JP2007293963A - Optical information recording and reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical information recording and reproducing device which can make both the correct focusing on a two-layered optical disk and correction of the spherical aberration by utilizing focusing error signals and also make quick and stabilized jumps between the layers. <P>SOLUTION: This device has an objective lens 10 to converge the light flux from the laser light source, and an SIL11 arranged between the objective lens 10 and the optical recording mediums 12, and converges the light flux from the laser light source into an light spot on one of the recording layers of the optical recording medium 12 by using the objective lens 10 and the SIL11. It has a focusing optical system to form a light spot on one of the recording layers of the optical recording medium 12 based on the focusing error signals, and a spherical aberration correction mechanism to correct the spherical aberration in the state focusing on one of the recording layers of the recording medium. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical information recording / reproducing apparatus such as an optical disk apparatus, and more particularly to a near-field recording light that performs recording / reproduction on an information recording layer of two or more optical disks using Solid Immersion Lens (hereinafter abbreviated as SIL). The present invention relates to an information recording / reproducing apparatus.

  In order to improve the recording density of the optical disc, it is required to shorten the wavelength of light used for recording and reproduction, increase the numerical aperture (NA) of the objective lens, and reduce the light spot diameter on the optical disc recording surface. . Conventionally, a so-called SIL is formed by bringing the tip of the objective lens close to a fraction of the recording wavelength (for example, 1/2) or less on the recording surface, and the NA is set to 1 or more even in the air. Has been made.

  For example, they are detailed in the following Non-Patent Document 1 or Non-Patent Document 2.

  A conventional technique will be described with reference to FIGS. The configuration of a conventional near-field recording optical pickup shown in Non-Patent Document 1 will be described with reference to FIG. A light beam emitted from the semiconductor laser 1 having a wavelength of 405 nm is converted into a parallel light beam by the collimator lens 2 and is incident on the beam shaping prism 3 to form an isotropic light amount distribution. The light beam that has passed through the non-polarizing beam splitter (NBS) 4 and transmitted through the polarizing beam splitter (PBS) 7 passes through the quarter-wave plate (QWP) 8 and is converted from linearly polarized light into circularly polarized light. Note that a photodetector (LPC-PD) 6 for receiving the light beam reflected by the non-polarizing beam splitter (NBS) 4 and controlling the emission power of the semiconductor laser 1 is provided.

  The light beam that has passed through the quarter wavelength plate enters the expander lens 9. The expander lens 9 is a lens for correcting spherical aberration that occurs in an objective lens and SIL, which will be described later, and is configured so that the distance between the two lenses can be controlled in accordance with the spherical aberration. The light beam from the expander lens 9 enters the rear lens 10 of the objective lens. The objective lens includes a rear lens 10 and a SIL (front lens) 11, which are mounted on a biaxial actuator (not shown) that integrally drives the two lenses in the focus and tracking directions. There are two types of SIL as described in FIG. 9 and FIG.

  FIG. 9 condenses the light beam focused by the objective lens rear lens 101 on the bottom surface of the hemispherical lens SIL 102-a. In this case, as is well known, if the refractive index of the hemispherical lens is N and the numerical aperture of the rear lens 101 of the objective lens is NA, a light spot equivalent to an effective numerical aperture N × NA (= NAeff) on the recording surface of the optical disk 14. Is obtained.

On the other hand, FIG. 10 condenses the light beam narrowed down by the rear lens of the objective lens on the bottom surface of the SIL 102-b of the super hemispheric lens. The bottom surface is a surface separated by R / N from the center of the super hemisphere 102-b. In this case, as is well known, if the refractive index of the hemispherical lens is N and the numerical aperture of the rear lens 101 of the objective lens is NA, a light spot equivalent to N ² × NA (= NAeff) is formed on the recording surface of the optical disk 14. can get.

  In any SIL, only when the distance between the bottom surface of the SIL and the optical disc 12 is a short distance of a fraction of a wavelength of 405 nm of the light source, for example, 100 nm or less, the SIL acts on the recording surface as evanescent light. As a result, recording / reproduction with a NAeff light spot diameter is possible. In order to maintain this distance, a gap servo described later is used. The optical disk 12 is a two-layer disk having two recording layers, which will be described in detail later with reference to FIGS.

  Returning to FIG. 8, the return path optical system will be described. The light beam reflected by the optical disk 12 becomes reverse circularly polarized light, enters the SIL 11 and the objective lens 10 and is converted again into a parallel light beam. The light beam that has passed through the expander lens 9 and the quarter-wave plate 8 and has been linearly polarized in the direction orthogonal to the forward path is reflected by the PBS 7. Of the light beam whose polarization plane has been rotated by 45 ° by the half-wave plate (HWP) 13, the S-polarized light component is reflected by the polarization beam splitter 14 and passes through the lens 15 onto the photodetector 1 (PD 1) 16. The light is condensed and the RF output 17 which is information on the optical disk 12 is reproduced.

  Of the light beam whose polarization plane has been rotated by 45 ° by the half-wave plate (HWP) 13, the P-polarized light component passes through the polarizing beam splitter 14 and is reflected by the non-polarizing beam splitter 18. The reflected light is condensed on the two-divided photodetector 2 (PD2) 20 via the lens 19 and a tracking error 21 is output.

  On the other hand, among the light beams reflected by the bottom surface of the SIL 11, a light beam of NAeff <1 that does not totally reflect is reflected as circularly polarized light that is reverse to the incident, similarly to the light reflected from the optical disk 12 described above. For a light flux of NAeff ≧ 1 that causes total reflection, a phase difference δ shown by the following equation is generated between the P-polarized component and the S-polarized component, and is shifted from circularly polarized light to become elliptically polarized light.

tan (δ / 2) = cos θi × √ (N ² × sin ² θi−1) / (N × sin ² θi) (2) Therefore, when the light passes through the quarter wavelength plate 8, it is polarized in the same direction as the forward path. Ingredients will be included. This polarized component passes through the PBS 7 and is reflected by the NBS 4, and is condensed on the photodetector 3 (PD 3) 27 via the lens 26. The light quantity of this light beam can be used as the gap error signal 28 because it monotonously decreases as the distance between the bottom surface of the SIL and the optical disk approaches in the near field region. If a target threshold value is determined in advance, the distance between the bottom surface of the SIL and the optical disk can be kept at a desired distance of 100 nm or less by performing gap servo. The gap servo is detailed in the paper of Non-Patent Document 1 described above. Further, since this light beam is not modulated by the recording information on the optical disc 12, a stable gap error signal can be obtained regardless of the presence or absence of the recording information.

  Next, details of the two-layer disc 12 and the hemispherical SIL will be described with reference to FIGS. 11 and 12. 11 and 12, the two-layer disc 12 is provided with an L0 recording layer 12-2 having tracks on which information tracks and pits are formed on a polycarbonate substrate 12-1. On the L0 recording layer, for example, an L1 recording layer 12-4 having a track on which information tracks and pits are similarly formed via an intermediate layer 12-3 having a constant thickness of 3 μm made of 2P (Photo Polymer), for example. Is provided. Furthermore, a cover layer 12-5 having a constant thickness of 3 μm made of, for example, 2P (Photo Polymer) is provided on the L1 recording layer.

  The center of the sphere of the virtual hemisphere SIL11 (the center of the circle indicated by the dotted line) is approximately between the L0 recording layer 12-2 and the L1 recording layer 12-4. When focusing on the L0 recording layer, the distance between the objective lens 10 and the SIL 11 is adjusted to d1 by the voice coil motor 201 as shown in FIG. The light beam made parallel by the expander lens 9 passes through the objective lens 10 and the SIL 11, and is focused on the L0 recording layer that is slightly farther from the SIL than the virtual center of the sphere.

  When focusing on the L1 recording layer, the distance between the objective lens 10 and the SIL 11 is adjusted to d2 (d2> d1) by the voice coil motor 201 as shown in FIG. The adjustment of the interval not only adjusts the focus but also plays a role of adjusting spherical aberration.

  The light beam collimated by the expander lens 9 passes through the objective lens 10 and the SIL 11, and is focused on the L1 recording layer that is slightly closer to the SIL than the virtual center of the sphere. The jump between the L0 layer and the L1 layer is performed by adjusting the distance between the objective lens 10 and the SIL 11 by the voice coil motor 201.

  Regarding these, it is detailed in the paper of the nonpatent literature 2 mentioned above.

The objective lens 10, the SIL 11, and a voice coil motor 201 that adjusts the distance between both lenses are mounted on a lens holder 202. The lens holder 202 is maintained at a predetermined value by a gap error signal 28 using a gap error signal 28 by a biaxial actuator (not shown), and the tracking error 21 follows the desired track.
Japan Journal Applied Physics, vol. 44 (2005), pages 3564-3567, “Near Field Recording on First-Surface Write-Once Media with NAI 1S. Optical Data Storage 2004, Proceedings of SPIE 5380 (2004) “Near Field read-out of first-surface disk with NA-1.9 and a proposal for a coer

  However, the optical information recording / reproducing apparatus for near-field recording using the conventional hemispherical SIL 11 and the two-layer optical disk 12 has the following problems. In the conventional example, the gap error signal 28 is used to keep the distance between the SIL and the disk 12 at a predetermined value and no focus error signal is detected. For this reason, in order to accurately focus on the L0 layer or the L1 layer, it is necessary to constantly monitor the reproduction signal quality such as the tracking error signal, the amplitude of the RF signal, and the modulation degree. For this reason, when performing an interlayer jump, there is a problem that it is difficult to perform a quick focus jump.

  In addition, the distance between the objective lens 10 and the SIL 11 has been changed for focus adjustment and spherical aberration adjustment. However, since this distance must be controlled with high accuracy, there are problems such as difficulty in control. It was.

  An object of the present invention is to provide an optical information recording / reproducing apparatus that uses a focus error signal and can accurately focus on a two-layer optical disc, and at the same time, corrects spherical aberration and enables quick and stable interlayer jump operation. Is to provide.

In order to solve the above problems, an optical information recording / reproducing apparatus of the present invention includes an objective lens that collects a light beam from a laser light source, and a SIL disposed between the objective lens and the optical recording medium, In an optical information recording / reproducing apparatus that records or reproduces information by condensing a light beam from the laser light source as one light spot on one of a plurality of recording layers of the optical recording medium by the objective lens and the SIL.
A focusing optical system for focusing the light spot on one of a plurality of recording layers of the optical recording medium based on a focus error signal; and one of the recording layers of the recording medium. And a spherical aberration correction mechanism that corrects spherical aberration in a focused state.

  As described above, in the optical information recording / reproducing apparatus for near-field recording according to the present invention that performs recording / reproduction on the information recording layer of two or more optical disks using the hemispherical SIL of the present invention, the L0 layer or the L1 layer is accurately set. A focus error signal can be used to focus. Therefore, when performing the interlayer jump, focusing can be performed based on the focus error signal, and the spherical aberration is also corrected at the same time, so that a quick and stable interlayer jump operation is possible.

  Next, embodiments for carrying out the invention will be described in detail with reference to the drawings.

(First embodiment)
A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 illustrates the configuration of an optical information recording / reproducing apparatus for near-field recording according to the present invention.

  A light beam emitted from the semiconductor laser 1 having a wavelength of 405 nm, which is a laser light source, is converted into a parallel light beam by the collimator lens 2 and is incident on the beam shaping prism 3 to form an isotropic light amount distribution. The light beam that has passed through the polarization beam splitter (PBS) 7 through the non-polarization beam splitter (NBS) 4 is incident on the expander lens 9. Note that a photodetector (LPC-PD) 6 for receiving the light beam reflected by the non-polarizing beam splitter (NBS) 4 and controlling the emission power of the semiconductor laser 1 is provided.

  Further, the expander lens 9 is configured so that the distance between the two lenses can be controlled in accordance with a focus error 25 described later. The light beam from the expander lens passes through the liquid crystal element 29 and the quarter wave plate (QWP) 8 and is converted from linearly polarized light to circularly polarized light. As will be described later, a voltage is applied to the liquid crystal element 29 so as to generate an antiphase component of spherical aberration that occurs at each in-focus position of the two-layer disc 12. The light beam that has passed through the quarter-wave plate enters the rear lens 10 of the objective lens.

  The objective lens includes a rear lens 10 and a SIL (front lens) 11, which are arranged on a biaxial actuator (not shown) that integrally drives two lenses in the focus and tracking directions, and the liquid crystal elements 29 and 1 /. It is mounted together with the four-wavelength plate 8. As the SIL, the hemispherical type SIL described in FIG. 9 is used. An NA = 0.7 objective lens (rear lens) 10 and an N = 2 hemispherical lens SIL 11 were combined to obtain NAeff = 1.4.

  Only when the distance between the bottom surface of the SIL and the optical disk 12 is a short distance of a fraction of the wavelength of the light source 405 nm, for example, 100 nm or less, the recording surface acts as evanescent light from the bottom surface of the SIL, and recording by the NAeff light spot diameter Playback is possible. The gap servo described above is used to maintain this distance. The optical disk 12 is a two-layer disk having two recording layers shown in FIGS.

  The light beam reflected by the optical disk 12 becomes reverse circularly polarized light, enters the SIL 11 and the objective lens 10 and is converted again into a parallel light beam. The light beam that has passed through the quarter-wave plate 8, the liquid crystal element 29, and the expander lens 9 and is linearly polarized in a direction orthogonal to the forward path is reflected by the PBS 7. Of the light beam whose polarization plane has been rotated by 45 ° by the half-wave plate (HWP) 13, the S-polarized light component is reflected by the polarization beam splitter 14 and passes through the lens 15 onto the photodetector 1 (PD 1) 16. The light is condensed and the RF output 17 which is information on the optical disk 12 is reproduced. Of the light beam whose polarization plane has been rotated by 45 ° by the half-wave plate (HWP) 13, the P-polarized light component passes through the polarizing beam splitter 14 and is reflected by the non-polarizing beam splitter 18. The reflected light is reflected and condensed on the two-divided photodetector 2 (PD2) 20 via the lens 19, and a tracking error 21 is output.

  A method for performing focus adjustment, which is one of the features of the present invention, will be described below using a portion surrounded by a dotted line in FIG.

  The light beam that has passed through the non-polarizing beam splitter 18 passes through the opening 22, the outer periphery of the light beam is shielded, and is condensed on the photodetector 4 (PD 4) 24 via the sensor lens 23, resulting in a focus error 25. Is output. Then, with reference to the focus error 25, the distance between the two lenses of the expander lens 9 is controlled, and the desired recording layer is focused.

  The part surrounded by the dotted line will be described in detail with reference to FIGS.

  In FIG. 2, the reflected light beam from the disk is NA = 1.4 (NA> 1) at the periphery of the pupil diameter. The aperture 22 transmits a light beam with NA <1 at the center, for example, NA = 0.85, and blocks a light beam with NA> 1 at the outer periphery. The reason why the transmitted light flux is made about 10% smaller than NA = 1 is that when the objective lens 10 and the SIL 11 are moved in the radial direction of the disk due to the eccentricity of the disk, the light flux with NA> 1 in the outer peripheral portion is not mixed. It is. The opening diameter is preferably in the range of NA = 0.75 to 0.95. This is because if the NA is remarkably lowered, the focus sensitivity is lowered. The sensor lens 23 is a toric lens, and a desired recording layer is focused by an astigmatism method using a four-divided photodetector 24.

  FIG. 3 schematically shows the light amount distribution in the pupil.

  This is a case where the gap between the SIL and the optical disk is maintained at a distance of a fraction of a wavelength of 405 nm, for example, 50 nm by the gap servo. The ring portion with NA> 1 contains a large amount of reflected light from the bottom surface of the SIL, and becomes a noise for the focus signal. Accordingly, the aperture 22 transmits a light beam with NA <1 or less, for example, NA <0.85, which is inside the dotted line in FIG. A light beam with NA <1 or less contains a lot of reflected light from the recording layer of the disk 12, and focus information can be easily obtained.

  The focus error signal 25 is obtained as shown in FIG. 4 corresponding to the L0 layer and the L1 layer by changing the distance between the two lenses of the expander lens 9 under the gap servo. Therefore, during the interlayer jump, the focus error 25 is referred to and the distance between the L0 layer focus position and the L1 layer focus position is changed by changing the distance between the two lenses of the expander lens 9. .

  Further, when focusing on the L0 layer and the L1 layer, a large difference in spherical aberration occurs due to the difference in layer thickness and the large NA. In order to solve this, a spherical aberration correction method and correction mechanism, which is another feature of the present invention, will be described with reference to FIGS.

  FIG. 5 is an explanatory diagram for correcting spherical aberration using a liquid crystal element, and schematically shows how correction is performed.

  The horizontal axis in FIG. 5 is the normalized radius of the light beam, and the vertical axis represents the amount of spherical aberration. In each of the three lines, the dotted line represents the spherical aberration before correction, the broken line represents the spherical aberration for correction, and the solid line represents the corrected spherical aberration. As can be seen from the solid line in FIG. 5, spherical aberration can be reduced by correcting spherical aberration using a liquid crystal element.

  FIG. 6A is a schematic diagram of electrodes of the liquid crystal element used in FIG. 5, and FIG. 6B is a diagram schematically showing a correction amount of spherical aberration in the liquid crystal element. FIG. 6 shows, as an example, electrodes of a liquid crystal element that performs aberration correction in eight divisions in five steps, but the number of steps and the number of divisions are not limited thereto. By controlling the voltage of the electrode of the liquid crystal element, the opposite phase component of the spherical aberration amount generated in the optical system of the optical information recording / reproducing apparatus for near-field recording at the L0 layer in-focus position and the L1 layer in-focus position, respectively, is liquid crystal. It is generated in the element to correct spherical aberration at each layer in-focus position. The spherical aberration amount generated by the liquid crystal element at the L0 layer in-focus position and the L1 layer in-focus position has a binary value that has the same absolute value and the opposite sign, and simply switches the sign. Also good.

  Further, among the light beams reflected by the bottom surface of the SIL 11, a light beam of NAeff <1 that does not totally reflect is reflected as circularly polarized light that is reverse to the incidence, similarly to the light reflected from the optical disk 12 described above. For a luminous flux of NAeff ≧ 1 that causes total reflection, a phase difference δ shown in the equation (2) is generated between the P-polarized component and the S-polarized component, and is shifted from circularly polarized light to become elliptically polarized light. When it passes, it includes a polarization component in the same direction as the forward path. This polarized component passes through the PBS 7 and is reflected by the NBS 4, and is collected on the photodetector 3 (PD 3) 27 via the lens 26. The light quantity of this light beam can be used as the gap error signal 28 because it decreases monotonously as the distance between the bottom surface of the SIL and the optical disk approaches in the near-field region. If the target threshold value is determined in advance, the distance between the bottom surface of the SIL and the optical disk can be kept at a desired distance of 100 nm or less by driving the biaxial actuator and performing the gap servo.

  Further, the gap error signal 28 can be normalized using the output of the photodetector (LPC-PD) 6 for controlling the emission power of the semiconductor laser 1.

  In the present invention, since a focus error signal can be used to accurately focus on the L0 layer or the L1 layer, even if a slight thickness unevenness occurs in the cover layer or the intermediate layer, the lens interval of the expander lens can be changed. It can follow quickly by driving. At the same time, since spherical aberration is corrected by the liquid crystal element, it is possible to accurately record and reproduce information. Further, even if the wavelength of the semiconductor laser 1 changes due to a temperature change or the like, it can be quickly followed by variable lens interval drive of the expander lens and control of the liquid crystal element applied voltage, so that accurate information recording and reproduction can be performed. It has become possible.

  Further, since the focus error signal can be referred to when performing the interlayer jump, the focusing is performed by the variable lens interval driving of the expander lens, and at the same time, the spherical aberration is corrected by controlling the voltage applied to the liquid crystal element. Therefore, it is possible to provide a device that can perform a quick and stable focus jump operation and has good recording and reproduction characteristics.

(Second Embodiment)
The configuration of an optical information recording / reproducing apparatus for near-field recording according to the second embodiment of the present invention will be described with reference to FIG.

  A light beam emitted from a semiconductor laser 31 having a wavelength of 405 nm enters a polarization beam splitter (PBS) 34 through a non-polarization beam splitter (NBS) 32. Note that a photodetector (LPC-PD) 33 for receiving the light beam reflected by the non-polarizing beam splitter (NBS) 32 and controlling the emission power of the semiconductor laser 31 is provided. The light beam that has passed through the polarization beam splitter (PBS) 34 enters the expander lens 36.

  The expander lens 36 is configured to control the distance between the two lens groups in accordance with a focus error 45 described later. It also has a collimator function that makes the luminous flux substantially parallel. The light beam from the expander lens 36 passes through the liquid crystal element 49 and enters the quarter-wave plate (QWP) 35. The light beam that has passed through the quarter-wave plate (QWP) 35 is converted from linearly polarized light into circularly polarized light, and enters the rear lens 38 of the objective lens. The objective lens includes a rear lens 38 and an SIL (front lens) 39, which are mounted on a biaxial actuator (not shown) that integrally drives the two lenses in the focus and tracking directions. As the SIL, the hemispherical type SIL described in FIG. 9 is used. NAeff = 1.4 was obtained by combining the SIL11 of hemispherical lens with N = 2 with the objective lens (rear lens) 38 with NA = 0.7.

  Only when the distance between the bottom surface of the SIL and the optical disk 40 is a short distance of a fraction of the wavelength of the light source 405 nm, for example, 100 nm or less, the recording surface acts as evanescent light from the bottom surface of the SIL, and recording is performed with the NAeff light spot diameter. Playback is possible. In order to maintain this distance, a gap servo is used as in the first embodiment. The optical disc 40 is a two-layer disc having two recording layers shown in FIGS.

  The light beam reflected by the optical disk 40 becomes reverse circularly polarized light, enters the SIL 39 and the objective lens 38, and is converted again into a parallel light beam. The light beam that has passed through the quarter-wave plate 35, the liquid crystal element 49, and the expander lens 36 and has been linearly polarized in the direction orthogonal to the forward path is reflected by the PBS 34.

  The reflected light beam is separated by the hologram 41 into a light beam of NA <1 and its surroundings, and is incident on the photodetector (PD) 43, and a focus error 45 and a light beam in the peripheral portion thereof from the light beam of NA <1. Accordingly, a tracking error 46 and an RF output 47 are output. Here, as in the first embodiment, it is preferable that the aperture diameter of the light beam with NA <1 is specifically in the range of NA = 0.75 to 0.95.

  Further, the light beam that has passed through the PBS 34 and reflected by the non-polarization beam splitter (NBS) 32 is incident on the photodetector (PD) 44 and a gap error 48 is output. The gap control method is the same as in the first embodiment.

  Also in the present embodiment, as in the first embodiment, the distance between the two lens groups of the expander lens 36 is controlled with reference to the focus error 45, and the desired recording layer is focused, and the liquid crystal element The spherical aberration is corrected by the voltage control 49. Therefore, during the interlayer jump, as in the first embodiment, the L0 layer focusing position and the L1 layer focusing are changed by changing the distance between the two lens groups of the expander lens 36 and the voltage applied to the liquid crystal element 49. Move between focal positions.

  Also in the invention of this embodiment, a focus error signal can be used to accurately focus on the L0 layer or the L1 layer. As a result, even if slight thickness unevenness occurs in the cover layer or the intermediate layer, it can be quickly followed by variable lens interval drive of the expander lens and control of the liquid crystal element applied voltage, and accurate information recording and reproduction can be performed. It has become possible. Further, even if the wavelength of the semiconductor laser 1 changes due to a temperature change or the like, it can be quickly followed by variable lens interval drive of the expander lens and control of the liquid crystal element applied voltage, so that accurate information recording and reproduction can be performed. It has become possible.

  In addition, since the focus error signal can be referred to when performing an interlayer jump, a quick and stable focus jump operation is possible by controlling the lens interval variable drive of the expander lens and the liquid crystal element applied voltage, and good recording and reproduction A device with characteristics can be provided.

  In the case of the present embodiment, the expander lens also has a collimator function for making the light beam substantially parallel, so that a PBS or NBS can be arranged between the semiconductor laser and the expander lens, and the apparatus can be made compact. It is useful for conversion.

It is a figure for demonstrating 1st Embodiment of the optical information recording / reproducing apparatus for near field recording in this invention. It is a figure for demonstrating the optical means which detects a focus error signal in 1st Embodiment of the optical information recording and reproducing apparatus for near field recording in this invention. It is a figure for demonstrating the opening used for the optical means which detects a focus error signal in 1st Embodiment of the optical information recording and reproducing apparatus for near field recording in this invention. It is a figure for demonstrating the focus error obtained with the double layer disk in this invention. It is a figure for demonstrating spherical aberration correction of the liquid crystal element in this invention. It is a figure for demonstrating the electrode of the liquid crystal element in this invention. It is a figure for demonstrating 2nd Embodiment of the optical information recording / reproducing apparatus for near field recording in this invention. It is a figure for demonstrating the optical information recording / reproducing apparatus for near field recording of a prior art example. It is a figure explaining the prior art example of hemisphere SIL. It is a figure explaining the prior art example of super hemisphere SIL. It is a figure explaining the prior art example of the optical means which performs focusing of the optical information recording / reproducing apparatus for near field recording corresponding to a multilayer medium. It is a figure explaining the prior art example of the optical means which performs focusing of the optical information recording / reproducing apparatus for near field recording corresponding to a multilayer medium.

Explanation of symbols

1,31 Semiconductor laser 2 Collimator lens 3 Beam shaping prism 4, 18, 32 Non-polarization beam splitter (NBS)
5,15,19,23,26,42 Lens 6,33 LPC-PD
7, 14, 34 Polarizing beam splitter 8, 35 1/4 wavelength plate 9, 36 Expander lens 10, 38 Objective lens (rear lens)
11, 39, 102-a, 102-b SIL (tip lens)
12,40 Double-layer optical disc (recording medium)
13 1/2 wavelength plate 16, 20, 24, 27, 43, 44 Photo detector 17, 47 RF output 21, 46 Tracking error 22 Aperture 25, 45 Focus error 28, 48 Gap error 29, 49 Liquid crystal element 103 Optical disc 201 Voice coil motor 202 2-axis actuator

Claims (5)

An objective lens for condensing a light beam from a laser light source; and an SIL disposed between the objective lens and the optical recording medium, and the optical recording medium transmits the light beam from the laser light source by the objective lens and the SIL. In an optical information recording / reproducing apparatus for recording or reproducing information by converging as one light spot on one of the plurality of recording layers,
A focusing optical system for focusing the light spot on one of a plurality of recording layers of the optical recording medium based on a focus error signal; and one of the recording layers of the recording medium. An optical information recording / reproducing apparatus comprising: a spherical aberration correction mechanism that corrects spherical aberration in a focused state.   2. The optical information recording / reproducing apparatus according to claim 1, wherein the focus optical system detects the focus error signal by using a light beam having an effective numerical aperture NAeff <1 by the objective lens and the SIL.   The optical information recording / reproducing apparatus according to claim 1, wherein the focus optical system includes an expander lens, and the focusing is performed by changing a lens interval of the expander lens.   The optical information recording / reproducing apparatus according to claim 1, wherein the spherical aberration correction mechanism is a liquid crystal element.   5. The optical information recording according to claim 4, wherein a voltage for controlling the liquid crystal element is binarized and switched in accordance with selection of a predetermined recording layer among a plurality of recording layers of the recording medium. Playback device.

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