WO2012133364A1

WO2012133364A1 - Objective lens for optical pickup device, optical pickup device, and optical information recorder / player

Info

Publication number: WO2012133364A1
Application number: PCT/JP2012/057854
Authority: WO
Inventors: 立山清乃
Original assignee: コニカミノルタアドバンストレイヤー株式会社
Priority date: 2011-03-30
Filing date: 2012-03-27
Publication date: 2012-10-04
Also published as: JPWO2012133364A1

Abstract

Provided are an optical pickup device with objective lens, an optical information recorder / player, and an objective lens optimal for use therein which, while simultaneously achieving both BD skew adjustment and off-axis characteristics suitable for CDs, keep away unnecessary diffracted light prone to result in error signals, and, while further having excellent off-axis characteristics with all BDs and CDs, are capable of achieving compatibility with at least two types of optical discs, BDs and CDs, with a common objective lens. When the paraxial power is adjusted giving priority to BDs, the CD sine condition may become inadequate and coma aberration occurring during incidence of off-axis light may increase. Then, using the fact that BDs and CDs have different effective diameters, in the CD effective diameter range, a design is used which gives priority to the CD sine condition, and outside of the CD effective diameter range, a design is used which gives priority to the BD sine condition. Specifically, in the CD effective diameter range, the offense against the sine condition of BDs is adjusted so as to have a maximum value SCmin on the negative side, and outside of the CD effective diameters, the offense against the sine condition of BDs is adjusted so as to have a maximum value SCmax on the positive side.

Description

Objective lens for optical pickup device, optical pickup device and optical information recording / reproducing device

The present invention relates to an objective lens for an optical pickup device, an optical pickup device, and an optical information recording / reproducing device capable of recording and / or reproducing information with respect to an optical disc having three or more information recording surfaces in the thickness direction.

There is known a high-density optical disk system capable of recording and / or reproducing information (hereinafter, “recording and / or reproduction” is referred to as “recording / reproduction”) using a blue-violet semiconductor laser having a wavelength of about 400 nm. As an example, an optical disc for recording / reproducing information with specifications of NA 0.85 and light source wavelength 405 nm, so-called Blu-ray Disc (hereinafter referred to as BD), DVD (NA 0.6, light source wavelength 650 nm, storage capacity 4. It is possible to record 25 GB of information per layer on an optical disk having a diameter of 12 cm, which is the same size as 7 GB).

By the way, simply saying that information can be recorded / reproduced appropriately with respect to a BD cannot be said to be sufficient as a product of an optical disc player / recorder (optical information recording / reproducing apparatus). 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 optical disc player / recorder for BD has a performance capable of appropriately recording / reproducing information while maintaining compatibility with BD and DVD and CD. Is desired.

As a method for recording / reproducing information appropriately while maintaining compatibility with BD and DVD / CD, information is recorded / reproduced between BD optical system and DVD / CD optical system. Although a method of selectively switching according to the recording density of the optical disk to be used is conceivable, a plurality of optical systems are required, which is disadvantageous for downsizing and increases the cost.

Therefore, in order to simplify the configuration of the optical pickup device and to reduce the cost, in the compatible optical pickup device, the optical system for BD and the optical system for DVD or CD are used in common. It is preferable to reduce the number of optical components constituting the apparatus 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 necessary to form an optical path difference providing structure such as a diffraction structure having a wavelength dependency of spherical aberration in the objective lens. is there.

Furthermore, many of the conventional BDs have one or two layers of information recording surface, but due to the market demand to store larger data on one BD, the information recording surface of three or more layers. Research is also progressing with the aim of commercialization of BDs having the same. However, since the NA of the luminous flux when recording / reproducing information is as large as 0.85, in a BD having three or more information recording surfaces, a minimum spherical aberration is imparted to one information recording surface. In this case, spherical aberration increases on other information recording surfaces with different substrate thicknesses, and there is a problem that information cannot be recorded / reproduced appropriately. The problem of spherical aberration becomes more apparent as the number of information recording surfaces increases (that is, as the distance between the information recording surface having the smallest distance from the surface and the information recording surface having the largest distance from the surface increases). On the other hand, by moving the coupling lens disposed between the light source and the objective lens in the optical axis direction, it is possible to correct spherical aberration caused by the difference in substrate thickness. However, in such a system, convergent light or divergent light is incident on the objective lens, and there is a problem of how to adjust the skew of the BD. The operation of changing the information recording surface on which information is to be recorded / reproduced from one information recording surface to another information recording surface may be referred to as “focus jump” in this specification.

Here, Patent Document 1 describes an objective lens that can be used for a BD, a DVD, and a CD having three or more information recording surfaces, and an optical pickup device equipped with the objective lens. However, the BD skew adjustment and securing of off-axis characteristics in CD are generally in a trade-off relationship. However, the technology of Patent Document 1 creates a lens tilt sensitivity for performing skew adjustment in BD as an issue. The off-axis characteristics of BD, DVD, and CD are not considered.

JP 2010-170634 A

The present invention has been made to solve the above-mentioned problems, and while keeping both the BD skew adjustment and the off-axis characteristics in the CD, the unnecessary diffracted light that causes an error signal is kept away, and further, the BD / CD. Optical pickup apparatus, optical information recording / reproducing apparatus, and optical information recording / reproducing apparatus including an objective lens capable of performing compatibility of at least two types of BD / CD optical discs with a common objective lens An object is to provide a suitable objective lens.

The objective lens according to claim 1, wherein a first light source that emits a first light beam with a wavelength λ1 (390 nm <λ1 <415 nm) and a third light beam with a third wavelength λ3 (760 nm ≦ λ3 ≦ 820 nm) are emitted. Information recording surfaces having three light sources and an objective lens and having different distances from the light incident surface (thickness of the transparent substrate, but the thickest transparent substrate thickness being TMAX (mm)) are 3 in the thickness direction. Recording and / or reproducing information by selecting any one information recording surface in the BD having two or more and condensing the first light flux on the selected information recording surface by the objective lens; An optical pickup for recording and / or reproducing information by condensing the third light flux on the information recording surface of a CD having a protective substrate having a transparent substrate thickness of t3 (mm) (t1 <t3) by the objective lens. An objective lens used in the apparatus,
A first optical path difference providing structure in a region where the first light flux and the third light flux are commonly incident;
At normal temperature (25 ± 3 ° C.) and a cover glass thickness T (mm) satisfying the expression (1), the magnification M at which the third-order spherical aberration is minimized in the objective lens on which the first light flux is incident is ( 2) When the formula is satisfied, the sine condition violation amount at the magnification M is the first maximum value at the pupil radius H1, the second maximum value at the pupil radius H2, and the pupil radius H3 is 0.9 or more. Equation (3) is satisfied (however, the pupil radii H1, H2, and H3 are relative values when the effective radius of the objective lens is 1), and the derivative Φ (h) of the sine condition violation amount is Satisfy equations (4) to (6)
TMAX × 0.78 ≦ T ≦ TMAX × 1.1 (1)
-0.003 ≦ M ≦ 0.003 (2)
H1 <H2 <H3 (3)
φ (h) <0.0 (h <H1) (4)
φ (h)> 0.0 (H1 <h <H2) (5)
φ (h) <0.0 (H2 <h <H3) (6)
Furthermore, the following formula is satisfied.
-0.01 ≦ m1 ≦ 0.01 (7)
-0.01 ≦ m3 ≦ 0.01 (8)
−0.05 ≦ (fB3−fB1) /d≦0.10 (9)
However,
fB1 = WD1 + t1 × (1-1 / n1)
fB3 = WD3 + t3 × (1-1 / n3)
ν: Abbe number m1 of the material of the objective lens m1: Imaging magnification when the light beam having the first wavelength λ1 is incident on the objective lens m3: Result when the light beam having the third wavelength λ3 is incident on the objective lens Image magnification d: On-axis thickness of the objective lens (mm)
WD1: Working distance when using the BD (mm)
WD3: Working distance when using the CD (mm)
n1: Refractive index of the protective substrate of the BD with respect to the light beam with the first wavelength λ1 n3: Refractive index of the protective substrate of the CD with respect to the light beam with the third wavelength λ3

The sine condition that defines the off-axis characteristics of the objective lens is determined by (a) the thickness of the protective substrate of the optical disc, (b) the magnification, and (c) the paraxial diffraction power. Since the protective substrate thickness of the optical disk is different, if the sine condition is satisfied in one optical disk, the sine condition may not be satisfied in another optical disk. In such a case, when an off-axis light beam enters an optical disk that does not satisfy the sine condition, a relatively large coma aberration is generated. Usually, since the sine condition at the time of BD use with strict spot standards is often satisfied, in such a case, there is a risk that the sine condition at the time of CD use may not be satisfied. In particular, in the case of a BD having three or more information recording surfaces in the thickness direction, skew adjustment is performed on the information recording surface having the thickest substrate, and a low-order spherical surface due to a difference in thickness due to a change in magnification. In order to suppress the occurrence of higher order spherical aberration when the aberration is corrected, it is necessary to shift the sine condition to the positive side at the substrate thickness at the design center (magnification M = 0). The sine condition will be greatly broken.

In contrast, (b) it is possible to satisfy the sine condition for each optical disk by changing the magnification. However, changing the magnification makes it difficult to match the optical paths of light beams of two different wavelengths, and the optical pickup device is also increased in size, and further coma aberration is likely to occur during tracking of the objective lens. This is not preferable.

Therefore, as a result of earnest research, the present inventor has adjusted the paraxial diffraction power and devised the shape of the BD sine condition under the premise that the optical system magnification satisfies (7) and (8). It was found that the optimum sine condition can be secured. Here, when the paraxial diffraction power is not used, (fB3-fB1) is almost uniquely determined by the refractive power of the lens. However, when the diffraction power is used, it is possible to give different diffraction power to each disk. Therefore, (fB3-fB1) can be set arbitrarily. Describing with a conceptual diagram, when the paraxial diffraction power is not used, each sine condition is as shown in FIG. 14, but when the paraxial diffraction power is within a certain range, it is as shown in FIG. On the other hand, if the paraxial diffraction power is kept too low, the CD sine condition changes to approach 0 as shown in [1] in FIG. 15 and the off-axis characteristics of the CD become good, but the first optical path difference providing structure Undesired diffracted light (diffracted light other than the used diffracted light used for recording / reproducing information) may approach the used diffracted light and be detected by the photodetector to generate an error signal, or the CD working distance In particular, in the slim type optical pickup device, the risk of the objective lens colliding with the CD is remarkably increased. On the other hand, when the paraxial diffraction power is increased, the CD sine condition changes to the positive side as shown in [2] in FIG. 15, the off-axis characteristics of the CD deteriorate, and the diffraction pitch decreases, but 1/1 / 1 structure can keep away unnecessary light, can suppress the false detection detected by the photodetector together with the main light, and can ensure a sufficient working distance in the CD. However, even if the adjustment of the paraxial diffraction power is effective, if the sine condition is adjusted with priority on BD, the CD sine condition may become inappropriate, and coma aberration generated when off-axis light is incident may increase. There is. Therefore, by utilizing the fact that the effective diameters of BD and CD are different, the CD sine condition and WD are prioritized within the effective diameter range of the CD, and the BD sine condition is prioritized outside the effective diameter of the CD. Design. Specifically, the BD sine condition violation amount is adjusted to have a minimum value SCmin on the negative side within the effective diameter range of the CD, and the BD sine condition violation amount is on the positive side outside the CD effective diameter range. It adjusted so that it might have local maximum SCmax (refer FIG. 1).

As a result, when the sine condition violation amount when using BD is plotted on the horizontal axis and the pupil radius (height from the optical axis) with the BD effective diameter being 1 is plotted on the vertical axis, the sine condition violation amount is The pupil radius H1 that takes the first maximum value, the pupil radius H2 that takes the second maximum value, and the pupil radius H3 that is 90% or more of the effective diameter satisfy the above equation (3), and from the optical axis The derivative φ (h) of the sine condition violation amount with the height h as a variable satisfies the equations (4) to (6). That is, the sine condition violation amount draws an inverted S-curve as shown in FIG.

If the paraxial diffraction power is too low, unnecessary diffracted light (diffracted light other than the used diffracted light used for recording / reproducing information) generated from the first optical path difference providing structure approaches the used diffracted light, and light detection is performed. May cause an error signal to be detected by the detector, or the working distance of the CD may be shortened and the objective lens may collide with the CD. Therefore, formula (9) is defined as the optimum range of paraxial diffraction power. More specifically, if the value of equation (9) is equal to or greater than the lower limit, unnecessary light emitted from the first optical path difference providing structure can be kept away, and a working distance in the CD is ensured, while ( 9) If the value of the equation is equal to or less than the upper limit, the difference between the sine conditions when using BD and when using CD becomes small, and off-axis characteristics when using CD can be improved.

Next, the following two effects can be obtained as characteristics suitable for a BD objective lens having three or more layers according to the equations (4) to (6).
(Characteristic 1) Residual higher order spherical aberration at the time of focus jump is small.
(Characteristic 2) The amount of movement of the coupling lens when performing a focus jump is small.
As a result of intensive studies, the present inventors have found an objective lens suitable for a BD having three or more layers having the above (Characteristic 1) and (Characteristic 2) at a level that can be practically used. This will be described in detail below.

Regarding (Characteristic 1) The present inventor has departed from the conventional common sense that the sine condition should be satisfied in the design of the objective lens, and examined whether the problem of the conventional technique could be solved by deliberately breaking the sine condition. However, as shown in Patent Literature 2, if the coma aberration correction state is set so that the design magnification is negative (incident divergent light) and the sine condition in the design magnification is satisfied in all regions within the effective radius, the magnification Since the ratio between the third-order spherical aberration and the fifth-order spherical aberration that occurs when the cover glass thickness changes, the ratio between the third-order spherical aberration and the fifth-order spherical aberration when the cover glass thickness changes (approximately 5: 1) greatly differs. It was found that higher-order spherical aberration remained during focus jump. Based on this knowledge, the present inventor can effectively suppress high-order spherical aberration at the time of focus jump by making the sine condition violation amount have a positive maximum value at the magnification M satisfying the equation (1). Was found.

(Characteristic 2) In order to reduce the amount of movement of the coupling lens when performing the focus jump, it is necessary to increase the amount of change in the third-order spherical aberration with respect to the change in magnification. As a result of the study, the present inventor increases the third-order spherical aberration change amount with respect to the magnification change by setting the sine condition violation amount to have a positive maximum value at the magnification M satisfying the expression (1). Found that it would be possible.

In addition, at least the following two characteristics are required for an objective lens that has high performance stability and is easy to manufacture.
(Characteristic 3) Even when the opposing optical surfaces are shifted in the direction perpendicular to the optical axis due to manufacturing errors (referred to as surface shift), the coma aberration does not become too large.
(Characteristic 4) Spherical aberration should not be too large even when the opposing optical surfaces are displaced in the optical axis direction due to manufacturing errors (referred to as lens thickness error).

As a result of diligent research by the present inventors, not only satisfying the two characteristics (characteristic 1) and (characteristic 2) suitable for the above-described BD having three or more layers, It has been found that, by satisfying the conditions, it is possible to provide an objective lens suitable for BD having three or more layers and having high performance stability and easy to manufacture.
(Characteristic 3) According to the present invention, the second maximum at the second pupil radius H2 is obtained by causing the sine condition violation amount to have the first minimum value at the position of the first pupil radius H1. Since it is possible to suppress the value from becoming too large, it is possible to suppress the amount of coma aberration generated during the surface shift.

(Characteristic 4) According to the present invention, the second maximum at the second pupil radius H2 is obtained by causing the sine condition violation amount to have the first minimum value at the position of the first pupil radius H1. Since it is possible to suppress the value from becoming too large, it is possible to suppress the generation amount of spherical aberration when a lens thickness error occurs, and thus it is possible to provide an objective lens that is easier to manufacture.

As described above, the objective lens according to claim 1 has (Characteristic 1) small residual high-order spherical aberration at the time of focus jump, and (Characteristic 2) small movement amount of the coupling lens at the time of focus jump. In addition, (Characteristic 3) it is possible to suppress the amount of coma aberration generated when the surface is shifted, and (Characteristic 4) it is also possible to suppress the amount of spherical aberration generated when the lens thickness error occurs. Since the objective lens of the present invention is used, an optical disc having three or more information recording surfaces that is small, low cost, and excellent in recording / reproducing characteristics can be provided. It becomes possible to provide an optical pickup device for use. In this specification, the “transparent substrate thickness” is the distance from the light beam incident surface of the optical disc to the information recording surface. In an optical disc having a plurality of information recording surfaces in the thickness direction, each information recording surface is transparent. The substrate thickness will be different from each other. In general, an objective lens for an optical pickup is combined with a cover glass having a predetermined thickness, and the correction state of the spherical aberration is determined so that the spherical aberration is minimized (the thickness of the cover glass is determined as the design cover glass). Also called thickness). The design cover glass thickness may be the same as or different from the transparent substrate thickness of any information recording surface of the optical disc. When the thickness of the cover glass changes, the characteristics of the objective lens also change. Therefore, when discussing the characteristics of the objective lens for the optical pickup, it is necessary to consider the cover glass thickness as a set. Therefore, in this specification, when describing the characteristics of the objective lens, the term “cover glass” is used to distinguish it from the “transparent substrate (also simply referred to as a substrate)” of the optical disk. (Note that although the term “cover glass” is used, the cover glass thickness is not limited to glass, but a resin may be added.)

The objective lens described in claim 2 is characterized in that, in the invention described in claim 1, equation (10) is satisfied.
0.7 ≦ H2 ≦ 0.9 (10)

By satisfying the expression (10), it is possible to suppress the amount of aberration generated when the two optical surfaces facing each other of the objective lens shift in the direction perpendicular to the optical axis due to manufacturing errors. Since it is possible to suppress the amount of aberration generated when the lens thickness is shifted in the optical axis direction due to a manufacturing error, it is possible to provide an objective lens that is easier to manufacture.

The objective lens according to a third aspect is the objective lens according to the first or second aspect, wherein only the objective lens is collected when condensing a light beam incident at a magnification M on the information recording surface of the transparent substrate thickness T of the BD. Is a third-order coma aberration LTCM3 (λrms) that occurs when the lens is tilted by a predetermined angle, and a third-order coma aberration DTCM3 (λrms) that occurs when only the BD is tilted at the predetermined angle in the same direction as the objective lens. The following formula is satisfied.
| LTCM3 | >> | DTCM3 | (11)

If the expression (11) is satisfied, skew adjustment can be performed even when a divergent light beam is incident on the information recording surface having the largest substrate thickness in the BD, and the assembly of the optical pickup device is facilitated. .

The objective lens described in claim 4 is characterized in that, in the invention described in any one of claims 1 to 3, the following expression is satisfied.
−0.05 ≦ (fB3−fB1) /d≦0.05 (6 ′)

If the expression (6 ′) is satisfied, the WD of the CD can be extended by the diffraction power, which is effective for a slim type objective lens.

According to a fifth aspect of the present invention, there is provided the objective lens according to any one of the first to third aspects, wherein the optical pickup device includes a second light flux having a second wavelength λ2 (630 nm ≦ λ2 ≦ 670 nm) at an imaging magnification m2. The objective lens condenses the second light flux on the information recording surface of a DVD having a protective substrate with a transparent substrate thickness of t2 (mm) (t1 <t2 <t3). Information is recorded and / or reproduced. Thereby, in addition to BD and CD, information can be recorded and / or reproduced on DVD.

The objective lens according to claim 6 is the invention according to claim 4 or 5, wherein the height h from the optical axis at which the sine condition when using the BD turns from negative to positive satisfies the following expression. It is characterized by.
_0.8h _CDNA ≤ h ≤ h _DVDNA (12)
However,
h _CDNA : Relative value representing the height in the optical axis direction corresponding to the numerical aperture when the CD is used as the BD effective radius of the objective lens is 1 h _DVDNA : Optical axis direction corresponding to the numerical aperture when the DVD is used Relative value expressing height as BD effective radius of the objective lens is 1

When the equation (12) is satisfied, the sine condition violation amount when using the BD within the CD effective diameter becomes negative, so that the sine condition violation amount when using the CD can be reduced.

The objective lens according to claim 7 is the invention according to claim 5 or 6,
The 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 has the first optical path difference providing structure,
The objective lens condenses the first light flux that passes through the central region so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux that passes through the central region. Are recorded on the information recording surface of the DVD so that information can be recorded and / or reproduced, and the third light flux passing through the central region is recorded and / or recorded on the information recording surface of the CD. Or collect it so that it can be regenerated,
The objective lens condenses the first light flux passing through the intermediate area so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux passes through the intermediate area. Is recorded on the information recording surface of the DVD so that information can be recorded and / or reproduced, and the third light flux passing through the intermediate region is recorded and / or recorded on the information recording surface of the CD. Or do not concentrate so that it can be regenerated,
The objective lens condenses the first light flux passing through the peripheral area so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux passes through the peripheral area. Is recorded on the information recording surface of the DVD so that information can be recorded and / or reproduced, and the third light flux passing through the peripheral area is recorded on the information recording surface of the CD. And / or do not collect light for playback
The first optical path difference providing structure is a structure in which at least a first basic structure and a second basic structure are overlapped,
The first basic structure makes the first-order diffracted light quantity of the first light beam that has passed through the first basic structure larger than any other order of diffracted light quantity, and 1 of the second light flux that has passed through the first basic structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, making the first order diffracted light quantity of the third light flux that has passed through the first basic structure larger than any other order diffracted light quantity,
The second basic structure makes the second-order diffracted light amount of the first light beam that has passed through the second basic structure larger than any other order of diffracted light amount, and 1 of the second light beam that has passed through the second basic structure. The next diffracted light amount is made larger than any other order diffracted light amount, and the first diffracted light amount of the third light beam that has passed through the second basic structure is made larger than any other order diffracted light amount. To do.

As in the objective lens of the present invention, the first optical path difference providing structure is a structure in which at least a first basic structure and a second basic structure are overlapped, and the first basic structure includes the first basic structure. The first-order diffracted light amount of the first light beam that has passed is made larger than any other order of diffracted light amount, and the first-order diffracted light amount of the second light beam that has passed through the first basic structure is greater than any other order of diffracted light amount. The first-order diffracted light amount of the third light flux that has passed through the first basic structure is made larger than any other order diffracted light amount (sometimes referred to as a 1/1/1 structure), and the second The basic structure makes the second-order diffracted light amount of the first light beam that has passed through the second basic structure larger than any other order of diffracted light amount, and the first-order diffraction of the second light beam that has passed through the second basic structure. Make the light intensity larger than any other order of diffracted light, By making the first-order diffracted light amount of the third light flux that has passed through the second basic structure larger than any other order diffracted light amount (sometimes referred to as a 2/1/1 structure), the common objective lens While used, it is possible to provide an objective lens having a balanced light utilization efficiency while maintaining a high light utilization efficiency for any of the three types of optical disks of BD / DVD / CD.

The objective lens according to claim 8 is the objective lens according to claim 7, wherein the first foundation structure and the second foundation structure are blazed, and one objective lens closest to the optical axis in the second foundation structure is provided. 2 to 6 ring zones of the first basic structure are included on the ring zone.

According to the present invention, two to six ring zones of the first basic structure are superimposed on one ring zone closest to the optical axis in the second basic structure, so that BD / DVD / CD compatibility is achieved. You can secure a working distance when using a CD. Further, it is possible to reduce the problem of unnecessary light (light flux reflected by other layers) when using an optical disk having a plurality of layers, and to improve the temperature characteristics and wavelength characteristics when using a DVD.

The objective lens according to claim 9 is the objective lens according to claim 8, wherein the step of the first basic structure provided at least in the vicinity of the optical axis of the central region is directed in a direction opposite to the optical axis. And
The second basic structure provided at least in the vicinity of the optical axis of the central region is characterized in that the step is directed in the direction of the optical axis.

As a result, in the first optical path difference providing structure in which the first basic structure and the second basic structure are overlapped, the level difference in the optical axis direction can be further reduced, thereby further suppressing the decrease in diffraction efficiency when the wavelength varies. it can.

An objective lens according to a tenth aspect is the invention according to the eighth or ninth aspect, wherein the intermediate region has a second optical path difference providing structure in which at least a third basic structure and a fourth basic structure are overlapped. ,
The third basic structure makes the first-order diffracted light quantity of the first light beam that has passed through the third basic structure larger than any other order of diffracted light quantity, so that 1 of the second light flux that has passed through the third basic structure. Make the next diffracted light quantity larger than any other order diffracted light quantity,
In the fourth basic structure, the second-order diffracted light amount of the first light beam that has passed through the fourth basic structure is made larger than any other order of diffracted light amount, and 1st of the second light beam that has passed through the fourth basic structure. It is characterized in that the next diffracted light quantity is made larger than any other order diffracted light quantity.

Thereby, in the second optical path difference providing structure in which at least the third basic structure and the fourth basic structure are overlapped, the step amount in the optical axis direction can be reduced, thereby reducing the diffraction efficiency at the time of wavelength variation. Can be suppressed. Further, the orders of the diffracted light having the highest light intensity in the first basic structure and the third basic structure are matched, and the orders of the diffracted light having the highest light intensity in the second basic structure and the fourth basic structure are matched. Therefore, the spherical aberration can be made continuous even when the temperature and the wavelength of the light flux passing through the central region and the intermediate region are changed, and the occurrence of higher order aberrations can be suppressed. In addition, the pupil transmittance distribution is almost flat between the intermediate region and the peripheral region, and it is possible to effectively suppress the spot thickening that occurs when the amount of light changes greatly at the boundary due to abolishment or the like. It is also possible to ensure the degree of freedom in designing the objective lens.

The objective lens according to claim 11 is the objective lens according to claim 10, wherein the third foundation structure and the fourth foundation structure are blazed, and one objective lens closest to the central region in the fourth foundation structure is provided. One to three annular zones of the third basic structure are included on the annular zone.

Thereby, when using a BD having a plurality of information recording layers or when using a DVD, the condensing position of unnecessary light generated by passing through the intermediate region is the information recording layer other than the information recording layer for recording / reproducing information. It can be separated from the information recording device. In addition, the wavelength characteristics when using a DVD can be improved.

According to a twelfth aspect of the present invention, in the invention according to the tenth or eleventh aspect, in the third basic structure provided near the boundary with the central region, the step is directed in a direction opposite to the optical axis. And
The fourth foundation structure provided in the vicinity of the boundary with the central region is characterized in that the step is directed in the direction of the optical axis.

As a result, in the second optical path difference providing structure in which the third basic structure and the fourth basic structure are overlapped, the level difference in the optical axis direction can be further reduced, thereby further suppressing the decrease in diffraction efficiency at the time of wavelength fluctuation. it can.

The objective lens according to claim 13 is the invention according to any one of claims 10 to 12, wherein the annular zone of the third foundation structure is disposed on one annular zone closest to the peripheral region in the fourth foundation structure. 1 to 5 are included.

An objective lens according to a fourteenth aspect is the invention according to any one of the tenth to thirteenth aspects, wherein the intermediate region is provided with only the third base structure and the fourth base structure, and the other bases. The structure is not provided.

The objective lens according to claim 15 is the invention according to any one of claims 1 to 14, wherein the annular zone of the first foundation structure is disposed on one annular zone closest to the intermediate region in the second foundation structure. 1 to 5 are included.

An objective lens according to a sixteenth aspect is characterized in that, in the invention according to any one of the first to fifteenth aspects, the following expression is satisfied.
160 (mm) ≤ N · f ≤ 210 (mm) (13)
Here, the total number of annular zones in the central region is N, and the focal length of the objective lens in the first light flux is f (mm).

By setting the value of equation (13) above the lower limit, the CD working distance can be secured, and the possibility of scratching by interference with the optical disk can be reduced. On the other hand, by setting the value of the expression (13) below the upper limit, it is possible to prevent the pitch from becoming too small, thereby preventing the workability from being lowered and reducing the shape error, and as a result, preventing the diffraction efficiency from being lowered.

An optical pickup device according to claim 17 has the objective lens according to any one of claims 1 to 16.

An optical information recording / reproducing device according to claim 18 has the optical pickup device according to claim 17.

The optical pickup device according to the present invention preferably includes at least two light sources, a first light source and a third light source, and further includes a second light source. Furthermore, the optical pickup device of the present invention has a condensing optical system for condensing the first light beam on the information recording surface of the BD and condensing the third light beam on the information recording surface of the CD. The condensing optical system preferably condenses the second light flux on the information recording surface of the DVD. The optical pickup device of the present invention preferably includes a light receiving element that receives a reflected light beam from the information recording surface of the BD and CD, and the light receiving element receives a reflected light beam from the information recording surface of the DVD.

BD has three or more information recording surfaces stacked in the thickness direction. In other words, the BD is an optical disc having three or more information recording surfaces in the thickness direction that have different distances from the light beam incident surface of the optical disc to the information recording surface (this is referred to as “transparent substrate thickness” in this specification). . Of course, you may have four or more information recording surfaces. The thickness of the protective substrate that is the thickest in the BD is t1. The DVD has a protective substrate having a thickness t2 (t1 <t2) and an information recording surface. The CD has a protective substrate having a thickness of t3 (t2 <t3) and an information recording surface. Note that the DVD or CD may also be a multi-layer optical disk 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 two or more information recording layers, and the like. Further, 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. Including DVD-ROM, DVD-Video, DVD- Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, and the like. 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 thickness of the protective substrate is 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, it is preferable to satisfy the following conditional expressions (15), (16), and (17), but is not limited thereto. 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.
0.01mm ≦ t1 ≦ 0.125mm (15)
0.5mm ≤ t2 ≤ 0.7mm (16)
1.0 mm ≤ t3 ≤ 1.3 mm (17)

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) preferably satisfies the following conditional expressions (18) and (19).
1.5 · λ1 <λ2 <1.7 · λ1 (18)
1.8 · λ1 <λ3 <2.0 · λ1 (19)

The first wavelength λ1 of the first light source is preferably 350 nm to 440 nm, more preferably 390 nm to 415 nm, and the second wavelength λ2 of the second light source is preferably 570 nm to 680 nm, more preferably. Is 630 nm or more and 670 nm or less, and the third wavelength λ3 of the third light source is preferably 750 nm or more and 880 nm or less, more preferably 760 nm or more and 820 nm or less.

Also, 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. Of course, the first light source, the second light source, and the third light source may all be fixedly housed in one package. 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. A light receiving element may be used. 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 light incident on the collimator 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 of the present invention is preferably a single plastic lens, but may be a glass lens. A convex lens is preferable. 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, it is preferable to use an alicyclic hydrocarbon-based polymer material such as a cyclic olefin-based resin material as a plastic material constituting the objective lens. 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 ) is -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, it is preferable that the coupling lens is also a plastic lens.

Some preferred examples of the alicyclic hydrocarbon polymer are shown below.

A first preferred example includes a polymer block [A] containing a repeating unit [1] represented by the following formula (I), a repeating unit [1] represented by the following formula (1) and the following formula ( II) and / or polymer block [B] containing a repeating unit [3] represented by the following formula (III), and repeating in the block [A] From the block copolymer in which the relationship between the molar fraction a (mol%) of the unit [1] and the molar fraction b (mol%) of the repeating unit [1] in the block [B] is a> b. It is the resin composition which becomes.

(Wherein R ¹ represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms, and R ^{2 to} R ¹² each independently represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a hydroxyl group, a carbon number of 1 ˜20 alkoxy groups or halogen groups.)

(In the formula, R ¹³ represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.)

(Wherein R ¹⁴ and R ¹⁵ each independently represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.)

Next, a second preferred example is obtained by addition polymerization of a monomer composition comprising at least an α-olefin having 2 to 20 carbon atoms and a cyclic olefin represented by the following general formula (IV). Polymer (B) obtained by addition polymerization of polymer (A) and a monomer composition comprising an α-olefin having 2 to 20 carbon atoms and a cyclic olefin represented by the following general formula (V) ).

[Wherein n is 0 or 1, m is 0 or an integer of 1 or more, q is 0 or 1, and R ¹ to R ¹⁸ , R ^a and R ^b are each independently a hydrogen atom, A halogen atom or a hydrocarbon group, R ¹⁵ to R ¹⁸ may be bonded to each other to form a monocycle or polycycle, and the monocycle or polycycle in parentheses may have a double bond Alternatively, R ¹⁵ and R ¹⁶ , or R ¹⁷ and R ¹⁸ may form an alkylidene group. ]

[Wherein, R ¹⁹ to R ²⁶ each independently represents a hydrogen atom, a halogen atom or a hydrocarbon group. ]

In order to add further performance to the resin material, the following additives may be added.

(Stabilizer)
It is preferable to add at least one stabilizer selected from a phenol stabilizer, a hindered amine stabilizer, a phosphorus stabilizer, and a sulfur stabilizer. By suitably selecting and adding these stabilizers, for example, it is possible to more highly suppress the white turbidity and the optical characteristic fluctuations such as the refractive index fluctuations when continuously irradiated with light having a short wavelength of 405 nm. .

As the preferred phenol-based stabilizer, conventionally known ones can be used. For example, 2-t-butyl-6- (3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2 , 4-di-t-amyl-6- (1- (3,5-di-t-amyl-2-hydroxyphenyl) ethyl) phenyl acrylate and the like, and JP-A Nos. 63-179953 and 1-168643. Acrylate compounds described in Japanese Patent Publication No. 1; octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 2,2′-methylene-bis (4-methyl-6-tert-butylphenol) ), 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1,3,5-trimethyl-2,4,6-tris ( , 5-di-t-butyl-4-hydroxybenzyl) benzene, tetrakis (methylene-3- (3 ', 5'-di-t-butyl-4'-hydroxyphenylpropionate)) methane [ie pentaerythris Limethyl-tetrakis (3- (3,5-di-tert-butyl-4-hydroxyphenylpropionate))], triethylene glycol bis (3- (3-tert-butyl-4-hydroxy-5-methylphenyl) ) Propionate) and other alkyl-substituted phenolic compounds; 6- (4-hydroxy-3,5-di-t-butylanilino) -2,4-bisoctylthio-1,3,5-triazine, 4-bisoctylthio -1,3,5-triazine, 2-octylthio-4,6-bis- (3,5-di-t-butyl-4-oxyanilino) -1,3,5- Triazine group-containing phenol compounds such as triazine; and the like.

Preferred hindered amine stabilizers include bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (2,2,6,6-tetramethyl-4-piperidyl) succinate, bis ( 1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, bis (N-octoxy-2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (N-benzyloxy-2, 2,6,6-tetramethyl-4-piperidyl) sebacate, bis (N-cyclohexyloxy-2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (1,2,2,6,6) -Pentamethyl-4-piperidyl) 2- (3,5-di-t-butyl-4-hydroxybenzyl) -2-butylmalonate, bis (1-acryloyl-2,2, , 6-Tetramethyl-4-piperidyl) 2,2-bis (3,5-di-t-butyl-4-hydroxybenzyl) -2-butylmalonate, bis (1,2,2,6,6- Pentamethyl-4-piperidyl) decandioate, 2,2,6,6-tetramethyl-4-piperidyl methacrylate, 4- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionyloxy] -1- [2- (3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy) ethyl] -2,2,6,6-tetramethylpiperidine, 2-methyl-2- ( 2,2,6,6-tetramethyl-4-piperidyl) amino-N- (2,2,6,6-tetramethyl-4-piperidyl) propionamide, tetrakis (2,2,6,6-tetramethyl -4-pi Lysyl) 1,2,3,4-butane tetracarboxylate, tetrakis (1,2,2,6,6-pentamethyl-4-piperidyl) 1,2,3,4-butane tetracarboxylate, and the like.

Further, the preferable phosphorus stabilizer is not particularly limited as long as it is a substance usually used in the general resin industry. For example, triphenyl phosphite, diphenylisodecyl phosphite, phenyl diisodecyl phosphite, tris (nonyl). Phenyl) phosphite, tris (dinonylphenyl) phosphite, tris (2,4-di-t-butylphenyl) phosphite, 10- (3,5-di-t-butyl-4-hydroxybenzyl) -9 Monophosphite compounds such as 1,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide; 4,4′-butylidene-bis (3-methyl-6-tert-butylphenyl-di-tridecyl) Phosphite), 4,4 'isopropylidene-bis (phenyl-di-alkyl (C12-C15)) Fight) and the like diphosphite compounds such as. Among these, monophosphite compounds are preferable, and tris (nonylphenyl) phosphite, tris (dinonylphenyl) phosphite, tris (2,4-di-t-butylphenyl) phosphite and the like are particularly preferable.

Preferred sulfur stabilizers include, for example, dilauryl 3,3-thiodipropionate, dimyristyl 3,3′-thiodipropionate, distearyl 3,3-thiodipropionate, lauryl stearyl 3,3- Thiodipropionate, pentaerythritol-tetrakis- (β-lauryl-thio) -propionate, 3,9-bis (2-dodecylthioethyl) -2,4,8,10-tetraoxaspiro [5,5] undecane Etc.

The amount of each of these stabilizers is appropriately selected within a range not to impair the purpose of the present invention, but is usually 0.01 to 2 parts by mass with respect to 100 parts by mass of the alicyclic hydrocarbon-based copolymer, The amount is preferably 0.01 to 1 part by mass.

(Surfactant)
A surfactant is a compound having a hydrophilic group and a hydrophobic group in the same molecule. The surfactant can prevent white turbidity of the resin composition by adjusting the rate of moisture adhesion to the resin surface and the rate of moisture evaporation from the surface.

Specific examples of the hydrophilic group of the surfactant include a hydroxy group, a hydroxyalkyl group having 1 or more carbon atoms, a hydroxyl group, a carbonyl group, an ester group, an amino group, an amide group, an ammonium salt, a thiol, a sulfonate, A phosphate, a polyalkylene glycol group, etc. are mentioned. Here, the amino group may be primary, secondary, or tertiary. Specific examples of the hydrophobic group of the surfactant include an alkyl group having 6 or more carbon atoms, a silyl group having an alkyl group having 6 or more carbon atoms, and a fluoroalkyl group having 6 or more carbon atoms. Here, the alkyl group having 6 or more carbon atoms may have an aromatic ring as a substituent. Specific examples of the alkyl group include hexyl, heptyl, octyl, nonyl, decyl, undecenyl, dodecyl, tridecyl, tetradecyl, myristyl, stearyl, lauryl, palmityl, cyclohexyl and the like. Examples of the aromatic ring include a phenyl group. The surfactant only needs to have at least one hydrophilic group and hydrophobic group as described above in the same molecule, and may have two or more groups.

More specifically, examples of such a surfactant include myristyl diethanolamine, 2-hydroxyethyl-2-hydroxydodecylamine, 2-hydroxyethyl-2-hydroxytridecylamine, 2-hydroxyethyl-2- Hydroxytetradecylamine, pentaerythritol monostearate, pentaerythritol distearate, pentaerythritol tristearate, di-2-hydroxyethyl-2-hydroxydodecylamine, alkyl (8-18 carbon atoms) benzyldimethylammonium chloride, ethylene Examples thereof include bisalkyl (carbon number 8 to 18) amide, stearyl diethanolamide, lauryl diethanolamide, myristyl diethanolamide, palmityl diethanolamide, and the like. Among these, amine compounds or amide compounds having a hydroxyalkyl group are preferably used. In the present invention, two or more of these compounds may be used in combination.

From the viewpoint of effectively suppressing the white turbidity of the molded product accompanying fluctuations in temperature and humidity and maintaining the light transmittance of the molded product high, the surfactant is added to 100 parts by mass of the alicyclic hydrocarbon-based polymer. On the other hand, it is preferable to add 0.01 to 10 parts by mass. The addition amount of the surfactant is more preferably 0.05 to 5 parts by mass, still more preferably 0.3 to 3 parts by mass with respect to 100 parts by mass of the alicyclic hydrocarbon-based polymer.

(Plasticizer)
The plasticizer is added as necessary to adjust the melt index of the copolymer.

Plasticizers include bis (2-ethylhexyl) adipate, bis (2-butoxyethyl) adipate, bis (2-ethylhexyl) azelate, dipropylene glycol dibenzoate, tri-n-butyl citrate, tricitrate citrate -N-butylacetyl, epoxidized soybean oil, 2-ethylhexyl epoxidized tall oil, chlorinated paraffin, tri-2-ethylhexyl phosphate, tricresyl phosphate, t-butylphenyl phosphate, tri-2-ethylhexyl phosphate Diphenyl, dibutyl phthalate, diisohexyl phthalate, diheptyl phthalate, dinonyl phthalate, diundecyl phthalate, di-2-ethylhexyl phthalate, diisononyl phthalate, diisodecyl phthalate, ditridecyl phthalate, butyl benzyl phthalate, dicyclyl phthalate Known materials such as hexyl, di-2-ethylhexyl sebacate, tri-2-ethylhexyl trimellitic acid, Santizer 278, Paraplex G40, Drapex 334F, Plastolein 9720, Mesamol, DNODP-610, HB-40, etc. are applicable. . The selection of the plasticizer and the addition amount are appropriately performed under the condition that the permeability of the copolymer and the resistance to environmental changes are not impaired.

As these resins, cycloolefin resins are preferably used. Specifically, ZEONEX manufactured by Nippon Zeon Co., Ltd., APEL manufactured by Mitsui Chemicals, Inc., TOPAS® ADVANCED® POLYMERS manufactured by TOPAS, and JSR manufactured by ARTON are preferable. Take as an example.

Further, the Abbe number of the material constituting the objective lens is preferably 50 or more.

The objective lens will be described below, but here, an objective lens for BD / DVD / CD compatibility will be described. In the case of an objective lens for BD / CD compatibility, there are only two regions, a central region and a peripheral region described below, and details thereof are omitted.

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. 2, 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. In addition, a first optical path difference providing structure is provided in the central area of the objective lens, and a second optical path difference providing structure is provided in the intermediate area. The peripheral region may be a refracting surface, or a third optical path difference providing structure may be provided in the peripheral region. 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 central area of the objective lens can be said to be a BD / DVD / CD shared area used for recording / reproducing BD, DVD and CD. That is, the objective lens condenses the first light flux passing through the central area so that information can be recorded / reproduced on the information recording surface of the BD, and the second light flux passing through the central area is recorded as information recording on the DVD. The light is condensed so that information can be recorded and / or reproduced on the surface, and the third light flux passing through the central region is condensed so that information can be recorded / reproduced on the information recording surface of the CD. In addition, the first optical path difference providing structure provided in the central region has the BD protective substrate thickness t1 and the DVD protective substrate thickness with respect to the first and second light fluxes passing through the first 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 first optical path difference providing structure is different from the thickness t1 of the BD protective substrate and the thickness t3 of the CD protective substrate with respect to the first and third light fluxes that have passed through the first 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 BD / DVD recording / reproduction and can be said to be a BD / DVD shared area not used for CD recording / reproduction. That is, the objective lens condenses the first light flux passing through the intermediate area so that information can be recorded / reproduced on the information recording surface of the BD, and the second light flux passing through the intermediate area is recorded as information recording on the DVD. Light is collected so that information can be recorded / reproduced on the surface. 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 CD. The third light flux passing through the intermediate region of the objective lens preferably forms a flare on the information recording surface of the CD. As shown in FIG. 3, in the spot formed on the information recording surface of the CD by the third light beam that has passed through the objective lens, the spot center having a high light quantity density in the order from the optical axis side (or the spot center) to the outside. It is preferable to have a portion SCN, a spot intermediate portion SMD whose light intensity density is lower than that of the spot central portion, and a spot peripheral portion SOT whose light intensity density is higher than that of the spot intermediate portion and lower than that of the spot central portion. 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. In other words, 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 CD.

The peripheral region of the objective lens is used for BD recording / reproduction, and can be said to be a BD-dedicated region that is not used for DVD / CD recording / reproduction. 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 BD. 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 DVD, and the third light flux that passes through the peripheral area does not converge. Do not collect light so that information can be recorded / reproduced on top. 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 surface of DVD and CD. 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 surface of DVD and CD.

The first 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 first optical path difference providing structure is provided on the entire surface of the central region. The second 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, the second optical path difference providing structure is provided on the entire surface of the intermediate region. When the peripheral region has the third optical path difference providing structure, the third 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 third optical path difference providing structure is provided on the entire surface of the peripheral region.

In addition, 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 a function 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, when the objective lens provided with the diffractive structure is a single aspherical lens, the incident angle of the light beam to the objective lens differs depending on the height from the optical axis, so the step amount of the diffractive structure is slightly different for each annular zone. It will be. 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.

Incidentally, it is preferable that the optical path difference providing structure has a plurality of concentric annular zones with the optical axis as the center. 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. 4A and 4B, the blaze-type structure means that the cross-sectional shape including the optical axis of the optical element having the optical path difference providing structure is a sawtooth shape. In the example of FIG. 4, 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 in the direction perpendicular to the optical axis of one blaze unit is called a pitch P. (See FIGS. 4A and 4B.) The length of the step in the direction parallel to the optical axis of the blaze is referred to as a step amount B. (See Fig. 4 (a))

In addition, as shown in FIGS. 4C and 4D, 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. 4C is referred to as a five-level step structure, and the optical path difference providing structure illustrated in FIG. 4D is referred to as a two-level step structure (also referred to as a binary structure). .

The optical path difference providing structure is preferably a structure in which a certain unit shape is periodically repeated. 「“ The unit shape is periodically repeated ”here 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. 4 (a), the same sawtooth shape may be repeated, and as shown in FIG. 4 (b), the shape of the sawtooth 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 structure 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.

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. 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. It is also conceivable to provide the first basic structure and the second basic structure on different optical surfaces without overlapping. Similarly, the third basic structure and the fourth basic structure may be provided on different optical surfaces without overlapping.

Next, the first optical path difference providing structure provided in the central region will be described. The first optical path difference providing structure is preferably a structure in which at least the first basic structure and the second basic structure are overlapped, but is not limited thereto. The first optical path difference providing structure is preferably a structure in which only the first basic structure and the second basic structure are overlapped.

The first basic structure is a blaze type structure. In addition, the first basic structure makes the first-order diffracted light quantity of the first light beam that has passed through the first basic structure larger than any other order of diffracted light quantity, and the first-order diffracted light quantity that has passed through the first basic structure. Is made larger than any other order of the diffracted light quantity, and the first order diffracted light quantity of the third light flux that has passed through the first basic structure is made larger than any other order of diffracted light quantity. This is called a (1/1/1) structure. In particular, if the first-order diffracted light that is low order is generated, the step amount of the first basic structure does not become too large, so that the manufacture is facilitated, and the light quantity loss due to the manufacturing error can be suppressed, and the wavelength It is preferable because the diffraction efficiency fluctuation at the time of fluctuation can be reduced.

Further, it is preferable that the first basic structure provided at least in the vicinity of the optical axis in the central region has a step in a direction opposite to the optical axis. “The step is directed in the direction opposite to the optical axis” means a state as shown in FIG. In addition, the first basic structure provided “at least in the vicinity of the optical axis of the central region” refers to a step at least closest to the optical axis among steps of the (1/1/1) structure. Preferably, at least a (1/1/1) structure step existing between the optical axis and the half-position in the direction orthogonal to the optical axis from the optical axis to the boundary between the central region and the intermediate region is the optical axis. Is pointing in the opposite direction.

For example, in the first basic structure provided near the middle region of the central region, the step may be directed in the direction of the optical axis. That is, as shown in FIG. 6 (b), when the first foundation structure is in the vicinity of the optical axis, the step is directed in the opposite direction to the optical axis. It is good also as a shape which faces the direction of an optical axis. However, it is preferable that all the steps of the first basic structure provided in the central region are directed in a direction opposite to the optical axis.

In this way, the direction of the step of the first basic structure in which the diffraction order of the first light beam is the first order is directed in the direction opposite to the optical axis, so that the three types of optical disks of BD / DVD / CD can be used interchangeably. Even with a thick objective lens having a large axial thickness, a sufficient working distance can be secured when the CD is used.

The first basic structure is the first basic structure from the viewpoint of securing a sufficient working distance when using a CD even in a thick objective lens having a thick on-axis thickness, which is used for compatibility with three types of optical disks of BD / DVD / CD. It is preferable to have a negative paraxial power with respect to the luminous flux. Here, “having negative paraxial power” means that C ₂ h ² > 0 when the optical path difference function of the first basic structure is expressed by the following equation ( ² ).

The second basic structure is also a blaze type structure. In the second basic structure, the second-order diffracted light amount of the first light beam that has passed through the second basic structure is made larger than the diffracted light amount of any other order, and the first-order diffraction of the second light beam that has passed through the first basic structure. The light quantity is made larger than any other order of diffracted light quantity, and the first order diffracted light quantity of the third light flux that has passed through the first basic structure is made larger than any other order of diffracted light quantity. This is called a (2/1/1) structure. In particular, if low-order second-order diffracted light or first-order diffracted light is generated, the step amount of the second basic structure does not become too large, which facilitates manufacturing and suppresses light loss caused by manufacturing errors. This is preferable because it can reduce the diffraction efficiency fluctuation at the time of wavelength fluctuation.

Further, it is preferable that the step of the second basic structure provided at least in the vicinity of the optical axis in the central region is directed in the direction of the optical axis. “The step is directed in the direction of the optical axis” means a state as shown in FIG. The second basic structure provided “at least in the vicinity of the optical axis of the central region” refers to a step at least closest to the optical axis among steps of the (2/1/1) structure. Preferably, at least a half of the optical axis orthogonal direction from the optical axis to the boundary between the central region and the intermediate region and the (2/1/1) structure step existing between the optical axis and the optical axis direction It is suitable.

For example, in the second basic structure provided near the middle region of the central region, the step may be directed in a direction opposite to the optical axis. That is, as shown in FIG. 6A, the step is directed in the direction of the optical axis when the second foundation structure is near the optical axis, but is switched halfway, and the step of the second foundation structure is near the optical axis near the intermediate region. It is good also as a shape which faces the reverse direction. However, preferably, the second basic structure provided in the central region is that all the steps are directed in the direction of the optical axis.

When the first optical path difference providing structure is formed by superimposing the first basic structure having the (1/1/1) structure and the second basic structure having the (2/1/1) structure, the height of the step is extremely high. Can be lowered. Therefore, it is possible to further reduce manufacturing errors, further reduce the light amount loss, and further suppress the change in diffraction efficiency when the wavelength changes.

Furthermore, at least near the optical axis of the central region, the first basic structure in which the step is directed in the direction opposite to the optical axis, and at least near the optical axis of the central region, the step is directed in the direction of the optical axis. By superimposing two foundation structures, the height of the step after superposition is higher than when superimposing the steps so that the first and second foundation structures have the same step direction. As a result, it is possible to further suppress the light amount loss due to manufacturing errors and the like, and to further suppress the fluctuation of the diffraction efficiency at the time of wavelength fluctuation.

Further, not only can the three types of optical discs of BD / DVD / CD be compatible, but also the light usage efficiency that can maintain high light usage efficiency for any of the three types of optical discs of BD / DVD / CD. It is preferable to provide a balanced objective lens. For example, it is preferable to provide an objective lens that has a diffraction efficiency of 80% or more for the wavelength λ1, a diffraction efficiency of 60% or more for the wavelength λ2, and a diffraction efficiency of 50% or more for the wavelength λ3. Furthermore, it is more preferable to provide an objective lens that has a diffraction efficiency of 80% or more for the wavelength λ1, a diffraction efficiency of 70% or more for the wavelength λ2, and a diffraction efficiency of 60% or more for the wavelength λ3. In addition, by orienting the step of the first basic structure in the direction opposite to the optical axis, it is easier to change the aberration in the direction of under (undercorrection) when the wavelength changes to the long wavelength side. .

Viewpoint of the shape and step amount of the first optical path difference providing structure after the first basic structure in which the step is opposite to the optical axis and the second basic structure in which the step is directed toward the optical axis are overlapped Therefore, the first optical path difference providing structure in which the first basic structure having the (1/1/1) structure and the second basic structure having the (2/1/1) structure are overlapped is expressed as follows. be able to. The first optical path difference providing structure provided at least in the vicinity of the optical axis of the central region has both a step facing in the opposite direction to the optical axis and a step facing in the direction of the optical axis. It is preferable that the step amount d11 of the step facing the direction opposite to the axis and the step amount d12 of the step facing the direction of the optical axis satisfy the following conditional expressions (20) and (21). More preferably, the following conditional expressions (20) and (21) are satisfied in all the regions of the central region. If the objective lens provided with the optical path difference providing structure is a single aspherical convex lens, the incident angle of the light flux to the objective lens differs depending on the height from the optical axis, so that the optical path difference providing structure that gives the same optical path difference Even so, in general, as the distance from the optical axis increases, the step amount tends to increase. In the following conditional expression, the upper limit is multiplied by 1.5 because the increase in the level difference is taken into account. Here, n represents the refractive index of the objective lens at the first wavelength λ1.
0.6 · (λ1 / (n-1)) <d11 <1.5 · (λ1 / (n-1)) (20)
0.6 · (λ1 / (n-1)) <d12 <1.5 · (2λ1 / (n-1)) (21)

The first optical path difference providing structure provided “at least in the vicinity of the optical axis of the central region” includes at least a step facing in a direction opposite to the optical axis closest to the optical axis and an optical axis closest to the optical axis. An optical path difference providing structure having both of the steps facing the direction of. Preferably, the optical path difference providing structure has a step existing between at least a half position in the direction perpendicular to the optical axis from the optical axis to the boundary between the central region and the intermediate region.

For example, when λ1 is 390 to 415 nm (0.390 to 0.415 μm) and n is 1.54 to 1.60, the above conditional expression can be expressed as follows.

0.39 μm <d11 <1.15 μm (22)
0.39 μm <d12 <2.31 μm (23)

Further, as a method of overlapping the first foundation structure and the second foundation structure, the shape of the foundation structure is finely adjusted so that the positions of all the steps of the second foundation structure and the positions of the steps of the first foundation structure are matched. Alternatively, it is preferable to finely adjust the shape of the foundation structure so that the positions of all the steps of the first foundation structure and the positions of the steps of the second foundation structure are matched.

As described above, when the positions of all the steps of the second foundation structure are matched with the positions of the steps of the first foundation structure, d11 and d12 of the first optical path difference providing structure are the following conditional expressions (24) and (25 ) Is preferably satisfied. More preferably, the following conditional expressions (24) and (25) are satisfied in all the regions of the central region.
0.6 · (λ1 / (n-1)) <d11 <1.5 · (λ1 / (n-1)) (24)
0.6 · (λ1 / (n-1)) <d12 <1.5 · (λ1 / (n-1)) (25)

0.39 μm <d11 <1.15 μm (22) ′
0.39 μm <d12 <1.15 μm (23) ′

More preferably, the following conditional expressions (22) ′ and (23) ′ are preferably satisfied. More preferably, the following conditional expressions (24) ′ and (25) ′ are satisfied in all the regions of the central region.
0.9 · (λ1 / (n−1)) <d11 <1.5 · (λ1 / (n−1)) (24) ′
0.9 · (λ1 / (n-1)) <d12 <1.5 · (λ1 / (n-1)) (25) '

0.59 μm <d11 <1.15 μm (22) ″
0.59 μm <d12 <1.15 μm (23) ″

Further, in the first basic structure having the (1/1/1) structure, when the wavelength of the incident light beam is changed to be longer, the spherical aberration is changed in the undercorrection direction (under), and (2 / In the second basic structure having the 1/1) structure, when the wavelength of the incident light beam is changed to be longer, it is preferable that the spherical aberration is changed in the undercorrection direction (under). With such a configuration, when the refractive index of the objective lens changes due to an increase in the temperature of the optical pickup device, the refractive index of the objective lens is also utilized by utilizing the fact that the wavelength of the light source increases due to the increase in the environmental temperature. It is possible to correct a change in spherical aberration due to a change in the rate and form an appropriate focused spot on the information recording surface of each optical disc. Thereby, even if the objective lens is made of plastic, it is possible to provide an objective lens that can maintain stable performance even when the temperature changes.

It is preferable that the paraxial power of the first foundation structure is larger than that of the second foundation structure. That is, it is preferable that the average pitch of the first foundation structure is smaller than the average pitch of the second foundation structure. Thereby, a working distance in the CD can be secured even in an objective lens having a large axial thickness, which is a BD / DVD / CD compatible objective lens. Furthermore, the chromatic aberration is reduced, a good light spot is formed even when the light source has a high frequency superposition, and the problem of stray light when the optical disk has a plurality of information recording surfaces is reduced. In order to improve the temperature characteristics and the wavelength characteristics at the time, in the first optical path difference providing structure, one ring zone closest to the optical axis of the second basic structure has two or more ring zones of the first basic structure. It is preferable that 6 (particularly preferably 2 to 3) are included. In this case, the “ring zone” closest to the optical axis of the second foundation structure is described, but in practice, it is usually a “circle” including the optical axis. Accordingly, the “annular zone closest to the optical axis” mentioned here includes a circular shape. Further, in one ring zone of the second foundation structure closest to the intermediate region, 1 to 5 ring zones of the first foundation structure (particularly preferably 2 to 3 rings) are included in one ring zone of the second foundation structure. ) Is included.

As shown in FIG. 7D, when the first basic structure and the second basic structure are superimposed as they are, a part may protrude as shown by a dotted line, but the width of the protruding part is 5 μm or less. If it is narrow, the projecting portion is shifted in parallel along the optical axis, and eliminating the projecting portion has no significant effect, so that one annular zone of the second foundation structure can have a plurality of the first foundation structure. The zonal is just like that (see the solid line). Therefore, in the example of FIG.7 (d), it handles as the ring zone of three 1st foundation structures on one ring zone of a 2nd foundation structure. When the first foundation structure and the second foundation structure are superimposed as they are, a dent may be eliminated in the same manner even when a dent having a width of 5 μm or less is generated.

Here, if Δλ (nm) is the amount of change in the first wavelength, and ΔWD (μm) is the chromatic aberration of the objective lens caused by the change in the first wavelength Δλ, the following equation is satisfied.
0.3 (μm / nm) ≦ ΔWD / Δλ ≦ 0.6 (μm / nm) (26)

In order to obtain such a configuration, as described above, in the first optical path difference providing structure, two annular zones N1 of the first basic structure are equal to one annular zone closest to the optical axis of the second basic structure. It is preferable to include ˜6 (particularly preferably 2 to 3). By setting the chromatic aberration to the above-described range, the optical disc has a plurality of information recording surfaces while ensuring a working distance in the CD even in an objective lens having a large axial thickness, which is a BD / DVD / CD compatible objective lens. This is preferable because the problem of stray light can be reduced and the temperature and wavelength characteristics can be improved when using a DVD. In addition, the number N2 of the first foundation structure annular zones superimposed on one annular zone closest to the intermediate region in the second foundation structure is preferably equal to or smaller than N1, for example, 1 to 5 overlapping zones. It should be done.

The first basic structure preferably has a positive diffractive power, so that a working distance when using a CD can be secured even for an objective lens having a large axial thickness such as an objective lens for BD / DVD / CD. Further, the second basic structure preferably has a negative diffraction power. As described above, since both the first basic structure and the second basic structure have diffraction power, when using an optical disk having a plurality of information recording surfaces, unnecessary light reflected by the information recording surface which is not a recording / reproducing object is required light. It is preferable because it can be further away from the center.

The first best focus position where the light intensity of the spot formed by the third light flux is the strongest by the third light flux passing through the first optical path difference providing structure, and the second strongest light intensity of the spot formed by the third light flux. It is preferable that the best focus position satisfies the following conditional expression (27). Here, the best focus position refers to a position where the beam waist becomes a minimum within a certain defocus range. The first best focus position is the best focus position of the necessary light used for CD recording / reproduction, and the second best focus position is the best of the luminous flux having the largest light quantity among the unnecessary light that is not used for CD recording / reproduction. The focus position.
0.05 ≦ L / f13 ≦ 0.35 (27)
However, f13 [mm] indicates the focal length of the third light flux that passes through the first optical path difference providing structure and forms the first best focus, and L [mm] indicates the first best focus and the second best focus. Refers to the distance between.

More preferably, the following conditional expression (27) ′ is satisfied.
0.10 ≦ L / f13 ≦ 0.25 (27) ′

Several preferable examples of the first optical path difference providing structure described above are shown in FIGS. 7A, 7B, and 7C. Although FIG. 7 shows the first optical path difference providing structure ODS1 as a flat plate for convenience, it may be provided on a single aspherical convex lens. The first basic structure BS1 which is a (1/1/1) diffraction structure is overlapped with the second basic structure BS2 which is a (2/1/1) diffraction structure. In FIG. 7A, the step of the second basic structure BS2 faces the direction of the optical axis OA, and the step of the first basic structure BS1 faces the direction opposite to the optical axis OA. Furthermore, it can be seen that the positions of all the steps of the second foundation structure BS2 are aligned with the positions of the steps of the first foundation structure BS1. Next, in FIG.7 (b), the level | step difference of 2nd foundation structure BS2 has faced the direction of optical axis OA, and the level | step difference of 1st foundation structure BS1 has also faced the direction of optical axis OA. Furthermore, it can be seen that the positions of all the steps of the second foundation structure BS2 are aligned with the positions of the steps of the first foundation structure BS1. Next, in FIG.7 (c), the level | step difference of 1st foundation structure BS1 has faced the direction opposite to optical axis OA, and the level | step difference of 2nd foundation structure BS2 has also faced the direction opposite to optical axis OA. . Furthermore, it can be seen that the positions of all the steps of the second foundation structure BS2 are aligned with the positions of the steps of the first foundation structure BS1.

Furthermore, when the total number of annular zones in the central region is N and the focal length of the first light flux of the objective lens is f (mm), it is preferable that the following expression is satisfied. As a result, it is possible to prevent the working distance of the CD from becoming too short and to suppress the workability from being lowered due to the ring zone pitch becoming too small. Note that the number of steps substantially parallel to the optical axis in the central region may be regarded as the total number of annular zones in the central region.
160 (mm) ≤ N · f ≤ 210 (mm) (13)

As described above, the preferable structure of the first optical path difference providing structure has been described focusing on the structure in which the blaze type (1/1/1) structure and the blaze type (2/1/1) structure are superimposed. Examples of other first optical path difference providing structures include the following.

For example, (A) in the case of only a single blazed structure, (B) in the case of a single staircase structure, (C) in the case of superimposing a plurality of blazed structures, (D) a blazed structure and a staircase structure For example. As a preferable example of (A), a first optical path difference providing structure composed only of a blazed (2/1/1) structure or a (1/1/1) structure alone while utilizing the magnification difference of the objective lens. The 1st optical path difference providing structure which becomes becomes. Preferred examples of (B) include a first optical path difference providing structure consisting only of a (1/3/4) structure which is a 7-level staircase structure, and a 7-level staircase structure (1 / -2 / -3) a first optical path difference providing structure consisting only of a structure, a first optical path difference providing structure consisting only of a (1 / -1 / -2) structure which is a six-level stepped structure, and the like. As a preferable example of (C), in addition to the first optical path difference providing structure in which the blaze type (2/1/1) structure and the blaze type (1/1/1) structure are superimposed, the blaze type (2 / 1/1) structure and a blaze-type (1/0/0) structure may be mentioned as a first optical path difference providing structure. As a preferred example of (D), there is a first optical path difference providing structure in which a blaze type (2/1/1) structure and a (1/0/0) structure that is a four-level step structure are overlapped. There is a first optical path difference providing structure in which a blaze type (2/1/1) structure and a (0/0/1) structure that is a two-level stepped structure are superimposed.

Next, the second optical path difference providing structure provided in the intermediate region will be described. The second optical path difference providing structure is preferably a structure in which at least two basic structures of the third basic structure and the fourth basic structure are overlapped, but is not limited thereto.

It is preferable that both the third basic structure and the fourth basic structure are blazed structures. Further, the third basic structure makes the first-order diffracted light quantity of the first light flux that has passed through the third basic structure larger than any other order of diffracted light quantity, and the first-order diffracted light quantity of the second light flux that has passed through the third basic structure Is preferably larger than any other order of diffracted light. In addition, it is preferable that the first-order diffracted light amount of the third light flux that has passed through the third basic structure is larger than any other order diffracted light amount. In addition, the fourth foundation structure makes the second-order diffracted light amount of the first light beam that has passed through the fourth foundation structure larger than any other order of diffracted light amount, and the first-order of the second light beam that has passed through the fourth foundation structure. Is preferably larger than any other order of diffracted light. Further, the first-order diffracted light amount of the third light flux that has passed through the fourth basic structure is made larger than any other order diffracted light amount. Thereby, in the second optical path difference providing structure in which at least the third basic structure and the fourth basic structure are overlapped, the amount of step in the optical axis direction can be reduced, thereby suppressing the decrease in diffraction efficiency at the time of wavelength variation. Further, the orders of the diffracted light having the highest light intensity in the first basic structure and the third basic structure are matched, and the orders of the diffracted light having the highest light intensity in the second basic structure and the fourth basic structure are matched. Therefore, the spherical aberration can be made continuous even when the temperature and the wavelength change for the light flux passing through the central region and the intermediate region, and as a result, the occurrence of higher order aberrations can be suppressed.

The second optical path difference providing structure may be a structure in which the fifth basic structure is overlapped in addition to the third and fourth basic structures. However, in order to simplify the structure and suppress a decrease in light utilization efficiency due to manufacturing errors. The second optical path difference providing structure preferably includes only the third basic structure and the fourth basic structure.

At this time, the fifth basic structure makes the 0th-order diffracted light quantity of the first light flux that has passed through the fifth basic structure larger than any other order diffracted light quantity, and the second light flux that has passed through the fifth basic structure. The 0th-order diffracted light amount is made larger than any other order diffracted light amount, and the G-th order diffracted light amount of the third light flux that has passed through the fifth basic structure is made larger than any other order diffracted light amount. It is preferable. By superimposing such a fifth basic structure, a phase shift occurs between the central region and the intermediate region without adversely affecting the first light beam and the second light beam passing through the intermediate region of the objective lens. Accordingly, it is possible to easily give only the third light flux an effect of forming a flare at a position far from the light spot on the information recording surface of the CD.

Preferably, G is ± 1. When G is ± 1, the fifth basic structure is preferably a two-level staircase structure (also referred to as a binary structure) as shown in FIG.

Further, the third-order diffracted light amount of the first light beam that has passed through the third basic structure is made larger than any other order of diffracted light amount, and the second-order diffracted light amount of the second light beam that has passed through the third basic structure is changed to other values. The diffraction light quantity of any order is made larger (also referred to as (3/2) structure), the second-order diffraction light quantity of the first light beam that has passed through the fourth basic structure is made larger than any other order of diffraction light quantity, The first-order diffracted light amount of the second light beam that has passed through the four basic structures may be made larger than any other order diffracted light amount (also referred to as a (2/1) structure). With such a configuration, the diffraction efficiency in BD can be further increased.

In addition, even when the 3rd foundation structure and the 4th foundation structure are the combination of the (1/1) structure and the (2/1) structure, it is the combination of the (3/2) structure and the (2/1) structure. Even in this case, the third basic structure provided at least in the middle region at the position closest to the central region has the step in the direction opposite to the optical axis, and at least in the middle region at the position closest to the central region. As for the 4th foundation structure provided, it is preferred that the level | step difference has faced the direction of an optical axis. More preferably, the steps of all the third foundation structures in the intermediate region are directed in the direction opposite to the optical axis, and the steps of all the fourth foundation structures in the intermediate region are directed in the direction of the optical axis. is there.

In the third basic structure, when the wavelength of the incident light beam changes so as to become longer, the spherical aberration changes in an undercorrected (under) direction, and in the fourth basic structure, the wavelength of the incident light beam becomes longer. If it changes, the spherical aberration may change in the direction of under-correction (under).

With such a configuration, even in the second optical path difference providing structure, when the refractive index of the objective lens changes due to the temperature increase of the optical pickup device, the wavelength of the light source also increases due to the increase in the environmental temperature. Is used to correct the deterioration of the spherical aberration due to the change in the refractive index of the objective lens, so that a more appropriate condensing spot can be formed on the information recording surface of each optical disc when the environmental temperature changes.

On the other hand, when one of the third basic structure and the fourth basic structure is changed so that the wavelength of the incident light beam becomes longer, the spherical aberration changes in the undercorrection (under) direction, and the incident light is incident on the other side. When the wavelength of the luminous flux to be changed is changed to be longer, the spherical aberration may be changed in the overcorrection (over) direction.

In one of the third basic structure and the fourth basic structure, when the wavelength of the incident light beam is changed so as to become longer, the spherical aberration changes in the undercorrection (under) direction. If the spherical aberration is changed in the overcorrection direction when the wavelength is changed to be longer, when the first light beam is condensed on the information recording surface of the BD as the entire objective lens, the first aberration is changed. The amount of change of the third-order spherical aberration when the wavelength of one light beam changes by +5 nm can be set to −30 mλrms to +50 mλrms, which is preferable. When the first light beam is condensed on the information recording surface of the BD as the entire objective lens, the amount of change in the third-order spherical aberration when the wavelength of the first light beam changes by +5 nm is -10 mλrms or more and +10 mλrms or less. More preferably. When the first light beam is condensed on the information recording surface of the BD as the entire objective lens, the amount of change in the fifth-order spherical aberration when the wavelength of the first light beam changes by +5 nm is -20 mλrms or more and 20 mλrms or less. It is preferable that More preferably, it is −10 mλrms or more and +10 mλrms or less.

With such a configuration, in either one of the third basic structure and the fourth basic structure, when the wavelength of the incident light beam is changed to be longer, the spherical aberration changes in the overcorrection direction. Even if the two-optical path difference providing structure is composed of only the third and fourth basic structures, flare can be easily produced when using the CD. Accordingly, flare out when using a CD can be performed with a simple second optical path difference providing structure, so that a decrease in light utilization efficiency due to a shadow effect is suppressed, and a decrease in light utilization efficiency due to manufacturing errors is also suppressed. As a result, the light use efficiency can be improved. This reduces the effect of correcting the temperature characteristics when using BD in the intermediate area, but the temperature characteristics are too poor because both the first basic structure and the second basic structure in the central area are insufficiently corrected at long wavelengths. This can be prevented, and the wavelength characteristic correction effect when using the BD can be increased. In addition, when the DVD is used, both the temperature characteristic and wavelength characteristic of the DVD can be improved.

When the wavelength of the incident light beam is changed to be longer in the fourth basic structure, the spherical aberration is changed in an undercorrected (under) direction, and the wavelength of the incident light beam is longer in the third basic structure. In this case, it is preferable that the spherical aberration changes in the overcorrected (over) direction because the flare can be easily moved farther when the CD is used.

Further, in order to improve the wavelength characteristics when using the DVD, in the second optical path difference providing structure, the ring zone of the third basic structure is 1 to 3 in one ring zone closest to the central region of the fourth basic structure. It is preferable that the number (particularly preferably 2 to 3) is included. More preferably, in the second optical path difference providing structure, 1 to 5 (particularly preferably 2 to 3) ring zones of the third foundation structure are provided for one ring zone closest to the peripheral region of the fourth foundation structure. It is included.

When providing the third optical path difference providing structure in the peripheral structure, it is possible to provide an arbitrary optical path difference providing structure. The third optical path difference providing structure preferably has a sixth basic structure. In the sixth basic structure, the P-order diffracted light amount of the first light beam that has passed through the sixth basic structure is made larger than any other order diffracted light amount, and the Q-order diffraction of the second light beam that has passed through the sixth basic structure. The light quantity is made larger than any other order of diffracted light quantity, and the R-order diffracted light quantity of the third light flux that has passed through the sixth basic structure is made larger than any other order of diffracted light quantity. Note that P is preferably 5 or less in order to suppress fluctuations in diffraction efficiency during wavelength fluctuations.

Here, FIG. 8 shows a schematic diagram of a preferable objective lens. It is the figure which showed the upper half from the optical axis among the cross sections of the objective lens containing optical axis OA. Note that FIG. 8 is a schematic diagram to the last, and is not a drawing showing an accurate length ratio or the like based on the embodiment.

8 has a central region CN, an intermediate region MD, and a peripheral region OT. A first optical path difference providing structure ODS1 is provided in the central area, a second optical path difference providing structure ODS2 is provided in the middle area, and a third optical path difference providing structure is provided in the peripheral area.

The first optical path difference providing structure ODS1 in FIG. 8 is a (2/1/1) blazed structure in which the step is directed toward the optical axis and a (1/1/1) second basic structure BS2. The blazed structure has a structure in which a first basic structure BS1 with a step facing away from the optical axis is superimposed. In FIG. 8, the second foundation structure BS2 has three annular zones, and four annular zones of the first foundation structure BS1 are included on the annular zone (circular shape) closest to the optical axis in the second foundation structure BS2. ing. In addition, two annular zones of the first foundation structure BS1 are included in one annular zone closest to the intermediate region in the second foundation structure BS2.

The second optical path difference providing structure ODS2 in FIG. 8 is a (2/1/1) blazed structure in which a step is directed toward the optical axis, and a (1/1/1) fourth basic structure BS4. The blazed structure has a structure in which a third basic structure BS3 having a level difference opposite to the optical axis is superimposed. In FIG. 8, the fourth foundation structure BS4 is a three-ring zone, and three ring zones of the third foundation structure BS3 are included on the zone closest to the central region in the fourth foundation structure BS4. Further, one ring zone of the third foundation structure BS3 is included in one ring zone closest to the peripheral region in the fourth foundation structure BS4.

The third optical path difference providing structure ODS3 in FIG. 8 is a (2/1/1) blazed structure, and is composed only of the sixth basic structure BS6 in which the step is directed toward the optical axis.

The NA on the image side of the objective lens necessary for reproducing / recording information on the BD is NA1, and the NA on the image side of the objective lens necessary for reproducing / recording information on the DVD is NA2 (NA1 > NA2), and the image side numerical aperture of the objective lens necessary for reproducing / recording information on the CD 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 CD, 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.

The objective lens preferably satisfies the following conditional expression (28).
0.8 ≦ d / f ≦ 1.5 (28)
Here, d represents the thickness (mm) on the optical axis of the objective lens, and f represents the focal length of the objective lens in the first light flux.

When an optical disk with a short wavelength and high NA such as BD is used, the objective lens is likely to generate astigmatism and decent coma, but the conditional expression (28) is satisfied. As a result, it is possible to suppress the generation of astigmatism and decentration coma.

In addition, since the objective lens becomes a thick objective lens with a thick on-axis thickness, the working distance at the time of CD recording / reproduction tends to be shortened, so the upper limit value of conditional expression (28) may not be exceeded. preferable.

In the objective lens according to the present invention, when the third-order spherical aberration is minimized in the objective lens incident with the first light beam at room temperature (25 ± 3 ° C.) and the cover glass thickness T (mm) satisfying the expression (1). The sine condition violation amount at the magnification M takes the first maximum value at the pupil radius H1, the second maximum value at the pupil radius H2, and the pupil radius H3 to 0.9. When the above is satisfied, the expression (3) is satisfied (however, the pupil radii H1, H2, and H3 are relative values when the effective radius of the objective lens is 1), and the derivative Φ ( h) satisfies the expressions (4) to (6).
TMAX × 0.78 ≦ T ≦ TMAX × 1.1 (1)
-0.003 ≦ M ≦ 0.003 (2)
H1 <H2 <H3 (3)
φ (h) <0.0 (h <H1) (4)
φ (h)> 0.0 (H1 <h <H2) (5)
φ (h) <0.0 (H2 <h <H3) (6)
Furthermore, the following expression is satisfied.
-0.01 ≦ m1 ≦ 0.01 (7)
-0.01 ≦ m3 ≦ 0.01 (8)
−0.05 ≦ (fB3−fB1) /d≦0.10 (9)
However,
fB1 = WD1 + t1 × (1-1 / n1)
fB3 = WD3 + t3 × (1-1 / n3)
ν: Abbe number of the material of the objective lens m1: Imaging magnification when the light beam having the first wavelength λ1 is incident on the objective lens m3: Imaging magnification when the light beam having the third wavelength λ3 is incident on the objective lens d: Objective Lens axial thickness (mm)
WD1: Working distance when using BD (mm)
WD3: Working distance when using CD (mm)
n1: Refractive index of the BD protective substrate for the light beam having the first wavelength λ1 n3: Refractive index of the CD protective substrate for the light beam having the third wavelength λ3

In the magnification M, it is preferable that the sine condition violation amount has a positive maximum value and the sine condition violation amount has a negative minimum value between 70% and 90% of the effective radius. The negative minimum value is preferably between 20% and 60% of the effective radius. Furthermore, it is preferable that the value of the sine condition violation amount at 100% of the effective radius is substantially zero. Incidentally, almost 0 means −0.001 to 0.001 mm.

Furthermore, it is preferable to satisfy the following formula.
0.7 ≦ H2 ≦ 0.9 (10)

In condensing a light beam incident at a magnification m1 on an information recording surface of a BD transparent substrate thickness t1, the third-order coma aberration LTCM3 generated when only the objective lens is tilted by a predetermined angle, and the same direction as the objective lens The third-order coma aberration DTCM3 generated when only the BD is tilted at the predetermined angle satisfies the following expression.
| LTCM3 | >> | DTCM3 | (11)

The following formula is satisfied.
−0.05 ≦ (fB3−fB1) /d≦0.05 (6 ′)

The height h from the optical axis at which the sine condition when using BD turns from negative to positive satisfies the following expression.
_0.8h _CDNA ≤ h ≤ h _DVDNA (12)
However,
h _CDNA : height in the optical axis direction corresponding to the image-side numerical aperture when using a CD h _DVDNA : height in the optical axis direction corresponding to the image-side numerical aperture when using a DVD

The first light beam, the second light beam, and the third light beam are incident on the objective lens as parallel light or substantially parallel light. The second 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. The imaging magnification m1 of the objective lens in the first light flux incident on the objective lens as parallel light or substantially parallel light satisfies the following formula (7).
-0.01 ≦ m1 ≦ 0.01 (7)

In addition, 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 satisfies the following expression (29). Is preferred.
-0.01 <m2 <0.01 (29)

Further, when the second light flux is incident on the objective lens as diverging light, it is preferable that the imaging magnification m2 of the objective lens when the second light flux is incident on the objective lens satisfies the following formula (29) ′.
m2 <0 (29) '
However, m2: The imaging magnification when the light beam having the second wavelength λ2 is incident on the objective lens preferably satisfies the following (29) ″.
−0.025 <m2 ≦ −0.01 (29) ”

Further, the imaging magnification m3 of the objective lens in the third light beam incident on the objective lens as the parallel light beam or the substantially parallel light beam satisfies the following formula (8).
-0.01 ≦ m3 ≦ 0.01 (8)

Also, 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 0.2 mm or more and 0.5 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.

In the optical pickup device, the coupling lens may have an actuator through which at least the first light beam and the second light beam pass and move the coupling lens in the optical axis direction. In particular, when the BD has a plurality of information recording surfaces such as two layers or three layers or more, when recording / reproducing one layer to another layer, the difference in the thickness of the transparent substrate is required. Therefore, spherical aberration generated due to the difference in thickness must be corrected. It is conceivable to correct the generated spherical aberration by moving the coupling lens in the optical axis direction and changing the magnification of the objective lens. Further, spherical aberration that occurs when the temperature or wavelength changes can be corrected by moving the coupling lens in the optical axis direction and changing the magnification of the objective lens.

However, even in the case of an optical pickup device that corrects various spherical aberrations by moving the coupling lens in the optical axis direction when using BD, the position of the coupling lens in the optical axis direction is fixed when using DVD. It is preferable.

The reason is that flare does not occur when using BD, but flare occurs when using DVD. By changing the coupling lens, the flare aberration changes, and as a result, the flare is recorded / reproduced. The reason is that there is a possibility of adversely affecting the driving force, and the reason why it is desired to simplify the control of the displacement of the coupling lens in the drive.

In order to fix the position of the coupling lens in the optical axis direction when using a DVD, the wavelength of the incident light beam in one of the third basic structure and the fourth basic structure constituting the second optical path difference providing structure of the objective lens. So that the spherical aberration changes in the direction of insufficient correction, and on the other side, the spherical aberration changes in the direction of overcorrection when the wavelength of the incident light beam changes longer. As a result, both the temperature characteristic and the wavelength characteristic when using the DVD can be improved, and as a result, when using the DVD, the position of the coupling lens in the optical axis direction is fixed when the second light beam passes. However, it is preferable because information can be recorded / reproduced with respect to the information recording surface of the DVD.

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

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.

The optical information recording / reproducing apparatus using each method described above 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 ensure compatibility between three types of BD / DVD / CD optical disks while ensuring a working distance, keeping unnecessary diffracted light causing an error signal away, and further improving off-axis characteristics. And an optical information recording / reproducing apparatus including an objective lens that can be performed in the above-described manner, and an objective lens suitable for the optical pickup apparatus.

It is an example of a graph in which the vertical axis represents the height (effective radius) from the optical axis, and the horizontal axis represents the sine condition violation amount (OSC). It is the figure which looked at the single objective lens OBJ concerning this Embodiment in the optical axis direction. It is a figure which shows the state which forms the spot which the 3rd light beam which passed the objective lens forms on the information recording surface of a 3rd optical disk. It is an axial direction sectional view showing an example of an optical path difference grant structure, (a) and (b) show an example of a blaze type structure, and (c) and (d) show an example of a step type structure. (A) shows a state where the step is directed in the direction of the optical axis, and (b) is a diagram showing a state where the step is directed in the direction opposite to the optical axis. (A) shows a shape in which the step is in the direction of the optical axis in the vicinity of the optical axis, but changes in the middle, and in the vicinity of the intermediate region, the step is in the direction opposite to the optical axis. FIG. 4 is a diagram showing a shape in which a step is directed in the opposite direction to the optical axis in the vicinity of the axis, but is switched in the middle, and the step is directed toward the optical axis in the vicinity of the intermediate region. It is a conceptual diagram of a 1st optical path difference providing structure, (a) thru | or (c) show the preferable example of a 1st optical path difference providing structure, (d) is the example which superimposed the 1st foundation structure and the 2nd foundation structure. Indicates. It is a schematic diagram of a preferable objective lens. 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 a figure which shows the longitudinal spherical aberration amount (SA) and sine condition unsatisfied amount (SC) of (a) BD of Example 1, (b) CD. It is a figure which shows the amount of longitudinal spherical aberration (SA) and sine condition dissatisfaction amount (SC) of (a) BD of Example 2, (b) CD. It is a figure which shows the amount of longitudinal spherical aberration (SA) and sine condition dissatisfaction amount (SC) of (a) BD of Example 3, (b) CD. It is a figure which shows the amount of longitudinal spherical aberration (SA) and sine condition unsatisfied amount (SC) of (a) BD of Example 4, (b) CD. It is a figure which shows each sine condition violation amount of BD and CD when not using paraxial diffraction power. It is a figure which shows each sine condition violation amount of BD and CD in the case of using paraxial diffraction power.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 9 shows BD, DVD, and CD, which are optical discs having three information recording surfaces RL1 to RL3 (referred to as RL1, RL2, and RL3 in ascending order of distance from the light incident surface of the optical disc) in the thickness direction. It is a figure which shows roughly the structure of optical pick-up apparatus PU1 of this Embodiment which can record / reproduce information appropriately with respect to this. Such an optical pickup device PU1 can be mounted on an optical information recording / reproducing device. The present invention is not limited to the present embodiment.

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

As shown in FIG. 2, in the single objective lens OBJ according to the present embodiment, a central region CN including the optical axis on the aspherical optical surface on the light source side, an intermediate region MD disposed around the central region CN, Further, a peripheral region OT disposed around the periphery is formed concentrically with the optical axis as the center. Although not shown, the first optical path difference providing structure already described in detail is formed in the center region CN, and the second optical path difference providing structure already described in detail is formed in the intermediate region MD. In addition, a third optical path difference providing structure is formed in the peripheral region OT. In the present embodiment, the third optical path difference providing structure is a blazed diffractive structure. The objective lens of the present embodiment is a plastic lens. As shown in FIG. 7, the first optical path difference providing structure formed in the center region CN of the objective lens OBJ is a structure in which the first basic structure and the second basic structure are overlapped. The first-order diffracted light amount of the first light beam that has passed through the first basic structure is made larger than any other order of diffracted light amount, and the first-order diffracted light amount of the second light beam that has passed through the first basic structure is set to any other order. The first order diffracted light amount of the third light flux that has passed through the first basic structure is made larger than any other order diffracted light amount, and is provided at least near the optical axis of the central region CN. In the basic structure, the step is directed in the direction opposite to the optical axis, and in the second basic structure, the second-order diffracted light quantity of the first light beam that has passed through the second basic structure is greater than the diffracted light quantity of any other order. 1 of the second light flux that has passed through the second basic structure. Diffracted light quantity of any other order is made larger, the first order diffracted light quantity of the third light flux that has passed through the second basic structure is made larger than any other order diffracted light quantity, and the room temperature (25 ± 3 [deg.] C. and a cover glass thickness T (mm) satisfying the expression (1), the magnification M at which the third-order spherical aberration is minimized in the objective lens on which the first light beam is incident satisfies the expression (2) When the sine condition violation amount at the magnification M is the first maximum value at the pupil radius H1 and the second maximum value at the pupil radius H2, the equation (3) is satisfied when the pupil radius H3 is 0.9 or more. (However, the pupil radii H1, H2, and H3 are relative values when the effective radius of the objective lens is set to 1.) Further, the derivative Φ (h) of the sine condition violation amount satisfies the equations (4) to (6). Fulfill.
TMAX × 0.78 ≦ T ≦ TMAX × 1.1 (1)
-0.003 ≦ M ≦ 0.003 (2)
H1 <H2 <H3 (3)
φ (h) <0.0 (h <H1) (4)
φ (h)> 0.0 (H1 <h <H2) (5)
φ (h) <0.0 (H2 <h <H3) (6)
Furthermore, the following expression is satisfied.
-0.01 ≦ m1 ≦ 0.01 (7)
-0.01 ≦ m3 ≦ 0.01 (8)
−0.05 ≦ (fB3−fB1) /d≦0.10 (9)
However,
fB1 = WD1 + t1 × (1-1 / n1)
fB3 = WD3 + t3 × (1-1 / n3)
ν: Abbe number of the material of the objective lens m1: Imaging magnification when the light beam having the first wavelength λ1 is incident on the objective lens m3: Imaging magnification when the light beam having the third wavelength λ3 is incident on the objective lens d: Objective Lens axial thickness (mm)
WD1: Working distance when using BD (mm)
WD3: Working distance when using CD (mm)
n1: Refractive index of the BD protective substrate for the light beam having the first wavelength λ1 n3: Refractive index of the CD protective substrate for the light beam having the third wavelength λ3

First, a case where recording / reproduction is performed on the first information recording surface RL1 of the BD will be described. In such a case, the coupling lens COL is moved to the first predetermined position by a single-axis actuator (not shown). Here, the divergent light beam of the light beam (λ1 = 405 nm) emitted from the blue-violet semiconductor laser LD1 passes through the dichroic prism DP and the polarization prism BS, passes through the coupling lens COL, and becomes a weakly convergent light beam. The first information recording surface is converted from linearly polarized light to circularly polarized light by the λ / 4 wave plate QWP, the diameter of the light beam is regulated by a diaphragm (not shown), and the objective lens OBJ passes through the transparent substrate PL1 having the first thickness. It becomes a spot formed on RL1.

The reflected light flux modulated by the information pits on the first information recording surface RL1 is again transmitted through the objective lens OBJ and the aperture, and then converted from circularly polarized light to linearly polarized light by the λ / 4 wavelength plate QWP, and coupled to the coupling lens COL. Is reflected by the polarizing prism BS, and then converged on the light receiving surface of the light receiving element PD by the sensor lens SL. Then, using the output signal of the light receiving element PD, the information recorded on the first information recording surface RL1 can be read by focusing or tracking the objective lens OBJ by the triaxial actuator AC2.

Next, a case where recording / reproduction is performed on the second information recording surface RL2 of the BD will be described. In such a case, the coupling lens COL is moved to the second predetermined position by a uniaxial actuator (not shown). Here, the divergent light beam of the light beam (λ1 = 405 nm) emitted from the blue-violet semiconductor laser LD1 passes through the dichroic prism DP and the polarization prism BS, passes through the coupling lens COL, and is converted into a parallel light beam. / 4 wavelength plate QWP converts linearly polarized light into circularly polarized light, the diameter of the light beam is regulated by a diaphragm (not shown), and the second information recording surface RL2 is passed through the transparent substrate PL2 having the second thickness by the objective lens OBJ. It becomes a spot formed on the top.

The reflected light flux modulated by the information pits on the second information recording surface RL2 is again transmitted through the objective lens OBJ and the stop, and then converted from circularly polarized light to linearly polarized light by the λ / 4 wavelength plate QWP, and coupled to the coupling lens COL. Is reflected by the polarizing prism BS, and then converged on the light receiving surface of the light receiving element PD by the sensor lens SL. Then, using the output signal of the light receiving element PD, the information recorded on the second information recording surface RL2 can be read by focusing or tracking the objective lens OBJ by the triaxial actuator AC2.

Next, a case where recording / reproduction is performed on the third information recording surface RL3 of the BD will be described. In such a case, the coupling lens COL is moved to a third predetermined position by a uniaxial actuator (not shown). Here, the divergent beam of the beam (λ1 = 405 nm) emitted from the blue-violet semiconductor laser LD1 passes through the dichroic prism DP and the polarization prism BS, passes through the coupling lens COL, and becomes a weak divergent beam. The linearly polarized light is converted into circularly polarized light by the λ / 4 wavelength plate QWP, the light beam diameter is regulated by a diaphragm (not shown), and the third information recording surface is passed through the transparent substrate PL3 having the third thickness by the objective lens OBJ. It becomes a spot formed on RL3.

The reflected light beam modulated by the information pits on the third information recording surface RL3 is again transmitted through the objective lens OBJ and the aperture, and then converted from circularly polarized light to linearly polarized light by the λ / 4 wavelength plate QWP. Is reflected by the polarizing prism BS, and then converged on the light receiving surface of the light receiving element PD by the sensor lens SL. Then, using the output signal of the light receiving element PD, the information recorded on the third information recording surface RL3 can be read by focusing or tracking the objective lens OBJ by the triaxial actuator AC2.

Furthermore, the case where information is recorded and / or reproduced on a DVD will be described. The divergent light beam of the second light beam (λ2 = 660 nm) emitted from the semiconductor laser LD2 of the laser unit LDP is reflected by the dichroic prism DP, passes through the polarization beam splitter BS and the collimating lens COL, as indicated by the dotted line, and λ The / 4 wavelength plate QWP converts the linearly polarized light into circularly polarized light and enters the objective lens OBJ. Here, the light beam collected by the central region and the intermediate region of the objective lens OBJ (the light beam that has passed through the peripheral region is flared to form a spot peripheral portion) is recorded on the DVD through the protection substrate PL4 It becomes a spot formed on the surface RL4 and forms the center of the spot.

The reflected light beam modulated by the information pits on the information recording surface RL4 is transmitted again through the objective lens OBJ, converted from circularly polarized light to linearly polarized light by the λ / 4 wave plate QWP, and converted into a parallel 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.

Furthermore, the case of recording and / or reproducing information on a CD will be described. The divergent light beam of the third light beam (λ3 = 785 nm) emitted from the semiconductor laser LD3 of the laser unit LDP is reflected by the dichroic prism DP, as shown by the one-dot chain line, and passes through the polarization beam splitter BS and the collimating lens COL. The linearly polarized light is converted into circularly polarized light by the λ / 4 wavelength plate QWP, and is incident on the objective lens OBJ. Here, the light beam collected by the central region of the objective lens OBJ (the light beam that has passed through the intermediate region and the peripheral region is flared to form a spot peripheral portion) is recorded on the CD through the protective substrate PL5 This is a spot formed on the surface RL5.

The reflected light flux modulated by the information pits on the information recording surface RL5 is again transmitted through the objective lens OBJ, converted from circularly polarized light to linearly polarized light by the λ / 4 wave plate QWP, and converted into a parallel light flux 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 CD can be read using the output signal of light receiving element PD.

(Example)
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 (with the light traveling direction being 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. .

(Equation 2)
Φ (h) = Σ (C _i h ²ⁱ × λ × m / λB)
Here, λ: wavelength used, m: diffraction order, λB: manufacturing wavelength, h: distance in the direction perpendicular to the optical axis from the optical axis.
Further, the pitch P (h) = λB / (Σ (2i × C _i × h ^2i-1 )).

Example 1
The objective lens of Example 1 is a plastic single lens. Table 1 shows lens data. A conceptual diagram of the first optical path difference providing structure of the first embodiment is shown in FIG. 6A (FIG. 6A is a conceptual diagram different from the actual shape of the first embodiment). In the first optical path difference providing structure of Example 1, the (1/1/1) blaze is added to the second basic structure BS2 that is a (2/1/1) blaze-type diffraction structure in the entire central region. The first basic structure BS1, which is a diffractive structure of the mold, is an optical path difference providing structure that is overlapped. Further, the step of the second foundation structure BS2 faces the direction of the optical axis OA, and the step of the first foundation structure BS1 faces the direction opposite to the optical axis OA. In this embodiment, the magnification of the objective lens is m1 = m2 = m3 = 0, the on-axis thickness d = 1.50 mm, (fB3-fB1) /d=0.008 (mm), (fB2-fB1) = 0.10 mm, | LTCM3 | = 0.060 (λrms), | DTCM3 | = 0.046 (λrms).

FIG. 10A is a diagram showing longitudinal spherical aberration SA and sine condition dissatisfaction amount SC when BD is used in the objective lens of Example 1, and FIG. 10B is the use of CD in the objective lens of Example 1. FIG. 6 is a diagram showing longitudinal spherical aberration SA and sine condition unsatisfactory amount SC, with the vertical axis indicating 1 as the height from the optical axis corresponding to each effective diameter of BD / CD. As is apparent from FIG. 10, the third-order spherical aberration is minimized in the objective lens on which the first light beam is incident at room temperature (25 ± 3 ° C.) and the cover glass thickness T (mm) satisfying the expression (1). The magnification M at the time satisfies the formula (2), and the sine condition violation amount at the magnification M is a negative first minimum value at the pupil radius H1 = 0.4, and the positive second value at the pupil radius H2 = 0.9. Since the maximum values are respectively taken, the expression (3) is satisfied when the pupil radius H3 is 0.9 or more, and the derivative Φ (h) of the sine condition violation amount satisfies the expressions (4) to (6). h = 0.61 and _0.8h _CDNA ≦ h ≦ h _DVDNA is satisfied.

(Example 2)
The objective lens of Example 2 is a plastic single lens. Table 2 shows lens data. A conceptual diagram of the first optical path difference providing structure of Example 2 is shown in FIG. 6A (FIG. 6A is a conceptual diagram different from the actual shape of Example 2). In the first optical path difference providing structure of Example 2, the (1/0/0) blaze is added to the second basic structure BS2 that is a (2/1/1) blaze type diffraction structure in the entire central region. Is an optical path difference providing structure in which another basic structure that is a diffractive structure of a mold is overlapped (in addition to a blazed (1/0/0) structure, a four-level stepped structure) (It may be a (1/0/0) structure). In this embodiment, the magnification of the objective lens is m1 = m2 = m3 = 0, the on-axis thickness is d = 2.18 mm, (fB3-fB1) /d=0.000 (mm), (fB2-fB1) = LTC3 | = 0.057 (λrms) and | DTCM3 | = 0.043 (λrms).

FIG. 11A is a diagram showing longitudinal spherical aberration SA and sine condition dissatisfaction amount SC when BD is used in the objective lens of Example 2, and FIG. 11B is a diagram showing CD use in the objective lens of Example 2. FIG. 6 is a diagram showing longitudinal spherical aberration SA and sine condition unsatisfactory amount SC, with the vertical axis indicating 1 as the height from the optical axis corresponding to each effective diameter of BD / CD. As is apparent from FIG. 11, the third-order spherical aberration is minimized in the objective lens on which the first light flux is incident at room temperature (25 ± 3 ° C.) and the cover glass thickness T (mm) satisfying the expression (1). The magnification M at the time satisfies the formula (2), and the sine condition violation amount at the magnification M is a negative first maximum value at the pupil radius H1 = 0.3, and the positive second value at the pupil radius H2 = 0.9. Since the maximum values are respectively taken, the expression (3) is satisfied when the pupil radius H3 is 0.9 or more, and the derivative Φ (h) of the sine condition violation amount satisfies the expressions (4) to (6). h = 0.48, _0.8h _CDNA ≦ h ≦ h _DVDNA is satisfied.

(Example 3)
The objective lens of Example 3 is a plastic single lens. Table 3 shows lens data. A conceptual diagram of the first optical path difference providing structure of the third embodiment is shown in FIG. 6A (FIG. 6A is a conceptual diagram different from the actual shape of the third embodiment). The first optical path difference providing structure of Example 3 is a two-level step-type structure in the second basic structure BS2 that is a (2/1/1) blazed diffraction structure in the entire central region ( This is an optical path difference providing structure in which the first basic structure BS1 which is another diffraction structure of 0/0/1) structure is overlapped. In this example, the magnification of the objective lens is m1 = m2 = 0, m3 = 0.0085, the on-axis thickness d = 1.63 mm, (fB3-fB1) /d=0.091 (mm), ( fB2−fB1) = − 0.06 mm, | LTCM3 | = 0.066 (λrms), and | DTCM3 | = 0.047 (λrms).

FIG. 12A is a diagram showing longitudinal spherical aberration SA and sine condition dissatisfaction amount SC when BD is used in the objective lens of Example 3, and FIG. 12B is CD use in the objective lens of Example 3. FIG. 6 is a diagram showing longitudinal spherical aberration SA and sine condition unsatisfactory amount SC, with the vertical axis indicating 1 as the height from the optical axis corresponding to each effective diameter of BD / CD. As is apparent from FIG. 10, the third-order spherical aberration is minimized in the objective lens on which the first light beam is incident at room temperature (25 ± 3 ° C.) and the cover glass thickness T (mm) satisfying the expression (1). The magnification M at the time satisfies the expression (2), the sine condition violation amount at the magnification M is a negative first maximum value at the pupil radius H1 = 0.35, and the positive second value at the pupil radius H2 = 0.9. Since the maximum values are respectively taken, the expression (3) is satisfied when the pupil radius H3 is 0.9 or more, and the derivative Φ (h) of the sine condition violation amount satisfies the expressions (4) to (6). h = 0.46, _0.8h _CDNA ≦ h ≦ h _DVDNA is satisfied.

Example 4
The objective lens of Example 4 is a plastic single lens. Table 4 shows the lens data. A conceptual diagram of the first optical path difference providing structure of the fourth embodiment is shown in FIG. 6A (FIG. 6A is a conceptual diagram different from the actual shape of the fourth embodiment). The first optical path difference providing structure of Example 4 is a (1/3/4) seven-level step-type diffractive structure in the entire central region. In this example, the magnification of the objective lens is m1 = m3 = 0, m2 = −0.0031, the on-axis thickness d = 2.64 mm, and (fB3-fB1) /d=−0.026 (mm). , (FB2-fB1) = 0.00 mm, | LTCM3 | = 0.056 (λrms), and | DTCM3 | = 0.042 (λrms).

FIG. 13A is a diagram showing longitudinal spherical aberration SA and sine condition unsatisfied amount SC when BD is used in the objective lens of Example 4, and FIG. 13B is CD use in the objective lens of Example 1. FIG. 6 is a diagram showing longitudinal spherical aberration SA and sine condition unsatisfactory amount SC, with the vertical axis indicating 1 as the height from the optical axis corresponding to each effective diameter of BD / CD. As is apparent from FIG. 13, the third-order spherical aberration is minimized in the objective lens that is incident with the first light flux at room temperature (25 ± 3 ° C.) and at the cover glass thickness T (mm) satisfying the expression (1). The magnification M at the time satisfies the expression (2), the sine condition violation amount at the magnification M is a negative first maximum value at the pupil radius H1 = 0.5, and the positive second value at the pupil radius H2 = 0.9. Since the maximum values are respectively taken, the expression (3) is satisfied when the pupil radius H3 is 0.9 or more, and the derivative Φ (h) of the sine condition violation amount satisfies the expressions (4) to (6). h = 0.66, _0.8h _CDNA ≦ h ≦ h _DVDNA is satisfied.

Table 5 summarizes the numerical values of the formulas defined in the claims corresponding to each example.

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.

AC1 Biaxial actuator BS Polarizing beam splitter CN Central region COL Collimating lens DP Dichroic prism LD1 First semiconductor laser or blue-violet 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 elements PL1 to RL5 Protective substrate PU1 Optical pickup device QWP λ / 4 wave plate RL1 to RL5 Information recording surface SEN Sensor lens

Claims

A first light source that emits a first light beam having a wavelength λ1 (390 nm <λ1 <415 nm); a third light source that emits a third light beam having a third wavelength λ3 (760 nm ≦ λ3 ≦ 820 nm); and an objective lens. Any information recording in a BD having three or more information recording surfaces in the thickness direction that have different distances from the light incident surface (thickness of the transparent substrate, but the thickest transparent substrate thickness is TMAX (mm)) By selecting a surface and condensing the first light beam on the selected information recording surface by the objective lens, information is recorded and / or reproduced, and the third light beam is transparent by the objective lens. An objective lens used in an optical pickup device that records and / or reproduces information by focusing on an information recording surface of a CD having a protective substrate with a substrate thickness of t3 (mm) (t1 <t3). What
A first optical path difference providing structure in a region where the first light flux and the third light flux are commonly incident;
At normal temperature (25 ± 3 ° C.) and a cover glass thickness T (mm) satisfying the expression (1), the magnification M at which the third-order spherical aberration is minimized in the objective lens on which the first light flux is incident is ( 2) When the expression is satisfied, the sine condition violation amount at the magnification M is the first minimum value at the pupil radius H1, the second maximum value at the pupil radius H2, and the pupil radius H3 is 0.9 or more. Equation (3) is satisfied (however, the pupil radii H1, H2, and H3 are relative values when the effective radius of the objective lens is 1), and the derivative Φ (h) of the sine condition violation amount is Satisfy equations (4) to (6)
TMAX × 0.78 ≦ T ≦ TMAX × 1.1 (1)
-0.003 ≦ M ≦ 0.003 (2)
H1 <H2 <H3 (3)
φ (h) <0.0 (h <H1) (4)
φ (h)> 0.0 (H1 <h <H2) (5)
φ (h) <0.0 (H2 <h <H3) (6)
Furthermore, the objective lens characterized by satisfy | filling the following formula | equation.
-0.01 ≦ m1 ≦ 0.01 (7)
-0.01 ≦ m3 ≦ 0.01 (8)
−0.05 ≦ (fB3−fB1) /d≦0.10 (9)
However,
fB1 = WD1 + t1 × (1-1 / n1)
fB3 = WD3 + t3 × (1-1 / n3)
ν: Abbe number m1 of the material of the objective lens m1: Imaging magnification when the light beam having the first wavelength λ1 is incident on the objective lens m3: Result when the light beam having the third wavelength λ3 is incident on the objective lens Image magnification d: On-axis thickness of the objective lens (mm)
WD1: Working distance when using the BD (mm)
WD3: Working distance when using the CD (mm)
n1: Refractive index of the protective substrate of the BD with respect to the light beam with the first wavelength λ1 n3: Refractive index of the protective substrate of the CD with respect to the light beam with the third wavelength λ3
The objective lens according to claim 1, wherein the following expression is satisfied.
0.7 ≦ H2 ≦ 0.9 (10)
In the case where the first light beam is condensed to a cover glass thickness T (mm) satisfying the expression (1) by the objective lens at a normal temperature (25 ± 3 ° C.) and a magnification M satisfying the expression (2), the objective lens And third-order coma aberration LTCM3 (λrms) that occurs when only the BD tilts at the predetermined angle in the same direction as the objective lens. The objective lens according to claim 1, wherein the following expression is satisfied.
| LTCM3 | >> | DTCM3 | (11)
The objective lens according to any one of claims 1 to 3, wherein the following expression is satisfied.
−0.05 ≦ (fB3−fB1) /d≦0.05 (6 ′)
The optical pickup device includes a second light source that emits a second light beam having a second wavelength λ2 (630 nm ≦ λ2 ≦ 670 nm), and the objective lens has an imaging magnification m2 and the second light beam is a transparent substrate thickness. 5. The information is recorded and / or reproduced by focusing on the information recording surface of the DVD having a protective substrate of t2 (mm) (t1 <t2 <t3). The objective lens according to Item 1.
Sine condition violation amount when the first light beam is condensed to the cover glass thickness T (mm) satisfying the expression (1) by the objective lens at the normal temperature (25 ± 3 ° C.) and the magnification M satisfying the expression (2). However, the height h from the optical axis which turns from negative to positive satisfies the following expression.
0.8h CDNA ≤ h ≤ h DVDNA (12)
However,
h CDNA : Relative value representing the height in the optical axis direction corresponding to the numerical aperture when the CD is used as the BD effective radius of the objective lens is 1 h DVDNA : Optical axis direction corresponding to the numerical aperture when the DVD is used Relative value expressing height as BD effective radius of the objective lens is 1
The 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 has the first optical path difference providing structure,
The objective lens condenses the first light flux that passes through the central region so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux that passes through the central region. Are recorded on the information recording surface of the DVD so that information can be recorded and / or reproduced, and the third light flux passing through the central region is recorded and / or recorded on the information recording surface of the CD. Or collect it so that it can be regenerated,
The objective lens condenses the first light flux passing through the intermediate area so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux passes through the intermediate area. Is recorded on the information recording surface of the DVD so that information can be recorded and / or reproduced, and the third light flux passing through the intermediate region is recorded and / or recorded on the information recording surface of the CD. Or do not concentrate so that it can be regenerated,
The objective lens condenses the first light flux passing through the peripheral area so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux passes through the peripheral area. Is recorded on the information recording surface of the DVD so that information can be recorded and / or reproduced, and the third light flux passing through the peripheral area is recorded on the information recording surface of the CD. And / or do not collect light for playback
The first optical path difference providing structure is a structure in which at least a first basic structure and a second basic structure are overlapped,
The first basic structure makes the first-order diffracted light quantity of the first light beam that has passed through the first basic structure larger than any other order of diffracted light quantity, and 1 of the second light flux that has passed through the first basic structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, making the first order diffracted light quantity of the third light flux that has passed through the first basic structure larger than any other order diffracted light quantity,
The second basic structure makes the second-order diffracted light amount of the first light beam that has passed through the second basic structure larger than any other order of diffracted light amount, and 1 of the second light beam that has passed through the second basic structure. The next diffracted light amount is made larger than any other order diffracted light amount, and the first diffracted light amount of the third light beam that has passed through the second basic structure is made larger than any other order diffracted light amount. The objective lens according to claim 5 or 6.
The first foundation structure and the second foundation structure are blazed, and 2 to 6 ring zones of the first foundation structure are included on one ring zone closest to the optical axis in the second foundation structure. The objective lens according to claim 7, wherein:
The first basic structure provided at least near the optical axis of the central region has a step in a direction opposite to the optical axis,
The objective lens according to claim 8, wherein the step of the second basic structure provided at least in the vicinity of the optical axis of the central region is directed in the direction of the optical axis.
The intermediate region has a second optical path difference providing structure in which at least a third basic structure and a fourth basic structure are overlapped,
The third basic structure makes the first-order diffracted light quantity of the first light beam that has passed through the third basic structure larger than any other order of diffracted light quantity, so that 1 of the second light flux that has passed through the third basic structure. Make the next diffracted light quantity larger than any other order diffracted light quantity,
In the fourth basic structure, the second-order diffracted light amount of the first light beam that has passed through the fourth basic structure is made larger than any other order of diffracted light amount, and 1st of the second light beam that has passed through the fourth basic structure. 10. The objective lens according to claim 7, wherein the next diffracted light quantity is made larger than any other order diffracted light quantity.
The third foundation structure and the fourth foundation structure are blazed, and include one to three ring zones of the third foundation structure on one ring zone closest to the central region of the fourth foundation structure. The objective lens according to claim 10, wherein the objective lens is provided.
In the third basic structure provided near the boundary with the central region, the step is directed in the direction opposite to the optical axis,
The objective lens according to claim 10 or 11, wherein the step of the fourth foundation structure provided in the vicinity of the boundary with the central region faces the direction of the optical axis.
The ring zone closest to the peripheral region in the fourth foundation structure includes 1 to 5 zones of the third foundation structure, according to any one of claims 10 to 12. Objective lens.
The intermediate region according to any one of claims 10 to 13, wherein only the third foundation structure and the fourth foundation structure are provided in the intermediate region, and no other foundation structure is provided. Objective lens.
The ring zone of the first foundation structure includes one to five zones of the first foundation structure in one zone of the second foundation structure closest to the intermediate region. Objective lens described in 1.
The objective lens according to any one of claims 1 to 15, wherein the following expression is satisfied.
160 (mm) ≤ N · f ≤ 210 (mm) (13)
Here, the total number of annular zones in the central region is N, and the focal length of the objective lens in the first light flux is f (mm).
An optical pickup device comprising the objective lens according to any one of claims 1 to 16.
An optical information recording / reproducing apparatus comprising the optical pickup apparatus according to claim 17.