JP2011187116A - Optical pickup device and optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a mutual interference between focus error signals in recording / reproducing of an optical disc having a plurality of information recording surfaces, to have a high sensitivity to defocus, and to detect a stable focus error signal. It is another object of the present invention to provide an optical disk device having the same mounted thereon.
An optical pickup device includes a laser light source, an objective lens for condensing a light beam on an information recording surface of an optical disc, a diffraction grating for dividing a light beam reflected by the information recording surface into a plurality of light beams, and a light beam divided into a plurality of light beams And a photodetector having a plurality of light receiving elements for receiving light,
Using the light flux of only the offset component not including the central region on the diffraction grating,
The light receiving element is a two-divided light receiving element in which a side in a direction substantially parallel to a direction in which the light beam is defocused is a short side, and a focus error signal is detected by a double knife edge method.
[Selection] Figure 3

Description

  The present invention relates to an optical pickup device and an optical disk device on which the optical pickup device is mounted.

  As background art regarding this technology, there is, for example, JP 2009-87402 A (Patent Document 1). This publication states that “the calculation of the focus error signal by the double knife edge method makes it difficult for an offset to occur in the focus error signal even when a position shift of the photodetector 112 occurs, and stable focus control is performed. Is possible. "

Japanese Patent Laying-Open No. 2009-87402 (page 15, FIG. 4)

  With regard to the servo technology necessary for recording and reproducing an optical recording information medium (hereinafter abbreviated as an optical disk), a servo control signal called a focus error signal is used to focus a light beam on the information recording surface of the optical disk. is necessary. One of the focus error signal detection methods is a double knife edge method. The double knife edge method detects the amount of movement of the light spot image on the light receiving surface of the light beam reflected by the disc when the objective lens is moved back and forth along the light beam traveling direction (hereinafter referred to as defocusing). In this way, the focus error signal is detected. In the double knife edge method, since the light receiving surface is arranged at a position where the reflected light beam is collected, the influence of the diffracted light disturbance compared to the astigmatism method, which is another focus error signal detection method, for example. Has the advantage of being less.

  In Patent Document 1, a light beam reflected by an optical disk is branched into a plurality of parts by a diffraction grating, and a focus error signal is detected by a double knife edge method using diffracted light in a region including the center of the diffraction grating. Therefore, when the objective lens defocuses from the focused position, the amount of light amount displacement with respect to the defocus becomes small, and the focus error signal forms a gentle waveform. At this time, in the case of an optical disc having a plurality of information recording surfaces, the focus error signals detected from the respective recording surfaces interfere with each other, and the mutual interference mainly causes unnecessary offset components and waveform distortion. This causes a problem that the quality of the focus error signal is significantly deteriorated.

  The present invention provides an optical pickup device capable of preventing mutual interference between focus error signals and detecting a stable focus error signal even in the case of an optical disc having a plurality of information recording surfaces, and an optical disc apparatus equipped with the same. The purpose is to provide.

  The above object can be achieved by the configuration described in the claims as an example.

  According to the present invention, it is possible to provide an optical pickup device capable of obtaining a stable focus error signal and an optical disk device equipped with the same when recording and reproducing an information recording medium having a plurality of information recording surfaces.

In Example 1, it is the figure which showed the optical system of this invention. In Example 1, it is the figure which showed the diffraction grating of this invention. In Example 1, it is the figure which showed the light-receiving surface structure of the photodetector of this invention. It is the figure which showed the optical path of the signal light and stray light which injected into the 3 layer optical disk. In Example 1, it is the figure which showed the shape of the stray light from the layer before and behind the recording layer used as object. It is the figure which showed the relationship between the diffracted signal light and stray light from each area | region of a diffraction grating. It is the figure which showed the change by defocusing of the signal light which injected into the photodetector. It is the figure which showed the relationship between the defocus direction of signal light, and the light-receiving surface which detects a focus error signal. In Example 1, it is the figure which showed the other optical system of this invention. In Example 1, it is the figure which showed the other diffraction grating of this invention. In Example 1, it is the figure which showed the other diffraction grating of this invention. It is the figure which showed the change by defocusing of the signal light which injected into the photodetector. It is the figure which showed the change by defocusing of the signal light which injected into the photodetector. In Example 2, it is the figure which showed the light-receiving surface structure of the photodetector of this invention. In Example 2, it is the figure which showed the shape of the stray light from the layer before and behind the recording layer used as object. In Example 3, it is the figure which showed the schematic block diagram of the optical information reproducing | regenerating apparatus carrying an optical pick-up apparatus, or an optical information recording / reproducing apparatus.

  An example of an embodiment of an optical pickup device and an optical disk device to which the present invention is applied will be described below with reference to the drawings.

  FIG. 1 shows an optical system of an optical pickup device according to Embodiment 1 of the present invention. Here, the recording method is not particularly described, but BD, DVD, and other recording methods may be used.

  A light beam is emitted from the laser light source 11 as divergent light. The semiconductor laser generally emits a linearly polarized light beam, and it is assumed that the laser light source 11 also emits a linearly polarized light beam. A central optical path (hereinafter abbreviated as an optical axis) of a light beam emitted from the laser light source 11 is shown by a chain line.

  A light beam emitted from the laser light source 11 is reflected by a polarization beam splitter (hereinafter abbreviated as PBS) 12. However, a part of the light flux passes through the PBS 12 and enters the front monitor 13. In general, in order to improve the accuracy of the recording / reproducing operation of the optical disc, it is essential to control the light amount of the light beam applied to the optical disc to a desired value. The front monitor 13 can control the light amount of the light flux by feeding back the change in the light amount from the laser light source to the control circuit.

  The light beam reflected from the PBS 12 is converted into a substantially parallel light beam by the collimating lens 14. The light beam that has passed through the collimator lens 14 passes through the polarizing diffraction grating 15 and enters the beam expander 16. The beam expander 16 shifts in a direction parallel to the optical axis, thereby changing the convergence / divergence state of the light beam and correcting the spherical aberration due to the cover layer thickness error of the optical disk.

  The light beam that has passed through the beam expander 16 passes through the quarter-wave plate 17, reflects off the rising mirror 18, and then passes through the objective lens 20 mounted on the actuator 19, on the recording layer of the optical disc (not shown). ).

  The light beam reflected from the recording layer of the optical disc passes through the objective lens 20, the rising mirror 18, the quarter wavelength plate 17, and the beam expander 16 and enters the polarizing diffraction grating 15. The polarizing diffraction grating is a diffraction grating having a function of diffracting a linearly polarized light beam in a predetermined direction and transmitting a linearly polarized light beam in a direction orthogonal to the direction. The polarizing diffraction grating 15 in this embodiment divides the light beam into a plurality of regions, and the divided light beam passes through the collimator lens 14 and the PBS 12 and is condensed on the photodetector 21.

  The light detector 21 is composed of a plurality of light receiving surfaces that can collect each of the light beams divided into a plurality by diffraction, and an RF signal or a focus error that is a reproduction signal according to the amount of light irradiated on the light receiving surface. A signal, a tracking error signal, and the like are generated.

  The quarter-wave plate 17 is not limited to the position shown in FIG. 1 because the light beam reflected by the optical disk may be transmitted before entering the polarizing diffraction grating 15 again.

  FIG. 2 shows an example of the configuration of the polarizing diffraction grating 15 in FIG. The polarizing diffraction grating 15 is divided into nine regions 15A, 15B, 15C, 15D, 15E, 15F, 15G, 15H, and 15I by solid lines, and each diffracts a light beam in a predetermined direction. Regions 15A to 15H are a direction corresponding to the track direction indicated by a one-dot chain line, that is, a line X1 passing through the center of the diffraction grating in a direction tangential to the optical disc (hereinafter referred to as Tan direction), and a direction substantially perpendicular to the track direction. That is, they are positioned symmetrically with respect to a line X2 passing through the center of the diffraction grating with a line in the radial direction of the optical disk (hereinafter abbreviated as Rad direction). A broken-line circle indicates the outer shape of a light beam that is reflected by the recording layer of the optical disc and enters the polarizing diffraction grating 15. The hatched portions 22 and 23 represent the interference region where the track diffraction zero-order light and the track diffraction ± first-order light of the optical disc overlap, that is, the push-pull component pattern generated by diffraction by the track of the optical disc. The light beam 24 excluding the hatched portions 22 and 23 represents only the track diffraction zero-order light of the optical disk, that is, only the offset component in which no interference occurs. Accordingly, diffracted light including a push-pull component is emitted from the regions 15A to 15D, and diffracted light having only an offset component is emitted from the regions 15E to 15H and 15I.

  FIG. 3 shows an example of the configuration of the photodetector 21 in FIG. The + 1st order diffracted lights of the light beams diffracted by the regions 15A, 15B, 15C, 15D, 15E, 15F, 15G, 15H, and 15I of the polarizing diffraction grating 15 shown in FIG. 2 are light receiving surfaces A1, B1, C1, D1, P1, Q1, R1, S1, and I1 are incident on the -1st order diffracted light, and the light receiving surfaces A2, B2, C2, D2, and the dark line portion between E1 and E2, the dark line portion between F1 and F2, and between G1 and G2, respectively. , And the dark line portion between H1 and H2. Since the + 1st order diffracted light and the −1st order diffracted light are diffracted symmetrically with respect to the optical axis center 25, the light receiving surfaces are also arranged symmetrically as shown in FIG.

  An RF signal which is a focus error signal, a tracking error signal, and a reproduction signal is generated from the signal light incident on each light receiving surface. Obtained by detecting on the light receiving surfaces A1, B1, C1, D1, P1, Q1, R1, S1, I1, A2, B2, C2, D2, E1, E2, F1, F2, G1, G2, H1, H2. The signals are sequentially a1, b1, c1, d1, p1, q1, r1, s1, i1, a2, b2, c2, d2, e1, e2, f1, f2, g1, g2, h1, and h2.

The double knife edge method is used to detect the focus error signal. In order to generate the focus error signal by the double knife edge method, the signal light is incident on the dark line portion between the light receiving surfaces divided into two in the light condensing state. The dark line portion detects light with a predetermined sensitivity according to the distance from the light receiving surface, even with light away from the light receiving surface. By using this dark line portion, the focus error with sensitivity to defocusing is detected. A signal can be generated. Using the signals e1 to h1 and e2 to h2 obtained by the double knife edge method, it is generated from the arithmetic expression shown in Equation 1.

  On the other hand, two methods of a push-pull method (PP: Push Pull) and a phase difference detection method (DPD: Differential Phase Detection) can be used to detect a tracking error signal. This is because, for example, it is difficult to detect a tracking error signal by the DPD method when the optical disc is a write-once type or a rewritable type, particularly when the optical disc is not recorded.

When the PP method is used and the signals are generated only from signals a1 to d1 including a push-pull component, when the objective lens is displaced in the Rad direction (hereinafter referred to as a lens shift), the left and right in FIG. An offset of the DC component occurs due to the unbalance of the amount of light. Therefore, an operation for canceling the offset is performed using the signals p1 to s1 having only the offset component. When a signal including a push-pull component is a main push-pull signal (hereinafter abbreviated as an MPP signal) and a signal having only an offset component is an offset signal, the PP signal is expressed by the following equation (2).

  Here, kt in Equation 2 is used to correct the offset component included in the signal of the first term in the equation and the offset component included in the signal of the second term in the equation when the objective lens is lens-shifted. It is a coefficient. By performing such calculation, it is possible to generate a stable tracking error signal without offset even when the objective lens is shifted.

On the other hand, when the DPD method is used, a DPD signal is generated from the phase difference of the signals generated from the region 15A + 15E, the region 15B + 15F, the region 15C + 1GE, and the region 15D + 15H in FIG. Therefore, for example, using the signals a2 to d2 and the signals p1 to s1, a DPD signal is generated by the phase difference between the four signals shown in Equation 3.

The spectral ratio of each region of the polarizing diffraction grating 15 is, for example, 0th order light: + 1st order light: −1st order light = 0: 7: 3 in the region other than the region 15I. Further, the region 15I has 0th order light: + 1st order light: -1st order light = 0: 1: 0. In this manner, forming the grating groove shape of the diffraction grating so that the spectral ratios of the + 1st order light and the −1st order light are different from each other is referred to as blazing. The reason for blazing is that the reproduction signal is generated as the sum of the + 1st order light, so that the amount of the reproduction signal is increased to reduce noise. An RF signal that is a reproduction signal is generated from an arithmetic expression shown in Equation 4.

  When a light beam is condensed on each recording layer using a multilayered optical disk, a part of the light amount is not reflected by the target recording layer but is reflected by the non-target recording layer. Therefore, there is a problem that not only the desired signal light beam reflected by the target recording layer but also the unnecessary light beam reflected by the non-target recording layer is incident on each light receiving surface of the photodetector. When an unnecessary light beam, that is, stray light, enters the light receiving surface, unnecessary noise leaks into the signal as a result. Therefore, it is necessary to prevent stray light from other layers from entering the light receiving surface.

  The polarizing diffraction grating 15 and the photodetector 21 shown in FIGS. 2 and 3 are configured to solve the stray light problem that is a problem in the multilayer optical disk. A description will be given by taking a three-layer optical disc 30 as shown in FIG. 4 as an example.

  FIG. 4A shows the reflected light of the recording layer 32 on the near side (lower side in the figure) when the light beam is condensed on the middle recording layer 31. At this time, the light beam incident on the three-layer optical disc 30 is condensed on the recording layer 31 in the middle and reflected as the signal light beam 34, but a part of the light beam is reflected by the recording layer 32 on the front side, and the unnecessary light beam 34. Become.

  Similarly, FIG. 4B shows the reflected light of the recording layer 33 at the back (upper side in the drawing) when the light beam is condensed on the middle recording layer 31. Among the light beams incident on the three-layer optical disk 30, some of the light beams pass through the middle recording layer 31 and are reflected by the inner recording layer 33 to become unnecessary light beams 35.

  FIG. 5A shows the recording layer from the previous recording layer (referred to as the recording layer 32 this time) when condensed on the target recording layer (referred to as the recording layer 31 this time) as shown in FIG. The stray light (unnecessary light beam) is shown when it is incident on the photodetector shown in FIG. Black dots indicate signal light diffracted by the polarizing diffraction grating 15, and hatched portions indicate stray light from the front recording layer. In this case, since the signal light 34 is focused on each light receiving surface so as to be collected on the photodetector 21, the unnecessary light beam 35 becomes non-convergent light, and therefore, stray light diffracted by the polarizing diffraction grating 15. Defocuses without condensing and enters the light detector 21, resulting in a stray light pattern as shown in FIG.

  Similarly, FIG. 5B shows a recording layer in the back (this time indicates the recording layer 33) when the light is focused on the target recording layer (this time indicates the recording layer 31) as shown in FIG. 4B. FIG. 4 shows a state when stray light (unnecessary light flux) from the light enters the photodetector shown in FIG. 3. A black dot indicates signal light diffracted by the polarizing diffraction grating 15, and a dotted line portion indicates stray light from the inner recording layer. In this case, since the signal light is focused on each light receiving surface so as to be collected on the photodetector 21, the unnecessary light beam 36 becomes non-convergent light, so that the stray light diffracted by the polarizing diffraction grating 15 is After condensing in front of the photodetector 21, it is defocused and incident on the photodetector 21, resulting in a stray light pattern as shown in FIG.

  The reason why stray light incident on the photodetector 21 can avoid the light receiving surface as shown in FIGS. 5 (a) and 5 (b) will be described.

  FIG. 6A shows the incidence of stray light 41a from the front recording layer 32 and stray light 41b from the back recording layer 33 when the signal light 41 from the target recording layer 31 enters the light receiving surface A1. Show the state. As shown in the figure, the stray lights 41a and 41b are incident on the signal light in the Rad direction, that is, in the horizontal direction in the figure. This applies to all the light receiving surfaces that receive the diffracted light from the regions 15A to 15D in FIG. Therefore, it is most effective to avoid stray light if the light receiving surfaces where stray light is generated on the left and right are arranged in the Tan direction, that is, the vertical direction in FIG.

  On the other hand, FIG. 6B shows the incidence of the stray light 42a from the front recording layer 32 and the stray light 42b from the back recording layer 33 when the signal light 42 from the target recording layer 31 enters the light receiving surface P1. The state of is shown. As shown in the figure, the stray lights 42a and 42b are incident on the signal light in the Tan direction, that is, in the vertical direction in the figure. This applies to all the light receiving surfaces that receive the diffracted light from the regions 15E to 15H in FIG. Therefore, it is most effective to avoid the stray light if the light receiving surfaces where the stray light is generated vertically are arranged in the Rad direction, that is, in the left-right direction in FIG.

  Since the photodetector 21 in FIG. 3 has a pattern that satisfies these conditions, it is possible to prevent stray light from entering other layers on each light receiving surface as shown in FIGS. 5 (a) and 5 (b). Problems such as noise leakage can be solved.

  Although the stray light from the grating region 15I is on the light receiving surface I1, the signal i1 obtained by I1 is used only for the reproduction signal, and is not used for servo control signals such as a focus error signal and tracking error signal. It doesn't matter if you do.

  In addition, since the servo control signal and the reproduction signal are generated by the + 1st order light and the −1st order light and the 0th order light is not used, there is no other layer stray light in the 0th order light, so that the light receiving surface has the optical axis center 22. It can be placed close to. Therefore, the size of the photodetector 21 can be reduced.

  Note that stray light from a non-target recording layer has the same shape as that shown in FIGS. 5A and 5B, even from a two-layer optical disk or a multilayer optical disk having four or more layers, and from each light receiving surface except I1. Since the light is incident on the photodetector 21 so as to be separated, stray light can be avoided.

  Now, in the multilayered optical disk, the layer interval is narrowed as the number of recording layers increases due to the limitation of the disk thickness.

  At this time, the focus error signals detected from the recording layers interfere with each other, and the mutual interference is the main factor, causing unnecessary offset components and waveform distortion, which degrades the quality of the focus error signal. Occurs.

  Therefore, in order to obtain a stable focus error signal in a multilayered optical disc, it is necessary to prevent mutual interference between focus error signals. For this reason, the focus error signal of each recording layer is sensitive to defocus. It needs to be high.

  The present invention has four grating region configurations of 15E, 15F, 15G, and 15H in FIG. 2 and light receiving surface configurations of E1 to H1 and E2 to H2 in FIG. High focus error signal is realized. Details of this will be described later with reference to FIGS.

  FIG. 7 shows changes due to defocusing of the signal light diffracted by the polarizing diffraction grating region 15H of FIG. 2 and incident on the photodetector.

  FIG. 7A shows a state where the diffracted signal light is collected on the photodetector, and the black dots indicate the signal light. It is assumed that the diffracted light is collected at the center of X1 indicating the Tan direction and X2 indicating the Rad direction in the condensed state. In addition, hatched portions (b) to (g) indicate signal light when defocused from the condensed state. When the objective lens is defocused in one direction, the signal light is sequentially blurred as shown in FIGS. 7B, 7C, and 7D. When the objective lens is defocused in the opposite direction, the signal light is blurred as shown in FIGS. 7 (e), (f), and (g). A broken line 50 indicates the defocus direction of the signal light by the region 15H.

  At this time, it is important that the signal light is incident with increasing distance from the centers of X1 and X2 as the defocus amount increases. This occurs because the central region 15I of the polarizing diffraction grating 15 of FIG. 2 is not included. For example, assuming that there is a light receiving surface at the center of X1 and X2 because the central region is not included, the signal light that does not include the central region is more defocused than the signal light that includes the central region as shown in FIG. The displacement of the amount of light with respect to the light receiving surface is large. That is, in general, it is possible to generate a focus error signal that is highly sensitive to defocus by using signal light that does not include the central region of the diffraction grating.

  FIG. 8 shows an example of the arrangement of a two-divided light receiving surface for detecting a focus error signal. As shown in FIG. 8A, the light receiving surface 51 and the light receiving surface 52 that detect the focus error signal are desirably arranged in a direction along the defocus direction 50. At the same time, the long side 51b of the light receiving surface 51 and the long side 52b of the light receiving surface 52 are defocused so that the short side 51a of the light receiving surface 51 and the short side 52a of the light receiving surface 52 are parallel to the defocus direction 50. It is desirable to arrange them so as to be perpendicular to the direction 50. This is because the state in which the short side of the light receiving surface is arranged along the defocus direction makes it possible to realize a focus error signal with a high sensitivity by making the light amount displacement with respect to defocus the steepest.

  However, if the light receiving surface is inclined with respect to X1 as shown in FIG. 8A, there is a problem that stray light easily enters due to lens shift.

  Therefore, as shown in FIG. 8B, the long side 51b of the light receiving surface 51 and the long side of the light receiving surface 52 are set so that the short side 51a of the light receiving surface 51 and the short side 52a of the light receiving surface 52 are parallel to X1. It is desirable to arrange 52b so as to be parallel to X2. This is because the signal light when defocused is blurred adjacent to X1 because the region 15H is adjacent to X1.

  On the contrary, as shown in FIG. 8C, when the short side 51a of the light receiving surface 51 and the short side 52a of the light receiving surface 52 are arranged so as to be parallel to X2, the light amount displacement is small with respect to defocusing. A focus error signal is generated.

  In addition, the grating regions 15E, 15F, 15G, and 15H are configured so that light of only an offset component is incident without including a push-pull component caused by diffraction on the optical disc. Therefore, it is possible to generate a focus error signal with a small push-pull component leakage.

  As described above, the optical pickup device of the present embodiment includes the laser light source 11, the objective lens 20 for condensing the light beam emitted from the laser light source on the information recording surface of the optical disk, and the plurality of light beams reflected by the information recording surface. And an optical pickup device having a plurality of light receiving surfaces for receiving a light beam divided into a plurality of parts by the diffraction grating, and the light beam reflected by the information recording surface is: As shown in FIG. 2, the diffraction grating includes the center of the diffraction grating and is incident on the region A where the track diffraction zero-order light enters (15I in FIG. 2). And the push-pull component indicated by the hatched portions 22 and 23, which does not include the center of the diffraction grating and overlaps the track diffraction zero-order light and the track diffraction ± first-order light. Region B (corresponding to 15A to 15D in FIG. 2) and the region C (not shown in FIG. 2) in which the track diffraction zero-order light, that is, the offset component 24 not including the push-pull component, does not include the center of the diffraction grating. 15E to 15H), and the focus error signal is detected using the region C, that is, the region from 15E to 15H.

  Further, the optical pickup device of the present embodiment has a region C1, a region C2, a region C3, a region C4 that divides light into at least four different directions, that is, a region 15E, a region 15F, a region 15G, A region 15H is included, and a focus error signal is detected using these.

  In the optical pickup device of this embodiment, the means for detecting the focus error signal is a double knife edge method.

  Further, in the optical pickup device of this embodiment, the light receiving surface for detecting the focus error signal among the light receiving surfaces is divided into at least two regions, such as the light receiving surfaces E1 to H1 and E2 to H2 in FIG. The diffracted light is condensed at the division position of the light receiving surface, that is, the dark line portion shown in FIG.

  In the optical pickup device of this embodiment, the light receiving surface divided into two regions for detecting the focus error signal in the light receiving surface is displaced on the light receiving surface by defocusing as shown in FIG. The direction substantially parallel to the direction 50 is defined as the short side, and the direction substantially perpendicular to the direction 50 in which the diffracted light is displaced on the light receiving surface by defocusing is defined as the long side.

  Further, in the optical pickup device of the present embodiment, the light receiving surface divided into two regions for detecting the focus error signal in the light receiving surface has a direction substantially corresponding to the track direction X1 of the optical disc as shown in FIG. The short side is the long side and the direction substantially perpendicular to the track direction X1 of the optical disk is the long side.

  Further, in the optical pickup device of this embodiment, the light receiving surface divided into two regions for detecting the focus error signal among the light receiving surfaces is the light receiving surface for detecting the focus error signal as shown in FIG. That is, they are arranged in a direction substantially perpendicular to the Tan direction.

  Further, in the optical pickup device of the present embodiment, the light receiving surface of the photodetector 21 is located at a position where an unnecessary light beam reflected from an information recording surface other than the focused information recording surface of the disk is not incident as shown in FIG. Has been placed.

  With the above configuration, a focus error signal with high sensitivity to defocus can be realized, and multilayer stray light can be effectively avoided.

  The position of the polarizing diffraction grating 15 is not limited to FIG. For example, there is no problem even if it is arranged between the PBS 12 and the photodetector 21 as shown in FIG. In the case of the optical system of FIG. 9, since the diffraction grating is included only in the return optical system, it is not necessary to use the polarizing diffraction grating 15, and the normal diffraction grating 60 may be used. By using the normal diffraction grating 60, it is possible to provide a cheaper optical pickup device.

  Further, the configuration of the polarizing diffraction grating 15 or the diffraction grating 22 is not limited to FIG. For example, even with the configuration shown in FIGS. 10 and 11, it is possible to generate a focus error signal that is highly sensitive to defocusing.

  In the case of the diffraction grating configuration as shown in FIG. 10, the change due to the defocusing of the signal light incident on the photodetector is as shown in FIG. Since the area of the central region 15I of the polarizing diffraction grating 15 is increased in the Tan direction, the amount of light amount displacement with respect to defocus is larger than that in FIG. 7, and a focus error signal with higher sensitivity than the grating pattern in FIG. 2 can be generated.

  In the case of the diffraction grating configuration as shown in FIG. 11, the change due to the defocusing of the signal light incident on the photodetector is as shown in FIG. Since the region 15H in FIG. 11 is closer to the Tan direction than the region 15H in FIG. 2, the defocus direction of the signal light is closer to the Tan direction X1. Therefore, in the case of the focus error signal light receiving surface arrangement shown in FIG. 3 or FIG. 8B, the light amount displacement amount with respect to defocus becomes larger than that in FIG. 7, and a focus error signal having higher sensitivity than the lattice pattern in FIG. Can be generated.

  Furthermore, in Example 1, the light receiving surface for the focus error signal has a simple rectangular shape as shown in FIG. 3, but the present invention is not limited to such a light receiving surface. As long as the length of the light receiving surface in the direction parallel to the defocus direction is shortened and a focus error signal with high sensitivity to the focus can be generated, the detection surface may have any shape.

  FIG. 14 shows an optical detector of the optical system of the optical pickup device according to the second embodiment of the present invention. The difference from the first embodiment is that the configuration of the photodetector 21 in FIG. 3 and the diffraction direction of the region of the polarizing diffraction grating 15 are different, but the other configuration is the same as that of the first embodiment.

  The polarizing diffraction grating 15 is the same as that of the first embodiment and is as shown in FIG. The incident light beam is diffracted by nine regions 15A, 15B, 15C, 15D, 15E, 15F, 15G, 15H, and 15I, and enters the photodetector 21 shown in FIG.

  The + 1st order diffracted light beams diffracted by the regions 15A, 15B, 15C, 15D, 15E, 15F, 15G, 15H, and 15I of the polarizing diffraction grating 15 are light receiving surfaces A1, B1, C1, D1, P1, Q1, and R1, respectively. , S1 and I1, and the −1st order diffracted lights are respectively A2, B2, C2, D2, E1 and E2, dark line portions between F1 and F2, dark line portions between G1 and G2, and H1 and H2. Incident in the dark line between.

  An RF signal which is a focus error signal, a tracking error signal, and a reproduction signal is generated from the signal light incident on each light receiving surface. Since the light receiving surface of the photodetector in FIG. 14 and the light receiving surface of the photodetector in FIG. 3 correspond to each other, these signals are generated by arithmetic expressions of Formulas 1 to 4.

  In FIG. 15A, when the light is focused on the target recording layer 31 as shown in FIG. 4A, the unnecessary light beam 35 from the front recording layer 32 is incident on the photodetector shown in FIG. It shows the state when it was done. Black dots indicate signal light diffracted by the polarizing diffraction grating 15, and hatched portions indicate stray light from the front recording layer. In this case, since the signal light 34 is focused on each light receiving surface so as to be collected on the photodetector 21, the unnecessary light beam 35 becomes non-convergent light, and therefore, stray light diffracted by the polarizing diffraction grating 15. Defocuses without condensing and enters the photodetector 21, resulting in a stray light pattern as shown in FIG.

  In FIG. 15B, when the light is focused on the target recording layer 31 as shown in FIG. 4B, the unnecessary light beam 36 from the inner recording layer 33 is incident on the photodetector shown in FIG. It shows the state when it was done. A black dot indicates signal light diffracted by the polarizing diffraction grating 15, and a dotted line portion indicates stray light from the inner recording layer. In this case, the signal light 34 is focused on each light receiving surface so as to be condensed on the light detector 21, but the unnecessary light beam 36 becomes non-convergent light, so that stray light diffracted by the polarizing diffraction grating 15. Is focused before the photodetector 21 and then defocused and incident on the photodetector 21, resulting in a stray light pattern as shown in FIG.

  Since the photodetector 21 in FIG. 14 has a pattern that can avoid the effective stray light described in FIGS. 6 and 7, each of the light receiving elements as shown in FIGS. 15A and 15B. Other layers of stray light can be prevented from entering the surface, and problems such as noise leakage can be solved.

  Although the stray light from the grating region 15I is on the light receiving surface I1, the signal i1 obtained by I1 is used only for the reproduction signal and not for the servo control signal such as the tracking error signal. It doesn't matter.

  In addition, since the servo control signal and the reproduction signal are generated by the + 1st order light and the −1st order light and the 0th order light is not used, there is no other layer stray light in the 0th order light, so that the light receiving surface has the optical axis center 22. It can be placed close to. 14 differs from FIG. 3 in that the light receiving surfaces of the diffracted light in the regions 15E to 15H are arranged near the optical axis center 22, but as in FIG. 3, the signal light and stray light are effectively separated. Is able to. Therefore, the size of the photodetector 21 can be reduced.

  Note that stray light from a non-target recording layer is incident on the photodetector 21 in the same shape as in FIGS. 14A and 14B even in a two-layer optical disk or a multilayer optical disk having four or more layers. Can avoid stray light.

  Since the grating region and the light receiving surface configuration used for detecting the focus error signal are exactly the same as those in the first embodiment, it is possible to realize a focus signal that is highly sensitive to defocusing and has a small push-pull component leakage. it can.

  Note that the position of the polarizing diffraction grating 15 is not limited to that shown in FIG. 1. For example, the polarizing diffraction grating 60 may be used at the position shown in FIG. 9. Further, the configuration of the polarizing diffraction grating 15 is not limited to that shown in FIG. 2, and for example, the configuration shown in FIGS. 10 and 11 may be used.

  In the third embodiment, an optical disk device (an optical information reproducing device or an optical information recording / reproducing device) on which the optical pickup device described in the first and second embodiments is mounted will be described with reference to FIG.

  FIG. 16 shows a schematic block diagram of an optical information recording / reproducing apparatus for recording and reproducing information. Reference numeral 200 denotes an optical pickup device of the present invention, and a signal detected from the photodetector 21 in the optical pickup device 200 is sent to a servo signal generation circuit 201 and an information signal reproduction circuit 202.

  The servo signal generation circuit 201 generates a focus error signal, a tracking error signal, a spherical aberration detection signal, a tilt control signal, and the like suitable for the optical disc 203 based on the signal detected by the optical pickup device 200, and based on these signals. Then, the position of the objective lens 205 is controlled by driving the objective lens actuator in the optical pickup device 200 via the actuator drive circuit 204.

  The information signal reproducing circuit 202 reproduces the information signal recorded on the optical disc 203 from the signal detected by the optical pickup device 200.

  Further, part of the signals obtained by the servo signal generation circuit 201 and the information signal reproduction circuit 202 are sent to the control circuit 206. A laser driving signal is sent from the control circuit 206, and the laser lighting circuit 207 is driven to supply a laser driving current to the laser light source 11 in the optical pickup device 200. In addition, the amount of light emitted from the laser light source 11 can be controlled using a front monitor in the optical pickup device 200. The laser lighting circuit 207 can also be incorporated in the optical pickup device 200.

  In addition to the servo signal control circuit 201 and the laser lighting circuit 207, a spindle motor drive circuit 208, an access control circuit 209, a spherical aberration correction element drive circuit 210, and the like are connected to the control circuit 206, and each rotates the optical disc 203. The rotation control of the spindle motor 211, the access direction position control of the optical pickup device 200, and the drive control of the correction lens of the spherical aberration correction optical system in the optical pickup device 200 are performed.

  During recording, the laser lighting circuit 207 is driven based on the recording control signal from the information signal recording circuit 212 provided between the control circuit 206 and the laser lighting circuit 207 to record information on the optical disc 203.

  In addition, this invention is not limited to an above-described Example, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. In addition, a part of the configuration of a certain embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of a certain embodiment.

11 ... Laser light source,
12 ... Polarizing beam splitter (PBS),
13 ... Front monitor,
14 ... Collimating lens,
15 ... Polarizing diffraction grating,
16 ... Beam expander,
17: 1/4 wavelength plate,
18 ... Launch mirror,
19 ... Actuator,
20 ... Objective lens,
21 ... photodetector,
30 ... 3 layer optical disc,
200: optical pickup device,
201. Servo signal generation circuit,
202 ... Information signal reproduction circuit,
203 ... optical disc,
206 ... control circuit,
207 ... Laser lighting circuit,

Claims (10)

A laser light source;
An objective lens for condensing the light beam emitted from the laser light source on the information recording surface of the optical disc;
A diffraction grating for dividing the light beam reflected by the information recording surface into a plurality of pieces,
A photodetector having a plurality of light receiving elements for receiving a light beam divided into a plurality of parts by the diffraction grating;
The diffraction grating is divided into a plurality of regions;
An optical pickup device that detects a focus error signal using a region excluding a region at a central position including a center of the diffraction grating. The optical pickup device according to claim 1,
The light beam reflected by the information recording surface is composed of track diffraction zero-order light and track diffraction ± first-order light of the optical disc,
The diffraction grating is
A region A that includes the center of the diffraction grating and on which the track diffraction zero-order light is incident;
A region B that does not include the center of the diffraction grating and is incident on a region where the track diffraction zero-order light and the track diffraction ± first-order light overlap;
It does not include the center of the diffraction grating and is divided into three regions C, where the track diffraction zero-order light is incident,
An optical pickup device that detects a focus error signal using the region C. The optical pickup device according to claim 1,
The light beam reflected by the information recording surface is composed of track diffraction zero-order light and track diffraction ± first-order light of the optical disc,
The diffraction grating is
A region A that includes the center of the diffraction grating and on which the track diffraction zero-order light is incident;
A region B that does not include the center of the diffraction grating and is incident on a region where the track diffraction zero-order light and the track diffraction ± first-order light overlap;
The center of the diffraction grating is not included, and the region is divided into three regions C in which only the track diffraction zero-order light is incident,
The region C includes at least four regions C1, C2, C3, and C4 that divide light in different directions.
An optical pickup device that detects a focus error signal using the region C1, the region C2, the region C3, and the region C4. The optical pickup device according to any one of claims 1 to 3,
An optical pickup apparatus characterized in that means for detecting a focus error signal is a double knife edge method. The optical pickup device according to claim 3,
The light receiving element for detecting the focus error signal is divided into at least two regions,
The optical pickup device characterized in that the diffracted light from the region C1, the region C2, the region C3, and the region C4 is condensed at a division position of the two-divided light receiving element. The optical pickup device according to claim 5,
The two-divided light receiving element for detecting a focus error signal has a short side in a direction substantially parallel to a direction in which the diffracted light is displaced on the light receiving element by defocusing, and the diffracted light is displaced on the light receiving element by defocusing. An optical pickup device having a long side in a direction substantially perpendicular to the direction. The optical pickup device according to claim 5,
The two-divided light receiving element for detecting a focus error signal has an optical pickup having a short side in a direction substantially corresponding to a track direction of the optical disc and a long side in a direction substantially perpendicular to the track direction of the optical disc. apparatus. The optical pickup device according to claim 5,
The two-divided light receiving element for detecting a focus error signal is:
An optical pickup device, characterized in that the other two-divided light receiving elements are arranged in a direction substantially perpendicular to the track direction of the optical disc. The optical pickup device according to claim 1, wherein:
The light receiving element of the photodetector is arranged to receive the signal light reflected from the focused information recording surface of the optical disc and avoid stray light reflected from an information recording surface other than the information recording surface. An optical pickup device characterized by that. An optical pickup device according to any one of claims 1 to 9,
A laser lighting circuit for driving the laser light source;
From the detection signal obtained by the photodetector of the optical pickup, a servo signal generation circuit for generating a stable servo signal with the multilayered optical disk,
An information signal reproducing circuit for reproducing information recorded on the optical disc from a detection signal obtained by a photodetector of the optical pickup;
An optical disc apparatus comprising: the laser lighting circuit; a control circuit for controlling the servo signal generation circuit or the information signal reproduction circuit.

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