JP2005038575A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small pickup device coping with a plurality of wavelengths/a plurality of substrates and provided with a small and high-performance wave surface conversion element which is simple in structure. <P>SOLUTION: In the optical pickup device provided with a plurality of wavelength light sources constituted of a blue layer DB, a red laser DR and an infrared layer DIR, a wave surface conversion element WC converts the wave surface shapes of red and infrared laser beams LR and LIR emitted from the plurality of wavelength light sources and passed through a collimator optical system CL. An objective lens OB is subjected to aberration correction to exhibit good aberration performance when the blue laser beam LB is used, and respective coefficients of the phase function of diffraction grating surfaces provided in the wave surface conversion element WC are set to desired values, thereby realizing the optical pickup coping with three different wavelengths and substrate thicknesses. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical pickup device. For example, a blue laser compatible optical information recording medium, a red laser compatible optical information recording medium, and a red, red, and infrared laser light source and one wavefront conversion element are used. The present invention relates to a multi-wavelength optical pickup device (optical information recording / reproducing device, magneto-optical recording / reproducing device) capable of recording and reproducing optical information with respect to any of the external laser compatible optical information recording media.

  Several standards have been proposed for next-generation recording media that use blue laser light, including the Blu-ray method (wavelength λ = 400 to 415 nm, NA 0.85, disk substrate thickness 0.1 mm) and HD. -There is a DVD system (wavelength λ = 400 to 415 nm, NA 0.65, disk substrate thickness 0.6 mm). Here, in an optical pickup device with a high NA (numerical aperture) using blue laser light, the conventional DVD method (use wavelength λ = 640 to 670 nm, NA 0.60, disk substrate thickness 0.6 mm) or CD method (use wavelength) There is a strong demand for media compatibility that is compatible with λ = 750 to 820 nm, NA 0.45, and disk substrate thickness 1.2 mm.

  Conventionally, an optical pickup optical system compatible with a plurality of wavelengths has been proposed. For example, Patent Document 1 transmits light having a wavelength λ = 400 to 415 nm, and wavelengths λ = 640 to 670 nm and λ = Using a wavelength selective filter that diffracts light of 750 to 820 nm, light of wavelength λ = 400 to 415 nm has an infinite conjugate length, light of wavelengths λ = 640 to 670 nm and λ = 750 to 820 nm has a finite conjugate length and an objective lens 1 shows an optical head device capable of three-wavelength compatibility in which a light beam is incident on. In Non-Patent Document 1, an optical element that transmits light having a wavelength λ = 400 to 415 nm and a wavelength λ = 640 to 670 nm and diffracts light having a wavelength λ = 750 to 820 nm is used. In addition, light having a wavelength λ = 640 to 670 nm has an infinite conjugate length, light having a wavelength λ = 750 to 820 nm has a finite conjugate length, and a method of making a light beam incident on an objective lens and making it compatible with three wavelengths is shown. Second, using a diffractive lens to make the incident light when using a blue laser with a wavelength of λ = 400 to 415 nm converged light, increasing the conjugate distance when using a DVD or CD and enabling media compatibility It is shown.

JP 2003-67972 A Proceedings of the Japan Society of Applied Physics (Autumn 2002) Proceedings of the Japan Society of Applied Physics (Spring 2003)

  When the Blu-ray method is adopted, the recording medium used for blue laser light (hereinafter referred to as “BD”) has a substrate thickness of 0.1 mm, DVD (substrate thickness 0.6 mm), and CD (substrate thickness 1.2 mm). ) Is extremely thin. Because of this large difference in substrate thickness, for example, as previously proposed, when using a blue laser BD with an objective lens shared with a DVD or CD, all substrates are used with an infinite conjugate length. Then, when using a thick substrate, the air space between the objective lens and the substrate (hereinafter referred to as “WD; working distance”) is shortened, and the objective lens and the substrate may collide. Therefore, in each of the three-wavelength compatible systems described in the above-mentioned documents, at least one wavelength light of the three wavelengths is incident on the objective lens with a finite conjugate length.

  In this case, particularly when using a DVD or CD with a thick substrate, it is necessary to secure the WD of the objective lens, so that the object point position becomes very close to the objective lens. Due to coma generated when moving in the vertical direction, it is very difficult to ensure optical performance (off-axis performance), which is a big problem in optical design. In order to solve this problem, Patent Document 1 proposes a method of preventing a decrease in optical performance during tracking by moving a relay optical system for setting a finite conjugate length together with an objective lens when using a DVD or CD. Since a mechanism for moving the objective lens and the relay optical system in a predetermined positional relationship is required, the configuration of the optical pickup device is complicated, which is not desirable. In addition, when the HD-DVD method is adopted, the BD substrate thickness is 0.6 mm, the same as DVD, but a spot image with good wavefront aberration is formed on the optical recording surface of the disc substrate due to the difference in the wavelength used. It was difficult.

  The present invention has been made in view of such a situation, and includes a wavefront conversion element that can prevent deterioration of optical performance due to tracking tracking or the like while ensuring the WD of an objective lens even when a DVD or CD is used. It is another object of the present invention to provide an optical pickup device that supports a plurality of wavelengths and a plurality of substrates.

In order to achieve the above object, an optical pickup device of a first invention includes a plurality of wavelength light sources composed of a plurality of light sources that emit laser beams having different wavelengths, and a plurality of thicknesses from the surface to the optical recording surface that are different from each other. An optical pickup device comprising: an objective lens for determining a wavelength of laser light corresponding to an optical information recording medium; and focusing an optical recording surface of the plurality of optical information recording media with laser light having a corresponding wavelength A wavefront conversion element having a function of converting a wavefront shape, comprising at least one diffraction grating surface for diffracting any one of a plurality of wavelengths of laser light emitted from the plurality of wavelength light sources. The wavefront conversion element and the objective lens move together, and satisfy the following conditional expression (A1).
2.5 <| fc / fOL | <50.0 (A1)
However,
fc: Wavefront conversion element focal length when using a wavelength corresponding to the thickest optical information recording medium,
fOL: Objective lens focal length when using a wavelength corresponding to the thickest optical information recording medium,
It is.

  An optical pickup device according to a second aspect of the invention is characterized in that, in the configuration of the first aspect, the wavefront conversion element is disposed closer to the light source than the objective lens.

  According to a third aspect of the present invention, there is provided the optical pickup device according to the first or second aspect, wherein the plurality of wavelength light sources includes three light sources that emit laser beams having three different wavelengths. The diffraction grating surface for diffracting the laser beam corresponding to the optical information recording medium having the two thicknesses up to the optical recording surface of the laser beam is located on the optical information recording medium side. The diffraction grating surface for diffracting the laser beam corresponding to the second thickest optical information recording medium is arranged so as to be positioned on the light source side.

  According to a fourth aspect of the present invention, there is provided the optical pickup device according to the first, second, or third aspect, wherein the wavefront conversion element is an optical information recording medium having the smallest thickness up to the optical recording surface of the laser light. The wavefront shape of the corresponding laser light is transmitted without being converted.

An optical pickup device according to a fifth aspect of the present invention is characterized in that, in the configuration of the first, second, third or fourth invention, the objective lens satisfies the following conditional expression (B1).
1.0 <d / fB <1.5 (B1)
However,
d: Center thickness of the objective lens,
fB: Focal length of the objective lens when using a wavelength corresponding to the thinnest optical information recording medium,
It is.

An optical pickup device of a sixth invention is characterized in that, in the configuration of the first, second, third, fourth or fifth invention, the wavefront conversion element satisfies the following conditional expression (C): To do.
｜ C2c ＊ fc ^ 3 | <800 ・ ・ ・ (C)
However,
C2c: the fourth-order coefficient of the optical path difference function of the diffraction grating surface acting when using the wavelength corresponding to the thickest optical information recording medium,
fc: Wavefront conversion element focal length when using a wavelength corresponding to the thickest optical information recording medium,
It is.

According to a seventh aspect of the present invention, there is provided an optical pickup device comprising: a multi-wavelength light source including a plurality of light sources that emit laser beams having different wavelengths corresponding to a plurality of optical information recording media; and an optical recording surface of the plurality of optical information recording media. An optical pickup device including an objective lens for focusing laser light of a corresponding wavelength, wherein the optical information recording medium corresponds to laser light emitted from any two of the plurality of light sources. A function of converting a wavefront shape, wherein the thickness from the surface to the optical recording surface is equal, and at least one diffraction grating surface that diffracts any one of the laser beams having a plurality of wavelengths emitted from the plurality of wavelength light sources is provided. The wavefront conversion element and the objective lens move together, and satisfy the following conditional expression (A2).
50 <| fc / fOL | <1000 (A2)
However,
fc: Wavefront conversion element focal length when using a wavelength corresponding to the thickest optical information recording medium,
fOL: Objective lens focal length when using a wavelength corresponding to the thickest optical information recording medium,
It is.

  According to an eighth aspect of the present invention, there is provided the optical pickup device according to the seventh aspect, wherein the wavefront conversion element is disposed closer to a light source than the objective lens.

  According to a ninth aspect of the present invention, in the configuration of the seventh or eighth aspect, the multi-wavelength light source includes three light sources that emit laser beams having three different wavelengths, and the wavefront conversion element includes The diffraction grating surface for diffracting the laser beam corresponding to the optical information recording medium having a thickness up to the optical recording surface among the laser beams is located on the optical information recording medium side, A diffraction grating surface for diffracting a laser beam corresponding to an optical information recording medium having a thin thickness up to the surface is disposed on the light source side.

  An optical pickup device according to a tenth aspect of the present invention is the optical pickup apparatus according to the seventh or eighth aspect, wherein the plurality of wavelength light sources includes three light sources that emit laser beams having three different wavelengths, and the wavefront conversion element and The objective lens has one each of the diffraction grating surfaces, and the diffraction grating surface for diffracting the laser light corresponding to the optical information recording medium having a large thickness up to the optical recording surface of the laser light is on the optical information recording medium side. The diffraction grating surface for diffracting the laser beam corresponding to the optical information recording medium having a small thickness up to the optical recording surface is located on the light source side.

  In an optical pickup device according to an eleventh aspect of the invention, in the configuration of the seventh, eighth, ninth, or tenth aspect, the diffraction grating surface provided on the objective lens diffracts laser light having three wavelengths. It is characterized by that.

  An optical pickup device according to a twelfth aspect of the invention is that the diffraction grating surface provided on the objective lens diffracts only laser light of one wavelength in the configuration of the seventh, eighth, ninth or tenth aspect. It is characterized by doing.

  An optical pickup device according to a thirteenth aspect of the present invention is the configuration of the seventh, eighth, ninth, tenth, eleventh or twelfth aspect, wherein the wavefront conversion element extends from the laser beam to the optical recording surface. The wavefront shape of the laser beam corresponding to the thinnest optical information recording medium is transmitted without conversion.

According to a fourteenth aspect of the present invention, there is provided the optical pickup device according to the seventh, eighth, ninth, tenth, eleventh, twelfth or thirteenth aspect, wherein the objective lens satisfies the following conditional expression (B2): It is characterized by satisfying.
0.4 <d / fB <0.8 (B2)
However,
d: Center thickness of the objective lens,
fB: Focal length of the objective lens when using a wavelength corresponding to the thinnest optical information recording medium,
It is.

An optical pickup apparatus according to a fifteenth aspect of the invention is characterized in that, in the configuration of any one of the first to fourteenth aspects, the objective lens satisfies the following conditional expression (D).
-0.8 <rOF / rOR <0.1 (D)
However,
rOF: radius of curvature of the side of the light source of the objective lens,
rOR: radius of curvature of the optical information recording medium side surface of the objective lens,
It is.

  According to a sixteenth aspect of the present invention, there is provided the optical pickup device according to any one of the first to fifteenth aspects, wherein the object distance of the objective lens is infinite when any of the optical information recording media is used. And

  According to the present invention, the wavefront conversion element that converts the wavefront shape of laser light having a plurality of wavelengths emitted from a plurality of wavelength light sources is disposed between the collimator optical system and the objective lens, and the wavefront conversion element and the objective lens are integrated. In addition, the optical arrangement that satisfies the conditional expression (A1) is used, and a compact optical pick-up device that supports multiple wavelengths with a simple, compact, and high-performance wavefront conversion element. Can be realized. If the optical pickup device according to the present invention is used, a plurality of types of optical information recording media having different substrate thicknesses can be compatible with a plurality of wavelengths, and the recording density can be improved. .

  Further, the thickness from the surface of the optical information recording medium corresponding to the laser light emitted from any two of the plurality of light sources to the optical recording surface is equal, and the wavefront conversion element and the objective lens move together. In addition, since the optical arrangement satisfies the conditional expression (A2), the optical information recording medium corresponding to two different wavelengths of laser light has the same thickness and is compatible with multiple wavelengths. An optical pickup device can be provided.

  Hereinafter, an optical pickup device embodying the present invention will be described with reference to the drawings. FIG. 1 shows an optical configuration corresponding to the first embodiment of the optical pickup device of the present invention. In FIG. 1, DB is a laser light source composed of a blue laser diode (hereinafter also simply referred to as “blue laser”), DR is a laser light source composed of a red laser diode (hereinafter also simply referred to as “red laser”), and DIR is infrared. A laser light source (hereinafter also simply referred to as “infrared laser”) composed of a laser diode, and these three light sources constitute a multi-wavelength light source. DP is a dichroic prism, CL is a collimator optical system, WC is a wavefront conversion element, OB is an objective lens, DK is a disk substrate, sD is an optical recording surface, and s1 is the first surface (light incident side surface) of the wavefront conversion element (WC) , S2 is the second surface (light emission side surface) of the wavefront conversion element (WC). In the Cartesian coordinate system (x, y, z), the direction in which the laser light is emitted from the blue laser (DB) and the red laser (DR) (the horizontal direction in FIG. 1) is the x direction, and the optical axis (AX) direction. FIG. 1 shows an xz section, where z (the vertical direction in FIG. 1) is the z direction, and y is the direction perpendicular to x and z.

  The optical pickup device shown in FIG. 1 can record and reproduce optical information on any of a blue laser compatible optical information recording medium, a red laser compatible optical information recording medium, and an infrared laser compatible optical information recording medium. This is an optical pickup device that supports multiple wavelengths. Examples of optical information recording media include CD, CD-R, CD-RW, CD-ROM, DVD, DVD-R, DVD-RW, DVD-ROM, DVD-RAM, BD, BD-R, BD-RW, There are optical disks such as BD-ROM, BD-RAM, and MD, and the disk substrate (DK) located on the image side of the objective lens (OB) corresponds to a cover glass for the optical recording surface (sD). The optical information recording medium for blue laser, the optical information recording medium for red laser, and the optical information recording medium for infrared laser are different from each other in the thickness of the disk substrate (DK) from the surface to the optical recording surface (sD), The blue wavelength (first wavelength) laser beam (LB) is focused on the optical recording surface (sD) of the blue laser compatible optical information recording medium, and the optical recording surface (sD) of the red laser compatible optical information recording medium is focused on. Is focused on the laser light (LR) of red wavelength (second wavelength), and the laser light of infrared wavelength (third wavelength) on the optical recording surface (sD) of the optical information recording medium for infrared laser ( The objective lens (OB) acts so that (LIR) is in focus.

  The blue laser (DB) as the first light source, the red laser (DR) as the second light source, and the infrared laser (DIR) as the third light source are arranged on separate chips, and two or more Are not lit at the same time. For example, which laser light source (DB, DR, DIR) is used depending on the difference in thickness of the disk substrate (DK) and some information written on the optical recording surface (sD) on the disk substrate (DK) Is judged. Each optical pickup device has means (not shown) for making the determination, and based on the determination, one of blue laser (DB), red laser (DR), and infrared laser (DIR) Lights up. Only one of blue, red, and infrared laser light (LB, LR, LIR) is emitted from the laser light source (DB, DR, DIR), and optical information is recorded on the optical recording surface (sD). Or reproduction will be performed. Note that the blue laser (DB), red laser (DR), and infrared laser (DIR) can be arranged on the same chip.

  The blue laser beam (LB) emitted from the blue laser (DB), the red laser beam (LR) emitted from the red laser (DR), and the infrared laser beam (LIR) emitted from the infrared laser (DIR) The light beam is incident on an optical path combining unit that combines the optical paths of the laser beams. Here, a dichroic prism (DP) is used as the optical path synthesis means. The dichroic prism (DP) reflects the first laser surface (M1) that reflects blue laser light and transmits infrared laser light, and the second mirror surface (M2) that reflects red laser light and transmits infrared laser light. The blue laser beam (LB) is reflected by the first mirror surface (M1) and the red laser beam (LR) is reflected by the second mirror surface (M2) and then the infrared laser. The light (LIR) passes through the first mirror surface (M1) and the second mirror surface (M2), and is then converted into a parallel light beam by the collimator optical system (CL). The first surface (s1) of the wavefront conversion element (WC) ).

  Here, the optical path of each laser beam is synthesized using one dichroic prism (DP) and guided to the collimator optical system, but a plurality of dichroic prisms (DP) may be provided in the optical path. Further, a dichroic mirror may be used instead of the dichroic prism (DP) as the optical path synthesis means, or a plane mirror may be used in combination. That is, any combination of a dichroic prism (DP), a dichroic mirror, and a plane mirror can be used as an optical path combining unit. In addition, when each laser light source (DB, DR, DIR) is provided on one optical path, or when it can be moved according to the position of the optical system, it is possible to adopt a configuration in which no optical path synthesizing means is provided. It is.

  2 to 4 show the wavefront conversion elements (WC) of the specific example 1 in this embodiment when using the wavelength λ = 400 to 415 nm, when using the wavelength λ = 640 to 670 nm, and when using the wavelength λ = 750 to 820 nm, respectively. FIG. 3 is a diagram showing a schematic optical path of a portion of the objective lens (OB) in a yz section. 2 to 4, the wavefront conversion element (WC) is a parallel plate, and the asterisk (**) on the first surface (s1) on the light incident side and the second surface (s2) on the light emission side is the first. It shows that the surface (s1) and the second surface (s2) are diffraction grating surfaces. The first surface (s1) is provided with a first diffraction grating surface (D1) that allows light of wavelengths 400 to 415 nm and 750 to 820 nm to pass through without being affected and diffracts only light of wavelengths 640 to 670 nm. The second surface (s2) is provided with a second diffraction grating surface (D2) that allows light of wavelengths 400 to 415 nm and 640 to 670 nm to pass through without being affected and diffracts only light of wavelengths 750 to 820 nm. It has been. With this configuration, an optical pickup optical system corresponding to three different wavelengths of 400 to 415 nm, 640 to 670 nm, and 750 to 820 nm is obtained. The first surface (s3) on the light incident side of the objective lens (OB) and the asterisk (*) on the second surface (s4) on the light emission side are the first surface (s3) and the second surface of the objective lens (OB). (s4) indicates an aspherical surface. A stop (ST) is arranged between the wavefront conversion element (WC) and the objective lens (OB), and the light beam emitted from the second surface (s2) of the wavefront conversion element (WC) is the objective lens (OB). ) To adjust the optical path so that it enters the effective area.

  Next, aberration correction at each wavelength in the first specific example will be described. When the wavelength λ = 400 to 415 nm is used, the blue laser (DB) is selected from the three laser light sources, and the blue laser light (LB) having the wavelength λ = 400 to 415 nm is emitted as diverging light. The blue laser beam (LB) passes through the dichroic prism (DP) and is collimated by the collimating optical system (CL), and then, as shown in FIG. 2, the first surface (s1) of the wavefront conversion element (WC) Is incident on. At this time, the first diffraction grating surface (D1) provided on the first surface (s1) and the second diffraction grating surface (D2) provided on the second surface (s2) are light waves having a wavelength λ = 400 to 415 nm. Since the light is transmitted without acting on the surface, a parallel light beam enters the objective lens (OB). Here, the objective lens (OB) has been subjected to aberration correction so as to have good aberration performance when using a disk substrate (DK) with a parallel light flux of wavelength λ = 400 to 415 nm and a substrate thickness of 0.1 mm. A spot image with good wavefront aberration is obtained on the optical recording surface (sD) of the substrate (DK).

  When the wavelength λ = 640 to 670 nm is used, a red laser (DR) is selected from the three laser light sources, and a red laser beam (LB) having a wavelength λ = 640 to 670 nm is emitted as diverging light. The red laser beam (LR) passes through the dichroic prism (DP) and is collimated by the collimating optical system (CL). Then, as shown in FIG. 3, the first surface (s1) of the wavefront conversion element (WC) Is incident on. At this time, since the first diffraction grating surface (D1) provided on the first surface (s1) diffracts the light wavefront having the wavelength λ = 640 to 670 nm, the parallel light beam is converted into a divergent light beam. Since the second diffraction grating surface (D2) provided on the second surface (s2) transmits the light wavefront having the wavelength λ = 640 to 670 nm without acting, the objective lens (OB) has the first diffraction grating surface ( The divergent light beam diffracted only by D1) enters. Here, the objective lens (OB) has been subjected to aberration correction so as to have good aberration performance when using a disk substrate (DK) with a parallel light flux of wavelength λ = 400 to 415 nm and a substrate thickness of 0.1 mm. When a disk substrate (DK) having a substrate thickness of 0.6 mm with a divergent light beam of λ = 640 to 670 nm is used, spherical aberration due to differences in wavelength, object distance, and disk substrate thickness occurs. However, this spherical aberration can be corrected by setting each coefficient of the phase function of the first diffraction grating surface (D1) to a desired value. As a result, the wavefront aberration is excellent on the optical recording surface (sD). A spot image can be obtained.

  When the wavelength λ = 750 to 820 nm is used, an infrared laser (DIR) is selected from the three laser light sources, and an infrared laser beam (LIR) having a wavelength λ = 750 to 820 nm is emitted as diverging light. The infrared laser beam (LIR) passes through the dichroic prism (DP) and is converted into a parallel beam by the collimating optical system (CL), and as shown in FIG. 4, the first surface (s1) of the wavefront conversion element (WC) ). At this time, the first diffraction grating surface (D1) provided on the first surface (s1) is transmitted without acting on the light wavefront having the wavelength λ = 750 to 820 nm. Since the second diffraction grating surface (D2) provided on the second surface (s2) diffracts the light wavefront with a wavelength λ = 750 to 820 nm, only the second diffraction grating surface (D2) is provided on the objective lens (OB). A diffracted divergent light beam enters. Here, the objective lens (OB) has been subjected to aberration correction so as to have good aberration performance when using a disk substrate (DK) with a parallel light flux of wavelength λ = 400 to 415 nm and a substrate thickness of 0.1 mm. When a disc substrate (DK) having a substrate thickness of 1.2 mm with a divergent light beam of λ = 750 to 820 nm is used, spherical aberration due to differences in wavelength, object distance, and disc substrate thickness occurs. However, this spherical aberration can be corrected by setting each coefficient of the phase function of the second diffraction grating surface (D2) to a desired value as in the case of the wavelength λ = 750 to 820 nm. A spot image with good wavefront aberration is obtained on the surface (sD).

  As described above, the first diffraction grating surface (D1) that allows the light of wavelengths λ = 400 to 415 nm and λ = 750 to 820 nm to pass through without being affected, and diffracts only the light of wavelength λ = 640 to 670 nm, and the wavelength λ Wavefront conversion element provided with a second diffraction grating surface (D2) that diffracts only light having a wavelength of λ = 750 to 820 nm on both sides while allowing light of 400 to 415 nm and λ = 640 to 670 nm to pass through without being affected (WC) and an objective lens (OB) that has been corrected for aberrations to achieve good aberration performance when using a disk substrate (DK) with a parallel light flux of wavelength λ = 400 to 415 nm and a substrate thickness of 0.1 mm Thus, when using three different wavelengths and disk substrate thicknesses, good aberration performance can be obtained. In addition, since the wavefront conversion element (WC) and the objective lens (OB) are configured to move together, the optical performance is improved even when the objective lens moves perpendicular to the optical axis due to tracking tracking or the like. In particular, even when an optical information recording medium having a large substrate thickness such as a CD or DVD is used, off-axis aberration is corrected well, and a high-performance optical pickup device can be realized.

  5 to 7 show yz cross-sections of the schematic optical paths of the wavefront conversion element (WC) and the objective lens (OB) when using the wavelength λ = 400 to 415 nm, respectively, in the specific examples 2 to 4 in the present embodiment. It is the figure shown by. Portions common to those in FIG. 2 are denoted by the same reference numerals and description thereof is omitted. Although not shown in the figure, each of these specific examples can also be used at wavelengths of λ = 640 to 670 nm and λ = 750 to 820 nm, and the optical path diagram is the same as in FIGS. become. The details of the aberration correction at each wavelength in these specific examples are the same as those in specific example 1, and thus the description thereof is omitted.

  8 and 9 show schematic optical paths of the wavefront conversion element (WC) and the objective lens (OB) in specific examples 5 and 6 in the present embodiment when the wavelength λ = 400 to 415 nm, respectively, in the yz section. FIG. Portions common to those in FIG. 2 are denoted by the same reference numerals and description thereof is omitted. Although not shown in the figure, each of these specific examples can also be used at wavelengths of λ = 640 to 670 nm and λ = 750 to 820 nm, and the optical path diagram is the same as in FIGS. become. 8 and 9, the wavefront conversion element (WC) is a plano-concave lens having a concave second surface (s2) on the disk side, and the first surface (s1) and the second surface are the same as in the first to fourth examples. A first diffraction grating surface (D1) and a second diffraction grating surface (D2) are provided on the surface (s2), respectively. Since the configuration of the diffraction grating surfaces (D1, D2) is the same as that of the first specific example, the description thereof is omitted.

  Next, aberration correction at each wavelength in specific examples 5 and 6 will be described. Since the laser beams (LB, LR, LIR) emitted from the laser light sources (DB, DR, DIR) are converted into parallel beams by the collimating optical system (CL), the description is omitted. . As shown in FIGS. 8 and 9, when the wavelength λ = 400 to 415 nm is used, a parallel light beam having a wavelength λ = 400 to 415 nm is incident on the first surface (s1) of the wavefront conversion element (WC). At this time, the first diffraction grating surface (D1) provided on the first surface (s1) and the second diffraction grating surface (D2) provided on the second surface (s2) are light waves having a wavelength λ = 400 to 415 nm. The light wavefront is not affected because it is transmitted without acting on the surface, but the wavefront conversion element (WC) has a plano-concave shape, so the parallel light beam becomes a divergent light beam due to its lens action, and the objective lens (OB) A divergent light beam is incident on. Here, the objective lens (OB) has been subjected to aberration correction so as to have good aberration performance when using a disk substrate (DK) having a substrate thickness of 0.1 mm with a divergent light beam by a lens action of wavelength λ = 400 to 415 nm. Therefore, a spot image with good wavefront aberration can be obtained on the optical recording surface (sD) of the disk substrate (DK).

  Further, when the wavelength λ = 640 to 670 nm is used, a parallel light beam having a wavelength λ = 640 to 670 nm is incident on the first surface (s1) of the wavefront conversion element (WC). At this time, since the first diffraction grating surface (D1) provided on the first surface (s1) diffracts the light wavefront having the wavelength λ = 640 to 670 nm, the parallel light beam is converted into a divergent light beam. Further, since the second diffraction grating surface (D2) provided on the second surface (s2) is transmitted without acting on the light wavefront having the wavelength λ = 640 to 670 nm, the light wavefront is not affected. Accordingly, a divergent light beam diffracted by the first diffraction grating surface (D1) and diverged by the lens action of the wavefront conversion element (WC) is incident on the objective lens (OB). Here, the objective lens (OB) has a good aberration performance when using a disk substrate (DK) having a substrate thickness of 0.1 mm with a divergent light beam generated by the lens action of a wavefront conversion element (WC) having a wavelength λ = 400 to 415 nm. As a result, the difference in wavelength, object distance, and disc substrate thickness is required when using a disc substrate (DK) with a substrate thickness of 0.6 mm with a divergent light beam due to diffraction and lens action at a wavelength λ = 640 to 670 nm. Will cause spherical aberration. However, this spherical aberration can be corrected by the same method as in Example 1, and as a result, a spot image with good wavefront aberration can be obtained on the optical recording surface (sD).

  Similarly, when the wavelength λ = 750 to 820 nm is used, a parallel light beam having a wavelength λ = 750 to 820 nm is incident on the first surface (s1) of the wavefront conversion element (WC). At this time, the first diffraction grating surface (D1) provided on the first surface (s1) is transmitted without acting on the light wavefront having the wavelength λ = 750 to 820 nm. Further, the second diffraction grating surface (D2) provided on the second surface (s2) diffracts the light wavefront having the wavelength λ = 750 to 820 nm, so that the parallel light beam is converted into a divergent light beam. Accordingly, a divergent light beam diffracted by the second diffraction grating surface (D2) and diverged by the lens action of the wavefront conversion element (WC) is incident on the objective lens (OB). Here, the objective lens (OB) has been subjected to aberration correction so as to have good aberration performance when using a disk substrate (DK) having a substrate thickness of 0.1 mm with a divergent light beam by a lens action of wavelength λ = 400 to 415 nm. Therefore, when using a disc substrate (DK) with a substrate thickness of 1.2 mm with a divergent light beam due to diffraction and lens action at a wavelength λ = 750 to 820 nm, spherical aberration due to differences in wavelength, object distance and disc substrate thickness may occur. It becomes. However, this spherical aberration can be corrected by the same method as in Example 1, and as a result, a spot image with good wavefront aberration can be obtained on the optical recording surface (sD).

  The wavefront conversion element (WC) will be described in more detail. FIG. 10 shows a schematic configuration of the wavefront conversion element (WC) used in the first embodiment and a schematic optical path of each laser beam (LB, LR, LIR) in the xz section. FIG. 11 is an enlarged xz cross section of the fine structure of the first diffraction grating surface (D1) provided on the first surface (s1). The first diffraction grating surface (D1) provided on the first surface (s1) of the wavefront conversion element (WC) transmits blue laser light (LB) and infrared laser light (LIR), and is a red laser. It has a structure that diffracts light (LR), and the second diffraction grating surface (D2) provided on the second surface (s2) of the wavefront conversion element (WC) is blue laser light (LB) and red It has a structure that transmits laser light (LR) and diffracts infrared laser light (LIR).

As shown in FIG. 11, the first diffraction grating surface (D1) on the light incident side is composed of stepped diffraction gratings having a number of steps p (here, four steps), and grooves are provided in a one-dimensional direction (y direction). It has a structured. When the blue laser beam (LB) is incident on the first diffraction grating surface (D1), the step (that is, the height of each step) is d, and the refractive index of the diffraction grating substrate medium with respect to the wavelength λBL of the blue laser beam is set. Assuming nBL, a difference in optical path length of d · (nBL−1) occurs in the wavefront passing through a certain step and the adjacent step. The same applies to red laser light (LR) and infrared laser light (LIR). Here, the difference in optical path length between the blue laser beam (LB) and the infrared laser beam (LIR) is an integral multiple of the blue laser wavelength and the infrared laser wavelength (M ₁ times and M ₂ times, respectively), q, When L is an integer, the height H of each diffraction grating is specified by a set of integers q, L, M ₁ , and M ₂ satisfying the following formula (DS1). As shown in (B), the blue laser beam (LB) and the infrared laser beam (LIR) are transmitted, and as shown in FIG. 11 (C), the red laser beam (LR) is transmitted to an arbitrary order D (height). (Order determined by H)). At this time, the width (pitch P) of each diffraction grating is determined from the objective lens magnification desired for each use.

H = p · d
= P ・ M ₁・ λBL / (nBL-1)
= P ・ M ₂・ λIR / (nIR-1)
= (L ± 1 / q) λR / (nR-1) (DS1)
here,
λBL: Blue laser light (LB) wavelength,
nBL: refractive index of the diffraction grating substrate medium with respect to the wavelength of the blue laser beam (LB),
λIR: wavelength of infrared laser light (LIR),
nIR: refractive index of the diffraction grating substrate medium with respect to the wavelength of infrared laser light (LIR),
λR: wavelength of red laser light (LR),
nR: refractive index of the diffraction grating substrate medium with respect to the wavelength of the red laser beam (LR),
It is. Furthermore, if the number of stages p and the integer q in the formula (DS1) are set to have the relationship of the following formula (DS2), the diffraction efficiency can be increased in the D-order.
p = D × q (DS2)

Although not shown in the figure, the second diffraction grating surface (D2) on the light emission side transmits blue laser light (LB) and red laser light (LR) and diffracts infrared laser light (LIR). Therefore, as in the case of the first diffraction grating surface (D1), the step of the diffraction grating is d, the number of steps is p, and the difference in the optical path length between the blue laser beam (LB) and the red laser beam (LR) is calculated. Integer q of the blue laser wavelength and the red laser wavelength (M ₃ times and M ₄ times respectively), and q and L are integers, the height q of each diffraction grating satisfies the following formula (DS3) q , L, M ₃ , and M ₄ , the blue laser beam (LB) and the red laser beam (LR) are transmitted, and the infrared laser beam (LIR) is in an arbitrary order. It becomes possible to diffract at D (order determined by height H). Furthermore, if the number of stages p and the integer q in the formula (DS3) have the relationship of the above-described formula (DS2), the diffraction efficiency can be increased in the D-order.

H = p · d
= P ・ M ₃・ λBL / (nBL-1)
= P ・ M ₄・ λR / (nR-1)
= (L ± 1 / q) λIR / (nIR-1) (DS3)
Here, λBL, nBL, λR, nR, λIR, and nIR are respectively synonymous with those in the formula (DS1). By using the wavefront conversion element (WC) provided with the first diffraction grating surface (D1) and the second diffraction grating surface (D2) based on such a principle, it becomes possible to interchange three different wavelengths.

  As described above, each laser beam (LB, LR, LIR) that has passed through the dichroic prism (DP) enters the collimator optical system (CL) and is collimated into a parallel light beam. Note that the collimator optical system (CL) preferably has a two-group two-lens configuration with one negative lens and one positive lens when one collimator optical system (CL) is to cope with a plurality of wavelengths. When there is one collimator optical system (CL), it is desirable to use at least one negative lens and one positive lens from the viewpoint of chromatic aberration correction. However, when the collimator optical system (CL) is composed of a single lens element composed of two lenses in one group, the wavelength is large like blue laser light (for example, wavelength 400 to 415 nm) and red laser light (for example, wavelength 640 to 670 nm). It becomes difficult to suppress the variation of the spherical aberration when changed, and it cannot be said to be a desirable configuration. Therefore, in order to secure the wavefront aberration performance while reducing the number of lenses and achieving cost reduction and downsizing, a two-group two-lens configuration with one negative lens and one positive lens as described above is desirable. .

  A plurality of collimator optical systems (CL) can be provided for each wavelength of laser light. In this case, the configuration is not limited to the two-group / two-element configuration as in the case of a single collimator optical system (CL). For example, when using blue laser light, the NA of the collimator optical system (CL) should be set high. In such a case, it is desirable to use a two-group configuration that facilitates spherical correction. In this case, since the diameter of the collimator optical system (CL) becomes large, it is desirable to use a beam expander optical system together in order to use a small objective lens (OB). Further, a beam expander optical system can be used instead of the collimator optical system (CL). The laser light (LB, LR, LIR) collimated by the collimator optical system (CL) passes through the first surface (s1) and the second surface (s2) of the wavefront conversion element (WC), and then the objective lens (OB ) And forms an image on the optical recording surface (sD) of the optical information recording medium via the disk substrate (DK).

  In order to correct on-axis spherical aberration and off-axis coma, the objective lens (OB) is preferably biconvex or meniscus, and both surfaces are aspheric. In addition, the wavefront conversion element (WC) may be flat on both sides, or at least one side may be spherical, but at least one side is spherical so that the wavelength can be used for a particularly thick substrate. This is more desirable because it increases the degree of design freedom for correcting off-axis coma at times.

  Next, an optical configuration corresponding to the second embodiment of the optical pickup device of the present invention is shown in FIG. 12 also defines an orthogonal coordinate system (x, y, z) as in FIG. 1, and FIG. 12 shows an xz cross section. Also, the same reference numerals are given to the parts common to FIG. In the present embodiment, no infrared laser (DIR) is provided, and only a blue laser (DB) and a red laser (DR) are arranged. As in the first embodiment, the blue laser (DB) and the red laser (DR) are not lit at the same time, the difference in thickness of the disk substrate (DK) and the optical recording surface (sD on the disk substrate (DK)). ) To determine which laser light source (DB, DR) to use. Each optical pickup device has means (not shown) for making the determination, and either the blue laser (DB) or the red laser (DR) is turned on based on the determination there. Only one of the blue and red laser beams (LB, LR) is emitted, and optical information is recorded or reproduced on the optical recording surface (sD).

  Both the blue laser beam (LB) emitted from the blue laser (DB) and the red laser beam (LR) emitted from the red laser (DR) are reflected by the mirror (MR), and then the optical path is synthesized by the dichroic prism (DP). Is done. The dichroic prism (DP) consists of a first mirror surface (M1) that reflects red laser light (LR) and a dichroic film that transmits blue laser light (LB) and reflects red laser light (LR). The second mirror surface (M2), and the two optical paths are combined by the second mirror surface (M2). After the blue laser beam (LB) is transmitted through the second mirror surface (M2), the red laser beam (LR) is reflected by the second mirror surface (M2) and then is collimated by the collimator optical system (CL). Then, it is incident on the first surface (s1) of the wavefront conversion element (WC). In this embodiment, the optical paths of the blue and red laser beams (LB, LR) are combined using a mirror (MR) and a dichroic prism (DP). However, as in the first embodiment, optical path combining means is used. Can be configured not to use a mirror (MR).

  FIG. 13 is a diagram illustrating a schematic optical path of the wavefront conversion element (WC) and the objective lens (OB) in the yz section when using the wavelength λ = 400 to 415 nm in the seventh specific example of the present embodiment. Portions common to those in FIG. 2 are denoted by the same reference numerals and description thereof is omitted. Although not shown in the figure, this specific example can also be used at a wavelength of λ = 640 to 670 nm, and its optical path diagram is the same as FIG. In FIG. 13, the wavefront conversion element (WC) is a parallel plate, and the first diffraction grating surface (D1) is provided only on the first surface (s1) on the light incident side. The first diffraction grating surface (D1) transmits light having a wavelength of 400 to 415 nm without being affected, and diffracts only light having a wavelength of 640 to 670 nm. With this configuration, an optical pickup optical system corresponding to two different wavelengths of 400 to 415 nm and 640 to 670 nm is obtained.

  Next, aberration correction at each wavelength in specific example 7 will be described. When the wavelength λ = 400 to 415 nm is used, the blue laser (DB) is selected from the two laser light sources, and the blue laser light (LB) having the wavelength λ = 400 to 415 nm is emitted as diverging light. The blue laser beam (LB) is reflected by the mirror (MR), passes through the dichroic prism (DP), and is collimated by the collimating optical system (CL). Then, as shown in FIG. ) On the first surface (s1). At this time, since the first diffraction grating surface (D1) provided on the first surface (s1) is transmitted without acting on the light wavefront having the wavelength λ = 400 to 415 nm, the light wavefront is not affected. A parallel light beam enters the objective lens (OB). Here, the objective lens (OB) has been subjected to aberration correction so as to have good aberration performance when using a disk substrate (DK) with a parallel light flux of wavelength λ = 400 to 415 nm and a substrate thickness of 0.1 mm. A spot image with good wavefront aberration is obtained on the optical recording surface (sD) of the substrate (DK).

  When the wavelength λ = 640 to 670 nm is used, the red laser (DR) is selected from the two laser light sources, and the red laser light (LR) having the wavelength λ = 640 to 670 nm is emitted as diverging light. The red laser beam (LR) is reflected by the mirror (MR), passes through the dichroic prism (DP), is converted into a parallel beam by the collimating optical system (CL), and then the first surface (s1) of the wavefront conversion element (WC). ). At this time, since the first diffraction grating surface (D1) provided on the first surface (s1) diffracts the light wavefront having the wavelength λ = 640 to 670 nm, the parallel light beam is converted into a divergent light beam. Accordingly, the divergent light beam diffracted by the first diffraction grating surface (D1) is incident on the objective lens (OB). Here, the objective lens (OB) has been subjected to aberration correction so as to have good aberration performance when using a disk substrate (DK) with a parallel light flux of wavelength λ = 400 to 415 nm and a substrate thickness of 0.1 mm. When a disk substrate (DK) having a substrate thickness of 0.6 mm with a divergent light beam of λ = 640 to 670 nm is used, spherical aberration due to differences in wavelength, object distance, and disk substrate thickness occurs. However, this spherical aberration can be corrected by the same method as in Example 1, and as a result, a spot image with good wavefront aberration can be obtained on the optical recording surface (sD).

  In this way, the wavefront conversion element (WC) provided with a diffraction grating surface provided on the side surface of the light source that transmits the light of the wavelength λ = 400 to 415 nm without affecting and diffracts only the light of the wavelength λ = 640 to 670 nm, When using a disk substrate (DK) with a parallel light flux of wavelength λ = 400 to 415 nm and a substrate thickness of 0.1 mm, combining two objective lenses (OB) that have been corrected for aberrations to achieve good aberration performance Good aberration performance can be obtained at both wavelength and disk substrate thickness.

  14 and 15 show the schematic optical paths of the wavefront conversion element (WC) and the objective lens (OB) when the wavelength λ = 400 to 415 nm and the wavelength λ = 640 to 670 nm, respectively, of the specific example 8 in this embodiment. It is the figure shown by the yz cross section. Portions common to FIGS. 2 and 3 are denoted by the same reference numerals and description thereof is omitted. 14 and 15, the wavefront conversion element (WC) is a parallel plate, and the second diffraction grating surface (D2) is provided only on the second surface (s2) on the disk side. The second diffraction grating surface (D2) transmits light having a wavelength of 400 to 415 nm without being affected, and diffracts only light having a wavelength of 640 to 670 nm. With this configuration, an optical pickup optical system corresponding to two different wavelengths of 400 to 415 nm and 640 to 670 nm is obtained. Aberration correction at each wavelength in this specific example is the same as in specific example 7 except that the diffraction grating surface is provided on the second surface (s2) on the disk side of the wavefront conversion element (WC), and thus description thereof is omitted. To do.

  FIGS. 16 and 17 show schematic optical paths of the wavefront conversion element (WC) and the objective lens (OB) in the yz section when the wavelength λ = 400 to 415 nm is used in specific examples 9 and 10 in the present embodiment. It is a figure. Portions common to those in FIG. 2 are denoted by the same reference numerals and description thereof is omitted. In these specific examples, the wavefront conversion element (WC) in which the second diffraction grating surface (D2) having the same configuration as that of the specific example 8 is provided only on the second surface (s2) on the disk side is used. Although not shown in the figure, each of these specific examples can also be used at a wavelength of λ = 640 to 670 nm, and its optical path diagram is the same as FIG. In addition, aberration correction at each wavelength is the same as in the eighth specific example, and a description thereof will be omitted.

  Next, a third embodiment of the optical pickup device of the present invention will be described. Since the optical configuration of this embodiment is the same as that of the first embodiment (FIG. 1), description thereof is omitted. In this embodiment, the thickness of the disk substrate (DK) corresponding to the blue laser (DB) and the red laser (DR) is equal, and only the thickness of the disk substrate (DK) corresponding to the infrared laser (DIR). Is different. As in the first embodiment, the blue laser (DB), red laser (DR), and infrared laser (DIR) do not turn on at the same time, and are written on the optical recording surface (sD) on the disk substrate (DK). It is determined which laser light source (DB, DR, DIR) is used according to some information. Each optical pickup device has means (not shown) for making the determination, and based on the determination, one of blue laser (DB), red laser (DR), and infrared laser (DIR) Lights up. Only one of blue, red, and infrared laser beams (LB, LR, LIR) is emitted, and optical information is recorded or reproduced on the optical recording surface (sD).

  FIG. 18 is a diagram illustrating a schematic optical path of the wavefront conversion element (WC) and the objective lens (OB) in the yz section when using the wavelength λ = 400 to 415 nm in the eleventh example of the present embodiment. Portions common to those in FIG. 2 are denoted by the same reference numerals and description thereof is omitted. Although not shown in the figure, this specific example can also be used at wavelengths of λ = 640 to 670 nm and λ = 750 to 820 nm, and its optical path diagram is the same as in FIGS. . In FIG. 18, the wavefront conversion element (WC) is a parallel plate, the first diffraction grating surface (D1) is on the first surface (s1) on the light incident side, and the second surface (s2) on the light emission side is the second surface (s2). Two diffraction grating planes (D2) are provided. The first diffraction grating surface (D1) transmits light of wavelengths 400 to 415 nm and 750 to 820 nm without being affected, diffracts only light of wavelength 640 to 670 nm, and the second diffraction grating surface (D2) is Light having wavelengths of 400 to 415 nm and 640 to 670 nm is transmitted without being affected, and only light having a wavelength of 750 to 820 nm is diffracted. With this configuration, an optical pickup optical system corresponding to three different wavelengths of 400 to 415 nm, 640 to 670 nm, and 750 to 820 nm is obtained.

  Next, aberration correction at each wavelength in specific example 11 will be described. When the wavelength λ = 400 to 415 nm is used, the blue laser (DB) is selected from the two laser light sources, and the blue laser light (LB) having the wavelength λ = 400 to 415 nm is emitted as diverging light. The blue laser beam (LB) is reflected by the mirror (MR), passes through the dichroic prism (DP), is converted into a parallel light beam by the collimating optical system (CL), and then, as shown in FIG. ) On the first surface (s1). At this time, since the first diffraction grating surface (D1) provided on the first surface (s1) is transmitted without acting on the light wavefront having the wavelength λ = 400 to 415 nm, the light wavefront is not affected. A parallel light beam enters the objective lens (OB). Here, the objective lens (OB) is corrected for aberration so as to have good aberration performance when using a disk substrate (DK) with a parallel light flux of wavelength λ = 400 to 415 nm and a substrate thickness of 0.6 mm. A spot image with good wavefront aberration is obtained on the optical recording surface (sD) of the substrate (DK).

  When the wavelength λ = 640 to 670 nm is used, a red laser (DR) is selected from the three laser light sources, and a red laser beam (LR) having a wavelength λ = 640 to 670 nm is emitted as diverging light. The red laser beam (LR) is reflected by the mirror (MR), passes through the dichroic prism (DP), is converted into a parallel beam by the collimating optical system (CL), and then the first surface (s1) of the wavefront conversion element (WC). ). At this time, since the first diffraction grating surface (D1) provided on the first surface (s1) diffracts the light wavefront having the wavelength λ = 640 to 670 nm, the parallel light beam is converted into a divergent light beam. Accordingly, the divergent light beam diffracted by the first diffraction grating surface (D1) is incident on the objective lens (OB). Here, the objective lens (OB) has been subjected to aberration correction so as to have good aberration performance when using a disk substrate (DK) with a parallel light flux of wavelength λ = 400 to 415 nm and a substrate thickness of 0.6 mm. When a disk substrate (DK) having a substrate thickness of 0.6 mm with a divergent light beam of λ = 640 to 670 nm is used, spherical aberration due to a difference in wavelength and object distance occurs. However, this spherical aberration can be corrected by the same method as in Example 1 in which each coefficient of the phase function of the first diffraction grating surface (D1) is set to a desired value, and as a result, on the optical recording surface (sD). In this case, a spot image with good wavefront aberration can be obtained.

  When the wavelength λ = 750 to 820 nm is used, an infrared laser (DIR) is selected from the three laser light sources, and an infrared laser beam (LIR) having a wavelength λ = 750 to 820 nm is emitted as diverging light. The infrared laser beam (LIR) passes through the dichroic prism (DP) and is converted into a parallel beam by the collimating optical system (CL), and as shown in FIG. 4, the first surface (s1) of the wavefront conversion element (WC) ). At this time, the first diffraction grating surface (D1) provided on the first surface (s1) is transmitted without acting on the light wavefront having the wavelength λ = 750 to 820 nm. Since the second diffraction grating surface (D2) provided on the second surface (s2) diffracts the light wavefront with a wavelength λ = 750 to 820 nm, only the second diffraction grating surface (D2) is provided on the objective lens (OB). A diffracted divergent light beam enters. Here, the objective lens (OB) has been subjected to aberration correction so as to have good aberration performance when using a disk substrate (DK) with a parallel light flux of wavelength λ = 400 to 415 nm and a substrate thickness of 0.6 mm. When a disc substrate (DK) having a substrate thickness of 1.2 mm with a divergent light beam of λ = 750 to 820 nm is used, spherical aberration due to differences in wavelength, object distance, and disc substrate thickness occurs. However, this spherical aberration can be corrected by the method of Example 1 as in the case of the wavelength λ = 640 to 670 nm, and as a result, a spot image with good wavefront aberration is obtained on the optical recording surface (sD). Will be.

  As described above, the first diffraction grating surface (D1) that allows the light of wavelengths λ = 400 to 415 nm and λ = 750 to 820 nm to pass through without being affected, and diffracts only the light of wavelength λ = 640 to 670 nm, and the wavelength λ Wavefront conversion element provided with a second diffraction grating surface (D2) that diffracts only light having a wavelength of λ = 750 to 820 nm on both sides while allowing light of 400 to 415 nm and λ = 640 to 670 nm to pass through without being affected Combining (WC) with an objective lens (OB) that has been corrected for aberrations to achieve good aberration performance when using a disk substrate (DK) with a parallel luminous flux of wavelength λ = 400 to 415 nm and a substrate thickness of 0.6 mm Accordingly, even when there are two types of disk substrate thicknesses corresponding to three different wavelengths, good aberration performance can be obtained. In addition,

  FIG. 19 is a diagram illustrating a schematic optical path of the wavefront conversion element (WC) and the objective lens (OB) in the yz section when using the wavelength λ = 400 to 415 nm in the twelfth example of the present embodiment. Portions common to those in FIG. 2 are denoted by the same reference numerals and description thereof is omitted. Although not shown in the figure, this specific example can also be used at wavelengths of λ = 640 to 670 nm and λ = 750 to 820 nm, and its optical path diagram is the same as in FIGS. . In FIG. 19, the wavefront conversion element (WC) is a parallel plate, and the second diffraction grating surface (D2) is provided only on the second surface (s2) on the disk side. The second diffraction grating surface (D2) transmits light having a wavelength of 400 to 415 nm and a wavelength of 640 to 670 nm without being affected, and diffracts only light having a wavelength of 750 to 820 nm. A third diffraction grating surface (D3) that diffracts only light having a wavelength λ = 640 to 670 nm is provided on the light incident side surface (s3) of the objective lens (OB). With this configuration, an optical pickup optical system corresponding to three different wavelengths of 400 to 415 nm, 640 to 670 nm, and 750 to 820 nm is obtained. For aberration correction at each wavelength in this specific example, the third diffraction grating surface (D3) is provided on the light incident side surface (s3) of the objective lens (OB), and the light of wavelengths 640 to 670 nm and 750 to 820 nm is emitted. Except for the difference in diffraction order, the description is omitted because it is the same as the specific example 11.

  FIG. 20 is a diagram illustrating a schematic optical path of the wavefront conversion element (WC) and the objective lens (OB) in the yz section when using the wavelength λ = 400 to 415 nm in the thirteenth example according to the present embodiment. Portions common to those in FIG. 2 are denoted by the same reference numerals and description thereof is omitted. Although not shown in the figure, this specific example can also be used at wavelengths of λ = 640 to 670 nm and λ = 750 to 820 nm, and its optical path diagram is the same as in FIGS. . In FIG. 20, the second diffraction grating surface (D2) having the same configuration as in the specific example 12 uses a wavefront conversion element (WC) provided on the second surface (s2) on the disk side, and a third diffraction grating surface ( D3) uses the objective lens (OB) provided with the first surface (s3) on the light source side. In addition, the aberration correction at each wavelength is the same as that in the specific example 12, and thus the description thereof is omitted.

  The wavefront conversion element (WC) and the objective lens (OB) used in specific examples 12 and 13 will be described in more detail. FIG. 21 shows the structures of the wavefront conversion element (WC) and objective lens (OB) used in Example 12 in the xz section. The second diffraction grating surface (D2) provided on the second surface (s2) of the wavefront conversion element (WC) transmits blue laser light (LB) and red laser light (LR), and is an infrared laser. It has a structure that diffracts light (LIR), and the third diffraction grating surface (D3) provided on the light incident side surface (s3) of the objective lens (OB) has blue laser light (LB) and infrared light. It has a structure that transmits laser light (LIR) and diffracts red laser light (LR).

  The second diffraction grating surface (D2) is provided only at the center of the second surface (s2) of the wavefront conversion element (WC), and its range is the numerical aperture when infrared laser light (LIR) is used. A range corresponding to (NA3) is desirable. Here, the effective diameters of the wavefront conversion element (WC) and the objective lens (OB) are the required numerical aperture when using the blue laser beam (LB) (assumed NA1) and the required numerical aperture when using the red laser beam (LR). Since (NA2) is larger than NA3, it becomes larger than the effective diameter at the outermost light beam position when using infrared laser light (LR), and the wavefront conversion element (WC) and objective lens (OB) ) Alone may cause unwanted luminous flux to be incident when using infrared laser light (LIR), which may be undesirable. In that case, it is necessary to use a light shielding means (not shown) for restricting the aperture corresponding to NA3 as a separate body, or for either the wavefront conversion element (WC) or the objective lens (OB).

  As the light shielding means, for example, a dichroic filter that transmits blue laser light (LB) and red laser light (LR) entirely and transmits infrared laser light (LIR) only at the central portion is used. Further, here, a comb-like diffraction grating is provided as the second diffraction grating surface (D2) instead of the step-like diffraction grating as shown in FIG. This is because the laser light diffracted by the second diffraction grating surface (D2) is infrared laser light (LIR), whereas it is red laser light (LR) in FIG. Note that the shape of the diffraction grating is not limited to a comb-like shape, and may be stepped depending on the material of the wavefront conversion element (WC).

  This light shielding means can also be used in the first embodiment or the second embodiment. In that case, the required numerical aperture of each laser beam is in the order of NA1> NA2> NA3, so when using red laser beam (LR) and infrared laser beam (LIR), or when using at least one of the laser beams In this case, it is possible to use a light shielding means that transmits only light having a necessary numerical aperture (NA2 or NA3). For example, when blocking red laser light (LR) and infrared laser light (LIR), only blue laser light (LB) does not transmit red laser light (LR) and infrared laser light (LIR) to the light shielding part. A dichroic filter that transmits light may be used.

  The third diffraction grating surface (D3) is provided on the entire light incident side surface (s3) of the objective lens (OB). As shown in the enlarged view (A) of FIG. A false-tooth diffraction grating (D3b) having the following is used. The red laser beam (LR) transmitted through the second diffraction grating surface (D2) is diffracted by the third diffraction grating surface (D3), and further converged by the lens action of the objective lens (OB) to be optically applied to the disk substrate (DK). An image is formed on the recording surface (sD). On the other hand, the blue laser beam (LB) and the infrared laser beam (LIR) are converged by the lens action of the objective lens (OB) without being influenced by the third diffraction grating surface (D3), and the optical of the disk substrate (DK). An image is formed on the recording surface (sD). Furthermore, by setting each coefficient of the phase function of the second diffraction grating surface (D2) and the third diffraction grating surface (D3) to a desired value, on the optical recording surface (sD) corresponding to the laser beam of each wavelength. A spot image with good wavefront aberration can be obtained. In addition, in the portion where the infrared laser light (LIR) diffracted by the second diffraction grating surface (D2) is not incident, a third diffraction having a diffraction power that flares the infrared laser light (LIR). By using the grating surface (D3), it is possible to adjust the optical path of the infrared laser light (LIR) without providing a light shielding means such as the dichroic filter described above.

  FIG. 22 shows the structures of the wavefront conversion element (WC) and the objective lens (OB) used in Example 13 in the xz section. The configuration and function of the second diffraction grating surface (D2) are the same as those in FIG. Here, the third diffraction grating surface (D3) provided on the light incident side surface (s3) of the objective lens (OB) is blue laser light (LB), red laser light (LR), and infrared laser light ( LIR) is diffracted.

  The light incident side surface (s3) of the objective lens (OB) is provided with a third diffraction grating surface (D3) made of a tooth-like diffraction grating. Here, if the above formulas (DS1), (DS2), and (DS3) are also applied to the blue laser beam (LB) so that the number of stages p and the integer q are in the relationship of the formula (DS2), the Dth order The diffraction efficiencies of blue, red, and infrared laser beams (LB, LR, LIR) can be increased. In this example, each laser beam (LB, LR, LIR) is diffracted by blue laser beam (LB) 8th order, red laser beam (LR) 5th order, and infrared laser beam (LIR) 4th order. ) Diffraction efficiency.

  In Example 13, the diffraction grating surface that diffracts infrared laser light (LIR) is diffracted to the first surface (s1) of the wavefront conversion element (WC) and all laser light (LB, LR, LIR) is diffracted. However, the type of laser light diffracted by the diffraction grating surface or the position where the diffraction grating surface and the total diffraction surface are provided is limited to this. Rather than the diffraction grating surface that diffracts any one of the laser beams (LB, LR, LIR) and all diffraction surfaces that diffract all the laser beams (LB, LR, LIR), the wavefront The first surface (s1), the second surface (s2) of the conversion element (WC), and the light incident side surface (s3) of the objective lens (OB) can be provided at any location.

  Also, phase difference between blue, red, and infrared laser beams (LB, LR, LIR) is generated on any surface of the wavefront conversion element (WC) or objective lens (OB) that does not have a diffraction grating surface. By providing such a surface structure, it is possible to improve chromatic aberration and further suppress changes in the refractive index and thermal expansion of the objective lens (OB) due to temperature changes. In particular, since the objective lens (OB) used in the specific examples 12 and 13 is provided with the third diffraction grating surface (D3) on the light incident side surface (s3), a plastic lens that is easy to manufacture is often used. For this reason, it is more desirable to provide a surface structure in which the optical characteristics of the objective lens (OB) are easily affected by temperature changes and generate a phase difference. In addition, by providing the diffraction grating surface with a phase difference generation function, the diffraction grating surface itself can be used also as the phase difference generation surface. Furthermore, a means for generating a phase difference may be provided in addition to the wavefront conversion element (WC) and the objective lens (OB).

  In the specific examples 7 to 13, the shape of the wavefront conversion element (WC) is a parallel plate. However, as in specific examples 5 and 6, a plano-concave lens shape in which the second surface (s2) on the disk side is a concave surface. It is good. In that case, aberration correction at each wavelength may be performed in the same manner as in the specific examples 5 and 6.

  Each of the above embodiments includes three light sources of blue laser (DB), red laser (DR), and infrared laser (DIR), or two light sources of blue laser (DB) and red laser (DR), Although the optical configuration corresponding to each wavelength is adopted, the wavelength and the number of light sources are not limited to this. If there is a multi-wavelength light source consisting of multiple laser light sources of multiple wavelengths, a wavefront conversion element (WC) is placed between the laser light source and the objective lens (OB) and is common to the laser light of multiple wavelengths By using the optical configuration, it is possible to appropriately use the optical configuration of the type of each embodiment. In other words, a plurality of wavelength light sources composed of a plurality of light sources emitting laser beams having different wavelengths and a plurality of optical information recording media having different thicknesses up to the optical recording surface correspond to the optical recording surfaces of the respective optical information recording media. In an optical pickup device for multiple wavelengths / multiple light sources equipped with an objective lens for focusing laser light of a wavelength, an optical path synthesis means, a collimator optical system, a wavefront conversion element, and an objective lens are arranged from the laser light source side. The optical configuration of each embodiment type may be employed.

In order to realize an easy-to-manufacture, small, high-performance optical pickup device with a wavefront conversion element (WC) that supports multiple wavelengths, blue, red, and infrared lasers (DB, DR) as in each embodiment , DIR), a wavefront conversion element (WC) that converts at least one wavefront shape among multiple wavelength laser beams (LB, LR, LIR) emitted from multiple wavelengths, collimates multiple wavelength laser beams (LB, LR, LIR) Between the collimator optical system (CL) and the objective lens (OB) for focusing a plurality of wavelengths of laser light (LB, LR, LIR) on the optical recording surface (sD) of the optical information recording medium An optical arrangement is desirable. In order to achieve this effectively, it is further desirable that the wavefront conversion element (WC) and the objective lens (OB) satisfy the following conditional expression (A).
2.5 <| fc / fOL | <1000 (A)
However,
fc: Wavefront conversion element focal length when using a wavelength corresponding to the thickest optical information recording medium,
fOL: Objective lens focal length when using a wavelength corresponding to the thickest optical information recording medium,
It is.

  Conditional formula (A) specifies a desirable condition range in order to ensure WD and maintain high performance at each wavelength and substrate thickness even when the disk substrate with the thickest substrate thickness is used. By satisfying the formula (A), it becomes possible to cope with a plurality of substrate thicknesses. Exceeding the upper limit of conditional expression (A) is not desirable because the WD when using the disk substrate with the thickest substrate thickness is shortened and the possibility of collision between the objective lens (OB) and the disk substrate increases. On the other hand, if the lower limit of conditional expression (A) is exceeded, the magnification of the objective lens (OB) when using the thickest substrate thickness increases, off-axis aberrations deteriorate, and This is not desirable because it becomes difficult to correct spherical aberration when the disk substrate thickness changes to a thick substrate thickness. Further, since the error sensitivity to the tilt of the disk substrate of the wavefront conversion element (WC) and the objective lens (OB) is increased, it is not desirable in manufacturing.

In particular, in the first and second embodiments, it is more preferable to satisfy the following conditional expression (A1).
2.5 <| fc / fOL | <50.0 (A1)
However,
fc: Wavefront conversion element focal length when using a wavelength corresponding to the thickest optical information recording medium,
fOL: Objective lens focal length when using a wavelength corresponding to the thickest optical information recording medium,
It is.

In the third embodiment, it is more preferable to satisfy the following conditional expression (A2).
50 <| fc / fOL | <1000 (A2)
However,
fc: Wavefront conversion element focal length when using a wavelength corresponding to the thickest optical information recording medium,
fOL: Objective lens focal length when using a wavelength corresponding to the thickest optical information recording medium,
It is.

Further, it is desirable that the objective lens (OB) used in the optical pickup device as in each embodiment satisfies the following conditional expression (B).
0.3 <d / fB <1.5 (B)
However,
d: Center thickness of the objective lens,
fB: Focal length of the objective lens when using a wavelength corresponding to the thinnest optical information recording medium,
It is.

  Conditional expression (B) defines a desirable condition range in order to ensure WD while achieving high NA and to maintain compactness. For example, when dealing with three substrate thicknesses of BD, DVD, and CD, it is necessary to ensure the WD of the objective lens (OB) when using BD in order to ensure WD when using CD. . If the upper limit of conditional expression (B) is exceeded, it is difficult to ensure WD and the weight of the objective lens (OB) increases, which is not desirable. On the other hand, if the lower limit of conditional expression (B) is exceeded, it is difficult to ensure the thickness of the copa portion of the objective lens (OB), which is not desirable.

In particular, in the first and second embodiments, it is more preferable to satisfy the following conditional expression (B1).
1.0 <d / fB <1.5 (B1)
However,
d: Center thickness of the objective lens,
fB: Focal length of the objective lens when using a wavelength corresponding to the thinnest optical information recording medium,
It is.

In the third embodiment, it is more preferable to satisfy the following conditional expression (B2).
0.4 <d / fB <0.8 (B2)
However,
d: Center thickness of the objective lens,
fB: Focal length of the objective lens when using a wavelength corresponding to the thinnest optical information recording medium,
It is.

Further, it is desirable that the wavefront conversion element (WC) used in the optical pickup device as in the first embodiment and the second embodiment satisfies the following conditional expression (C).
｜ C2c ＊ fc ^ 3 | <800 ・ ・ ・ (C)
However,
C2c: the fourth-order coefficient of the optical path difference function of the diffraction grating surface acting when using the wavelength corresponding to the thickest optical information recording medium,
fc: Wavefront conversion element focal length when using a wavelength corresponding to the thickest optical information recording medium,
It is.

  Conditional expression (C) defines a condition range for correcting spherical aberration generated when a disk substrate having a different substrate thickness is used in an optical pickup device having a high NA to ensure high performance. Exceeding the upper limit of conditional expression (C) is not desirable because the diffraction coefficient becomes too large and high-order aberrations occur. Also, in some cases, the focal length of the wavefront conversion element (WC) when using light with the wavelength corresponding to the thinnest substrate thickness becomes long, and the WD when using light with the wavelength corresponding to the thickest substrate is used. Since securing becomes difficult, it is not desirable.

Furthermore, it is desirable that the light incident side surface (s3) and the disk side surface (s4) of the objective lens (OB) satisfy the following conditional expression (D).
-0.8 <rOF / rOR <0.1 (D)
However,
rOF: radius of curvature of the side of the light source of the objective lens,
rOR: radius of curvature of the optical information recording medium side surface of the objective lens,
It is.

  Conditional expression (D) defines a desirable condition range for securing WD while achieving high NA and maintaining high performance. If the upper limit or lower limit of conditional expression (D) is exceeded, it is difficult to ensure off-axis performance while ensuring the WD of the objective lens (OB), which is not desirable.

Further, it is desirable that the objective lens (OB) satisfies the following conditional expression (E).
0.5 <rOF / fB <0.95 (E)
However,
rOF: radius of curvature of the side of the light source of the objective lens,
fB: Focal length of the objective lens when using a wavelength corresponding to the thinnest optical information recording medium,
It is.

  Conditional expression (E) defines a desirable range of conditions for ensuring ease of manufacture and maintaining high performance in an optical pickup lens having a high NA. Exceeding the upper limit of conditional expression (E) is not desirable because it is difficult to ensure off-axis performance. On the other hand, when the lower limit of conditional expression (E) is exceeded, the radius of curvature becomes too small, and when high NA is achieved, the local tilt of the lens around the objective lens (OB) becomes tight, and the objective lens (OB) is manufactured. This is not desirable because it makes it difficult to manufacture a mold for use in the manufacturing process. In each of the above embodiments, it is particularly preferable that the range is 0.6 to 0.8.

Further, it is desirable that the objective lens (OB) satisfies the following conditional expression (F).
1.1 <| rOR / fB | (F)
However,
rOR: radius of curvature of the disc side of the objective lens,
fB: Focal length of the objective lens when using a wavelength corresponding to the thinnest optical information recording medium,
It is.

  Conditional expression (F) defines a desirable condition range for maintaining high performance in an optical pickup lens having a high NA. Exceeding the lower limit of conditional expression (F) is not desirable because the radius of curvature of the objective lens (OB) becomes too small to ensure off-axis performance. In each of the above embodiments, the range of 1.1 to 50 is particularly preferable.

Further, it is desirable that the objective lens (OB) satisfies the following conditional expression (G).
-10 <θOF-θOR <30 (G)
However,
θOF: an angle formed by a light beam (outermost light beam) incident on the outermost periphery of the effective diameter of the light source side surface of the objective lens with the light source side surface,
θOR: an angle formed by a light beam (outermost light beam) emitted from the outermost periphery of the disk side effective diameter of the objective lens and the disk side surface;
It is.

  Conditional expression (G) defines a desirable condition range for maintaining high performance in an optical pickup lens having a high NA. Exceeding the upper limit or lower limit of conditional expression (G) is not desirable because the off-axis characteristics of the objective lens (OB) deteriorate and the sensitivity to decentering becomes severe. In the first and second embodiments, a range of −10 to 10 is particularly preferable. In the third embodiment, a range of 10 to 20 is preferable.

Furthermore, it is desirable that the objective lens (OB) satisfies the following conditional expression (H).
0.35 <(NO-1) sinθOF <0.8 (H)
However,
NO: refraction at a wavelength corresponding to the thinnest substrate thickness of the objective lens,
θOF: an angle formed by a light beam (outermost light beam) incident on the outermost periphery of the effective diameter of the light source side surface of the objective lens with the light source side surface,
It is.

  Conditional expression (H) defines a desirable range of conditions for ensuring ease of manufacture and maintaining high performance in an optical pickup lens having a high NA. Exceeding the lower limit of conditional expression (H) is not desirable because it becomes difficult to ensure a high NA. On the other hand, if the upper limit of conditional expression (H) is exceeded, θOF becomes extremely large, making it difficult to manufacture the objective lens (OB), or there is no practical optical glass that satisfies the refractive index requirement. Not desirable. In each of the above embodiments, it is particularly preferable that the range is 0.4 to 0.7.

Furthermore, it is desirable that the objective lens (OB) satisfies the following conditional expression (I).
0.2 <(rOR + rOF) / (rOR-rOF) <1.5 (I)
However,
rOF: radius of curvature of the side of the light source of the objective lens,
rOR: radius of curvature of the optical information recording medium side surface of the objective lens,
It is.

  Conditional expression (I) defines a desirable condition range for maintaining high performance in an optical pickup lens having a high NA, and is a conditional expression for correcting spherical aberration in particular. Exceeding the upper limit or lower limit of conditional expression (I) is not desirable because the tilting of the spherical aberration in the third order range becomes large, and the aberration is swelled by correction by higher order, making it difficult to increase the NA.

In addition, the optical pickup device as in each embodiment desirably satisfies the following conditional expression (J).
0.2 <WDb / fB <0.6 (J)
However,
WDb: Working distance when using wavelengths corresponding to the thinnest substrate thickness,
fB: Focal length of the objective lens when using a wavelength corresponding to the thinnest optical information recording medium,
It is.

  Conditional expression (J) defines a desirable condition range in order to secure WD and achieve compactness while achieving high NA. Exceeding the upper limit of conditional expression (J) is not desirable because it is difficult to ensure off-axis aberration performance and the lens diameter increases. On the other hand, if the lower limit of conditional expression (J) is exceeded, the WD is too short and the possibility of collision between the objective lens (OB) and the disk substrate increases, which is not desirable. In the first and second embodiments, a range of 0.2 to 0.4 is particularly preferable, and in the third embodiment, a range of 0.4 to 0.6 is preferable.

When an aspherical surface is used for the light incident side surface (s3) of the objective lens (OB), it is desirable that the following conditional expression (K) is satisfied.
0.2 <αmax-αmin <1.5 (K)
However,
α (h) ≡dz (h) / dh-h / r / (1- (1 + k) * (h / r) ^ 2) ^ 1/2
h: the incident height from the optical axis of the axial ray incident on the aspheric surface,
hmax: the incident height from the optical axis of the on-axis marginal ray incident on the aspheric surface,
z (h): aspherical shape (distance along the optical axis from the apex of the aspherical surface at each height,
z (h) = r- [r ^ 2- (1 + k) ・ h ^ 2] ^ 1/2 (A4 ・ H ^ 4 + A6 ・ H ^ 6 + A8 ・ H ^ 8 ...)
r: aspherical paraxial radius of curvature,
k: conic coefficient,
Ai: i-order aspheric coefficient of h,
dz (h) / dh: differential value with respect to the incident height of the aspheric shape,
f: objective lens focal length,
It is.

When an aspherical surface is used for the disk side surface (s4) of the objective lens (OB), it is desirable that the following conditional expression (L) is satisfied.
0.01 <αmax-αmin <0.2 (L)
However,
α (h) ≡dz (h) / dh-h / r / (1- (1 + k) * (h / r) ^ 2) ^ 1/2
h: the incident height from the optical axis of the axial ray incident on the aspheric surface,
hmax: the incident height from the optical axis of the on-axis marginal ray incident on the aspheric surface,
z (h): aspherical shape (distance along the optical axis from the apex of the aspherical surface at each height,
z (h) = r- [r ^ 2- (1 + k) ・ h ^ 2] ^ 1/2 (A4 ・ H ^ 4 + A6 ・ H ^ 6 + A8 ・ H ^ 8 ...)
r: aspherical paraxial radius of curvature,
k: conic coefficient,
Ai: i-order aspheric coefficient of h,
dz (h) / dh: differential value with respect to the incident height of the aspheric shape,
f: objective lens focal length,
It is.

  Conditional expressions (K) and (L) define a desirable condition range for maintaining high performance in an optical pickup lens having a high NA. If the upper limit of conditional expressions (K) and (L) is exceeded, higher-order aberrations due to aspherical surfaces will occur, making it difficult to correct aberrations.If the lower limit of conditional expressions (K) and (L) is exceeded, aspherical surfaces will occur. Since the aberration correction effect is reduced and spherical aberration correction is particularly difficult, it is not desirable for achieving high performance.

When an aspherical surface is used for the light incident side surface (s3) of the objective lens (OB), it is desirable that the following conditional expression (M) is satisfied.
0.01 <Δ (hmax) / f <0.3 (M)
However,
Δ (h): Distance [Z (H)] in the direction along the optical axis from the apex of the aspherical surface at height h from the optical axis, and the reference quadric surface [≡dz (h) / dh-h / r / (1- (1 + k) * (h / r) ^ 2) ^ 1/2] The difference in the distance along the optical axis from the top of the surface,
h: the incident height from the optical axis of the axial ray incident on the aspheric surface,
hmax: the incident height from the optical axis of the on-axis marginal ray incident on the aspheric surface,
z (h): aspherical shape (distance along the optical axis from the apex of the aspherical surface at each height,
z (h) = r- [r ^ 2- (1 + k) ・ h ^ 2] ^ 1/2 (A4 ・ H ^ 4 + A6 ・ H ^ 6 + A8 ・ H ^ 8 ...)
r: aspherical paraxial radius of curvature,
k: conic coefficient,
Ai: i-order aspheric coefficient of h,
dz (h) / dh: differential value with respect to the incident height of the aspheric shape,
f: objective lens focal length,
It is.

When an aspherical surface is used for the disk side surface (s4) of the objective lens (OB), it is desirable that the following conditional expression (N) is satisfied.
0.001 <Δ (hmax) / f <0.1 (N)
However,
Δ (h): Distance [Z (H)] in the direction along the optical axis from the apex of the aspherical surface at height h from the optical axis, and the reference quadric surface [≡dz (h) / dh-h / r / (1- (1 + k) * (h / r) ^ 2) ^ 1/2] The difference in the distance along the optical axis from the top of the surface,
h: the incident height from the optical axis of the axial ray incident on the aspheric surface,
hmax: the incident height from the optical axis of the on-axis marginal ray incident on the aspheric surface,
z (h): aspherical shape (distance along the optical axis from the apex of the aspherical surface at each height,
z (h) = r- [r ^ 2- (1 + k) ・ h ^ 2] ^ 1/2 (A4 ・ H ^ 4 + A6 ・ H ^ 6 + A8 ・ H ^ 8 ...)
r: aspherical paraxial radius of curvature,
k: conic coefficient,
Ai: i-order aspheric coefficient of h,
dz (h) / dh: differential value with respect to the incident height of the aspheric shape,
f: objective lens focal length,
It is.

  Conditional expressions (M) and (N) define a conditional range desirable for maintaining high performance in an optical pickup lens having a high NA. If the upper limit of conditional expressions (M) and (N) is exceeded, higher-order aberrations due to aspherical surfaces will occur, making it difficult to correct aberrations.If the lower limit of conditional expressions (M) and (N) is exceeded, aspherical surfaces will occur. Since the aberration correction effect is reduced and spherical aberration correction is particularly difficult, it is not desirable for achieving high performance.

  In the above conditional expressions, the preferable condition ranges in the first and second embodiments and the third embodiment are different because of the difference in NA and the thickness of the disk substrate used.

  Moreover, it is desirable that the object distance of the objective lens is infinite when using a disk substrate having all the substrate thicknesses as in the optical pickup device of each embodiment. This is a condition for securing a high NA. As the NA of the objective lens (OB) increases, performance degradation due to errors such as disc substrate tilt and lens eccentricity becomes a problem, but if the lens object distance is finite. This performance deterioration becomes a non-negligible size, which is a practical problem.

  In addition, when the three wavelengths are compatible as in the first and third embodiments, it is possible to cope with using two wavefront conversion elements having a diffraction grating surface on at least one surface. It is preferable to use a single wavefront conversion element having diffraction grating surfaces on both sides because the number of components is reduced. In this case, it is desirable to provide the diffraction grating surface corresponding to the thickest substrate thickness on the disk side surface of the wavefront conversion element and the diffraction grating surface corresponding to the second thickest substrate thickness on the light source side surface of the wavefront conversion element. As the substrate thickness increases, the WD cannot be sufficiently secured unless the total focal length is increased. Therefore, the diffraction grating surface corresponding to the thickest substrate thickness requires more power, but the diffraction power is too strong. This is not desirable because the pitch of the diffraction grating is reduced, which is not preferable in manufacturing, and higher order aberrations are likely to occur. In this case, the power required for a shorter air gap between the diffraction grating surface and the objective lens can be made relatively small. Therefore, it is desirable to provide a diffraction grating surface corresponding to the thickest substrate thickness requiring strong power on the side surface of the disk where the power of the diffraction grating surface can be made relatively small. Even when two or more wavefront conversion elements are used, it is desirable that the wavefront conversion element having the diffraction grating surface corresponding to the thickest substrate thickness is disposed on the most disk side.

  In each of the above specific examples 1 to 11, red laser light is used in the case where laser beams of three wavelengths of blue laser light (LB), red laser light (LR), and infrared laser light (LIR) are compatible. (LR) and infrared laser light (LIR) wavefront conversion element (WC) that converts the wavefront shape is used, and red is used when the two wavelengths of blue laser light (LB) and red laser light (LR) are compatible. A wavefront conversion element (WC) that converts the wavefront shape of laser light (LR) is used. The intensity of currently known blue laser light (LB) is smaller than that of red laser light (LR) and infrared laser light (LIR). Since the diffraction efficiency by the diffraction grating surfaces (D1, D2) is not 100%, when the blue laser light (LB) is diffracted by the wavefront conversion element (WC), the intensity of the blue laser light is undesirably lowered. In addition, when the two wavelengths of blue laser light (LB) and infrared laser light (LIR) are compatible, the wavelength of the infrared laser light (LIR) is λ = 750 nm to 820 nm, and the wavelength λ = 400 to 415 nm. Since it is about twice as much as the laser beam (LB), it is difficult to produce a wavefront conversion element (WC) that diffracts either the blue laser beam (LB) or the infrared laser beam (LIR). Is also not preferred. Therefore, it is desirable that the wavefront shape of the blue laser light (LB) that needs to secure the maximum intensity as in each specific example is transmitted without being converted.

Each of the embodiments described above includes inventions (1) to (16) having the following configuration, and the configuration allows for a compact, high-performance multiple wavelength / multiple substrate equipped with a wavefront conversion element. A laser optical device can be realized.
(1) The wavelength of laser light corresponding to a plurality of wavelength light sources composed of a plurality of light sources that emit laser beams having different wavelengths and a plurality of optical information recording media having different thicknesses from the surface to the optical recording surface are determined. An optical pickup device comprising: an objective lens that focuses laser light of a corresponding wavelength on an optical recording surface of each of the plurality of optical information recording media; A wavefront conversion element having at least one diffraction grating surface that diffracts any one of a plurality of laser beams emitted from a light source and having a function of converting a wavefront shape; and An optical pickup device, wherein the objective lens moves as a unit and satisfies the conditional expression (A1).

(2) The optical pickup device according to (1), wherein the wavefront conversion element is disposed closer to the light source than the objective lens.
(3) The multiple-wavelength light source includes three light sources that emit laser beams having three different wavelengths, and the wavefront conversion element includes two diffraction grating surfaces, and the optical recording surface of the laser beams is included. A diffraction grating surface for diffracting laser light corresponding to the optical information recording medium having the thickest thickness is positioned on the optical information recording medium side, and a diffraction grating surface for diffracting laser light corresponding to the second thickest optical information recording medium is provided. The optical pickup device according to (1) or (2), wherein the optical pickup device is disposed so as to be positioned on a light source side.

(4) The wavefront conversion element allows the wavefront shape of the laser beam corresponding to the optical information recording medium having the smallest thickness to the optical recording surface of the laser beam to pass through without being converted (1) ), (2) or (3).
(5) The optical pickup device according to (1), (2), (3) or (4), wherein the wavefront conversion element satisfies the conditional expression (B1).
(6) The optical pickup device according to (1), (2), (3), (4) or (5), wherein the wavefront conversion element satisfies the conditional expression (C).
(7) A multi-wavelength light source composed of a plurality of light sources emitting laser beams having different wavelengths corresponding to a plurality of optical information recording media, and a laser beam having a wavelength corresponding to the optical recording surface of the plurality of optical information recording media. An optical pickup device including an objective lens that focuses the light from the surface of the optical information recording medium corresponding to the laser light emitted from any two of the plurality of light sources to the optical recording surface. A wavefront conversion element having a function of converting a wavefront shape, having at least one diffraction grating surface that is equal in thickness and diffracts any one of a plurality of laser beams emitted from the plurality of wavelength light sources; The optical pickup device, wherein the wavefront conversion element and the objective lens move together and satisfy the conditional expression (A2).

(8) The optical pickup device according to (7), wherein the wavefront conversion element is disposed closer to the light source than the objective lens.
(9) The multi-wavelength light source includes three light sources that emit laser beams having three different wavelengths, and the wavefront conversion element includes two diffraction grating surfaces, up to an optical recording surface of the laser light. The diffraction grating surface that diffracts the laser beam corresponding to the optical information recording medium with a large thickness is located on the optical information recording medium side, and the diffraction that diffracts the laser beam corresponding to the optical information recording medium with a small thickness to the optical recording surface The optical pickup device according to (7) or (8), wherein the grating surface is disposed on the light source side.

  (10) The multiple-wavelength light source includes three light sources that emit laser beams having three different wavelengths, and the wavefront conversion element and the objective lens each include one diffraction grating surface, and the laser light. Among them, the diffraction grating surface for diffracting the laser beam corresponding to the optical information recording medium having a large thickness up to the optical recording surface is located on the optical information recording medium side, and corresponds to the optical information recording medium having a small thickness up to the optical recording surface. The optical pickup device as described in (7) or (8) above, wherein the diffraction grating surface for diffracting the laser light is disposed on the light source side.

(11) The light described in (7), (8), (9) or (10) above, wherein the diffraction grating surface provided on the objective lens diffracts laser light having three wavelengths Pickup device.
(12) The diffraction grating surface provided on the objective lens diffracts only laser light of one wavelength, (7), (8), (9), or (10) Optical pickup device.
(13) The wavefront conversion element transmits, without converting, the wavefront shape of the laser beam corresponding to the optical information recording medium having the smallest thickness up to the optical recording surface among the laser beams (7). ), (8), (9), (10), (11) or (12).
(14) The objective lens according to (7), (8), (9), (10), (11), (12) or (13), wherein the objective lens satisfies the conditional expression (B2) Optical pickup device.
(15) The optical pickup device according to any one of (1) to (14), wherein the objective lens satisfies the conditional expression (D).
(16) The optical pickup device according to any one of (1) to (15), wherein the object distance of the objective lens is infinite when any of the optical information recording media is used.

  Hereinafter, the optical configurations of the wavefront conversion element (WC) and the objective lens (OB) of the optical pickup device embodying the present invention will be described more specifically with reference to construction data and the like. Examples 1 to 13 listed here are specific examples of the optical configuration from the wavefront conversion element (WC) to the optical recording surface (sD) in each of the above-described embodiments (FIGS. 1 and 12). The wavefront conversion element (WC) and the objective lens (OB) used correspond to the specific examples 1 to 13 (FIGS. 2, 5 to 9, FIGS. 13, 14, and 16 to 20).

  In the construction data of each example, NA (405), NA (408), NA (650), NA (655), NA (780), NA (785) have a wavelength of 405 nm, a wavelength of 408 nm, a wavelength of 650 nm, and a wavelength of 655 nm. , 780nm, NA at wavelength 785nm, OD (405), OD (408), OD (650), OD (655), OD (780), OD (785) are wavelength 405nm, wavelength 408nm, wavelength 650nm , The distance between lens objects at a wavelength of 655 nm, a wavelength of 780 nm, and a wavelength of 785 nm. sj (j = 1, 2, 3,...) is the jth surface counted from the object side. For example, s1 is the light incident side surface (first surface) of the wavefront conversion element (WC), and s2 is the wavefront. It is the light emission side surface (2nd surface) of a conversion element (WC). Rj (j = 1, 2, 3,...) Is the radius of curvature (mm) of the surface sj (j = 1, 2, 3,...), And Tj (j = 1, 2, 3). ,...) Is the j-th axis upper surface interval (heart thickness, mm) counted from the wavefront conversion element (WC) side.

  T5 (405), T5 (408), T5 (650), T5 (655), T5 (780), T5 (785) are at wavelength 405nm, wavelength 408nm, wavelength 650nm, wavelength 655nm, wavelength 780nm, wavelength 785nm, respectively Variable distance (WD, mm) between the light exit side (s4) of the objective lens (OB) and the light entrance side (s5) of the disc substrate (DK), T6 (405), T6 (408), T6 (650), T6 (655), T6 (780), and T6 (785) are disk substrates (DK) used as optical information recording media at wavelengths of 405 nm, 408 nm, 650 nm, 655 nm, 780 nm, and 785 nm, respectively. ) Substrate thickness (mm). Regarding the lens material of each optical element, N (405), N (408), N (650), N (655), N (780), N (785) are wavelength 405nm, wavelength 408nm, wavelength 650nm, wavelength Refractive index at 655 nm, wavelength 780 nm, wavelength 785 m. In addition, the corresponding values of the conditional expressions in each example are as shown in Table 1, Table 2, and Table 3.

The first surface (s1) and / or the second surface (s2) of the wavefront conversion element (WC) used in each embodiment and / or the light incident side surface (s3) of the objective lens (OB) have the following optical paths: It is a diffraction grating surface defined by the formula of the difference function. Wavelength conversion function coefficient (HOE coefficient) with respect to wavelength 650 nm and wavelength 780 nm of the first surface (s1) and / or second surface (s2) of the wavefront conversion element (WC) used in Examples 1 to 11, and Examples 11 is used for the first and second surfaces (s1) and (s2) of the wavefront conversion element (WC) used for the wavelength 11, the wavelength 785 nm, and the coefficient of the optical path difference function (HOE coefficient) with respect to the wavelength 655 nm. The optical path difference function coefficient (HOE coefficient) for the wavelength 785nm and wavelength 408nm of the second surface (s2) of the wavefront conversion element (WC) and the light incident side surface (s3) of the objective lens (OB) is shown together with other data. .
φ (R) = C1 ・ R ² + C2 ・ R ⁴ + C3 ・ R ⁶ + C4 ・ R ⁸ + C5 ・ R ¹⁰
However,
R: distance from the optical axis in the vertical direction from the optical axis,
C1 to C5: HOE coefficients.

The light incident side surface (s3) and the light emission side surface (s4) of the objective lens (OB) used in each example are aspherical surfaces having a surface shape defined by the following equations. The aspherical data of the objective lenses (OB) of Examples 1 to 13 are shown together with other data.
X = CO · Y ² / [1+ {1- (1 + k) · CO ² · Y ² } ^1/2 ] + Σ (Ai · Y ⁱ )
However,
X: Amount of displacement in the optical axis (AX) direction at the position of height Y (based on the surface vertex),
Y: height in the direction perpendicular to the optical axis (AX),
CO: Paraxial curvature (= 1 / rj),
k: cone coefficient,
Ai: i-th order aspheric coefficient,
It is.

  FIGS. 23 to 35 are aberration diagrams corresponding to Examples 1 to 13, respectively. FIGS. 23 to 28 are rays of light having wavelengths λ = 405 nm, wavelength λ = 650 nm, and wavelength λ = 780 nm in Examples 1 to 6, respectively. 29 to 32 show axial wavefront aberrations for the light beams having the wavelengths λ = 405 nm and λ = 650 nm in Examples 7 to 10, and FIGS. 33 to 35 show the axial wavefront aberrations for Examples 11 to 13, respectively. The on-axis wavefront aberration for each light beam having a wavelength λ = 408 nm, a wavelength λ = 655 nm, and a wavelength λ = 785 nm is shown. In each figure, (A) shows the wavefront aberration (Y-FAN) in the y direction, and (B) shows the wavefront aberration (X-FAN) in the x direction.

Example 1
NA (405) = 0.85, NA (650) = 0.60, NA (780) = 0.45
OD (405) = ∞, OD (650) = ∞, OD (780) = ∞
[Surface] [Radius of curvature] [Spacing of shaft upper surface]
s1 r1 = ∞ T1 = 1.000 ・ ・ ・ Wavefront conversion element (WC)
s2 r2 = ∞ T2 = 0.100
Stop r = ∞ T3 = 0.000 ・ ・ ・ Aperture (ST)
s3 r3 = 1.063 T4 = 1.728 ・ ・ ・ Objective lens (OB)
s4 r4 = -6.419 T5 (405) = 0.393, T5 (650) = 0.236, T5 (780) = 0.200
s5 r5 = ∞ T6 (405) = 0.100, T6 (650) = 0.600, T6 (780) = 1.200
s6 r6 = ∞ ・ ・ ・ Optical recording surface (sD)

[Lens material of wavefront conversion element (WC)]
N (405) = 1.52403, N (650) = 1.50619, N (780) = 1.50261
[Lens material for objective lens (OB)]
N (405) = 1.71490, N (650) = 1.69056, N (780) = 1.68568
[Disk substrate (DK) lens material]
N (405) = 1.62100, N (650) = 1.58149, N (780) = 1.57466

[HOE coefficient for wavelength 650nm of first surface (s1)]
C1 = 2.86956 × 10 ^-2 , C2 = 5.23067 × 10 ^-4 , C3 = 2.23798 × 10 ^-3 , C4 = -6.16062 × 10 ^-3 ,
C5 = 1.70385 × 10 ^-3
[HOE coefficient for wavelength 780nm of second surface (s2)]
C1 = 8.50396 × 10 ^-2 , C2 = -2.06007 × 10 ^-3 , C3 = 6.27967 × 10 ^-2 , C4 = -1.03441 × 10 ^-1 ,
C5 = 7.93942 × 10 ^-2

[Aspherical data of 3rd surface (s3)]
k = -0.78777
A4 = 3.57378 × 10 ^-2 , A6 = 1.16622 × 10 ^-2 , A8 = -4.81811 × 10 ^-3 , A10 = 8.89572 × 10 ^-3 ,
A12 = -2.60970 × 10 ^-3 , A14 = -8.85884 × 10 ^-4 , A16 = -2.23337 × 10 ^-4
[Aspherical data of the 4th surface (s4)]
k = -8.17005
A4 = 2.65232 × 10 ^-1 , A6 = -3.95146 × 10 ^-1 , A8 = -2.20783 × 10 ^-1 , A10 = 1.31888,
A12 = -1.26826, A14 = 6.97559 × 10 ^-2 , A16 = 2.83338 × 10 ^-1

Example 2
NA (405) = 0.85, NA (650) = 0.60, NA (780) = 0.45
OD (405) = ∞, OD (650) = ∞, OD (780) = ∞
[Surface] [Radius of curvature] [Spacing of shaft upper surface]
s1 r1 = ∞ T1 = 1.000 ・ ・ ・ Wavefront conversion element (WC)
s2 r2 = ∞ T2 = 0.200
Stop r = ∞ T3 = 0.000 ・ ・ ・ Aperture (ST)
s3 r3 = 1.006 T4 = 1.790 ・ ・ ・ Objective lens (OB)
s4 r4 = -2.777 T5 (405) = 0.382, T5 (650) = 0.224, T5 (780) = 0.220
s5 r5 = ∞ T6 (405) = 0.100, T6 (650) = 0.600, T6 (780) = 1.200
s6 r6 = ∞ ・ ・ ・ Optical recording surface (sD)

[Lens material of wavefront conversion element (WC)]
N (405) = 1.52403, N (650) = 1.50619, N (780) = 1.50261
[Lens material for objective lens (OB)]
N (405) = 1.63279, N (650) = 1.61258, N (780) = 1.60854
[Disk substrate (DK) lens material]
N (405) = 1.62100, N (650) = 1.58149, N (780) = 1.57466

[HOE coefficient for wavelength 650nm of first surface (s1)]
C1 = 2.95000 × 10 ^-2 , C2 = -5.09935 × 10 ^-3 , C3 = 1.39481 × 10 ^-2 , C4 = -1.51340 × 10 ^-2 ,
C5 = 5.02284 × 10 ^-3
[HOE coefficient for wavelength 780nm of second surface (s2)]
C1 = 9.42800 × 10 ^-2 , C2 = -3.45380 × 10 ^-2 , C3 = 1.79465 × 10 ^-1 , C4 = -3.17577 × 10 ^-1 ,
C5 = 2.63999 × 10 ^-1

[Aspherical data of 3rd surface (s3)]
k = -0.76860
A4 = 4.29817 × 10 ^-2 , A6 = 1.74401 × 10 ^-2 , A8 = -6.99716 × 10 ^-3 , A10 = 1.13681 × 10 ^-2 ,
A12 = -1.63368 × 10 ^-3 , A14 = -5.85638 × 10 ^-4 , A16 = -6.08733 × 10 ^-4
[Aspherical data of the 4th surface (s4)]
k = -215.32132
A4 = 1.76621 × 10 ^-1 , A6 = -3.01445 × 10 ^-1 , A8 = -1.47640 × 10 ^-1 ,
A10 = 9.28718 × 10 ^-1 , A12 = -7.45903 × 10 ^-1 , A14 = 0.00000, A16 = 0.00000

Example 3
NA (405) = 0.85, NA (650) = 0.60, NA (780) = 0.45
OD (405) = ∞, OD (650) = ∞, OD (780) = ∞
[Surface] [Radius of curvature] [Spacing of shaft upper surface]
s1 r1 = ∞ T1 = 1.000 ・ ・ ・ Wavefront conversion element (WC)
s2 r2 = ∞ T2 = 0.100
Stop r = ∞ T3 = 0.000 ・ ・ ・ Aperture (ST)
s3 r3 = 1.017 T4 = 1.790 ・ ・ ・ Objective lens (OB)
s4 r4 = -2.023 T5 (405) = 0.380, T5 (650) = 0.220, T5 (780) = 0.309
s5 r5 = ∞ T6 (405) = 0.100, T6 (650) = 0.600, T6 (780) = 1.200
s6 r6 = ∞ ・ ・ ・ Optical recording surface (sD)

[Lens material of wavefront conversion element (WC)]
N (405) = 1.52403, N (650) = 1.50619, N (780) = 1.50261
[Lens material for objective lens (OB)]
N (405) = 1.63279, N (650) = 1.61258, N (780) = 1.60854
[Disk substrate (DK) lens material]
N (405) = 1.62100, N (650) = 1.58149, N (780) = 1.57466

[HOE coefficient for wavelength 650nm of first surface (s1)]
C1 = 2.99211 × 10 ^-2 , C2 = -7.67951 × 10 ^-3 , C3 = 9.91761 × 10 ^-3 , C4 = -4.20539 × 10 ^-3 ,
C5 = -1.55738 × 10 ^-3
[HOE coefficient for wavelength 780nm of second surface (s2)]
C1 = 1.15540 × 10 ^-1 , C2 = -9.86989 × 10 ^-2 , C3 = 4.02044 × 10 ^-1 , C4 = -7.00453 × 10 ^-1 ,
C5 = 5.31749 × 10 ^-1

[Aspherical data of 3rd surface (s3)]
k = -0.76112
A4 = 4.65822 × 10 ^-2 , A6 = 1.31091 × 10 ^-2 , A8 = -5.87111 × 10 ^-3 , A10 = 1.34153 × 10 ^-2 ,
A12 = -3.09232 × 10 ^-3 , A14 = -5.85638 × 10 ^-4 , A16 = -6.08733 × 10 ^-4
[Aspherical data of the 4th surface (s4)]
k = -171.21842
A4 = 2.07813 × 10 ^-1 , A6 = -3.32883 × 10 ^-1 , A8 = -3.57057 × 10 ^-1 ,
A10 = 1.45901, A12 = -1.10995, A14 = 0.00000, A16 = 0.00000

Example 4
NA (405) = 0.85, NA (650) = 0.60, NA (780) = 0.45
OD (405) = ∞, OD (650) = ∞, OD (780) = ∞
[Surface] [Radius of curvature] [Spacing of shaft upper surface]
s1 r1 = ∞ T1 = 1.000 ・ ・ ・ Wavefront conversion element (WC)
s2 r2 = ∞ T2 = 0.100
Stop r = ∞ T3 = 0.000 ・ ・ ・ Aperture (ST)
s3 r3 = 1.014 T4 = 1.790 ・ ・ ・ Objective lens (OB)
s4 r4 = -2.380 T5 (405) = 0.386, T5 (650) = 0.195, T5 (780) = 0.126
s5 r5 = ∞ T6 (405) = 0.100, T6 (650) = 0.600, T6 (780) = 1.200
s6 r6 = ∞ ・ ・ ・ Optical recording surface (sD)

[Lens material of wavefront conversion element (WC)]
N (405) = 1.52403, N (650) = 1.50619, N (780) = 1.50261
[Lens material for objective lens (OB)]
N (405) = 1.63279, N (650) = 1.61258, N (780) = 1.60854
[Disk substrate (DK) lens material]
N (405) = 1.62100, N (650) = 1.58149, N (780) = 1.57466

[HOE coefficient for wavelength 650nm of first surface (s1)]
C1 = 2.25731 × 10 ^-2 , C2 = -8.55794 × 10 ^-3 , C3 = 1.87681 × 10 ^-2 , C4 = -2.18397 × 10 ^-2 ,
C5 = 8.19854 × 10 ^-3
[HOE coefficient for wavelength 780nm of second surface (s2)]
C1 = 8.02340 × 10 ^-2 , C2 = -2.76430 × 10 ^-2 , C3 = 1.05807 × 10 ^-1 , C4 = -1.37306 × 10 ^-1 ,
C5 = 9.29306 × 10 ^-2

[Aspherical data of 3rd surface (s3)]
k = -0.74956
A4 = 5.26687 × 10 ^-2 , A6 = 4.87770 × 10 ^-3 , A8 = -1.77499 × 10 ^-3 , A10 = 1.52966 × 10 ^-2 ,
A12 = -4.31430 × 10 ^-3 , A14 = -5.85638 × 10 ^-4 , A16 = -6.08733 × 10 ^-4
[Aspherical data of the 4th surface (s4)]
k = -365.90830
A4 = 1.75704 × 10 ^-1 , A6 = -2.70446 × 10 ^-1 , A8 = -4.09287 × 10 ^-1 ,
A10 = 1.42390, A12 = -1.04317, A14 = 0.00000, A16 = 0.00000

Example 5
NA (405) = 0.85, NA (650) = 0.60, NA (780) = 0.45
OD (405) = ∞, OD (650) = ∞, OD (780) = ∞
[Surface] [Radius of curvature] [Spacing of shaft upper surface]
s1 r1 = ∞ T1 = 1.000 ・ ・ ・ Wavefront conversion element (WC)
s2 r2 = 52.111 T2 = 0.200
Stop r = ∞ T3 = 0.000 ・ ・ ・ Aperture (ST)
s3 r3 = 1.019 T4 = 1.790 ・ ・ ・ Objective lens (OB)
s4 r4 = -1.761 T5 (405) = 0.390, T5 (650) = 0.223, T5 (780) = 0.202
s5 r5 = ∞ T6 (405) = 0.100, T6 (650) = 0.600, T6 (780) = 1.200
s6 r6 = ∞ ・ ・ ・ Optical recording surface (sD)

[Lens material of wavefront conversion element (WC)]
N (405) = 1.52403, N (650) = 1.50619, N (780) = 1.50261
[Lens material for objective lens (OB)]
N (405) = 1.63279, N (650) = 1.61258, N (780) = 1.60854
[Disk substrate (DK) lens material]
N (405) = 1.62100, N (650) = 1.58149, N (780) = 1.57466

[HOE coefficient for wavelength 650nm of first surface (s1)]
C1 = 3.02583 × 10 ^-2 , C2 = -6.43972 × 10 ^-3 , C3 = 6.35280 × 10 ^-3 , C4 = -7.43016 × 10 ^-3 ,
C5 = 2.19687 × 10 ^-3
[HOE coefficient for wavelength 780nm of second surface (s2)]
C1 = 1.02932 × 10 ^-1 , C2 = -4.93484 × 10 ^-2 , C3 = 1.59277 × 10 ^-1 , C4 = -2.25979 × 10 ^-1 ,
C5 = 1.58002 × 10 ^-1

[Aspherical data of 3rd surface (s3)]
k = -0.78858
A4 = 4.01842 × 10 ^-2 , A6 = 1.39060 × 10 ^-2 , A8 = -8.47108 × 10 ^-3 , A10 = 1.16961 × 10 ^-2 ,
A12 = -1.09175 × 10 ^-3 , A14 = -4.80114 × 10 ^-4 , A16 = -1.30279 × 10 ^-3
[Aspherical data of the 4th surface (s4)]
k = -59.68950
A4 = 2.21321 × 10 ^-1 , A6 = -3.06 150 × 10 ^-1 , A8 = -2.48208 × 10 ^-1 , A10 = 8.99027 × 10 ^-1 ,
A12 = -7.17574 × 10 ^-1 , A14 = 2.29657 × 10 ^-1 , A16 = -9.55758 × 10 ^-2

Example 6
NA (405) = 0.85, NA (650) = 0.60, NA (780) = 0.45
OD (405) = ∞, OD (650) = ∞, OD (780) = ∞
[Surface] [Radius of curvature] [Spacing of shaft upper surface]
s1 r1 = ∞ T1 = 1.000 ・ ・ ・ Wavefront conversion element (WC)
s2 r2 = 27.538 T2 = 0.200
Stop r = ∞ T3 = 0.000 ・ ・ ・ Aperture (ST)
s3 r3 = 1.265 T4 = 2.239 ・ ・ ・ Objective lens (OB)
s4 r4 = -2.082 T5 (405) = 0.520, T5 (650) = 0.407, T5 (780) = 0.440
s5 r5 = ∞ T6 (405) = 0.100, T6 (650) = 0.600, T6 (780) = 1.200
s6 r6 = ∞ ・ ・ ・ Optical recording surface (sD)

[Lens material of wavefront conversion element (WC)]
N (405) = 1.52403, N (650) = 1.50619, N (780) = 1.50261
[Lens material for objective lens (OB)]
N (405) = 1.63279, N (650) = 1.61258, N (780) = 1.60854
[Disk substrate (DK) lens material]
N (405) = 1.62100, N (650) = 1.58149, N (780) = 1.57466

[HOE coefficient for wavelength 650nm of first surface (s1)]
C1 = 2.66979 × 10 ^-2 , C2 = -3.47076 × 10 ^-3 , C3 = 2.84247 × 10 ^-3 , C4 = -1.69027 × 10 ^-3 ,
C5 = 4.13606 × 10 ^-4
[HOE coefficient for wavelength 780nm of second surface (s2)]
C1 = 7.96581 × 10 ^-2 , C2 = -2.37808 × 10 ^-2 , C3 = 4.50089 × 10 ^-2 , C4 = -3.88942 × 10 ^-2 ,
C5 = 1.74021 × 10 ^-2

[Aspherical data of 3rd surface (s3)]
k = -0.79369
A4 = 1.96775 × 10 ^-2 , A6 = 5.04797 × 10 ^-3 , A8 = -1.86623 × 10 ^-3 , A10 = 1.50610 × 10 ^-3 ,
A12 = -8.11143 × 10 ^-5 , A14 = -6.00306 × 10 ^-6 , A16 = -4.25533 × 10 ^-5
[Aspherical data of the 4th surface (s4)]
k = -54.13169
A4 = 1.22106 × 10 ^-1 , A6 = -9.63378 × 10 ^-2 , A8 = -5.69181 × 10 ^-2 , A10 = 1.18928 × 10 ^-1 ,
A12 = -5.30769 × 10 ^-2 , A14 = -4.84329 × 10 ^-4 , A16 = 3.46641 × 10 ^-3

Example 7
NA (405) = 0.85, NA (650) = 0.60
OD (405) = ∞, OD (650) = ∞
[Surface] [Radius of curvature] [Spacing of shaft upper surface]
s1 r1 = ∞ T1 = 1.000 ・ ・ ・ Wavefront conversion element (WC)
s2 r2 = ∞ T2 = 0.500
Stop r = ∞ T3 = 0.000 ・ ・ ・ Aperture (ST)
s3 r3 = 1.056 T4 = 1.728 ・ ・ ・ Objective lens (OB)
s4 r4 = -11.334 T5 (405) = 0.394, T5 (650) = 0.227
s5 r5 = ∞ T6 (405) = 0.100, T6 (650) = 0.600
s6 r6 = ∞ ・ ・ ・ Optical recording surface (sD)

[Lens material of wavefront conversion element (WC)]
N (405) = 1.52403, N (650) = 1.50619
[Lens material for objective lens (OB)]
N (405) = 1.71490, N (650) = 1.69056
[Disk substrate (DK) lens material]
N (405) = 1.62100, N (650) = 1.58149

[HOE coefficient for wavelength 650nm of first surface (s1)]
C1 = 2.60000 × 10 ^-2 , C2 = 5.23067 × 10 ^-4 , C3 = 2.23798 × 10 ^-3 , C4 = -6.16062 × 10 ^-3 ,
C5 = 1.70385 × 10 ^-3

[Aspherical data of 3rd surface (s3)]
k = -0.77796
A4 = 3.67561 × 10 ^-2 , A6 = 1.34312 × 10 ^-2 , A8 = -3.65185 × 10 ^-3 , A10 = 9.06049 × 10 ^-3 ,
A12 = -2.87131 × 10 ^-3 , A14 = -9.77510 × 10 ^-4 , A16 = 1.16698 × 10 ^-4
[Aspherical data of the 4th surface (s4)]
k = 34.11457
A4 = 2.50452 × 10 ^-1 , A6 = -4.08886 × 10 ^-1 , A8 = -1.51988 × 10 ^-1 , A10 = 1.22193,
A12 = -9.37990 × 10 ^-1 , A14 = -3.23790 × 10 ^-1 , A16 = 2.83338 × 10 ^-1

Example 8
NA (405) = 0.85, NA (650) = 0.60
OD (405) = ∞, OD (650) = ∞
[Surface] [Radius of curvature] [Spacing of shaft upper surface]
s1 r1 = ∞ T1 = 0.500 ・ ・ ・ Wavefront conversion element (WC)
s2 r2 = ∞ T2 = 3.000
Stop r = ∞ T3 = 0.000 ・ ・ ・ Aperture (ST)
s3 r3 = 1.261 T4 = 2.261 ・ ・ ・ Objective lens (OB)
s4 r4 = -3.733 T5 (405) = 0.480, T5 (650) = 0.250
s5 r5 = ∞ T6 (405) = 0.100, T6 (650) = 0.600
s6 r6 = ∞ ・ ・ ・ Optical recording surface (sD)

[Lens material of wavefront conversion element (WC)]
N (405) = 1.53020, N (650) = 1.51452
[Lens material for objective lens (OB)]
N (405) = 1.63768, N (650) = 1.61752
[Disk substrate (DK) lens material]
N (405) = 1.62040, N (650) = 1.58093

[HOE coefficient for wavelength 650nm of second surface (s2)]
C1 = 7.08758 × 10 ^-3 , C2 = -1.07758 × 10 ^-3 , C3 = -1.00520 × 10 ^-3 , C4 = 0.00000,
C5 = 0.00000

[Aspherical data of 3rd surface (s3)]
k = -2.44625
A4 = 1.24905 × 10 ^-1 , A6 = -3.90946 × 10 ^-2 , A8 = 2.67850 × 10 ^-2 , A10 = -1.19723 × 10 ^-2 ,
A12 = 2.83223 × 10 ^-3 , A14 = 1.96274 × 10 ^-4 , A16 = -1.80641 × 10 ^-4
[Aspherical data of the 4th surface (s4)]
k = -49.23979
A4 = 2.07900 × 10 ^-1 , A6 = -3.66273 × 10 ^-1 , A8 = 3.37123 × 10 ^-1 , A10 = -1.76649 × 10 ^-1 ,
A12 = 3.99927 × 10 ^-2 , A14 = 0.00000, A16 = 0.00000

Example 9
NA (405) = 0.85, NA (650) = 0.60
OD (405) = ∞, OD (650) = ∞
[Surface] [Radius of curvature] [Spacing of shaft upper surface]
s1 r1 = ∞ T1 = 0.500 ・ ・ ・ Wavefront conversion element (WC)
s2 r2 = ∞ T2 = 3.000
Stop r = ∞ T3 = 0.000 ・ ・ ・ Aperture (ST)
s3 r3 = 1.249 T4 = 2.146 ・ ・ ・ Objective lens (OB)
s4 r4 = -4.437 T5 (405) = 0.530, T5 (650) = 0.300
s5 r5 = ∞ T6 (405) = 0.100, T6 (650) = 0.600
s6 r6 = ∞ ・ ・ ・ Optical recording surface (sD)

[Lens material of wavefront conversion element (WC)]
N (405) = 1.53020, N (650) = 1.51452
[Lens material for objective lens (OB)]
N (405) = 1.63768, N (650) = 1.61752
[Disk substrate (DK) lens material]
N (405) = 1.62040, N (650) = 1.58093

[HOE coefficient for wavelength 650nm of second surface (s2)]
C1 = 6.95093 × 10 ^-3 , C2 = -1.31762 × 10 ^-3 , C3 = -8.79435 × 10 ^-4 , C4 = 0.00000,
C5 = 0.00000

[Aspherical data of 3rd surface (s3)]
k = -2.38871
A4 = 1.25852 × 10 ^-1 , A6 = -3.81552 × 10 ^-2 , A8 = 2.71289 × 10 ^-2 , A10 = -1.21086 × 10 ^-2 ,
A12 = 2.87343 × 10 ^-3 , A14 = 2.04921 × 10 ^-4 , A16 = -1.95906 × 10 ^-4
[Aspherical data of the 4th surface (s4)]
k = -67.66554
A4 = 2.05310 × 10 ^-1 , A6 = -3.68803 × 10 ^-1 , A8 = 3.44747 × 10 ^-1 , A10 = -1.79896 × 10 ^-1 ,
A12 = 3.98869 × 10 ^-2 , A14 = 0.00000, A16 = 0.00000

Example 10
NA (405) = 0.85, NA (650) = 0.60
OD (405) = ∞, OD (650) = ∞
[Surface] [Radius of curvature] [Spacing of shaft upper surface]
s1 r1 = ∞ T1 = 0.500 ・ ・ ・ Wavefront conversion element (WC)
s2 r2 = ∞ T2 = 3.000
Stop r = ∞ T3 = 0.000 ・ ・ ・ Aperture (ST)
s3 r3 = 1.375 T4 = 1.982 ・ ・ ・ Objective lens (OB)
s4 r4 = 23.148 T5 (405) = 0.570, T5 (650) = 0.400
s5 r5 = ∞ T6 (405) = 0.100, T6 (650) = 0.600
s6 r6 = ∞ ・ ・ ・ Optical recording surface (sD)

[Lens material of wavefront conversion element (WC)]
N (405) = 1.53020, N (650) = 1.51452
[Lens material for objective lens (OB)]
N (405) = 1.79976, N (650) = 1.76881
[Disk substrate (DK) lens material]
N (405) = 1.62040, N (650) = 1.58093

[HOE coefficient for wavelength 650nm of second surface (s2)]
C1 = 1.48188 × 10 ^-2 , C2 = -9.21870 × 10 ^-4 , C3 = -7.85189 × 10 ^-4 , C4 = 0.00000,
C5 = 0.00000

[Aspherical data of 3rd surface (s3)]
k = -0.78085
A4 = 1.82393 × 10 ^-2 , A6 = 5.37349 × 10 ^-3 , A8 = -5.80627 × 10 ^-4 , A10 = 7.29054 × 10 ^-4 ,
A12 = -9.87191 × 10 ^-5 , A14 = 1.16531 × 10 ^-4 , A16 = -6.97588 × 10 ^-5
[Aspherical data of the 4th surface (s4)]
k = 461.90878
A4 = 1.25913 × 10 ^-1 , A6 = -1.20455 × 10 ^-1 , A8 = -7.57245 × 10 ^-2 , A10 = 1.53229 × 10 ^-1 ,
A12 = -6.46724 × 10 ^-2 , A14 = 0.00000, A16 = 0.00000

Example 11
NA (408) = 0.67, NA (655) = 0.65, NA (785) = 0.51
OD (408) = ∞, OD (655) = ∞, OD (785) = ∞
[Surface] [Radius of curvature] [Spacing of shaft upper surface]
s1 r1 = ∞ T1 = 1.000 ・ ・ ・ Wavefront conversion element (WC)
s2 r2 = ∞ T2 = 0.500
Stop r = ∞ T3 = 0.000 ・ ・ ・ Aperture (ST)
s3 r3 = 1.968 T4 = 1.700 ・ ・ ・ Objective lens (OB)
s4 r4 = -7.892 T5 (408) = 1.702, T5 (655) = 1.778, T5 (785) = 1.423
s5 r5 = ∞ T6 (408) = 0.600, T6 (655) = 0.600, T6 (785) = 1.200
s6 r6 = ∞ ・ ・ ・ Optical recording surface (sD)

[Lens material of wavefront conversion element (WC)]
N (408) = 1.52424, N (655) = 1.50650, N (785) = 1.50497
[Lens material for objective lens (OB)]
N (408) = 1.55965, N (655) = 1.54073, N (785) = 1.53724
[Disk substrate (DK) lens material]
N (408) = 1.61830, N (655) = 1.57721, N (785) = 1.57042

[HOE coefficient for the first surface (s1) wavelength 655nm]
C1 = -2.54097 × 10 ^-4 , C2 = -1.74855 × 10 ^-4 , C3 = 3.62257 × 10 ^-5 , C4 = -9.70091 × 10 ^-6 ,
C5 = 5.27765 × 10 ^-7
[HOE coefficient for the second surface (s2) wavelength 785nm]
C1 = 3.68962 × 10 ^-4 , C2 = -6.80890 × 10 ^-4 , C3 = 2.10821 × 10 ^-4 , C4 = -8.61298 × 10 ^-5 ,
C5 = 1.05135 × 10 ^-5

[Aspherical data of 3rd surface (s3)]
k = -0.97649
A4 = 1.26572 × 10 ^-2 , A6 = -8.21879 × 10 ^-4 , A8 = 3.58163 × 10 ^-4 , A10 = -5.23840 × 10 ^-5 ,
A12 = 6.12599 × 10 ^-6 , A14 = -3.89913 × 10 ^-7 , A16 = 0.00000
[Aspherical data of the 4th surface (s4)]
k = -154.86307
A4 = 3.39545 × 10 ^-3 , A6 = -7.91767 × 10 ^-4 , A8 = 1.37764 × 10 ^-4 , A10 = -3.28007 × 10 ^-6 ,
A12 = -3.77706 × 10 ^-6 , A14 = 4.66609 × 10 ^-7 , A16 = 0.00000

Example 12
NA (408) = 0.67, NA (655) = 0.65, NA (785) = 0.51
OD (408) = ∞, OD (655) = ∞, OD (785) = ∞
[Surface] [Radius of curvature] [Spacing of shaft upper surface]
s1 r1 = ∞ T1 = 1.000 ・ ・ ・ Wavefront conversion element (WC)
s2 r2 = ∞ T2 = 0.500
Stop r = ∞ T3 = 0.000 ・ ・ ・ Aperture (ST)
s3 r3 = 1.957 T4 = 1.700 ・ ・ ・ Objective lens (OB)
s4 r4 = -8.132 T5 (408) = 1.696, T5 (655) = 1.813, T5 (785) = 1.434
s5 r5 = ∞ T6 (408) = 0.600, T6 (655) = 0.600, T6 (785) = 1.200
s6 r6 = ∞ ・ ・ ・ Optical recording surface (sD)

[Lens material of wavefront conversion element (WC)]
N (408) = 1.52424, N (655) = 1.50650, N (785) = 1.50497
[Lens material for objective lens (OB)]
N (408) = 1.55965, N (655) = 1.54073, N (785) = 1.53724
[Disk substrate (DK) lens material]
N (408) = 1.61830, N (655) = 1.57721, N (785) = 1.57042

[HOE coefficient for the second surface (s2) wavelength 785nm]
C1 = 1.20588 × 10 ^-3 , C2 = -5.69695 × 10 ^-4 , C3 = 1.37827 × 10 ^-4 , C4 = -5.84823 × 10 ^-5 ,
C5 = 6.74986 × 10 ^-6

[HOE coefficient for wavelength 655nm of the third surface (s3)]
C1 = 1.84116 × 10 ^-3 , C2 = -1.53108 × 10 ^-4 , C3 = 6.17271 × 10 ^-5 , C4 = -1.48865 × 10 ^-5 ,
C5 = 9.43634 × 10 ^-7
[Aspherical data of 3rd surface (s3)]
k = -0.99113
A4 = 1.24046 × 10 ^-2 , A6 = -7.64394 × 10 ^-4 , A8 = 3.66967 × 10 ^-4 , A10 = -5.93650 × 10 ^-5 ,
A12 = 6.67568 × 10 ^-6 , A14 = -1.96648 × 10 ^-7 , A16 = 0.00000
[Aspherical data of the 4th surface (s4)]
k = -150.88807
A4 = 2.79389 × 10 ^-3 , A6 = -6.61623 × 10 ^-4 , A8 = 1.51863 × 10 ^-4 , A10 = -6.93035 × 10 ^-6 ,
A12 = -3.60706 × 10 ^-6 , A14 = 4.79148 × 10 ^-7 , A16 = 0.00000

Example 13
NA (408) = 0.67, NA (655) = 0.65, NA (785) = 0.51
OD (408) = ∞, OD (655) = ∞, OD (785) = ∞
[Surface] [Radius of curvature] [Spacing of shaft upper surface]
s1 r1 = ∞ T1 = 1.000 ・ ・ ・ Wavefront conversion element (WC)
s2 r2 = ∞ T2 = 0.500
Stop r = ∞ T3 = 0.000 ・ ・ ・ Aperture (ST)
s3 r3 = 1.817 T4 = 1.700 ・ ・ ・ Objective lens (OB)
s4 r4 = -6.882 T5 (408) = 1.728, T5 (655) = 1.822, T5 (785) = 1.423
s5 r5 = ∞ T6 (408) = 0.600, T6 (655) = 0.600, T6 (785) = 1.200
s6 r6 = ∞ ・ ・ ・ Optical recording surface (sD)

[Lens material of wavefront conversion element (WC)]
N (408) = 1.52424, N (655) = 1.50650, N (785) = 1.50497
[Lens material for objective lens (OB)]
N (408) = 1.55965, N (655) = 1.54073, N (785) = 1.53724
[Disk substrate (DK) lens material]
N (408) = 1.61830, N (655) = 1.57721, N (785) = 1.57042

[HOE coefficient for the second surface (s2) wavelength 785nm]
C1 = -1.01425 × 10 ^-3 , C2 = -5.95922 × 10 ^-4 , C3 = 1.02287 × 10 ^-4 , C4 = -4.75436 × 10 ^-5 ,
C5 = 5.64793 × 10 ^-6

[HOE coefficient for the third surface (s3) wavelength 408nm]
C1 = 1.96332 × 10 ^-3 , C2 = -3.74687 × 10 ^-4 , C3 = 5.66213 × 10 ^-5 , C4 = -1.79483 × 10 ^-5 ,
C5 = 8.10532 × 10 ^-7
[Aspherical data of 3rd surface (s3)]
k = -1.02821
A4 = 1.13640 × 10 ^-2 , A6 = -1.00473 × 10 ^-3 , A8 = 4.84374 × 10 ^-4 , A10 = -9.64162 × 10 ^-5 ,
A12 = 1.28122 × 10 ^-6 , A14 = 9.81309 × 10 ^-7 , A16 = 0.00000
[Aspherical data of the 4th surface (s4)]
k = -127.49381
A4 = 5.75901 × 10 ^-3 , A6 = -1.01375 × 10 ^-3 , A8 = 8.00435 × 10 ^-5 , A10 = 3.63035 × 10 ^-6 ,
A12 = 1.39188 × 10 ^-6 , A14 = -2.98809 × 10 ^-7 , A16 = 0.00000

  As described above, according to the present invention, the wavefront conversion element that converts the wavefront shape of the laser light having a plurality of wavelengths emitted from the plurality of wavelength light sources is disposed between the collimator optical system and the objective lens, and the wavefront conversion element The objective lens and the objective lens move together, and the optical arrangement satisfies the conditional expression (A1). A small optical pickup device can be realized. If the optical pickup device according to the present invention is used, a plurality of types of optical information recording media having different substrate thicknesses can be compatible with a plurality of wavelengths, and the recording density can be improved. . Therefore, when a Blu-ray system is adopted in the next-generation recording media using blue laser light, an optical pickup device having media compatibility capable of supporting the conventional DVD system and CD system is provided. Can do.

  Further, the wavefronts of the laser beams having a plurality of wavelengths emitted from the plurality of wavelength light sources are equal in thickness from the surface of the optical information recording medium to the optical recording surface corresponding to the laser beams emitted from any two of the plurality of light sources. Because it has a wavefront conversion element having a function of converting the shape, and the wavefront conversion element and the objective lens move together, and the optical arrangement satisfies the conditional expression (A2) In the next-generation recording media using blue laser light, when the HD-DVD system is adopted, an optical pickup device having media compatibility with the conventional DVD system and CD system can be provided.

1 is an optical configuration diagram showing a first embodiment of an optical pickup device. FIG. FIG. 5 is a schematic optical path diagram when using a wavelength λ = 400 to 415 nm in a specific example 1 (Example 1) of the wavefront conversion element and the objective lens used in the optical pickup device. The schematic optical path figure at the time of wavelength (lambda) = 640-670nm use of the specific example 1 (Example 1). The schematic optical path figure at the time of wavelength (lambda) = 750-820nm use of the specific example 1 (Example 1). FIG. 6 is a schematic optical path diagram when using a wavelength λ = 400 to 415 nm of a specific example 2 (Example 2) of the wavefront conversion element and the objective lens used in the optical pickup device. FIG. 6 is a schematic optical path diagram when using a wavelength λ = 400 to 415 nm of a specific example 3 (Example 3) of the wavefront conversion element and the objective lens used in the optical pickup device. FIG. 10 is a schematic optical path diagram when using a wavelength λ = 400 to 415n of a specific example 4 (Example 4) of the wavefront conversion element and the objective lens used in the optical pickup device. FIG. 6 is a schematic optical path diagram when using a wavelength λ = 400 to 415 nm of a specific example 5 (Example 5) of the wavefront conversion element and the objective lens used in the optical pickup device. FIG. 10 is a schematic optical path diagram when using a wavelength λ = 400 to 415 nm in a specific example 6 (Example 6) of the wavefront conversion element and the objective lens used in the optical pickup device. The schematic diagram which shows schematic structure of the wavefront conversion element used for 1st Embodiment. The enlarged view which shows the fine structure of the diffraction grating surface in the laser beam incident surface of the wavefront conversion element used for 1st Embodiment. The optical block diagram which shows 2nd Embodiment of an optical pick-up apparatus. FIG. 11 is a schematic optical path diagram when using a wavelength λ = 400 to 415 nm of a specific example 7 (Example 7) of the wavefront conversion element and the objective lens used in the optical pickup device. FIG. 11 is a schematic optical path diagram when using a wavelength λ = 400 to 415 nm in a specific example 8 (Example 8) of the wavefront conversion element and objective lens used in the optical pickup device. The schematic optical path figure at the time of wavelength (lambda) = 640-670nm use of the specific example 8 (Example 8). FIG. 10 is a schematic optical path diagram when using a wavelength λ = 400 to 415 nm of a specific example 9 (Example 9) of the wavefront conversion element and the objective lens used in the optical pickup device. FIG. 11 is a schematic optical path diagram when using a wavelength λ = 400 to 415 nm in a specific example 10 (Example 10) of the wavefront conversion element and the objective lens used in the optical pickup device. FIG. 16 is a schematic optical path diagram when using a wavelength λ = 400 to 415 nm in a specific example 11 (Example 11) of the wavefront conversion element and the objective lens used in the optical pickup device. FIG. 16 is a schematic optical path diagram when using a wavelength λ = 400 to 415 nm in a specific example 12 (Example 12) of the wavefront conversion element and the objective lens used in the optical pickup device. FIG. 14 is a schematic optical path diagram when using a wavelength λ = 400 to 415 nm of a specific example 13 (Example 13) of the wavefront conversion element and the objective lens used in the optical pickup device. FIG. 14 is a schematic diagram showing a schematic configuration of a wavefront conversion element and an objective lens used in Specific Example 12; FIG. 14 is a schematic diagram showing a schematic configuration of a wavefront conversion element and an objective lens used in Specific Example 13; FIG. 6 is an aberration diagram showing on-axis wavefront aberration (wavelength 405 nm, wavelength 650 nm, wavelength 780 nm) of Example 1. FIG. 6 is an aberration diagram showing on-axis wavefront aberration (wavelength 405 nm, wavelength 650 nm, wavelength 780 nm) of Example 2. FIG. 6 is an aberration diagram showing on-axis wavefront aberration (wavelength 405 nm, wavelength 650 nm, wavelength 780 nm) of Example 3. FIG. 6 is an aberration diagram showing on-axis wavefront aberration (wavelength 405 nm, wavelength 650 nm, wavelength 780 nm) of Example 4. FIG. 6 is an aberration diagram showing on-axis wavefront aberration (wavelength 405 nm, wavelength 650 nm, wavelength 780 nm) of Example 5. FIG. 6 is an aberration diagram showing on-axis wavefront aberration (wavelength 405 nm, wavelength 650 nm, wavelength 780 nm) of Example 6. FIG. 10 is an aberration diagram showing on-axis wavefront aberration (wavelength 405 nm, wavelength 650 nm) of Example 7. FIG. 10 is an aberration diagram showing on-axis wavefront aberration (wavelength 405 nm, wavelength 650 nm) of Example 8. FIG. 10 is an aberration diagram showing on-axis wavefront aberration (wavelength 405 nm, wavelength 650 nm) of Example 9. FIG. 11 is an aberration diagram showing on-axis wavefront aberration (wavelength 405 nm, wavelength 650 nm) of Example 10. FIG. 10 is an aberration diagram showing on-axis wavefront aberration (wavelength 408 nm, wavelength 655 nm, wavelength 785 nm) of Example 11. FIG. 18 is an aberration diagram showing the on-axis wavefront aberration (wavelength 408 nm, wavelength 655 nm, wavelength 785 nm) of Example 12. FIG. 14 is an aberration diagram showing the on-axis wavefront aberration (wavelength 408 nm, wavelength 655 nm, wavelength 785 nm) of Example 13.

Explanation of symbols

DB ・ ・ ・ Blue laser (laser light source, first light source)
DR ・ ・ ・ Red laser (laser light source, second light source)
DIR: Infrared laser (laser light source, third light source)
LB ... Blue laser light (laser light of the first wavelength)
LR ... Red laser light (laser light of the second wavelength)
LIR: Infrared laser beam (third wavelength laser beam)
WC ... wavefront conversion element
s1 ・ ・ ・ First surface of wavefront conversion element (light incident side surface)
s2 ・ ・ ・ Second surface of wavefront conversion element (light emission side surface)
D1 ... 1st diffraction grating surface
D2 ... Second diffraction grating surface
D3 ... Third diffraction grating surface
OB ... Objective lens
s3 ・ ・ ・ First surface of objective lens (light incident side surface)
s4 ・ ・ ・ Second surface of the objective lens (light exit side)
DP ... Dichroic prism (light path synthesis means)
CL: Collimator optical system
DK ... Disk substrate (optical information recording medium)
sD ・ ・ ・ Optical recording surface (optical information recording medium)

Claims (16)

A multi-wavelength light source comprising a plurality of light sources that emit laser beams of different wavelengths;
The wavelength of laser light corresponding to a plurality of optical information recording media having different thicknesses from the surface to the optical recording surface is determined, and laser light having a corresponding wavelength is applied to the optical recording surfaces of the plurality of optical information recording media. An objective lens for focusing;
An optical pickup device comprising:
A wavefront conversion element having a function of converting a wavefront shape, comprising at least one diffraction grating surface that diffracts any one of a plurality of laser beams emitted from the plurality of wavelength light sources; An optical pickup device characterized in that the element and the objective lens move together and satisfy the following conditional expression (A1).
2.5 <| fc / fOL | <50.0 (A1)
However,
fc: Wavefront conversion element focal length when using a wavelength corresponding to the thickest optical information recording medium,
fOL: Objective lens focal length when using a wavelength corresponding to the thickest optical information recording medium,
It is.   The optical pickup device according to claim 1, wherein the wavefront conversion element is disposed closer to a light source than the objective lens.   The multi-wavelength light source includes three light sources that emit laser beams having three different wavelengths, the wavefront conversion element includes two diffraction grating surfaces, and the thickness of the laser light to the optical recording surface is The diffraction grating surface that diffracts the laser light corresponding to the thickest optical information recording medium is located on the optical information recording medium side, and the diffraction grating surface that diffracts the laser light corresponding to the second thickest optical information recording medium is on the light source side. The optical pickup device according to claim 1, wherein the optical pickup device is disposed so as to be positioned.   4. The wavefront conversion element according to claim 1, wherein the wavefront conversion element transmits the wavefront shape of the laser light corresponding to the optical information recording medium having the smallest thickness up to the optical recording surface of the laser light without being converted. The optical pick-up apparatus in any one. The optical pickup device according to claim 1, wherein the objective lens satisfies the following conditional expression (B1).
1.0 <d / fB <1.5 (B1)
However,
d: Center thickness of the objective lens,
fB: Focal length of the objective lens when using a wavelength corresponding to the thinnest optical information recording medium,
It is. 6. The optical pickup device according to claim 1, wherein the wavefront conversion element satisfies the following conditional expression (C).
｜ C2c ＊ fc ^ 3 | <800 ・ ・ ・ (C)
However,
C2c: the fourth-order coefficient of the optical path difference function of the diffraction grating surface acting when using the wavelength corresponding to the thickest optical information recording medium
fc: Wavefront conversion element focal length when using a wavelength corresponding to the thickest optical information recording medium,
It is. A multi-wavelength light source comprising a plurality of light sources that emit laser beams of different wavelengths corresponding to a plurality of optical information recording media;
An objective lens that focuses laser light of a corresponding wavelength on the optical recording surfaces of the plurality of optical information recording media;
An optical pickup device comprising:
The thickness from the surface of the optical information recording medium corresponding to the laser light emitted from any two of the plurality of light sources to the optical recording surface is equal, and the laser light of a plurality of wavelengths emitted from the plurality of light sources A wavefront conversion element having at least one diffraction grating surface for diffracting any one of them and having a function of converting a wavefront shape, and the wavefront conversion element and the objective lens move together, An optical pickup device satisfying the following conditional expression (A2):
50 <| fc / fOL | <1000 (A2)
However,
fc: Wavefront conversion element focal length when using a wavelength corresponding to the thickest optical information recording medium,
fOL: Objective lens focal length when using a wavelength corresponding to the thickest optical information recording medium,
It is.   The optical pickup device according to claim 7, wherein the wavefront conversion element is disposed closer to a light source than the objective lens.   The multi-wavelength light source includes three light sources that emit laser beams having three different wavelengths, the wavefront conversion element includes two diffraction grating surfaces, and the thickness of the laser light to the optical recording surface is The diffraction grating surface that diffracts the laser light corresponding to the thick optical information recording medium is located on the optical information recording medium side, and the diffraction grating surface that diffracts the laser light corresponding to the thin optical information recording medium up to the optical recording surface The optical pickup device according to claim 7, wherein the optical pickup device is disposed so as to be positioned on a light source side.   The multi-wavelength light source includes three light sources that emit laser beams having three different wavelengths, and the wavefront conversion element and the objective lens each include one surface of the diffraction grating surface. The diffraction grating surface that diffracts the laser beam corresponding to the optical information recording medium having a large thickness up to the recording surface is positioned on the optical information recording medium side, and the laser beam corresponding to the optical information recording medium having a small thickness to the optical recording surface is used. 9. The optical pickup device according to claim 7, wherein the diffraction grating surface to be diffracted is disposed on the light source side.   11. The optical pickup device according to claim 7, wherein the diffraction grating surface provided on the objective lens diffracts laser light having three wavelengths.   11. The optical pickup device according to claim 7, wherein the diffraction grating surface provided on the objective lens diffracts only one wavelength of laser light.   13. The wavefront converting element transmits the wavefront shape of the laser beam corresponding to the optical information recording medium having the smallest thickness up to the optical recording surface of the laser beam without converting it. The optical pick-up apparatus in any one. The optical pickup device according to claim 7, wherein the objective lens satisfies the following conditional expression (B2).
0.4 <d / fB <0.8 (B2)
However,
d: Center thickness of the objective lens,
fB: Focal length of the objective lens when using a wavelength corresponding to the thinnest optical information recording medium,
It is. The optical pickup device according to claim 1, wherein the objective lens satisfies the following conditional expression (D).
-0.8 <rOF / rOR <0.1 (D)
However,
rOF: radius of curvature of the side of the light source of the objective lens,
rOR: radius of curvature of the optical information recording medium side surface of the objective lens,
It is.   16. The optical pickup device according to claim 1, wherein the object distance of the objective lens is infinite when any of the optical information recording media is used.

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