JP4339222B2 - Optical pickup device - Google Patents

Description

  The present invention relates to a polarizing lens element and an optical pickup device including the polarizing lens element, and more specifically, a polarizing lens for performing recording or reproduction on a plurality of types of optical disks using objective lenses having different numerical apertures. The present invention relates to an element and an optical pickup device including the element.

  In recent years, many types of optical discs using a blue-violet semiconductor laser having a wavelength of about 400 nm to 415 nm as light sources have been proposed as next-generation high-density optical discs. In such a plurality of types of optical discs, a light transmission layer (hereinafter referred to as a cover glass) is provided on the objective lens side in the recording layer. Some optical discs have different cover glass thicknesses, and others have different physical properties of the optical disc itself such as track pitch. Some optical disks have different numerical apertures of objective lenses to be used.

  The larger the numerical aperture (NA) of the objective lens, the smaller the beam diameter of the focused spot focused on the optical disc. For this reason, the larger the numerical aperture of the objective lens, the higher the recording density of the optical disc. However, when the numerical aperture of the objective lens increases, the amount of coma generated by the tilting of the optical disk increases. The amount of coma generated is proportional to the cube of the numerical aperture and also proportional to the thickness of the cover glass of the optical disk.

  Therefore, a next-generation high-density optical disk that uses an objective lens with a large numerical aperture has been proposed in which the cover glass is made thinner in order to reduce the amount of coma generated. As such a next-generation high-density optical disc, for example, a cover glass having a thickness of 0.6 mm and an objective lens having a numerical aperture of 0.65, or a cover glass having a thickness of 0.1 mm, and An objective lens with a numerical aperture of 0.85 has been proposed. In the next-generation high-density optical disc with the objective lens having a numerical aperture of 0.85, the diameter of the focused beam focused on the recording layer by the objective lens is small. For this reason, the next-generation high-density optical disc with the numerical aperture of the objective lens of 0.85 has a higher recording density than the next-generation high-density optical disc with the numerical aperture of the objective lens of 0.65.

  In addition to the numerical aperture of the objective lens and the wavelength of light emitted from the light source, the size of the focused spot focused on the optical disk by the objective lens is influenced by the intensity distribution of the incident light beam incident on the objective lens. . Generally, when the intensity distribution of the incident light beam incident on the objective lens is uniform, the smallest focused spot can be obtained. Conversely, when the intensity distribution of the incident light beam incident on the objective lens is non-uniform, the condensing spot becomes large.

  The intensity distribution of the light beam emitted from the semiconductor laser used in the optical pickup device is an intensity distribution that approximates a Gaussian distribution, that is, a distribution in which the light intensity decreases from the center to the periphery of the light beam. Yes. In general, Rim intensity is an index that defines the uniformity of the intensity distribution of a light beam incident on an objective lens. The Rim intensity is defined by the ratio between the intensity of the light beam incident on the center of the objective lens and the intensity of the light beam incident on the outermost side of the objective lens in the intensity distribution of the light beam incident on the objective lens. That is, the Rim intensity is expressed by Rim intensity = (outermost incident light beam intensity) / (center incident light beam intensity). Usually, the Rim intensity is set as a standard for each type of optical disc.

  Therefore, in order to improve the recording density of the optical disc, it is preferable that the Rim intensity is large. However, increasing the Rim intensity means that, of the light beams emitted from the semiconductor laser, only the light beam near the center of the intensity distribution is incident on the objective lens. For this reason, when the Rim intensity is increased, the utilization efficiency of the light emitted from the semiconductor laser is lowered.

  The Rim intensity is defined as shown in Table 1 below for optical discs that can be recorded and reproduced, such as DVD-R and DVD-RAM.

  Further, the numerical aperture of the objective lens is determined as follows.

  Thus, as a standard, the numerical aperture of the objective lens and the Rim intensity are set within a certain range because the size of the focused spot focused on the recording layer of the optical disc is different between different optical pickup devices. The intention is to unify.

  The intention of unifying the size of the focused spot collected on the recording layer of the optical disc between different optical pickup devices is that when the size of the focused spot is recorded or reproduced with a large focused beam that does not meet the standard, This is because the signal already recorded on the optical disk cannot be read. In addition, when the optical disk is recorded with a focused beam having a small focused spot size, the following problems may occur when reproduction is performed by another optical pickup device having a different focused spot size.

  That is, when recording is performed with an optical pickup device that forms a recording mark with a focused beam having a small focused spot size on an optical disc that can be recorded once or multiple times, The recording mark is formed so that the length of the recording mark in the circumferential direction becomes small. For this reason, in order to reproduce such a small recording mark, an optical pickup device having a higher resolution, that is, capable of forming a condensed spot with a smaller size is required. However, in the objective lens having the numerical aperture defined by the above-mentioned standard and the optical pickup device having Rim intensity, the condensed spot condensed on the recording layer is relatively large. For this reason, when an optical disc recorded with a focused beam having a small focused spot size is reproduced, there is a problem that information recorded on the optical disc cannot be reproduced as a signal or the quality of reproduction is reduced. Further, when the recording mark is formed short in the circumferential direction of the optical disk, when processing such as signal decoding is performed, it may be recognized as a signal with an incorrect recording mark length, and error data may be generated.

  As described above, the optical pickup device is designed to have the Rim intensity defined in the standard in consideration of the radiation angle of the semiconductor laser to be used and the numerical aperture of the objective lens. Hereinafter, the design of such an optical pickup device will be described with reference to FIG.

  FIG. 18 is a sectional view showing a schematic configuration of a conventionally used optical pickup device 17. As shown in FIG. 18, the optical pickup device 17 includes a semiconductor laser 1700, a collimating lens 1701, and an objective lens 1702. Light emitted from the semiconductor laser 1700 enters the collimator lens 1701 and becomes parallel light. Then, the light emitted from the collimator lens 1701 enters the objective lens 1702 and is condensed on the recording layer 1704 of the optical disc 1703. The design conditions regarding such an optical pickup device 17 will be described below.

In the optical pickup device 17, the light beam emitted from the semiconductor laser 1700 has a distribution approximate to a Gaussian distribution. Normally, the intensity distribution of the light beam emitted from the semiconductor laser 1700 is an angle at which the intensity of the light beam is 50% with respect to the intensity at the center of the intensity distribution of the emitted light (hereinafter referred to as full width at half maximum θ). It is prescribed by. Therefore, for example, when the optical pickup device is designed so that the Rim intensity becomes 0.5, the light beam radiated at a half angle (θ / 2) of the full angle at half maximum with respect to the optical axis is the objective lens. What is necessary is just to design so that it may inject into the outermost periphery part of 1702. Therefore, when the effective diameter of the objective lens 1702 is Φ and the focal length of the collimating lens 1701 is f, the optical pickup device is designed so as to satisfy the following expression (5).
θ / 2 = sin ⁻¹ ((Φ / 2) / f) (1)
In general, since the radiation angle of the semiconductor laser differs between the horizontal direction and the vertical direction, the Rim intensity of the light beam incident on the objective lens differs between the horizontal direction and the vertical direction, resulting in an elliptical intensity distribution. Therefore, if necessary, in order to eliminate the asymmetry of the Rim intensity, as shown in FIG. 19, a shaping prism 1802 which is an anamorphic prism is disposed between the collimating lens 1801 and the objective lens 1803, and the horizontal A method of ensuring symmetry of Rim intensity by enlarging or reducing at least one of the vertical beam diameters is adopted.

  Further, increasing the Rim intensity means that only the light beam in the central region of the light beam emitted from the semiconductor laser is incident on the objective lens as described above, so that the light use efficiency is lowered. . Therefore, a light source that emits light of higher output is required.

  Usually, when a plurality of types of optical discs are recorded / reproduced with one optical pickup device or one objective lens, the following problems arise. That is, when a plurality of types of optical disks are recorded / reproduced with one objective lens, one aperture limiting aperture corresponds to one objective lens. Problem. In addition, since a plurality of types of optical disks have different cover glass thicknesses as described above, it is technically possible to correct spherical aberration caused by the difference in cover glass thickness while using one objective lens. It has the problem of being difficult. Therefore, when recording and reproducing a plurality of types of optical discs with one optical pickup device or one objective lens, a plurality of optical pickup devices or an optical disc recording / reproducing device equipped with a plurality of objective lenses has been proposed. ing.

  However, optical disks (hereinafter referred to as heterogeneous optical disk optical recording media) having different numerical apertures of the corresponding objective lenses, the cover glass thickness of the optical disk, the recording density of the recording layer, the number of recording layers included in one optical disk, and the like are different. There is a great demand for an optical pickup device capable of recording and reproducing using one objective lens. For example, Non-Patent Document 1 describes an optical pickup device using a special objective lens system as an optical pickup device that can handle different types of optical disks with a single objective lens.

  Non-Patent Document 1 describes a compatible objective lens having compatibility with a CD and a DVD as a special objective lens. This compatible objective lens has different cover glass thicknesses, and is compatible with different types of optical disks having different numerical apertures of the objective lenses used. In addition, the cover glass thickness of CD is 1.2 mm, and the numerical aperture of the objective lens to be used is 0.45. Moreover, the cover glass thickness of DVD is 0.6 mm, and the numerical aperture of the objective lens used is 0.6. Further, the effective diameter of the compatible objective lens is set to an effective diameter corresponding to a numerical aperture of 0.6, and the incident light flux to the objective lens is infinite parallel when recording and reproducing CDs and DVDs. Light.

  Hereinafter, the compatible objective lens will be described with reference to FIGS. FIG. 20 is a sectional view schematically showing the shape of the compatible objective lens. FIG. 21 is a graph showing the wavefront on the recording surface of the condensed beam condensed on the different type optical disk by the compatible objective lens, FIG. 21A is the wavefront on the DVD recording surface, and FIG. Is the wavefront on the CD recording surface.

  As shown in FIG. 20, the compatible objective lens 1900 is provided with a ring-shaped step 1901 on the side where the light source is provided. The step 1901 is provided on the lens surface optimized for DVD recording / reproduction. The step 1901 is provided in a region corresponding to a numerical aperture of the compatible objective lens 1900 of 0.37 to 0.41. When the step 1901 is provided in this way, as shown in FIG. 21, a phase difference corresponding to the step 1901 is also generated on the wavefront of the light emitted from the compatible objective lens 1900.

  For example, in the wavefront on the DVD recording surface, a phase difference is generated in a region corresponding to the step 1901 as shown in FIG. On the other hand, on the wavefront on the CD recording surface, as shown in FIG. 21B, aberration (phase difference) is generated in the peripheral portion of the compatible objective lens 1900 due to the influence of spherical aberration. This is because the cover glass thickness of the CD is different from that of the DVD.

  However, in the case of a DVD, even if a phase difference occurs in an area corresponding to the step 1901, there is no particular problem with the light collecting performance of the compatible objective lens 1900. In the case of a CD, in the compatible objective lens 1900, the depth of the step 1901 is designed so that the aberration in the portion corresponding to the step 1901 is reduced. Therefore, the beam diameter of the condensed beam condensed on the CD recording surface effectively corresponds to the beam diameter corresponding to the numerical aperture of the objective lens corresponding to 0.40 when converted from the size of the condensed beam. . Therefore, there is no problem in the light collecting performance with respect to the CD. In addition, since the light around the compatible objective lens 1900 becomes flare in the recording layer of the optical disk, the light collecting performance of the compatible objective lens 1900 is not affected.

  As described above, in the compatible objective lens 1900, by forming the annular step 1901 on the lens surface of the objective lens, the effective effective diameter of the objective lens when recording and reproducing CDs and DVDs, that is, effective The numerical aperture is switched. That is, in the optical pickup device provided with the compatible objective lens 1900, when recording / reproducing a DVD, the light emitted from both the inside and outside of the step 1901 is used, while the opening of the corresponding objective lens is used. When a CD having a smaller number than DVD is recorded / reproduced, light emitted from an area inside the step 1901 is used, and light emitted from an area outside the step 1901 is flare light.

  Further, Non-Patent Document 1 describes a liquid crystal shutter system as a system in which different types of optical disks can be interchanged with one objective lens in addition to the special objective lens system described above. The liquid crystal shutter system is a system in which a TN liquid crystal and an annular polarizing plate are arranged between an objective lens and a light source to switch the numerical aperture of the objective lens. That is, in the liquid crystal shutter method, the polarization direction of the light emitted from the TN liquid crystal is switched by turning on / off the TN liquid crystal, and the numerical aperture of the objective lens is switched depending on whether the light is transmitted through the polarizing plate. .

The annular polarizing plate is disposed at a position corresponding to the outer peripheral portion of the objective lens, and the inner peripheral diameter is set so as to substantially correspond to the numerical aperture of the objective lens used for the CD. . With this liquid crystal shutter system, the effective effective diameter of the objective lens, that is, the effective numerical aperture, is switched when recording and reproducing CDs and DVDs.
Noriichi Arai, “Optical system of DVD / CD compatible objective lens”, Optical Technology Contact, 2001, Vol. 39, No. 9. p.30-36

  However, the conventional compatible method has a problem that the light utilization efficiency is low when the prescribed Rim intensity optimum for recording / reproduction of different types of optical disks is secured.

  As a conventional compatible method, for example, a method using a special objective lens 1900 shown in FIG. 20 will be described.

  In an optical pickup device provided with a compatible objective lens 1900, the effective effective diameter and numerical aperture of the objective lens differ when recording / reproducing different types of optical disks. Hereinafter, in the conventional optical pickup device 17 shown in FIG. 18, a configuration in which the objective lens 1702 is replaced with a compatible objective lens 1900 will be described. A case where a DVD and a CD are used as different types of optical disks will be described.

If the effective diameter of the objective lens in the case of supporting DVD is ΦDVD, and the effective diameter in the case of supporting the CD (diameter near the boundary region between the stepped portion and the outer portion) is ΦCD, ΦDVD and ΦCD are
ΦDVD> ΦCD (2)
It has become.

Here, regarding the Rim intensity when the special objective lens 1900 is used, the effective diameter Φ of the objective lens in the above formula (1) is replaced with ΦDVD or ΦCD, respectively. The emission angles θDVD and θCD at which the semiconductor laser 1700 emits the light beam incident on the outermost diameter of the effective diameter of the objective lens are:
θDVD = 2 × sin ⁻¹ ((ΦDVD / 2) / f) (3)
θCD = 2 × sin ⁻¹ ((ΦCD / 2) / f) (4)
It becomes. Therefore, from the above equations (2) to (4), θDVD> θCD (5)
It becomes.

  In other words, in the optical pickup device provided with the compatible objective lens 1900, the effective effective diameter of the objective lens when recording / reproducing different types of optical disks is different. That is, the intensity of the light beam that determines the effective numerical aperture is different, and the Rim intensity is also different.

  When a next-generation high-density optical disk is applied as a heterogeneous optical disk, for example, an optical disk using a numerical aperture of 0.85 is compatible with an optical disk using a numerical aperture of 0.65. When applied, an objective lens that is effectively used in the case of a large numerical aperture (0.85) (in the case of DVD in the above) and in the case of a small numerical aperture (0.65) (in the case of CD in the above). The effective numerical aperture of the objective lens is switched by switching the effective diameter of the objective lens. Therefore, the Rim intensity also changes.

  Next, consider the case where the numerical aperture is switched by the special objective lens when a next-generation high-density optical disk is applied as the heterogeneous optical disk. In addition, the thing with the corresponding numerical aperture of 0.85 and 0.65 was used as a heterogeneous optical disk. The Rim intensity was set under conditions 1 and 2 in Tables 3 and 4 below.

Condition 1 was designed such that the Rim intensity was set to 0.6 and the Rim intensity satisfied the specification in the corresponding optical disk having a large numerical aperture, that is, the corresponding optical disk having a numerical aperture of 0.85. On the other hand, Condition 2 was designed so that the Rim intensity was set to 0.6 and the Rim intensity satisfied the specification in the corresponding optical disk with a small numerical aperture, that is, the corresponding optical disk with a numerical aperture of 0.65. .

  When the optical pickup device is designed based on the above condition 1 or 2, the semiconductor laser has a radiation angle of θ horizontal (radial direction) of 10 degrees and θ vertical (tangential direction). What was 20 degrees was used. In the cases 1) and 4) of Tables 3 and 4, the collimating lens focal length was set so as to satisfy the Rim intensity condition. In the case of 1), the collimating lens has a focal length of 10 (mm). In the case of 4), the collimating lens has a focal length of 7.7 (mm).

  The rim intensity was matched in the radial direction and the tangential direction by doubling the beam diameter in the θ horizontal direction by an anamorphic prism.

  As described above, when the Rim intensity is set based on the conditions 1 and 2, the Rim intensity and the coupling efficiency are as shown in Tables 5 and 6 below.

  As shown in Tables 5 and 6, in both conditions 1 and 2, when the effective diameter is different, the coupling efficiency is different by about 1.5 times. Condition 1 requires 1.5 times the light output of the light source in order to perform recording or reproduction of the optical disc in the case of 2) as compared to the case of 1). On the other hand, in condition 2, in order to perform recording or reproduction of the optical disc in the case of 4), the light output of the light source is required to be about 1.5 times the case of 3).

  In addition, it is technically difficult to manufacture a blue-violet semiconductor laser used in a next-generation high-density optical disk, and it is difficult to generate a high output of 1.5 times. For example, in the current technology, a semiconductor laser capable of obtaining an output of 100 mW is required for recording an optical disc having two recording layers. Development is difficult. Also, if a semiconductor laser is used at a high output, the life of the semiconductor laser will be shortened, so an optical pickup capable of recording or reproducing multiple types of optical disks with one semiconductor laser and one objective lens. The device itself does not hold and cannot be put to practical use. In addition, in order to improve the recording speed of an optical disc, or to support an optical disc having a plurality of recording layers, a light source having a high output is required. Is very disadvantageous.

  Furthermore, under condition 1 2), the Rim intensity is larger than the specification, so the beam diameter is about 1% smaller than the focused beam diameter in the optical pickup device that satisfies the specification. The above-mentioned problem may occur due to the small beam diameter. On the other hand, condition 2) 3) has a Rim intensity smaller than the specification, so that the focused beam diameter is increased by about 2%. Therefore, there is a possibility that a recording mark recorded by another optical pickup device cannot be read or the signal level is lowered. Further, in contrast to the above example, when the effective effective diameter of the objective lens corresponding to different types of optical disks or the difference in numerical aperture is large, the change of the condensed beam diameter is further increased. The influence of the instability of the reproduced signal quality due to the difference becomes more remarkable.

  When the Rim intensity for the two target optical disks in the heterogeneous optical disk is the same, the optical pickup so that the Rim intensity in the optical disk having a relatively small numerical aperture of the corresponding objective lens satisfies the prescribed Rim intensity. When the apparatus is designed, the Rim intensity in the other optical disc is smaller than the specified Rim intensity. Further, when the optical pickup device is designed so that the Rim intensity of the optical disk having a relatively large numerical aperture of the corresponding objective lens satisfies the specified Rim intensity, the Rim intensity of the other optical disk is determined to be the specified Rim intensity. Greater than strength. In any of the above cases, it becomes difficult to ensure a prescribed Rim intensity that is optimal for recording / reproduction of a different type of optical disk.

  Therefore, in the conventional optical pickup device to which the compatible system is applied, when the rim intensity that is optimal for recording / reproduction of either one of the different types of optical disks is secured, the light utilization efficiency of the other optical disk is poor, and There is a problem that the size of the light spot is reduced, or a problem that the focused spot is increased.

  The present invention has been made in view of the above-described conventional problems, and an object thereof is to make it possible to interchange a plurality of types of optical discs with a single lens, and to ensure Rim strength suitable for recording and reproduction of each optical disc. In addition, it is an object of the present invention to provide a polarizing lens element that can further improve the light utilization efficiency and an optical pickup device including the same.

  In order to solve the above problem, the polarizing lens element of the present invention emits linearly polarized light having a light beam diameter different from the light beam diameter of incident light when linearly polarized light in a predetermined direction is incident. In the case where the polarization direction of the incident light is perpendicular to the predetermined direction, linearly polarized light having the same light beam diameter as that of the incident light is emitted.

  According to said structure, when the polarization direction of the light which injects into the said polarizing lens element is the said predetermined direction, the light which radiate | emits a polarizing lens element has a light beam diameter different from the light beam diameter of the incident light. Further, when the polarization direction of the light incident on the polarizing lens element is a direction orthogonal to the predetermined direction, the light exiting the polarizing lens element has the same light beam diameter as the light beam diameter of the incident light. For this reason, it becomes possible to convert the beam diameter according to the polarization direction of linearly polarized light.

  The polarizing lens element of the present invention includes a first polarizing lens that functions as a concave lens with respect to the linearly polarized light in the predetermined direction, and a second polarizing lens that functions as a convex lens with respect to the linearly polarized light in the predetermined direction. Are preferably provided.

  According to the above configuration, even if the conversion magnification of the beam diameter is the same and the distance between the two lenses is the same as that of the polarizing lens element including two polarizing lenses functioning as a convex lens, each polarizing lens The focal length can be increased. For this reason, when a refractive lens is used as the first and second polarizing lenses, according to the above configuration, since the radius of curvature of the lens can be increased, a cheaper lens can be used, and two lenses can be used. An effect is obtained that the amount of coma generated by the optical axis deviation is relatively small.

  In the polarizing lens element of the present invention, a light transmitting member that transmits light passing between the first polarizing lens and the second polarizing lens is further provided. It is preferable that the second polarizing lens and the light transmitting member are integrated.

  According to said structure, the said light transmissive member is provided between the 1st polarizing lens and the 2nd polarizing lens, and is integrated, ie, the 1st and 1st on both surfaces of the said light transmissive member. Since the two polarizing lenses are integrally formed, the polarizing lens element can be easily assembled to the optical device. Further, according to the above configuration, in such an optical device, a change in the lens interval due to a change in the environmental temperature after the polarization lens element is assembled, and an optical axis misalignment between the polarization lenses are less likely to occur, and aberrations It is possible to suppress problems such as the occurrence of Here, the “optical device” is a device using an optical action, and examples thereof include an optical pickup device and an illumination device.

  Further, when the first polarizing lens functions as a concave lens and the second polarizing lens functions as a convex lens, according to the above configuration, it is compared with a polarizing lens element including a polarizing lens that functions as two convex lenses. Thus, no light is collected inside the light transmitting member, and there is no possibility that the material of the light transmitting member is deteriorated due to heat generation.

  In the polarizing lens element of the present invention, it is preferable that each of the first polarizing lens and the second polarizing lens is a blazed hologram lens.

  According to the above configuration, since each of the first polarizing lens and the second polarizing lens is a blazed hologram lens, the thickness of each polarizing lens can be reduced compared to a refractive lens. Therefore, according to said structure, the thickness of a polarizing lens element also becomes thin and can be reduced in size.

  Further, according to the above configuration, the focal length of each polarizing lens becomes longer when compared with a polarizing lens element having a polarizing lens functioning as two convex lenses, which has the same thickness. The grating pitch at the periphery of the polarizing lens can be increased. For this reason, it is possible to reduce a light amount loss due to an error in creating a blazed hologram such as etching. Thereby, according to said structure, it has further the effect that the fall of coupling efficiency can be prevented.

  In the polarizing lens element of the present invention, it is preferable that the focal length and the lens interval of the first and second polarizing lenses are set so that the parallel light is emitted when the parallel light is incident.

  According to said structure, the light which injected into the polarizing lens element with parallel light radiate | emits a polarizing lens element with parallel light. For this reason, according to the above configuration, the amount of coma generated due to the optical axis deviation between the two polarizing lenses is compared with the configuration in which the polarizing lens element is arranged in the divergent light beam or the focused light beam. Therefore, the position adjustment accuracy in a plane perpendicular to the optical axis of the lens can be relaxed.

  In order to solve the above-described problems, an optical pickup device of the present invention includes the polarizing lens element described above, a light source, and a condensing unit that condenses light emitted from the light source onto a recording layer of the optical recording medium. The polarizing lens element is provided between the light source and the light condensing means.

  According to said structure, when the polarization direction of the light which injects into the said polarizing lens element from a light source is the said predetermined direction, the light radiate | emitted from a polarizing lens element has a light beam diameter different from the light beam diameter of the incident light. Further, when the polarization direction of the light incident on the polarizing lens element is a direction orthogonal to the predetermined direction, the light exiting the polarizing lens element has the same light beam diameter as the light beam diameter of the incident light. For this reason, it becomes possible to convert the light beam diameter of the light incident on the objective lens in accordance with the polarization direction of the linearly polarized light.

  Therefore, for example, it is possible to change the Rim intensity of the light incident on the condensing means and change the diameter of the condensed beam condensed on the recording layer of the optical recording medium by the condensing means. Therefore, according to the above configuration, the diameter of the focused beam can be changed according to various optical recording media and the recording layers provided in the optical recording medium. It is also possible to change the light coupling efficiency. “Coupling efficiency” refers to the efficiency with which light intensity is transmitted from a light source to an optical recording medium via a condensing means in an optical pickup device.

  In the optical pickup device of the present invention, it is preferable that the light collecting means have effective diameters that are effectively different from each other.

  According to the above configuration, when condensing light by the corresponding light condensing means on the optical recording medium in which the corresponding effective diameter in the light condensing means is effectively different or the recording layer provided in the optical recording medium. The Rim intensity can be appropriately set for each optical recording medium or each recording layer. For example, the Rim intensity and the optical coupling efficiency can be set to different values or can be matched.

  For this reason, the condensing spot can be appropriately sized for each optical recording medium or each recording layer, and the stability in recording and reproduction can be improved. In addition, since a reduction in coupling efficiency can be prevented, it is advantageous for reducing power consumption and increasing the recording rate.

  The light collecting means includes a single light collecting means having a plurality of effective diameters and a plurality of light collecting means having effective effective diameters different from each other.

  In the optical pickup device of the present invention, the effective effective diameter that is relatively large corresponds to light having a relatively large light beam diameter in the light emitted from the polarizing lens element. It is preferable.

  According to the above configuration, the light having a large luminous flux diameter among the light emitted from the polarizing lens element corresponds to the light having a relatively large effective effective diameter in the condensing means. The range of the Rim intensity that can be set can be expanded.

  For example, when light having a large beam diameter is “linearly polarized light having a beam diameter different from the beam diameter of incident light” to the polarizing lens element, the incident light is changed by changing the magnification of the polarizing lens. Rim intensity of linearly polarized light having the same light beam diameter as the light beam diameter of the light to be transmitted (that is, light having a small light beam diameter) is defined as the reference Rim intensity, and the Rim intensity of light having a large light beam diameter matches the reference Rim intensity. It can be set to be large or small.

  In addition, when light having a large light beam diameter is “linearly polarized light having the same light beam diameter as the light beam diameter of the incident light” to the polarizing lens element, the light beam diameter can be changed by changing the magnification of the polarizing lens. The Rim intensity of light having a large beam diameter is defined as the reference Rim intensity, and the Rim intensity of “linearly polarized light having a light beam diameter different from the light beam diameter of incident light” (that is, light having a small light beam diameter) matches the reference Rim intensity. It can be set to be large or small.

  In the optical pickup device of the present invention, it is preferable that the condensing means having effective diameters different from each other have different effective numerical apertures as well as the effective diameters.

  According to the above configuration, the condensing means has an effective numerical aperture, so that in addition to the above effects, an optical pickup device corresponding to an optical recording medium with greatly different recording density, cover glass thickness, etc. Can do.

  In the optical pickup device of the present invention, in the condensing means, a relatively large effective diameter corresponds to linearly polarized light having a relatively large light beam diameter among the linearly polarized light emitted from the polarizing lens element. The optical recording medium is selected from a plurality of types of optical recording media having different effective effective diameters corresponding to the condensing means, and the light source is a semiconductor laser and the plurality of types of optical recording Among the media, the light beam diameter of the light emitted from the polarizing lens element is relatively smaller than the corresponding optical recording medium having a relatively large effective effective diameter. It corresponds to a large light, and it is preferable that the light condensed at the time of information recording corresponds to light having a relatively small light beam diameter among the light emitted from the polarizing lens element.

  According to the above configuration, particularly when a semiconductor laser having a large noise is used at the time of low-output light emission, the corresponding effective effective diameter is emitted from the polarization lens element at the time of information reproduction of an optical recording medium having a relatively large effective diameter. Since the linearly polarized light having a relatively large light beam diameter is used, the Rim intensity is increased. And, as the Rim intensity increases, the light coupling efficiency decreases. As described above, when the light coupling efficiency at the time of information reproduction on the optical recording medium is lowered, the semiconductor laser is caused to emit light at a higher output, so that noise can be reduced. The noise referred to here is output fluctuation noise of the semiconductor laser, and is generally called RIN noise.

  In addition, according to the above configuration, when a semiconductor laser having a large noise is used, particularly at low output light emission, the corresponding effective effective diameter is emitted from the polarizing lens element when recording information on an optical recording medium having a relatively large effective diameter. Since the linearly polarized light having a relatively small light beam diameter is used, the Rim intensity becomes small. Further, the light coupling efficiency is increased by reducing the Rim intensity. Thus, the maximum output of the semiconductor laser can be reduced by providing high light coupling efficiency when recording information on the optical recording medium.

  In the optical pickup device of the present invention, the light source is a semiconductor laser, and the light focused on the optical recording medium during information reproduction has a relative light beam diameter in the light emitted from the polarizing lens element. The light that is focused on the optical recording medium during information recording corresponds to the light having a relatively small luminous flux diameter among the light emitted from the polarizing lens element, The effective diameter of the light collecting means at the time of information recording and information reproduction may be the same.

  In addition, the light source is a semiconductor laser, and the light condensed when reproducing the information on the optical recording medium with respect to the effective effective diameter of the light condensing means is the light emitted from the polarizing lens element. Among them, it may correspond to light having a relatively large light beam diameter.

  Further, the condensing means has one effective effective diameter, the light source is a semiconductor laser, and light condensed when information is recorded on the optical recording medium is emitted from the polarizing lens element. It may correspond to light having a relatively small luminous flux diameter.

  In the optical pickup device of the present invention, the polarization direction of the light incident on the polarization lens element from the light source side between the light source and the polarization lens element is orthogonal to the predetermined direction. It is preferable to provide polarization direction switching means for switching between the directions.

  In the optical pickup device of the present invention, the above-described operational effect can be obtained also by providing a plurality of light sources that emit light having different polarization directions. According to the above configuration, the polarization direction switching means is a light source. Since the polarization direction of the light emitted from the light source is switched, it is not necessary to provide a plurality of light sources to change the polarization direction. Therefore, according to the above configuration, it is possible to provide an optical pickup device that has a small number of components and can realize low cost and downsizing.

  In the optical pickup device of the present invention, the polarization direction switching means is preferably a liquid crystal element.

  Examples of the polarization direction switching means include a Faraday rotator or a liquid crystal element. Among these, since the liquid crystal element has high light transmittance, the coupling efficiency can be further improved. Further, since the liquid crystal element is small, the optical pickup device can be miniaturized.

In the optical pickup device of the present invention, further, between the polarizing lens element and the condensing means,
It is preferable to include spherical aberration correction means for correcting the spherical aberration of the light condensed on the optical recording medium.

  According to the above configuration, the spherical aberration correcting unit corrects the spherical aberration of the light condensed on the optical recording medium. For this reason, it is possible to improve the light condensing performance in recording / reproducing of the optical recording medium, and it is possible to improve the signal quality. According to the above configuration, the effect of correcting the spherical aberration and improving the light condensing performance is increased in the optical recording medium corresponding to the light condensing means having a larger numerical aperture.

  In the optical pickup device of the present invention, it is preferable that the spherical aberration correcting unit includes a plurality of lenses and a driving unit that drives the lenses in the optical axis direction.

  As a spherical aberration correction means, there is a liquid crystal element having a concentric electrode pattern, but a spherical surface called a so-called beam expander comprising a plurality of lenses and having a drive means for driving the lenses in the optical axis direction. Aberration correction means is desirable. In that case, there is no reduction in efficiency due to an increase in the electrode pattern as compared with a spherical aberration correction element using a liquid crystal element. Moreover, there is no influence on the frequency characteristics of the movable part of the objective lens by the lead-out wiring from the electrode.

  In the optical pickup device of the present invention, the polarization aperture restriction is further provided between the polarizing lens element and the condensing unit to restrict the beam diameter corresponding to the numerical aperture according to the polarization direction of the light incident on the condensing unit. Preferably means are provided.

  According to the above configuration, the polarization aperture limiting unit limits the beam diameter corresponding to the numerical aperture in accordance with the polarization direction of the light incident on the condensing unit. Therefore, the change rate of the light beam diameter can be set more strictly for the optical recording medium. As a result, the flare of the spot formed on the optical recording medium is reduced and the outline of the spot becomes clear, so that the quality of the reproduction signal can be further improved.

  In the optical pickup device of the present invention, a light receiving means for receiving the return light reflected from the optical recording medium, and a signal detection means for detecting at least a focus error signal based on the light received by the light receiving means. Preferably, the signal detecting means detects a focus error signal by a knife edge method.

  According to the above configuration, the light receiving means receives the return light reflected from the optical recording medium. Then, the signal detection unit detects an information signal, a radial error signal, and a focus error signal recorded on the optical recording medium based on the light received by the light receiving unit.

  According to the above configuration, since the signal detection unit detects the focus error signal by the knife edge method, even if the beam diameter of the return light reflected from the optical recording medium varies from one optical recording medium to another, the beam For focus error signal detection by the size method, it is not necessary to switch the light receiving means, and the number of light receiving elements can be reduced, so that the delay difference of the light output signal from the light receiving means can be reduced. Become. Therefore, it is possible to prevent the focus error signal from being detected as error data.

  Further, when the spherical lens correcting means for correcting the spherical aberration of the light condensed on the optical recording medium is provided between the polarizing lens element and the condensing means, the polarizing lens element has both forward and backward paths. Parallel light can be incident. Accordingly, it is possible to prevent occurrence of an offset in the focus error signal.

  In the optical pickup device of the present invention, a light receiving means for receiving the return light reflected from the optical recording medium, and a signal detection means for detecting at least a focus error signal based on the light received by the light receiving means. Preferably, the signal detecting means detects a focus error signal by an astigmatism method.

  According to the above configuration, the light receiving means receives the return light reflected from the optical recording medium. Then, the signal detection unit detects an information signal, a radial error signal, and a focus error signal recorded on the optical recording medium based on the light received by the light receiving unit.

  According to the above configuration, since the signal detection unit detects the focus error signal by the astigmatism method, even if the luminous flux diameter of the return light reflected from the optical recording medium changes for each optical recording medium, For focus error signal detection by the beam size method, it is not necessary to switch the light receiving means, and the number of light receiving elements can be reduced, so that the delay difference in the light output signal from the light receiving means can be reduced. become. Therefore, it is possible to prevent the focus error signal from being detected as error data.

  Further, when the spherical lens correcting means for correcting the spherical aberration of the light condensed on the optical recording medium is provided between the polarizing lens element and the condensing means, the polarizing lens element has both forward and backward paths. Parallel light can be incident. Accordingly, it is possible to prevent occurrence of an offset in the focus error signal.

  As described above, the polarizing lens element of the present invention emits light having a light beam diameter different from the light beam diameter of incident light when linearly polarized light in a predetermined direction is incident, while the polarization direction of incident light is Is a direction orthogonal to the predetermined direction, light having the same light beam diameter as that of the incident light is emitted, so that the conversion magnification of the light beam diameter of the incident light can be changed. As a result, in the optical pickup device provided with the polarizing lens element of the present invention, the Rim intensity can be set so as to optimize recording / reproduction, and the coupling efficiency can be further improved.

[Embodiment 1]
An embodiment of the present invention will be described below with reference to FIGS.

  The optical pickup device of the present embodiment performs recording or reproduction by condensing a light beam having the same wavelength on optical disks having different numerical apertures of corresponding objective lenses. In the present embodiment, a light beam having a wavelength of 405 nm is used as a light beam having the same wavelength that is focused on the optical disk. However, the light beam having the same wavelength is not limited to this, and a conventionally known light beam having an arbitrary wavelength can be used.

  In the present embodiment, as an optical disc (optical recording medium), the numerical aperture of the corresponding objective lens is 0.85 and 0.65, respectively, and the cover glass thickness is 0.1 mm and The one with 0.6 mm was used. However, the optical disk used in this embodiment is not limited to this, and any optical disk may be used as long as the corresponding objective lens has a different numerical aperture.

  In this case, when the numerical aperture of the corresponding objective lens is large, the recording density of the optical disc is generally relatively high, so that the optical disc having a large numerical aperture of the corresponding objective lens (having a numerical aperture of 0.85). ) Is called a high density optical disk, and an optical disk having a small numerical aperture of the corresponding objective lens (having a numerical aperture of 0.65) is called a low density optical disk.

  Further, the high-density optical disk and the low-density optical disk used in the present embodiment have two recording layers. The thicknesses of the intermediate layers existing between the two recording layers in the high-density optical disk and the low-density optical disk are 25 μm and 20 μm, respectively.

  FIG. 1 shows a schematic configuration of a main part of the optical pickup device 100 of the present embodiment. As shown in FIG. 1, an optical pickup device 100 includes a light source 13, a collimating lens 3, a shaping prism 4, a TN type liquid crystal element (polarization direction switching means) 5, a polarization lens element 6, and a beam expander (spherical aberration correction means). 7 and an objective lens unit 18 that condenses the light beam from the λ / 4 wavelength plate 8 and the light source 13 onto the optical disk 12 (low-density optical disk or high-density optical disk).

  The light source 13 is a hologram laser light source, and includes a semiconductor laser 1, a hologram element 2, and a light receiving element 21 as light beam irradiation means. The semiconductor laser 1 emits a blue-violet light beam having a wavelength of 405 nm and linearly polarized light in the X direction. The hologram element 2 is provided on the side from which the semiconductor laser 1 emits a light beam. A three-beam generating diffraction grating 2b used for detecting a radial signal is formed on the surface of the hologram element 2 on the semiconductor laser 1 side. A three-part hologram 2a for diffracting the light beam reflected by the optical disk 12 is formed on the surface of the hologram element 2 opposite to the semiconductor laser 1 side. Further, the light receiving element 28 is provided in the light source 13 and receives the light beam reflected by the optical disc 12.

  The light beam irradiation means in the light source 13 is not limited to the semiconductor laser 1 that emits linearly polarized light in a predetermined direction. As the light beam irradiation means, for example, a solid laser light source or a gas laser light source may be used. The light beam irradiating means may emit a non-polarized light beam. However, when a light beam irradiating means that emits a non-polarized light beam is used, a linearly polarized light beam in a predetermined direction can be obtained by arranging a polarizing plate between the light source 13 and the polarizing lens element 6. What should I do?

  The light beam emitted from the semiconductor laser 1 is divided into three light beams of zero-order diffracted light and ± first-order diffracted light by a three-beam generating diffraction grating 2b formed on the surface of the hologram element 2 on the semiconductor laser 1 side. The This light beam enters the collimating lens 3 and becomes parallel light. Then, the light beam emitted from the collimating lens 3 enters the shaping prism 4, and the light beam diameter in the X direction is expanded so that the light beam intensity distribution becomes a substantially circular intensity distribution.

  The light beam emitted from the shaping prism 4 enters the liquid crystal element 5. The light beam incident on the liquid crystal element 5 is linearly polarized light in the X direction.

  The liquid crystal element 5 emits a light beam to the polarizing lens element 6 as linearly polarized light in the X direction or linearly polarized light in the Y direction according to the type of the optical disk 12, that is, a high density optical disk or a low density optical disk. .

  The optical axis direction is the Z direction, and the plane perpendicular to the Z direction is the XY plane.

  The light beam emitted from the liquid crystal element 5 enters the polarizing lens element 6 as parallel light. The polarizing lens element 6 includes two polarizing lenses, a polarizing lens (first polarizing lens) 14 and a polarizing lens (second polarizing lens) 15. The polarizing lens element 6 functions as a lens for linearly polarized light in the X direction, the polarizing lens 14 is provided on the light source 13 side, and the polarizing lens 15 is provided on the opposite side to the light source 13. The polarizing lens 14 functions as a concave lens for linearly polarized light in the X direction. The polarizing lens 15 functions as a convex lens with respect to linearly polarized light in the X direction. In the polarizing lens element 6, the focal lengths of the polarizing lens 14 and the polarizing lens 15 are set so that a light beam having a light beam diameter larger than the light beam diameter of the incident parallel light is emitted as parallel light. The lens interval is set. This setting condition will be described later.

  The light beam emitted from the polarizing lens element 6 enters the beam expander 7 as parallel light. The beam expander 7 includes a concave lens 16, a convex lens 17, a driving unit that drives the lens in the optical axis direction, and a lens interval control unit 61. In the beam expander 7, the concave lens 16 is provided on the incident side, and the convex lens 17 is provided on the output side. Accordingly, the parallel light incident on the beam expander is emitted as expanded parallel light. The lens interval control unit 61 controls the lens interval between the concave lens 16 and the convex lens 17 based on a spherical aberration adjustment method to be described later, and corrects the spherical aberration of the light beam collected on the recording layer by the objective lens. is doing.

  The light beam emitted from the beam expander 7 enters the λ / 4 wavelength plate 8 and is emitted with the polarization direction being circularly polarized. Then, the light beam emitted from the λ / 4 wavelength plate 8 enters the objective lens unit 18.

  The objective lens unit 18 includes an objective lens holder 9, an aperture 10, and an objective lens (condensing means) 11. The objective lens holder 9 holds the objective lens 11. In addition, the aperture 10 shields the light beam at the outer peripheral portion of the light beam in the incident light beam. For this reason, the light beam emitted from the λ / 4 wavelength plate 8 is blocked by the aperture 10 from the outer peripheral portion of the light beam, enters the objective lens 11, and is condensed on the optical disk 12. Here, an optical path until the light beam emitted from the semiconductor laser 1 is collected on the optical disk 12 by the objective lens 11 is defined as an outward path.

  The objective lens 11 is not particularly limited as long as it can be condensed on the optical disk 12, and a conventionally known objective lens can be used. In the optical pickup device 100, a special objective lens compatible objective lens having a ring-shaped step 19 as described in FIG. 20 or FIG. 21 is used as the optical disk 12. In this special objective lens, the effective numerical aperture calculated from the diameter of the condensed beam focused on the CD recording layer and the numerical aperture obtained from the diameter of the step provided in the objective lens are slightly different. However, in the following description, the numerical aperture determined by the outer shape of the objective lens, that is, the numerical aperture obtained from the diameter of the stepped portion is treated as an effective numerical aperture for the CD. However, even if the numerical aperture calculated from the focused beam diameter as the effective numerical aperture is handled as the effective numerical aperture, the effect of the present invention does not change.

  Next, an optical path (hereinafter referred to as a return path) of a light beam (hereinafter referred to as a return light beam) that has been focused on the optical disk 12 and then reflected by the optical disk 12 will be described.

  The return light beam reflected by the optical disk 12 passes through the objective lens unit 18 and enters the λ / 4 wavelength plate 8. The λ / 4 wavelength plate 8 becomes parallel light having a polarization direction that is 90 degrees different from that of the forward path. Then, the return light beam emitted from the λ / 4 wavelength plate 8 enters the beam expander 7 and further enters the polarizing lens element 6.

  Then, the return light beam emitted from the polarizing lens element 6 enters the liquid crystal element 5, enters the light source 13 through the shaping prism 4 and the collimating lens 3. In the light source 13, the return light beam is diffracted by the three-part hologram 2 a formed on the surface of the hologram element 2 opposite to the semiconductor laser 1 and guided to the light receiving element 28.

  The return light beam received by the light receiving element 28 is converted into an electric signal, and the obtained electric signal is processed. As a result of the arithmetic processing, an information signal called an RF signal and servo signals such as a focus error signal and a radial error signal are detected.

  In the optical pickup device 100, signal processing for reproducing the optical disc 12 and adjusting spherical aberration is performed by processing the detected RF signal. Further, the objective lens holder 9 is driven by objective lens driving means (not shown) based on the detected focus error signal or radial error signal, so that the objective lens 11 is driven in the focus direction or radial direction. Yes.

  Next, referring to FIG. 2 and FIG. 3, regarding the state of the polarization direction of the light beam transmitted through each member of the optical pickup device 100 when a low-density optical disk or a high-density optical disk is used as the optical disk 12, This will be described in detail below. 2 is a cross-sectional view showing the state of the polarization direction of the light beam transmitted through each member of the optical pickup device 100 when the high-density optical disk 20 is used as the optical disk 12, and FIG. FIG. 2B shows the return path. FIG. 3 is a cross-sectional view showing the state of the polarization direction of the light beam transmitted through each member of the optical pickup device 100 when the low-density optical disk 30 is used as the optical disk 12, and FIG. FIG. 3B shows the return path. 2 and 3, members from the liquid crystal element 5 to the light source 13 in the optical pickup device 100 are omitted.

  First, in the optical pickup device 100 using the high-density optical disk 20 as the optical disk 12, the state of the forward polarization direction until the light beam emitted from the light source 13 is emitted from the liquid crystal element 5 will be described. The light beam emitted from the light source 13 passes through the collimating lens 3 and the shaping prism 4 and enters the liquid crystal element 5 with the polarization direction maintained in the X direction. The liquid crystal element 5 is provided with voltage application means (not shown). When this voltage application means applies a voltage to the liquid crystal layer provided inside the liquid crystal element 5, the major axis of the liquid crystal molecules present in the liquid crystal layer is directed in the Z direction. At this time, the light beam transmitted through the liquid crystal element 5 enters the polarizing lens element 6 without changing its polarization direction. That is, when a high-density optical disk is used as the optical disk 12, in the optical pickup device 100, the light beam emitted from the liquid crystal element 5 is linearly polarized in the X direction.

  As shown in FIG. 2A, the light beam emitted from the liquid crystal element 5 is incident on the polarizing lens element 6 while being linearly polarized in the X direction. As described above, the polarizing lens element 6 includes the polarizing lens 14 that functions as a concave lens for the linearly polarized light in the X direction and the concave lens 15 that functions as a convex lens for the linearly polarized light in the X direction. Therefore, the light beam incident on the polarizing lens element 6 is first diverged by the polarizing lens 14 having its light beam diameter enlarged. Then, the light is again converted into parallel light by the polarizing lens 15 and emitted from the polarizing lens element 6. That is, the light beam incident on the polarizing lens element 6 is expanded in diameter by the polarizing lens 14 and the polarizing lens 15.

  The light beam emitted from the polarizing lens element 6 is further expanded in beam diameter by the beam expander 7 and becomes circularly polarized light whose polarization direction is counterclockwise by the λ / 4 wavelength plate 8. Then, the light beam emitted from the λ / 4 wavelength plate 8 is shielded by the aperture 10 provided in the objective lens holder 9, and the light beam corresponding to the effective diameter of the objective lens 11 is changed into the objective lens 11. 11 is incident.

  In the optical pickup device 100, the objective lens 11 corresponding to the high-density optical disk 20 is an infinite objective lens. For this reason, in the optical pickup device 100, the aperture 10 provided in the objective lens holder 9 determines the effective diameter of the objective lens 11, that is, the numerical aperture. In other words, the light beam that has passed through the outermost portion of the inner diameter of the aperture 10 is a light beam having the largest angle when being focused by the objective lens 11, that is, a light beam that determines the numerical aperture. In general, when the objective lens 11 is an infinite objective lens, an aperture 10 whose inner diameter matches the effective diameter of the objective lens 11 is used. Therefore, also in the optical pickup device 100, the inner diameter of the aperture 10 and the effective diameter of the objective lens 11 are the same. Here, the effective diameter of the objective lens 11 is a diameter set at the time of designing the objective lens 11 so that the incident light beam is almost aberration-free and is well collected. Further, when a light beam having a beam diameter that matches the effective diameter is incident on the objective lens 11, the numerical aperture is the original numerical aperture of the objective lens 11.

  Further, in the optical pickup device 100, the Rim intensity is determined based on the intensity of the light beam that has entered the objective lens 11 through the outermost part of the inner diameter of the aperture 10 and the intensity of the light beam that has entered the center of the objective lens 11. It is specified as the ratio of.

  In the optical pickup device 100, various members are designed so that the Rim intensity is 0.6 in both the radial direction and the tangential direction. The design method will be described below.

In general, the laser emission angle is defined by the angle (θ _{full width at half maximum} ) formed by the light beam, which is half the intensity (I / 2) of the intensity (I) at the center of the intensity distribution. Therefore, ± θ _{full width at half maximum} for the optical axis / 2
The light beam emitted from the laser at an angle of (1/2) is half the intensity (I) at the center of the intensity distribution. The _{full width} at _{half maximum} of θ does not change even if the distance between the observation point and the laser changes.

In addition, the angle at which the intensity (0.6 × I) is 60% of the intensity at the center of the intensity distribution can be calculated from the function expression of the intensity distribution actually indicating the Gaussian distribution and the above-mentioned full width at half maximum. . Here, ± θ _0.6 / 2 with respect to the optical axis
The light beam emitted from the laser at the angle is 60% of the intensity (I) at the center of the intensity distribution.

  The point where the intensity distribution of the laser is observed is at a distance f from the laser in the optical axis direction. A collimating lens is disposed there, and the divergent light emitted from the laser is parallel light. Therefore, the focal length of the collimating lens is f. Further, an objective lens is disposed further forward.

In the light beam emitted from the collimating lens, assuming that the diameter of the light beam having a light beam with an intensity of 0.6 × I at both ends is Φ _0.6 , the light beam diameter can be obtained by the following equation.

Φ _0.6 = 2 × f × sin (θ _0.6 / 2) (6)
When an objective lens having an effective diameter of Φ _0.6 is used as the objective lens arranged in front of the collimating lens, the intensity of the light beam passing through the center of the objective lens is less than that of the light beam passing through the outermost periphery of the objective lens. Since the intensity is 0.6 × I, the Rim intensity is 0.6.

  Actually, the radiation angle of the semiconductor laser varies depending on the individual semiconductor laser. For this reason, as the radiation angle of the semiconductor laser 1, a value obtained by measuring the radiation angle for each semiconductor laser is applied, or the radiation angle is measured in advance for each semiconductor laser, and an average value of the variation is applied. Thus, the optical pickup device 100 is designed.

  Next, the state of the polarization direction in the return path until the return light beam reflected by the high-density optical disk 20 enters the light source 13 will be described.

  After condensing on the high-density optical disk 20, the reflected return light beam becomes clockwise circularly polarized light and enters the λ / 4 wavelength plate 8 as shown in FIG. 2B. Then, the return light beam becomes linearly polarized light in the Y direction at the λ / 4 wavelength plate 8. The return light beam emitted from the λ / 4 wavelength plate 8 is incident on the polarizing lens element 6 with the beam diameter reduced by the beam expander 7.

  The polarizing lens element 6 does not have a function as a lens for linearly polarized light in the Y direction, and functions as a simple parallel plate. For this reason, the return light beam incident on the polarizing lens element 6 is transmitted through the polarizing lens element 6 while maintaining the beam diameter. Then, the return light beam emitted from the polarizing lens element 6 enters the light source 13 through the liquid crystal element 5, the shaping prism 4, and the collimating lens 3. The return light beam on the return path is incident on the light source 13 with a light beam diameter larger than that of the light beam on the forward path by the action of the polarizing lens element 6 described above.

  Next, in the optical pickup device 100 using the low-density optical disc 30 as the optical disc 12, the state of the forward polarization direction until the light beam emitted from the light source 13 exits the liquid crystal element 5 will be described. The light beam emitted from the light source 13 passes through the collimating lens 3 and the shaping prism 4 and enters the liquid crystal element 5 with the polarization direction maintained in the X direction.

  When the low-density optical disk 30 is used as the optical disk 12, the voltage applying means of the liquid crystal element 5 does not apply a voltage to the liquid crystal layer provided inside the liquid crystal element 5. Therefore, the light beam transmitted through the liquid crystal element 5 changes its polarization direction by 90 degrees and enters the polarizing lens element 6. That is, when the low-density optical disc 30 is used as the optical disc 12, the optical pickup device 100 is configured such that the light beam emitted from the liquid crystal element 5 becomes linearly polarized light in the Y direction.

  As shown in FIG. 3A, the light beam emitted from the liquid crystal element 5 is incident on the polarizing lens element 6 while being linearly polarized in the Y direction. As described above, the polarizing lens element 6 has no function as a lens for linearly polarized light in the Y direction, and functions as a simple parallel plate. For this reason, the light beam incident on the polarizing lens element 6 is transmitted through the polarizing lens element 6 while maintaining the beam diameter.

  The light beam emitted from the polarizing lens element 6 is enlarged by the beam expander 7 and becomes circularly polarized light whose polarization direction is clockwise by the λ / 4 wavelength plate 8. Then, the light beam emitted from the λ / 4 wavelength plate 8 is shielded by the aperture 10 provided in the objective lens holder 9, and the light beam corresponding to the effective diameter of the objective lens 11 is changed into the objective lens 11. 11 is incident.

  When the low-density optical disk 30 is used as the optical disk 12, in the optical pickup device 100, the portion of the ring-shaped step 19 provided in the objective lens 11 and the light beam incident on the inner peripheral region of the step 19 are The light is condensed on the recording layer of the low density optical disc 30. In addition, the light beam incident on the outer peripheral portion at the step 19 becomes a flare and is not used for recording or reproduction of the low density optical disc 30. That is, when the low-density optical disk 30 is used as the optical disk 12, the numerical aperture of the corresponding objective lens is effectively determined by the step 19. In the optical pickup device 100, the step 19 is provided in a portion where the numerical aperture of the objective lens 11 is 0.6 to 0.65. Therefore, the effective numerical aperture of the objective lens is set to 0.65 corresponding to the diameter of the outer peripheral portion in the step 19. Therefore, in the optical pickup device 100, the Rim intensity is set corresponding to the numerical aperture of the objective lens 0.65. In the optical pickup device 100, various members are designed so that the Rim intensity is 0.6 in both the radial direction and the tangential direction.

  In reality, a light beam having a light beam diameter larger than the diameter of the aperture 10 is incident on the aperture 29. However, in order to make the contents of the present invention easier to understand, a portion of the light beam diameter corresponding to the effective numerical aperture is used. Only shown.

  Next, the state of the polarization direction in the return path until the return light beam reflected by the low density optical disk 30 enters the light source 13 will be described.

  After returning to the low density optical disk 30, the reflected return light beam becomes counterclockwise circularly polarized light and enters the λ / 4 wavelength plate 8 as shown in FIG. Then, the returning light beam becomes linearly polarized light in the X direction at the λ / 4 wavelength plate 8. The return light beam emitted from the λ / 4 wavelength plate 8 is incident on the polarizing lens element 6 with the beam diameter reduced by the beam expander 7.

  As described above, the polarizing lens element 6 includes the polarizing lens 14 that functions as a concave lens for linearly polarized light in the X direction and the polarizing lens 15 that functions as a convex lens for linearly polarized light in the X direction. Therefore, the return light beam incident on the polarization lens element 6 is first converged by the polarization lens 15 with the light beam diameter reduced. Then, the light is again converted into parallel light by the polarizing lens 15 and emitted from the polarizing lens element 6. That is, the light beam diameter of the return light beam incident on the polarizing lens element 6 is reduced by the polarizing lens 15 and the polarizing lens 14. The return light beam incident on the polarizing lens element 6 as parallel light is emitted as parallel light.

  The return light beam emitted from the polarizing lens element 6 changes its polarization direction by 90 degrees in the liquid crystal element 5 and becomes linearly polarized light in the Y direction. The return light beam emitted from the liquid crystal element 5 is incident on the three-part hologram 2 a of the light source 13 through the shaping prism 4 and the collimating lens 3.

  Thus, when linearly polarized light in a predetermined direction is incident, the polarizing lens element 6 emits light having a light beam diameter different from the light beam diameter of the incident light, while the polarization direction of the incident light is the predetermined direction. When the direction is perpendicular to the direction, light having the same light beam diameter as that of the incident light is emitted. Therefore, the conversion magnification of the luminous flux diameter of incident light can be changed. As a result, in the optical pickup device 100, the Rim intensity can be set so that recording / reproduction is optimized. Further, it is possible to prevent the coupling efficiency from being lowered and to relatively increase the coupling efficiency. Since the coupling efficiency is relatively high, the amount of light emitted from the objective lens can be increased when semiconductor laser light sources having the same maximum output are used. On the other hand, in order to increase the recording rate of the optical disc, it is necessary to rotate the optical disc faster and record more information per unit time. However, if the optical disc is rotated at a high speed, the recording film of the information recording layer is irradiated. The total amount of light to be emitted (the amount of light to be irradiated × the irradiation time) becomes small. However, as described above, in the optical pickup device 100, the amount of light emitted from the objective lens can be increased, so that a reduction in the integrated amount of light can be prevented. That is, the recording rate can be increased. Here, the “perpendicular direction” and the “same beam diameter” may be within the design range of the optical pickup device in actual use.

Hereinafter, (1) the configuration of the polarizing lens element 6 and the manufacturing method thereof, (2) the specific configuration of the light source 13 and the signal detection method thereof, (3) the polarization direction switching element, (4) the spherical aberration correction element, (5 ) Applicable optical disc, (6) Polarizing lens element of the present invention, and (7) Comparison between the conventional optical pickup device and the optical pickup device 100 of the present embodiment will be described. Configuration and Manufacturing Method Thereof Next, the configuration of the polarizing lens element 6 in the optical pickup device 100 and the manufacturing method thereof will be described in detail below with reference to FIG. 4A and 4B are diagrams showing the configuration of the polarizing lens element 6 in the optical pickup device 100, FIG. 4A is a plan view, and FIG. 4B is a cross-sectional view.

  As shown in FIG. 4B, the polarizing lens element 6 includes a polarizing lens 14, a polarizing lens 15, a glass substrate 21, a protective glass plate 22, and a protective glass plate 23. Between the polarizing lens 14 and the polarizing lens 15, a glass substrate (light transmitting member) 21 that is a parallel plate is provided. A protective glass plate 22 is provided on the surface of the polarizing lens 14 opposite to the glass substrate 21 side. A protective glass plate 23 is provided on the surface of the polarizing lens 15 opposite to the glass substrate 21 side.

  The polarizing lens 14 includes a blazed hologram 24 and a filling layer 25 made of a photocurable resin that is an isotropic material. A blaze hologram 24 is formed on the surface of the filling layer 25 facing the glass substrate 21. The polarizing lens 15 includes a blazed hologram 26 and a filling layer 27 made of a photocurable resin that is an isotropic material. A blazed hologram 26 is formed on the surface of the filling layer 27 facing the glass substrate 21.

  The blaze holograms 24 and 26 are made of polymer liquid crystals 24a and 26a which are birefringent materials. Further, as shown in FIG. 4A, the blazed holograms 24 and 26 are formed concentrically with respect to the optical axis. The cross-sectional shape of the blazed holograms 24 and 26 is a sawtooth shape as shown in FIG. By making the cross-sectional shape of the hologram serrated, any one of the ± first-order diffracted lights is diffracted by the blaze holograms 24 and 26. Note that the blazed holograms 24 and 26 shown in FIG. 4 have a schematic configuration. In practice, these blazed holograms are formed from tens to hundreds of sawtooth-shaped gratings.

The polymer liquid crystal 26a has refractive index anisotropy, and Nx and Ny are Nx and Ny when the refractive index in the linearly polarized light in the X direction and the refractive index in the linearly polarized light in the Y direction are Nx and Ny, respectively. (7)
And here,
Nx> Ny (8)
It is.

Further, when the refractive index of the filling layer 27 is N,
N = Ny (9)
It is set to become.

  Therefore, when linearly polarized light in the Y direction is incident on the polarizing lens 15, the refractive index of the blazed hologram 26 and the filling layer 27 are equal to each other according to the formula (9). It functions as a simple parallel plate for polarized light and does not function as a lens. On the other hand, when linearly polarized light in the X direction is incident on the polarizing lens 15, the refractive index Nx of the blazed hologram 26 made of the polymer liquid crystal 26 a is larger than the refractive index N of the filling layer 27. For this reason, the polarizing lens 15 has a function as a lens.

  Thus, the polarizing lens element 6 functions as a lens for linearly polarized light in the X direction. Further, in the polarizing lens element 6, a polarizing lens 14 that functions as a concave lens with respect to linearly polarized light in the X direction is provided on the incident side, and polarized light that functions as a convex lens with respect to linearly polarized light in the X direction on the output side. A lens 15 is provided. Therefore, when the high-density optical disk 20 is used as the optical disk 12, the beam diameter of the light beam emitted from the liquid crystal element 5 is enlarged at a predetermined magnification (β) in the forward path. On the other hand, when the low-density optical disk 30 is used as the optical disk 12, the beam diameter of the return light beam reflected from the low-density optical disk 30 is reduced at a predetermined magnification β in the return path. Hereinafter, the setting of the focal length between the polarizing lens 14 and the polarizing lens 15 and the lens interval in the polarizing lens element 6 of the optical pickup device 100 will be described with reference to FIGS. FIG. 5 is a cross-sectional view showing the focal length and the lens interval in the polarizing lens 14 and the polarizing lens 15.

  First, the setting of the predetermined magnification β in the polarizing lens element 6 will be described.

  The effective diameter of the objective lens 11 corresponding to the numerical aperture (hereinafter referred to as Na) of the high-density optical disk 20 is defined as Φa. In addition, an effective diameter corresponding to the numerical aperture (hereinafter referred to as Nb) of the low density optical disc 30 is defined as Φb. Furthermore, it is assumed that the beam expander 7 expands the beam diameter of the light beam at a predetermined magnification α. In the present embodiment, the Rim intensity of the condensed light beam is set to be the same between the high-density optical disc 20 and the low-density optical disc 30. Therefore, in each of the high-density optical disc 20 and the low-density optical disc 30, when a light beam having the same luminous flux diameter among the light beams emitted from the collimating lens 3 enters the objective lens 11, each has a predetermined numerical aperture. The predetermined magnification β of the polarizing lens element 6 may be determined so that the light beam has an effective diameter corresponding to Na and Nb.

First, consider the beam diameter expansion magnification of the beam expander 7 when the polarizing lens element 6 does not function as a lens in the forward path, that is, when the low-density optical disk 30 is used as the optical disk 12. Assuming that the polarization lens element incident light beam diameter ΦPL is a light beam diameter of an effective diameter Φb corresponding to the numerical aperture of the objective lens corresponding to the low density optical disk 30, ΦPL is expressed by the following equation (10).
ΦPL = Φb / (α) (10)
The polarization lens incident light beam diameter ΦPL described here is a light beam diameter corresponding to the effective effective diameter of the objective lens 11, and actually considers that the objective lens 11 shifts in the radial direction. A light beam having a large light beam diameter enters the polarized lens element 6 and is emitted.

When the high-density optical disk 20 is used as the optical disk 12, the polarizing lens element 6 functions as a lens in the forward path of the light beam. Therefore, when the light flux of ΦPL is enlarged by the polarizing lens element 6 and further enlarged by the beam expander 7 and enters the objective lens 11, it is sufficient that the diameter of the light flux is Φa. The magnification β satisfies the following formula (11),
ΦPL × β × α = Φa (11)
Thus, the predetermined magnification β of the polarizing lens element 6 is
β = Φb / (ΦPL × α) (12)
It becomes.

  In the present embodiment, as an example, when the effective diameter Φb corresponding to the numerical aperture of the objective lens corresponding to the low density optical disc 30 is Φ2.29 and α is 1.5, the polarization is based on the equation (10). The lens incident light beam diameter ΦPL is Φ1.53. Further, when the light beam of Φ1.53 is expanded by the polarizing lens element 6 and further expanded by the beam expander 7 and enters the objective lens 11, the light beam diameter of Φa = Φ3 suffices. The predetermined magnification β is β = 1.31 from the equation (12).

  In the present embodiment, when the objective lens 11 is used with a different numerical aperture, both are used in an infinite system, so the magnification β of the polarizing lens element 6 is equal to the numerical aperture ratio or the effective diameter ratio. I'm doing it. By doing so, it is possible to make light incident on objective lenses having effective effective diameters different from each other in a state in which the Rim intensity is matched.

  In the present embodiment, it is possible to change the Rim intensity by changing the magnification β of the polarizing lens element 6. For example, when the Rim intensity is the same at the magnification β = 1.31, if the polarizing lens element 6 is designed so that the magnification β is larger than 1.31, the beam diameter is expanded, and the effective effective diameter of the objective lens is increased. In the intensity distribution of the light incident on, the difference in intensity between the central portion and the outer peripheral portion becomes small, so that the Rim intensity becomes large.

  In addition, when the polarizing lens element 6 is designed so that the magnification β is smaller than 1.31, the beam diameter is reduced, and in the intensity distribution of light incident on the effective effective diameter of the objective lens, the central portion and the outer peripheral portion Therefore, the Rim intensity becomes small.

Therefore, when linearly polarized light having a lens effect is incident on the polarizing lens element 6, assuming that the incident light beam diameter on the light source side is Di and the light beam diameter on the objective lens side is Do, the polarizing lens element 6 The predetermined magnification β is expressed by the following equation (13).
β = Do / Di (13)
Further, when the focal length of the polarizing lens 14 on the light source side in the polarizing lens element 6 is fi, the focal length of the polarizing lens 15 on the objective lens side is fo, and the distance between the polarizing lens 14 and the polarizing lens 15 is s, the following ( 14) and (15) are satisfied.
fi + s = fo (14)
β = fo / fi (15)
A glass substrate 21 is provided between the polarizing lens 14 and the polarizing lens 15 constituting the polarizing lens element 6. For this reason, when the distance between the polarizing lens 14 and the polarizing lens 15 is s, the thickness d of the glass substrate 21 takes into account the air equivalent thickness. That is, s takes the refractive index n of the glass substrate into consideration, and when the thickness of the glass substrate is d, the following equation (16) is obtained.
s = d / n (16)
Note that the above relational expressions of the focal length fi · fo and the lens interval s are based on the paraxial formula of the lens, and may be designed in consideration of light aberration.

  The focal length fi of the polarizing lens 14 and the focal length fo of the polarizing lens 15 are related to a predetermined magnification β of the light beam in the polarizing lens element 6, an incident light beam diameter, an output light beam diameter, or a lens interval. Is set.

  In the present embodiment, as the polarizing lens element, the polarizing lens 14 that functions as a concave lens on the incident side and the polarizing lens 15 that has a convex lens effect on the output side are arranged with respect to light in the polarization direction in the X direction. The configuration of the polarizing lens element 6 is not limited to this, and may be any configuration that expands the light beam with respect to the linearly polarized light in the X direction. For example, the configuration of the polarizing lens element may be a configuration in which a polarizing lens that functions as a convex lens is provided for linearly polarized light in the X direction on both the incident side and the outgoing side.

  Hereinafter, a configuration in which a polarizing lens functioning as a convex lens for linearly polarized light in the X direction will be described with reference to FIG. FIG. 6 is a cross-sectional view showing another configuration of the polarizing lens element in the present embodiment.

  As shown in FIG. 6, the polarizing lens element 66 has the same configuration as the polarizing lens element 6 except that the configurations of the polarizing lens 14 and the polarizing lens 15 in the polarizing lens element 6 described above are different. As shown in the figure, the polarizing lens element 66 includes a polarizing lens 614 that functions as a convex lens for linearly polarized light in the X direction, and a polarizing lens 615, and between the polarizing lens 614 and the polarizing lens 615. In addition, the focal point of the light beam is located.

  The polarizing lenses 614 and 615 include blazed holograms 624 and 626, respectively. Therefore, the light beam incident on the polarizing lens element 66 passes through the polarizing lens 614 and is condensed in the glass substrate 621, and then is emitted with the light beam diameter being enlarged by the polarizing lens 615.

When the focal length of the polarizing lens 614 is fi, the focal length of the polarizing lens 615 is fo, and the distance between the polarizing lens 614 and the polarizing lens 615 is s, the following equation (17) is obtained.
fi + fo = s (17)
Based on the equation (17), the focal length of the polarizing lens 614 and the focal length of the polarizing lens 615 can be determined. Further, the relationship between the distance s between the two polarizing lenses and the thickness d of the glass substrate 621 can employ the above formula (16).

  In the polarization lens element 66, the beam diameter conversion magnification β is the same, and the distance between the polarization lens 614 and the polarization lens 615 is the same as that of the combination of the concave lens and the convex lens. It is necessary to make the focal length of the lens 614 and the focal length of each of the polarizing lenses 615 shorter. When the focal length of the polarizing lens 614 and the focal length of each of the polarizing lenses 615 become shorter, the peripheral portions of the blaze holograms 624 and 626 change the direction of the light beam more greatly, so that the pitch of the diffraction grating becomes narrower. For this reason, there is a possibility that a light amount loss due to an error in creating a blaze hologram such as etching increases.

  On the other hand, when the focal lengths of the two polarizing lenses are long, the pitch of the diffraction grating is changed in order to change the direction of the light beam smaller than when the focal lengths of the two polarizing lenses are short. Becomes wider.

  For this reason, as a structure of the polarizing lens element 6, the structure by the combination of a concave lens and a convex lens is more desirable. When the polarizing lens element is a combination of a concave lens and a convex lens, the focal length of the lens can be increased compared to the case where the two polarizing lenses are formed of a convex lens, so that the pitch of the peripheral part of the blaze hologram is widened. Thus, it is possible to reduce a loss of light amount due to an error in creating a blazed hologram such as etching. In addition, since the alignment accuracy of the photomask when creating the blazed hologram can be relaxed, it is possible to reduce the manufacturing cost of the lens. Furthermore, an effect is obtained that the amount of coma generated by the optical axis shift between the two polarizing lenses is relatively small.

  Moreover, since light is not condensed inside the glass substrate, it is possible to prevent the glass substrate from being deteriorated by heat generated in the vicinity of the condensing spot. In addition, since polarizing lenses are integrally formed on both surfaces of a glass substrate, which is a flat plate that transmits light, the polarizing lens element can be used for other devices (optical devices) such as an optical recording / reproducing device and an illumination device. And easy to assemble. In other words, the position between the two lenses is adjusted in advance, and a fixed one is installed. This makes it difficult for the center of the optical axis to shift between the lenses due to changes in the ambient temperature during assembly or after assembly, resulting in aberrations, etc. The problem can be suppressed. These effects are not limited to the hologram lens, and similar effects can be obtained even with a normal refraction type lens.

  Hereinafter, a manufacturing method of the polarizing lens in the polarizing lens element 6 will be described with reference to FIG. As an example, a method for manufacturing the polarizing lens 15 will be described. 7A to 7D are cross-sectional views illustrating an example of the manufacturing process of the polarizing lens element 6.

  First, as shown in FIG. 7A, a polymer liquid crystal 26a is applied between a glass substrate 21 on which an alignment film is formed and a glass plate 116 on which an alignment film is formed on the surface facing the glass substrate 21. To do. In this step, the alignment direction of the polymer liquid crystal 26 a is determined by the action of the alignment film provided on the glass substrate 21 and the glass plate 116.

  Next, as shown in FIG. 7B, the polymer liquid crystal 26a is cured by light irradiation, and the glass plate 116 and the alignment film are removed.

  Then, as shown in FIG. 7C, the shape of the blazed hologram 26 is formed by etching the cured polymer liquid crystal 26a.

  Next, as shown in FIG. 7D, a filler made of a photo-curing resin, which is an isotropic material, is applied onto the blaze hologram 26. Then, the protective glass plate 23 is adhered and irradiated with light to cure the filler and form the filling layer 27.

  In the polarizing lens element 6, the polarizing lens 14 and the polarizing lens 15 are formed on both surfaces of the glass substrate 21. However, the polarizing lens element 6 is manufactured using the same process as described above except that the shape of the blazed hologram is different. Can do.

  In the polarizing lens 14 and the polarizing lens 15, the shape of the blazed hologram is a so-called sawtooth shape, but may be a stepped shape. It can be designed by a general hologram lens design method. Furthermore, it may be a refraction type instead of a hologram lens using diffraction. In that case, an isotropic material having a refractive index that matches the refractive index of one of the materials is created by etching or polishing a material such as a polymer liquid crystal material or crystal having birefringence in the same manner as the blazed hologram lens. What is necessary is just to fill and comprise. However, the reason why the blazed hologram lens is used in the present embodiment is that the thickness in the optical axis direction can be made thinner than that of a refractive polarizing lens.

  Further, in the optical pickup device 100, the polarizing lens element 6 has a focal distance between the polarizing lens 14 and the polarizing lens 15 and a lens interval (that is, a glass substrate) so that the light incident as parallel light is emitted as parallel light. 21) is preferably set. The reason will be described below with reference to FIG. FIG. 8 is a cross-sectional view showing the state of the polarization direction of the light beam transmitted through each member of the optical pickup device 101 when the polarization lens element 6 is designed to emit a non-parallel light beam. FIG. 8A shows the forward path, and FIG. 8B shows the backward path.

  As shown in FIG. 8A, in the optical pickup device 101, the focal length and the lens interval between the polarizing lens 14 and the polarizing lens 15 are such that the parallel light incident on the polarizing lens element 36 is emitted as diverging light. Is set. In this case, as shown in FIG. 8B, in the return path of the return light beam from the optical disk 12, the return light beam emitted from the polarization lens element 36 becomes focused light and travels toward the shaping prism 4.

  Here, when the convergent light is incident on the shaping prism 4, coma and astigmatism occur. For this reason, the condensed beam diameter of the return light beam received by the light source 13 is widened, which causes a problem in servo signal detection.

  Further, in the optical pickup device 101, the return light beam is condensed before reaching the light source 13, and the return light beam reaching the light receiving element provided in the light source 13 becomes divergent light. For this reason, a problem arises in servo signal and RF signal detection. This causes the same problem even when the shaping prism 4 is not used in the optical pickup device 101. Therefore, in the optical pickup device 101, it is difficult to use a light receiving / emitting element in which a light source such as a hologram laser light source and a light receiving element are integrated as the light source 13, for example.

  On the other hand, in the optical pickup device 100, the polarizing lens element 6 sets the focal length and the lens interval between the polarizing lens 14 and the polarizing lens 15 so that the light incident as parallel light is emitted as parallel light. Has been. For this reason, regardless of which one of the high-density optical disk 20 and the low-density optical disk 30 is used as the optical disk 12, the polarizing lens element 6 does not function as a lens in either the forward path or the return path, but the optical disk 12 In the case where either the high-density optical disk 20 or the low-density optical disk 30 is used, the return light beam emitted from the polarization lens element 6 enters the shaping prism 4 in the parallel light state in the return path of the return light beam. To do. For this reason, as the light source 13, a light receiving / emitting element in which a light source such as a hologram laser light source and a light receiving element are integrated can be used.

  In general, a light receiving element arranged in a hologram laser light source as the light source 13 is arranged so that the laser (semiconductor laser 1) and the Z direction which is the optical axis direction are substantially at the same position. Thereby, it is possible to arrange the light source and the light receiving element in the integrated package.

As described above, since the focal length and the lens interval between the polarizing lens 14 and the polarizing lens 15 are set so that the polarized lens element 6 emits the parallel incident light as the parallel light, the hologram A light emitting / receiving element in which a laser such as a laser light source and a light receiving element are integrated can be used. Further, as shown in FIG. 8A, when the polarizing lens element 36 is arranged in a divergent light beam or a convergent light beam, the position adjustment accuracy in the X / Y plane is improved due to the occurrence of coma aberration or the like. It becomes severe. However, in the optical pickup device 100, the positional adjustment accuracy of the polarizing lens element 6 in the X and Y planes can be relaxed.
(2) Specific Configuration of Light Source 13 and its Signal Detection Method Next, the configuration of the light source 13 and its signal detection method will be described below with reference to FIGS. 9 and 10. FIG. 9 is a cross-sectional view showing a schematic configuration of the light source 13.

  As shown in FIG. 9, the light source 13 includes a laser package 31 and a hologram element 2. The hologram element 2 is provided on the emission surface of the laser package 31. In the laser package 31, a semiconductor laser 1 and a light receiving element 28 on which a photodetector is disposed are disposed. Further, a three-part hologram 2a is formed on the exit surface of the hologram element 2, and a diffraction grating 2b for generating three beams is formed on the surface opposite to the exit surface of the hologram element 2. A pin terminal 31 a is formed on the surface opposite to the emission surface of the laser package 31, and the pin terminal 31 a is connected to a signal detection unit (signal detection means) 62.

  The return light beam from the optical disk 12 is diffracted by the three-part hologram 2 a of the hologram element 2 and received by the light receiving element 28. Then, an electrical signal of the return light beam received by the light receiving element 28 is output from the pin terminal 31a. Based on the output of the electrical signal, the signal detection unit (signal detection means) 62 generates a radial error signal (RES signal), a focus error signal (FES), a reproduction signal (RF signal), and a reproduction signal. A signal for adjusting the spherical aberration is detected. The number of pin terminals 31a that can output the electrical signal can be set as appropriate depending on the design of the laser package and the like.

  Hereinafter, a method for generating the various signals will be described with reference to FIG. FIG. 10 is a plan view of the three-part hologram 2a and the light-receiving element 28 formed on the hologram element 2 as seen from the side from which the light source 13 emits the light beam. In FIG. 10, the left side shows the three-part hologram 2a. It is a plan view, and the right side is a plan view of the light receiving element 28.

  In FIG. 10, the light spot patterns received by the photodetectors a to h are semicircular or quarter-circular, but this is because each region of the three-divided hologram 2 a and each of the light receiving elements 28. This is for the purpose of facilitating understanding of the relationship with the photodetector, and in actuality, it is designed so that substantially collected light is incident on the photodetectors a to h.

  As shown in FIG. 10, the three-divided hologram 2a is divided into three regions 291 to 293. Each area is divided into two parts, an area 291 and another area (292 + 293) by a dividing line L1 corresponding to the radial direction of the optical disc, and the divided areas are divided lines corresponding to the tangential direction of the optical disc. The area 292 and the area 293 are divided into two by L2.

The light receiving element 28 includes light receiving portions R291 to R293 as shown in FIG. These light receiving units receive the return light beam diffracted in the regions 291 to 293. The light receiving unit R291 is a two-divided photo detector including the photo detectors a and b, and receives the return light beam diffracted in the region 291. The light receiving unit R292 includes photo detectors c to e and receives the return light beam diffracted in the region 292. Further, the light receiving unit R293 includes the photodetectors f to h, and receives the return light beam diffracted in the region 293. If the electrical signals output from the photodetectors a to h are Va to Vh, the radial error signal (RES signal), the focus error signal (FES), and the reproduction signal (RF signal) are detected by the following arithmetic expressions. The
FES = Va−Vb (18)
RES (DPP) = Phase {(Vd−Vg)} (19)
RES (DPD) = (Vd−Vg) −k {(Vc−Vf) + (Ve−Vh)} (20)
RF = Va + Vb + Vd + Vg (21)
In the arithmetic expressions (18) to (21), “Phase” means the output of the phase difference between the output electrical signal waveforms, and the constant k is the three-beam generating diffraction grating 29b in the forward path. The push-pull signal (Vd−Vg) calculated from the output obtained by receiving the light beam obtained by diffracting the zero-order diffracted light diffracted by the three-part hologram 2a with the light receiving element and ± 1st order diffracted light are received by the light receiving element This means an output ratio with the sum of push-pull signals ((Vc−Vf) + (Ve−Vh)) calculated from the obtained outputs.

  A focus error signal (FES signal) is detected from the differential output of the electrical signal output from the light receiving unit R291. Here, the focus error signal is detected by a knife edge method using a hologram pattern. The three-beam generating diffraction grating 29b diffracts the forward light beam, that is, the light beam emitted from the semiconductor laser 1, into 0th-order diffracted light and ± 1st-order diffracted light. For this reason, the light receiving unit R291 also receives ± first-order diffracted light among the forward light beams diffracted by the three-beam generating diffraction grating 29b. In the light receiving unit R291, these ± first-order diffracted lights are incident in a direction corresponding to the tangential direction of the photodetectors a and b. However, in the detection of the focus error signal, the ± first-order diffracted light is not used as the detection signal, and the 0th-order diffracted light is used as the detection signal. For this reason, in the light receiving unit R291, no photodetector is disposed at a position where the ± first-order diffracted light is incident.

  Further, a radial error signal (RES signal) is detected by performing arithmetic processing on the electrical signals output from the light receiving units R292 and R293 based on the arithmetic expression (14) or (15). Here, the radial error signal is detected by the DPP method or the DPD method. As described above, the three-beam generating diffraction grating 29b diffracts the forward light beam into zero-order diffracted light and ± first-order diffracted light. When detecting a radial error signal, 0th-order diffracted light and ± 1st-order diffracted light diffracted by the three-beam generating diffraction grating 29b are used as detection signals. For this reason, in the light receiving unit R292, the photodetector d is disposed as a photodetector that receives the 0th-order diffracted light, and the photodetectors c and e are disposed as photodetectors that receive the ± 1st-order diffracted light. Similarly, in the light receiving portion R293, a photodetector g is disposed as a photodetector that receives 0th-order diffracted light, and photodetectors f and h are disposed as photodetectors that receive ± 1st-order diffracted light.

  Further, the reproduction signal (RF signal) is detected as the sum of the signals output from the photo detector a, photo detector b, photo detector d, and photo detector g based on the arithmetic expression (16).

  The spherical aberration is adjusted by the following method based on the RF signal. The amplitude of the RF signal detected by the light receiving element 28 is affected by the amount of spherical aberration. That is, when the amount of spherical aberration is large, the amplitude of the RF signal is small, and when the amount of spherical aberration is small, the amplitude of the RF signal is large. Therefore, in the present embodiment, the driving means is controlled by the control means, and one of the two lenses constituting the beam expander that is a spherical aberration correction element is moved in the optical axis direction so that the RF signal amplitude is maximized. It is adjusted.

  In the present embodiment, the knife edge method is used as the focus error signal detection method, but the present invention is not limited to this. For example, an astigmatism method may be applied as a focus error signal detection method.

  When the knife edge method or the astigmatism method is used, it is preferable for the following reasons as compared with the case of using the beam size method (also called spot size method). The beam size method here is a method for detecting a focus error signal by utilizing the fact that the beam size on the light receiving element changes according to the change in the relative position between the objective lens and the optical disc.

  Like the optical pickup device 100, one objective lens is used with different numerical apertures corresponding to two different types of optical disks, and further, the beam diameter reduction action by the polarizing lens element is different in the return path (on the other hand). In the case of this optical disc, the beam diameter does not change before and after the polarizing lens element, and changes on the other side). Therefore, when the beam diameter of the return light itself is different, even if the relative positional relationship between the objective lens and the optical disk is appropriate, in the case of the light receiving element appropriately designed for one of the two optical disks, the other May be detected as defocus (also referred to as focus offset). As a method for avoiding this problem, for example, in the case of a high-density optical disk using a five-divided photodetector and a large beam diameter of the return light, all five-divided photodetectors are used, and the low beam density of the return beam is small. In the case of an optical disc, there is a method using an inner three-part photo detector.

  A light source for detecting a focus error signal using a five-divided photodetector will be described below with reference to FIG. FIG. 11 is a cross-sectional view showing a schematic configuration of a light source 213 that detects a focus error signal using a five-divided photodetector.

  As shown in FIG. 11, the light source 213 includes a laser package 231 and a hologram element 32. In the laser package 231, the semiconductor laser 1 and the light receiving elements 38a and 38b on which the photodetectors are arranged are arranged. Further, a three-part hologram 32a is formed on the exit side surface of the hologram element 32, and a three-beam generating diffraction grating 32b is formed on the opposite side of the exit surface of the hologram element 32.

  The return light beam from the optical disk 12 is diffracted by the three-part hologram 32a of the hologram element 32 and received by the light receiving elements 38a and 38b. The three-beam generating diffraction grating 32b diffracts the forward light beam, that is, the light beam emitted from the semiconductor laser 1, into 0th-order diffracted light and ± 1st-order diffracted light. The light receiving element 38a receives the + 1st order diffracted light among the forward light beams diffracted by the three-part hologram 32a. On the other hand, the light receiving element 38b receives −1st order diffracted light. As shown in FIG. 11, in the light source 213, the position of the condensing point of ± first-order diffracted light diffracted by the three-part hologram 32a is shifted from the light receiving elements 38a and 38b in the optical axis direction. It is a configuration set to.

  In the light source 213, an electrical signal of the return light beam received by the light receiving elements 38a and 39b is output. The light source 213 calculates a radial error signal (RES signal), a focus error signal (FES), and a reproduction signal (RF signal) by calculating the output of this electric signal.

  Hereinafter, a method of generating a focus error signal in the light source 213 will be described with reference to FIG. FIG. 12 is a plan view of the three-segment hologram 32a formed on the hologram element 222 and the light-receiving element 38a that receives the + 1st order diffracted light as viewed from the emission side of the light source 213. In FIG. 32a is a plan view, and the right side is a plan view of the light receiving element 38a. The light receiving element 38a differs from the light receiving element 28 shown in FIG. 10 in that the beam size on the photodetector is a plan view reflecting the actual beam size. This is to make it easier to understand the difference in beam size.

  That is, in FIG. 12, the focused beam incident on the photodetector for detecting the radial error signal is drawn with small dots so as to be actually focused, and is divided into five parts for detecting the focus error signal. The light beam incident on the photodetector is also drawn as a large semicircle as in practice.

  As shown in FIG. 12, the three-divided hologram 32a is divided into three regions 391-393. Each of the areas is divided into an area 391 and another area (392 + 393) by a dividing line L1 corresponding to the radial direction of the optical disk, and the divided areas are divided lines corresponding to the tangential direction of the optical disk. By L2, the area 392 and the area 393 are divided into two.

  In addition, the light receiving element 38a includes light receiving portions R391 to R393 as shown in FIG. These light receiving units receive + 1st order diffracted light among the return light beams diffracted in the regions 391 to 393. The light receiving unit R391 is a five-divided photo detector including photo detectors a 'to f', and receives the return light beam diffracted in the region 391. The light receiving unit R392 includes photo detectors g 'to i' and receives the return light beam diffracted in the region 392. Further, the light receiving unit R393 includes photo detectors j 'to l', and receives the return light beam diffracted in the region 393.

  In FIG. 12, the light spots indicated by dotted lines in the photodetectors a ′ to f ′ of the light receiving unit R391 are light spots corresponding to the return light beam from the high-density optical disc. On the other hand, the light spot indicated by the solid line is a light spot corresponding to the return light beam from the low-density optical disk. That is, the light spot indicated by the dotted line is the light spot of the return light beam when the corresponding objective lens 11 having a large numerical aperture is used, and the light spot indicated by the solid line is: This is a light spot of the return light beam when the corresponding objective lens 11 having a small numerical aperture is used.

As described above, when two types of optical disks having different effective effective diameters or different numerical apertures are used, the size of the light spot condensed on the photodetectors a ′ to f ′ of the light receiving unit R391 is large. Different. For this reason, the detection method using the light source 213 is devised to switch the calculation method in accordance with the numerical aperture. In the light source 213, assuming that the electrical signals output from the photodetectors a ′ to e ′ are V2a ′ to V2e ′, the focus error signal (FES) is detected by the following arithmetic expression.
When the corresponding numerical aperture is large (when using a high-density optical disc)
FES = (V2a ′ + V2b ′ + V2c ′) − (V2d ′ + V2e ′) (22)
When the corresponding numerical aperture is small (when using a low-density optical disk)
FES = (V2a ′) − (V2b ′ + V2c ′ + V2d ′ + V2e ′) (23)
That is, when using a high-density optical disc, among the five-divided photodetectors of the light receiving unit R391, outputs from the photodetectors a ′ to c ′ inside and the photodetectors d ′ and e ′ outside the photodetectors a ′ to c ′. The difference from this output is used as a focus error signal. On the other hand, when a low density optical disk is used, the difference between the output from the photodetector a ′ at the center of the five-divided photodetectors of the light receiving unit R391 and the output from the photodetectors b ′ to e ′ outside the photodetector a ′ is calculated. Focus error signal.

  As described above, in the light source 213, the number of photodetectors in the light receiving unit R391 is increased, and the calculation for detecting the focus error signal according to the numerical aperture of the objective lens, that is, the beam diameter of the return light beam. The expression is switched. By doing so, when the beam diameter of the return light itself is different, even if the relative positional relationship between the objective lens and the optical disk is appropriate, it is not detected as defocus. Further, there is no need for a control and a circuit such as switching a photodetector that obtains an output for performing focus error signal detection. However, when the number of photodetectors in the light receiving unit R391 increases, a reproduction signal (RF signal) is detected as the sum of output signals from all the photodetectors, so that the signal error occurs due to the delay difference of the signals from each photodetector. May be detected as data. Therefore, it is preferable that the number of photodetectors of the light receiving unit R391 that detects the focus error signal is smaller.

  Further, when the focus error signal is detected by the astigmatism method, the optical pickup device may be configured to detect the focus error signal by separating the return light beam on the return path, as shown in FIG. .

  As shown in FIG. 13, the optical pickup device 102 includes a polarization beam splitter 32, a composite lens 33, and a light receiving element 34. A compound lens 33 is disposed between the polarization beam splitter 32 and the light receiving element 34.

  The polarization beam splitter 32 separates the return light beam from the optical disk 12. The compound lens 33 includes a convex lens and a cylindrical lens, and guides the return light beam separated by the polarization beam splitter 32 to the light receiving element 34. The light receiving element 34 includes a square-shaped quadrant photodetector and receives an incident return light beam. In the optical pickup device 102, a focus error signal is detected based on the output from the quadrant photodetector of the light receiving element 34.

  As described above, in the case of the knife edge method or the astigmatism method, unlike the beam size method, the focus error signal is not detected depending on the size of the beam, so that it is influenced by the size of the beam received by the photodetector. It is more preferable because no offset is generated.

  In the present invention, a semiconductor laser is used as the light source. The light emitted from the semiconductor laser includes output fluctuation noise called RIN noise. Generally, the RIN noise is large when the output is low, and decreases when the output is high. The allowable value of RIN noise of a semiconductor laser used in an optical pickup device is desired to be −125 dB / Hz ^ (1/2) or −130 dB / Hz ^ (1/2) or less. In the currently developed blue-violet semiconductor laser, the noise tolerance may be exceeded during reproduction, that is, at low output (about 1 to 6 mW). In such a case, a method of increasing the output during reproduction by deliberately degrading the light coupling efficiency and reducing the RIN noise may be used. In that case, on the contrary, a large output is required at the time of recording, which is a problem in developing a semiconductor laser.

  In such a case, for example, an object lens having only one effective diameter is used as an objective lens that is a condensing means used in the optical pickup device, and the light beam incident on the objective lens is obtained by the polarizing lens element of the present invention. By changing the diameter, it becomes possible to change the light coupling efficiency between information reproduction and information recording on the optical recording medium.

  That is, when information is reproduced from the optical recording medium, the Rim intensity can be increased by using linearly polarized light having a relatively large light beam diameter among the linearly polarized light emitted from the polarizing lens element. And by increasing the Rim intensity, the light coupling efficiency is lowered. As described above, the low light coupling efficiency at the time of reproducing information from the optical recording medium enables the semiconductor laser to emit light at a higher output, thereby reducing noise. In addition, when recording information on the optical recording medium, it is possible to reduce the Rim intensity by using linearly polarized light having a relatively small beam diameter among linearly polarized light emitted from the polarizing lens element. Further, by reducing the Rim intensity, the light coupling efficiency is increased. Thus, the maximum output of the semiconductor laser can be reduced by providing high light coupling efficiency when recording information on the optical recording medium.

  As described above, by reducing the coupling efficiency during information reproduction and increasing it during information recording, it is possible to ensure recording power even with a semiconductor laser having a lower output.

  In addition, said effect is not restricted to what has one effective diameter as an objective lens. One objective lens may have effective diameters that are effectively different from each other used in the present embodiment. Further, in an optical pickup device including two objective lenses, the objective lenses may have different effective diameters. There may be.

  That is, in the light condensing means, when the relatively large effective effective diameter corresponds to the linearly polarized light having a relatively large light beam diameter among the linearly polarized light emitted from the polarizing lens element, the optical recording medium Is selected from a plurality of types of optical recording media having different effective effective diameters corresponding to the objective lens, and among the plurality of types of optical recording media, the corresponding effective effective diameter is a relatively large optical recording medium. On the other hand, the light condensed during information reproduction corresponds to the linearly polarized light having a relatively large light beam diameter among the linearly polarized light emitted from the polarizing lens element, and the light condensed during information recording is the polarized light. The linearly polarized light emitted from the lens element may correspond to linearly polarized light having a relatively small beam diameter.

In the light collecting means, when the relatively small effective diameter corresponds to the linearly polarized light having a relatively large light beam diameter among the linearly polarized light emitted from the polarizing lens element, Each of the recording media is selected from a plurality of types of optical recording media having different effective effective diameters corresponding to the objective lens, and the corresponding effective effective diameter of the plurality of types of optical recording media is relatively small. Light that is condensed during information reproduction on the recording medium corresponds to linearly polarized light having a relatively large light beam diameter among the linearly polarized light emitted from the polarizing lens element, and is condensed during information recording. May correspond to linearly polarized light having a relatively small light beam diameter among the linearly polarized light emitted from the polarizing lens element.
(3) Polarization Direction Switching Element In the optical pickup device 100, a TN liquid crystal element 5 is provided between the polarizing lens element 6 and the light source 13 as a polarization direction switching element. Thereby, the linearly polarized light in a predetermined direction emitted from the light source 13 can be converted into linearly polarized light in two directions.

  The polarization direction switching element is not particularly limited as long as it can switch linearly polarized light in two directions, that is, a predetermined direction and another direction, and enter the polarized lens element 6. For example, even with the configuration as shown in FIG. 14, it is possible to switch linearly polarized light in two directions of a predetermined direction and the other direction to enter the polarization lens element 6. Hereinafter, an optical pickup device including a polarization direction switching element having another configuration will be described.

  As shown in FIG. 14, the optical pickup device 103 includes two light sources, light sources 13a and 13b. The optical pickup device 103 includes collimating lenses 3a and 3b, shaping prisms 4a and 4b, a beam splitter 42, and a light source irradiation control unit 43.

  In the optical pickup device 103, the light beams emitted from the light source 13a and the light source 13b are arranged so that the polarization directions thereof are orthogonal to each other. That is, in the optical pickup device 103, the light source 13a emits linearly polarized light in the X direction, while the light source 13b emits linearly polarized light in the Y direction. Further, the light source irradiation control unit 43 controls which of the light source 13a and the light source 13b emits light according to the type of the optical disk 12 to be applied. Alternatively, which of the two light sources emits light is controlled according to the required light beam diameter. For example, when the coupling efficiency is switched between recording and reproduction, the light source that emits light is switched between recording and reproduction.

  In the optical pickup device 103, the light beam (linearly polarized light in the X direction) emitted from the light source 13 a passes through the collimator lens 3 a and the shaping prism 4 a, passes through the beam splitter 42, and enters the polarizing lens element 6. On the other hand, the light beam (linearly polarized light in the Y direction) emitted from the light source 13 b is reflected by the beam splitter 42 through the collimating lens 3 b and the shaping prism 4 b and enters the polarizing lens element 6. Then, the light source irradiation control unit 43 controls which of the light source 13 a and the light source 13 b emit light according to the type of the optical disk 12, thereby switching the polarization direction of the light beam incident on the polarization lens element 6. It becomes possible.

  Further, the optical pickup device 103 may be configured such that the light sources 13a and 13b emit linearly polarized light having the same polarization direction. In this case, the optical pickup device 103 is provided with a λ / 2 wavelength plate that rotates the polarization direction of one of the light beams emitted from the light sources 13a and 13b.

  However, as described above, the configuration including the TN-type liquid crystal element 5 as the polarization direction switching element has a smaller number of components and is less expensive than the configuration including the two light sources as the polarization direction switching element. In addition, it is advantageous for reducing the size of the optical pickup device. Therefore, the polarization direction switching element is more preferably a TN liquid crystal element 5.

In addition to the above configuration, a Faraday rotator or the like can be used as the polarization direction switching element. However, since the liquid crystal element has higher transmittance than the Faraday rotator, it is advantageous in improving the coupling efficiency. Moreover, since it is small, it is advantageous for miniaturization of the optical pickup.
(4) Spherical Aberration Correction Element Normally, the objective lens 11 is designed so that the spherical aberration is reduced at a focused spot that has passed through a cover glass having a predetermined thickness. More precisely, the spherical aberration is also affected by the refractive index of the glass material constituting the cover glass of the optical disk 12. For this reason, the objective lens 11 is designed in consideration of the refractive index of the glass material constituting the cover glass.

  On the other hand, when an optical disc different from the thickness of the cover glass assumed when designing the objective lens 11 or the refractive index of the constituting glass material is applied, the light spot condensed on the recording layer of the optical disc 12 has spherical aberration. appear. This spherical aberration (third-order spherical aberration) is proportional to the fourth power of the numerical aperture with respect to the cover glass thickness error or the refractive index error. For this reason, the influence of this spherical aberration increases as the numerical aperture of the objective lens 11 increases.

  Further, when the objective lens 11 is designed assuming an optical disk having a single recording layer, the thickness error of the cover glass of the optical disk is a target. However, in the case of an optical disc having two recording layers, the thickness of the intermediate layer between the two recording layers is also a factor that causes spherical aberration. For example, an optical disk 12 shown in FIG. 1 is given as an optical disk having two recording layers.

  As shown in FIG. 1, the optical disc 12 includes a first recording layer 12a and a second recording layer 12b. In the optical disc 12, the first recording layer 12a and the second recording layer 12b are formed in this order from the surface closer to the objective lens 11 side. An intermediate layer 12c is formed between the first recording layer 12a and the second recording layer 12b. When the objective lens 11 is designed so that the spherical aberration of the light spot condensed on the first recording layer 12a of the optical disk 12 is reduced, spherical aberration occurs when the light beam is condensed on the second recording layer 12b of the optical disk 12. Occurs. When the amount of this spherical aberration is large, there is an effect that the error rate is deteriorated when the signal recorded on the optical disk 12 is reproduced. For this reason, the amount of spherical aberration in the first recording layer 12a and the second recording layer 12b needs to be reduced to such an extent that there is no problem in signal recording or reproduction.

  In the optical pickup device 100, a beam expander is used to correct a cover glass thickness error, an intermediate layer thickness between two recording layers, or a spherical aberration caused by the refractive index error.

  Below, the structure of the beam expander 7 in the optical pick-up apparatus 100 is demonstrated with reference to FIG.

  As shown in FIG. 1, the beam expander 7 includes a concave lens 16 and a convex lens 17. The concave lens 16 is disposed on the light source 13 side, and the convex lens 17 is disposed on the objective lens 11 side. For this reason, the beam expander 7 is configured to expand and emit the light beam of the light beam incident from the light source 13 side. By adjusting the lens interval between the concave lens 16 and the convex lens 17, the beam expander 7 is arranged on the optical disk 12. The generated spherical aberration is corrected. In the reference state of the beam expander 7, the focal length and the lens interval between the concave lens 16 and the convex lens 17 are set so that parallel light incident from the light source 13 side is emitted as parallel light to the objective lens 11 side. ing.

  Further, the beam expander 7 can emit diverging light or focused light to the objective lens 11 side by changing the lens interval between the concave lens 16 and the convex lens 17. By making a light beam having such a divergence angle enter the objective lens 11, spherical aberration due to an error in the cover glass thickness of the optical disk 12 can be corrected.

  The objective lens 11 receives parallel light and focuses a light beam near the center between the first recording layer 12a and the second recording layer 12b, that is, near the center of the intermediate layer 12c. In addition, the spherical aberration that occurs is designed to be the smallest in a high-density optical disc. For this reason, when the optical disk 12 is a high-density optical disk, when a light beam is condensed on the first recording layer 12a, the beam expander 7 widens the distance between the concave lens 16 and the convex lens 17 to thereby focus the focused light. It is incident on the lens 11 to correct spherical aberration. Further, when condensing the light on the second recording layer 12b, the beam expander 7 makes the divergent light incident on the objective lens 11 by narrowing the lens interval between the concave lens 16 and the convex lens 17, thereby causing spherical aberration. Is corrected.

  On the other hand, when the optical disk 12 is a low density optical disk having a cover glass thickness larger than that of the high density optical disk, the effective numerical aperture is limited by the effect of the step provided on the objective lens 11, so that the low density optical disk is used. Spherical aberration in the focused light beam is also reduced. However, since the objective lens 11 is designed to reduce the spherical aberration that occurs when the light beam is focused near the center of the intermediate layer of the high-density optical disc, the two recording layers provided in the low-density optical disc. Even when the light beam is focused on either of them, an excessive spherical aberration occurs. Therefore, when condensing light on the recording layer of the low-density optical disk, the beam expander 7 narrows the lens interval between the concave lens 16 and the convex lens 17 so that divergent light is incident on the objective lens 11 and spherical aberration. Can be reduced.

  In this example, the objective lens 11 is a high-density optical disk and designed to have the smallest spherical aberration near the center of the intermediate layer 12c. However, the objective lens 11 is not limited to this and is designed by other methods. There may be another objective lens.

  As in this embodiment, a low density optical disk is often an optical disk having a cover glass that is thicker than a high density optical disk. For this reason, even if the effective numerical aperture is reduced, the remaining spherical aberration may be large and the spherical aberration may be excessive. In the present embodiment, an objective lens having a small spherical aberration is used in the intermediate layer of the two recording layers of the high-density optical disc having a thinner cover glass thickness. For example, the objective lens 11 is the first lens of the low-density optical disc. It may be designed so that the spherical aberration of the light beam condensed on one recording layer 12a is minimized. In this case, the lens interval between the concave lens 16 and the convex lens 17 of the beam expander 7 is narrowed, and diverging light is incident on the objective lens 11, thereby condensing the light on the other second recording layer 12b of the low-density optical disk. In order to correct the spherical aberration of the light beam, and to correct the spherical aberration of the light beam condensed on the two recording layers of the high-density optical disc, the lens interval between the concave lens 16 and the convex lens 17 is What is necessary is just to make it wide and to make convergent light inject into the objective lens 11. FIG.

  In addition, the objective lens 11 is designed so that the spherical aberration of the light beam that collects the light at any position between the first recording layer 12a of the low-density optical disk and the second recording layer 12b of the high-density optical disk becomes small. May be. In this case, the beam expander 7 narrows the lens interval between the concave lens 16 and the convex lens 17 and makes divergent light incident on the objective lens 11, so that the first recording layer 12 a or the second recording layer of the low-density optical disk is obtained. It is possible to correct the spherical aberration of the light beam focused on the layer 12b. Moreover, the lens interval between the concave lens 16 and the convex lens 17 is widened, and diverging light is incident on the objective lens 11, thereby condensing the light on the first recording layer 12a or the second recording layer 12b of the high-density optical disc. The spherical aberration of the light beam can be corrected.

  The spherical aberration correction element is not limited to the beam expander 7 described above, and any conventionally known spherical aberration correction element can be applied to the optical pickup device 100. For example, the spherical aberration correction element includes an element provided with a liquid crystal element.

  Hereinafter, the configuration of a liquid crystal spherical aberration correction element including a liquid crystal element will be described with reference to FIG. FIG. 15 is a plan view showing a schematic configuration of the liquid crystal type spherical aberration correction element 47.

  The liquid crystal spherical aberration correction element 47 includes a liquid crystal element 44 in which a liquid crystal layer is sandwiched between a pair of glass substrates, and an electrode pattern 45. The electrode pattern 45 is provided on one of the pair of glass substrates of the liquid crystal element 44. The liquid crystal element 44 is an electric field birefringence type liquid crystal element. As shown in FIG. 15, the electrode pattern 45 has an annular electrode pattern.

  In the liquid crystal type spherical aberration correction element 47, the voltage applied to the electrode pattern 45 is changed according to the amount of spherical aberration to be corrected. Thereby, a phase distribution is generated in the wavefront of the light transmitted through the liquid crystal element 44, and the spherical aberration is corrected.

  As described above, in the optical pickup device 100, the liquid crystal type spherical aberration correction element 47 can be used as a spherical aberration correction element. However, in the optical pickup device 100, as in the beam expander 7, it is more preferable to correct the spherical aberration by changing the distance between the two lenses. The reason for this will be described below.

  The electrode pattern 45 is formed with an annular electrode pattern corresponding to the diameter of the incident light beam. Therefore, in order to correct the spherical aberration generated in two types of optical discs having different beam diameters or different numerical apertures, the electrode pattern 45 has two types of beam diameters according to the size of the numerical aperture. (Only the electrode pattern corresponding to one type of optical disk is shown in FIG. 15, but in order to support two types of optical disks, another electrode pattern having a similar shape is required.) Pair is required). For this reason, the number of electrode patterns of the electrode pattern 45 increases, and there is a problem that the number of power supply wires connected to the electrode patterns to supply current from an external power supply to the electrode patterns also increases. . Moreover, since light is shielded by the electrode pattern, there is a demerit such as a decrease in transmittance.

Further, in order to generate a large phase distribution in the light beam transmitted through the liquid crystal element 44, it is necessary to increase the thickness of the liquid crystal layer of the liquid crystal element 44. The response time of the liquid crystal element 44 becomes longer in proportion to the square of the thickness of the liquid crystal layer. For this reason, in the liquid crystal type spherical aberration correction element 47, in order to reduce the amount of phase difference to be generated, the generated phase distribution W (ρ) appears to approximate the wavefront given by the following equation (24). There is something.
W (ρ) = 6ρ ^ 4-6ρ ^ 2 + 1 (24)
ρ represents the distance in the radial direction from the center of the electrode pattern.

On the other hand, when the beam expander 7 is used as the spherical aberration correction element, the wave front is such that the phase distribution W (ρ) generated by the beam expander 7 is approximated by the following equation (25).
W (ρ) = 2ρ ^ 2-1 (25)
In the case of the wavefront of the above formula (24), the amount of coma generated due to the shift of the center of the objective lens 11 and the center of the electrode pattern 45 of the liquid crystal element is large, and there is a problem when the objective lens 11 is driven in the radial direction. It becomes. When the liquid crystal spherical aberration correction element 47 is used as the spherical aberration correction element, the liquid crystal element 44 is often mounted on the objective lens holder so as to be driven integrally with the objective lens 11. For this reason, many feed wires are fastened from the driven portion to the fixed portion (the portion that is not driven). Therefore, there is a possibility of affecting the frequency characteristics of the movable part of the objective lens holder.

  On the other hand, since the beam expander 7 corrects spherical aberration by changing the lens interval between the concave lens 16 and the convex lens 17, even the light with different light beam diameters can be used without any problem. Therefore, the beam expander 7 is more preferable as the spherical aberration correction element than the liquid crystal type spherical aberration correction element 47.

  Moreover, although the beam expander 7 is a structure which consists of a concave lens and a convex lens, it is not limited to this, The structure which consists of two convex lenses may be sufficient. Hereinafter, a beam expander 57 including two convex lenses will be described with reference to FIG.

  As shown in FIG. 16, the beam expander 57 includes a convex lens 516 and a convex lens 517. The convex lens 516 is disposed on the light source 13 side, and the convex lens 517 is disposed on the objective lens 11 side. The beam expander 57 is configured to expand and emit the light beam of the light beam incident from the light source 13 side, and by adjusting the lens interval between the convex lens 516 and the convex lens 517, a spherical surface generated on the optical disk 12. Aberration is corrected. In the reference state of the beam expander 57, the focal length and the lens interval between the convex lens 516 and the convex lens 517 are set so that parallel light incident from the light source 13 side is emitted as parallel light to the objective lens 11 side. ing.

  Further, the beam expander 57 can emit diverging light or focused light to the objective lens 11 side by changing the lens interval between the convex lens 516 and the convex lens 517. By making a light beam having such a divergence angle enter the objective lens 11, spherical aberration due to an error in the cover glass thickness of the optical disk 12 can be corrected.

  As described above, the spherical aberration correction element can correct spherical aberration even in the case of an optical disc having a plurality of recording layers, and further uses corresponding objective lenses having different numerical apertures and optical discs having different cover glass thicknesses. Even in the case of using, since it is possible to correct spherical aberration, it is possible to improve signal quality in recording / reproducing.

  The spherical aberration correction element corrects the spherical aberration by changing the divergence of the emitted light beam. The spherical aberration correcting element is disposed between the polarizing lens element 6 and the objective lens 11. Therefore, in the optical pickup device 100, parallel light can be incident on the polarization lens element 6 in both the forward path and the return path. In addition to the beam expander type spherical aberration correction element composed of two lenses, even in the case of the liquid crystal element type, two liquid crystal elements whose working polarization directions are orthogonal to each other are used. By using a λ / 4 wavelength plate in between, the above action can be realized.

When the spherical aberration correction element is arranged on the light source side with respect to the polarizing lens element, the light traveling from the spherical aberration correction element to the optical disk is divergent, or in order to correct the spherical aberration in the light beam condensed on the recording layer of the optical disk. For example, in the optical pickup device 100, the diverging light is incident on the polarizing lens element 6 in the forward path of the light beam, and the diverging light whose beam diameter is expanded by the lens effect of the polarizing lens element 6 is the polarizing lens element. Since the polarizing lens element has no lens effect on the return light from the optical disk when the light is emitted from the optical disc, the condensing point position of the light passing through the polarizing lens element according to the correction amount of the spherical aberration is the optical axis. Due to the above change, an offset occurs in focus error signal detection. In the configuration of the present embodiment, it is possible to prevent occurrence of an offset in the focus error signal. Therefore, it is desirable to arrange the spherical aberration correcting element between the polarizing lens element and the objective lens.
(5) Applicable Optical Disc Although the optical disc having two recording layers has been described as the optical disc 12, the optical disc that can be applied to the optical pickup device 100 is not limited to this. For example, the optical disc 12 may be an optical disc having a larger number of recording layers or an optical disc having a single recording layer. In addition, the number of recording layers may be different between the two types of optical disks. In addition, one optical disc may have a plurality of recording layers and have different recording densities.

  Further, when a plurality of types of optical discs that require different numerical apertures are compatible with a single objective lens, the optical pickup device 100 sets the Rim intensity objective lens incident light intensity distribution suitable for each optical disc, It is intended to suppress a decrease in light utilization efficiency during reproduction. For this reason, in this embodiment, the case where a high-density optical disk and a low-density optical disk having different recording densities are used as two different types of optical disks has been described. However, as the optical disk 12, the recording densities of different types of optical disks are the same. It may be an optical disc. The optical disc 12 may be an optical disc having the same cover glass thickness, intermediate layer thickness between recording layers, and refractive index. Moreover, as an optical disk to which one of the different numerical apertures corresponds, for example, a plurality of types of optical disks having different cover glass thicknesses, intermediate layer thicknesses between recording layers, and refractive indexes may be used.

  Further, the objective lens which is a condensing means has been described as an objective lens having an effectively different numerical aperture as one objective lens, but is not limited to this. For example, two objective lenses having different numerical apertures are used. You may switch and use a lens.

  The optical pickup device 100 can also support at least two types of optical disks that require different numerical apertures, that is, two or more types of optical disks. For example, the present invention can be applied to a total of three types of optical discs, one type of optical disc having a relatively large numerical aperture and two types of optical discs having a relatively small numerical aperture. In such a case, an optical disk having a relatively large numerical aperture is made to correspond to linearly polarized light in a predetermined direction, while an optical disk having a relatively small numerical aperture is made to correspond to linearly polarized light in a direction orthogonal to the predetermined direction. By doing so, it becomes possible to realize compatibility of the optical disc.

  Here, as two types of optical disks having a relatively small numerical aperture, for example, those having different recording layers, those having different track pitches, those having different recording data formats, those for reproduction only, or those for recording / reproduction are used. It is possible to deal with various things such as possible. Further, two types of optical discs having a relatively large numerical aperture and one type of optical disc having a relatively small numerical aperture can be used. Further, it is possible to deal with more types of optical disks.

  Further, the optical disk 12 may be an optical disk in which the corresponding condensing means has the same effective diameter and numerical aperture. For example, in an optical pickup device having one objective lens and a polarizing lens element, the light coupling efficiency can be changed by switching the diameter of the light beam emitted from the polarizing lens element. As a result, the output emitted from the light source is constant, and it is possible to change the output focused on the optical disk from the objective lens by switching the beam diameter, thereby switching the recording / reproducing power. In addition, when the optical disk has two recording layers and the recording density is different for each recording layer, the intensity distribution of the light beam incident on the objective lens, that is, the Rim intensity is changed by switching the light beam diameter by the polarizing lens element. By utilizing this, it is possible to change the diameter of the condensed beam condensed on each recording layer so as to correspond to different recording densities.

Further, the optical disk 12 may have the same numerical aperture although the effective diameter of the corresponding condensing means is different. In the case of the condensing means having the same effective diameter, the Rim intensity changes by switching the light beam diameter by the polarizing lens element. However, when the effective diameters are different, the Rim intensity in each case can be matched. Become.
(6) Polarizing Lens Element of the Present Invention The polarizing lens element 60 is not limited to an optical pickup device, and can be used as a beam diameter conversion optical system.

  In that case, as described above, the polarizing lens element 6 includes two polarizing lenses that function as lenses for linearly polarized light in one direction incident from the light source side, and parallel light is incident on the polarizing lens element from the light source side. In addition, when the polarization direction of the incident light beam is the same as the direction of the linearly polarized light, the light beam emitted from the polarization lens element is parallelized with a light beam diameter different from the light beam diameter of the incident light beam. The focal length of the lens and the distance between the polarizing lenses may be set. By setting in this way, when the polarization direction of the light beam incident on the polarizing lens element is orthogonal to the linearly polarized light, parallel light having the same light beam diameter as that of the incident light beam is emitted. When two light sources that emit linearly polarized light with orthogonal polarization directions are provided, the diameter of the light beam emitted from the polarizing lens element can be switched by switching the light source to be turned on. Therefore, in the case of a beam expander composed of two normal lenses (for example, the one used as the spherical aberration correction element of the present invention), a drive mechanism for changing the lens interval is necessary to change the outgoing beam diameter. The divergence angle of the emitted light also changes with the change of the beam diameter, but the polarizing lens element of the present invention can emit parallel light with different beam diameters and does not require a driving mechanism. It is.

  Also, since the focal length of the two polarizing lenses and the distance between the two polarizing lenses are set so that the light incident as parallel light is emitted as parallel light, for example, it is arranged in a divergent light beam or a focused light beam. In this configuration, the positional adjustment accuracy in the X and Y planes becomes severe due to the occurrence of coma aberration, etc., but the positional adjustment accuracy in the X and Y planes of the polarizing lens element is relaxed compared to that case. Can do.

  Further, as the polarizing lens element 6, two polarizing lenses are integrally formed on both sides of a glass substrate that transmits one light, and the first polarizing lens functions as a concave lens with respect to linearly polarized light in one direction; A polarizing lens element composed of a second polarizing lens that functions as a convex lens for linearly polarized light in the same direction as the linearly polarized light may be used. If the thickness of the glass substrate between the two polarizing lenses is the same, the focal length of the lens can be increased compared to the case where the two polarizing lenses are formed of convex lenses. The pitch of the peripheral portion can be widened, and the light amount loss due to errors in creating a blazed hologram such as etching can be reduced. In the case of a normal refraction type lens, since the focal length can be increased, the radius of curvature of the lens can be increased, and the cost can be further reduced. Further, it is possible to reduce the amount of coma generated due to the optical axis shift between the two lenses. Moreover, since light is not condensed inside the glass substrate, it is possible to prevent the glass substrate from being deteriorated by heat generated in the vicinity of the condensing spot. In the case of a blazed hologram, it can be made thinner than a refraction type polarizing lens, which is advantageous for downsizing of the apparatus.

  Also, polarized light that switches between the polarization lens element 6 and the light source 13 to output the polarization direction of linearly polarized light incident from the light source side as linearly polarized light in the same direction or as orthogonally linearly polarized light. A direction switching element may be provided. When the polarization direction switching element is used, for example, it is not necessary to provide a plurality of light sources that emit light having polarization directions orthogonal to each other. Therefore, the number of components is small, the cost is low, and the optical system can be made compact.

  Further, the polarization direction switching element may be a liquid crystal element. A Faraday rotator or the like can be used as the polarization direction switching element, but the liquid crystal element is advantageous in improving the coupling efficiency because the transmittance is higher. Moreover, since it is small, it is advantageous for making the optical system compact.

  As described above, the optical pickup device 100 includes the polarizing lens element 60 that converts the beam diameter according to the polarization direction of the incident light beam. For this reason, the conversion magnification of the light beam diameter of the incident light beam can be set according to the high-density optical disk and the low-density optical disk in which both the effective diameter and numerical aperture of the objective lens that is the corresponding condensing means are different. As a result, in the optical pickup device 100, the two types of optical disks can be set to have the same Rim intensity, and the coupling efficiencies can be made to be the same.

  Further, in the optical pickup device 100, when different types of optical disks are interchanged with one objective lens, the Rim intensity can be appropriately set for both optical disks. For this reason, the condensing spot of both optical disks can be appropriately sized, and the stability in recording and reproduction can be improved.

  In addition, since a reduction in coupling efficiency can be prevented, it is advantageous for reducing power consumption, increasing the recording rate of the optical disk, and increasing the number of optical disks.

  Further, in the optical pickup device 100, the polarizing lens element 6 emits a light beam having a different beam diameter depending on the direction of incident linearly polarized light, and is applied to an objective lens that is a condensing unit having an effective diameter that is effectively different. It is configured to receive light. In such a configuration, for example, in the light collecting means having effective diameters that are effectively different from each other, the luminous flux diameter in the light emitted from the polarizing lens element is smaller than the case where the effective effective diameter is relatively small. When the effective effective diameter is relatively large when dealing with relatively large linearly polarized light, the Rim intensity is inevitably smaller than when the effective effective diameter is relatively small. Therefore, the Rim intensity cannot be matched in the case of different effective diameters.

  However, in the light collecting means having effective diameters that are effectively different from each other, the light having a relatively large light beam diameter in the linearly polarized light emitted from the polarizing lens element, compared to the case where the effective effective diameter is relatively large. , Rim intensities can be matched in the case of different effective diameters. Further, compared to the case where the effective diameter is small, the Rim intensity when the effective diameter is large can be increased or decreased. That is, it is desirable because the range of Rim intensity that can be set by the polarizing lens element can be expanded.

  This will be described in further detail with reference to FIG. FIG. 22 is an explanatory diagram showing the relationship between the effective effective diameter of the objective lens and the Rim intensity. FIG. 22A shows the relatively small effective effective diameter of the objective lens from the polarizing lens element. FIG. 22B shows a case where the linearly polarized light having a relatively large luminous flux diameter (hereinafter referred to as “Type.1”) among the emitted linearly polarized light is shown. FIG. FIG. 22 (c) shows a case where the effective diameter is made to correspond to linearly polarized light having a relatively small light beam diameter among the linearly polarized light emitted from the polarizing lens element (hereinafter referred to as Type 2). When the relatively large effective diameter of the objective lens is made to correspond to the linearly polarized light having a relatively large light beam diameter among the linearly polarized light emitted from the polarizing lens element (hereinafter referred to as Type.3). FIG. 22 (d) shows a relatively small effective effective diameter of the objective lens. If the light beam diameter in the linearly polarized light emitted from the lens element is made to correspond to a relatively small linear polarization shows a (hereinafter referred to as Type.4).

  In FIG. 22, Type.1 and Type.2 are one combination. Type.3 and Type.4 are different combinations.

  First, in the case of the combination of Type.1 and Type.2, the effective diameter of the objective lens is small in the case of Type.1 compared to the case of Type.2, and the linearly polarized light beam emitted from the polarizing lens element Since the diameter is large, the Rim intensity in the case of Type.1 inevitably becomes larger than that in the case of Type.2. The relationship between the Rim intensity does not change even when the conversion magnification of the linearly polarized light emitted from the polarizing lens element is changed. The reason is that the diameter of linearly polarized light emitted from the polarizing lens element in Type.1 is larger than that in Type.2 and the objective lens is effective in Type.1. This is because the diameter is smaller than that of Type.2.

  Next, in the case of the combination of Type.3 and Type.4, the effective diameter of the objective lens is large in the case of Type.3 compared to the case of Type.4, and the linearly polarized light emitted from the polarizing lens element Large beam diameter. For this reason, when the ratio of the effective diameters of the objective lenses differing from each other and the ratio of the diameter of the linearly polarized light emitted from the polarizing lens element are matched, the type 3 and type 4 cases are different. Rim intensity matches. FIGS. 22C and 22D are diagrams showing such a state. In the case of Type.3, if the diameter of the linearly polarized light emitted from the polarizing lens element is reduced in relation to the relationship between the ratio of the effective diameter and the ratio of the light beam diameter so that the Rim intensities coincide with each other, The Rim intensity is smaller than that of Type 4. On the contrary, in the case of Type.3, when the diameter of the linearly polarized light emitted from the polarizing lens element is increased, the Rim intensity in the case of Type.3 becomes larger than that in the case of Type.4. That is, in the combination of Type.3 and Type.4, the Rim intensity of the other type can be increased or decreased with respect to the Rim intensity in the case of one type. Further, it is possible to match the Rim intensity in both types.

Therefore, when the effective effective diameter is relatively large, when the light having a relatively large luminous flux diameter is made to correspond to the light emitted from the polarizing lens element, the Rim intensities coincide with each other in the case of different effective diameters. Can be made. Further, compared to the case where the effective diameter is small, the Rim intensity when the effective diameter is large can be increased or decreased. That is, the range of Rim intensity that can be set by the polarizing lens element can be expanded.
[Embodiment 2]
The following will describe another embodiment of the present invention with reference to FIG. In the present embodiment, differences from the first embodiment will be mainly described, and the same reference numerals are given to the constituent elements having the same functions as the constituent elements used in the first embodiment. A description thereof will be omitted. In addition, the various feature points described in the first embodiment can be applied in combination with the present embodiment. FIG. 17 is a cross-sectional view showing a schematic configuration of the optical pickup device 104 according to the present embodiment. FIG. 17A shows a case where the high-density optical disc 20 is used as the optical disc 12, and FIG. The case where the low density optical disk 30 is used as the optical disk 12 is shown.

  The optical pickup device 100 according to the first embodiment has a configuration in which the objective lens 11 has a step 19. On the other hand, the objective lens of the optical pickup device 104 of the present embodiment does not have a step. Unlike the optical pickup device 100 of the first embodiment, the optical pickup device 104 includes a polarization aperture limiting unit. The optical pickup device 104 is different from the configuration of the optical pickup device 100 in that it does not include a λ / 4 wavelength plate. Further, in the optical pickup device 104, an optical disk 12 having two recording layers is used.

  As shown in FIG. 17A, the optical pickup device 104 includes an objective lens 211 and a polarization aperture limiting element 208.

  The objective lens 211 has a numerical aperture corresponding to the high density optical disc 20 of 0.85 and an effective diameter of Φ3, while the numerical aperture corresponding to the low density optical disc 30 is 0.65 and has an effective diameter. Is an objective lens with Φ2.29.

  The objective lens 211 is designed so that spherical aberration becomes small when the high-density optical disk 20 is used. The objective lens 211 is designed so that spherical aberration generated by the light beam condensed at a position closer to the second recording layer 20b (including the second recording layer 20b) than near the center of the intermediate layer 20c is reduced. ing. In this case, the second recording layer 20b of the high density optical disc 20 is located at a position of 125 μm from the surface of the high density optical disc 20. On the other hand, the first recording layer 30 a of the low density optical disc 30 is located at a position 600 μm from the surface of the low density optical disc 30. Therefore, in the optical pickup device 104, when the low-density optical disc 30 is used as the optical disc 12, the over spherical surface is also obtained when the light beam is condensed on either the first recording layer 30a or the second recording layer 30b. Aberration occurs. Therefore, when the low-density optical disk 30 is used as the optical disk 12, the spherical aberration is corrected by adjusting the distance between the two lenses of the beam expander 7 which is a spherical aberration correcting element.

  In addition, an aperture limiting method for realizing a numerical aperture corresponding to two types of optical disks in the optical pickup device 104 is as follows. When the high-density optical disk 20 is used as the optical disk 12, in the optical pickup device 104, the aperture is limited by the aperture 10 provided in the objective lens holder 9 shielding the incident light beam, as in the above embodiment. . That is, the optical pickup device 104 is configured such that a light beam having an effective diameter Φ3 of the objective lens 211 is incident on the objective lens 211. Further, the objective lens holder 9 of the optical pickup device 104 is provided with a polarization aperture limiting element 208.

  The polarization aperture limiting element 208 includes a polarizing plate 201, a glass substrate 202, and a phase correction film 203. A phase correction film 203 is provided at the center of the surface of the glass substrate 202 on the beam expander 7 side, and a polarizing plate 201 is provided at the periphery of the phase correction film 203.

  Also, as shown in FIG. 17B, the inner diameter of the polarizing plate 201 is a diameter corresponding to the numerical aperture 0.65 of the objective lens 211 corresponding to the low density optical disc 30. That is, the inner diameter of the polarizing plate 201 is a diameter corresponding to the effective diameter Φ2.29 of the objective lens 211. In the optical pickup device 104, the light beam is incident on the objective lens 211 as divergent light, and thus the inner diameter of the polarizing plate 201 is smaller than the effective diameter Φ2.29 of the objective lens 211. However, the inner diameter of the polarizing plate 201 is not limited to this, and when the light beam is incident on the objective lens 1606 as parallel light, it may be the same diameter as the effective diameter Φ2.29 of the objective lens 211. .

  The polarizing plate 201 absorbs the linearly polarized light in the Y direction and transmits the linearly polarized light in the X direction, and absorbs the light beam in the polarization direction in the Y direction at the outer peripheral portion of the light beam toward the objective lens 211. It is supposed to be.

  Therefore, when the low-density optical disk 30 is used as the optical disk 12, the outer peripheral portion of the light beam directed toward the objective lens 211 is blocked by being absorbed by the polarizing plate 201. For this reason, when the low density optical disk 30 is used as the optical disk 12, only the light at the center of the light beam of the light beam is incident on the objective lens 211.

On the other hand, when the high-density optical disk 20 is used as the optical disk 12, the light beam directed toward the objective lens 211 is linearly polarized light in the X direction. For this reason, when the high-density optical disk 20 is used as the optical disk 12, the light beam is not absorbed by the polarizing plate 201, and the light beam that has passed through the aperture 10 enters the objective lens 211 as it is. In this case, a phase difference occurs between the light transmitted through the polarizing plate 201 and the light transmitted through the central portion of the light beam. The phase correction film 203 corrects the phase difference between the light beam that has passed through the polarizing plate 201 and the light beam that has passed through the central portion of the light beam so that such a phase difference does not occur. The phase correction film 203 may be a dielectric film such as TiO ₂ or SiO ₂ , or may be a film obtained by bonding a film made of an isotropic resin material.

  Further, the optical pickup device 104 is not provided with a λ / 4 wavelength plate. For this reason, the polarization direction of the light beam incident on the polarization aperture limiting element 208 and the return light beam reflected by the optical disk and incident on the polarization aperture limitation element 208 are the same.

  Conversely, when a λ / 4 wavelength plate is provided, when the high-density optical disk 20 is used as the optical disk 12, the light having the polarization direction in the X direction in the forward path of the light beam is returned in the return path of the return light beam. , The light is polarized in the Y direction. For this reason, the outer peripheral portion of the light beam of the return light beam is shielded by the polarizing plate 201. Therefore, when the high-density optical disk 20 is used as the optical disk 12, the S / N ratio decreases because the amount of return light is lost. In addition, the interference pattern (also referred to as a ball pattern) of diffracted light in the high-density optical disk 20 used for detecting the radial error signal is lost, which also affects the detection of the radial error signal.

  In the optical pickup device 104, the polarization direction incident on the polarization lens element 6 and the polarization aperture limiting element 208 is switched by the TN liquid crystal element 5 which is a polarization direction switching element. That is, in the optical pickup device 104, the polarization direction corresponding to each of the high density optical disk 20 and the low density optical disk 30 is switched. Therefore, the number of parts can be reduced as compared with the case where the polarization direction switching element is used individually.

  Further, by using the beam expander 7 which is a spherical aberration correction element, it is possible to effectively correct spherical aberration occurring in optical disks having different cover glass thicknesses.

  In the optical pickup device 104, the polarizing plate 201 that absorbs linearly polarized light in one direction is provided as the polarizing aperture limiting element. However, the polarizing aperture limiting element is not limited to this. For example, a polarization aperture limiting element provided with a polarization diffraction element that diffracts only light in one polarization direction may be used. In that case, when the low-density optical disk 30 is used as the optical disk 12, the light at the outer peripheral portion of the light beam is diffracted, but the diffracted light does not enter the objective lens, or even if it enters, flare is formed on the recording layer. A diffraction angle and a diffraction direction may be set in. The polarization aperture limiting element may be a reflective polarizing plate that reflects linearly polarized light in one direction.

  As described above, the optical pickup device of the present invention includes a light source and a condensing unit that condenses the light emitted from the light source onto the recording layer of the optical recording medium, and between the light source and the condensing unit. Since a polarizing lens element that changes the beam diameter according to the polarization direction of linearly polarized light is provided, the Rim intensity can be ensured so that the recording / reproducing is optimized in the optical recording medium, and the coupling efficiency is improved. It becomes possible to improve further. Therefore, the present invention can be used in the industry of optical disc recording / reproducing apparatuses.

It is sectional drawing which shows schematic structure of the principal part of the optical pick-up apparatus of one Embodiment of this invention. When a high-density optical disk is used as an optical disk, it is a cross-sectional view showing the state of the polarization direction of a light beam transmitted through each member of the optical pickup device, (a) shows the forward path, (b), Indicates a return trip. FIG. 5 is a cross-sectional view showing a state of a polarization direction of a light beam transmitted through each member of the optical pickup device when a low-density optical disc is used as an optical disc, (a) showing a forward path, and (b) showing Indicates a return trip. It is a figure which shows the structure of the polarizing lens element in the said optical pick-up apparatus, (a) is a top view, (b) is sectional drawing. It is sectional drawing which shows the focal distance and lens space | interval of two polarizing lenses in the said polarizing lens element. It is sectional drawing which shows another structure of the said polarizing lens element. (A)-(d) is sectional drawing which shows an example of the manufacturing process of the said polarizing lens element. FIG. 5 is a cross-sectional view showing a polarization direction of a light beam transmitted through each member of the optical pickup device when the polarization lens element is designed to emit a non-parallel light beam; The forward path is shown, and (b) shows the return path. It is sectional drawing which shows schematic structure of the light source in the said optical pick-up apparatus. FIG. 2 is a plan view of a three-part hologram formed on a hologram element and a light receiving element as seen from the side from which a light source emits a light beam. In the drawing, the left side is a plan view of the three-part hologram and the right side is a light receiving element. FIG. It is sectional drawing which shows schematic structure of the light source which detects a focus error signal using a 5-part photodetector. FIG. 2 is a plan view of a three-part hologram formed on a hologram element and a light receiving element as seen from the side from which a light source emits a light beam. In the drawing, the left side is a plan view of the three-part hologram and the right side is a light receiving element. FIG. It is sectional drawing which shows schematic structure of the optical pick-up apparatus which isolate | separates the return light beam of a return path and detects a focus error signal. It is sectional drawing which shows schematic structure of the optical pick-up apparatus provided with two light sources as a polarization direction switching element. It is a top view which shows another structure of the spherical aberration correction element in the said optical pick-up apparatus. It is sectional drawing which shows schematic structure of the optical pick-up apparatus provided with the spherical aberration correction element which consists of two convex lenses. FIG. 6 is a cross-sectional view showing a schematic configuration of an optical pickup device according to another embodiment of the present invention, where (a) shows a case where a high-density optical disk is used as an optical disk, and (b) uses a low-density optical disk as an optical disk. Indicates the case where It is sectional drawing which showed schematic structure of the optical pick-up apparatus used conventionally. It is sectional drawing which showed schematic structure of the conventional optical pick-up apparatus provided with the shaping prism. It is sectional drawing which showed the outline of the shape of the compatible objective lens used for the conventional optical pick-up apparatus. It is a graph which shows the wave front in the recording surface of the condensing beam condensed on the different optical disk by the compatible objective lens, (a) is a wave front in a DVD recording surface, (b) is a wave front in a CD recording surface. It is explanatory drawing which shows the relationship between the effective effective diameter of an objective lens, and Rim intensity | strength, (a) is a relatively small effective effective diameter of an objective lens, and shows linearly polarized light radiate | emitted from a polarizing lens element. (B) shows a relatively large effective effective diameter of the objective lens in the linearly polarized light emitted from the polarizing lens element. (C) shows the case where the effective effective diameter of the objective lens is relatively large, and the effective diameter of the objective lens is the diameter of the light beam in the linearly polarized light emitted from the polarizing lens element. (D) shows a relatively small effective effective diameter of the objective lens and a relative light beam diameter in the linearly polarized light emitted from the polarizing lens element. The case where it corresponds to small linearly polarized light is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Hologram element 3 Collimate lens 4 Shaping prism 5 Liquid crystal element (polarization direction switching means)
6 Polarizing lens element 7 Beam expander (spherical aberration correction means)
8 λ / 4 wave plate 9 Objective lens holder 10 Aperture 11 Objective lens (condensing means)
12 Optical disc (different optical recording medium)
12a, 12b Recording layer 13 Light source 14 Polarizing lens (first polarizing lens)
15 Polarized lens (second polarized lens)
16 Concave lens (first lens)
17 Convex lens (second lens)
28 Light receiving element (light receiving means)
20 High-density optical disk (optical recording medium)
30 Low density optical disc (optical recording medium)
60 Polarized beam conversion unit 61 Lens interval control unit 62 Signal detection unit (signal detection means)
208 Polarization aperture limiting element (polarization aperture limiting means)
516 Convex lens 517 Convex lens

Claims (17)

A polarizing lens element;
A light source;
Condensing means for condensing the light emitted from the light source on the recording layer of the optical recording medium,
An optical pickup device in which the polarizing lens element and the λ / 4 wavelength plate are provided in order from the light source side between the light source and the light collecting means,
The polarizing lens element includes a first polarizing lens and a second polarizing lens . When the first linearly polarized light that is linearly polarized light in a predetermined direction is incident on the polarizing lens element, the polarizing lens element is incident. When the linearly polarized light having a light beam diameter different from the light beam diameter is emitted and the second linearly polarized light whose polarization direction is orthogonal to the predetermined direction is incident, the light beam diameter of the incident light The polarization lens element that emits linearly polarized light having the same light beam diameter, and the focal length and the lens interval of the first and second polarization lenses are determined when parallel light is incident on the polarization lens element. , Is set to emit parallel light,
Between the polarizing lens element and the condensing means, spherical aberration correcting means for correcting the spherical aberration of the light condensed on the optical recording medium is arranged, and
A light receiving means for receiving the diffracted light of the return light reflected from the optical recording medium and emitted from the polarizing lens element;
An optical pickup device comprising: signal detection means for detecting at least a focus error signal based on light received by the light receiving means . The first polarizing lens functions as a concave lens with respect to the linearly polarized light in the predetermined direction,
The second polarizing lenses, relative to the predetermined direction of the linearly polarized light, the optical pickup apparatus of claim 1, wherein the benzalkonium to function as a convex lens. Furthermore, a light transmitting member that transmits light passing between the first polarizing lens and the second polarizing lens is provided,
It said a first polarization lens, the second polarizing lens, the optical pick-up apparatus according to claim 1 or 2, characterized in that the said light transmitting member are integrated. First polarization lens, and an optical pickup apparatus according to any one of claim 1 to 3, the second polarizing lenses, characterized in that each is a blazed hologram lens. The condensing means is effective when the first linearly polarized light is emitted from the polarizing lens element to the condensing means and when the second linearly polarized light is emitted from the polarizing lens element to the condensing means. 5. The optical pickup device according to claim 1, wherein the first and second effective diameters are different from each other. Further, among the first and second effective diameters of the light collecting means, a relatively large effective diameter is the first and second linearly polarized light emitted from the polarizing lens element to the light collecting means. The optical pickup device according to claim 5, which corresponds to light having a relatively large light beam diameter . 7. The optical pickup device according to claim 5, wherein the condensing means having the first and second effective diameters have different effective numerical apertures together with the effective diameters. The optical recording medium is selected from a plurality of types of optical recording media having different effective effective diameters corresponding to the light collecting means,
The light source is a semiconductor laser,
Among the plurality of types of optical recording media, the corresponding effective recording diameter is relatively large,
The light condensed at the time of information reproduction corresponds to light having a relatively large light beam diameter in the first and second linearly polarized light emitted from the polarizing lens element to the light collecting means,
The light condensed at the time of information recording corresponds to light having a relatively small beam diameter in the first and second linearly polarized light emitted from the polarizing lens element to the condensing means. The optical pickup device according to claim 6 or 7. The light source is a semiconductor laser,
The light condensed on the optical recording medium during information reproduction corresponds to the light having a relatively large light beam diameter among the first and second linearly polarized light emitted from the polarizing lens element to the condensing means. And
The light condensed on the optical recording medium during information recording corresponds to light having a relatively small light beam diameter in the first and second linearly polarized light emitted from the polarizing lens element to the condensing means. And
2. The optical pickup device according to claim 1, wherein the effective diameter of the light collecting means is the same during information recording and information reproduction. The light source is a semiconductor laser,
The first and second linearly polarized lights emitted from the polarizing lens element to the light collecting means are condensed with respect to the effective effective diameter of the light collecting means. The optical pickup device according to claim 1, wherein the optical pickup device corresponds to light having a relatively large light beam diameter. Further, the light condensed when recording information on the optical recording medium corresponds to light having a relatively small light beam diameter in the first and second linearly polarized light emitted from the polarizing lens element to the condensing means. The optical pickup device according to claim 10, wherein: Between the light source and the polarizing lens element, a polarization direction switching unit that switches a polarization direction of light incident on the polarizing lens element from the light source side between the predetermined direction and a direction orthogonal to the predetermined direction. The optical pickup device according to claim 1, wherein the optical pickup device is provided. The optical pickup device according to claim 12, wherein the polarization direction switching means is a liquid crystal element. 14. The optical pickup device according to claim 1, wherein the spherical aberration correcting unit includes a plurality of lenses and a driving unit that drives the lenses in the optical axis direction. Furthermore, a polarization aperture limiting unit that limits the beam diameter corresponding to the numerical aperture according to the polarization direction of light incident on the focusing unit is provided between the polarizing lens element and the focusing unit. The optical pickup device according to any one of claims 1 to 14. The optical pickup device according to claim 1, wherein the signal detection unit detects a focus error signal by a knife edge method. The optical pickup device according to claim 1, wherein the signal detecting unit detects a focus error signal by an astigmatism method.

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