JPWO2011114895A1 - Objective lens, optical pickup device, and optical information recording / reproducing device - Google Patents

Abstract

To provide an objective lens for an optical pickup device, an optical pickup device, and an optical information recording / reproducing device that can suppress the occurrence of an error signal or the like when using three different optical disks interchangeably, the first wavelength that passes through the objective lens a first optical path difference providing structure that imparts a diffraction action to the first light flux of λ1, but does not give a diffraction action to the second light flux of the second wavelength λ2 and the third light flux of the third wavelength λ3, and a second optical path having a blaze shape A difference providing structure is provided, and power is provided to the first optical path difference providing structure and the second optical path difference providing structure so that information is recorded / reproduced on / from different optical disks using light beams having three different wavelengths. To. As a result, for example, a combination of the diffracted light having the highest diffraction efficiency in the first optical path difference providing structure and the diffracted light having the highest diffraction efficiency in the second optical path difference providing structure is caused by a manufacturing error or the like. Even when the diffraction efficiency of diffracted light of different orders is increased, erroneous detection can be avoided.

Description

  The present invention relates to an optical pickup device capable of recording and / or reproducing information interchangeably with different types of optical discs, an objective lens for the optical pickup device, and an optical information recording / reproducing device.

  In recent years, in an optical pickup device, a laser light source used as a light source for reproducing information recorded on an optical disc and recording information on the optical disc has been shortened. For example, a wavelength 390 such as a blue-violet semiconductor laser is used. A laser light source of ˜420 nm has been put into practical use. When these blue-violet laser light sources are used, when an objective lens having the same numerical aperture (NA) as that of a DVD (digital versatile disk) is used, it is possible to record information of 15 to 20 GB on an optical disk having a diameter of 12 cm. When the NA of the objective optical element is increased to 0.85, 23 to 25 GB of information can be recorded on an optical disk having a diameter of 12 cm.

  As an example of an optical disk using the above-described objective lens with NA of 0.85, there is a BD (Blu-ray disk). When NA is large, it becomes sensitive to the tilt (skew) of the optical disk and coma aberration generated due to the tilt increases. Therefore, in BD, the protective substrate is designed to be thinner than in the case of DVD (to 0.6 mm of DVD). On the other hand, the amount of coma due to skew is reduced by 0.1 mm.

  By the way, the value as a product of an optical disc player / recorder (optical information recording / reproducing apparatus) is sufficient just to be able to record and / or reproduce information appropriately (hereinafter referred to as recording / reproducing) with respect to the BD. It's not a good thing. In light of the reality that DVDs and CDs (compact discs) on which a wide variety of information is recorded are currently being sold, it is not possible to record / reproduce information with respect to BDs. For example, DVDs owned by users, Similarly, it is possible to appropriately record / reproduce information on a CD, which leads to an increase in the commercial value of an optical disc player / recorder for BD. From such a background, the optical pickup device mounted on the BD optical disc player / recorder can record / reproduce information appropriately while maintaining compatibility with any of BD, DVD, and CD. It is desirable to have

  As a method for appropriately recording / reproducing information while maintaining compatibility with both BD and DVD, and further with CD, information between BD optical system and DVD or CD optical system is used. Although a method of selectively switching according to the recording density of the optical disc to be recorded / reproduced is conceivable, it requires a plurality of optical systems, which is disadvantageous for miniaturization and increases the cost.

  Therefore, in order to simplify the configuration of the optical pickup device and reduce the cost, even in an optical pickup device having compatibility, the optical system for BD and the optical system for DVD or CD can be shared. It is preferable to reduce the number of optical components constituting the pickup device as much as possible. And, it is most advantageous to simplify the configuration of the optical pickup device and to reduce the cost to make the objective lens arranged facing the optical disc in common. In order to obtain a common objective lens for a plurality of types of optical disks having different recording / reproducing wavelengths, it is desirable to form a diffractive structure having a wavelength dependency of spherical aberration in the objective lens.

  In particular, in an optical pickup device that uses three different wavelengths, it is common to provide two diffractive structures to realize BD / DVD / CD compatibility using chromatic spherical aberration. It is also necessary to correct chromatic spherical aberration that occurs due to variations in oscillation wavelength. On the other hand, Patent Document 1 describes an objective lens that has two diffractive structures and can be used in common for three types of optical disks, and an optical pickup device equipped with the objective lens.

JP 2009-199707 A

  According to the objective lens of Patent Document 1, the first diffractive structure generates primary light as the strongest diffracted light in the light beam with the first wavelength λ1, and the 0th-order light as the strongest diffracted light in the light beam with the second wavelength λ2. The second-order light is generated as the strongest diffracted light by the second diffractive structure, and the second-order light is generated as the strongest diffracted light by the second-diffractive structure. The primary light is generated as the strongest diffracted light in the light beam with the second wavelength λ2, and the primary light is generated as the strongest diffracted light in the light beam with the third wavelength λ3. Here, when the DVD / CD is used, the first diffractive structure generates zero-order diffracted light, and therefore does not receive a diffractive action, so that the occurrence of chromatic spherical aberration can be suppressed. In addition, when the DVD / CD is used, first-order diffracted light is generated in any of the second diffractive structures, so that it is possible to use a conventionally designed DVD / CD compatible objective lens.

  By the way, in the objective lens of patent document 1, it is clear from the fact that the value of P2 in the first region (circled character 2) is zero with reference to, for example, the numerical value of the optical path difference function (Table 30). As such, the second diffractive structure is designed to have no power. However, since the second diffractive structure does not have power, for example, in the BD, the second-order diffracted light used has light of other orders superimposed on the position of the longitudinal spherical aberration on the optical axis. Here, as compared with the second-order diffracted light, the efficiency of diffraction of the first-order diffracted light and the third-order diffracted light generated on both sides is extremely low in design, so that an inherently erroneous spot may be detected on the photodetector. Should be low. However, since the diffractive structure is a fine structure that requires an accuracy of several tens of nanometers, the diffraction efficiency of first-order diffracted light, third-order diffracted light, or the like may be higher than the theoretical value due to manufacturing errors or the like. In such a case, there is a possibility that the light spot such as the first-order diffracted light or the third-order diffracted light may be erroneously detected by the photodetector while being superimposed on the second-order diffracted light.

  An object of the present invention is to solve the above-described problems. In the case where three different optical discs are used interchangeably, an objective lens and an optical pickup device for an optical pickup device capable of suppressing the generation of an error signal and the like, and An object of the present invention is to provide an optical information recording / reproducing apparatus.

The objective lens according to claim 1, wherein a first light source that emits a first light flux having a first wavelength λ1 (nm) and a second light flux that emits a second light flux having a second wavelength λ2 (nm) (λ2> λ1). A first optical disc having a light source and a third light source that emits a third light beam having a third wavelength λ3 (nm) (λ3> λ2), and having a protective substrate having a thickness t1 using the first light beam. Information is recorded and / or reproduced, information is recorded and / or reproduced on a second optical disc having a protective substrate having a thickness t2 (t1 <t2) using the second light flux, and the third light flux is reflected on the third light flux. An objective lens used in an optical pickup device for recording and / or reproducing information on a third optical disk having a protective substrate having a thickness of t3 (t2 <t3).
The objective lens imparts a diffractive action to the first light beam having the first wavelength λ1 passing therethrough, but does not give a diffractive action to the second light beam having the second wavelength λ2 and the third light beam having the third wavelength λ3. Having a structure and a second optical path difference providing structure having a blaze shape,
The step d1 (nm) of the second optical path difference providing structure satisfies the following formula when the refractive index of the objective lens material with respect to the first wavelength is n1:
(1.8 × λ1 / (n1-1)) ≦ d1 ≦ (3.0 × λ1 / (n1-1))
(1)
The first optical path difference providing structure and the second optical path difference providing structure both have power.

  According to the present invention, the first optical path difference that gives a diffractive action to the first light flux having the first wavelength λ1 passing therethrough but does not give the diffractive action to the second light flux having the second wavelength λ2 and the third light flux having the third wavelength λ3. By providing the providing structure and the second optical path difference providing structure having a blaze shape, information can be recorded / reproduced on / from different optical disks using light beams having three different wavelengths. In addition, since both the first optical path difference providing structure and the second optical path difference providing structure have power, for example, the n-th order diffracted light having the highest diffraction efficiency in the first optical path difference providing structure and the second optical path difference structure. Even if the diffraction efficiency of the diffracted light of a different order from the combination with the m-th order diffracted light that has the highest diffraction efficiency in the applied structure is increased due to manufacturing error, the paraxial power is given to the paraxial Misdetection can be effectively avoided by shifting the condensing position in the optical axis direction.

The objective lens according to claim 2 is the following formula in the invention according to claim 1,
0.08 ≦ P1 / P ≦ 0.15 (2)
0.02 ≦ | P2 / P | ≦ 0.05 (3)
However,
P1: Power of the first optical path difference providing structure P2: Power of the second optical path difference providing structure P: Power of the entire objective lens, P> 0
It is characterized by satisfying.

  By setting the value of the expression (2) to be equal to or higher than the lower limit value, the working distance of the third optical disc with respect to the first disc can be increased, and the nth-order diffracted light with the highest diffraction efficiency emitted from the first optical path difference providing structure. On the other hand, even when the diffraction efficiency of adjacent (n-1) th order diffracted light or (n + 1) th order diffracted light is increased, false detection can be effectively performed by providing a paraxial power and shifting the condensing position in the optical axis direction. Can be avoided. However, if the value of the expression (2) exceeds the upper limit value, the pitch of the diffractive structure may be too fine. Further, by setting the value of the expression (3) to be equal to or higher than the lower limit value, the (m−1) th order diffracted light adjacent to the mth order diffracted light having the highest diffraction efficiency emitted from the second optical path difference providing structure or Even when the diffraction efficiency of the (m + 1) th order diffracted light is increased, erroneous detection can be effectively avoided by providing paraxial power and shifting the condensing position in the optical axis direction. However, if the value of the expression (3) exceeds the upper limit value, the pitch of the diffractive structure may be too fine.

  The objective lens described in claim 3 is characterized in that, in the invention described in claim 2, P2 / P is positive. As a result, the chromatic aberration when using the first optical disk can be suppressed as compared with the case where P2 / P is negative, the pitch of the second optical path difference providing structure is increased, and the mold for molding the objective lens is produced. It can be easily processed and has excellent processability.

  The objective lens described in claim 4 is characterized in that, in the invention described in claim 2, P2 / P is negative. As a result, the working distance of the third optical disc with respect to the first disc can be made longer than when P2 / P is positive.

  The objective lens according to claim 5 is the invention according to any one of claims 1 to 4, wherein the first optical path difference providing structure has a blaze shape. Thereby, the diffraction efficiency in a reference wavelength can be maintained high.

  The objective lens according to claim 6 is the invention according to any one of claims 1 to 4, wherein the first optical path difference providing structure has a stepped shape. Thereby, the change of the diffraction efficiency at the time of wavelength fluctuation can be suppressed small. Moreover, highly efficient unnecessary light can be kept away from the diffracted light used for recording and reproduction.

  An objective lens according to a seventh aspect is the invention according to any one of the first to sixth aspects, wherein the first optical path difference providing structure is a primary beam of the first light beam that has passed through the first optical path difference providing structure. The diffracted light quantity is made larger than any other order diffracted light quantity, the 0th-order diffracted light quantity of the second light flux that has passed through the first optical path difference providing structure is made larger than any other order diffracted light quantity, The 0th-order diffracted light amount of the third light beam that has passed through the optical path difference providing structure is made larger than any other order diffracted light amount, and the second optical path difference providing structure is the first light beam that has passed through the second optical path difference providing structure. The second order diffracted light quantity of the light beam is made larger than any other order diffracted light quantity, and the first order diffracted light quantity of the second light flux that has passed through the second optical path difference providing structure is made larger than any other order diffracted light quantity. And the third light flux that has passed through the second optical path difference providing structure A first-order diffracted light, characterized in that larger than the other diffracted light of any order. This makes it possible to effectively record / reproduce information with respect to three different optical discs using light beams having three different wavelengths.

  An objective lens according to an eighth aspect is the invention according to any one of the first to seventh aspects, wherein the first optical path difference providing structure and the second optical path difference providing structure are superimposed. .

  An optical pickup device according to a ninth aspect includes the objective lens according to any one of the first to eighth aspects.

  An optical information recording / reproducing apparatus according to a tenth aspect has the optical pickup apparatus according to the ninth aspect.

  The optical pickup device according to the present invention has at least three light sources: a first light source, a second light source, and a third light source. Furthermore, the optical pickup device of the present invention condenses the first light flux on the information recording surface of the first optical disc, condenses the second light flux on the information recording surface of the second optical disc, and causes the third light flux to be third. It has a condensing optical system for condensing on the information recording surface of the optical disc. The optical pickup device of the present invention includes a light receiving element that receives a reflected light beam from the information recording surface of the first optical disc, the second optical disc, or the third optical disc.

  The first optical disc has a protective substrate having a thickness t1 and an information recording surface. The second optical disc has a protective substrate having a thickness t2 (t1 <t2) and an information recording surface. The third optical disc has a protective substrate having a thickness t3 (t2 <t3) and an information recording surface. The first optical disc is preferably a BD, the second optical disc is a DVD, and the third optical disc is preferably a CD, but is not limited thereto. The first optical disc, the second optical disc, or the third optical disc may be a multi-layer optical disc having a plurality of information recording surfaces.

  In this specification, BD means that information is recorded / reproduced by a light beam having a wavelength of about 390 to 415 nm and an objective lens having an NA of about 0.8 to 0.9, and the thickness of the protective substrate is 0.05 to 0.00 mm. It is a generic term for a BD series optical disc of about 125 mm, and includes a BD having only a single information recording layer, a BD having a plurality of information recording layers, and the like. Furthermore, in this specification, DVD is a general term for DVD series optical discs in which information is recorded / reproduced by an objective lens having an NA of about 0.60 to 0.67 and the thickness of the protective substrate is about 0.6 mm. And includes DVD-ROM, DVD-Video, DVD-Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, and the like. Further, in this specification, CD is a general term for CD-series optical discs in which information is recorded / reproduced by an objective lens having an NA of about 0.45 to 0.51 and the protective substrate has a thickness of about 1.2 mm. Including CD-ROM, CD-Audio, CD-Video, CD-R, CD-RW, and the like. As for the recording density, the recording density of BD is the highest, followed by the order of DVD and CD.

In addition, regarding the thicknesses t1, t2, and t3 of the protective substrate, the following conditional expressions (4), (5), (6),
0.050 mm ≦ t1 ≦ 0.125 mm (4)
0.5mm ≦ t2 ≦ 0.7mm (5)
1.0mm ≦ t3 ≦ 1.3mm (6)
However, the present invention is not limited to this.

  The thickness of the protective substrate referred to here is the thickness of the protective substrate provided on the surface of the optical disk. That is, the thickness of the protective substrate from the optical disc surface to the information recording surface closest to the surface.

In the present specification, the first light source, the second light source, and the third light source are preferably laser light sources. As the laser light source, a semiconductor laser, a silicon laser, or the like can be preferably used. The first wavelength λ1 of the first light beam emitted from the first light source, the second wavelength λ2 (λ2> λ1) of the second light beam emitted from the second light source, and the third of the third light beam emitted from the third light source. The wavelength λ3 (λ3> λ2) is defined by the following conditional expressions (7), (8),
1.5 · λ1 <λ2 <1.7 · λ1 (7)
1.8 · λ1 <λ3 <2.0 · λ1 (8)
It is preferable to satisfy.

  When BD, DVD, and CD are used as the first optical disc, the second optical disc, and the third optical disc, respectively, the first wavelength λ1 of the first light source is preferably 350 nm or more and 440 nm or less, more preferably 390 nm. The second wavelength λ2 of the second light source is preferably 570 nm or more and 680 nm or less, more preferably 630 nm or more and 670 nm or less, and the third wavelength λ3 of the third light source is preferably 415 nm or less. It is 750 nm or more and 880 nm or less, More preferably, it is 760 nm or more and 820 nm or less.

  Further, at least two of the first light source, the second light source, and the third light source may be unitized. The unitization means that the first light source and the second light source are fixedly housed in one package, for example. In addition to the light source, a light receiving element to be described later may be packaged.

  As the light receiving element, a photodetector such as a photodiode is preferably used. Light reflected on the information recording surface of the optical disc enters the light receiving element, and a read signal of information recorded on each optical disc is obtained using the output signal. Furthermore, it detects the change in the light amount due to the spot shape change and position change on the light receiving element, performs focus detection and track detection, and based on this detection, the objective lens can be moved for focusing and tracking I can do it. The light receiving element may comprise a plurality of photodetectors. The light receiving element may have a main photodetector and a sub photodetector. For example, two sub photodetectors are provided on both sides of a photodetector that receives main light used for recording and reproducing information, and the sub light for tracking adjustment is received by the two sub photodetectors. It is good also as a simple light receiving element. The light receiving element may have a plurality of light receiving elements corresponding to the respective light sources.

  The condensing optical system has an objective lens. The condensing optical system preferably has a coupling lens such as a collimator in addition to the objective lens. The coupling lens is a single lens or a lens group that is disposed between the objective lens and the light source and changes the divergence angle of the light beam. The collimator is a type of coupling lens, and is a lens that emits incident light as parallel light. In this specification, the objective lens refers to an optical system that is disposed at a position facing the optical disk in the optical pickup device and has a function of condensing the light beam emitted from the light source onto the information recording surface of the optical disk. The objective lens may be composed of two or more plural lenses and / or optical elements, may be composed of only a single lens, and is more preferably an objective lens composed of a single convex lens. . The objective lens may be a glass lens or a plastic lens, or an optical path difference providing structure is provided on the glass lens with a photo-curing resin, a UV-curing resin, or a thermosetting resin. A hybrid lens may also be used. When the objective lens has a plurality of lenses, a glass lens and a plastic lens may be mixed and used. When the objective lens includes a plurality of lenses, it may be a combination of a flat optical element having an optical path difference providing structure and an aspherical lens (which may or may not have an optical path difference providing structure). The objective lens preferably has a refractive surface that is aspheric. In the objective lens, the base surface on which the optical path difference providing structure is provided is preferably an aspherical surface.

  Moreover, when using an objective lens as a glass lens, it is preferable to use the glass material whose glass transition point Tg is 450 degrees C or less, More preferably, it is 400 degrees C or less. By using a glass material having a glass transition point Tg of 450 ° C. or lower, molding at a relatively low temperature becomes possible, so that the life of the mold can be extended. Examples of such a glass material having a low glass transition point Tg include K-PG325 and K-PG375 (both product names) manufactured by Sumita Optical Glass Co., Ltd.

  By the way, since the specific gravity of a glass lens is generally larger than that of a resin lens, if the objective lens is a glass lens, the mass becomes large and a load is imposed on the actuator that drives the objective lens. Therefore, when the objective lens is a glass lens, it is preferable to use a glass material having a small specific gravity. Specifically, the specific gravity is preferably 4.0 or less, more preferably the specific gravity is 3.0 or less.

When the objective lens is a plastic lens, it is preferable to use an alicyclic hydrocarbon polymer material such as a cyclic olefin resin material. The resin material has a refractive index within a range of 1.54 to 1.60 at a temperature of 25 ° C. with respect to a wavelength of 405 nm, and a wavelength of 405 nm associated with a temperature change within a temperature range of −5 ° C. to 70 ° C. The refractive index change rate dN / dT (° C. ⁻¹ ) with respect to the range of −20 × 10 ^{−5 to} −5 × 10 ⁻⁵ (more preferably −10 × 10 ^{−5 to} −8 × 10 ⁻⁵ ). It is more preferable to use a certain resin material. When the objective lens is a plastic lens, the coupling lens is preferably a plastic lens.

  As the plastic, cycloolefin resin is preferably used. Specifically, ZEONEX manufactured by Nippon Zeon, APEL manufactured by Mitsui Chemicals, TOPAS manufactured by TOPAS ADVANCED POLYMERS, ARTON manufactured by JSR, and the like are preferable examples. Can be mentioned.

  Moreover, it is preferable that the Abbe number of the material which comprises an objective lens is 50 or more.

  The objective lens will be described below. It is preferable that at least one optical surface of the objective lens has at least a central region, an intermediate region around the central region, and a peripheral region around the intermediate region. The central region is preferably a region including the optical axis of the objective lens, but a minute region including the optical axis is used as an unused region or a special purpose region, and the surroundings are defined as a central region (also referred to as a central region). Also good. The central region, the intermediate region, and the peripheral region are preferably provided on the same optical surface. As shown in FIG. 1, the central region CN, the intermediate region MD, and the peripheral region OT are preferably provided concentrically around the optical axis on the same optical surface. The central region, the intermediate region, and the peripheral region are preferably adjacent to each other, but there may be a slight gap between them. The region including the optical axis (the central region in the case of being divided into the central region, the intermediate region, and the peripheral region) gives a diffractive action to the first light beam having the first wavelength λ1 that passes therethrough, but has the second wavelength λ2 in the first region. A first optical path difference providing structure that does not give diffraction action to the two light beams and the third light beam having the third wavelength λ3, and a second optical path difference providing structure having a blaze shape, Both of the second optical path difference providing structures have power.

  In the present specification, “does not give a diffractive action” means that the light having the strongest light intensity among the light beams that have passed through the optical path difference providing structure is zero-order diffracted light. Means that the diffracted light of the order other than 0 has the strongest light intensity among the light beams that have passed through the optical path difference providing structure.

  It can be said that the central area of the objective lens is a shared area of the first, second, and third optical disks used for recording / reproduction of the first optical disk, the second optical disk, and the third optical disk. That is, the objective lens condenses the first light flux that passes through the central area so that information can be recorded / reproduced on the information recording surface of the first optical disc, and the second light flux that passes through the central area becomes the second light flux. Focusing on the information recording surface of the optical disc so that information can be recorded and / or reproduced, and allowing the third light flux passing through the central area to be recorded / reproduced on the information recording surface of the third optical disc Condensate. In addition, the optical path difference providing structure provided in the central region has the thickness t1 of the protective substrate of the first optical disc and the protective substrate of the second optical disc with respect to the first light flux and the second light flux passing through the optical path difference providing structure. It is preferable to correct spherical aberration generated due to the difference in thickness t2 / spherical aberration generated due to the difference in wavelength between the first light beam and the second light beam. Further, the optical path difference providing structure is different from the thickness t1 of the protective substrate of the first optical disc and the thickness t3 of the protective substrate of the third optical disc with respect to the first and third light fluxes that have passed through the optical path difference providing structure. It is preferable to correct the spherical aberration caused by the difference in the wavelength of the first light beam and the third light beam.

  The intermediate area of the objective lens is used for recording / reproduction of the first optical disk and the second optical disk, and can be said to be the first and second optical disk shared areas not used for recording / reproduction of the third optical disk. That is, the objective lens condenses the first light flux that passes through the intermediate area so that information can be recorded / reproduced on the information recording surface of the first optical disc, and the second light flux that passes through the intermediate area becomes the second light flux. The light is condensed on the information recording surface of the optical disc so that information can be recorded / reproduced. On the other hand, the third light flux passing through the intermediate region is not condensed so that information can be recorded / reproduced on the information recording surface of the third optical disk. The third light flux passing through the intermediate region of the objective lens preferably forms a flare on the information recording surface of the third optical disc. In the spot formed on the information recording surface of the third optical disc by the third light flux that has passed through the objective lens, the spot center portion having a high light amount density and the light amount density in order from the optical axis side (or the spot center portion) to the outside. It is preferable to have a spot middle part lower than the spot center part and a spot peripheral part whose light intensity is higher than the spot middle part and lower than the spot center part. The center portion of the spot is used for recording / reproducing information on the optical disc, and the middle portion of the spot and the peripheral portion of the spot are not used for recording / reproducing information on the optical disc. In the above, this spot peripheral part is called flare. However, there is no spot middle part around the center part of the spot and there is a spot peripheral part, that is, even when a light spot is formed thinly around the condensing spot, the spot peripheral part may be called a flare. Good. That is, it can be said that the third light flux that has passed through the intermediate region of the objective lens preferably forms a spot peripheral portion on the information recording surface of the third optical disc.

  The peripheral area of the objective lens is used for recording / reproduction of the first optical disk, and can be said to be an area dedicated to the first optical disk that is not used for recording / reproduction of the second optical disk and the third optical disk. That is, the objective lens condenses the first light flux passing through the peripheral region so that information can be recorded / reproduced on the information recording surface of the first optical disc. On the other hand, the second light flux that passes through the peripheral area is not condensed so that information can be recorded / reproduced on the information recording surface of the second optical disc, and the third light flux that passes through the peripheral area does not converge. The light is not condensed so that information can be recorded / reproduced on the information recording surface. The second light flux and the third light flux that pass through the peripheral area of the objective lens preferably form a flare on the information recording surfaces of the second optical disc and the third optical disc. That is, it is preferable that the second light flux and the third light flux that have passed through the peripheral area of the objective lens form a spot peripheral portion on the information recording surfaces of the second optical disc and the third optical disc.

  The optical path difference providing structure is preferably provided in a region of 70% or more of the area of the central region of the objective lens, and more preferably 90% or more. More preferably, the optical path difference providing structure is provided on the entire surface of the central region. Further, another optical path difference providing structure is preferably provided in a region of 70% or more of the area of the intermediate region of the objective lens, and more preferably 90% or more. More preferably, another optical path difference providing structure is provided on the entire surface of the intermediate region. When the peripheral region has an optical path difference providing structure, the optical path difference providing structure is preferably provided in a region of 70% or more of the area of the peripheral region of the objective lens, and more preferably 90% or more. More preferably, the optical path difference providing structure is provided on the entire surface of the peripheral region.

  The optical path difference providing structure referred to in this specification is a general term for structures that add an optical path difference to an incident light beam. The optical path difference providing structure also includes a phase difference providing structure for providing a phase difference. The phase difference providing structure includes a diffractive structure. The optical path difference providing structure of the present invention is preferably a diffractive structure. The optical path difference providing structure has a step, preferably a plurality of steps. This step adds an optical path difference and / or phase difference to the incident light flux. The optical path difference added by the optical path difference providing structure may be an integer multiple of the wavelength of the incident light beam or a non-integer multiple of the wavelength of the incident light beam. The steps may be arranged with a periodic interval in the direction perpendicular to the optical axis, or may be arranged with a non-periodic interval in the direction perpendicular to the optical axis. When the objective lens provided with the optical path difference providing structure is a single aspherical lens, the incident angle of the light flux to the objective lens differs depending on the height from the optical axis. Each will be slightly different. For example, when the objective lens is a single-lens aspherical convex lens, even if it is an optical path difference providing structure that provides the same optical path difference, generally the distance from the optical axis tends to increase.

  In addition, the diffractive structure referred to in this specification is a general term for structures that have a step and have an action of converging or diverging a light beam by diffraction. For example, a plurality of unit shapes are arranged around the optical axis, and a light beam is incident on each unit shape, and the wavefront of the transmitted light is shifted between adjacent annular zones, resulting in new It includes a structure that converges or diverges light by forming a simple wavefront. The diffractive structure preferably has a plurality of steps, and the steps may be arranged with a periodic interval in the direction perpendicular to the optical axis, or may be arranged with a non-periodic interval in the direction perpendicular to the optical axis. In addition, in the case of a single aspherical lens having a diffractive structure on the light source side lens surface, the exit angle from the diffractive structure and the optical path length to enter the lens differ depending on the height from the optical axis. The amount will vary slightly for each zone. For example, when the objective lens is a single aspherical convex lens, even if it is a diffractive structure that generates diffracted light of the same diffraction order, generally, the distance from the optical axis tends to increase.

  By the way, it is preferable that the optical path difference providing structure has a plurality of concentric annular zones centered on the optical axis. In addition, the optical path difference providing structure can generally have various cross-sectional shapes (cross-sectional shapes on the plane including the optical axis), and the cross-sectional shapes including the optical axis are roughly classified into a blazed structure and a staircase structure.

  As shown in FIGS. 2A and 2B, the blazed structure means that the cross-sectional shape including the optical axis of an optical element having an optical path difference providing structure is a sawtooth shape. In the example of FIG. 2, it is assumed that the upper side is the light source side and the lower side is the optical disk side, and the optical path difference providing structure is formed on a plane as a mother aspherical surface. In the blazed structure, the length of one blaze unit in the direction perpendicular to the optical axis is referred to as the pitch Ph (see FIGS. 2A and 2B). The length of the step in the direction parallel to the optical axis of the blaze is referred to as a step amount d (see FIG. 2A).

When the first optical path difference providing structure is a blazed structure, the step d can be expressed by the following equation.
d = (1 × λB) / (n1-1) (9)
Where λB is the blazed wavelength (220 nm ≦ λB ≦ 330 nm), and n1 is the refractive index with respect to the wavelength λ1 (nm) of the blazed structure.

More preferably, the following formula (9) ′,
(0.54λ1 / (n1-1)) ≦ d ≦ (0.81λ1 / (n1-1))
(9) '
It can be expressed as

  In addition, as shown in FIGS. 2C and 2D, the staircase structure has a small staircase shape in cross section including the optical axis of an optical element having an optical path difference providing structure (referred to as a staircase unit). ). In the present specification, “V level” means a ring-shaped surface (hereinafter also referred to as a terrace surface) corresponding to (or facing) the vertical direction of the optical axis in one step unit of the step structure. In other words, it is divided by V steps and divided into V ring zones. Particularly, a three-level or higher staircase structure has a small step and a large step.

  For example, the optical path difference providing structure illustrated in FIG. 2C is referred to as a five-level step structure, and the optical path difference providing structure illustrated in FIG. 2D is referred to as a two-level step structure (also referred to as a binary structure). . A two-level staircase structure is described below. A plurality of annular zones including a plurality of concentric annular zones around the optical axis, and a plurality of annular zones including the optical axis of the objective lens have a plurality of stepped surfaces Pa and Pb extending in parallel to the optical axis, The light source side terrace surface Pc for connecting the light source side ends of the adjacent step surfaces Pa and Pb and the optical disk side terrace surface Pd for connecting the optical disk side ends of the adjacent step surfaces Pa and Pb are formed. The surface Pc and the optical disc side terrace surface Pd are alternately arranged along the direction intersecting the optical axis.

  In the staircase structure, the length of one staircase unit in the direction perpendicular to the optical axis is referred to as a pitch Ph (see FIGS. 2C and 2D). The length of the step in the direction parallel to the optical axis of the staircase is referred to as step amounts B1 and B2. In the case of a three-level or higher staircase structure, a large step amount B1 and a small step amount B2 exist (see FIG. 2C).

  The optical path difference providing structure is preferably a structure in which a certain unit shape is periodically repeated. As used herein, “unit shape is periodically repeated” naturally includes shapes in which the same shape is repeated in the same cycle. In addition, the unit shape that is one unit of the cycle has regularity, and the shape in which the cycle gradually increases or decreases gradually is also included in the “unit shape is periodically repeated”. Suppose that

  When the optical path difference providing structure has a blazed structure, the sawtooth shape as a unit shape is repeated. As shown in FIG. 2 (a), the same serrated shape may be repeated, or as shown in FIG. 2 (b), the serrated shape gradually increases as it moves away from the optical axis. A shape in which the pitch becomes longer or a shape in which the pitch becomes shorter may be used. In addition, in some areas, the blazed structure has a step opposite to the optical axis (center) side, and in other areas, the blazed structure has a step toward the optical axis (center). It is good also as a shape in which the transition area | region required in order to switch the direction of the level | step difference of a blaze | braze type | mold structure is provided in the meantime. In addition, when it is set as the structure which switches the direction of the level | step difference of a blaze | braze type | mold in this way, it becomes possible to widen an annular zone pitch and it can suppress the transmittance | permeability fall by the manufacturing error of an optical path difference providing structure.

  In the case where the optical path difference providing structure has a staircase structure, there may be a shape such that a 5-level stair unit as shown in FIG. 2C is repeated. Furthermore, it may be a shape in which the pitch of the staircase unit gradually increases as it moves away from the optical axis, or a shape in which the pitch of the staircase unit gradually decreases.

  The first optical path difference providing structure and the second optical path difference providing structure may be provided on different optical surfaces of the objective lens, respectively, but are preferably provided on the same optical surface. In addition, when the first optical path difference providing structure and the second optical path difference providing structure are provided on the same optical surface, it is preferable to overlap the first optical path difference providing structure and the second optical path difference providing structure at the same position, that is, to overlap. . Furthermore, also when providing a 3rd optical path difference providing structure, it is preferable to provide in the same optical surface as a 1st optical path difference providing structure and a 2nd optical path difference providing structure. Providing them on the same optical surface is preferable because it makes it possible to reduce eccentricity errors during manufacturing. In addition, the first optical path difference providing structure, the second optical path difference providing structure, and the third optical path difference providing structure are preferably provided on the light source side surface of the objective lens rather than the surface of the objective lens on the optical disk side. In other words, the first optical path difference providing structure, the second optical path difference providing structure, and the third optical path difference providing structure are preferably provided on the optical surface having the smaller absolute value of the radius of curvature of the objective lens.

  The first optical path difference providing structure is a blazed structure or a staircase structure. Further, the first optical path difference providing structure makes the first-order diffracted light quantity of the first light flux that has passed through the first optical path difference-providing structure larger than any other order of diffracted light quantity, and passed through the first optical path difference providing structure. The 0th-order diffracted light amount of the second light beam is made larger than any other order diffracted light amount, and the 0th-order diffracted light amount of the third light beam that has passed through the first optical path difference providing structure is made higher than any other order diffracted light amount. Larger is preferable.

  The second optical path difference providing structure is a blazed structure. Further, the second optical path difference providing structure makes the second-order diffracted light amount of the first light beam that has passed through the second optical path difference providing structure larger than any other order diffracted light amount, and passed through the second optical path difference providing structure. The first order diffracted light amount of the second light beam is made larger than any other order diffracted light amount, and the first order diffracted light amount of the third light beam that has passed through the second optical path difference providing structure is made higher than any other order diffracted light amount. Larger is preferable.

The blaze step d1 (nm) in the second optical path difference providing structure satisfies the following expression when the refractive index for the first wavelength λ1 of the blazed structure is n1:
(1.8 × λ1 / (n1-1)) ≦ d1 ≦ (3.0 × λ1 / (n1-1))
(1)
Both the first optical path difference providing structure and the second optical path difference providing structure have paraxial power.

And the following formula:
0.08 ≦ P1 / P ≦ 0.15 (2)
0.02 ≦ | P2 / P | ≦ 0.05 (3)
However,
P1: Power of the first optical path difference providing structure P2: Power of the second optical path difference providing structure P: Power of the entire objective lens, P> 0
It is preferable to satisfy

  P2 / P may be positive or negative. The first optical path difference providing structure and the second optical path difference providing structure may be superimposed on one optical surface.

The thick on-axis objective lens used for compatibility with the three types of optical discs of BD / DVD / CD according to the present invention affects the condensed spot on the information recording surface even if the efficiency of unnecessary diffracted light increases due to manufacturing errors. In order to avoid this, the first optical path difference providing structure and the second optical path difference providing structure have paraxial power with respect to the first light flux (also referred to as power in this specification). Here, “having paraxial power” means that C ₂ h ² is not 0 when the optical path difference functions of the first optical path difference providing structure and the second optical path difference providing structure are expressed by the following equation ( ^2). means. The paraxial power P in the diffractive structure can be generally expressed by the following equation.
P = −2 × B ₁ × mλ (10)
Where B ₁ is an optical path difference function coefficient, m is a diffraction order, and λ is a wavelength.

  FIG. 3A is a diagram illustrating a change in diffraction efficiency with respect to wavelength variation of the blazed diffraction structure and the staircase diffraction structure. FIG. 3B is a diagram showing the relationship between the order of diffracted light generated with respect to the wavelength used and the diffraction efficiency. Here, the first-order diffracted light amount of the first light beam that has passed through the diffractive structure is made larger than any other order of diffracted light amount, and the zero-order diffracted light amount of the second light beam that has passed through the diffractive structure is set to any other order. An example will be described in which the 0th-order diffracted light amount of the third light flux that has passed through the diffractive structure is made larger than any other order diffracted light amount. In FIG. 3, the diffraction efficiency of the blazed diffraction structure is 74.1% at the reference wavelength λ1 = 405 nm, and the diffraction efficiency of the staircase diffraction structure is 71.5%. Is expensive. However, when the wavelength variation of ± 5 nm occurs with respect to the reference wavelength due to the variation of the oscillation wavelength, the variation of the diffraction efficiency of the blazed diffraction structure is about 3% as shown in FIG. The fluctuation of the diffraction efficiency is about 2%, and the fluctuation of the diffraction efficiency of the staircase type diffraction structure is smaller. That is, it is preferable to use a blazed diffraction structure if the light source has a small variation in oscillation wavelength, and it is preferable to use a staircase diffraction structure if the light source has a large variation in oscillation wavelength.

  The numerical aperture on the image side of the objective lens necessary for reproducing / recording information on the first optical disc is NA1, and the numerical aperture on the image side of the objective lens necessary for reproducing / recording information on the second optical disc. Is NA2 (NA1> NA2), and the image-side numerical aperture of the objective lens necessary for reproducing / recording information on the third optical disk is NA3 (NA2> NA3). NA1 is preferably 0.75 or more and 0.9 or less, and more preferably 0.8 or more and 0.9 or less. In particular, NA1 is preferably 0.85. NA2 is preferably 0.55 or more and 0.7 or less. In particular, NA2 is preferably 0.60 or 0.65. NA3 is preferably 0.4 or more and 0.55 or less. In particular, NA3 is preferably 0.45 or 0.53.

  The boundary between the central region and the intermediate region of the objective lens is 0.9 · NA 3 or more and 1.2 · NA 3 or less (more preferably 0.95 · NA 3 or more, 1.15 · NA 3) when the third light beam is used. It is preferably formed in a portion corresponding to the following range. More preferably, the boundary between the central region and the intermediate region of the objective lens is formed in a portion corresponding to NA3. Further, the boundary between the intermediate region and the peripheral region of the objective lens is 0.9 · NA 2 or more and 1.2 · NA 2 or less (more preferably 0.95 · NA 2 or more, 1.15) when the second light flux is used. -It is preferably formed in a portion corresponding to the range of NA2 or less. More preferably, the boundary between the intermediate region and the peripheral region of the objective lens is formed in a portion corresponding to NA2.

  When the third light flux that has passed through the objective lens is condensed on the information recording surface of the third optical disc, it is preferable that the spherical aberration has at least one discontinuous portion. In that case, the discontinuous portion has a range of 0.9 · NA 3 or more and 1.2 · NA 3 or less (more preferably 0.95 · NA 3 or more and 1.15 · NA 3 or less) when the third light flux is used. It is preferable that it exists in.

Moreover, it is preferable that an objective lens satisfy | fills the following conditional expression (11).
1.0 ≦ dt / f ≦ 1.5 (11)
However, dt represents the thickness (mm) of the objective lens on the optical axis, and f represents the focal length (mm) of the objective lens in the first light flux.

  When dealing with an optical disk with a short wavelength and high NA such as BD, the objective lens has a problem that astigmatism is likely to occur and decentration coma is likely to occur, but the conditional expression (11) is satisfied. As a result, it is possible to suppress the generation of astigmatism and decentration coma.

  Further, by satisfying conditional expression (11), the objective lens becomes a thick objective lens having a thick on-axis thickness, so that the working distance during CD recording / reproduction tends to be shortened. By providing the objective lens with the first optical path difference providing structure, the working distance in CD recording / reproduction can be sufficiently ensured, and the effect of the present invention becomes more remarkable.

The first light beam, the second light beam, and the third light beam may be incident on the objective lens as parallel light, or may be incident on the objective lens as divergent light or convergent light. Even during tracking, in order to prevent coma from occurring, it is preferable that all of the first light beam, the second light beam, and the third light beam be incident on the objective lens as parallel light or substantially parallel light. By using the first optical path difference providing structure of the present invention, all of the first light beam, the second light beam, and the third light beam can be incident on the objective lens as parallel light or substantially parallel light. The effect becomes more remarkable. When the first light flux becomes parallel light or substantially parallel light, the imaging magnification m1 of the objective lens when the first light flux enters the objective lens is expressed by the following equation (12):
−0.01 <m1 <0.01 (12)
It is preferable to satisfy.

When the second light beam is incident on the objective lens as parallel light or substantially parallel light, the imaging magnification m2 of the objective lens when the second light beam is incident on the objective lens is expressed by the following equation (13):
-0.01 <m2 <0.01 (13)
It is preferable to satisfy.

On the other hand, when the second light flux is incident on the objective lens as diverging light, the imaging magnification m2 of the objective lens when the second light flux is incident on the objective lens is expressed by the following equation (13) ′,
−0.025 <m2 ≦ −0.01 (13) ′
It is preferable to satisfy.

When the third light beam is incident on the objective lens as a parallel light beam or a substantially parallel light beam, the imaging magnification m3 of the objective lens when the third light beam is incident on the objective lens is expressed by the following equation (14):
-0.01 <m3 <0.01 (14)
It is preferable to satisfy.

On the other hand, when the third light beam is incident on the objective lens as diverging light, the imaging magnification m3 of the objective lens when the third light beam enters the objective lens is expressed by the following equation (14) ′,
−0.025 <m3 ≦ −0.01 (14) ′
It is preferable to satisfy.

  In addition, the working distance (WD) of the objective optical element when using the third optical disk is preferably 0.15 mm or more and 1.5 mm or less. Preferably, it is 0.3 mm or more and 0.9 mm or less. Next, the WD of the objective optical element when using the second optical disc is preferably 0.2 mm or more and 1.3 mm or less. Furthermore, the WD of the objective optical element when using the first optical disk is preferably 0.25 mm or more and 1.0 mm or less.

  An optical information recording / reproducing apparatus according to the present invention includes an optical disc drive apparatus having the optical pickup device described above.

  Here, the optical disk drive apparatus provided in the optical information recording / reproducing apparatus will be described. The optical disk drive apparatus can hold an optical disk mounted from the optical information recording / reproducing apparatus main body containing the optical pickup apparatus or the like. There are a system in which only the tray is taken out, and a system in which the optical disc drive apparatus main body in which the optical pickup device is stored is taken out to the outside.

  An optical information recording / reproducing apparatus using each of the above-described methods is generally equipped with the following components, but is not limited thereto. An optical pickup device housed in a housing or the like, a drive source of an optical pickup device such as a seek motor that moves the optical pickup device together with the housing toward the inner periphery or outer periphery of the optical disc, and the optical pickup device housing the inner periphery or outer periphery of the optical disc These include a transfer means of an optical pickup device having a guide rail or the like that guides toward the head, a spindle motor that rotates the optical disk, and the like.

  In addition to these components, the former method is provided with a tray that can be held in a state in which an optical disk is mounted and a loading mechanism for sliding the tray, and the latter method has no tray and loading mechanism. It is preferable that each component is provided in a drawer corresponding to a chassis that can be pulled out to the outside.

  According to the present invention, it is possible to provide an objective lens for an optical pickup device, an optical pickup device, and an optical information recording / reproducing device that can suppress the occurrence of an error signal or the like when three different optical disks are used interchangeably. .

It is the figure which looked at the single objective lens OL concerning this Embodiment in the optical axis direction. It is an axial direction sectional view showing an example of an optical path difference grant structure. (A) is a figure which shows the change of the diffraction efficiency with respect to the wavelength fluctuation of a blaze | braze type | mold diffraction structure and a staircase type diffraction structure, (b) is the relationship between the order of the diffracted light generate | occur | produced with respect to a use wavelength, and diffraction efficiency. FIG. It is a figure which shows schematically the structure of optical pick-up apparatus PU1 of this Embodiment which can record and / or reproduce | regenerate information appropriately with respect to BD, DVD, and CD which are different optical disks. It is the schematic which shows the staircase type structure as an example of a 1st optical path difference providing structure. FIG. 4 is a longitudinal spherical aberration diagram of Example 1, and B1 to B5, D1 to D5, and C1 to C5 in the drawing respectively correspond to light beams indicated by the same reference numerals on the upper side of Table 4. FIG. 4 is a longitudinal spherical aberration diagram of Example 2, and B1 to B5, D1 to D5, and C1 to C5 in the drawing respectively correspond to light beams indicated by the same reference numerals on the upper side of Table 4. FIG. 6 is a longitudinal spherical aberration diagram of Example 3. B1 to B5, D1 to D5, and C1 to C5 in the drawing respectively correspond to light beams indicated by the same reference numerals on the lower side of Table 4.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 4 is a diagram schematically showing a configuration of the optical pickup apparatus PU1 of the present embodiment that can appropriately record and / or reproduce information on BD, DVD, and CD, which are different optical disks. Such an optical pickup device PU1 can be mounted on an optical information recording / reproducing device. Here, the first optical disc is a BD, the second optical disc is a DVD, and the third optical disc is a CD. The present invention is not limited to the present embodiment.

  The optical pickup device PU1 shown in FIG. 4 emits light when recording / reproducing information with respect to the objective lens OL, the λ / 4 wavelength plate QWP, the collimating lens COL, the polarization beam splitter BS, the dichroic prism DP, and BD. A first semiconductor laser LD1 (first light source) that emits a laser beam (first beam) of λ1 = 405 nm, and a laser beam (first beam) emitted when recording / reproducing information on a DVD (wavelength λ2 = 660 nm) A second semiconductor laser LD2 (second light source) that emits two light beams) and a third semiconductor that emits a laser beam (third light beam) having a wavelength λ3 = 785 nm, which is emitted when information is recorded / reproduced with respect to the CD. It has a laser unit LDP integrated with a laser LD3, a sensor lens SEN, a light receiving element PD as a photodetector, and the like.

The first optical path difference providing structure formed on the objective lens OL makes the first light amount of the first light flux that has passed through the first optical path difference providing structure larger than any other order of the diffracted light amount. The 0th-order diffracted light amount of the second light beam that has passed through the providing structure is made larger than any other order diffracted light amount, and the 0th-order diffracted light amount of the third light beam that has passed through the first optical path difference providing structure is set to any other order. To be larger than the diffracted light quantity. Further, the second optical path difference providing structure formed on the objective lens OL makes the second order diffracted light quantity of the first light beam that has passed through the second optical path difference providing structure larger than any other order diffracted light quantity. The first-order diffracted light amount of the second light beam that has passed through the optical path difference providing structure is made larger than any other order of diffracted light amount, and the first-order diffracted light amount of the third light beam that has passed through the second optical path difference providing structure is It is made larger than the diffracted light quantity of any order. Furthermore, the following formula:
0.08 ≦ P1 / P ≦ 0.15 (2)
0.02 ≦ | P2 / P | ≦ 0.05 (3)
However,
P1: Power of the first optical path difference providing structure P2: Power of the second optical path difference providing structure P: Power of the entire objective lens, P> 0
Meet.

  The divergent light beam of the first light beam (λ1 = 405 nm) emitted from the first semiconductor laser LD1 passes through the dichroic prism DP, passes through the polarization beam splitter BS, and then passes through the collimating lens COL as indicated by the solid line. It becomes parallel light, is converted from linearly polarized light into circularly polarized light by the λ / 4 wavelength plate QWP, the light beam diameter is regulated by a diaphragm (not shown), and enters the objective lens OL. Here, the light beam condensed by the central region, the intermediate region, and the peripheral region of the objective lens OL becomes a spot formed on the information recording surface RL1 of the BD through the protective substrate PL1 having a thickness of 0.1 mm. .

  The reflected light beam modulated by the information pits on the information recording surface RL1 is again transmitted through the objective lens OL and a diaphragm (not shown), and then converted from circularly polarized light to linearly polarized light by the λ / 4 wavelength plate QWP, and by the collimating lens COL. A converged light beam is reflected by the polarization beam splitter BS, and converges on the light receiving surface of the light receiving element PD via the sensor lens SEN. The information recorded on the BD can be read by using the output signal of the light receiving element PD to focus or track the objective lens OL by the biaxial actuator AC1. Here, when the wavelength fluctuation occurs in the first light flux or when recording / reproducing of a BD having a plurality of information recording layers, the spherical aberration generated due to the wavelength fluctuation or different information recording layers is changed in magnification. Correction can be made by changing the divergence angle or convergence angle of the light beam incident on the objective optical element OL by changing the collimating lens COL as means in the optical axis direction.

  The divergent light beam of the second light beam (λ2 = 660 nm) emitted from the second semiconductor laser LD2 of the laser unit LDP is reflected by the dichroic prism DP and passes through the polarization beam splitter BS and the collimating lens COL as indicated by the dotted line. The λ / 4 wavelength plate QWP converts the linearly polarized light into circularly polarized light and enters the objective lens OL. Here, the light beam condensed by the central region and the intermediate region of the objective lens OL (the light beam that has passed through the peripheral region is flared and forms a spot peripheral part) is passed through the protective substrate PL2 having a thickness of 0.6 mm. Thus, the spot is formed on the information recording surface RL2 of the DVD and forms the center of the spot.

  The reflected light beam modulated by the information pits on the information recording surface RL2 is transmitted again through the objective lens OL, converted from circularly polarized light to linearly polarized light by the λ / 4 wave plate QWP, and converted into a convergent light beam by the collimator lens COL. The light is reflected by the polarization beam splitter BS and converges on the light receiving surface of the light receiving element PD via the sensor lens SEN. And the information recorded on DVD can be read using the output signal of light receiving element PD.

  The divergent light beam of the third light beam (λ3 = 785 nm) emitted from the third semiconductor laser LD3 of the laser unit LDP is reflected by the dichroic prism DP and passes through the polarization beam splitter BS and the collimating lens COL as indicated by the one-dot chain line. Then, it is converted from linearly polarized light into circularly polarized light by the λ / 4 wavelength plate QWP, and enters the objective lens OL. Here, the light beam condensed by the central region of the objective lens OL (the light beam that has passed through the intermediate region and the peripheral region is flared to form a spot peripheral portion) is passed through the protective substrate PL3 having a thickness of 1.2 mm. Thus, the spot is formed on the information recording surface RL3 of the CD.

  The reflected light beam modulated by the information pits on the information recording surface RL3 passes through the objective lens OL again, is converted from circularly polarized light to linearly polarized light by the λ / 4 wave plate QWP, and is converged by the collimating lens COL. The light is reflected by the polarization beam splitter BS and converges on the light receiving surface of the light receiving element PD via the sensor lens SEN. And the information recorded on CD can be read using the output signal of light receiving element PD.

Examples that can be used in the above-described embodiment will be described below. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻³ ) may be expressed using E (for example, 2.5 × E−3). The optical surface of the objective lens is formed as an aspherical surface that is symmetric about the optical axis and is defined by a mathematical formula in which the coefficients shown in Table 1 are substituted into Formula 1.

  Here, X (h) is an axis in the optical axis direction (the light traveling direction is positive), κ is a conical coefficient, Ai is an aspherical coefficient, h is a height from the optical axis, and r is a paraxial radius of curvature. It is.

  Further, in the case of the embodiment using the diffractive structure, the optical path difference given to the light flux of each wavelength by the diffractive structure is defined by an equation in which the coefficient shown in the table is substituted into the optical path difference function of Formula 2. .

Here, λ is the wavelength of the incident light beam, λ _B is the design wavelength (also called a blazed wavelength in the case of a blazed diffraction structure), dor is the diffraction order, and C _2i is a coefficient of the optical path difference function.

In addition, B ₁ in the equation (10) is represented by B ₁ = C ₂ / λ _B.

Example 1
Table 1 shows lens data of Example 1. Further, FIG. 5 shows a conceptual diagram of the first optical path difference providing structure (diffractive structure 1) that is the step type of the first embodiment (FIG. 5 is a conceptual diagram different from the actual shape of the first embodiment). . The second optical path difference providing structure of Example 1 is a blazed diffractive structure. The objective lens of Example 1 has a focal length of f = 2.2 mm with respect to the light flux with wavelength λ1, P2 / P is negative, and the design wavelength λ _B of the first optical path difference providing structure is 0.25 × 0. .405 μm, the level difference d of the first optical path difference providing structure is d = 0.25 × 0.405 μm / (1.525-1) = 0.193 μm. Further, assuming that the first wavelength λ1 is 0.405 μm (= 405 nm), the step difference d1 = 2 × 0.405 μm / (1.525-1) = 1.543 μm of the second optical path difference providing structure, the formula (1) (However, the refractive index n1 of the objective lens material is assumed to be 1.525). The steps d and d1 in the examples indicate the theoretical steps in the optical axis direction when the optical path difference providing structure is formed on the parallel plate, and the on-axis thickness is the thickest as in the present embodiment. If a ring-shaped optical path difference providing structure centered on the optical axis is formed on the aspheric lens, the step tends to increase as the distance from the optical axis increases. However, in the case of an objective lens having an NA of about 0.8, the step d1 hardly exceeds (3.0 × λ1 / (n1-1)).

(Example 2)
Table 2 shows lens data of Example 2. Further, the first optical path difference providing structure (diffraction structure 1) of the step type of the second embodiment is the same as that shown in FIG. The second optical path difference providing structure of Example 2 is a blazed diffractive structure. The objective lens of Example 2 has a focal length of f = 2.2 mm with respect to the light flux with wavelength λ1, P2 / P is positive, and the design wavelength λ _B of the first optical path difference providing structure is 0.25 × 0. .405 μm, the level difference d of the first optical path difference providing structure is d = 0.25 × 0.405 μm / (1.525-1) = 0.193 μm. Further, assuming that the first wavelength λ1 is 0.405 μm (= 405 nm), the step difference d1 = 2 × 0.405 μm / (1.525-1) = 1.543 μm of the second optical path difference providing structure, the formula (1) (However, the refractive index n1 of the objective lens material is assumed to be 1.525).

(Example 3)
Table 3 shows lens data of Example 3. Further, the first optical path difference providing structure of Example 3 is a blazed diffractive structure, and the second optical path difference providing structure is a blazed diffractive structure. The objective lens of Example 3 has a focal length of f = 1.8 mm with respect to the light flux with wavelength λ1, P2 / P is negative, and the blazed wavelength λ _{B is} 0.2847 μm. Step d = 0.2847 μm / (1.525-1) = 0.542 μm. Further, assuming that the first wavelength λ1 is 0.405 μm (= 405 nm), the step difference d1 = 2 × 0.405 μm / (1.525-1) = 1.543 μm of the second optical path difference providing structure, the formula (1) (However, the refractive index n1 of the objective lens material is assumed to be 1.525).

  Table 4 shows the relationship of the light intensity of the diffracted light of each example. In the first optical path difference providing structure (diffractive structure 1) of the first and second embodiments, the first-order diffracted light is generated as the strongest diffracted light when the light beam having the wavelength λ1 = 405 nm is incident, and the second strongest diffracted light is generated. A third-order diffracted light is generated as light, and a zeroth-order diffracted light is generated as the third strongest diffracted light. Further, when a light beam having a wavelength λ2 = 660 nm is incident, 0th order diffracted light is generated as the strongest diffracted light, 1st order diffracted light is generated as the second strongest diffracted light, and −1st order diffracted light is generated as the third strongest diffracted light. Is generated. Further, when a light beam having a wavelength λ3 = 790 nm is incident, 0th order diffracted light is generated as the strongest diffracted light, 1st order diffracted light is generated as the second strongest diffracted light, and −1st order diffracted light is generated as the third strongest diffracted light. Is generated.

  Next, in the second optical path difference providing structure (diffractive structure 2) of the first and second embodiments, the second-order diffracted light is generated as the strongest diffracted light when the light beam having the wavelength λ1 = 405 nm is incident. The third order diffracted light is generated as the strongest diffracted light, and the first order diffracted light is generated as the third strongest diffracted light. Further, when a light beam having a wavelength λ2 = 660 nm is incident, the first-order diffracted light is generated as the strongest diffracted light, the second-order diffracted light is generated as the second strongest diffracted light, and the zero-order diffracted light is generated as the third strongest diffracted light. Occur. Further, when a light beam having a wavelength of λ3 = 790 nm is incident, first-order diffracted light is generated as the strongest diffracted light, zero-order diffracted light is generated as the second strongest diffracted light, and second-order diffracted light is generated as the third strongest diffracted light. Occur.

  A structure in which the diffraction structure 1 and the diffraction structure 2 are superposed by multiplying the diffraction efficiency of each order of diffracted light generated in the diffraction structure 1 and the diffraction efficiency of each order generated in the diffraction structure 2. It can be seen which order of diffraction light is generated most. For example, in a light beam of 405 nm, the diffraction structure 1 generates the most first-order diffracted light, and the diffraction structure 2 generates the most second-order diffracted light. Therefore, naturally, the diffraction order of the diffraction structure 1 and the diffraction structure 2 are diffracted. The combination of order> = <1,2> is the most frequently generated diffracted light. The next most common is a value obtained by multiplying the diffraction efficiency of the third-order diffracted light generated second most in the diffraction structure 1 by the diffraction efficiency of the second-order diffracted light generated most frequently in the diffraction structure 2 (0.079 * 1). ) = 0.079, a value obtained by multiplying the diffraction efficiency of the first-order diffracted light generated most frequently in the diffraction structure 1 by the diffraction efficiency of the third-order diffracted light generated second most in the diffraction structure 2 (0.715 * 0) ) = 0 values are compared, and the larger one is the second largest. As a result, the combination of the diffracted light with the next largest amount of light is <−3, 2>. By repeating such calculation, as shown in Table 4, the order of the light quantity in the combination of the diffracted light of each diffraction order can be known.

  6 is a longitudinal spherical aberration diagram of the objective lens in Example 1. FIG. In FIG. 6A, which is a longitudinal spherical aberration diagram for the wavelength λ1 = 405 nm, referring to Table 4, the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure. When the second-order diffracted light (B1) is emitted, the amount of light emitted becomes maximum (efficiency 72%), and the third-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure for the second time. The amount of light emitted when the folded light (B2) is emitted is the second highest, and the 0th-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and exits the second-order diffracted light (B3). The third-order diffracted light is the third highest, and the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference-providing structure and the third-order diffracted light (B4) is emitted. The first-order diffracted light emitted from the first optical path difference providing structure is the second optical path difference. The amount of light emitted upon exiting the first-order diffracted light (B5) and enters the given structure is high fifth. Here, as apparent from FIG. 6A, the spherical aberration curves of the light beams B4 and B5 which are unnecessary light are close to the spherical aberration of the light beam B1 used when the BD is used. However, even when the efficiency of the unnecessary light beams B4 and B5 increases due to a manufacturing error or the like, the first optical path difference providing structure and the second optical path difference providing structure are given power so that the unnecessary light beams B4 and B5 are on the optical axis. The condensing position can be shifted from the used light beam B1, thereby suppressing reading errors and the like.

  In FIG. 6B, which is a longitudinal spherical aberration diagram for the wavelength λ2 = 660 nm, the 0th-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and the first-order diffracted light ( D1) is emitted in the maximum amount (efficiency 42%), and the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure to emit the first-order diffracted light (D2). The amount of light emitted when the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and is emitted from the first-order diffracted light (D3). The third highest light output when the 0th-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and the second-order diffracted light (D4) is emitted is the fourth highest, and the first The 0th-order diffracted light emitted from the optical path difference providing structure enters the second optical path difference providing structure. To 0 the amount of light emitted upon exiting order diffracted light (D5) is high fifth. Here, as is apparent from FIG. 6B, the spherical aberration curves of the light beams D4 and D5 that are unnecessary light are close to the spherical aberration of the light beam D1 used when the DVD is used. However, even when the efficiency of the unnecessary light beams D4 and D5 increases due to manufacturing errors or the like, the first optical path difference providing structure and the second optical path difference providing structure are given power so that the unnecessary light beams D4 and D5 are on the optical axis. The condensing position can be shifted from the used light beam D1, thereby suppressing reading errors and the like.

  Further, in FIG. 6C, which is a longitudinal spherical aberration diagram for the wavelength λ3 = 790 nm, the 0th-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and the first-order diffracted light ( The amount of light emitted when C1) is emitted is maximized (efficiency 60%), and the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure to emit the first-order diffracted light (C2). The amount of light emitted when the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and emitted first-order diffracted light (not shown) is emitted. Is the third highest, and the amount of emitted light when the 0th-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and exits the 0th-order diffracted light (C4) is the fourth highest, The 0th-order diffracted light emitted from the 1 optical path difference providing structure is the second optical path difference providing structure. Quantity of light emitted when emitted incident to the second-order diffracted light (C5) is high fifth. Here, as is apparent from FIG. 6C, the spherical aberration curves of the light beams C4 and C5 which are unnecessary light are close to the spherical aberration of the light beam C1 used when the CD is used. However, even when the efficiency of the unnecessary light beams C4 and C5 increases due to a manufacturing error or the like, by giving power to the first optical path difference providing structure and the second optical path difference providing structure, the unnecessary light beams C4 and C5 on the optical axis. The condensing position can be shifted from the used light beam C1, thereby suppressing reading errors and the like.

  FIG. 7 is a longitudinal spherical aberration diagram of the objective lens in Example 2. In FIG. 7A, which is a longitudinal spherical aberration diagram for the wavelength λ1 = 405 nm, referring to Table 4, the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure. When the second-order diffracted light (B1) is emitted, the amount of emitted light is maximized (efficiency 72%), and the 0th-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure. When the amount of emitted light is the second highest when emitting (B2), and the second-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and emits second-order diffracted light (B3) Is the third highest, and the first order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and the third order diffracted light (B4) is emitted fourth. The first-order diffracted light emitted from the first optical path difference providing structure is high and has the second optical path difference. The amount of light emitted upon exiting the first-order diffracted light (B5) is incident on the structure is high fifth. Here, as apparent from FIG. 7A, the spherical aberration curves of the light beams B4 and B5 that are unnecessary light are close to the spherical aberration of the light beam B1 used when the BD is used. However, even when the efficiency of the unnecessary light beams B4 and B5 increases due to a manufacturing error or the like, the first optical path difference providing structure and the second optical path difference providing structure are given power so that the unnecessary light beams B4 and B5 are on the optical axis. The condensing position can be shifted from the used light beam B1, thereby suppressing reading errors and the like.

  In FIG. 7B, which is a longitudinal spherical aberration diagram for the wavelength λ2 = 660 nm, the 0th-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and the first-order diffracted light ( D1) is emitted in the maximum amount (efficiency 42%), and the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure to emit the first-order diffracted light (D2). The amount of light emitted when the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and is emitted from the first-order diffracted light (D3). The third highest light output when the 0th-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and the second-order diffracted light (D4) is emitted is the fourth highest, and the first The 0th-order diffracted light emitted from the optical path difference providing structure enters the second optical path difference providing structure. To 0 the amount of light emitted upon exiting order diffracted light (D5) is high fifth. Here, as apparent from FIG. 7B, the spherical aberration curves of the light beams D4 and D5 which are unnecessary light are close to the spherical aberration of the light beam D1 used when the DVD is used. However, even when the efficiency of the unnecessary light beams D4 and D5 increases due to manufacturing errors or the like, the first optical path difference providing structure and the second optical path difference providing structure are given power so that the unnecessary light beams D4 and D5 are on the optical axis. The condensing position can be shifted from the used light beam D1, thereby suppressing reading errors and the like.

  Further, in FIG. 7C, which is a longitudinal spherical aberration diagram for the wavelength λ3 = 790 nm, the 0th-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and the first-order diffracted light ( The amount of light emitted when C1) is emitted is maximized (efficiency 60%), and the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure to emit the first-order diffracted light (C2). The amount of emitted light when the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and emitted the first-order diffracted light (C3) is the second highest. The third highest light output when the 0th order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and the 0th order diffracted light (C4) is emitted is the fourth highest, and the first The zero-order diffracted light emitted from the optical path difference providing structure enters the second optical path difference providing structure. It shines light emission amount at the time of exiting the second-order diffracted light (C5) with a high fifth. Here, as apparent from FIG. 7C, the spherical aberration curves of the light beams C4 and C5 which are unnecessary light are close to the spherical aberration of the light beam C1 used when the CD is used. However, even when the efficiency of the unnecessary light beams C4 and C5 increases due to a manufacturing error or the like, by giving power to the first optical path difference providing structure and the second optical path difference providing structure, the unnecessary light beams C4 and C5 on the optical axis. The condensing position can be shifted from the used light beam C1, thereby suppressing reading errors and the like.

  FIG. 8 is a longitudinal spherical aberration diagram of the objective lens in Example 3. In FIG. 8A, which is a longitudinal spherical aberration diagram for the wavelength λ1 = 405 nm, referring to Table 4, the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure. When the second-order diffracted light (B1) is emitted, the amount of light emitted becomes maximum (efficiency 72%), and the third-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure for the second time. The amount of light emitted when the folded light (B2) is emitted is the second highest, and the 0th-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and exits the second-order diffracted light (B3). The third-order diffracted light is the third highest, and the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference-providing structure and the third-order diffracted light (B4) is emitted. The first-order diffracted light emitted from the first optical path difference providing structure is the second optical path difference. The amount of light emitted upon exiting the first-order diffracted light (B5) and enters the given structure is high fifth. Here, as apparent from FIG. 8A, the spherical aberration curves of the light beams B4 and B5 which are unnecessary light are close to the spherical aberration of the light beam B1 used when the BD is used. However, even when the efficiency of the unnecessary light beams B4 and B5 increases due to a manufacturing error or the like, the first optical path difference providing structure and the second optical path difference providing structure are given power so that the unnecessary light beams B4 and B5 are on the optical axis. The condensing position can be shifted from the used light beam B1, thereby suppressing reading errors and the like.

  In FIG. 8B, which is a longitudinal spherical aberration diagram for the wavelength λ2 = 660 nm, the 0th-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and the first-order diffracted light ( D1) is emitted in the maximum amount (efficiency 42%), and the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure to emit the first-order diffracted light (D2). The amount of light emitted when the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and is emitted from the first-order diffracted light (D3). The third highest light output when the 0th-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and the second-order diffracted light (D4) is emitted is the fourth highest, and the first The 0th-order diffracted light emitted from the optical path difference providing structure enters the second optical path difference providing structure. To 0 the amount of light emitted upon exiting order diffracted light (D5) is high fifth. Here, as apparent from FIG. 8B, the spherical aberration curves of the light beams D4 and D5 that are unnecessary light are close to the spherical aberration of the light beam D1 used when the DVD is used. However, even when the efficiency of the unnecessary light beams D4 and D5 increases due to manufacturing errors or the like, the first optical path difference providing structure and the second optical path difference providing structure are given power so that the unnecessary light beams D4 and D5 are on the optical axis. The condensing position can be shifted from the used light beam D1, thereby suppressing reading errors and the like.

  Furthermore, in FIG. 8C, which is a longitudinal spherical aberration diagram for the wavelength λ3 = 790 nm, the 0th-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and the first-order diffracted light ( The amount of light emitted when C1) is emitted is maximized (efficiency 60%), and the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure to emit the first-order diffracted light (C2). The amount of emitted light when the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and emitted the first-order diffracted light (C3) is the second highest. The third highest light output when the 0th order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and the 0th order diffracted light (C4) is emitted is the fourth highest, and the first The zero-order diffracted light emitted from the optical path difference providing structure enters the second optical path difference providing structure. It shines light emission amount at the time of exiting the second-order diffracted light (C5) with a high fifth. Here, as apparent from FIG. 8C, the spherical aberration curves of the light beams C4 and C5 which are unnecessary light are close to the spherical aberration of the light beam C1 used when the CD is used. However, even when the efficiency of the unnecessary light beams C4 and C5 increases due to a manufacturing error or the like, by giving power to the first optical path difference providing structure and the second optical path difference providing structure, the unnecessary light beams C4 and C5 on the optical axis. The condensing position can be shifted from the used light beam C1, thereby suppressing reading errors and the like.

  Table 5 summarizes the numerical values that are characteristic of Examples 1 to 3.

  The present invention is not limited to the embodiments described in the specification, and other embodiments and modifications are apparent to those skilled in the art from the embodiments and ideas described in the present specification. It is. The description and examples are for illustrative purposes only, and the scope of the invention is indicated by the following claims. For example, the light beam emitted from the light source may first pass through the second optical path difference providing structure and then pass through the first optical path difference providing structure.

AC1 Biaxial actuator BS Polarizing beam splitter CN Central region COL Collimating lens DP Dichroic prism LD1 First semiconductor laser LD2 Second semiconductor laser LD3 Third semiconductor laser LDP Laser unit MD Intermediate region OL Objective lens OT Peripheral region PD Light receiving element PL1 Protective substrate PL2 protective substrate PL3 protective substrate PU1 Optical pickup device QWP λ / 4 wave plate RL1 Information recording surface RL2 Information recording surface RL3 Information recording surface SEN Sensor lens

Claims (10)

A first light source that emits a first light flux having a first wavelength λ1 (nm), a second light source that emits a second light flux having a second wavelength λ2 (nm) (λ2> λ1), and a third wavelength λ3 (nm) A third light source that emits a third light beam of (λ3> λ2), and recording and / or reproducing information of a first optical disk having a protective substrate with a thickness of t1 using the first light beam, Information is recorded and / or reproduced on the second optical disc having the protective substrate having a thickness t2 (t1 <t2) using the second light flux, and the thickness t3 (t2 <t3) using the third light flux. An objective lens used in an optical pickup device for recording and / or reproducing information on a third optical disk having a protective substrate of
The objective lens imparts a diffractive action to the first light beam having the first wavelength λ1 passing therethrough, but does not give a diffractive action to the second light beam having the second wavelength λ2 and the third light beam having the third wavelength λ3. Having a structure and a second optical path difference providing structure having a blaze shape,
The step d1 (nm) of the second optical path difference providing structure satisfies the following formula when the refractive index of the objective lens material with respect to the first wavelength is n1:
(1.8 × λ1 / (n1-1)) ≦ d1 ≦ (3.0 × λ1 / (n1-1))
(1)
The first optical path difference providing structure and the second optical path difference providing structure both have power. The objective lens according to claim 1, wherein the following expression is satisfied.
0.08 ≦ P1 / P ≦ 0.15 (2)
0.02 ≦ | P2 / P | ≦ 0.05 (3)
However,
P1: Power of the first optical path difference providing structure P2: Power of the second optical path difference providing structure P: Power of the entire objective lens, P> 0   The objective lens according to claim 2, wherein P2 / P is positive.   The objective lens according to claim 2, wherein P2 / P is negative.   The objective lens according to claim 1, wherein the first optical path difference providing structure has a blaze shape.   The objective lens according to claim 1, wherein the first optical path difference providing structure has a step shape. The first optical path difference providing structure makes the first-order diffracted light quantity of the first light beam that has passed through the first optical path difference-providing structure larger than any other order diffracted light quantity, and passes through the first optical path difference providing structure. The 0th-order diffracted light quantity of the second light flux is made larger than any other order diffracted light quantity, and the 0th-order diffracted light quantity of the third light flux passing through the first optical path difference providing structure is changed to any other order diffracted light quantity. Bigger than
The second optical path difference providing structure makes the second-order diffracted light quantity of the first light beam that has passed through the second optical path difference providing structure larger than any other order of diffracted light quantity, and passes through the second optical path difference providing structure. The first order diffracted light quantity of the second light flux is made larger than any other order diffracted light quantity, and the first order diffracted light quantity of the third light flux that has passed through the second optical path difference providing structure is changed to any other order diffracted light quantity. The objective lens according to claim 1, wherein the objective lens is made larger.   The objective lens according to claim 1, wherein the first optical path difference providing structure and the second optical path difference providing structure are superimposed.   An optical pickup device comprising the objective lens according to claim 1.   An optical information recording / reproducing apparatus comprising the optical pickup apparatus according to claim 9.