JP2008165920A - Objective lens optical system, optical pickup optical system - Google Patents

Abstract

Condensation is performed on three or more optical recording media having the same wavelength of light beams condensed on two or more optical recording media and different wavelengths of light beams condensed on two or more optical recording media. To improve the light utilization efficiency of the objective lens optical system and reduce unnecessary light.
The present invention relates to a second optical recording having a light beam having a wavelength λ1 and a light beam having a wavelength λ1 on a data recording surface of a first optical recording medium having a transparent substrate having a thickness t1. This is an objective lens optical system that focuses a light beam having a wavelength λ3 on the information recording surface of a third optical recording medium having a transparent substrate having a thickness t3 on the information recording surface of the medium. The objective lens optical system is divided into regions that are compatible with the same wavelength, and aberrations that cancel out chromatic aberration and the like caused by the difference in the wavelength λ of the light beam are generated in compatible technologies of different wavelengths. The optical path length difference between the first optical recording medium area and the two shared areas adjacent inside and outside was set to 0.5λ or more.
[Selection] Figure 1

Description

  The present invention relates to an objective lens optical system and an optical pickup optical system capable of recording or reproducing information with respect to optical recording media having a plurality of different thicknesses.

  Conventionally, an objective lens optical system for condensing light onto different optical recording media has been developed (for example, see Patent Document 1). The technique disclosed in Patent Document 1 uses a chromatic aberration generated by a difference in wavelength and a wavefront aberration generated by a thickness of a transparent substrate to collect light on two different optical recording media (hereinafter referred to as a compatible technique). Called). However, it is difficult to apply this interchangeable technique when condensing light onto optical recording media having different thicknesses using light of the same wavelength.

  Moreover, there is a technique disclosed in Patent Document 2 as a compatible technique at the same wavelength. In this technique, a polarization plane switching element that selectively switches the polarization direction of the light beam is necessary, and there are problems of increasing the number of components, increasing the size of the objective lens optical system, and increasing the weight of the objective lens optical system.

  As another compatible technology at the same wavelength, as introduced in Patent Document 3, there is a technology for focusing on different optical recording media by dividing the objective lens optical system into regions. However, since each region of the objective lens optical system that focuses on each optical recording medium can be focused only on each of the optical recording media, when focusing on three or more optical recording media, There have been problems such as an increase in laser power due to a decrease in light utilization efficiency and unnecessary light processing.

  Patent Document 4 discloses a technique for solving the problem that each region of the objective lens optical system that focuses on each optical recording medium can be focused only on each optical recording medium. In this technique, an area for condensing two media is provided. However, the diffractive structure is used in the compatible technology in this area, and there is a decrease in the light utilization efficiency due to the diffraction efficiency, and there are still problems such as an increase in laser power and a treatment of unnecessary light due to the decrease in the light utilization efficiency .

JP 2001-195769 A JP 2006-12391 A Japanese Patent Laid-Open No. 10-143905 JP 2000-28917 A

  When the objective lens optical system according to the prior art is used, as described above, there has been a problem of increased laser power and unnecessary light processing due to a decrease in light utilization efficiency.

  According to the present invention, at least three or more light beams having the same wavelength of light beams condensed on at least two or more optical recording media and different wavelengths of light beams condensed on at least two or more optical recording media. An object of the present invention is to provide a high-performance objective lens optical system by improving the light use efficiency of the objective lens optical system for focusing on a recording medium and reducing unnecessary light.

  First, the basic technology of the present invention will be outlined, and then the specific configuration of the present invention will be described.

  In the present invention, first, the objective lens optical system is divided into regions for the same wavelength compatible technology (hereinafter referred to as “compatible technology A”), and the compatible technology for different wavelengths is used on the information recording surface for an arbitrary light beam height. A structure (hereinafter referred to as compatible technology B) that changes the phase so that the aberration at the focal point falls within an allowable range was used.

  In the compatible technology B, wavefront aberration generated when recording / reproducing on the optical recording medium 2 having the substrate thickness t1 with the laser beam having the wavelength λ1 and recording / reproducing on the information recording medium having the substrate thickness t3 with the laser beam having the wavelength λ3 are performed. This is realized by a structure in which the phase is changed so as to compensate for the wavefront aberration generated in the above. Aberrations to be considered in the interchangeable technology B include wavefront aberration (aberration α) caused by a difference in substrate thickness, chromatic aberration (aberration) caused by a difference in refractive index between the objective lens and the optical recording medium substrate based on the difference in laser beam wavelength β), there is chromatic aberration (aberration γ) generated by making the surface of the objective lens a higher-order aspheric surface using the difference in wavelength.

  The interchangeable technology B includes a technology (B1) that enables compatibility by canceling aberration α by aberration β and aberration γ, and a technology (B2) that enables compatibility by canceling aberration β by aberration γ. There is. The former B1 compatible technology is, for example, a high-order that changes the phase so that chromatic aberration (aberration β) caused by a difference in wavelength cancels out wavefront aberration (aberration α) caused by a difference in the thickness of the transparent substrate. This is realized by forming an aspherical structure, and is disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-270528. The latter B2 is a chromatic aberration (aberration γ) that causes a chromatic aberration (aberration β) caused by a difference in wavelength when the substrate thickness is the same as in HDDVD and DVD, but different in wavelength, in a higher-order aspheric structure. It is realized to offset each other.

  As described above, the configuration using both the compatible technology A and the compatible technology B enables compatibility at the same wavelength, enables improvement of light use efficiency in compatibility of different wavelengths, and reduction of unnecessary light. A high-performance objective lens optical system can be provided.

  Second, at least part of the objective lens optical system, the region of the structure that changes the phase is divided by the region of the recording medium that is not condensed in the region of the structure that changes the phase, and inside the divided region, The optical path length difference in the outer region was set to 0.5λ or more for each optical recording medium condensed in the region having a structure for changing the phase. In other words, when it is assumed that the shared area is provided in the entire area of the objective lens, the dedicated area is provided in the area where the absolute value of the wavefront aberration for one of the shared optical recording media or the change thereof is the largest. By adopting such a configuration, it becomes possible to reduce a large aberration of the structure that changes the phase generated by the compatible technology B, and it is possible to provide a high-performance objective lens optical system.

  Third, the relationship between the thickness t1 of the transparent substrate corresponding to the light beam λ1, the thickness t2 of the transparent substrate corresponding to the light beam λ1, and the thickness t3 of the transparent substrate corresponding to the light beam λ3 is expressed as | t3-t1 |> | t3-t2. In the NA area corresponding to t3, the light is not condensed on the optical recording medium corresponding to t1 (Compatible Technology A), but is condensed on the optical recording medium corresponding to t2 and t3 (Compatible Technology B). It was. By adopting such a configuration, in the vicinity of the NA that is difficult to focus on the optical recording medium corresponding to t3, the difference in wavefront aberration due to the difference in thickness corresponds to t2, which is smaller than that in the optical recording medium corresponding to t1. Compatibility with an optical recording medium can be performed, and a high-performance objective lens optical system can be provided.

  Fourth, a region for condensing light onto the optical recording medium corresponding to t1 and t3 is provided inside the NA region corresponding to t3. With such a configuration, the use area of t1 increases, so that the light use efficiency can be improved and unnecessary light can be reduced, and a high-performance objective lens optical system can be provided.

  Fifth, a step shape on the lens surface is used for the structure for changing the phase. By adopting such a configuration, a compatible technique can be provided without adding a new element that changes the phase, so that the objective lens optical system can be reduced in size and weight.

  Sixth, the objective lens optical system has a single lens configuration. By adopting such a configuration, it is possible to provide a compatible technique without adding a compatible element, so that the objective lens optical system can be reduced in size and weight.

  Specifically, the objective lens optical system according to the present invention condenses the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium having the transparent substrate having the thickness t1, and the light beam having the wavelength λ1 has a thickness. A second optical recording medium having a transparent substrate having a thickness t3 and condensing the light beam having a wavelength λ3 (λ3 ≠ λ1) on the information recording surface of the second optical recording medium having a transparent substrate having t2 (t2 ≠ t1). An objective lens optical system having a positive power that focuses light on an information recording surface of a medium and forms a light spot on each information recording surface, wherein the light beam having the wavelength λ1 is converted into information on the second optical recording medium. The first optical recording medium region to be condensed on the information recording surface of the first optical recording medium without condensing on the recording surface, and the luminous flux having the wavelength λ1 are Without condensing on the information recording surface, it is condensed on the information recording surface of the second optical recording medium, And a common area for condensing the light beam having the wavelength λ3 on the information recording surface of the third optical recording medium, and the common area cancels chromatic aberration caused by the difference in the wavelength λ of the light beam. An aspherical shape that generates an aberration is set, and an optical path length difference between the first optical recording medium region and two shared regions adjacent inside and outside is either wavelength λ1 or wavelength λ3. It is characterized by being 0.5λ or more.

  An objective lens optical system according to another aspect of the present invention condenses a light beam having a wavelength λ1 on an information recording surface of a first optical recording medium having a transparent substrate having a thickness t1, and the light beam having a wavelength λ1 has a thickness t2. A third optical recording medium having a transparent substrate having a thickness of t3 and condensing the information recording surface of the second optical recording medium having a transparent substrate of (t2 ≠ t1) and having a wavelength λ3 (λ3 ≠ λ1). An objective lens optical system having a positive power for condensing light on each information recording surface and forming a light spot on each information recording surface, wherein the light beam having the wavelength λ1 is recorded on the information recording surface of the second optical recording medium. A first optical recording medium region to be condensed on the information recording surface of the first optical recording medium without condensing on the surface, and a light beam having the wavelength λ1 to the information on the first optical recording medium Instead of focusing on the recording surface, the light is focused on the information recording surface of the second optical recording medium. And a common area for condensing the light beam having the wavelength λ3 on the information recording surface of the third optical recording medium, and the common area is set to an aspherical shape, and the thickness of the transparent substrate of the optical recording medium is The wavefront aberration caused by the difference, the chromatic aberration caused by the difference in the wavelength λ of the light beam, and the aberration caused by the aspherical shape are canceled out, and the first optical recording medium region and the two common adjacent inside and outside The optical path length difference between the regions is 0.5λ or more for either wavelength λ1 or wavelength λ3.

  An objective lens optical system according to another aspect of the present invention condenses a light beam having a wavelength λ1 on an information recording surface of a first optical recording medium having a transparent substrate having a thickness t1, and the light beam having a wavelength λ1 has a thickness t2. A third optical recording medium having a transparent substrate having a thickness of t3 and condensing the information recording surface of the second optical recording medium having a transparent substrate of (t2 ≠ t1) and having a wavelength λ3 (λ3 ≠ λ1). An objective lens optical system having a positive power for condensing light on each information recording surface and forming a light spot on each information recording surface, wherein the light beam having the wavelength λ1 is recorded on the information recording surface of the second optical recording medium. A first optical recording medium region to be condensed on the information recording surface of the first optical recording medium without condensing on the surface, and a light beam having the wavelength λ1 to the information on the first optical recording medium Instead of focusing on the recording surface, the light is focused on the information recording surface of the second optical recording medium. And a common area for condensing the light beam having the wavelength λ3 on the information recording surface of the third optical recording medium, and the common area cancels chromatic aberration caused by the difference in the wavelength λ of the light beam. When an aspherical shape that generates aberration is set and the common area is provided in the entire area of the objective lens, the wavefront aberration changes relative to the second optical recording medium or the third optical recording medium. The first optical recording medium area is provided.

  An objective lens optical system according to another aspect of the present invention condenses a light beam having a wavelength λ1 on an information recording surface of a first optical recording medium having a transparent substrate having a thickness t1, and the light beam having a wavelength λ1 is thick. Third light having a transparent substrate having a thickness of t3 and condensing the light beam of wavelength λ3 (λ3 ≠ λ1) on the information recording surface of the second optical recording medium having a transparent substrate having a thickness t2 (t2 ≠ t1) An objective lens optical system having a positive power that focuses light on the information recording surface of the recording medium and forms a light spot on each information recording surface, wherein the light beam having the wavelength λ1 is reflected on the second optical recording medium. A first optical recording medium region that is focused on the information recording surface of the first optical recording medium without condensing on the information recording surface, and a light beam having the wavelength λ1 is converted into the first optical recording medium. Without focusing on the information recording surface of the second optical recording medium. And a common area for condensing the light beam having the wavelength λ3 on the information recording surface of the third optical recording medium, the common area having an aspherical shape, and a transparent substrate of the optical recording medium. When the wavefront aberration caused by the difference in thickness and the chromatic aberration caused by the difference in the wavelength λ of the light beam and the aberration caused by the aspherical shape are offset, the second region is provided when the common area is provided in the entire area of the objective lens. The first optical recording medium region is provided in a region where the change in wavefront aberration is largest with respect to the third optical recording medium or the third optical recording medium.

  Here, in a preferred embodiment, the wavelength λ1 is approximately 405 nm, the wavelength λ3 is approximately 655 nm, the substrate thickness t1 is approximately 0.1 mm, the substrate thickness t2 is approximately 0.6 mm, and the substrate thickness t3 is approximately 0. .6 mm.

  An objective lens optical system according to another aspect of the present invention condenses a light beam having a wavelength λ1 on an information recording surface of a first optical recording medium having a transparent substrate having a thickness t1, and the light beam having a wavelength λ1 is thick. Third light having a transparent substrate having a thickness of t3 and condensing the light beam of wavelength λ3 (λ3 ≠ λ1) on the information recording surface of the second optical recording medium having a transparent substrate having a thickness t2 (t2 ≠ t1) An objective lens optical system having a positive power that focuses light on the information recording surface of the recording medium and forms a light spot on each information recording surface, wherein the light beam having the wavelength λ1 is reflected on the second optical recording medium. A first optical recording medium region that is focused on the information recording surface of the first optical recording medium without condensing on the information recording surface, and a light beam having the wavelength λ1 is converted into the first optical recording medium. Without focusing on the information recording surface of the second optical recording medium. And a common area for condensing the light flux of wavelength λ3 on the information recording surface of the third optical recording medium, and the light flux of wavelength λ3 and the light flux of wavelength λ1 incident on the common area are mutually The optical path length difference between the first optical recording medium region and the two shared regions adjacent to the inside and outside is 0.5λ with respect to either wavelength λ1 or wavelength λ3. It is the above, It is characterized by the above.

  Further, the light beam having the wavelength λ1 is condensed on the information recording surface of the first optical recording medium having the transparent substrate having the thickness t1, and the light beam having the wavelength λ1 is condensed to the second having the transparent substrate having the thickness t2 (t2 ≠ t1). And the light beam having the wavelength λ3 (λ3 ≠ λ1) is condensed on the information recording surface of the third optical recording medium having the transparent substrate having the thickness t3. An objective lens optical system having a positive power for forming a light spot on the recording surface, wherein the first light beam having the wavelength λ1 is not condensed on the information recording surface of the second optical recording medium. The first optical recording medium region to be condensed on the information recording surface of the optical recording medium and the light beam having the wavelength λ1 are not condensed on the information recording surface of the first optical recording medium, The light beam having the wavelength λ3 is condensed on the information recording surface of the second optical recording medium, and the third optical recording medium And a light beam having the wavelength λ3 and a light beam having the wavelength λ1 incident on the common area are incident at different angles of incidence, and the common area is formed on the entire objective lens. The first optical recording medium area is provided in an area where the change in wavefront aberration relative to the second optical recording medium or the third optical recording medium is the largest when provided in the area. It is.

  Here, in a preferred embodiment, the wavelength λ1 is about 405 nm, the wavelength λ3 is about 790 nm, the substrate thickness t1 is about 0.1 mm, the substrate thickness t2 is about 0.6 mm, and the substrate thickness t3 is about 1. .2 mm.

  An objective lens optical system according to another aspect of the present invention condenses a light beam having a wavelength λ1 on an information recording surface of a first optical recording medium having a transparent substrate having a thickness t1, and the light beam having a wavelength λ1 has a thickness t2. The light beam having the wavelength λ3 (λ3 ≠ λ1) is condensed on the information recording surface of the second optical recording medium having the transparent substrate (t2 ≠ t1), and the third optical recording medium having the transparent substrate having the thickness t3. The light is condensed on the information recording surface, and the light beam having the wavelength λ4 (λ4 ≠ λ1) is condensed on the information recording surface of the fourth optical recording medium having the transparent substrate having the thickness t4, and a light spot is formed on each information recording surface. An objective lens optical system having a positive power for forming the first optical recording medium without condensing the light beam having the wavelength λ1 on the information recording surface of the second optical recording medium. A first optical recording medium region to be condensed on the information recording surface, and a light beam having the wavelength λ1. The light is condensed on the information recording surface of the second optical recording medium without condensing on the information recording surface of the first optical recording medium, and the light beam having the wavelength λ3 is recorded on the information recording surface of the third optical recording medium. A common region for condensing the light beam having the wavelength λ4 on the information recording surface of the fourth optical recording medium, and collecting the light beam having the wavelength λ3 and the light beam having the wavelength λ1 incident on the common region. Has an aspherical shape that is incident at different incident angles and cancels out chromatic aberration caused by the difference between the wavelengths λ4 and λ1 of the light beam, and is adjacent to the first optical recording medium area on the inner side and the outer side. The optical path length difference between the two shared areas is 0.5λ or more for any one of the wavelengths λ1, λ3, and λ4.

  An objective lens optical system according to another aspect of the present invention condenses a light beam having a wavelength λ1 on an information recording surface of a first optical recording medium having a transparent substrate having a thickness t1, and the light beam having a wavelength λ1 has a thickness t2. The light beam having the wavelength λ3 (λ3 ≠ λ1) is condensed on the information recording surface of the second optical recording medium having the transparent substrate (t2 ≠ t1), and the third optical recording medium having the transparent substrate having the thickness t3. The light is condensed on the information recording surface, and the light beam having the wavelength λ4 (λ4 ≠ λ1) is condensed on the information recording surface of the third optical recording medium having the transparent substrate with the thickness t4, and a light spot is formed on each information recording surface. An objective lens optical system having a positive power for forming the first optical recording medium without condensing the light beam having the wavelength λ1 on the information recording surface of the second optical recording medium. A first optical recording medium region to be condensed on the information recording surface, and a light beam having the wavelength λ1. The light is condensed on the information recording surface of the second optical recording medium without condensing on the information recording surface of the first optical recording medium, and the light beam having the wavelength λ3 is recorded on the information recording surface of the third optical recording medium. A common region for condensing the light beam having the wavelength λ4 on the information recording surface of the fourth optical recording medium, and collecting the light beam having the wavelength λ3 and the light beam having the wavelength λ1 incident on the common region. Is formed with an aspherical shape that is incident at different incident angles and cancels out chromatic aberration caused by the difference between the wavelengths λ4 and λ1 of the light beam, and the common area is provided in the entire area of the objective lens. The first optical recording medium region is provided in a region where the change in wavefront aberration relative to the second optical recording medium, the third optical recording medium, or the fourth optical recording medium is the largest. Is.

  An objective lens optical system according to another aspect of the present invention condenses a light beam having a wavelength λ1 on an information recording surface of a first optical recording medium having a transparent substrate having a thickness t1, and the light beam having a wavelength λ1 has a thickness t2. The light beam having the wavelength λ3 (λ3 ≠ λ1) is condensed on the information recording surface of the second optical recording medium having the transparent substrate (t2 ≠ t1), and the third optical recording medium having the transparent substrate having the thickness t3. The light is condensed on the information recording surface, and the light beam having the wavelength λ4 (λ4 ≠ λ1) is condensed on the information recording surface of the fourth optical recording medium having the transparent substrate having the thickness t4, and a light spot is formed on each information recording surface. An objective lens optical system having a positive power for forming the first optical recording medium without condensing the light beam having the wavelength λ1 on the information recording surface of the second optical recording medium. A first optical recording medium region to be condensed on the information recording surface, and a light beam having the wavelength λ1. The light is condensed on the information recording surface of the second optical recording medium without condensing on the information recording surface of the first optical recording medium, and the light beam having the wavelength λ3 is recorded on the information recording surface of the third optical recording medium. A common region for condensing the light beam having the wavelength λ4 on the information recording surface of the fourth optical recording medium, and collecting the light beam having the wavelength λ3 and the light beam having the wavelength λ1 incident on the common region. Are incident at different angles of incidence, and the shared area is set to be aspherical, and the wavefront aberration caused by the difference in the thickness of the transparent substrate of the second optical recording medium and the fourth optical recording medium The chromatic aberration caused by the difference between the wavelengths λ4 and λ1 of the light beam and the aberration caused by the aspherical shape are canceled out, and the optical path length between the first optical recording medium area and the two shared areas adjacent to the inside and outside The difference between the wavelength λ1, the wavelength λ3, and the wavelength λ4 And 0.5λ or more.

  An objective lens optical system according to another aspect of the present invention condenses a light beam having a wavelength λ1 on an information recording surface of a first optical recording medium having a transparent substrate having a thickness t1, and the light beam having a wavelength λ1 is thick. A second optical recording medium having a transparent substrate having a thickness t3 is focused on the information recording surface of the second optical recording medium having a transparent substrate having a thickness t2 (t2 ≠ t1), and a light beam having a wavelength λ3 (λ3 ≠ λ1) is provided. The light is condensed on the information recording surface of the medium, and the light beam having the wavelength λ4 (λ4 ≠ λ1) is condensed on the information recording surface of the fourth optical recording medium having the transparent substrate having the thickness t4. An objective lens optical system having a positive power for forming a light spot, wherein the first optical recording is performed without condensing the light beam having the wavelength λ1 on the information recording surface of the second optical recording medium. A first optical recording medium region to be condensed on the information recording surface of the medium, and the wavelength λ1 The bundle is not condensed on the information recording surface of the first optical recording medium, but is condensed on the information recording surface of the second optical recording medium, and the light flux having the wavelength λ3 is condensed on the information recording surface of the third optical recording medium. A common region for condensing the light beam having the wavelength λ4 on the information recording surface of the fourth optical recording medium, and collecting the light beam having the wavelength λ3 and the wavelength λ1 incident on the common region. Are incident at different angles of incidence, and the common area is set to be aspheric, and wavefront aberration is caused by the difference in thickness of the transparent substrates of the second and fourth optical recording media. And the chromatic aberration generated by the difference between the wavelengths λ4 and λ1 of the light beam and the aberration generated by the aspherical shape are canceled, and the second optical recording medium, For the third optical recording medium or the fourth optical recording medium The largest area is the change in surface aberration and is characterized in that a first optical recording medium area.

  Here, in a preferred embodiment, the wavelength λ1 is approximately 405 nm, the wavelength λ3 is approximately 790 nm, the wavelength λ4 is approximately 655 nm, the substrate thickness t1 is approximately 0.1 mm, the substrate thickness t2 is approximately 0.6 mm, and the substrate The thickness t3 is approximately 1.2 mm, and the substrate thickness t4 is approximately 0.6 mm.

  On the other hand, the optical pickup optical system according to the present invention condenses the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium having the transparent substrate having the thickness t1, and the light beam having the wavelength λ1 has the thickness t2 ( The second optical recording medium having a transparent substrate with t2 ≠ t1) is focused on the information recording surface of the second optical recording medium, and the light beam with wavelength λ3 (λ3 ≠ λ1) is condensed with the third optical recording medium having the transparent substrate with thickness t3. An optical pickup optical system having a positive power that focuses light on an information recording surface and forms a light spot on each information recording surface, wherein the light beam having the wavelength λ1 is reflected on the information recording surface of the second optical recording medium The first optical recording medium region to be condensed on the information recording surface of the first optical recording medium without condensing the light beam having the wavelength λ1 and the information recording on the first optical recording medium. Condensing on the information recording surface of the second optical recording medium without condensing on the surface. And a common area for condensing the light beam having the wavelength λ3 on the information recording surface of the third optical recording medium, and the common area cancels chromatic aberration caused by the difference in the wavelength λ of the light beam. An aspherical shape that generates an aberration is set, and an optical path length difference between the first optical recording medium region and two shared regions adjacent inside and outside is either wavelength λ1 or wavelength λ3. It is characterized by being 0.5λ or more.

  An optical pickup optical system according to another aspect of the present invention condenses a light beam having a wavelength λ1 on an information recording surface of a first optical recording medium having a transparent substrate having a thickness t1, and a light beam having a wavelength λ1 has a thickness t2. A third optical recording medium having a transparent substrate having a thickness of t3 and condensing the information recording surface of the second optical recording medium having a transparent substrate of (t2 ≠ t1) and having a wavelength λ3 (λ3 ≠ λ1). An optical pickup optical system having a positive power for condensing light on each information recording surface and forming a light spot on each information recording surface, wherein the light beam having the wavelength λ1 is recorded on the information recording surface of the second optical recording medium. A first optical recording medium region to be condensed on the information recording surface of the first optical recording medium without condensing on the surface, and a light beam having the wavelength λ1 to the information on the first optical recording medium Without focusing on the recording surface, the information recording surface of the second optical recording medium And a common area for condensing the light beam having the wavelength λ3 on the information recording surface of the third optical recording medium, and the common area cancels chromatic aberration caused by the difference in the wavelength λ of the light beam. When an aspherical shape that generates such an aberration is set and the common area is provided in the entire area of the objective lens, the change in wavefront aberration with respect to the second optical recording medium or the third optical recording medium is the largest. The first optical recording medium area is provided in a large area.

  An optical pickup optical system according to another aspect of the present invention condenses a light beam having a wavelength λ1 on an information recording surface of a first optical recording medium having a transparent substrate having a thickness t1, and a light beam having a wavelength λ1 has a thickness t2. A third optical recording medium having a transparent substrate having a thickness of t3 and condensing the information recording surface of the second optical recording medium having a transparent substrate of (t2 ≠ t1) and having a wavelength λ3 (λ3 ≠ λ1). An optical pickup optical system having a positive power for condensing light on each information recording surface and forming a light spot on each information recording surface, wherein the light beam having the wavelength λ1 is recorded on the information recording surface of the second optical recording medium. A first optical recording medium region to be condensed on the information recording surface of the first optical recording medium without condensing on the surface, and a light beam having the wavelength λ1 to the information on the first optical recording medium Without focusing on the recording surface, the information recording surface of the second optical recording medium And a common area for condensing the light beam having the wavelength λ3 on the information recording surface of the third optical recording medium, and the common area is set to an aspherical shape, and the transparent substrate of the optical recording medium The wavefront aberration caused by the difference in the thickness of the light beam, the chromatic aberration caused by the difference in the wavelength λ of the light beam, and the aberration caused by the aspherical shape are offset, and the first optical recording medium region is adjacent to the inner side and the outer side. The optical path length difference between the two shared areas is 0.5λ or more for either wavelength λ1 or wavelength λ3.

  An optical pickup optical system according to another aspect of the present invention condenses a light beam having a wavelength λ1 on an information recording surface of a first optical recording medium having a transparent substrate having a thickness t1, and a light beam having a wavelength λ1 has a thickness t2. A third optical recording medium having a transparent substrate having a thickness of t3 and condensing the information recording surface of the second optical recording medium having a transparent substrate of (t2 ≠ t1) and having a wavelength λ3 (λ3 ≠ λ1). An optical pickup optical system having a positive power for condensing light on each information recording surface and forming a light spot on each information recording surface, wherein the light beam having the wavelength λ1 is recorded on the information recording surface of the second optical recording medium. A first optical recording medium region to be condensed on the information recording surface of the first optical recording medium without condensing on the surface, and a light beam having the wavelength λ1 to the information on the first optical recording medium Without focusing on the recording surface, the information recording surface of the second optical recording medium And a common area for condensing the light beam having the wavelength λ3 on the information recording surface of the third optical recording medium, and the common area is set to an aspherical shape, and the transparent substrate of the optical recording medium The wavefront aberration caused by the difference in thickness of the light beam, the chromatic aberration caused by the difference in wavelength λ of the light beam, and the aberration caused by the aspherical shape are offset, and the common area is provided in the entire area of the objective lens. The first optical recording medium region is provided in a region where the change of the wavefront aberration relative to the second optical recording medium or the third optical recording medium is the largest.

  An optical pickup optical system according to another aspect of the present invention condenses a light beam having a wavelength λ1 on an information recording surface of a first optical recording medium having a transparent substrate having a thickness t1, and a light beam having a wavelength λ1 has a thickness t2. A third optical recording medium having a transparent substrate having a thickness of t3 and condensing the information recording surface of the second optical recording medium having a transparent substrate of (t2 ≠ t1) and having a wavelength λ3 (λ3 ≠ λ1). An optical pickup optical system having a positive power for condensing light on each information recording surface and forming a light spot on each information recording surface, wherein the light beam having the wavelength λ1 is recorded on the information recording surface of the second optical recording medium. A first optical recording medium region to be condensed on the information recording surface of the first optical recording medium without condensing on the surface, and a light beam having the wavelength λ1 to the information on the first optical recording medium Without focusing on the recording surface, the information recording surface of the second optical recording medium A shared region that causes light to be collected and collects the light beam having the wavelength λ3 on the information recording surface of the third optical recording medium, and the light beam having the wavelength λ3 and the light beam having the wavelength λ1 incident on the shared region are: The optical path length difference between the first optical recording medium area and the two shared areas adjacent to the inside and outside is incident at different incident angles. It is characterized by being 5λ or more.

  An optical pickup optical system according to another aspect of the present invention condenses a light beam having a wavelength λ1 on an information recording surface of a first optical recording medium having a transparent substrate having a thickness t1, and a light beam having a wavelength λ1 has a thickness t2. A third optical recording medium having a transparent substrate having a thickness of t3 and condensing the information recording surface of the second optical recording medium having a transparent substrate of (t2 ≠ t1) and having a wavelength λ3 (λ3 ≠ λ1). An optical pickup optical system having a positive power for condensing light on each information recording surface and forming a light spot on each information recording surface, wherein the light beam having the wavelength λ1 is recorded on the information recording surface of the second optical recording medium. A first optical recording medium region to be condensed on the information recording surface of the first optical recording medium without condensing on the surface, and a light beam having the wavelength λ1 to the information on the first optical recording medium Without focusing on the recording surface, the information recording surface of the second optical recording medium A shared region that causes light to be collected and collects the light beam having the wavelength λ3 on the information recording surface of the third optical recording medium, and the light beam having the wavelength λ3 and the light beam having the wavelength λ1 incident on the shared region are: When the incident light is incident at different angles of incidence and the shared area is provided in the entire area of the objective lens, the second optical recording medium or the third optical recording medium has the largest change in wavefront aberration. One optical recording medium area is provided.

  An optical pickup optical system according to another aspect of the present invention condenses a light beam having a wavelength λ1 on an information recording surface of a first optical recording medium having a transparent substrate having a thickness t1, and a light beam having a wavelength λ1 has a thickness t2. The light beam having the wavelength λ3 (λ3 ≠ λ1) is condensed on the information recording surface of the second optical recording medium having the transparent substrate (t2 ≠ t1), and the third optical recording medium having the transparent substrate having the thickness t3. The light is condensed on the information recording surface, and the light beam having the wavelength λ4 (λ4 ≠ λ1) is condensed on the information recording surface of the fourth optical recording medium having the transparent substrate having the thickness t4, and a light spot is formed on each information recording surface. An optical pickup optical system having a positive power for forming the first optical recording medium without condensing the light beam having the wavelength λ1 on the information recording surface of the second optical recording medium. A first optical recording medium region to be condensed on the information recording surface; and the wavelength λ1. The light beam is condensed on the information recording surface of the second optical recording medium without being condensed on the information recording surface of the first optical recording medium, and the light beam having the wavelength λ3 is condensed on the information recording surface of the third optical recording medium. A common region for condensing the light beam having the wavelength λ4 on the information recording surface of the fourth optical recording medium and condensing the light beam having the wavelength λ4 and the wavelength λ1 incident on the common region. Are incident at different angles of incidence, and an aspherical shape that cancels out chromatic aberration caused by the difference between the wavelengths λ4 and λ1 of the light beam is set, inside and outside the first optical recording medium region. The optical path length difference between two adjacent shared areas is 0.5λ or more for either wavelength λ1 or wavelength λ3.

  An optical pickup optical system according to another aspect of the present invention condenses a light beam having a wavelength λ1 on an information recording surface of a first optical recording medium having a transparent substrate having a thickness t1, and a light beam having a wavelength λ1 has a thickness t2. The light beam having the wavelength λ3 (λ3 ≠ λ1) is condensed on the information recording surface of the second optical recording medium having the transparent substrate (t2 ≠ t1), and the third optical recording medium having the transparent substrate having the thickness t3. The light is condensed on the information recording surface, and the light beam having the wavelength λ4 (λ4 ≠ λ1) is condensed on the information recording surface of the fourth optical recording medium having the transparent substrate having the thickness t4, and a light spot is formed on each information recording surface. An optical pickup optical system having a positive power for forming the first optical recording medium without condensing the light beam having the wavelength λ1 on the information recording surface of the second optical recording medium. A first optical recording medium region to be condensed on the information recording surface; and the wavelength λ1. The light beam is condensed on the information recording surface of the second optical recording medium without being condensed on the information recording surface of the first optical recording medium, and the light beam having the wavelength λ3 is condensed on the information recording surface of the third optical recording medium. A common region for condensing the light beam having the wavelength λ4 on the information recording surface of the fourth optical recording medium and condensing the light beam having the wavelength λ4 and the wavelength λ1 incident on the common region. Are incident at different incident angles, and an aspherical shape that cancels out chromatic aberration caused by the difference between the wavelengths λ4 and λ1 of the light beam is set, and the common area is provided in the entire area of the objective lens In addition, the first optical recording medium region is provided in a region where the change in wavefront aberration relative to the second optical recording medium, the third optical recording medium, or the fourth optical recording medium is the largest. It is what.

  An optical pickup optical system according to another aspect of the present invention condenses a light beam having a wavelength λ1 on an information recording surface of a first optical recording medium having a transparent substrate having a thickness t1, and a light beam having a wavelength λ1 has a thickness t2. The light beam having the wavelength λ3 (λ3 ≠ λ1) is condensed on the information recording surface of the second optical recording medium having the transparent substrate (t2 ≠ t1), and the third optical recording medium having the transparent substrate having the thickness t3. The light is condensed on the information recording surface, and the light beam having the wavelength λ4 (λ4 ≠ λ1) is condensed on the information recording surface of the fourth optical recording medium having the transparent substrate having the thickness t4, and a light spot is formed on each information recording surface. An optical pickup optical system having a positive power for forming the first optical recording medium without condensing the light beam having the wavelength λ1 on the information recording surface of the second optical recording medium. A first optical recording medium region to be condensed on the information recording surface; and the wavelength λ1. The light beam is condensed on the information recording surface of the second optical recording medium without being condensed on the information recording surface of the first optical recording medium, and the light beam having the wavelength λ3 is condensed on the information recording surface of the third optical recording medium. A common region for condensing the light beam having the wavelength λ4 on the information recording surface of the fourth optical recording medium, and collecting the light beam having the wavelength λ3 and the wavelength λ1 incident on the common region. Are incident at different angles of incidence, and the common area is set to be aspheric, and wavefront aberration is caused by the difference in the thickness of the transparent substrates of the second optical recording medium and the fourth optical recording medium. And the chromatic aberration generated by the difference between the wavelengths λ4 and λ1 of the light beam and the aberration generated in the aspherical shape are canceled out, and the first optical recording medium region and the two shared regions adjacent to the inner side and the outer side are arranged. The optical path length difference is either wavelength λ1, wavelength λ3, or wavelength λ4. It is characterized in that at least 0.5λ the length lambda.

  An optical pickup optical system according to another aspect of the present invention condenses a light beam having a wavelength λ1 on an information recording surface of a first optical recording medium having a transparent substrate having a thickness t1, and a light beam having a wavelength λ1 has a thickness t2. The light beam having the wavelength λ3 (λ3 ≠ λ1) is condensed on the information recording surface of the second optical recording medium having the transparent substrate (t2 ≠ t1), and the third optical recording medium having the transparent substrate having the thickness t3. The light is condensed on the information recording surface, and the light beam having the wavelength λ4 (λ4 ≠ λ1) is condensed on the information recording surface of the fourth optical recording medium having the transparent substrate having the thickness t4, and a light spot is formed on each information recording surface. An optical pickup optical system having a positive power for forming the first optical recording medium without condensing the light beam having the wavelength λ1 on the information recording surface of the second optical recording medium. A first optical recording medium region to be condensed on the information recording surface; and the wavelength λ1. The light beam is condensed on the information recording surface of the second optical recording medium without being condensed on the information recording surface of the first optical recording medium, and the light beam having the wavelength λ3 is condensed on the information recording surface of the third optical recording medium. A common region for condensing the light beam having the wavelength λ4 on the information recording surface of the fourth optical recording medium, and collecting the light beam having the wavelength λ3 and the wavelength λ1 incident on the common region. Are incident at different angles of incidence, and the common area is set to be aspheric, and wavefront aberration is caused by the difference in thickness of the transparent substrates of the second and fourth optical recording media. And the chromatic aberration generated by the difference between the wavelengths λ4 and λ1 of the light beam and the aberration generated by the aspherical shape are canceled, and the second optical recording medium, For the third optical recording medium or the fourth optical recording medium The largest area change of the wavefront aberration and is characterized in that a first optical recording medium area.

  In this specification, the laser wavelength corresponding to the first optical recording medium having the thickness t1 and the laser wavelength corresponding to the second optical recording medium having the thickness t2 are described as λ1, but they are limited to use of the same laser. Instead, different lasers may be used. Therefore, λ1 in the present specification has a certain width.

  According to the present invention, at least three or more of the wavelengths of the light beams condensed on at least two or more optical recording media are the same, and the wavelengths of the light beams collected on at least two or more optical recording media are different. It is possible to provide a high-performance objective lens optical system by improving the light use efficiency of the objective lens optical system that focuses light on the optical recording medium and reducing unnecessary light.

An objective lens optical system according to an embodiment of the present invention, which will be described in detail later, basically uses a CD such as a BD (Blu-ray Disc), an HDDVD (High Definition Digital Versatile Disc), and a CD (Compact Disc: CD-R). And 4 (DVD) (Digital Versatile Disc) compatibility is realized. In order to realize 4 compatibility, three degrees of freedom are required. As a result of searching for the degrees of freedom as candidates, it was found that the degrees of freedom could be secured by the following three measures, thereby realizing compatibility with four systems.
(Measure 1) Measure by dividing the region (light flux) (corresponding to the above compatible technology A)
(Countermeasure 2) Measure by higher-order aspherical surface (equivalent to the above compatible technology B)
(Measure 3) Measure by incident angle

  In addition, the compatibility of the three measures described above was examined.

  First, the combinations to which Strategy 1 should be applied were examined. Policy 1 by this region division can be determined by selecting a combination to which policy 2 or policy 3 cannot be applied. Here, Measure 2 cannot be applied to compatibility of the same wavelength, and Measure 3 cannot be applied to compatibility using the same laser light source. Then, since BD and HDDVD have the same blue wavelength (408 nm or 405 nm), Measure 2 cannot be applied, and the use of two lasers for the same wavelength can reduce the cost of the optical pick optical system and the number of parts. In order to increase, it is preferable to use the same laser. In this case, since the method 3 cannot be applied, the method 1 is applied. At this time, the division of the region can be selected in the range of 2 to 4 divisions, but the light use efficiency decreases as the number of divisions increases, so that the division is made into 2 divisions. In addition, in order to reduce the optical system by ensuring the working distance of the CD, it is possible to further divide into three by providing a dedicated CD area.

  Next, the combinations to which the measures 2 and 3 should be applied were examined from the two viewpoints of aberration performance and light utilization efficiency. Measure 2 is a measure that enables compatibility by canceling aberration α by aberration β and aberration γ, as described in Compatibility Technology B above.

First, it was considered to make the compatibility between the blue wavelength use medium (BD or HDDVD) and the CD by the measure 2. Optical path length difference OPD _Blue = 2λ _Blue (where λ _Blue is the wavelength of the blue wavelength laser light) with respect to the blue wavelength laser light, and the optical path length difference is determined so as to be insensitive to the blue wavelength laser light. , Because the optical path length difference OPD _{CD with} respect to the laser beam of _CD is d (n _Blue −1) × 2 × 405 nm, 0.9913λ _CD (where λ _CD is the wavelength of the laser beam of the CD) as follows: It becomes.

OPD _CD = d (n _CD −1) = (n _CD −1) / (n _Blue −1) × 2 × 405 nm / 790 nm = 0.9913λ _CD
Here, the step is d, the refractive index for the blue laser beam is n _Blue , and the refractive index for the CD laser beam is n _CD, and the values shown in FIG. 10 are used.

In terms of aberrations, an aberration can be generated only by 9 mλ _CD (1/13 in the case of DVD) with one step, so that the desired aberration is generated unless the number of steps is increased. I can't. Here, when the number of steps is increased, scattering occurs at the steps, resulting in problems such as reduced light use efficiency, generation of unnecessary light, and difficulty in processing with high accuracy. Therefore, it is not appropriate to make the compatibility between the blue wavelength use medium (BD or HDDVD) and the CD by the measure 2.

  On the other hand, the difference in substrate thickness between BD and CD is 1.1 mm, whereas between HDDVD and CD is only 0.6 mm, it is preferable to achieve compatibility between HDDVD and CD. . Thereby, the difference in incident angle can be reduced, and the deterioration of the lens shift characteristic due to the increase in incident angle can be prevented. For example, when an infinite system is used for HDDVD and a finite system is used for CD, aberration α and aberration β can be compensated even if the difference in incident angle is small. Here, basically, it is optimal to achieve compatibility between the HDDVD and the CD by the measure 3.

  Up to this point, it has been determined that it is optimal that BD and HDDVD be compatible with Measure 1 and that CD be compatible with HDDVD and Measure 3.

  Finally, DVD can be interchanged with HDDVD by Measure 2. Although compatibility between DVD and BD may be considered for DVD, the difference in substrate thickness between DVD and HDDVD is smaller than that between DVD and BD. Is optimal.

In this way, it has been found that it is an optimal four-system compatible form to use the BD as a dedicated area and the other HDDVD, CD and DVD as a shared area.
Here, it examined from the viewpoint of light utilization efficiency. In the light beam splitting strategy, since the focal length of each region can be set freely, the effective diameter can be set freely. For blue wavelength media (BD or HDDVD), it is necessary to divide the speed of light because it is a single laser for the reasons described above, but in the end it is not necessary to divide the speed of light because DVDs and CDs are often dedicated lasers. It is. For example, consider the case where the BD dedicated area and the three-wavelength shared area of HDDVD, DVD, and CD are divided. The area ratio with respect to the luminous flux of BD and HDDVD using a blue laser is divided into two regions of 50% and 50%. At this time, since the effective diameters Φ _BD and Φ _HD are Φ _BD ² × π−Φ _HD ² × π: Φ _HD ² × π = 1: 1, 2 × Φ _HD ² = Φ _BD ² is satisfied. The HDDVD area is arranged in the inner area, and the BD dedicated area is arranged outside. Here, if the required NAs are 0.85 and 0.65, respectively, the paraxial theory represents the effective diameter Φ = 2 × f × NA. Therefore, the respective focal lengths are expressed as f _BD : f _HD = Φ _BD /1.7:Φ _HD /1.3≈0.924:1. At this time, since the DVD and CD are formed in a shared area with the _HD , the area in the Φ _HD is used. For this reason, DVD lasers and CD lasers can enter a light beam with respect to each effective diameter, and can use an area of 100% with respect to the light beam. That is, 50%, 50%, 100%, and 100% of the use area of BD, HD, DVD, and CD can be realized.

  In addition, as a structure in which the HD dedicated area and the shared area of BD, DVD, and CD are divided, it is possible to realize 50%, 50%, 100%, and 100% use areas of the light beam splitting BD, HD, DVD, and CD as described above. I understand that. However, the former configuration is optimal from the consideration of the compatibility method. Further, although it is desirable to divide into two areas from the viewpoint of the use area, the BD dedicated area is allocated in the common area in consideration of the light beam interference and the working distance.

  The objective lens optical system of the present embodiment has a configuration capable of focusing on the four types of optical recording media specified in FIG. Specifically, the optical recording medium 1 is BD, the optical recording medium 2 is HDDVD, the optical recording medium 3 is CD, and the optical recording medium 4 is DVD. As shown in the figure, the optical recording medium 1 and the optical recording medium 2 have the same wavelength of the condensed light beam.

  In addition, the optical recording medium 3 and the optical recording medium 4 have different wavelengths of light beams to be collected, and the optical recording medium 3 and the optical recording medium 4 have different wavelengths of light beams to be collected. . Further, the optical recording medium 2 and the optical recording medium 4 have the same transparent substrate thickness, but are different from the optical recording medium 1 and the optical recording medium 4. The thicknesses of the transparent substrates of the optical recording medium 1 and the optical recording medium 4 are different.

Comparative example.
In order to explain the superiority of the present invention, a comparative example will be described first. This comparative example does not constitute a known technique.

  The objective lens optical system according to the comparative example is composed of a single lens. FIG. 10 shows the effective diameter of the light beam incident on each optical recording medium and the refractive index of the lens material used for this objective lens.

  Lens data and surface shape data of the objective lens optical system according to the comparative example are shown in FIGS. Here, the surface shape data shown in FIG. 13 is expressed by the following equation (1). The objective lens surface 1 was divided into medium regions and surface regions using aspherical coefficients up to the sixth order, and each surface region formed a step shape. The objective lens surface 2 used aspherical coefficients up to the 16th order.

z is an aspherical zag amount and indicates a distance from the tangential plane on the optical axis of the aspherical surface at a coordinate point on the aspherical surface where the height from the optical axis is r. k represents a conic constant (coefficient). c represents the curvature (1 / curvature radius) on the optical axis of the aspherical surface. r is the height of the light beam from the optical axis. α ₁ , ₂ ,... indicate aspheric coefficients. Zshift indicates the amount of deviation of the optical axis intersection when each surface region is formed up to the optical axis.

  Next, a schematic configuration of an objective lens optical system according to a comparative example and each embodiment described later will be described with reference to FIG.

  In the figure, 100 is an objective lens, 200 is an optical recording medium (transparent substrate), 201 is an information recording surface, and 300 is a light beam. The objective lens 100 is used in common for each of the optical recording media 1 to 4. In FIGS. 1A to 1D, a light beam 300 indicates only a light beam condensed on the information recording surface 201 of each optical recording medium 200.

  As is clear from FIGS. 1A and 1B, on the incident surface of the objective lens 100, a region that is focused on the optical recording medium 1 and a region that is focused on the optical recording medium 2 are a partial region. It is designed so that it does not overlap except for (in this example, the central region). This is because the optical recording medium 1 and the optical recording medium 2 have the same wavelength of the light beam to be used, but have different transparent substrate thicknesses, so that it is not possible to use the compatible technology B that utilizes the difference in wavelength. Therefore, the compatible technology A that divides the area is used.

  Further, as is apparent from FIGS. 1A, 1C, and 1D, on the incident surface of the objective lens 100, an area focused on the optical recording medium 1, an area focused on the optical recording medium 3, and The areas focused on the optical recording medium 4 are basically the same. However, in the optical recording medium 1, the optical recording medium 3, and the optical recording medium 4, the NAs are different and the effective lens diameters are different as shown in FIGS. Absent.

In the objective lens optical system according to the comparative example, the optical path length difference between the regions was set as follows. That is, with respect to the areas of surface area numbers _{2, 4,} 6, _12, and 14, the optical recording medium 2 is approximately “−0.06 ± 0.06λ”, that is, −0.12λ _{2 to} 0λ _2. The optical path length difference was set to approximately “+ 0.06 ± 0.06λ”, that is, 0λ _{4 to} 0.12λ ₄ with respect to the optical recording medium 4. With regard to the region of the surface region numbers 7, 9, 11, substantially "-2.06 ± 0.06λ" That -2.12Ramuda ₂ a ~-2 [lambda] ₂ as an optical path length difference to the optical recording medium 2 The optical path length difference is approximately “−0.94 ± 0.06λ”, that is, −1λ ₄ to −0.88λ ₄ with respect to the optical recording medium 4. By setting the optical path length difference in this way, compatibility between the optical recording medium 2 and the optical recording medium 4 is realized by the compatibility technique B described above.

  In the objective lens optical system according to the comparative example, the optical recording medium 2 and the optical recording medium 3 are compatible in the medium area of the NA portion of the optical recording medium 3. Furthermore, in the first and second embodiments, the optical recording medium 1 and the optical recording medium 4 are compatible in the medium area of the NA portion of the optical recording medium 4, but in the medium area of the NA portion of the optical recording medium 4, The optical recording medium 2 and the optical recording medium 4 are compatible. By adopting such a configuration, the lens shift characteristic can be improved, and both the on-axis characteristic and the lens shift characteristic can be suppressed to 0.06λ or less, and a high-performance objective lens optical system is provided. I was able to.

  Further, since both the optical recording media 3 and 4 having different wavelengths from the optical recording media 1 and 2 are compatible with the optical recording medium 2 having a small difference in substrate thickness, the number of surface regions can be reduced. It is possible to reduce the level difference formed between them, making it easier to manufacture and improving performance by suppressing light scattering caused by the level difference.

  However, as a result of studies by the inventors, it has been found that in order to further improve the characteristics relating to wavefront aberration, the setting of the dedicated area and the shared area should be devised as described in the following embodiments of the invention. did.

Embodiment 1 of the Invention
The objective lens optical system according to the first embodiment is configured to focus on four optical recording media using the objective lens optical system shown in FIGS. 16 to 20 as in the comparative example. The characteristics of the objective lens optical system are shown in FIG. 4, FIG. 5, and FIG.

  In the objective lens optical system according to the first embodiment, the lens shape of the region that condenses on the optical recording medium 1 and the lens shape of the region that condenses on the optical recording media 2, 3, and 4 are the same as those in the comparative example, Only the position is changed. As shown in FIG. 17, medium area numbers 1, 3, 5, and 7 are dedicated areas of the optical recording medium 1, and medium area numbers 2, 4, and 6 are shared by the optical recording media 2, 3, and 4. It is an area.

  In the first embodiment, as in the comparative example, the compatibility technique B is used to achieve compatibility between the optical recording medium 2 and the optical recording medium 4. Here, an optical path length difference OPD represented by Expression (2) occurs in the stepped portion of the compatible technology B.

OPD = d (N−N ₀ ) / λ (2)
Here, d is the step amount, N is the refractive index of the material constituting the step, and N ₀ is the refractive index of air.

  As one method for realizing the compatible technology B, in each optical recording medium (each wavelength), mod (OPD)> 0.5 when mod (OPD)> 0.5, and mod (OPD) <0.5 when mod (OPD) <0.5 OPD) (this value is hereinafter referred to as W) to generate aberration γ, thereby canceling aberration α, aberration β, and aberration γ in each optical recording medium (each wavelength), aberration β, and aberration γ. There is a technology to offset Here, mod means that the maximum integer that does not exceed the value of OPD is subtracted from OPD. For example, when OPD = -1.9, mod (OPD) = 0.1 and W is 0. If, for example, OPD = 1.6, mod (OPD) = 0.6 and W = −0.4.

  In this case, depending on the combination of the wavelength and the material constituting the step, the W given by the step increases, resulting in deterioration of optical performance due to the jump of wavefront aberration occurring at the step, or difficulty in manufacturing due to an increase in the step amount. There has been a problem of deterioration in optical performance due to an increase in unnecessary light at the step portion. On the other hand, if W is small, the aberration γ generated at one step by the compatible technology B is small, and if many steps are not used, cancellation cannot be realized. There was a problem of deterioration in optical performance due to an increase in unnecessary light.

  From this point of view, the phase difference given to the optical recording medium 1 or 2 and the optical recording medium 4 in both the comparative example and the first and second embodiments of the present invention is expressed by the following equation from the equation (2). Satisfied.

| W2-W4 | ≒ 0.24λ
Here, W2 is W of the optical recording medium 1 or 2, and W4 is W of the optical recording medium 4.

  At this time, 0.24λ is distributed to each of the recording medium 1 or 2 and the optical recording medium 4 so that the performance is high, and W2≈0.12λ and W4 = −0.12λ. The aberration γ is generated at one step.

  As a result, in the comparative example, OPD2 = −2nλ + 0.12λ and OPD4 = −nλ−0.12λ can be realized. Aberration α, aberration β, aberration γ cancellation, or aberration β and aberration can be achieved. γ cancellation is realized.

  Here, as shown in the schematic diagram of FIG. 6, the sum of the aberration α and the aberration β is usually a curve, and in order to cancel this, it must be a curve as shown by the aberration γi. . However, as described above, since the aberration γ is generated by providing the step, the actual aberration γ becomes a step-shaped aberration. Therefore, how to reduce the amount of aberration W generated by one step is an important factor in reducing the amount of wavefront aberration and improving performance.

  Therefore, in the first embodiment, a surface area corresponding to the optical recording medium 1 using the compatible technology A is arranged at the step portion. As a result, the difference between the maximum value and the minimum value of the wavefront aberration can be made W or less, and the wavefront aberration can be reduced.

  Here, in the comparative example, as shown in FIG. 2B, the wavefront aberration amount is rapidly increased between the surface region number 6 and the surface region number 7 and between the surface region number 11 and the surface region number 12. Changes have occurred.

  In the first embodiment, as shown in FIG. 5, a medium that focuses on an optical recording medium that does not use the compatible technology B in a step region where the change of the wavefront aberration is the largest and the absolute value of the wavefront aberration is large. The area is arranged. Specifically, as shown in FIG. 5, the surface area number 2 and the surface area number 4 that are focused on the optical recording media 2, 3, and 4 are not focused on the optical recording media 2, 3, and 4. Are divided by a surface area number 3 that is focused only on the optical recording medium 1.

  As shown in FIG. 6, the optical path length difference OPD of the optical recording medium 2 is approximately −0.0729 to −0.0173λ in the surface area number 2 and −2.0155 to −2.0296 in the surface area number 4. It is. The optical path length difference OPD of the optical recording medium 4 was approximately 0.0206 to 0.0362λ in the surface area number 2 and −0.9794 to −0.9338 in the surface area number 4. In this way, the difference between the optical path lengths of the front and rear surface area numbers 2 and 4 divided by the surface area number 3 is set to 0.5λ or more, and the change of the wavefront aberration amount of 0.12λ is suppressed. Since the area number 3 is arranged, as shown in FIG. 5, the change width of the wavefront aberration amount of the surface area numbers 2 and 4 is 0.057λ for the optical recording medium 2 and 0 for the optical recording medium 3. It can be seen that the values can be reduced to 0.065λ, which are smaller than 0 and 12λ, respectively. As a result, as shown in FIG. 21, an on-axis characteristic of 0.03λ or less and a lens shift characteristic of 0.06λ or less can be achieved, and a high-performance objective lens optical system can be provided.

Embodiment 2 of the Invention
The objective lens optical system according to the second embodiment has the same basic configuration as that of the comparative example, and uses the objective lens optical system shown in FIGS. 22 to 26 to focus on four types of optical recording media. It was. FIG. 7 shows the characteristics of the objective lens optical system according to the second embodiment, and FIG. 27 shows the RMS wavefront aberration values.

The objective lens optical system according to the second embodiment is the same as that of the comparative example except for the configuration related to the compatible technology B of the optical recording media 2 and 4. That is, in the objective lens optical system according to the second embodiment, the optical path length difference between regions is set as follows. That is, with respect to the areas of the surface area numbers 2 and 4, the optical path length difference is approximately “0 ± 0.06λ”, that is, −0.06λ ₂ to + 0.06λ ₂ with respect to the optical recording medium 2. The optical path length difference was approximately “0 ± 0.06λ”, that is, −0.06λ ₄ to + 0.06λ ₄ with respect to the medium 4. Further, the areas of the surface area numbers 5, 7, 9, and 11 are approximately “−2.0 ± 0.06λ”, that is, −2.06λ ₂ to −1.94λ ₂ with respect to the optical recording medium 2. The optical path length difference was approximately “−1.0 ± 0.06λ”, that is, −1.06λ ₄ to −0.94λ ₄ with respect to the optical recording medium 4. Further, regarding the area of surface area number 13, the optical recording medium 2 has an optical path length difference that is approximately “−0 ± 0.06λ”, that is, −0.06λ ₂ to + 0.06λ _2. 4, the optical path length difference was approximately “+ 0 ± 0.06λ”, that is, −0.06λ ₄ to + 0.06λ ₄ . By setting the optical path length difference in this way, compatibility between the optical recording medium 2 and the optical recording medium 4 is realized by the compatibility technique B described above.

  Further, in the second embodiment, the technique according to the present invention described in the first embodiment of the present invention is applied in the vicinity of NA 0.7 of the optical recording medium 2 and the optical recording medium 4.

  In the objective lens optical system according to the second embodiment, with such a configuration, as shown in FIG. 27, the on-axis characteristic is 0.04λ or less, and the lens shift characteristic (at the time of 0.2 mm shift). In this case, 0.06λ or less could be achieved, and a high-performance objective lens optical system could be provided.

Other embodiments.
In the first and second embodiments, the objective lens optical system is realized by a single lens. However, as shown in FIG. 8, the objective lens optical system may be realized by using two components of the objective lens 100 and the aberration correction element 400. Good. Specifically, as shown in FIG. 8B, both the compatible technology A and the compatible technology B may be applied to the incident surface or the output surface of the aberration correction element 400. Further, as shown in FIG. 8C, the compatible technology A may be applied to the aberration correction element 400 and the compatible technology B may be applied to the objective lens 100. Further, as shown in FIG. 8D, the compatible technology B may be applied to the aberration correction element 400 and the compatible technology A may be applied to the objective lens 100. Even if the objective lens optical system is realized by such a configuration, the same effects as those of the first and second embodiments of the invention can be obtained. However, in order to reduce the size and weight of the objective lens optical system, it is preferable to realize the objective lens optical system with a single lens as in the objective lens optical systems according to the first and second embodiments.

  In the above-described example, the objective lens optical system that enables compatibility of four types of optical recording media has been described. However, the wavelengths of the light beams condensed on at least two or more optical recording media are the same, and at least two or more optical recording media are used. The present invention is applicable to an objective lens optical system that focuses light on at least three or more optical recording media that have different wavelengths of light beams that are focused on the other optical recording media.

It is a schematic block diagram of the objective-lens optical system concerning embodiment of invention and a comparative example. It is a wave aberration diagram of the objective lens optical system concerning a comparative example. It is a figure which shows OPD of the objective-lens optical system concerning a comparative example. It is a wavefront aberration diagram of the objective lens optical system according to the first embodiment of the invention. It is a figure which shows OPD of the objective-lens optical system concerning Embodiment 1 of invention. FIG. 3 is a schematic wavefront aberration diagram for explaining the cancellation of aberrations in the objective lens optical system according to the first embodiment of the invention. It is a wave aberration diagram of the objective lens optical system concerning Embodiment 2 of invention. It is a schematic block diagram of the objective-lens optical system concerning other embodiment. It is a table | surface which shows the various quantities of the optical recording medium which can be used in the objective-lens optical system concerning embodiment of invention. It is a table | surface which shows the effective diameter and refractive index of the objective-lens optical system concerning a comparative example. It is a table | surface which shows the characteristic of each area | region of the objective-lens optical system concerning a comparative example. It is a table | surface which shows the lens data of the objective-lens optical system concerning a comparative example. It is a table | surface which shows the surface shape data (objective lens surface 1) of the objective-lens optical system concerning a comparative example. It is a table | surface which shows the surface shape data (objective lens surface 2) of the objective-lens optical system concerning a comparative example. It is a table | surface which shows the RMS wavefront aberration value of the objective-lens optical system concerning a comparative example. It is a table | surface which shows the effective diameter and refractive index of the objective-lens optical system concerning Embodiment 1 of invention. It is a table | surface which shows the characteristic of each area | region of the objective-lens optical system concerning Embodiment 1 of invention. It is a table | surface which shows the lens data of the objective-lens optical system concerning Embodiment 1 of invention. It is a table | surface which shows the surface shape data (objective lens surface 1) of the objective lens optical system concerning Embodiment 1 of invention. It is a table | surface which shows the surface shape data (objective lens surface 2) of the objective lens optical system concerning Embodiment 1 of invention. It is a table | surface which shows the RMS wavefront aberration value of the objective lens optical system concerning Embodiment 1 of invention. It is a table | surface which shows the effective diameter and refractive index of the objective-lens optical system concerning Embodiment 2 of invention. It is a table | surface which shows the characteristic of each area | region of the objective-lens optical system concerning Embodiment 2 of invention. It is a table | surface which shows the lens data of the objective-lens optical system concerning Embodiment 2 of invention. It is a table | surface which shows the surface shape data (objective lens surface 1) of the objective lens optical system concerning Embodiment 2 of invention. It is a table | surface which shows the surface shape data (objective lens surface 2) of the objective lens optical system concerning Embodiment 2 of invention. It is a table | surface which shows the RMS wavefront aberration value of the objective lens optical system concerning Embodiment 2 of invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Objective lens 200 Transparent substrate 201 Information recording surface 300 Light beam 400 Aberration correction element

Claims (23)

The light beam having the wavelength λ1 is condensed on the information recording surface of the first optical recording medium having the transparent substrate having the thickness t1, and the light beam having the wavelength λ1 is condensed to the second light having the transparent substrate having the thickness t2 (t2 ≠ t1). The light is condensed on the information recording surface of the recording medium, and the light beam having the wavelength λ3 (λ3 ≠ λ1) is condensed on the information recording surface of the third optical recording medium having the transparent substrate having the thickness t3. An objective lens optical system having a positive power for forming a light spot on
A first optical recording medium region for condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium without condensing the light flux on the information recording surface of the second optical recording medium; ,
The light beam having the wavelength λ1 is condensed on the information recording surface of the second optical recording medium without condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium. A common area for condensing on the information recording surface of the third optical recording medium,
In the common area, an aspherical shape that generates an aberration that cancels chromatic aberration caused by a difference in wavelength λ of the light beam is set,
The optical path length difference between the first optical recording medium area and two shared areas adjacent to the inside and outside is 0.5λ or more for either wavelength λ1 or wavelength λ3. Objective lens optical system. The light beam having the wavelength λ1 is condensed on the information recording surface of the first optical recording medium having the transparent substrate having the thickness t1, and the light beam having the wavelength λ1 is condensed to the second light having the transparent substrate having the thickness t2 (t2 ≠ t1). The light is condensed on the information recording surface of the recording medium, and the light beam having the wavelength λ3 (λ3 ≠ λ1) is condensed on the information recording surface of the third optical recording medium having the transparent substrate having the thickness t3. An objective lens optical system having a positive power for forming a light spot on
A first optical recording medium region for condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium without condensing the light flux on the information recording surface of the second optical recording medium; ,
The light beam having the wavelength λ1 is condensed on the information recording surface of the second optical recording medium without condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium. A common area for condensing on the information recording surface of the third optical recording medium,
The common area has an aspheric shape, and a wavefront aberration caused by a difference in the thickness of the transparent substrate of the optical recording medium, a chromatic aberration caused by a difference in the wavelength λ of the light beam, and an aberration caused by the aspheric shape. Offset,
The optical path length difference between the first optical recording medium area and two shared areas adjacent to the inside and outside is 0.5λ or more for either wavelength λ1 or wavelength λ3. Objective lens optical system. The light beam having the wavelength λ1 is condensed on the information recording surface of the first optical recording medium having the transparent substrate having the thickness t1, and the light beam having the wavelength λ1 is condensed to the second light having the transparent substrate having the thickness t2 (t2 ≠ t1). The light is condensed on the information recording surface of the recording medium, and the light beam having the wavelength λ3 (λ3 ≠ λ1) is condensed on the information recording surface of the third optical recording medium having the transparent substrate having the thickness t3. An objective lens optical system having a positive power for forming a light spot on
A first optical recording medium region for condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium without condensing the light flux on the information recording surface of the second optical recording medium; ,
The light beam having the wavelength λ1 is condensed on the information recording surface of the second optical recording medium without condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium. A common area for condensing on the information recording surface of the third optical recording medium,
In the common area, an aspherical shape that generates an aberration that cancels chromatic aberration caused by a difference in wavelength λ of the light beam is set,
When the shared area is provided in the entire area of the objective lens, the first optical recording medium area is formed in an area where the change in wavefront aberration with respect to the second optical recording medium or the third optical recording medium is the largest. An objective lens optical system provided. The light beam having the wavelength λ1 is condensed on the information recording surface of the first optical recording medium having the transparent substrate having the thickness t1, and the light beam having the wavelength λ1 is condensed to the second light having the transparent substrate having the thickness t2 (t2 ≠ t1). The light is condensed on the information recording surface of the recording medium, and the light beam having the wavelength λ3 (λ3 ≠ λ1) is condensed on the information recording surface of the third optical recording medium having the transparent substrate having the thickness t3. An objective lens optical system having a positive power for forming a light spot on
A first optical recording medium region for condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium without condensing the light flux on the information recording surface of the second optical recording medium; ,
The light beam having the wavelength λ1 is condensed on the information recording surface of the second optical recording medium without condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium. A common area for condensing on the information recording surface of the third optical recording medium,
The common area has an aspheric shape, and a wavefront aberration caused by a difference in the thickness of the transparent substrate of the optical recording medium, a chromatic aberration caused by a difference in the wavelength λ of the light beam, and an aberration caused by the aspheric shape. Offset,
When the shared area is provided in the entire area of the objective lens, the first optical recording medium area is formed in an area where the change in wavefront aberration with respect to the second optical recording medium or the third optical recording medium is the largest. An objective lens optical system provided.   The wavelength λ1 is approximately 405 nm, the wavelength λ3 is approximately 655 nm, the substrate thickness t1 is approximately 0.1 mm, the substrate thickness t2 is approximately 0.6 mm, and the substrate thickness t3 is approximately 0.6 mm. The objective lens optical system according to any one of 1 to 4. The light beam having the wavelength λ1 is condensed on the information recording surface of the first optical recording medium having the transparent substrate having the thickness t1, and the light beam having the wavelength λ1 is condensed to the second light having the transparent substrate having the thickness t2 (t2 ≠ t1). The light is condensed on the information recording surface of the recording medium, and the light beam having the wavelength λ3 (λ3 ≠ λ1) is condensed on the information recording surface of the third optical recording medium having the transparent substrate having the thickness t3. An objective lens optical system having a positive power for forming a light spot on
A first optical recording medium region for condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium without condensing the light flux on the information recording surface of the second optical recording medium; ,
The light beam having the wavelength λ1 is condensed on the information recording surface of the second optical recording medium without condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium. A common area for condensing on the information recording surface of the third optical recording medium,
The light beam having the wavelength λ3 and the light beam having the wavelength λ1 incident on the common area are incident at different incident angles.
The optical path length difference between the first optical recording medium area and two shared areas adjacent to the inside and outside is 0.5λ or more for either wavelength λ1 or wavelength λ3. Objective lens optical system. The light beam having the wavelength λ1 is condensed on the information recording surface of the first optical recording medium having the transparent substrate having the thickness t1, and the light beam having the wavelength λ1 is condensed to the second light having the transparent substrate having the thickness t2 (t2 ≠ t1). The light is condensed on the information recording surface of the recording medium, and the light beam having the wavelength λ3 (λ3 ≠ λ1) is condensed on the information recording surface of the third optical recording medium having the transparent substrate having the thickness t3. An objective lens optical system having a positive power for forming a light spot on
A first optical recording medium region for condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium without condensing the light flux on the information recording surface of the second optical recording medium; ,
The light beam having the wavelength λ1 is condensed on the information recording surface of the second optical recording medium without condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium. A common area for condensing on the information recording surface of the third optical recording medium,
The light beam having the wavelength λ3 and the light beam having the wavelength λ1 incident on the common area are incident at different incident angles.
When the shared area is provided in the entire area of the objective lens, the first optical recording medium area is formed in an area where the change in wavefront aberration with respect to the second optical recording medium or the third optical recording medium is the largest. An objective lens optical system provided.   The wavelength λ1 is about 405 nm, the wavelength λ3 is about 790 nm, the substrate thickness t1 is about 0.1 mm, the substrate thickness t2 is about 0.6 mm, and the substrate thickness t3 is about 1.2 mm. The objective lens optical system according to 6 or 7. The light beam having the wavelength λ1 is condensed on the information recording surface of the first optical recording medium having the transparent substrate having the thickness t1, and the light beam having the wavelength λ1 is condensed to the second light having the transparent substrate having the thickness t2 (t2 ≠ t1). A light beam having a wavelength λ3 (λ3 ≠ λ1) is condensed on an information recording surface of a third optical recording medium having a transparent substrate having a thickness t3, and a wavelength λ4 (λ4 ≠). This is an objective lens optical system having a positive power for focusing a light beam of λ1) on an information recording surface of a fourth optical recording medium having a transparent substrate having a thickness t4 and forming a light spot on each information recording surface. And
A first optical recording medium region for condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium without condensing the light flux on the information recording surface of the second optical recording medium; ,
The light beam having the wavelength λ1 is not condensed on the information recording surface of the first optical recording medium, but is condensed on the information recording surface of the second optical recording medium, and the light beam having the wavelength λ3 is condensed on the third optical recording medium. A common area for condensing on the information recording surface of the optical recording medium and condensing the light beam having the wavelength λ4 on the information recording surface of the fourth optical recording medium,
The light beam having the wavelength λ3 and the light beam having the wavelength λ1 incident on the common area are incident at different incident angles.
An aspherical shape that cancels out chromatic aberration caused by the difference between the wavelengths λ4 and λ1 of the light beam is set,
The optical path length difference between the first optical recording medium region and the two shared regions adjacent inside and outside is 0.5λ or more for any one of the wavelengths λ1, λ3, and λ4. An objective lens optical system. The light beam having the wavelength λ1 is condensed on the information recording surface of the first optical recording medium having the transparent substrate having the thickness t1, and the light beam having the wavelength λ1 is condensed to the second light having the transparent substrate having the thickness t2 (t2 ≠ t1). A light beam having a wavelength λ3 (λ3 ≠ λ1) is condensed on an information recording surface of a third optical recording medium having a transparent substrate having a thickness t3, and a wavelength λ4 (λ4 ≠). This is an objective lens optical system having a positive power for focusing a light beam of λ1) on an information recording surface of a fourth optical recording medium having a transparent substrate having a thickness t4 and forming a light spot on each information recording surface. And
A first optical recording medium region for condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium without condensing the light flux on the information recording surface of the second optical recording medium; ,
The light beam having the wavelength λ1 is not condensed on the information recording surface of the first optical recording medium, but is condensed on the information recording surface of the second optical recording medium, and the light beam having the wavelength λ3 is condensed on the third optical recording medium. A common area for condensing on the information recording surface of the optical recording medium and condensing the light beam having the wavelength λ4 on the information recording surface of the fourth optical recording medium,
The light beam having the wavelength λ3 and the light beam having the wavelength λ1 incident on the common area are incident at different incident angles.
An aspherical shape that cancels out chromatic aberration caused by the difference between the wavelengths λ4 and λ1 of the light beam is set,
When the shared area is provided in the entire area of the objective lens, the second optical recording medium, the third optical recording medium, or the fourth optical recording medium has the largest change in wavefront aberration. 1. An objective lens optical system, wherein one optical recording medium region is provided. The light beam having the wavelength λ1 is condensed on the information recording surface of the first optical recording medium having the transparent substrate having the thickness t1, and the light beam having the wavelength λ1 is condensed to the second light having the transparent substrate having the thickness t2 (t2 ≠ t1). A light beam having a wavelength λ3 (λ3 ≠ λ1) is condensed on an information recording surface of a third optical recording medium having a transparent substrate having a thickness t3, and a wavelength λ4 (λ4 ≠). This is an objective lens optical system having a positive power for focusing a light beam of λ1) on an information recording surface of a fourth optical recording medium having a transparent substrate having a thickness t4 and forming a light spot on each information recording surface. And
A first optical recording medium region for condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium without condensing the light flux on the information recording surface of the second optical recording medium; ,
The light beam having the wavelength λ1 is not condensed on the information recording surface of the first optical recording medium, but is condensed on the information recording surface of the second optical recording medium, and the light beam having the wavelength λ3 is condensed on the third optical recording medium. A common area for condensing on the information recording surface of the optical recording medium and condensing the light beam having the wavelength λ4 on the information recording surface of the fourth optical recording medium,
The light beam having the wavelength λ3 and the light beam having the wavelength λ1 incident on the common area are incident at different incident angles.
The common area has an aspherical shape, and the wavefront aberration caused by the difference in thickness between the transparent substrates of the second optical recording medium and the fourth optical recording medium and the difference between the wavelengths λ4 and λ1 of the optical beam. The chromatic aberration that occurs and the aberration that occurs in the aspheric shape are offset,
The optical path length difference between the first optical recording medium region and the two shared regions adjacent inside and outside is 0.5λ or more for any one of the wavelengths λ1, λ3, and λ4. An objective lens optical system. The light beam having the wavelength λ1 is condensed on the information recording surface of the first optical recording medium having the transparent substrate having the thickness t1, and the light beam having the wavelength λ1 is condensed to the second light having the transparent substrate having the thickness t2 (t2 ≠ t1). A light beam having a wavelength λ3 (λ3 ≠ λ1) is condensed on an information recording surface of a third optical recording medium having a transparent substrate having a thickness t3, and a wavelength λ4 (λ4 ≠). This is an objective lens optical system having a positive power for focusing a light beam of λ1) on an information recording surface of a fourth optical recording medium having a transparent substrate having a thickness t4 and forming a light spot on each information recording surface. And
A first optical recording medium region for condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium without condensing the light flux on the information recording surface of the second optical recording medium; ,
The light beam having the wavelength λ1 is not condensed on the information recording surface of the first optical recording medium, but is condensed on the information recording surface of the second optical recording medium, and the light beam having the wavelength λ3 is condensed on the third optical recording medium. A common area for condensing on the information recording surface of the optical recording medium and condensing the light beam having the wavelength λ4 on the information recording surface of the fourth optical recording medium,
The light beam having the wavelength λ3 and the light beam having the wavelength λ1 incident on the common area are incident at different incident angles.
The common area has an aspherical shape, and the wavefront aberration caused by the difference in thickness between the transparent substrates of the second optical recording medium and the fourth optical recording medium and the difference between the wavelengths λ4 and λ1 of the optical beam. The chromatic aberration that occurs and the aberration that occurs in the aspheric shape are offset,
When the shared area is provided in the entire area of the objective lens, the second optical recording medium, the third optical recording medium, or the fourth optical recording medium has the largest change in wavefront aberration. 1. An objective lens optical system, wherein one optical recording medium region is provided.   Wavelength λ1 is approximately 405 nm, wavelength λ3 is approximately 790 nm, wavelength λ4 is approximately 655 nm, substrate thickness t1 is approximately 0.1 mm, substrate thickness t2 is approximately 0.6 mm, substrate thickness t3 is approximately 1.2 mm, and substrate thickness The objective lens optical system according to claim 9, wherein the length t4 is approximately 0.6 mm. The light beam having the wavelength λ1 is condensed on the information recording surface of the first optical recording medium having the transparent substrate having the thickness t1, and the light beam having the wavelength λ1 is second light having the transparent substrate having the thickness t2 (t2 ≠ t1). The light is condensed on the information recording surface of the recording medium, and the light beam having the wavelength λ3 (λ3 ≠ λ1) is condensed on the information recording surface of the third optical recording medium having the transparent substrate having the thickness t3. An optical pickup optical system having a positive power for forming a light spot on
A first optical recording medium region for condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium without condensing the light flux on the information recording surface of the second optical recording medium; ,
The light beam having the wavelength λ1 is condensed on the information recording surface of the second optical recording medium without condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium. A common area for condensing on the information recording surface of the third optical recording medium,
In the common area, an aspherical shape that generates an aberration that cancels chromatic aberration caused by a difference in wavelength λ of the light beam is set,
The optical path length difference between the first optical recording medium area and two shared areas adjacent to the inside and outside is 0.5λ or more for either wavelength λ1 or wavelength λ3. Optical pickup optical system. The light beam having the wavelength λ1 is condensed on the information recording surface of the first optical recording medium having the transparent substrate having the thickness t1, and the light beam having the wavelength λ1 is condensed to the second light having the transparent substrate having the thickness t2 (t2 ≠ t1). The light is condensed on the information recording surface of the recording medium, and the light beam having the wavelength λ3 (λ3 ≠ λ1) is condensed on the information recording surface of the third optical recording medium having the transparent substrate having the thickness t3. An optical pickup optical system having a positive power for forming a light spot on
A first optical recording medium region for condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium without condensing the light flux on the information recording surface of the second optical recording medium; ,
The light beam having the wavelength λ1 is condensed on the information recording surface of the second optical recording medium without condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium. A common area for condensing on the information recording surface of the third optical recording medium,
In the common area, an aspherical shape that generates an aberration that cancels chromatic aberration caused by a difference in wavelength λ of the light beam is set,
When the shared area is provided in the entire area of the objective lens, the first optical recording medium area is formed in an area where the change in wavefront aberration with respect to the second optical recording medium or the third optical recording medium is the largest. An optical pickup optical system characterized by being provided. The light beam having the wavelength λ1 is condensed on the information recording surface of the first optical recording medium having the transparent substrate having the thickness t1, and the light beam having the wavelength λ1 is condensed to the second light having the transparent substrate having the thickness t2 (t2 ≠ t1). The light is condensed on the information recording surface of the recording medium, and the light beam having the wavelength λ3 (λ3 ≠ λ1) is condensed on the information recording surface of the third optical recording medium having the transparent substrate having the thickness t3. An optical pickup optical system having a positive power for forming a light spot on
A first optical recording medium region for condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium without condensing the light flux on the information recording surface of the second optical recording medium; ,
The light beam having the wavelength λ1 is condensed on the information recording surface of the second optical recording medium without condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium. A common area for condensing on the information recording surface of the third optical recording medium,
The common area has an aspheric shape, and a wavefront aberration caused by a difference in the thickness of the transparent substrate of the optical recording medium, a chromatic aberration caused by a difference in the wavelength λ of the light beam, and an aberration caused by the aspheric shape. Offset,
The optical path length difference between the first optical recording medium area and two shared areas adjacent to the inside and outside is 0.5λ or more for either wavelength λ1 or wavelength λ3. Optical pickup optical system. The light beam having the wavelength λ1 is condensed on the information recording surface of the first optical recording medium having the transparent substrate having the thickness t1, and the light beam having the wavelength λ1 is condensed to the second light having the transparent substrate having the thickness t2 (t2 ≠ t1). The light is condensed on the information recording surface of the recording medium, and the light beam having the wavelength λ3 (λ3 ≠ λ1) is condensed on the information recording surface of the third optical recording medium having the transparent substrate having the thickness t3. An optical pickup optical system having a positive power for forming a light spot on
A first optical recording medium region for condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium without condensing the light flux on the information recording surface of the second optical recording medium; ,
The light beam having the wavelength λ1 is condensed on the information recording surface of the second optical recording medium without condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium. A common area for condensing on the information recording surface of the third optical recording medium,
The common area has an aspheric shape, and a wavefront aberration caused by a difference in the thickness of the transparent substrate of the optical recording medium, a chromatic aberration caused by a difference in the wavelength λ of the light beam, and an aberration caused by the aspheric shape. Offset,
When the shared area is provided in the entire area of the objective lens, the first optical recording medium area is formed in an area where the change in wavefront aberration with respect to the second optical recording medium or the third optical recording medium is the largest. An optical pickup optical system characterized by being provided. The light beam having the wavelength λ1 is condensed on the information recording surface of the first optical recording medium having the transparent substrate having the thickness t1, and the light beam having the wavelength λ1 is condensed to the second light having the transparent substrate having the thickness t2 (t2 ≠ t1). The light is condensed on the information recording surface of the recording medium, and the light beam having the wavelength λ3 (λ3 ≠ λ1) is condensed on the information recording surface of the third optical recording medium having the transparent substrate having the thickness t3. An optical pickup optical system having a positive power for forming a light spot on
A first optical recording medium region for condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium without condensing the light flux on the information recording surface of the second optical recording medium; ,
The light beam having the wavelength λ1 is condensed on the information recording surface of the second optical recording medium without condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium. A common area for condensing on the information recording surface of the third optical recording medium,
The light beam having the wavelength λ3 and the light beam having the wavelength λ1 incident on the common area are incident at different incident angles.
The optical path length difference between the first optical recording medium area and two shared areas adjacent to the inside and outside is 0.5λ or more for either wavelength λ1 or wavelength λ3. Optical pickup optical system. The light beam having the wavelength λ1 is condensed on the information recording surface of the first optical recording medium having the transparent substrate having the thickness t1, and the light beam having the wavelength λ1 is condensed to the second light having the transparent substrate having the thickness t2 (t2 ≠ t1). The light is condensed on the information recording surface of the recording medium, and the light beam having the wavelength λ3 (λ3 ≠ λ1) is condensed on the information recording surface of the third optical recording medium having the transparent substrate having the thickness t3. An optical pickup optical system having a positive power for forming a light spot on
A first optical recording medium region for condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium without condensing the light flux on the information recording surface of the second optical recording medium; ,
The light beam having the wavelength λ1 is condensed on the information recording surface of the second optical recording medium without condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium. A common area for condensing on the information recording surface of the third optical recording medium,
The light beam having the wavelength λ3 and the light beam having the wavelength λ1 incident on the common area are incident at different incident angles.
When the shared area is provided in the entire area of the objective lens, the first optical recording medium area is formed in an area where the change in wavefront aberration with respect to the second optical recording medium or the third optical recording medium is the largest. An optical pickup optical system characterized by being provided. The light beam having the wavelength λ1 is condensed on the information recording surface of the first optical recording medium having the transparent substrate having the thickness t1, and the light beam having the wavelength λ1 is condensed to the second light having the transparent substrate having the thickness t2 (t2 ≠ t1). A light beam having a wavelength λ3 (λ3 ≠ λ1) is condensed on an information recording surface of a third optical recording medium having a transparent substrate having a thickness t3, and a wavelength λ4 (λ4 ≠). An optical pickup optical system having a positive power for converging a light beam of λ1) onto an information recording surface of a fourth optical recording medium having a transparent substrate having a thickness t4 and forming a light spot on each information recording surface. And
A first optical recording medium region for condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium without condensing the light flux on the information recording surface of the second optical recording medium; ,
The light beam having the wavelength λ1 is not condensed on the information recording surface of the first optical recording medium, but is condensed on the information recording surface of the second optical recording medium, and the light beam having the wavelength λ3 is condensed on the third optical recording medium. A common area for condensing on the information recording surface of the optical recording medium and condensing the light beam having the wavelength λ4 on the information recording surface of the fourth optical recording medium,
The light beam having the wavelength λ3 and the light beam having the wavelength λ1 incident on the common area are incident at different incident angles.
An aspherical shape that cancels out chromatic aberration caused by the difference between the wavelengths λ4 and λ1 of the light beam is set,
The optical path length difference between the first optical recording medium area and two shared areas adjacent to the inside and outside is 0.5λ or more for either wavelength λ1 or wavelength λ3. Optical pickup optical system. The light beam having the wavelength λ1 is condensed on the information recording surface of the first optical recording medium having the transparent substrate having the thickness t1, and the light beam having the wavelength λ1 is condensed to the second light having the transparent substrate having the thickness t2 (t2 ≠ t1). A light beam having a wavelength λ3 (λ3 ≠ λ1) is condensed on an information recording surface of a third optical recording medium having a transparent substrate having a thickness t3, and a wavelength λ4 (λ4 ≠). An optical pickup optical system having a positive power for converging a light beam of λ1) onto an information recording surface of a fourth optical recording medium having a transparent substrate having a thickness t4 and forming a light spot on each information recording surface. And
A first optical recording medium region for condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium without condensing the light flux on the information recording surface of the second optical recording medium; ,
The light beam having the wavelength λ1 is not condensed on the information recording surface of the first optical recording medium, but is condensed on the information recording surface of the second optical recording medium, and the light beam having the wavelength λ3 is condensed on the third optical recording medium. A common area for condensing on the information recording surface of the optical recording medium and condensing the light beam having the wavelength λ4 on the information recording surface of the fourth optical recording medium,
The light beam having the wavelength λ3 and the light beam having the wavelength λ1 incident on the common area are incident at different incident angles.
An aspherical shape that cancels out chromatic aberration caused by the difference between the wavelengths λ4 and λ1 of the light beam is set,
When the shared area is provided in the entire area of the objective lens, the second optical recording medium, the third optical recording medium, or the fourth optical recording medium has the largest change in wavefront aberration. 1. An optical pickup optical system comprising an optical recording medium area. The light beam having the wavelength λ1 is condensed on the information recording surface of the first optical recording medium having the transparent substrate having the thickness t1, and the light beam having the wavelength λ1 is condensed to the second light having the transparent substrate having the thickness t2 (t2 ≠ t1). A light beam having a wavelength λ3 (λ3 ≠ λ1) is condensed on an information recording surface of a third optical recording medium having a transparent substrate having a thickness t3, and a wavelength λ4 (λ4 ≠). This is an optical pickup optical system having a positive power that focuses a light beam of λ1) on an information recording surface of a third optical recording medium having a transparent substrate having a thickness t4 and forms a light spot on each information recording surface. And
A first optical recording medium region for condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium without condensing the light flux on the information recording surface of the second optical recording medium; ,
The light beam having the wavelength λ1 is not condensed on the information recording surface of the first optical recording medium, but is condensed on the information recording surface of the second optical recording medium, and the light beam having the wavelength λ3 is condensed on the third optical recording medium. A common area for condensing on the information recording surface of the optical recording medium and condensing the light beam having the wavelength λ4 on the information recording surface of the fourth optical recording medium,
The light beam having the wavelength λ3 and the light beam having the wavelength λ1 incident on the common area are incident at different incident angles.
The common area has an aspherical shape, and the wavefront aberration caused by the difference in thickness between the transparent substrates of the second and fourth optical recording media and the difference between the wavelengths λ4 and λ1 of the light beam. The chromatic aberration that occurs and the aberration that occurs in the aspheric shape are offset,
The optical path length difference between the first optical recording medium area and the two shared areas adjacent to the inside and outside is 0.5λ or more for any one of the wavelengths λ1, λ3, or λ4. An optical pickup optical system characterized by the above. The light beam having the wavelength λ1 is condensed on the information recording surface of the first optical recording medium having the transparent substrate having the thickness t1, and the light beam having the wavelength λ1 is condensed to the second light having the transparent substrate having the thickness t2 (t2 ≠ t1). A light beam having a wavelength λ3 (λ3 ≠ λ1) is condensed on an information recording surface of a third optical recording medium having a transparent substrate having a thickness t3, and a wavelength λ4 (λ4 ≠). An optical pickup optical system having a positive power for converging a light beam of λ1) onto an information recording surface of a fourth optical recording medium having a transparent substrate having a thickness t4 and forming a light spot on each information recording surface. And
A first optical recording medium region for condensing the light beam having the wavelength λ1 on the information recording surface of the first optical recording medium without condensing the light flux on the information recording surface of the second optical recording medium; ,
The light beam having the wavelength λ1 is not condensed on the information recording surface of the first optical recording medium, but is condensed on the information recording surface of the second optical recording medium, and the light beam having the wavelength λ3 is condensed on the third optical recording medium. A common area for condensing on the information recording surface of the optical recording medium and condensing the light beam having the wavelength λ4 on the information recording surface of the fourth optical recording medium,
The light beam having the wavelength λ3 and the light beam having the wavelength λ1 incident on the common area are incident at different incident angles.
The common area has an aspherical shape, and the wavefront aberration caused by the difference in thickness between the transparent substrates of the second optical recording medium and the fourth optical recording medium and the difference between the wavelengths λ4 and λ1 of the optical beam. The chromatic aberration that occurs and the aberration that occurs in the aspheric shape are offset,
When the shared area is provided in the entire area of the objective lens, the second optical recording medium, the third optical recording medium, or the fourth optical recording medium has the largest change in wavefront aberration. An optical pickup optical system characterized in that one optical recording medium region is provided.

Images