WO2008044475A1

WO2008044475A1 - Objective optical element unit and optical pickup device

Info

Publication number: WO2008044475A1
Application number: PCT/JP2007/068795
Authority: WO
Inventors: Eiji Nomura; Kohei Ota
Original assignee: Konica Minolta Opto, Inc.
Priority date: 2006-10-12
Filing date: 2007-09-27
Publication date: 2008-04-17
Also published as: JPWO2008044475A1

Abstract

Disclosed is an easily produced low-cost optical pickup device, which has good temperature characteristics and is capable of adequately recording and/or reproducing information on and/or from different optical disks. Also disclosed is an objective optical element unit for such an optical pickup device. For the purpose of providing such objective optical element unit and optical pickup device, the cost is reduced by making a first optical element and a second optical element from a plastic, and aberration deterioration of a focusing spot due to temperature change and thickness difference of a protection substrate is suppressed by providing first to third phase structures, thereby forming an optimum focusing spot on the information recording surfaces of different optical information recording media.

Description

Specification

Objective optical element unit and optical pickup device

Technical field

The present invention relates to an objective optical element unit used in an optical pickup device capable of recording and / or reproducing information interchangeably with different types of optical discs, and an optical pickup device using the objective optical element unit.

Background art

In recent years, a high-density optical disc 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. System research and development is progressing rapidly. As an example, an optical disc that records and reproduces information with specifications of NA 0.85 and light source wavelength 405 nm, so-called Blu-ray Disc (hereinafter referred to as BD), 15-25 GB per layer for an optical disc with a diameter of 12 cm This information can be recorded. Hereinafter, in the present specification, such an optical disc is referred to as a “high density optical disc”.

[0003] By the way, the value of optical disc players and recorders (optical information recording / reproducing devices), and the value of these products, can be described simply by being able to record / reproduce information appropriately for such high-density optical discs. It's not enough. Based on the current situation in which DV D and CD (compact discs) that record a wide variety of information are sold, it is not possible to record / reproduce information on high-density optical discs. Similarly, making it possible to properly record / reproduce information on DVDs and CDs in the same way increases the commercial value of optical disc players and recorders for high-density optical discs. Against this background, optical pickup devices mounted on optical disc players and recorders for high-density optical discs are suitable for maintaining high compatibility with both high-density optical discs, DVDs, and CDs. It is desirable to have a function capable of recording / reproducing data.

[0004] As a method for recording / reproducing information appropriately while maintaining compatibility with both high-density optical discs, DVDs, and even CDs, optical systems for high-density optical discs and DV The power to selectively switch between the optical system for D and CD according to the recording density of the optical disk for recording / reproducing information. Multiple optical systems are required, which is disadvantageous for miniaturization. Cost increases.

[0005] Therefore, in order to simplify the configuration of the optical pickup device and reduce the cost, an optical system for high-density optical discs and an optical system for DVDs and CDs are also used in compatible optical pickup devices. It is advantageous to simplify the configuration of the optical pickup device and reduce the cost by reducing the number of optical components constituting the optical pickup device as much as possible.

[0006] Patent Document 1 describes an objective optical element that is compatible with both HD DVD, DVD, and CD, and an optical pickup device equipped with the objective optical element.

Patent Document 1: Japanese Unexamined Patent Publication No. 2006-92720

Disclosure of the invention

Problems to be solved by the invention

[0007] However, the objective optical element disclosed in Patent Document 1 is used in an optical pickup device that records / reproduces information for both HD DVD, DVD, and CD. Since the HD DVD has the same protective substrate thickness and numerical aperture as the DVD, the common objective optical element is used to record / reproduce information for both BD, DVD, and CD. It can be said that the difficulty level is lower than that. In Patent Document 1, a diffractive structure is provided on the optical element (condensing optical element) on the optical disc side. However, if a diffractive structure is provided on an optical surface having a large curvature, a mold for forming the diffractive structure is manufactured. In addition, there is a problem that the light transmittance is likely to be lowered due to vignetting of light. In contrast, by using a glass lens as the condensing optical element, the ability to eliminate the diffraction structure that corrects the aberration deterioration of the condensing spot caused by temperature changes required when a plastic lens is used. There is a problem that increases. In addition, when a glass lens is used as the condensing optical element, there is a problem that the weight of the objective optical element unit increases, which is disadvantageous for increasing the speed of the optical pickup device.

[0008] From the above, in order to realize high-performance compatibility for at least three types of optical discs of different standard types, such as high-density optical discs, DVDs, and CDs, For example, it is required to be an objective optical element unit with a large numerical aperture of ΝΑ0 · 8 or higher for high-density optical discs, and it occurs due to the difference in the protective substrate thickness of these three different types of optical discs. Light transmission is possible for a light beam of a predetermined wavelength used for each optical disc while providing a structure such as a phase structure required for suppressing deterioration of spherical aberration or the like, or a structure for compensating temperature characteristics. It is important to prevent the rate from falling, and to suppress the increase in manufacturing force and manufacturing cost.

[0009] The present invention takes the above-mentioned problems into consideration, has good temperature characteristics, and records / records information on at least three types of optical discs having different light source wavelengths and protective substrate thicknesses. An object of the present invention is to provide an objective optical element unit and an optical pickup device that can be manufactured easily and can be manufactured at a low cost while appropriately reproducing. Means for solving the problem

In order to solve the above problems, the objective optical element unit according to claim 1 includes a first light source that emits a light beam having a wavelength λ 1, and a wavelength 2 (λ 1 <λ 2). A second light source that emits a light beam having a wavelength of 3, a third light source that emits a light beam having a wavelength of 3 (λ 2 <λ 3), and a condensing optical system including an objective optical element unit. The optical optical system condenses the light beam having the first light source power on the information recording surface of the first optical information recording medium through the protective substrate having a thickness of tl, thereby recording and / or reproducing information. And the light flux from the second light source is condensed on the information recording surface of the second optical information recording medium through a protective substrate having a thickness t2 (tl <t2). Thus, information can be recorded and / or reproduced, and the light beam from the third light source is further transmitted through a protective substrate having a thickness t3 (t2 <t3). An objective optical element unit of an optical pickup device capable of recording and / or reproducing information by focusing on the information recording surface of the recording medium, each of which is made of a single plastic material. A first optical element and a second optical element;

The first optical element is caused by a difference between a first phase structure that suppresses aberration deterioration of a condensing spot caused by a temperature change with respect to the light beam having the wavelength λ1, and a thickness tl, t2 of the protective substrate. do it It has a second phase structure that suppresses the spherical aberration deterioration that occurs and a third phase structure that suppresses the spherical aberration deterioration that occurs due to the difference between the thicknesses tl and t3 of the protective substrate.

Note that the second phase structure preferably has a function of suppressing spherical aberration deterioration caused by at least the difference between the protective substrate thicknesses tl and t2, but the difference between the protective substrate thicknesses tl and t2 It is more preferable to have a function of suppressing the spherical aberration deterioration caused by the above and the function of suppressing the spherical aberration deterioration based on the difference between the wavelengths λ 1 and λ 2.

[0012] In addition, the first phase structure is the amount of change in wavefront aberration on the information recording surface of the first optical information recording medium with respect to the light flux with wavelength λ 1 when the temperature rises by 30 ° C from 25 ° C. It is preferable that the structure suppresses 0.1 λ lrms or less.

[0013] Further, it is preferable that the objective optical element unit has the first optical element disposed on the light source side and the second optical element disposed on the optical information recording medium side.

[0014] According to the present invention, the first optical element and the second optical element are formed of plastic, so that the cost can be reduced as compared with the case where the second optical element is a glass lens. In addition, the use of the first optical element and the second optical element increases the degree of design freedom compared with the case of using a single optical element. Furthermore, by providing the first to third phase structures on the first optical element, information recording on three different types of optical information recording media can be performed while suppressing aberration deterioration of the focused spot due to temperature changes. A force S is used to form a good focused spot or optimum focused spot on the surface.

[0015] Each of the first to third phase structures can take various cross-sectional shapes as schematically shown in Figs. Fig. 6 shows the case of a sawtooth shape, and Fig. 7 shows the case of a stepped shape with all steps being in the same direction. In this specification, a structure that gives a specific action to a light beam having a predetermined phase difference is given to a light beam having a wavelength of at least one of the incident light beams as a phase structure (or phase difference providing structure). For example, as shown in Fig. 6 and Fig. 7, it refers to a structure that has a sawtooth shape or a step shape along the optical axis direction when the cross section is viewed in a plane including the optical axis. In addition, in Fig. 8, when the step is stepped in the opposite direction in the middle, that is, when the cross-sectional shape including the optical axis is at a predetermined height from the optical axis, the optical path length increases as the distance from the optical axis increases. After the predetermined height from the optical axis, a staircase structure (phase difference providing structure) in which the optical path length decreases as the distance from the optical axis increases, or at a predetermined height from the optical axis, the optical axis It shows the case of a staircase structure (phase difference providing structure) in which the optical path length becomes shorter as the force is separated and the optical path length becomes longer as the distance from the optical axis is increased from the optical axis.

[0016] FIG. 9 shows a pattern in which the cross-sectional shape including the optical axis is stepwise arranged in a concentric manner.

For each given number of level surfaces (the number of level surfaces is 5 in the example shown in Fig. 9), the level is shifted by the height corresponding to each level surface (4 levels in the example shown in Fig. 9). This shows the case where In this specification, a structure formed by shifting the steps is also referred to as a staircase, a staircase shape, or a staircase structure, and the shift amount by which the steps are shifted is also referred to as a step. Note that the width of each level surface in one pattern may be the same or different.

FIG. 6 shows the case where the directions of the saw blades are the same, and FIG. 9 shows the force _S showing the case where the directions of the patterns whose cross-sectional shapes are stepped are the same, as shown in FIG. 10 and FIG. In this way, the sawtooth having the phase reversal part PR, the sawtooth having a sawtooth direction opposite to the sawtooth closer to the optical axis than the phase reversal part PR and the sawtooth farther from the optical axis than the phase reversal part PR The pattern may include a pattern in which the direction of the steps is opposite between the pattern closer to the optical axis than the phase inversion part PR and the pattern farther from the optical axis than the phase inversion part PR. 6 to 11 show a force S, which is a case where each structure is formed on a plane, and each structure may be formed on a spherical surface or an aspheric surface. In FIGS. 9 and 11, the number of predetermined level planes is set to 5. This is not limited to this.

The objective optical element unit according to claim 2 includes a first light source that emits a light beam having a wavelength λ 1, a second light source that emits a light beam having a wavelength 2 (λ 1 <λ 2), and A third light source that emits a light beam having a wavelength of 3 (λ 2 <λ 3), and a condensing optical system that includes an objective optical element unit, and the condensing optical system includes a light beam from the first light source Information can be recorded and / or reproduced by focusing the light on the information recording surface of the first optical information recording medium through a protective substrate having a thickness of tl. Information can be recorded and / or reproduced by focusing the light beam from the light source on the information recording surface of the second optical information recording medium via the protective substrate with thickness t2 (tl <t2). Furthermore, the light flux from the third light source is collected on the information recording surface of the third optical information recording medium through a protective substrate having a thickness t3 (t2 <t3). By Rukoto, recording and / or optical pin which it is possible to reproduce information An objective optical element unit of a backup device,

Each has a single first optical element and second optical element made of plastic,

The first optical element changes the amount of change in wavefront aberration on the information recording surface of the first optical information recording medium with respect to the light beam having the wavelength λ 1 when the temperature rises by 30 ° C. from 25 ° C. The first phase structure that suppresses 0.1 λ lr ms or less and the second phase structure that suppresses spherical aberration deterioration caused by the difference between the thickness tl and t2 of the protective substrate and the thickness tl of the protective substrate , and a third phase structure that suppresses spherical aberration deterioration caused by the difference in t3.

According to the present invention, the cost is reduced by forming the first optical element and the second optical element from plastic. In addition, by providing the first to third phase structures, it is possible to achieve good light collection on the information recording surface of three different types of optical information recording media while suppressing aberration deterioration of the light collecting spot due to temperature change. A spot or an optimum focused spot can be formed.

[0020] The objective optical element unit according to claim 3 is the invention according to claim 1, wherein the first phase structure, the second phase structure, and the third phase structure At least two of them are superimposed on one optical surface. “Superimposition” means literally overlapping. In this specification, even if the first phase structure and the second phase structure are provided on different optical surfaces, respectively, or even if the first phase structure and the second phase structure are on the same optical surface, These are provided in different areas, and when there is no overlapping area, this is not a superposition in this specification. Further, another phase structure may be superimposed as long as at least two phase structures are superimposed. For example, a third phase structure may be further superimposed in addition to the first phase structure and the second phase structure.

[0021] The phase structure such as the first phase structure and the second phase structure is preferably a concentric structure centered on the optical axis when viewed from the optical axis direction.

[0022] Further, the first phase structure and the second phase structure are preferably structures in which a blaze shape is periodically repeated. Here, the blazed shape is a sawtooth shape in cross section including the optical axis of the optical element as shown in FIGS. 1 (a), (b), 2 (a), and (b). In other words, the base surface topological structure has a base surface (for example, in FIGS. 1 and 2). In other words, it has an oblique surface C that is neither perpendicular nor parallel to B) and a step D that intersects the oblique surface C and the base surface B. The base surface means a flat plate surface when the first optical element is a flat plate type, and an envelope surface of a phase structure when it is a lens. In addition, “the blazed shape is periodically repeated” naturally includes a shape in which the same blazed shape is repeated in the same cycle. In addition, a blazed shape, which is a unit of period, has regularity, and a shape in which the period gradually increases or decreases gradually is also referred to as “blazed shape is repeated periodically. It is included in what is!

[0023] When the phase structure has a blazed shape, a triangular shape (including a case where the oblique surface is a curved surface) is repeated. The same triangle may be repeated, or it may have a shape in which the size of the triangle gradually increases or decreases as the distance from the optical axis increases. However, even in the case where the size of the triangle changes gradually, it is preferable that the length of the triangle in the optical axis direction (or the direction of the passing light) hardly changes. In a blazed shape, the length in the direction of the optical axis of one triangle (may be the length in the direction of light passing through the triangle) is called the pitch depth, and the direction along the base surface of one triangle. Is called the pitch width.

[0024] Furthermore, the shape of the superposition structure formed by superimposing the first phase structure and the second phase structure may leave behind the blazed shape of the first phase structure and the second phase structure. . In other words, the superposition structure formed by superimposing the first phase structure and the second phase structure is an oblique surface that is neither perpendicular nor parallel to the base surface on which the optical element superposition structure is provided. You may have.

[0025] In addition, among the first phase structure and the second phase structure, a blazed-type phase structure (see FIGS. 1 and 2 (a)) having a larger pitch width (or period width), When at least two phase structures of a blazed-type phase structure (see Figs. 1 and 2 (b)) with a small pitch width (or period width) are superimposed, At least one force at the position of the step of the phase structure (i.e., the first phase structure) having a large pitch width (or periodic width) (surface D substantially perpendicular to the base surface B in Fig. 1), a small pitch width ( Alternatively, it may or may not coincide with the position of the step D of the phase structure having a period width (ie, the second phase structure). The positions of all the steps D in the first phase structure are the same as the positions of the steps D in the second phase structure. An example of the optical path difference providing structure superimposed so as to match is shown in Fig. 1 (c). Note that the blazed triangular shape S in the first phase structure and the blazed triangular force S in the second phase structure are similar to each other if they are similar to each other. As described above, it has a surface parallel to the base surface and does not have a surface oblique to the base surface. On the other hand, if the blazed triangle of the first phase structure and the blazed triangle force S of the second phase structure are not similar to each other, that is, if they are dissimilar to each other, all of the first phase structure Even if the position of the step D is superimposed so as to coincide with the position of the step D of the second phase structure, as shown in the structure on the right side of FIG. It is possible to leave a remnant of the blaze shape. On the other hand, by making the position of the step D of the first phase structure not coincide with the position of the step D of at least one second phase structure, it is more preferable that the first phase structure (Fig. 2 (a)) By shifting the position of each step D so that the period does not match the integer multiple of the period of the second phase structure (Figure 2 (b)), a blaze shape as shown in Figure 2 (c) It becomes possible to leave a remnant of.

[0026] The objective optical element unit according to claim 4 is the invention according to claim 3, wherein the first phase structure and the second phase structure are the first optical element. It is superimposed on the optical surface on the light source side.

[0027] The objective optical element unit according to claim 5 is the invention according to any one of claims 1 to 4, wherein the third optical information is the third optical information. The working distance WD3 with respect to the recording medium satisfies the following expression (1), and further, the paraxial power of the first optical element with respect to the light beam with the wavelength λ 1 is pi, and the first distance with respect to the light beam with the wavelength λ 1 When the paraxial power of the optical element 2 is ρ2, the following equation (2) is satisfied.

[0028] 0. 20 (mm) ≤WD3≤0. 50 (mm) (1)

0 <pl / p2≤0. 30 (2)

Giving the first optical element power so that pl / p2 exceeds the lower limit of equation (2) has an advantage that spherical aberration deterioration caused by temperature changes can be easily suppressed. On the other hand, if the first optical element has too much power, the working distance WD3 for the third optical information recording medium may be shortened. Therefore, by setting pl / p2 below the upper limit of equation (2), the working distance WD3 is set within the range shown in equation (1). Can be determined.

[0029] It is more preferable to satisfy the following expression (2 ').

[0030] 0. 03 <pl / p2≤0. 30 (2 ')

The objective optical element unit according to claim 6 is the paraxial axis of the first optical element with respect to the light beam having the wavelength λ 1 in the invention according to any one of claims 1 to 4. When the power is pi and the paraxial power of the second optical element with respect to the light beam having the wavelength λ1 is ρ2, the following expression (3) is satisfied.

[0031] pl / p2 = 0 (3)

As shown in the formula (3), when the first optical element is not provided with power (for example, a parallel plate), it is preferable to install the first optical element in an inclined state.

[0032] The objective optical element unit according to claim 7 is the invention according to any one of claims 1 to 6 in the claims 1 to 6, and the second optical element. Since the optical surface of the element consists only of a refracting surface, it is easier to design than the case where a phase structure is provided on the optical surface of the second optical element. Costs can be reduced and light utilization efficiency can be increased.

[0033] The objective optical element unit according to claim 8 is the invention according to any one of claims 1 to 7, and the invention according to any one of claims 1 to 7, and the first phase structure. In the cross-sectional shape including the optical axis, the optical path length increases with increasing distance from the optical axis at a predetermined height from the optical axis, and the optical path length decreases with increasing distance from the optical axis after the predetermined height from the optical axis. The optical path length decreases as the distance from the optical axis increases at a predetermined height from the optical axis, or the optical path length increases as the distance from the optical axis increases from the predetermined height. It is characterized by a phase difference providing structure.

[0034] The principle of correction of temperature aberration by the annular structure of the first phase structure determined as in claim 8 will be described. The line (Α) in Fig. 3 represents the wavefront of a single lens having two aspherical optical surfaces when the temperature rises from the design reference temperature, and the horizontal axis is the optical surface. It represents the effective radius, and the vertical axis represents the optical path difference. A single lens generates spherical aberration due to the change in refractive index with temperature rise, and the wavefront changes as shown by the line (Α). In particular, when the single lens is made of resin, the refractive index change with temperature changes is large, so spherical aberration is generated. The amount gets bigger.

[0035] Line (B) is an optical path difference added to the transmitted wavefront by the annular structure determined as in claim 8. Line (C) has a temperature from the design reference temperature. It is a figure showing the mode of the wave front which permeate | transmitted the ring zone structure and single lens at the time of rising. From the line (B) and the line (C), the wave front transmitted through the annular structure and the wave front of the single lens when the temperature rises from the design reference temperature cancel each other on the information recording surface of the optical disc. It can be understood that the wavefront of the condensed laser beam is a good wavefront with no optical path difference when viewed macroscopically, and the temperature aberration of the single lens is corrected by such an annular structure.

The objective optical element unit according to claim 9 is the same as the phase at the position of the predetermined height of the first phase structure in the invention according to claim 8. This region includes a position of 70% of the effective light beam diameter of the first light beam.

[0037] The change in the wavefront accompanying the change in temperature is maximum at around 70% of the effective beam diameter. Therefore, as in the third aspect of the claims, the annular zone that is the turning point of the phase structure, that is, a predetermined height. If the region with the same phase as the phase at the position (optical path difference) is set so as to include the position of 70% of the effective beam diameter, the effect of improving the temperature characteristics can be most expected.

[0038] The objective optical element unit according to claim 10 is the invention according to any one of claims 1 to 9, wherein the first phase structure is a light beam having the wavelength λ1. When X is incident, the light intensity of the X-order outgoing light is made larger than the light intensity of any other order of outgoing light, and when the luminous flux of wavelength λ 2 is incident, the light intensity of the y-order outgoing light Is a phase structure that increases the light intensity of any other order of emitted light, and satisfies the following formula (4).

0 (9) (χλ1) / (nl-l) ≤ (y λ2) / (η2-1) ≤ 1.2 (χλ1) / (η1-1)

(Four)

Where χ represents an integer other than 0, y represents an integer other than 0, nl represents the refractive index at the wavelength λ 1 of the first optical element, and η2 represents the wavelength of the first optical element. Refractive index at λ 2.

According to the invention described in claim 10, the first optical element exhibits high transmittance with respect to the wavelength λ 1 and the wavelength λ 2 by satisfying the equation (4). 1st because it can be secured Recording / reproducing speed on the optical information recording medium and the second optical information recording medium can be increased.

Yes

[0040] The objective optical element unit according to claim 11 is the invention according to any one of claims 1 to 10, wherein the second phase structure includes the first light flux and the front beam. The diffractive structure diffracts the second light beam without diffracting the third light beam.

[0041] By making the second phase structure a diffractive structure that selectively diffracts only the second light beam, the aberration with respect to the second light beam can be controlled independently, and the first information recording medium and the second information can be controlled. Good condensing characteristics can be obtained for both recording media.

[0042] The objective optical element unit according to claim 12 is the invention according to claim 11, wherein the second phase structure is a butterfly whose cross-sectional shape including the optical axis is stepped. It is a staircase structure with concentric rings arranged in a concentric circle, with the steps shifted by the height corresponding to each level surface for each predetermined number A of the level surfaces. Features.

[0043] According to the invention described in claim 12, it is possible to give the second phase structure the diffraction characteristics as described in claim 11.

[0044] In the objective optical element unit according to Claim 13, in the invention according to Claim 12, the number A of the predetermined level surfaces is any one of 4, 5, and 6. It is characterized by this.

[0045] According to the invention described in claim 13, high transmittance can be secured for the three light beams. In order to ensure the highest transmittance for the three luminous fluxes, it is more preferable to set the number A of predetermined level surfaces to 5! /.

[0046] The objective optical element unit according to claim 14 is characterized in that the objective optical element unit according to claim 12 or

In the invention described in item 13, the optical path difference caused by one step of the staircase is 1.9 times or more and 2.1 times or less of the wavelength λΐ.

[0047] According to the invention described in claim 14, high transmittance can be secured for the three light beams.

[0048] The objective optical element unit according to claim 15 is the invention according to any one of claims 1 to 14, wherein the third phase structure includes the first light flux and the front beam. The diffractive structure diffracts the third light beam without diffracting the second light beam.

[0049] According to the invention of claim 15, the third phase structure is a diffractive structure that selectively diffracts only the third light beam, thereby independently controlling the aberration with respect to the third light beam. As a result, good light condensing characteristics can be obtained for both the first information recording medium and the third information recording medium.

[0050] The objective optical element unit according to claim 16 is the invention according to claim 15, wherein the third phase structure is a butterfly having a stepped cross section including an optical axis. It is a staircase structure with concentric rings arranged in a concentric circle, with the steps shifted by a height corresponding to each level surface for each predetermined number of level surfaces B Features. B is preferably 2.

[0051] According to the invention described in claim 16, it is possible to give the third phase structure diffraction characteristics as in claim 15.

[0052] The objective optical element unit according to claim 17 is characterized in that the object optical element unit according to claim 15 or

In the invention described in item 16, the optical path difference caused by one step of the step structure is 4.9 times or more and 5.1 times or less of the wavelength λΐ.

[0053] According to the invention of claim 17, high transmittance is ensured for the first optical information recording medium and the second optical information recording medium, which are required to increase the recording / reproducing speed. it can. Then, as described in claim 17, this effect becomes more prominent by making the optical path difference caused by one step of the staircase approximately 5 times the wavelength 1.

[0054] The objective optical element unit according to claim 18 is the objective optical element unit according to any one of claims 1 to 7, in which the wavelength λ1 that has passed through the first phase structure is The light flux has the highest light intensity of the 10th-order diffracted light, and the light beam having the wavelength λ 2 that has passed through the first phase structure has the highest light intensity of the 6th-order diffracted light and has passed through the first phase structure. The light beam with the wavelength λ 3 has the highest light intensity of the fifth-order diffracted light,

The light beam having the wavelength λ 1 that has passed through the second phase structure has the highest light intensity of the second-order diffracted light, and the light beam having the wavelength λ 2 that has passed through the second phase structure has the light intensity of the first-order diffracted light. The light beam having the wavelength 3 that has passed through the second phase structure has the highest light intensity of the first-order diffracted light, The light beam having the wavelength λ 1 that has passed through the third phase structure has the highest light intensity of the 0th-order diffracted light, and the light beam having the wavelength λ 2 that has passed through the third phase structure has the light intensity of the 0th-order diffracted light. The light beam of wavelength 3 that has the highest value and has passed through the third phase structure has the highest light intensity of the first-order diffracted light.

[0055] The objective optical element unit according to Claim 19 is the invention according to any one of Claims 1 to 18, wherein the second phase structure has a thickness tl of a protective substrate. , the spherical aberration deterioration caused by the difference between t2 and the spherical aberration deterioration based on the difference between the wavelengths λ 1 and λ 2 are suppressed.

[0056] The optical pickup device according to claim 20, wherein the optical pickup device emits a light flux having a wavelength of λ1.

A first light source, a second light source that emits a light beam having a wavelength of 2 (λ 1 <λ 2), a third light source that emits a light beam of a wavelength of 3 (λ 2 <λ 3), and claim 1 A condensing optical system including the object optical element unit according to any one of claims 19 to 19, wherein the condensing optical system converts the first light source power and the luminous flux into a protective substrate having a thickness of tl. The information is recorded and / or reproduced by collecting light on the information recording surface of the first optical information recording medium via the first optical information recording medium. Information can be recorded and / or reproduced by focusing on the information recording surface of the second optical information recording medium via a protective substrate of t2 (tl <t2). Information is recorded and / or collected by focusing the light beam from the light source on the information recording surface of the third optical information recording medium through a protective substrate having a thickness of t3 (t2 <t3). Characterized in that it is possible to reproduce.

[0057] In this specification, as an example of a high-density optical disk, information is recorded / reproduced by an objective lens of NAO. 85, and a standard light whose protective substrate thickness is about 0.1 mm is used. Discs (for example, BD: Blu-ray Disc) are listed. A high-density optical disc includes an optical disc having a protective film with a thickness of several to several tens of nanometers on the information recording surface (in this specification, the protective substrate includes the protective film), and the thickness of the protective substrate. This includes optical disks with a length of zero. Further, in this specification, DVD is a DVD series optical disc in which information is recorded / reproduced with an objective lens of NA 0.60-0.67 and the thickness of the protective substrate is 0.6 mm. It is a generic term and includes DVD-ROM, DVD-Video, DVD-Audio, DV D—RAM, DVD-R, DVD—RW, DVD + R, DVD + RW, and the like. Also, this In the booklet, CD is a general term for CD series optical discs in which information is recorded / reproduced by an objective lens of NA 0.45-0.51 and the thickness of the protective substrate is about 1.2 mm. — Includes ROM, CD-Audio, CD-Video, CD-R, CD-RW, etc. As for the recording density, the recording density of the high-density optical disc is the highest, followed by DVD and CD.

[0058] Note that, regarding the thicknesses tl, t2, and t3 of the protective substrate, it is preferable to satisfy the following conditional expression, but the present invention is not limited to this.

[0059] 0. 070mm≤tl≤0. 125mm

0. 5mm≥≥t2≤0. 7mm

0. 8mm≥≥td≤1.3mm

The thickness tl and t3 of the protective substrate are

0. 0750mm≤tl≤0. 125mm

1. 0mm≤t3≤1.3mm

It is preferable that

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, it is preferable to use a semiconductor laser, a silicon laser, or the like.

[0061] When BD, DVD, and CD are used as the first optical disc, the second optical disc, and the third optical disc, respectively, the wavelength λ1 of the first light source is preferably 350 nm or more and 440 ηm or less, more preferably Is 380 nm or more and 415 nm or less, and the wavelength 2 of the second light source is preferably 570 or more, 680 or less, more preferably 630 or more and 670 or less, and the wavelength of the third light source 3 Is preferably 750 or more and 880 or less, more preferably 760 or more and 820 or less.

[0062] Further, at least two of the first light source, the second light source, and the third light source may be unitized. Unitization means, for example, that the first light source and the second light source are fixedly housed in one package, but is not limited to this, and the two light sources are fixed so that aberration correction is not possible Is widely included. In addition to the light source, a light receiving element to be described later may be packaged. [0063] As a light receiving element that receives reflected light from the optical information recording medium, a photodetector such as a photodiode is preferably used. The light reflected on the information recording surface of the optical disc enters the light receiving element, and the read signal of the information recorded on each optical disc is obtained using the output signal. Furthermore, it detects the change in the amount of light due to the shape change and position change of the focused spot on the light receiving element, and performs focus detection and track detection. Based on this detection, the objective optical element is used for focusing and tracking. You can move the unit. The light receiving element may be composed of a plurality of photodetectors. The light receiving element may have a main photodetector and a sub photodetector. For example, two sub-light detectors are provided on both sides of a light detector that receives main light used for recording and reproducing information, and the sub light for tracking adjustment is received by the two sub-light detectors. It is good also as a simple light receiving element. The light receiving element has a plurality of light receiving elements corresponding to each light source.

[0064] The condensing optical system may have only the objective optical element unit, but in addition, other optical elements such as a coupling lens such as a collimator lens and a flat plate optical element having an optical function may be provided. You may have. The coupling lens is a single lens or a lens group that is disposed between the objective optical element unit and the light source and changes the divergence angle of the light beam. Furthermore, the condensing optical system has an optical element such as a diffractive optical element that divides the light beam emitted from the light source into a main light beam used for recording and reproducing information and two sub light beams used for tracking and the like. It may be. In this specification, the objective optical element unit 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. . Preferably, the objective optical element unit is 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. Further, it refers to an optical system that can be integrally displaced at least in the optical axis direction by an actuator.

The invention's effect

[0065] According to the present invention, it is possible to appropriately record and / or reproduce information with respect to at least three types of optical discs having favorable temperature characteristics and having different light source wavelengths and protective substrate thicknesses. An optical picker that is easy to manufacture and can reduce manufacturing costs. It is possible to provide an objective optical element unit and an optical pickup device for the optical device. Brief Description of Drawings

[0066] FIG. 1 is a diagram showing a phase difference providing structure (c) in which a first phase structure (a) and a second phase structure (b) are overlapped with the positions of steps being matched.

FIG. 2 is a diagram showing a phase difference providing structure (c) in which a first phase structure (a) and a second phase structure (b) are overlapped by shifting the position of a step.

FIG. 3 is a drawing for explaining the principle of temperature aberration correction by the ring structure of the first phase structure.

FIG. 4 is a diagram schematically showing a configuration of an optical pickup device according to the present invention.

FIG. 5 is a cross-sectional view schematically showing an example of an objective optical element unit OL according to the present invention.

FIG. 6 is a diagram showing an example of a phase structure.

FIG. 7 is a diagram showing an example of a phase structure.

FIG. 8 is a diagram showing an example of a phase structure.

FIG. 9 is a diagram showing an example of a phase structure.

FIG. 10 is a diagram showing an example of a phase structure.

FIG. 11 is a diagram showing an example of a phase structure.

Explanation of symbols

[0067] AC1 2-axis actuator

AC 2 1-axis actuator

B Base surface

C Diagonal surface

C1 central area

C2 peripheral area

C3 Central area

C4 peripheral area

CL collimating optics

D Step

DOE1 first diffraction structure DOE2 second diffraction structure

DOE3 3rd diffraction structure

L blaze dimensions

L1 aberration correction element

L2 condensing element

LD1 Blue-violet semiconductor laser

LD2 Red semiconductor laser

LD3 infrared semiconductor laser

ML mirror

OL Objective optical element unit

P1 prism

P2 prism

P3 prism

PD photodetector

PL1 protection board

PL2 protection board

PL3 protection board

PU optical pickup device

RL1 information recording surface

RL2 information recording surface

RL3 information recording surface

SE sensor optics

STO aperture

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, an optical pickup device using the objective optical element unit according to the present invention will be described with reference to FIG. Figure 4 shows the information stored in the high-density optical information recording medium BD (first optical information recording medium), DVD (second optical information recording medium), and CD (third optical information recording medium). Record and playback 1 is a diagram schematically showing a configuration of an optical pickup device PU. BD specification is 1st wavelength λ l = 405nm, protective substrate PL1 thickness tl = 0.1mm, numerical aperture NA1 = 0.85, DVD specification is 2nd wavelength 2 = 655nm, protection Substrate PL2 thickness t2 = 0.6mm, numerical aperture NA2 = 0.65, CD specification is 3rd wavelength 3 = 785nm, protective substrate PL3 thickness t3 = 1.2mm, numerical aperture NA3 = 0.51. However, the combination of wavelength, protective substrate thickness, and numerical aperture is not limited to this.

[0069] The optical pickup device PU includes a blue-violet semiconductor laser LD1 (first light source) for BD, a red semiconductor laser LD2 (second light source) for DVD, an infrared semiconductor laser LD3 (third light source) for CD, BD / DVD / CD shared photodetector PD, objective optical element OL, collimating optical system CL, 2-axis actuator AC1, 1-axis actuator AC2, first prism PI, second prism P2, third prism P3, vertical It consists of a lifting mirror ML and a sensor optical system SE for adding astigmatism to the reflected light flux from the information recording surface of each optical disk. A blue-violet SHG laser may be used as a light source for BD.

[0070] When recording / reproducing information with respect to the BD in the optical pickup device PU, the uniaxial actuator AC2 is used so that the blue-violet laser beam is emitted from the collimating optical system CL in the state of a parallel beam. After adjusting the position of the collimating optical system CL in the optical axis direction, the blue-violet semiconductor laser LD1 is caused to emit light. The divergent light beam emitted from the blue-violet semiconductor laser LD1 is reflected by the first prism P1 and then the second prism P2 and the third prism P3, as shown in FIG. Are sequentially transmitted and converted into a parallel light beam by the collimating optical system CL. After that, after being reflected by the rising mirror ML, the beam diameter is regulated by the stop STO, and it becomes a condensed spot formed on the information recording surface RL1 by the objective optical element unit OL via the BD protective substrate P L1. . The objective optical unit OL is focused and tracked by the 2-axis actuator AC1 placed around it. A detailed description of the objective optical element unit OL will be given later.

[0071] The reflected light beam modulated by the information pits on the information recording surface RL1 is transmitted again through the objective optical element unit OL, then reflected by the rising mirror ML, and is reflected as a convergent light beam when passing through the collimating optical system CL. Become. Then, the third prism P3, the second prism P2, and the first prism After sequentially passing through PI, astigmatism is added by the sensor optical system SE and converges on the light receiving surface of the photodetector PD. Information recorded on the BD can be read using the output signal of the photodetector PD.

[0072] Further, when recording / reproducing information on / from a DVD to the optical pickup device PU, the red laser beam is emitted in the state of a parallel beam from the collimating optical system CL. In addition, after adjusting the position of the collimating optical system CL in the direction of the optical axis by the single-axis actuator AC2, the red semiconductor laser LD2 is caused to emit light. The divergent light beam emitted from the red semiconductor laser LD2 is reflected by the second prism P2 and then transmitted through the third prism P3, as shown by the broken line in FIG. 4, and is transmitted by the collimating optical system CL. Converted to parallel light flux. After that, after being reflected by the rising mirror ML, it becomes a focused spot formed on the information recording surface RL2 by the objective optical element unit OL via the DVD protective substrate PL2. The objective optical element unit OL is connected to the 2-axis actuator AC1 located around it.

[0073] The reflected light beam modulated by the information pits on the information recording surface RL2 is transmitted again through the objective optical element unit OL, then reflected by the rising mirror ML, and is reflected as a convergent light beam when passing through the collimating optical system CL. Become. Thereafter, after passing through the third prism P3, the second prism P2 and the first prism P1 in order, astigmatism is added by the sensor optical system SE and converges on the light receiving surface of the photodetector PD. The information recorded on the DVD can be read using the output signal of the photodetector PD.

[0074] Further, when recording / reproducing information to / from the optical pickup device PU, the infrared laser beam is emitted in the state of a parallel beam from the collimating optical system CL. In addition, after adjusting the position of the collimating optical system CL in the direction of the optical axis by the uniaxial actuator AC2, the infrared semiconductor laser LD3 is caused to emit light. The divergent light beam emitted from the infrared semiconductor laser LD3 is reflected by the third prism P3 and then converted into a parallel light beam by the collimating optical system CL, as shown by the dashed line in FIG. The After that, after being reflected by the rising mirror ML, it becomes a focused spot formed on the information recording surface RL3 by the objective optical element unit OL via the CD protective substrate PL3. The objective optical element unit OL is focused by a two-axis actuator AC1 arranged around it. Fi.

[0075] The reflected light beam modulated by the information pits on the information recording surface RL2 is transmitted again through the objective optical element unit OL, then reflected by the rising mirror ML, and is reflected as a convergent light beam when passing through the collimating optical system CL. Become. Thereafter, after passing through the third prism P3, the second prism P2 and the first prism P1 in order, astigmatism is added by the sensor optical system SE and converges on the light receiving surface of the photodetector PD. The information recorded on the CD can be read using the output signal of the photodetector PD.

In the optical pickup device PU, the spherical aberration when using the BD can be corrected by driving the collimating optical system CL in the optical axis direction by the uniaxial actuator AC2. This spherical aberration correction mechanism enables wavelength variations due to manufacturing errors of the blue-violet semiconductor laser LD1, changes in the refractive index and refractive index distribution of the objective optical system due to temperature changes, focus jumps between information recording layers of multilayer discs, protective substrate PL1 It is possible to correct spherical aberration caused by thickness variation and thickness distribution due to manufacturing errors. Note that this spherical aberration correction mechanism may correct spherical aberration when using a DVD or CD.

Next, the configuration of the objective optical element unit OL will be described. FIG. 5 schematically shows the configuration of the object optical element unit OL according to the present invention. The objective optical element unit OL has an aberration correction element (first optical element) L1 and a condensing element (second optical element) L2 arranged in order from the laser light source side through a lens barrel (holding member) HL. In other words, the optical axis X is held so as to be coaxial.

[0078] The aberration correction element L1 is made of plastic having an Abbe number of 50 or more and 60 or less, and the optical surface on the optical disk side corresponds to the central region C1 corresponding to the numerical aperture NA3 and the numerical aperture NA3 to the numerical aperture NA1. The optical surface on the laser light source side is divided into a central region C3 corresponding to the numerical aperture NA2 and a peripheral region C4 corresponding to the numerical aperture NA2 to numerical aperture NA1. Yes.

[0079] The first diffractive structure DOE1 is formed in the central region C1 of the optical surface on the optical disc side, and the third diffractive structure DOE3 is formed in the peripheral region C2. The first diffractive structure DOE1 is a superposed structural force of the first phase structure and the third phase structure, and the third diffractive structure DOE3 consists only of the third phase structure. The first phase structure reduces aberrations in the focused spot due to temperature changes. The third phase structure is for correcting the spherical aberration caused by the difference in thickness between the protective substrate PL1 and the protective substrate PL3.

[0080] In addition, a second diffractive structure (also referred to as an optical path difference providing structure) DOE2 is formed in the central region C3 of the optical surface on the laser light source side, and the peripheral region C4 includes fine structures such as a diffractive structure and a phase structure. The plane is such that no fine structure is formed. The second diffractive structure DOE2 is composed of a second phase structure that corrects the spherical aberration caused by the difference in thickness between the protective substrate PL1 and the protective substrate PL2 and the wavelength difference between the blue-violet laser beam and the red laser beam. The specific diffraction orders of the first phase structure, the second phase structure, and the third phase structure are (10, 6, 5), (0, 1, 0), (0, 0, 1), respectively.

[0081] Note that without providing the first diffractive structure DOE1 in which the first phase structure and the third phase structure are superimposed, only the first phase structure is provided in the region of the first diffractive structure DOE1, and the second diffractive structure DOE2 When correcting the spherical aberration caused by the difference in the protective substrate thickness of three different optical discs by superimposing the second phase structure and the third phase structure, when the light beam with wavelength λ1 passes as the first phase structure , 5 (= u) When the diffracted light has the highest light intensity and the light beam with wavelength 2 passes, 3 (= v) When the diffracted light with the highest light intensity passes and the light beam with wavelength 3 passes The value of the step D and the dimension of one blaze in the direction perpendicular to the optical axis (pitch width P) may be determined so that the light intensity of the 2 (= w) order diffracted light is the highest. The first diffractive structure DOE1 may be superimposed on the second diffractive structure DOE2.

Further, the first phase structure may be provided on the optical surface on the light source side of the aberration correction element L1, or may be provided on the optical surface on the optical disk side. The first phase structure has the second-order (= u) diffracted light having the highest light intensity when the light beam with wavelength λ 1 passes, and the first-order (= v) when the light beam with wavelength 2 passes. When the diffracted light has the highest light intensity and a light beam with a wavelength of 3 has passed, the first-order (= w) diffracted light has the highest light intensity. , w) may be (10, 6, 5), (5, 3, 2), or (2, 1, 1).

[0083] Furthermore, it is more preferable that the first phase structure and the second phase structure overlap with the optical surface on the light source side of the aberration correction element L1. As the diffraction order of the second phase structure, when the light beam having the wavelength λ 1 passes, the 0th order diffracted light has the highest light intensity, and when the light beam having the wavelength 2 passes, the first order diffracted light has the highest light intensity. When the light beam with wavelength λ3 passes, Also, it is preferable that the light intensity is high (0, 1, 0).

[0084] In the cross-sectional shape including the optical axis of the first phase structure, the optical path length increases as the distance from the optical axis increases from the optical axis at a predetermined height, and from the optical axis after the predetermined height from the optical axis. A phase difference providing structure in which the optical path length is shortened as the distance is increased, or at a predetermined height from the optical axis, the optical path length is decreased as the distance from the optical axis is increased. A phase difference providing structure in which the optical path length increases as the distance increases is preferable.

[0085] It is preferable that the position includes 70% of the effective light beam diameter of the light flux having the region force wavelength λ 1 in the same phase as the phase at the position of the predetermined height of the first phase structure.

The second phase structure is preferably a diffractive structure that does not diffract a light beam having a wavelength λ 1 and a light beam having a wavelength λ 3 but diffracts a light beam having a wavelength λ 2. The specific diffraction orders are (0, 1,

0) is preferred.

[0087] The second phase structure is a structure in which patterns whose cross-sectional shape including the optical axis is stepped are arranged concentrically, and the number of level planes is equal to the number of level planes every predetermined number of level planes. A structure in which the steps are shifted by a height corresponding to the number of steps is preferable.

[0088] The number A of the predetermined level surfaces is preferably 4, 5, or 6.

[0089] The optical path difference caused by one step of the staircase is preferably twice the wavelength λ1.

[0090] The third phase structure is preferably a diffractive structure that diffracts the third light beam without diffracting the light beam having the wavelength λ1 and the light beam having the wavelength λ2. The specific diffraction order is preferably (0, 0, 1).

[0091] The third phase structure is a structure in which patterns whose cross-sectional shape including the optical axis is stepped are arranged concentrically, and the number of level planes is the number of level planes every predetermined number of level planes. A structure in which the steps are shifted by a height corresponding to the number of steps is preferable.

[0092] The optical path difference caused by one step of the staircase is preferably 5 times the wavelength λ1.

Example

An example that can be used in the optical pickup device of FIG. 4 will be described. Examples 1 and 2 below are examples in which the first phase structure and the second phase structure are superimposed on the light source side optical surface of the first optical element. The third phase structure is an example formed on the optical surface of the first optical element on the optical disc side. In the following, a power of 10 (for example, 2.5 X 1CT ³ ) It shall be expressed using E (for example, 2 · 5E−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 Equation (1).

[0095] [Equation 1] A ₂ ² i

[0096] where X (h) is the coordinate axis of the aspherical surface in the optical axis direction (the light traveling direction is positive), _κ is the conic coefficient, Α is the aspherical coefficient, h is the height from the optical axis, r is the radius of curvature on the optical axis of the aspheric surface

2i

Further, the optical path length 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.

[0098] [Equation 2]

[0099] where λ is the wavelength of the incident light beam, λ 製造 is the manufacturing wavelength (blazed wavelength), dor is the diffraction order, and C is the coefficient of the optical path difference function.

2i

(Example 1)

Tables 1 and 2 below show the lens data of Example 1. In Example 1, the first optical element has no power with respect to the design wavelength λ l = 408 nm. In Example 1, the amount of aberration change when the temperature rises from the design reference temperature of 25 ° C to 30 ° C is 165m rms for the comparative example without the 10th / 6th / 5th diffraction structures. On the other hand, in the case of the present embodiment having the 10th / 6th / 5th diffraction structures, it is 38 m rms. However, the laser wavelength shift due to temperature change + and 0. 05nm / ° C, the material refractive index variation - are a 9 X 10- ⁵ / ° C.

[0100] [Table 1] Design wavelength λ1: 408nra λ2: 658nm λ3: 785nm Focal length of objective lens fl: 2.20mm f2: 2.23mm f3: 2.47mm Image surface side numerical aperture Ml: 0.85 NA2: 0.61 NA3: 0.46 pi (first element Of paraxial power) 0.000

p2 (Paraxial power of the second element) 0.455

pl / p2 0.000

[Paraxial axis

[2nd and 3rd data]

(Example 2)

Tables 3 and 4 below show the lens data of Example 2. In Example 2, the first optical element has power with respect to the design wavelength λ l = 408 nm. In Example 2, the amount of aberration change when the temperature rose by 30 ° C from the design reference temperature of 25 ° C was 87 rms for the comparative example without the 10th / 6th / 5th diffraction structures. In the case of the present embodiment having a 10th order / 6th order / 5th order diffraction structure, 9 m rms is obtained. However, temperature change Design wavelength λ 1: 408 nm 2: 658 nm 3: 785

Focal length of objective lens fl: 2.20mm f2: 2.27ram f3: 2.51mm

Image side numerical aperture NA1: 0.85 NA2: 0.60 NA3: 0.45

pi (Paraxial power of the first element) 0.028

p2 (Paraxial power of the second element) 0.435 pl / p2 0.064

[Paraxial data]

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Claims

The scope of the claims

[1] A first light source that emits a light beam of wavelength λλ, a second light source that emits a light beam of wavelength 2 (λ 1 <λ 2), and a light beam of wavelength 3 (λ 2 <λ 3) And a condensing optical system including an objective optical element unit, and the condensing optical system transmits the light beam having the first light source power via the protective substrate having a thickness of tl to the first optical information. By focusing on the information recording surface of the recording medium, it is possible to record and / or reproduce information, and protect the light flux from the second light source with a thickness t2 (tl <t2). It is possible to record and / or reproduce information by condensing on the information recording surface of the second optical information recording medium through the substrate, and further, the light flux from the third light source is Information is recorded and / or reproduced by focusing on the information recording surface of the third optical information recording medium via the protective substrate of t3 (t2 <t3). A objective optical element unit of an optical pickup apparatus has become possible, have a respectively single first optical element to the material of plastic and a second optical element,

The first optical element is caused by a difference between a first phase structure that suppresses aberration deterioration of a condensing spot caused by a temperature change with respect to the light beam having the wavelength λ1, and a thickness tl, t2 of the protective substrate. Objective light, comprising: a second phase structure that suppresses spherical aberration degradation that occurs as a result; and a third phase structure that suppresses spherical aberration degradation caused by the difference between the thicknesses tl and t3 of the protective substrate. Scientific element unit.

[2] A first light source that emits a light beam of wavelength λλ, a second light source that emits a light beam of wavelength 2 (λ 1 <λ 2), and a light beam of wavelength 3 (λ 2 <λ 3) And a condensing optical system including an objective optical element unit, and the condensing optical system transmits the light beam having the first light source power via the protective substrate having a thickness of tl to the first optical information. By focusing on the information recording surface of the recording medium, it is possible to record and / or reproduce information, and protect the light flux from the second light source with a thickness t2 (tl <t2). It is possible to record and / or reproduce information by condensing on the information recording surface of the second optical information recording medium through the substrate, and further, the light flux from the third light source is Information is recorded and / or reproduced by focusing on the information recording surface of the third optical information recording medium via the protective substrate of t3 (t2 <t3). A objective optical element unit of an optical pickup apparatus has become possible, Each has a single first optical element and second optical element made of plastic,

The first optical element changes the amount of change in wavefront aberration on the information recording surface of the first optical information recording medium with respect to the light beam having the wavelength λ 1 when the temperature rises by 30 ° C. from 25 ° C. The first phase structure that suppresses 0.1 λ lr ms or less and the second phase structure that suppresses spherical aberration deterioration caused by the difference between the thickness tl and t2 of the protective substrate and the thickness tl of the protective substrate , a third phase structure that suppresses spherical aberration deterioration caused by the difference in t3.

[3] The first aspect of the invention is characterized in that at least two of the first phase structure, the second phase structure, and the third phase structure are superimposed on one optical surface. Alternatively, the objective optical element unit according to Item 2.

[4] The objective optical according to claim 3, wherein the first phase structure and the second phase structure are superimposed on an optical surface on the light source side of the first optical element. Element unit.

[5] The working distance WD3 for the third optical information recording medium satisfies the following expression (1), and further, the paraxial power of the first optical element with respect to the light beam having the wavelength λ 1 is pi, and Any one of claims 1 to 4, wherein the following expression (2) is satisfied, where p2 is a paraxial power of the second optical element with respect to a light beam having a wavelength λ1: An objective optical element unit as described above.

0. 20 (mm) ≤WD3≤0.50 (mm) (1)

0 <pl / p2≤0. 30 (2)

[6] When the paraxial power of the first optical element with respect to the light flux with wavelength λ1 is pi and the paraxial power of the second optical element with respect to the light flux with wavelength λ1 is ρ2, The object optical element unit according to any one of claims 1 to 4, wherein the following expression (3) is satisfied.

pl / p2 = 0 (3)

[7] The objective optical element unit according to any one of [1] to [6], wherein the optical surface of the second optical element comprises only a refractive surface.

[8] The cross-sectional shape including the optical axis of the first phase structure has an optical path length that increases as it is away from the optical axis at a predetermined height from the optical axis. A phase difference providing structure in which the optical path length is shortened as it is away from the axis, or at a predetermined height from the optical axis, the optical path length is shortened as it is away from the optical axis, and after the predetermined height from the optical axis, the optical axis 8. The objective optical element unit according to any one of claims 1 to 7, wherein the objective optical element unit has a phase difference providing structure in which an optical path length is increased as the force is separated.

[9] The region having the same phase as the phase at the position of the predetermined height of the first phase structure includes a position of 70% of the effective light beam diameter of the first light beam. Objective optical element unit as described in item 8.

[10] The first phase structure makes the light intensity of the X-order outgoing light larger than the light intensity of any other order of outgoing light when the light flux having the wavelength λ1 is incident, This is a phase structure that makes the light intensity of the y-order outgoing light larger than the light intensity of any other order of outgoing light when the second luminous flux is incident, and satisfies the following formula (4). The objective optical element unit according to any one of claims 1 to 9 of claim 1.

0.9 (χlλl) / (nl-l) ≤ (yλ2) / (η2-1) ≤1.22 (χlλl) / (nl-l)

(Four)

11. The second phase structure according to claim 1, wherein the second phase structure is a diffractive structure that does not diffract the first light flux and the third light flux but diffracts the second light flux. The objective optical element unit according to any one of the above.

[12] The second phase structure is a staircase structure in which a pattern whose cross-sectional shape including the optical axis is a staircase pattern is concentrically arranged, and for each predetermined number of level surfaces, each level surface 12. The objective optical element unit according to claim 11, wherein the objective optical element unit has a structure in which the steps are shifted by a height corresponding to the number of steps.

13. The objective optical element unit according to claim 12, wherein the number A of the predetermined level surfaces is any one of 4, 5, and 6.

[14] The optical path difference produced by one step of the staircase structure is not less than 1.9 times and not more than 2.1 times the wavelength λ1. Objective optical element unit.

15. The third phase structure according to any one of claims 1 to 14, wherein the third phase structure is a diffractive structure that does not diffract the first light flux and the second light flux but diffracts the third light flux. The objective optical element unit according to any one of the above.

[16] The third phase structure is a staircase structure in which patterns whose cross-sectional shapes including the optical axis are stepped are arranged concentrically, and each level plane is provided for each predetermined number of level planes. 16. The objective optical element unit according to claim 15, wherein the objective optical element unit has a structure in which the steps are shifted by a height corresponding to the number of steps.

[17] The optical path difference produced by one step of the step structure is not less than 4.9 times and not more than 5.1 times the wavelength λ1. Objective optical element unit.

[18] The light beam with the wavelength λ 1 that has passed through the first phase structure has the highest light intensity of the 10th-order diffracted light, and the light beam with the wavelength λ 2 that has passed through the first phase structure has The light beam with the wavelength λ 3 that has the highest light intensity and has passed through the first phase structure has the highest light intensity of the fifth-order diffracted light,

The light beam having the wavelength λ 1 that has passed through the second phase structure has the highest light intensity of the second-order diffracted light, and the light beam having the wavelength λ 2 that has passed through the second phase structure has the light intensity of the first-order diffracted light. The light beam having the wavelength 3 that has passed through the second phase structure has the highest light intensity of the first-order diffracted light,

The light beam having the wavelength λ 1 that has passed through the third phase structure has the highest light intensity of the 0th-order diffracted light, and the light beam having the wavelength λ 2 that has passed through the third phase structure has the light intensity of the 0th-order diffracted light. 8. The light beam of wavelength 3 having the highest value and having passed through the third phase structure has the highest light intensity of the first-order diffracted light. 8. Objective optical element unit.

[19] The second phase structure is a structure that suppresses spherical aberration deterioration caused by the difference between the thicknesses tl and t2 of the protective substrate and spherical aberration deterioration based on the difference between the wavelengths λ 1 and λ 2. Features The objective optical element unit according to any one of claims 1 to 18, wherein:

[20] A first light source that emits a light beam of wavelength λ と, a second light source that emits a light beam of wavelength 2 (λ 1 <λ 2), and a light beam of wavelength 3 (λ 2 <λ 3) And a condensing optical system including the objective optical element unit according to any one of claims 1 to 19, wherein the condensing optical system has the first light source power Information can be recorded and / or reproduced by focusing the light beam on the information recording surface of the first optical information recording medium via a protective substrate having a thickness of tl. (2) Information can be recorded and / or reproduced by focusing the light beam from the light source on the information recording surface of the second optical information recording medium via a protective substrate with a thickness t2 (tl <t2). Further, the light beam from the third light source is condensed on the information recording surface of the third optical information recording medium through a protective substrate having a thickness t3 (t2 <t3). Thus, the optical pickup device according to feature that it is possible to perform recording and / or reproducing information.