JP2011023065A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device that efficiently eliminates crosstalk light even for a multilayer disk with a simple configuration. <P>SOLUTION: An optical pickup device 1 makes a luminous flux incident on an optical disk 11 having a plurality of recording layers via an objective lens 8, focuses a luminous flux reflected by the optical disk 11 by a condensing lens 5, and makes the focused luminous flux incident on a light receiving element 9 via a condensing lens 4. The optical pickup device 1 includes, between the condensing lens 5 and the condensing lens 4, an optical filter 10 having a plurality of masks spaced in the optical axis direction of the reflected luminous flux and configured to reduce crosstalk light which is reflected from a recording layer other than the target layer of the optical disk 11 by the masks. At lest one mask of the optical filter 10 is arranged on both sides across a focus O, which is formed by the condensing lens 5, of signal light reflected from the target layer of the optical disk 11. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical pickup device used for recording and reproducing information signals on an optical disc.

  In recent years, due to the explosive increase in the amount of information accompanying the spread of terrestrial digital broadcasting and the like, large capacity optical discs are required. Following CD (Compact Disk) and DVD (Digital Versatile Disk), larger capacity BDs are required. (Blu-ray Disk) is becoming popular. In addition, for the purpose of further increasing the capacity, research and development of a multilayer disk in which recording layers are stacked and the capacity is increased several times as much as the number of stacked layers are being actively conducted.

  2. Description of the Related Art A recording / reproducing apparatus that records and reproduces information signals on an optical disc is provided with an optical pickup device that irradiates the optical disc with laser light. In the optical pickup device, the light beam emitted from the laser light source is condensed on the recording layer of the optical disk by the objective lens, and the light beam reflected by the recording layer is incident on the light receiving element.

  When recording or reproducing an information signal with respect to a multi-layer disc by an optical pickup device, a reflected light beam from a recording layer other than the target layer which is a recording layer on which recording or reproduction is performed becomes crosstalk light, which is the target. The signal may fluctuate due to interference with the signal light that is a reflected light beam from the layer, and the servo signal may be deteriorated. In order to avoid this inconvenience, the dual-layer discs that are currently popular mainly use one servo signal beam and devise hologram division.

  In an optical pickup apparatus for BD using an objective lens having a high NA (numerical aperture), means for correcting spherical aberration due to a difference in spacer thickness between recording layers of BD is required. There is a limit to the amount of correction, and considering the simplification and miniaturization of the overall configuration of the optical pickup device, it is desirable to reduce the amount of correction of spherical aberration even in a multilayer disk. For this reason, in an optical disc having three or more recording layers, it is necessary to narrow the interval between the recording layers with respect to the two-layer disc. However, if the interval between the recording layers is narrowed, the defocus difference between the signal light and the crosstalk light becomes small. Therefore, it is difficult to avoid the influence of the crosstalk light by using one beam and dividing the hologram as described above. Become.

  Therefore, it has been proposed to install a dedicated element for removing crosstalk light in the optical pickup device. For example, in the optical pickup device disclosed in Patent Document 1, an element having a mask region that diffracts or blocks only a region overlapping with a light receiving element of crosstalk light, and a light beam reflected by an optical disk is received by the light receiving element. It is arranged in the optical path of the return path until it is incident on.

  In Patent Document 2, a pinhole that allows only signal light to pass through is provided in the vicinity of the focus of the signal light in the expander optical system provided in the optical path of the return path, or the crosstalk light is crossed at the focal position of the crosstalk light. An optical pickup device in which a mask for shielding only talk light is arranged is disclosed.

  In the optical pickup device described in Patent Document 3, in the optical system in which the signal light is focused in the expander optical system provided in the optical path of the return path, a prism 100 as shown in FIG. It is installed. The prism 100 includes a transmission film 101 and absorption films 102 and 103 parallel to the optical axis direction. The transmissive film 101 is disposed in a region including the signal light focal point 104 and transmits light. The absorption films 102 and 103 are disposed adjacent to both sides of the transmission film 101 and absorb light.

  In the optical pickup device described in Patent Document 3 in which such a prism 100 is installed, the crosstalk light is focused on the absorption films 102 and 103, and the crosstalk light is absorbed by the absorption films 102 and 103. Is removed.

JP 2005-203090 A Special table 2007-511023 gazette JP 2007-141357 A

  In the above-mentioned Patent Document 1, since the mask area is arranged at a position where there is no difference in the light beam diameter between the signal light and the crosstalk light in the substantially parallel light beam, the mask area becomes larger than the light beam diameter of the signal light. , The loss of signal light increases. Such a loss of signal light is particularly noticeable when the recording layer that reflects the crosstalk light is close to the recording layer that reflects the signal light, and thus becomes larger as the recording layer of the optical disc becomes multilayered.

  Further, in Patent Document 2, when crosstalk light is removed by providing a pinhole that allows only signal light to pass through, coherent noise cannot be removed. When a mask that blocks only the crosstalk light is arranged, 2 (N-1) masks are required for the N-layer disk because the mask is arranged at the focal point of the crosstalk light.

  For this reason, especially in the case of dealing with an optical disk having three or more layers, the configuration of an element including a mask becomes complicated. Further, as the number of optical discs increases, the total thickness between the recording layer (surface layer) on the outermost surface and the recording layer (lowermost layer) on the innermost side of the optical disc becomes thicker. Since the focal point of the crosstalk light from the lower layer and the focal point of the crosstalk light from the surface layer when the lowermost layer is the target layer are separated from the focal position of the signal light in the expander optical system, the entire element including the mask is large. Become.

  Further, in the optical pickup device disclosed in Patent Document 3, if the multi-layer disc is to be used, the cross-talk light is separated from the focal position of the signal light in the multi-layer disc as described above. Need to expand to. This increases the size of the prism 100 and makes it difficult to manufacture the prism 100.

  The present invention has been made in view of the above, and an object of the present invention is to provide an optical pickup device that can efficiently remove crosstalk light even with respect to a multilayer disk with a simple configuration.

  In order to achieve the above object, an optical pickup device according to a first aspect includes an objective lens that makes a light beam incident on an optical disk having a plurality of recording layers, and a reflected light beam that is a light beam reflected by the optical disk. An optical axis of the reflected light beam between a light receiving element that is focused through an optical lens and then incident through a second condenser lens, and the first condenser lens and the second condenser lens. A plurality of masks arranged to be spaced apart from each other to reduce the amount of light passing through a predetermined region including the optical axis of the reflected light beam, and other than the recording layer on which the information signal of the optical disc is recorded or reproduced An optical filter unit that reduces crosstalk light, which is a reflected light beam from the recording layer, by the mask, and the mask is a reflected light beam from the recording layer on which an information signal is recorded or reproduced. Across the signal light focus a focal by the first condenser lens issue light, characterized in that it is arranged one by at least one on the optical disk side and the light receiving element side.

  An optical pickup device according to a second aspect is the optical pickup device according to the first aspect, wherein the mask is used when an information signal is recorded or reproduced on a recording layer on the outermost surface side of the optical disc. At least one piece of crosstalk light from the innermost recording layer of the optical disc is disposed between the focal point of the first condenser lens and the signal light focal point, and is disposed on the innermost recording layer of the optical disc. On the other hand, when the information signal is recorded or reproduced, at least between the focal point of the first condenser lens of the crosstalk light from the recording layer on the most surface side of the optical disc and the focal point of the signal light One sheet is arranged.

The optical pickup device according to claim 3 is the optical pickup device according to claim 1 or 2, wherein a distance from the signal light focus of the mask on the optical disc side closest to the signal light focus is dm ₁ , corresponding to a radius. of the size and hm _1, the distance from the signal light focus farthest the optical disk side of the mask from the signal light focus and dm _K, a radius corresponding to the size and hm _K, closest to the signal light focus Dm' 1 the distance from the signal light focus of the mask of the light-receiving element _side, the size of the radius corresponds with Hm' _1, from the signal light focus farthest the optical disk side of the mask from the signal light focus wherein _L a distance Dm', when the size of the radius corresponding to _{hm' L, hm 1, hm K} , hm' 1, hm' L is to satisfy the following (equation 1) through (formula 4) When To do.
2 × (tmin ⁺ ) × Me ² / n ≧ he × dm ₁ / (he + hm ₁ ) (Formula 1)
2 × (tmax ⁺ ) × Me ² / n ≦ he × dm _K / (he−hm _K ) (Formula 2)
2 × (tmin ⁻ ) × Me ² / n ≧ he × dm ′ ₁ / (he + hm ′ ₁ ) (Formula 3)
^{2 × (tmax -) × Me} 2 / n ≦ he × dm' L / (he-hm' L) ... ( Equation 4)
However,
Me: Ratio of the focal length of the first condenser lens and the focal length of the objective lens n: Refractive index of the optical disc he: Radius when the light receiving portion of the light receiving element is projected at the position of the signal light focal point Substantial size tmin ⁺ : effective reflection position, which is a reflection position in the optical disk when the crosstalk light is regarded as light reflected only once in the optical disk, is more than the reflection position of the signal light. Minimum value of the distance in the thickness direction of the optical disc between the effective reflection position of the crosstalk light and the reflection position of the signal light in the crosstalk light on the back side of the optical disk tmin ⁻ : the effective reflection position is the The light between the effective reflection position of the crosstalk light and the reflection position of the signal light in the crosstalk light closer to the surface of the optical disc than the reflection position of the signal light. Disc in the thickness direction of the minimum distance value tmax of ^+: in the cross-talk light effective reflection position is on the back side of the optical disc than the reflection position of the signal light, and the effective reflection position of the cross talk light, the signal light The maximum value of the distance in the thickness direction of the optical disk between the reflection position of the optical disk tmax ⁻ : the crosstalk light in the crosstalk light whose effective reflection position is on the surface side of the optical disk from the reflection position of the signal light The maximum value of the distance in the thickness direction of the optical disc between the effective reflection position and the reflection position of the signal light

  According to the present invention, it is possible to provide an optical pickup device that can efficiently remove crosstalk light even for a multilayer disk with a simple configuration.

1 is a schematic configuration diagram of an optical pickup device according to a first embodiment of the present invention. It is a schematic block diagram which shows an example of the optical pick-up apparatus which has an expander optical system. It is a figure which shows the focus in the expander optical system in case crosstalk light and signal light are mixed. It is a perspective view which shows schematic structure of the optical filter part in the optical pick-up apparatus shown in FIG. It is sectional drawing along the AA line in FIG. It is a figure which shows the crosstalk light which generate | occur | produces in a 2 layer disc. It is a figure which shows the positional relationship of the mask in a optical filter part, the focus of crosstalk light, and the focus of signal light. It is a figure for demonstrating the method of calculating the magnitude | size equivalent to the radius of a mask, and the distance of a mask and the focus of signal light. It is a figure which shows the other structural example of the optical filter part in 1st Embodiment. It is a schematic block diagram of the optical pick-up apparatus which concerns on 2nd Embodiment. It is a perspective view which shows schematic structure of the optical filter part in the optical pick-up apparatus shown in FIG. It is a figure which shows arrangement | positioning of the mask in the optical filter part shown in FIG. It is a figure which shows a mode that the light reception cell and crosstalk light of the light receiving element in Example 1 overlap. It is a figure which shows the cross-sectional structure of the optical disk which the optical pick-up apparatus based on Example 1 assumed correspondence. It is a figure which shows the crosstalk light generate | occur | produced with the optical disk shown in FIG. FIG. 3 is a diagram illustrating a positional relationship between a focus of signal light, a mask, and a focus of crosstalk light in an expander optical system of the optical pickup device in Embodiment 1. FIG. 10 is a diagram illustrating a cross-sectional structure of an optical disc assumed to be supported by the optical pickup device in the second embodiment. It is a figure which shows the multiple reflection crosstalk light generate | occur | produced with the optical disk shown in FIG. It is a figure which shows the positional relationship of the focus of the signal light in the expander optical system of the optical pick-up apparatus in Example 2, the focus of crosstalk light and multiple reflection crosstalk light, and a mask. FIG. 10 is a diagram illustrating a cross-sectional structure of an optical disc assumed to be supported by the optical pickup device in the third embodiment. It is a figure which shows the crosstalk light generate | occur | produced with the optical disk shown in FIG. FIG. 10 is a diagram illustrating a positional relationship between a focus of signal light, a focus of crosstalk light, and a mask in an expander optical system of an optical pickup device in Embodiment 3. FIG. 10 is a perspective view illustrating a schematic configuration of an optical filter unit according to a third embodiment. FIG. 10 is a diagram showing a cross-sectional structure of an optical disc assumed to be supported by an optical pickup device in Example 4. It is a figure which shows the multiple reflection crosstalk light generate | occur | produced with the optical disk shown in FIG. FIG. 10 is a diagram illustrating a positional relationship between a focal point of signal light, a focal point of crosstalk light and multiple reflection crosstalk light, and a mask in an expander optical system of an optical pickup device in Example 4. FIG. 10 is a diagram illustrating a positional relationship between a focal point of signal light, a focal point of crosstalk light and multiple reflection crosstalk light, and a mask in an expander optical system of an optical pickup device in Example 5. FIG. 10 is a perspective view illustrating a schematic configuration of an optical filter unit according to a fifth embodiment. It is a perspective view which shows an example of the prism which removes crosstalk light with the conventional optical pick-up apparatus.

  Embodiments of the present invention will be described below with reference to the drawings. Throughout the drawings, the same or equivalent parts and components are denoted by the same or equivalent reference numerals, and the description thereof is omitted or simplified.

(First embodiment)
FIG. 1 is a schematic configuration diagram of an optical pickup device according to a first embodiment of the present invention. As shown in FIG. 1, the optical pickup device 1 according to the first embodiment includes a light source 2, a polarizing beam splitter 3, condensing lenses 4 and 5, a quarter-wave plate 6, and a start-up. A mirror 7, an objective lens 8, a light receiving element 9, and an optical filter unit 10 are provided.

  In the optical pickup device 1, the laser light emitted from the light source 2 is reflected by the optical disc 11, which is a multilayer disc having a plurality of recording layers, and finally received by the light receiving element 9. The light path from the light source 2 until it enters the optical disk 11 is defined as the forward path, and the light path from the light reflected by the optical disk 11 to the light receiving element 9 is defined as the return path.

  The light source 2 is composed of a semiconductor laser or the like, and emits laser light having a predetermined wavelength. The polarizing beam splitter 3 transmits the light beam incident from the light source 2, reflects the return light beam incident from the condenser lens 4 by the polarizing film 3 a, and causes the light receiving element 9 to enter. In the optical pickup device 1, the light source 2 emits an S-polarized light beam, and the polarizing film 3a transmits the S-polarized light beam and reflects the P-polarized light beam.

  The condensing lens 4 condenses the forward light beam that has passed through the polarizing beam splitter 3 at the focal point O, and makes the returning light beam incident via the optical filter unit 10 converged light and enter the polarizing beam splitter 3. The condensing lens 5 converts the outward light beam incident through the optical filter unit 10 into substantially parallel light and makes it enter the quarter-wave plate 6, and returns the return light beam incident from the quarter-wave plate 6. The light is condensed at the focal point O ′.

  The quarter-wave plate 6 converts the forward light beam from S-polarized light to circularly-polarized light, and converts the return light beam from circularly-polarized light to P-polarized light. The rising mirror 7 bends the optical path of the outgoing light beam from the quarter-wave plate 6 and makes it incident on the objective lens 8, and bends the optical path of the return light beam that is transmitted through the objective lens 8 and becomes 4 minutes. The first wavelength plate 6 is made incident.

  The light receiving element 9 converts the incident light into an electric signal and outputs the electric signal to an external arithmetic processing circuit.

  The optical filter unit 10 is disposed between the condensing lenses 4 and 5 so as to include the focal point O ′ therein, and transmits the forward light flux and filters the crosstalk light contained in the return light flux.

  In the optical pickup device 1, the condenser lenses 4 and 5 constitute an expander optical system having one focal point O ′ in the middle.

  Here, the expander optical system generally refers to an optical system that emits parallel light and emits parallel light, such as the condensing lenses 42 and 5 of the optical pickup device 1A shown in FIG.

  The optical pickup device 1A of FIG. 2 is obtained by replacing the condenser lens 4 of the optical pickup device 1 of FIG. 1 with a lens system 4A. The lens system 4 </ b> A includes condenser lenses 41 and 42. The condensing lens 41 causes the forward light beam that has passed through the polarizing beam splitter 3 to enter the condensing lens 42 as substantially parallel light, and the returning light beam that is incident from the condensing lens 42 is used as convergent light. Make it incident. The condensing lens 42 condenses the forward light flux incident from the condensing lens 41 at the focal point O, and causes the return light flux incident via the optical filter unit 10 to enter the condensing lens 41 as substantially parallel light.

  In the present embodiment, it is assumed that the magnification of the expander optical system is 1, and that the condensing lenses 41 and 42 in FIG. 2 are shared to form the condensing lens 4 in FIG. The condenser lens 4 to the condenser lens 5 are referred to as an expander optical system as described above.

  FIG. 3 is a diagram showing a state near the focal point O ′ on the return path in the expander optical system when crosstalk light and signal light are mixed. Here, the signal light is a reflected light beam from a target layer that is a recording layer on which an information signal is recorded or reproduced on the optical disc 11, and the crosstalk light is a reflected light beam from a recording layer other than the target layer. is there.

  Since the signal light is focused on the target layer of the optical disc 11, the focal point O ′ coincides with the focal point O in the forward path. Therefore, hereinafter, the focus of the signal light in the expander optical system (signal light focus) will be described as the focus O.

  On the other hand, the crosstalk light is condensed at a focal point P at a position different from the focal point O because the reflection position on the optical disc 11 is defocused. That is, the expander optical system plays a role of spatially separating the focus O of the signal light and the focus P of the crosstalk light.

  Here, when the distance between the focal points O and P is Δ and the defocus amount (air conversion) of the optical disk 11 is δ, the following (Equation 5) is established in the paraxial region. However, the ratio Me is the ratio between the focal length of the condenser lens 5 and the focal length of the objective lens 8.

2 × δ × Me ² = Δ (Formula 5)
Next, the configuration of the optical filter unit 10 will be described with reference to FIGS. 4 and 5. 4 is a perspective view illustrating a schematic configuration of the optical filter unit 10, and FIG. 5 is a cross-sectional view taken along line AA in FIG.

  As shown in FIGS. 4 and 5, the optical filter unit 10 is formed in a rectangular parallelepiped shape using a material such as glass that transmits light, and the opposed planes 10a and 10b are substantially perpendicular to the optical axis of the incident light beam, It arrange | positions so that O may be located inside the optical filter part 10 (between plane 10a, 10b).

  Masks 12A and 12B are arranged on the planes 10a and 10b, respectively, for reducing the amount of light passing through a predetermined region including the optical axis of the incident light beam. The masks 12 </ b> A and 12 </ b> B have a transmittance of 0%, or a transmittance that attenuates the crosstalk light to the extent that there is no problem even if it enters the light receiving element 9.

  The masks 12A and 12B include, for example, a binary diffraction grating with the depth set to the maximum diffraction efficiency, a mirror structure with a metal thin film, a diffusion structure by ground glass processing, and a refractive structure processed into a wedge shape, but are not limited thereto. Not. However, care must be taken so that stray light generated by diffraction, refraction, reflection, diffusion, etc. in the masks 12A and 12B does not enter the light receiving element 9.

  With the optical filter unit 10 as described above, a mask 12A is disposed on the optical disc 11 side (condensing lens 5 side, objective lens 8 side) and a mask 12B is disposed on the light receiving element 9 side (condensing lens 4 side) across the focal point O. Is done. As shown in FIG. 3, since the focus O of the signal light and the focus P of the crosstalk light are spatially separated, the masks 12A and 12B have a difference in the beam diameters of the signal light and the crosstalk light. Will be placed in place.

  The distances dm, dm ′ (air equivalent) between the focal point O and the masks 12A, 12B in the optical axis direction of the incident light flux, and the sizes hm, hm ′ corresponding to the radii of the masks 12A, 12B It is determined based on the effective size he of the light receiving element, which is a size corresponding to the radius when the light receiving cell (light receiving unit) is projected at the position of the focal point O, the defocus amount of crosstalk light that can be generated by the optical disc 11, and the like.

  The light receiving element effective size he shown in FIG. 5 will be described. The light receiving element 9 has a light receiving cell (not shown) for detecting the amount of light, and its size is represented by he ′ corresponding to a radius around the optical axis. When the ratio of the distance from the condensing lens 4 to the focal point O and the distance from the light receiving element 9 to the condensing lens 4 is a magnification M, the light receiving element effective size he in the expander optical system is as follows (Formula 6): It is represented by In other words, the light receiving element effective size he is equivalent to the effective size when the light receiving cell size he ′ is projected onto the focal point O in the expander optical system.

he = M × he ′ (Formula 6)
Next, the range of the defocus amount of crosstalk light that can be generated by the optical disk 11 will be described. FIG. 6 is a diagram showing crosstalk light when the optical disc 11 is a two-layer disc having two recording layers of L0 layer and L1 layer.

  In FIG. 6, the recording layer on the back side of the optical disc 11 is the L0 layer, the recording layer on the front side is the L1 layer, and the interlayer spacing is t0. FIG. 6 (a) shows the L0 layer, and FIG. 6 (b) shows the L1 layer. Signal light and crosstalk light in the case of a target layer are shown.

As shown in FIG. 6A, the crosstalk light from the L1 layer when the L0 layer is the target layer is defocused from the L0 layer to the surface side (minus side) of the optical disc 11, and the defocus amount δ ⁻ = t0 / n. Here, n is the refractive index of the optical disk 11.

Further, as shown in FIG. 6B, the crosstalk light from the L0 layer when the L1 layer is the target layer is defocused from the L1 layer to the back side (plus side) of the optical disc 11, and the defocused light is defocused. The focus amount is δ ⁺ = t0 / n.

When the optical disk 11 is a multi-layer disk having three or more layers, there can be a plurality of crosstalk lights as shown in FIGS. The range of the magnitude of the focus amount δ ⁺ and the defocus amount δ ⁻ on the minus side is expressed as in the following (Expression 7) and (Expression 8).

tmin ⁺ / n ≦ δ ⁺ ≦ tmax ⁺ / n (Expression 7)
^{tmin - / n ≦ δ - ≦} tmax - / n ... ( Equation 8)
here,
tmin ⁺ : Thickness of the optical disk 11 between the reflection position of the crosstalk light and the reflection position of the signal light in the crosstalk light in which the reflection position in the optical disk 11 is located behind the reflection position of the signal light Minimum value of distance in the vertical direction tmin ⁻ : between the reflection position of the crosstalk light and the reflection position of the signal light in the crosstalk light in which the reflection position in the optical disk 11 is closer to the surface of the optical disk 11 than the reflection position of the signal light The minimum value tmax ⁺ of the distance in the thickness direction of the optical disk 11 between the reflection position of the crosstalk light in the crosstalk light in which the reflection position in the optical disk 11 is behind the signal light and the reflection position of the optical disk 11 between the reflection position of the signal light, the thickness direction of the distance maximum tmax of the optical disc 11 ^-: anti-reflection position in the optical disc 11 is the signal light In crosstalk light on the surface side of the optical disk 11 than the position, between the reflection position of the reflected position and the signal light of the crosstalk light is the maximum value of the thickness direction of the distance of the optical disk 11.

In the above (Expression 7) and (Expression 8), tmin ⁺ , tmin ⁻ , tmax ⁺ , and tmax ⁻ are values determined by the interlayer spacing of the recording layers of the optical disc 11, and n is a material of the spacer between the recording layers (polycarbonate or the like). Therefore, the range of the defocus amount of the crosstalk light that can be generated is determined by the design value of the optical disc 11 from (Expression 7) and (Expression 8).

Crosstalk light having a positive defocus amount δ ⁺ is filtered by the mask 12A on the optical disk 11 side (condenser lens 5 side) in FIG. 5 and is related to hm and dm. Crosstalk light having a negative defocus amount δ ⁻ is filtered by the mask 12B on the light receiving element 9 side (condenser lens 4 side) and is related to hm ′ and dm ′. For this reason, masks 12A and 12B that are spaced apart from each other in the optical axis direction with the focus O of the signal light interposed therebetween are required.

  Next, how to determine the size hm corresponding to the radius of the mask 12A and the distance dm between the mask 12A and the focal point O will be described with reference to FIGS.

  FIG. 7 is a diagram showing the positional relationship between the mask 12A in the optical filter unit 10 and the focal point P and the focal point O of the crosstalk light filtered by the mask 12A. FIG. FIG. 7B is a diagram showing a state intermediate between the state where the focal point P is closest to the focal point O and the farthest state, and FIG. 7C is a diagram showing the state closest to the focal point O. FIG. It is a figure which shows the farthest state. The size hm corresponding to the radius of the mask 12A is made smaller than the effective light receiving element size he.

  FIG. 7A shows a state in which the light flux of crosstalk light leaks from the outside of the mask 12A to the light receiving cell of the light receiving element 9 when the focal point P becomes closer to the focal point O, and the cross filtered by the mask 12A. This corresponds to crosstalk light having the smallest defocus amount on the plus side among talk light. At this time, the position of the mask 12A is farther from the focal point O of the signal light than the focal point P of the crosstalk light. For this reason, compared with the case where the mask 12A is arranged at the position of the focal point P, it is advantageous for the crosstalk light having a small defocus amount.

  On the other hand, FIG. 7C shows a state in which the point on the outermost periphery of the light receiving cell of the light receiving element 9 projected onto the focal point O coincides with the extension line of the straight line connecting the focal point P and the point on the outer periphery of the mask 12A. It is. When the focal point P is further away from the focal point O, the light flux leaks from the outside of the mask 12A to the light receiving cell of the light receiving element 9. This state corresponds to the crosstalk light having the largest positive defocus amount among the crosstalk light filtered by the mask 12A. At this time, the position of the mask 12A is closer to the focal point O of the signal light than the focal point P of the crosstalk light. For this reason, compared with the case where the mask 12A is arranged at the position of the focal point P, the optical filter unit 10 can be made smaller, which is advantageous in simplifying the configuration of the optical pickup device 1.

  From the above, the range of the distance Δ between the focal point P and the focal point O of the crosstalk light that can be completely filtered by the mask 12A is set to minimize Δ1 shown in FIG. 8A and maximize Δ2 shown in FIG. To do. FIG. 8A shows that the distance between the focal point P and the focal point O of the crosstalk light having the smallest defocus amount on the plus side is minimum when all the generated crosstalk light can be completely filtered by the mask 12A. FIG. 8B is a schematic diagram showing a state in which crosstalk light having the largest plus-side defocus amount and the focus P when the mask 12A can completely filter all possible crosstalk light. It is a schematic diagram which shows the state from which the distance with O becomes the maximum.

  Δ1 in FIG. 8A is expressed by the following (formula 9) from the similar relationship between ΔPOQ and ΔPSR.

Δ1 = he × dm / (he + hm) (Formula 9)
Δ2 in FIG. 8B is expressed by the following (formula 10) from the similar relationship between ΔPOQ and ΔRTQ.

Δ2 = he × dm / (he−hm) (Expression 10)
Here, the distance Δmin ⁺ between the focal point P and the focal point O of the crosstalk light having the smallest positive defocus amount among the generated crosstalk light, and the positive defocus amount of the generated crosstalk light is Assuming the distance Δmax ⁺ between the focal point P and the focal point O of the largest crosstalk light, Δmin ⁺ and Δmax ⁺ are expressed by the following (Expression 11) and (Expression 12) from (Expression 5) and (Expression 7). Is done.

Δmin ⁺ = 2 × (tmin ⁺ ) × Me ² / n (Expression 11)
Δmax ⁺ = 2 × (tmax ⁺ ) × Me ² / n (Expression 12)
In order to filter all the crosstalk light having the defocus amount on the plus side with the mask 12A, it is necessary to satisfy Δmin ⁺ ≧ Δ1 and Δmax ⁺ ≦ Δ2. The following (Expression 13) and (Expression 14) are obtained from the relations of (Expression 9) to (Expression 12) and Δmin ⁺ ≧ Δ1 and Δmax ⁺ ≦ Δ2.

2 × (tmin ⁺ ) × Me ² / n ≧ he × dm / (he + hm) (Equation 13)
2 × (tmax ⁺ ) × Me ² / n ≦ he × dm / (he−hm) (Formula 14)
The size hm corresponding to the radius of the mask 12A on the optical disc 11 side (condenser lens 5 side) and the distance dm between the mask 12A and the focal point O are determined so as to satisfy the above (Expression 13) and (Expression 14). .

  The size hm ′ corresponding to the radius of the mask 12B on the light receiving element 9 side (condenser lens 4 side) and the distance dm ′ between the mask 12B and the focal point O are also determined in the same manner as in the mask 12A described above. (Equation 15) and (Equation 16) are obtained.

2 × (tmin ⁻ ) × Me ² / n ≧ he × dm ′ / (he + hm ′) (Equation 15)
^{2 × (tmax -) × Me} 2 / n ≦ he × dm' / (he-hm') ... ( Equation 16)
The values of hm ′ and dm ′ relating to the mask 12B are determined so as to satisfy the above (Expression 15) and (Expression 16).

  As described above, since the defocus amount of the crosstalk light that can be generated is determined from the design value of the optical disk 11, hm, within a range satisfying (Expression 13) to (Expression 16) according to the optical disk 11 to be used. dm, hm ′, dm ′ are determined, and the optical filter unit 10 is configured.

Note that, for a crosstalk light component having a very large defocus amount, the light beam may be sufficiently diffused and the amount of light may be weak. It is also conceivable to combine the optical filter unit 10 with other crosstalk light countermeasure methods. Therefore, tmin ⁺ , tmin ⁻ , tmax ⁺ , and tmax ⁻ can be limited as necessary.

  Further, the masks 12A and 12B may be designed to be slightly larger in size to ensure a margin.

  Next, the operation of the optical pickup device 1 will be described.

  When the light source 2 emits laser light, the emitted S-polarized light beam passes through the polarization beam splitter 3, becomes convergent light by the condenser lens 4, and is condensed at the focal point O while passing through the optical filter unit 10. After that, it becomes divergent light again and becomes substantially parallel light by the condenser lens 5. The light beam that has passed through the condenser lens 5 passes through the quarter-wave plate 6 and is converted into circularly polarized light, enters the objective lens 8 through the rising mirror 7, and is incident on the target layer of the optical disk 11 by the objective lens 8. It is focused on.

  The light incident on the optical disk 11 is reflected by the optical disk 11. The reflected light flux on the return path includes signal light and crosstalk light.

  The light flux on the return path passes through the objective lens 8, enters the quarter-wave plate 6 through the rising mirror 7, is converted to P-polarized light, and is collected in the expander optical system by the condenser lens 5.

  Among the light fluxes on the return path, the signal light flux is condensed at the focal point O while passing through the optical filter unit 10, then becomes divergent light again, enters the condenser lens 4, and is converged by the condenser lens 4. It becomes light, is reflected by the polarizing film 3 a of the polarizing beam splitter 3, and enters the light receiving element 9.

  Of the return beam, the crosstalk beam is filtered by the masks 12A and 12B of the optical filter unit 10.

  As described above, the optical filter unit 10 is configured by determining the values of hm, dm, hm ′, and dm ′ regarding the sizes and arrangement positions of the masks 12A and 12B according to the design value of the optical disk 11 to be used. Therefore, the crosstalk light having a positive defocus amount is filtered by the mask 12A on the optical disc 11 side (the condenser lens 5 side and the objective lens 8 side), and the crosstalk light having a negative defocus amount is obtained. Filtering is performed by the mask 12B on the light receiving element 9 side (condenser lens 4 side). As a result, the crosstalk light is prevented from entering the light receiving cell of the light receiving element 9.

  As described above, according to the first embodiment, by providing the optical filter unit 10 having the masks 12A and 12B whose sizes and arrangement positions are determined according to the design value of the optical disk 11, three optical disks 11 are provided. Even in the case of a multi-layer disc having more than one layer, the crosstalk light can be efficiently removed with a simple configuration. The optical filter unit 10 is easy to design even when it is compatible with filtering of crosstalk light with a small defocus amount, and the increase in size is suppressed even when it is compatible with filtering of crosstalk light with a large defocus amount.

  Further, since the masks 12A and 12B are arranged at locations where the beam diameters of the signal light and the crosstalk light are different, the size of the masks 12A and 12B can be suppressed to be small, and the loss of the signal light due to the masks 12A and 12B is reduced. be able to.

  The optical filter unit 10 is not limited to the configuration shown in FIG. 4, and masks 12 </ b> A and 12 </ b> B that are equivalent to the radius and have a size of hm and hm ′ are arranged at a distance of dm and dm ′ from the focal point O. Any configuration may be used. For example, as shown in FIG. 9, a configuration in which two glass plates 13 and 14 are arranged side by side with a focal point O, and masks 12A and 12B are arranged on one flat surface 13a and 14a, respectively.

  Further, the same effects as those of the optical pickup device 1 can be obtained in the optical pickup device 1A of FIG. 2 in which the condenser lens 4 of the optical pickup device 1 of FIG.

(Second Embodiment)
FIG. 10 is a schematic configuration diagram of an optical pickup device according to the second embodiment of the present invention. As shown in FIG. 10, the optical pickup device 1 </ b> B according to the second embodiment has a configuration in which the optical filter unit 10 is replaced with an optical filter unit 20 with respect to the optical pickup device 1 shown in FIG. 1.

  The configuration of the optical filter unit 20 will be described with reference to FIGS. 11 and 12. FIG. 11 is a perspective view illustrating a schematic configuration of the optical filter unit 20, and FIG. 12 is a diagram illustrating a mask arrangement in the optical filter unit 20.

  As shown in FIG. 11, the optical filter unit 20 includes a translucent plate 21 made of a material such as glass that transmits light. The translucent plate 21 is arranged so that the opposed planes 21a and 21b are substantially perpendicular to the optical axis, and the focal point O is located inside (between the planes 21a and 21b). The optical filter unit 20 is made of the same material as that of the translucent plate 21, and a plurality of translucent plates 22 arranged side by side on the optical disc 11 side with respect to the translucent plate 21. And a plurality of translucent plates 23 arranged side by side on the light receiving element 9 side with respect to the translucent plate 21.

  On the planes 21a and 21b of the translucent plate 21 and the planes 22a and 23a perpendicular to the optical axis of the translucent plates 22 and 23, masks similar to the masks 12A and 12B in the first embodiment are provided. Is formed.

Masks respectively formed on the flat surface 21a of the translucent plate 21 and the flat surface 22a of the translucent plate 22 on the optical disc 11 side (the condensing lens 5 side and the objective lens 8 side) with respect to the focal point O are masks. 26A _k (k = 1, 2,..., K), the plane 21b of the translucent plate 21 and the translucent plate 23 on the light receiving element 9 side (condenser lens 4 side) with respect to the focal point O. The masks respectively formed on the plane 23a are referred to as masks 26B _l (l = 1, 2,..., L). As shown in FIG. 11, the masks 26A ₁ and 26B ₁ are closest to the focal point O, and the masks 26A _K and 26B _L are disposed farthest from the focal point O.

Here, as shown in FIG. 12, the distances (air conversion) between the focal point O and the masks 26A _k and 26B _l in the optical axis direction are dm _k and dm ′ _l , respectively, and the masks 26A _k and 26B _{l. hm} k radius considerable size, respectively, and hm' _l.

The optical filter unit 20 is not limited to the configuration shown in FIG. 11, _dm k from the focal point O, the distance dm' _{l, hm} k radius equivalent size of the mask 26A _k of Hm' _l, mask 26B Any configuration is possible as long as _l is arranged.

Next, how to determine the size hm _k corresponding to the radius of the k-th mask 26A _k on the optical disc 11 side and the distance dm _k between the mask 26A _k and the focal point O will be described.

  The following (Expression 17) and (Expression 18) are obtained by the same method as that used to derive (Expression 9) and (Expression 10) in the first embodiment.

Δ1 (k) = he × dm _k / (he + hm _k ) (Expression 17)
Δ2 (k) = he × dm _k / (he−hm _k ) (Expression 18)
Here, .DELTA.1 (k), of the k-th mask 26A _k only completely filterable crosstalk light, at a distance of the defocus amount on the positive side is the focal point P and the focal point O of the smallest cross-talk light is there. Δ2 (k) is the distance between the focal point P and the focal point O of the crosstalk light having the largest positive defocus amount among the crosstalk light that can be completely filtered only by the _kth mask 26Ak. .

If Δ1 (1) is equal to or smaller than Δmin ⁺ shown in (Expression 11) and Δ2 (K) is equal to or greater than Δmax ⁺ shown in (Expression 12), the range shown in (Expression 7) with K masks It is possible to design so that the crosstalk light having the defocus amount is not incident on the light receiving cell of the light receiving element 9. Thus, for the mask 26A _k of the optical disk 11 side, the following equation (1), is designed to satisfy the equation (2).

2 × (tmin ⁺ ) × Me ² / n ≧ he × dm ₁ / (he + hm ₁ ) (Formula 1)
2 × (tmax ⁺ ) × Me ² / n ≦ he × dm _K / (he−hm _K ) (Formula 2)
The size hm _k radius corresponding mask 26A _k is smaller than the light-receiving element effective size he.

For even mask 26B _l of the light receiving element 9 side, in the same manner as in the above-described mask 12A, the following equation (3), obtained (Equation 4), it is designed to meet these.

2 × (tmin ⁻ ) × Me ² / n ≧ he × dm ′ ₁ / (he + hm ′ ₁ ) (Formula 3)
^{2 × (tmax -) × Me} 2 / n ≦ he × dm' L / (he-hm' L) ... ( Equation 4)
The mask _26A k, the radius sizeable _hm k of 26B _l, hm' _l is smaller than the light-receiving element effective size he.

As described above, since the defocus amount of the crosstalk light that can be generated is determined from the design value of the optical disk 11, hm _k within a range that satisfies (Expression 1) to (Expression 4) according to the optical disk 11 to be used. , Dm _k , hm ′ _l , dm ′ _l are determined, and the optical filter unit 20 is configured.

  When K = L = 1, (Expression 1) to (Expression 4) correspond to (Expression 13) to (Expression 16) shown in the first embodiment.

In the optical pickup device 1B configured as described above, crosstalk light having a positive defocus amount is converted into a plurality of masks 26A ₁ and 26A ₂ on the optical disc 11 side (the condenser lens 5 side and the objective lens 8 side). ,..., And crosstalk light having a negative defocus amount is filtered by a plurality of masks 26B ₁ , 26B ₂ ,... On the light receiving element 9 side (condenser lens 4 side). As a result, the crosstalk light is prevented from entering the light receiving cell of the light receiving element 9.

As described above, according to the second embodiment, the same effect as that of the optical pickup device 1 of the first embodiment can be obtained, and a plurality of masks 26A ₁ , 26A ₂ , ..., by arranging the masks 26B ₁ , 26B ₂ , ..., the size of each mask can be further reduced, and attenuation of the signal light by the mask can be further reduced.

  Next, specific examples of the above-described embodiments of the present invention will be described.

Example 1
Since the optical pickup device of Example 1 has the same overall configuration as the optical pickup device 1 of the first embodiment shown in FIG. 1, it will be described with reference to FIG. However, in the first embodiment, the optical pickup device 1 includes a diffraction element (not shown) that divides the laser light from the light source 2 into three beams in the outward optical system, and the light receiving element 9 has three beams. The three-beam DPP (Differential Push Pull) method is applied to convert the light received by the three light receiving cells into electrical signals and detect the tracking error signal from the differential calculation. Shall.

  The constants of the optical system are: NA of the objective lens 8 is 0.85, and the focal lengths of the objective lens 8 and the condenser lenses 4 and 5 are 1.8 mm, 9 mm, and 18 mm, respectively. The magnification Me = 10, which is the ratio of the focal lengths of the two. Further, the magnification M = 1, which is the ratio of the distance from the condenser lens 4 to the focal point O and the distance from the light receiving element 9 to the condenser lens 4. The light source 2 emits laser light having a wavelength of 405 nm corresponding to BD.

  FIG. 13 shows how the light receiving cells 91 to 93 of the light receiving element 9 overlap with the crosstalk light. Since the three-beam DPP method is applied in the first embodiment as described above, the cell range is different in the TAN direction that is the direction along the recording track of the optical disc 11 and the RAD direction perpendicular thereto.

  Therefore, in order to minimize the loss of signal light, the masks 12A and 12B have a rectangular shape that is long in the TAN direction. As shown in FIG. 13, the projected sizes of the masks 12A and 12B on the light receiving element 9 are 300 μm in the TAN direction and 100 μm in the RAD direction including the margin, and the distance corresponding to the radius from the optical axis is he_tan ′. = 150 μm and he_rad ′ = 50 μm were set. Here, “_tan” is a symbol indicating the TAN direction and “_rad” is a symbol indicating the RAD direction, and will be omitted when discussing the TAN direction and the RAD direction together.

  In Example 1, since M = 1, the light receiving element effective size he_tan in the TAN direction and the light receiving element effective size he_rad in the RAD direction at the focal point O in the expander optical system are the same as those on the light receiving element 9. Thus, he_tan = he_tan ′ = 150 μm and he_rad = he_rad ′ = 50 μm.

  FIG. 14 shows a cross-sectional structure of an optical disc 11 that is a three-layer disc assumed to be supported by the optical pickup device 1 according to the first embodiment. As shown in FIG. 14, the lowermost layer, the intermediate layer, and the outermost layer of the optical disc 11 are the L0 layer, the L1 layer, and the L2 layer, respectively, and the spacer thickness t0 = 15 μm between the L0 layer and the L1 layer, The thickness of the spacer between the L2 layer was t1 = 10 μm, and the refractive index n of the optical disk 11 was 1.6.

  Next, crosstalk light that can be generated in the optical disk 11 will be described with reference to FIG.

  When the L0 layer is the target layer, as shown in FIG. 15A, crosstalk lights C1 and C2 reflected by the L1 layer and the L2 layer are generated. When the L1 layer is the target layer, as shown in FIG. 15B, crosstalk lights C3 and C4 reflected by the L0 layer and the L2 layer are generated. When the L2 layer is the target layer, as shown in FIG. 15C, crosstalk lights C5 and C6 reflected by the L0 layer and the L2 layer are generated.

Table 1 summarizes the distance td (μm) in the thickness direction of the optical disk 11 between the reflection positions of the crosstalk lights C1 to C6 and the reflection positions of the signal lights in FIGS.

  In Table 1, the crosstalk layer indicates a recording layer in which crosstalk light is reflected. Further, a value corresponding to the crosstalk light reflected by the recording layer on the back side of the optical disk 11 with respect to the target layer is added with a plus sign, and a value corresponding to the crosstalk light reflected by the recording layer on the surface side is added with a minus sign. Is written. For example, for the crosstalk light C1 reflected by the L1 layer when the target layer is the L0 layer, td = t0 = 15 μm, and the reflection position of the crosstalk light C1 is at the back of the optical disc 11 with respect to the target layer. Therefore, in Table 1, it is written as -15.

From Table 1, in Example 1, the values of tmin ⁺ , tmin ⁻ , tmax ⁺ , tmax ^{− in} the above (Formula 7) and (Formula 8) are as follows.

tmax ⁺ = tmax ⁻ = 25 μm
tmin ⁺ = tmin ⁻ = 10 μm
Here, tmax ⁺ crosstalk light C5, tmax ^- crosstalk light C2, tmin ⁺ crosstalk light C6, tmin ^- respectively correspond to the cross talk light C4.

  The design value of the mask 12A can be obtained by substituting the values obtained above into (Expression 13) and (Expression 14). In the first embodiment, since masks having different lengths are used in the RAD direction and the TAN direction, the following (Expression 19), (Expression 20), and TAN obtained from (Expression 13) and (Expression 14) in the RAD direction are used. The direction is designed by the following (Expression 21) and (Expression 22) obtained from (Expression 13) and (Expression 14).

2 × 10 × 10 ² /1.6≧50×dm/(50+hm_rad) (Equation 19)
2 × 25 × 10 ² /1.6≦50×dm/(50−hm_rad) (Equation 20)
2 × 10 × 10 ² /1.6≧150×dm/(150+hm_tan) (Formula 21)
2 × 25 × 10 ² /1.6≦150×dm/(150−hm_tan) (Formula 22)
Since tmax ⁺ = tmax ⁻ and tmin ⁺ = tmin ⁻ , the mask 12B may be designed with dm = dm ′ and hm = hm ′. Therefore, the calculation using (Expression 15) and (Expression 16) is omitted.

  In Example 1, hm_rad = 23 μm, hm_tan = 69 μm, and dm = 1.8 mm were selected as values satisfying the ranges of the above (formula 19) to (formula 22).

  FIG. 16 is a diagram illustrating the positional relationship between the focal point O of signal light, the masks 12A and 12B, and the focal point of crosstalk light in the expander optical system according to the first embodiment. In FIG. 16, (Lsi, Lcj) indicates the position of the focal point of the crosstalk light from the Lj layer when the Li layer is the target layer (i ≠ j). A thick dotted line indicates signal light, and a thin dotted line indicates crosstalk light.

  Temporarily, if it is the structure which arrange | positions a mask in the focus of crosstalk light and removes crosstalk light, the range of (Ls2, Lc0)-(Ls2, Lc1) and (Ls1, Lc2)-(Ls0, Lc2) All of them need masking. On the other hand, in the first embodiment, all the crosstalk light can be removed by arranging the masks one by one in the application range of the masks 12A and 12B shown in FIG. Simplification and miniaturization are possible.

  As shown in FIG. 9, the optical filter unit 10 according to the first embodiment has masks 12A and 12B formed at the center of the flat surfaces 13a and 14a of the thin glass plates 13 and 14, and the glass plates 13 and 14 are arranged in parallel. It is. The glass plates 13 and 14 are arranged so that the distance between the masks 12A and 12B is dm = dm ′ in consideration of the refractive index and thickness.

  Further, the masks 12A and 12B are made of an aluminum thin film of 46 μm × 138 μm from the above-mentioned hm_rad = 23 μm and hm_tan = 69 μm, and the light incident on the masks 12A and 12B is reflected by 100%. It is assumed that the reflected light does not reach the light receiving cell of the light receiving element 9. The masks 12A and 12B as described above can be easily realized by a known method, for example, etching is performed after forming a resist pattern by photolithography.

  As described above, in Example 1, it is possible to prevent the crosstalk light in the three-layer disc from entering the light receiving element 9. Further, even with the three-beam DPP method, a stable crosstalk light removing action can be obtained.

  Depending on the configuration of the optical system, the NA of the target layer and the corresponding crosstalk light in the expander optical system is different, so that dm, dm ′, hm, and hm ′ are further optimized in consideration thereof. It is conceivable that dm ≠ dm ′ and hm ≠ hm ′.

In the first embodiment, a case where a three-layer disk is used is shown, but for other multi-layer disks, values of tmin ⁺ , tmin ⁻ , tmax ⁺ , tmax ⁻ are obtained in the same manner as in the first embodiment, and this is used as a mask. What is necessary is just to design 12A and 12B. In an N-layer disc (N ≧ 2), when the outermost layer is LN-1 layer, the lowermost layer is L0 layer, and the spacer thickness ti is between Li layer and Li + 1 layer (0 ≦ i ≦ N-2), The values of tmin ⁺ , tmin ⁻ , tmax ⁺ and tmax ⁻ are calculated by the following (Expression 23) and (Expression 24). However, Min (ti) is the minimum value of ti.

tmin ⁺ = tmin ⁻ = Min (ti) (Equation 23)
tmax ⁺ = tmax ⁻ = Σ (ti) (Equation 24)
(Example 2)
Since the optical pickup device of the second embodiment has the same configuration as that of the first embodiment, it will be described with reference to FIG. The second embodiment is different from the first embodiment in the structure of an optical disc that is assumed to be compatible.

  FIG. 17 shows a cross-sectional structure of the optical disc 11A assumed to be supported by the optical pickup device 1 in the second embodiment. A difference from the optical disk 11 corresponding to Example 1 shown in FIG. 14 is that the thickness t0 of the spacer between the L0 layer and the L1 layer is 17 μm.

  The crosstalk light that can be generated in the optical disc 11A is the same as that described with reference to FIG. 15 in the first embodiment. However, the second embodiment further removes the multiple reflected crosstalk light C7 shown in FIG. This is a difference from the first embodiment.

  18, when the L0 layer is the target layer, the crosstalk light reflected by the L1 layer to the front surface side (L2 layer side) of the optical disc 11A is reflected by the back surface of the L2 layer. And reflected again by the L1 layer.

  The multi-reflection crosstalk light C7 is twice as many times as the number of reflections than the normal crosstalk light and weak in intensity. However, in some cases, the multi-reflection crosstalk light C7 may affect the tracking error signal. The light C7 is also removed.

  The multi-reflection crosstalk light C7 is equivalent to a light beam reflected from a position away from the surface side by t0−t1 = 7 μm with respect to the L0 layer as the target layer. That is, the multiple reflection crosstalk light C7 can be regarded as light reflected only once at an arbitrary position (effective reflection position) on the effective reflection layer 41 which is a virtual reflection surface shown in FIG.

The distance td in the thickness direction of the optical disc 11A between the effective reflection position of the crosstalk light C1 to C6 and the multiple reflection crosstalk light C7 in FIG. 15A to FIG. Table 2 summarizes (μm). Note that the effective reflection positions of the crosstalk lights C1 to C6 that are not multiple reflections are actual reflection positions.

From Table 2, in Example 2, the values of tmin ⁺ , tmin ⁻ , tmax ⁺ , and tmax ^{− in} the above (Formula 7) and (Formula 8) are as follows. When multiple reflection is considered as in the second embodiment, the reflection position of the crosstalk light when obtaining the values of tmin ⁺ , tmin ⁻ , tmax ⁺ , tmax ⁻ in (Expression 7) and (Expression 8) is as follows. The effective reflection position.

tmax ⁺ = tmax ⁻ = 27 μm
tmin ⁺ = 10 μm
tmin ⁻ = 7 μm
Here, tmax ⁺ crosstalk light C5, tmax ^- crosstalk light C2, tmin ⁺ crosstalk light C6, tmin ^- respectively correspond to the multiple reflection crosstalk light C7.

  The design values of the masks 12A and 12B can be obtained by substituting the values obtained above into (Expression 13) to (Expression 16). For the RAD direction, the following (Expression 25) to (Expression 28) obtained from (Expression 13) to (Expression 16), and for the TAN direction, the following (Expression 29) obtained from (Expression 13) to (Expression 16) Designed by (Equation 32).

2 × 10 × 10 ² /1.6≧50×dm/(50+hm_rad) (Equation 25)
2 × 27 × 10 ² /1.6≦50×dm/(50−hm_rad) (Equation 26)
2 × 7 × 10 ² /1.6≧50×dm′/(50+hm_rad ′) (Expression 27)
2 × 25 × 10 ² /1.6≦50×dm′/(50−hm_rad ′) (Equation 28)
2 × 10 × 10 ² /1.6≧150×dm/(150+hm_tan) (Equation 29)
2 × 27 × 10 ² /1.6≦150×dm/(150−hm_tan) (Equation 30)
2 × 7 × 10 ² /1.6≧150×dm′/(150+hm_tan ′) (Equation 31)
2 × 27 × 10 ² /1.6≦150×dm′/(150−hm_tan ′)
... (Formula 32)
In Example 2, hm_rad = 23 μm, hm_tan = 69 μm, dm = 1.8 mm, hm_rad ′ = 29 μm, hm_tan ′ = 87 μm, dm ′ = 1 as values satisfying the ranges of (Expression 25) to (Expression 32) above. .35mm was chosen.

  As in the first embodiment, the optical filter unit 10 according to the second embodiment has a configuration in which masks 12A and 12B are formed at the center of the flat surfaces 13a and 14a of the glass plates 13 and 14. However, the distance between the masks 12A and 12B is dm + dm ′ = 1.8 + 1.35 = 1.15 μm in terms of the distance in vacuum. Further, the distance between the mask 12A and the focal point O is 1.8 μm, and the distance between the mask 12B and the focal point O is 1.35 μm.

  FIG. 19 is a diagram illustrating the positional relationship between the focal point O of signal light, the focal points of crosstalk light and multiple reflection crosstalk light, and the masks 12A and 12B in the expander optical system according to the second embodiment.

  In FIG. 19, (Lsi, Lcj) has the same meaning as in FIG. 16 described in the first embodiment, and (Lsi, Lcjkj) represents Li layer → Lk layer → Lj when the Li layer is the target layer. The position of the focal point of the multi-reflection crosstalk light that multi-reflects with the layer is shown. A thick dotted line indicates signal light, a thin dotted line indicates crosstalk light, and a one-dot chain line indicates multiple reflection crosstalk light.

  In the second embodiment, the crosstalk light is removed by the small optical filter unit 10 with a simple configuration as in the first embodiment by arranging the masks one by one in the application range of the masks 12A and 12B shown in FIG. In addition, multiple reflection crosstalk light can be removed.

  Further, the mask 12B in which the multiple reflection crosstalk light collected at the position (Ls0, Lc121) close to the focal point O of the signal light is disposed farther than the focal point (Ls0, Lc121) of the multiple reflection crosstalk light when viewed from the focal point O. Therefore, high stability can be obtained while suppressing loss of signal light.

Multi-layer discs with four or more layers generate more complex multiple reflections. However, when the Li layer is the target layer, the multi-reflection crosstalk light that is reflected three times, that is, Li + 1 layer → Li + 2 layer → Li + 1 layer, is the most. High reflectivity. For this reason, even in a multi-layer disc having four or more layers, it is only necessary to determine the values of tmin ⁺ and tmin ^{− in} consideration of only the three-time reflection as described above for multiple reflection crosstalk light. The values of tmax ⁺ and tmax ⁻ may be obtained from (Equation 24) as in the first embodiment.

In an N-layer disc with N ≧ 3, when only the above-described three-time reflected multi-reflection crosstalk light is considered, tmin ⁺ and tmin ⁻ are obtained as follows. First, when the spacer thickness ti monotonously decreases from the L0 layer, which is the lowermost layer, toward the LN-1 layer, which is the outermost layer (ti> ti + 1), tmin ⁺ and tmin ⁻ are as follows: It is calculated by (Expression 33) and (Expression 34).

tmin ⁺ = Min (ti) (Expression 33)
tmin ⁻ = Min (| ti− (ti + 1) |, ti) (Expression 34)
On the other hand, when the interlayer spacer thickness ti monotonously increases from the L0 layer to the LN-1 layer (ti <ti + 1), tmin ⁺ and tmin ⁻ are expressed by the following (formula 35) and (formula 36).

tmin ⁺ = Min (| ti− (ti + 1) |, ti) (Expression 35)
tmin ⁻ = Min (ti) (Expression 36)
When the optical disk spacer thickness ti is neither monotonously decreased nor monotonously increased, tmin ⁺ is obtained by using (Expression 35) for a set of ti corresponding to i where ti <ti + 1. For a set of ti corresponding to i satisfying> ti + 1, tmin ⁻ can be obtained by using (Expression 34).

Even when other multiple reflections are supported, similarly, the defocus amount can be indicated based on the thicknesses of the plurality of spacers. Therefore, tmin ⁺ and tmin ⁻ are appropriately set by the corresponding multiple reflections. Then, the optical filter unit 10 can be designed.

(Example 3)
The optical pickup device of Example 3 has the same overall configuration as the optical pickup device 1B of the second embodiment shown in FIG. 10, and will be described with reference to FIG. However, the optical pickup device 1B according to the third embodiment applies the three-beam DPP method as in the first embodiment, and a diffractive element that divides the laser light from the light source 2 into three beams in the outward optical system. As shown in FIG. 13, the light receiving element 9 has three light receiving cells 91 to 93 corresponding to three beams.

  The optical system constants are also the same as in Example 1. The NA of the objective lens 8 is 0.85, and the focal lengths of the objective lens 8 and the condenser lenses 4 and 5 are 1.8 mm, 9 mm, and 18 mm, respectively. The magnification Me = 10, which is the ratio of the focal lengths of the condenser lens 5 and the objective lens 8. Further, the magnification M = 1, which is the ratio of the distance from the condenser lens 4 to the focal point O and the distance from the light receiving element 9 to the condenser lens 4.

  Further, the light receiving element effective size he_tan in the TAN direction and the light receiving element effective size he_rad in the RAD direction are the same as in the first embodiment, and he_tan = 150 μm and he_rad = 50 μm.

  FIG. 20 shows a cross-sectional structure of the optical disc 11B assumed to be supported by the optical pickup device 1B in the third embodiment. As shown in FIG. 20, the L0 layer, the L1 layer, the L2 layer, and the L3 layer are sequentially formed from the lowermost layer to the outermost layer of the optical disc 11B, and the spacer thickness t0 = 10 μm between the L0 layer and the L1 layer, L1. The spacer thickness t1 between the L2 layer and the L2 layer was 15 μm, the spacer thickness t2 between the L2 layer and the L3 layer was 10 μm, and the refractive index n of the optical disk 11 was 1.6.

  Next, crosstalk light that can be generated in the optical disc 11B will be described with reference to FIG.

  When the L0 layer is the target layer, as shown in FIG. 21A, crosstalk lights C11, C12, and C13 reflected by the L1, L2, and L3 layers, respectively, are generated. When the L1 layer is the target layer, as shown in FIG. 21B, crosstalk lights C14, C15, and C16 reflected by the L0 layer, the L2 layer, and the L3 layer are generated. When the L2 layer is the target layer, as shown in FIG. 21C, crosstalk lights C17, C18, C19 reflected by the L0 layer, the L1 layer, and the L3 layer are generated. When the L3 layer is the target layer, as shown in FIG. 21 (d), crosstalk lights C20, C21, and C22 reflected by the L0 layer, the L1 layer, and the L2 layer are generated.

Table 3 summarizes the distance td (μm) in the thickness direction of the optical disc 11B between the reflection positions of the crosstalk lights C11 to C22 and the reflection positions of the signal lights in FIGS.

From Table 3, in Example 3, the values of tmin ⁺ , tmin ⁻ , tmax ⁺ , tmax ^{− in} the above (Formula 7) and (Formula 8) are as follows.

tmax ⁺ = tmax ⁻ = 35 μm
tmin ⁺ = tmin ⁻ = 10 μm
Here, tmax ⁺ crosstalk light C20, tmax ^- crosstalk light C13, tmin ⁺ crosstalk light C14, C22, tmin ^- respectively correspond to the cross talk light C11, C19.

The design values of the masks 26A ₁ and 26A _K can be obtained by substituting the values obtained above into (Expression 1) and (Expression 2).

Since tmax ⁺ = tmax ⁻ and tmin ⁺ = tmin ⁻ , the masks 26B ₁ and 26B are set as dm ₁ = dm ′ ₁ , dm _K = dm ′ _L , hm ₁ = hm ′ ₁ , and hm _K = hm ′ _{L. What} is necessary is _just to design _K. Therefore, the calculation using (Expression 3) and (Expression 4) is omitted.

  In Example 3, K = L = 2, that is, two masks are arranged on the optical disc 11B side and the light receiving element 9 side with respect to the focal point O.

  For the RAD direction, the following (Expression 37) and (Expression 38) obtained from (Expression 1) and (Expression 2), and for the TAN direction, the following (Expression 39) obtained from (Expression 1) and (Expression 2) , (Equation 40).

2 × 10 × 10 ² /1.6≧50×dm ₁ / (50 + hm ₁ _rad) (Expression 37)
_{^{2 × 35 × 10 2 /1.6≦50×dm 2}} / (50-hm 2 _rad) ... ( Equation 38)
2 × 10 × 10 ² /1.6≧150×dm ₁ / (150 + hm ₁ _tan)
... (Formula 39)
_{^{2 × 35 × 10 2 /1.6≦150×dm 2}} / (150-hm 2 _tan)
... (Formula 40)
In Example 3, hm ₁ _rad = 14 μm, hm ₁ _tan = 41 μm, dm ₁ = 1.3 mm, hm ₂ _rad = 24 μm, and hm ₂ _tan as values satisfying the ranges of (Expression 37) to (Expression 40) above. = 73 μm and dm ₂ = 2.3 mm were selected.

FIG. 22 is a diagram illustrating the positional relationship between the focal point O of signal light, the focal point of crosstalk light, and the masks 26A ₁ , 26A ₂ , 26B ₁ , and 26B ₂ in the expander optical system according to the third embodiment. In FIG. 22 (a), the dotted line, close to the focal point O, and indicates the range of removable crosstalk light mask 26A ₁ and the light receiving element 9 side of the mask 26B ₁ of the optical disc 11B side, FIG. 22 (b in), the dotted line, away from the focus O, shows a range of removable crosstalk light mask 26A ₂ and the light receiving element 9 side of the mask 26B ₂ of the optical disc 11B side.

  Further, in FIG. 22A, the position of the focal point in the expander optical system of the crosstalk light that can be generated is shown together with the value of td based on Table 3.

According to FIGS. 22A and 22B, everything that can occur within the range A in which the application ranges of the masks 26A ₁ and 26A ₂ are combined and the range B in which the application ranges of the masks 26B ₁ and 26B ₂ are combined is generated. It can be seen that the crosstalk light is condensed.

  Accordingly, since all the crosstalk lights C11 to C22 shown in FIGS. 21A to 21D can be removed with a total of four masks in the third embodiment, the configuration of the optical filter unit 20 is simplified and reduced in size. Is possible.

As shown in FIG. 23, the optical filter unit 20 according to the third embodiment forms masks 26A ₁ and 26A ₂ at the center of both surfaces 31a and 31b of the glass plate 31, and the center of both surfaces 32a and 32b of the glass plate 32. The masks 26B ₁ and 26B ₂ are formed on the glass plates 31 and 32 in parallel.

For the masks 26A ₁ and 26A ₂ , the thickness of the glass plate 31 and the distance from the focal point O to the masks 26A ₁ and 26A ₂ are dm ₁ = 1.3 mm and dm ₂ = 2.3 mm in terms of air. The distance from the focal point O is adjusted.

Further, the masks 26A ₁ and 26A ₂ are rectangles having different sizes in the TAN direction and the RAD direction as described above. The mask _{26A 1, hm 1 _rad = 14μm} , since hm ₁ _tan = 41μm, a rectangle 28 .mu.m × 82 .mu.m, for mask _{26A 2, hm 2 _rad = 24μm} , hm 2 _tan = 73μm because, 48μm × 146μm rectangular And Since the masks 26B ₁ and 26B ₂ are dm = dm ′ and hm = hm ′, they may be configured in the same manner as the masks 26A ₁ and 26A ₂ and arranged at symmetrical positions with the focus O as the center.

The masks 26A ₁ , 26A ₂ , 26B ₁ and 26B ₂ are made of an aluminum thin film like the masks 12A and 12B of the first embodiment. The incident light has a structure that reflects 100%, and the reflected light is a light receiving element. It is assumed that the light receiving cell 9 is not reached.

  As described above, in Example 3, it is possible to prevent the crosstalk light in the four-layer disc from entering the light receiving element 9.

In the third embodiment, a case where a four-layer disk is used is shown. However, for other multi-layer disks, tmin ⁺ , tmin ⁻ , tmax ⁺ , tmax are also obtained according to (Equation 23) and (Equation 24) shown in the first embodiment. The value of ⁻ may be obtained and used to design the masks 26A ₁ , 26A _K , 26B ₁ , 26B _K.

Depending on the configuration of the optical system, the NA of the target layer and the crosstalk light corresponding to the target layer in the expander optical system is different, so that the masks 26A ₁ , 26A ₂ , 26B ₁ , 26B ₂ are taken into consideration. Is further optimized to satisfy dm ₁ ≠ dm ′ ₁ , dm _K ≠ dm ′ _L , hm ₁ ≠ hm ′ ₁ , hm _K ≠ hm ′ _L.

Example 4
Since the optical pickup device of the fourth embodiment has the same configuration as that of the third embodiment, it will be described with reference to FIG. The fourth embodiment is different from the third embodiment in the structure of the optical disc that is assumed to be compatible.

  FIG. 24 shows a cross-sectional structure of an optical disc 11C assumed to be supported by the optical pickup device 1B in the fourth embodiment. The optical disk 11C is different from the optical disk 11B corresponding to the third embodiment shown in FIG. 20 in that the spacer thickness t1 = 17 μm between the L1 layer and the L2 layer.

  The crosstalk light that can be generated in the optical disc 11C is the same as that described with reference to FIG. 21 in the third embodiment, but in the fourth embodiment, the multiple reflection crosstalk light C31 shown in FIG. The difference from the third embodiment is that the multiple reflected crosstalk light C32 shown in FIG.

  The multi-reflection crosstalk light C31 shown in FIG. 25A is obtained when the L0 layer is the target layer and the crosstalk light reflected by the L1 layer to the front surface side (L2 layer side) of the optical disc 11C is the L2 layer first. Reflected on the back surface and again reflected on the L1 layer. In the multi-reflection crosstalk light C32 shown in FIG. 25B, when the L1 layer is the target layer, the crosstalk light reflected by the L2 layer to the surface side (L3 layer side) of the optical disc 11C is first of the L3 layer. Reflected on the back surface and again reflected on the L2 layer.

  The multiple reflection crosstalk lights C31 and C32 have twice the number of reflections than ordinary crosstalk light and are weak in intensity. However, in some cases, the multiple reflection crosstalk lights C31 and C32 may affect the tracking error signal. The crosstalk lights C31 and C32 are also removed.

  The multiple reflection crosstalk light C31 in FIG. 25A is equivalent to a light beam reflected from a position away from the back side by t1-t0 = 7 μm with respect to the L0 layer as the target layer. That is, the multiple reflection crosstalk light C31 can be regarded as light that is reflected only once at an arbitrary position (effective reflection position) on the effective reflection layer 51 that is a virtual reflection surface shown in FIG. .

  In addition, the multiple reflection crosstalk light C32 in FIG. 25B is equivalent to a light beam reflected from a position away from the front side by t1−t2 = 7 μm with respect to the L1 layer as the target layer. That is, the multiple reflection crosstalk light C32 can be regarded as light that is reflected only once at an arbitrary position (effective reflection position) on the effective reflection layer 52 that is a virtual reflection surface shown in FIG. .

21 (a) to 21 (d) and FIGS. 25 (a) and 25 (b), between the effective reflection positions of the crosstalk light C11 to C22 and the multiple reflection crosstalk lights C31 and C32 and the reflection position of the signal light. Table 4 summarizes the distance td (μm) in the thickness direction of the optical disc 11C. Note that the effective reflection positions of the crosstalk lights C11 to C22 that are not multiple reflections are actual reflection positions.

From Table 4, in Example 4, the values of tmin ⁺ , tmin ⁻ , tmax ⁺ , and tmax ^{− in} the above (Formula 7) and (Formula 8) are as follows.

tmax ⁺ = tmax ⁻ = 37 μm
tmin ⁺ = tmin ⁻ = 7 μm
Here, tmax ⁺ crosstalk light C20, tmax ^- crosstalk light C13, tmin ⁺ multiplex reflected crosstalk light C31, tmin ^- respectively correspond to the multiple reflection crosstalk light C32.

The design values of the masks 26A ₁ and 26A _K can be obtained by substituting the values obtained above into (Expression 1) and (Expression 2).

Since tmax ⁺ = tmax ⁻ and tmin ⁺ = tmin ⁻ , the masks 26B ₁ and 26B are set as dm ₁ = dm ′ ₁ , dm _K = dm ′ _L , hm ₁ = hm ′ ₁ , and hm _K = hm ′ _{L. What} is necessary is _just to design _K. Therefore, the calculation using (Expression 3) and (Expression 4) is omitted.

  In the fourth embodiment, as in the third embodiment, K = L = 2, that is, with respect to the focal point O, the optical disc 11B side (condensing lens 5 side, objective lens 8 side) and the light receiving element 9 side (condensing lens 4). Two masks are arranged on the side).

  Regarding the RAD direction, the following (Expression 41) and (Expression 42) obtained from (Expression 1) and (Expression 2), and for the TAN direction, the following (Expression 43) obtained from (Expression 1) and (Expression 2) , (Equation 44).

2 × 7 × 10 ² /1.6≧50×dm ₁ / (50 + hm ₁ _rad) (Formula 41)
2 × 37 × 10 ² /1.6≦50×dm ₂ / (50−hm ₂ _rad) (Formula 42)
2 × 7 × 10 ² /1.6≧150×dm ₁ / (150 + hm ₁ _tan) (Formula 43)
_{^{2 × 37 × 10 2 /1.6≦150×dm 2}} / (150-hm 2 _tan)
... (Formula 44)
In Example 4, hm ₁ _rad = 15 μm, hm ₁ _tan = 45 μm, dm ₁ = 1.0 mm, hm ₂ _rad = 30 μm, hm ₂ _tan as values satisfying the ranges of the above (formula 41) to (formula 44). = 89 μm and dm ₂ = 2.0 mm were selected.

FIG. 26 is a diagram illustrating the positional relationship between the focal point O of signal light, the focal points of crosstalk light and multiple reflection crosstalk light, and masks 26A ₁ , 26A ₂ , 26B ₁ , and 26B ₂ in the expander optical system according to the fourth embodiment. It is. In FIG. 26 (a), the dotted line, close to the focal point O, and indicates the range of removable crosstalk light mask 26A ₁ and the light receiving element 9 side of the mask 26B ₁ of the optical disc 11C side, FIG. 26 (b in), the dotted line, away from the focus O, shows a range of removable crosstalk light mask 26A ₂ and the light receiving element 9 side of the mask 26B ₂ of the optical disc 11C side.

  Further, in FIG. 26A, the position of the focal point in the expander optical system of the crosstalk light and the multiple reflection crosstalk light that can be generated is shown together with the value of td based on Table 4.

According to FIGS. 26 (a) and (b), all that can occur within the range C obtained by combining the application ranges of the masks 26A ₁ and 26A ₂ and the range D obtained by combining the application ranges of the masks 26B ₁ and 26B _2. It can be seen that the crosstalk light and the multiple reflection crosstalk light are condensed.

  Therefore, in the fourth embodiment, a total of four crosstalk lights C11 to C22 and multiple reflection crosstalk lights C31 and C32 shown in FIGS. 21 (a) to 21 (d) and FIGS. 25 (a) and 25 (b) are used. Therefore, the configuration of the optical filter unit 20 can be simplified and downsized.

The optical filter unit 20 in the fourth embodiment has the same configuration as that of the third embodiment shown in FIG. 23, and is different only in the size of the masks 26A ₁ , 26A ₂ , 26B ₁ , 26B ₂ and the distance from the focal point O. That is, for the masks 26A ₁ and 26A ₂ , the thickness of the glass plate 31 is set so that the distance from the focal point O to the masks 26A ₁ and 26A ₂ is dm ₁ = 1.0 mm and dm ₂ = 2.0 mm in terms of air. And the distance from the focal point O are adjusted.

Further, the masks 26A ₁ and 26A ₂ are rectangles having different sizes in the TAN direction and the RAD direction as described above. The mask 26A ₁ has a rectangular shape of 30 μm × 90 μm because hm ₁ _rad = 15 μm and hm ₁ _tan = 45 μm, and the mask 26A ₂ has a rectangular shape of 60 μm × 178 μm because hm ₂ _rad = 30 μm and hm ₂ _tan = 89 μm. And Since the masks 26B ₁ and 26B ₂ are dm = dm ′ and hm = hm ′, they may be configured in the same manner as the masks 26A ₁ and 26A ₂ and arranged at symmetrical positions with the focus O as the center.

As described above, in the fourth embodiment, the crosstalk light can be removed by the small optical filter unit 20 with a simple configuration as in the third embodiment, and the multi-reflection crosstalk light can also be removed. Further, since the multiple reflection crosstalk light collected at a position close to the focal point O of the signal light is removed by the masks 26A ₁ and 26B ₁ arranged farther from the focal point of the multiple reflection crosstalk light when viewed from the focal point O, the signal High stability is obtained by suppressing light loss.

(Example 5)
The optical pickup device of the fifth embodiment has the same configuration as that of the third embodiment, and the fifth embodiment is different from the fourth embodiment in the structure of an optical disk that is assumed to be compatible.

  In the fifth embodiment, the optical pickup device 1B assumes correspondence, as in the first embodiment, in the three-layer optical disk 11 shown in FIG.

  The crosstalk light and multiple reflection crosstalk light that can be generated in the optical disk 11 are the same as those described in the first and second embodiments with reference to FIGS. 15 and 18, but since t0−t1 = 5 μm, the multiplexing is possible. The effective reflection position of the reflected crosstalk light C7 is different from that of the second embodiment.

Table 5 shows the distance td (μm) in the thickness direction of the optical disk 11 between the effective reflection position of the crosstalk light C1 to C6 and the multiple reflection crosstalk light C7 that can be generated in the fifth embodiment and the reflection position of the signal light. It summarizes and shows.

From Table 5, in Example 5, the values of tmin ⁺ , tmin ⁻ , tmax ⁺ , and tmax ^{− in} the above (Formula 7) and (Formula 8) are as follows.

tmax ⁺ = tmax ⁻ = 25 μm
tmin ⁺ = 10 μm
tmin ⁻ = 5 μm
Since the effective reflection position of the multiple reflection crosstalk light C7 is the minus side (front side) with respect to the target layer, the multiple reflection crosstalk light C7 is condensed from the focal point O to the light receiving element 9 side in the expander optical system. . Further, since the value of t0-t1 is smaller than t0 and t1, the multiple reflection crosstalk light C7 is condensed closer to the focal point O than the crosstalk lights C1 to C6.

The design values of the masks 26A ₁ and 26A _K and the masks 26B ₁ and 26B _L can be obtained by substituting the values obtained above into (Expression 1) to (Expression 4).

In Example 5, the range of the defocus amount is different between the optical disc 11 side (the condenser lens 5 side and the objective lens 8 side) and the light receiving element 9 side (the condenser lens 4 side) (tmin ⁺ ≠ tmin ⁻ ). Therefore, K = 1, L = 2, that is, one mask on the optical disk 11 side and two masks on the light receiving element 9 side with respect to the focal point O are arranged.

  The following (Formula 45) to (Formula 48) obtained from (Formula 1) to (Formula 4) for the RAD direction, and the following (Formula 49) obtained from (Formula 1) to (Formula 4) for the TAN direction. Designed by (Equation 52).

2 × 10 × 10 ² /1.6≧50×dm ₁ / (50 + hm ₁ _rad) (Formula 45)
2 × 25 × 10 ² /1.6≦50×dm ₁ / (50−hm ₁ _rad) (Formula 46)
2 × 5 × 10 ² /1.6≧50×dm ′ ₁ / (50 + hm ₁ _rad ′) (Expression 47)
2 × 25 × 10 ² /1.6≦50×dm ′ ₂ / (50−hm ₂ _rad ′)
... (Formula 48)
2 × 10 × 10 ² /1.6≧150×dm ₁ / (150 + hm ₁ _tan)
... (Formula 49)
2 × 25 × 10 ² /1.6≦150×dm ₁ / (150−hm ₁ _tan)
... (Formula 50)
2 × 5 × 10 ² /1.6≧150×dm ′ ₁ / (150 + hm ₁ _tan ′)
... (Formula 51)
2 × 25 × 10 ² /1.6≦150×dm ′ ₂ / (150−hm ₂ _tan ′)
... (Formula 52)
In Example 4, hm ₁ _rad = 23 μm, hm ₁ _tan = 69 μm, dm ₁ = 1.8 mm, hm ₁ _rad ′ = 8 μm, hm ₁ as values satisfying the ranges of (Expression 45) to (Expression 52) above. _tan ′ = 24 μm, dm ′ ₁ = 0.6 mm, hm ₂ _rad ′ = 23 μm, hm ₂ _tan ′ = 69 μm, and dm ′ ₂ = 1.8 mm were selected.

FIG. 27 is a diagram illustrating a positional relationship among the focal point O of signal light, the focal points of crosstalk light and multiple reflection crosstalk light, and masks 26A ₁ , 26B ₁ , and 26B ₂ in the expander optical system according to the fifth embodiment. In FIG. 27A, the dotted line indicates the range of crosstalk light that can be removed by the mask 26A ₁ on the optical disc 11 side and the mask 26B ₂ far from the focal point O on the light receiving element 9 side, and FIG. in), the dotted line indicates the range of removable crosstalk light receiving element 9 side of the mask 26B ₁ close to the focal point O.

  Further, in FIG. 27A, the positions of the focal points in the expander optical system of the crosstalk light and the multiple reflection crosstalk light that can be generated are shown together with the value of td based on Table 5.

According to FIGS. 27A and 27B, all the possible crosstalk light and multi-reflection crosstalk light are collected within the application range of the masks 26A ₁ , 26B ₁ , 26B _2. Recognize.

  Accordingly, since all the crosstalk light C1 to C6 and the multiple reflection crosstalk light C7 that can be generated can be removed with a total of three masks in the fifth embodiment, the configuration of the optical filter unit 20 can be simplified and downsized. Is possible.

The optical filter unit 20 in the fifth embodiment, as shown in FIG. 28, the mask 26A ₁ is formed in a central portion of one surface 31b of the glass plate 31, both sides 32a of the glass plate 32, the mask 26B at the center portion of the 32b ₁ and 26B ₂ and glass plates 31 and 32 are juxtaposed. The method for forming the mask is the same as that in the first embodiment.

The distance from the focal point O to the glass plate 31 on the optical disc 11 side, the glass plate 32 on the light receiving element 9 side, and the focal point O to the masks 26A ₁ , 26B ₁ , 26B ₂ is dm ₁ = The thickness of the glass plates 31 and 32 and the distance from the focal point O are adjusted so that 1.8 mm, dm ′ ₁ = 0.6 mm, and dm ′ ₂ = 1.8 mm.

In addition, each mask has a rectangular shape with different sizes in the TAN direction and the RAD direction as described above. The mask _{26A 1, hm 1 _rad = 23μm} , since hm ₁ _tan = 69μm, and a rectangular 46μm × 138μm, the mask 26B ₁ is, hm ₁ _rad' = 8μm, since _{hm 1 _tan' = 24μm, 16μm ×} 48μm The rectangle of Mask 26B ₁ is the same size as the mask 26A _1.

  Note that the optical filter unit 20 is not limited to the configuration of FIG. 28, and may be a configuration in which, for example, three glass plates each having a mask formed on one side are arranged in an appropriate distance relationship.

As described above, in Embodiment 5, by providing the mask 26B ₁ dedicated for removing multiple reflections crosstalk light C7, can be removed multiple reflection crosstalk light C7 with a simple structure.

  In Examples 4 and 5, in the case of four-layer and three-layer optical discs, the multiple reflection crosstalk light is reflected three times as Li + 1 layer → Li + 2 layer → Li + 1 layer when the Li layer is the target layer. Only the crosstalk light is removed. As described in the second embodiment, the above-described three-reflection multi-reflection crosstalk light has the highest reflectance among all the multi-reflection cross-talk lights. It is sufficient to consider only the reflected crosstalk light.

The same applies to the case of dealing with multi-layer discs other than the 4-layer and 3-layer shown in Embodiments 4 and 5, and tmin ⁺ and tmin ⁻ use (Equation 33) to (Equation 36) described in Embodiment 2. It is required by the method that was used. The values of tmax ⁺ and tmax ⁻ can also be obtained from (Equation 24) described above.

DESCRIPTION OF SYMBOLS 1,1A, 1B Optical pick-up apparatus 2 Light source 3 Polarizing beam splitter 4,5 Condensing lens 6 1/4 wavelength plate 7 Standing mirror 8 Objective lens 9 Light receiving element 10,20 Optical filter part 11,11A-11C Optical disk 12A , 12B, 26A _k , 26B _l mask

Claims (3)

An objective lens for making a light beam incident on an optical disc having a plurality of recording layers;
A light receiving element that causes a reflected light beam, which is a light beam reflected by the optical disc, to be incident through a second condenser lens after being focused by the first condenser lens;
The amount of light passing through a predetermined region including the optical axis of the reflected light beam, which is arranged in the optical axis direction of the reflected light beam between the first condensing lens and the second condensing lens, is reduced. An optical filter unit that reduces a crosstalk light that is a reflected light beam from a recording layer other than a recording layer on which recording or reproduction of an information signal of the optical disc is performed, using the mask.
The mask sandwiches the signal light focus, which is the focal point of the first condensing lens, of the signal light, which is the reflected light beam from the recording layer on which the information signal is recorded or reproduced, and the light receiving side An optical pickup device, wherein at least one piece is arranged on the element side.   The mask includes the first condensing of the crosstalk light from the innermost recording layer of the optical disc when an information signal is recorded or reproduced on the outermost recording layer of the optical disc. At least one sheet is disposed between the focal point of the lens and the signal light focal point, and when the information signal is recorded or reproduced on the innermost recording layer of the optical disk, the outermost surface side of the optical disk 2. The optical pickup device according to claim 1, wherein at least one piece of crosstalk light from the recording layer is disposed between the focal point of the first condenser lens and the signal light focal point. The distance of the mask on the optical disc side closest to the signal light focus from the signal light focus is dm ₁ , the size corresponding to the radius is hm _1, and the mask on the optical disc side farthest from the signal light focus The distance from the signal light focus is dm _K , the size corresponding to the radius is hm _K , the distance from the signal light focus of the mask on the light receiving element closest to the signal light focus is dm ′ ₁ , and the radius is equivalent to the size and Hm' _1, distance Dm' L from the signal light focus farthest the optical disk side of the mask from the signal light _focus, when the size of the radius corresponding to hm' _L, hm 1, hm The optical pickup device according to claim ₁ , wherein _{K 1} , hm ′ ₁ , and hm ′ _L satisfy the following (Expression 1) to (Expression 4).
2 × (tmin ⁺ ) × Me ² / n ≧ he × dm ₁ / (he + hm ₁ ) (Formula 1)
2 × (tmax ⁺ ) × Me ² / n ≦ he × dm _K / (he−hm _K ) (Formula 2)
2 × (tmin ⁻ ) × Me ² / n ≧ he × dm ′ ₁ / (he + hm ′ ₁ ) (Formula 3)
^{2 × (tmax -) × Me} 2 / n ≦ he × dm' L / (he-hm' L) ... ( Equation 4)
However,
Me: Ratio of the focal length of the first condenser lens and the focal length of the objective lens n: Refractive index of the optical disc he: Radius when the light receiving portion of the light receiving element is projected at the position of the signal light focal point Substantial size tmin ⁺ : effective reflection position, which is a reflection position in the optical disk when the crosstalk light is regarded as light reflected only once in the optical disk, is more than the reflection position of the signal light. Minimum value of the distance in the thickness direction of the optical disc between the effective reflection position of the crosstalk light and the reflection position of the signal light in the crosstalk light on the back side of the optical disk tmin ⁻ : the effective reflection position is the The light between the effective reflection position of the crosstalk light and the reflection position of the signal light in the crosstalk light closer to the surface of the optical disc than the reflection position of the signal light. Disc in the thickness direction of the minimum distance value tmax of ^+: in the cross-talk light effective reflection position is on the back side of the optical disc than the reflection position of the signal light, and the effective reflection position of the cross talk light, the signal light The maximum value of the distance in the thickness direction of the optical disk between the reflection position of the optical disk tmax ⁻ : the crosstalk light in the crosstalk light whose effective reflection position is on the surface side of the optical disk from the reflection position of the signal light The maximum value of the distance in the thickness direction of the optical disc between the effective reflection position and the reflection position of the signal light

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