JP4861934B2 - Optical pickup, optical disc apparatus, and optical element - Google Patents

Description

  The present invention relates to an optical pickup that reproduces information recorded on an optical disc and an optical disc apparatus equipped with the optical pickup.

  As background art of this technical field, for example, there is Patent Document 1 below. Patent Document 1 discloses that “a light that can suppress interference light from an adjacent layer during recording and / or reproduction of a multi-layer optical disc having a plurality of recording layers on one side and improve fluctuation of a tracking error signal detected by DPP. "I will provide a pickup."

JP 2005-203090 A

  In the optical disc system, there is a double-layer disc in which the signal recording surface is doubled in order to increase the recording capacity. For example, in a DVD, a double-layer disc exists in DVD-R and DVD-RW, and a capacity approximately twice that of a single-layer optical disk is realized. Similarly, in a high-density recording optical disk system called Blu-ray Disc (hereinafter referred to as BD) or HD-DVD Disc (hereinafter referred to as HD), a dual-layer disk exists.

  In an optical pickup mounted on an optical disc apparatus, reflected light from the optical disc is used to generate a servo control signal in the focus direction and tracking direction of the objective lens. Therefore, if unnecessary light is added to the reflected light to be used for the signal, a problem occurs in signal detection.

  In particular, an optical pickup that divides a light beam emitted from a laser light source into at least three light beams of zero-order light and ± first-order light, irradiates the optical disk, and receives reflected light from the optical disk with a photodetector. However, when a reproducing operation of a two-layer disc is performed, there is a problem that reflected light from other layers becomes an unnecessary light component and becomes a disturbance component of a tracking signal.

  With respect to such a problem, in Patent Document 1 described above, a predetermined optical member is disposed immediately below the objective lens in order to prevent unnecessary light from an adjacent layer other than the signal reproduction layer from being received by the photodetector. Means for doing so are disclosed. However, in this disclosed means, in order to prevent interference light from being received by the photodetector, not only unnecessary light from the adjacent layer but also part of the important signal reproduction light cannot be received by the photodetector. End up. As a result, there is a problem that bad effects such as deterioration of the quality of the reproduced signal and a decrease in light utilization efficiency during signal reproduction are unavoidable.

  In light of the above situation, the present invention satisfactorily suppresses unnecessary light from adjacent layers other than the signal reproduction layer, while maintaining a high reliability without substantially reducing the quality of the signal reproduction light and the light utilization efficiency. An object is to provide an optical pickup and an optical disc apparatus.

  The above object can be achieved by, for example, the invention described in the claims.

  The following is a brief description of an outline of typical inventions disclosed in the present application.

  In the optical pickup of the present invention, the objective lens and the light detection are performed so that the light beam reflected by the recording layer other than the recording layer focused by the objective lens for reproduction is not incident on the light receiving surface of the photodetector. An optical element is placed between the two.

  The optical element has a function of diffracting a light beam having a predetermined wavelength incident on the incident surface at a predetermined incident angle α in a predetermined diffraction angle direction with a predetermined diffraction efficiency η, and with respect to the incident angle α. An optical element having a function of transmitting a light beam incident on the incident surface with an incident angle shifted by a predetermined minute angle error ± δ or more as it is with a predetermined transmittance T is preferable.

  Further, the optical element has a function of reflecting or absorbing a light beam incident on a predetermined region including the central optical axis of the incident light beam and transmitting the light beam incident outside the predetermined region as it is. A partial light shielding filter element may be used.

  According to the present invention, it is possible to provide an optical pickup and an optical disc apparatus having high reliability.

  A specific configuration for carrying out the present invention will be described below.

  Hereinafter, the configuration of an optical pickup will be described as Embodiment 1 of the present invention with reference to the drawings. FIG. 1 is a schematic diagram showing an optical system configuration of an optical pickup 20 according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a semiconductor laser light source that emits a laser beam having a wavelength of 405 nm, for example.

  The light beam emitted from the semiconductor laser light source 1 reaches the diffraction grating 2 immediately after. Here, the diffraction grating 2 separates the incident light beam into three light beams of 0th-order light and ± 1st-order diffracted light. In the optical path after the diffraction grating 2, three light beams are actually traveling. However, for the sake of simplicity in this specification, the description will be limited to only the main 0th-order light beam in principle.

  In an actual optical pickup, it is necessary to monitor the light emission intensity of the semiconductor laser 1 by the front monitor 5 as will be described later. For this reason, the forward light beam emitted from the semiconductor laser light source 1 and separated into three light beams by the diffraction grating 2 does not direct the total light amount toward the objective lens 7 as will be described later. It is necessary to enter the monitor 5. Therefore, not only the S-polarized light component that is completely perpendicular to the paper surface, but also the P-polarized light component that is substantially parallel to the paper surface remains in the forward light beam.

  In this way, in order to adjust the polarization component of the light beam emitted from the semiconductor laser light source, for example, the semiconductor laser light source 1 itself is attached by being rotated slightly around the optical axis, or a half immediately after the laser light source 1. What is necessary is just to arrange | position the optical element provided with the function which can convert the polarization direction of a light beam like a wavelength plate. However, the present invention is not limited to such a configuration, and the present invention can be sufficiently applied to an optical pickup in which such a polarization direction conversion element is not mounted. Therefore, in FIG. 1, a polarization direction conversion element such as a half-wave plate is not particularly shown, and further detailed explanation is omitted.

    Next, the light beam emitted from the half-wave plate 2 reaches the PBS prism 3. The PBS prism 3 is an optical element having a function of reflecting almost 100% of the S-polarized component of the incident light beam and transmitting almost 100% of the P-polarized component. Therefore, most of the light amount of the light beam that has reached the PBS prism 3 is reflected in the direction of 90 ° with respect to the incident direction, and only a small amount of remaining light (P-polarized component) is transmitted through the PBS prism 3. To the front monitor 5 for monitoring the light quantity of the light beam.

  On the other hand, the light beam reflected from the PBS prism 3 is converted into a substantially parallel light beam by the collimator lens 4, is converted into circularly polarized light by passing through the quarter-wave plate 6, and then enters the objective lens 7. To do. The objective lens 7 is a lens that can be focused on the information recording surface of the first optical disc 11 having a substrate thickness of 0.1 mm, such as BD, when a 405 nm band light beam is incident as parallel light. It is.

  The objective lens 7 is held by an actuator 8 including a drive coil 9 and a magnet 10 disposed at a position facing the drive coil 9, and a predetermined objective lens position control signal is transmitted to the actuator 8. , The position of the objective lens 7 can be adjusted in the radial direction of the optical disk 11 and the optical axis direction substantially perpendicular to the disk surface. The light beam transmitted through the objective lens 7 has its disk irradiation light intensity controlled based on the amount of light detected by the front monitor 5 during recording or reproduction.

  Next, the light beam reflected from the optical disk 11 returns to the quarter-wave plate 6 through the objective lens 7 through the same optical path as the forward light in the opposite direction to the forward path, and this quarter-wave plate 6. Is converted to P-polarized light orthogonal to the polarization direction of forward light (S-polarized light). Thereafter, the disk reflected light beam passes through the collimating lens 4, is converted from a parallel light beam into a convergent light beam, and reaches the PBS prism 3 again. Unlike the forward path, the PBS prism 3 is transmitted with a transmittance of about 100%, passes through the detection lens 12, the first unnecessary light removing filter 13, and the second unnecessary light removing filter 14, and then the photodetector. The light is condensed on a predetermined light receiving surface in 15 and a predetermined photoelectric conversion signal is detected.

  Of the optical system configuration of the optical pickup outlined above, the first unnecessary light removal filter 13 and the second unnecessary light removal filter 14 are the core part of the present invention, and the configuration, function, and effect thereof. Will be explained in detail later.

  By the way, signals used for position control of the objective lens 7 such as a focus control signal and a tracking control signal are generated from the photoelectric conversion signals detected by the respective light receiving surfaces (not shown) of the photodetector 15. Each control signal is supplied to the actuator 8 to control the position of the objective lens 7. An information signal recorded on the disk is also reproduced from a photoelectric conversion signal detected from a predetermined light receiving surface among the light receiving surfaces.

  As a means for detecting the focus control signal and tracking control signal described above, as a representative method, there are an astigmatism method for the focus control signal and a push-pull method or a differential push-pull method for the tracking control signal. Of course, the optical pickup of this embodiment can also be employed. However, since these focus or tracking control signal detection methods are all known techniques and are not directly related to the contents of the present invention, detailed description thereof will be omitted.

  Further, as a matter of course, the present invention is not limited to the focus and tracking control signal detection method as described above, and the present invention can be applied to an optical pickup employing any focus and tracking control signal detection method. .

  Incidentally, there are two cases as shown in FIGS. 2A and 2B when an information signal is recorded on a double-layer disc, or when an information signal is reproduced from a double-layer disc.

  That is, as shown in FIG. 2 (a), the recording layer 100 in the optical disc 11 and on the far side (back side) with respect to the objective lens 7 (hereinafter, this recording layer is referred to as L0 layer) is recorded / reproduced. A case where the light beam 50 is focused on a point P on the L0 layer as an object layer (hereinafter referred to as case A) and a side closer to the objective lens 7 as shown in FIG. A case where the recording layer 101 on the front side (hereinafter, this recording layer is referred to as L1 layer) is a recording / reproducing target layer, and the light beam 50 is condensed at a point Q on the L1 layer (hereinafter this case is referred to as Case B). ).

  In any case, the light beam 50 condensed at a predetermined position on the recording / reproducing target layer (P point or Q point in FIG. 2) reflects each recording / reproducing target layer and travels as a signal light beam 51. The optical path travels in the opposite direction and reaches the objective lens 7 again. Then, after passing through the objective lens 7, it follows the return optical path as described above, and finally converges on predetermined light receiving surfaces 70, 71, 72 in the photodetector 15 as shown in FIG. Signal light spots 52, 53, and 54 having a predetermined size are formed.

  On the other hand, a part of the condensed beam 50 reflects the other recording layer (L1 layer 101 in case A, L0 layer 100 in case B), and is applied to the objective lens 7 as the unnecessary light beam 61 in the same manner as the signal light beam 51. Reach. In the conventional optical pickup, the unnecessary light beam 61 also passes through the objective lens 7 and follows the same return optical path as that of the signal light beam 51. Finally, for example, as shown in FIG. A predetermined light receiving surface 70, 71, 72 and the vicinity thereof are irradiated as an unnecessary light spot 62 that is largely blurred.

  As a result, as shown in FIG. 4, the signal light spots 52, 53, and 54 and the unnecessary light spot 62 overlap on the light receiving surfaces 70, 71, and 72 in the photodetector 15, respectively. An interference phenomenon occurs between the spots, and as a result, unnecessary fluctuation components and noise components are superimposed on the photoelectric conversion signals detected on the respective light receiving surfaces. The unnecessary fluctuation component and noise component cause a disadvantage that the signal quality of the focus control signal, tracking control signal or information reproduction signal generated or reproduced from each photoelectric conversion signal is significantly deteriorated.

  Therefore, in the following, the first unnecessary light removing filter 13 and the second unnecessary light removing filter 14 disclosed in the present invention are such that the unnecessary light beams generated in the cases A and B are respectively the photodetector 15. And a function of preventing interference with a signal light spot that causes signal quality degradation.

  Hereinafter, specific configurations, functions, and effects of the filter elements will be described as Example 2 and Example 3.

  First, the first unnecessary light removing filter 13 will be described. Now, assuming that the distance between the two recording layers in the optical disk 11, that is, the L0 layer 100 and the L1 layer 101 is Δ, in the case A, that is, in the case of FIG. The point P ′ approaching the objective lens 7 side by a distance corresponding to about 2Δ from the condensing point P on the L0 layer 100 is divergent light having a virtual light emission point and enters the objective lens 7.

  Therefore, when the signal light beam 51 after passing through the objective lens 7 is compared with the unnecessary light beam 61, the signal light beam 51 is converted into a light beam substantially parallel to the optical axis, whereas the unnecessary light beam 61 is Clearly converted into a predetermined divergent light beam. As a result, when each light beam incident on the photodetector 15 is compared, as shown in FIG. 5A, the signal light beam 51 is incident in the state of a predetermined convergent light beam as shown by a solid line. The convergence degree of the unnecessary light beam 61 is obviously reduced. Therefore, depending on the optical design of the detection optical system, for example, as shown by the broken line in FIG. 5A, it is possible to make the light beam substantially parallel to the optical axis (indicated by a one-dot chain line in the figure).

  FIG. 6 shows that in the above-described state, each light beam is regarded as a bundle of a plurality of light beams on the light beam cross section (XY plane), and the distribution of the traveling angle with respect to the optical axis of each light beam is a ray tracing simulation. It is the figure which calculated and plotted by the method of. As is clear from this figure, each light beam constituting the signal light beam 51 (indicated by X in the figure) is distributed almost evenly in the range of about ± 2 ° in both the X-axis direction and the Y-axis direction. On the other hand, the rays (circles in the figure) constituting the unnecessary light beam 61 are concentrated in the X-axis direction and the Y-axis direction at 0 ° and in the vicinity thereof, and are clearly markedly different with respect to the distribution of the ray travel angles. Is seen.

  Therefore, by making use of the remarkable difference in the distribution of the light beam traveling angle, a light beam having a light beam traveling angle of 0 ° with respect to the optical axis and an angle in the vicinity thereof, that is, substantially parallel to the optical axis, by some optical element. If the optical path is largely deflected only by a light beam, for example, by an optical action such as reflection or diffraction, or if the light beam itself can be extinguished, the signal light beam 51 is hardly affected and the unnecessary light beam 51 is not affected. It is possible to remove only from the light receiving surface of the photodetector. The first unnecessary light removing filter 13 is an optical element having such a function.

  By the way, as a specific example of an optical element having such a high sensitivity selectivity with respect to the light beam traveling angle, there is an optical element called a volume type (or volume type) hologram. As is apparent from the name, this optical element called a volume hologram is a kind of hologram element, but a general hologram element has a planar configuration, that is, forms a holographic diffraction grating on a predetermined surface. On the other hand, it has a predetermined thickness D as shown in FIG. 7, and forms a holographic lattice-like structure not only on the surface but also in the thickness direction.

  A specific example of the manufacturing method will be briefly described. As shown in FIG. 7A, an element 13 made of a substantially transparent material and two parallel lights having a predetermined wavelength λ and having coherence with each other. Beams 80 and 81 are prepared. For example, a light beam 80 (hereinafter referred to as a reference light beam) is irradiated perpendicularly to the element 13 while the light beam 81 is irradiated at a predetermined angle with respect to the reference light beam 80. Irradiate at an angle of θ. Then, a holographic lattice-like structure is three-dimensionally formed by the change in the refractive index of the material at the position of the interference fringes formed on the surface and inside of the element 13 by both light beams.

By forming the holographic lattice-like structure three-dimensionally in this way, so-called Bragg diffraction conditions can be made highly sensitive. That is, the volume hologram element 13 manufactured by the above-described manufacturing means has a wavelength λ incident on the element 13 perpendicularly as in the case of the reference light beam 80, as indicated by the solid line in FIG. The light beam 82 becomes a light beam 83 diffracted in the angle θ direction with an efficiency of almost 100%. However, when the incident angle of the incident light beam 82 is slightly inclined from the vertical direction, the diffraction efficiency is rapidly lowered. For example, as shown by a broken line in FIG. 7B, the incident light beam 84 whose incident angle has a slope of δ ₀ has almost zero diffraction efficiency, and a light amount of almost 100% is a simple transmitted light beam. It will be 85.

  According to academic literature (for example, “Optical Data Storage Topic Training Course Notes”, IEEE, SPIEA & OSA [23, April, 2006]), etc., the angular error (tilt) δ of the incident light beam in this volume hologram element The relationship with the diffraction efficiency η is generally expressed by the following formula 1, and further plotting the relationship gives a graph as shown in FIG.

ただし、ｎ：ホログラム素子の屈折率
Ｄ：ホログラム素子の板厚さ
θ：回折光の回折角度
λ：入射光ビームの波長

そして上記数式１から導出すると、回折効率１００％から最初に０％にまで低下する傾き幅δ₀（以下、これを傾き角の感度幅と記す。）は、以下の数式２で表される。

Where n is the refractive index of the hologram element
D: Thickness of hologram element
θ: Diffraction angle of diffracted light
λ: wavelength of incident light beam

Then, when derived from Equation 1 above, an inclination width δ ₀ (hereinafter referred to as an inclination angle sensitivity width) that decreases from 100% diffraction efficiency to 0% first is expressed by Equation 2 below.

ここで数式２を用いて具体的な数値例を当てはめると、例えば、
波長λ＝４０５ｎｍ
屈折率ｎ＝１．５
素子板厚さ＝１．５ｍｍ
回折角度＝３０°
以上の値を上記数式２に代入すると、傾き角の感度幅δ₀は約０．０２°と極めて急峻な感度幅が得られることがわかる。

Here, when applying a specific numerical example using Formula 2, for example,
Wavelength λ = 405 nm
Refractive index n = 1.5
Element plate thickness = 1.5mm
Diffraction angle = 30 °
By substituting the above values into Equation 2, it can be seen that the sensitivity range δ ₀ of the tilt angle is about 0.02 °, and a very steep sensitivity range is obtained.

As described above, if the sensitivity range of the tilt angle is a very steep value such as 0.02 °, it is conjectured that it is difficult to be practically used. However, in the volume hologram, a method of multiplexing is possible in order to arbitrarily widen the sensitivity range. This is because the hologram reference light beam 80 is not only perpendicularly incident but also repeatedly incident at different angles, and a holographic grating structure is formed in multiple positions at the position of the interference fringe with the light beam 81 formed each time. It is a technique to go. In the volume hologram produced in this way, the relationship between the angle error (tilt) δ of the incident light beam and the diffraction efficiency η is 2 of the Sinc function with the peak position gradually moved as shown in FIG. By superimposing the power graph, as a result, for example, as indicated by a broken line in the figure, it is possible to obtain a diffraction efficiency characteristic having a sensitivity width δ ₁ of an arbitrary inclination angle.

  Since the volume hologram itself is a well-known technique, further detailed explanation is omitted, but the volume hologram produced by the above-described method can be used with respect to the ray traveling angle as described above. Since a good selectivity can be given with an arbitrary sensitivity range, the first unnecessary light removing filter 13 is a very effective optical element.

  That is, as shown in FIG. 10, when the volume hologram is arranged as the first unnecessary light removing filter element 13 in the return optical path of the optical pickup 20, the signal light beam 51 is hardly affected. Only the unnecessary light beam 61 is selectively diffracted at a predetermined diffraction angle θ, and the optical path after the filter element 13 is greatly deflected in an arbitrary direction so that it is not incident on the light receiving surface in the photodetector 15 and the vicinity thereof. Can be.

  FIG. 11 shows light receiving surfaces 70, 71, 72 in the photodetector 15 when the above-mentioned volume hologram is arranged in the return light of the optical pickup 20 as the first unnecessary light removing filter element 13 in the case A. 2 is a spot diagram in which unnecessary light beams irradiated on the periphery thereof are calculated and plotted using a calculation method of ray tracing simulation. Each small black circle in the figure is the arrival point of each light beam when the unnecessary light beam is regarded as a bundle of a plurality of light beams. As shown in the figure, it can be confirmed that the unnecessary light beam that should have entered the light receiving surface and the vicinity thereof is almost completely removed by the unnecessary light removing action of the filter element 13.

  In this embodiment, as a representative example of a filter element for removing unnecessary light using a volume hologram, an example of diffracting a light beam substantially perpendicularly incident on the volume hologram has been described. However, the present invention is not limited thereto.

  For example, a volume hologram that selectively diffracts light incident at an angle α designed in the vicinity and an angle near the angle α instead of normal incidence is also possible, and such a volume hologram is used for removing unnecessary light. Even if it is used as a filter element, it does not matter.

  In this case, it goes without saying that when the volume hologram is manufactured, the reference light beam 80 is not incident perpendicularly to the element but is incident at a predetermined design angle α. Of course, such a volume hologram is used as a filter element for removing unnecessary light when the light beam incident on the filter element at the angle α and the vicinity thereof is used as an unnecessary light beam. It is.

  Furthermore, in the present embodiment, a volume hologram has been described as a specific example of the first unnecessary light removing filter element 13. However, the present invention is not limited thereto. When the sensitivity of the light beam angle does not require so high sensitivity, a general hologram element may be used, and other than the hologram element, for example, the traveling angle of the light beam or light beam such as a dielectric multilayer film or a photonic crystal Any material that can utilize dependency or selectivity may be used as the first unnecessary light removing filter element 13.

  Next, the second unnecessary light removing filter 14 will be described. In the case B, that is, the case of FIG. 2B, the unnecessary light beam 61 is separated from the objective lens 7 side by a distance corresponding to about 2Δ from the condensing point Q on the L1 layer 101 which is the recording / reproducing target layer. It enters into the objective lens 7 as divergent light having 'as a virtual light emitting point.

  Therefore, when the signal light beam 51 after passing through the objective lens 7 is compared with the unnecessary light beam 61, the signal light beam 51 is converted into a light beam substantially parallel to the optical axis, whereas the unnecessary light beam 61 is Obviously, it is converted into a predetermined convergent light beam. As a result, when each light beam incident on the photodetector 15 is compared, as shown in FIG. 5B, the signal light beam 51 is incident in a predetermined convergent light beam state as shown by a solid line. The unnecessary light beam 61 obviously has a stronger convergence as shown by a broken line in the figure, for example, and converges the light beam at a predetermined position on the optical axis between the detection lens 12 and the photodetector 15 in the return optical path. Point R is formed.

  Therefore, when the cross sections of the two light beams when the signal light beam 51 and the unnecessary light beam 61 are cut on the plane 21 including the convergence point R and perpendicular to the optical axis are shown in FIG. Has a substantially circular light beam cross section having a predetermined size, whereas the unnecessary light beam 61 is concentrated only on the optical axis center point R and a very small region in the vicinity thereof. There is clearly a marked difference in the size of the light beam cross section.

  Therefore, using this difference, as shown in FIG. 13, a minute light-shielding mask 22 for completely blocking the amount of light is provided only in a very small area on a transparent substrate having a transmittance of almost 100%. An optical element 14 is prepared, and this optical element 14 is disposed in the return optical path of the optical pickup 20 as a second unnecessary light removing filter, and the light shielding mask 22 has the optical axis center point R in the plane 21 and its optical path. By adjusting the position so as to cover the vicinity, almost no influence is exerted on the signal light beam 51, and only the unnecessary light beam 61 is almost completely blocked and is not irradiated on each light receiving surface in the photodetector 15. Can be.

  The size of the light shielding mask 22 of the optical element 14 can be any size and shape as long as it can block only the unnecessary light beam among the passing light beams, for example, a size of about several tens of μm. Can be formed. In the current optical pickup configuration, the size of the light-shielding mask may be about 50 μm. The position of the light shielding mask 22 of the optical element 14 is preferably arranged at a position substantially coincident with the focal position of the unnecessary light beam in the return path.

  FIG. 14 shows the light receiving surface in the photodetector 15 when the optical element having the above-described minute light shielding mask in the case B is arranged in the return light of the optical pickup 20 as the second unnecessary light removing filter element 14. 70 is a spot diagram in which unnecessary light beams 70, 71, 72 and their surroundings are calculated and plotted using a calculation method of ray tracing simulation. Each small black circle in the figure is the arrival point of each light beam when the unnecessary light beam is regarded as a bundle of a plurality of light beams. As shown in the figure, it can be confirmed that the unnecessary light beam that should have entered the light receiving surface and the vicinity thereof is almost completely removed by the unnecessary light blocking action of the filter element 14.

  As described above, by arranging both the first unnecessary light removing filter 13 and the second unnecessary light removing filter 14 in the same optical pickup, it is possible to determine which recording layer in the two-layer disc. Even if it is used as a recording / playback layer, the signal light beam is hardly affected, and only unnecessary light beams generated from other recording layers are selectively excluded from the light-receiving surface of the photodetector. It is possible to satisfactorily solve the problem of signal quality degradation of each detection signal or reproduction signal caused by interference with an unnecessary light beam.

In the return optical system (detection optical system) configuration of the optical pickup 20 shown in FIGS. 1, 5, 10, etc., the first unnecessary light removing filter 13 is provided on the side far from the photodetector 15. Although the second unnecessary light removing filter 14 is arranged on the near side, it is needless to say that this arrangement order may be completely reversed. Also, the first unnecessary light removing filter 13 and the second unnecessary light removing filter 14 may be joined to form one optical element. Furthermore, the first and second unnecessary light removal filters may be joined together or individually to another optical element such as the detection lens 12 or the polarization beam splitter 3. By thus joining the filter elements or other optical elements and integrating them as optical elements, the number of parts of the entire optical pickup can be reduced, and the optical system configuration can be simplified.
By the way, all of the embodiments so far have been directed to the double-layer disc of high-density media such as BD and HD, but the present invention is not limited to this. The present invention may be applied to a double-layer disc in an existing medium such as a DVD or a CD, and the present invention is applicable and effective to a high-layer disc having three or more layers.

  Next, as Example 4, an optical information reproducing apparatus equipped with the optical pickup 20 of the present invention shown in Example 1 will be described. FIG. 15 shows a schematic block diagram of an optical information reproducing apparatus equipped with the optical pickup 20 in this embodiment. A part of the signal detected by the optical pickup 20 is sent to the optical disc discrimination circuit 121. When the optical disc discriminating operation in the optical disc discriminating circuit 121 corresponds to the oscillation wavelength of the semiconductor laser in which the substrate thickness of the optical disc is lit, and the case where it corresponds to a different oscillation wavelength In addition, the fact that the focus control signal amplitude level detected by the optical pickup 20 is increased in the former case is utilized. The determination result is sent to the control circuit 124. Further, a part of the detection signal detected by the optical pickup 20 is sent to the servo signal generation circuit 122 or the information signal detection circuit 123. The servo signal generation circuit 122 generates a focus control signal and a tracking control signal from various signals detected by the optical pickup 20 and sends them to the control circuit 124. On the other hand, the information signal detection circuit 123 detects the information signal recorded on the optical disc 11 from the detection signal of the optical pickup 20 and outputs it to the reproduction signal output terminal. The control circuit 124 selects whether the optical disc 11 is a normal single-layer disc or a double-layer disc based on the signal from the optical disc discrimination circuit 121, and according to the result, the focus control signal generated by the servo signal generation circuit 122 and the tracking are selected. A predetermined objective lens drive signal is generated from the control signal and sent to the actuator drive circuit 125. In response to the objective lens drive signal, the actuator drive circuit 125 drives the objective lens actuator in the optical pickup 20 to control the position of the objective lens 7. The control circuit 124 controls the position of the optical pickup 20 in the access direction by the access control circuit 126, and controls the spindle motor 130 to rotate by the spindle motor control circuit 127 to rotate the disk 11 or the double-layer disk 22. Further, the control circuit 124 drives the laser lighting circuit 128 to light the semiconductor laser 1 mounted on the optical pickup 20 as appropriate, thereby realizing a recording / reproducing operation in the optical disc apparatus.

  Here, an optical disk reproducing apparatus is configured by including an information signal reproducing unit that reproduces an information signal from a signal output from the optical pickup 20 and an output unit that outputs a signal output from the information signal reproducing unit. Is possible. An optical disc recording apparatus includes an information input unit that inputs an information signal, and a recording signal generation unit that generates a signal to be recorded on the optical disc from information input from the information input unit and outputs the signal to the optical pickup 20. It is also possible to configure.

  The embodiments of the optical pickup and the optical disc apparatus according to the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various improvements and modifications can be made without departing from the gist of the present invention.

Schematic showing an example of the configuration of the optical pickup optical system of the present invention FIG. 1 is an enlarged view of the vicinity of an objective lens in the optical pickup optical system configuration example of FIG. FIG. 1 is an enlarged view of the vicinity of a light detection surface in the configuration example of the optical pickup optical system in FIG. FIG. 1 is an enlarged view of the vicinity of a light detection surface in the configuration example of the optical pickup optical system in FIG. The figure which expanded and displayed the return path detection system part in the optical pick-up optical system structural example of FIG. The figure which showed the light ray travel angle distribution of the signal light and unnecessary light in 1st Example of this invention FIG. 1 is a schematic side view showing a basic method for producing a volume hologram used in the first embodiment of the present invention and its optical characteristics. The diagram which showed an example of the relationship between the light beam incident angle and diffraction efficiency of the volume type hologram used in 1st Example of this invention FIG. 4 is a diagram for explaining a diffraction sensitivity width expansion method by multiple recording of volume holograms used in the first embodiment of the present invention. FIG. 3 is an enlarged view of a detection optical system portion for explaining the function of an optical pickup equipped with a volume hologram used in the first embodiment of the present invention. The spot diagram which shows the result of the ray tracing simulation implemented in order to verify the unnecessary light removal effect in 1st Example of this invention The enlarged view of the filter element 14 for demonstrating the 2nd Example of this invention The enlarged view of the filter element 14 for demonstrating the 2nd Example of this invention The spot diagram which shows the result of the ray tracing simulation implemented in order to verify the unnecessary light removal effect in 2nd Example of this invention The block diagram for demonstrating the function of the optical disk apparatus carrying the optical pick-up of this invention

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 2 ... Diffraction grating, 3 ... PBS prism, 4 ... Collimator lens, 5 ... Front monitor, 6 ... Quarter wavelength plate, 7 ... Objective lens, 8 ... Actuator, 11 ... Optical disk, 12 ... Detection Lens: 13... First unnecessary light removal filter, 14. Second unnecessary light removal filter, 15... Photodetector, 20... Optical pickup, 70, 71, 72.

Claims (6)

An optical pickup that irradiates an optical disc having at least two recording layers with a light beam and detects a reflected light beam from the optical disc,
A laser light source that emits a light beam having a predetermined wavelength;
An objective lens for condensing the light beam on any recording layer of the optical disc;
A photodetector arranged to receive part or all of the reflected light beam from the recording layer of the optical disc;
An optical element disposed in an optical path from the objective lens to the photodetector,
The optical element diffracts the light beam incident on the incident surface at a predetermined incident angle α in a predetermined diffraction angle direction with a predetermined diffraction efficiency η, and a predetermined minute angle error with respect to the incident angle α. The light beam incident on the incident surface at an incident angle shifted by ± δ or more is transmitted as it is with a predetermined transmittance T,
A light beam incident on the optical element after being reflected by any recording layer of the optical disc and diffracted in the predetermined diffraction angle direction by the optical element is prevented from irradiating the light receiving surface in the photodetector. An optical pickup characterized by being configured as follows. The optical pickup according to claim 1,
Furthermore, it has a partial light shielding filter element disposed in the optical path from the objective lens to the photodetector,
The partial light blocking filter reflects or absorbs a light beam incident within a predetermined region including the central optical axis of the incident light beam, and transmits the light beam incident outside the predetermined region as it is. ,
A light beam reflected by any recording layer of the optical disc and incident on the light shielding filter element and then reflected or absorbed by the light shielding filter element is configured not to irradiate the light receiving surface in the photodetector. An optical pickup characterized by The optical pickup according to claim 1 or 2,
The light beam diffracted in the predetermined diffraction angle direction by the optical element is reflected by the recording layer located closer to the objective lens than the recording layer focused by the objective lens for reproduction. An optical pickup characterized by being a light beam. The optical pickup according to claim 2,
The light beam reflected or absorbed by the predetermined region of the partial light-shielding filter element is a recording layer located on the side farther from the objective lens than the recording layer focused by the objective lens for reproduction. An optical pickup characterized by being a reflected light beam. An optical pickup that irradiates an optical disc having at least two recording layers with a light beam and detects a reflected light beam from the optical disc,
A laser light source that emits a light beam having a predetermined wavelength;
An objective lens for condensing the light beam on any recording layer of the optical disc;
A photodetector arranged to receive part or all of the reflected light beam from the recording layer of the optical disc;
A composite optical element disposed in an optical path from the objective lens to the photodetector,
The composite optical element is
A function of diffracting a light beam having a predetermined wavelength incident on the incident surface at a predetermined incident angle α in a predetermined diffraction angle direction with a predetermined diffraction efficiency η;
A function of transmitting a light beam incident on the incident surface at an incident angle shifted by a predetermined minute angle error ± δ or more with respect to the incident angle α as it is with a predetermined transmittance T;
A function of reflecting or absorbing a light beam incident within a predetermined region including the central optical axis of the incident light beam and transmitting the light beam incident outside the predetermined region as it is;
A light beam that is configured so that a light beam diffracted, reflected, or absorbed by the composite optical element after being incident on the composite optical element is not irradiated onto a light receiving surface in the photodetector. pick up. An optical pickup according to any one of claims 1 to 5 ,
A servo signal generation circuit that generates a focus error signal and a tracking error signal using a signal output from the optical pickup,
The optical disc apparatus, wherein the servo signal generation circuit can generate a tracking signal by an arithmetic method similar to the differential push-pull method.

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