JP2006338782A - Optical pickup apparatus and information recording and reproducing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To remove a noise component from layers except a desired recording layer when a recording medium having multilayered recording layers is reproduced. <P>SOLUTION: When an optical disk 60 having the multilayered recording layers is reproduced, a polarization diffraction element 132 having polarization dependence and a polarization separation element 211 including a polarization beam splitter are used in a spot forming means 100 and a reflected light separating means 200, respectively. Thereby, a second condensed spot is formed on the recording layer except the desired recording layer to be reproduced on the same axis as a first condensed spot for obtaining a reproducing signal, and a cross-talk component included in the reproducing signal and leaked from the other layer is removed by using a signal obtained from reflected light of the second condensed spot. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical pickup device for irradiating light for recording or reproducing information on a recording medium having a multilayer recording layer, and an optical disc for recording or reproducing information on a recording medium having a multilayer recording layer. The present invention relates to an information recording / reproducing apparatus including a drive.

In recent years, the demand for higher recording density and larger capacity for optical discs has been increasing. In order to improve the in-plane recording density of the optical disk, the numerical aperture NA of the objective lens used in the optical pickup is increased, and the wavelength of the light used is shortened to reduce the spot diameter of the light collected by the objective lens. It is effective to reduce the diameter.
However, recently, as seen in Blu-ray discs, both the numerical aperture NA and the wavelength of light are approaching the limits.

In view of this, hologram memory and multilayer three-dimensional memory have been proposed as a technique for greatly breaking the current situation and improving the recording density in the direction perpendicular to the optical disk surface.
For example, although the volume recording hologram memory can be said to be the “ultimate multilayer three-dimensional memory”, no recording material that satisfies practical specifications has been found so far.
In addition, for multi-layer 3D memories, two-photon absorption and fluorescent recording materials are being actively developed, but for multi-layer reproduction technology, a pinhole optical system that applies conventional confocal microscope technology is assumed. There is only.

Conventionally, a condensing lens that condenses the return light from the recording layer that is reading out before the detector, and a recording layer other than the recording layer that is arranged at the condensing point position of the condensing lens and that performs the reading out. There has been an information recording / reproducing apparatus (see, for example, Patent Document 1) that provides a pinhole that suppresses the passage of return light from a recording layer to remove flare light from another layer.
In addition, there has been an information recording / reproducing apparatus (for example, see Patent Document 2) that detects reflected light from other layers with a photodetector of an appropriate size installed on the image plane and processes a signal from the readout layer. .

Furthermore, three spots having different rotational positions on the same track, of which two spots read information from the recording layers above and below the target recording layer, and for each of the three signals, a delay circuit In addition, there is an information recording / reproducing apparatus that performs processing by a transversal filter and removes flare light from other layers (see, for example, Patent Document 3).
Furthermore, an information recording / reproducing apparatus (for example, patent) that obtains a spherical aberration detection signal that is not affected by interlayer crosstalk and corrects it by detecting and correcting the spherical aberration of the multilayer optical disk with a pinhole optical system. Reference 4).
Japanese Unexamined Patent Publication No. 63-306546 JP 2001-273640 A JP 2002-197666 A JP 2003-323736 A

However, in the conventional information recording / reproducing apparatus, it is effective when the distance between the recording layers of the optical disk is several tens of μm or more as before, but the distance between the recording layers is assumed as “multilayer three-dimensional memory”. There was a problem that the other layer noise signal at the level of several μm could not be removed.
The reason will be described below.
FIG. 14A shows a ROM disk having three recording layers L0, L1, and L2, and the recording layers are filled with media having refractive indexes of n1, n2, n3, and n4. . Reference numeral 50 denotes an objective lens.
If all the values of n1 to n3 are equal and the concave / convex shape of the pits is considered as a diffraction grating, the light beam (0th-order light) transmitted through each layer is not subjected to intensity modulation.

However, when the values of n1 to n3 are different from each other, the transmitted light beam undergoes intensity modulation.
FIG. 14B shows a multi-layered R or RW disc. Even if all the values of n1 to n3 are equal, the recording pit itself is considered to be an amplitude-modulated diffraction grating, so that it passes through each layer. The light beam (0th order light) is subjected to intensity modulation.
Therefore, (1) In the case of a ROM disk having different refractive indexes of the medium between the recording layers and an R or RW disk having pits whose intensity or phase of the transmitted light changes, the transmitted light itself is intensity-modulated. Therefore, even if the flare light from the recording layer other than the desired recording layer is eliminated, the crosstalk from other layers cannot be removed from the reproduction signal.

There is also the influence of the reading depth of the objective lens.
FIG. 15 shows measured signals from four types of two-layer CD-ROM discs having different thickness T of the intermediate layer between recording layers under the condition of wavelength 780 nm / objective lens NA 0.53.
In FIGS. 15A to 15D, signals are a reproduction signal (RF signal), a focus signal (Fo signal), and a track signal (Tr signal) in order from the top in the drawing.
Here, since focus and track servo are not applied, two peaks are generated in the RF signal only at a certain position during rotation.
The two peaks are due to the reflected light of the recording layers L0 and L1, each generating a pit signal near the peak of the peaks, and it can be seen that the lines are thick in each figure.
The thick part (the part where the RF signal is generated = reading depth) of the lines (a) to (d) in FIG. 15 is about ± 6 μm.

As the intermediate layer thickness T is reduced in FIGS. 15A to 15D, the interval between the two peaks is also reduced, and in FIG. 15D, thick lines overlap.
The degree of overlap can be separated to some extent when a pinhole is inserted on the detection system side, but finally it cannot be separated when the intermediate layer thickness approaches the focal depth of the objective lens.
Therefore, (2) when the thickness of the intermediate layer is made thinner than the reading depth of the objective lens (the range in which the RF signal remains when defocused) or the focal depth, the other layer is also positioned at the position where the desired recording layer is read. Therefore, even if the flare light from the recording layer other than the desired recording layer is eliminated, the crosstalk from the other layers cannot be removed from the reproduction signal.
Thus, for the reasons of (1) and (2) above, even if the flare light from other layers is eliminated by using, for example, a pinhole as in the technique described in Patent Document 1, other layer noise signals are used. Cannot be removed.

The technique described in Patent Document 2 detects reflected light from other layers with a photodetector having an appropriate size installed on the image plane, and processes a signal from the readout layer. For this reason, the signal SN ratio of the reflected light from the other layer is poor, so that the other layer noise signal cannot be accurately removed.
FIG. 16 shows a two-layer disc having an L0 layer and an L1 recording layer having an intermediate layer thickness T, 50 is an objective lens, and A in the figure is a condensing point on the L0 layer.
FIG. 17 is a waveform diagram showing an RF signal when the objective lens is defocused in the optical axis direction.
The S0 curve indicated by an arrow b1 in the figure indicates a signal change due to reflected light from the L0 layer, and the S1 curve indicated by an arrow b2 in the figure indicates a signal change due to reflected light from the L1 layer. The signal amplitude at each in-focus position indicates the peak value of the reproduction signals RF0 and RF1.

Now, when the defocus amount is 0 μm and the focal point is located in the L0 layer as shown in FIG. 16, the reproduction signal RF0 is transmitted from the L0 layer and the other layer noise signal (“ A signal of k * RF1 (referred to as “kRF1” in the figure) (k <1) is also detected.
That is, the reproduction signal RF0 from the desired recording layer and the other layer noise signal kRF1 are detected simultaneously.
The technique described in Patent Document 2 is to detect the other layer noise signal kRF1 at that time and correct the reproduction signal, but as can be seen from FIG. 17, the signal of the other layer noise signal kRF1 is level. Is low and SN is bad.
Further, when the thickness T of the intermediate layer is reduced, the signal level of the other-layer noise signal kRF1 increases, but this time, the signal levels of the reproduction signal RF0 and the other-layer noise signal kRF1 approach each other and separation detection becomes difficult.

Furthermore, the technology described in Patent Document 3 is three spots having different positions in the rotation direction on the same track, and two of the spots read information from recording layers above and below the target recording layer, Each of the three signals is processed by a delay circuit or a transversal filter to remove flare light from other layers. However, the positions in the rotation direction are made different in order to separate and detect the three spots. Therefore, a delay circuit and a transversal filter are required for each spot, and the electric circuit becomes complicated.
Further, the three spots have a drawback in that a stable signal cannot be obtained over the entire disk because a relative track shift occurs when the disk radial position is different.
The present invention has been made in view of the above points, and an object thereof is to remove noise components from layers other than a desired recording layer at the time of reproduction of a recording medium having a plurality of recording layers.

In order to achieve the above object, the present invention provides the following optical pickup device and information recording / reproducing device.
(1) Using a recording medium having multiple recording layers, a light source, an objective lens for condensing a light beam from the light source on the desired recording layer, and the objective lens are formed on the desired recording layer. In the optical pickup device provided with the first detection means for detecting the signal from the reflected light of the first focused spot, the first focused light is recorded on the recording layer other than the desired recording layer by the objective lens. Spot forming means for forming at least one or more second focused spots coaxially with the spot, and reflected light for separating the reflected light of the first focused spot and the reflected light of the second focused spot Using the separation means, the second detection means for detecting a signal from the reflected light of the second focused spot, and the signal obtained from the reflected light of the second focused spot, the first focused spot The signal obtained from the reflected light of the spot Optical pickup device provided with correction arithmetic means for correcting operation on.

(2) The optical pickup device according to (1), wherein the spot forming means includes a diffraction element.
(3) The optical pickup device according to (2), wherein the diffraction element has a plurality of diffraction surfaces.
(4) The optical pickup device according to (1), wherein the reflected light separating means is configured using a pinhole element.
(5) In the optical pickup device of (1), the spot forming means is a polarization diffraction element, and the reflected light separation means is a polarization separation element that separates an optical path according to a difference in polarization direction. .
(6) The optical pickup device according to (5), wherein a plurality of diffraction surfaces of the polarization diffraction element are provided.

(7) In the optical pickup device of (1), the spot forming means is a birefringent element having a different degree of convergence and divergence of the transmitted light beam depending on the polarization direction, and the reflected light separating means is polarized light that separates the optical path according to the difference in polarization direction. An optical pickup device configured by using each separation element.
(8) In the optical pickup device of (1), the spot forming means is a second light source different from the wavelength of the light source, and the reflected light separating means is a wavelength separation element that separates the optical path according to the wavelength difference. An optical pickup device configured by using.
(9) In the optical pickup device of (1), the spot forming means is a second light source having a polarization component orthogonal to the polarization direction of the light source, and the reflected light separating means is an optical path depending on the difference in polarization direction. Pickup device constructed by using each of the polarization separation elements for separating the light.

(10) In the optical pickup device according to any one of (1) to (9), the diameter of the second focused spot on the recording layer other than the desired recording layer is the first concentration on the desired recording layer. An optical pickup device that is larger than the diameter of the light spot.
(11) The optical pickup device of (10), wherein the wavefront aberration of the second focused spot is larger than the wavefront aberration of the first focused spot.
(12) The optical pickup device according to (10), wherein the numerical aperture of the second focused spot is smaller than the numerical aperture of the first focused spot.
(13) In the optical pickup device of any one of (1) to (12), the correction calculation means outputs a correction signal obtained by multiplying a signal obtained from the reflected light of the second focused spot by a predetermined gain. An optical pickup device that is a means for generating and subtracting a signal obtained from the reflected light of the first focused spot.
(14) An information recording / reproducing apparatus equipped with the optical pickup device according to any one of (1) to (13).

  The optical pickup apparatus and information recording / reproducing apparatus according to the present invention eliminates noise components from layers other than a desired recording layer when reproducing a recording medium having a multi-layered recording layer, so Even if the recording density is increased, it can be reproduced with high accuracy.

Hereinafter, the best mode for carrying out the present invention will be specifically described with reference to the drawings.
[Example 1]
FIG. 1 is a block diagram showing a functional configuration of a main part according to the present invention of an optical disc drive according to Embodiment 1 of the present invention.
Reference numeral 10 denotes a light source (also referred to as “hologram unit”) having a semiconductor laser chip 11. The divergent light beam from the light source 10 passes through the collimator lens 20 to become parallel light, and then is reflected by the optical path synthesis / separation element 110, passes through the second optical path synthesis / separation element 30, and is opened by the aperture limiting element 40. It is limited and enters the objective lens 50.
The objective lens 50 condenses the incident light beam on any recording surface of the optical disc 60 which is a recording medium having two recording layers, L0 and L1.

Assuming that the parallel light beam reflected by the optical path combining / separating element 110 and incident on the objective lens 50 is collected on the L0 plane on the optical axis of the objective lens 50, the reflected light passes through the optical path combining / separating element 110 and is reflected by three reflections. By the mirrors 115 to 117 and the concave lens 120, the luminous flux that is divergent and enters the objective lens 50 is condensed on the L1 layer surface on the optical axis of the objective lens 50.
Therefore, two focused spots (indicated by a solid line and a broken line in the figure) are formed on the optical axis of the objective lens 50.
The optical path combining / separating element 110, the three reflecting mirrors 115 to 117, and the concave lens 120 constitute the spot forming means 100 according to the present invention.

Next, the two reflected lights from each recording layer are reflected by the second optical path synthesis / separation element 30 and separated again by the third optical path synthesis / separation element 210 while being condensed by the detection lens 70.
Optical axis direction of light receiving element 220 as a first detector corresponding to the first detecting means according to the present invention and light receiving element 221 as the second detector corresponding to the second detecting means according to the present invention Is in an imaging relationship with the condensing point positions of the L0 layer and the L1 layer.
Therefore, if each light receiving region is limited to a certain range, a reproduction signal (RF signal) mainly from the L0 layer is obtained from the light receiving element 220, and an RF signal mainly from the L1 layer is obtained from the light receiving element 221. This will be described in detail later.
That is, the third optical path combining / separating element 210, the light receiving element 220, and the light receiving element 221 constitute the reflected light separating means 200 according to the present invention.

Here, each light receiving element 220, 221 has a light receiving region (not shown) and generates various signals including a track signal and a focus signal for each recording layer by a known method.
Further, the objective lens 50 and the aperture limiting element 40 are servoed according to the track signal and the focus signal by a biaxial actuator (not shown) and follow the movement of either the L0 layer or the L1 layer on the recording surface. It is assumed that the spot is condensed.
Here, the effect of reducing crosstalk from other layers will be described.
2 and 3 are explanatory diagrams for explaining the effect of reducing crosstalk from other layers.
As shown in FIG. 2, the objective lens 50 and the optical disk 60 are the same as those shown in FIG. 1, and the first condensing spot s0 and the second condensing spot s1 are condensed on the L0 layer and the L1 layer, respectively. is doing.

As shown in FIG. 3A, the light receiving element 220 has a light receiving region 223 whose size is limited, and the reflected light r0 from the focused spot s0 is inside the received light region 223 and from the focused spot s1. Since the reflected light r1 protrudes beyond the light receiving region 223, the reproduced signal S0 obtained is mainly from the L0 layer.
Similarly, as shown in FIG. 3B, the light receiving element 221 has a light receiving region 224 whose size is limited, and the reflected light r0 from the focused spot s0 reaches the light receiving region 224 and reaches. Since the reflected light r1 from the condensed spot s1 reaches the inside of the light receiving region 224, the reproduction signal S1 mainly from the L1 layer is obtained.
FIG. 4 is a waveform diagram showing the reproduction signals S0 and S1 when focus and track servo are applied to the focused spot s0.
As shown in the figure, the reproduction signal S0 (arrow a1 in the figure) is a reproduction signal based on the presence or absence of pits in the L0 layer, but the reproduction signal S1 (arrow a2 in the figure) is a relative signal between the L0 layer and the L1 layer. The reproduction signal of the L1 layer appears instantaneously due to the eccentricity or surface blurring.

FIG. 5 is a diagram showing envelopes of curves S0 and S1 indicating reproduction signals S0 and S1 when the focused spots s0 and s1 are servoed.
The S0 curve indicated by an arrow b1 in the figure indicates a signal change due to reflected light from the L0 layer, and the S1 curve indicated by an arrow b2 in the figure indicates a signal change due to reflected light from the L1 layer. The signal amplitude at each in-focus position indicates the peak value of the reproduction signals RF0 and RF1.
As shown in the figure, when focus and track servo are applied to the focused spot s0, the reproduction signal S1 appears instantaneously when there is no relative eccentricity or surface blur between the L0 layer and the L1 layer. In other cases, the signal is smaller than this.
At this time, the reproduction signal S0 includes a reproduction signal RF0 from the L0 layer and a crosstalk signal k * RF1 (denoted as “kRF1” in the drawing) (k <1) from the L1 layer. That is, the relationship shown in Equation 1 is established.

(Expression 1) S0 = RF0 + kRF1
The reproduction signal S1 includes a reproduction signal RF1 from the L1 layer and a crosstalk signal k ′ * RF0 (denoted as “k′RF0” in the drawing) (k ′ <1) from the L0 layer. That is, the relationship shown in Equation 2 is established.
(Expression 2) S1 = RF1 + k′RF0
The value of the reproduction signal S1 varies depending on the relative eccentricity and surface blur between the L0 layer and the L1 layer.
Therefore, if the value of k is obtained in advance as the characteristic value of the optical disk or optical system, a reproduction signal from the L0 layer without crosstalk can be detected by the arithmetic processing based on Equation 3.

(Equation 3) RF0 = S0-kRF1 = S0-k (S1-k'RF0) ≈S0-kS1
The arithmetic processing based on Equation 3 is performed by the signal processing circuit 300 in FIG. 310 is a multiplier, and 320 is an adder / subtractor. That is, the signal processing circuit 300 functions as a correction calculation unit according to the present invention.
The light source 10, the collimating lens 20, the spot forming means 100, the second optical path synthesis / separation element 30, the aperture limiting element 40, the objective lens 50, the detection lens 70, the reflected light separation means 200, the interlock switch SW, and the signal processing circuit 300 are provided. This corresponds to the optical pickup device according to the present invention.
1 is a servo circuit, which generates a servo signal from signals other than the reproduction signal S0 of the light receiving element 220 and drives an objective lens actuator not shown.
The interlock switch SW switches downward when the recording layer to be reproduced changes from the L0 layer to the L1 layer. As a result, the servo circuit 400 servos the L1 layer, and the signal processing circuit 300 outputs the reproduction signal RF1.

In this way, the crosstalk component of the other layer is removed from the reproduction signal by the arithmetic processing using the constant, so that the noise component is removed even when the intermediate layer becomes thin and the reproduction signal itself has a crosstalk component. be able to.
In addition, since the crosstalk component in the other layer is detected with high accuracy using the second light-collecting spot, the noise component can be accurately removed without adversely affecting the reproduction signal.

In the optical disk drive of the first embodiment, the crosstalk component from the other layer is detected by the second converging spot focused on the reproducing condensing spot and the other concentric layer on the same axis and removed by calculation. Even when the layer thickness is thinner than the reading depth of the first focused spot and the reproduction signal itself has a crosstalk component, the noise component for the desired recording layer can be accurately removed.
Accordingly, it is possible to improve the recording density in the direction orthogonal to the disk surface of the recording medium having a multi-layered recording layer, thereby realizing an increase in the capacity of the optical disk.

[Example 2]
FIG. 6 is a block diagram showing the functional configuration of the main part according to the present invention of the optical disk drive of Embodiment 2 of the present invention, and the same reference numerals are given to the parts common to FIG.
In the optical disk drive of the second embodiment, the diffraction element 130 is used for the spot forming means 100.
The diffractive element 130 transmits the light beam incident from the collimating lens 20 as zero-order light and diffracts it as primary light. The diffracted light is given a slight optical power equivalent to a concave lens or convex lens by the grating pattern of the diffractive element 130, and enters the objective lens 50 as divergent light or convergent light in the same manner as in the first embodiment.
In the optical disk drive of the second embodiment, by using the diffraction element 130 for the spot forming means 100, an optical path branching element including a beam splitter is unnecessary, and the optical system can be simplified and miniaturized.

Example 3
In the optical disk drive of Example 2, the optical power of the diffracted light is very small corresponding to the thickness of the intermediate layer, so that the grating pitch may be too large to produce the diffraction element with high accuracy. In such a case, a diffraction element having a plurality of diffraction surfaces may be used.
FIG. 7 is an explanatory diagram of a diffraction element having a plurality of diffraction surfaces.
As shown in the figure, the diffraction element 131 has concentric diffraction gratings on two diffraction surfaces 131a and 131b.
Now, when a light beam is incident on the diffractive element 131 from the left side in the figure, it is separated into three light beams of 0th order light, + 1st order light, and −1st order light by the diffraction surface 131a. When the lattice shape is concentric, for example, + 1st order light becomes divergent light and -1st order light becomes convergent light.
Further, each of the three light beams is diffracted and separated into three light beams by the diffraction surface 131b. Of these light beams, three of B + 1 / -1, B0 / 0 and B-1 / + 1 shown in Table 1 are separated. A light beam is used.

In this way, by slightly changing the pitch of the concentric diffraction gratings of the diffraction surface 131a and the diffraction surface 131b of the diffraction element 131, the absolute value of the optical power of the diffracted light generated on each surface is slightly changed.
Therefore, by combining the signs of the orders of the diffracted light shown in Table 1, both the diffractive surface 131a and the diffractive surface 131b of the diffractive element 131 have an appropriate grating pitch on the two surfaces, and very little optical for the three light beams. A difference in dynamic power can be generated.
The optical disk drive of Example 3 uses a diffractive element having a plurality of diffractive surfaces, so that even if the intermediate layer is thin and the grating pitch is too large for a single diffractive grating, the diffractive element cannot be accurately produced. The grating pitch can be made with sufficient accuracy, and the optical system can be simplified and miniaturized.

Example 4
Instead of limiting the light receiving area of the light receiving elements 220 and 221, a pinhole element may be used.
FIG. 8 is a block diagram showing the functional configuration of the main part according to the present invention of the optical disk drive of Embodiment 4 of the present invention, and the same reference numerals are given to the parts common to FIGS.
The optical disc drive of this embodiment 4, by using a diffraction element 131 having a diffraction grating on both surfaces as a spot forming means, the recording layer on both sides of the L _i layer of a desired recording layer to be reproduced (i is a positive integer) The crosstalk components from the L _{i + 1} layer and the L _i−1 layer are removed.

The optical disc 60 has a L _i−1 layer, a L _i layer, and a L _{i + 1} layer as multilayer recording layers.
The expander 80 includes a concave lens 81 and a convex lens 82, and corrects the spherical aberration of the substrate thickness on which the desired recording layer to be reproduced is located by moving one of the lenses in the optical axis direction.
The pinholes 230, 231 and 232 are arranged at the spot imaging positions on the surfaces of the L _i-1 layer, the _Li layer, and the _{Li + 1} layer of the recording layer, respectively, and separate only the signals from the respective layers. Thus, the light beams are allowed to pass through the light receiving elements 220, 221, 222 having no light receiving area limitation.
Assuming that the signals from the light receiving elements 220, 221, and 222 are S _i , S _{i + 1} , and S _i−1 , respectively, L _{i having} no crosstalk component is obtained by the arithmetic processing based on the mathematical expression 4 in the same manner as the arithmetic processing based on the mathematical expression 3. A reproduction signal RF _i from the layer is obtained. k is a constant.

(Expression 4) RF _i = S _i −k (S _{i + 1} + S _i−1 )
However, here, the values of k in both adjacent layers are set to the same value, but may be set to different values.
The optical disk drive of the fourth embodiment removes crosstalk components from the recording layers adjacent to the desired recording layer to be always reproduced even when the three focused spots jump between the layers due to the movement of the objective lens 50. can do.
In addition, when limiting the light receiving area of the light receiving element, it is difficult to reduce the size of the limited area to several μm due to manufacturing limitations and light leakage, but by using a pinhole element, Since it is possible to obtain a light beam with a clear restriction boundary, it is possible to realize a reflected light separating means with high separation accuracy.
Further, the arithmetic circuit is simplified, and for example, signals from other layers obtained by the light receiving elements 221 and 222 can be processed together.

Example 5
FIG. 9 is a block diagram showing the functional configuration of the main part according to the present invention of the optical disk drive of Embodiment 5 of the present invention. Components common to those in FIGS. 1, 6, and 8 are given the same reference numerals. Yes.
In the optical disk drive of the fifth embodiment, the diffraction element of the spot forming means 100 is a polarization diffractive element having polarization dependency.
As shown in the figure, the diffraction efficiency of the polarization diffraction element 132 changes depending on the polarization direction of incident light.
Accordingly, by appropriately shifting the polarization direction of the light source and the polarization axis of the polarization diffraction element, it is possible to simultaneously generate 0th order light, ± 1st order light, or higher order diffracted light. This figure shows a case where 0th order light and ± 1st order light are generated.

Of course, the polarization diffraction element 132 may have diffraction gratings on both sides of the substrate for the same reason as in the fourth embodiment.
The polarization separation element 211 of the reflected light separation means 200 is an element that transmits the polarization direction of the zero-order light and reflects the polarization direction of the ± first-order light.
The optical disk drive of the fifth embodiment uses a polarization diffractive element having polarization dependency as a spot forming unit and a polarization separating element including a polarizing beam splitter as a reflected light separating unit, so that a light receiving element or pinhole with limited area is used. Can be eliminated, and the component configuration can be simplified to reduce the assembly accuracy. In addition, the separation accuracy can be improved.

Example 6
Instead of the polarization diffraction element 132, a birefringence element may be used.
FIG. 10 is a diagram showing the configuration of the birefringent element.
The birefringent element 134 is configured by attaching a lens made of a birefringent material to at least one of the lenses 134a and 134b.
When a light beam having two directions of polarization components is incident on the birefringence element 134, for example, the polarization components in the direction of the paper in the figure pass through because the refractive indexes of the lenses 134a and 134b are equal.
The polarized light component in the direction perpendicular to the paper surface of the figure passes through the diverging action because the refractive index of the lens 134b is larger than that of the lens 134a. Therefore, a second spot similar to that in the first embodiment can be formed.
Note that a polarized light separating element similar to that in the fifth embodiment may be used as the reflected light separating means.

In the optical disk drive of Example 6, by using a birefringent element as a spot forming means, the divergence when the wavelength is changed and the fluctuation to the convergence degree are smaller than the polarization diffraction element, and the second spot is always stable. Thus, it can be formed in the adjacent recording layer.
Therefore, a stable crosstalk removal effect can be expected even when the wavelength varies.

Example 7
FIG. 11 is a block diagram showing a functional configuration of a main part according to the present invention of an optical disc drive according to Embodiment 7 of the present invention. Components common to those in FIGS. 1, 6, 8, and 9 are denoted by the same reference numerals. It is attached.
In the optical disk drive of the seventh embodiment, the second spot is formed with a light source wavelength different from the first light source wavelength.
The light source 10 ′ includes a semiconductor laser chip 11 that is a first light source, a light receiving element 12, and a hologram 13 that diffracts reflected light from the disk to the light receiving element 12.
The light beam from the semiconductor laser chip 11 passes through the wavelength separation element 240 including the dichroic prism as the reflected light separating means 200 and is collected on the L0 layer of the optical disc 60 having two recording layers of the L0 layer and the L1 layer. Shine.

On the other hand, the light source 14 includes a semiconductor laser chip 15 having a wavelength different from that of the semiconductor laser chip 11, a light receiving element 16 and a hologram 17 similar to the light source 10 '.
The light beam from the semiconductor laser chip 15 is reflected by the wavelength separation element 240 of the reflected light separating means 200 and condensed on the L1 layer of the optical disk 60.
Here, the light flux from the semiconductor laser chip 11 is focused on the L0 layer and the light flux from the semiconductor laser chip 15 is focused on the L1 layer because the positions of the respective light emitting points are in an imaging relationship with respect to each layer, and the lens system. This is because of chromatic aberration.
The difference between the wavelengths of the two light sources is preferably about several tens of nm in consideration of the performance of the wavelength separation element and the accuracy of crosstalk signal detection.
Since the operation of the interlock switch SW, the signal processing circuit 300, and the servo circuit 400 is the same as that of the first embodiment, the description thereof is omitted.

In the optical disk drive of the seventh embodiment, since the second light source having a wavelength different from that of the first light source is used as the spot forming unit, the two wavelengths can be efficiently synthesized and separated by the wavelength separation element. No elements or pinholes are required, and the component configuration can be simplified and the assembly accuracy can be reduced.
Further, if a polarization hologram and a λ / 4 plate are used for the holograms 13 and 17, the utilization efficiency of each wavelength can be increased more than before, so that the recording power and the reproduction signal level are improved, and high-speed recording and high-speed reproduction are possible. become.

Example 8
The semiconductor laser chip 15 may be a light source having a polarization component orthogonal to the semiconductor laser chip 11, and the wavelength separation element 240 may be replaced with a polarization separation element including a polarization beam splitter.
In this case, a polarization hologram cannot be used for the holograms 13 and 17, but complete synthesis and separation can be performed even with the same wavelength by the polarization separation element, so that the accuracy of crosstalk signal detection is improved.
The optical disk drive of the eighth embodiment uses a light source having a polarization component orthogonal to the first light source as the second light source, and a polarization separation element including a polarization beam splitter as the reflected light separation means, respectively. Therefore, the accuracy of noise removal can be improved because a crosstalk component reproduced faithfully at the same wavelength can be detected for a reproduced signal.

Example 9
In each of the embodiments described above, the second focused spot is focused on the recording layer adjacent to the desired recording layer to detect the crosstalk component of the signal from the desired recording layer. In some cases, the talk component can be detected with higher accuracy by slightly increasing the diameter of the second focused spot.
Therefore, in the optical disk drive of Example 9, the diameter of the second focused spot is made larger than the diameter of the first focused spot.
FIG. 12 is an explanatory diagram of making the diameter of the second focused spot larger than the diameter of the first focused spot.
When the L1 layer is a desired recording layer, the first focused spot s0 includes the crosstalk component of the L0 layer.

When the distance between the two layers is within the reading depth, there is no problem with the conventional detection method. However, when the distance is larger than that, the spot diameter in the L0 layer is larger than that in the L1 layer, and thus the second focused spot s1. The accuracy is better when the area on the disk is made the same by making the diameter of the disk equal to that of the disk.
In order to increase the diameter of s1 of the second focused spot, the spot position may be changed by defocusing.
For example, in the optical disk drive shown in FIG. 1, the position of the concave lens 120 in the optical axis direction is changed, and the diffraction pattern is changed in the diffraction element. In the optical disk drive shown in FIG. 11, the position of the light source 14 in the optical axis direction may be changed.
In the optical disk drive of Example 9, the diameter of the second focused spot is made larger than the diameter of the first focused spot, so that the second focused spot has the same area as the first focused spot. A pit row can be detected, and more accurate crosstalk component detection can be performed.

Example 10
In Example 9, the position of the second focused spot was defocused in order to increase the spot diameter. However, if there is a recording layer at the defocused position, the cross of the target layer for the signal of the recording layer. The talk signal may be hidden.
In that case, the minimum spot diameter may be increased by giving wavefront aberration to the second focused spot.
Therefore, in the optical disk drive of Example 10, wavefront aberration is given to the second focused spot to increase the minimum spot diameter.

For example, in the optical disk drive shown in FIG. 1, the surface shape of the reflecting mirror 115 and the concave lens 120 may be an aspherical shape that generates spherical aberration. Moreover, it is preferable to change the diffraction pattern in the diffraction element in the same manner. Furthermore, in the optical disk drive shown in FIG. 11, an aberration generating plate may be inserted between the light source 14 and the wavelength separation element 240 so that the transmitted wavefront generates aberration.
The optical disk drive of Example 10 can always detect the crosstalk signal of the target layer with high accuracy by giving wavefront aberration to the second focused spot to increase the minimum spot diameter.

Example 11
To increase the minimum spot diameter of the second focused spot, the numerical aperture may be decreased.
Therefore, in the optical disk drive of Example 11, the numerical aperture of the aperture limiting element 40 is decreased to increase the minimum spot diameter of the second focused spot.
FIG. 13 is an explanatory diagram of a wavelength filter type aperture limiting element.
In the aperture limiting element 40, the light flux of the first condensing spot s0 transmits the original aperture diameter a, but the light flux of the second condensing spot s1 is limited by the aperture diameter b due to the difference in wavelength.
Therefore, the diameter of the second focused spot s1 is larger than that of the first focused spot due to the difference in numerical aperture.

In the optical disk drive of the eighth embodiment, the aperture limiting element 40 may be a polarizing filter type.
Further, in the optical disk drive shown in FIG. 1, the second aperture limiting element may be inserted into the optical path of the spot forming means 100. In the diffraction element, the region of the diffraction pattern is preferably limited.
The optical disk drive of Example 11 can always detect the crosstalk signal of the target layer with high accuracy by limiting the numerical aperture of the second focused spot and increasing the minimum spot diameter.
In addition, since there is no aberration in the second focused spot, a crosstalk signal equivalent to that when the first focused spot is defocused can be detected.

Example 12
In the optical disk drive of Embodiment 12, each signal processing circuit 300 generates a correction signal obtained by multiplying a signal obtained from the reflected light of the second focused spot by a predetermined gain, and reflects the first focused spot. A circuit that performs subtraction processing on a signal obtained from light is used.
Therefore, crosstalk can be corrected with a simple configuration.
In particular, in the optical disk drive shown in FIGS. 1, 6, and 11, it is possible to move between recording phases instantaneously only by switching the interlock switch SW, and the access time can be shortened.
The optical disk drive of Example 12 is equipped with an optical pickup device that removes noise components due to crosstalk from other layers even when the thickness of the intermediate layer becomes thinner than the depth of reading of the focused spot. The recording density in the direction orthogonal to the disk surface of the recording medium having a multi-layered recording layer can be improved more than ever, and the capacity of the optical disk can be increased.

  The optical pickup device and the information recording / reproducing apparatus according to the present invention can be applied to all types of optical disc drives that record or reproduce information on a recording medium having multiple recording layers.

It is a block diagram which shows the function structure of the principal part which concerns on this invention of the optical disk drive of Example 1 of this invention. It is explanatory drawing with which it uses for description of the crosstalk reduction effect from another layer. It is explanatory drawing similarly used for description of the crosstalk reduction effect from another layer. FIG. 6 is a waveform diagram showing reproduction signals S0 and S1 when focus and track servo are applied to the focused spot s0.

It is a figure which shows the envelope of curve S0, S1 which shows reproduction signal S0, S1 when the servo is applied to the condensing spots s0, s1. It is a block diagram which shows the function structure of the principal part which concerns on this invention of the optical disk drive of Example 2 of this invention. It is explanatory drawing of the diffraction element with a several diffraction surface. It is a block diagram which shows the function structure of the principal part which concerns on this invention of the optical disk drive of Example 4 of this invention.

It is a block diagram which shows the function structure of the principal part which concerns on this invention of the optical disk drive of Example 5 of this invention. It is a figure which shows the structure of a birefringent element. It is a block diagram which shows the function structure of the principal part which concerns on this invention of the optical disk drive of Example 7 of this invention.

It is explanatory drawing of making the diameter of a 2nd condensing spot larger than the diameter of a 1st condensing spot. It is explanatory drawing of the aperture limiting element of a wavelength filter type. It is sectional drawing of the recording layer of a ROM disc, R disc, and RW disc which has a multilayer recording layer

FIG. 5 is a waveform diagram of measured values of signals from four types of two-layer CD-ROM discs having different thickness T of an intermediate layer between recording layers. A two-layer disc having an L0 layer and an L1 recording layer having an intermediate layer thickness T is shown, 50 is an objective lens, and A in the figure is a condensing point on the L0 layer. It is a wave form diagram which shows RF signal when an objective lens is defocused to an optical axis direction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 10 ', 14: Light source 11, 15: Semiconductor laser chip 12, 16, 220, 221, 222: Light receiving element 13, 17: Hologram 20: Collimating lens 30: 2nd optical path synthetic | combination separation element 40: Aperture limiting element 50: Objective lens 60: Optical disc 70: Detection lens 80: Expander 81: Concave lens 82: Convex lens 100: Spot forming means 110: Optical path synthesis / separation element 115 to 117: Reflection mirror 120: Concave lens 130: Diffraction element 131: Diffraction element 131a 131b: Diffraction surface 132: Polarization diffraction element 134: Birefringence element 134a, 134b: Lens 200: Reflected light separation means 210: Third optical path composition separation element 211: Polarization separation element 223, 224: Light receiving region 23 , 231, 232: Pinhole 240: wavelength demultiplexing element 300: a signal processing circuit 310: Multiplier 320: Acceleration 400: servo circuit SW: interlock switch

Claims (14)

Using a recording medium having a multi-layer recording layer, a light source, an objective lens for condensing a light beam from the light source on a desired recording layer, and a first formed on the desired recording layer by the objective lens In the optical pickup device comprising the first detection means for detecting a signal from the reflected light of the condensing spot of
Spot forming means for forming at least one second focused spot coaxially with the first focused spot by the objective lens on a recording layer other than the desired recording layer; and the first Reflected light separating means for separating reflected light from the focused spot and reflected light from the second focused spot; second detecting means for detecting a signal from the reflected light from the second focused spot; An optical pickup comprising: a correction operation means for performing a correction operation on a signal obtained from the reflected light of the first condensed spot using a signal obtained from the reflected light of the second condensed spot. apparatus.   2. The optical pickup device according to claim 1, wherein the spot forming means is configured using a diffraction element.   3. The optical pickup device according to claim 2, wherein the diffraction element has a plurality of diffraction surfaces.   2. The optical pickup device according to claim 1, wherein the reflected light separating means is configured using a pinhole element.   2. The optical pickup apparatus according to claim 1, wherein the spot forming means is a polarization diffraction element, and the reflected light separation means is a polarization separation element that separates an optical path according to a difference in polarization direction. Pickup device.   6. The optical pickup device according to claim 5, wherein the polarization diffraction element has a plurality of diffraction surfaces.   2. The optical pickup apparatus according to claim 1, wherein the spot forming means includes a birefringent element having a degree of convergence and divergence of a transmitted light beam depending on a polarization direction, and the reflected light separating means includes a polarization separation element that separates an optical path according to a difference in polarization direction. An optical pickup device characterized by being configured by using each.   2. The optical pickup apparatus according to claim 1, wherein the spot forming means uses a second light source different from the wavelength of the light source, and the reflected light separating means uses a wavelength separation element that separates an optical path according to a difference in wavelength. An optical pickup device characterized by that.   2. The optical pickup device according to claim 1, wherein the spot forming unit separates a second light source having a polarization component orthogonal to a polarization direction of the light source, and the reflected light separating unit separates an optical path according to a difference in polarization direction. An optical pickup device comprising a polarization separation element.   10. The optical pickup device according to claim 1, wherein the diameter of the second focused spot on the recording layer other than the desired recording layer is equal to the first focused spot on the desired recording layer. An optical pickup device characterized in that it is larger than the diameter of the optical pickup device.   11. The optical pickup device according to claim 10, wherein the wavefront aberration of the second focused spot is larger than the wavefront aberration of the first focused spot.   11. The optical pickup device according to claim 10, wherein a numerical aperture of the second focused spot is made smaller than a numerical aperture of the first focused spot.   13. The optical pickup device according to claim 1, wherein the correction calculation unit generates a correction signal obtained by multiplying a signal obtained from the reflected light of the second focused spot by a predetermined gain. The optical pickup device is a means for performing a subtraction process on a signal obtained from the reflected light of the first focused spot.   An information recording / reproducing apparatus comprising the optical pickup device according to claim 1.

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