Optical pickup device with correcting element

RELATED APPLICATION

0001This application is based on patent application No. <patcit id="pcit0001" dnum="JP2003374616A"><text>2003-374616</text></patcit> filed in Japan, the entire content of which is hereby incorporated by reference.

BACKGROUND

1.

Field of the Invention

0002The present invention relates to an optical pickup device and to a correcting element used in the optical pickup device.

2.

Description of the Related Art

0003In recent years, there have been made research and development on the so-called high density optical disc wherein recording density of an optical information recording medium (optical disc) has been enhanced by using a blue laser beam having a wavelength of about 400 nm, and thereby, a storage capacity has been increased.

0004As a standard of the high density optical disc, there are known, for example, the one wherein an image-side numerical aperture of an objective lens (NA) is about 0.85 and a protective substrate thickness is about 0.1 mm and the one wherein NA and a protective substrate thickness are controlled to be respectively about 0.65 and about 0.6 mm which are similar to those of a conventional DVD (digital versatile disc). In the following explanation, the high density optical disc whose NA and protective substrate thickness are respectively about 0.65 and about 0.6 mm will be indicated as "HD-DVD (High Density DVD)".

0005There are proposed various technologies relating to optical pickup devices each having compatibility between the high density optical disc of this kind and an optical disc which has been used widely such as DVD and CD (compact disc).

0006Incidentally, light flux wavelengths λ1, λ2 and λ3 used respectively for HD-DVD, DVD and CD are respectively about 400 nm, about 650 nm and about 780 nm, and protective substrate thickness t1, t2 and t3 are respectively about 0.6 mm, about 0.6 mm and about 1.2 mm.

0007To achieve compatibility among the optical discs in plural types of this kind, it is necessary to correct aberrations each being generated by a difference between wavelengths or a difference between protective substrate thicknesses, while securing an amount of a light flux used for each optical disc, and Japanese laid-open patent No. <patcit id="pcit0002" dnum="JP2001060336A"><text>2001-60336</text></patcit>, for example, discloses a technology to provide a diffractive structure on an optical surface of an optical element that constitutes an optical pickup device.

0008The invention disclosed in Japanese laid-open patent No. <patcit id="pcit0003" dnum="JP2001060336A"><text>2001-60336</text></patcit> is an optical pickup device having an compatibility between HD-DVD and DVD or an compatibility among HD-DVD, DVD and CD, wherein chromatic aberration of HD-DVD is corrected by combining a diffractive optical element and an objective lens.

0009However, in the high density optical disc such as HD-DVD, a tolerance of a value of chromatic aberration in a light-converging spot is narrower than that of DVD, and it is necessary to secure an amount of light sufficiently, thus, in the invention disclosed in Japanese laid-open patent No. <patcit id="pcit0004" dnum="JP2001060336A"><text>2001-60336</text></patcit>, correction of chromatic aberration has not always been sufficient.

0010<patcit id="pcit0005" dnum="US6370103B"><text>US-B-6 370 103</text></patcit>, which is used for the two-part form delimitation, discloses a system for reproducing information from one of different kinds of optical information recording medium, each having a transparent substrate in different thickness. The system disclosed comprises a light source for omitting light flux, a converging optical system having an optical axis, a ring-zonal diffraction section, and a refracting surface including a first divisional portion, a second divisional portion and a third divisional portion. The first divisional portion and the third divisional portion are capable of converging the light flux on a first information recording plane of a first optical information recording medium having a first transparent substrate of thickness t1, to reproduce information recorded in the first optical information recording medium. The first divisional portion and the second divisional portion are capable of converging the light flux on a second information recording plane of a second optical information recording medium having a second transparent substrate of thickness t2, to reproduce information recorded in the second optical information recording medium, wherein t2 is greater than t1.

0011<patcit id="pcit0006" dnum="WO03075267A"><text>WO-A-03075267</text></patcit> discloses a system for recording or reproducing conventional optical disks such as CDs and DVDs at high light usage efficiency, using an optical head capable of recording or reproduce high-density optical discs. A diffraction optical element is disposed in a light path of a first light beam of a first wavelength (400 nm to 415 nm) and a second light beam of a second wavelength (650 nm to 680 nm). An arrangement is disclosed in which principally fifth order diffracted light is emitted with respect to the first light beam and principally third order diffracted light is emitted with respect to the second light beam, from the diffraction optical element. Thus, a light diffraction efficiency of substantially 100% can be obtained with respect to both wavelengths.

0012<patcit id="pcit0007" dnum="US2001036018A"><text>US-A-2001/036,018</text></patcit> discloses an optical element comprising an optical surface provided with a stepped level difference, wherein when the stepped level difference is viewed from a direction of an optical axis, the stepped level difference is provided in a form of a single continuous line in which a starting point of the line does not agree with an ending point of the line.

SUMMARY

0013In view of the problems stated above, an object of the invention is to provide an optical pickup device wherein at least a high density disc such as HD-DVD is compatible with DVD, and securing an amount of light is compatible with correction of chromatic aberration and to provide a correcting element representing an optical system used for the aforementioned optical pickup device.

0014The scope of the invention is defined in the appended claims.

0015In the present specification, the "chromatic aberration" means the one wherein an amount of the position change for the minimum wavefront aberration in the optical axis direction for the light-converging spot on the optical information recording medium in the case of the change of a wavelength of light by +1 µm is indicated using the sign in which the direction to leave the light-converging optical element is positive.

0016The "chromatic aberration owned by the element itself" is in the case of evaluating on the individual element, and it means the one wherein an amount of fluctuation of the position for the minimum wavefront aberration in the optical axis direction for the light-converging spot in the case of the change of a wavelength of light by +1 µm is indicated using the sign in which the direction to leave the light-converging optical element is positive.

0017The "image-surface-side numerical aperture" means a numerical aperture (beam-diameter-converted NA) obtained by diameter of the light-converging spot formed on an information recording surface of the optical information recording medium.

0018Compared with HD-DVD, a demand for correction of chromatic aberration in DVD is lower, and therefore, no diffractive structure is provided on second correcting element L2 as in the second invention, and it is possible to control chromatic aberration of the second light-converging spot to be within a range necessary for reproducing and/or recording of information, even in the case of the structure in which the second correcting element itself has chromatic aberration for the second light flux. In this case, a large amount of light can be secured because for the second light flux it is not case that an amount of light is lost in passing through diffractive ring-shaped zones.

0019It is further possible that the second correcting element is provided with a diffractive structure, and that an absolute value of chromatic aberration owned by the second correcting element itself is controlled to be 3.5 µm/nm or less for the light flux emitted from the second light source. In this way, worse of wavefront aberration can be suppressed, even when wavelength change are caused in the case of tracking in reproducing and/or recording for DVD, by controlling chromatic aberration of the light-converging optical element for the second light flux and that of the second correcting element itself to be nearly zero. The light-converging optical element may be made of plastic.

0020The first correcting element may also be made of plastic.

0021The second correcting element may also be made of plastic.

0022Focal length f of the light-converging optical element for the light flux with wavelength λ1 may also be made to satisfy 1 mm ≤ f ≤ 4 mm.

0023Focal length f1 of the first correcting element for the light flux with wavelength λ1 may also be made to satisfy 5.5 mm ≤ f1 ≤ 32 mm.

0024Focal length f2 of the second correcting element for the light flux with wavelength λ2 may also be made to satisfy 5.5 mm ≤ f12 ≤ 32 mm.

0025Magnification m1 of the optical system including the first light source up to the first optical information recording medium for the light flux with wavelength λ1 may also be made to satisfy -1/3 ≤ m1 ≤ -1/10.

0026Further, magnification m2 of the optical system including the second light source up to the second optical information recording medium may also be made to satisfy -1/3 ≤ m2 ≤ -1/10.

0027Further, image-surface-side numerical aperture NA1 of the light-converging optical element for the light flux with wavelength λ1 in the case of using the optical pickup device may also be made to satisfy 0.63 ≤ NA1 ≤ 0.67.

0028Further, image-surface-side numerical aperture NA2 of the light-converging optical element for the light flux with wavelength λ2 in the case of using the optical pickup device may also be made to satisfy 0.59 ≤ NA2 ≤ 0.67.

0029At least one of the first correcting element and the second correcting element may also be made to be a collimator.

0030A combination of the n1 and n2 may also be made to be any one of (n1, n2) = (0, 1), (2, 1), (3, 2), (5, 3) and (8, 5).

0031It is also possible to arrange to provide a third light source emitting a light flux with wavelength λ3 (750 nm ≤ λ3 ≤ 800 nm) and to conduct reproducing and/or recording of information for a third optical information recording medium having protective substrate thickness t3 (1.1 mm ≤ t3 ≤ 1.3 mm) by using n3^th (n3 is a natural number) diffracted light of the light flux with wavelength λ3 generated by diffractive effects of the light-converging optical element in the case of using the optical pickup device.

0032Magnification m3 of the optical system including the third light source up to the third optical information recording medium for the light flux with wavelength λ3 may also be made to satisfy -1/4 ≤ m3 ≤ -1/10.

0033A combination of the n1, n2 and n3 may also be made to be any one of (n1, n2, n3) = (0, 1, 0), (2, 1, 1), (3, 2, 2), (5, 3, 3) and (8, 5, 4).

0034It is also possible to arrange so that the light flux with wavelength λ3 may pass through the second correcting element.

0035The second light source and the third light source may also constitute a packaged light source.

0036When a diffractive structure is provided on the second correcting element, the diffractive structure may also be provided on a plane of incidence and on a plane of emergence of the second correcting element.

0037It is also possible to arrange the chromatic aberration of the first light-converging spot and the chromatic aberration of the second light-converging spot to be controlled within a range necessary for reproducing and/or recording of information, by controlling an absolute value of the chromatic aberration of the first light-converging spot to be 0.15 µm/nm or less and by controlling an absolute value of the chromatic aberration of the second light-converging spot to be 0.25 µm/nm or less. The invention itself, together with further objects and attendant advantages, will best be understood by reference to the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

0038<ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Fig. 1</figref> is a plan view of primary portions showing the structure of an optical pickup device relating to the invention.</li><li><figref idref="f0002">Fig. 2</figref> is a plan view of primary portions showing the structure of a light-converging optical system.</li><li>Each of <figref idref="f0003">Figs. 3(a) - 3(e)</figref> shows chromatic aberration of a light-converging optical element.</li><li><figref idref="f0004">Fig. 4</figref> is a plan view of primary portions showing the structure of a light-converging optical system.</li><li><figref idref="f0005">Fig. 5</figref> is a plan view of primary portions showing the structure of an optical pickup device relating to the invention.</li></ul>

0039In the following description, like parts are designated by like reference numbers throughout the several drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT

0040The preferred embodiment to practice the invention will be explained in detail as follows, referring to the drawings.

(First Embodiment)

0041<figref idref="f0001">Fig. 1</figref> is a drawing showing schematically the structure of first pickup device PU1 capable of conducting recording/reproducing of information properly for any one of HD-DVD (first optical information recording medium), DVD (second optical information recording medium) and CD (third optical information recording medium). In the optical specifications of HD-DVD, wavelength λ1 is 407 nm, thickness t1 of protective layer PL1 is 0.6 mm and numerical aperture NA1 is 0.65, in the optical specifications of DVD, wavelength λ2 is 655 nm, thickness t2 of protective layer PL2 is 0.6 mm and numerical aperture NA2 is 0.65, and in the optical specifications of CD, wavelength λ3 is 785 nm, thickness t3 of protective layer PL3 is 1.2 mm and numerical aperture NA3 is 0.51. However, a combination of a wavelength, a thickness of the protective layer and a numerical aperture is not limited to the foregoing.

0042Optical pickup device PU1 is composed of light source unit LU 23 wherein there are united solidly violet semiconductor laser LD1 (first light source) that emits a laser light flux (first light flux) with wavelength 407 nm when conducting recording/reproducing of information for HD-DVD, red semiconductor laser LD2 (second light source) that emits a laser light flux (second light flux) with wavelength 655 nm when conducting recording/reproducing of information for photodetector PD1 for the first light flux and DVD, and infrared semiconductor laser LD3 (third light source) that emits a laser light flux (third light flux) with wavelength 785 nm when conducting recording/reproducing of information for CD, photodetector PD 23 that is common for both the second light flux and the third light flux, first correcting element L1 through which only the first light flux passes, second correcting element L2 through which the second and third light fluxes pass, objective lens (light-converging optical element) OBJ having a function to converge each laser light flux on each of information recording surfaces RL1, RL2 and RL3, first beam splitter BS1, second beam splitter BS2, third beam splitter BS3, diaphragm STO and sensor lenses SEN1 and SEN2.

0043Incidentally, a diffractive structure is provided on each of the first correcting element L1, the second correcting element L2 and objective lens OBJ, for which the detailed explanation will be given later.

0044When conducting recording/reproducing of information for HD-DVD in optical pickup device PU1, violet semiconductor laser LD1 is first driven to emit light as shown in <figref idref="f0001">Fig. 1</figref> where a light path is indicated with solid lines. A divergent light flux emitted from the violet semiconductor laser LD1 passes through the first beam splitter BS1, then, is transmitted through the first correcting element L1 to be converted into a collimated light flux, and passes through the second beam splitter BS2 to arrive at light-converging optical element OBJ.

0045Then, n1^th diffracted light (n1 is a natural number) of the first light flux generated by diffractive effects of the diffractive structure of the light-converging optical element OBJ is converged on information recording surface RL1 through protective layer PL1 of HD-DVD to form a spot (first light-converging spot). This first light-converging spot is controlled to be within a range necessary for reproducing and/or recording of information in terms of chromatic aberration, and an absolute value of chromatic aberration for the first light-converging spot is controlled specifically to be 0.15 µm/nm or less.

0046Then, the light-converging optical element OBJ conducts focusing and tracking with biaxial actuator AC (not shown) that is arranged on the periphery of the light-converging optical element OBJ. A reflected light flux modulated by information pits on information recording surface RL1 passes again through the light-converging optical element OBJ, the second beam splitter BS2 and the first correcting element L1, to be branched by the first beam splitter BS1, and is given astigmatism by sensor lens SEN 1 to be converged on a light-receiving surface of photodetector PD 1. Thus, information recorded on HD-DVD by the use of output signals of the photodetector PD 1 can be read.

0047Further, when conducting recording/reproducing of information for DVD, the red semiconductor laser LD2 is first driven to emit light as shown in <figref idref="f0001">Fig. 1</figref> where a light path is indicated with one-dot chain lines. A divergent light flux emitted from the red semiconductor laser LD2 passes through the third beam splitter BS3, then, is transmitted through the second correcting element L2 to be converted into a collimated light flux, and is reflected on the second beam splitter BS2 to arrive at light-converging optical element OBJ.

0048Then, n2^th diffracted light (n2 is a natural number satisfying n1 ≠ n2) of the second light flux generated by diffractive effects of the diffractive structure of light-converging optical element OBJ is converged on information recording surface RL2 through protective layer PL2 of DVD to form a spot (second light-converging spot). This second light-converging spot is controlled, in terms of chromatic aberration, to be within a range necessary for reproducing and/or recording of information, and an absolute value of chromatic aberration of the second light-converging spot is specifically controlled to be 0.25 µm/nm or less.

0049Then, the light-converging optical element OBJ conducts focusing and tracking with biaxial actuator AC that is arranged on the periphery of the light-converging optical element OBJ. A reflected light flux modulated by information pits on information recording surface RL2 passes again through the light-converging optical element OBJ, the second beam splitter BS2 and the second correcting element L2, to be branched by the third beam splitter BS3, and is converged on the light-receiving surface of photodetector PD 23. Thus, information recorded on DVD by the use of output signals of photodetector 23 can be read.

0050Further, when conducting recording/reproducing of information for CD, the infrared semiconductor laser LD3 is first driven to emit light as shown in <figref idref="f0001">Fig. 1</figref> where a light path is indicated with dotted lines. A divergent light flux emitted from the infrared semiconductor laser LD3 passes through the third beam splitter BS3, then, it emerges from the second correcting element L2, and is reflected on the second beam splitter BS2 to arrive at light-converging optical element OBJ.

0051Then, n3^th diffracted light (n3 is a natural number) of the third light flux generated by diffractive effects of the diffractive structure of light-converging optical element OBJ is converged on information recording surface RL3 through protective layer PL3 of CD to form a spot (third light-converging spot). This third light-converging spot is controlled, in terms of chromatic aberration, to be within a range necessary for reproducing and/or recording of information.

0052Then, the light-converging optical element OBJ conducts focusing and tracking with biaxial actuator AC that is arranged on the periphery of the light-converging optical element OBJ. A reflected light flux modulated by information pits on information recording surface RL3 passes again through the light-converging optical element OBJ, the second beam splitter BS2 and the second correcting element L2, to be branched by the third beam splitter BS3, and is converged on the light-receiving surface of photodetector PD 23. Thus, information recorded on CD by the use of output signals of photodetector 23 can be read.

0053The light-converging optical element OBJ is a plastic single lens with aspheric surfaces on both sides having a function to make the first - third light fluxes to be converged respectively on information recording surfaces RL1 - RL3. Incidentally, the light-converging optical element may also be constructed by combining a plurality of optical elements.

0054On a plane of incidence of the light-converging optical element OBJ, there is formed blaze-formed diffractive structure DOE shown in <figref idref="f0002">Fig. 2</figref>. The blaze-formed diffractive structure DOE is provided for the purpose of correcting chromatic aberration that is owned by light-converging optical element OBJ itself for the light flux emitted from the first light source, and it is designed specifically so that an absolute value of the chromatic aberration may be 0.15 µm/nm or less.

0055First correcting element L1 has a collimating function to convert the first light flux emitted from the first light source LD1 as a divergent light into a collimated light, and on its plane of emergence, there is formed blaze-formed diffractive structure DOE that is the same as one shown in <figref idref="f0002">Fig. 2</figref>. The blaze-formed diffractive structure DOE is provided for the purpose of correcting chromatic aberration that is owned by the first correcting element L1 itself for the light flux emitted from the first light source, and it is designed specifically so that an absolute value of the chromatic aberration may be 2.1 µm/nm or less.

0056First correcting element L2 has a collimating function to convert the second light flux emitted from the second light source LD2, and has a function to change a divergent angle of the third light flux emitted from the third light source LD3 as a. divergent light to be a smaller divergent angle, and on each of its plane of incidence and plane of emergence, there is formed blaze-formed diffractive structure DOE that is the same as one shown in <figref idref="f0002">Fig. 2</figref>.

0057<figref idref="f0003">Fig. 3 (a)</figref> is a diagram showing the values of chromatic aberration owned by the light-converging optical element itself for the first light flux and the second light flux, in which the value of chromatic aberration owned by the light-converging optical element itself for the first light flux is shown with a circle, while, the value of chromatic aberration owned by the light-converging optical element itself for the second light flux is shown with a square.

0058<figref idref="f0003">Fig. 3 (a)</figref> shows that an absolute value of chromatic aberration owned by the light-converging optical element itself for the first light flux is made to be 0.15 µm/nm or less, namely, to be zero substantially, by the blaze-formed diffractive structure DOE formed on the light-converging optical element, as stated above.

0059Although an illustration is omitted; an absolute value of the chromatic aberration owned by the first correcting element itself for the first light flux is also made to be 2.1 µm/nm or less, namely, to be zero substantially, by the blaze-formed diffractive structure DOE formed on the first correcting element.

0060As stated above, by making chromatic aberration of the light-converging optical element itself for the first light source and chromatic aberration of the first correcting element itself to be substantially zero respectively, it is possible to control chromatic aberration of the first light-converging spot in the case of using an optical pickup device to be within a range that is necessary for reproducing and/or recording of information.

0061If the blaze-formed diffractive structure DOE of the light-converging optical element is designed so that the chromatic aberration of the light-converging optical element itself for the first light flux may be substantially zero, the chromatic aberration of the light-converging optical element for the second light flux remains and a value of the chromatic aberration becomes negative specifically, as shown in <figref idref="f0003">Fig. 3 (a)</figref>.

0062In the present embodiment, therefore, the blaze-formed diffractive structure DOE on each of the plane of incidence and the plane of emergence of the second correcting element is designed so that a value of chromatic aberration owned by the second correcting element itself for the second light flux may be positive, although an illustration thereof is omitted.

0063As stated above, by making negative chromatic aberration of the light-converging optical element itself for the second light flux to be cancelled by positive chromatic aberration of the second correcting element itself, it is possible to control chromatic aberration of the second light-converging spot in the case of using an optical pickup device to be within a range that is necessary for reproducing and/or recording of information.

0064Incidentally, since the design technology to change properly the value of chromatic aberration owned by the optical element itself for the specific light flux by the use of a diffractive structure formed on the optical element is known widely, an explanation thereof will be omitted here.

0065Further, a diffractive structure formed on each of light-converging optical element OBJ, first correcting element L1 and second correcting element L2 may also be superimposed-type diffractive structure HOE representing a structure wherein there are arranged plural ring-shaped zones R in each of which a staircase structure is formed as shown in <figref idref="f0004">Fig. 4</figref> in a way that their centers are on the optical axis.

0066In the structure and the design method for ordinary superimposed-type diffractive structure HOE, depth of one step d0 in the staircase structure formed in each ring-shaped zone R is set to a value calculated by an expression of d0 = k x λ1 / (n1 - 1) µm, and number of division N for respective ring-shaped zones R is set to 5. In the expression above, λ1 represents a wavelength that is of a laser light flux emitted from a violet semiconductor laser and is expressed with a unit of micron (λ1 = 0.408 µm, in this case), and n1 is a refractive index of aberration correcting element L1 for wavelength λ1 (n1 = 1.5242, in this case).

0067When laser light flux with wavelength λ1 enters the superimposed-type diffractive structure HOE, there is generated an optical path difference of k x λ1 µm between adjoining steps of the staircase, and a laser light flux with wavelength λ1 is not diffracted and is transmitted as it is, because no phase difference is given to the laser light flux. Incidentally, in the following explanation, a light flux that is transmitted as it is without being given a phase difference substantially by superimposed-type diffractive structure is called a zero-order diffracted light.

0068In the case of k = 2, for example, when a laser light flux with wavelength λ2 (λ2 = 0.658 µm, in this case) emitted from a red semiconductor laser enters the superimposed-type diffractive structure HOE, there is generated an optical path difference of d0 x (n2 - 1) - λ2 = 0.13 µm between adjoining staircases, and wavefronts transmitted through adjoining ring-shaped zones R are superposed while being staggered by one wavelength, because there is generated an optical path difference equivalent to a difference between 0.13 x 5 = 0.65 µm and one wavelength of wavelength λ2, for single ring-shaped zone R equivalent to one fifth of ring-shaped zones R. Namely, a light flux with wavelength λ2 is made to be a diffracted light diffracted in the first-order direction by the superimposed-type diffractive structure HOE. Incidentally, n2 represents a refractive index of aberration correcting element L2 for wavelength λ2 (n2 = 1.5064, in this case). The diffraction efficiency of the first-order diffracted light for the laser light flux with wavelength λ2 in this case is 87.5% which is a sufficient amount of light for recording/reproducing of information for DVD.

0069When superimposed-type diffractive structure HOE is formed on light-converging optical element OBJ, it is possible to correct spherical aberration caused by a difference of a protective layer thickness between HD-DVD and DVD.

0070When a laser light flux with wavelength λ3 (λ3 = 0.785 µm, in this case) emitted from an infrared semiconductor laser enters the superimposed-type diffractive structure HOE having the aforementioned structure, there is generated an optical path difference of 1 x λ3 µm between adjoining staircases because of λ3 ≈ 2 x λ1, and a laser light flux with wavelength λ3 is also transmitted as it is, like the laser light flux with wavelength λ1 because no phase difference is given to the laser light flux substantially (zero-order diffracted light).

0071When superimposed-type diffractive structure HOE is formed on light-converging optical element OBJ, it is possible to correct spherical aberration caused by a difference of a protective layer thickness between HD-DVD and DVD, by making the magnification for λ1 and the magnification for λ3 to be different each other, for the light-converging optical element OBJ.

0072Incidentally, in the present embodiment, it is not necessary to utilize the aforesaid wavelength selectivity of superimposed-type diffractive structure HOE, because only the first light flux passes through the first correcting element L1. However, when the first correcting element L1, for example, is arranged between the second beam splitter BS2 and light-converging optical element OBJ, the first - third light fluxes pass through the first correcting element L1. In this case, therefore, it is possible to contrive an arrangement wherein superimposed-type diffractive structure HOE is formed on the first correcting element L1, and thereby, wavelength selectivity of superimposed-type diffractive structure HOE is utilized so that the first light flux only may be subjected to diffractive effects and the second and third light fluxes may not be subjected to the diffractive effects.

0073As stated above, the first correcting element L1, the second correcting element L2 and optical pickup device PU1 shown in the present embodiment make it possible to prevent increase of wavefront aberration by controlling chromatic aberration of a light-converging optical element itself and of the first correcting element itself to be zero substantially, even when wavelength fluctuations are caused in the case of tracking in reproducing and/or recording for HD-DVD.

0074Further, by contriving an arrangement wherein light source unit LU23 in which the second light source LD2 and the third light source LD3 are united solidly is used, and the second light flux and the third light flux enter the second correcting element, it is possible to obtain sufficient amount of light and aberration controlling functions, by using diffracting structures provided respectively on the plane of incidence and the plane of emergence of the second correcting element L2.

0075Incidentally, as a combination of n1 and n2, any one of (n1, n2) = (0, 1), (2, 1), (3, 2), (5, 3) and (8, 5) is preferable, and as a combination of n1, n2 and n3, any one of (n1, n2, n3) = (0, 1, 0), (2, 1, 1), (3, 2, 2), (5, 3, 3) and (8, 5, 4) is preferable.

(Second Embodiment)

0076Next, there will be explained Second Embodiment of the invention, wherein an arrangement of each element constituting the present embodiment is the same as that in the aforesaid First Embodiment, for which an illustration is omitted, and the same structure is given the same symbol and an explanation thereof will be omitted.

0077In optical pickup device PU2 of the present embodiment, a diffractive structure is provided on each of first correcting element L1, second correcting element L2 and objective lens OBJ.

0078<figref idref="f0003">Fig. 3 (b)</figref> is a diagram showing the values of chromatic aberration owned by the light-converging optical element itself for the first light flux and the second light flux, in which the value of chromatic aberration owned by the light-converging optical element itself for the first light flux is shown with a circle, while, the value of chromatic aberration owned by the light-converging optical element itself for the second light flux is shown with a square.

0079It is shown that an absolute value of chromatic aberration owned by the light-converging optical element itself for the second light flux is made to be 0.25 µm/nm or less, namely, to be zero substantially, by the blaze-formed diffractive structure DOE formed on the light-converging optical element OBJ, as stated above.

0080Though an illustration will be omitted, an absolute value of chromatic aberration owned by the second light-converging optical element itself for the second light flux is made to be 3.5 µm/nm or less, namely, to be zero substantially, by the blaze-formed diffractive structure DOE formed on the second correcting element L2, as stated above.

0081In this way, by making chromatic aberration of the light-converging optical element itself for the second light flux and chromatic aberration of the second correcting element itself to be substantially zero respectively, it is possible to control chromatic aberration of the second light-converging spot in the case of using an optical pickup device to be within a range that is necessary for reproducing and/or recording of information.

0082If the blaze-formed diffractive structure DOE of the light-converging optical element OBJ is designed so that the chromatic aberration of the light-converging optical element itself for the second light flux may be substantially zero, the chromatic aberration of the light-converging optical element itself for the first light flux remains and a value of the chromatic aberration becomes positive specifically, as shown in <figref idref="f0003">Fig. 3 (b)</figref>.

0083In the present embodiment, therefore, the blaze-formed diffractive structure DOE of the first correcting element L1 is designed so that a value of chromatic aberration owned by the first correcting element itself for the first light flux may be negative, although an illustration thereof is omitted.

0084As stated above, by making positive chromatic aberration of the light-converging optical element itself for the first light flux to be cancelled by negative chromatic aberration of the first correcting element itself, it is possible to control chromatic aberration of the first light-converging spot in the case of using an optical pickup device to be within a range that is necessary for reproducing and/or recording of information.

0085As stated above, the first correcting element L1, the second correcting element L2 and optical pickup device PU2 shown in the present embodiment make it possible to prevent a change for the worse of wavefront aberration by controlling chromatic aberration of a light-converging optical element itself and of the first correcting element itself for the first light flux to be zero substantially, even when wavelength fluctuations are caused in the case of tracking in reproducing and/or recording for DVD.

0086Incidentally, in DVD, a demand for chromatic aberration correction is low, compared with HD-DVD, therefore, it is possible to control chromatic aberration of the second light-converging spot to be within a range necessary for reproducing and/or recording of information, even in the case of an arrangement where a diffractive structure is not provided on the second correcting element L2, and the second correcting element itself has chromatic aberration for the second light flux. In this case, a sufficient amount of light can be secured, because a loss of an amount of light in the occasion for the second light flux to pass through the diffractive ring-shaped zones is not caused.

(Third Embodiment)

0087Next, there will be explained Third Embodiment of the invention, wherein an arrangement of each element constituting the present embodiment is the same as that in the aforesaid First Embodiment, for which an illustration is omitted, and the same structure is given the same symbol and an explanation thereof will be omitted.

0088In optical pickup device PU3 of the present embodiment, a diffractive structure is provided on each of first correcting element L1, second correcting element L2 and objective lens OBJ.

0089<figref idref="f0003">Fig. 3 (c)</figref> is a diagram showing the values of chromatic aberration owned by the light-converging optical element itself for the first light flux and the second light flux, in which the value of chromatic aberration owned by the light-converging optical element itself for the first light flux is shown with a circle, while, the value of chromatic aberration owned by the light-converging optical element itself for the second light flux is shown with a square.

0090As is clear from <figref idref="f0003">Fig. 3 (c)</figref>, a value of chromatic aberration owned by the light-converging optical element itself for the first light flux is positive.

0091In the present embodiment, therefore, the blaze-formed diffractive structure DOE of the first correcting element L1 is designed so that a value of chromatic aberration owned by the first correcting element itself for the first light flux may be negative, although an illustration thereof is omitted.

0092As stated above, by making positive chromatic aberration of the light-converging optical element itself for the first light flux to be cancelled by negative chromatic aberration of the first correcting element itself, it is possible to control chromatic aberration of the first light-converging spot in the case of using an optical pickup device to be within a range that is necessary for reproducing and/or recording of information.

0093A value of chromatic aberration owned by the light-converging optical element itself for the second light flux is positive.

0094In the present embodiment, therefore, the blaze-formed diffractive structure DOE of the second correcting element L2 is designed so that a value of chromatic aberration owned by the second correcting element itself for the second light flux may be negative, although an illustration thereof is omitted.

0095As stated above, by making the positive chromatic aberration of the light-converging optical element itself for the second light flux to be cancelled by negative chromatic aberration of the second correcting element itself, it is possible to control chromatic aberration of the second light-converging spot in the case of using an optical pickup device to be within a range that is necessary for reproducing and/or recording of information.

0096As stated above, the first correcting element L1, the second correcting element L2 and optical pickup device PU3 shown in the present embodiment make it possible to make values of chromatic aberration owned by the light-converging optical element itself for the first and second light fluxes to be of the same signs (positive), and thereby to weaken diffractive effects of the blaze-formed diffractive structure DOE formed on light-converging optical element OBJ. Therefore, an improvement of processability and reduction of a loss of an amount of light can be attained by expanding a pitch of diffraction.

0097Further, by contriving an arrangement wherein light source unit LU23 in which the second light source LD2 and the third light source LD3 are united solidly is used, and the second light flux and the third light flux enter the second correcting element, it is possible to obtain sufficient amount of light and aberration controlling functions in DVD and CD, by using a diffracting structure provided on the second correcting element L2.

(Fourth Embodiment)

0098Next, there will be explained Fourth Embodiment of the invention, wherein an arrangement of each element constituting the present embodiment is the same as that in the aforesaid First Embodiment, for which an illustration is omitted, and the same structure is given the same symbol and an explanation thereof will be omitted.

0099In optical pickup device PU4 of the present embodiment, a diffractive structure is provided on each of first correcting element L1, second correcting element L2 and objective lens OBJ.

0100<figref idref="f0003">Fig. 3 (d)</figref> is a diagram showing the values of chromatic aberration owned by the light-converging optical element itself for the first light flux and the second light flux, in which the value of chromatic aberration owned by the light-converging optical element itself for the first light flux is shown with a circle, while, the value of chromatic aberration owned by the light-converging optical element itself for the second light flux is shown with a square.

0101As is clear from <figref idref="f0003">Fig. 3 (d)</figref>, a value of chromatic aberration owned by the light-converging optical element itself for the first light flux is negative.

0102In the present embodiment, therefore, the blaze-formed diffractive structure DOE of the first correcting element L1 is designed so that a value of chromatic aberration owned by the first correcting element itself for the first light flux may be positive, although an illustration thereof is omitted.

0103As stated above, by making negative chromatic aberration of the light-converging optical element itself for the first light flux to be cancelled by positive chromatic aberration of the first correcting element itself, it is possible to control chromatic aberration of the first light-converging spot in the case of using an optical pickup device to be within a range that is necessary for reproducing and/or recording of information.

0104A value of chromatic aberration owned by the light-converging optical element itself for the second light flux is negative.

0105In the present embodiment, therefore, the blaze-formed diffractive structure DOE of the second correcting element L2 is designed so that a value of chromatic aberration owned by the second correcting element itself for the second light flux may be positive, although an illustration thereof is omitted.

0106As stated above, by making the negative chromatic aberration of the light-converging optical element itself for the second light flux to be cancelled by positive chromatic aberration of the second correcting element itself, it is possible to control chromatic aberration of the second light-converging spot in the case of using an optical pickup device to be within a range that is necessary for reproducing and/or recording of information.

0107Further, by contriving an arrangement wherein light source unit LU23 in which the second light source LD2 and the third light source LD3 are united solidly is used, and the second light flux and the third light flux enter the second correcting element, it is possible to obtain sufficient amount of light and aberration controlling functions in DVD and CD, by using a diffracting structure provided on the second correcting element L2.

0108Further, in DVD, a demand for chromatic aberration correction is low, compared with HD-DVD, therefore, it is possible to control chromatic aberration of the second light-converging spot to be within a range necessary for reproducing and/or recording of information, even in the case of an arrangement where a diffractive structure is not provided on the second correcting element L2, and the second correcting element itself has chromatic aberration for the second light flux. In this case, a sufficient amount of light can be secured, because a loss of an amount of light in the occasion for the second light flux to pass through the diffractive ring-shaped zones is not caused.

(Fifth Embodiment)

0109Next, there will be explained Fifth Embodiment of the invention, wherein an arrangement of each element constituting the present embodiment is the same as that in the aforesaid First Embodiment, for which an illustration is omitted, and the same structure is given the same symbol and an explanation thereof will be omitted.

0110In optical pickup device PU5 of the present embodiment, a diffractive structure is provided on each of second correcting element L2 and objective lens OBJ.

0111<figref idref="f0003">Fig. 3 (e)</figref> is a diagram showing the values of chromatic aberration owned by the light-converging optical element itself for the first light flux and the second light flux, in which the value of chromatic aberration owned by the light-converging optical element itself for the first light flux is shown with a circle, while, the value of chromatic aberration owned by the light-converging optical element itself for the second light flux is shown with a square.

0112As is clear from <figref idref="f0003">Fig. 3 (e)</figref>, a value of chromatic aberration owned by the light-converging optical element itself for the first light flux is positive, and this positive chromatic aberration is canceled by a value (negative) of chromatic aberration owned by the first correcting element itself for the first light flux in the structure, though an illustration thereof is omitted.

0113As stated above, by making the positive chromatic aberration of the light-converging optical element itself for the first light flux to be cancelled by negative chromatic aberration of the first correcting element itself, it is possible to control chromatic aberration of the first light-converging spot in the case of using an optical pickup device to be within a range that is necessary for reproducing and/or recording of information.

0114A value of chromatic aberration owned by the light-converging optical element itself for the second light flux is negative.

0115In the present embodiment, therefore, the blaze-formed diffractive structure DOE of the second correcting element L2 is designed so that a value of chromatic aberration owned by the second correcting element itself for the second light flux may be positive, although an illustration thereof is omitted.

0116As stated above, by making negative chromatic aberration of the light-converging optical element itself for the second light flux to be cancelled by positive chromatic aberration of the second correcting element itself, it is possible to control chromatic aberration of the second light-converging spot in the case of using an optical pickup device to be within a range that is necessary for reproducing and/or recording of information.

0117As stated above, in the present embodiment, a loss in an amount of light in the case for the first light flux to pass through the first correcting element is not caused, and processability can be improved.

(Sixth Embodiment)

0118<figref idref="f0005">Fig. 5</figref> is a diagram showing schematically the structure of optical pickup device PU6 capable of conducting recording/reproducing of information properly for any one of HD-DVD (first optical information recording medium) and DVD (second optical information recording medium). The structure which is the same as that in the aforesaid First Embodiment is given the same symbol and an explanation thereof will be omitted.

0119Optical pickup device PU6 is composed of violet semiconductor laser LD1 (first light source) that emits a laser light flux (first light flux) with wavelength 407 nm that is emitted when conducting recording/reproducing of information for HD-DVD, photodetector PD1 for the first light flux, red semiconductor laser LD2 (second light source) that emits a laser light flux (second light flux) with wavelength 655 nm that is emitted when conducting recording/reproducing of information for DVD, photodetector PD2 for the second light flux, first correcting element L1 through which the first and second light fluxes pass, second correcting element L2 through which only the second light flux passes, objective lens (light-converging optical element) OBJ having a function to converge each laser light flux on each of information recording surfaces RL1 and RL2, first beam splitter BS1, second beam splitter BS2, third beam splitter BS3, diaphragm STO, and sensor lenses SEN1 and SEN2.

0120Incidentally, a diffractive structure is provided on each of the first correcting element L1, the second correcting element L2 and objective lens OBJ, for which the detailed explanation will be given later.

0121When conducting recording/reproducing of information for HD-DVD in optical pickup device PU6, violet semiconductor laser LD1 is first driven to emit light as shown in <figref idref="f0005">Fig. 5</figref> where a light path is indicated. A divergent light flux emitted from the violet semiconductor laser LD1 passes through the first beam splitter BS1, then, is reflected on the second beam splitter BS2 and is transmitted through the first correcting element L1 to be converted into a collimated light flux, and arrives at light-converging optical element OBJ.

0122Then, n1^th diffracted light (n1 is a natural number) of the first light flux generated by diffractive effects of the diffractive structure of the light-converging optical element OBJ is converged on information recording surface RL1 through protective layer PL1 of HD-DVD to form a spot (first light-converging spot). This first light-converging spot is controlled to be within a range necessary for reproducing and/or recording of information in terms of chromatic aberration, and an absolute value of chromatic aberration for the first light-converging spot is controlled specifically to be 0.15 µm/nm or less.

0123Then, the light-converging optical element OBJ conducts focusing and tracking with biaxial actuator AC (not shown) that is arranged on the periphery of the light-converging optical element OBJ. A reflected light flux modulated by information pits on information recording surface RL1 passes again through the light-converging optical element OBJ and the first correcting element L1, and is reflected on the second beam splitter BS2, then is branched by the first beam splitter BS1, and is given astigmatism by sensor lens SEN 1 to be converged on a light-receiving surface of photodetector PD 1. Thus, information recorded on HD-DVD by the use of output signals of the photodetector PD 1 can be read.

0124When conducting recording/reproducing of information for DVD, the red semiconductor laser LD2 is first driven to emit light as shown in <figref idref="f0005">Fig. 5</figref> where a light path is indicated. A divergent light flux emitted from the red semiconductor laser LD2 passes through the second correcting element L2, the third beam splitter BS3 and the second beam splitter BS2, and then, is converted into a collimated light flux after being transmitted through the first correcting element L1, to arrive at light-converging optical element OBJ.

0125Then, n2^th diffracted light (n2 is a natural number satisfying n1 ≠ n2) of the second light flux generated by diffractive effects of the diffractive structure of light-converging optical element OBJ is converged on information recording surface RL2 through protective layer PL2 of DVD to form a spot (second light-converging spot). This second light-converging spot is controlled, in terms of chromatic aberration, to be within a range necessary for reproducing and/or recording of information, and an absolute value of chromatic aberration of the second light-converging spot is specifically controlled to be 0.25 µm/nm or less.

0126Then, the light-converging optical element OBJ conducts focusing and tracking with biaxial actuator AC that is arranged on the periphery of the light-converging optical element OBJ. A reflected light flux modulated by information pits on information recording surface RL2 passes again through the light-converging optical element OBJ, the first correcting element L1, the second beam splitter BS2 to be branched by the third beam splitter BS3, and is given astigmatism by sensor lens SEN 2, and is converged on the light-receiving surface of photodetector PD 2. Thus, information recorded on DVD can be read by the use of output signals of photodetector 2.

0127The light-converging optical element OBJ is a plastic single lens with aspheric surfaces on its both sides having a function to make the first and second light fluxes to be converged respectively on information recording surfaces RL1 and RL2. Incidentally, the light-converging optical element may also be constructed by combining a plurality of optical elements.

0128On a plane of incidence of the light-converging optical element OBJ, there is formed blaze-formed diffractive structure DOE shown in <figref idref="f0002">Fig. 2</figref>. The blaze-formed diffractive structure DOE is provided for the purpose of correcting chromatic aberration that is owned by light-converging optical element OBJ itself for the light flux emitted from the second light source, and it is designed specifically so that an absolute value of the chromatic aberration may be 0.25 µm/nm or less.

0129The first correcting element L1 has a collimating function to make the first light flux emitted from the first light source LD1 as a divergent light and the second light flux emitted from the second light source LD2 as a divergent light to emerge as collimated light, and on a plane of emergence of the first correcting element L1, there is formed blaze-formed diffractive structure DOE that is the same as one shown in <figref idref="f0002">Fig. 2</figref>.

0130On a plane of emergence of the second correcting element L2, there is formed blaze-formed diffractive structure DOE that is the same as one shown in <figref idref="f0002">Fig. 2</figref>.

0131<figref idref="f0003">Fig. 3 (b)</figref> is a diagram showing the values of chromatic aberration owned by the light-converging optical element itself for the first light flux and the second light flux, in which the value of chromatic aberration owned by the light-converging optical element itself for the first light flux is shown with a circle, while, the value of chromatic aberration owned by the light-converging optical element itself for the second light flux is shown with a square.

0132It is understood that an absolute value of chromatic aberration owned by the light-converging optical element itself for the second light flux is made to be 0.25 µm/nm or less, namely, to be zero substantially, by the blaze-formed diffractive structure DOE formed on the light-converging optical element OBJ, as stated above.

0133If the blaze-formed diffractive structure DOE of the light-converging optical element OBJ is designed so that the chromatic aberration of the light-converging optical element itself for the second light flux may be substantially zero, the chromatic aberration of the light-converging optical element for the first light flux remains and a value of the chromatic aberration becomes positive specifically, as shown in <figref idref="f0003">Fig. 3 (b)</figref>.

0134In the present embodiment, therefore, the blaze-formed diffractive structure DOE of the first correcting element L1 is designed so that a value of chromatic aberration owned by the first correcting element itself for the first light flux may be negative, although an illustration thereof is omitted.

0135As stated above, by making positive chromatic aberration of the light-converging optical element itself for the first light flux to be cancelled by negative chromatic aberration of the first correcting element itself, it is possible to control chromatic aberration of the first light-converging spot in the case of using an optical pickup device to be within a range that is necessary for reproducing and/or recording of information.

0136If the blaze-formed diffractive structure DOE of the first correcting element L1 is designed so that a value of the chromatic aberration owned by the first correcting element itself for the first light flux may be negative, the chromatic aberration of the first correcting element itself remains even for the second light flux, and a value of the chromatic aberration becomes negative specifically.

0137In the present embodiment, therefore, the blaze-formed diffractive structure DOE of the second correcting element L2 is designed so that a value of chromatic aberration owned by the second correcting element itself for the second light flux may be positive, although an illustration thereof is omitted.

0138As stated above, by making negative chromatic aberration of the first correcting element itself for the second light flux to be cancelled by positive chromatic aberration of the second correcting element itself, it is possible to control chromatic aberration of the second light-converging spot in the case of using an optical pickup device to be within a range that is necessary for reproducing and/or recording of information.

0139It is preferable that a combination of the n1 and n2 is any one of (n1, n2) = (0, 1), (2, 1), (3, 2), (5, 3) and (8, 5).

(Seventh Embodiment)

0140Next, there will be explained Seventh Embodiment of the invention, wherein an arrangement of each element constituting the present embodiment is the same as that in the aforesaid Sixth Embodiment, for which an illustration is omitted, and the same structure is given the same symbol and an explanation thereof will be omitted.

0141In optical pickup device PU7 of the present embodiment, a diffractive structure is provided on each of the first correcting element L1, the second correcting element L2 and objective lens OBJ.

0142On the plane of incidence of light-converging optical element OBJ, there is formed blaze-formed diffractive structure DOE as shown in <figref idref="f0002">Fig. 2</figref>. The blaze-formed diffractive structure DOE is provided for the purpose of correcting chromatic aberration that is owned by light-converging optical element OBJ itself for the light flux emitted from the first light source, and it is designed specifically so that an absolute value of chromatic aberration may be 0.15 µm/nm or less.

0143<figref idref="f0003">Fig. 3 (a)</figref> is a diagram showing the values of chromatic aberration owned by the light-converging optical element itself for the first light flux and the second light flux, in which the value of chromatic aberration owned by the light-converging optical element itself for the first light flux is shown with a circle, while, the value of chromatic aberration owned by the light-converging optical element itself for the second light flux is shown with a square.

0144As is clear from <figref idref="f0003">Fig. 3 (a)</figref>, an absolute value of chromatic aberration owned by the light-converging optical element itself for the first light flux is made by the blaze-formed diffractive structure DOE formed on the light-converging optical element to be 0.15 µm/nm or less, namely, to be zero substantially, as stated above.

0145Further, an absolute value of the chromatic aberration owned by the first correcting element itself for the first light flux is also made by the blaze-formed diffractive structure DOE formed on the first correcting element to be 2.1 µm/nm or less, namely, to be zero substantially, as stated above, though an illustration thereof will be omitted here.

0146As stated above, by making chromatic aberration of the light-converging optical system itself for the first light flux and chromatic aberration of the first correcting element itself to be zero substantially, it is possible to control chromatic aberration of the first light-converging spot in the case of using an optical pickup device to be within a range that is necessary for reproducing and/or recording of information.

0147If the blaze-formed diffractive structure DOE of the light-converging optical element is designed so that the chromatic aberration of the light-converging optical element itself for the first light flux may be substantially zero, the chromatic aberration of the light-converging optical element for the second light flux remains and a value of the chromatic aberration becomes negative specifically, as shown in <figref idref="f0003">Fig. 3 (a)</figref>.

0148If the blaze-formed diffractive structure DOE of the first correcting element L1 is designed so that a value of the chromatic aberration owned by the first correcting element itself for the first light flux may be zero substantially, the chromatic aberration of the first correcting element itself remains for the second light flux, and a value of the chromatic aberration becomes negative specifically.

0149In the present embodiment, therefore, the blaze-formed diffractive structure DOE of the second correcting element L2 is designed so that a value of chromatic aberration owned by the second correcting element itself for the second light flux may be positive, although an illustration thereof is omitted.

0150As stated above, by making negative chromatic aberration of the light-converging optical element itself for the second light flux and negative chromatic aberration of the first correcting element itself to be cancelled by positive chromatic aberration of the second correcting element itself, it is possible to control chromatic aberration of the second light-converging spot in the case of using an optical pickup device to be within a range that is necessary for reproducing and/or recording of information.

(Example 1)

0151Next, the first example of each of the optical pickup device, the first correcting element and the second correcting element all shown in the aforementioned embodiment will be explained.

0152The present example is one relating to an optical pickup device wherein it is possible to control chromatic aberration of the first light-converging spot in the case of using an optical pickup device to be within a range that is necessary for reproducing and/or recording of information, by making the negative chromatic aberration of the light-converging optical element itself for the first light flux to be cancelled with positive chromatic aberration of the first correcting element itself, like the Fourth Embodiment stated above, and it is possible to control chromatic aberration of the second light-converging spot in the case of using an optical pickup device to be within a range that is necessary for reproducing and/or recording of information, by making negative chromatic aberration of the light-converging optical element itself for the second light flux to be cancelled by positive chromatic aberration of the second correcting element itself.

0153Lens data of respective optical elements are shown in Table 1 and Table 2. <tables id="tabl0001" num="0001"><img file="EP1530207B1_D0001.tif" /></tables><tables id="tabl0002" num="0002"><table frame="all"><title>(Table 2)</title><tgroup cols="2"><colspec colnum="1" colname="col1" colwidth="89mm" /><colspec colnum="2" colname="col2" colwidth="63mm" /><tbody><row><entry namest="col1" nameend="col2" rowsep="0" align="left">Aspheric surface data</entry></row><row><entry namest="col1" nameend="col2" align="left">First correcting element</entry></row><row><entry namest="col1" nameend="col2" align="left">Third surface</entry></row><row><entry>Aspheric surface coefficient</entry><entry>κ -6.6436 x E+1</entry></row><row><entry namest="col1" nameend="col2" align="left">Fourth surface (HD-DVD: First-order Blazed wavelength 1 mm)</entry></row><row><entry>Aspheric surface coefficient</entry><entry>κ -8.3465 x E-1</entry></row><row><entry morerows="1" valign="middle">Optical path difference function</entry><entry rowsep="0">C2 -6.2961 x E-0</entry></row><row><entry>C4 -1.5298 x E-2</entry></row><row><entry namest="col1" nameend="col2" align="left">Second correcting element</entry></row><row rowsep="0"><entry namest="col1" nameend="col2" align="left">Third surface</entry></row><row><entry namest="col1" nameend="col2" align="center">(DVD: Second-order, CD: First-order Blazed wavelength 1 mm)</entry></row><row><entry>Aspheric surface coefficient</entry><entry>κ -1.0000 x E+3</entry></row><row><entry morerows="1" valign="middle">Optical path difference function</entry><entry rowsep="0">C2 +2.4248 x E+0</entry></row><row><entry>C4 +6.2330 x E-4</entry></row><row rowsep="0"><entry namest="col1" nameend="col2" align="center">Fourth surface</entry></row><row><entry namest="col1" nameend="col2" align="center">(DVD: First-order, CD: First-order Blazed wavelength 1 mm)</entry></row><row><entry>Aspheric surface coefficient</entry><entry>κ -4.7604 x E-1</entry></row><row><entry morerows="1" valign="middle">Optical path difference function</entry><entry rowsep="0">C2 +2.0944 x E+1</entry></row><row><entry>C4 +1.2308 x E-1</entry></row><row><entry namest="col1" nameend="col2" align="left">Objective lens</entry></row><row rowsep="0"><entry>Sixth surface</entry><entry /></row><row><entry namest="col1" nameend="col2" align="center">(AOD: Third-order, DVD: Second-order, CD: Second-order (HD-DVD: First-order Blazed wavelength 1 mm)</entry></row><row rowsep="0"><entry morerows="6" rowsep="1" align="center" valign="middle">Aspheric surface coefficient</entry><entry>κ -4.4715 x E-1.</entry></row><row rowsep="0"><entry>A2 -7.2396 x E-4</entry></row><row rowsep="0"><entry>A4 -1.3187 x E-3</entry></row><row rowsep="0"><entry>A6 +5.4370 x E-4</entry></row><row rowsep="0"><entry>A8 -1.0983 x E-4</entry></row><row rowsep="0"><entry>A10 +8.5286 x E-6</entry></row><row><entry>A12 -1.3509 x E-6</entry></row><row rowsep="0"><entry morerows="4" rowsep="1" align="center" valign="middle">Optical path difference function</entry><entry>C2 -8.1308 x E-0</entry></row><row rowsep="0"><entry>C4 -4.6175 x E-1</entry></row><row rowsep="0"><entry>C6 -2.8616 x E-1</entry></row><row rowsep="0"><entry>C8 +6.6346 x E-2</entry></row><row><entry>C10 -7.9277 x E-3</entry></row><row><entry namest="col1" nameend="col2" align="left">Seventh surface</entry></row><row rowsep="0"><entry morerows="6" rowsep="1" align="center" valign="middle">Aspheric surface coefficient</entry><entry>κ -4.1355 x E+2</entry></row><row rowsep="0"><entry>A2 -9.4311 x E-3</entry></row><row rowsep="0"><entry>A4 +1.1572 x E-2</entry></row><row rowsep="0"><entry>A6 -5.3553 x E-3</entry></row><row rowsep="0"><entry>A8 +1.2651 x E-3</entry></row><row rowsep="0"><entry>A10 -1.5851 x E-4</entry></row><row><entry>A12 +8.2943 x E-6</entry></row></tbody></tgroup></table></tables>

0154As shown in Table 1, in the objective lens of the present example, focal length f1 and image-side numerical aperture NA1 both for wavelength λ1 = 407 nm are established respectively to be 3.1 mm and 0.65, focal length f2 and image-side numerical aperture NA2 both for wavelength λ2 = 655 nm are established respectively to be 3.19 mm and 0.65, and focal length f3 and image-side numerical aperture NA3 both for wavelength λ3 = 785 nm are established respectively to be 3.16 mm and 0.51.

0155Further, in the present example, a blaze-formed diffractive structure is formed on a plane of emergence (fourth surface) of the first correcting element, a plane of incidence (third surface) and a plane of emergence (fourth surface) both of the second correcting element, and on a plane of incidence (sixth surface) of a light-converging optical element (objective lens).

0156In the constitution, magnifications m1 and m2 of the objective lens for the first light flux and the second light flux are zero substantially, the first light flux and the second light flux enter the objective lens as parallel rays, magnification m3 for the third light flux is negative, and the third light flux enters the objective lens as divergent rays.

0157On each of a plane of incidence (third surface) and a plane of emergence (fourth surface) of the first correcting element, a plane of incidence (third surface) and a plane of emergence (fourth surface) of the second correcting element and on a plane of incidence (sixth surface) and a plane of emergence (seventh surface) of the light-converging optical element (objective lens), there is formed an aspheric surface that is stipulated by the expression wherein the coefficients shown in Tables 1 and 2 are substituted in the following expression (Numeral 1), and is axially symmetric around optical axis L. <maths id="math0001" num="(Numeral 1)"><math display="block"><mi>Expression of aspheric form</mi><mspace width="1em" /><mi>X</mi><mfenced><mi>h</mi></mfenced><mo>=</mo><mfrac><mfenced><msup><mi>h</mi><mn>2</mn></msup><mo>/</mo><mi>R</mi></mfenced><mrow><mn>1</mn><mo>+</mo><msqrt><mn>1</mn><mo>-</mo><mfenced><mn>1</mn><mo>+</mo><mi>κ</mi></mfenced><mo>⁢</mo><msup><mfenced><mi>h</mi><mo>/</mo><mi>R</mi></mfenced><mn>2</mn></msup></msqrt></mrow></mfrac><mo>+</mo><mstyle displaystyle="true"><munderover><mo>∑</mo><mrow><mi>i</mi><mo>=</mo><mn>0</mn></mrow><mn>9</mn></munderover></mstyle><mo>+</mo><msub><mi>A</mi><mrow><mn>2</mn><mo>⁢</mo><mi>i</mi></mrow></msub><mo>⁢</mo><msup><mi>h</mi><mrow><mn>2</mn><mo>⁢</mo><mi>i</mi></mrow></msup></math><img file="EP1530207B1_D0002.tif" /></maths>

0158In the expression above, X (h) represents an axis in the optical axis direction (advancing direction of light is positive), κ represents a conic constant and A_2i represents a coefficient of aspheric surface.

0159Further, a pitch of the diffractive ring-shaped zones is stipulated by the expression wherein a coefficient shown in Table 2 is substituted in the optical path difference function of Numeral 2. <maths id="math0002" num="(Numeral 2)"><math display="block"><mi>Optical path difference function</mi><mspace width="2em" /><mi>φ</mi><mfenced><mi>h</mi></mfenced><mo>=</mo><mfenced><mstyle displaystyle="true"><munderover><mo>∑</mo><mrow><mi>i</mi><mo>=</mo><mn>0</mn></mrow><mn>5</mn></munderover></mstyle><msub><mi>B</mi><mrow><mn>2</mn><mo>⁢</mo><mi>i</mi></mrow></msub><mo>⁢</mo><msup><mi>h</mi><mrow><mn>2</mn><mo>⁢</mo><mi>i</mi></mrow></msup></mfenced><mo>×</mo><mi>n</mi><mo>×</mo><mmultiscripts><msub><mo>/</mo><mi mathvariant="italic">λB</mi></msub><mprescripts /><none /><mi mathvariant="italic">λ</mi></mmultiscripts></math><img file="EP1530207B1_D0003.tif" /></maths>

0160In the expression above, B_2i represents a coefficient of the optical path difference function, λ represents a working wavelength and λB represents the blazed wavelength (λB = 1 mm) for diffraction.

(Example 2)

0161Next, the second example of each of the optical pickup device, the first correcting element and the second correcting element all shown in the aforementioned embodiment will be explained.

0162The present example is one relating to an optical pickup device wherein it is possible to control chromatic aberration of the first light-converging spot in the case of using an optical pickup device to be within a range that is necessary for reproducing and/or recording of information, by making the chromatic aberration of the light-converging optical element for the first light source itself and the chromatic aberration of the first correcting element itself to be zero substantially, like the First Embodiment, and it is possible to control chromatic aberration of the second light-converging spot in the case of using an optical pickup device to be within a range that is necessary for reproducing and/or recording of information, by making negative chromatic aberration of the light-converging optical element itself for the second light flux to be cancelled by positive chromatic aberration of the second correcting element itself.

0163Lens data of respective optical elements are shown in Table 3 and Table 4. <tables id="tabl0003" num="0003"><img file="EP1530207B1_D0004.tif" /></tables><tables id="tabl0004" num="0004"><table frame="all"><title>(Table 4)</title><tgroup cols="2"><colspec colnum="1" colname="col1" colwidth="74mm" /><colspec colnum="2" colname="col2" colwidth="48mm" /><tbody><row><entry namest="col1" nameend="col2" rowsep="0" align="left">Aspheric surface data</entry></row><row><entry namest="col1" nameend="col2" align="left">First correcting element</entry></row><row><entry namest="col1" nameend="col2" align="left">Third surface</entry></row><row><entry align="center">Aspheric surface coefficient</entry><entry>κ -2.9816 x E+0</entry></row><row><entry namest="col1" nameend="col2" align="center">Fourth surface (HD-DVD: First-order Blazed wavelength 1 mm)</entry></row><row rowsep="0"><entry morerows="2" rowsep="1" align="center" valign="middle">Aspheric surface coefficient</entry><entry>κ -6.6298 x E-1</entry></row><row rowsep="0"><entry>A2 +6.8060 x E-4</entry></row><row><entry>A4 +4.2157 x E-7</entry></row><row><entry morerows="1" valign="middle">Optical path difference function</entry><entry rowsep="0">C2 +1.6953 x E+1</entry></row><row><entry>C4 +9.7909 x E-1</entry></row><row><entry namest="col1" nameend="col2" align="left">Second correcting element</entry></row><row><entry namest="col1" nameend="col2" align="left">Third surface</entry></row><row><entry align="center">Aspheric surface coefficient</entry><entry>κ -6.8225 x E-0</entry></row><row rowsep="0"><entry namest="col1" nameend="col2" align="left">Fourth surface</entry></row><row><entry namest="col1" nameend="col2" align="center">(DVD: First-order, CD: First-order Blazed wavelength 1 mm)</entry></row><row><entry align="center">Aspheric surface coefficient</entry><entry>κ -8.8682 x E-1</entry></row><row><entry morerows="1" valign="middle">Optical path difference function</entry><entry rowsep="0">C2 +3.4941 x E+1</entry></row><row><entry>C4 +2.0110 x E-2</entry></row><row><entry namest="col1" nameend="col2" align="left">Objective lens</entry></row><row rowsep="0"><entry namest="col1" nameend="col2" align="left">Sixth surface</entry></row><row><entry namest="col1" nameend="col2" align="center">(AOD: Third-order, DVD: Second-order, CD: Second-order Blazed wavelength 1 mm)</entry></row><row rowsep="0"><entry morerows="6" rowsep="1" align="center" valign="middle">Aspheric surface coefficient</entry><entry>κ -4.3741 x E-1</entry></row><row rowsep="0"><entry>A2 +1.1713 x E-4</entry></row><row rowsep="0"><entry>A4 -1.2104 x E-3</entry></row><row rowsep="0"><entry>A6 +5.3927 x E-4</entry></row><row rowsep="0"><entry>A8 -1.1589 x E-4</entry></row><row rowsep="0"><entry>A10 +1.1395 x E-5</entry></row><row><entry>A12 -1.3946 x E-6</entry></row><row rowsep="0"><entry morerows="4" rowsep="1" align="center" valign="middle">Optical path difference function</entry><entry>C2 -1.7589 x E+1</entry></row><row rowsep="0"><entry>C4 -6.7834 x E-1</entry></row><row rowsep="0"><entry>C6 -2.1641 x E-1</entry></row><row rowsep="0"><entry>C8 +3.2057 x E-2</entry></row><row><entry>C10 -3.4960 x E-3</entry></row><row><entry namest="col1" nameend="col2" align="left">Seventh surface</entry></row><row rowsep="0"><entry morerows="6" rowsep="1" align="center" valign="middle">Aspheric surface coefficient</entry><entry>κ -1.1243 x E+3</entry></row><row rowsep="0"><entry>A2 -7.9648 x E-3</entry></row><row rowsep="0"><entry>A4 +1.1269 x E-2</entry></row><row rowsep="0"><entry>A6 -5.3948 x E-3</entry></row><row rowsep="0"><entry>A8 +1.2875 x E-3</entry></row><row rowsep="0"><entry>A10 -1.6243 x E-4</entry></row><row><entry>A12 +8.5641 x E-6</entry></row></tbody></tgroup></table></tables>

0164As shown in Table 3, in the objective lens of the present example, focal length f1 and image-side numerical aperture NA1 both for wavelength λ1 = 407 nm are established respectively to be 3.1 mm and 0.65, focal length f2 and image-side numerical aperture NA2 both for wavelength λ2 = 655 nm are established respectively to be 3.19 mm and 0.65, and focal length f3 and image-side numerical aperture NA3 both for wavelength λ3 = 785 nm are established respectively to be 3.16 mm and 0.51.

0165Further, in the present example, a blaze-formed diffractive structure is formed on a plane of emergence (fourth surface) of the first correcting element, a plane of emergence (fourth surface) of the second correcting element and a plane of incidence (sixth surface) of the light-converging optical element.

0166In the constitution, magnifications m1 and m2 of the objective lens for the first light flux and the second light flux are zero substantially, the first light flux and the second light flux enter the objective lens as parallel rays, magnification m3 for the third light flux is negative, and the third light flux enters the objective lens as divergent rays.

0167On each of a plane of incidence (third surface) and a plane of emergence (fourth surface) of the first correcting element, a plane of incidence (third surface) and a plane of emergence (fourth surface) of the second correcting element and on a plane of incidence (sixth surface) and a plane of emergence (seventh surface) of the light-converging optical element (objective lens), there is formed an aspheric surface that is stipulated by the expression wherein the coefficients shown in Tables 3 and 4 are substituted in the aforesaid Numeral 1, and is axially symmetric around optical axis L.

0168A pitch of the diffractive ring-shaped zones is stipulated by the expression wherein a coefficient shown in Table 4 is.substituted in the optical path difference function of the Numeral 2.

(Example 3)

0169Next, the third example of each of the optical pickup device, the first correcting element and the second correcting element all shown in the aforementioned embodiment will be explained.

0170The present example is one relating to an optical pickup device wherein it is possible to control chromatic aberration of the second light-converging spot in the case of using an optical pickup device to be within a range that is necessary for reproducing and/or recording of information, by making the chromatic aberration of the light-converging optical element for the second light flux itself and the chromatic aberration of the second correcting element itself to be zero substantially, like the aforesaid Second Embodiment, and it is possible to control chromatic aberration of the first light-converging spot in the case of using an optical pickup device to be within a range that is necessary for reproducing and/or recording of information, by making negative chromatic aberration of the light-converging optical element itself for the first light flux to be cancelled by positive chromatic aberration of the first correcting element itself.

0171Lens data of respective optical elements are shown in Table 5 and Table 6. <tables id="tabl0005" num="0005"><img file="EP1530207B1_D0005.tif" /></tables><tables id="tabl0006" num="0006"><table frame="all"><title>(Table 6)</title><tgroup cols="2"><colspec colnum="1" colname="col1" colwidth="74mm" /><colspec colnum="2" colname="col2" colwidth="48mm" /><tbody><row><entry namest="col1" nameend="col2" rowsep="0" align="left">Aspheric surface data</entry></row><row><entry namest="col1" nameend="col2" align="left">First correcting element</entry></row><row><entry colsep="0">Third surface</entry><entry colsep="0" /></row><row><entry align="center">Aspheric surface coefficient</entry><entry>κ -1.2865 x E-1</entry></row><row><entry namest="col1" nameend="col2" align="center">Fourth surface (HD-DVD: First-order Blazed wavelength 1 mm)</entry></row><row rowsep="0"><entry morerows="2" rowsep="1" align="center" valign="middle">Aspheric surface coefficient</entry><entry>κ -5.6016 x E-0</entry></row><row rowsep="0"><entry>A2 -1.2220 x E-4</entry></row><row><entry>A4 +8.2772 x E-7</entry></row><row><entry morerows="1" valign="middle">Optical path difference function</entry><entry rowsep="0">C2 -3.4973 x E+1</entry></row><row><entry>C4 -3.1167 x E-1</entry></row><row><entry namest="col1" nameend="col2" align="left">Second correcting element</entry></row><row><entry namest="col1" nameend="col2" align="left">Third surface</entry></row><row><entry align="center">Aspheric surface coefficient</entry><entry>κ +5.0000 x E-0</entry></row><row rowsep="0"><entry namest="col1" nameend="col2" align="left">Fourth surface</entry></row><row><entry namest="col1" nameend="col2" align="center">(DVD: Second-order, CD: First-order Blazed wavelength 1 mm)</entry></row><row><entry align="center">Aspheric surface coefficient</entry><entry>κ -3.0979 x E-1</entry></row><row><entry morerows="1" align="center" valign="middle">Optical path difference function</entry><entry rowsep="0">C2 -6.8329 x E-0</entry></row><row><entry>C4 -9.6489 x E-4</entry></row><row><entry namest="col1" nameend="col2" align="left">Objective lens</entry></row><row rowsep="0"><entry namest="col1" nameend="col2" align="left">Sixth surface</entry></row><row><entry namest="col1" nameend="col2" align="center">(AOD: Third-order, DVD: Second-order, CD: Second-order Blazed wavelength 1 mm)</entry></row><row rowsep="0"><entry morerows="6" rowsep="1" align="center" valign="middle">Aspheric surface coefficient</entry><entry>κ -4.6387 x E-1</entry></row><row rowsep="0"><entry>A2 -1.8195 x E-4</entry></row><row rowsep="0"><entry>A4 -1.9297 x E-3</entry></row><row rowsep="0"><entry>A6 +7.6730 x E-4</entry></row><row rowsep="0"><entry>A8 -1.4669 x E-4</entry></row><row rowsep="0"><entry>A10 +4.2269 x E-6</entry></row><row><entry>A12 -3.3768 x E-7</entry></row><row rowsep="0"><entry morerows="4" rowsep="1" align="center" valign="middle">Optical path difference function</entry><entry>C2 0</entry></row><row rowsep="0"><entry>C4 -4.3190 x E-1</entry></row><row rowsep="0"><entry>C6 -2.3777 x E-1</entry></row><row rowsep="0"><entry>C8 +7.3114 x E-2</entry></row><row><entry>C10 -1.0422 x E-2</entry></row><row><entry colsep="0">Seventh surface</entry><entry colsep="0" /></row><row rowsep="0"><entry morerows="6" rowsep="1" align="center" valign="middle">Aspheric surface coefficient</entry><entry>κ -2.8743 x E+2</entry></row><row rowsep="0"><entry>A2 -9.7882 x E-3</entry></row><row rowsep="0"><entry>A4 +1.1311 x E-2</entry></row><row rowsep="0"><entry>A6 -5.3137 x E-3</entry></row><row rowsep="0"><entry>A8 +1.2888 x E-3</entry></row><row rowsep="0"><entry>A10 -1.6378 x E-4</entry></row><row><entry>A12 +8.6619 x E-6</entry></row></tbody></tgroup></table></tables>

0172As shown in Table 5, in the objective lens of the present example, focal length f1 and image-side numerical aperture NA1 both for wavelength λ1 = 407 nm are established respectively to be 3.1 mm and 0.65, focal length f2 and image-side numerical aperture NA2 both for wavelength λ2 = 655 nm are established respectively to be 3.21 mm and 0.65, and focal length f3 and image-side numerical aperture NA3 both for wavelength λ3 = 785 nm are established respectively to be 3.23 mm and 0.51.

0173Further, in the present example, a blaze-formed diffractive structure is formed on a plane of emergence (fourth surface) of the first correcting element, a plane of emergence (fourth surface) of the second correcting element and a plane of incidence (sixth surface) of the light-converging optical element.

0174In the constitution, magnifications m1 and m2 of the objective lens for the first light flux and the second light flux are zero substantially, the first light flux and the second light flux enter the objective lens as parallel rays, magnification m3 for the third light flux is negative, and the third light flux enters the objective lens as divergent rays.

0175On each of a plane of incidence (third surface) and a plane of emergence (fourth surface) of the first correcting element, a plane of incidence (third surface) and a plane of emergence (fourth surface) of the second correcting element and on a plane of incidence (sixth surface) and a plane of emergence (seventh surface) of the light-converging optical element (objective lens), there is formed an aspheric surface that is stipulated by the expression wherein the coefficients shown in Tables 5 and 6 are substituted in the aforesaid Numeral 1, and is axially symmetric around optical axis L.

0176A pitch of the diffractive ring-shaped zones is stipulated by the expression wherein a coefficient shown in Table 6 is substituted in the optical path difference function of the Numeral 2. "

(Example 4)

0177Next, the fourth example of each of the optical pickup device, the first correcting element and the second correcting element all shown in the aforementioned embodiment will be explained.

0178The present example is one relating to an optical pickup device wherein it is possible to control chromatic aberration of the second light-converging spot in the case of using an optical pickup device to be within a range that is necessary for reproducing and/or recording of information, by making the negative chromatic aberration of the first correcting element for the second light flux by the positive chromatic aberration of the second correcting element itself, and it is possible to control chromatic aberration of the first light-converging spot in the case of using an optical pickup device to be within a range that is necessary for reproducing and/or recording of information, by making positive chromatic aberration of the light-converging optical element itself for the first light flux to be cancelled by negative chromatic aberration of the first correcting element itself.

0179Lens data of respective optical elements are shown in Table 7 and Table 8. <tables id="tabl0007" num="0007"><img file="EP1530207B1_D0006.tif" /></tables><tables id="tabl0008" num="0008"><table frame="all"><title>(Table 8)</title><tgroup cols="2"><colspec colnum="1" colname="col1" colwidth="128mm" /><colspec colnum="2" colname="col2" colwidth="38mm" /><tbody><row><entry namest="col1" nameend="col2" align="left">Correcting element for DVD</entry></row><row><entry namest="col1" nameend="col2" align="left">Second surface</entry></row><row><entry morerows="1" align="center" valign="middle">Optical path difference function (DVD: First-order Blazed wavelength 661 nm)</entry><entry rowsep="0">C2 2.6331E-02</entry></row><row><entry>C4 1.2847E-04</entry></row><row><entry namest="col1" nameend="col2" align="left">Collimator to be used commonly for HD-DVD/DVD</entry></row><row><entry namest="col1" nameend="col2" align="left">Sixth surface (HD-DVD: Fifth-order, DVD: Third-order Blazed wavelength 407.9 nm)</entry></row><row rowsep="0"><entry morerows="2" rowsep="1" align="center" valign="middle">Aspheric surface coefficient</entry><entry>κ -1.0000E-01</entry></row><row rowsep="0"><entry>A1 -9.6629E-06</entry></row><row><entry>A2 -2.5101E-08</entry></row><row><entry namest="col1" nameend="col2" align="left">Optical path difference function C2 -2.4248 x E+0</entry></row><row><entry namest="col1" nameend="col2" align="left">Objective lens</entry></row><row><entry namest="col1" nameend="col2" align="left">Eighth surface (1.015mm≤h)</entry></row><row rowsep="0"><entry morerows="6" rowsep="1" align="center" valign="middle">Aspheric surface coefficient</entry><entry>κ -5.7409E-01</entry></row><row rowsep="0"><entry>A1 7.1066E-04</entry></row><row rowsep="0"><entry>A2 -2.4404E-03</entry></row><row rowsep="0"><entry>A3 1.1090E-03</entry></row><row rowsep="0"><entry>A4 -1.9304E-04</entry></row><row rowsep="0"><entry>A5 1.4092E-05</entry></row><row><entry>A6 -7.7600E-07</entry></row><row rowsep="0"><entry morerows="4" rowsep="1" align="center" valign="middle">Optical path difference function (DVD: First-order Blazed wavelength 661 nm)</entry><entry>C2 -2.5443E-03</entry></row><row rowsep="0"><entry>C4 -7.4686E-04</entry></row><row rowsep="0"><entry>C6 -4.8639E-04</entry></row><row rowsep="0"><entry>C8 1.2462E-04</entry></row><row><entry>C10 -7.6259E-06</entry></row><row><entry namest="col1" nameend="col2" align="left">Eighth surface (0mm≤h&lt;1.015mm)</entry></row><row rowsep="0"><entry morerows="6" rowsep="1" align="center" valign="middle">Aspheric surface coefficient</entry><entry>κ -5.4894E-01</entry></row><row rowsep="0"><entry>A1 1.0603E-03</entry></row><row rowsep="0"><entry>A2 -1.3250E-03</entry></row><row rowsep="0"><entry>A3 5.0847E-04</entry></row><row rowsep="0"><entry>A4 -3.9760E-05</entry></row><row rowsep="0"><entry>A5 -1.4261E-05</entry></row><row><entry>A6 1.1184E-06</entry></row><row rowsep="0"><entry morerows="3" rowsep="1" align="center" valign="middle">Optical path difference function C2 (HD DVD: Third-order,DVD: Second-order Blazed wavelength C6 -1.7645E-04 417 nm)</entry><entry>-5.4303E-04</entry></row><row rowsep="0"><entry>C4 -5.8842E-05</entry></row><row rowsep="0"><entry>C8 5.1044E-05</entry></row><row><entry>C10 -6.1711E-06</entry></row><row><entry namest="col1" nameend="col2" align="left">Ninth surface</entry></row><row rowsep="0"><entry morerows="6" rowsep="1" align="center" valign="middle">Aspheric surface coefficient</entry><entry>κ -2.2653E+02</entry></row><row rowsep="0"><entry>A1 -8.3958E-03</entry></row><row rowsep="0"><entry>A2 1.0917E-02</entry></row><row rowsep="0"><entry>A3 -5.3410E-03</entry></row><row rowsep="0"><entry>A4 1.3141E-03</entry></row><row rowsep="0"><entry>A5 -1.6618E-04</entry></row><row><entry>A6 8.5718E-06</entry></row></tbody></tgroup></table></tables><tables id="tabl0009" num="0009"><table frame="all"><tgroup cols="3"><colspec colnum="1" colname="col1" colwidth="45mm" /><colspec colnum="2" colname="col2" colwidth="45mm" /><colspec colnum="3" colname="col3" colwidth="44mm" /><thead><row><entry align="center" valign="top" /><entry align="center" valign="top">nd (Refractive index for d line)</entry><entry align="center" valign="top">vd (Abbe's number for d line)</entry></row></thead><tbody><row><entry align="center">Material of the first surface</entry><entry align="char" char="." charoff="4">1.5422</entry><entry align="char" char="." charoff="9">56.5</entry></row><row><entry align="center">Material of the fifth surface</entry><entry align="char" char="." charoff="4">1.5422</entry><entry align="char" char="." charoff="9">56.5</entry></row><row><entry align="center">Material of the eighth surface</entry><entry align="char" char="." charoff="4">1.5422</entry><entry align="char" char="." charoff="9">56.5</entry></row><row><entry align="center">Material of 8'^th surface</entry><entry align="char" char="." charoff="4">1.5422</entry><entry align="char" char="." charoff="9">56.5</entry></row></tbody></tgroup></table></tables>

0180As shown in Table 7, in the objective lens of the present example, focal length f1 and image-side numerical aperture NA1 both for wavelength λ1 = 407.9 nm are established respectively to be 3.1 mm and 0.65 and focal length f2 and image-side numerical aperture NA2 both for wavelength λ2 = 661 nm are established respectively to be 3.19 mm and 0.65.

0181Further, in the present example, a blaze-formed diffractive structure is formed on each of a plane of emergence (sixth surface) of the first correcting element, a plane of emergence (second surface) of the second correcting element and on a plane of incidence (eighth surface, 8'^th surface) of the light-converging optical element (objective lens).

0182In the constitution, magnifications m1 and m2 of the objective lens for the first light flux and the second light flux are zero substantially, and the first light flux and the second light flux enter the objective lens as parallel rays.

0183On each of a plane of emergence (sixth surface) of the first correcting element and planes of incidence (8^th and 8'^th surfaces) and a plane of emergence (ninth surface) of the light-converging optical element (objective lens), there is formed an aspheric surface that is stipulated by the expression wherein the coefficients shown in Tables 7 and 8 are substituted in the aforesaid Numeral 1, and is axially symmetric around optical axis L.

0184A pitch of the diffractive ring-shaped zones is stipulated by the expression wherein a coefficient shown in Table 8 is substituted in the optical path difference function of the Numeral 2.

(Example 5)

0185Next, the fifth example of each of the optical pickup device, the first correcting element and the second correcting element all shown in the aforementioned embodiment will be explained.

0186The present example is one relating to an optical pickup device wherein it is possible to control chromatic aberration of the first light-converging spot in the case of using an optical pickup device to be within a range that is necessary for reproducing and/or recording of information, by making the chromatic aberration of the light-converging optical element itself for the first light flux and chromatic aberration of the first correcting element itself to be zero substantially, and it is possible to control chromatic aberration of the second light-converging spot in the case of using an optical pickup device to be within a range that is necessary for reproducing and/or recording of information, by making negative chromatic aberration of the light-converging optical element itself for the second light flux and negative chromatic aberration of the first correcting element itself to be cancelled by positive chromatic aberration of the second correcting element itself.

0187Lens data of respective optical elements are shown in Table 9 and Table 10. <tables id="tabl0010" num="0010"><img file="EP1530207B1_D0007.tif" /></tables><tables id="tabl0011" num="0011"><table frame="all"><title>(Table 10)</title><tgroup cols="2"><colspec colnum="1" colname="col1" colwidth="135mm" /><colspec colnum="2" colname="col2" colwidth="31mm" /><tbody><row><entry namest="col1" nameend="col2" rowsep="0" align="left">Aspheric surface data</entry></row><row><entry namest="col1" nameend="col2" align="left">Correcting element for DVD</entry></row><row><entry namest="col1" nameend="col2" align="left">Second surface</entry></row><row><entry morerows="1" align="center" valign="middle">Optical path difference function (DVD: First-order Blazed wavelength 655 nm)</entry><entry rowsep="0">C2 2.2008E-02</entry></row><row><entry>C4 1.0027E-04</entry></row><row><entry namest="col1" nameend="col2" align="left">Collimator to be used commonly for HD-DVD/DVD</entry></row><row><entry namest="col1" nameend="col2" align="left">Sixth surface</entry></row><row rowsep="0"><entry morerows="2" rowsep="1" align="center" valign="middle">Aspheric surface coefficient</entry><entry>κ -1.0000E-01</entry></row><row rowsep="0"><entry>A1 2.4710E-05</entry></row><row><entry>A2 1.1294E-07</entry></row><row><entry align="center" valign="middle">Optical path difference function (HD-DVD: Second-order, DVD: First-order Blazed wavelength 407 nm)</entry><entry valign="middle">C2 -1.1527E-03</entry></row><row><entry namest="col1" nameend="col2" align="left">Objective lens</entry></row><row><entry namest="col1" nameend="col2" align="left">Eighth surface</entry></row><row rowsep="0"><entry morerows="6" rowsep="1" align="center" valign="middle">Aspheric surface coefficient</entry><entry>κ -4.4715E-01</entry></row><row rowsep="0"><entry>A1 -7.2396E-04</entry></row><row rowsep="0"><entry>A2 -1.3187E-03</entry></row><row rowsep="0"><entry>A3 5.4370E-04</entry></row><row rowsep="0"><entry>A4 -1.0983E-04</entry></row><row rowsep="0"><entry>A5 8.5286E-06</entry></row><row><entry>A6 -1.3509E-06</entry></row><row rowsep="0"><entry morerows="4" rowsep="1" align="center" valign="middle">Optical path difference function (HD DVD: Third-order, DVD:Second-order Blazed wavelength 422 nm)</entry><entry>C2 -3.4312E-03</entry></row><row rowsep="0"><entry>C4 -1.9486E-04</entry></row><row rowsep="0"><entry>C6 -1.2076E-04</entry></row><row><entry rowsep="0">C8 2.7998E-05</entry></row><row><entry>C10 -3.345-5E-06</entry></row><row><entry namest="col1" nameend="col2" align="left">Ninth surface</entry></row><row rowsep="0"><entry morerows="6" rowsep="1" align="center" valign="middle">Aspheric surface coefficient</entry><entry>κ -4.1355E+02</entry></row><row rowsep="0"><entry>A1 -9.4311E-03</entry></row><row rowsep="0"><entry>A2 1.1572E-02</entry></row><row rowsep="0"><entry>A3 -5.3553E-03</entry></row><row rowsep="0"><entry>A4 1.2651E-03</entry></row><row rowsep="0"><entry>A5 -1.5851E-04</entry></row><row><entry>A6 8.2943E-06</entry></row></tbody></tgroup></table></tables><tables id="tabl0012" num="0012"><table frame="all"><tgroup cols="3"><colspec colnum="1" colname="col1" colwidth="45mm" /><colspec colnum="2" colname="col2" colwidth="45mm" /><colspec colnum="3" colname="col3" colwidth="44mm" /><thead><row><entry align="center" valign="top" /><entry align="center" valign="top">nd (Refractive index for d line)</entry><entry align="center" valign="top">vd (Abbe's number for d line)</entry></row></thead><tbody><row><entry align="center">Material of the first surface</entry><entry align="char" char="." charoff="4">1.5435</entry><entry align="char" char="." charoff="9">56.7</entry></row><row><entry align="center">Material of the fifth surface</entry><entry align="char" char="." charoff="4">1.5422</entry><entry align="char" char="." charoff="9">56.5</entry></row><row><entry align="center">Material of the eighth surface</entry><entry align="char" char="." charoff="4">1.5435</entry><entry align="char" char="." charoff="9">56.7</entry></row></tbody></tgroup></table></tables>

0188As shown in Table 9, in the objective lens of the present example, focal length f1 and image-side numerical aperture NA1 both for wavelength λ1 = 407 nm are established respectively to be 3.1 mm and 0.65 and focal length f2 and image-side numerical aperture NA2 both for wavelength λ2 = 655 nm are established respectively to be 3.21 mm and 0.65.

0189Further, in the present example, a blaze-formed diffractive structure is formed on each of a plane of emergence (sixth surface) of the first correcting element, a plane of emergence (second surface) of the second correcting element and on a plane of incidence (eighth surface) of the light-converging optical element (objective lens).

0190In the constitution, magnifications m1 and m2 of the objective lens for the first light flux and the second light flux are zero substantially, and the first light flux and the second light flux enter the objective lens as parallel rays.

0191On each of a plane of emergence (sixth surface) of the first correcting element and a plane of incidence (eighth surface) and a plane of emergence (ninth surface) of the light-converging optical element (objective lens), there is formed an aspheric surface that is stipulated by the expression wherein the coefficients shown in Tables 9 and 10 are substituted in the aforesaid Numeral 1, and is axially symmetric around optical axis L.

0192A pitch of the diffractive ring-shaped zones is stipulated by the expression wherein a coefficient shown in Table 10 is substituted in the optical path difference function of the Numeral 2.

0193Table 11 shows chromatic aberration (abbreviated as HD-DVD) for the first light flux in the combination of the objective lens and the first correcting element and chromatic aberration (abbreviated as DVD) for the second light flux in the combination of the objective lens and the second correcting element, in Examples 1 - 3. <tables id="tabl0013" num="0013"><table frame="all"><title>(Table 11)</title><tgroup cols="3"><colspec colnum="1" colname="col1" colwidth="50mm" /><colspec colnum="2" colname="col2" colwidth="44mm" /><colspec colnum="3" colname="col3" colwidth="44mm" /><thead><row><entry namest="col1" nameend="col3" align="center" valign="top">Chromatic aberration (µm/nm) in the case of combination of objective lens and correcting element</entry></row><row><entry align="center" valign="top" /><entry align="center" valign="top">HD DVD</entry><entry align="center" valign="top">DVD</entry></row></thead><tbody><row><entry align="center">Example 1</entry><entry align="center">0.04</entry><entry align="center">-0.02</entry></row><row><entry align="center">Example 2</entry><entry align="center">0.04</entry><entry align="center">-0.01</entry></row><row><entry align="center">Example 3</entry><entry align="center">-0.01</entry><entry align="center">-0.19</entry></row></tbody></tgroup></table></tables>

0194It is understood from Table 11 that chromatic aberrations for HD-DVD and DVD in Examples 1 - 3 are controlled to be within a range wherein the chromatic aberration is not problematic in practical use.

0195Table 12 shows chromatic aberration (abbreviated as HD-DVD) for the first light flux in the combination of the objective lens and the first correcting element and chromatic aberration (abbreviated as DVD) for the second light flux in the combination of the objective lens, the first correcting element and the second correcting element, in Examples 4 and 5. <tables id="tabl0014" num="0014"><table frame="all"><title>(Table 12)</title><tgroup cols="3"><colspec colnum="1" colname="col1" colwidth="50mm" /><colspec colnum="2" colname="col2" colwidth="44mm" /><colspec colnum="3" colname="col3" colwidth="44mm" /><thead><row><entry namest="col1" nameend="col3" align="center" valign="top">Chromatic aberration (µm/nm) in the case of combination of objective lens and correcting element</entry></row><row><entry align="center" valign="top" /><entry align="center" valign="top">HD DVD</entry><entry align="center" valign="top">DVD</entry></row></thead><tbody><row><entry align="center">Example 4</entry><entry>0</entry><entry align="center">0.02</entry></row><row><entry align="center">Example 5</entry><entry>0.1</entry><entry align="center">-0.08</entry></row></tbody></tgroup></table></tables>

0196It is understood from Table 12 that chromatic aberrations for HD-DVD and DVD in Examples 4 and 5 are controlled to be within a range wherein the chromatic aberration is not problematic in practical use.

0197Incidentally, in the examples stated above, HD-DVD has been exemplified as a high density optical disc. However, the high density optical disc is not limited to HD-DVD, in the invention.