JP2013175260A - Focus error detection device and optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a focus error detection device and an optical pickup device such that positioning of a diffraction element is made easy and stable focus control can be performed.SOLUTION: A light receiving element 2 includes a focus light receiving region that is divided into focus light receiving regions 2a and 2b by a division line. A diffraction element 4 includes: in a focus state, diffraction regions E that diffract a part of reflection light emitted from a light source 1 and reflected from an optical recording medium 7 and form a spot on the division line; and diffraction regions E and F that diffract the other part of the reflection light toward the focus light receiving regions 2a and 2b and form spots at positions symmetrical with respect to the division line.

Description

  The present invention relates to a focus error detecting device for detecting a focus error when irradiating light to an optical recording medium and receiving reflected light from the optical recording medium for reproducing and recording information recorded on the optical recording medium. And an optical pickup device.

  FIG. 20 is a diagram illustrating the configuration of the optical pickup device 108 according to the first conventional technique. FIG. 21 is a plan view of the diffraction region 104 and the light receiving element 102 of the diffraction element 103 in the first prior art. FIG. 22 is a characteristic diagram showing a focus error signal (hereinafter abbreviated as FES) detected by the first conventional optical pickup device 108 in accordance with the movement distance of the objective lens 106 in the Z direction, which is the focus direction. It is.

  The optical pickup device 108 collects a light source 101 composed of a semiconductor laser, a collimating lens 105 for collimating the emitted light, and a light bundle that has been collimated by the collimating lens 105 toward the optical recording medium 107. It includes an objective lens 106 that emits light, a light receiving element 102, and a diffraction element 103.

  In the light receiving element 102, a plurality of light receiving regions are formed. A part of the plurality of light receiving regions is used as the focus light receiving regions 102a and 102b, and the other part is used as the radial light receiving regions 102c and 102d. The focus light receiving areas 102a and 102b are used for focus servo, and the radial light receiving areas 102c and 102d are used for radial servo. The diffractive element 104 has a function of diffracting the reflected light 112 from the optical recording medium 7 toward the light receiving element 102 and has a diffraction region divided into a plurality of parts, and a part of the reflected light is reflected light. 112 is used as a diffraction region that diffracts 112 toward the focus light receiving regions 102a and 102b.

  The diffractive element 104 includes a radial diffraction region formed in the −Y direction and a focus formed in the + Y direction, with a dividing line 109 in the X direction passing through the center O serving as the optical axis as a boundary in a circular outer edge. Consists of diffraction regions. Further, the radial diffraction region is composed of a diffraction region C in the -X direction and a diffraction region D in the + X direction with a dividing line 111 extending from the center O in the -Y direction as a boundary. The focus diffraction region is a dividing line. 109, the diffraction regions E to K having a plurality of dividing lines 110 extending at a predetermined interval in the + Y direction orthogonal to the dividing line 109 as boundaries.

  The light receiving element 102 includes focus light receiving areas 102a and 102b arranged in the + X direction with respect to the diffraction element 104, a radial light receiving area 102c arranged in the + Y direction, and a radial light receiving area 102d arranged in the -Y direction. Has been. The dividing line serving as the boundary between the focus light receiving regions 102a and 102b is formed in a direction of an angle α slightly inclined from the direction of the dividing line 109 of the diffraction element 104. The outer dimensions of the light receiving regions 102a to 102d are set so that the X direction is longer than the Y direction. This is because when the arrangement of the light source 101, the light receiving element 102, and the diffraction element 104 is deviated from a predetermined position, the Y direction position shift can be adjusted by the rotation angle θ in the XY plane, but on the light receiving element 102 This is because the position of the light spot incident on the screen moves in the X direction.

  When the reflected light 112 from the optical recording medium 107 enters the diffraction region 104, the light diffracted by the diffraction regions C and D is diffracted so as to be incident on the light receiving regions 102c and 102d. The light diffracted by the diffraction regions E to K is diffracted toward the vicinity of the dividing line of the light receiving regions 102a and 102b, and the diffracted light of the diffraction regions E, G, I, and K is divided into the light receiving regions 102a and 102b. Slightly deviates in the + Y direction from the line and is diffracted at a certain interval in the ± X direction and is incident on the light spots e, g, i, k. The diffracted light in the diffraction regions F, H, J is divided into 102a and 102b. The light is diffracted slightly from the line in the −Y direction and at a certain interval in the ± X direction and is incident on the light spots f, h, and j.

  However, the optical arrangement of the light source 101, the diffraction element 104, and the light receiving element 102 is set so that the incident light spots c, d, e to k on the light receiving element 102 are condensed like the light spot 113. However, if there is a tolerance that shifts in the Z direction in the optical arrangement, for example, the light spot moves in the −X direction while the spot becomes a large light spot 114 or moves in the + X direction. In some cases, the light spot is inverted to become a larger light spot 115. Even in such a case, in order to ensure the FES characteristic, the angle of the dividing line of the focus light receiving regions 102a and 102b is inclined by the angle α, and the diffraction element 103 is centered within the XY plane perpendicular to the optical axis direction Z. It is rotated around the center.

  Next, the operation principle of the optical pickup device 108 according to the first prior art will be described. When the values obtained by converting the light incident on the light receiving regions 102a to 102d into electrical signals are Sa, Sb, Sc, and Sd, the subsequent servo signal generation unit generates the focus error signal FES and the radial error signal RES. In accordance with the servo signal, the servo signal processing unit performs focus servo control and radial servo control, and an objective lens equipped with an actuator so as to follow the focal point of the objective lens 106 with respect to a predetermined track of the optical recording medium 107 The position control in the focus direction and the track direction of 106 is performed.

Specifically, the focus error signal FES can be obtained by the following equation.
FES = Sa−Sb (1)
If the radial error signal is a push-pull method,
RES = Sc-Sd (2)
If the DPD method can be obtained,
RES = Phase (Sc-Sd) (3)
The light can be collected on a desired track of the optical recording medium 107 by performing servo control.

Furthermore, the reproduction signal RF is
RF = Sa + Sb + Sc + Sd (4)
By performing the above calculation, the reproduction signal RF of the track can be reproduced.

  When the electric signal amount of the focus error signal FES obtained here is taken as the vertical axis and the movement distance (hereinafter referred to as defocus amount) of the objective lens 106 in the Z direction as the focus direction is taken as the X axis, the FES as shown in FIG. A curve (hereinafter referred to as FES curve) is obtained. When the intersection of the FES curve and the X axis deviates from the defocus amount = 0, the position of the objective lens 106 in the Z direction, which is the focus direction, deviates by that distance, and the focal point for condensing light on the optical recording medium is increased. Therefore, a stable RF signal cannot be reproduced.

  Further, when the light is focused on the optical recording medium 107, the vicinity of the intersection with the X axis of the FES curve is linear, and the focus servo is controlled so that the focus servo is always drawn at the intersection. Further, the focus error signal FES is detected by the knife edge method using the dividing line 109 on the diffraction region 104 as a knife edge. In particular, the focus error signal FES is diffracted by the diffraction regions E to K, and near the dividing line of the light receiving regions 102a and 102b. Since the light spot focused on is composed of a plurality of light spots e to k, the slope of the straight line of the FES curve at the zero cross point becomes gentle compared to the case of one light spot, and the focus error signal FES is detected. Since sensitivity can be reduced, focus servo control can be performed more easily.

  However, the plurality of light spots ek on the dividing lines of the light receiving regions 102a and 102b have a tolerance in the arrangement of the light source 101, the diffractive element 103, and the light receiving element 102, and if the positions of the light spots ek shift, The posture of the light receiving element 102 that rotates the 103 in the XY plane perpendicular to the optical axis direction Z can be adjusted by rotating in the XY direction in the plane perpendicular to the optical axis direction Z. The position sensitivity of the plurality of light spots e to k with respect to the dividing line of the light receiving regions 102 a and 102 b is X with respect to the rotation angle θ of the diffraction element 103. Since the position of the light spot is shifted slightly in the direction, the defocus amount can be made slightly small, and high accuracy is required for adjusting the rotation angle θ of the diffraction element 103. . For example, when the number of light spots on the dividing line of the light receiving elements 102a and 102b is one point, a plurality of defocus amounts = ± 0.7 μm are generated at the rotation angle θ = ± 1 degree of the diffraction element 103. In the case of the light spots e to k, the rotation angle θ of the same diffraction element 103 is ± 1 degree, and the defocus amount is slightly reduced to ± 0.6 μm.

  Therefore, in the optical pickup device 108 as the first conventional technique, the detection sensitivity of the focus error signal FES is lowered, but in order to reduce the defocus amount, it is necessary to perform the rotation angle θ of the diffraction element 103 with high accuracy. There is.

Next, an optical pickup device according to the second prior art will be described.
The optical pickup device according to the second prior art is similar to the optical pickup device 108 according to the first prior art, and is provided with a dividing line constituting the diffraction region 116 on the diffraction element 103 and the dividing line. The positions of the light spots diffracted from the individual diffraction regions are different. FIG. 23 is a plan view of the diffraction region 116 and the light receiving element 102 of the diffraction element 103 in the second prior art. FIG. 24 shows two light spots e and f out of three light spots incident on the light receiving regions 102a and 102b, and two types of diffraction regions (E1, E2) and (F1, F2) that are diffracted. Are a diagram showing a state when the focal point of the objective lens 106 is focused on the optical recording medium and a case where the objective lens 106 is blurred, and a characteristic diagram showing a focus error signal obtained from each of the diffraction region (E1, E2) and each diffraction region (F1, F2). FIG. 25 is a characteristic diagram showing the focus error signal FES detected in accordance with the movement distance in the Z direction that is the focus direction of the objective lens 106 in the second conventional optical pickup device. Since other components are the same as those of the first prior art, description thereof is omitted.

  The diffractive element 116 includes a dividing line 117 that is parallel to the X direction and offset from the center O that is the optical axis by a distance Lh, a diffraction region I that is surrounded by an arc centered on the center O, and a dividing line 117. The boundary is composed of a radial diffraction region formed in the −Y direction and a focus diffraction region including a diffraction region I formed in the + Y direction. Further, the radial diffraction region is composed of a diffraction region C in the −X direction and a diffraction region D in the + X direction with a dividing line 118 extending from the center O in the −Y direction as a boundary. Diffracting regions E1, F1, G1, H1, H2, G2, F2, and E2 surrounded by a plurality of dividing lines 119 that are divided into eight at equal angles with respect to the intersection of the axis in the + Y direction and the dividing line 117; And a diffraction region I.

  When the reflected light 112 from the optical recording medium 107 enters the diffraction region 116, the light diffracted by the diffraction regions C and D is diffracted so as to be incident on the light receiving regions 102c and 102d (first conventional technique). Is omitted because it is the same as). The light diffracted by the diffraction areas E1, F1, G1, H1, H2, G2, F2, E2, and I is diffracted toward the vicinity of the dividing line of the light receiving areas 102a and 102b. Among them, the diffraction region I is incident as a light spot i at the center of the dividing line of the light receiving regions 102a and 102b. The diffraction areas G1 and G2 are reflected as light spots g at positions shifted by a distance Gw in the −Y direction from the light spot i on the dividing line of the light receiving areas 102a and 102b. The diffraction areas H1 and H2 are reflected as light spots h at positions shifted by a distance Gw in the + Y direction from the light spot i on the dividing lines of the light receiving areas 102a and 102b. The diffraction areas E1 and E2 are reflected as light spots e at positions shifted by a distance Gw in the −Y direction from the light spot g on the dividing line of the light receiving areas 102a and 102b. The diffraction areas F1 and F2 are reflected as light spots h at positions shifted by a distance Gw in the + Y direction from the light spots h on the dividing lines of the light receiving areas 102a and 102b. That is, five light spots on the dividing lines of the light receiving regions 102a and 102b are collected at a constant interval Gw in the ± Y direction with respect to the light spot i.

  The second conventional technique can similarly obtain the focus error signal FES, the radial error signal RES, and the reproduction signal RF. However, what greatly depends on the amplitude of the focus error signal FES is the distance of the knife edge in the + Y direction from the optical axis center O, the dimension in the + Y direction of the diffraction region from the dividing line that becomes the knife edge, and the incidence. It is a light intensity distribution of the reflected light 112 to be. Furthermore, the light spot position in the ± Y direction with respect to the dividing line of the light receiving regions 102a and 102b greatly depends on the offset (defocus amount) of the focus error signal FES.

  The focus error signals FESe and FESf to be generated are compared with the light spots e and f at positions symmetrical to the dividing lines of the light receiving regions 102a and 102b.

  Since the light spot e is focused at a position on the light receiving area 102a away from the reference line in the X direction passing through the optical axis center O by +2 Gw in the Y direction at the time of focusing, the focus error signal FESe is on the plus side. Offset. Conversely, the light spot f at a position symmetric with respect to the light spot position i is a position on the light receiving region 102b away from the reference line in the X direction passing through the optical axis center O by −2 Gw in the Y direction at the time of focusing. The focus error signal FESf is offset to the minus side.

  Further, a semiconductor laser is used as the light source 1, and the emission angle thereof has a light intensity distribution with an aspect ratio of Y direction / X direction = 1.5 to 2, so that the light spots e, f and When only the light amounts Ie and If are compared, Ie <If. Accordingly, the amplitude of the focus error signal FESf is larger than that of the focus error signal FESe, and the focus error signal FESef obtained by adding them is offset to the minus side.

  Further, when the shapes of the light spots e and f incident on the light receiving regions 102a and 102b when the objective lens 106 is moved in the + Z direction (Near side) of the focus direction from the time of focusing, the optical axis center is compared. The shape of the light spot e and the light spot f is not symmetrical with respect to the reference line in the X direction passing through O. This is because the diffraction areas E1, E2 and the diffraction areas F1, F2 have different shapes, and the Y-direction dimension Fy of the light spot f is longer than the Y-direction dimension Ey of the light spot e. Similarly, the shape of the light spots e and f incident on the light receiving regions 102a and 102b when the objective lens 106 is moved in the −Z direction (far side) of the focus direction is the same, and the Y direction of the light spot e is the same. The Y-direction dimension Fy of the light spot f is longer than the dimension Ey. Therefore, even when the light amounts Ie and If of the light spots e and f are the same, the amplitude of the FESf is larger than that of the focus error signal FESe.

  Therefore, the focus error signal FESef generated by the light spots e and f incident on the light receiving regions 102a and 102b at positions symmetrical to the Y direction with respect to the reference line passing through the optical axis center O is larger than the light spot e. As a result, the influence of the light spot f is strong, and as a result, the offset is offset to the minus side, and the amplitude is larger on the minus side than the plus side, resulting in a shape with an unbalanced balance.

  Similarly, although not shown, the same applies to the diffraction regions G and H that are symmetric with respect to the reference line in the X direction from the optical axis center O, and generated by the focus error signal FESg generated by the light spot g and the light spot h. The focus error signal FESgh, which is the sum of the focus error signals FESh, is more affected by the light spot h than the light spot g. As a result, the offset is offset to the minus side, and the amplitude is larger on the minus side than the plus side, resulting in a balance. It becomes an uneven shape. However, when the light amounts Ie to Ih of the light spots e to h are compared, since Ie <If <Ig <Ih, the influence of the focus error signal FESgh is stronger than the focus error signal FESef.

  The light spot i has the largest amount of light because the diffraction region I is in the vicinity of the optical axis center, but the distance Lh from the X axis passing through the optical axis center O to the dividing line is short, so the offset and amplitude of the focus error signal FESi. Is small.

  As described above, the focus error signal FESi has different polarities of offset and amplitude balance compared to the focus error signals FESef and FESgh, but the influence thereof is small. Therefore, the focus error signal FES obtained by adding the FESef, FESgh, and FESi. Is offset in the minus direction, and the balance of the amplitude of the FES curve is greatly shifted to the minus side. Therefore, the defocus is greatly deviated and the FES balance is also biased. Therefore, the focus servo control cannot be performed accurately and stably, and the reproduction signal cannot be detected stably.

Next, an optical pickup device according to the third prior art will be described.
The optical pickup device according to the third prior art has a structure in which the configurations of the light source 101, the light receiving element 102, and the diffraction element 103 of the optical pickup device 108 according to the first and second conventional techniques are different. FIG. 26 is a diagram illustrating a configuration of an optical pickup device 128 according to the third related art. FIG. 27 is a plan view of the composite element 121 in which the light source 130 and the light receiving elements 132 and 133 in the third prior art are integrated as seen from the optical axis direction. FIG. 28 is a plan view of the diffraction region 124 of the third prior art diffraction element 123. FIG. 29 is a characteristic diagram showing a focus error signal detected by the optical pickup device 128 according to the movement distance of the objective lens 126 in the Z direction, which is the focus direction.

  The diffractive element 123 is a circular region surrounded by a circumference centered on the center O serving as an optical axis. This circular region is defined by dividing lines 123x and 123y extending from the center O in the X direction and the Y direction, respectively. Are divided into large areas A, B, C, and D, and each area is further divided into strip-shaped areas by a plurality of straight lines extending in the Y direction. Each large area is divided into six small areas. Here, every other small area is set as Ab1, Ab2, and Ab3, and these are set as one group, and every other small area is set as Af1, Af2, and Af3, and these are set as another group. In addition, the large areas B, C, and D are similarly composed of groups of three areas. The diffractive element 123 has a polarization characteristic that transmits linearly polarized light in the X direction and diffracts linearly polarized light in the Y direction.

  In the composite element 121, a light receiving element is formed on a silicon substrate, and light emitted from the light source 130 is reflected from the Y direction to the Z direction by a rising mirror 131 formed by etching on the light receiving element. Light receiving areas 132 and 133 are provided in the ± X direction of the rising mirror 131. In the light receiving area 132, the light receiving areas FE1 to FE4 and FE5 to FE8 for detecting the focus error signal are divided into four areas in the Y direction, and the light receiving area 133 includes the light receiving areas TE1 to TE4 for detecting the radial error signal. , And divided into four regions by dividing lines in the X direction and the Y direction.

  A quarter-wave plate 124 is provided between the diffraction element 123 and the collimating lens 125.

  The light in the Y direction emitted from the light source 130 is reflected in the Z direction by the rising mirror 131 and enters the diffraction element 123. The diffractive element 123 transmits linearly polarized light L0 in the X direction, becomes circularly polarized light by the quarter wavelength plate 124, passes through the collimator lens 125 and the objective lens 126, and is irradiated onto the optical recording medium 127. The reflected light reflected by the optical recording medium 127 passes through the collimator lens 125 and the objective lens 126, passes through the quarter wavelength plate 124 again, becomes linearly polarized light in the Y direction, enters the diffraction element 123, and enters the light receiving region 132. A + 1st order diffracted light L1 diffracted toward the light receiving direction and a −1st order diffracted light L2 diffracted toward the light receiving region 133 are generated.

  In the small areas Ab1 to Ab3 of the diffractive element 123, the + 1st-order diffracted light L1 out of the incident light is condensed behind the light receiving area 132 (in the −Z direction), and on the light receiving area 132, the light receiving area FE5 and the light received. A diffraction groove is provided to form a light spot L1Ab that enters the center of the dividing line of the region FE6. In addition, in the areas Af <b> 1 to Af <b> 3 of the diffraction element 123, the incident light is collected forward (+ Z direction) from the light receiving area 132, and on the light receiving area 132, the center of the dividing lines of the light receiving areas FE <b> 5 and FE <b> 6. A diffraction groove is provided to form a light spot L1Af that is incident on the beam. The −1st-order diffracted light forms a light spot L2Ab and a light spot L2Af at symmetrical positions with respect to the center O of the diffraction element 123, and is incident on the TE1 center of the light receiving region 133, respectively.

  In the regions Bb <b> 1 to Bb <b> 3 of the diffractive element 123, the + 1st order diffracted light L <b> 1 out of the incident light is condensed behind (−Z direction) from the light receiving region 132, and on the light receiving region 132, the light receiving region FE <b> 1 and the light receiving region. A diffraction groove is provided to form a light spot L1Bb that enters the center of the dividing line of FE2. In addition, in the regions Bf <b> 1 to Bf <b> 3 of the diffraction element 123, incident light is collected forward (+ Z direction) from the light receiving region 132, and on the light receiving region 132, the center of the dividing line between the light receiving region FE <b> 1 and the light receiving region FE <b> 2. A diffraction groove is provided to form a light spot L1Bf that is incident on the beam. The −1st-order diffracted light L2 is formed with a light spot L2Bb and a light spot L2Bf at symmetrical positions with respect to the center O of the diffraction element 123, and is incident on the center of TE2 in the light receiving region 133, respectively.

  In the regions Cb <b> 1 to Cb <b> 3 of the diffractive element 123, the + 1st-order diffracted light L <b> 1 of the incident light is condensed behind (−Z direction) from the light receiving region 132, and on the light receiving region 132, the light receiving region FE <b> 1 and the light receiving region. A diffraction groove is provided to form a light spot L1Cb that enters the center of the dividing line of FE2. In addition, in the regions Cf <b> 1 to Cf <b> 3 of the diffractive element 123, incident light is collected forward (+ Z direction) from the light receiving region 132, and on the light receiving region 132, the center of the dividing line between the light receiving region FE <b> 1 and the light receiving region FE <b> 2. A diffraction groove is formed so that a light spot L1Cf that enters the light is formed. The light spot L2Cb and the light spot L2Cf are formed at symmetric positions with respect to the center O of the diffraction element 123, and the −1st order diffracted light L2 is incident on the center of TE3 of the light receiving region 133, respectively.

  In the regions Db <b> 1 to Db <b> 3 of the diffractive element 123, the + 1st-order diffracted light L <b> 1 of the incident light is condensed behind (−Z direction) from the light receiving region 132, while the light receiving region FE <b> 5 and the light receiving region are on the light receiving region 132. A diffraction groove is provided to form a light spot L1Db that enters the center of the dividing line of FE6. In addition, in the regions Df <b> 1 to Df <b> 3 of the diffraction element 123, incident light is collected forward (+ Z direction) from the light receiving region 132, and on the light receiving region 132, the center of the dividing line of the light receiving regions FE <b> 5 and FE <b> 6. A diffraction groove is provided to form a light spot L1Df that enters the light source. The −1st-order diffracted light L2 is formed with a light spot L2Db and a light spot L2Df at symmetrical positions with respect to the center O of the diffraction element 123, and is incident on the center of TE4 of the light receiving region 133, respectively.

Next, the operation principle of the optical pickup device 128 according to the third prior art will be described. Assuming that the values obtained by converting the light incident on the light receiving regions FE1 to FE8 and TE1 to TE4 into electric signals are SF1 to SF8 and ST1 to ST4, respectively, the focus error signal FES can be obtained by the following equation if the beam size method is used. Can do.
FES = {(SF1 + SF6)-(SF2 + SF5)}
-{(SF3 + SF8)-(SF4 + SF7)} (5)
If the radial error signal is a push-pull method,
RES = {(TE1 + TE2)-(TE3 + TE4)} (6)
If the DPD method can be obtained,
RES = Phase {(TE1 + TE4)-(TE2 + TE3) (7)
The light can be collected on a desired track of the optical recording medium 127 by performing servo control.

  Further, the small areas Ab1 to Ab3 each reduce the interference of the light spot L1Ab on the light receiving areas FE5 to FE8 by changing the phase of the diffracted light. Further, the small regions Af1 to Af3, the small regions Bb1 to Bb3, the small regions Bf1 to Bf3, the small regions Cb1 to Cb3, the small regions Cf1 to Cf3, the small regions Db1 to Db3, and the small regions Df1 to Df3 are similarly diffracted. By changing the phase, the interference of the light spots L1Af, L1Bb, L1Bf, L1Cb, L1Cf, L1Db, and L1Df is reduced, and the undulations of the regions NF1 and NF2 excluding between the + direction peak and the −direction peak of the focus error signal FES are reduced. To do.

Japanese Patent Laid-Open No. 2005-1000047 JP 2006-24285 A JP 2001-27710 A

  In the first conventional technique, the detection sensitivity of the focus error signal FES is lower than that in the case where the number of light spots collected on the dividing lines of the light receiving regions 102a and 102b is one, but in order to reduce the defocus amount. Therefore, it is necessary to adjust the rotation angle of the diffraction element 103 with high accuracy. Therefore, in order to reduce the variation in the defocus amount, it is necessary to introduce a highly accurate rotation adjusting device. On the other hand, if the adjustment device has low accuracy, the variation in the defocus amount increases, and defective products are likely to occur.

  In the second conventional technique, as in the first conventional technique, the detection sensitivity of the focus error signal FES is lower than that in the case where the number of light spots condensed on the dividing lines of the light receiving regions 102a and 102b is one. The light amounts of the respective light spots incident symmetrically on the light receiving regions 102a and 102b are not equal. Further, since the Y-direction dimension of each diffraction region is different, the offset and FES balance deviation of the focus error signal FES generated by each region cannot be absorbed, and as a result, the offset and FES balance are added to the focus error signal FES obtained by adding up all regions. Deviation remains and it is difficult to perform focus servo control accurately.

  In the third prior art, the undulation in the regions NF1 and NF2 excluding the + peak to −peak of the focus error signal FES is reduced, but the deviation due to the positional tolerance of the light source 130, the diffraction element 123, and the composite element 121 is reduced. A variation in focus amount cannot be suppressed, and a highly accurate assembly adjustment device is required.

  An object of the present invention is to provide a focus error detection device and an optical pickup device that can easily adjust the position of a diffraction element and can perform stable focus control.

The present invention includes a light source that emits light irradiated to an optical recording medium,
A light receiving element that receives light reflected and irradiated on the optical recording medium, and converts the received light into an electric signal to control a focus of the light irradiated on the optical recording medium, and is firstly divided by a dividing line. A light receiving element including a focus light receiving region divided into a light receiving region and a second light receiving region;
A part of the reflected light reflected by the optical recording medium is diffracted, and in a focused state, a first diffraction region that forms a spot on the dividing line, and another part of the reflected light is received by the first light reception. The first light-receiving region symmetrical to the spot on the dividing line formed by diffracting toward the region and the second light-receiving region and being diffracted by the dividing line and the first diffraction region in a focused state A second diffraction region that forms a spot at a position with respect to the second light receiving region, a first region including the first diffraction region and the second diffraction region that passes near the center of the optical axis, and a region other than the one region A diffractive element including a boundary line between the first diffraction area and the second diffraction area that is at least partially shared as an outer edge. Detection equipment It is.

  In the invention, it is preferable that the first diffraction region diffracts light at a central portion of the reflected light.

  In the invention, it is preferable that the second diffraction region diffracts the other part of the reflected light toward the first light receiving region and a plurality of first belt-shaped regions that are diffracted toward the first light receiving region. And a plurality of second belt-like regions.

  In addition, the present invention is characterized in that the band-like regions are provided so as to have different areas.

  Further, the present invention is characterized in that the first belt-like region and the second belt-like region are alternately arranged.

  Further, the present invention is characterized in that the first belt-like region and the second belt-like region are arranged adjacent to each other.

  According to the present invention, the first belt-shaped region and the second belt-shaped region include one region including the first diffraction region and the second diffraction region, the extending direction passing through the center of the optical axis, and the other region than the one region. It is provided so as to be orthogonal to the boundary line with the other area, which is the area of the above, or to form an angle of 30 ° to 150 ° with the boundary line.

  The present invention also provides a spot shape formed in the focus light receiving region when the first belt region and the second belt region are not in focus and the focal point is located on the light source side with respect to the optical recording medium. And the spot shape formed in the focus light receiving region when the focal point is located on the opposite side of the light source with respect to the optical recording medium is on the dividing line formed by being diffracted by the dividing line and the first diffraction region. It is provided to be symmetrical with respect to the spot.

  According to the present invention, the light source is configured to be capable of emitting light of a plurality of types of wavelengths, and the first diffraction region and the second diffraction region are a plurality of types of diffraction regions that diffract light of different wavelengths. It is characterized by comprising.

  Further, the present invention is characterized in that the diffraction regions constituting the first diffraction region are provided so as to diffract light of different wavelengths to form spots at the same position on the dividing line.

  According to the present invention, the diffraction regions constituting the second diffraction region diffract light of at least one wavelength among light of different wavelengths, and form spots at positions symmetrical to the dividing line, respectively. It is provided as follows.

  In the invention, it is preferable that the diffraction regions constituting the second diffraction region are provided so that the distances from the dividing line of spots formed at positions symmetrical to the dividing line are different for each wavelength. It is characterized by.

  Further, the present invention is characterized in that the diffraction regions constituting the second diffraction region are provided so that defocus amounts of spots respectively formed at positions symmetrical to the dividing line are different for each wavelength. To do.

Further, the present invention is characterized in that a focus error is detected by a knife edge method.
Further, the present invention is characterized in that a focus error is detected by a beam spot method.
According to another aspect of the present invention, there is provided an optical pickup device comprising the above-described focus error detection device.

  According to the present invention, the light receiving element includes a focus light receiving area that is divided into a first light receiving area and a second light receiving area by a dividing line, and the diffractive element is emitted from the light source in the focused state, and the optical element A first diffraction area that diffracts part of the reflected light reflected by the recording medium to form a spot on the dividing line, and another part of the reflected light, the first light receiving area and the second light receiving area. And a second diffraction region that forms a spot at a position symmetrical to the spot on the dividing line and the dividing line formed by being diffracted by the first diffraction region. The diffractive element has a boundary line between one region including the first diffractive region and the second diffractive region passing through the vicinity of the center of the optical axis and the other region other than the one region. In the line, the first diffraction region and the second diffraction region are at least partially shared as an outer edge.

  As a result, the intensity distribution of the reflected light in the light receiving element becomes a symmetrical intensity distribution with respect to the dividing line, and does not require a high-accuracy rotation adjustment device and is stable by suppressing the offset of the focus error signal FES and the FES balance deviation. Focus control can be performed.

  Further, according to the present invention, the first diffraction region diffracts the light at the central portion of the reflected light, so that the amount of light to be formed increases, and the decrease in the amplitude of the focus error signal FES can be prevented.

  According to the invention, the second diffraction region has a plurality of first band-like regions that diffract another part of the reflected light toward the first light receiving region, and toward the second light receiving region. A plurality of second belt-shaped regions to be diffracted.

  As a result, the spot shape formed by diffracting by the second diffraction region becomes a shape extending in a direction orthogonal to the dividing line, so that a decrease in the amplitude of the focus error signal FES can be prevented and rotation adjustment can be performed. Thus, the influence of displacement of the light source, the light receiving element, and the diffraction element can be reduced.

  Further, according to the present invention, since the belt-like regions are provided so as to have different areas, the defocus amount of the spot formed by diffracting can be made different for each region, and the spot shape is further extended. As a result, it is possible to further reduce the offset of the focus error signal FES.

  Further, according to the present invention, since the first belt-like region and the second belt-like region are alternately arranged, the amount of light received by each of the first light-receiving region and the second light-receiving region can be reduced. The bias is reduced, and the offset of the focus error signal FES and the FES balance deviation can be further suppressed.

  According to the invention, the first belt-like region and the second belt-like region are arranged adjacent to each other. Thereby, even if the objective lens moves in the radial direction and the spot position fluctuates, the difference in the amount of light diffracted in the adjacent region is small, so that each of the first light receiving region and the second light receiving region The deviation of the amount of received light is reduced, and the offset of the focus error signal FES and the FES balance deviation can be further suppressed.

  Further, according to the present invention, the extending direction of the first belt-like region and the second belt-like region is perpendicular to the knife edge or forms an angle of 30 ° or more and 150 ° or less with the knife edge. Provided.

  One region including the first diffraction region and the second diffraction region, in which the extending direction of the first belt region and the second belt region passes through the center of the optical axis, and the other region that is a region other than the one region If it is parallel to the boundary line, the amount of light received by each of the first light receiving region and the second light receiving region is biased, but it is orthogonal or forms an angle of 30 ° to 150 °. If provided in such a manner, the light quantity is not biased, and the noise of the focus error signal curve can be reduced.

  According to the invention, the first belt-like region and the second belt-like region are formed in the focus light-receiving region when the focal point is located on the light source side with respect to the optical recording medium in a state where it is not in focus. A division formed by diffracting the spot shape and the spot shape formed in the focus light receiving region when the focal point is located on the side opposite to the light source with respect to the optical recording medium, by the dividing line and the first diffraction region It is provided so as to be symmetric with respect to the spot on the line.

  As a result, the spot shapes formed in each of the first light receiving region and the second light receiving region extend in directions opposite to each other in the direction orthogonal to the dividing line, so that the focal depth of the spot is increased and the focus is increased. The error signal FES offset and FES balance deviation can be suppressed.

  According to the invention, the light source is configured to be capable of emitting light of a plurality of types of wavelengths, and the first diffraction region and the second diffraction region are a plurality of types of light that diffract light of different wavelengths. It consists of a diffraction region.

  Accordingly, for example, it is possible to cope with a plurality of types of optical recording media having different wavelengths of light irradiated for reproduction.

  Further, according to the present invention, the diffraction regions constituting the first diffraction region are provided so as to diffract light of different wavelengths and form spots at the same position on the dividing line. As a result, the position of the diffraction element can be adjusted with light of any one type of wavelength.

  According to the invention, the diffraction region constituting the second diffraction region diffracts light of at least one wavelength among light of different wavelengths, and sets spots at positions symmetrical to the dividing line. It is provided to form. As a result, when light having a wavelength other than that used for position adjustment of the diffractive element is irradiated, it is possible to obtain an effect that the spot shape is further extended and the depth of focus is longer, so that the offset of the focus error signal FES is reduced. Further reduction is possible.

  According to the invention, the diffraction region constituting the second diffraction region is provided such that the distance from the dividing line of each spot formed at a position symmetrical to the dividing line differs for each wavelength. It is done. As a result, it is possible to perform stable focus control while suppressing the offset of the focus error signal FES and the FES balance deviation for the light irradiated from the center of the optical axis such as the objective lens.

  According to the invention, the diffraction regions constituting the second diffraction region are provided such that the defocus amounts of the spots formed at positions symmetrical to the dividing line are different for each wavelength. Thereby, even with respect to the light irradiated from the center of the optical axis such as the objective lens, stable focus control can be performed by further suppressing the offset of the focus error signal FES and the FES balance deviation.

  Further, according to the present invention, when the knife edge method is used, the dividing line serving as the knife edge of the first diffraction region and the second diffraction region is arranged on the common straight line so that the boundary line serving as the knife edge is disposed. Stable focus control can be performed by suppressing the offset of the focus error signal FES and the FES balance deviation generated by the spots diffracted in the first diffraction region and the second diffraction region.

According to the present invention, when the beam spot method is used, a plurality of near-side and far-side spots incident on the first light receiving region and the second light receiving region are formed at positions symmetrical to the dividing line of the light receiving element. By doing so, it is possible to perform stable focus control while suppressing the offset and FES balance deviation of the generated focus error signal FES.
In addition, according to the present invention, it is possible to provide an optical pickup device capable of performing stable focus control by including the above-described focus error detection device.

FIG. 1 is a schematic diagram showing a configuration of an optical pickup device 8 according to the first embodiment of the present invention. It is a top view showing the relationship between the diffraction element 4 among each example of the focus error detection apparatus contained in 1st Embodiment, and each light reception area | region of the light receiving element 2 which the light diffracted by this arrives. In the first embodiment, when the light condensed by the objective lens 6 is condensed on the optical recording medium 7 and when it moves to the plus side / minus side in the Z direction which is the focus direction from the position, A plan view showing the shape of a light spot incident on the diffraction element 4 and the light receiving element 2 and a characteristic diagram of the focus error signal FES detected according to the Z-direction movement distance of the objective lens 6 are shown in FIG. It is the figure represented independently for every area | region. FIG. 6 is a characteristic diagram of the focus error signal FES, and shows that the characteristics differ for each rotation adjustment angle of the diffraction element 8. It is a schematic diagram which shows the structure of the optical pick-up apparatus 28 which concerns on 2nd Embodiment of this invention. It is the top view which looked at the arrangement configuration of the light source 21 and the light receiving element 22 from the optical axis direction. Of the example of the focus error detection device included in the second embodiment, the diffraction element 24 when the light source 21 emits light of the first wavelength, and the light receiving regions of the light receiving element 22 where the light diffracted thereby reaches, It is a top view showing the relationship. Of the example of the focus error detection device included in the second embodiment, the diffraction element 24 when the light source 21 emits light of the second wavelength, and the light receiving regions of the light receiving element 22 where the light diffracted thereby reaches, It is a top view showing the relationship. It is a schematic diagram when the light which injects into the light receiving element 22 is seen from the direction orthogonal to an optical axis direction. In the second embodiment, when the light collected by the objective lens 26 is collected on the optical recording medium 27 and moved to the plus side / minus side in the Z direction, which is the focus direction from the position, 3 is a plan view showing the shape of a light spot that falls on the diffraction element 24 and the light receiving element 22. FIG. FIG. 11 is a characteristic diagram of a focus error signal FES in which all the focus error signals FES for each diffraction area shown in FIG. 10 are collected, and a focus error signal FES detected according to a movement distance of the objective lens 26 in the Y direction that is a focus direction. It is the characteristic view which represented for every wavelength. It is a schematic diagram showing the structure of the optical pick-up apparatus 48 which concerns on 3rd Embodiment of this invention. It is the top view which looked at the arrangement configuration of the light source 41 and the light receiving element 42 from the optical axis direction. In 3rd Embodiment, it is a top view showing the relationship between the diffraction element 44 when the light source 41 radiate | emits the light of 1st wavelength, and each light reception area | region of the light receiving element 42 which the light diffracted by this arrives. In 3rd Embodiment, it is a top view showing the relationship between the diffraction element 44 when the light source 41 radiate | emits the light of 2nd wavelength, and each light reception area | region of the light receiving element 42 which the light diffracted by this arrives. In 3rd Embodiment, it is a top view showing the relationship between the diffraction element 44 when the light source 41 radiate | emits the light of the 3rd wavelength, and each light reception area | region of the light receiving element 42 which the light diffracted by this arrives. It is a figure showing the structure of the optical pick-up apparatus 68 which concerns on 4th Embodiment. It is the top view which looked at the composite element 61 with which the light source 70 and the light receiving elements 72 and 73 in 4th Embodiment were united from the optical axis direction. It is a top view of the diffraction area 64 of the diffraction element 63 of 4th Embodiment. It is a figure showing the structure of the optical pick-up apparatus 108 which concerns on a 1st prior art.

It is a top view of the diffraction area 104 of the diffraction element 103 in the 1st prior art, and the light receiving element 102. FIG. 6 is a characteristic diagram showing a focus error signal (hereinafter abbreviated as FES) detected in accordance with the movement distance in the Z direction, which is the focus direction of the objective lens 106, in the first conventional optical pickup device. It is a top view of the diffraction area | region 116 and the light receiving element 102 of the diffraction element 103 in a 2nd prior art. The focal point of the objective lens 106 matches the optical recording medium with two light spots e and f out of the three light spots incident on the light receiving areas 102a and 102b, and two types of diffracted diffraction areas. The figure which shows the state at the time of having been blurred, and the characteristic figure showing the focus error signal obtained from each are shown for every diffraction area | region. FIG. 10 is a characteristic diagram showing a focus error signal FES detected in accordance with the movement distance in the Z direction that is the focus direction of the objective lens 106 in the second conventional optical pickup device. It is a figure showing the structure of the optical pick-up apparatus 128 which concerns on a 3rd prior art. It is the top view which looked at the composite element 121 with which the light source 130 and the light receiving elements 132 and 133 in 3rd prior art were united from the optical axis direction. It is a top view of the diffraction area 124 of the diffraction element 123 of the 3rd prior art. 6 is a characteristic diagram showing a focus error signal detected by the optical pickup device 128 according to a movement distance in the Z direction that is a focus direction of the objective lens 126. FIG.

  Hereinafter, a plurality of modes for carrying out the present invention will be described with reference to the drawings. In the following description, parts corresponding to items already described in the forms preceding each form may be denoted by the same reference numerals, and overlapping descriptions may be omitted. When only a part of the configuration is described, the other parts of the configuration are the same as those described in the preceding section. In addition to the combination of parts specifically described in each embodiment, the embodiments may be partially combined as long as the combination is not particularly troublesome. Moreover, each embodiment is illustrated in order to embody the technique which concerns on this invention, and does not limit the technical scope of this invention. The technical contents according to the present invention can be variously modified within the technical scope described in the claims.

(First embodiment)
FIG. 1 is a schematic diagram showing a configuration of an optical pickup device 8 according to the first embodiment of the present invention. FIG. 2 is a plan view showing the relationship between the diffraction element 4 and each light receiving region of the light receiving element 2 to which the light diffracted thereby reaches in the example of the focus error detection apparatus included in the first embodiment. FIG. 3 shows that in the first embodiment, when the light collected by the objective lens 6 is collected on the optical recording medium 7 and moved to the plus / minus side in the Z direction, which is the focus direction from that position. The plan view showing the shape of the light spot incident on the diffraction element 4 and the light receiving element 2 and the characteristic diagram of the focus error signal FES detected according to the movement distance of the objective lens 6 in the Z direction are diffracted. FIG. 5 is a diagram independently representing each diffraction region of the element 4. FIG. 4 is a characteristic diagram of the focus error signal FES in which all the focus error signals FES for each diffraction region shown in FIG. 3 are combined. The characteristic diagram shows that the characteristics are different for each rotation angle of the diffraction element 4. is there.

  The optical pickup device 8 is a device that irradiates the optical recording medium 7 with light and receives reflected light from the optical recording medium 7 in order to read information recorded on the optical recording medium 7.

  In the first embodiment, the optical pickup device 8 optically records a light source 1 composed of a semiconductor laser, a collimating lens 5 for converting emitted light into parallel light, and a light beam converted into parallel light by the collimating lens 5. The objective lens 6 that condenses the light toward the medium 7, the light receiving element 2, and the hologram element 3 provided with the diffraction element 4 are configured.

  The light source 1 emits light to be irradiated on the optical recording medium 7. In the light receiving element 2, a plurality of light receiving regions are formed, a part of the plurality of light receiving regions is used as the focus light receiving regions 2a and 2b, and the other part is used as the radial light receiving regions 2c and 2d. The focus light receiving areas 2a and 2b are used for focus servo control, and the radial light receiving areas 2c and 2d are used for radial servo control. The diffractive element 4 has a function of diffracting the reflected light 12 from the optical recording medium 7 toward the light receiving element 2 and has a diffraction region divided into a plurality of parts, and a part of the reflected light is reflected light. 12 is used as a diffraction region for diffracting 12 toward the focus light receiving regions 2a and 2b.

  In FIG. 1, the optical axes of a plurality of optical components that guide light emitted from the light source 1 to the optical recording medium 7 are arranged on one straight line. Hereinafter, the optical axis direction of the light emitted from the light source 1 is simply referred to as “optical axis direction” (Z direction). The objective lens 6 and the collimating lens 5 are arranged so that their centers pass through the optical axis. FIG. 2 shows the diffraction element 4 and the light receiving element 2 as viewed in the Z direction.

  A condensing point where light emitted from the light source 1 is condensed on the recording surface of the optical recording medium 7 is located on a track formed on the recording surface. The tangential direction at the condensing point of this track is referred to as “tangential direction” (Y direction). Similarly, the directions in the diffraction element 4 and the light receiving element 2 corresponding to the tangential direction at the focal point of the track will be described as “tangential direction” (Y direction). A direction perpendicular to the Z direction and perpendicular to the Y direction is defined as a “radial direction” (X direction).

  The light receiving element 2 is disposed at a position away from the light source 1 in the X direction. Of the radial directions, the direction from the light source 1 toward the light receiving element 2 is the + X direction, and the opposite direction is the -X direction. Further, with respect to the dividing line 9 on the diffraction element 4 passing through the optical axis center O in the tangential direction, the direction toward the focus diffraction regions E to G is the + Y direction, and the opposite direction is the −Y direction. To do.

  The diffraction element 4 includes a radial diffraction region formed in the −Y direction and a + Y direction in a circular outer edge with a dividing line 9 that is a straight line parallel to the X direction passing through the center O serving as the optical axis. And a focus diffraction region. Further, the radial diffraction region is composed of a diffraction region C in the −X direction and a diffraction region D in the + X direction, with a dividing line 11 extending from the center O in the −Y direction as a boundary. The focus diffraction region is composed of a plurality of strip-shaped diffraction regions E, F, and G that are bordered by a plurality of division lines 10 extending from the division line 9 in the + Y direction orthogonal to the division line 9 at a predetermined interval.

  Only one diffraction region E is arranged at the center of the focus diffraction region so that the optical axis center O is positioned at the center in the width direction. The diffraction region F and the diffraction region G are alternately arranged in the order of the diffraction region F and the diffraction region G from the diffraction region E in the −X direction and with the same width in the X direction, and from the diffraction region E to the + X direction. On the other hand, the diffraction regions G and F are alternately arranged in this order and with the same width in the X direction.

  The X-direction widths of the diffraction area E, the diffraction area F, and the diffraction area G are all set to the same width. Accordingly, each of the diffraction regions E to G has a configuration including a boundary line that shares the dividing line 9. The width in the X direction is set such that at least two or more diffraction regions F or G are included in the radius of the light spot when the reflected light 12 enters the diffraction element 4. Further, in each of the diffraction regions E to G, a plurality of concave and convex diffractive grooves are formed in parallel or close to each other in a periodic manner, and these diffractive grooves are formed in one diffractive region. The width in the X direction is such that five or more are arranged. These diffraction regions C to G diffract the + 1st order diffracted light by directing the reflected light 12 from the optical recording medium 7 toward the light receiving regions 2a to 2d for signal detection, respectively.

  The light receiving element 2 includes focus light receiving areas 2a and 2b arranged in the + X direction with respect to the diffraction element 4, a radial light receiving area 2c arranged in the + Y direction with respect to the focus light receiving areas 2a and 2b, and a focus light receiving area 2a. 2b, and a radial light receiving region 2d arranged in the -Y direction with respect to 2b. A dividing line serving as a boundary between the focus light receiving region 2a that is the first light receiving region and the focus light receiving region 2b that is the second light receiving region is provided in parallel with the X direction or inclined by an angle α with respect to the X direction. . The inclination angle α varies with the wavelength variation of the light source 1, and the diffraction angle when diffracted in the diffraction region varies, and the shape of the light spot incident on the dividing line of the light receiving regions 2a and 2b becomes large and deforms. This is an angle for inclining the dividing line to absorb the offset generated in the focus error signal FES caused by the influence.

  The outer dimensions of the light receiving regions 2a to 2d are set so that the length in the X direction is longer than the length in the Y direction. This is because, in the arrangement of the light source 1, the light receiving element 2 and the diffraction element 4, when the position in the Z direction is shifted, the position of the light spot condensed on the light receiving element 2 is shifted in the X direction due to the wavelength shift of the light source 1. This is to move. The positional deviation in the Y direction can be adjusted by adjusting the diffractive element 4 to move horizontally in the Y direction within the XY plane, and further rotating the optical axis about the rotation axis.

  When the reflected light 12 from the optical recording medium 7 is incident on the diffraction element 4, the light incident on the diffraction areas C and D is diffracted so as to be incident on the light receiving areas 2c and 2d. The light incident on the diffraction regions E to G is diffracted so as to be incident toward the vicinity of the dividing line between the light receiving region 2a and the light receiving region 2b. Of the diffracted light diffracted by the diffraction regions E to G, the light diffracted by the band-shaped diffraction region E defined as the first diffraction region is 1 as a light spot e at the center of the dividing line of the light receiving regions 2a and 2b. It falls on the spot to concentrate. Of the band-like diffraction regions F and G defined as the second diffraction region, the light diffracted by the diffraction region F is collected at one point as a light spot f at a position −Ty in the + Y direction from the light spot e. It is reflected in the light. Of the band-like diffraction regions F and G defined as the second diffraction region, the light diffracted by the diffraction region G is one point as a light spot g at a position + Ty in the −Y direction from the light spot e. It falls on the light to concentrate.

  As an optical recording medium 7 capable of recording or reproducing information, a compact disc (abbreviation “CD”), a digital versatile disc (abbreviation “DVD”), and a Blu-ray disc (abbreviation). “BD”: registered trademark). In the first embodiment, any one of these may be used. In the CD, light in the infrared region near 780 nm is used for recording and reproducing information. DVD uses light in the red region near 650 nm for recording and reproducing information. In BD, light in the blue-violet region near 405 nm is used for recording and reproducing information. Further, the optical recording medium 7 may have a larger capacity in which a plurality of recording layers are stacked.

  In order to perform focus servo control and tracking servo control on the optical recording medium 7, the optical signal of the light received in the light receiving area on the light receiving element 2 is converted into an electrical signal, and the servo signal is detected. Focus servo control and tracking servo control are performed based on detection results of these servo signals. A knife edge method is used for focus servo control. For radial servo control, a DPD method (differential phase detection method), a push-pull method (push-pull method), or the like is used depending on the type of the optical recording medium 7.

  Next, the operation principle of the optical pickup device 8 according to the first embodiment will be described. Assuming that the values obtained by converting the light incident on the light receiving areas 2a to 2d into electrical signals are Sa, Sb, Sc, and Sd, the servo signal generator at the subsequent stage generates the focus error signal FES and the radial error signal RES. Based on these servo signals, the servo signal processing unit performs focus servo control and radial servo control. By the focus servo control and the radial servo control, the position of the objective lens 6 in the focus direction and the track direction is controlled by the actuator so that the focal point of the objective lens 6 follows a predetermined track of the optical recording medium 7. These are realized by a servo signal generator, a servo signal processor, and a drive controller that controls the actuator.

Specifically, the focus error signal FES can be obtained by the following equation.
FES = Sa−Sb (8)
Further, if the radial error signal RES is a push-pull method,
RES = Sc-Sd (9)
If the DPD method can be obtained,
RES = Phase (Sc-Sd) (10)
By performing servo control, light can be condensed on a desired track of the optical recording medium 7.

Furthermore, the reproduction signal RF is
RF = Sa + Sb + Sc + Sd (11)
By performing the above calculation, the reproduction signal RF of the track can be reproduced.

  If the electric signal amount of the focus error signal FES obtained here is the vertical axis and the movement distance (hereinafter referred to as defocus amount) in the Z direction that is the focus direction of the objective lens 6 is the horizontal axis, the FES as shown in FIG. A curve (hereinafter referred to as FES curve) is obtained. When the intersection with the horizontal axis of the FES curve is greatly deviated from the defocus amount = 0 to, for example, 1 μm or more, the position of the objective lens 6 in the Z direction, which is the focus direction, is deviated by the distance, and collected on the optical recording medium 7. The light condensing point is blurred and a stable RF signal cannot be reproduced. Further, when the light is focused on the optical recording medium 7, the vicinity of the intersection with the horizontal axis of the FES curve is linear, and focus servo control is performed so that the focus servo is always drawn at the intersection.

  Further, the FES curve detects a focus error signal by a knife edge method using a dividing line 9 serving as a common boundary line of the diffraction regions E to G as a knife edge.

  First, the focus error signal FESe generated only from the light spot e diffracted in the diffraction region E of the diffraction element 4 will be described. The light spot e is focused in a dot shape on an extension of the reference line in the X direction passing through the optical axis center O in a state where the light spot e is focused on the optical recording medium 7. Further, when the objective lens 6 is moved from the in-focus state in the + Z direction of the focus direction (a direction approaching the optical recording medium 7 and set to the Near side), the light spot e incident on the light receiving regions 2a and 2b becomes a knife edge. With the dividing line 9 as a boundary, the light spot shape is inverted in the −Y direction and incident on the light receiving region 2a. Therefore, no light is incident on the light receiving region 2b, and light is incident only on the light receiving region 2a side. On the contrary, when the objective lens 6 is moved from the in-focus state in the −Z direction of the focus direction (the direction away from the optical recording medium 7, the Far side), the light spot incident on the light receiving regions 2 a and 2 b becomes a knife edge. With the dividing line 9 as a boundary, the light spot remains in its shape without being inverted in the −Y direction. For this reason, light does not enter the light receiving region 2a, and light enters only the light receiving region 2b.

  The shape of the diffraction region E is a substantially rectangular shape in which one side opposite to the dividing line 9 is an arc shape. When the position of the objective lens 6 is further shifted in the near direction, the shape of the light spot e on the light receiving region 2a. The shape further extends in the −Y direction. At the point where the arc-shaped side reaches the end of the light receiving region 2a, the positive amplitude of the focus error signal FESe becomes maximum, and when it protrudes from the end of the light receiving region 2a, the focus error signal FESe gradually decreases. Similarly, when the position of the objective lens 6 is further shifted in the Far direction, the shape of the light spot e on the light receiving region 2b becomes a shape further extending in the + Y direction. When the arc-shaped side reaches the end of the light receiving region 2b, the negative amplitude of the focus error signal FESe becomes maximum, and when it protrudes from the end of the light receiving region 2b, the focus error signal FESe gradually decreases.

  Therefore, the FES curve of the focus error signal FESe generated only with the light spot e has no offset, and the amplitudes on the plus side and the minus side are the same, resulting in a well-balanced curve shape.

  Next, the focus error signal FESf generated only from the light spot f diffracted by the diffraction region F of the diffraction element 4 will be described. The light spot f is focused in a dotted manner on an extension that is shifted by −Ty in the Y direction from the reference line in the X direction passing through the optical axis center O in a state of being focused on the optical recording medium 7. Further, similarly to the light spot e, when the objective lens 6 is moved in the near direction from the focused state, the light spot f incident on the light receiving regions 2a and 2b is from the reference line in the X direction passing through the optical axis center O. A light spot shape that is inverted in the −Y direction and incident on the light receiving region 2a with the dividing line 9 serving as a knife edge at a position shifted by −Ty in the Y direction as a boundary. Therefore, no light is incident on the light receiving region 2b, and light is incident only on the light receiving region 2a side. Conversely, when the objective lens 6 is moved in the Far direction from the in-focus state, the light spot incident on the light receiving areas 2a and 2b is not reversed in the -Y direction with the dividing line 9 serving as the knife edge as a boundary. The light spot remains in its shape, and light is incident on a base point that is a position in the light receiving region 2 a that is shifted by −Ty in the Y direction from the X-direction reference line passing through the optical axis center O.

  Since the shape of the diffraction region F is a strip shape with a semicircle as the outer edge, if the position of the objective lens 6 in the focus direction is further shifted in the near direction, the light spot f on the light receiving region 2a is -Y from the base point. When the outer edge reaches the end of the light receiving region 2a, the plus side amplitude FESP of the focus error signal FESf becomes maximum, and when it protrudes from the end of the light receiving region 2a, the focus error signal FESf gradually increases. To drop. Similarly, when the position of the objective lens 6 is further shifted in the Far direction from the in-focus state, the shape of the light spot f on the light receiving region 2b becomes a shape further extending in the + Y direction from the base point. When the objective lens 6 further shifts in the Far direction, the shape of the light spot f exceeds the dividing line of the light receiving areas 2a and 2b and enters the light receiving area 2b. When the outer edge reaches the other end of the light receiving region 2b, the minus side amplitude FESM of the focus error signal FESf becomes maximum, and when the outer edge protrudes from the end of the light receiving region 2b, the focus error signal FESf gradually decreases.

  Therefore, the FES curve of the focus error signal FESf generated only by the light spot f is offset to the minus side (defocus amount = −βf). Further, since the light spot f when shifted in the Far direction straddles the light receiving regions 2a and 2b, the peak of the amplitude of the focus error signal FESf when shifted in the Far direction is larger than that when shifted in the Near direction. The absolute value becomes smaller. Therefore, the positive side amplitude is larger than the negative side amplitude, and the curve shape is out of balance.

"FES-B" which shows FES balance is
FES-B = (FESP-FESM) / (FESP + FESM) (12)
And FES−B = + γ.

  Similarly, the focus error signal FESg generated only from the light spot g diffracted from the diffraction region G of the diffraction element 4 will be described. The light spot g is focused in the form of dots on an extension shifted by + Ty in the Y direction from the reference line in the X direction passing through the optical axis center O in a state of being focused on the optical recording medium 7. Further, similarly to the light spot e, when the objective lens 6 is moved in the Far direction from the in-focus state, the light spot g incident on the light receiving regions 2a and 2b is from the reference line in the X direction passing through the optical axis center O. With the dividing line 9 serving as the knife edge at a position shifted by + Ty in the Y direction as a boundary, the light spot remains in its shape without being inverted, and no light is incident on the light receiving region 2a, but only on the light receiving region 2b side. Is incident. Conversely, when the objective lens 6 is moved in the near direction from the focused state, the light spot incident on the light receiving regions 2a and 2b has a shape reversed in the −Y direction with the dividing line 9 serving as a knife edge as a boundary. There is incident light whose base point is a position in the light receiving region 2b that is shifted by + Ty in the Y direction from the reference line in the X direction passing through the optical axis center O.

  Since the shape of the diffraction region G is a strip shape with a semicircle as an outer edge, when the position of the objective lens 6 is further shifted in the Far direction, the light spot g on the light receiving region 2b becomes a semicircle with reference to the base point. The strip shape with the outer edge extending in the + Y direction further extends in the + Y direction, and at the point where the outer edge reaches the end of the light receiving region 2b, the minus side amplitude FESM of the focus error signal FESg is minimized and protrudes from the end of the light receiving region 2b. Then, the focus error signal FESg gradually increases. Similarly, when the position of the objective lens 6 is further shifted in the Near direction from the focused state, the shape of the light spot g on the light receiving region 2b is a strip shape with a semicircle as an outer edge based on the base point in the -Y direction. The shape further extends. When the objective lens 6 further shifts in the near direction, the light spot g passes the dividing line of the light receiving areas 2a and 2b and enters the light receiving area 2a. When the outer edge reaches the other end of the light receiving area 2a, the plus-side amplitude FESP of the focus error signal FESg becomes maximum, and when it protrudes from the end of the light receiving area 2a, the focus error signal FESg gradually decreases.

  Therefore, the FES curve of the focus error signal FESg generated only from the light spot g is offset to the plus side (defocus amount = + βg). Further, since the light spot g when shifted in the Near direction straddles the light receiving region 2a and the light receiving region 2b, the amplitude peak of the focus error signal FESg when shifted in the Near direction is shifted in the Far direction. Rather than the absolute value. Therefore, the negative side amplitude FESM becomes larger than the positive side amplitude FESP, resulting in a curve shape out of balance. FES-B is obtained by the above equation (12), and FES-B = −γg.

  Here, the light spot e is incident on the dividing line of the light receiving regions 2a and 2b, and the light spots f and g are incident on symmetrical positions in the ± Ty direction from the position, and the ends of the light receiving regions 2a and 2b in the Y direction. Are at the same distance from the center of the dividing line, and the diffraction regions F and G have the same Y-direction dimension in the region obtained by dividing the diffraction element 4 into a plurality of defocuses generated in the focus error signals FESf and FESg. The absolute values βf and βg of the quantities become equal, and the absolute values γf and γg of FES-B become equal.

Therefore, the focus error signal FES by all the focus diffraction regions E to G is expressed by the following formula (13), and the defocus amount and the FES balance almost cancel each other, so that the generated defocus amount and the FES balance are biased. As a result, the focus servo control can be performed stably, and as a result, the reproduction signal can be detected stably.
FES = FESE + FESf + FESg (13)

  However, the photoelectric conversion sensitivities Ma and Mb of the light receiving regions 2a and 2b with respect to the Y direction position of the dividing line of the light receiving regions 2a and 2b are equal to Ma = Mb at the center of the dividing line, respectively, but if it shifts in the + Y direction, Ma <Mb, and when it shifts to a certain position, the photoelectric conversion sensitivity Ma of the light receiving region 2a becomes 0, and the photoelectric conversion sensitivity Mb of the light receiving region 2b becomes maximum. Conversely, when it shifts in the -Y direction, Ma> Mb, and when it shifts to a certain position, the photoelectric conversion sensitivity Mb of the light receiving region 2b becomes 0, and the photoelectric conversion sensitivity Ma of the light receiving region 2a becomes maximum.

  The distance Ty in the Y direction of the light spots f and g far from the light spot e takes too large values, for example, the absolute value of the defocus βf of the focus error signal FESf and the absolute value of the defocus βg of the focus error signal FESg. However, if the focus error signals are too far apart so as to exceed the plus and minus peaks of the focus error signal amplitude, the FES curve of the focus error signal FES has a secondary peak. Such a peak becomes noise, and stable focus servo control cannot be performed. Therefore, it is preferable to provide the Y-direction position Ty where the light spots f and g fall off at a position where the light conversion sensitivity does not become zero.

  Further, when the shape of the diffraction region is such that the light amount difference between the light spots f and g is large, or when the boundary line serving as the knife edge is at a different position, the focus error generated by each of the light spots f and g. The defocus amount, which is the opposite polarity of the signals FESf and FESg, deviates from the absolute value of the FES balance amount, and the focus error signal FES is defocused and FES balanced, which makes stable focus servo control impossible. .

  For this reason, the apparent light spots f and g incident on the light receiving regions 2a and 2b have the strongest light intensity distribution at the center of the dividing line and extend long in the Y direction, which is approximately perpendicular to the dividing line direction, and By making the light spot having a substantially symmetrical light intensity distribution, the optical arrangement deviation of the light source 1, the light receiving element 2, and the diffraction element 4, the defocus deviation of the focus error signal FES with respect to the wavelength deviation of the light source 1, and the FES balance deviation are caused. , Less likely to occur.

  For example, when the rotation adjustment angle of the diffraction element 4 is θ, the tolerance of the amount of defocus that occurs is large with respect to θ. When the number of light spots on the dividing line of the light receiving regions 2a and 2b is one point, the first adjustment is made as compared with the case where the rotation adjustment angle θ of the diffraction element 4 is ± 1 degree and the defocus amount is ± 0.7 μm. In the optical pickup device 8 according to the embodiment, when the rotation adjustment angle θ of the same diffraction element 4 is ± 1 degree, the defocus amount is ± 0.5 μm, and the defocus amount with respect to the rotation adjustment angle θ can be reduced.

  Further, in the optical pickup device 8 of the first embodiment, three light spots are generated in the vicinity of the dividing lines of the light receiving regions 2a and 2b, and are symmetrically positioned in the Y direction with respect to the central light spot e. Although the auxiliary light spots f and g are arranged, when the positions of the light spots f and g are shifted only in the Y direction, the light spots are almost the same as the dividing line direction of the light receiving regions 2a and 2b. The FES curves of the focus error signals FESf and FESg generated from f and g are substantially the same as the FES curve of the focus FESe generated at the light spot e. Therefore, the defocus amount and the FES balance are almost the same, and there is not much difference from the characteristics of the focus error signal FES when there is one light spot.

  That is, the apparent light spot incident on the dividing line of the light receiving regions 2a and 2b is only elongated in the same direction as the dividing line of the light receiving regions 2a and 2b, so that the light source 1, the light receiving element 2, and the diffraction element 4 The change in the optical arrangement deviation, the defocus deviation of the focus error signal FES with respect to the wavelength deviation of the light source 1, and the FES balance deviation are small compared to the case where there is one light spot.

  In the above description, the diffraction region E having the strongest light intensity distribution in the focus diffraction region of the diffraction element 4 has only one configuration. However, the present invention is not limited to this, and the Y-direction axis passing through the center O is not limited thereto. A plurality of regions may be provided as long as the positions are symmetrical with respect to each other.

  In the above description, the width of the diffraction region E having the strongest light intensity distribution in the focus diffraction region of the diffraction element 4 is the same as that of the diffraction regions F and G. However, the width of the diffraction region E is not limited thereto. May be different from the diffraction regions F and G. Even when different, the width may be set such that the number of diffraction gratings provided in each of the plurality of diffraction regions F and G is at least 5 or more.

  In the above description, the light spot incident on the vicinity of the dividing line of the light receiving regions a and b is set to three points of the light spot e, the light spot f, and the light spot g. However, the present invention is not limited to this. The number may be larger as long as the position is symmetrical with respect to the light spot incident on the center.

  In the above description, the positions of the other light spots are arranged only at positions separated in the Y direction with respect to the light spot incident on the center of the light receiving areas a and b. However, the present invention is not limited to this. As long as the position is symmetric with respect to the direction, it is also possible to dispose at a position shifted by combining both the Y direction and the X direction.

  In the above description, the divided regions of the diffraction regions F and G are divided into a plurality of regions in the Y direction and arranged alternately when viewed from one direction in the X direction. You may arrange | position alternately with respect to the area | region E in the symmetrical position. In the above description, the dividing lines of the diffraction regions E to G are in a direction parallel to the Y direction and linear, but are not limited thereto, and may be a polygonal line, a curved line, or the like.

(Second Embodiment)
FIG. 5 is a schematic diagram showing a configuration of an optical pickup device 28 according to the second embodiment of the present invention. FIG. 6 is a plan view of the arrangement configuration of the light source 21 and the light receiving element 22 as viewed from the optical axis direction. FIG. 7 shows an example of the focus error detection apparatus included in the second embodiment. The diffraction element 24 when the light source 21 emits light of the first wavelength and the light receiving element 22 to which the light diffracted thereby reaches. It is a top view showing the relationship with each light reception area | region. FIG. 8 shows the diffraction element 24 when the light source 21 emits light of the second wavelength and the light receiving element 22 to which the light diffracted thereby reaches, among examples of the focus error detection apparatus included in the second embodiment. It is a top view showing the relationship with each light reception area | region. FIG. 9 is a schematic diagram when light incident on the light receiving element 22 is viewed from a direction orthogonal to the optical axis direction. FIG. 10 shows that the light collected by the objective lens 26 moves to the plus / minus side in the Z direction, which is the focus direction from the position, when the light collected by the objective lens 26 is collected in the second embodiment. It is a top view showing the light spot shape which falls on the diffraction element 24 and the light receiving element 22 when it does. FIG. 11 is a characteristic diagram of the focus error signal FES in which all the focus error signals FES for each diffraction area shown in FIG. 10 are collected, and is detected according to the movement distance of the objective lens 26 in the Y direction which is the focus direction. FIG. 6 is a characteristic diagram illustrating a focus error signal FES for each wavelength.

  The optical pickup device 28 according to the second embodiment is similar to the configuration of the optical pickup device 8 of the first embodiment, and hereinafter, description will be made focusing on differences between the second embodiment and the first embodiment.

  The light source 21 of the optical pickup device 28 according to the second embodiment can emit a plurality of types of light having different wavelengths using the light to be irradiated on the optical recording medium 27. For example, the first light emitting point 21a and a second light emitting point 21b, the first light emitting point 21a emits light near the first wavelength of 650 nm, and the second light emitting point 21b emits light near the second wavelength of 780 nm. . Such a light source 21 can be realized by, for example, a monolithic semiconductor laser element.

  The light source 21 emits with the first light emitting point 21a as the center of the optical axis, and is arranged such that the second light emitting point 21b is located at a position shifted by a distance LDx in the + X direction with respect to the first light emitting point 21a. The optical axis of the first wavelength light is disposed so as to pass through the centers of the collimating lens 25 and the objective lens 26, and is condensed on the optical recording medium 27a corresponding to the first wavelength light. Further, since the optical axis of the second wavelength light is deviated from the center of the optical system of the collimating lens 25 and the objective lens 26 by the distance LDx, the principal ray direction is inclined by the magnification of the optical system, and the second wavelength light. Is condensed on the optical recording medium 27b corresponding to the above.

  The light receiving element 22 has substantially the same structure as that of the light receiving element 2 of the first embodiment, and the focus light receiving areas 22a and 22b and the focus light receiving areas 22a and 22b disposed on the + X direction side with respect to the light sources 21a and 21b. And a radial light receiving region 22c arranged in the + Y direction and a radial light receiving region 22d arranged in the -Y direction. The dividing line serving as the boundary between the focus light receiving regions 22a and 22b is provided parallel to the X direction, which is the arrangement direction of the first light emitting point 21a and the second light emitting point 21b, or inclined by an angle α2 with respect to the X direction. It is done. The tilt angle α2 is caused by the diffraction angle when diffracted in the diffraction region due to the wavelength variation of the light source 21, and the shape of the light spot incident on the dividing line of the light receiving regions 22a and 22b is increased and deformed. This is an angle for inclining the dividing line to absorb the offset generated in the focus error signal FES caused by the influence.

  The diffraction element 24 is configured so that only the focus diffraction region is different from the first embodiment. The focus diffraction region 24 has a certain angle δ from the dividing line 29 with respect to the dividing line 29 with a dividing line 29 parallel to the X direction passing through the center O serving as the optical axis in a circular outer edge. The band-shaped diffraction regions E, F, G, and H (each of which is divided into the first diffraction region and the second diffraction region) divided by a plurality of dividing lines 30 that extend in parallel at predetermined intervals. Equivalent to).

  Only one diffraction region E is arranged at a position slightly shifted from the optical axis center O in the −X direction. The diffraction regions F to H are repeatedly arranged in the −X direction from the diffraction region E, with the diffraction region H → the diffraction region G → the diffraction region H → the diffraction region F as one cycle. That is, it arrange | positions so that the diffraction area H may appear every other area, and the diffraction area F and the diffraction area G which adjoin the diffraction area H are arrange | positioned so that it may appear alternately.

  Similarly, in the + X direction from the diffraction area E, the diffraction area H → the diffraction area F → the diffraction area H → the diffraction area G is repeatedly arranged as one cycle. That is, it arrange | positions so that the diffraction area H may appear every other area, and the diffraction area F and the diffraction area G which adjoin the diffraction area H are arrange | positioned so that it may appear alternately.

  The X-direction widths of the diffraction region E and the diffraction region H are made equal, and the X-direction widths of the diffraction region F and the diffraction region G are half of the X-direction widths of the diffraction regions E and H.

  The diffraction region H is a focus diffraction region for light of the first wavelength, and the diffraction regions E to G are configured as focus diffraction regions for light of the second wavelength. However, the reflected light 32a obtained by reflecting the light of the first wavelength by the optical recording medium 27a is within the radius of the light spot 32a when entering the diffraction element 24, and the diffraction region H is on both sides of the diffraction region E in the X direction. It is set to include at least two or more. In addition, the diffraction region F or the diffraction region G is within the radius of the light spot 32b when the reflected light 32b of the second wavelength light reflected by the optical recording medium 27b is incident on the diffraction element 24. It is set so that at least two are included on both sides in the direction.

  In addition, in each of the diffraction regions E to H, a plurality of diffractive grooves having a concavo-convex shape are formed in parallel or close to each other and periodically arranged, and the diffraction grooves are formed in one diffraction region. The width in the X direction is such that five or more are arranged. The diffraction region H diffracts the + 1st order diffracted light by directing the reflected light 32a having the first wavelength from the optical recording medium 27a toward the light receiving regions 22a to 22d for signal detection. Further, the diffraction regions E to G diffract the + 1st order diffracted light by directing the reflected light 32b of the second wavelength from the optical recording medium 27b toward the light receiving regions 22a to 22d for signal detection, respectively.

  When the reflected light 32a having the first wavelength reflected by the optical recording medium 27a enters the diffraction element 24, it is diffracted by the diffraction region H toward the vicinity of the dividing line between the light receiving region 22a and the light receiving region 22b. The reflected light 32a becomes a circular light spot centered on the optical axis center O on the diffraction element 24, and the light diffracted by the diffraction region H is located at a distance Tx from the optical axis center O in the + X direction. Then, it is incident on the light spot h so as to be condensed at one point.

  When the reflected light 32b having the second wavelength from the optical recording medium 27b is incident on the diffraction element 24, the light diffracted by the diffraction regions E to G is diffracted toward the vicinity of the dividing line between the light receiving regions 22a and 22b. . Since the light source 21b is shifted in the + X direction, the reflected light 32b becomes a circular light spot centered on the position O ′ shifted in the + X direction from the optical axis center O on the diffraction element 24. The light diffracted by the region E is reflected as a light spot e in the center of the light receiving regions 22a and 22b dividing line so as to be condensed at one point in the position + X from the optical axis center O in the + X direction. Is done. The light diffracted by the diffraction region F is reflected as a light spot f at a position away from the light spot e in the + Y direction by a distance Ty so as to defocus in the −Z direction by a distance Tz. The light diffracted by the diffraction region G is reflected as a light spot g at a position away from the light spot e by the distance Ty in the −Y direction so as to be defocused by the distance Tz in the + Z direction. That is, the light spot f and the light spot g are condensed at a position that is symmetrical with respect to the Y direction and the Z direction with respect to the light spot e collected at the center of the dividing line of the light receiving regions 22a and 22b. Is set as follows.

  In the vicinity of the dividing line between the light receiving region 22a and the light receiving region 22b, the light spot f and the light spot g have a blurred spot shape in which the circumscribed shape of the plurality of belt-like spots is a half-moon shape. The straight portions that become the knife edges corresponding to the dividing lines 29 of the region are reflected as a plurality of light spot groups so that they are separated from the light spot e and the arc portions face each other.

  In this way, even if light of the first wavelength and light of the second wavelength are incident, the condensing positions of the light receiving regions 22a and 22b are positions separated from the optical axis center O by the distance Tx.

  When the diffraction direction of the diffraction regions E to H and the condensing position of the light spots e to h are set as described above, the reflected light 32a of the first wavelength causes the diffraction regions E to G to diffract the light of the second wavelength. The diffraction angle of the light incident on and diffracted differs from the diffraction angle of the light incident on the diffraction region H and diffracted. Since the second wavelength light to be incident on the diffraction regions E to G has a longer wavelength than the first wavelength light to be diffracted in the diffraction region H, the reflected light 32a of the first wavelength is reflected in the diffraction regions E to G. The diffraction angle of the light incident on and diffracted becomes larger and falls on a position farther than the distance Tx.

  Similarly, the reflected light 32b of the second wavelength is incident on the diffraction region H for diffracting the light of the first wavelength and is diffracted by entering the diffraction regions E to G. The diffraction angle of light is different.

Since the first wavelength light to be diffracted in the diffraction region H has a shorter wavelength than the second wavelength light to be incident on the diffraction regions E to G, the second wavelength reflected light 32b is incident on the diffraction region H. Thus, the diffraction angle of the diffracted light becomes small and falls on a position closer than the distance Tx.

  By reducing the X-direction dimensions of the light receiving region 22a and the light receiving region 22b so that these light spots do not enter the light receiving region 22a and the light receiving region 22b, the light spot is affected by light other than the light that should originally be diffracted. There is no.

  The operation principle of the optical pickup device 28 according to the second embodiment will be described. Since the effective diameters of the objective lens 26 corresponding to the light of the first wavelength and the light of the second wavelength are different, the characteristics such as the detection sensitivity and the amplitude of the focus error signal FES corresponding to each light change, but in principle. Is the same as the optical pickup device 8 of the first embodiment.

  When the light of the first wavelength is emitted, the effective diameter corresponding to the light of the first wavelength of the objective lens 26 is large, and one light spot h is collected on the dividing line of the light receiving region 22a and the light receiving region 22b. Therefore, the detection sensitivity is increased.

  When the second wavelength light is emitted, the effective diameter corresponding to the second wavelength light of the objective lens 26 is smaller than the effective diameter for the first wavelength light. As in the first embodiment, the apparent light spot becomes longer in the Y direction. The light spot f is shifted by the distance Tz in the −Z direction as well as the −Y direction with respect to the light spot e. This is the same effect as the objective lens 26 is shifted to the Far side. At the position of the objective lens at which the light spot e is in focus, the shape of the light spot f is blurred by the distance −Tz on the light receiving area 22a and becomes a large spot extending in the direction of the light receiving area 22b. As it shifts, the spot becomes smaller, eventually converges, and inverts to become larger. Conversely, when shifting to the Far side, it becomes larger without inversion. Therefore, as a characteristic of the focus error signal FESf2 generated only from the light spot f, the offset βf2 is set when the light spot f when the light of the first wavelength is emitted is temporarily condensed as in the first embodiment. It becomes smaller compared to the offset βf generated at.

  Similarly, the light spot g is shifted by the distance Tz in the + Z direction as well as in the + Y direction with respect to the light spot e. This is the same effect as the objective lens 26 is shifted to the Near side. At the position of the objective lens where the light spot e is in focus, the shape of the light spot g is blurred by the distance + Tz on the light receiving area 22b and becomes a large spot extending in the direction of the light receiving area 22a. As it shifts, the spot becomes smaller, eventually converges, and inverts to become larger. Conversely, when shifting to the Near side, it becomes larger without inversion. Therefore, as a characteristic of the focus error signal FESg2 generated only from the light spot g, the offset βg2 is obtained when the light spot f when the light of the first wavelength is emitted is temporarily condensed as in the first embodiment. It becomes smaller compared to the offset βg generated in.

  The focus error signal FESe2 generated only from the light spot e and the focus error signal FES2 obtained by synthesizing all the light spots e to g are the same principle as in the first embodiment, and thus description thereof is omitted.

  However, the positions of the light spot e and the light spot f in the Y direction are such that the spot outer shape becomes larger toward the dividing line, but as in the first embodiment, the positions in the vicinity of the dividing lines of the light receiving region 22a and the light receiving region 22b. It is preferable to provide the Y-direction position Ty so that the light conversion sensitivity does not become zero. In addition, if the Z-direction position Tz of the light spot e and the light spot f is too long, the amplitude of the focus error signal FES is decreased and the dynamic range is decreased.

  As described above, in the second embodiment, the apparent light spot incident on the light receiving region 22a and the light receiving region 22b increases in the Y direction, and at the same time, the effect of increasing the depth of focus can be obtained. That is, even if a deviation occurs in the optical arrangement of the second light emitting point 21b, the light receiving element 22, and the diffraction element 23 with respect to the first light emitting point 21a, it occurs more than the optical pickup device 8 of the first embodiment. It is possible to further reduce the defocus amount. Therefore, if the position of the diffractive element is accurately adjusted (XYθ direction) in a state where the light of the first wavelength is emitted, the light of the second wavelength is in the XYZ direction on the dividing line of the light receiving region 22a and the light receiving region 22b. Even if there is a slight deviation, the apparent light spot is large in the Y direction and the depth of focus is also long in the Z direction, so that variations in the defocus amount can be reduced.

  In the state where the light of the first wavelength is emitted, the rotation adjustment angle θ of the diffraction element 23 is ± 1 degree, the defocus amount is ± 0.4 μm, and the defocus amount with respect to the rotation adjustment angle θ can be reduced. Further, when the position of the light receiving element 22 is shifted by ± 10 μm in the Y direction, the diffraction element 23 is moved and rotated in a state where the light of the first wavelength is emitted, and the defocus amount is adjusted to be 0 μm. The defocus amount generated by the light of the second wavelength is suppressed to about ± 0.1 μm. This is because the straight line connecting the first light emitting point 21a and the second light emitting point 21b and the dividing line of the light receiving regions 22a and 22b are parallel or close to each other (the angle formed is at most an angle α2). If the position adjustment (XYθ direction) is performed and the variation in the defocus amount is suppressed within ± 0.4 μm, the defocus amount with the light of the second wavelength can be suppressed within ± 0.5 μm.

  Here, the Y-direction positions of the light spots f and g due to the second wavelength incident on the light receiving regions 22a and 22b are arranged so that the linear portions that are the knife edges of the light spots f and g are separated from each other. On the other hand, if they are arranged so as to face each other in the Y direction, the offset of the FES curve between the focus error signal FESf2 generated only from the light spot f and the focus error signal FESg2 generated only from the light spot g increases. The focus error signal FES obtained by combining e to g is not preferable because the offset increases when the optical arrangement is shifted.

  In addition, since the condensing position in the X direction from the optical axis center O to the light receiving regions 22a and 22b is the same distance for both the first wavelength light and the second wavelength light by the distance Tx, the light receiving element 22 Even when rotated in the XY plane, the light spot position deviation of the second wavelength light with respect to the first wavelength light is small, and the variation in the defocus amount of the generated second wavelength light can be reduced.

  In the above description, a monolithic type semiconductor laser element is exemplified as the light source 21. However, the light source 21 is not limited to this, and may be a hybrid type in which two semiconductor laser elements are arranged in parallel.

  In the above, only one light of the second wavelength is arranged with three types of diffraction regions that generate a plurality of spots in which light incident on the light receiving regions 22a and 22b is shifted in the Y direction and the Z direction. However, the present invention is not limited to this, and a diffraction region that generates a plurality of light spots generated by both the first wavelength light and the second wavelength light may be arranged.

  Further, the inclination angle δ of the focus diffraction regions E to H may be arranged within a range of 30 ° to 150 °. Furthermore, the dividing line 30 does not have to be a parallel straight line, and may be a parallel curve.

  In the above description, the diffraction regions F and G for diffracting the light of the second wavelength are disposed adjacent to each other. However, the present invention is not limited thereto, and the diffraction region H for diffracting the light of the first wavelength is not limited thereto. Are arranged adjacent to each other, for example, the diffraction region H → the diffraction region G → the diffraction region H → the diffraction region F is set to one cycle, so that the symmetry of the light spots F and G may be improved. .

(Third embodiment)
FIG. 12 is a schematic diagram showing a configuration of an optical pickup device 48 according to the third embodiment of the present invention. FIG. 13 is a plan view of the arrangement configuration of the light source 41 and the light receiving element 42 as viewed from the optical axis direction. FIG. 14 is a plan view showing the relationship between the diffraction element 44 when the light source 41 emits light of the first wavelength and each light receiving region of the light receiving element 42 where the light diffracted thereby reaches in the third embodiment. It is. FIG. 15 is a plan view showing the relationship between the diffraction element 44 when the light source 41 emits light of the second wavelength and each light receiving region of the light receiving element 42 where the light diffracted thereby reaches in the third embodiment. It is. FIG. 16 is a plan view showing the relationship between the diffraction element 44 when the light source 41 emits light of the third wavelength and each light receiving region of the light receiving element 42 where the light diffracted thereby reaches in the third embodiment. It is.

  The optical pickup device 48 according to the third embodiment is similar to the configuration of the optical pickup devices 8 and 28 according to the first embodiment and the second embodiment. Hereinafter, the optical pickup device 48 according to the first embodiment and the second embodiment will be described. The difference between the three embodiments will be mainly described.

  The light source 41 of the optical pickup device 48 according to the third embodiment can emit three types of light having different wavelengths as light to be irradiated to the optical recording medium 47. In the light source 41, the first emission point 41a emits light in the vicinity of 405 nm which is the first wavelength, the second emission point 41b emits light in the vicinity of 650 nm which is the second wavelength, and the third emission point 41c is , And emits light in the vicinity of 780 nm, which is the third wavelength. The light source 41 includes a semiconductor laser element that emits light of a first wavelength and a monolithic semiconductor laser element that emits light of a second wavelength and light of a third wavelength. The light source 41 emits with the first light emitting point 41a as the optical axis center, and is disposed such that the second light emitting point 41b is located at a position shifted by the distance LDx1 in the −X direction with respect to the first light emitting point 41a. The third light emitting point 41c is arranged at a position shifted by the distance LDx2 in the -X direction with respect to the one light emitting point 41a. There is almost no displacement in the Y direction and Z direction of the first light emitting point 41a, the second light emitting point 41b, and the third light emitting point 41c.

  The optical axis of the first light emitting point 41a is disposed so as to pass through the centers of the collimator lens 45 and the objective lens 46, and is condensed on the optical recording medium 47a corresponding to the light of the first wavelength. Further, since the optical axis of the second light emitting point 41b is deviated by a distance LDx1 from the center of the optical system of the collimating lens 45 and the objective lens 46, the principal ray direction is inclined by the magnification of the optical system, and the light of the second wavelength. The light is focused on the optical recording medium 47b corresponding to. Further, since the optical axis of the third light emitting point 41c is shifted from the center of the collimating lens 45 and the objective lens 46 by the distance LDx2, the principal ray direction is further inclined by the magnification of the optical system, and corresponds to the light of the third wavelength. The light is focused on the optical recording medium 47c.

  In addition, a wave plate 61 that converts polarization characteristics of the first to third wavelengths is provided between the collimating lens 45 and the objective lens 46 of the optical pickup device 48 according to the third embodiment. The wave plate 61 converts linearly polarized light emitted from the light source 41 into circularly polarized light or elliptically polarized light, and is made of quartz, plastic, liquid crystal or the like having birefringence.

  In addition, the optical pickup device 48 according to the third embodiment includes a polarizing beam splitter (hereinafter abbreviated as PBS) 60 above the hologram element 43 including the diffraction element 44. The PBS 60 includes a polarizing film 60a that transmits P-polarized light and reflects S-polarized light, and a reflective film 60b that reflects S-polarized light. The first to third light emitting points 41 a to 41 c of the light source 41 emit P-polarized light, pass through the diffraction element 44, and pass through the polarizing film 60 a of the PBS 60. Then, the light is converted into circularly polarized light or elliptically polarized light by the wave plate 61 through the collimating lens 45, and collected in one of the optical recording media 47 a to 47 c of the optical recording medium 47 corresponding to each wavelength through the objective lens 46. Reflect with light. When this reflected light passes through the objective lens 46 and the wave plate 61 again, the polarization directions of the circularly polarized light and the elliptically polarized light are changed to become S polarized light. Then, the light passes through the collimating lens 45 and enters the PBS 60. The S-polarized light incident on the PBS 60 is reflected by the polarizing film 60a, and the optical path is changed in the + X direction. Thereafter, the light is reflected by the reflective film 60b and the optical path is changed in the -Z direction. Thus, the S-polarized light reflected by the PBS 60 enters the diffraction element 44 and is diffracted by the diffraction region 44.

  The light receiving element 42 has substantially the same structure as that of the first and second embodiments, but further includes light receiving regions 42e to 42g that receive zero-order diffracted light (transmitted light) that is not diffracted by the diffraction region. Since the structures of the focus light receiving areas 42a and 42b and the radial light receiving areas 42c and 42d are the same as those in the first and second embodiments, the description thereof is omitted.

  Since the first light emitting point 41a, the second light emitting point 41b, and the third light emitting point 41c are arranged apart from each other in the −X direction, the corresponding light receiving regions 42e, 42f, and 42g are also separated in the X direction. It is provided at the position. The distance is determined by the distance between the first to third light emitting points 41a to 41c and the magnification of the optical system. By detecting the 0th-order diffracted light incident on these light receiving regions 42e, 42f, and 42g, the RF signal of the optical recording medium is reproduced.

  The diffraction element 44 is different from the first and second embodiments only in the focus diffraction region. The focus diffraction region 44 has a circular outer edge with a dividing line 49 in the X direction passing through the center O serving as the optical axis as a boundary, and from the dividing line 49 to the + Y direction orthogonal to the dividing line 49 at a predetermined interval. The band-shaped diffraction regions E to M are divided by a plurality of dividing lines 30 extending. Like the diffraction regions E to G of the second embodiment, three regions are provided for each wavelength, the diffraction region is arranged in the region having the highest light intensity distribution, and is incident on the center of the dividing line of the light receiving regions 42a and 42b. And a diffraction region where the spot is condensed is provided. The diffraction regions corresponding to the first to third wavelengths are the diffraction regions K, H, and E, respectively, and the light spots incident on the light receiving regions 42a and 42b correspond to the light spots k, h, and e, respectively. In the diffraction region where the light intensity distribution decreases, the light spot is incident at a position symmetrical in the ± Y direction with respect to the light spot incident on the center of the dividing line. Light incident in the −Y direction simultaneously becomes a spot blurred in the −Z direction, and light incident in the + Y direction becomes a blurred spot in the + Z direction. The diffraction regions corresponding to the first to third wavelengths of light incident in the −Y direction are the diffraction regions L, I, and F, respectively, and the light spots incident on the light receiving regions 42a and 42b are the light spots l and i, respectively. , F correspond. The diffraction regions corresponding to the first to third wavelengths of light incident in the + Y direction are the diffraction regions M, J, and G, respectively, and the light spots incident on the light receiving regions 42a and 42b are the light spots m, j, and g corresponds.

  The light spot k having the first wavelength that is the center of the optical axis is incident on the center of the dividing line of the light receiving regions 42a and 42b. The position is incident on a position shifted from the optical axis center O by + Tx in the + X direction. The light spots l and m are symmetrical in the ± Y direction with respect to the light spot k, and in the ± Z direction so that the outer edges corresponding to the respective knife edges are located at positions separated by the distance Ty1. The light is condensed by shifting by the distance Tz1.

  The light spot h of the second wavelength light is incident on the center of the dividing line of the light receiving regions 42a and 42b. The position is incident on a position shifted from the optical axis center O by + Tx in the + X direction. The light spots i and j are symmetrical in the ± Y direction with respect to the light spot h, and in the ± Z direction so that the outer edges corresponding to the respective knife edges are located at positions separated by the distance Ty2. The light is condensed by shifting by the distance Tz2. The distance Ty2 and the distance Tz2 are set to be larger than the distance Ty1 and the distance Tz1, respectively.

  The light spot e of the third wavelength light is incident on the center of the dividing line of the light receiving regions 42a and 42b. The position is incident on a position shifted from the optical axis center O by + Tx in the + X direction. The light spots f and g are symmetrical in the ± Y direction with respect to the light spot e, and the diffracted light from the diffraction area close to the light spot center is located far from the light spot center by a distance Ty3. The diffracted light from the diffracted region near the light spot center is shifted by the distance Tz3 in the ± Z direction so that the outer edge corresponding to each knife edge is located at a position separated by the distance Ty4. Diffracted light from the diffraction region far from the light is condensed at a distance Tz4. The magnitude relationships of the distances Ty2 to Ty4 and Tz2 to Tz4 are set as Ty2 <Ty3 <Ty4 and Tz2 <Tz3 <Tz4, respectively.

  If the position adjustment of the diffraction element 44 is performed when the light of the first wavelength is emitted, the optical arrangement of the second light emitting point 41b and the third light emitting point 41c, the light receiving element 42, the diffraction element 44, and the PBS 60 is displaced. The positions of the light spots on the dividing lines of the light receiving regions 42a and 42b of the reflected second wavelength light and third wavelength light are shifted. Here, similarly to the optical pickup device 28 of the second embodiment, the light spots i to j of the second wavelength light and the light spots e to g of the third wavelength light on the dividing lines of the light receiving regions 42a and 42b. By increasing the ± Y direction dimension to make the apparent spot longer in the Y direction and widening the ± Z direction, the focal depth of the apparent light spot can be increased, and the amount of defocus generated and It becomes possible to suppress the deviation of the FES balance. Furthermore, since the third light emitting point 41c is farther from the center of the optical axis than the second light emitting point 41b, the influence on the defocus amount and the FES balance with respect to the deviation of the optical arrangement is great. Therefore, when a plurality of diffraction regions that diffract the light spots f and g are diffracted so that the light intensity distribution is weaker and the region farther from the optical axis center is further away in both the ± Y direction and the ± Z direction, f and g have a larger spot shape with respect to the light spot e. This further increases the apparent Y-direction dimension of the light spot and increases the depth of focus, thereby reducing the defocus amount and FES balance deviation that occur with respect to the deviation of the optical arrangement.

  Further, as in the case of emitting the light of the third wavelength, the light spot incident on the symmetrical position with respect to the center of the dividing line of the light receiving regions 42a and 42b is simply moved in the ± Y direction and the ± Z direction. Alternatively, it may be shifted in the ± X direction. When the objective lens 46 moves in the focus direction, the light spot increases on the light receiving element 42. Even when focused on the optical recording medium 47, when the light spot incident on the symmetrical position with respect to the center of the dividing line of the light receiving areas 42a and 42b is blurred, the spot is moved when the objective lens 46 moves in the focus direction. May become even larger. Therefore, the diffraction positions of the diffraction regions F and G for diffracting the light spots f and g may be determined individually so that the X-direction dimension of the light spot of the plus side peak and the minus side peak of the focus error signal FES is minimized. .

  Note that the operation principle of the third embodiment is the same as that of the second embodiment, and a description thereof will be omitted.

  By adopting the above-described structure, it is possible to reduce the defocus amount and FES balance deviation generated in the focus error signal FES for all three wavelengths of light, and perform stable focus servo control. it can.

  In the present embodiment, the optical axis of the light emitted from the first light emitting point 41a is arranged so as to pass through the centers of the collimating lens 45 and the objective lens 46, but the second light emitting point is not limited thereto. 41b or the third light emitting point 41c may be arranged so as to be the center of the optical axis.

  In the above description, the first to third light emitting points 41a to 41c are arranged in parallel. However, the present invention is not limited to this, and the emission is performed so that the shift amount of the light intensity distribution center of light of each wavelength is reduced. The direction may be adjusted.

  In the above description, the arrangement of the first to third light emitting points 41a to 41c is shifted only in the X direction. However, the arrangement is not limited to this, and the first to third light emitting points 41a to 41c are shifted from each other in the Y direction and Z direction. May be. It is possible to adjust the position of the incident spot to the light receiving region by making each diffraction region in the diffraction region 44 have a corresponding grating shape and changing the diffraction angle also in the YZ direction. Furthermore, in the above description, an example in which two semiconductor laser elements are used as the light source 41 has been described. However, the present invention is not limited to this, and light of three wavelengths is emitted from each semiconductor laser element, or light of three wavelengths is emitted. A monolithic semiconductor laser element that can emit light may be used. If the position of each light emitting point is determined, the grating shape of the diffraction region can be set, and the position of the incident spot to the light receiving region can be adjusted. .

  In the above description, the polarization beam splitter 60 and the diffractive element 44 are used and not only the first-order diffracted light but also the zero-order diffracted light is used for the return path light. Similarly to the second embodiment, the structure may be such that only the diffraction element 44 is used and only the first-order diffracted light is used for the return path light. In this case, the diffraction region of the diffractive element 44 has a polarization characteristic, which increases the zero-order diffraction efficiency of the forward polarization and increases the first-order diffraction efficiency of the return polarization whose polarization direction is changed by 90 ° by the wave plate 61. It is possible to improve the round-trip use efficiency.

  In the above description, the half-wave plate 61 is disposed between the collimator lens 45 and the objective lens 46. However, the present invention is not limited thereto, and is disposed between the polarization beam splitter 60 and the objective lens 46. For example, it may be a structure that is attached to the upper surface of the polarization beam splitter 60. Furthermore, a structure in which a hologram is integrated with the polarization beam splitter 50 may be employed.

  In the above description, the light spots of the second wavelength light and the third wavelength light incident on the light receiving regions 42a and 42b are diffracted into a plurality of spots, and the light spot of the first wavelength light is one spot. However, the present invention is not limited to this, and the light spot of the first wavelength light may be a plurality of spots.

  In the above description, the single knife edge method using only the + 1st order diffracted light diffracted from the diffraction region 44 is used. However, it is also possible to use the double knife edge method using the −1st order diffracted light generated simultaneously.

(Fourth embodiment)
Next, an optical pickup device according to a fourth embodiment will be described.
In the above description, the knife edge method has been mainly described. However, the present invention is not limited to this, and an optical pickup device to which the beam size method is applied may be used. In the beam size method, one of the lights diffracted from two types of diffraction areas on the light receiving element is set to the near side, and the other light is set to the far side. The focus error signal FES is generated based on the detected difference. For example, a near-side spot and a far-side spot are formed by a plurality of light spots, and are arranged so that the positions thereof are spread with respect to the dividing line of the light-receiving element, so that the light source, light-receiving element, diffraction element, etc. It is possible to alleviate the defocus amount and the FES balance deviation with respect to the optical arrangement deviation.

  FIG. 17 is a diagram illustrating a configuration of an optical pickup device 68 according to the fourth embodiment. FIG. 18 is a plan view of the composite element 61 in which the light source 70 and the light receiving elements 72 and 73 are integrated in the fourth embodiment when viewed from the optical axis direction. FIG. 19 is a plan view of the diffraction region 64 of the diffraction element 63 of the fourth embodiment. The optical pickup device 68 according to the fourth embodiment has a structure in which the configurations of the light source, the light receiving element, and the diffraction element are different from those of the optical pickup devices according to the first to third embodiments.

  The diffractive element 63 is a circumferential region centered on the center O serving as an optical axis. Of the circular region, the diffraction element 63 is largely separated by dividing lines 63x and 63y extending from the center O in the X direction and the Y direction. The areas are divided into areas A, B, C, and D, and each area is further divided into strip-shaped areas by a plurality of straight lines extending in the Y direction. Each large area is divided into six small areas. Here, every other small area is set as Ab1, Ab2, and Ab3, and these are set as one group, and every other small area is set as Af1, Af2, and Af3, and these are set as another group. In addition, the large areas B, C, and D are similarly composed of groups of three areas. The diffractive element 63 has a polarization characteristic that transmits linearly polarized light in the X direction and diffracts linearly polarized light in the Y direction.

  In the composite element 61, a light receiving element is formed on a silicon substrate, and light emitted from the light source 70 is reflected from the Y direction to the Z direction by a rising mirror 71 which is also formed on the light receiving element by etching. Light receiving areas 72 and 73 are provided in the ± X direction of the rising mirror 71. In the light receiving area 72, the light receiving areas FE1 to FE4 and FE5 to FE8 for detecting focus error signals are divided into four areas in the Y direction, and the light receiving area 73 includes light receiving areas TE1 to TE4 for detecting radial error signals. , And divided into four regions by dividing lines in the X direction and the Y direction.

A quarter wavelength plate 64 is provided between the diffraction element 63 and the collimating lens 65.
The light in the Y direction emitted from the light source 70 is reflected in the Z direction by the rising mirror 71 and enters the diffraction element 63. The diffractive element 63 transmits linearly polarized light L0 in the X direction, becomes circularly polarized light by the quarter wavelength plate 64, passes through the collimator lens 65 and the objective lens 66, and is irradiated onto the optical recording medium 67. The reflected light reflected by the optical recording medium 67 passes through the collimator lens 65 and the objective lens 66, passes through the quarter wavelength plate 64 again, becomes linearly polarized light in the Y direction, enters the diffraction element 63, and enters the light receiving region 72. A + 1st order diffracted light L1 that is diffracted toward the light source and a −1st order diffracted light L2 that is diffracted toward the light receiving region 73 are generated.

  In the regions Ab1 to Ab3 of the diffractive element 63, the + 1st-order diffracted light L1 out of the incident light is condensed behind the light receiving region 72 (in the −Z direction), and on the light receiving region 72, the light receiving region FE5 and the light receiving region. In the vicinity of the center of the dividing line of FE6, the light spot L1Ab1 is incident on the center of the dividing line of the light receiving areas FE5 and FE6, the light spot L1Ab2 is incident on the position shifted in the -Y direction, and the light spot L1Ab3 is shifted in the + Y direction. A diffraction groove is provided in which the light spots L1Ab1 to L1Ab3 are formed. In addition, in the areas Af <b> 1 to Af <b> 3 of the diffraction element 63, incident light is collected forward (+ Z direction) with respect to the light receiving area 72, and on the light receiving area 72, the center of the dividing line of the light receiving areas FE <b> 5 and FE <b> 6. In the vicinity, the light spots L1Af1 to L1Af3 are such that the light spot L1Af1 is incident on the center of the dividing line of the light receiving areas FE5 and FE6, the light spot L1Af2 is shifted in the + Y direction, and the light spot L1Af3 is shifted in the -Y direction. A diffraction groove is formed so that is formed. The light spots L2Ab1 to L2Ab3 and L2Af1 to L2Af3 are formed at symmetrical positions with respect to the center O of the diffraction element 63, and the −1st order diffracted light is incident on the vicinity of the center of TE1 of the light receiving region 73, respectively.

  In the regions Bb <b> 1 to Bb <b> 3 of the diffractive element 63, the + 1st-order diffracted light L <b> 1 out of the incident light is condensed behind (−Z direction) from the light receiving region 72, while the light receiving region FE <b> 1 and the light receiving region are on the light receiving region 72. In the vicinity of the center of the dividing line of FE2, the light spot L1Bb1 is incident on the center of the dividing line of the light receiving area FE1 and the light receiving area FE2, the light spot L1Bb2 is shifted in the + Y direction, and the light spot L1Bb3 is shifted in the -Y direction. A diffraction groove is provided in which the light spots L1Bb1 to L1Bb3 are formed. In addition, in the regions Bf <b> 1 to Bf <b> 3 of the diffraction element 63, the incident light is collected forward (+ Z direction) from the light receiving region 72, and on the light receiving region 72, the center of the dividing line between the light receiving region FE <b> 1 and the light receiving region FE <b> 2. In the vicinity, light spots L1Bf1 to L1Bf3 such that the light spot L1Bf1 is incident on the center of the dividing line between the light receiving area FE1 and the light receiving area FE2, the light spot L1Bf2 is shifted in the −Y direction, and the light spot L1Bf3 is shifted in the + Y direction. A diffraction groove is formed so that is formed. The light spots L2Bb1 to L2Bb3 and L2Bf1 to L2Bf3 are formed at symmetric positions with respect to the center O of the diffraction element 63, and the −1st order diffracted light is incident on the vicinity of the center TE2 of the light receiving region 73, respectively.

  In the regions Cb <b> 1 to Cb <b> 3 of the diffractive element 63, the + 1st order diffracted light L <b> 1 out of the incident light is condensed behind (−Z direction) from the light receiving region 72, and on the light receiving region 72, the light receiving region FE <b> 1 and the light receiving region. In the vicinity of the center of the dividing line of FE2, the light spot L1Cb1 is incident on the center of the dividing line of the light receiving area FE1 and the light receiving area FE2, the light spot L1Cb2 is incident in the −Y direction, and the light spot L1Cb3 is incident in the + Y direction. A diffraction groove is provided so that the light spots L1Cb1 to L1Cb3 are formed. In addition, in the regions Cf <b> 1 to Cf <b> 3 of the diffractive element 63, the incident light is collected forward (+ Z direction) from the light receiving region 72, and on the light receiving region 72, the center of the dividing line between the light receiving region FE <b> 1 and the light receiving region FE <b> 2. In the vicinity, the light spots L1Cf1 to L1Cf3 are such that the light spot L1Cf1 is incident on the center of the dividing line between the light receiving area FE1 and the light receiving area FE2, the light spot L1Cf2 is shifted in the + Y direction, and the light spot L1Cf3 is shifted in the -Y direction. A diffraction groove is formed so that is formed. Light spots L2Cb1 to L2Cb3 and L2Cf1 to L2Cf3 are formed at symmetric positions with respect to the center O of the diffraction element 63, and the −1st order diffracted light is incident on the vicinity of the center of TE3 of the light receiving region 73, respectively.

  In the regions Db <b> 1 to Db <b> 3 of the diffractive element 63, the + 1st-order diffracted light L <b> 1 out of the incident light is condensed behind (−Z direction) from the light receiving region 72, while the light receiving region FE <b> 5 and the light receiving region are on the light receiving region 72. In the vicinity of the center of the dividing line of FE6, the light spot L1Db1 is incident on the center of the dividing line of the light receiving areas FE5 and FE6, the light spot L1Db2 is incident in the + Y direction, and the light spot L1Db3 is shifted in the −Y direction. A diffraction groove is provided in which the light spots L1Db1 to L1Db3 are formed. In addition, in the regions Df <b> 1 to Df <b> 3 of the diffraction element 63, incident light is collected forward (+ Z direction) from the light receiving region 72, and on the light receiving region 72, the center of the dividing line of the light receiving regions FE <b> 5 and FE <b> 6. In the vicinity, the light spots L1Df1 to L1Df3 such that the light spot L1Df1 is incident on the center of the dividing line of the light receiving areas FE5 and FE6, the light spot L1Df2 is shifted in the -Y direction, and the light spot L1Df3 is shifted in the + Y direction. A diffraction groove is formed so that is formed. The light spots L2Db1 to L2Db3 and L2Df1 to L2Df3 are formed at symmetric positions with respect to the center O of the diffraction element 63, and the −1st order diffracted light is incident on the vicinity of the center of TE1 of the light receiving region 73, respectively.

Next, the operation principle of the optical pickup device 68 according to the fourth embodiment will be described. Assuming that the values obtained by converting the light incident on the light receiving regions FE1 to FE8 and TE1 to TE4 into electric signals are SF1 to SF8 and ST1 to ST4, respectively, the focus error signal FES can be obtained by the following equation if the beam size method is used. Can do.
FES = {(SF1 + SF6)-(SF2 + SF5)}
-{(SF3 + SF8)-(SF4 + SF7)} (14)
If the radial error signal is a push-pull method,
RES = {(TE1 + TE2)-(TE3 + TE4)} (15)
If the DPD method can be obtained,
RES = Phase {(TE1 + TE4)-(TE2 + TE3) (16)
And you can get it.

  As in the first embodiment, the apparent light spot is obtained by shifting the light spot in the Y direction which is the orthogonal direction of the dividing line with respect to the dividing line between the light receiving regions FE1 to FE2 and FE5 to FE5. Therefore, the defocus amount and FES balance deviation due to tolerances of the light source 61, the composite element 61, and the diffraction element 62 are reduced.

  Further, as in the second and third embodiments, the one corresponding to a plurality of wavelengths, or the plurality of spots on the light receiving region moved to the plus side / minus side in the Z direction which is the focus direction may be used. .

1, 21, 41 Light source 2, 22, 42 Light receiving element 2a, 2b, 22a, 22b, 42a, 42b Focus light receiving area 2c, 2d, 22c, 22d, 42c, 42d Radial light receiving area 4, 24, 44 Diffraction element 5, 25, 45 Collimating lens 6, 26, 46 Objective lens 7, 27, 47 Optical recording medium 8, 28, 48 Optical pickup device

Claims (16)

A light source that emits light applied to the optical recording medium;
A light receiving element that receives light reflected and irradiated on the optical recording medium, and converts the received light into an electric signal to control a focus of the light irradiated on the optical recording medium, and is firstly divided by a dividing line. A light receiving element including a focus light receiving region divided into a light receiving region and a second light receiving region;
A part of the reflected light reflected by the optical recording medium is diffracted, and in a focused state, a first diffraction region that forms a spot on the dividing line, and another part of the reflected light is received by the first light reception. The first light-receiving region symmetrical to the spot on the dividing line formed by diffracting toward the region and the second light-receiving region and being diffracted by the dividing line and the first diffraction region in a focused state A second diffraction region that forms a spot at a position with respect to the second light receiving region, a first region including the first diffraction region and the second diffraction region that passes near the center of the optical axis, and a region other than the one region A diffractive element including a boundary line between the first diffraction area and the second diffraction area that is at least partially shared as an outer edge. Detection equipment .   The focus error detection device according to claim 1, wherein the first diffraction region diffracts light at a central portion of the reflected light.   The second diffraction region includes a plurality of first band regions that diffract other portions of the reflected light toward the first light receiving region and a plurality of second band shapes that diffract the light toward the second light receiving region. The focus error detection apparatus according to claim 1, wherein the focus error detection apparatus has a region.   The focus error detection device according to claim 3, wherein the belt-like regions are provided so as to have different areas.   5. The focus error detection device according to claim 3, wherein the first belt-like region and the second belt-like region are alternately arranged.   The focus error detection device according to claim 5, wherein the first belt-like region and the second belt-like region are arranged adjacent to each other.   The first belt-like region and the second belt-like region extend in one direction including the first diffraction region and the second diffraction region, and the other is a region other than the one region, the extending direction passing through the center of the optical axis. The focus according to any one of claims 3 to 6, wherein the focus is provided so as to be orthogonal to a boundary line with a region or to form an angle of 30 ° or more and 150 ° or less with the boundary line. Error detection device.   The first belt-like region and the second belt-like region have a spot shape formed in a focus light-receiving region when the focal point is located on the light source side with respect to the optical recording medium and the focal point is optical in an unfocused state. The spot shape formed in the focus light receiving region when positioned on the opposite side of the light source with respect to the recording medium is symmetric with respect to the spot on the dividing line formed by diffracting by the dividing line and the first diffraction region. The focus error detection device according to claim 3, wherein the focus error detection device is provided so as to satisfy the following.   The light source is configured to be capable of emitting light of a plurality of types of wavelengths, and the first diffraction region and the second diffraction region include a plurality of types of diffraction regions that diffract light of different wavelengths. The focus error detection device according to any one of claims 3 to 8.   The focus error according to claim 9, wherein the diffraction regions constituting the first diffraction region are provided so as to diffract light of different wavelengths to form spots at the same position on the dividing line. Detection device.   The diffractive region constituting the second diffractive region is provided so as to diffract at least one wavelength of light having different wavelengths and form spots at positions symmetrical to the dividing line. The focus error detection device according to claim 9 or 10, wherein:   The diffractive region constituting the second diffractive region is provided such that a distance of a spot formed at a symmetric position with respect to the dividing line from the dividing line differs for each wavelength. Item 12. The focus error detection device according to Item 11.   12. The diffractive region constituting the second diffractive region is provided such that a defocus amount of a spot formed at a position symmetric with respect to the dividing line is different for each wavelength. Focus error detection device.   The focus error detection apparatus according to claim 1, wherein the focus error is detected by a knife edge method.   The focus error detection apparatus according to claim 1, wherein the focus error is detected by a beam spot method.   An optical pickup device comprising the focus error detection device according to claim 1.