JP2011060383A - Optical pickup device and optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device that reduces a signal offset caused by variation in spectral ratio of a diffraction grating while preventing an unnecessary luminous flux reflected by an unintended recording layer from entering a light receiving surface when recording and reproducing a multilayered optical disk, to obtain a stable tracking error signal, and to provide an optical disk device equipped with the optical pickup device. <P>SOLUTION: The optical pickup includes a laser light source, an objective lens for condensing luminous flux on an information recording surface of an optical disk, a diffraction grating for dividing the luminous flux reflected on the information recording surface into a plurality of regions, and a light detector having a plurality of light receiving surfaces for receiving the luminous flux divided into a plurality of regions by the diffraction grating. A plurality of grating regions are formed in the diffraction grating so that they are line-symmetric with respect to the center line in the direction corresponding to the track direction of the optical disk, or point-symmetric with respect to the center position. The grating pitches of the grating regions which are line-symmetric with respect to the center line or point-symmetric with respect to the center position are substantially the same. <P>COPYRIGHT: (C)2011,JPO&INPIT

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, Japanese Patent Application Laid-Open No. 2004-281026 (Patent Document 1). In this publication, as a problem, “when an optical storage medium that has an error when creating a groove that is a track of the optical storage medium and the TE signal amplitude varies, the fluctuation of the TE signal amplitude is reduced” is stated. As a solving means, “a tracking error signal generating means for generating a tracking error signal that is a signal for performing control to irradiate a beam to a desired track is used, and the light detecting means has a plurality of light receiving portions. The plurality of beams irradiate different positions in a direction orthogonal to the track, and the tracking error signal generation unit generates a push-pull signal by operating the signal output from the light receiving unit, ”Manipulates the signal obtained from the beam”.

JP2004-281026

  With respect to the servo technology necessary for recording / reproducing an optical recording information medium (hereinafter abbreviated as an optical disk), a tracking error signal is used to cause a spot focused on the optical disk to follow a predetermined position on the track. Servo control signal is required. Among tracking error signal detection methods, the push-pull method is usually used for recording media.

  In the push-pull method, the light beam is divided into a main beam and two sub beams in the forward path system, and the main beam and the sub beam are incident on the recording surface while being shifted by a 1/2 track pitch. A so-called differential push-pull method (hereinafter, abbreviated as DPP method) is known in which only the offset component of a signal is subtracted when calculating.

  Since the DPP method is realized by three beams, it is called a three-beam DPP method. On the other hand, there is a so-called 1-beam DPP method in which a beam is split using a beam splitting element in the return path while maintaining one beam, and an offset component is canceled in the calculation.

  Patent Document 1 describes a technique related to the three-beam DPP method, and does not use or cancel the area near the center of the sub-beam, and detects TES with little fluctuation. (For example, refer to Patent Document 1, FIG. 7 and FIG. 8). However, since the three-beam DPP system is not configured to avoid other layer stray light, for example, when a multilayer film is formed to increase the recording capacity of the optical disc, the fluctuation of the DPP signal is caused by interference of the other layer stray light. There is a growing problem.

  Patent Document 1 also describes a technique related to the 1-beam DPP method, in which a light-receiving surface for detecting a focus error signal with zero-order light is arranged on the center of the optical axis, and tracking error signal with ± primary light. A DPP signal is calculated by arranging a light-receiving surface for detecting (see, for example, Patent Document 1, FIG. 22 and FIG. 24). However, since it is necessary to arrange the light receiving surface of the ± 1st order diffracted light so as to avoid the other layer stray light of the 0th order light in order to reduce the fluctuation of the DPP signal, there is a problem that the size of the photodetector is increased. is there.

  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 tracking error signal that is more stable than the conventional one-beam DPP method, and an optical disk device equipped with the optical pickup device.

In Example 1, it is the figure which showed the optical system of the optical pick-up apparatus according to this invention. In Example 1, it is the figure which showed the diffraction grating of the optical pick-up apparatus according to this invention. In Example 1, it is the figure which showed the light-receiving surface structure of the photodetector of the optical pick-up apparatus according to this invention. It is the figure which showed the optical path of the light beam which injected into the multilayered optical disk. In Example 1, it is the figure which showed the shape of the other layer stray light from a 2 layer optical disk. It is the figure which showed the other layer stray light when the diffracted light of an offset signal area | region entered into the light-receiving surface. FIG. 6 is a diagram for explaining a relationship between an optimum light receiving surface configuration for detecting an offset signal and other layer stray light in the first embodiment. It is the figure which showed the other layer stray light when the diffracted light of PP signal area injects into the light-receiving surface. It is a figure explaining the relationship between the optimal light-receiving surface structure of PP signal area | region, and other layer stray light. It is a figure explaining the relationship between the grating pitch of a diffraction grating, and the light-receiving surface position on the photodetector in which diffracted light injects. It is a figure explaining the significance of the light-receiving surface which has symmetry with respect to an optical axis. In Example 1, it is the figure which showed the other optical system of the optical pick-up apparatus according to this invention. In Example 1, it is the figure which showed the other diffraction grating of the optical pick-up apparatus according to this invention. In Example 2, it is the figure which showed the light-receiving surface structure of the photodetector of the optical pick-up apparatus according to this invention. It is a figure explaining the relationship between the optimal light-receiving surface configuration which detects an offset signal, and other-layer stray light in Example 2. FIG. In Example 2, it is the figure which showed the shape of the other layer stray light from a 2 layer optical disk. In Example 3, it is the figure which showed the light-receiving surface structure of the photodetector of the optical pick-up apparatus according to this invention. In Example 3, it is the figure which showed the diffraction grating of the optical pick-up apparatus according to this invention. In Example 3, it is the figure which showed the shape of the other layer stray light from a 2 layer optical disk. In Example 3, it is the figure which showed the light-receiving surface structure of the other photodetector of the optical pick-up apparatus according to this invention. In Example 4, 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 optical pickup and an optical disc apparatus to which the present invention is applied will be described in the following examples.

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. The broken line indicates the outer shape of the light beam. The shaded area represents a push-pull component pattern generated by diffraction on the optical disk. That is, diffracted light including a push-pull component is emitted from the regions 15A to 15D, and diffracted light having only a DC 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, E1, F1, G1, H1, and I1 are incident, and the −1st order diffracted light beams are dark line portions between the light receiving surfaces MN, dark line portions between KL, dark line portions between NO, dark line portions between JK, E2, F2, Incident on G2 and H2.

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.
The signals obtained by detecting at the light receiving surfaces A1, B1, C1, D1, E1, F1, G1, H1, I1, E2, F2, G2, H2, J, K, L, M, N, and O are sequentially a1. , B1, c1, d1, e1, f1, g1, h1, i1, e2, f2, g2, h2, j, k, l, m, n, o.
Although the DPP method is used for detecting the tracking error signal, even if it is generated only by signals a1 to d1 including push-pull components, the objective lens is in the radial direction of the optical disk radial direction (hereinafter abbreviated as Rad direction). When the lens is shifted to, the DC component offset occurs due to the left and right light quantity imbalance in FIG. Therefore, an operation for canceling the offset is performed using the signals e2 to h2 having only the offset component. The signals e1 to h1 are added to the push-pull signal for use as a reproduction signal. When a signal including a push-pull component is a push-pull signal (hereinafter abbreviated as a PP signal) and a signal having only an offset component is an offset signal, the tracking error signal is represented by the following arithmetic expression.

  Here, kt of Equation 1 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.

  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 light amount related to the focus error signal that does not contribute to the reproduction signal is reduced in order to reduce the noise by increasing the light amount of the reproduction signal. is there. A focus error signal and an RF signal as a reproduction signal are generated from the following arithmetic expression using the signal obtained by incidence.

  As the focus error signal, −1st order diffracted light is used. The focus error signal detection method uses the knife edge method, but since this method is known, the description thereof is omitted.

  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 two-layer optical disc 30 as shown in FIG. 4 as an example.

  FIG. 4A shows a case where light is condensed on the recording layer 31 at the back (upper side in the figure), that is, the recording layer 31 is the target layer, and the recording layer 32 on the front side (lower side in the figure) is the non-target layer. Shows the case. At this time, the light beam incident on the two-layer optical disc 30 passes through the front recording layer 32 and is condensed on the back recording layer 31, and is reflected as the signal light beam 33. It is reflected by 32 and becomes an unnecessary light beam 34.

  On the other hand, FIG. 4B shows a case where light is focused on the front recording layer 32, that is, the recording layer 32 is the target layer and the back recording layer 31 is the non-target layer. At this time, the light beam incident on the two-layer optical disc 30 is reflected by the front recording layer 32 and becomes the signal light beam 33, but a part of the light beam passes through the front recording layer 32 and is reflected by the back recording layer 31. Thus, an unnecessary light beam 35 is obtained.

  FIG. 5A shows a case where stray light (unnecessary light flux) 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, the signal light is focused on each light receiving surface so as to be collected on the photodetector 21, but the unnecessary light beam 34 becomes non-convergent light, so that the stray light diffracted by the polarizing diffraction grating 15 is The light is defocused without being collected and is incident on the photodetector 21 to form a stray light pattern as shown in FIG. The stray light of the + 1st order light diffracted from the regions 15A, 15B, 15C, 15D, 15E, 15F, 15G, 15H, and 15I of the polarizing diffraction grating 15 is sequentially converted into A1a, B1a, C1a, D1a, E1a, F1a, G1a, H1a, and I1a are set, and the stray light of the −1st order light is sequentially set as A2a, B2a, C2a, D2a, E2a, F2a, G2a, and H2a.

  Similarly, in FIG. 5B, stray light (unnecessary light flux) from the back recording layer 31 is collected on the photodetector shown in FIG. 3 when condensed on the front recording layer 32 as shown in FIG. 4B. It shows a state when it is incident on. 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 35 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 stray light of the + 1st order light diffracted from the regions 15A, 15B, 15C, 15D, 15E, 15F, 15G, 15H, and 15I of the polarizing diffraction grating 15 is sequentially converted into A1b, B1b, C1b, D1b, E1b, F1b, G1b, H1b, and I1b are set, and the stray light of the −1st order light is sequentially set to A2b, B2b, C2b, D2b, E2b, F2b, G2b, and H2b.

  Unnecessary light beams diffracted by the regions 15A, 15B, 15C, and 15D of the polarizing diffraction grating 15 deviate from the light receiving surface and enter the disc in the radial direction. Therefore, in order to avoid unnecessary light fluxes, it is necessary that a plurality of light receiving surfaces on which the signal light diffracted in the regions 15A, 15B, 15C, and 15D is incident are not arranged in the disk radial direction. Further, the unnecessary light beam diffracted in the regions 15E, 15F, 15G, and 15H deviates from the light receiving surface and enters the disc tangential direction after being defocused. For this reason, in order to avoid unnecessary light fluxes, it is necessary that a plurality of light receiving surfaces on which the signal light diffracted in the regions 15E, 15F, 15G, and 15H is incident are not arranged in the disk tangential direction.

  Therefore, by making the configuration of the photodetector 21 as shown in FIG. 3, 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). The problem of noise leakage can be solved. Details of this will be described later with reference to FIGS.

  FIG. 6 shows a light receiving surface 61 (corresponding to the light receiving surface E2 in FIG. 3) for detecting an offset signal on which the −1st order diffracted light diffracted by the region 15E of the polarizing diffraction grating 15 in FIG. It shows the relationship. The other-layer stray light 61a indicated by the hatched portion and the other-layer stray light 61b indicated by the dotted-line portion are received from the non-target recording layer when condensed on each recording layer, assuming a two-layer disc as shown in FIG. A state of incidence on the surface 61 is shown. The other-layer stray lights 61a and 61b are not generated simultaneously because the target recording layers are different.

  Further, when so-called lens shift is performed in which the objective lens is displaced in the Rad direction, the other-layer stray light is shifted in the Rad direction with respect to the light receiving surface. That is, the other-layer stray light 61a, 61b is shifted in the direction of 60 in FIG. Since other layer stray light as shown in FIG. 6 is seen on the light receiving surface for detecting the offset signal, a light receiving surface configuration for avoiding these stray light is required.

  FIG. 7 shows an optimal combination of four light receiving surfaces for detecting an offset signal. As shown in FIG. 2, there are four areas 15E, 15F, 15G, and 15H for diffracting the offset signal. Is provided. In addition, the other layer stray light for the light receiving surface 61, the light receiving surface 62, the light receiving surface 63, and the light receiving surface 64 when the two-layer disc 30 is assumed is 61a and 61b, 62a and 62b, 63a and 63b, 64a and 64b, respectively.

  At this time, two each in the Rad direction and the Tan direction, that is, the square-shaped light receiving surfaces are arranged adjacent to each other in the Tan direction, so that as shown in FIGS. 7A and 7B It is the structure which can avoid other-layer stray light. The reason why it is not arranged in a straight line in the Rad direction, but in a square shape will be described later with reference to FIG. Further, even when the lens is shifted, the stray light in the other layer moves in the direction of 60 in the figure with respect to the light receiving surface, so that the stray light can be avoided.

FIG. 8 shows the relationship between the light receiving surface 71 (corresponding to the light receiving surface A1 in FIG. 3) on which the + 1st order diffracted light diffracted in the region 15A of the polarizing diffraction grating 15 in FIG. Is shown. The other-layer stray light 71a indicated by the hatched portion and the other-layer stray light 71b indicated by the dotted-line portion are received from the non-target recording layer when condensed on each recording layer, assuming a two-layer disc as shown in FIG. A state in which the light is incident on the surface 71 is shown. The other-layer stray lights 71a and 71b are not generated simultaneously because the target recording layers are different.
Further, when so-called lens shift is performed in which the objective lens is displaced in the Rad direction, the other-layer stray light is shifted in the Rad direction with respect to the light receiving surface. Unlike FIG. 6, there is a concern that stray light in other layers may enter the light receiving surface when the lens is largely shifted in FIG. 8.

  Therefore, as shown in FIG. 9, the four light receiving surfaces 71, 72, 73, and 74 are arranged in a straight line in the Tan direction. At this time, the other-layer stray lights 71a to 74a and 71b to 74b with respect to the light receiving surfaces 71 to 74 do not enter the light receiving surface as shown in FIGS. Is the least. For example, when the light receiving surface is arranged in the Rad direction, that is, in the left-right direction in the drawing, the other layer stray light enters the light receiving surface with a lens shift amount smaller than that in FIG. As shown in FIG. 9, the light receiving surface is arranged in a straight line in the Tan direction to effectively avoid other layer stray light.

  As described above, the photodetector 21 shown in FIG. 3 that satisfies FIGS. 7 and 9 has a configuration capable of effectively separating the signal light and the stray light.

  Now, as shown in FIG. 2, when the light beam is divided for each region using the polarizing diffraction grating 15, there is a problem that the spectral ratio varies for each diffraction grating region because the position of the light receiving surface on the photodetector is different.

  FIG. 10 simply shows the diffraction angle and the incident position when the light beam diffracted by the diffraction grating 80 enters the photodetector 81. Now, as shown in FIG. 10, it is assumed that the light beam diffracted at the diffraction angle θ1 enters the light receiving surface 83 on the photodetector 81, and the light beam diffracted at the diffraction angle θ2 enters the light receiving surface 84 on the photodetector 81. At this time, the diffraction angle θ and the distance from the optical axis center 82 of the light receiving surface are correlated. In FIG. 6, since θ1 <θ2, the light receiving surface 84 is located farther from the optical axis center 82 of the photodetector 81 than the light receiving surface 83.

  The light diffracted by the diffraction grating has the following relational expression based on the light diffraction principle.

  In Equation 3, d is the grating pitch of the diffraction grating, θ is the diffraction angle when emitted from the diffraction grating, λ is the wavelength of the incident light beam, and m is the diffraction order. From Equation 3, when diffracted light of the same order when light of the same wavelength is incident on the diffraction grating is observed, the grating pitch d and the diffraction angle θ are inversely proportional. Therefore, it can be seen from FIG. 10 and Equation 3 that the grating pitch of the diffraction grating varies depending on the position of the light receiving surface.

  Actually, when the diffraction grating is manufactured, a manufacturing error of the grating groove depth depending on the grating pitch occurs. Since the spectral ratio of the diffraction grating depends on the grating groove depth, a problem arises in that the detection signal varies as a result of this manufacturing error.

  In particular, in the polarizing diffraction grating 15 of FIG. 2, the regions other than the region 15I take a large amount of light of the reproduction signal, so that 0th order light: + 1st order light: −1st order light = 0: 7: 3 by blazing. It is said. For this reason, the offset signal necessary for canceling the offset component of the tracking error signal uses −1st order light, so the amount of light is small, and the signal is generated by amplifying the signal by that amount. It is easy to be affected by the manufacturing error of the groove depth, and the signal variation due to the variation in the spectral ratio is likely to be remarkable.

However, on the contrary, if the grating pitch is the same, a manufacturing error of the same grating groove depth occurs, and this can be used to cancel the offset.
FIG. 11 shows the distance from the optical axis center 65 with respect to the square-shaped light-receiving surface for detecting the offset signal shown in FIG. The distances of the light receiving surfaces 61 and 63 from the optical axis center 65 are equal to w1, and the distances of the light receiving surfaces 62 and 64 from the optical axis center 65 are equal to w2. Therefore, the lattice pitch of the grating regions of the light beams incident on the light receiving surfaces 61 and 63 is the same, and the lattice pitch of the grating regions of the light beams incident on the light receiving surfaces 62 and 64 is also the same. That is, the signal variation due to the spectral ratio between the light receiving surfaces 61 and 63 and the signal variation due to the spectral ratio between the light receiving surfaces 62 and 64 are approximately the same, so that the offset component can be canceled by calculating with a differential combination. . For example, diffracted light from the regions 15E and 15F in FIG. 2 is incident on the light receiving surface 61 and the light receiving surface 62, and diffracted light from the regions 15G and 15H in FIG. The offset caused by the spectral ratio variation of the diffraction grating can be canceled.

As described above, the light receiving surface for detecting the offset signal is configured and combined with symmetry as shown in FIG. 11 to avoid stray light in other layers and minimize the offset caused by the dispersion of the spectral ratio of the diffraction grating. Can be suppressed.
Even if the optical disk is multi-layered with two or more layers, stray light from other layers can be avoided except for the light receiving surface I1 as shown in FIGS. 5 (a) and 5 (b), so that fluctuations in the DPP signal can be suppressed. is there. 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. It can be placed close to. Therefore, the size of the photodetector 21 can be reduced.

  Note that the position of the polarizing diffraction grating 15 is not limited to that shown in FIG. 1, and is disposed in the return path on the laser light source 11 side of the beam expander 16, that is, below the beam expander 16 in the drawing. Just do it. 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. 12, since the diffraction grating 90 is included only in the return path optical system, it is not necessary to use the polarizing diffraction grating 15, and a normal diffraction grating may be used.

  Further, the configuration of the polarizing diffraction grating 15 is not limited to that shown in FIG. 2, and there is no problem even if the grating pattern is as shown in FIG.

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 the polarizing diffraction grating 15 by nine regions 15A, 15B, 15C, 15D, 15E, 15F, 15G, 15H, and 15I, and enters the photodetector 21 shown in FIG. The + 1st order 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, E1, F1, and G1, respectively. , H1 and I1, and −1st order light is incident on the dark line portion between the light receiving surfaces NO, the dark line portion between JK, the dark line portion between MN, and the dark line portion between KL, E2, F2, G2, and H2, respectively. To do. The arithmetic expressions for generating the tracking error signal, the focus error signal, and the RF signal are the same as those in Expression 1 and Expression 2. The spectral ratio of each region of the polarizing diffraction grating 15 is set to 0th order light: + 1st order light: −1st order light = 0: 7: 3 in the region other than the region 15I as in the first embodiment, and the region 15I. Is 0th order light: + 1st order light: -1st order light = 0: 1: 1.

  Here, when the configuration of the light receiving surface of the photodetector 21 shown in FIG. 14 and the configuration of the light receiving surface of the photodetector 21 shown in FIG. 3 are compared, the light receiving surfaces A1 to H1 that generate the PP signals have optical axes. The light receiving surfaces J to O and E2 to H2, which are arranged in the Tan positive direction when taking the axis in the Rad direction from the center, that is, in the upper half in the drawing and generate the focus error signal and the offset signal, are Rad from the optical axis center. It differs in the Tan negative direction when the axis is taken in the direction, that is, in the lower half in the figure.

  Since the light receiving surface for detecting the offset signal is E2 to H2, the structure is not the rice field shape shown in FIGS. 7 to 11 of the first embodiment. However, when only the light receiving surface for detecting the offset signal in the photodetector of FIG. 14 is extracted as shown in FIG. 15, the four light receiving surfaces are arranged in a straight line in the Rad direction, that is, in the horizontal direction in the drawing. The other-layer stray lights 61a to 64a and 61b to 64b for the light receiving surfaces E2 to H2 do not enter the light receiving surface as shown in FIGS. 15 (a) and 15 (b). Even if the lens is shifted, the other-layer stray light is displaced in the Rad direction indicated by 60 in the figure, so that it does not enter the light receiving surface.

  The light receiving surfaces E <b> 2 to H <b> 2 are arranged with symmetry with respect to the optical axis center 65 of the photodetector 21. Since the light receiving surface F2 and the light receiving surface G2, and the light receiving surface E2 and the light receiving surface H2 are in the same distance, the diffraction pitch of the diffraction region and the groove depth of the diffraction region are the same. The signal variations due to the spectral ratio variations of the surfaces E2 and H2 are approximately the same. Therefore, for example, the diffracted light from the regions 15E and 15F in FIG. 2 is incident on the light receiving surface E2 and the light receiving surface F2, and the diffracted light from the regions 15G and 15H in FIG. 2 is incident on the light receiving surface G2 and the light receiving surface H2. When combined, the offset can be canceled even if the spectral ratio varies.

  In FIG. 16A, when the light is condensed on the recording layer 31 at the back as shown in FIG. 4A, stray light (unnecessary light flux) 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, the signal light is focused on each light receiving surface so as to be collected on the photodetector 21, but the unnecessary light beam 34 becomes non-convergent light, so that the stray light diffracted by the polarizing diffraction grating 15 is The light is defocused without being collected and is incident on the photodetector 21 to form a stray light pattern as shown in FIG. The stray light diffracted from the polarizing diffraction grating 15 is the same as that in the first embodiment, and the details are omitted.

  Similarly, FIG. 16B shows a photodetector in which the stray light (unnecessary light beam) from the back recording layer 31 when condensed on the front recording layer 32 as shown in FIG. 4B is shown in FIG. The state when it is incident on the top is shown. 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 35 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 stray light diffracted from the polarizing diffraction grating 15 is the same as that in the first embodiment, and the details are omitted.

  16 (a) and 16 (b), even in a pattern such as the photodetector 21 in FIG. 14, it is possible to prevent other-layer stray light from entering each light receiving surface, such as noise leakage. The problem can be solved. It goes without saying that stray light in other layers can be avoided even in an optical disc having two or more layers, and fluctuations in the DPP signal can be suppressed. Further, since the configuration of the light receiving surface of the photodetector 21 shown in FIG. 14 is substantially the same as the configuration of the light receiving surface of the photodetector 21 shown in FIG. 3, the size of the photodetector 21 can be reduced. .

  Further, the light receiving surface configuration of the photodetector 21 shown in FIG. 14 is compared with the light receiving surface configuration of the photodetector 21 shown in FIG. 3, and the grating pitch of the region incident on A1 to D1 that generates the PP signal. Are equally arranged in the Rad direction, that is, in the horizontal direction in the drawing. In FIG. 2, the grating pitches of the signal beams incident on A1 and B1 are equal, and the grating pitches of the signal beams incident on C1 and D1 are equal, but the calculation formula of the PP signal is (a1 + e1 + b1 + f1) − (c1 + g1 + d1 + h1) Therefore, the signal varies due to the variation in the spectral ratio. However, since the amount of light is large, there is no practical problem. On the other hand, in FIG. 14, since the grating pitches of the signal beams incident on A1 and D1 are equal, and the grating pitches of the signal beams incident on B1 and C1 are equal, signal variation caused by variation in the spectral ratio from the PP signal calculation formula. Will be cancelled. Accordingly, the configuration of the light receiving surface in FIG. 14 is a configuration that suppresses the offset that occurs due to the variation in the spectral ratio of the PP signal.

  Needless to say, the position and configuration of the polarizing diffraction grating 15 are not limited to those shown in FIGS.

FIG. 17 shows an optical detector of the optical system of the optical pickup device according to the third embodiment of the present invention.
The difference from the first embodiment is that the configuration of the polarizing diffraction grating 15 in FIG. 2 is as shown in FIG. 18 and the configuration of the photodetector 21 is different. It is the same composition.

  The polarizing diffraction grating 15 is as shown in FIG. The incident light beam is diffracted by the polarizing diffraction grating 15 by 12 regions 15A, 15B, 15C, 15D, 15E, 15F, 15G, 15H, 15Ia, 15Ib, 15Ic, and 15Id, and enters the photodetector 21. The difference from FIG. 2 is that the 15I area is divided into four parts, 15Ia to 15Id.

The + 1st order light beams diffracted by the regions 15A, 15B, 15C, 15D, 15E, 15F, 15G, 15H, 15Ia, 15Ib, 15Ic, and 15Id of the polarizing diffraction grating 15 are light receiving surfaces A1, B1, C1, and D1, respectively. , E1, F1, G1, H1, Ia, Ib, Ic, Id, and the −1st order light is between the dark line part between the light receiving surfaces KL, the dark line part between MN, the dark line part between JK, and between NO, respectively. The light enters the dark line portion, E2, F2, G2, and H2. Here, signals obtained by detection on the light receiving surfaces Ia, Ib, Ic, and Id are sequentially referred to as ia, ib, ic, and id.
The arithmetic expressions for generating the tracking error signal and the focus error signal are the same as those in Equations 1 and 2. An arithmetic expression for generating the RF signal is as follows.

  The spectral ratio of each region of the polarizing diffraction grating 15 is set to 0th order light: + 1st order light: −1st order light = 0: 7: 3 in the region other than the region 15I as in the first embodiment, and the region 15I. Is 0th order light: + 1st order light: -1st order light = 0: 1: 1.

  Although the light receiving surface configuration of the photodetector 21 shown in FIG. 17 is different from the light receiving surface configuration of the photodetector 21 shown in FIG. 3, the light receiving surface that generates the offset signal has been described with reference to FIGS. Thus, because of the symmetrical U-shaped configuration, it is possible to avoid stray light in other layers and cancel offset caused by variations in the spectral ratio of the diffraction grating. Since the light receiving surface for generating the PP signal is arranged in a straight line in the Tan direction as described with reference to FIG. 9, it is a structure that can effectively avoid other layer stray light including lens shift.

  FIG. 19A shows the state of stray light (unnecessary light flux) from the front recording layer 32 on the photodetector when the light is condensed on the recording layer 31 in the back as shown in FIG. 4A. It is. In this case, since the unnecessary light beam 34 becomes non-convergent light, the stray light diffracted by the polarizing diffraction grating 15 is incident on the photodetector 21 without being collected, and has a stray light pattern as shown in FIG. . The stray light of the + 1st order light diffracted from the regions Ia, Ib, Ic, and Id of the polarizing diffraction grating 15 is sequentially referred to as Iaa, Iba, Ica, and Ida. Since others are the same as those in the first embodiment, a description thereof will be omitted.

  Similarly, FIG. 19B shows a state of stray light (unnecessary light flux) from the back recording layer 31 on the photodetector when the light is condensed on the front recording layer 32 as shown in FIG. 4B. It is a thing. In this case, since the unnecessary light beam 35 becomes non-convergent light, the stray light diffracted by the polarizing diffraction grating 15 is collected before the light detector 21 and then enters the light detector 21, as shown in FIG. Such a stray light pattern is obtained. The stray light of the + 1st order light diffracted from the regions Ia, Ib, Ic, and Id of the polarizing diffraction grating 15 is sequentially referred to as Iab, Ibb, Icb, and Idb. Since others are the same as those in the first embodiment, a description thereof will be omitted.

  In the configuration of Example 3, the central region of the polarizing diffraction grating 15 is divided into four parts as 15 Ia to 15 Id, but other layer stray light related to this region is also incident on other light receiving surfaces as can be seen from FIG. It is possible to avoid it without doing.

  19 (a) and 19 (b), even in a pattern such as the photodetector 21 in FIG. 17, it is possible to prevent other layers of stray light from entering each light receiving surface, such as noise leakage. The problem can be solved. It goes without saying that stray light in other layers can be avoided even in an optical disc having two or more layers, and fluctuations in the DPP signal can be suppressed.

  The light receiving surface configuration of the photodetector 21 shown in FIG. 17 has an offset component compared to the light receiving surface configuration of the photodetector 21 shown in FIG. 3 and the light receiving surface configuration of the photodetector 21 shown in FIG. The light receiving surfaces E1 to H1 and E2 to H2 to be detected are different from the optical axis center in the disk tangential direction, that is, in the vertical direction on the drawing. For this reason, the light receiving surfaces A1 to D1 and J to O for detecting the push-pull component can be arranged closer to the center of the optical axis. Further, the diffracted light receiving surface in the central region of the polarizing diffraction grating 15 can also be disposed near the optical axis center as indicated by Ia to Id in FIG. Therefore, the light receiving surface configuration of FIG. 17 makes it possible to make the photodetector 21 smaller.

  Needless to say, the position and configuration of the polarizing diffraction grating 15 are not limited to those shown in FIGS. Further, even if the light receiving surface configuration of the photodetector 21 is as shown in FIG. 20, for example, there is no problem.

  In the fourth embodiment, an optical information reproducing apparatus or an optical information recording / reproducing apparatus equipped with the optical pickup device described in the first to third embodiments will be described with reference to FIG.

FIG. 21 is a schematic block diagram of an optical information recording / reproducing apparatus that records and reproduces 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 to drive the laser lighting circuit 207 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. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

DESCRIPTION OF SYMBOLS 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 ... Standing mirror DESCRIPTION OF SYMBOLS 19 ... Actuator, 20 ... Objective lens, 21 ... Photo detector, 15A-15I ... Diffraction grating area | region, A1-I1 ... + 1st order light side light-receiving surface on a photo detector, JO and E2-H2 ... Photodetection -1 primary light side light receiving surface, a1 to i1, jo and e2 to h2 on the vessel, signals obtained from the light receiving surface, 30 ... double layer optical disc, 31 to 32 ... recording layer, 33 ... signal light beam, 34 35, unwanted light flux, A1a to I1a, A2a to H2a, A1b to I1b, and A2b to H2b ... stray light, 60 ... other layer stray light displacement direction during lens shift, 61 to 64 ... light receiving surface, 61a to 64a and 61b to 64b ... other layer stray light, 65 ... optical axis center, 71-74 ... light-receiving surface, 71a-74a and 71b-74b ... other layer stray light, 80 ... diffraction grating, 81 ... photodetector, 82 ... optical axis center, 83-84 ... light receiving surface, 90 ... diffraction grating, 15Ia-15Id ... diffraction grating region, Ia-Id ... light receiving surface on photodetector, ia-id ... signal obtained from light receiving surface, Iaa-Ida and Iab-- Idb ... stray light, 200 ... optical pickup device, 201 ... servo signal generation circuit, 202 ... information signal reproduction circuit, 203 ... optical disk, 204 ... actuator drive circuit, 205 ... objective lens, 206 ... control circuit, 207 ... laser lighting circuit, 208: Spindle motor drive circuit, 209 ... Access control circuit, 210 ... Spherical aberration correction element drive circuit, 211 ... Spindle motor, 21 ... information signal recording circuit

Claims (14)

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;
An optical branching element that divides the light beam reflected by the information recording surface into a plurality of parts;
A photodetector having a plurality of light receiving surfaces for receiving a light beam divided into a plurality of parts by the light branching element;
An optical pickup device comprising:
The optical branching element is:
Divided into at least two at the center line in the direction corresponding to the track direction of the optical disc,
One of the divided areas is area a, the other area is area a,
The optical pickup apparatus characterized in that the periodic structure pitch is substantially the same between the area A and the area A. 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 surfaces for receiving a light beam divided into a plurality of parts by the light branching element;
An optical pickup device comprising:
The diffraction grating is
Divided into at least two at the center line in the direction corresponding to the track direction of the optical disc,
One of the divided areas is area a, the other area is area a,
An optical pickup device characterized in that the area a and the area a have substantially the same lattice pitch. The optical pickup device according to claim 1 or 2,
The diffraction grating is
A plurality of lattice regions are formed so as to be line symmetric with respect to the center line or point symmetric with respect to the center position,
An optical pickup device characterized in that lattice pitches of lattice regions that are line-symmetric with respect to the center line or point-symmetric with respect to the center position are substantially the same. The optical pickup device according to claim 2 or 3,
The diffraction grating is
It is divided into nine areas: area A, area B, area C, area D, area E, area F, area G, area H, area I,
The region A and the region D, the region B and the region C, the region E and the region H, and the region with respect to the center line in the direction corresponding to the track direction of the optical disc passing through the center of the diffraction grating. F and the region G are in line symmetrical positions,
The region A and the region C, the region B and the region D, the region E and the region G, the region F and the region H are respectively point-symmetric with respect to the center position of the diffraction grating,
The region I is at a central position including the center of the diffraction grating,
In the region A and the region B, an interference region where the track diffraction zero-order light and the track diffraction plus first-order light of the optical disc overlap is incident,
In the region C and the region D, an interference region where the track diffraction zero-order light and the track diffraction minus first-order light overlap is incident,
In the region E, the region F, the region G, the region H, and the region I, only track diffraction zero-order light is incident,
The lattice pitch of the region E and the region H is substantially the same,
The lattice pitch of the region F and the region G is substantially the same, or the lattice pitch of the region E and the region G is substantially the same,
The optical pickup device, wherein the region F and the region H have substantially the same lattice pitch. An optical pickup device according to any one of claims 2 to 4,
Among the light receiving surfaces on which the + 1st order light or the −1st order light of the region E, the region F, the region G, and the region H is incident,
An optical pickup device, wherein two light receiving surfaces are disposed adjacent to each other in a direction substantially parallel to the track direction. An optical pickup device according to any one of claims 2 to 5,
The light receiving surface on which the + 1st order light or the −1st order light of the region E, the region F, the region G, and the region H is incident on the photodetector is arranged in a square shape. Pickup device The optical pickup device according to any one of claims 2 to 6,
With respect to the midpoint of the line segment connecting the + 1st order light and the −1st order light diffracted in the same region of the diffraction grating and incident on the photodetector,
The light receiving surface on which the + 1st order light or the −1st order light of the region E, the region F, the region G, and the region H is incident is:
Than the light receiving surface on which the + 1st order light or the −1st order light of the region A, the region B, the region C, and the region D is incident,
An optical pickup device, which is disposed near the midpoint of a line segment connecting the + 1st order light and the −1st order light. An optical pickup device according to any one of claims 2 to 7,
The diffraction grating is
The lattice pitch of the region A and the region D is substantially the same,
The lattice pitch of the region B and the region C is substantially the same, or the lattice pitch of the region A and the region C is substantially the same,
The optical pickup device, wherein the region B and the region D have substantially the same lattice pitch. An optical pickup device according to any one of claims 2 to 8,
A light-receiving surface on the photodetector on which the + 1st order light or the −1st order light of the region A, the region B, the region C, and the region D is incident,
An optical pickup device arranged in a direction substantially parallel to a track direction of the optical disc An optical pickup device according to any one of claims 2 to 9,
2. An optical pickup device according to claim 1, wherein a light receiving surface for detecting + 1st order light or −1st order light diffracted from the region I of the diffraction grating is one to four light receiving surfaces. The optical pickup device according to any one of claims 2 to 10,
The optical pickup device, wherein the diffraction grating is blazed. The optical pickup device according to any one of claims 2 to 11,
A focus error signal is detected by −1st order light diffracted from the region A, the region B, the region C, and the region D of the diffraction grating;
+ 1st order light diffracted from the region A, the region B, the region C, the region D, the region E, the region F, the region G, and the region H of the diffraction grating;
A tracking error signal is detected by −1st order light diffracted from the region E, the region F, the region G, and the region H of the diffraction grating;
Reproduction by the sum of + 1st order light diffracted from the region A, the region B, the region C, the region D, the region E, the region F, the region G, the region H, and the region I of the diffraction grating. An optical pickup device for detecting a signal. The optical pickup device according to any one of claims 2 to 12,
The unnecessary luminous flux reflected from the information recording surface other than the focused information recording surface of the optical disc is
An optical pickup device that does not enter a light receiving surface on the photodetector. An optical pickup device according to any one of claims 2 to 13,
A laser lighting circuit for driving the laser light source;
A servo signal generation circuit for generating a servo signal from a detection signal obtained by a photodetector of the optical pickup;
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;
A control circuit for controlling the laser lighting circuit, the servo signal generation circuit or the information signal reproduction circuit;
An optical information recording / reproducing apparatus comprising:

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