JP2008010020A - Optical element and optical pickup - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the following problem: in an optical pickup for recording/reproducing information in/from different kinds of optical recording media such as a DVD and a CD, using light beams having different wavelengths, it is difficult for a polarizer used with two or more wavelengths in common to be compatible with both efficiency and measures against a birefringent disk with each other. <P>SOLUTION: About an area (area F) where an opening of a distributed wavelength plate 6 is large, areas (area D1 and area D2) with different properties in counter positions are arranged to oppose each other, and about an area (area E) where an opening is small, areas which have similarly the areas D1 and D2 and the same properties are arranged at counter angular positions. Thus, the efficiency is compatible with the measures against the birefringent disk without sacrificing a signal light quantity and signal quality. Moreover, since the arrangement requires only to change the arrangement pattern of the distributed wavelength plate, productivity is not spoiled either. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention has a wave plate having the property of performing different polarization conversion on light of different wavelengths and a laser light source of different wavelengths, and is used for optical discs having various specifications and standards such as CD, DVD, Blu-ray disc, etc. The present invention relates to an optical pickup used for recording or reproducing signals.

  In recent years, as an optical disk device used for an external storage device of a computer, a video recorder or the like, for example, a CD (CD-ROM disk or CD-R / RW disk), DVD (DVD-ROM disk, DVD-RAM disk, DVD-R / RW discs), Blu-ray discs, etc., products for multi-disc applications that support a variety of recording media with different standards, such as recording density / capacity, groove specifications, and substrate thickness, with a single device are increasing.

  In such an apparatus, an optical pickup for recording / reproducing information on / from an optical disc uses a laser light source having a different wavelength, or light detection for receiving light reflected from the optical disc and obtaining control signals such as an RF signal, focus, and tracking. A plurality of devices are mounted, and writing, erasing, and reading are performed on a medium suitable for each using a laser light source, a photodetector, and the like.

  In order to reduce the size and cost of the device while maintaining stable performance for discs of various different standards, there is a technology that balances adaptability to different types of discs and downsizing of the optical system of the optical pickup. It becomes important.

  As one condition for obtaining adaptability to different types of discs, for example, it is necessary to ensure stable signal reproduction performance for discs with a thick transparent base material and larger birefringence, and optical systems. In order to make the system compact, it is necessary to share optical components for light of different wavelengths as much as possible to reduce the number of components as much as possible and to configure in a small space.

  Conventionally, an optical pickup having a compact optical system corresponding to a plurality of recording media is disclosed in Patent Document 1.

  FIG. 5 shows the overall configuration of the optical pickup device in Patent Document 1.

  The optical pickup device shown in FIG. 5 collects light beams having different wavelengths for the purpose of writing data to or reading data from different types of optical disks, and collects the light beams on the signal surface of the optical disk. An objective lens for forming a light spot, a polarizing element comprising a hologram element and a wave plate, and a photodetector for detecting the intensity of the light beam reflected from the optical disk. A polarizing element made up of a hologram element and a wave plate is disposed at a portion where the optical path from the light source to the objective lens and the optical path from the signal surface of the optical disk to the photodetector are common.

  Hereinafter, the configuration of the optical pickup device and the action of the polarizing element in Patent Document 1 will be described with reference to FIGS. 5 and 6.

  In FIG. 5, the photodetector 103 is formed on a semiconductor substrate 102 such as a silicon chip, and a laser chip 101 that emits two types of laser light having wavelengths λ <b> 1 and λ <b> 2 is mounted on the substrate 102. The photodetector 103 is composed of a plurality of photodiodes that convert light into an electrical signal by a photoelectric effect. Of the laser light emitted by the laser chip 101, for example, the wavelength λ1 is about 650 nm and the wavelength λ2 is about 800 nm. For example, laser light with a wavelength λ1 is used for DVD, and laser light with a wavelength λ2 is used for CD.

  The light of wavelength λ1 emitted from the laser chip 101 is converted into parallel light by the collimator lens 104 and then transmitted through the polarizing element 107. The polarizing element 107 is an element in which a polarizing hologram element 105 and a wave plate 106 are integrated. The polarizing element 107 is attached to the support member 135 together with the objective lens 108, and is driven integrally with the objective lens 108 by the actuator 136.

  In the following description, the optical path of light traveling from the light source to the disk is referred to as the forward path of the optical system, and the optical path of light reflected by the disk and directed to the photodetector is referred to as the return path of the optical system.

  The light (wavelength λ 1) transmitted through the polarizing element 107 is collected and reflected on the recording surface 109 of the optical disk by the objective lens 108. The reflected light again passes through the objective lens 108 and is diffracted by the polarizing element 107 due to the polarization dependence of the hologram 105. The light diffracted by the polarizing element 107 enters the photodetector 103 through the collimator lens 104. The photodetector 103 generates an electrical signal corresponding to the change in the amount of light. This electric signal is a focus control signal, a tracking control signal, and an RF signal.

  The polarization hologram element 105 completely transmits the linearly polarized light in the forward path (P-polarized light component), and completely diffracts the polarization direction component (S-polarized light component) orthogonal to the forward path in the backward path.

  Such an optical system that uses different polarizations in the round trip path of the optical system is generally called a polarization optical system. Since the optical transmission rate of the round trip path is high, the recording power and the signal from the recording medium with low reflectivity are transmitted. It is used in recording optical systems that are required to be compatible with S / N.

  The light having the wavelength λ 2 emitted from the laser chip 101 is also converted into parallel light by the collimator lens 104 and transmitted through the polarizing element 107. The light transmitted through the polarizing element 107 is collected on the recording surface 110 of the optical disk having a different substrate thickness by the objective lens 108 and reflected by the recording surface 110. The reflected light is diffracted by the polarizing element 107 again through the objective lens 108. The diffracted light enters the photodetector 103 through the collimating lens 104. The photodetector 103 generates an electrical signal corresponding to a change in the amount of light, and the electrical signal is a focus control signal, a tracking control signal, and an RF signal.

  That is, the optical pickup in Patent Document 1 has one laser chip 101 that emits light of two types of wavelengths for DVD and CD, and has a wavelength obtained from reflected information from different optical information media 109 or 110. The common light detector 103 receives signal light of different light.

  According to such a configuration, an optical pickup corresponding to optical recording media of different standards can be made compact. This is because, in general, the light from the disk is guided to independent photodetectors by using a branching unit that splits light of different wavelengths in the middle of the optical path, whereas in this configuration, the same one branching unit is used. Because it can be realized with a certain hologram element and the same photodetector, the optical path from the laser light source to the optical recording medium (outward path) and the optical path from the optical recording medium to the optical detector (return path) are different. This is because they can be completely shared, the number of parts of the optical system can be reduced, and the optical system can be stored in a small space.

  6A is a plan view of the wave plate 106 shown in FIG. 5, and FIG. 6B is a wave plate in which light traveling from the light source side to the optical information medium 110 and reflected light from the optical information medium 110 are reflected. FIG. 6 is a diagram showing a state in which the lens 106 and the polarization hologram 105 are reciprocated. FIG. 6C is a diagram illustrating an example of polarization conversion by the wavelength plate 106 with respect to light having the wavelength λ1, and FIG. 6D is a diagram illustrating an example of polarization conversion by the wavelength plate 106 with respect to light having the wavelength λ2.

  As shown in the plan view of the wave plate in FIG. 6A, the wave plate is divided into four regions by lines (x-axis and y-axis) passing through the center of the optical axis. Regions of the same nature (region A and region B) are formed. Region A has an axial direction of optical anisotropy in a direction that forms an angle of θ1 with respect to the x-axis direction in the drawing, and region B is optically anisotropic in a direction that forms an angle of θ2 with respect to the x-axis direction in the drawing. Has an axial direction. It is assumed that the direction of linearly polarized light incident on the wave plate 106 from the light source side coincides with the x axis. The angles θ1 and θ2 are 45 ° −α, 45 ° + α, and (0 <α ≦ 15 °) with respect to the x-axis direction, respectively.

  Hereinafter, a wave plate in which regions having different properties are distributed will be expressed as a distributed wave plate.

  By the area division shown in FIG. 6A, the light passing through the area A out of the light from the light source as shown in FIG. 6B is collected by the lens 108 and reflected by the optical information medium 110, and the optical axis. It passes through a region A having the same property at a symmetrical position. On the other hand, the light passing through the region B is reflected by the optical information medium 110 and passes through the region B at a symmetrical position on the return path.

  Of the reflected light, the polarization component in the direction orthogonal to the forward linear polarization (that is, the y-axis) is diffracted by the polarization hologram 105 to become signal light, and light of the other components returns to the laser light source as zero-order light.

  Here, when the refractive index anisotropy of the wave plate is Δn, the thickness is d, and the wavelength is λ1 (wavelength for DVD), the retardation of the wave plate represented by 360 ° × Δnd / λ1 is an odd multiple of 90 °. be equivalent to. Specifically, for example, about 270 ° is desirable.

  The retardation 270 ° is equivalent to a 3/4 wavelength plate, that is, a 1/4 wavelength plate, and is a conventional uniform 1/4 wavelength plate if α of the optical anisotropy axis direction 45 ° ± α is 0, When linearly polarized light having a vibration direction parallel to the x-axis direction (P-polarized light component) is incident, it becomes circularly polarized light, exits the wave plate, and light reflected by the optical information medium passes through the wave plate in the opposite direction again. It becomes linearly polarized light (S-polarized light component) having a polarization direction in the y-axis direction perpendicular to the forward linearly polarized light.

  In the wave plate shown in FIG. 6A, since α is not 0, the polarization conversion of the light that reciprocates through the regions A and B having different optical anisotropy axis directions is different from each other.

  FIG. 6C shows a change in the polarization state of the light having the wavelength λ1 when it passes through the distributed wave plate 106 in a reciprocating manner.

  The light of wavelength λ1 is linearly polarized light (P wave) as indicated by I when passing through the polarization hologram and entering the wave plate in the outward path of the optical system. Since the conditions of the retardation and optical axis orientation of the distributed wave plate 106 are close to a quarter wave plate, the region A and the region B are converted into elliptically polarized light that is slightly close to a circle with a different ellipse principal axis (state II). This is reflected by the disk (assuming no birefringence) and passes through the wave plate again on the return path of the optical system, so that it becomes elliptically polarized light (state III) close to linearly polarized light almost orthogonal to the forward path. Among these, the S wave component (light of the vibration component in the y-axis direction in FIG. 6A) is diffracted by the hologram 105.

  Since the retardation of the wave plate is approximately inversely proportional to the wavelength, assuming that the wavelength λ1 (wavelength for DVD) is 270 degrees, the light of wavelength λ2 (wavelength for CD) is about 225 ° (270 ° × 650 / 800≈ 270 ° × 5/6 = 225 °), that is, about 5λ / 8 plate.

  That is, if the light having the wavelength λ2 is used, the light reciprocates twice through the distributed wave plate 106, which is equivalent to a 5λ / 8 × 2 = 5/4 wave plate, that is, a quarter wave plate.

  FIG. 6D shows a process of converting the polarization state by the distributed wavelength plate 106 for the light of wavelength λ2 (light of the wavelength for CD). Similarly, linearly polarized light I having a polarization direction in the x-axis direction is transmitted through the wave plate 106, undergoes different polarization conversions in the regions A and B, and enters an elliptical polarization state as shown in II. To do.

  If the disc substrate has no birefringence, the light traveling back and forth through the region A and the light traveling back and forth through the region B have different principal axis directions, but both are nearly circularly polarized (III in FIG. 6 (d)). The light enters the polarization hologram 105 along the return path of the optical system. Therefore, approximately half of the light (S wave component) is diffracted by the polarization hologram 105, and the other half of the light (P wave component) is transmitted through the hologram 105 without being diffracted.

  On the other hand, consider the case where the disk base material has a large birefringence, for example, a birefringence equivalent to a half-wave plate by reciprocation as described in the background art. At this time, polarized light (III ′ in FIG. 6D) whose elliptical principal axis is just orthogonal to the polarization state in the case where the light incident on the polarization hologram 5 does not have birefringence by polarization conversion equivalent to a half-wave plate. In this case as well, although the principal axis direction differs between the light traveling back and forth through the region A and the light traveling back and forth through the region B, both are substantially circularly polarized.

  That is, in this case as well, about half of the light (S wave component) is diffracted by the polarization hologram 105 and about half of the light (P wave component) is transmitted without being diffracted. Therefore, the amount of light diffracted by the polarization hologram 105, that is, the amount of signal light, has a very small change compared to the case where the disk base material has no birefringence.

  For light of wavelength λ2, the amount of signal is less than that of light of wavelength λ1 because it deviates from the perfect diffraction condition in the return path of the optical system even if the substrate has no birefringence. However, long wavelength lasers for CDs and the like are less affected by a decrease in efficiency because it is easy to increase the output.

That is, the base material is thin like a DVD, and the birefringence of the base material is unlikely to occur during the manufacturing process, but it is highly efficient for both the return path of the optical system for light with a wavelength λ1 that is short in wavelength and difficult to achieve high output. On the other hand, even if the efficiency is low, the amount of light can be covered with a high-power laser, but since the base material is thick, a product having a large optical birefringence in the production process can be easily produced. For light, signal light can be obtained even if light whose polarization state has changed due to the birefringence of the substrate returns from the disk.
JP 2005-339766 A

  According to the wave plate as shown in the background art and the optical pickup using the wave plate, while ensuring the efficiency of the round-trip path with respect to the light of a short wavelength laser used for a DVD or the like, a longer wavelength such as a CD or the like The laser beam is always diffracted by the hologram in any region in the plane, so that the optical transmission loss of the element is relatively small for short-wavelength laser light, which is difficult to achieve high output. There is a merit that it is possible to cope with variations in optical characteristics of an optical disk substrate using a long-wavelength laser that can easily achieve high output.

  On the other hand, the use of such a distributed wave plate does not significantly reduce the efficiency, but there is a demerit that the amount of signal light is reduced as compared with the case of using a uniform wave plate.

  For example, in the case of a distributed wave plate in which the azimuth angle of the optical anisotropy axis of the wave plates in the two regions A and B as shown in FIG. 6 is α = 5 ° to 15 °, it is 4 to the optical wavelength of the DVD. The amount of signal light is lower than that of a uniform wave plate by about% to 12% (when the disk has no birefringence).

  That is, it is advantageous to increase the shift amount α of the optic axis direction of the distributed wave plate in order to reduce the amount of signal light on a disk such as a CD having a large birefringence, but on the other hand, if the value of α is too large, the birefringence is increased. However, the amount of signal light loss for a recording medium such as a DVD having a low reflectivity becomes a problem. In addition, the quality of the reproduced signal is slightly reduced due to the distributed wave plate.

  FIG. 7 shows calculated values of the signal light amount and the optical jitter with respect to the birefringence of the disc for the light having the wavelength of DVD. That is, when the birefringence of the disk is extreme, the optical jitter is infinite because there is no signal in the uniform wave plate, but the signal light quantity does not become zero in the distributed wave plate. However, in the uniform wavelength plate, the optical jitter does not change so much with respect to a certain amount of birefringence, whereas in the distributed wavelength plate, the optical jitter gradually deteriorates, that is, the signal quality deteriorates as the birefringence increases.

  Further, there is a problem of stray light as another problem in an optical pickup that shares an optical system with light of different wavelengths as shown in FIG. 5 and performs recording / reproduction of a disc according to each wavelength with one objective lens. .

  That is, in such an optical pickup, the aperture of light incident on the objective lens is often limited by the wavelength, but the light reflected by such aperture limiting means (for example, a wavelength-selective aperture limiting film) becomes stray light. May enter the detector and adversely affect the signal quality.

  Conventionally, such stray light may vary due to errors such as assembly / adjustment of an optical pickup, which may affect the quality of servo signals and RF signals.

  In order to solve the above-described problems, the present invention provides, as a first invention, an optical element disposed in an optical path through which light of at least two types of wavelengths reciprocates, and the element comprises a polarization hologram and a wavelength plate. And the axial direction of the optical anisotropy of the wave plate is different from each other among a plurality of regions in the element plane, and a certain region is symmetrically the same with respect to the optical axis center of the light passing through the element. The other region is characterized in that regions having different anisotropic axis orientations are arranged symmetrically with respect to the optical axis center.

  Or as 2nd invention, it is an optical element arrange | positioned in the optical path through which the light of at least 2 types of wavelength reciprocates, Comprising: An element has a polarization hologram and a wavelength plate as a structure, and the retardation of a wavelength plate is an element A plurality of in-plane regions are different from each other. In one region, the same retardation region is arranged symmetrically with respect to the optical axis center of light passing through the element, and in another region, different retardation regions are symmetrically arranged with respect to the optical axis center. It is arranged.

  In the first invention, the axial direction of the optical anisotropy of the wave plate is different in two ways between a plurality of regions in the element plane, and each is 45 ° with respect to the polarization direction of light incident on the element. It may be ± α (0 <α ≦ 15 °).

  In the second invention, the wave plate is disposed in an optical path through which light of at least two types of wavelengths reciprocates, and a phase difference between ordinary light and extraordinary light generated when passing through the wave plate is within the element plane. The plurality of regions may be different from each other, and the phase difference may be 270 ° ± δ (0 ° <δ ≦ 30 °) with respect to light of one wavelength.

  Further, in the above invention, the openings through which light of different wavelengths reciprocate are different, and a plurality of regions having the same property are arranged in an axial symmetry within the common opening, and an opening through which only some wavelengths reciprocate One or a plurality of regions having different properties in axial symmetry may be disposed in the.

  Further, in the above invention, the divided area of the region in which the regions having different properties in the axial symmetry are formed may be relatively larger than the divided area in the region in which the plurality of regions having the same properties in the axial symmetry are arranged. .

  In the above invention, the optical element has a wavelength-selective aperture limiting film as a configuration, and in the region where the wavelength-selective aperture limiting film is formed, the wavelength plate has an axially symmetric region having different properties. In other regions, regions having the same property may be formed in axial symmetry.

  Further, in the above invention, the optical element in which regions having different properties alternately arranged in a fine lattice or stripe shape are formed in an axially symmetrical manner in the region where the aperture limiting film is formed is inclined with respect to the optical axis. It is also possible that the light reflected by the wavelength-selective aperture limiting film passes through the wave plate again, partly passes through a region having the same property, and partly passes through a region having a different property.

  In the above invention, when the distance between the wave plate and the aperture limiting film is d, the distribution pattern pitch of the wave plate is P, and the inclination with respect to the optical axis of the element is θ, the relationship of Sin θ = P / 2d is established. It may be.

  The present invention also provides one or a plurality of laser light sources that emit at least two or more wavelengths, condensing means for condensing light emitted from the laser light sources onto the optical information medium, and light reflected from the optical information medium. The optical element according to any one of the above inventions is provided in a portion where the optical path of light from the light source toward the optical information medium and the optical path of light from the optical information medium toward the optical detector are common. May be. Further, a photodetector that receives light from the optical information medium may be shared by light of two or more different wavelengths.

  In addition, the present invention includes a unit in which a laser that emits light of different wavelengths and a photodetector that is shared by two or more types of light that receives light from an optical information medium are integrated. The optical element according to any one of the above inventions may be provided in a common part of an optical path from the light source to the optical information medium and an optical path from which the light from the optical information medium reaches the photodetector.

  According to the present invention, in an optical pickup that records and reproduces information on optical information media having different substrate thicknesses and areal densities using light of different wavelengths, the effect of reducing the influence of birefringence of the substrate is ensured for one wavelength On the other hand, it is possible to prevent a loss of light quantity of the light of the other wavelength, and it is possible to realize an optical pickup having a simple configuration with high efficiency and more stable performance. Alternatively, it is possible to reduce the influence of stray light caused by the aperture limiting means. In addition, the productivity and cost reduction effects as shown in the background art are not impaired.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the component which has the same function as what was demonstrated by background art is shown with the same code | symbol.

(Embodiment 1)
Embodiment 1 of an optical pickup and an optical element according to the present invention will be described with reference to FIGS. Hereinafter, the same numbers are assigned to the same components.

  FIG. 1 is a configuration diagram of an optical pickup to which an optical element according to the present invention is applied. In FIG. 1, the wave plate 6 formed integrally with the polarization hologram 5 has a feature as compared with the optical pickup of FIG. 6 described in the background art. However, the optical system layout and light in which light from the light source 1 that emits light of two wavelengths integrated with the detector 2 is reflected by the disk 9 or 10 and detected as signal light by the photodetector 2. Since the transmission operation is the same as that of the pickup shown in FIG. 6 of the background art, a detailed description thereof will be omitted.

  In the present embodiment, a pickup configuration in which the light source and the detector are integrated is shown, but the present invention can be applied even if they are independent. Further, the wave plate 6 is integrated with the polarization hologram 5, but these may be separate, or may be a polarizing filter such as PBS instead of the hologram.

  FIG. 2A shows a part of the configuration of the optical pick-up according to the present invention, that is, a side view of the polarization hologram 5, the distributed wavelength plate 6, and the objective lens 8, and a wavelength λ1 (DVD optical wavelength) that reciprocates through the hologram. It is a figure which shows the light ray of wavelength (lambda) 2 (light wavelength of CD).

  As shown in FIG. 2A, the light of wavelength λ1 and wavelength λ2 passes through the polarization hologram 5 as it is in the outward path of the optical system, and passes through the distributed wavelength plate 6 in the region composed of E and F having a large aperture. The polarization state changes.

  This light is focused by the objective lens 8 on the recording surface of the disk 9 having a thin substrate thickness, and the light having the wavelength λ2 is condensed on the recording surface of the disk 10 having a thick substrate thickness.

  Here, the objective lens 8 is designed so that the light of wavelength λ1 is ideally condensed on the recording surface of the disk 9 in the entire aperture region, while the aperture ratio of light of wavelength λ2 is designed. Condensation is good in the inner peripheral area of E with a small A, but in the outer peripheral area F having a high aperture ratio, a condensing state with extremely large aberration is achieved.

  Therefore, the light having the wavelength λ1 is reflected by the disk in the entire aperture region (E + F) and passes through the distributed wavelength plate 6 along the return path of the optical system. At this time, forward and backward light passes through diagonal positions with respect to a point where the axis passing through the center of the objective lens 8 and the surface of the distributed wave plate 6 intersect.

  The light of the wavelength λ2 is well focused by the objective lens 8 and the forward and backward light passes through diagonal positions in the low aperture region (in the region E). The outside (area F) is sufficiently diffused because it is not well focused on the disk.

  FIG. 2B is a plan view of the distributed wave plate 6 in the present invention.

  As shown in FIG. 2B, in the low aperture region (E region), regions D1 and D2 having the same property are arranged diagonally with respect to the center point O.

  In the region D1, the azimuth of the optical axis is 45 ° + α (0 <α ≦ 15 °) with respect to the x axis (coincident with the incident polarization direction of the forward path), and in the region D2, the azimuth of the optical axis is the x axis. It is 45 ° −α (0 <α ≦ 15 °) with respect to the incident polarization direction of the forward path.

  The retardation of the wave plate is 270 ° with respect to the wavelength λ1 (DVD light) and 225 ° with respect to the light with wavelength λ2 (CD light).

  That is, the low aperture CD light region is completely equivalent to that described in the background art.

  On the other hand, in the high aperture region (the ring zone region of F), regions D1 and D2 having different properties with respect to the center point O at diagonal positions are arranged.

  In this case, the light beams having the wavelength λ1 pass through the optical axis direction of 45 ° + α (or 45 ° -α) on the forward path and the optical axis direction of 45 ° -α (or 45 ° + α) on the return path. In other words, it is equivalent to passing through a uniform wave plate with 45 degrees orientation and no distribution.

  FIG. 3 shows the signal light amount of the light having the wavelength λ1 (that is, the light amount diffracted by the polarization hologram in the return path) in the configuration shown in FIG. 2, and the reproduction performance obtained from this signal, that is, the calculated value of the optical jitter.

  As shown in FIG. 3, the signal amplitude is larger than that in the conventional example in which the diagonal regions are the same for all the openings by making the regions at the opposite positions in the high aperture region different from each other. And jitter performance is improved.

  When the birefringence is large, both the signal light quantity and the jitter are reversed. However, a thin disk such as a DVD does not actually have such a large birefringence, so that the improvement effect is greater.

  Further, the function and performance in the opening area of the CD are kept exactly the same as in the prior art.

  Although it is conceivable to use a uniform wavelength plate with a 45 ° azimuth for all the high aperture regions, in that case, there are three types of azimuths of the optical axis: 45 °, 45 ° + α, and 45 ° -α, resulting in poor productivity.

  On the other hand, in the configuration of the present invention, it is only necessary to change the region arrangement, and the manufacturability is not impaired.

  Further, in the configuration of the present invention, the configuration of the distributed wave plate is made different in the optical anisotropy axis direction, but the effect is the same in the type in which the retardation of the wave plate is changed instead.

  In this case, for example, the same effect can be obtained by setting the optical axis direction to 45 ° and the retardation to 270 ° + δ (0 <δ ≦ 30 °), 270 ° −δ.

  Further, the pattern of the wave plate is not limited to that shown in FIG. 2B, and any shape may be used as long as the opposing positions are arranged so as to be a pair of the same properties or a pair of different properties.

  Furthermore, in the present embodiment, two wavelengths of light for DVD and light for CD have been described. However, even in the case of simultaneously using light of the wavelength of Blu-ray or HD-DVD that uses a high aperture area of the lens, this high wavelength is also used. By making the aperture region a pair of regions having different properties at diagonal positions, it is possible to prevent the loss of light amount and the deterioration of signal quality.

(Embodiment 2)
FIG. 4A shows a part of the configuration of the optical pickup according to the second embodiment of the present invention. Here, the description of the same components as those in FIG.

  In the present embodiment, a wavelength-selective aperture limiting film 13 is included as a configuration, and a polarizing element (including the polarization hologram 5, the distributed wavelength plate 6, and the aperture limiting film 13) including the wavelength selective aperture limiting film 13 is arranged with respect to the optical axis. It is characteristic that it is inclined by a predetermined angle β.

  In the first embodiment, it is assumed that the light having the wavelength λ2 passing through the region F on the outer peripheral side is not well collected by the objective lens, and thus the light reflected by the disk is sufficiently diffused.

  However, depending on the design of the lens, the amount of aberration of the wavelength λ2 on the outer peripheral side is low, so the amount reflected on the disk and mixed into the signal light on the return path may not be negligible.

  Alternatively, in the case of a diffractive objective lens, high-order diffracted light generated in the low aperture region may be reflected by the disk and mixed into the signal through the outer periphery of the objective lens.

  In such a case, a wavelength-selective aperture pattern film is formed in the high aperture region of the device, and the light having the wavelength λ1 is reciprocally transmitted, and the light having the wavelength λ2 is shielded from entering from the outer peripheral side in the return path. Is done.

  However, in this case, since the aperture pattern film reflects the light having the wavelength λ2, the light on the outer peripheral side is reflected in the outward path of the optical system, passes through the same wavelength plate region in the return path, and is polarized and diffracted by the hologram pattern. This becomes a noise component.

  FIG. 4B is a plan view showing a pattern of the distributed wavelength plate 6 in the present embodiment.

  Also in the present embodiment, in the inner peripheral side region (E region), regions having the same properties (a pair of D1 or a pair of D2) are arranged with respect to the center O, and the outer peripheral region (F In the region (2), regions (D1 and D2 pairs) having different properties in the diagonal position with respect to the center O are arranged.

  It is assumed that the distributed wave plate 6 is inclined by β around the y axis. In this embodiment, D1 and D2 regions having different properties periodically along the x-axis direction are alternately formed in the F region on the outer peripheral side.

  FIG. 4C is a schematic diagram showing the progress of light in the F region. The solid line arrow in the figure passes through the D2 region in the forward path, reflects off the opening limiting film 13 having an inclination, and passes through the adjacent D1 region in the return path. On the other hand, the wavy arrow passes through the D1 region in the forward path and is reflected by the opening limiting film 13 having an inclination, but passes through the same D1 region in the return path.

  When the distance between the distributed wavelength plate 6 and the aperture limiting film 13 is d, the distribution pattern pitch of the distributed wavelength plate 6 is P, and the inclination with respect to the optical axis of the element is θ, the relationship of Sunθ = P / 2d is established. If it does so, the area | region which passes the same property and the area | region which passes a different property will be located in a line periodically by the half-pitch of a wavelength plate pattern.

  When such light with different polarization states periodically present at a small pitch is viewed through a polarizing hologram, a bright and dark pattern with high contrast as shown in FIG. 4C is obtained.

  That is, the light reflected by the aperture pattern in the outer peripheral region is diffused under the same action as passing through a periodic bright and dark filter with a fine pitch.

  As described above, according to the second embodiment, it is possible to eliminate the influence that the light returning to the detector is diffused on the signal.

  The optical pickup according to the present invention is a device of an optical information recording apparatus that performs recording / reproduction on a plurality of different optical recording media with one apparatus, in particular by integrally forming a light source and a photodetector with different wavelengths. Therefore, the present invention can be applied to applications such as CD, DVD, and Blu-ray recording type optical disc apparatuses that are required to be small and low cost.

Configuration diagram of an optical pickup according to Embodiment 1 of the present invention A partial side view of a pickup including the wave plate in the first embodiment and a plan view of the wave plate Characteristic diagram of signal level and jitter value with respect to disc base birefringence in optical pickup by optical element of embodiment 1 The partial side view of the pick-up containing the wave plate in Embodiment 2, the top view of a wave plate, and the schematic diagram which shows the mode of reflection of CD light by an aperture film Configuration of conventional optical pickup A plan view of a conventional optical element, a partial side view of a pickup including the optical element, a schematic diagram showing a change in the polarization state of the DVD wavelength light by the wave plate, and a polarization state of the CD wavelength light by the wave plate Schematic diagram showing changes Characteristics of signal level and jitter value for disc birefringence by an optical pickup equipped with a conventional distributed wave plate

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser light source 3 Photodetector 4 Collimate lens 5 Polarization hologram 6 Distribution wavelength plate 8 Objective lens 13 Aperture restriction film

Claims (12)

An optical element disposed in an optical path through which light of at least two types of wavelengths passes reciprocally, the element having a polarization hologram and a wave plate, and the axis direction of the optical anisotropy of the wave plate is in the element plane A plurality of regions are different from each other, and in one region, a region having the same anisotropic axis orientation is arranged at a diagonal position with respect to the optical axis center of the light passing through the element, and another region is diagonal with respect to the optical axis center. An optical element, wherein regions having different anisotropic axis orientations are arranged at positions. An optical element disposed in an optical path through which light of at least two types of wavelengths reciprocates, the element having a polarization hologram and a wave plate, and the retardation of the wave plate between a plurality of regions in the element surface Different regions are located in the same retardation region in the diagonal position with respect to the optical axis center of the light passing through the element, and different regions are disposed in the diagonal position in the diagonal position with respect to the optical axis center. An optical element. The axial direction of the optical anisotropy of the wave plate is different in two ways between a plurality of regions in the element plane, and each is 45 ° ± α (0 <α ≦ 15 with respect to the polarization direction of the light incident on the element. The optical element according to claim 1, wherein A wave plate arranged in an optical path through which light of at least two types of wavelengths reciprocates, and the phase difference between ordinary light and extraordinary light generated when passing through the wave plate is different among a plurality of regions in the element plane. 3. The optical element according to claim 2, wherein the phase difference is 270 ° ± δ (0 ° <δ ≦ 30 °) with respect to light of one wavelength. The apertures through which light of different wavelengths reciprocate are different, and a plurality of regions having the same property are arranged in an axial symmetry within the common aperture, and the apertures through which only a part of the wavelengths pass are different in axisymmetric manner. 5. The optical element according to claim 1, wherein one or a plurality of property regions are arranged. 2. A divided area of a region in which regions having different properties in axial symmetry are formed is relatively larger than a divided area in a region in which a plurality of regions having the same properties are arranged in axial symmetry. The optical element according to any one of 5. The optical element has a wavelength-selective aperture limiting film as a configuration, and in the region where the wavelength-selective aperture limiting film is formed, regions having different properties of the wavelength plate are arranged in an axial symmetry. 7. The optical element according to claim 1, wherein a region having the same property is formed in an axial symmetry in the region. In the region where the aperture limiting film is formed, an optical element in which regions having different properties alternately arranged in a fine lattice pattern or stripe pattern are arranged in an axially symmetrical manner is arranged with an inclination relative to the optical axis. 8. The optical element according to claim 7, wherein the light reflected by the selective aperture limiting film passes through the wave plate again and partially passes through a region having the same property and partly having a different property. The relationship of Sinθ = P / 2d is established, where d is the distance between the waveplate and the aperture limiting film, P is the distribution pattern pitch of the waveplate, and θ is the inclination with respect to the optical axis of the element. 8. The optical element according to 8. One or a plurality of laser light sources that emit light of at least two types of wavelengths, light collecting means for condensing the light emitted from the laser light source onto an optical information medium, and light reflected from the optical information medium are received 10. The optical detector according to claim 1, wherein the optical path of light from the laser light source toward the optical information medium and the optical path of light from the optical information medium toward the photodetector are common. An optical pickup comprising the optical element described in 1. 11. The optical pickup according to claim 10, wherein a photodetector for receiving light from the optical information medium is shared by light of two or more different wavelengths. A unit comprising a laser light source that emits light of different wavelengths and a photodetector shared by light of two or more wavelengths that receives light from an optical information medium is provided, and light of different wavelengths is emitted from the laser light source. The optical element according to any one of claims 1 to 9 is provided in a common part of an optical path toward the optical information medium and an optical path where light from the optical information medium reaches the photodetector. Optical pickup.

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