JP2005276245A - Optical pickup apparatus, wave front compensating element, and optical disk apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup apparatus in which spherical aberration caused in a laser beam for next generation DVD, a laser beam for DVD, and a laser beam for CD can be compensated smoothly with simple constitution. <P>SOLUTION: A spherical aberration compensating element is arranged in a common optical path of each laser beam. This spherical aberration compensating element is constituted so that a liquid crystal element in which molecules having double refractive index are arranged in one direction is sandwiched between two resistive film having a light transmission property. Four transparent electrodes (electrode 1 to electrode 4) are arranged in a concentric circle state on one side of the resistive film, also, the other resistive film is grounded. Then, the electrode 1 to electrode 4 are arranged, so that when distance from the electrode 1 to the electrode 4 is assumed as 1, distance from the electrode 1 to the electrode 3 is 1/√2, and distance from the electrode 1 to the electrode 2 is 1/2. Also, distance from the electrode 1 to the electrode 4 is set so as to be coincident almost to an effective diameter (radius) of the laser beam for next generation DVD. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to an optical pickup device, a wavefront correction element, and an optical disk device, and is particularly suitable for use in compatible optical pickup devices and optical disk devices that irradiate a recording medium with several types of laser beams having different wavelengths.

  Currently, various optical discs such as CD (Compact Disc) and DVD (Digital Versatile Disc) have been commercialized and spread. Furthermore, recently, the standardization of the next-generation DVD for recording / reproducing information using a blue-violet laser beam has been advanced. This next-generation DVD records and reproduces information using blue-violet laser light having a wavelength of about 405 nm. A further increase in density can be achieved by shortening the wavelength of the laser beam.

  Thus, with the diversification of discs, development of a so-called compatible optical pickup device capable of recording / reproducing on different types of discs is required. Here, in order to irradiate the disk with laser beams having different wavelengths, a technique of individually arranging semiconductor lasers that emit laser beams of the respective wavelengths may be employed. Alternatively, a plurality of laser elements having different wavelengths can be simultaneously provided in one laser CAN. In the former case, the laser light of each wavelength is guided to the objective lens after optical axis alignment by a dichroic prism or the like. In the latter case, the laser light of each wavelength is guided to the objective lens after being optically aligned by a birefringent element or the like, for example, as shown in Patent Document 1 below.

  Here, when such a compatible optical pickup device is used for, for example, a CD / DVD / next-generation DVD, it is necessary to appropriately perform wavefront correction on the laser light of each wavelength. For example, when the objective lens is designed to support the laser beam for the next generation DVD, if the laser beam for the DVD is converged by the objective lens, the laser beam for the DVD and the laser beam for the next generation DVD are Wavefront aberrations occur in the laser light according to the wavelength shift. Even when the objective lens is designed to support next-generation DVD laser light in this way, wavefront aberration also occurs in the next-generation DVD laser light due to the film formation error of the disc substrate thickness. Further, since the substrate thickness of the CD is larger than the substrate thickness of the other discs, the objective lens is usually often designed as a finite system with respect to the CD laser beam. It is necessary to correct the wavefront state of the light to a wavefront state corresponding to the objective lens and then enter the objective lens.

As described above, when the optical pickup device is a compatible type, it is necessary to appropriately perform wavefront correction on the laser light of each wavelength. On the other hand, Patent Document 2 shown below describes an optical pickup device that performs wavefront correction on a laser beam that does not correspond to the design of the objective lens among two types of laser beams having different wavelengths. . That is, such an optical pickup device includes a polarizing phase correction element that has a refractive index different from that of two types of linearly polarized light and that has been subjected to surface processing so that wavefront correction can be performed only on one of the linearly polarized light. In this element, two kinds of laser beams are made incident on this element so that the polarization planes are different from each other, thereby correcting the wavefront of the laser beam that does not correspond to the design of the objective lens. .
JP 2001-283457 A JP 2003-149443 A

  However, in such a conventional technique, only wavefront correction for the laser beam that does not correspond to the design of the objective lens is considered, and wavefront correction for the laser beam that corresponds to the design of the objective lens, for example, No consideration has been given to the wavefront aberration correction of the next-generation DVD laser light caused by the above-described film substrate thickness film formation error. Further, in the above-described conventional technology, there is a structural limitation such that laser light is incident on the polarization phase correction element with different polarization planes, and it is necessary to perform fine surface processing on the polarization phase correction element. There is also.

Therefore, an object of the present invention is to provide an optical pickup device, a wavefront correction element, and an optical disk device using the same, which can appropriately perform wavefront correction on laser light of each wavelength with a simple configuration.

  In view of the above problems, the present invention has the following features.

  According to a first aspect of the present invention, there is provided an optical pickup device that irradiates a disc with at least a CD laser beam and a next-generation DVD laser beam and / or a DVD laser beam according to the magnitude of a potential applied in the light transmission direction. A wavefront correction element in which the phase state of the light is changed is arranged in a common optical path of each laser beam, and four types of electrodes for applying a potential to the wavefront correction element are defined as an optical axis position through which the laser light penetrates. The distance from the optical axis position is approximately 1: 1 / √2: 1/2.

  According to a second aspect of the present invention, in the optical pickup device according to the first aspect of the invention, the wavefront correction element includes a liquid crystal element that is molecularly oriented in one direction, and the liquid crystal is applied according to the potential applied from the electrode. The refractive index with respect to the transmitted light is changed by changing the potential distribution with respect to the element.

  A third invention is a wavefront correction element used in an optical pickup device that irradiates at least a CD laser beam and a next-generation DVD laser beam and / or a DVD laser beam onto a disk, and is applied in the light transmission direction. An optical axis position through which the laser beam penetrates four types of electrodes for providing a potential to the light transmission layer, the light transmission layer having a light phase state that changes in accordance with the magnitude of the applied potential; The distance from the optical axis position is approximately 1: 1 / √2: 1/2.

  According to a fourth aspect of the present invention, in the wavefront correction element according to the third aspect of the invention, the light transmission layer includes a liquid crystal element that is molecularly oriented in one direction, and the liquid crystal element according to a potential applied from the electrode. The refractive index with respect to the transmitted light is changed by changing the potential distribution with respect to.

  According to a fifth aspect of the present invention, there is provided an optical disc apparatus for performing recording and / or reproduction on a disc using at least a CD laser beam and a next-generation DVD laser beam and / or a DVD laser beam. A wavefront correction element in which the phase state of light changes according to the magnitude of the potential is arranged in a common optical path of each laser beam, and four types of electrodes for applying a potential to the wavefront correction element are provided by the laser beam. Depending on the optical axis position penetrating through, the optical pickup device disposed at a position where the distance from the optical axis position is approximately 1: 1 / √2: 1/2, and the disc type to be recorded and / or reproduced And wavefront control means for controlling the application state of the potential to the electrode.

  According to a sixth invention, in the optical disk device according to the fifth invention, the wavefront correction element includes a liquid crystal element having molecular orientation in one direction, and the liquid crystal element is applied to the liquid crystal element according to a potential applied from the electrode. The refractive index with respect to the transmitted light is changed by changing the potential distribution.

  According to a seventh aspect of the present invention, in the optical disc apparatus according to the fifth or sixth aspect, the wavefront control means is configured such that, when CD laser light is used, an outer peripheral side from the second electrode from the outside with respect to the optical axis. A potential is applied to the electrode so as to scatter light.

The features of the above invention will become more apparent from the following description of embodiments. However, the following embodiment is merely one embodiment of the present invention, and the meaning of the term of the present invention or each constituent element is not limited to that described in the following embodiment. Absent.

According to the Zernike polynomial, when the effective diameter (radius) of the laser beam is 1, the third-order spherical aberration is represented by 6r ⁴ -6r ² +1 (r is a radial distance from the optical axis). This is illustrated in FIG. When this polynomial is differentiated by r, the maximum value of spherical aberration is
r = 1 / √2≈0.7 (1)
It can be seen that it appears at the position.

On the other hand, the effective diameter Φ (diameter) of the laser light is expressed by the following equation from the focal length f of the objective lens and the numerical aperture NA.
Φ = 2 * NA * f (2)

Here, the NA required for the next-generation DVD laser light or the DVD laser light is about 0.65, and the NA required for the CD laser light is about 0.45. Since the focal length f of the laser light differs only by about several percent, the ratio of the effective diameter Φ1 of the CD laser light to the objective lens and the effective diameter Φ2 of the next-generation DVD laser light or DVD laser light is
Φ1 / Φ2 = 0.45 / 0.65 = 0.7 (3)
It becomes.

On the other hand, if the effective diameter of the next-generation DVD laser beam or DVD laser beam is R0 (radius), and the maximum position of spherical aberration in this laser beam is Rmax (radius), The ratio of
Rmax / R0 = 0.7 (4)
Thus, it almost coincides with the ratio of effective diameters expressed by the above equation (3). That is, it can be seen that the effective diameter of the laser beam for CD substantially matches the maximum position of the next-generation DVD laser beam or the DVD laser beam.

  The first invention focuses on the analysis result.

  That is, if the four types of electrodes arranged on the wavefront correction element are first, second, third, and fourth electrodes in order from the inside, the third electrode position is the above ( Since the relationship shown in the formula 1) or formula (4) is satisfied, when the fourth electrode position is adjusted to the effective diameter of the next-generation DVD laser beam or the DVD laser beam, the third electrode position becomes The position at which the spherical aberration becomes a maximum value with respect to the effective diameter. Therefore, among these four types of electrodes, by applying a potential to the first, third, and fourth electrodes as appropriate, a wavefront state that cancels the spherical aberration that occurs in the next-generation DVD laser light or DVD laser light, These laser beams can be introduced.

  At the same time, the third electrode position substantially coincides with the position of the effective diameter of the laser beam for CD (see the above formula (3)), and the second electrode position corresponds to the above (1 ) Or the position represented by the formula (4), that is, the position at which the spherical aberration becomes a maximum with respect to the effective diameter of the laser beam for CD, among these four types of electrodes, the first, second, The wavefront state of the laser beam for CD can be corrected by appropriately adjusting the potential applied to the third electrode.

  Thus, according to the first aspect of the present invention, the wavefront state of the laser beam for CD and the laser beam for next-generation DVD or the DVD laser beam is controlled by controlling the application state of the potential to the first to fourth electrodes. Can be corrected to an appropriate state. In addition, since the third electrode can be used for wavefront correction of the next-generation DVD laser beam or DVD laser beam and for wavefront correction of the CD laser beam, the configuration of the wavefront correction element or electrode is simplified. it can. That is, according to the first invention, the wavefront correction of each laser beam can be smoothly performed by the wavefront correction element having a simple configuration.

  Such operational effects are also exhibited in the third and fifth inventions.

  According to the seventh aspect, the wavefront correcting element can be further provided with an aperture limiting function for the CD laser beam. For example, by applying a potential necessary to scatter the outer periphery of the CD laser light to the fourth electrode, it is possible to realize the aperture restriction for the CD laser light. At this time, it is not necessary to add a new configuration separately to the wavefront correction element itself, and the configuration of the wavefront correction element can be simplified as described above.

The effects of the present invention will become more apparent from the following description of embodiments.

  Embodiments of the present invention will be described below with reference to the drawings. In the present embodiment, the present invention is applied to a CD / DVD / next-generation DVD (substrate thickness 0.6 mm) compatible optical disc apparatus.

  First, FIG. 1 shows a configuration of an optical disc apparatus according to the embodiment. In the figure, the semiconductor laser 101 to the photodetector 123 are arranged in an optical pickup device. Further, the circuit configuration on the optical disc apparatus side shows only the reproduction circuit 200 and the servo circuit 300, and other circuit configurations such as a controller, a memory, an input / output interface, etc. are omitted.

  In the figure, a semiconductor laser (LD) 101 emits a laser beam for CD (wavelength: 780 nm). The collimator lens 102 converts the laser light emitted from the semiconductor laser 101 into parallel light. The aperture limiting element 103 blocks the outer peripheral portion of the parallel light converted by the collimator lens 102 and adjusts the beam diameter of the laser light to an effective diameter required by the objective lens 117. The polarization beam splitter (PBS) 104 substantially totally reflects the light that has passed through the aperture limiting element 103.

  The semiconductor laser (LD) 105 emits DVD laser light (wavelength: 655 nm). The collimator lens 106 converts the laser light emitted from the semiconductor laser 105 into parallel light. A polarization beam splitter (PBS) 107 substantially totally reflects the parallel light converted by the collimator lens 106.

  The semiconductor laser (LD) 108 emits next-generation DVD laser light (wavelength: 407 nm). The collimator lens 109 converts the laser light emitted from the semiconductor laser 108 into parallel light. The polarization beam splitter (PBS) 110 substantially totally reflects the parallel light converted by the collimator lens 109.

  The dichroic prism 111 substantially totally transmits the CD laser light having a wavelength of 780 nm and substantially totally reflects the DVD laser light having a wavelength of 655 nm. The position of the dichroic prism 111 is adjusted so that the optical axes of these two laser beams coincide with each other.

  The dichroic prism 112 substantially totally transmits the laser beam for CD having a wavelength of 780 nm and the laser beam for DVD having a wavelength of 655 nm, and substantially totally reflects the laser beam for next-generation DVD having a wavelength of 407 nm. The position of the dichroic prism 112 is adjusted so that the optical axes of these three laser beams coincide.

  The mirror 113 reflects each laser beam in the direction of the objective lens 117.

  The spherical aberration correction element 114 adjusts the wavefront state of the laser beam for CD, the laser beam for DVD, and the laser beam for next-generation DVD according to the servo signal from the servo circuit 300. The configuration of the spherical aberration correction element 114 will be described later.

  The ¼λ plate 115 converts the laser light from the spherical aberration correction element 114 toward the objective lens 117 from linearly polarized light to circularly polarized light. Further, the laser beam reflected from the disk is converted from circularly polarized light into linearly polarized light orthogonal to the polarization direction at the time of incidence. Thereby, the reflected light of each wavelength reflected from the disk is almost completely transmitted through the polarization beam splitters 104, 107, and 110, respectively.

  The objective lens actuator 116 drives the objective lens 117 in the focus direction, the tracking direction, and the tilt direction according to the servo signal from the servo circuit 300. The configuration of the objective lens actuator 116 is well known in the art and will not be described here.

  The objective lens 117 is designed so that each laser beam for next-generation DVD, DVD, and CD can be properly converged on the corresponding disk. In the present embodiment, the objective lens 117 is an infinite system for the next-generation DVD laser beam and the DVD laser beam, and is a finite system only for the CD laser beam. A design example of the objective lens 117 will be described later.

  The condensing lens 118 converges the reflected light (wavelength: 780 nm) from the disc on the photodetector 119 so that the photodetector 119 can properly derive the reproduction signal and various error signals. The photodetector 119 includes a sensor pattern for deriving a reproduction signal and various error signals, and outputs a signal corresponding to the received reflected light to the reproduction circuit 200 and the servo circuit 300.

  The condensing lens 120 converges the reflected light (wavelength: 655 nm) from the disc to the photodetector 121 so that the photodetector 121 can properly derive the reproduction signal and various error signals. The photodetector 121 includes a sensor pattern for deriving a reproduction signal and various error signals, and outputs a signal corresponding to the received reflected light to the reproduction circuit 200 and the servo circuit 300.

  The condensing lens 122 converges the reflected light (wavelength: 407 nm) from the disc to the photodetector 123 so that the photodetector 123 can properly derive the reproduction signal and various error signals. The photodetector 123 includes a sensor pattern for deriving a reproduction signal and various error signals, and outputs a signal corresponding to the received reflected light to the reproduction circuit 200 and the servo circuit 300.

  The reproduction circuit 200 performs arithmetic processing on the sensor signals received from the photodetectors 119, 121, and 123 to derive a reproduction signal, and demodulates the signal to generate reproduction data. The servo circuit 300 performs arithmetic processing on the sensor signals received from the photodetectors 119, 121, and 123 to derive various error signals such as tracking error signals, and generates various servo signals in accordance therewith to correct spherical aberration. Output to the element 114 and the objective lens actuator 116. In addition, a servo signal is output to the spherical correction element 114 in response to a command from a controller (not shown).

  FIG. 2 shows the configuration of the spherical aberration correction element 114.

  The spherical aberration correction element 114 is configured such that a liquid crystal element in which molecules having a birefringence index are aligned in one direction is sandwiched between two light-transmissive resistance films. Here, four transparent electrodes (electrode 1 to electrode 4) are arranged concentrically on one resistance film, and the other resistance film is grounded.

  When a predetermined potential is applied to each electrode, a potential difference is generated between the resistance films, and a voltage is applied to the liquid crystal element. Here, the distribution state of the voltage applied to the liquid crystal element depends on the application state of the potential to each electrode. When a voltage is applied to the liquid crystal element in this way, the alignment molecules in the liquid crystal element are tilted accordingly, and the refractive index of the liquid crystal element is locally changed according to the distribution state of the applied voltage. When laser light is incident on such a liquid crystal element in a polarization state in which the refractive index changes, the wavefront state of the laser light changes according to the refractive index distribution state. Therefore, the wavefront state of the laser light transmitted through the spherical aberration correction element 114 can be set to a desired state by appropriately adjusting the potential applied to the electrodes 1 to 4.

  FIG. 3 is a diagram illustrating a voltage distribution state and a refractive index distribution state in the liquid crystal element when the potential Vc2 is applied to the electrode 3 while the potential Vc1 is applied to the electrode 1 and the electrode 4. As shown in the figure, the potential in the liquid crystal element monotonously increases from the electrode 1 and the electrode 4 with the electrode 3 as a peak. Further, according to the potential distribution, the refractive index of the liquid crystal element also monotonously increases from the positions of the electrodes 1 and 4 with the position of the electrode 3 as a peak.

  FIG. 4 is a diagram illustrating a voltage distribution state and a refractive index distribution state in the liquid crystal element when the potential Vc2 is applied to the electrode 2 while the potential Vc1 is applied to the electrode 1 and the electrode 3. As shown in the figure, the potential in the liquid crystal element monotonously increases from the electrode 1 and the electrode 3 with the electrode 2 as a peak. Further, according to the potential distribution, the refractive index of the liquid crystal element also monotonously increases from the position of the electrode 1 and the electrode 3 with the position of the electrode 2 as a peak.

  In the above-described electrodes 1 to 4, when the distance from the electrode 1 to the electrode 4 is 1, the distance from the electrode 1 to the electrode 3 is 1 / √2, and the distance from the electrode 1 to the electrode 2 is It arrange | positions so that distance may become 1/2. The distance from the electrode 1 to the electrode 4 substantially matches the effective diameter (radius) of the next-generation DVD laser light, and the distance from the electrode 1 to the electrode 3 is the effective diameter (radius) of the CD laser light. ). By arranging the electrodes 1 to 4 in this way, as described in the section “Effects of the Invention”, it is appropriate for all of the next-generation DVD laser light, DVD laser light, and CD laser light. Wavefront correction can be performed.

  FIG. 5 shows the relationship between the numerical aperture (NA) and the effective diameter for next-generation DVD laser light (wavelength: 407 nm), DVD laser light (wavelength: 605 nm), and CD laser light (wavelength: 780 nm). When the numerical aperture for the laser light of each wavelength is set as shown in the table of the figure, the effective diameter of each laser light is 3.9 mm, 3.9 mm, and 2.79 mm from the above equation (2), respectively. Become. When the expression (1) in the section “Effects of the Invention” is applied to the effective diameters of the next-generation DVD laser light and the DVD laser light, the maximum position of the spherical aberration with respect to these laser lights is 2 in diameter. The position is approximately .76 mm, which substantially coincides with the effective diameter of 2.79 mm of the laser beam for CD (see the lower part of the figure).

  FIG. 6 shows the relationship between the arrangement positions of the electrodes 1 to 4 and the spherical aberration generated in each laser beam, and the potential distribution and refractive index distribution of the spherical aberration correction element 114 when a potential is applied to each electrode.

  As shown in the figure, when a potential Vc2 is applied to the electrode 3 while the potential Vc1 is applied to the electrode 1 and the electrode 4, a change state of spherical aberration generated in the next-generation DVD laser light and DVD laser light (same figure). The refractive index of the spherical aberration correction element 114 can be distributed in the same change state as in the uppermost solid line (the lowermost solid line in the figure). Therefore, when the optical axis of the laser beam penetrates the electrode 1, the spherical aberration generated in the next-generation DVD laser beam and the DVD laser beam is canceled by appropriately adjusting the applied potential Vc1 and the applied potential Vc2. The wavefront state of these laser beams can be corrected.

  Further, as shown in the figure, when the potential Vc2 is applied to the electrode 2 while the potential Vc1 is applied to the electrodes 1 and 3, the change state of the spherical aberration generated in the laser beam for CD (the dotted line at the top in the figure). The refractive index of the spherical aberration correcting element 114 can be distributed in the same change state as (dotted line at the bottom of the figure). Therefore, when the optical axis of the laser beam passes through the electrode 1, the wavefront state of the laser beam is adjusted so as to cancel the spherical aberration generated in the CD laser beam by appropriately adjusting the applied potential Vc1 and the applied potential Vc2. Can be corrected.

  FIG. 7 shows a design example of the objective lens 117. The design values shown in the figure are those when the objective lens 117 is designed to correspond to the next-generation DVD laser light as described above. The objective lens designed as shown in the figure is an infinite system for the next-generation DVD laser light and the DVD laser light, and a finite system for the CD laser light.

  FIG. 8 shows the state of occurrence of spherical aberration when laser light of each wavelength is incident on the objective lens 117 designed in this way.

  As shown in the figure, when the next-generation DVD laser light (wavelength: 407 nm) is incident, the PV value is 0.83λ when the substrate thickness is 0.7 mm (0.1 mm thicker than the reference value). Spherical aberration occurs. Further, when DVD laser light (wavelength: 655 nm) is incident, spherical aberration with a PV value of 0.79λ is generated according to the wavelength shift with the next-generation DVD laser light. When a laser beam for CD (wavelength: 780 nm) is incident, spherical aberration with a PV value of 0.61λ is generated in response to the incident laser beam as parallel light (infinite system). .

  In this case, each electrode (electrode 1 to electrode 4) of the spherical aberration correcting element 114 is given a potential that causes a refractive index distribution that cancels the spherical aberration.

  That is, when next-generation DVD laser light or DVD laser light is used, an appropriate potential (servo signal) is applied from the servo circuit 300 to the electrodes 1, 3, and 4. For example, the potential applied to the electrode 3 is changed in a state where a constant voltage is applied to the electrodes 1 and 4, the reproduced signal at that time is monitored, and the potential (servo that gives the most appropriate potential to the reproduced signal) is applied to the electrode 3 (servo Signal).

  In addition, when CD laser light is used, an appropriate potential (servo signal) is applied from the servo circuit 300 to the electrode 1, electrode 2, and electrode 3. For example, the potential applied to the electrode 2 is changed in a state where a constant voltage is applied to the electrodes 1 and 3, the reproduced signal at that time is monitored, and the potential (servo that gives the most appropriate potential to the reproduced signal is applied to the electrode 2) Signal).

  As described above, according to the present embodiment, as shown in FIG. 2, the two resistance films are formed so as to sandwich the liquid crystal element, and the four electrodes are arranged on one resistance film. It is possible to correct spherical aberration generated in generation DVD laser light, DVD laser light, and CD laser light. Further, such correction can be performed only by applying a predetermined potential to each electrode, and the spherical aberration of each laser beam can be corrected by extremely simple control. As described above, according to the present embodiment, the spherical aberration of the next-generation DVD laser beam, DVD laser beam, and CD laser beam can be corrected smoothly with a simple configuration.

  Needless to say, the present invention is not limited to the above embodiment, and various other modifications are possible.

  For example, in the above embodiment, three semiconductor lasers are arranged and the respective laser beams are integrated by the dichroic prism, but instead, three laser elements are arranged in the same can, The optical axis of the laser beam from the element may be adjusted.

  In the above embodiment, the compatible optical disk apparatus using the next-generation DVD laser beam, the DVD laser beam, and the CD laser beam has been exemplified. However, the next-generation DVD laser beam and the CD laser beam, or the DVD In the optical disk apparatus using the laser beam for CD and the laser beam for CD, the spherical aberration of each laser beam can be corrected by the similar spherical aberration correction element 114.

  In the above embodiment, the aperture limiting element 103 is used to limit the opening of the laser beam for CD. However, the aperture limiting element 103 is omitted and the spherical aberration correcting element 114 is used to open the aperture of the laser beam for CD. It can also be restricted. For example, when a CD laser beam is used, a large potential is applied to the electrode 4 to greatly change the refractive index of the region between the electrode 3 and the electrode 4. As a result, the laser light incident on the region is greatly deflected from the optical axis, and only the laser light inside the electrode 3 is allowed to pass. In this way, the aperture limiting element 103 can be omitted, and the number of parts can be reduced. Further, since only the potential needs to be applied to the electrode 4, the control processing in the servo circuit 300 is not complicated.

In addition, the embodiment of the present invention can be variously modified as appropriate within the scope of the technical idea shown in the claims.

The figure which shows the structure of the optical disk apparatus which concerns on embodiment The figure which shows the structure of the spherical aberration correction element which concerns on embodiment The figure explaining operation | movement of the spherical aberration correction element which concerns on embodiment The figure explaining operation | movement of the spherical aberration correction element which concerns on embodiment The figure explaining arrangement | positioning of the electrode of the spherical aberration correction element which concerns on embodiment The figure explaining the correction | amendment operation | movement by the spherical aberration correction element which concerns on embodiment The figure which shows the example of a design of the objective lens which concerns on embodiment The figure which shows the example of generation | occurrence | production of the spherical aberration which concerns on embodiment The figure which shows the change state of a 3rd-order spherical aberration

Explanation of symbols

101 Semiconductor laser (wavelength: 780 nm)
105 Semiconductor laser (wavelength: 655 nm)
109 Semiconductor laser (wavelength: 407 nm)
114 Spherical Aberration Correction Element

Claims (7)

In an optical pickup device that irradiates at least a laser beam for CD and a laser beam for next generation DVD and / or a laser beam for DVD on a disk,
A wavefront correction element whose phase state of light changes in accordance with the magnitude of the potential applied in the light transmission direction is arranged in the common optical path of each laser beam, and four types for applying a potential to the wavefront correction element Are arranged at positions where the optical axis position through which the laser beam penetrates and the distance from the optical axis position is approximately 1: 1 / √2: 1/2,
An optical pickup device characterized by that. In claim 1,
The wavefront correction element includes a liquid crystal element that is molecularly oriented in one direction, and the refractive index with respect to transmitted light is changed by changing a potential distribution with respect to the liquid crystal element according to a potential applied from the electrode.
An optical pickup device characterized by that. A wavefront correction element used in an optical pickup device that irradiates at least a laser beam for CD and a laser beam for next generation DVD and / or a laser beam for DVD on a disk,
The laser beam penetrates through four kinds of electrodes for providing a potential to the light transmission layer, including a light transmission layer whose phase state of light changes according to the magnitude of the potential applied in the light transmission direction. The optical axis position and the distance from the optical axis position are approximately 1: 1 / √2: 1/2.
A wavefront correction element characterized by that. In claim 3,
The light transmission layer is composed of a liquid crystal element that is molecularly oriented in one direction, and the refractive index for the transmitted light is changed by changing the potential distribution with respect to the liquid crystal element according to the potential applied from the electrode.
A wavefront correction element characterized by that. In an optical disc apparatus that records and / or reproduces a disc using at least a CD laser beam and a next-generation DVD laser beam and / or a DVD laser beam,
A wavefront correction element that changes the phase state of the light according to the magnitude of the potential applied in the light transmission direction is arranged in the common optical path of each laser beam, and four types for applying a potential to the wavefront correction element An optical pickup device in which an electrode is disposed at an optical axis position through which the laser beam penetrates and at a position where the distance from the optical axis position is approximately 1: 1 / √2: 1/2;
Wavefront control means for controlling the applied state of the potential to the electrode according to the disc type to be recorded and / or reproduced;
An optical disc apparatus comprising: In claim 5,
The wavefront correction element includes a liquid crystal element that is molecularly oriented in one direction, and the refractive index with respect to transmitted light is changed by changing a potential distribution with respect to the liquid crystal element according to a potential applied from the electrode.
An optical disc device characterized by the above. In claim 5 or 6,
The wavefront control means applies a potential to the electrode so as to scatter light on the outer peripheral side from the second electrode from the outside with respect to the optical axis when CD laser light is used.
An optical disc device characterized by the above.

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