JP2001307370A - Optical recording and reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical recording and reproducing device capable of properly recording and reproducing information even for a high density optical disk having more recording layers than before. SOLUTION: The recording and reproducing optical system of the device includes a laser diode 12, a polarizing beam splitter 14, a collimator lens 16, a 1/4 wavelength plate 18, a mirror 20, an aberration compensator 22, a dichroic prism 30, an objective optical part 32, a pinhole 38 and a photodetector 40. The objective optical part 32 is provided with an objective lens 34 and an actuator 36 for moving the lens along the optical axis. The aberration compensator 22 is equipped with a relay lens 24, an image forming lens 26, and an actuator 28 for changing an interval between the two lenses. The numerical aperture NAimg of the image forming lens 26 and that NAobj of the objective lens 34 satisfy the relation of 0.45<NAimg/NAobj<0.8; the numerical apertures are, for example, NAobj=0.6 and NAimg=0.313.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical recording / reproducing apparatus for optically recording / reproducing information on / from an optical disk. In particular, it relates to an optical recording / reproducing apparatus for an optical disk having a plurality of recording layers.

[0002]

2. Description of the Related Art Japanese Patent Laying-Open No. 7-21565 discloses an optical recording / reproducing apparatus.

This optical recording / reproducing apparatus is a device for recording / reproducing on / from an optical disk having a guide layer for focus and tracking and a plurality of recording layers for holding information, and is used for accessing the guide layer. It has a laser light source and a laser light source for accessing the recording layer.

The divergent light beams emitted from the respective laser light sources are converted into parallel light beams by the corresponding collimator lenses, then combined by a half mirror, and condensed on an optical disk by a common objective lens. You.

The focus operation for the guide layer is performed by moving the objective lens along the optical axis, and the focus operation for selecting the recording layer is performed by moving the collimator lens of the recording / reproducing laser light source back and forth. .

The light reflected from the guide layer passes through a half mirror, enters a photodetector, and performs focus and tracking operations based on the signal.

[0007] As the reflected light from the recording layer, only the reflected light from the desired recording layer is selected by a pinhole, enters the photodetector, and is converted into a reproduction signal.

As described above, the optical disc has the guide layer, and the optical recording / reproducing apparatus has a dedicated focus and track detection optical system. Thus, a stable following operation is performed on the surface deflection of the optical disk.

However, this optical recording / reproducing apparatus is not suitable for application to a currently mainstream separation optical system.

The optical system of most optical disk drive devices such as MOs currently on the market is a separation optical system, and includes a movable portion including an objective lens and its actuator, and a fixed portion including a light source, a collimator lens, and a detection system. Are separated. The movable part and the fixed part are connected by a beam of parallel light,
Only the movable part can move in the radial direction of the optical disk, and the movable part accesses a desired track.

In such a separation optical system, since the movable portion is light in weight, the movable portion can be moved by a motor having a small output, so that the power consumption can be reduced. In addition, since the inertial mass of the movable portion is small, a desired track can be formed. This has the advantage that the movable part can be moved quickly.

Japanese Patent Application Laid-Open No. 5-174395 discloses an optical recording / reproducing apparatus using such a separation optical system. In the optical recording / reproducing device, the focus operation on the optical disc is performed by moving a collimator lens provided on a fixed portion along the optical axis, and the focus and track detection system includes:
It is arranged between the laser light source and the collimator lens.

[0013]

The conventional optical recording / reproducing apparatus for an optical disk having a plurality of recording layers has a drawback that it cannot cope with a high-density optical disk having a large number of recording layers. .

This is because, as the focal point of the beam becomes deeper from the surface of the optical disk, the aberration becomes larger, so that the beam is not properly focused. For this reason, it is difficult to appropriately record and reproduce information on a recording layer at a deep position.

FIG. 5 shows the relationship between the focal point shift and the wavefront aberration.
With respect to a typical objective lens having a numerical aperture of 0.5 to 0.6, it can be seen that the wavefront aberration exceeds the wavefront aberration limit value 0.07λ for beam focusing even with a focus movement of about 100 μm. .

Further, the conventional recording / reproducing apparatus of the separation optical system has a disadvantage that the intensity of the beam irradiated on the optical disk fluctuates.

This is because the collimator lens is moved along the optical axis for the focus operation for selecting the recording layer. Therefore, the beam connecting the fixed part and the movable part is not a parallel light beam but a non-parallel light beam. As a result, as shown in FIG. 6, the diameter of the beam incident on the objective lens changes according to the position of the movable part. For this reason, the beam incident on the objective lens protrudes from the objective lens depending on the position of the movable part. As a result, the intensity of the laser irradiated on the optical disk changes.

The present invention has been made in view of such a situation, and its main purpose is to appropriately apply to a high-density optical disk having a larger number of recording layers than in the past. An object of the present invention is to provide an optical recording / reproducing apparatus capable of recording and reproducing information.

[0019]

SUMMARY OF THE INVENTION The present invention is an optical recording / reproducing apparatus for recording / reproducing information on / from an optical disk having a plurality of recording layers, and for emitting a beam of diverging light for recording / reproducing. A collimator lens for converting the divergent light beam from the light source into a parallel light beam,
An aberration corrector for changing the degree of focusing of the parallel light beam from the collimator lens, and an objective lens for focusing the beam from the aberration corrector on one of the recording layers of the optical disc. By changing the degree of converging of the parallel light beam by the aberration corrector, focus shift and aberration correction between a plurality of recording layers of the optical disc are performed.

Preferably, the aberration correction section includes a relay lens disposed on the collimator lens side, an imaging lens disposed on the object lens side, and an actuator for adjusting a distance between the relay lens and the imaging lens. The imaging lens numerical aperture NA _img and the objective lens numerical aperture NA _obj are
0.45 <NA _img / NA _obj <0.8.

[0021]

FIG. 1 shows an optical recording / reproducing apparatus according to an embodiment of the present invention. This optical recording / reproducing apparatus includes an optical system for recording / reproducing, and an optical system for focusing and tracking.

An optical system for recording and reproducing includes a laser diode (LD) 12 and a polarizing beam splitter (PBS) 14.
, A collimator lens 16, a quarter-wave plate 18, a mirror 20, an aberration corrector 22, a dichroic prism 30, an objective optical unit 32, a pinhole 38, and a photodetector (PD) 40. Contains.

An optical system for focusing and tracking includes an LD 42, a polarizing beam splitter 44, a collimator lens 46, a quarter-wave plate 48, a dichroic prism 30, an objective optical section 32, a cylindrical lens 50, And a photodetector 52.

Among the above-mentioned optical elements, the mirror 20, the aberration correcting section 22, the dichroic prism 30, and the objective optical section 32 are provided on a movable section 54 that can move in the radial direction of the optical disk 70. Other optical elements are provided on the fixed portion 56 that does not move.

As shown in FIG. 2, the optical disk 70 has a guide layer 72, a protective layer 76, and a plurality of recording layers between which information is written, for example, three recording layers 74a, 74b, 74c. The optical disk 70 is rotatably held by a motor 80 as shown in FIG.

The recording / reproducing optical system and the focusing / tracking optical system commonly include a dichroic prism 30 and an objective optical section 32. That is, the optical system for recording and reproduction and the optical system for focusing and tracking are coupled to each other in the section between the dichroic prism 30 and the optical disk 70.

The LD 12 of the recording / reproducing optical system is 680
The light beam having a wavelength of 780 nm is emitted, and the LD 42 of the optical system for focusing and tracking emits a light beam having a wavelength of 780 nm. Dichroic prism 30
Transmits a beam of light having a wavelength of 680 nm and 780 n
It reflects a beam of light of wavelength m. Accordingly, the dichroic prism 30 combines the recording / reproducing light beam heading toward the optical disk 70 with the focusing / tracking light beam, and also returns the recording / reproducing light beam returning from the optical disk 70 to the focusing / tracking light. From the beam.

The objective optical section 32 includes an objective lens 34 and an actuator 36 for moving the objective lens 34 along the optical axis.
And The objective lens 34 has an NA of 0.6 and has a focal length of 2.6 mm.

[Optical system for recording / reproducing]
A beam of divergent light of linearly polarized light (p-polarized light) having a wavelength of 0 nm is emitted. The PBS 14 transmits p-polarized light from the LD 12, and reflects linearly polarized light (s-polarized light) orthogonal to the p-polarized light. The collimator lens 16 changes the divergent light beam from the LD 12 into a parallel light beam, and changes the return light beam from the optical disk 70 into a convergent light beam. The quarter-wave plate 18 changes the p-polarized light from the LD 12 into circularly polarized light and changes the circularly polarized light returned from the optical disk 70 into s-polarized light orthogonal to the p-polarized light from the LD 12. The mirror 20
The light beam from the LD 12 is deflected toward the aberration corrector 22.

The aberration corrector 22 includes a relay lens 24,
It has an imaging lens 26 and an actuator 28 for changing the distance between the two. Both the relay lens 24 and the imaging lens 26 have an NA of 0.313. In one example, the relay lens 24 is fixed, and the imaging lens 26 is movably supported by the actuator 28 along the optical axis.

The aberration corrector 22 adjusts the position of the imaging lens 26 as necessary to convert the incident parallel light beam into a non-parallel light beam, ie, a convergent light beam or a divergent light beam. Change. That is, the aberration correction unit 2
2 changes the degree of focusing of the incident parallel light beam as needed.

The dichroic prism 30 is 680n
It transmits light of wavelength m. The objective lens 34 converges the light beam for recording and reproduction, and the recording layer 74 of the optical disc 70.
A beam spot is formed on any one of a to 74c.

The pinhole 38 is located in front of the PD 40 and has a hole having a diameter substantially the same as the diameter of the beam spot formed on the recording layer. Are located in For this reason, the pinhole 38 blocks light from other than the beam spot, selectively passes only light from the beam spot, and
Allow incidence on

The beam of p-polarized divergent light emitted from the LD 12 passes through the PBS 14 and passes through the collimator lens 16.
Is converted into a parallel light beam, and passes through the quarter-wave plate 18 to become a circularly polarized light beam. The circularly polarized parallel light beam is reflected by the mirror 20, passes through the aberration corrector 22 and the dichroic prism 30, is condensed by the objective lens 34, and is condensed by the objective lens 34.
Focus on any one of 4a, 74b and 74c to form a beam spot. This focus control is performed by moving the imaging lens 26 along the optical axis by the actuator 28.

The circularly polarized beam returning from the optical disk 70 is supplied to the objective lens 34 and the dichroic prism 30.
, The light passes through the aberration corrector 22, is reflected by the mirror 20, passes through the quarter-wave plate 18, becomes a s-polarized beam, is converted into a convergent light beam by the collimator lens 16, and is The light is reflected toward the PD 40.

Since the pinhole 38 is arranged at a confocal position with respect to the beam spot, the light from the beam spot out of the return light toward the PD 40 is the pinhole 3.
8, but light from other portions cannot pass through the pinhole 38. The return light passing through the pinhole 38 is converted by the PD 40 into an electric signal corresponding to the recorded content of the recording layer.

[Focusing and Tracking Optical System] The LD 42 is a linearly polarized light (p-polarized light) having a wavelength of 780 nm.
Emits a beam of divergent light. PBS44 is LD42
, And reflects linearly polarized light (s-polarized light) orthogonal thereto. The collimator lens 46 changes the divergent light beam from the LD 42 into a parallel light beam and changes the return light beam from the optical disc 70 into a convergent light beam. The 波長 wavelength plate 48 is provided with the p
The polarization is changed to circular polarization, and the circular polarization returning from the optical disk 70 is changed to s-polarization orthogonal to p-polarization from the LD 42.

The dichroic prism 30 is 780n
Reflects light of wavelength m. The objective lens 34 converges a beam of light for focusing and tracking, and forms a beam spot on the guide layer 72 of the optical disc 70. The cylindrical lens 50 gives astigmatism to the beam of the return light from the optical disk 70.

The p-polarized divergent light beam emitted from the LD 42 passes through the PBS 44 and is collimated by the collimator lens 46.
Is converted into a parallel light beam, and passes through a quarter-wave plate 48 to become a circularly polarized light beam. This parallel beam of circularly polarized light is reflected by the dichroic prism 30 and condensed on the guide layer 72 of the optical disk 70 by the objective lens 34. Focus control for the guide layer 72 is performed by moving the objective lens 34 along the optical axis by the actuator 36.

The circularly polarized beam returning from the guide layer 72 of the optical disk 70 passes through the objective lens 34, is reflected by the dichroic prism 30, passes through the quarter-wave plate 48, becomes an S-polarized beam, and becomes a collimator. The light is converted into a convergent light beam by the lens 46, reflected by the PBS 44, passes through the cylindrical lens 50, and
Incident on.

The light beam that has passed through the cylindrical lens 50 has astigmatism. For this reason, the shape and position of the beam spot formed on the light receiving surface of the PD 52 change according to the focus and the track position. PD52
Outputs an electric signal corresponding to the focus and track position based on the shape and position of the beam spot formed on the light receiving surface. Thus, the focus error signal and the track error signal are obtained according to the astigmatism method which is a known technique.

[Focus control and tracking control] P
The focus error signal obtained from D52 is sent to the control circuit 62 of the objective optical unit 32. The control circuit 62 controls the position of the objective lens 34 along the optical axis by the actuator 36 based on the input focus error signal. The objective lens 34 is controlled so that the beam of the light for focusing and tracking follows the vertical vibration of the optical disk 70 and always focuses on the guide layer 72 of the optical disk 70.

On the other hand, since the recording / reproducing light beam is also condensed by the common objective lens 34, the recording / reproducing light beam follows the vertical runout of the optical disk 70, and moves to the guide layer 72. On the other hand, the recording layer 74 at a certain height
a, 74b, and 74c are always kept in focus.

The track control is performed by moving the movable section 54 including the objective lens 34 in the radial direction of the optical disk 70 based on the track error signal obtained from the PD 52.

[Movement of focal point of recording / reproducing light beam and correction of aberrations associated therewith] Movement of the focal point of recording / reproducing light beam between recording layers by actuator 28 moves imaging lens 26 along the optical axis. It is performed by moving. To shift the focus of the beam from the current recording layer to the lower recording layer, the imaging lens 26 is moved upward. Conversely, to shift the focus of the beam from the current recording layer to the upper recording layer,
The imaging lens 26 is moved downward.

More specifically, in FIG. 1, the focus shift amount is transmitted from the focus control circuit 64 to the aberration correction circuit 66. The aberration correction circuit 66 sends a control voltage corresponding to the movement amount of the focal position to the actuator 28. The actuator 28 moves the imaging lens 26 along the optical axis according to the control voltage.

At this time, the moving amount Δz of the imaging lens 26
Is given by the following equation for the distance d between the recording layers.

△ z = β × d / n where β = (numerical aperture of the objective lens NA _obj / numerical aperture of the imaging lens NA _img ) ² , n is the recording layers 74 a, 74 b, 74
c is the refractive index.

As the focal point of the beam moves, the objective lens 3
The aberration w _obj of 4 occurs under, and the aberration w
_dsk occurs over.

With respect to the objective lens alone, the aberration associated with the movement of the focal point is given by w _dsk −w _obj , as shown in FIG.

On the other hand, in FIG.
The beam of light between the objective lens 34 and the imaging lens 26
Is converged, and diverged to the objective lens 34. Therefore, the aberration w
_img is the objective lens 34 as indicated by the dashed optical path.
Is opposite to the aberration w _obj of. Therefore, the aberration of the entire optical system is w _dsk −w _{obj +} w _img .

Since the aberration of the lens associated with the focus movement depends on its numerical aperture, the aberration associated with the focus movement can be completely canceled by appropriately selecting the numerical aperture of the imaging lens 26.

The present applicant has studied a typical objective lens and an optical disc, and as a result, as shown in FIG.
By selecting a numerical aperture of 6, as shown in FIG. 4, the occurrence of wavefront aberration due to focus movement is reduced to rms <0.0.
It has been found that it can be corrected to 05λ.

As can be seen from FIG. 3C, the imaging lens 2
6 numerical aperture NA _img and objective lens 34 numerical aperture NA
_obj preferably satisfies the relationship 0.45 <NA _img / NA _obj <0.8.

Specifically, as described above, the objective lens 34 has a numerical aperture of 0.6, while the imaging lens 26 has a numerical aperture of 0.313. In this relationship, as shown in FIG. 4, the occurrence of wavefront aberration due to the movement of the focal point is suppressed to rms <0.005λ.

[Advantage] In the optical recording / reproducing apparatus according to the present embodiment, the aberration generated due to the focal point movement of the recording / reproducing light beam between the plurality of recording layers can be canceled by the aberration corrector. . This makes it possible to appropriately focus the light beam for recording and reproduction on a desired recording layer. Therefore, it is possible to appropriately record and reproduce information even on a high-density optical disk having a larger number of recording layers than before.

In the optical recording / reproducing apparatus, since the aberration correcting section and the objective lens are mounted on the movable section, the movable section and the fixed section are provided in both the recording / reproducing optical system and the focusing and tracking optical system. It is always linked by a parallel light beam. For this reason, the beam diameter is kept constant irrespective of the movement of the movable part.

Accordingly, the recording / reproducing light beam is always applied to the optical disk at a constant intensity. Therefore, stable recording and reproduction of information can be performed on any track of the optical disc.

Also, a beam of light for focusing and tracking is always applied to the optical disk at a constant intensity.
Therefore, stable track and focus tracking are performed on any track of the optical disc.

Although some embodiments have been described in detail with reference to the drawings, the present invention is not limited to the above-described embodiments, and may be carried out without departing from the scope of the invention. Including all implementations.

[0061]

According to the present invention, there is provided an optical recording / reproducing apparatus capable of appropriately recording / reproducing information even on a high-density optical disk having a larger number of recording layers than before.

[Brief description of the drawings]

FIG. 1 shows an optical recording / reproducing apparatus according to an embodiment of the present invention.

FIG. 2 is a sectional view of the optical disc shown in FIG.

FIG. 3A shows an aberration correction operation of an imaging lens, and FIG.
Indicates the aberration associated with the focal point movement of the objective lens alone,
(c) shows a preferable combination of numerical apertures of the objective lens and the imaging lens.

FIG. 4 shows a wavefront aberration with respect to a focal point movement with and without an aberration correction unit.

FIG. 5 shows a wavefront aberration with respect to a focal point shift in an optical disc in an objective lens having various numerical apertures (NA).

FIG. 6 shows the relationship between the position of a movable part and the beam diameter in a conventional recording / reproducing apparatus of a separation optical system.

[Explanation of symbols]

 12 Laser Diode 16 Collimator Lens 22 Aberration Correction Unit 24 Relay Lens 26 Imaging Lens 28 Actuator 34 Objective Lens

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[Procedure amendment]

[Submission date] August 30, 2000 (2008.3.
0)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Name of invention

[Correction method] Change

[Correction contents]

[Title of the Invention] Optical recording / reproducing device

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G11B 11/105 551 G11B 11/105 551L 586 586A

Claims (3)

[Claims] 1. An optical recording / reproducing apparatus for recording / reproducing information on / from an optical disk having a plurality of recording layers, comprising: a light source for emitting a beam of diverging light for recording / reproducing; A collimator lens for changing the diverging light beam into a parallel light beam, an aberration correcting unit for changing the degree of converging of the parallel light beam from the collimating lens, and a beam from the aberration correcting unit for a recording layer of the optical disc. And an objective lens for converging light onto one of the optical discs. By changing the degree of converging of the parallel light beam by the aberration corrector, the focus shift and aberration between the multiple recording layers of the optical disc An optical recording or other raw device in which correction is performed. 2. The aberration correction unit according to claim 1, wherein the aberration correction unit adjusts a relay lens disposed on the collimator lens side, an imaging lens disposed on the objective lens side, and a distance between the relay lens and the imaging lens. the actuator includes a number of the imaging lens aperture NA _img and objective lens numerical aperture NA _obj to 0.45 <satisfy the relationship of _{NA img / NA o bj <0.8} , the optical recording and reproducing apparatus. 3. The optical recording / reproducing apparatus according to claim 1,
It has a movable part movable with respect to the optical disk, and a fixed part that does not move. The light source and the collimator lens are provided in the fixed part, and the aberration correction part and the objective lens are provided in the movable part. apparatus.