JP2007250072A - Optical information recording and reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce costs by miniaturization of a device and reduction of the number of parts while attaining precise recording and reproducing of information utilizing an SIL (solid immersion lens). <P>SOLUTION: This device is provided with a collimator 30 which collimates a luminous flux outgoing from a light source to be a parallel luminous flux; an objective lens which is for irradiating an optical recording medium with the parallel luminous flux, which is composed of a lens 10 satisfying NA<1 and the SIL 11 and whose numerical aperture is >1; and photodetectors 27 and 29 which photodetect only the luminous flux of NA<1 of the objective lens in reflected light from the optical recording medium 12. The photodetectors 27 and 29 are arranged so as to photodetect the luminous flux collected by the collimator 30. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical information recording / reproducing apparatus such as an optical disk apparatus, and more particularly to an optical information recording / reproducing apparatus for near-field recording that performs recording / reproducing on an information recording layer of an optical disk using Solid Immersion Lens (hereinafter abbreviated as SIL). It is about.

  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 an NA is set to 1 or more even in the air. Has been made. For example, they are described in “Japan Field Applied on First-Surface Write-Once Media with ID” in Non-patent Document 1 of Japanese Journal Applied Physics, Vol. 44 (2005) P3564-357. 1). Also, in Optical Data Storage 2004, Proceedings of SPIE 5380 (2004) “Near Field read-out of first-surface disk with NA = 1.9 and a proposal. Detailed (Non-Patent Document 2).

  The prior art will be described with reference to FIGS. The configuration of an optical pickup for near-field recording in a conventional example (Japan Journal Applied Physics, Vol. 44 (2005) P3564-357) 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. A light beam that has passed through the non-polarizing beam splitter (NBS) 4 and transmitted through the polarizing beam splitter (PBS) 7 passes through a 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-wave plate enters the expander lens 9. The expander lens 9 is a lens for correcting spherical aberration generated in an objective lens and SIL described later, and is configured to control the distance between the two lenses in accordance with the spherical aberration. The light beam from the expander lens enters the rear lens 10 of the objective lens. The objective lens is composed of 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 FIGS.

  FIG. 7 condenses the light beam focused by the objective lens rear lens 101 on the bottom surface of the hemispherical lens SIL 102-a. The light beam enters the hemisphere lens's spherical surface perpendicularly, and is condensed on the bottom surface through the same optical path as when there is no hemisphere, so it is equivalent to shortening the wavelength by the refractive index of the hemisphere lens and reducing the light spot diameter. There is an effect to. That is, if the refractive index of the hemispherical lens is N and the numerical aperture of the objective lens rear lens 101 is NA, a light spot equivalent to N × NA is obtained on the recording surface of the optical disk 14. For example, when the SIL of the hemispherical lens of N = 2 is combined with the objective lens 101 of NA = 0.7, NAeff = 1.4 is reached with the effective NA as NAeff. Since the thickness error of the hemispherical lens 102-a can be allowed to be about 10 μm, mass production is easy.

On the other hand, FIG. 8 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 hemispherical lens. When the radius of the super hemisphere 102-b is R, the bottom surface is a surface separated from the center of the super hemisphere 102-b by R / N. If the angle between the optical axis and the light beam on the bottom surface is θt, the relationship of equation (1) is established between the angle θi between the light beam incident on the SIL and the optical axis.
sin θt = N × sin θ i (1) Since sin θ i is nothing but the NA of the objective lens rear lens 101, N ² × A light spot equivalent to NA is obtained. The NA of the objective lens rear lens 101 is limited to 1 / N or less from the equation (1) because the light beam can enter the SIL 102-b. If a glass material of N = 2 is used for the SIL 102-b, a light spot corresponding to NAeff = 2.0 can be obtained even if a relatively low NA, for example, an NA = 0.5 objective lens is used for the rear lens 101 of the objective lens. Is possible. However, it is difficult that the thickness error of the super hemispherical lens 102-b is only allowed to be about 1 μm.

  In any SIL, only when the distance between the bottom surface of the SIL and the optical disk 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. Returning to FIG. 6, the return 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 RF photodetector (RFPD) 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 is rotated by 45 ° by the half-wave plate (HWP) 13, the P-polarized light component passes through the polarization beam splitter 14, is reflected by the non-polarization beam splitter 18, and passes through the lens 19 to be 2 The light is condensed on the divided Tr photodetector (TRPD) 20 and a tracking error 21 is output.

On the other hand, among the light beams reflected from the bottom surface of the SIL 11, a light beam of NAeff <1 that does not totally reflect is reflected as circularly polarized light in the reverse direction to the incident, similarly to the light reflected from the optical disk 12 described above. For a beam of NAeff ≧ 1 that causes total reflection, a phase difference δ expressed by the following equation is generated between the P-polarized component and the S-polarized component, and becomes elliptically polarized light that deviates from circularly polarized light.
tan (δ / 2) = cos θi × √ (N ² × sin ² θi−1) / (N × sin ² θi) (2) Therefore, when passing through the quarter wavelength plate 8, the polarization component in the same direction as the forward path Will be included. This polarized light component passes through the PBS 7 and is reflected by the NBS 4, and is condensed on the GE photodetector (GEPD) 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 above-mentioned paper of Japan Journal Applied Physics Vol. 44 (2005) P3564-357. Further, since this light beam is not modulated by the recording information on the optical disk 12, a stable gap error signal can be obtained regardless of the presence or absence of the recording information.

  As described above, the super hemisphere SIL has an advantage that the NA can be easily increased. For example, if NAeff = 2, 150 GB can be recorded on a disk having a diameter of 120 mm. However, it is necessary to strictly manage the SIL lens thickness manufacturing error. Further, since the evanescent light does not reach the recording layer unless the refractive index of the protective layer protecting the recording layer is higher than NAeff, the material of the protective layer is necessarily an inorganic material having a refractive index exceeding 2. Must-have. That is, the super hemisphere SIL can be applied at low cost by spin coating or the like, but an organic material protective layer having a low refractive index (N = about 1.6) cannot be used. Since the protective layer for preventing the recording layer from being damaged by rubbing or the like is required to be at least several μm, it is expensive to produce them with an inorganic material. On the other hand, the hemispherical SIL has a limit of NAeff = 1.5 considering the NA of an objective lens that can be used at low cost. In this case, 84 GB can be recorded on a disk having a diameter of 120 mm. However, since the refractive index of the protective layer protecting the recording layer can be selected to be about 1.6, an inexpensive organic material protective layer can be used. The comparison of these SILs is detailed in the above-mentioned paper of Optical Data Storage 2004, Proceedings of SPIE 5380 (2004).

  Details of the disk 12 and the hemisphere SIL will be described with reference to FIG. In FIG. 9, the disk 12 is provided with a recording layer 12-2 having tracks on which information tracks and pits are formed on a polycarbonate substrate 12-1. On the recording layer, for example, a cover layer 12-5 having a constant thickness of 3 μm made of 2P (Photo Polymer) is provided.

  The center of the sphere of the virtual hemisphere SIL11 (the center of the circle indicated by the dotted line) substantially coincides with the recording layer 12-2, and the light beam made parallel by the expander lens 9 in FIG. Through the SIL 11, the recording layer which is the virtual center of the sphere is focused.

The objective lens is maintained at a predetermined distance between the SIL and the disk 12 by using a gap error signal 28 by a biaxial actuator (not shown), and a desired track is tracked by a tracking error 21.
Japan Journal Applied Physics vol. 44 (2005) P. 3564-3567 “Near Field Recording on First-Surface Write-Once Media with NA” = 1.9 mm Solid. 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 conventional optical information recording / reproducing apparatus for near-field recording has the following problems. In the configuration of the conventional example described above, since the separation elements PBS7 and NBS4 are arranged in parallel light, the return light separated from the forward path also becomes parallel light. For this reason, the lens 15, the lens 19, and the lens 26 for condensing the light detectors are separately required, and there is a problem that the apparatus is increased in size and cost.

  In the conventional example, since the gap error signal 28 is used to keep the distance between the SIL and the disk 12 at a predetermined value, the tracking error signal and the amplitude of the RF signal, It was necessary to constantly monitor the degree of modulation. The focus error signal cannot be used because, as described above, the reflected light from the bottom surface of the SIL 11 is mixed as noise.

  Therefore, even if a slight thickness unevenness occurs in the cover layer, it cannot be quickly followed, and accurate information recording / reproduction becomes difficult. Or, even if the wavelength of the semiconductor laser 1 changes due to a temperature change or the like, it cannot quickly follow the wavelength, making it difficult to accurately record and reproduce information.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to realize cost reduction by reducing the size of the apparatus and reducing the number of parts while realizing accurate information recording / reproduction.

  In order to solve the above problems, in an optical information recording / reproducing apparatus, NA <1 for irradiating a light source, a collimator for converting the light beam emitted from the light source into a parallel light beam, and the parallel light beam on the optical recording medium. An objective lens having an effective numerical aperture larger than 1 and a photodetector that detects only the luminous flux of NA <1 of the objective lens out of the reflected light from the optical recording medium. The optical detector is arranged so as to receive the light beam collected by the collimator. An optical information recording / reproducing apparatus is provided.

  According to the configuration of the present invention, in the return path, the light beam incident on the NBS4 and the PBS7 that are the separation elements becomes the focused light. For this reason, it is possible to eliminate the lens for focusing on each photodetector as shown in the conventional example, and the cost can be reduced by reducing the number of parts, and the device can be downsized along with the shortening of the optical path length. The

  Furthermore, a focus error signal can be used to accurately focus the recording layer. For this reason, even if a slight thickness unevenness occurs in the cover layer, it can be quickly followed, and accurate information recording and reproduction can be performed. Further, even if the wavelength of the semiconductor laser 1 changes due to a temperature change or the like, it can quickly follow the wavelength, and accurate information recording and reproduction can be performed. In this configuration, as compared with the conventional example, at least a lens for focusing on the GE photodetector (GEPD) 27 is not required, so that the cost and size can be reduced by reducing the number of components. .

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Example 1
A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 illustrates the configuration of an optical pickup for near-field recording according to the present invention.

  A light beam emitted from the semiconductor laser 1 having a wavelength of 405 nm passes through a non-polarizing beam splitter (NBS) 4 such as a half mirror, passes through a polarizing beam splitter (PBS) 7, and a quarter wavelength plate (QWP) 8, Conversion from linearly polarized light to circularly polarized light. The light beam reflected by the non-polarizing beam splitter (NBS) 4 is directed to a photodetector (LPC-PD) 6 for controlling the emission power of the semiconductor laser 1. The light beam that has passed through the QWP 8 enters the collimator 30, becomes a parallel light beam, and enters the rear lens 10 of the objective lens. The collimator 30 is configured to be movable along the forward optical axis by a voice coil motor or a rack (not shown). Further, the collimator moves along the optical axis direction based on a focus error signal, which will be described later, thereby focusing on the recording layer of the optical disc 12. The objective lens is composed of 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. As the SIL, the hemispherical type SIL described in FIG. 8 made of a material having a refractive index N larger than 1 is used. An NA = 0.7 objective lens (rear lens) 10 was combined with an N = 2 hemispherical lens SIL11 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 light source wavelength of 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. The gap servo described above is used to maintain this distance.

  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 parallel light flux passes through the collimator 30 to become focused light, and passes through the QWP 8 to become linearly polarized light in a direction orthogonal to the forward path, and is reflected by the PBS 7. The light beam reflected by the PBS 7 enters the hologram 33. The hologram 33 is provided with the hologram pattern shown in FIG.

  More specifically, in FIG. 2, the reflected light beam from the disk is NA = 1.4 (NA> 1) at the periphery of the pupil diameter. In this embodiment, a part of the light beam with NA <1, for example, NA = 0.85, at the center thereof is diffracted while generating astigmatism for generating a focus error signal. The method of diffracting while generating astigmatism with the hologram 33 is well known and will not be described. The reason why the transmitted light beam is made about 10% smaller than NA = 1 is that when the objective lens 10 and the SIL 11 move in the radial direction of the disk due to the eccentricity of the disk, a light beam 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 diffracted light beam for generating the focus error signal is condensed on a light receiving surface (not shown) divided into four on an RF / Tr / Fo photodetector (RF / Tr / Fo-PD) 29. The focus error signal 34 is obtained by a known astigmatism method.

  When the gap servo maintains the distance between the SIL and the optical disc at a fraction of a wavelength of 405 nm, for example, at a distance of 50 nm, the ring portion with NA> 1 contains a lot of reflected light from the bottom surface of the SIL. Therefore, it becomes noise for the focus error signal 34. Therefore, the hologram pattern for generating the focus error signal of the hologram 33 diffracts a beam of NA <1 or less, for example, NA <0.85 which is inside the dotted line in FIG. The light flux with NA <1 contains a large amount of reflected light from the recording layer of the disk 12, so that focus information can be easily obtained.

  Further, the light beam (the total light beam with NA> 0.85 and the 0th-order light with NA <0.85) transmitted through the hologram 33 shown in FIG. 2 is an RF / Tr / Fo detector (RF / Tr / Fo). The light is condensed on a light receiving surface (not shown) divided into two, which is arranged in parallel with the light receiving surface divided into four on the PD) 29. As a result, the RF output 17 and the tracking error signal 21 are output from the photodetector. In this embodiment, the tracking error signal is generated by a known push-pull method.

  On the other hand, among the light beams reflected from the bottom surface of the SIL 11, a light beam of NAeff <1 that does not totally reflect is reflected as circularly polarized light in the reverse direction to the incident, similarly to the light reflected from the optical disk 12 described above. For a beam 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 passing through QWP8, the same as the forward path Direction polarization component. This polarized light component passes through the PBS 7 and is reflected by the NBS 4 and is collected on the GE photodetector (GEPD) 27. 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 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 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.

  The focus error signal 34 is supplied to a drive source (not shown) of the collimator 30 via a servo circuit (not shown). As a result, the collimator 30 is driven to focus on the recording layer of the optical disc 12.

  As described above in detail, according to the configuration of the present invention, in the return path, the light beam incident on the NBS 4 and the PBS 7 serving as the separation elements becomes the focused light. For this reason, it is possible to eliminate the lens 15, the lens 19, and the lens 26 for condensing light on each photodetector as shown in the conventional example, thereby realizing downsizing and cost reduction of the apparatus.

  In the present invention, since a focus error signal can be used to accurately focus the recording layer, even if a slight thickness unevenness occurs in the cover layer, it can be quickly followed and accurate information recording can be performed. Playback is possible. Further, even if the wavelength of the semiconductor laser 1 changes due to a temperature change or the like, it can quickly follow the wavelength, and accurate information recording and reproduction can be performed. Furthermore, according to the configuration of the present invention, in the return path, the light beam incident on the NBS4 and PBS7 which are the separation elements becomes the focused light. For this reason, it becomes possible to abolish the lens for condensing light on each photodetector as shown in the conventional example, and the device can be downsized along with the shortening of the optical path length. In addition, since a lens for condensing at least on the GE photodetector (GEPD) 27 is unnecessary as compared with the conventional example, cost reduction and downsizing can be realized by reducing the number of components.

(Example 2)
A second embodiment of the present invention will be described with reference to FIG. In the present embodiment, the same reference numerals are used for the same elements as in the first embodiment.

  A light beam emitted from the semiconductor laser 1 having a wavelength of 405 nm passes through the non-polarizing beam splitter (NBS) 4, passes through the polarizing beam splitter (PBS) 7, and enters the collimator 30. The light beam reflected by the non-polarizing beam splitter (NBS) 4 is directed to a photodetector (LPC-PD) 6 for controlling the emission power of the semiconductor laser 1. The light beam incident on the collimator 30 is converted into a parallel light beam and is incident on the rear lens 10 of the objective lens. The collimator 30 includes a first collimator 30a and a second collimator 30b. In the present embodiment, the first collimator 30a moves along the optical axis direction based on a focus error signal described later, thereby focusing on the recording layer of the optical disc 12. The objective lens is composed of 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. As the SIL, the hemispherical type SIL described in FIG. 8 is used. An NA = 0.7 objective lens (rear lens) 10 was combined with an N = 2 hemispherical lens SIL11 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 light source wavelength of 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. The gap servo described above is used to maintain this distance.

  The light beam reflected by the optical disk 12 enters the SIL 11 and the objective lens 10 and is converted again into a parallel light beam. The parallel light beam passes through the collimator 30 to become focused light, and the linearly polarized light beam in the same direction as the forward path passes through the PBS 7 and is reflected by the NBS 4. The means for generating the RF output 17, the tracking error signal 21, and the focus error signal 34 from the light beam reflected by the NBS 4 is the same as that in the first embodiment, and the description thereof is omitted.

  The focus error signal 34 is supplied to a drive source (not shown) of the collimator 30a via a servo circuit (not shown). As a result, the collimator 30a is driven to focus on the recording layer of the optical disc 12. On the other hand, among the light beams reflected from the bottom surface of the SIL 11, a light beam of NAeff <1 that does not totally reflect is reflected as linearly polarized light similar to that at the time of incidence, similar to the light reflected from the optical disk 12 described above. For a light flux of NAeff ≧ 1 that causes total reflection, in the light flux incident on the bottom surface of the SIL with an azimuth other than the incident polarization direction and the direction orthogonal thereto, the expression (2) is used between the P polarization component and the S polarization component of the reflected light. The phase difference δ shown is produced, resulting in elliptically polarized light. As a result, the reflected light includes a polarization component orthogonal to the forward path. This polarized component is reflected by the PBS 7 and collected on the GE photodetector (GEPD) 27. 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 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 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 embodiment, not only the effects of the first embodiment but also the QWP can be abolished, so that further cost reduction can be realized.

  Further, as shown in FIG. 4, by further disposing the GEPD 27 at a distance c from the optical axis of the forward path, further downsizing of the apparatus can be realized. The optical system of the present invention uses the fact that the light flux of the return path in the NBS 4 and PBS 7 is focused by the collimator 30 and focuses it on each photodetector. For this reason, as shown in FIGS. 1 and 3, the distance from each separation element to each photodetector is longer on the separation element (PBS 7) side closer to the collimator 30. More specifically, a distance approximately equivalent to the distance n from the semiconductor laser 1 to the center of the NBS 4 (intersection of the optical axis and the reflecting surface) and a distance from the center of the NBS 4 to RF / Tr / Fo-PD are required. is there. Similarly, if the distance from the semiconductor laser 1 to the center of the PBS 7 is p, the distance from the center of the PBS 7 to the GEPD 27 is also about p.

However, in this embodiment, the light beam separated by the PBS 7 generates a gap error signal 28. Since the gap error signal 28 is detected by the total amount of light, a sensor similar to the photodetector (LPC-PD) 6 for controlling the emission power of the semiconductor laser 1 can be used. Therefore, as shown in FIG. 4, if the distance from the optical axis of the forward path to the LPC-PD is a and the distance from the center of the NBS 4 to the center of the PBS 7 is b, the distance c from the optical axis of the forward path to the GEPD 27 Is
If c ≧ (b−a) (3), the received light flux does not exceed the detection area of the photodetector. Since it is obvious that the distance p from the semiconductor laser 1 to the PBS 7 is p> b, the minimum value of c is c <p, and the distance from the center of the PBS 7 to the GEPD 27 can be reduced. The downsizing of the device is realized.

(Example 3)
A third embodiment of the present invention will be described with reference to FIG. In this embodiment, the same reference numerals are used for the same elements as in the second embodiment.

  A light beam emitted from the semiconductor laser 1 having a wavelength of 405 nm enters the collimator 30 through an optical integrated unit 32 described later. The optical integrated unit 32 includes an LPC / GE photodetector (LPC / GE-PD) in which the photodetector for controlling the emission power of the semiconductor laser 1 and the above-described gap error signal generating photodetector are integrally formed. ) 31, NBS4, and PBS7 are integrally formed. The light beam reflected by the non-polarizing beam splitter (NBS) 4 is directed to the LPC / GE-PD 31 in order to control the emission power of the semiconductor laser 1. Further, the light beam incident on the collimator 30 is converted into a parallel light beam and is incident on the rear lens 10 of the objective lens. The collimator 30 includes a first collimator 30a and a second collimator 30b. In the present embodiment, the second collimator 30b moves along the optical axis direction based on a focus error signal described later, thereby focusing on the recording layer of the optical disc 12. The objective lens is composed of 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. As the SIL, the hemispherical type SIL described in FIG. 8 is used. An NA = 0.7 objective lens (rear lens) 10 was combined with an N = 2 hemispherical lens SIL11 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 light source wavelength of 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. The gap servo described above is used to maintain this distance.

  The light beam reflected by the optical disk 12 enters the SIL 11 and the objective lens 10 and is converted again into a parallel light beam. The parallel light beam passes through the collimator 30 to become focused light, and the linearly polarized light beam in the same direction as the forward path passes through the PBS 7 and is reflected by the NBS 4. The means for generating the RF output 17, the tracking error signal 21, and the focus error signal 34 from the light beam reflected by the NBS 4 is the same as that in the first embodiment, and the description thereof is omitted.

  The focus error signal 34 is supplied to a drive source (not shown) of the collimator 30a via a servo circuit (not shown). Thereby, the collimator 30b is driven and the recording layer of the optical disc 12 is focused.

  On the other hand, among the light beams reflected from the bottom surface of the SIL 11, a light beam of NAeff <1 that does not totally reflect is reflected as linearly polarized light similar to that at the time of incidence, similar to the light reflected from the optical disk 12 described above. For a light flux of NAeff ≧ 1 that causes total reflection, in the light flux incident on the bottom surface of the SIL with an azimuth other than the incident polarization direction and the direction orthogonal thereto, the expression (2) is used between the P polarization component and the S polarization component of the reflected light. The phase difference δ shown is produced, resulting in elliptically polarized light. As a result, the reflected light includes a polarization component orthogonal to the forward path. This polarization component is reflected by the PBS 7 in the optical integrated unit 32 and collected on the LPC / GE-PD 31. 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 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 gap servo. Further, the gap error signal 28 can be normalized using the output of the photodetector for controlling the emission power of the semiconductor laser 1.

  In the present embodiment, not only the effect of the second embodiment but also the NBS4, PBS7, and LPC / GE-PD31 are integrally configured, so that further downsizing of the apparatus is realized. In addition, since there is no need to adjust the position of each part, the cost can be reduced by reducing the number of assembly steps. Further, as described above, when the gap error signal 28 is normalized by using the output of the photodetector for controlling the emission power of the semiconductor laser 1, it is possible to perform computation within the same sensor. Improvements are also possible.

  Note that the present invention is not limited to the above-described embodiment. For example, a surface-recording optical disk can be used.

It is a figure which shows the 1st Example of the optical information recording / reproducing apparatus for near field recording of this invention. It is a figure explaining the hologram pattern in a 1st Example. It is a figure which shows the 2nd Example of the optical information recording / reproducing apparatus for near field recording of this invention. It is a figure explaining arrangement | positioning of GEPD in a 2nd Example. It is a figure which shows the 3rd Example of the optical information recording / reproducing apparatus for near field recording of 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 structure of the conventional recording medium.

Explanation of symbols

1 Semiconductor laser 4 Non-polarizing beam splitter (NBS)
6 LPC-PD
7 Polarizing beam splitter 8 1/4 wavelength plate 10,101 Objective lens (rear lens)
11, 102-a, 102-b SIL (tip lens)
12 Optical disc (recording medium)
17 RF output 21 Tracking error signal 27 GE photodetector 28 Gap error signal 29 RF / Tr / Fo photodetector 30 Collimator 30a First collimator 30b Second collimator 31 LCP / GE photodetector 32 Optical integrated unit 33 Hologram 34 Focus error signal 103 Optical disc

Claims (6)

In an optical information recording / reproducing apparatus,
An effective numerical aperture of 1 from a light source, a collimator that collimates the light beam emitted from the light source, and a lens satisfying NA <1 and an SIL lens for irradiating the parallel light beam on the optical recording medium. A large objective lens, and a photodetector that detects only the light flux of NA <1 of the objective lens among the reflected light from the optical recording medium, and the photodetector detects the light flux collected by the collimator. An optical information recording / reproducing apparatus, which is arranged to receive light.   2. The optical information recording according to claim 1, wherein a focus error signal is generated using an output of the photodetector, and the collimator is configured to be movable in a focus direction based on the focus error signal. Playback device.   The optical information recording / reproducing apparatus according to claim 2, wherein the collimator includes two lenses, and one of the lenses is configured to be movable in a focus direction.   Two light beam separating means are arranged between the light source and the collimator, the light beam separating means arranged on the light source side is a non-polarizing beam splitter, and the light beam separating means arranged on the objective lens side is a polarized beam. A splitter that generates a gap error signal used to control a gap interval between the SIL and the optical recording medium using a reflected light beam from the bottom surface of the SIL separated by the polarizing beam splitter, and is separated by the non-polarizing beam splitter. 3. The optical information recording / reproducing apparatus according to claim 2, wherein the focus error signal is generated using a reflected light beam from the optical recording medium.   Between the light source and the collimator, a λ / 4 plate and two light beam separating means are disposed. The light beam separating means disposed on the light source side is a non-polarizing beam splitter, and the light beam disposed on the objective lens side. The separating means is a polarizing beam splitter, and the λ / 4 plate is disposed between the polarizing beam splitter and a collimator, and a focus error signal is generated using a reflected light beam from the optical recording medium separated by the polarizing beam splitter. The gap error signal used for controlling the gap interval between the SIL and the optical recording medium is generated using a reflected light beam from the bottom surface of the SIL generated and separated by the non-polarizing beam splitter. The optical information recording / reproducing apparatus described. A first photodetector for receiving the light beam separated by the polarization beam splitter; and a second photodetector for receiving the light beam separated by the non-polarization beam splitter, the first photodetector. 5. The optical information recording / reproducing apparatus according to claim 4, wherein the distance from the center of the polarizing beam splitter is smaller than the distance from the center of the second photodetector and the non-polarizing beam splitter.

Images