent light. Converted. The converted weak convergent light is incident on the polarization beam splitter 7c as P-polarized light and is almost 100% transmitted, and is condensed in the disk 2b by the objective lens 12c. The beam reflected in the disk 2b passes through the objective lens 12c in the reverse direction, enters the polarization beam splitter 7c as P-polarized light, and almost 100% is transmitted, and passes through the relay lens system including the convex lenses 4c and 4b. It is converted from weak divergent light to parallel light. The converted parallel light is reflected by the interference filter 9, is incident on the polarization beam splitter 7b as P-polarized light, and almost 100% is transmitted, and about 50% is reflected by the half mirror 6, and is transmitted through the convex lens 4f and parallel. The light is converted into convergent light and received by the photodetector 13a. Based on the output from the photodetector 13a, a reproduction signal indicating information recorded on the disk 2b is generated.

The beam emitted from the laser 3b passes through the convex lens 4g and is converted from divergent light to weak divergent light, enters the polarization beam splitter 7d as P-polarized light, and almost 100% is transmitted, and is diffracted by the active diffraction lens 14. , And passes through the interference filter 9. The transmitted light passes through the relay lens system including the convex lenses 4b and 4c, is converted from weak divergent light into parallel light, passes through the polarization beam splitter 7c, and is condensed in the disk 2b by the objective lens 12c. The beam reflected in the disk 2b passes through the objective lens 12c in the reverse direction, passes through the polarizing beam splitter 7c, passes through the relay lens system constituted by the convex lenses 4c and 4b, and converts from parallel light to weakly convergent light. Then, it passes through the interference filter 9. The transmitted light is diffracted by the active diffractive lens 14, is incident on the polarizing beam splitter 7d as S-polarized light, is reflected by almost 100%, passes through the convex lens 4h, and is converted from weakly convergent light to convergent light, and the cylindrical lens 15 Astigmatism is given through the light and is received by the photodetector 13b. Based on the output from the photodetector 13b, a focus error signal for controlling the condensing position of the recording / reproducing beam in the optical axis direction is generated by a known astigmatism method.

10A to 10B are diagrams showing optical paths of an incident beam to the disk 2b and a reflected beam from the disk 2b when information is recorded on the disk 2b. FIG. 10A is a diagram when the beam 26a is selectively generated. FIG. 10B is a diagram when the beam 26i is selectively generated.

11A to 11B are diagrams showing optical paths of an incident beam to the disk 2b and a reflected beam from the disk 2b when information is reproduced from the disk 2b. FIG. 11A is a diagram when the beam 26a is selectively generated. FIG. 11B is a diagram when the beam 26i is selectively generated.

The disk 2b is configured to sandwich the recording layer 17b, the quarter-wave plate layer 19, and the reflective layer 20 in this order between the substrates 16c and 16d. Here, the reflective layer 20 corresponds to a focus control reference surface. For example, glass is used as the material of the substrates 16c and 16d. For example, a photopolymer is used as the material of the recording layer 17b. As the material of the quarter-wave plate layer 19, for example, liquid crystal is used. For example, aluminum is used as the material of the reflective layer 20.

10A to 10B, a beam 24a represents a beam transmitted through the polarization beam splitter 7b among the beams emitted from the laser 3a, and a beam 24b is formed by the polarization beam splitter 7b among the beams emitted from the laser 3a. It represents the reflected beam. In FIGS. 11A and 11B, a beam 24a represents a beam emitted from the laser 3a and transmitted through the polarization beam splitter 7b. Beams 26a to 26i in FIGS. 10A to 10B and FIGS. 11A to 11B represent beams that can be selectively generated by the active diffraction lens 14 from the beams emitted from the laser 3b. A solid line and a dotted line in the figure respectively indicate a beam that is actually generated and a beam that is not actually generated. FIGS. 10A and 11A show the optical path of the beam when the beam 26a is selectively generated, and FIGS. 10B and 11B show the optical path of the beam when the beam 26i is selectively generated.

In FIG. 10A, either one of the convex lenses 4b and 4c is driven in the optical axis direction by an actuator (not shown) so that the beam 26a is condensed on the reflection layer 20. The beam 26a is reflected by the reflective layer 20 and received by the photodetector 13b. At this time, since the distance between the condensing position of the beam 24a and the condensing position of the beam 26a is wide, the beam 24a is a position far from the reflective layer 20 on the way to the reflective layer 20 side in the recording layer 17b. The light is condensed at a condensing point 21c in the recording layer 17b. The beam 24b is transmitted through the recording layer 17b, is transmitted through the quarter-wave plate layer 19, is converted from linearly polarized light to circularly polarized light, is reflected by the reflective layer 20, and is transmitted through the quarter-wave plate layer 19. Either one of the convex lenses 4d and 4e is not shown so that it is converted from circularly polarized light into linearly polarized light and is condensed at the condensing point 21c on the way to the side opposite to the reflective layer 20 in the recording layer 17b. It is driven in the optical axis direction by an actuator. Therefore, the beam 24a and the beam 24b interfere at the condensing point 21c, and a minute diffraction grating is formed at the condensing point 21c.

In FIG. 10B, either one of the convex lenses 4b and 4c is driven in the optical axis direction by an actuator (not shown) so that the beam 26i is condensed on the reflection layer 20. The beam 26i is reflected by the reflective layer 20 and received by the photodetector 13b. At this time, since the distance between the condensing position of the beam 24a and the condensing position of the beam 26i is narrow, the beam 24a is close to the reflective layer 20 on the way to the reflective layer 20 side in the recording layer 17b. The light is condensed at a condensing point 21d in the recording layer 17b. The beam 24b is transmitted through the recording layer 17b, is transmitted through the quarter-wave plate layer 19, is converted from linearly polarized light to circularly polarized light, is reflected by the reflective layer 20, and is transmitted through the quarter-wave plate layer 19. Either one of the convex lenses 4d and 4e is not shown so that it is converted from circularly polarized light to linearly polarized light and is condensed at the condensing point 21d on the way to the side opposite to the reflective layer 20 in the recording layer 17b. It is driven in the optical axis direction by an actuator. The beam 24a and the beam 24b interfere at the condensing point 21d, and a minute diffraction grating is formed at the condensing point 21d.

In FIG. 11A, one of the convex lenses 4b and 4c is driven in the optical axis direction by an actuator (not shown) so that the beam 26a is condensed on the reflective layer 20. The beam 26a is reflected by the reflective layer 20 and received by the photodetector 13b. At this time, the distance between the condensing position of the beam 24a and the condensing position of the beam 26a is wide, and the beam 24a is a recording at a position far from the reflective layer 20 on the way to the reflective layer 20 side in the recording layer 17b. The light is condensed on the diffraction grating 22c in the layer 17b. The diffraction grating 22c is a diffraction grating formed at the condensing point 21c in FIG. 10A. The beam 24a is reflected by the diffraction grating 22c and received by the photodetector 13a.

In FIG. 11B, either one of the convex lenses 4b and 4c is driven in the optical axis direction by an actuator (not shown) so that the beam 26i is condensed on the reflection layer 20. The beam 26i is reflected by the reflective layer 20 and received by the photodetector 13b. At this time, the interval between the condensing position of the beam 24a and the condensing position of the beam 26i is narrow, and the beam 24a is a position near the reflective layer 20 on the way to the reflective layer 20 side in the recording layer 17b. The light is condensed on the diffraction grating 22d in the layer 17b. The diffraction grating 22d is a diffraction grating formed at the condensing point 21d in FIG. 10B. The beam 24a is reflected by the diffraction grating 22d and received by the photodetector 13a.

Here, the diffraction grating formed at the condensing position has bit data information. One of the beams 26a to 26i is selectively generated by the active diffractive lens 14, and the interval between the condensing position of the beam 24a and the condensing position of the selectively generated beam is changed in nine steps. By driving one of the convex lenses 4b and 4c so that the selectively generated beam is condensed on the reflection layer 20, the condensing position of the beam 24a is set in the optical axis direction in the recording layer 17b. It can be changed in 9 steps. Therefore, information can be recorded / reproduced in nine layers in the thickness direction of the recording layer 17b by using the beams 24a and 24b.

In the present embodiment, a single beam selectively generated by the active diffraction lens 14 is used as the focus control beam among the beams 26a to 26i. For this reason, the light quantity of the selectively generated beam can be increased. In addition, when the beam focused on the reflection layer 20 is received by the photodetector 13b, there is no unnecessary beam received by the photodetector 13b. As a result, noise and crosstalk are not mixed in the focus error signal, and the condensing position of the beam 24a can be correctly controlled in the optical axis direction.

The cross-sectional view of the active diffractive lens 14 is the same as that shown in FIG. Further, the relationship between the voltage applied to the liquid crystal layer in the active diffractive lens 14 and the focal length of the diffractive lens is the same as that shown in FIG.

If the thickness of the active diffractive lens 14 is ignored and the object point position and the image point position with respect to the active diffractive lens 14 are ad and bd, respectively, 1 / ad + 1 / bd = 1 / fd is established. If the thickness of the convex lens 4b is ignored, the focal length of the convex lens 4b is fr, the object point position and the image point position with respect to the convex lens 4b are ar1 and br1, respectively, 1 / ar1 + 1 / br1 = 1 / fr holds. If the thickness of the convex lens 4c is ignored, the focal length of the convex lens 4c is fr, and the object point position and the image point position with respect to the convex lens 4c are ar2 and br2, respectively, 1 / ar2 + 1 / br2 = 1 / fr holds. Further, ignoring the thickness of the objective lens 12c, if the focal length of the objective lens 12c is fo, and the object point position and the image point position with respect to the objective lens 12c are ao and bo, respectively, 1 / ao + 1 / bo = 1 / fo. It holds.

(A) to (i) shown in FIG. 7 correspond to the state in which the beams 26a to 26i in FIGS. 10A to 10B or 11A to 11B are selectively generated by the active diffraction lens 14, respectively. In order from (a) to (i), 1 / fd changes in nine steps from / 4/3 Fd to +4/3 Fd at 1/3 Fd intervals. Assuming that ad = fo ² / ΔF, 1 / bd changes from −4 / 3Fd−ΔF / fo ² to + 4 / 3Fd−ΔF / fo ² in 9 steps at 1 / 3Fd intervals. When Fd, fo ² / ΔF is sufficiently larger than the distance between the active diffractive lens 14 and the convex lens 4b, ar1 = −bd, so 1 / ar1 is changed from + 4 / 3Fd + ΔF / fo ² to −4 / 3Fd + ΔF / Changes to 9 levels at -1/3 Fd intervals up to fo ² . When Fd and fo ² / ΔF are sufficiently larger than fr, br1 is 9 steps from fr + 4fr ² / 3Fd + fr ² ΔF / fo ² to fr-4fr ² / 3Fd + fr ² ΔF / fo ² at −fr ² / 3Fd intervals. To change. Assuming that br1 + ar2 = 2fr + fr ² ΔF / fo ² , ar2 changes from fr-4fr ² / 3Fd to fr + 4fr ² / 3Fd in nine steps at fr ² / 3Fd intervals. When Fd is sufficiently larger than fr, 1 / br2 changes in nine steps from -4/3 Fd to +4/3 Fd at 1/3 Fd intervals. When Fd is sufficiently larger than the distance between the convex lens 4c and the objective lens 12c, ao = −br2, so 1 / ao is divided into nine stages at intervals of −1 / 3Fd from + 4 / 3Fd to −4 / 3Fd. Change. When Fd is sufficiently larger than fo, bo changes in nine steps from −fo + 4fo ² / 3Fd to fo−4fo ² / 3Fd at −fo ² / 3Fd intervals.

On the other hand, regarding the beam 24a in FIGS. 10A to 10B or FIGS. 11A to 11B, when ar1 = ∞, br1 = fr. When br1 + ar2 = 2fr + fr ² and a [Delta] F / fo ^2, the ^{ar2 = fr + fr 2 ΔF /} fo 2. When fo ² / ΔF is sufficiently larger than fr, 1 / br ² = ΔF / fo ² . When fo ² / ΔF is sufficiently larger than the distance between the convex lens 4c and the objective lens 12c, ao = −br2, so 1 / ao = −ΔF / fo ² . When fo ² / ΔF is sufficiently larger than fo, bo = fo−ΔF. Assuming that the focal position of the beam 24a with reference to the focal positions of the beams 26a to 26i is Δf, Δf is in nine stages from -4fo ² / 3Fd−ΔF to + 4fo ² / 3Fd−ΔF at intervals of fo ² / 3Fd. Change. For example, if ΔF = 13fo ² / 6Fd, Fd = 300 mm, and fo = 3 mm, Δf changes in nine steps from −105 μm to −25 μm at 10 μm intervals. Here, even if the voltage applied to the first and second liquid crystal layers varies slightly, the diffraction efficiency of the first and second diffractive lenses varies only slightly, and the focal length does not vary. Therefore, Δf does not vary.

In the present embodiment, the active diffractive lens 14 is a first and second diffractive lens that selectively generates one of three diffracted lights of −1st order diffracted light, 0th order light, and + 1st order diffracted light from incident light. It has. By changing the focal length of the first diffractive lens in three steps of -Fd, ∞, and + Fd and changing the focal length of the second diffractive lens in three steps of -3Fd, ∞, and + 3Fd, Δf becomes -4fo ² From / 3Fd−ΔF to + 4fo ² / 3Fd−ΔF, it changes in 9 steps at intervals of fo ² / 3Fd. As a result, information is recorded / reproduced on nine layers.

The active diffractive lens also includes first, second, and third diffractive lenses that selectively generate one of three diffracted lights of −1st order diffracted light, 0th order light, and + 1st order diffracted light from incident light. Good. The focal length of the first diffractive lens is changed in three steps of -Fd, ∞, + Fd, the focal length of the second diffractive lens is changed in three steps of -3Fd, ∞, + 3Fd, and the focal length of the third diffractive lens is changed. By changing in three steps of −9Fd, ∞, and + 9Fd, Δf changes from −13fo ² / 9Fd−ΔF to + 13fo ² / 9Fd−ΔF in 27 steps at a fo ² / 9Fd interval. As a result, information can be recorded and reproduced on the 27th layer.

In addition, the active diffractive lens selectively generates one of five diffracted lights, that is, a −2nd order diffracted light, a −1st order diffracted light, a 0th order light, a + 1st order diffracted light, and a + 2nd order diffracted light from the incident light. A second diffractive lens may be provided. The focal length of the first diffractive lens is changed in five steps: -Fd / 2, -Fd, ∞, + Fd, + Fd / 2, and the focal length of the second diffractive lens is -5Fd / 2, -5Fd, ∞, + 5Fd, By changing to 5 steps of + 5Fd / 2, Δf changes from −12fo ² / 5Fd−ΔF to + 12fo ² / 5Fd−ΔF in 25 steps at an interval of fo ² / 5Fd. As a result, it is possible to record and reproduce information on 25 layers.

FIG. 12 is a block diagram showing a configuration of an optical information recording / reproducing apparatus according to the second embodiment of the present invention. The optical information recording / reproducing apparatus includes an optical unit 1b, a positioner 33b, a spindle 34b, a controller 35, an active wave plate driving circuit 36, a modulation circuit 37, a recording signal generating circuit 38, and a laser driving circuit 39. An amplifier circuit 40, a reproduction signal processing circuit 41, a demodulation circuit 42, a laser drive circuit 43, an active diffraction lens drive circuit 44, an amplification circuit 45, an error signal generation circuit 46, and a relay lens drive circuit 48 A positioner driving circuit 49 and a spindle driving circuit 50.

The optical unit 1b corresponds to the optical unit according to the second embodiment described above, and is mounted on the positioner 33b. The disk 2b is mounted on the spindle 34b. The controller 35 includes an active wave plate driving circuit 36, a circuit from the modulation circuit 37 to the laser driving circuit 39, a circuit from the amplification circuit 40 to the demodulation circuit 42, a laser driving circuit 43, and an active diffractive lens driving circuit 44. The circuit from the amplifier circuit 45 to the relay lens drive circuit 48, the positioner drive circuit 49, and the spindle drive circuit 50 are controlled.

The active wave plate driving circuit 36 which is a beam switching means driving circuit, when recording information on the disk 2b, makes the active wave plate 5 so that the active wave plate 5 in the optical unit 1b has the effect of a quarter wave plate. An AC voltage having an effective value of 2.5 volts is applied to the liquid crystal layer included in. Further, when reproducing information from the disk 2b, the active wave plate driving circuit 36 has an effective value on the liquid crystal layer of the active wave plate 5 so that the active wave plate 5 in the optical unit 1b has the effect of all wave plates. Apply an AC voltage of 5 volts.

The modulation circuit 37 modulates a signal input from the outside as recording data according to a modulation rule when recording information on the disk 2b. The recording signal generation circuit 38 generates a recording signal for driving the laser 3a in the optical unit 1b based on the signal modulated by the modulation circuit 37. When recording information on the disk 2b, the laser driving circuit 39 drives the laser 3a by supplying a current corresponding to the recording signal to the laser 3a based on the recording signal generated by the recording signal generating circuit 38. When reproducing information from the disk 2b, the laser drive circuit 39 drives the laser 3a by supplying a constant current to the laser 3a so that the power of the emitted light from the laser 3a is constant.

The amplification circuit 40 amplifies the voltage signal output from the photodetector 13a in the optical unit 1b when reproducing information recorded in the form of a diffraction grating on the disk 2b. The reproduction signal processing circuit 41 performs generation, waveform equalization, and binarization of the disk 2b reproduction signal based on the voltage signal amplified by the amplifier circuit 40. The demodulation circuit 42 demodulates the signal binarized by the reproduction signal processing circuit 41 according to a demodulation rule, and outputs it as reproduction data to the outside.

When recording information on the disk 2b and reproducing information from the disk 2b, the laser drive circuit 43 applies to the laser 3b so that the power of the laser light emitted from the laser 3b in the optical unit 1b is constant. A constant current is supplied to drive the laser 3b.

The active diffractive lens driving circuit 44, which is a variable focus unit driving circuit, has an effective value of 0 in the liquid crystal layers 28a to 28d of the active diffractive lens 14 when recording information on the disk 2b and reproducing information from the disk 2b. An AC voltage of any one of volts, 2.5 volts, and 5 volts is applied. The active diffractive lens 14 in the optical unit 1b selectively generates one of the beams 26a to 26i according to the applied voltage.

The amplification circuit 45 amplifies a voltage signal output from the photodetector 13b in the optical unit 1b when recording information on the disk 2b and reproducing information from the disk 2b. Based on the voltage signal amplified by the amplifier circuit 45, the error signal generation circuit 46 drives a focus error signal for driving one of the convex lenses 4b and 4c and one of the convex lenses 4d and 4e in the optical unit 1b. Is generated. The relay lens driving circuit 48 is a focus moving unit driving circuit that corrects a deviation in the optical axis direction with respect to the reflective layer 20 of a condensing position of a beam selectively generated from the beams 26a to 26i. The relay lens driving circuit 48 supplies a current corresponding to the focus error signal to an actuator (not shown) based on the focus error signal generated by the error signal generation circuit 46, and either one of the convex lenses 4b and 4c, the convex lens 4d, Either one of 4e is driven in the optical axis direction.

Positioner drive circuit 49 supplies current to a motor (not shown) to move the positioner 33b in the radial direction of the disk 2b. Thus, when information is recorded on the disk 2b, the condensing positions of the beams 24a and 24b move in the radial direction of the disk 2b, and when information is reproduced from the disk 2b, the condensing position of the beam 24a is the radius of the disk 2b. Move in the direction.

The spindle drive circuit 50 supplies a current to a motor (not shown) to rotate the spindle 34b. Thus, when information is recorded on the disk 2b, the converging positions of the beams 24a and 24b move in the tangential direction of the disk 2b. When information is reproduced from the disk 2b, the converging position of the beam 24a is tangent to the disk 2b. Move in the direction.

In the second embodiment, the optical unit forms tracks parallel to the tangential direction of the disk 2b on the reflective layer 20 and moves the tracks 24a and 24b in the radial direction of the disk 2b. Means may be provided. The optical information recording / reproducing apparatus includes an error signal generation circuit that generates a track error signal for controlling the condensing positions of the beams 24a and 24b in the radial direction of the disk 2b based on the output from the photodetector 13b. And a track moving means driving circuit for driving the track moving means based on the track error signal.

At this time, the relay lens system including the convex lenses 4b and 4c and the relay lens system including the convex lenses 4d and 4e correspond to not only the focus moving means but also the track moving means. One of the convex lenses 4b and 4c and one of the convex lenses 4d and 4e are mounted on an actuator (not shown). Based on the voltage signal amplified by the amplifier circuit 45, the error signal generation circuit 46 drives a focus error signal for driving either one of the convex lenses 4b and 4c and one of the convex lenses 4d and 4e in the optical unit 1b. As well as a track error signal. The relay lens driving circuit 48 corrects the deviation in the radial direction of the disk 2b with respect to the track formed on the reflective layer 20 at the condensing position of the beam selectively generated from the beams 26a to 26i. For this purpose, the relay lens drive circuit 48 supplies a current corresponding to the track error signal to an actuator (not shown) based on the track error signal generated by the error signal generation circuit 46, and either one of the convex lenses 4b and 4c, One of the convex lenses 4d and 4e is driven in the radial direction of the disk 2b.

In the second embodiment, the optical unit includes another photodetector for receiving the recording / reproducing beam reflected in the disk 2b when information is recorded on the disk 2b, and the condensing position of the beam 24a. There may be provided beam moving means capable of moving the condensing position of the beam 24b with respect to the optical axis direction, the radial direction of the disk 2b, and the tangential direction. Further, the optical information recording / reproducing apparatus sets the condensing position of the beam 24b relative to the condensing position of the beam 24a based on the output from another amplifier circuit and another optical detector in the optical axis direction and the radial direction of the disk 2b. A position shift signal generating circuit that generates a position shift signal for controlling in the tangential direction and a beam moving means driving circuit that drives the beam moving means based on the position shift signal may be provided.

At this time, the relay lens system including the convex lenses 4d and 4e corresponds to beam moving means, and one of the convex lenses 4d and 4e is mounted on an actuator (not shown). Another amplifier circuit amplifies a voltage signal output from another photodetector in the optical unit 1b when recording information on the disk 2b. The position shift signal generation circuit generates a position shift signal for driving one of the convex lenses 4d and 4e in the optical unit 1b based on the voltage signal amplified by another amplifier circuit. Another relay lens driving circuit, which is a beam moving means driving circuit, corrects deviations in the optical axis direction, the radial direction of the disk 2b, and the tangential direction of the condensing position of the beam 24b with respect to the condensing position of the beam 24a. For this purpose, another relay lens drive circuit supplies a current corresponding to the position shift signal to an actuator (not shown) based on the position shift signal generated by the position shift signal generation circuit, and either one of the convex lenses 4d and 4e. Are driven in the optical axis direction, the radial direction of the disk 2b, and the tangential direction.

As described above, in the first and second embodiments, the bit-type hologram recording optical unit and the bit-type hologram recording optical information recording / reproducing apparatus are exemplified. However, the present invention is not limited to bit-type hologram recording and page-type hologram recording, as long as it is an optical unit and an optical information recording / reproducing apparatus for performing three-dimensional information recording / reproduction on an optical recording medium. It can also be applied to two-photon absorption recording.

It should be noted that the specific numerical values used in describing each of the above-described embodiments are merely examples, and can be freely changed within a range where there is no physical or technical contradiction.

As described above, according to the optical unit according to the present invention, the optical information recording / reproducing apparatus using the optical unit, and the optical information recording / reproducing method, a single beam is used as the focus control beam. The amount of light of the beam can be increased, and when the beam collected on the focus control reference surface is received by the photodetector, there is no other unnecessary beam received by the photodetector. Therefore, noise and crosstalk are not mixed in the focus error signal, and the focusing position of the recording / reproducing beam can be correctly controlled in the optical axis direction.

The present invention has been described above with reference to the embodiments, but the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

Note that this application claims priority based on Japanese Application No. 2008-084952, and the disclosure content in Japanese Application No. 2008-084952 is incorporated by reference into this application.

Claims (10)

1. For an optical recording medium having a recording layer and a focus control reference surface, a recording / reproduction beam is condensed in the recording layer, and a focus control beam is condensed on the focus control reference surface. In the optical unit for recording and reproducing information by
   A light source for emitting the recording / reproducing beam and the focus control beam;
   An objective lens system for condensing the recording / reproducing beam and the focus control beam on the optical recording medium;
   A photodetector that receives the reflected light of the recording / reproducing beam and the reflected light of the focus control beam incident from the optical recording medium;
   Variable focus means for enabling the interval between the focusing position of the recording / reproducing beam and the focusing position of the focus control beam to be changed;
   An optical unit comprising: a focus moving means for enabling the focusing positions of the recording / reproducing beam and the focus control beam to move in the optical axis direction.
2. The optical unit according to claim 1, wherein the variable focus unit includes a diffractive lens system capable of changing a focal length.
3. The diffractive lens system includes a plurality of diffractive lenses capable of changing a focal length,
   The optical unit according to claim 2, wherein the plurality of diffractive lenses have different focal length changes.
4. Using the objective lens system as the focal point moving means,
   The optical unit according to any one of claims 1 to 3, wherein the objective lens system is movable in an optical axis direction.
5. The focal point moving means includes a relay lens system having a plurality of lenses,
   The optical unit according to any one of claims 1 to 3, wherein any one of the plurality of lenses is movable in an optical axis direction.
6. The beam recording means further comprises a beam switching means capable of switching between two beams or a single beam which are focused on the same position so as to oppose each other in the recording layer. The optical unit according to 1.
7. An optical unit according to any one of claims 1 to 5,
   A variable focus means driving circuit for driving the variable focus means;
   An error signal generation circuit for generating a focus error signal for controlling the focusing position of the recording / reproducing beam in the optical axis direction based on an output from the photodetector;
   An optical information recording / reproducing apparatus comprising: a focus moving means driving circuit for driving the focus moving means based on the focus error signal.
8. Beam switching means capable of switching between the two beams that are focused on the same position facing each other in the recording layer or a single beam in the recording layer;
   The beam switching is performed so that the recording / reproducing beam becomes the two beams when information is recorded on the optical recording medium, and the recording / reproducing beam becomes the single beam when information is reproduced from the optical recording medium. The optical information recording / reproducing apparatus according to claim 7, further comprising: a beam switching unit driving circuit that drives the unit.
9. Emitting a recording / reproducing beam and a focus control beam from a light source;
   Condensing the recording / reproducing beam in a recording layer of an optical recording medium;
   Condensing the focus control beam on a focus control reference surface of the optical recording medium;
   Receiving reflected light of the recording / reproducing beam and reflected light of the focus control beam from the optical recording medium;
   Changing the distance between the focusing position of the recording / reproducing beam and the focusing position of the focus control beam;
   An optical information recording / reproducing method comprising: moving a focusing position of the recording / reproducing beam and the focus control beam in an optical axis direction.
10. In the optical information recording / reproducing method according to claim 9,
    An optical information recording / reproducing method further comprising the step of switching the recording / reproducing beam between two beams focused on the same position facing each other in the recording layer or a single beam.

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