JP2004158169A - Optical disk device and light branching device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk device capable of simultaneously dealing with configurations of two radiated light sources without causing an offtrack during tracking control even when there is eccentricity in the disk diameter direction of an objective lens and an eccentric light hologram substrate, and also to provide a light branching means. <P>SOLUTION: A light from a radiated light source 1 is reflected on the signal surface 6a of an optical disk, passed through an objective lens 5 to enter light branching means 2, 4, and divided into four image limits Ak (k=1, 2, 3, 4) at two straight lines crossing an optical axis 7. A photodetector 9 is divided into at least four areas Bk. Each of lights made incident on the image limit Ak by the light branching means 2, 4 generates a primary diffracted light ak to be projected to the area Bk on the photodetector 9. The cuts of the primary diffracted lights a2 and a3 by the x axis are almost superposed on the boundary lines B2 and B3, and the distributions of the primary diffracted lights a1 and a4 are isolated from each other on the photodetector 9. <P>COPYRIGHT: (C)2004,JPO

Description

  The present invention relates to an optical disk device and an optical branching device used for recording a signal on an optical disk or reproducing a signal from the optical disk.

  As a conventional technique, for example, there is Patent Document 1. Here, based on this precedent, a part will be described with reference to FIGS. FIG. 9 shows a cross-sectional configuration of an optical disk device in a conventional example, and a side view of the radiation light source 1 and its periphery is added below.

  In FIG. 9, a laser beam emitted from a radiation light source 1 such as a semiconductor laser mounted on a light detection substrate 9 reflects on a reflection mirror 10 mounted on the light detection substrate 9, and is collimated by a collimating lens 4. It is converted into light, transmitted through the polarizing hologram substrate 2, converted from linearly polarized light (S wave or P wave) into circularly polarized light by the １ ／ wavelength plate 3, condensed by the objective lens 5, and It converges on the signal surface 6a.

  The light reflected from the signal surface 6a passes through the objective lens 5, is converted into linearly polarized light (P wave or S wave) by the １ ／ wavelength plate 3, and is incident on the hologram surface 2a in the polarizing hologram substrate 2. Is diffracted into a first-order diffracted light 8 and a -1st-order diffracted light 8 ′ having the optical axis 7 as a symmetry axis, and each diffracted light becomes convergent light via the collimating lens 4. 9a. The 波長 wavelength plate 3 is formed on the same substrate as the hologram surface 2 a and moves integrally with the objective lens 6. The detection surface 9a is located substantially at the focal plane position of the collimator lens 4 (that is, the virtual light emitting point position of the light source 1).

  FIG. 10 shows a configuration of a detection surface (FIG. 10A) and a hologram surface (FIG. 10B) of an optical disk device in a conventional example, and both show a case where the hologram surface side and the light detection surface side are viewed from the optical disk side. Assuming that the intersection point between the hologram surface 2a and the optical axis 7 is 20, the hologram surface 2a is divided into four straight lines (X-axis and Y-axis) orthogonal to each other at the point 20, and each quadrant has a rectangular area along the X-axis. 21B, 21F, 22B, 22F, 23B, 23F, 24B, and 24F.

  On the other hand, the point of intersection of the detection surface 9a and the optical axis 7 is a point 90, and two straight lines perpendicular to the point 90 and parallel to the X axis and the Y axis are the x axis and the y axis. Comb-shaped focus detection cells F1a, F2a, F1b, F2b, F1c, F2c, F1d, F2d, F1e, and F2e are arranged, and trapezoidal tracking detection cells 7T1, 7T2, 7T3, and 7T4 are provided on the minus side of the y-axis. Are located. These detection cells are symmetric with respect to the y-axis. The light emitted from the light emitting point 1a of the radiation light source 1 intersects the x-axis and travels in a plane perpendicular to the plane of the paper in parallel with the x-axis. Is reflected.

  The first-order diffracted lights 81B and 81F diffracting the comb-tooth regions 21B and 21F in the first quadrant of the hologram surface 2a are detected by light spots 81BS and 81FS crossing the detection cells F2a and F1b, and the -1st-order diffracted lights 81B 'and 81F' are detected. The light is condensed on light spots 81BS 'and 81FS' that fit in the cell 7T1. The first-order diffracted lights 82B and 82F diffracting the comb-tooth regions 22B and 22F in the second quadrant fall in the light spots 82BS and 82FS that straddle the detection cells F1b and F2b, and the -1st-order diffracted lights 82B 'and 82F' fall in the detection cell 7T2. The light is focused on the light spots 82BS 'and 82FS'.

  The first-order diffracted lights 83B and 83F diffracting the comb-teeth regions 23B and 23F in the third quadrant fall in the light spots 83BS and 83FS that straddle the detection cells F1d and F2d, and the -1st-order diffracted lights 83B 'and 83F' fall in the detection cell 7T3. Light is condensed on light spots 83BS 'and 83FS'. The first-order diffracted lights 84B and 84F diffracting the comb-tooth regions 24B and 24F in the fourth quadrant fall in the light spots 84BS and 84FS that straddle the detection cells F2d and F1e, and the -1st-order diffracted lights 84B 'and 84F' fall in the detection cell 7T4. The light is focused on the light spots 84BS 'and 84FS'.

  The first-order diffracted lights 81B, 82B, 83B, and 84B are lights that are condensed on the back side of the detection surface 9a (on the side away from the hologram surface 2a), so that the spot shape on the detection surface 9a is different from the light distribution on the hologram surface 2a. Since the -1st-order diffracted lights 81B ', 82B', 83B ', and 84B' are light rays that converge before the detection surface 9a (on the side approaching the hologram surface 2a), the spot shape on the detection surface 9a has a hologram shape. This is similar to a shape in which the light distribution on the surface 2 a is inverted with respect to the point 20.

  Since the first-order diffracted lights 81F, 82F, 83F, and 84F are lights that converge before the detection surface 9a, the spot shape on the detection surface 9a is similar to a shape obtained by inverting the light distribution on the hologram surface 2a with respect to the point 20. Since the -1st-order diffracted lights 81F ', 82F', 83F ', and 84F' are lights condensed behind the detection surface 9a, the spot shape on the detection surface 9a is similar to the light distribution on the hologram surface 2a. It is.

Some of the detection cells are conductive and are configured to result in the following six signals.
F1 = signal obtained by detection cell F1a + signal obtained by detection cell F1b + signal obtained by detection cell F1c + signal obtained by detection cell F1d + signal obtained by detection cell F1e F2 = signal obtained by detection cell F2a + Signal obtained by detection cell F2b + Signal obtained by detection cell F2c + Signal obtained by detection cell F2d + Signal obtained by detection cell F2e T1 = Signal obtained by detection cell 7T1 T2 = Signal obtained by detection cell 7T2 T3 = signal obtained by the detection cell 7T3 T4 = signal obtained by the detection cell 7T4 In FIG. 10, the y-axis is the radial direction of the optical disk 6, the focus error signal FE on the optical disk signal surface, and the tracking error on the optical disk track. The signal TE and the reproduction signal RF of the optical disk signal surface are detected based on the following equation.

FE = F1-F2 (Equation 1)
TE = T1 + T2-T3-T4 (Equation 2)
RF = F1 + F2 + T1 + T2 + T3 + T4 (Equation 3)
JP 2000-132848 A

  Such a conventional optical disk device has the following problems. In general, assuming that the off-track amount with respect to the optical disk track is Δ and the eccentricity of the objective lens 5 and the polarizing hologram substrate 2 along the disk radial direction (Y-axis direction) is δ, the TE signal obtained by (Equation 2) has an appropriate coefficient a , B using the following equation.

TE = aΔ + bδ (Equation 4)
That is, as in the conventional example, in the TE detection method according to (Equation 2), the eccentricity of the objective lens 5 and the polarizing hologram substrate 2 that moves integrally with the objective lens 5 along the disk radial direction (this eccentricity is always required during tracking control). Occurs) and an offset occurs. The reason why TE is a function of δ is that the light emitted from the radiation light source 1 has a non-uniform intensity distribution such that it is strong in the paraxial direction and becomes weaker as the distance from the optical axis increases. This is because the intensity distribution of the return light 80 on the hologram surface 2a becomes asymmetric with respect to the X axis due to the eccentricity of the hologram substrate 2 along the radial direction.

  When the optical disk is a DVD-RAM or the like, the depth of the guide groove is deep (optical depth D = approximately λ / 6, where λ is the wavelength of the light source), and the pitch is wide (groove pitch Λ = 1.21 to 1.48 μm) In the case of an optical disk, since the intensity distribution of the return light 80 on the hologram surface 2a becomes substantially uniform in the Y-axis direction due to the diffraction effect in the groove, the coefficient b becomes substantially zero, and there is no problem. However, an optical disk such as a DVD-R or DVD-RW having a shallow guide groove (optical depth D = approximately λ / 10 to λ / 20) and a narrow pitch (groove pitch Λ = 0.74 μm) In this case, the asymmetry of the return light 80 increases, and the coefficient b ≠ 0.

In general, tracking control is performed so that TE = 0, so that when b ≠ 0, from (Equation 4),
Δ = −bδ / a (Equation 5)
Off-track occurs.

  As an example, for a disk having a groove depth D = λ / 12 and Λ = 0.74 μm, b / a = about 2.4 / 10000, and when δ = 200 μm, an off-track of Δ = 0.048 μm occurs. This is a size that cannot be ignored for a disc having a track pitch of 0.74 μm, and causes track skipping, deterioration of a reproduction signal, deterioration of an adjacent track signal at the time of recording, and the like.

  SUMMARY OF THE INVENTION The present invention provides an optical disc device in which off-track does not occur during tracking control even if there is an eccentricity of an objective lens and a polarizing hologram substrate along a disc radial direction in order to solve the conventional problem. It is an object of the present invention to provide an optical disk device and an optical branching means that can simultaneously cope with the configuration of two radiation light sources provided close to each other on a substrate.

  In order to achieve the above object, a first optical disk device of the present invention is an optical disk device including a radiation light source, an objective lens, a light splitting unit, and a photodetector, wherein light emitted from the radiation light source is the objective light. The light condensed on the signal surface of the optical disk via the lens, the light reflected on the signal surface is incident on the optical branching unit via the objective lens, and the light branching unit is connected to two straight lines intersecting the optical axis (in the radial direction of the optical disk). The quadrant is divided into four quadrants Ak (where k = 1, 2, 3, 4) by a parallel y-axis and an x-axis orthogonal thereto, and the photodetector is divided into at least four regions Bk. The light incident on the quadrant Ak by the branching means derives a first-order diffracted light ak and is projected on each of the regions Bk on the photodetector, and cuts of the first-order diffracted lights a2 and a3 by the x-axis correspond to the region B2. B1 substantially overlaps the boundary line, The distribution of the second-order diffracted lights a1 and a4 is characterized in that they are separated from each other on the photodetector.

  The detection signal in the area Bk (where k = 1, 2, 3, 4) is Ck, m is a numerical value of 1 or more, and the tracking error signal TE of the optical disk is TE = C1-C4- (C2-C3). / M.

  The light incident on the quadrant Ak by the light splitting means derives a -1st-order diffracted light ak '(where k = 1, 2, 3, 4), and the -1st-order diffracted light a2' is substantially y-axis. It is preferable that an image is formed on the detection surface without inversion with respect to the azimuth, and the -1st-order diffracted light a3 ′ is imaged on the detection surface with inversion with respect to the substantial y-axis azimuth.

  A second optical disk device according to the present invention includes a first radiation light source, a second radiation light source, an objective lens, a light branching unit, and a photodetector, wherein the first and second radiation light sources are Light emitted from the first radiation light source, which is formed on the photodetector, is focused on a signal surface of a first optical disc through the objective lens, and light reflected from the signal surface is passed through the objective lens. The light enters the light splitting means, and the light splitting means is divided into four quadrants Ak (where k = 1, 2, and 4) by two straight lines intersecting the optical axis (the y axis parallel to the optical disk radial direction and the x axis orthogonal thereto). 3, 4), the photodetector is divided into at least four regions Bk, and the light incident on the quadrant Ak by the light branching unit derives a first-order diffracted light ak to generate a region on the photodetector. Bk, respectively, exits the second radiation source and is different from the first radiation source The light having the wavelength is condensed on the signal surface of the second optical disk via the objective lens, and the light reflected on the signal surface is incident on the light splitting means via the objective lens, and the light is split by the light splitting means into the quadrant. The light incident on Ak derives the first-order diffracted light bk and is projected on each of the regions Bk on the photodetector.

  The cut of the first-order diffracted lights a2 and a3 or b2 and b3 along the x-axis substantially overlaps the boundary between the regions B2 and B3, and the distribution of the first-order diffracted lights a1 and a4 or b1 and b4 is determined by the photodetector. Preferably, they are separated from each other.

  The detection signal in the area Bk (where k = 1, 2, 3, 4) is Ck, m is a numerical value of 1 or more, and the tracking error signal TE of the first or second optical disk is TE = C1. It is preferred to be formed by -C4- (C2-C3) / m.

  The light incident on the quadrant Ak by the light branching unit derives the -1st-order diffracted light ak 'or bk' (k = 1, 2, 3, 4), and the -1st-order diffracted light a2 'or b2'. Forms an image on the detection surface without being inverted with respect to the substantial y-axis direction, and the -1st-order diffracted light a3 'or b3' is formed on the detection surface with being inverted with respect to the substantial y-axis direction. It is preferred to image.

  Also, the optical disc apparatus and the light branching means of the present invention comprise a first radiation light source, a second radiation light source, an objective lens, a light branching means, and a photodetector, wherein the light branching means is a periodic light source. It has a structure in which an uneven cross section is filled with a birefringent medium, and light having a wavelength of λ1 emitted from the first radiation light source is incident on the light branching means and is periodically substantially 2nπ (where n is an integer other than 0) ) Is converted into light having a phase difference, and the light is condensed on the signal surface of the first optical disc via the objective lens, and the light reflected on the signal surface is transmitted to the light splitting means via the objective lens. The light is periodically converted into light having a phase difference of approximately 2nπ + α (where α is a real number other than 0), and the diffracted light of the light is detected by being incident on the photodetector. The outgoing light of wavelength λ2 is incident on the optical branching means and periodically becomes approximately 2nπλ1 / λ2. The light is converted into light having a phase difference, the light is condensed on the signal surface of the second optical disk via the objective lens, and the light reflected on the signal surface is incident on the light splitting means via the objective lens. The light is periodically converted into light having a phase difference of approximately (2nπ + α) λ1 / λ2, and the diffracted light of the light is incident on the photodetector and detected.

  With the above-described configuration, it is possible to cancel off-track generated during tracking control. In addition, for a configuration having two adjacent radiation light sources, the same photodetector can detect a control signal and a reproduction signal for each light source light, and cancel off-track generated during tracking control, In particular, for one light source, the diffraction efficiency does not become zero under any birefringence condition of the optical disk substrate, and the optical disk signal can be reliably detected.

  According to the present invention, even if the objective lens and the polarizing hologram substrate have eccentricity along the radial direction of the optical disk, it is possible to cancel off-track generated during tracking control. Also, for a configuration having two adjacent radiation light sources, the same photodetector can detect a control signal and a reproduction signal, and can cancel off-track generated during tracking control. On the other hand, the diffraction efficiency does not become zero under any birefringence condition of the optical disk base material, and the optical disk signal can be reliably detected.

  According to the present invention, light emitted from a radiation light source is condensed on a signal surface of an optical disk via an objective lens, reflected light from the signal surface is divided into four parts, two of which are separated, and the other two are separated. It is characterized in that the joints of the detectors are arranged so as to overlap each other, a difference signal is detected from each combination, and a tracking error (TE) signal is detected by calculating these difference signals. As a result, the present invention can provide an optical disk device in which off-track does not occur during tracking control even if the objective lens and the polarizing hologram substrate have eccentricity along the disk radial direction. In addition, it is possible to provide an optical disk device and an optical branching unit that can simultaneously cope with the configuration of two radiation light sources provided close to each other on the light detection substrate.

(Embodiment 1)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. Elements common to the conventional example will be described using the same reference numerals. FIG. 1 shows a cross-sectional configuration of the optical disk device according to the first embodiment, and a side view relating to the radiation light source 1 and its periphery is also added below.

  In FIG. 1, a laser beam emitted from a radiation light source 1 such as a semiconductor laser mounted on a light detection substrate 9 reflects on a reflection mirror 10 mounted on the light detection substrate 9, and is collimated by a collimating lens 4. The light is converted into light, passes through the polarizing hologram substrate 2 as a light branching unit, is converted from linearly polarized light (S wave or P wave) into circularly polarized light by the quarter wavelength plate 3, and is condensed by the objective lens 5. It converges on the signal surface 6a of the optical disk substrate 6. The light reflected from the signal surface 6a passes through the objective lens 5, is converted into linearly polarized light (P wave or S wave) by the quarter wavelength plate 3, and is incident on the hologram surface 2a in the polarizing hologram substrate 2, and The light is diffracted and split into a first-order diffracted light 8 and a -1st-order diffracted light 8 ′ having the optical axis 7 as a symmetry axis, and each of the diffracted lights becomes a convergent light through the collimating lens 4. Incident.

  The 波長 wavelength plate 3 is formed on the same substrate as the hologram surface 2 a and moves integrally with the objective lens 6. The detection surface 9a is located substantially at the focal plane position of the collimator lens 4 (that is, the virtual light emitting point position of the light source 1). The diffraction efficiency of the return light by the hologram 2 is, for example, about 0% for the zero-order light and about 41% for the ± first-order lights.

  FIG. 2 shows a configuration of a light detection surface (FIG. 2A) and a hologram surface (FIG. 2B) of the optical disk device according to the first embodiment, both showing a case where the hologram surface side and the light detection surface side are viewed from the optical disk side. . Assuming that the intersection point between the hologram surface 2a and the optical axis 7 is 20, the hologram surface 2a is divided into four by two straight lines (X axis and Y axis) orthogonal to each other at the point 20, and the first quadrant and the fourth quadrant are divided into the X axis. It is divided into regions 21B, 21F, 24B, and 24F by strips along it, and the second quadrant is a region 22, and the third quadrant is a region 23.

  On the other hand, the point of intersection of the detection surface 9a and the optical axis 7 is a point 90, and two straight lines perpendicular to the point 90 and parallel to the X axis and the Y axis are the x axis and the y axis. Comb-shaped focus detection cells F1a, F2a, F1b, F2b, F1c, and F2c are arranged, and square tracking detection cells 7T1, 7T2, 7T3, and 7T4 are arranged on the negative side of the y-axis. These detection cells are symmetric with respect to the y-axis. The light emitted from the light emitting point 1a of the radiation light source 1 intersects the x-axis and travels in a plane perpendicular to the plane of the paper in parallel with the x-axis. Is reflected.

  The first-order diffracted lights 81B and 81F diffracting the comb-tooth regions 21B and 21F in the first quadrant of the hologram surface 2a are detected by light spots 81BS and 81FS crossing the detection cells F2a and F1b, and the -1st-order diffracted lights 81B 'and 81F' are detected. The first-order diffracted light 82 diffracting the second quadrant area 22 into the light spots 81BS 'and 81FS' that fit in the cell 7T1, the light spot 82S straddling the detection cells F1b and F2b, and the -1st-order diffracted light 82 'into the detection cell 7T2. The first-order diffracted light 83 diffracting the third quadrant region 23 into the light spot 82S 'that fits into the light spot 83S that straddles the detection cells F1b and F2b, and the -1st-order diffracted light 83' into the light spot 83S 'that fits in the detection cell 7T3. , The first-order diffracted lights 84B, 84F diffracting the comb teeth regions 24B, 24F in the fourth quadrant are light spots 84BS that straddle the detection cells F2b, F1c. The 84FS, -1-order diffracted light 84B ', 84F' are light spots 84BS fit into the detection cell 7T4 ', 84FS' focused on.

  FIG. 3 shows the focal point positions before and after the light detection surface 9a in a cross section along the optical axis in the first embodiment at the time of focusing on the optical disk signal surface 6a. For the first-order diffracted lights 81B, 84B, 81F, 84F and the -1st-order diffracted lights 81B ', 84B', 81F ', 84F', FIG. 3B shows the first-order diffracted light 82 and the -1st-order diffracted light 82 ', and FIG. This is the case of the folded light 83 and the -1st-order diffracted light 83 '. The 0th-order diffraction component corresponding to each diffracted light is condensed on a point 90 on the detection surface 9a, but the light is not actually irradiated because the diffraction efficiency of the 0th-order light is almost zero.

  As shown in FIG. 3A, of the light 80 diffracted by the hologram surface 2a, the first-order diffracted lights 81B and 84B diffracted in the first quadrant and the fourth quadrant, respectively, are points at the position of the distance L1 behind the detection surface 9a. 8B, and the -1st-order diffracted lights 81B 'and 84B' are condensed at a point 8B 'located at a distance of L1 in front of the detection surface 9a (light ray paths are indicated by solid lines). Also, of the light 80 diffracted by the hologram surface 2a, the first-order diffracted lights 81F and 84F diffracted in the first quadrant and the fourth quadrant, respectively, converge on a point 8F at a distance of L2 before the detection surface 9a, The -1st-order diffracted lights 81F 'and 84F' are condensed at a point 8F 'located at a distance of L2 behind the detection surface 9a (the ray trajectories are indicated by dotted lines). However, L2 is approximately equal to L1.

As shown in FIG. 3B, among the light 80 diffracted by the hologram surface 2a, the first-order diffracted light 82 diffracted in the second quadrant has a different condensing point between a cross section parallel to the paper surface and a cross section orthogonal to the paper surface. In a section perpendicular to the plane of the paper, the light is condensed at a point 82x located at a distance L1 behind the detection surface 9a (this diffracted light is indicated by 82X). In a section parallel to the plane of the paper, the distance between L3 behind the detection surface 9a (The diffracted light is indicated by 82Y). On the other hand, the −1st-order diffracted light 82 ′ diffracted in the second quadrant has a different condensing point between a cross section parallel to the paper surface and a cross section orthogonal to the paper surface. The light is condensed on a point 82x 'at a distance position (this diffracted light is indicated by 82X'), and is condensed on a point 82y 'at a distance L3 in front of the detection surface 9a in a cross section parallel to the paper surface. (The diffracted light is indicated by 82Y ')
As shown in FIG. 3C, among the light 80 diffracted by the hologram surface 2a, the first-order diffracted light 83 diffracted in the third quadrant has different condensing points in a cross section parallel to the paper and a cross section orthogonal to the paper. In a cross section orthogonal to the paper surface, light is condensed at a point 83x at a position of L1 in front of the detection surface 9a (this diffracted light is indicated by 83X), and in a cross section parallel to the paper surface, the distance of L3 is behind the detection surface 9a. (The diffracted light is indicated by 83Y). On the other hand, the -1st-order diffracted light 83 ′ diffracted in the third quadrant also has different condensing points between a section parallel to the plane of the paper and a section perpendicular to the plane of the paper. The light is condensed at a point 83x 'at a distance position (this diffracted light is indicated by 83X'), and is condensed at a point 83y 'at a distance L3 in front of the detection surface 9a in a cross section parallel to the paper surface. Diffracted light is indicated by 83Y ')
2 and 3, since the first-order diffracted lights 81B and 84B are lights condensed on the back side of the detection surface 9a (the side away from the hologram surface 2a), the spot shape on the detection surface 9a has a spot shape on the hologram surface 2a. Similar to the light distribution, the -1st-order diffracted lights 81B 'and 84B' are lights condensed in front of the detection surface 9a (on the side approaching the hologram surface 2a), so that the spot shape on the detection surface 9a is on the hologram surface 2a. Is similar to the shape obtained by inverting the light distribution at the point 20 with respect to the point 20.

  Since the first-order diffracted lights 81F and 84F are lights that converge before the detection surface 9a, the spot shape on the detection surface 9a is similar to a shape obtained by inverting the light distribution on the hologram surface 2a with respect to the point 20; Since the first-order diffracted lights 81F 'and 84F' are lights condensed behind the detection surface 9a, the spot shape on the detection surface 9a is similar to the light distribution on the hologram surface 2a.

  Further, since the first-order diffracted light 82 is a light that is condensed on the back side of the detection surface 9a in both a cross section parallel to the paper surface and a cross section orthogonal to the paper surface, the spot shape on the detection surface 9a is represented by Y Since the -1st-order diffracted light 82 ′ is a light that converges in front of the detection surface 9a in both the cross section parallel to the paper surface and the cross section orthogonal to the paper surface, the spot shape on the detection surface 9a is This is similar to a shape in which the light distribution on the hologram surface 2a is inverted with respect to the point 20 and elongated in the Y-axis direction.

  Further, since the first-order diffracted light 83 condenses before the detection surface 9a in a cross section orthogonal to the paper surface and converges behind the detection surface 9a in a cross section parallel to the paper surface, the spot shape on the detection surface 9a is The light distribution on the hologram surface 2a is inverted with respect to the Y-axis and is similar to a shape elongated in the Y-axis direction, and the -1st-order diffracted light 83 'is focused at the depth of the detection surface 9a in a cross section orthogonal to the paper surface. On the other hand, in a section parallel to the plane of the drawing, since the light is focused before the detection surface 9a, the spot shape on the detection surface 9a is obtained by inverting the light distribution on the hologram surface 2a with respect to the X axis and extending in the Y axis direction. Similar in shape.

  The light spots 81BS 'and 81FS' and the light spots 84BS 'and 84FS' are completely contained inside the photodetectors 7T1 and 7T4, respectively, but the light spots 82S 'and 83S' are spots connected in the y-axis direction. And the joint between the two substantially coincides with the dividing line 7Ta of the photodetectors 7T2 and 7T3. In addition, the light spot 82S is not inverted with respect to the Y axis, whereas the light spot 83S is inverted with respect to the Y axis with respect to the light distribution on the hologram surface 2a.

Some of the detection cells are conductive and are configured to result in the following six signals.
F1 = signal obtained from detection cell F1a + signal obtained from detection cell F1b + signal obtained from detection cell F1c F2 = signal obtained from detection cell F2a + signal obtained from detection cell F2b + signal obtained from detection cell F2c T1 = signal obtained from the detection cell 7T1 = signal obtained from the detection cell 7T2 T3 = signal obtained from the detection cell 7T3 = signal obtained from the detection cell 7T4 In FIG. The focus error signal FE on the optical disk signal surface, the tracking error signal TE on the optical disk track, and the reproduction signal RF on the optical disk signal surface are detected based on the following equations.

FE = F1-F2 (Equation 6)
TE = (T1-T4)-(T2-T3) / m (Equation 7)
RF = F1 + F2 + T1 + T2 + T3 + T4 (Equation 8)
In general, the behavior of the light spot on the light detection surface with respect to the defocus of the optical disc is determined by the relative positional relationship between the condensing point position of each spot and the light detection surface 9a. Particularly, the shape of the spot in the x-direction is related to the FE signal, and the shape of the spot is determined by the relative position between the light-condensing point position in the cross section orthogonal to the paper surface of the light spot in FIG. It is a positional relationship.

  Since the light spots 82FS and 83BS of the conventional example have the same behavior as the light spots 83FS and 82BS with respect to the defocus of the optical disk, the characteristics of the FE signal are the same without the light spots 82FS and 83BS. Further, the spread of the light spots 81BS, 81FS, 82S, 83S, 84BS, and 84FS in the x-axis direction in the first embodiment is the same as the spread of the light spot 81BS and the like in the conventional example in the x-axis direction.

  Accordingly, the light spots 81BS, 81FS, 84BS, and 84FS have the same behavior with respect to the defocus of the optical disk as in the conventional example, and the light spot 82S has the same position of the light-converging point in the cross section orthogonal to the paper surface. The light spot 82BS and the light spot 83S of the conventional example have the same behavior as the light spot 83FS of the conventional example (the light spots 82S and 83S are wider in the y-axis direction than the light spots 82BS and 83FS, but have a behavior for FE detection. Is determined by the spread in the x-axis direction, so that the characteristics of the FE signal are the same.) Therefore, the FE signal characteristics of the first embodiment are the same as those of the conventional example.

  The signal (T1-T4) and the signal (T2-T3) are basically the same signal for off-track, but have different characteristics. For example, assuming that the off-track amount with respect to the optical disk track is Δ and the eccentricity of the objective lens 5 and the polarizing hologram substrate 2 moving integrally therewith along the disk radial direction (Y-axis direction) is δ, the signal (T1-T4) is Are related by the following equation using the same coefficients a and b as in the conventional example.

T1−T4 = aΔ + bδ (Equation 9)
On the other hand, the signal (T2-T3) is related by the following equation.

T2−T3 = aΔ + b′δ (Equation 10)
The reason why the signal (T1−T4) is a function of δ is that the light emitted from the radiation light source 1 exhibits a non-uniform intensity distribution such that the light emitted from the radiation light source 1 is strong in the paraxial direction and becomes weaker as the distance from the optical axis increases. This is because, due to the eccentricity of the objective lens 5 and the polarizing hologram substrate 2 along the radial direction, the intensity distribution of the return light 80 on the hologram surface 2a becomes asymmetric with respect to the X axis.

  On the other hand, the reason why the dependence of the signal (T2−T3) on δ is different from the dependence on the signal (T1−T4) (b ′ ≠ b) is that the intensity distribution of the return light 80 on the hologram surface 2a is In addition to being asymmetric with respect to the X-axis, the effect of the light spot on the detection surface 9a shifting in the y-axis direction with the radial eccentricity of the objective lens 5 and the polarizing hologram substrate 2 This is because there is.

  That is, since the light spots 81BS 'and 81FS' and the light spots 84BS 'and 84FS' are completely contained in the photodetectors 7T1 and 7T4, respectively, even if the light spot is shifted in the y-axis direction, the light amount shifts. Although it does not occur (this is the same as the conventional example), the light spots 82S 'and 83S' are spots connected in the y-axis direction, and the joint between the two substantially coincides with the dividing line of the photodetectors 7T2 and 7T3. Therefore, when these spots are integrally shifted in the y-axis direction, there is a shift in the amount of light straddling the dividing line.

  Optical discs such as DVD-RAMs with a deep guide groove (optical depth D = approximately λ / 6, where λ is the wavelength of the light source) and a wide pitch (groove pitch Λ = 1.21 to 1.48 μm) In the case of, the intensity distribution of the return light 80 on the hologram surface 2a becomes substantially uniform in the Y-axis direction due to the diffraction effect at the groove, so that the coefficient b becomes substantially zero. At this time, if the coefficient m = ∞, that is, TE = (T1−T4), the off-track during tracking control (TE = 0) is zero.

In the case of an optical disk such as a DVD-R or DVD-RW having a shallow guide groove (optical depth D = approximately λ / 10 to λ / 20) and a narrow pitch (groove pitch Λ = 0.74 μm), The asymmetry of the return light 80 increases, and the coefficient b ≠ 0. If the coefficient m in (Equation 7) is set so as to satisfy m = b '/ b, TE = (1-1 / m) aΔ (Equation 7), (Equation 9), and (Equation 10). 11)
It becomes. Therefore, the influence of the eccentricity δ of the objective lens 5 and the polarizing hologram substrate 2 moving integrally therewith is almost eliminated, and even if the eccentricity δ exists, the off-track during tracking control (TE = 0) is zero. It is.

  The magnitude of the coefficient ratio b '/ b is substantially determined by the optical system and the groove shape of the optical disk. In the case of a DVD-R or DVD-RW optical disk, the coefficient b' is about 2 to 4 times the coefficient b. It becomes the size of. In the above embodiment, the light spots 82S 'and 83S' are described as spots connected in the y-axis direction. However, even if these light spots are shifted and deviated in the x-axis direction, the effect of removing the influence of the eccentricity δ is changed. There is no.

  If the light emitting point position 1a is shifted in the y-axis direction, the joint between the light spots 82S 'and 83S' is shifted from the dividing line 7Ta of the photodetectors 7T2 and 7T3, so that an offset is added to the signal (T2-T3). , This component can be removed by initial learning. Furthermore, even if the light emitting point position 1a is displaced in the y-axis direction, the light spots 82S 'and 83S' are spread in the y-axis direction, so that the ratio of the displacement amount to the spot diameter can be kept small, and the margin of error can be increased. Have been.

  Although the light detection surface 9a has been described as being located at the focal plane position of the collimator lens 4, it may be near the light detection surface 9a, and the light source and the light detector are arranged on the same substrate, but may be separate.

(Embodiment 2)
Hereinafter, a second embodiment of the present invention will be described with reference to FIG. The second embodiment is the same as the first embodiment except that the pattern of the polarization hologram surface 2a, the detection pattern on the photodetector surface 9a and the light distribution thereon are different, and the description of the common parts is omitted. Elements common to the first embodiment will be described with the same numbers. FIG. 4 shows the state of the hologram pattern, the light detection pattern, and the light distribution thereon, according to the second embodiment. When viewed from the optical disk side, the hologram surface (FIG. 4B) side and the light detection surface (FIG. 4A) side are both viewed. Is the case.

  Assuming that the intersection point between the hologram surface 2a and the optical axis 7 is 20, the hologram surface 2a is divided into four by two straight lines (X axis and Y axis) orthogonal to each other at the point 20, the first quadrant is an area 21B, and the second quadrant is an area. 22, the third quadrant is a region 23, and the fourth quadrant is a region 24F.

  The point of intersection of the detection surface 9a and the optical axis 7 is a point 90, and two straight lines perpendicular to the point 90 and parallel to the X axis and the Y axis are the x axis and the y axis, and the comb teeth along the y axis on the + side of the y axis Focus detection cells F1a, F2a, F1b, F2b, F1c, F2c are arranged, and square tracking detection cells 7T1, 7T2, 7T3, 7T4 are arranged on the negative side of the y-axis. These detection cells are symmetric with respect to the y-axis. The light emitted from the light emitting point 1a of the radiation light source 1 intersects the x-axis and travels in a plane perpendicular to the plane of the paper in parallel with the x-axis. Is reflected.

  The first-order diffracted light 81B diffracted in the first quadrant 21B of the hologram surface 2a is focused on the light spot 81BS straddling the detection cells F2a and F1b, and the -1st-order diffracted light 81B 'is focused on the light spot 81BS' that fits in the detection cell 7T1. The first-order diffracted light 82 diffracting the area 22 in the second quadrant is focused on the light spot 82S straddling the detection cells F1b and F2b, and the -1st-order diffracted light 82 'is focused on the light spot 82S' that fits in the detection cell 7T2.

  The first-order diffracted light 83 diffracting the region 23 in the third quadrant converges on a light spot 83S straddling the detection cells F1b and F2b, and the -1st-order diffracted light 83 'converges on a light spot 83S' that fits in the detection cell 7T3. The first-order diffracted light 84F diffracting the area 24F in the fourth quadrant is focused on the light spot 84FS that straddles the detection cells F2b and F1c, and the -1st-order diffracted light 84F 'is focused on the light spot 84FS' that fits in the detection cell 7T4.

  At the time of focusing on the optical disk signal surface 6a, the focal point positions before and after the photodetector in the cross section along the optical axis are the same as in the first embodiment, and the first-order diffracted lights 81F and 84B in FIG. , And −1st-order diffracted light 81F ′, 84B ′. Therefore, in FIG. 3A, in FIG. 3A, in the case of the first-order diffracted lights 81B and 84F and the −1st-order diffracted lights 81B ′ and 84F ′ in the present embodiment, and in FIG. In the case of the folded light 82 ', FIG. 3C corresponds to the case of the first-order diffracted light 83 and the -1st-order diffracted light 83' in this embodiment.

  Since the light spots 81FS and 84BS in the first embodiment behave the same as the light spots 84FS and 81BS with respect to the defocus of the optical disk, the characteristics of the FE signal are the same without the light spots 81FS and 84BS. The second embodiment is a form in which the light spots 81FS and 84BS in the first embodiment are omitted, and is the same as the first embodiment with respect to the eccentricity of the objective lens 5 and the polarizing hologram substrate 2 along the radial direction. It is clear that the same effect can be obtained in principle.

(Embodiment 3)
Hereinafter, a third embodiment of the present invention will be described with reference to FIGS. In the third embodiment, the number of light emitting points from the light source is increased to two, the structure of the polarization hologram substrate 2 which is a light branching unit is changed, the pattern of the polarization hologram surface 2a and the position on the photodetector surface 9a are changed. Are the same as in the first embodiment except that the detection pattern and the light distribution thereover are different, the description of the common parts is omitted, and the same elements as those in the first embodiment are denoted by the same reference numerals. I do.

  FIG. 5 shows a cross-sectional configuration of the optical disk device according to the third embodiment, and a side view relating to the radiation light source 1 and its periphery is also added below. In FIG. 5, a first laser beam (wavelength λ1) emitted from the first light emitting point 1a of the radiation light source 1 such as a semiconductor laser mounted on the light detection substrate 9 is mounted on the light detection substrate 9. The reflected light is reflected by the reflecting mirror 10, converted into parallel light by the collimating lens 4, transmitted through the polarizing hologram substrate 2, and converted from linearly polarized light (S wave or P wave) into circularly polarized light by the ４ wavelength plate 3. The light is condensed by the objective lens 5 and converges on the signal surface 6a of the first optical disc substrate 6.

  The light reflected from the signal surface 6a passes through the objective lens 5, is converted into linearly polarized light (P wave or S wave) by the quarter wavelength plate 3, and is incident on the hologram surface 2a in the polarizing hologram substrate 2, and The light is diffracted and split into a first-order diffracted light 8 and a -1st-order diffracted light 8 ′ having the optical axis 7 as a symmetry axis, and each of the diffracted lights becomes a convergent light through the collimating lens 4. Incident. The 波長 wavelength plate 3 is formed on the same substrate as the hologram surface 2 a and moves integrally with the objective lens 6. The detection surface 9a is located substantially at the focal plane position of the collimating lens 4 (that is, the virtual light emitting point position of the light emitting point 1a). The diffraction efficiency of the return light by the hologram surface 2a is, for example, about 0% for the zero-order light and about 41% for the ± first-order lights.

  Further, the radiation light source 1 can emit light having a wavelength different from that of the first laser light, and the second laser light (wavelength λ2, where λ2> λ1) emitted from the second light emitting point 1a ′ of the radiation light source 1 is Is reflected by a reflecting mirror 10 mounted on a light detection substrate 9, converted into parallel light by a collimating lens 4, transmitted (partially diffracted) through the polarizing hologram substrate 2, and Is converted from linearly polarized light (S wave or P wave) into elliptically polarized light, condensed by the objective lens 5, and converges on the signal surface 6a 'of the second optical disk substrate 6'.

  The light reflected from the signal surface 6a 'passes through the objective lens 5, passes through the quarter-wave plate 3, enters the hologram surface 2a in the polarizing hologram substrate 2, and diffracts the light to symmetrically align the optical axis 7'. The light is branched into the first-order diffracted light 11 and the -1st-order diffracted light 11 ′ having the axes, and each of the diffracted lights becomes convergent light through the collimator lens 4 and is incident on the detection surface 9 a on the detector 9. The optical disk substrate 6 is a disk having a low birefringence such as a DVD, and the optical disk substrate 6 'is a disk having a large birefringence such as a CD.

  FIG. 6 shows a cross-sectional configuration of the polarization hologram substrate 2 and the quarter-wave plate 3 in the third embodiment. The polarization hologram substrate 2 has a configuration in which a birefringent medium 2B is sandwiched between transparent substrates 2A and 2C having a uniform refractive index (na is the refractive index of the transparent substrate 2A). A grating having a depth d is formed on the surface facing.

  A ４ wavelength plate 3 serving as a 波長 wavelength plate for the light of wavelength λ1 is bonded to the surface on the opposite side of the substrate 2C, and its fast axis is 45 ° with respect to the X axis and the Y axis. The azimuth is in degrees. The Z axis is set in the light propagation direction, the X axis and the Y axis are set in a plane parallel to the hologram surface 2a, and the refractive index of the medium 2B is defined as x direction nx and y direction ny. Actually, the refractive index is a function of the wavelength, but the difference is small in the vicinity of visible to infrared light, and the same value is used instead. Further, FIG. 6 shows the orientation of the grating along the Y axis, but the orientation may be arbitrary. Further, the polarization direction of the outward light 12a (the light traveling from the light source 1 toward the polarization hologram 2) of the two lights is in the Y direction.

  Here, it is assumed that the following expression holds between the grating depth d and each refractive index.

(Na-ny) d = Nλ1 (Equation 12)
(Na-nx) d = nλ1 + λ1 / 2 (Equation 13)
Here, N is an integer other than 0, and n is an integer.

  The polarization hologram in the conventional example and the first embodiment has a so-called N = 0 form, but this embodiment is characterized by N ≠ 0.

  First, in the case of the light having the wavelength λ1, the polarization direction of the outward light 12a is in the Y direction. Therefore, from equation (12), the phase difference of Nλ1 between the concave and convex portions of the grating (that is, 2π Phase difference). This phase difference is substantially the same as that having no phase difference, and the light 12b transmitted through the medium 2B is not diffracted by the grating. The polarization direction of the light 12b remains in the Y direction, and the light 12b passes through the quarter-wave plate 3 to become circularly polarized light 12c. The polarization state of the return light 13a from the optical disk signal surface 6a is the same circular polarization as that of the light 12c, assuming that the optical disk substrate 6 has no birefringence. It becomes the polarized light 13b.

  Accordingly, according to (Equation 13), when the light passes through the polarization hologram substrate 2, a phase difference of nλ1 + λ1 / 2 (ie, a phase difference of π) is generated between the concave and convex portions of the grating. (0% light is about 0% and ± 1st light is about 41% each).

  Next, in the case of the light having the wavelength λ2, the polarization direction of the outward light 12a is in the Y direction. Therefore, according to (Equation 12), by transmitting through the polarization hologram substrate 2, the phase difference of λ2−Nλ1 between the concave and convex portions of the grating ( That is, a phase difference of 2π (1-Nλ1 / λ2) occurs. Generally, the light 12b transmitted through the medium 2B undergoes diffraction due to the grating, but only the 0th-order diffracted light is involved in recording and reproduction of signals, and other higher-order (first-order or higher) diffracted light is symmetrical to removal stray light. Since it becomes a component, higher-order diffracted light on the outward path is ignored in the following discussion.

  The polarization direction of the light 12b remains in the Y direction, and is transmitted through the を wavelength plate 3 (corresponding to a / 4 × λ1 / λ2 wavelength plate for light of the wavelength λ2), thereby forming the elliptically polarized light 12c. Become. The polarization state of the return light 13a from the optical disk signal surface 6a 'is considered to be birefringent from the optical disk substrate 6', from circularly polarized light, elliptically polarized light to linearly polarized light, and the light 13b after passing through the quarter wavelength plate 3 is considered. It must be considered that the polarization direction covers the X direction to the Y direction.

  Therefore, according to (Equation 13), the phase difference between λ2-nλ1-λ1 / 2 and λ2-Nλ1 between the concave and convex portions of the grating by transmitting through the polarization hologram substrate 2 (that is, 2π ｛1- (n + 1/2) λ1 / λ2). ｝ And 2π (1−Nλ1 / λ2) are mixed. Generally, the light 13c transmitted through the substrate 2 is diffracted by the grating and diffracted under any birefringence condition of the optical disk substrate 6 ′. Efficiency never goes to zero.

  For example, when λ1 = 660 nm, λ2 = 792 nm, N = 1, and n = 0, the diffraction efficiency of ± first-order light on the outward path is about 10% (the phase difference is π / 3), while the diffraction efficiency on the return path is about 10%. Has a phase difference of 7π / 6 and π / 3, the former ± 1st-order light diffraction efficiency is 38%, and the latter ± 1st-order light diffraction efficiency is about 10%. % Diffraction efficiency. When λ1 = 660 nm, λ2 = 792 nm, N = 1, and n = 1, the diffraction efficiency of ± first-order light on the outward path is about 10% (the phase difference is π / 3), while the diffraction efficiency on the return path is about 10%. The phase difference is a mixture of -π / 2 and π / 3, the former ± 1st-order light has a diffraction efficiency of 20%, and the latter ± 1st-order light has a diffraction efficiency of about 10%. % Diffraction efficiency.

  In any case, the diffraction efficiency does not fall below 10% under any birefringence condition of the optical disk substrate 6 ', and the optical disk signal is reliably detected by the photodetector even for an optical disk having a large birefringence such as a CD disk. There is. Therefore, for the light of wavelength λ2, the light transmission efficiency on the outward path and the light detection efficiency on the return path are slightly inferior, but stable signal detection performance can be secured against the influence of birefringence of the optical disk substrate.

  In FIG. 6, the medium 2B is made of a birefringent material, but the substrate 2A or 2A, 2B may be made of a birefringent material.

7A and 7B are cross-sectional views of a polarization hologram substrate 2 according to another example. The polarization hologram substrate 2 shown in FIG. 7A is obtained by forming a proton exchange region 200B by patterning a medium 200A of LiNbO ₃ crystal and then etching a part thereof. The proton exchange region 200B is formed in the Y-axis direction in FIG. 6, but may be in any direction.

  As an example of the polarization hologram substrate 2 as shown in FIG. 7A, the proton exchange region 200B has a refractive index ne of 2.33 in the P-wave incident direction, a refractive index no of 2.24 in the S-wave incident direction, and a P-wave incidence of the medium 200A. The refractive index no in the direction is 2.20, the refractive index no in the S-wave incident direction is 2.28, the etching depth h1 is 0.46 μm, and the proton exchange depth h2 is 2.1 μm.

In the polarization hologram substrate 2 shown in FIG. 7B, a proton exchange region 210B is formed by patterning on a LiNbO ₃ crystal medium 210A, and a Ta ₂ O ₃ film is further formed thereon by patterning. The proton exchange region 210B is formed in the Y-axis direction in FIG. 6, but may be in any direction.

As an example of the polarization hologram substrate 2 as shown in FIG. 7B, the refractive index of the medium 210A and the proton exchange region 210B is the same as that of the example of FIG. 7A, the refractive index n of the Ta ₂ O ₃ film is 2.10, and the film thickness t. Is 0.30 μm and the proton exchange depth h2 is 2.1 μm.

  7A and 7B, a broken line indicates a transmitted wavefront when light having a wavelength λ1 (0.66 μm) has passed through the polarization hologram substrate 2, and a phase difference λ1 is generated. This is the same as that without any phase difference. Other than this, the operation of the polarization hologram substrate 2 shown in each of these figures is the same as that shown in FIG. 6, and it is possible to surely obtain diffraction efficiency for both lights of wavelengths λ1 and λ2. Can be.

  FIG. 8 shows a state of a light detection pattern and light distribution on the light detection pattern according to the third embodiment, when the hologram surface side is viewed from the optical disk side. The hologram pattern and the focal point positions before and after the photodetector in the cross section along the optical axis are the same as those in the first embodiment, and a description thereof will be omitted. The light detection pattern is the same as that of the first embodiment except that the shape extends in the y direction, and the description thereof is omitted.

  FIG. 8A shows the state of the light spot of the return light with respect to the first laser light emitted from the first light emitting point 1a, and FIG. 8B shows the light of the return light with respect to the second laser light emitted from the second light emitting point 1a '. The state of the spot is shown.

  In FIG. 8A, the joint between the light spots 82S 'and 83S' is located at a distance of 11 from the point 90 as measured in the y-axis direction (the same applies to the joint between the light spots 82S and 83S). The joint between the light spots 81FS 'and 81BS' and the joint between the light spots 84FS 'and 84BS' are located at a distance of l1 + l1 'from the point 90 when measured in the y-axis direction (the joint between the light spots 81FS and 81BS and the light spot). 84FS, 84BS joint).

  On the other hand, in FIG. 8B, the joint between the light spots 82S 'and 83S' is located at a distance of 12 from the point 90 'measured in the y-axis direction (the same applies to the joint between the light spots 82S and 83S). The joint between the light spots 81FS 'and 81BS' and the joint between the light spots 84FS 'and 84BS' are both located in the y-axis direction at a distance of l2 + l2 'from the point 90' (the joint between the light spots 81FS and 81BS and the light). The same applies to the joint between the spots 84FS and 84BS). The distance between the light emitting points 1a and 1a ', that is, between the points 90 and 90', is separated by [epsilon] along the y-axis. Here, it is assumed that the following relationship is established.

l2 = l1 + ε (Equation 14)
At this time, if the joint between the light spots 82S 'and 83S' substantially coincides with the division line 7Ta of the photodetectors 7T2 and 7T3 with respect to the first laser light, it also coincides with the second laser light. become.

  On the other hand, the distance from the virtual light emitting point (i.e., the points 90 and 90 ') is approximately proportional to the diffraction angle, and the diffraction angle is approximately proportional to the wavelength.

l2 / l1 = l2 '/ l1' = λ2 / λ1 (Equation 15)
For example, when λ1 = 660 nm, λ2 = 792 nm, and ε = 100 μm, l1 = 500 μm and l2 = 600 μm.

  Since the shape of the light detection pattern of this embodiment extends in the y direction, the light spots 81FS 'and 81BS' and the light spots 84FS 'and 84BS' fall within the photodetectors 7T1 and 7T4 even if the wavelengths are different. I have. Further, the light spots 82S and 83S, and the light spots 81FS and 81BS and the light spots 84FS and 84BS have a small spread in the x-axis direction and are arranged almost along the y-axis. Therefore, the influence on the FE signal is small.

  Therefore, while maintaining good FE signal characteristics with respect to the two laser beams, the same effect as that of the first embodiment can be obtained with respect to the eccentricity of the objective lens 5 and the polarizing hologram substrate 2 along the radial direction. Is obtained.

  As described above, the present invention can be used for an optical disk device or an optical branching device, and cancels off-track generated during tracking control even if the objective lens and the polarizing hologram substrate have eccentricity along the radial direction of the optical disk. can do.

  Further, even for a configuration having two adjacent radiation light sources, the same light detector can detect a control signal and a reproduction signal, and can cancel off-track generated during tracking control. However, the diffraction efficiency does not become zero under any birefringence condition of the optical disk substrate, and the optical disk signal can be detected reliably. Therefore, it is useful for an optical disk device or an optical branching device having two radiation light sources.

FIG. 1 is a cross-sectional configuration diagram of an optical disc device according to a first embodiment of the present invention. FIG. 2 is a configuration diagram of a detection surface of the optical disc device according to the first embodiment of the present invention. FIG. 2 is a configuration diagram of a hologram surface of the optical disc device according to the first embodiment of the present invention. FIG. 8 is an explanatory diagram showing the positions of condensing points before and after the photodetector in a cross section along the optical axis when focusing on the optical disk signal surface according to the first embodiment of the present invention, and showing first-order diffracted lights 81B, 84B, and 81F. , 84F and −1st-order diffracted light 81B ′, 84B ′, 81F ′, 84F ′. FIG. 7 is an explanatory diagram showing the converging point positions before and after the photodetector in the cross section along the optical axis at the time of focusing on the optical disc signal surface according to the first embodiment of the present invention. The figure in the case of folding light 82 '. FIG. 4 is an explanatory diagram showing the converging point positions before and after the photodetector in a cross section along the optical axis at the time of focusing on the optical disc signal surface according to the first embodiment of the present invention. The figure in the case of folding light 83 '. FIG. 9 is an explanatory diagram showing a state of a light detection pattern and a light distribution thereon on the second embodiment of the present invention. FIG. 7 is an explanatory diagram showing a hologram pattern according to the second embodiment of the present invention. FIG. 13 is a sectional configuration diagram of an optical disc device according to a third embodiment of the present invention. FIG. 7 is a cross-sectional configuration diagram of a polarization hologram 2 and a 波長 wavelength plate 3 according to a third embodiment of the present invention. FIG. 13 is a sectional configuration diagram of another example of the polarization hologram according to the third embodiment of the present invention. Sectional view of yet another example of a polarization hologram according to Embodiment 3 of the present invention. FIG. 13 is a diagram showing a state of a light spot of return light with respect to a first laser beam emitted from a first light emitting point 1a according to the third embodiment of the present invention. FIG. 14 is a diagram illustrating a state of a light spot of return light with respect to a second laser beam emitted from a second light emitting point 1a ′ according to the third embodiment of the present invention. FIG. 2 is a cross-sectional configuration diagram of an optical disk device in a conventional example. FIG. 4 is a configuration diagram of a detection surface of an optical disk device in a conventional example. FIG. 3 is a configuration diagram of a hologram surface of an optical disc device in a conventional example.

Explanation of reference numerals

Reference Signs List 1 light source 2 polarizing hologram substrate 2a hologram surface 4 collimating lens 3 1/4 wavelength plate 5 objective lens 6 optical disk substrate 6a optical disk signal surface 7 optical axis 8 first-order diffracted light 8'-first-order diffracted light 9 light detection substrate 9a light detection Surface 10 Reflecting mirror

Claims (9)

An optical disc device including a radiation light source, an objective lens, a light branching unit, and a photodetector,
Light emitted from the radiation light source is focused on the signal surface of the optical disk via the objective lens,
Light reflected from the signal surface enters the light splitting means via the objective lens,
The light splitting means is divided into four quadrants Ak (where k = 1, 2, 3, 4) by two straight lines intersecting the optical axis (a y-axis parallel to the optical disk radial direction and an x-axis orthogonal thereto),
The photodetector is divided into at least four regions Bk;
The light incident on the quadrant Ak by the light branching unit derives a first-order diffracted light ak and is respectively projected on a region Bk on the photodetector.
The cuts of the first-order diffracted lights a2 and a3 along the x-axis substantially overlap the boundary between the regions B2 and B3,
An optical disk device, wherein the distributions of the first-order diffracted lights a1 and a4 are separated from each other on the photodetector.   The detection signal in the area Bk (where k = 1, 2, 3, 4) is Ck, m is a numerical value of 1 or more, and the tracking error signal TE of the optical disk is TE = C1-C4- (C2-C3). The optical disk device according to claim 1, wherein the optical disk device is generated by / m.   The light incident on the quadrant Ak by the light branching unit derives a -1st-order diffracted light ak '(where k = 1, 2, 3, 4), and the -1st-order diffracted light a2' has a substantial y-axis orientation. 3. The optical disk according to claim 1, wherein an image is formed on the detection surface without being inverted, and the -1st-order diffracted light a3 'is inverted with respect to a substantial y-axis direction and formed on the detection surface. apparatus. An optical disc device including a first radiation light source, a second radiation light source, an objective lens, a light branching unit, and a photodetector,
The first and second radiation sources are configured on the photodetector;
The light exiting the first radiation source is focused on the signal surface of the first optical disc via the objective lens,
Light reflected from the signal surface enters the light splitting means via the objective lens,
The light splitting means is divided into four quadrants Ak (where k = 1, 2, 3, 4) by two straight lines intersecting the optical axis (a y-axis parallel to the optical disk radial direction and an x-axis orthogonal thereto),
The photodetector is divided into at least four regions Bk;
The light incident on the quadrant Ak by the light branching unit derives a first-order diffracted light ak and is respectively projected on a region Bk on the photodetector.
Light having a wavelength different from that of the first radiation light source exiting from the second radiation light source is condensed on the signal surface of the second optical disk via the objective lens,
The light reflected from the signal surface is incident on the light splitting means via the objective lens, and the light incident on the quadrant Ak by the light splitting means derives a first-order diffracted light bk to generate an area Bk on the photodetector. An optical disk device characterized by being projected onto each of optical disks.   The cut of the first-order diffracted lights a2 and a3 or b2 and b3 along the x-axis substantially overlaps the boundary between the regions B2 and B3, and the distribution of the first-order diffracted lights a1 and a4 or b1 and b4 is determined by the photodetector. The optical disk device according to claim 4, wherein the optical disk device is separated from each other.   The detection signal in the area Bk (where k = 1, 2, 3, 4) is Ck, m is a numerical value of 1 or more, and the tracking error signal TE of the first or second optical disk is TE = C1-C4. The optical disk device according to claim 4, wherein the optical disk device is generated by − (C2−C3) / m.   The light incident on the quadrant Ak by the light branching unit derives a -1st-order diffracted light ak 'or bk' (k = 1, 2, 3, 4), and the -1st-order diffracted light a2 'or b2' is substantially An image is formed on the detection surface without being inverted with respect to a typical y-axis azimuth, and the -1st-order diffracted light a3 'or b3' is formed on the detection surface with being inverted with respect to the substantial y-axis azimuth. An optical disk device according to any one of claims 4 to 6. An optical disc device including a first radiation light source, a second radiation light source, an objective lens, a light branching unit, and a photodetector,
The light branching means has a structure in which a birefringent medium is filled in a periodic uneven cross section,
The light of wavelength λ1 that exits the first radiation light source enters the light branching unit and is periodically converted into light having a phase difference of approximately 2nπ (where n is an integer other than 0),
The light is focused on the signal surface of the first optical disc via the objective lens,
The light reflected from the signal surface is incident on the light splitting means via the objective lens, and is periodically converted into light having a phase difference of approximately 2nπ + α (where α is a real number other than 0). Is incident on the photodetector and detected,
The light of wavelength λ2 exiting the second radiation light source is incident on the light branching means and is periodically converted into light having a phase difference of approximately 2nπλ1 / λ2,
The light is focused on the signal surface of the second optical disc via the objective lens,
The light reflected from the signal surface is incident on the light splitting means via the objective lens, and is periodically converted into light having a phase difference of approximately (2nπ + α) λ1 / λ2,
An optical disc device, wherein the diffracted light of the light is incident on the photodetector and detected. An optical branching device including a first radiation source, a second radiation source, an objective lens, a light branching unit, and a photodetector,
The light branching means has a structure in which a birefringent medium is filled in a periodic uneven cross section,
The light of wavelength λ1 that exits the first radiation light source enters the light branching unit and is periodically converted into light having a phase difference of approximately 2nπ (where n is an integer other than 0),
The light is focused on the signal surface of the first optical disc via the objective lens,
The light reflected from the signal surface is incident on the light splitting means via the objective lens, and is periodically converted into light having a phase difference of approximately 2nπ + α (where α is a real number other than 0). Is incident on the photodetector and detected,
The light of wavelength λ2 exiting the second radiation light source is incident on the light branching means and is periodically converted into light having a phase difference of approximately 2nπλ1 / λ2,
The light is focused on the signal surface of the second optical disc via the objective lens,
The light reflected from the signal surface is incident on the light splitting means via the objective lens, and is periodically converted into light having a phase difference of approximately (2nπ + α) λ1 / λ2,
An optical branching device, wherein the diffracted light of the light enters the photodetector and is detected.

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