JP4497542B2 - Optical pickup device, optical disk device, and information processing device - Google Patents

Description

  The present invention relates to an optical pickup device, an optical disc device, and an information processing device. More specifically, the present invention relates to an optical pickup used for performing at least one of data recording, reproduction, and erasing on a plurality of types of optical discs. The present invention relates to a device, an optical disk device including the optical pickup device, and an information processing device including the optical disk device.

  In recent years, with the advancement of digital technology and the improvement of data compression technology, CD (compact) is used as an information recording medium (media) for recording information (hereinafter also referred to as “content”) such as music, movies, photographs, and computer software. Optical discs such as discs and DVDs (digital versatile discs) have attracted attention, and along with the reduction in price, optical disc apparatuses that use optical discs as information recording media have become widespread.

  In an optical disc apparatus, information is recorded by forming a micro-spot of laser light on a recording surface on which spiral or concentric tracks of an optical disc are formed, and information is reproduced based on reflected light from the recording surface. Is going. This optical disc apparatus is provided with an optical pickup device for irradiating the recording surface of the optical disc with laser light and receiving reflected light from the recording surface.

  In general, an optical pickup device emits laser light with a predetermined light emission power (output), guides the laser light emitted from the light source to the recording surface of the information recording medium, and reflects the laser light reflected by the recording surface. An optical system that leads to a predetermined light receiving position and a light receiving element arranged at the light receiving position are provided.

  The CD uses a light source having a substrate thickness of 1.2 mm, which is a distance between the incident surface of the light beam and the recording surface, an oscillation wavelength of 780 nm, and an objective lens having a numerical aperture of 0.4. The DVD is supposed to use a light source having a substrate thickness of 0.6 mm, an oscillation wavelength of 660 nm, and an objective lens having a numerical aperture of 0.6.

  Further, the amount of content information tends to increase year by year, and a further increase in the recording capacity of the optical disc is expected. Therefore, standards for Blu-ray Disc (hereinafter abbreviated as “BD”) and HD-DVD (High Definition DVD, abbreviated as “HD”) have been proposed. The BD uses a light source having a substrate thickness of 0.1 mm, an oscillation wavelength of 405 nm, and an objective lens having a numerical aperture of 0.85. On the other hand, HD uses a light source having a substrate thickness of 0.6 mm, an oscillation wavelength of 405 nm, and an objective lens having a numerical aperture of 0.65.

  By the way, downsizing and cost reduction of information processing apparatuses such as personal computers (hereinafter simply referred to as “personal computers”) are rapidly progressing, and as a result, a plurality of types of optical disks are installed as optical disk apparatuses mounted on the information processing apparatuses. There is a need for an optical disk device that can access the disk. In order to realize this, an optical pickup device that can handle a plurality of types of optical disks is required. In this case, since it is desirable for the optical pickup device to share most of the optical system including the objective lens, the optical pickup device is provided with a plurality of light sources corresponding to the optical disc and emits light with a necessary numerical aperture to the recording surface with one objective lens. Various converging optical pickup devices have been proposed (see, for example, Patent Document 1 and Patent Document 2). A so-called diffractive lens is disclosed in, for example, Patent Document 3.

  However, in the apparatus disclosed in Patent Document 1, if the wavelength of the light beam emitted from the light source fluctuates due to a temperature change or the like, aberration may occur and recording and reproduction may not be performed normally. It was. Further, in the apparatus disclosed in Patent Document 2, since the chromatic aberration correcting unit needs to be interlocked with the objective lens, the design is restricted, miniaturization is inhibited, and the load on the actuator that drives the objective lens is large. As a result, the power consumption increases.

JP 2003-207714 A JP 2003-255114 A JP 2001-195769 A

  The present invention has been made under such circumstances, and a first object of the present invention is to provide an optical pickup device capable of accurately and stably acquiring desired signals from a plurality of types of optical disks without causing an increase in size. Is to provide.

  A second object of the present invention is to provide an optical disc apparatus capable of accurately and stably accessing a plurality of types of optical discs without causing an increase in size.

  A third object of the present invention is to provide an information processing apparatus that can correctly acquire information from a plurality of types of optical disks without causing an increase in size.

From the first viewpoint, the present invention is used when at least one of information recording, reproduction, and erasing is performed on a plurality of types of optical disks, and the first wavelength that emits light of the first wavelength is used. A plurality of light sources, and a plurality of light sources including a second light source that emits light having a second wavelength different from the first wavelength; optimized for a first optical disc corresponding to the light having the first wavelength A light beam from the first light source between the objective lens for condensing the light emitted from each light source on the recording surface of the corresponding optical disc, and the first and second light sources and the objective lens. And a phase shifter surface arranged on a common optical path of the light flux from the second light source, divided into a plurality of annular zones centered on the optical axis, and provided with a step at the boundary between adjacent annular zones And an optical system including a phase shift element. In the up-apparatus, the first aperture diameter of the objective lens corresponding to the first optical disc is larger than the second aperture diameter of the objective lens corresponding to the second optical disc. A step is formed on the inner side of the diameter corresponding to the second opening diameter with the optical axis as the center so that the thickness in the optical axis direction of each annular zone decreases as the distance from the optical axis increases. the size is the size of the optical path difference of even multiples of the first wavelength is generated, the light flux from the second light source to be incident on the phase shift element is divergent light, the object distance of the diverging light In the optical pickup device, the wavefront aberration on the recording surface of the second optical disk is smaller than the object point distance at which the wavefront aberration is minimized when the phase shift element is not provided.

From the second point of view, the present invention is used when at least one of recording, reproducing, and erasing information on a plurality of types of optical disks, and emits light of a first wavelength. A plurality of light sources, and a plurality of light sources including a second light source that emits light having a second wavelength different from the first wavelength; optimized for a first optical disc corresponding to the light having the first wavelength A light beam from the first light source between the objective lens for condensing the light emitted from each light source on the recording surface of the corresponding optical disc, and the first and second light sources and the objective lens. And a phase shifter surface arranged on a common optical path of the light flux from the second light source, divided into a plurality of annular zones centered on the optical axis, and provided with a step at the boundary between adjacent annular zones And an optical system including a phase shift element. In the up-apparatus, the first aperture diameter of the objective lens corresponding to the first optical disc is larger than the second aperture diameter of the objective lens corresponding to the second optical disc. A step is formed on the inner side of the diameter corresponding to the second opening diameter with the optical axis as the center so that the thickness in the optical axis direction of each annular zone decreases as the distance from the optical axis increases. The magnitude is such that an optical path difference that is an even multiple of the first wavelength is generated, the luminous flux from the second light source incident on the phase shift element is divergent light, and the objective lens is orthogonal to the optical axis. The polarity of the coma aberration applied by the objective lens when it is shifted in the direction of the rotation and the polarity of the coma aberration applied when it is assumed that the objective lens is optimized for the second optical disc And each other So that the opposite polarity, it is an optical pickup device according to claim in which the object distance of the diverging light is set.

In the above SL each optical pickup device, before Symbol phase shift element may be a be an element the phase shifter surface is formed on one surface of the parallel plate.

In the above SL each optical pickup device is disposed in front Symbol common optical path, the divergence angle of the divergence angle and light beam emitted from the second light source of the light beam emitted from the first light source, respectively optimum divergence A conversion optical element for converting into a corner may be further provided, and the phase shift element may be integrated with the conversion optical element. In this specification, “integration” includes not only bonding two elements with an adhesive or the like but also providing a single substrate with the function of each element.

In the above SL each optical pickup device is disposed in a position where the front Stories optical paths of the light beam emitted from the second light source of the light flux emitted from the first light source intersect with the common optical path of each optical path The phase shift element may be integrated with the optical path synthesis element.

According to a third aspect of the present invention , an optical disc apparatus capable of at least one of recording, reproducing and erasing information on a plurality of types of optical discs includes the optical pickup device of the present invention. It is an optical disk device.

According to this, since the optical pickup device of the present invention capable of accurately and stably acquiring desired signals from a plurality of types of optical discs without causing an increase in size is provided, without increasing the size, Access to a plurality of types of optical disks can be performed accurately and stably.

According to a fourth aspect of the present invention , an information processing apparatus capable of accessing a plurality of types of optical disks includes the optical disk apparatus of the present invention .

According to this, since the optical drive device of the present invention is provided, it is possible to correctly acquire information from a plurality of types of optical discs without causing an increase in size.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of an optical pickup device 23 according to an embodiment of the present invention.

  1 includes a light source 51a, a collimating lens 52, a beam splitter 54a, a polarizing beam splitter 54b, a prism 53, a phase shifter 103, a quarter wavelength plate 55, an aperture limiting element 105, an objective lens 60, A divergence angle conversion lens 107, a hologram unit 110, a detection lens 58, a light receiver 59a, a drive system (not shown), and the like are provided.

  The optical pickup device 23 is compatible with optical discs conforming to a plurality of types of standards. In the present embodiment, as an example, an optical disc conforming to the Blu-ray Disc standard (hereinafter abbreviated as “BD”) and a conventional one. It is possible to support an optical disc (hereinafter abbreviated as “DVD”) conforming to the DVD standard.

  The distance from the incident surface of the light beam to the recording surface in the optical disc, the so-called substrate thickness, is 0.1 mm for BD and 0.6 mm for DVD. The appropriate numerical aperture of the objective lens is 0.85 for BD and 0.6 for DVD. In the present embodiment, in particular, when distinguishing between BD and DVD, the optical disk 15a is BD and the optical disk 15b is DVD.

  The light source 51a includes a semiconductor laser that emits laser light having a central wavelength of 405 nm. Note that the maximum intensity emission direction of the light beam emitted from the light source 51a is the + Z direction. As an example, it is assumed that a light beam of linearly polarized light (here, P-polarized light) is emitted from the light source 51a.

  The hologram unit 110 includes a light source 51b, a light receiver 59b, a hologram element 109, and the like. The light source 51b has a semiconductor laser that emits laser light having a center wavelength of 660 nm. Note that the maximum intensity emission direction of the light beam emitted from the light source 51b is defined as the -Y direction. The light source 51b emits the same linearly-polarized light beam (here, P-polarized light) as the light source 51a. The light receiver 59b is disposed in the vicinity of the light source 51b, and receives the return light beam emitted from the light source 51b and reflected by the optical disc 15 (more precisely, the optical disc 15b). The light receiver 59b includes a plurality of light receiving elements (or light receiving regions) for generating a signal (photoelectric conversion signal) including an RF signal, a wobble signal, a servo signal, and the like. The hologram element 109 is disposed on the −Y side of the light source 51b and deflects the returning light beam toward the light receiving surface of the light receiver 59b.

  The collimating lens 52 is disposed on the + Z side of the light source 51a, and the light beam emitted from the light source 51a is made into substantially parallel light.

  The divergence angle conversion lens 107 is disposed on the −Y side of the hologram unit 110, and converts the divergence angle of the light beam emitted from the light source 51b and transmitted through the hologram element 109 into an appropriate divergence angle set in advance.

  The beam splitter 54 a is disposed on the + Z side of the collimating lens 52 and on the −Y side of the divergence angle conversion lens 107. This beam splitter 54a has wavelength selectivity, and has a high transmittance for a light beam having a wavelength of 405 nm, and a high reflectance for a light beam having a wavelength of 660 nm. Accordingly, the beam splitter 54a transmits most of the light beam from the collimating lens 52 as it is, and branches the light beam from the divergence angle conversion lens 107 in the + Z direction.

  The polarizing beam splitter 54b is disposed on the + Z side of the beam splitter 54a. The polarization beam splitter 54b has a different reflectance depending on the polarization state of the incident light beam. Here, the polarization beam splitter 54b has a low reflectance for P-polarized light and a high reflectance for S-polarized light. Accordingly, the polarization beam splitter 54b transmits most of the light beam from the beam splitter 54a as it is.

  The prism 53 is disposed on the + Z side of the polarization beam splitter 54b and bends the optical path of the light beam from the polarization beam splitter 54b in the -Y direction. Note that a reflecting mirror may be used instead of the prism 53.

  The phase shifter 103 is disposed on the −Y side of the prism 53, and changes the phase of the wavefront of the incident light beam discontinuously, thereby correcting the aberration caused by the difference in the wavelength of the light beam and the difference in the substrate thickness. The structure and operation of the phase shifter 103 will be described later.

  The quarter wavelength plate 55 is disposed on the −Y side of the phase shifter 103, and imparts an optical phase difference of a quarter wavelength to the incident light beam.

  The aperture limiting element 105 is disposed on the −Y side of the quarter-wave plate 55 and defines the beam diameter of the light beam incident on the objective lens 60 according to an appropriate numerical aperture on the optical disc 15. Here, the aperture limiting element 105 has wavelength selectivity, and for a light beam having a wavelength of 405 nm, a beam diameter is defined so that a light beam corresponding to a numerical aperture of 0.85 is incident on the objective lens 60, For a light beam having a wavelength of 660 nm, the beam diameter is defined so that a light beam corresponding to a numerical aperture of 0.6 is incident on the objective lens 60. Further, the aperture limiting element 105 is interlocked with the objective lens 60. Specifically, the aperture limiting element 105 is fixed to the lens holder 110 that holds the objective lens 60. Thereby, a good light spot can be formed even if the objective lens 60 is shifted in the tracking direction.

  The objective lens 60 is disposed on the −Y side of the aperture limiting element 105 and condenses the light beam from the aperture limiting element 105 on the recording surface of the optical disc 15. The objective lens 60 has a numerical aperture of 0.85 and is optimized for BD by design as an example. That is, the design wavelength of the objective lens 60 is 405 nm, and as an example, as shown in FIG. 2, the wavefront aberration is designed to be 0.01 λrms or less when the wavelength of the incident light beam is 405 nm. In the present embodiment, the objective lens 60 has, as an example, as shown in FIGS. 3 to 4B, one surface in the optical axis direction and the other surface have different aspheric shapes. . As for the eccentricity tolerance, a value capable of mass production is secured.

  The detection lens 58 is disposed on the + Y side of the polarization beam splitter 54b and condenses the return light beam branched in the + Y direction by the polarization beam splitter 54a on the light receiving surface of the light receiver 59a. The light receiver 59a includes a plurality of light receiving elements (or light receiving regions) for generating a signal (photoelectric conversion signal) including an RF signal, a wobble signal, a servo signal, and the like.

  The drive system (not shown) has a focusing actuator for minutely driving the objective lens 60 in the focus direction, which is the optical axis direction of the objective lens 60, and a tracking actuator for minutely driving the objective lens 60 in the tracking direction. is doing.

  Here, the output signals of the light source 51a and the light receiver 59a are selected when the optical disk 15 is a BD, and the output signals of the light source 51b and the light receiver 59b are selected when the optical disk 15 is a DVD.

  Here, the structure of the phase shifter 103 will be described.

  In the present embodiment, as an example, the phase shifter 103 is made of resin as a glass material. The refractive index of a light beam having a wavelength of 405 nm is 1.563, and the refractive index of a light beam having a wavelength of 660 nm is 1.536. The refractive index of a light beam having a wavelength of 780 nm is 1.531.

  As shown in FIG. 5 and FIG. 6 as an example, the phase shifter 103 is divided into a plurality of annular zones centered on the optical axis, and a phase shifter surface having a step between the adjacent annular zones, It is formed on one surface of the parallel plate. Here, the phase shifter surface is divided into 11 ring-shaped regions (r1 to r11), and the thickness of the ring-shaped region decreases as the distance from the optical axis increases to the position of the diameter d2. Further, the step at the boundary with the adjacent annular zone is set so that an optical path difference 2N (N is an integer) times the design wavelength (here, 405 nm) of the objective lens 60 is generated in the phase shifter 103. In the present embodiment, as an example, the size of one step is 1.44 μm. As a result, a double optical path difference is generated in the annular regions r5 and r7 with respect to the annular region r6, a four times optical path difference is generated in the annular regions r4 and r8, and six times in the annular regions r3 and r9. An optical path difference of 8 times occurs in the annular regions r2 and r10, and an optical path difference of 10 times occurs in the annular regions r1 and r11. The distance from the optical axis of each step in the Z-axis direction is 0.37 mm, 0.57 mm, 0.73 mm, 0.93 mm, 1.19 mm, 1.81 mm, 1.87 mm, 1.90 mm, 1.97 mm, respectively. , And 2.00 mm. Here, d1 is a diameter corresponding to a numerical aperture of 0.85, and d2 is a diameter corresponding to a numerical aperture of 0.6.

  The size of the step on the phase shifter surface and the distance from the optical axis of each step are not limited to the present embodiment, but the shape and design wavelength of the objective lens 60, the material constituting the phase shifter 103, It depends on the appropriate numerical aperture.

  Next, the operation of the phase shifter 103 will be described.

  When the optical disk 15 is a BD, the light beam from the light source 51a is incident on the phase shifter 103 in a substantially parallel light state as indicated by a symbol La in FIG. When the wavelength variation of the light beam is small, the light beam incident on the phase shifter 103 is insensitive to the step on the phase shifter surface, and is transmitted through the phase shifter 103 as it is without any action.

  On the other hand, when the optical disk 15 is a DVD, the light beam from the light source 51b is incident on the phase shifter 103 in a divergent light state as indicated by a symbol Lb in FIG. In the present embodiment, the object point distance of divergent light is 34.5 mm. Note that the object point distance when the difference in wavelength, the difference in numerical aperture, and the difference in substrate thickness are corrected only by the finite magnification conversion of the objective lens 60 is 38 mm. A light beam incident at an object point distance of 34.5 mm has an aberration that the phase is delayed as the distance from the optical axis is increased, as shown in FIG. 8 as an example before correction. As shown in FIG. 8 after correction, the phase of the wavefront changes discontinuously at the stepped portion of the phase shifter surface, the difference in wavelength, the appropriate numerical aperture, and the substrate from the BD Aberrations caused by differences in thickness are corrected. The horizontal axis in FIG. 8 indicates the distance from the optical axis. As in this case, when the luminous flux from the light source 51b is divergent light and the object point distance is smaller than the object point distance when the object lens 60 is corrected only by the finite magnification conversion, the step between d2 and d1. Is not required.

  An example of a conventional phase shifter is shown in FIGS. 9 (A) and 9 (B). The phase shifter S1 shown in FIG. 9A has 17 steps, and the light beam Lb is incident in a substantially parallel light state. The phase shifter S2 shown in FIG. 9B has six steps, and the light beam Lb is incident in a divergent light state with an object distance of 54 mm. In each of the phase shifters S1 and S2, in the region where the light beam Lb is incident, unlike the phase shifter 103 in the present embodiment, the thickness of the region near the optical axis is thinner than the thickness of the outer region. The phase shifters S1 and S2 are arranged so as to be interlocked with the objective lens 60 together with the aperture limiting element 105.

  In general, it is known that the temperature in the vicinity of the light source changes in the range of 25 ° C. to 80 ° C., thereby changing the center wavelength of the light beam emitted from the light source by about 3 nm. In consideration of other factors, the center wavelength of the light beam emitted from the light source is expected to vary by about ± 5 nm.

  An example of the state of the wavefront when a light beam having a wavelength of 412 nm is incident on the phase shifter S1 is shown in FIG. According to this, it can be seen that a large aberration occurs. Further, the influence of the wavelength change of the light beam emitted from the light source 51a on the wavefront aberration is shown in FIG. 11 for each phase shifter. For example, if the allowable value of the degradation amount of the wavefront aberration is 0.02λrms, the conventional phase shifters S1 and S2 can only allow the wavelength change amounts of about 1 nm and about 3 nm, respectively. On the other hand, in the phase shifter 103 in the present embodiment, a wavelength change amount of about 7 nm can be allowed. That is, 398 nm to 412 nm are acceptable.

  This is because in the conventional phase shifters S1 and S2, the chromatic aberration generation direction of the phase shifter caused by the wavelength change and the chromatic aberration generation direction of the objective lens are the same direction, for example, when the wavelength shifts to the longer wavelength side. This is because the chromatic aberration of the phase shifter and the chromatic aberration of the objective lens both increase in phase as they move away from the optical axis, and the respective chromatic aberrations are added.

  On the other hand, in the phase shifter 103, the chromatic aberration generation direction of the phase shifter caused by the wavelength change and the chromatic aberration generation direction of the objective lens are opposite to each other, and a step is also formed between d2 and d1. Thus, for example, when the wavelength shifts to the longer wavelength side, the phase shifter chromatic aberrations become slower as they move away from the optical axis, and the objective lens chromatic aberrations move forward as they move away from the optical axis. Negate each other. Therefore, even when the wavelength of the light beam emitted from the light source 51a changes from the design wavelength due to variations between products in the light source, temperature changes in the vicinity of the light source, and output changes, a good wavefront can be maintained. As a result, it is possible to provide a highly accurate optical pickup device that is resistant to wavelength fluctuations.

  FIG. 12 also shows the amount of coma generated due to the axis deviation for each phase shifter. In the conventional phase shifters S1 and S2, the deterioration of the coma due to the axis deviation is large. Assuming that the coma aberration deterioration tolerance is 0.02λrms or less, the respective axis deviation tolerances are as small as about 8 μm and about 23 μm, and the tolerance of the phase shifter assembly position is severe. On the other hand, in the phase shifter 103, when the amount of axial deviation is 0.1 mm or less, coma aberration hardly occurs. Therefore, not only the tolerance of the assembly position is increased, but it is not necessary to interlock with the objective lens 60, and the burden on the tracking actuator can be reduced.

  In the phase shifter 103 according to the present embodiment, the reason why the deterioration amount of coma aberration due to the axis deviation is smaller than that of the conventional phase shifter will be described with reference to FIGS. FIG. 13 shows a case where there is no phase shifter 103 and the light beam Lb is incident on the objective lens 60 in a divergent light state. FIG. 14 shows a case where an objective lens 60 ′ optimized for DVD is used in place of the objective lens 60, and the light beam Lb is incident on the objective lens 60 ′ in a parallel light state. In FIG. 13, the wavefront shape when the axis deviation is 0 mm is shown in FIG. 15A, the wavefront shape when 0.1 mm is shown in FIG. 15B, and the wavefront shape when 0.2 mm is shown. It is shown in FIG. Further, in FIG. 14, the wavefront shape when the axis deviation is 0 mm is shown in FIG. 16A, and the wavefront shape when 0.2 mm is shown in FIG. 16B. That is, when the axis deviation is 0 mm, spherical aberration is shown, and when the axis deviation is other than 0 mm, spherical aberration + coma aberration is shown.

  Comparing the wavefront shapes when the axial deviation is 0 mm, the wavefront aberration in FIG. 15A and the wavefront aberration in FIG. 16A have opposite polarities. As a result, the spherical aberration due to the objective lens 60 and the spherical aberration due to the phase shifter 103 cancel each other, and thereby the spherical aberration caused by the difference in wavelength, substrate thickness, and numerical aperture is corrected. .

  Comparing the wavefront shapes when the axial deviation is 0.2 mm, the coma aberration in FIG. 15C and the coma aberration in FIG. 16B have opposite polarities. Thereby, coma aberration of the entire optical system can be canceled out, and even in an optical system with a high finite magnification, the coma aberration caused by the axis deviation is corrected without interlocking the phase shifter 103 with the objective lens 60. be able to. As a result, it is possible to provide a highly accurate and stable optical pickup device having a large assembly tolerance.

  As described above, according to the optical pickup device 23 according to the present embodiment, a step is formed from the center of the optical axis to d2 such that the thickness in the optical axis direction of the phase shifter surface decreases toward the periphery, Since a step is also formed between d2 and d1, aberrations caused by a difference in wavelength, a difference in substrate thickness, and a difference in numerical aperture can be corrected without causing a decrease in light utilization efficiency in DVD. . Further, even when the wavelength of the light beam from the light source 51a is changed from the design wavelength, the chromatic aberration generated on the phase shifter surface and the chromatic aberration generated on the objective lens can be canceled each other. That is, it is resistant to wavelength fluctuations, and desired signals can be acquired from a plurality of types of optical disks with high accuracy and stability.

  In addition, since the phase shifter 103 has a function of correcting the chromatic aberration of the objective lens 60, it is not necessary to separately provide an element for correcting chromatic aberration, and the number of parts can be reduced, the cost can be reduced, and the size can be reduced. Can do.

  Further, since the light beam from the light source 51b incident on the phase shifter 103 is divergent light, the phase difference imparted by the phase shifter 103 can be reduced. Thereby, the number of steps can be reduced.

  Further, the phase shifter 103 can correct the coma aberration due to the axial deviation without interlocking with the objective lens 60, and therefore, it is possible to suppress an increase in the load of the tracking actuator. Thereby, the freedom degree of design of an optical pick-up apparatus is not restrict | limited, and size reduction can be accelerated | stimulated. In addition, an increase in power consumption can be suppressed.

  Further, since the object point distance of the diverging light is set so that the coma aberration in the phase shifter 103 and the coma aberration in the objective lens 60 are opposite to each other, the objective lens 60 and the phase shifter 103 are set. Can be increased.

  In addition, since the phase shifter surface is formed on a parallel plate, the cost can be reduced.

  In addition, since an inexpensive objective lens can be used, the cost can be reduced.

  Furthermore, regardless of whether the optical disk to be accessed is a BD or a DVD, a good light spot is formed on the recording surface with a single objective lens, so that the apparatus can be reduced in size and cost.

  As an example, as shown in FIG. 17, the optical disc device 20 including the optical pickup device 23 according to this embodiment has a signal with a high S / N ratio regardless of whether the optical disc 15 is a BD or a DVD. Since it is output from the device 23, it is possible to access both BD and DVD with high accuracy. Therefore, it is possible to access a plurality of types of optical disks with high accuracy. Further, the optical pickup device 23 can be reduced in size and cost by reducing the size and cost thereof.

  In addition, since the information processing apparatus including the optical disc apparatus 20 can accurately access both the BD and the DVD, it is possible to correctly acquire information from a plurality of types of optical discs. Further, the downsizing and cost reduction of the optical pickup device 23 enables the downsizing and cost reduction of the information processing device.

  In the above embodiment, the phase shifter 103 and the polarization beam splitter 54b may be integrated as shown in FIG. Specifically, the surface of the phase shifter 103 where no step is formed may be bonded to the polarization beam splitter 54b. Further, a phase shifter surface equivalent to the phase shifter 103 may be formed on the surface on the + Z side of the polarization beam splitter 54b. That is, the phase shifter 103 and the polarization beam splitter 54b may be provided on the same substrate. The component integrated with the phase shifter 103 is not limited to the polarization beam splitter 54b. For example, as shown in FIG. 19, the collimator lens 52 is disposed between the beam splitter 54a and the polarization beam splitter 54b. The collimating lens 52 may be integrated. In short, the phase shifter 103 can be integrated with any one of the optical elements disposed in the common optical path. Thereby, the number of parts can be reduced, and cost reduction and size reduction can be further promoted.

  Moreover, although the said embodiment demonstrated the case where the aperture restriction element 105 interlock | cooperates with the objective lens 60, it is not limited to this.

  In the above-described embodiment, the case where the optical disc 15 is designed to be recorded and reproduced with high accuracy when the optical disc 15 is a BD has been described. It may be designed to be able to. In this case, the phase shifter 103 is formed with a phase shifter surface so as to correct aberrations caused by differences in wavelength, numerical aperture, and substrate thickness when the optical disk 15 is a BD. The Rukoto.

  Moreover, although the said embodiment demonstrated the case where there were two light sources, this invention is not limited to this. For example, as shown in FIG. 20, three light sources may be provided. In FIG. 20, the phase shifter 113, the beam splitter 54 c, and the divergence angle conversion are added to the optical pickup device 23 in the above embodiment so as to be compatible with an optical disc (hereinafter abbreviated as “CD”) compliant with the CD standard. A lens 117, a phase shifter 113, and a hologram unit 120 are added. The substrate thickness of the CD is 1.2 mm. In this case as well, regardless of whether the optical disk 15 is a BD, a DVD, or a CD, a desired signal can be obtained with high accuracy and stability.

  The hologram unit 120 includes a light source 51c, a light receiver 59c, a hologram element 119, and the like. The light source 51c has a semiconductor laser that is selected when the optical disk 15 is a CD and emits a laser beam having a center wavelength of 780 nm. Note that the maximum intensity emission direction of the light beam emitted from the light source 51c is defined as the -Y direction. In addition, as an example, it is assumed that the light source 51c emits the same linearly polarized light beam (here, P-polarized light) as the light source 51a. The light receiver 59c is disposed in the vicinity of the light source 51c, and receives the return light beam emitted from the light source 51c and reflected by the optical disc 15. The light receiver 59c includes a plurality of light receiving elements (or light receiving regions) for generating a signal (photoelectric conversion signal) including an RF signal, a wobble signal, a servo signal, and the like. The hologram element 119 is disposed on the −Y side of the light source 51c, and deflects the return light beam toward the light receiving surface of the light receiver 59c.

  The divergence angle conversion lens 117 is disposed on the −Y side of the hologram unit 120, and converts the divergence angle of the light beam emitted from the light source 51c.

  The beam splitter 54c is disposed on the −Y side of the divergence angle conversion lens 117 on the optical path between the beam splitter 54a and the polarization beam splitter 54b. The beam splitter 54c has wavelength selectivity, and is set so that the transmittance is high for a light beam having a wavelength of 405 nm and 660 nm, and the reflectance is high for a light beam having a wavelength of 780 nm. Therefore, the beam splitter 54c transmits most of the light beam from the beam splitter 54a as it is, and branches the light beam from the divergence angle conversion lens 117 in the + Z direction.

  The aperture limiting element 115 has wavelength selectivity, and for a light beam having a wavelength of 405 nm, the beam diameter is defined so that a light beam corresponding to a numerical aperture of 0.85 is incident on the objective lens 60. For a 660 nm light beam, the beam diameter is defined so that a light beam corresponding to a numerical aperture of 0.65 is incident on the objective lens 60, and for a light beam having a wavelength of 780 nm, a numerical aperture of 0.40 is supported. The beam diameter is defined so that the luminous flux to be incident on the objective lens 60.

  The phase shifter 113 is disposed between the phase shifter 103 and the quarter wavelength plate 55. As shown in FIG. 21 as an example, the phase shifter 113 is divided into three annular regions (R1 to R3) centered on the optical axis, and each annular region is separated from the optical axis. The thickness is set to be thin. Further, the thickness step in each annular zone is set such that an optical path difference of 5N (N is an integer) times the design wavelength (here, 405 nm) of the objective lens 60 is generated. Accordingly, the light flux having a wavelength of 405 nm and the light flux having a wavelength of 660 nm do not feel the step of the phase shifter 113. As an example, the phase shifter 113 uses resin as a glass material, the refractive index n of a light beam having a wavelength of 405 nm is 1.563, the refractive index n of a light beam having a wavelength of 660 nm is 1.536, and the wavelength is The refractive index n of the light beam of 780 nm is 1.531. Further, the height of one step is 3.6 μm. As a result, a five-fold optical path difference is generated in the annular zone R2 and a ten-fold optical path difference is generated in the annular zone R1 with respect to the annular zone R3. The position of each step in the Z-axis direction is 1.11 mm, 1.22 mm, and 1.28 mm, respectively, with respect to the optical axis. D3 is a diameter corresponding to a numerical aperture of 0.40.

  The height of the step in the phase shifter 113 and the radial position of the step are not limited to the present embodiment. The shape of the objective lens 60, the design wavelength of the objective lens 60, the material constituting the phase shifter 113, It depends on the numerical aperture.

  As an example, as shown in FIG. 22, the light beam La from the light source 51a is incident on the phase shifter 113 and the objective lens 60 in a parallel light state, and the light beam Lb from the light source 51b is divergent light having an object point distance of 34.5 mm. The light beam Lc from the light source 51c enters the phase shifter 113 in a divergent light state with an object point distance of 40.0 mm.

  In FIG. 22, the aperture limiting element 115, the quarter wavelength plate 55, and the phase shifter 113 are linked to the objective lens 60, respectively, but may be fixed on the optical path.

  The light beam Lc from the light source 51c incident on the phase shifter 113 at an object point distance of 34.5 mm has an aberration that the phase is delayed as the distance from the optical axis is increased as shown in FIG. However, the phase shifter 113 corrects the aberration by changing the phase of the wavefront discontinuously at the step as shown in FIG. 23 as an example after correction. Note that the horizontal axis in FIG. 23 indicates the distance from the optical axis.

  In this case, as shown in FIG. 24 as an example, the aperture limiting element 115, the quarter wavelength plate 55, the phase shifter 113, and the phase shifter 103 may be driven in conjunction with the objective lens 60, respectively.

  In this case, all the light beams from the respective light sources may be in a parallel light state.

  Further, in this case, as shown in FIG. 25 as an example, the phase shifter surface of the phase shifter 103 is formed on one surface of the parallel plate and the phase shifter surface of the phase shifter 113 is formed on the other surface. good. Thereby, the number of parts can be reduced, and further downsizing and cost reduction can be further promoted.

  In this case, as shown in FIG. 26 as an example, the phase shift surface obtained by adding the step of the phase shift surface of the phase shifter 103 and the step of the phase shift surface of the phase shifter 113 is one of the parallel plates. It may be formed on the surface. Thereby, the number of parts can be reduced, and further downsizing and cost reduction can be realized.

  Further, a function equivalent to the quarter-wave plate 55 or a function equivalent to the aperture limiting element 115 may be added to the other surface of the parallel plate shown in FIG. Thereby, the number of parts can be reduced, and further downsizing and cost reduction can be realized.

In this case, as an example, a hologram element 104 may be used in place of the phase shifter 103 as shown in FIGS. The hologram element 104 has a diffractive structure represented by an optical path difference function Φb (mm) defined by the following equation (1). In the formula (1), h is a height (mm) in a direction perpendicular to the optical axis. Also, b ₂ = 1.4384 × 10 ⁻² , b ₄ = 5.1678 × 10 ⁻⁴ , b ₆ = −3.2876 × 10 ⁻⁴ , b ₈ = 1.7535 × 10 ⁻⁴ , b ₁₀ = −5.2368 × 10 ⁻⁵ , b ₁₂ = 6.3337 × 10 ⁻⁶ .

Φb = b ₂ h ² + b ₄ h ⁴ + b ₆ h ⁶ + b ₈ h ⁸ + b ₁₀ h ¹⁰ + b ₁₂ h ¹² + (1)

  As an example, the hologram element 104 uses resin as a glass material, the refractive index of a light beam having a wavelength of 405 nm is 1.563, the refractive index of a light beam having a wavelength of 660 nm is 1.536, and the wavelength is 780 nm. The refractive index of the light beam is 1.531. Further, the groove is formed in a blazed shape, and its depth is 5.8 μm. This depth is such that a light beam having a wavelength of 405 nm and a light beam having a wavelength of 780 nm are transmitted as they are, and a light beam having a wavelength of 660 nm is such that the diffraction efficiency of the first-order diffracted light is 60%. The hologram element 104 corrects aberrations caused by the difference in wavelength and the difference in substrate thickness in the case of DVD. Even in this case, an effect equivalent to that of the above embodiment can be obtained.

  Further, the hologram element 104 and the phase shifter 113 may be integrally formed. For example, an element in which a diffraction element equivalent to the hologram element 104 is formed on one surface of a parallel plate and a phase shifter surface equivalent to the phase shifter 113 is formed on the other surface may be used. Thereby, the number of parts can be reduced, and further downsizing and cost reduction can be achieved.

  The light emitted from the hologram element 104 is divergent light and is incident on the objective lens 60 as divergent light. Thereby, even if the objective lens 60 and the hologram element 104 are misaligned with each other, coma aberration generated when divergent light passes through the objective lens 60 and the wavefront to which an optical phase difference is given by the hologram element 104. Since the coma generated when the light passes through the objective lens 60 has the opposite polarity, they can cancel each other, and the increase of the coma aberration of the entire optical system is suppressed. Therefore, the assembly tolerance of the hologram element 104 can be increased.

  Further, instead of the phase shifter 113, a hologram element that diffracts the light beam from the light source 51c and corrects the aberration generated in the case of CD may be used.

  As described above, the pickup device of the present invention is suitable for accurately obtaining desired signals from a plurality of types of optical disks without causing an increase in size. Moreover, the optical disk apparatus of the present invention is suitable for accurately accessing a plurality of types of optical disks without causing an increase in size. The information processing apparatus according to the present invention is suitable for correctly acquiring information from a plurality of types of optical discs without increasing the size.

It is a figure for demonstrating the optical pick-up apparatus which concerns on one Embodiment of this invention. It is a figure for demonstrating the influence of the wavelength change which acts on a wavefront aberration. FIG. 3 is a first diagram for explaining the objective lens in FIG. 1. 4A and 4B are views (No. 2) for explaining the objective lens in FIG. 1, respectively. FIG. 3 is a diagram (part 1) for describing a shape of a phase shifter in FIG. 1; FIG. 3 is a second diagram for explaining the shape of the phase shifter in FIG. 1; FIG. 3 is a diagram (part 1) for explaining the operation of the phase shifter in FIG. 1; FIG. 3 is a diagram (part 2) for explaining the operation of the phase shifter in FIG. 1; FIG. 9A and FIG. 9B are diagrams for explaining the shape of a conventional phase shifter, respectively. It is a figure for demonstrating the effect | action of the conventional phase shifter of FIG.9 (B). FIG. 3 is a diagram (part 1) for explaining a difference between the phase shifter in FIG. 1 and a conventional phase shifter. FIG. 8 is a diagram (No. 2) for explaining a difference between the phase shifter in FIG. 1 and a conventional phase shifter; FIG. 6 is a diagram (No. 3) for explaining the operation of the phase shifter in FIG. 1; FIG. 6 is a diagram (part 4) for explaining the operation of the phase shifter in FIG. 1; FIGS. 15A to 15C are views (No. 5) for explaining the operation of the phase shifter in FIG. FIGS. 16A and 16B are views (No. 6) for explaining the operation of the phase shifter in FIG. It is a figure for demonstrating the optical disk apparatus based on one Embodiment of this invention. It is a figure for demonstrating the optical pick-up apparatus with which the phase shifter and the polarizing beam splitter were integrated. It is a figure for demonstrating the optical pick-up apparatus with which the phase shifter and the collimating lens were integrated. It is a figure for demonstrating an optical pick-up apparatus provided with three light sources. It is a figure for demonstrating the shape of the phase shifter 113 in FIG. It is FIG. (1) for demonstrating the effect | action of the phase shifter 113 in FIG. It is FIG. (2) for demonstrating the effect | action of the phase shifter 113 in FIG. It is a figure for demonstrating the case where the phase shifter 113 interlock | cooperates with an objective lens. It is FIG. (1) for demonstrating integration of the phase shifter 113 and the phase shifter 103 in FIG. FIG. 21 is a diagram (No. 2) for describing integration of the phase shifter 113 and the phase shifter 103 in FIG. 20; FIG. 21 is a diagram for describing a case where a hologram element is used instead of the phase shifter 103 in FIG. 20. It is a figure for demonstrating the effect | action of the hologram element in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 15 ... Optical disk, 15a ... BD (one of several optical disks), 15b ... DVD (one of several optical disks), 15c ... CD (one of several optical disks), 20 ... Optical disk apparatus, 23 ... Optical pick-up apparatus , 51a ... light source (first light source), 51b ... light source (second light source), 51c ... light source (third light source), 52 ... collimator lens, 54a ... beam splitter (branch optical element), 54b ... polarized beam Splitter (branch optical element), 54c ... Beam splitter (branch optical element), 59a ... Light receiver (photodetector), 60 ... Objective lens, 103 ... Phase shifter (phase shift element), 104 ... Hologram element (diffractive optical element) ), 113... Phase shifter (second phase shift element).

Claims (8)

A first light source that emits light of a first wavelength, which is used when at least one of recording, reproduction, and erasing of information is performed on a plurality of types of optical disks, and is different from the first wavelength A plurality of light sources including a second light source that emits light of a second wavelength; and optimized for the first optical disc corresponding to the light of the first wavelength, and the light emitted from each light source A common light beam from the first light source and a light beam from the second light source between the objective lens for focusing on the recording surface of the corresponding optical disc, and the first and second light sources and the objective lens. An optical system including: a phase shift element disposed on the optical path, divided into a plurality of annular regions centered on the optical axis, and having a phase shifter surface provided with a step at a boundary between adjacent annular regions; In an optical pickup device comprising:
The first aperture diameter of the objective lens corresponding to the first optical disc is larger than the second aperture diameter of the objective lens corresponding to the second optical disc,
On the phase shifter surface, a step is formed on the inner side of the diameter corresponding to the second opening diameter centered on the optical axis so that the thickness in the optical axis direction of each annular zone decreases as the distance from the optical axis increases. Formed and the size of the step is such that an optical path difference that is an even multiple of the first wavelength is generated.
The phase of light flux from the second light source incident on the shift element is divergent light, the object distance of the diverging light, wavefront aberration on the recording surface of the second optical disk in the absence of the phase shift element optical pickup device it is smaller than smallest object distance. The optical pickup device according to claim 1, wherein the phase shift element is fixed on the common optical path. A first light source that emits light of a first wavelength, which is used when at least one of recording, reproduction, and erasing of information is performed on a plurality of types of optical disks, and is different from the first wavelength A plurality of light sources including a second light source that emits light of a second wavelength; and optimized for the first optical disc corresponding to the light of the first wavelength, and the light emitted from each light source A common light beam from the first light source and a light beam from the second light source between the objective lens for focusing on the recording surface of the corresponding optical disc, and the first and second light sources and the objective lens. An optical system including: a phase shift element disposed on the optical path, divided into a plurality of annular regions centered on the optical axis, and having a phase shifter surface provided with a step at a boundary between adjacent annular regions; In an optical pickup device comprising:
The first aperture diameter of the objective lens corresponding to the first optical disc is larger than the second aperture diameter of the objective lens corresponding to the second optical disc,
On the phase shifter surface, a step is formed on the inner side of the diameter corresponding to the second opening diameter centered on the optical axis so that the thickness in the optical axis direction of each annular zone decreases as the distance from the optical axis increases. Formed and the size of the step is such that an optical path difference that is an even multiple of the first wavelength is generated.
The light flux from the second light source incident on the phase shift element is divergent light,
When it is assumed that when the objective lens is shifted in a direction perpendicular to the optical axis, the polarity of the coma aberration applied by the objective lens and the objective lens are optimized for the second optical disc and the polarity of the coma aberration applied to is to have opposite polarities to each other, the optical pickup device you characterized in that the object distance of the diverging light is set. Wherein the phase shift element, an optical pickup apparatus according to any one of claims 1 to 3, characterized in that the one element the phase shifter surface is formed on a surface of the parallel plate. A conversion optical element that is disposed on the common optical path and converts the divergence angle of the light beam emitted from the first light source and the divergence angle of the light beam emitted from the second light source into optimum divergence angles, respectively. Prepared,
Wherein the phase shift element, an optical pickup apparatus according to any one of claims 1 to 4, characterized in that it is integrated with the conversion optical element. An optical path combining element that is disposed at a position where the optical path of the light beam emitted from the first light source intersects with the optical path of the light beam emitted from the second light source, and uses each optical path as the common optical path;
Wherein the phase shift element, an optical pickup apparatus according to any one of claims 1 to 4, characterized in that it is integrated with the light path combining element. In an optical disc apparatus capable of recording, reproducing and erasing information on a plurality of types of optical discs,
An optical disc device comprising the optical pickup device according to any one of claims 1 to 6 . In an information processing apparatus that can access multiple types of optical discs,
An information processing apparatus comprising the optical disc apparatus according to claim 7 .

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