WO2011078022A1 - 光ピックアップ装置用の対物レンズ及び光ピックアップ装置 - Google Patents
光ピックアップ装置用の対物レンズ及び光ピックアップ装置 Download PDFInfo
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- WO2011078022A1 WO2011078022A1 PCT/JP2010/072530 JP2010072530W WO2011078022A1 WO 2011078022 A1 WO2011078022 A1 WO 2011078022A1 JP 2010072530 W JP2010072530 W JP 2010072530W WO 2011078022 A1 WO2011078022 A1 WO 2011078022A1
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- objective lens
- lens
- optical
- information recording
- transparent substrate
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B13/00—Optical objectives specially designed for the purposes specified below
- G02B13/16—Optical objectives specially designed for the purposes specified below for use in conjunction with image converters or intensifiers, or for use with projectors, e.g. objectives for projection TV
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
- G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
- G11B7/1372—Lenses
- G11B7/1374—Objective lenses
Definitions
- the present invention relates to an objective lens for an optical pickup device and an optical pickup device capable of recording and / or reproducing information with respect to an optical disc having three or more information recording surfaces in the thickness direction.
- a high-density optical disk system capable of recording and / or reproducing information (hereinafter, “recording and / or reproduction” is referred to as “recording / reproduction”) using a blue-violet semiconductor laser having a wavelength of about 400 nm.
- Patent Document 1 the magnification of the objective lens is changed by moving a coupling lens arranged between the light source and the objective lens in the optical axis direction, and the selected information recording surface is tertiary.
- An optical pickup device capable of condensing a light beam with reduced spherical aberration is disclosed.
- the operation of changing the information recording surface on which information is to be recorded / reproduced from one information recording surface to another information recording surface may be referred to as “focus jump” in this specification.
- the objective lens of Patent Document 2 has the following problems. (1) In the objective lens of Patent Document 2, since the sine condition in the design magnification is corrected in the entire area of the effective radius, the residual higher-order spherical aberration at the time of focus jump tends to increase. That is, the ratio between the third-order spherical aberration and the fifth-order spherical aberration when the magnification is changed is far from the ratio between the third-order spherical aberration and the fifth-order spherical aberration when the cover glass thickness is changed (about 5: 1).
- the objective lens of Patent Document 2 is suitable for condensing a light beam on the information recording surface of a BD having three or more layers, where the maximum difference in the transparent substrate thickness of the information recording surface is larger than that of the two layers of BD.
- the objective lens of Patent Document 2 requires a large amount of movement of the coupling lens at the time of focus jump, and is therefore used for a thin optical pickup device. Not suitable for.
- the present invention has been made in consideration of the above-mentioned problems, and the amount of movement of the coupling lens can be reduced without causing high-order spherical aberration such as fifth-order spherical aberration to remain even at the time of focus jump. It is another object of the present invention to provide an objective lens for an optical pickup device and an optical pickup device capable of recording / reproducing information with respect to an optical disc having a multi-layer information recording surface at a low cost.
- the “transparent substrate thickness” is the distance from the light beam incident surface of the optical disc to the information recording surface.
- each information recording surface is transparent.
- the substrate thickness will be different from each other.
- an objective lens for an optical pickup is combined with a cover glass having a predetermined thickness, and the correction state of the spherical aberration is determined so that the spherical aberration is minimized (the thickness of the cover glass is determined as the design cover glass). Also called thickness).
- the design cover glass thickness may be the same as or different from the transparent substrate thickness of any information recording surface of the optical disc. When the thickness of the cover glass changes, the characteristics of the objective lens also change.
- cover glass thickness is used to distinguish it from the “transparent substrate” of the optical disk. (Note that although the term “cover glass” is used, the cover glass thickness is not limited to glass, but a resin may be added.)
- the objective lens according to claim 1 which includes a light source that emits a light beam having a wavelength ⁇ 1 (390 nm ⁇ 1 ⁇ 415 nm) and an objective lens, and information recording surfaces having different distances (transparent substrate thicknesses) from the light beam incident surface.
- An objective lens for an optical pickup device for recording and / or reproducing information is a single lens,
- the image-side numerical aperture (NA) is 0.8 or more and 0.95 or less,
- the sine condition violation amount at the magnification M satisfying the expression (1) takes the first maximum value at the pupil radius H1, the second maximum value at the pupil radius H2, and the pupil radius.
- H3 is 0.9 or more
- the expression (2) is satisfied, and the derivative ⁇ (h) of the sine condition violation amount satisfies the expressions (3) to (5).
- H1 ⁇ H2 ⁇ H3 (2) ⁇ (h) ⁇ 0.0 (h ⁇ H1) (3) ⁇ (h)> 0.0 (H1 ⁇ h ⁇ H2) (4) ⁇ (h) ⁇ 0.0 (H2 ⁇ h ⁇ H3) (5)
- the pupil radii H1, H2, and H3 are relative values when the effective radius of the objective lens is 1.
- the characteristics required for an objective lens suitable for a BD having three or more layers are at least the following two.
- (Characteristic 2) The amount of movement of the coupling lens when performing a focus jump is small.
- the present inventors set the focus jump by setting the sine condition violation amount to the second maximum value at the position of the second pupil radius H2 at the magnification M satisfying the equation (1). It has been found that higher order spherical aberration can be effectively suppressed.
- At least the following two characteristics are required for an objective lens that has high performance stability and is easy to manufacture.
- (Characteristic 3) Even when the opposing optical surfaces are shifted in the direction perpendicular to the optical axis due to manufacturing errors (referred to as surface shift), the coma aberration does not become too large.
- the sine condition violation amount has the first maximum value at the position of the first pupil radius H1, whereby the second maximum at the second pupil radius H2. Since it is possible to suppress the value from becoming too large, it is possible to suppress the amount of coma aberration generated during the surface shift.
- the second maximum at the second pupil radius H2 is obtained by causing the sine condition violation amount to have the first maximum at the position of the first pupil radius H1. Since it is possible to suppress the value from becoming too large, it is possible to suppress the generation amount of spherical aberration when a lens thickness error occurs, and thus it is possible to provide an objective lens that is easier to manufacture.
- the objective lens according to claim 1 has (Characteristic 1) small residual high-order spherical aberration at the time of focus jump, and (Characteristic 2) small movement amount of the coupling lens at the time of focus jump.
- (Characteristic 3) it is possible to suppress the amount of coma aberration generated when the surface is shifted
- (Characteristic 4) it is also possible to suppress the amount of spherical aberration generated when the lens thickness error occurs. Since the objective lens of the present invention is used, an optical disc having three or more information recording surfaces that is small, low cost, and excellent in recording / reproducing characteristics can be provided. It becomes possible to provide an optical pickup device for use.
- the objective lens described in claim 2 is characterized in that, in the invention described in claim 1, the following expression is satisfied.
- the sine condition violation amount can be optimized and the above (characteristics 1 to 4) can be realized in a well-balanced manner.
- (Characteristic 3) and (Characteristic 4) can be improved by satisfying the expression (6)
- (Characteristic 1) and (Characteristic 2) are improved by satisfying the expression (7). It becomes possible to do.
- the objective lens according to claim 3 is the objective lens according to claim 1 or 2, wherein the first maximum value of the sine condition violation amount is the OSC min (mm) in the ambient temperature (25 ⁇ 3 ° C) environment.
- the focal length at the wavelength ⁇ 1 is f (mm)
- OSC min / f When OSC min / f is taken on the horizontal axis and coma aberration generated when the surface of the objective lens is shifted is taken on the vertical axis, the relationship between them can be approximated by a downwardly convex parabolic function. Therefore, by making OSC min / f exceed the lower limit and lower than the upper limit of the expression (10), it is possible to prevent the coma aberration generated at the time of the surface shift of the objective lens from becoming too large, and to improve (Characteristic 3). It becomes possible to improve.
- the objective lens according to claim 4 is the objective lens according to claim 1 or 2, wherein the second maximum value of the sine condition violation amount is the OSC max (mm) in an environment at room temperature (25 ⁇ 3 ° C).
- the focal length at the wavelength ⁇ 1 is f (mm)
- the equation (11) ⁇ 0.0001 ⁇ OSC max /f ⁇ 0.0062 (11) It is characterized by satisfying.
- the objective lens includes a light source that emits a light beam having a wavelength ⁇ 1 (390 nm ⁇ 1 ⁇ 415 nm) and an objective lens, and distances (transparent substrate thicknesses) from the light beam incident surface are different from each other.
- An objective lens for an optical pickup device for recording and / or reproducing information is a single lens
- the image-side numerical aperture (NA) is 0.8 or more and 0.95 or less
- the cover glass thickness that minimizes the spherical aberration at the magnification M satisfying the expression (1) is T (mm)
- the half angle of view is 1 degree with respect to the objective lens.
- the third-order coma aberration CM3 ( ⁇ rms) of the spot condensed through the cover glass thickness T in the case where the oblique light beam is incident satisfies the expression (12) and is condensed through the cover glass thickness T.
- the fifth-order coma aberration CM5 ( ⁇ rms) of the spot satisfies the equation (13), -0.003 ⁇ M ⁇ 0.003 (1) 0 ⁇
- the third coma aberration CM3 and the fifth coma aberration CM5 have different signs.
- the invention according to claim 5 is an invention in which the invention according to claim 1 is expressed from the viewpoint of coma aberration, not the sine condition violation amount.
- the design magnification is set to be negative (incident divergent light), and the sine condition at the design magnification is satisfied in the entire region within the effective radius.
- the aberration correction state is set, the residual higher-order spherical aberration becomes too large at the time of focus jump, and the ratio of the third-order spherical aberration to the fifth-order spherical aberration when the magnification is changed is the third-order when the cover glass thickness is changed.
- the ratio was significantly different from the ratio of spherical aberration to fifth-order spherical aberration (about 5: 1). Therefore, when the luminous flux having the magnification M satisfying the expression (1) is incident, the light is condensed through the cover glass thickness T when the oblique luminous flux having a half angle of view is incident on the objective lens. So that the third-order coma aberration CM3 ( ⁇ rms) of the spot satisfies the formula (12), and the fifth-order coma aberration CM5 ( ⁇ rms) of the spot condensed through the cover glass thickness T satisfies the formula (13).
- the objective lens according to claim 6, which has a light source that emits a light beam having a wavelength ⁇ 1 (390 nm ⁇ 1 ⁇ 415 nm) and an objective lens, and information recording surfaces having different distances (transparent substrate thicknesses) from the light beam incident surface.
- An objective lens for an optical pickup device for recording and / or reproducing information is a single lens,
- the image-side numerical aperture (NA) is 0.8 or more and 0.95 or less, In a normal temperature (25 ⁇ 3 ° C.) environment, when the thickness of the cover glass that minimizes the spherical aberration at the magnification M satisfying the expression (1) is T (mm), the objective lens is tilted by 1 degree.
- the third-order coma aberration CM3 * ( ⁇ rms) and the fifth-order coma aberration CM5 * ( ⁇ rms) of the spot condensed through the cover glass thickness T are expressed by the following equation (14): -0.003 ⁇ M ⁇ 0.003 (1) 0.145 ⁇
- the present invention is an invention expressed from the viewpoint of coma aberration different from the invention described in claim 5. That is, in the case where the light beam having the magnification M satisfying the expression (1) is incident, the third-order coma aberration CM3 * (3) of the spot condensed through the cover glass thickness T when the objective lens is tilted by 1 degree. ( ⁇ rms) and fifth-order coma aberration CM5 * ( ⁇ rms) satisfy the equation (14), so that the balance can be optimized and high-order spherical aberration at the time of focus jump can be effectively suppressed (ie, ( It was found that the characteristic 1) is improved).
- the amount of movement of the coupling lens when performing the focus jump can be reduced (that is, (characteristic 2) can be improved), and coma aberration at the time of surface shift can be suppressed ( That is, (characteristic 3) can be improved), and spherical aberration can be suppressed (that is, (characteristic 4) can be improved) even when a lens thickness error occurs.
- the sine condition violation amount From the state where the sine condition violation amount is zero, the sine condition violation amount has the first maximum value at the position of the first pupil radius H1, and the sine condition is larger at the second pupil radius H2 position.
- the third order coma aberration CM3 * increases from the positive value or decreases from the negative value, but the fifth order coma aberration CM5. since * decreases or increases in the opposite direction to the third-order coma CM3 *, as a range of optimal balance, may 3 and order coma aberration CM3 * sign, the sign of the fifth-order coma aberration CM5 * different is there.
- An information recording surface having a light source that emits a light beam having a wavelength ⁇ 1 (390 nm ⁇ 1 ⁇ 415 nm) and an objective lens according to claim 7, and having different distances (transparent substrate thicknesses) from the light beam incident surface.
- the information recording surface is selected by selecting any one information recording surface of the optical disk having three or more light sources, and condensing the light beam having the wavelength ⁇ 1 emitted from the light source onto the selected information recording surface by the objective lens.
- the objective lens is a single lens
- the image-side numerical aperture (NA) is 0.8 or more and 0.95 or less
- the aspherical shape X (h) of the optical surface on the image side is characterized by having two inflection points within the effective radius and satisfying the expressions (15) to (18).
- PV The difference between the maximum value and the minimum value of the second-order derivative of the aspherical shape X (h) of the optical surface on the image side Absolute value.
- the present invention is an invention expressing the invention according to claim 1 from the viewpoint of lens shape.
- a preferable optical surface shape condition on the optical disk side of the objective lens for satisfying the sine condition violation amount defined in claim 1 is defined. That is, if the optical surface has a shape that satisfies the equations (15) to (18), (Characteristic 1) the residual higher-order spherical aberration at the time of the focus jump can be reduced, and (Characteristic 2) the cup at the time of the focus jump. The amount of movement of the ring lens can be reduced.
- the objective lens according to claim 8 is the invention according to any one of claims 1 to 7, wherein the minimum transparent substrate thickness of the transparent substrate thickness is T MIN (mm), and the transparent substrate thickness is When the maximum transparent substrate thickness is T MAX (mm), the cover glass thickness T (mm) that minimizes the spherical aberration at the magnification M is (19) in a normal temperature (25 ⁇ 3 ° C.) environment.
- the objective lens is made of a plastic material.
- the objective lens is tilted along the radial direction and / or tangential direction of the optical disc (in this specification, the lens tilt).
- the coma that occurs due to the warp or tilt of the optical disc (referred to as disc tilt in this specification) can be canceled. Therefore, if the amount of coma generated when the lens is tilted is small, the amount of lens tilt required to correct the coma due to disc tilt increases, so it is necessary to ensure a sufficiently large dynamic range of the lens tilt. As a result, problems such as an increase in the size of the optical pickup device and an increase in power consumption of the actuator occur.
- the coupling lens when recording / reproducing information on the information recording surface L0 (100 ⁇ m) having the thicker transparent substrate, the coupling lens is moved in the optical axis direction. As a result, the divergent light beam enters the objective lens, so that the coma aberration amount when the lens is tilted is smaller than when the parallel light beam is incident.
- an objective lens made of a plastic material is used to achieve a high NA, spherical aberration is generated in a beam spot due to a temperature change (referred to as temperature aberration in this specification).
- a plastic having a focal length of 1.41 mm The amount of change in spherical aberration due to a 30 ° C. change in the objective lens made of material is about 100 m ⁇ rms, which exceeds the Marshall limit value of 70 m ⁇ rms.
- the NA is about 0.60 to 0.67
- the amount of spherical aberration caused by temperature change is relatively small, and it is not necessary to correct this spherical aberration.
- the objective lens for BD is used, This is because the aberration is proportional to the fourth power of NA, and the amount of spherical aberration generated due to a temperature change increases. Therefore, in a BD optical pickup device equipped with a plastic objective lens, it is necessary to correct temperature aberration by moving the coupling lens in the optical axis direction.
- the tilt sensitivity of the objective lens when recording / reproducing information on the information recording surface with the thicker transparent substrate is not too small.
- the lens tilt sensitivity when the environmental temperature becomes high during recording / reproduction of information on the information recording surface with the thicker transparent substrate is high. It is necessary not to become too small.
- BD plastic objective lens for three or more layers with respect to coma generated when the lens is tilted.
- some optical pickup devices that record / reproduce information with respect to a two-layer BD have a plastic objective lens mounted on the information recording surface L0 having a thicker transparent substrate. (100 ⁇ m) and a spherical aberration by combining a cover glass thickness of 87.5 ⁇ m between the information recording surface L1 (75 ⁇ m) of the thinner transparent substrate and zero magnification (corresponding to the case where a parallel light beam is incident). Is designed to be minimal.
- the amount of coma generated when the lens is tilted is minimized when information is recorded / reproduced on the information recording surface L0.
- the amount of third-order coma aberration due to the tilt of the objective lens is defined as CM (LT).
- CM LT
- a plastic objective lens for BD having three or more layers can withstand practical use if it is designed so that the minimum amount of coma generated when the lens is tilted is greater than CM (LT). It can be said.
- CM (LT) of the objective lens is about 0.02 ⁇ rms
- CM (DT) generated when the optical disk is tilted by the same amount in the same state and CM (LT) The ratio is about 0.36.
- the present inventors have obtained a spherical surface at a magnification satisfying normal temperature (25 ⁇ 3 ° C.) and (1). It has been found that the target value of CM (LT) is satisfied by setting the correction state of the spherical aberration so that the cover glass thickness T when the aberration is minimized is equal to or greater than the lower limit of the equation (19). By setting the cover glass thickness T to be equal to or less than the upper limit of the equation (19), the CM (LT) is sufficiently increased, and the objective lens is used when information is recorded / reproduced on the information recording surface having the thinnest transparent substrate thickness.
- the degree of convergence of the light beam incident on the lens is prevented from becoming too large, and the lens shift characteristic (indicating the amount of aberration generated when the objective lens performs tracking in the optical pickup device) is deteriorated, or the transparent substrate thickness is It is possible to prevent the problem that the residual higher-order spherical aberration is increased when the focus jump is made to the thinnest information recording surface.
- the objective lens according to claim 9 is the invention according to claim 8, wherein the following expression (20): T MAX ⁇ 0.85 ⁇ T ⁇ T MAX ⁇ 1.0 (20) It is characterized by satisfying.
- the cover glass thickness at which spherical aberration is corrected By making the cover glass thickness at which spherical aberration is corrected to zero not thicker than T MAX , the light flux incident on the objective lens when information is recorded / reproduced on the information recording surface having the thinner transparent substrate thickness is used. An increase in the degree of convergence can be further prevented. Therefore, when information is recorded / reproduced on the information recording surface with the thinner transparent substrate, it is possible to further prevent the occurrence of coma aberration when the objective lens is shifted.
- the invention according to the present invention can solve such a larger problem unique to a BD having three or more layers. That is, when the cover glass thickness T satisfies the upper limit of the expression (20), the degree of convergence of the light beam incident on the objective lens becomes too large when information is recorded / reproduced on the information recording surface with the thinnest transparent substrate thickness.
- the objective lens according to claim 10 is the invention according to any one of claims 1 to 7, wherein the minimum transparent substrate thickness of the transparent substrate thickness is T MIN (mm), and the transparent substrate thickness is When the maximum transparent substrate thickness is T MAX (mm), the cover glass thickness T (mm) that minimizes the spherical aberration at the magnification M is (21) in a normal temperature (25 ⁇ 3 ° C.) environment.
- the objective lens is made of a glass material.
- the present inventors examined (Characteristic 5) related to a glass objective lens. That is, a target value to be satisfied by a three-layer or more glass objective lens for BD with respect to coma generated when the lens is tilted was examined.
- the glass objective lens since the influence of temperature change can be almost ignored, the degree of divergence of the incident light to the objective lens is not so large as compared with the case where a plastic objective lens is used. Therefore, it is found that the cover glass thickness becomes smaller when the spherical aberration is minimized at the normal temperature (25 ⁇ 3 ° C.) and the magnification M satisfying (1), and as a result, the upper limit of the expression (21) is exceeded.
- the target value of the third-order coma aberration generation amount CM (LT) due to the lens tilt is satisfied by setting the spherical aberration correction state.
- the cover glass thickness T not exceed the upper limit of the formula (21)
- the degree of convergence of the light beam incident on the objective lens when information is recorded / reproduced on the information recording surface having the thinnest transparent substrate thickness. Is prevented from becoming too large, and it is possible to prevent the lens shift characteristic from being deteriorated and the increase in residual higher-order spherical aberration when the focus jump is made to the information recording surface having the thinnest transparent substrate thickness.
- the objective lens according to claims 8 and 10 has (Characteristic 1) small residual high-order spherical aberration at the time of focus jump, and (Characteristic 2) the amount of movement of the coupling lens at the time of focus jump. (Characteristic 3) It is possible not only to suppress the amount of aberration generated during surface shift, and (Characteristic 4) to suppress the amount of aberration generated when a lens thickness error occurs. (Characteristic 5) Even when information is recorded / reproduced on the information recording surface having a larger transparent substrate thickness, the lens shift tilt sensitivity does not become too small, and the lens shift characteristic can be maintained well. Since it has characteristics that can withstand practical use, the objective lens of the present invention can be used to reduce the size and cost of the optical recording medium having three or more information recording surfaces with excellent recording / reproducing characteristics. It is possible to provide an optical pickup device for click.
- the objective lens according to claim 11 is the following expression (22) in the invention according to claim 10, T MAX ⁇ 0.8 ⁇ T ⁇ T MAX ⁇ 0.95 (22) It is characterized by satisfying.
- conditional expression (22) the lens shift characteristics can be further improved, and the residual higher-order spherical aberration when the focus jump is made to the information recording surface with the thinnest transparent substrate thickness can be further reduced.
- the objective lens according to a twelfth aspect of the present invention is the objective lens according to any one of the first to eleventh aspects, wherein the refractive index N of the wavelength ⁇ 1 in the ambient temperature (25 ⁇ 3 ° C.) environment and the object side
- the inclination angle ⁇ (degrees) at the outermost periphery of the effective diameter of the optical surface is expressed by equation (23), -59.8 ⁇ N + 158 ⁇ ⁇ 59.8 ⁇ N + 166 (23) It is characterized by satisfying.
- the refractive index N of the lens and the inclination angle ⁇ in the outermost periphery of the effective diameter of the optical surface on the object side are constant. It was found to exist within the range of conditions. From this knowledge, the objective lens of the present invention is defined from the viewpoint of a preferable shape, which is represented by the equation (23).
- the objective lens according to a thirteenth aspect is the invention according to any one of the first to twelfth aspects, wherein a minimum transparent substrate thickness among the transparent substrate thicknesses is T MIN (mm), and the transparent substrate thickness is Where the maximum transparent substrate thickness is T MAX (mm), 0.03 (mm) ⁇ T MAX -T MIN ⁇ 0.06 (mm) (24) It is characterized by satisfying.
- An optical pickup device includes the objective lens according to any one of the first to thirteenth aspects, and a coupling lens that is movable in an optical axis direction. One of the information recording surfaces of the optical disc is selected by moving in the axial direction.
- An optical pickup device corresponding to an optical disc having an information recording surface of three or more layers tends to have a large residual high-order spherical aberration at the time of (Problem 1) focus jump, and (Problem 2) coupling at the time of focus jump
- the movement amount of the lens tends to be large
- by mounting the objective lens of the present invention and moving the coupling lens in the optical axis direction and selecting one of the information recording surfaces (Characteristic 1) Residual high-order spherical aberration at the time of focus jump can be reduced, (Characteristic 2) the amount of movement of the coupling lens during focus jump can be kept small, and (Characteristic 3) two optical surfaces facing each other due to manufacturing errors
- the amount of aberration that occurs when shifting in the direction perpendicular to the optical axis can be suppressed, and (Characteristic 4) the lens thickness on the optical axis varies depending on the manufacturing error.
- the optical pickup device is characterized in that, in the invention according to claim 14, the coupling lens is a single lens.
- the optical pickup device according to the fourteenth aspect, wherein the coupling lens has a two-group configuration including a positive lens group and a negative lens group, and at least one of the positive lens groups. Any information recording surface of the optical disk is selected by moving the lens.
- the moving amount of the coupling lens can be further reduced, and a more compact optical pickup device can be provided.
- the optical pickup device has at least one light source (first light source).
- first light source a plurality of types of light sources may be provided so as to support a plurality of types of optical disks.
- the optical pickup device of the present invention has a condensing optical system for condensing at least the first light flux from the first light source on the information recording surface of the first optical disc.
- the condensing optical system condenses the second light beam on the information recording surface of the second optical disk, and the third light beam on the information recording surface of the third optical disk. You may make it condense.
- the optical pickup device of the present invention includes a light receiving element that receives at least a reflected light beam from the information recording surface of the first optical disc.
- the light receiving element receives a reflected light beam from the information recording surface of the second optical disk and receives a reflected light beam from the information recording surface of the third optical disk. Also good.
- object side means the light source side
- image side means the optical disk side.
- the first optical disk has a transparent substrate having a thickness t1 and an information recording surface.
- the second optical disc has a transparent substrate having a thickness t2 (t1 ⁇ t2) and an information recording surface.
- the third optical disc has a transparent substrate having a thickness of t3 (t2 ⁇ t3) and an information recording surface.
- the first optical disc is preferably a BD
- the second optical disc is a DVD
- the third optical disc is preferably a CD, but is not limited thereto.
- the first optical disc has three or more information recording surfaces stacked in the thickness direction.
- the first optical disc has three or more information recording surfaces in the thickness direction that have different distances from the light incident surface of the optical disc to the information recording surface (this is referred to as “transparent substrate thickness” in this specification). It is. Of course, you may have four or more information recording surfaces.
- the second optical disc and the third optical disc may also have a plurality of information recording surfaces.
- the “maximum transparent substrate thickness” means the transparent substrate thickness of the information recording surface farthest from the light incident surface of the optical disc among the plurality of information recording surfaces
- the “minimum transparent substrate thickness” means the optical disc. The thickness of the transparent substrate on the information recording surface closest to the incident surface of the light beam in FIG.
- T MIN the minimum transparent substrate thickness among the transparent substrate thicknesses
- T MAX 0.03 (mm) ⁇ T MAX -T MIN ⁇ 0.06 (mm)
- the optical pickup device selects one of the plurality of information recording surfaces of the first optical disc, and condenses the light beam emitted from the light source onto the selected information recording surface by the objective lens. By doing so, information is recorded and / or reproduced.
- BD means that information is recorded / reproduced by a light beam having a wavelength of about 390 to 415 nm and an objective lens having an NA of about 0.8 to 0.9, and the thickness of the transparent substrate is 0.05 to 0.00 mm.
- the optical pickup device of the present invention has at least three layers. It is possible to deal with a BD having the above information recording surface.
- DVD is a general term for DVD series optical discs in which information is recorded / reproduced by an objective lens having an NA of about 0.60 to 0.67 and the thickness of the transparent substrate is about 0.6 mm.
- CD is a general term for CD series optical discs in which information is recorded / reproduced by an objective lens having an NA of about 0.45 to 0.51 and the transparent substrate has a thickness of about 1.2 mm.
- CD-ROM, CD-Audio, CD-Video, CD-R, CD-RW and the like As for the recording density, the recording density of BD is the highest, followed by the order of DVD and CD.
- the present invention is not limited to this.
- the first light source, the second light source, and the third light source are preferably laser light sources.
- the laser light source a semiconductor laser, a silicon laser, or the like can be preferably used.
- the wavelength ⁇ 3 ( ⁇ 3> ⁇ 2) is expressed by the following equations (28) and (29): 1.5 ⁇ ⁇ 1 ⁇ 2 ⁇ 1.7 ⁇ ⁇ 1 (28) 1.8 ⁇ ⁇ 1 ⁇ 3 ⁇ 2.0 ⁇ ⁇ 1 (29) It is preferable to satisfy.
- the first wavelength ⁇ 1 of the first light source is preferably 350 nm or more and 440 nm or less, more preferably 390 nm.
- the second wavelength ⁇ 2 of the second light source is preferably 570 nm or more and 680 nm or less, more preferably 630 nm or more and 670 nm or less
- the third wavelength ⁇ 3 of the third light source is preferably 750 nm. As mentioned above, it is 880 nm or less, More preferably, it is 760 nm or more and 820 nm or less.
- the first light source, the second light source, and the third light source may be unitized.
- the unitization means that the first light source and the second light source are fixedly housed in one package, for example.
- a light receiving element to be described later may be packaged.
- a photodetector such as a photodiode is preferably used.
- Light reflected on the information recording surface of the optical disc enters the light receiving element, and a read signal of information recorded on each optical disc is obtained using the output signal. Furthermore, it detects the change in the light amount due to the spot shape change and position change on the light receiving element, performs focus detection and track detection, and based on this detection, the objective lens can be moved for focusing and tracking I can do it.
- the light receiving element may comprise a plurality of photodetectors.
- the light receiving element may have a main photodetector and a sub photodetector.
- two sub photodetectors are provided on both sides of a photodetector that receives main light used for recording and reproducing information, and the sub light for tracking adjustment is received by the two sub photodetectors. It is good also as a simple light receiving element.
- the light receiving element may have a plurality of light receiving elements corresponding to the respective light sources.
- the condensing optical system has a coupling lens and an objective lens.
- the coupling lens is a lens group that is disposed between the objective lens and the light source and changes the divergence angle of the light beam.
- the collimator is a kind of coupling lens, and is a coupling lens that emits an incident light beam as parallel light or substantially parallel light.
- the coupling lens may be composed of only a positive lens group or may have a positive lens group and a negative lens group.
- the positive lens group has at least one positive lens.
- the positive lens group may include only one positive lens or may include a plurality of lenses.
- the negative lens group includes at least one negative lens.
- the negative lens group may include only one negative lens or may include a plurality of lenses. Examples of a preferable coupling lens include only a single positive lens or a combination of a single positive lens and a single negative lens.
- a lens that is movable in the optical axis direction in the coupling lens may be referred to as a “movable lens”.
- “movement amount of the coupling lens” is used in the same meaning as “movement amount of the movable lens”.
- the power of the lens group moved in the optical axis direction is increased (that is, in the optical axis direction). It is conceivable to shorten the focal length of the lens group that is moved to (1). This is because the amount of movement of the lens group moved in the optical axis direction decreases as the power of the lens group increases (that is, as the focal length of the lens group decreases).
- the coupling lens has a group configuration
- the focal length of the lens group moved in the optical axis direction that is, equal to the focal length of the coupling lens
- the spot condensed by the objective lens becomes an ellipse.
- the recording and / or reproduction of information on the BD may be hindered. The reason for this will be described below.
- the coupling lens has a two-group configuration including a positive lens group and a negative lens group, and at least one lens in the positive lens group is moved in the optical axis direction, thereby It is preferable to select whether to collect light on the information recording surface.
- the coupling lens is a two-group thin lens system composed of a positive lens and a negative lens, and the positive lens is moved along the optical axis direction during focus jump.
- the power of the positive lens is P P
- the focal length of the positive lens is f P
- the power of the negative lens is P N
- the focal length of the negative lens is f N
- the distance between the positive lens and the negative lens is L
- the coupling lens The system power P C and the focal length f C of the entire coupling lens system are expressed by the following equation (30):
- P C P + P N ⁇ L ⁇ P P ⁇ P N
- P C 1 / f C
- P C 1 / f P + 1 / f N ⁇ L / (f P ⁇ f N )
- the system magnification M is about -0.1. Further, in consideration of a space in which an optical element such as a polarizing beam splitter disposed between the light source and the coupling lens is considered, the focal length f C of the entire coupling lens system cannot be extremely shortened.
- the distance between the objective lens and the BD (also referred to as a working distance) is not too short, and in order to reduce the thickness of the optical pickup device, optimal range of the focal length f O of the lens naturally determined.
- the focal length range of the entire system needs to be a certain predetermined range, and the movement of the coupling lens required at the time of focus jump Considering only the amount, the focal length f C of the entire coupling lens system cannot be reduced unnecessarily.
- the power P P of the positive lens is increased, and further, the power P of the negative lens is set so that the focal length f C of the entire coupling lens system is not too short. It is preferable to increase the absolute value of N (see equation (30)).
- the movement amount of the positive lens group required at the time of focus jump is reduced by moving the positive lens group in the optical axis direction.
- the arrangement of the positive lens group and the negative lens group may be arranged in the order of the negative lens group and the positive lens group from the light source side, or may be arranged in the order of the positive lens group and the negative lens group from the light source side. good.
- the preferred arrangement is the former.
- the optimum example of the coupling lens in the optical pickup device is composed of a combination of one positive lens and one negative lens, and the negative lens and the positive lens from the light source side. Are arranged in this order.
- the present invention is not limited to this, and from the viewpoint of simplifying the configuration of the coupling lens as much as possible, there can be an option of a single positive lens coupling lens.
- At least one lens (preferably a positive lens) of the positive lens group is movable in the optical axis direction in order to correct spherical aberration occurring on the selected information recording surface of the first optical disk. It is preferable that For example, when recording and / or reproducing on one information recording surface of the first optical disk and then recording and / or reproducing on another information recording surface of the first optical disk, the positive lens group of the coupling lens group Spherical aberration that occurs at the time of focus jump to a different information recording surface of the first optical disk by moving at least one lens in the optical axis direction, changing the divergence of the light beam, and changing the magnification of the objective lens Correct.
- the maximum moving distance from the reference position of the movable lens to the light source side is shorter than the maximum moving distance from the reference position of the movable lens to the optical disk side.
- FIG. 1 is a diagram showing the results of studies conducted by the present inventors.
- the first optical disc (BD) having a surface, when the maximum spherical aberration difference A generated when the optimum focused spot is formed on each of the information recording surfaces that are separated as much as possible, and when the environmental temperature changes by ⁇ 30 ° C.
- the maximum spherical aberration B that occurred and the maximum spherical aberration C that occurred when the wavelength of the light source changed by ⁇ 5 nm were determined.
- Such spherical aberration can be corrected by moving the coupling lens in the optical axis direction and changing the magnification of the objective lens. However, if the same coupling lens is used, the total amount of spherical aberration is the amount of movement of the coupling lens. It is equivalent to.
- the amount of spherical aberration is obtained regardless of whether the optical surface is an aspherical refractive surface or a diffractive surface. Is about 410 to 430 m ⁇ rms, and it can be said that the amount of movement of the coupling lens is relatively small.
- the total amount of spherical aberration is 680 m ⁇ rms in an objective lens having an aspherical refractive surface. The amount of movement is required to be about 1.5 times that required when an optical disc having two information recording surfaces is used. Furthermore, as shown in FIG.
- the objective lens is made of glass and the optical surface is an aspherical refracting surface
- the objective lens is made of glass and the optical surface is a diffractive surface that corrects spherical aberration that occurs when the wavelength varies, in addition to spherical aberration B caused by environmental temperature changes, spherical aberration C caused by wavelength fluctuations of the light source due to the function of the diffractive surface.
- the amount of movement of the coupling lens is smaller (corresponding to the correction amount of the spherical aberration of 500 m ⁇ rms in FIG. 1C). That is, in order to reduce the amount of movement of the coupling lens, the objective lens is preferably made of a glass material. However, even if the objective lens is improved in this way, the amount of movement of the coupling lens when the optical disk having two information recording surfaces is used is smaller than that of the coupling lens when the optical disk having four information recording surfaces is used. Since the amount of movement is still about twice, it is preferable to further devise in order to suppress the amount of movement of the coupling lens. The same applies to the amount of movement of the coupling lens when using an optical disc having three information recording surfaces or five or more information recording surfaces. Therefore, in the present invention, it is possible to further reduce the amount of movement of the coupling lens by breaking the sine condition of the objective lens.
- an optical disc having two information recording surfaces an information recording surface having a smaller distance from the light beam incident surface of the optical disc is RL1, an information recording surface having a larger distance from the light beam incident surface of the optical disc is RL2
- optical disk having four information recording surfaces (assuming that the information recording surface having the smallest distance from the light beam incident surface of the optical disk is RL1, and the information recording surface having the largest distance from the light beam incident surface of the optical disk is RL4), An optical disk was assumed in which the distance from the light beam incident surface of the optical disk to RL1 was 50 ⁇ m and the distance from the light beam incident surface of the optical disk to RL4 was 100 ⁇ m.
- the objective lens refers to an optical system that is disposed at a position facing the optical disk in the optical pickup device and has a function of condensing a light beam emitted from the light source onto the information recording surface of the optical disk.
- the objective lens is a single plastic lens or glass lens.
- the objective lens is a single convex lens.
- the objective lens may be composed of only a refractive surface or may have an optical path difference providing structure.
- the hybrid lens which provided the optical path difference providing structure with the photocurable resin, UV curable resin, or thermosetting resin etc. on the glass lens may be sufficient.
- the objective lens preferably has a refractive surface that is aspheric.
- the base surface on which the optical path difference providing structure is provided is preferably an aspherical surface.
- the optical surface on the light source side of the objective lens may be referred to as the optical surface on the object side, and the optical surface on the optical disk side may be referred to as the optical surface on the image side.
- the absolute value of the radius of curvature of the optical surface on the light source side is preferably smaller than the absolute value of the radius of curvature of the optical surface on the image side.
- the objective lens is a glass lens, as described with reference to FIG. 1, it is not necessary to move the coupling lens in order to correct the spherical aberration caused by the temperature change. This is preferable because it can be reduced and the optical pickup device can be downsized.
- the objective lens is a glass lens
- a glass material having a glass transition point Tg of 500 ° C. or lower more preferably 400 ° C. or lower.
- a glass material having a glass transition point Tg of 500 ° C. or lower molding at a relatively low temperature is possible, so that the life of the mold can be extended.
- Examples of such a glass material having a low glass transition point Tg include K-PG325 and K-PG375 (both product names) manufactured by Sumita Optical Glass Co., Ltd.
- a physical property value which is important when molding and manufacturing a glass lens is a linear expansion coefficient ⁇ . Even if a material having a Tg of 400 ° C. or lower is selected, the temperature difference from room temperature is still large compared to the resin material. When lens molding is performed using a glass material having a large linear expansion coefficient ⁇ , cracks are likely to occur when the temperature is lowered.
- the linear expansion coefficient ⁇ of the glass material is preferably 200 ( ⁇ 10 ⁇ 7 / K) or less, more preferably 120 ( ⁇ 10 ⁇ 7 / K) or less.
- the specific gravity of a glass lens is generally larger than that of a plastic lens, if the objective lens is a glass lens, the mass becomes large and a load is imposed on the actuator that drives the objective lens. Therefore, when the objective lens is a glass lens, it is preferable to use a glass material having a small specific gravity.
- the specific gravity is preferably 4.0 or less, more preferably the specific gravity is 3.0 or less.
- the objective lens is a plastic lens
- an alicyclic hydrocarbon polymer material such as a cyclic olefin resin material.
- the resin material has a refractive index of 1.54 to 1.60 at a temperature of 25 ° C. with respect to a wavelength of 405 nm, and a wavelength of 405 nm according to a temperature change within a temperature range of ⁇ 5 ° C. to 70 ° C.
- the coupling lens is preferably a plastic lens.
- a first preferred example is a polymer block [A] containing a repeating unit [1] represented by the following formula (1), a repeating unit [1] represented by the following formula (1) and the following formula ( 2) and / or polymer block [B] containing the repeating unit [3] represented by the following formula (3), and the repeating unit in the block [A] It consists of a block copolymer in which the relationship between the molar fraction a (mol%) of [1] and the molar fraction b (mol%) of the repeating unit [1] in the block [B] is a> b. It is a resin composition.
- R 1 represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms
- R 2 to R 12 each independently represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a hydroxyl group, a carbon number of 1 ⁇ 20 alkoxy groups or halogen groups.
- R 13 represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.
- each of R 14 and R 15 independently represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.
- the second preferred example is obtained by addition polymerization of a monomer composition comprising at least an ⁇ -olefin having 2 to 20 carbon atoms and a cyclic olefin represented by the following general formula (4).
- Polymer (B) obtained by addition polymerization of polymer (A) and a monomer composition comprising an ⁇ -olefin having 2 to 20 carbon atoms and a cyclic olefin represented by the following general formula (5) ).
- R 1 to R 18 , R a and R b are each independently a hydrogen atom, A halogen atom or a hydrocarbon group, R 15 to R 18 may be bonded to each other to form a monocycle or polycycle, and the monocycle or polycycle in parentheses may have a double bond Alternatively, R 15 and R 16 , or R 17 and R 18 may form an alkylidene group. ]
- R 19 to R 26 each independently represents a hydrogen atom, a halogen atom or a hydrocarbon group.
- the following additives may be added.
- Stabilizer It is preferable to add at least one stabilizer selected from a phenol stabilizer, a hindered amine stabilizer, a phosphorus stabilizer, and a sulfur stabilizer. By suitably selecting and adding these stabilizers, for example, it is possible to more highly suppress the white turbidity and the optical characteristic fluctuations such as the refractive index fluctuations when continuously irradiated with light having a short wavelength of 405 nm. .
- phenol-based stabilizer conventionally known ones can be used.
- 2-t-butyl-6- (3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate
- 2 4-di-t-amyl-6- (1- (3,5-di-t-amyl-2-hydroxyphenyl) ethyl) phenyl acrylate and the like
- JP-A Nos. 63-179953 and 1-168643 JP-A Nos. 63-179953 and 1-168643.
- Preferred hindered amine stabilizers include bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (2,2,6,6-tetramethyl-4-piperidyl) succinate, bis ( 1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, bis (N-octoxy-2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (N-benzyloxy-2, 2,6,6-tetramethyl-4-piperidyl) sebacate, bis (N-cyclohexyloxy-2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (1,2,2,6,6) -Pentamethyl-4-piperidyl) 2- (3,5-di-t-butyl-4-hydroxybenzyl) -2-butylmalonate, bis (1-acryloyl-2,2, , 6-Tetramethyl-4-piperidyl) 2,2-bis (3,5-di-t-but
- the preferable phosphorus stabilizer is not particularly limited as long as it is a substance usually used in the general resin industry.
- triphenyl phosphite diphenylisodecyl phosphite, phenyl diisodecyl phosphite, tris (nonyl).
- Phenyl) phosphite tris (dinonylphenyl) phosphite, tris (2,4-di-t-butylphenyl) phosphite, 10- (3,5-di-t-butyl-4-hydroxybenzyl) -9 Monophosphite compounds such as 1,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide; 4,4′-butylidene-bis (3-methyl-6-tert-butylphenyl-di-tridecyl) Phosphite), 4,4 'isopropylidene-bis (phenyl-di-alkyl (C12-C15)) Fight) and the like diphosphite compounds such as.
- monophosphite compounds are preferable, and tris (nonylphenyl) phosphite, tris (dinonylphenyl) phosphite, tris (2,4-di-t-butylphenyl) phosphite and the like are particularly preferable.
- Preferred sulfur stabilizers include, for example, dilauryl 3,3-thiodipropionate, dimyristyl 3,3′-thiodipropionate, distearyl 3,3-thiodipropionate, lauryl stearyl 3,3- Thiodipropionate, pentaerythritol-tetrakis- ( ⁇ -lauryl-thio) -propionate, 3,9-bis (2-dodecylthioethyl) -2,4,8,10-tetraoxaspiro [5,5] undecane Etc.
- each of these stabilizers is appropriately selected within a range not to impair the purpose of the present invention, but is usually 0.01 to 2 parts by mass with respect to 100 parts by mass of the alicyclic hydrocarbon-based copolymer, The amount is preferably 0.01 to 1 part by mass.
- a surfactant is a compound having a hydrophilic group and a hydrophobic group in the same molecule.
- the surfactant can prevent white turbidity of the resin composition by adjusting the rate of moisture adhesion to the resin surface and the rate of moisture evaporation from the surface.
- hydrophilic group of the surfactant examples include a hydroxy group, a hydroxyalkyl group having 1 or more carbon atoms, a hydroxyl group, a carbonyl group, an ester group, an amino group, an amide group, an ammonium salt, a thiol, a sulfonate, A phosphate, a polyalkylene glycol group, etc. are mentioned.
- the amino group may be primary, secondary, or tertiary.
- the hydrophobic group of the surfactant include an alkyl group having 6 or more carbon atoms, a silyl group having an alkyl group having 6 or more carbon atoms, and a fluoroalkyl group having 6 or more carbon atoms.
- the alkyl group having 6 or more carbon atoms may have an aromatic ring as a substituent.
- Specific examples of the alkyl group include hexyl, heptyl, octyl, nonyl, decyl, undecenyl, dodecyl, tridecyl, tetradecyl, myristyl, stearyl, lauryl, palmityl, cyclohexyl and the like.
- the aromatic ring include a phenyl group.
- the surfactant only needs to have at least one hydrophilic group and hydrophobic group as described above in the same molecule, and may have two or more groups.
- examples of such a surfactant include myristyl diethanolamine, 2-hydroxyethyl-2-hydroxydodecylamine, 2-hydroxyethyl-2-hydroxytridecylamine, 2-hydroxyethyl-2- Hydroxytetradecylamine, pentaerythritol monostearate, pentaerythritol distearate, pentaerythritol tristearate, di-2-hydroxyethyl-2-hydroxydodecylamine, alkyl (8-18 carbon atoms) benzyldimethylammonium chloride, ethylene
- examples thereof include bisalkyl (carbon number 8 to 18) amide, stearyl diethanolamide, lauryl diethanolamide, myristyl diethanolamide, palmityl diethanolamide, and the like.
- amine compounds or amide compounds having a hydroxyalkyl group are preferably used. In the present invention, two or more of these compounds may be used in combination.
- the surfactant is added to 100 parts by mass of the alicyclic hydrocarbon-based polymer.
- the addition amount of the surfactant is more preferably 0.05 to 5 parts by mass, still more preferably 0.3 to 3 parts by mass with respect to 100 parts by mass of the alicyclic hydrocarbon-based polymer.
- Plasticizer The plasticizer is added as necessary to adjust the melt index of the copolymer.
- Plasticizers include bis (2-ethylhexyl) adipate, bis (2-butoxyethyl) adipate, bis (2-ethylhexyl) azelate, dipropylene glycol dibenzoate, tri-n-butyl citrate, tricitrate citrate -N-butylacetyl, epoxidized soybean oil, 2-ethylhexyl epoxidized tall oil, chlorinated paraffin, tri-2-ethylhexyl phosphate, tricresyl phosphate, t-butylphenyl phosphate, tri-2-ethylhexyl phosphate Diphenyl, dibutyl phthalate, diisohexyl phthalate, diheptyl phthalate, dinonyl phthalate, diundecyl phthalate, di-2-ethylhexyl phthalate, diisononyl phthalate, diisode
- cycloolefin resins are preferably used.
- ZEONEX manufactured by Nippon Zeon, APEL manufactured by Mitsui Chemicals, TOPAS ADVANCED, TOPAS manufactured by POLYMERS, and ARTON manufactured by JSR are preferable. Take as an example.
- the Abbe number of the material constituting the objective lens is preferably 50 or more.
- the maximum transparent substrate thickness (at the deepest position) among the transparent substrate thicknesses of the optical disk At a normal temperature (25 ⁇ 3 ° C.) and a cover glass thickness T (mm) satisfying the following expression (19 ′), where T MAX (mm) is a distance between a certain information recording surface and the surface of the optical disk:
- T MAX (mm) is a distance between a certain information recording surface and the surface of the optical disk:
- CM Third-order coma aberration CM (DT) generated when the optical disk is tilted when the environmental temperature becomes high during the recording / reproducing of information with respect to the information recording surface having the largest substrate thickness), and CM The ratio with (LT) was set to about 0.36. As described above, the value of this ratio is the information recording surface of the thicker transparent substrate in the optical pickup device equipped with the plastic objective lens that records / reproduces information with respect to the two-layer BD.
- CM (LT) As a result of studying a plastic objective lens suitable for three or more layers of BD using these values as target values, the present inventors have obtained a spherical surface at a magnification satisfying normal temperature (25 ⁇ 3 ° C.) and (1). It has been found that the target value of CM (LT) is satisfied by setting the correction state of the spherical aberration so that the cover glass thickness T when the aberration is minimized is equal to or greater than the lower limit of the equation (19). CM (LT) can be increased as the cover glass thickness T is increased. However, when the cover glass thickness T exceeds the upper limit of the equation (19), information is recorded on the information recording surface with the thinnest transparent substrate.
- the cover glass thickness T satisfies the upper limit of the expression (3), the degree of convergence of the light beam incident on the objective lens becomes too large when information is recorded / reproduced on the information recording surface with the thinnest transparent substrate thickness. Further suppression is preferable, and as a result, the lens shift characteristic can be further improved, and the residual higher-order spherical aberration when the focus jump is made to the information recording surface having the thinnest transparent substrate can be further reduced.
- the objective lens is a single lens made of a glass material having an image-side numerical aperture (NA) of 0.8 or more and 0.95 or less
- the largest transparent substrate thickness most of the transparent substrate thicknesses of the optical disk
- the cover glass thickness T satisfies the following formula (21) at room temperature (25 ⁇ 3 ° C.).
- the magnification M when the spherical aberration is minimized is the expression (1), T MAX ⁇ 0.75 ⁇ T ⁇ T MAX ⁇ 1.0 (21) -0.003 ⁇ M ⁇ 0.003 (1) It is preferable to satisfy.
- the cover glass thickness T not exceed the upper limit of the formula (21), the degree of convergence of the light beam incident on the objective lens when information is recorded / reproduced on the information recording surface having the thinnest transparent substrate thickness. Is prevented from becoming too large, and it is possible to prevent the lens shift characteristic from being deteriorated and the increase in residual higher-order spherical aberration when the focus jump is made to the information recording surface having the thinnest transparent substrate thickness.
- the sine condition is h when a light beam having a height h 1 from the optical axis is incident on the lens parallel to the optical axis, and when the light beam is emitted from the lens at an emission angle U. 1 / sinU satisfies a certain value.
- U. 1 / sinU a constant value regardless of the height from the height h 1 from the optical axis
- the sine condition is satisfied and the lateral magnification of each light ray within the effective diameter can be regarded as constant.
- This sine condition is a calculated value on the axis, but is effective in correcting off-axis lateral magnification error (ie off-axis coma).
- FIG. 3 is a graph showing the sine condition violation amount in the objective lens on the horizontal axis and the height from the optical axis on the vertical axis.
- the graph matches the vertical axis, but in the case of an objective lens that does not satisfy the sine condition, the graph moves away from the vertical axis to the positive side and / or the negative side as shown in FIG. It becomes.
- the sine condition violation amount For an objective lens that does not satisfy the sine condition, if the sine condition is satisfied near the optical axis and effective diameter, the sine condition violation amount always has a maximum value.
- the maximum value on the positive side of the sine condition violation amount is OSCmax (the value of the maximum value is not positive but may be negative), and the maximum value on the negative side is OSCmin.
- the objective lens having the characteristics shown in FIG. 3A is an example in which the sine condition violation amount has one negative maximum value OSCmin and does not have a positive maximum value OSCmax. According to such an objective lens, since the surface shift sensitivity is small and the on-axis thickness error sensitivity is small, it is easy to manufacture. On the other hand, as the coupling lens moves, the higher-order spherical aberration increases and the magnification changes. It has the characteristic that the change in spherical aberration due to is small. Therefore, when the coupling lens is moved to select an information recording surface in an optical disc having three or more layers, there is a possibility that the necessary movement amount increases.
- the objective lens having the characteristics shown in FIG. 3B which is the objective lens of the present invention, has a maximum value OSCmax (not necessarily a positive value) with the sine condition violation amount on the positive side at the magnification M described above. At least one (preferably only one).
- OSCmax not necessarily a positive value
- At least one preferably only one.
- OSCmax the higher-order spherical aberration generated with the movement of the coupling lens is reduced, and the magnification change is caused. Since the change in spherical aberration is large, the amount of movement required when the coupling lens is moved for selecting an information recording surface in an optical disc having three or more layers can be reduced.
- the sine condition violation amount has one negative maximum value on the optical axis side than the maximum value on the positive side so as to draw an inverted S-shaped curve.
- the derivative ⁇ (h) of the sine condition violation amount is the first derivative in the curve of the sine condition violation amount when the pupil radius is taken on the vertical axis and the sine condition violation amount is taken on the horizontal axis shown in FIG. Say. That is, if the derivative ⁇ (h) is less than the pupil radius H1 and negative, the sine condition violation amount curve is inclined to the negative side (left side in FIG.
- H1 and H2 are the following formulas (6) and (7), 0.19 ⁇ H1 ⁇ 0.62 (6) 0.74 ⁇ H2 ⁇ 0.88 (7) It is preferable to satisfy.
- f is the focal length of the objective lens at the wavelength ⁇ 1 in a normal temperature (25 ⁇ 3 ° C.) environment
- ⁇ F (mm) is the PV value of the sine condition violation amount, and the sine condition violation at the pupil radii H1 and H2
- the objective lens may be set in a shape that violates the sine condition, giving priority to reducing the amount of movement of the coupling lens, or giving priority to minimizing residual aberration during focus jump.
- the shape of the condition violation amount may be set.
- the cover glass thickness that minimizes the spherical aberration at the magnification M satisfying the expression (1) is T (mm)
- the half angle of view is 1 with respect to the objective lens.
- the third-order coma aberration CM3 satisfies the equation (12)
- the light is collected through the cover glass thickness T.
- the fifth-order coma aberration CM5 satisfies the expression (13).
- the signs of the third-order coma aberration CM3 and the fifth-order coma aberration CM5 are different.
- the cover glass thickness at which the spherical aberration at the magnification M is the minimum is T (mm)
- the cover glass thickness T is passed through.
- the third-order coma aberration CM3 * ( ⁇ rms) and the fifth-order coma aberration CM5 * ( ⁇ rms) of the focused spot satisfy the expression (14).
- the aspherical shape X (h) of the optical surface on the image side (preferably the optical surface having the larger radius of curvature) has two inflection points within the effective radius, and the expressions (15) to (18) It is preferable to satisfy.
- the refractive index N of the objective lens for the wavelength ⁇ 1 at normal temperature (25 ⁇ 3 ° C.) and the optical surface on the light source side (object side) (preferably the optical surface with the smaller radius of curvature) are effective.
- the inclination angle ⁇ (degrees) in the outermost periphery of the diameter is the expression (23), -59.8 ⁇ N + 158 ⁇ ⁇ 59.8 ⁇ N + 166 (23) It is preferable to satisfy.
- the embodiment of the present invention finds that the refractive index N of the lens and the inclination angle ⁇ in the outermost periphery of the effective diameter of the optical surface on the object side are within the range of a certain condition. It was. From this knowledge, the objective lens of the present invention is defined from the viewpoint of a preferable shape, which is represented by the equation (23).
- the horizontal axis represents the refractive index N of the wavelength ⁇ 1 at room temperature (25 ⁇ 3 ° C.), and the vertical axis represents the tilt angle ⁇ (degrees) at the outermost effective diameter of the optical surface on the object side.
- FIG. 6 is a diagram in which Examples 1 to 14 are plotted.
- NA1 The numerical aperture on the image side of the objective lens necessary for reproducing / recording information on the first optical disc is NA1, and the numerical aperture on the image side of the objective lens necessary for reproducing / recording information on the second optical disc.
- NA2 NA1> NA2
- NA3 NA2> NA3
- NA1 is preferably 0.8 or more and 0.95 or less, and more preferably 0.8 or more and 0.9 or less.
- NA1 is preferably 0.85.
- NA2 is preferably 0.55 or more and 0.7 or less.
- NA2 is preferably 0.60 or 0.65.
- NA3 is preferably 0.4 or more and 0.55 or less.
- NA3 is preferably 0.45 or 0.53.
- the objective lens satisfies the following expression (32).
- d represents the thickness (mm) on the optical axis of the objective lens
- f represents the focal length of the objective lens in the first light flux. Note that f is preferably 1.0 mm or more and 1.8 mm or less.
- the working distance of the objective lens when using the first optical disk is preferably 0.15 mm or more and 1.0 mm or less.
- An optical information recording / reproducing apparatus includes an optical disc drive apparatus having the above-described optical pickup apparatus.
- the optical disk drive apparatus can hold an optical disk mounted from the optical information recording / reproducing apparatus main body containing the optical pickup apparatus or the like. There are a system in which only the tray is taken out, and a system in which the optical disc drive apparatus main body in which the optical pickup device is stored is taken out to the outside.
- the optical information recording / reproducing apparatus using each method described above is generally equipped with the following components, but is not limited thereto.
- An optical pickup device housed in a housing or the like, a drive source of an optical pickup device such as a seek motor that moves the optical pickup device together with the housing toward the inner periphery or outer periphery of the optical disc, and the optical pickup device housing the inner periphery or outer periphery of the optical disc include a transfer means of an optical pickup device having a guide rail or the like that guides toward the head, a spindle motor that rotates the optical disk, and the like.
- the former method is provided with a tray that can be held in a state in which an optical disk is mounted and a loading mechanism for sliding the tray, and the latter method has no tray and loading mechanism. It is preferable that each component is provided in a drawer corresponding to a chassis that can be pulled out to the outside.
- an optical pickup device capable of recording / reproducing information with respect to an optical disc having a multilayer information recording surface while being compact and low in cost.
- FIG. 5 is a graph showing the effective radius on the vertical axis and the sine condition violation amount on the horizontal axis for Example 1.
- FIG. 6 is a graph showing the effective radius on the vertical axis and the sine condition violation amount on the horizontal axis for Example 2.
- FIG. 10 is a graph showing the effective radius on the vertical axis and the sine condition violation amount on the horizontal axis for Example 3.
- FIG. FIG. 5 is a graph showing the effective radius on the vertical axis and the sine condition violation amount on the horizontal axis for Example 1.
- FIG. 6 is a graph showing the effective radius on the vertical axis and the sine condition violation amount on the horizontal axis for Example 2.
- FIG. 10 is a graph showing the effective radius on the vertical axis and the sine condition violation amount on the horizontal axis for Example 3.
- FIG. 10 is a graph showing the effective radius on the vertical axis and the sine condition violation amount on the horizontal axis for Example 4.
- FIG. 10 is a graph showing the effective radius on the vertical axis and the sine condition violation amount on the horizontal axis for Example 6.
- FIG. 10 is a graph showing the effective radius on the vertical axis and the sine condition violation amount on the horizontal axis for Example 7.
- FIG. It is a graph which takes an effective radius on a vertical axis
- FIG. 10 It is a graph which takes an effective radius on a vertical axis
- FIG. It is a graph which takes the effective radius on the vertical axis and shows the sine condition violation amount on the horizontal axis for Example 10.
- Example 11 the effective radius is plotted on the vertical axis and the sine condition violation amount is plotted on the horizontal axis.
- Example 12 the effective axis is taken on the vertical axis and the sine condition violation amount is taken on the horizontal axis.
- Example 13 the effective radius is plotted on the vertical axis and the sine condition violation amount is plotted on the horizontal axis.
- FIG. 14 is a diagram in which ⁇ 14 are plotted.
- FIG. 3 is a diagram showing an optical surface shape (sag amount) on the optical disc side of the objective lens according to Example 1;
- FIG. 6 is a diagram showing an optical surface shape (sag amount) on the optical disc side of the objective lens according to Example 2;
- FIG. 3 is a diagram showing an optical surface shape (sag amount) on the optical disc side of the objective lens according to Example 1;
- FIG. 6 is a diagram showing an optical surface shape (sag amount) on the optical disc side of the objective lens according to Example 2;
- FIG. 10 is a diagram illustrating an optical surface shape (sag amount) on the optical disc side of the objective lens according to Example 3;
- FIG. 10 is a diagram showing an optical surface shape (sag amount) of an objective lens according to Example 4 on the optical disc side.
- FIG. 10 is a diagram showing the optical surface shape (sag amount) of the objective lens according to Example 5 on the optical disc side.
- FIG. 10 is a diagram showing the optical surface shape (sag amount) of the objective lens according to Example 6 on the optical disc side.
- FIG. 10 is a diagram showing the optical surface shape (sag amount) of the objective lens according to Example 7 on the optical disc side.
- FIG. 10 is a diagram showing the optical surface shape (sag amount) of the objective lens according to Example 8 on the optical disc side.
- FIG. 10 is a diagram showing the optical surface shape (sag amount) of the objective lens according to Example 9 on the optical disc side.
- FIG. 10 is a diagram showing the optical surface shape (sag amount) of the objective lens according to Example 10 on the optical disc side. It is a figure which shows the optical surface shape (sag amount) by the side of the optical disk of the objective lens concerning Example 11.
- FIG. It is a figure which shows the optical surface shape (sag amount) by the side of the optical disk of the objective lens concerning Example 12.
- FIG. It is a figure which shows the optical surface shape (sag amount) by the side of the optical disk of the objective lens concerning Example 13.
- FIG. It is a figure which shows the optical surface shape (sag amount) by the side of the optical disk of the objective lens concerning Example 14.
- FIG. 10 is a diagram showing the optical surface shape (sag amount) of the objective lens according to Example 9 on the optical disc side.
- FIG. 10 is a diagram showing the optical surface shape (sag
- FIG. 4 shows that information is appropriately recorded on a BD that is an optical disk having three information recording surfaces RL1 to RL3 (referred to as RL1, RL2, and RL3 in order of increasing distance from the light beam incident surface of the optical disk) in the thickness direction.
- FIG. 2 is a diagram schematically showing a configuration of an optical pickup device PU1 of the present embodiment that can perform reproduction. Such an optical pickup device PU1 can be mounted on an optical information recording / reproducing device.
- the present invention is not limited to the present embodiment. For example, FIG.
- the objective lens OBJ is made compatible with BD / DVD / CD, or the objective lens for DVD / CD is separately arranged, so that the BD / DVD is used.
- An optical pickup device compatible with CD can be used.
- the optical pickup device PU1 moves the objective lens OBJ, the objective lens OBJ in the focusing direction and the tracking direction, and tilts in the radial direction and / or tangential direction of the optical disc, the ⁇ / 4 wavelength plate QWP, A coupling lens CL having a positive lens unit L2 composed of one positive lens having a refractive power and a negative lens unit L3 composed of one negative lens having a negative refractive power, and only the positive lens unit L2 is in the optical axis direction.
- a light-receiving element PD that receives reflected light beams from the information recording surfaces RL1 to RL3 of the uniaxial actuator AC1, the polarizing prism PBS, the semiconductor laser LD that emits a laser beam (light beam) of 405 nm, the sensor lens SL, and the BD.
- the coupling lens CL is disposed between the polarizing prism PBS and the ⁇ / 4 wavelength plate QWP, but may be a single lens.
- the objective lens OBJ is a single lens made of plastic or glass.
- the positive lens group L2 of the coupling lens CL is moved to the position of the solid line by the uniaxial actuator AC1.
- the positive lens unit L2 After passing through the positive lens unit L2 to be a weakly convergent light beam, it is converted from linearly polarized light to circularly polarized light by the ⁇ / 4 wavelength plate QWP, the diameter of the light beam is regulated by a diaphragm (not shown), and the first lens OBJ It becomes a spot formed on the first information recording surface RL1 as shown by a solid line through the transparent substrate PL1 having a thickness.
- the reflected light flux modulated by the information pits on the first information recording surface RL1 is again transmitted through the objective lens OBJ and the aperture, and then converted from circularly polarized light to linearly polarized light by the ⁇ / 4 wavelength plate QWP, and coupled to the coupling lens CL.
- the light beam After passing through the positive lens group L2 and the negative lens group L3, the light beam is converged and reflected by the polarizing prism PBS, and then converged on the light receiving surface of the light receiving element PD by the sensor lens SL.
- the information recorded on the first information recording surface RL1 can be read by focusing or tracking the objective lens OBJ by the triaxial actuator AC2.
- the positive lens group L2 of the coupling lens CL is moved to the position of the alternate long and short dash line by the uniaxial actuator AC1.
- the positive lens unit L2 After passing through the positive lens unit L2 and made into a substantially parallel light beam, it is converted from linearly polarized light to circularly polarized light by the ⁇ / 4 wave plate QWP, the diameter of the light beam is regulated by a diaphragm (not shown), and the second lens by the objective lens OBJ. It becomes a spot formed on the second information recording surface RL2 through the transparent substrate PL2 having a thickness (thicker than the first thickness), as indicated by a one-dot chain line.
- the reflected light beam modulated by the information pits on the second information recording surface RL2 is again transmitted through the objective lens OBJ and the diaphragm, and then converted from circularly polarized light to linearly polarized light by the ⁇ / 4 wavelength plate QWP, and coupled to the coupling lens CL.
- the light beam After passing through the positive lens group L2 and the negative lens group L3, the light beam is converged and reflected by the polarizing prism PBS, and then converged on the light receiving surface of the light receiving element PD by the sensor lens SL. Then, using the output signal of the light receiving element PD, the information recorded on the second information recording surface RL2 can be read by focusing or tracking the objective lens OBJ by the triaxial actuator AC2.
- the positive lens group L2 of the coupling lens CL is moved to the dotted line position by the uniaxial actuator AC1.
- the positive lens unit L2 After passing through the positive lens unit L2 to be a weakly divergent light beam, it is converted from linearly polarized light to circularly polarized light by the ⁇ / 4 wave plate QWP, the diameter of the light beam is regulated by a diaphragm (not shown), and the third lens OBJ It becomes a spot formed on the third information recording surface RL3 through the transparent substrate PL3 having a thickness (thicker than the second thickness) as shown by a dotted line.
- the reflected light beam modulated by the information pits on the third information recording surface RL3 is again transmitted through the objective lens OBJ and the aperture, and then converted from circularly polarized light to linearly polarized light by the ⁇ / 4 wavelength plate QWP, and coupled to the coupling lens CL.
- the light beam After passing through the positive lens group L2 and the negative lens group L3, the light beam is converged and reflected by the polarizing prism PBS, and then converged on the light receiving surface of the light receiving element PD by the sensor lens SL.
- the information recorded on the third information recording surface RL3 can be read by focusing or tracking the objective lens OBJ by the triaxial actuator AC2.
- the objective lens OBJ is attached by the triaxial actuator AC2. Tilt along the radial direction and / or tangential direction of the optical disc. As a result, it is possible to stably record and / or reproduce information on the warped optical disc, and to maintain a good spot quality on the information recording surface even when the optical disc is tilted during rotation.
- the design wavelength of the objective lens is 405 nm or 407.5 nm
- R in the table below is the radius of curvature
- NA is the numerical aperture of the objective lens
- n (OBL) is the refractive index at the design wavelength of the objective lens
- n (C. G.) represents the refractive index at the design wavelength of the transparent substrate of the optical disk.
- a power of 10 for example, 2.5 ⁇ 10 ⁇ 3
- E for example, 2.5 ⁇ E ⁇ 3
- the optical surface of the objective lens is formed as an aspherical surface that is axisymmetric about the optical axis, each of which is defined by an equation in which the coefficient shown in Table 1 is substituted into Equation (1).
- X (h) is an axis in the optical axis direction (the light traveling direction is positive)
- ⁇ is a conical coefficient
- a 2i is an aspherical coefficient
- h is a height from the optical axis
- r is a paraxial curvature. Radius.
- Example 1 shows lens data of Example 1.
- Table 2 shows the third-order spherical aberration CM3 and fifth-order spherical aberration CM5 generated in the spot when an oblique light beam having a half angle of view is incident on the objective lens of Example 1, and the objective lens is tilted by 1 degree.
- FIG. 20 shows the optical surface shape of the objective lens according to the present embodiment on the optical disk side.
- FIG. 5 shows a sine condition violation amount curve of the first embodiment.
- f 1.41
- H1 0.62
- H2 0.87
- ⁇ F / f 0.0013
- OSC max /f 0.006
- OSC min /f ⁇ 0.0008
- CM3 0.002
- CM5 ⁇ 0.004
- CM3 * ⁇ 0.163
- CM5 * ⁇ 0.017.
- Table 3 shows lens data of Example 2.
- Table 4 shows the third-order spherical aberration CM3 and fifth-order spherical aberration CM5 generated in a spot when an oblique light beam having a half angle of view of 1 degree is incident on the objective lens of Example 2, and the objective lens is tilted by 1 degree.
- FIG. 21 shows the optical surface shape of the objective lens according to the present embodiment on the optical disk side.
- FIG. 6 shows a sine condition violation amount curve of the second embodiment.
- f 1.41
- H1 0.61
- H2 0.88
- ⁇ F / f 0.020
- OSC max /f ⁇ 0.0001
- OSC min / f ⁇ 0.
- Table 5 shows lens data of Example 3.
- Table 6 shows the third-order spherical aberration CM3 and fifth-order spherical aberration CM5 generated in the spot when an oblique light beam having a half angle of view of 1 degree is incident on the objective lens of Example 3, and the objective lens is tilted by 1 degree.
- FIG. 22 shows an optical surface shape of the objective lens according to the present embodiment on the optical disk side.
- FIG. 7 shows a sine condition violation amount curve of the third embodiment.
- f 1.41
- H1 0.5
- H2 0.85
- ⁇ F / f 0.002
- OSC max /f 0.0003
- OSC min /f ⁇ 0.0009
- CM3 0.007
- CM5 ⁇ 0.021
- CM3 * ⁇ 0.087
- CM5 * 0.008.
- Example 4 shows lens data of Example 4.
- Table 8 shows the third-order spherical aberration CM3 and fifth-order spherical aberration CM5 generated in the spot when an oblique light beam having a half angle of view of 1 degree is incident on the objective lens of Example 4, and the objective lens is tilted by 1 degree.
- FIG. 23 shows the optical surface shape of the objective lens according to the present embodiment on the optical disk side.
- FIG. 8 shows a sine condition violation amount curve of the fourth embodiment.
- f 1.41
- H1 0.395
- H2 0.84
- ⁇ F / f 0.004
- OSC max /f 0.004
- OSC min /f ⁇ 0.0014
- CM3 0.019
- CM5 ⁇ 0.022
- CM3 * ⁇ 0.098
- CM5 * 0.010.
- Table 9 shows lens data of Example 5.
- Table 10 shows the third-order spherical aberration CM3 and fifth-order spherical aberration CM5 generated in the spot when an oblique light beam having a half angle of view of 1 degree is incident on the objective lens of Example 5, and the objective lens is tilted by 1 degree.
- FIG. 24 shows the optical surface shape of the objective lens according to the present embodiment on the optical disk side.
- FIG. 9 shows a sine condition violation amount curve of the fifth embodiment.
- Table 11 shows lens data of Example 6.
- Table 12 shows the third-order spherical aberration CM3 and fifth-order spherical aberration CM5 generated in a spot when an oblique light beam having a half angle of view of 1 degree is incident on the objective lens of Example 6, and the objective lens is tilted by 1 degree.
- FIG. 25 shows the optical surface shape of the objective lens according to the present embodiment on the optical disk side.
- FIG. 10 shows a sine condition violation amount curve of the sixth embodiment.
- f 1.41
- H1 0.455
- H2 0.82
- ⁇ F / f 0.005
- OSC max /f 0.0009
- CM5 ⁇ 0.012
- CM3 * ⁇ 0.087
- CM5 * 0.000.
- Example 7 Table 13 shows lens data of Example 7.
- Table 14 shows the third-order spherical aberration CM3 and fifth-order spherical aberration CM5 generated in the spot when an oblique light beam with a half angle of view of 1 degree is incident on the objective lens of Example 7, and the objective lens is tilted by 1 degree.
- FIG. 26 shows the optical surface shape of the objective lens according to the present embodiment on the optical disk side.
- FIG. 11 shows a sine condition violation amount curve of the seventh embodiment.
- f 1.41
- H1 0.435
- H2 0.805
- ⁇ F 0.005
- OSC max /f 0.0012
- OSC min /f ⁇ 0.0013
- CM3 0.006
- CM5 -0.013
- CM3 * -0.172
- CM5 * 0.003.
- Table 15 shows lens data of Example 8.
- Table 15 shows the third-order spherical aberration CM3 and fifth-order spherical aberration CM5 generated in the spot when an oblique light beam having a half angle of view of 1 degree is incident on the objective lens of Example 8, and the objective lens is tilted by 1 degree.
- FIG. 27 shows the optical surface shape of the objective lens according to the present embodiment on the optical disk side.
- FIG. 12 shows a sine condition violation amount curve of the eighth embodiment.
- f 1.41
- H1 0.195
- H2 0.74
- ⁇ F / f 0.050
- CM5 ⁇ 0.031
- CM3 * ⁇ 0.133
- CM5 * 0.036.
- Example 9 shows lens data of Example 9.
- Table 18 shows the third-order spherical aberration CM3 and fifth-order spherical aberration CM5 generated in the spot when an oblique light beam with a half angle of view is incident on the objective lens of Example 9, and the objective lens is tilted by 1 degree.
- FIG. 28 shows the optical surface shape of the objective lens according to the present embodiment on the optical disk side.
- FIG. 13 shows a sine condition violation amount curve of the ninth embodiment.
- f 1.27
- H1 0.345
- H2 0.765
- ⁇ F / f 0.636
- OSC max /f 0.026
- OSC min /f ⁇ 0.0009
- CM3 ⁇ 0.003
- CM5 ⁇ 0.022
- CM3 * ⁇ 0.083
- CM5 * 0.008.
- Table 19 shows lens data of Example 10.
- Table 20 shows the third-order spherical aberration CM3 and fifth-order spherical aberration CM5 generated in the spot when an oblique light beam having a half angle of view of 1 degree is incident on the objective lens of Example 10, and the objective lens is tilted by 1 degree.
- FIG. 29 shows the optical surface shape of the objective lens according to the present embodiment on the optical disk side.
- FIG. 14 shows a sine condition violation amount curve of the tenth embodiment.
- f 1.27
- H1 0.3
- H2 0.77
- ⁇ F / f 0.004
- OSC max /f 0.005
- CM5 ⁇ 0.022
- CM3 * ⁇ 0.083
- CM5 * 0.008.
- Table 21 shows lens data of Example 11.
- Table 22 shows the third-order spherical aberration CM3 and fifth-order spherical aberration CM5 generated in the spot when an oblique light beam having a half angle of view of 1 degree is incident on the objective lens of Example 11, and the objective lens is tilted by 1 degree.
- FIG. 30 shows an optical surface shape of the objective lens according to the present embodiment on the optical disk side.
- FIG. 15 shows a sine condition violation amount curve of the eleventh embodiment.
- f 1.27
- H1 0.19
- H2 0.955
- ⁇ F / f 0.003
- OSC max /f 0.006
- OSC min /f ⁇ 0.0001
- CM3 0.001
- CM5 ⁇ 0.036
- CM3 * ⁇ 0.085
- CM5 * 0.023.
- Table 23 shows lens data of Example 12.
- Table 24 shows the third-order spherical aberration CM3 and the fifth-order spherical aberration CM5 generated in the spot when an oblique light beam having a half angle of view is incident on the objective lens of Example 12, and the objective lens is tilted by 1 degree.
- FIG. 31 shows the optical surface shape of the objective lens according to the present embodiment on the optical disk side.
- FIG. 16 shows a sine condition violation amount curve of the twelfth embodiment.
- f 1.27
- H1 0.405
- H2 0.815
- ⁇ F / f 0.0015
- OSC max /f 0.020
- OSC min /f ⁇ 0.0015
- CM3 0.008
- CM5 ⁇ 0.019
- CM3 * ⁇ 0.093
- CM5 * 0.006.
- Table 25 shows lens data of Example 13.
- Table 26 shows the third-order spherical aberration CM3 and fifth-order spherical aberration CM5 generated in the spot when an oblique light beam having a half angle of view of 1 degree is incident on the objective lens of Example 13, and the objective lens is tilted by 1 degree.
- FIG. 32 shows the optical surface shape of the objective lens according to the present embodiment on the optical disk side.
- FIG. 17 shows a sine condition violation amount curve of Example 13.
- f 1.27
- H1 0.385
- H2 0.82
- ⁇ F / f 0.004
- OSC max /f 0.002
- CM5 ⁇ 0.025
- CM3 * ⁇ 0.094
- CM5 * 0.012.
- Table 27 shows lens data of Example 14.
- Table 28 shows the third-order spherical aberration CM3 and fifth-order spherical aberration CM5 generated in a spot when an oblique light beam having a half angle of view of 1 degree is incident on the objective lens of Example 14, and the objective lens is tilted by 1 degree.
- FIG. 33 shows the optical surface shape of the objective lens according to the present embodiment on the optical disk side.
- FIG. 18 shows a sine condition violation amount curve of the fourteenth embodiment.
- f 1.27
- H1 0.305
- H2 0.815
- ⁇ F / f 0.006
- OSC max /f 0.004
- CM5 ⁇ 0.039
- CM3 * ⁇ 0.089
- CM5 * ⁇ 0.025.
- Table 29 summarizes the characteristic values of Examples 1 to 7
- Table 30 summarizes the characteristic values of Examples 8 to 14.
- OBJ Objective lens PU1 Optical pickup device LD Blue-violet semiconductor laser AC1 Single-axis actuator AC2 Three-axis actuator PBS Polarizing prism CL Coupling lens L2 Positive lens group L3 Negative lens group PL1 First transparent substrate PL2 Second transparent substrate PL3 Third Transparent substrate RL1 first information recording surface RL2 second information recording surface RL3 third information recording surface QWP ⁇ / 4 wavelength plate
Abstract
Description
(1)特許文献2の対物レンズでは、設計倍率における正弦条件を有効半径の全領域にて補正しているため、フォーカスジャンプ時の残留高次球面収差が大きくなる傾向がある。つまり、倍率変化した際の3次球面収差と5次球面収差の比が、カバーガラス厚が変化した際の3次球面収差と5次球面収差の比(約5:1)から大きくかけ離れてしまうので、特許文献2の対物レンズは、2層のBDよりも情報記録面の透明基板厚の最大差が大きい3層以上のBDの情報記録面に光束を集光する為に用いるのには適していない。
(2)倍率変化した際の3次球面収差の変化量が小さいので、特許文献2の対物レンズは、フォーカスジャンプ時に大きなカップリングレンズの移動量が必要となり、従って薄型の光ピックアップ装置に用いるのに適していない。
前記対物レンズは、単玉レンズであり、
像側開口数(NA)は0.8以上、0.95以下であり、
常温(25±3℃)環境下において、(1)式を満たす倍率Mでの正弦条件違反量が瞳半径H1で第1極大値を、瞳半径H2で第2極大値をそれぞれとり、瞳半径H3を0.9以上としたときに(2)式を満たし、更に正弦条件違反量の導関数Φ(h)が(3)~(5)式を満たすことを特徴とする。
H1<H2<H3 (2)
Φ(h) <0.0(h<H1) (3)
Φ(h) >0.0(H1<h<H2) (4)
Φ(h) <0.0(H2<h<H3) (5)
ただし、前記瞳半径H1、H2、H3は前記対物レンズの有効半径を1としたときの相対値とする。
(特性1)フォーカスジャンプ時の残留高次球面収差が小さいこと。
(特性2)フォーカスジャンプをする際のカップリングレンズの移動量が小さいこと。
本発明者らは、対物レンズの設計において正弦条件を満たすべきとする従来の技術常識から離れ、正弦条件をあえて崩すことによって従来技術の問題を解消できないか検討した。しかしながら、特許文献2に示すように、設計倍率を負(発散光入射)とし、かつ、設計倍率における正弦条件を有効半径内の全領域において満足するようにコマ収差の補正状態を設定すると、フォーカスジャンプ時に残留高次球面収差が大きくなり過ぎ、また倍率変化した際の3次球面収差と5次球面収差の比が、カバーガラス厚が変化した際の3次球面収差と5次球面収差の比(約5:1)から大きくかけ離れてしまうことがわかった。かかる知見に基づき本発明者らは、(1)式を満たす前記倍率Mにおいて、第2瞳半径H2の位置で、正弦条件違反量が第2の極大値を持つようにすることで、フォーカスジャンプ時における高次球面収差を有効に抑制できることを見出したのである。
フォーカスジャンプをする際のカップリングレンズの移動量を小さくするためには、倍率変化に対する球面収差変化量を大きくする必要がある。本発明者らは、検討の結果、(1)式を満たす前記倍率Mにおいて、第2の瞳半径の位置で、正弦条件違反量が第2の極大値を持つようにすることで、フォーカスジャンプ時における高次球面収差を有効に抑制できるだけでなく、倍率変化に対する3次球面収差変化量も増大させることが可能となることを見出した。
(特性3)対向する光学面が製造誤差によって光軸直交方向にシフトしてずれた時(面シフトという)であっても、コマ収差が大きくなりすぎないこと。
(特性4)対向する光学面が製造誤差によって光軸方向にずれた時(レンズ厚誤差という)であっても、球面収差が大きくなりすぎないこと。
本発明によれば、第1の瞳半径H1の位置で、正弦条件違反量が第1の極大値を持つようにすることで、第2の瞳半径H2における第2の極大値が大きくなりすぎることを抑制できるため、面シフト時のコマ収差の発生量を抑えることができる。
本発明によれば、第1の瞳半径H1の位置で、正弦条件違反量が第1の極大値を持つようにすることで、第2の瞳半径H2における第2の極大値が大きくなりすぎることを抑制できるため、レンズ厚誤差発生時の球面収差の発生量も抑えることが可能となるため、より製造しやすい対物レンズを提供することが可能となる。
0.74≦H2≦0.88 (7)
0.0013≦δF/f≦0.0064 (8)
但し、fは常温(25±3℃)環境下での前記波長λ1における前記対物レンズの焦点距離であり、またδF(mm)は、正弦条件違反量のPV値として、前記瞳半径H1、H2における正弦条件違反量をそれぞれOSCmin(mm)、OSCmax(mm)とした場合に、以下の(9)式、
δF=|OSCmin-OSCmax| (9)
で表わされるものとする。
-0.0021≦OSCmin/f≦-0.0001 (10)
を満たすことを特徴とする。
-0.0001≦OSCmax/f≦0.0062 (11)
を満たすことを特徴とする。
前記対物レンズは、単玉レンズであり、
像側開口数(NA)は0.8以上、0.95以下であり、
常温(25±3℃)環境下において、(1)式を満たす倍率Mでの球面収差が最小となるカバーガラス厚をT(mm)としたとき、前記対物レンズに対して半画角1度の斜め光束を入射させた場合における、前記カバーガラス厚Tを介して集光したスポットの3次コマ収差CM3(λrms)が(12)式を満たし、前記カバーガラス厚Tを介して集光したスポットの5次コマ収差CM5(λrms)が(13)式を満たし、
-0.003≦M≦0.003 (1)
0<|CM3|≦0.026 (12)
0.002≦|CM5|≦0.039 (13)
前記3次コマ収差CM3と前記5次コマ収差CM5の符号が異なることを特徴とする。
前記対物レンズは、単玉レンズであり、
像側開口数(NA)は0.8以上、0.95以下であり、
常温(25±3℃)環境下において、(1)式を満たす倍率Mでの球面収差が最小となるカバーガラス厚をT(mm)としたとき、前記対物レンズを1度傾けた場合に前記カバーガラス厚Tを介して集光したスポットの3次コマ収差CM3*(λrms)と5次コマ収差CM5*(λrms)が(14)式、
-0.003≦M≦0.003 (1)
0.145≦|CM3*-CM5*|≦0.229 (14)
を満たすことを特徴とする。
前記対物レンズは、単玉レンズであり、
像側開口数(NA)は0.8以上、0.95以下であり、
像側の光学面の非球面形状X(h)は、有効半径内に変極点を2つ有するとともに、(15)~(18)式を満たすことを特徴とする。
0.270≦D1≦0.340 (16)
0.780≦D2≦0.930 (17)
0.530≦D3≦0.640 (18)
但し、
D1(mm):前記対物レンズの有効半径に対する、像側の光学面の非球面形状X(h)が第1変曲点をとる半径高さの比
D2(mm):前記対物レンズの有効半径に対する、像側の光学面の非球面形状X(h)が第2変曲点をとる半径高さの比
D3(mm):前記対物レンズの有効半径に対する、像側の光学面の非球面形状X(h)の2階の導関数が極大値をとる半径高さの比
PV:像側の光学面の非球面形状X(h)の2階の導関数の最大値と最小値の差の絶対値
である。
TMAX×0.85≦T≦TMAX×1.1 (19)
を満たすとともに、前記対物レンズはプラスチック材料からなることを特徴とする。
また、本発明者らは、レンズチルトした際に発生するコマ収差に関して、3層以上のBD用のプラスチック製の対物レンズが満たすべき目標値を検討した。現在、2層BDに対して情報の記録/再生を行う光ピックアップ装置にはプラスチック製の対物レンズが搭載されているものがあり、かかる対物レンズは、透明基板厚が厚いほうの情報記録面L0(100μm)と透明基板厚が薄いほうの情報記録面L1(75μm)の中間のカバーガラス厚87.5μmと、ゼロの倍率(平行光束が入射する場合に相当する)との組み合わせにて球面収差が最小となるように設計されている。このように設計されたプラスチック製の対物レンズでは、上述したように、レンズチルトした際に発生するコマ収差量が最小となるのは、情報記録面L0に対して情報の記録/再生を実行中に環境温度が高温になる場合であり、この状態において対物レンズが傾いたこと(レンズチルト)による3次コマ収差発生量をCM(LT)とする。逆にいうと3層以上のBD用のプラスチック製の対物レンズは、レンズチルトした際に発生するコマ収差量の最小値がCM(LT)より大きくなるように設計されていれば実用に耐えうる、ということが出来る。
TMAX×0.85≦T≦TMAX×1.0 (20)
を満たすことを特徴とする。
TMAX×0.75≦T≦TMAX×1.0 (21)
を満たすとともに、前記対物レンズはガラス材料からなることを特徴とする。
TMAX×0.8≦T≦TMAX×0.95 (22)
を満たすことを特徴とする。
-59.8×N+158<θ<-59.8×N+166 (23)
を満たすことを特徴とする。
0.03(mm)<TMAX-TMIN<0.06(mm) (24)
を満たすことを特徴とする。
0.03(mm)<TMAX-TMIN<0.06(mm) (24)
を満たすことが好ましい。
0.050mm≦t1≦0.125mm (25)
0.5mm≦t2≦0.7mm (26)
1.0mm≦t3≦1.3mm (27)
を満たすことが好ましいが、これに限られない。
1.5・λ1<λ2<1.7・λ1 (28)
1.8・λ1<λ3<2.0・λ1 (29)
を満たすことが好ましい。
PC=PP+PN-L・PP・PN
PC=1/fC
PC=1/fP+1/fN-L/(fP・fN) (30)
で表される。
M=-fO/fC (31)
となる。
次に、第2の好ましい例は、少なくとも炭素原子数2~20のα-オレフィンと下記一般式(4)で表される環状オレフィンからなる単量体組成物とを付加重合させることにより得られる重合体(A)と、炭素原子数2~20のα-オレフィンと下記一般式(5)で表される環状オレフィンからなる単量体組成物とを付加重合させることにより得られる重合体(B)とを含む樹脂組成物である。
樹脂材料に更なる性能を付加するために、以下のような添加剤を添加してもよい。
フェノール系安定剤、ヒンダードアミン系安定剤、リン系安定剤及びイオウ系安定剤から選ばれた少なくとも1種の安定剤を添加することが好ましい。これらの安定剤を適宜選択し添加することで、例えば、405nmといった短波長の光を継続的に照射した場合の白濁や、屈折率の変動等の光学特性変動をより高度に抑制することができる。
界面活性剤は、同一分子中に親水基と疎水基とを有する化合物である。界面活性剤は樹脂表面への水分の付着や上記表面からの水分の蒸発の速度を調節することで、樹脂組成物の白濁を防止することが可能となる。
可塑剤は共重合体のメルトインデックスを調節するため、必要に応じて添加される。
TMAX×0.85≦T≦TMAX×1.1 (19)
-0.003≦M≦0.003 (1)
より好ましくは、(19)式を満たすことである。
TMAX×0.85≦T≦TMAX×1.0 (20)
を満たすことである。この時、M=0であると特に好ましい。
TMAX×0.9≦T≦TMAX×0.95 (20′)
を満たすことである。この時、M=0であると特に好ましい。
TMAX×0.75≦T≦TMAX×1.0 (21)
-0.003≦M≦0.003 (1)
を満たすことが好ましい。
TMAX×0.8≦T≦TMAX×0.95 (22)
を満たすことである。この時、M=0であると特に好ましい。
0.19≦H1≦0.62 (6)
0.74≦H2≦0.88 (7)
を満たすのが好ましい。
0.0013≦δF/f≦0.0064 (8)
δF=|OSCmin-OSCmax| (9)
を満たすと好ましい。
-0.0021≦OSCmin/f≦-0.0001 (10)
-0.0001≦OSCmax/f≦0.0062 (11)
を満たすように両者のバランスをとるのが望ましい。
0<|CM3|≦0.026 (12)
0.002≦|CM5|≦0.039 (13)
更に好ましくは、3次コマ収差CM3と5次コマ収差CM5の符号が異なることである。
このときも、CM3*とCM5*の符号が異なることが好ましい。
0.270≦D1≦0.340 (16)
0.780≦D2≦0.930 (17)
0.530≦D3≦0.640 (18)
但し、
D1(mm):対物レンズの有効半径に対する、像側の光学面の非球面形状X(h)が第1変曲点をとる半径高さの比
D2(mm):対物レンズの有効半径に対する、像側の光学面の非球面形状X(h)が第2変曲点をとる半径高さの比
D3(mm):対物レンズの有効半径に対する、像側の光学面の非球面形状X(h)の2階の導関数が極大値をとる半径高さの比
PV:像側の光学面の非球面形状X(h)の2階の導関数の最大値と最小値の差の絶対値
である。
-59.8×N+158<θ<-59.8×N+166 (23)
を満たすことが好ましい。
但し、dは、対物レンズの光軸上の厚さ(mm)を表し、fは、第1光束における対物レンズの焦点距離を表す。なお、fは、1.0mm以上、1.8mm以下となることが好ましい。
表1に実施例1のレンズデータを示す。表2に、実施例1の対物レンズに対して半画角1度の斜め光束を入射させた場合におけるスポットに生じる3次球面収差CM3及び5次球面収差CM5と、同対物レンズを1度傾けた場合にカバーガラス厚Tを介して集光したスポットに生じる3次球面収差CM3*及び5次球面収差CM5*を示す。更に、図20に、本実施例にかかる対物レンズの光ディスク側の光学面形状を示す。本実施例は3層以上の多層BD(TMAX=0.1mm、TMIN=0.05mm)に対応したプラスチック製の対物レンズであり、T=0.08mmとした。図5に実施例1の正弦条件違反量カーブを示す。本実施例においては、f=1.41、H1=0.62,H2=0.87,δF/f=0.0013、OSCmax/f=0.0006,OSCmin/f=-0.0008、CM3=0.002、CM5=-0.004,CM3*=-0.163、CM5*=-0.017である。
表3に実施例2のレンズデータを示す。表4に、実施例2の対物レンズに対して半画角1度の斜め光束を入射させた場合におけるスポットに生じる3次球面収差CM3及び5次球面収差CM5と、同対物レンズを1度傾けた場合にカバーガラス厚Tを介して集光したスポットに生じる3次球面収差CM3*及び5次球面収差CM5*を示す。更に、図21に、本実施例にかかる対物レンズの光ディスク側の光学面形状を示す。本実施例は3層以上の多層BD(TMAX=0.1mm、TMIN=0.05mm)に対応したプラスチック製の対物レンズであり、T=0.08mmとした。図6に実施例2の正弦条件違反量カーブを示す。本実施例においては、f=1.41、H1=0.61,H2=0.88,δF/f=0.0020、OSCmax/f=-0.0001,OSCmin/f=-0.0021、CM3=0.008、CM5=-0.002,CM3*=-0.088、CM5*=-0.011である。
表5に実施例3のレンズデータを示す。表6に、実施例3の対物レンズに対して半画角1度の斜め光束を入射させた場合におけるスポットに生じる3次球面収差CM3及び5次球面収差CM5と、同対物レンズを1度傾けた場合にカバーガラス厚Tを介して集光したスポットに生じる3次球面収差CM3*及び5次球面収差CM5*を示す。更に、図22に、本実施例にかかる対物レンズの光ディスク側の光学面形状を示す。本実施例は3層以上の多層BD(TMAX=0.1mm、TMIN=0.05mm)に対応したプラスチック製の対物レンズであり、T=0.08mmとした。図7に実施例3の正弦条件違反量カーブを示す。本実施例においては、f=1.41、H1=0.5,H2=0.85,δF/f=0.0032、OSCmax/f=0.0023,OSCmin/f=-0.0009、CM3=0.007、CM5=-0.021,CM3*=-0.087、CM5*=0.008である。
表7に実施例4のレンズデータを示す。表8に、実施例4の対物レンズに対して半画角1度の斜め光束を入射させた場合におけるスポットに生じる3次球面収差CM3及び5次球面収差CM5と、同対物レンズを1度傾けた場合にカバーガラス厚Tを介して集光したスポットに生じる3次球面収差CM3*及び5次球面収差CM5*を示す。更に、図23に、本実施例にかかる対物レンズの光ディスク側の光学面形状を示す。本実施例は3層以上の多層BD(TMAX=0.1mm、TMIN=0.05mm)に対応したガラス製の対物レンズであり、T=0.08mmとした。図8に実施例4の正弦条件違反量カーブを示す。本実施例においては、f=1.41、H1=0.395,H2=0.84、δF/f=0.0043、OSCmax/f=0.0029,OSCmin/f=-0.0014、CM3=0.019、CM5=-0.022,CM3*=-0.098、CM5*=0.010である。
表9に実施例5のレンズデータを示す。表10に、実施例5の対物レンズに対して半画角1度の斜め光束を入射させた場合におけるスポットに生じる3次球面収差CM3及び5次球面収差CM5と、同対物レンズを1度傾けた場合にカバーガラス厚Tを介して集光したスポットに生じる3次球面収差CM3*及び5次球面収差CM5*を示す。更に、図24に、本実施例にかかる対物レンズの光ディスク側の光学面形状を示す。本実施例は3層以上の多層BD(TMAX=0.1mm、TMIN=0.05mm)に対応したガラス製の対物レンズであり、T=0.08mmとした。図9に実施例5の正弦条件違反量カーブを示す。本実施例においては、f=1.41、H1=0.42,H2=0.85,δF/f=0.0045、OSCmax/f=0.0025,OSCmin/f=-0.0020、CM3=0.026、CM5=-0.018,CM3*=-0.106、CM5*=0.006である。
表11に実施例6のレンズデータを示す。表12に、実施例6の対物レンズに対して半画角1度の斜め光束を入射させた場合におけるスポットに生じる3次球面収差CM3及び5次球面収差CM5と、同対物レンズを1度傾けた場合にカバーガラス厚Tを介して集光したスポットに生じる3次球面収差CM3*及び5次球面収差CM5*を示す。更に、図25に、本実施例にかかる対物レンズの光ディスク側の光学面形状を示す。本実施例は3層以上の多層BD(TMAX=0.1mm、TMIN=0.05mm)に対応したガラス製の対物レンズであり、T=0.08mmとした。図10に実施例6の正弦条件違反量カーブを示す。本実施例においては、f=1.41、H1=0.455,H2=0.82,δF/f=0.0025、OSCmax/f=0.0009,OSCmin/f=-0.0015、CM3=0.007、CM5=-0.012,CM3*=-0.087、CM5*=0.000である。
表13に実施例7のレンズデータを示す。表14に、実施例7の対物レンズに対して半画角1度の斜め光束を入射させた場合におけるスポットに生じる3次球面収差CM3及び5次球面収差CM5と、同対物レンズを1度傾けた場合にカバーガラス厚Tを介して集光したスポットに生じる3次球面収差CM3*及び5次球面収差CM5*を示す。更に、図26に、本実施例にかかる対物レンズの光ディスク側の光学面形状を示す。本実施例は3層以上の多層BD(TMAX=0.1mm、TMIN=0.05mm)に対応したガラス製の対物レンズであり、T=0.08mmとした。図11に実施例7の正弦条件違反量カーブを示す。本実施例においては、f=1.41、H1=0.435,H2=0.805,δF=0.0025、OSCmax/f=0.0012,OSCmin/f=-0.0013、CM3=0.006、CM5=-0.013,CM3*=-0.172、CM5*=0.003である。
表15に実施例8のレンズデータを示す。表15に、実施例8の対物レンズに対して半画角1度の斜め光束を入射させた場合におけるスポットに生じる3次球面収差CM3及び5次球面収差CM5と、同対物レンズを1度傾けた場合にカバーガラス厚Tを介して集光したスポットに生じる3次球面収差CM3*及び5次球面収差CM5*を示す。更に、図27に、本実施例にかかる対物レンズの光ディスク側の光学面形状を示す。本実施例は3層以上の多層BD(TMAX=0.1mm、TMIN=0.05mm)に対応したガラス製の対物レンズであり、T=0.08mmとした。図12に実施例8の正弦条件違反量カーブを示す。本実施例においては、f=1.41、H1=0.195,H2=0.74,δF/f=0.0050、OSCmax/f=0.0048,OSCmin/f=-0.0002、CM3=-0.014、CM5=-0.031,CM3*=-0.133、CM5*=0.036である。
表17に実施例9のレンズデータを示す。表18に、実施例9の対物レンズに対して半画角1度の斜め光束を入射させた場合におけるスポットに生じる3次球面収差CM3及び5次球面収差CM5と、同対物レンズを1度傾けた場合にカバーガラス厚Tを介して集光したスポットに生じる3次球面収差CM3*及び5次球面収差CM5*を示す。更に、図28に、本実施例にかかる対物レンズの光ディスク側の光学面形状を示す。本実施例は3層以上の多層BD(TMAX=0.1mm、TMIN=0.05mm)に対応したプラスチック製の対物レンズであり、T=0.08mmとした。図13に実施例9の正弦条件違反量カーブを示す。本実施例においては、f=1.27、H1=0.345,H2=0.765,δF/f=0.0036、OSCmax/f=0.0026,OSCmin/f=-0.0009、CM3=-0.003、CM5=-0.022,CM3*=-0.083、CM5*=0.008である。
表19に実施例10のレンズデータを示す。表20に、実施例10の対物レンズに対して半画角1度の斜め光束を入射させた場合におけるスポットに生じる3次球面収差CM3及び5次球面収差CM5と、同対物レンズを1度傾けた場合にカバーガラス厚Tを介して集光したスポットに生じる3次球面収差CM3*及び5次球面収差CM5*を示す。更に、図29に、本実施例にかかる対物レンズの光ディスク側の光学面形状を示す。本実施例は3層以上の多層BD(TMAX=0.1mm、TMIN=0.05mm)に対応したプラスチック製の対物レンズであり、T=0.08mmとした。図14に実施例10の正弦条件違反量カーブを示す。本実施例においては、f=1.27、H1=0.3,H2=0.77,δF/f=0.0041、OSCmax/f=0.0035,OSCmin/f=-0.0005、CM3=-0.003、CM5=-0.022,CM3*=-0.083、CM5*=0.008である。
表21に実施例11のレンズデータを示す。表22に、実施例11の対物レンズに対して半画角1度の斜め光束を入射させた場合におけるスポットに生じる3次球面収差CM3及び5次球面収差CM5と、同対物レンズを1度傾けた場合にカバーガラス厚Tを介して集光したスポットに生じる3次球面収差CM3*及び5次球面収差CM5*を示す。更に、図30に、本実施例にかかる対物レンズの光ディスク側の光学面形状を示す。本実施例は3層以上の多層BD(TMAX=0.1mm、TMIN=0.05mm)に対応したプラスチック製の対物レンズであり、T=0.08mmとした。図15に実施例11の正弦条件違反量カーブを示す。本実施例においては、f=1.27、H1=0.19,H2=0.795,δF/f=0.0063、OSCmax/f=0.0062,OSCmin/f=-0.0001、CM3=0.001、CM5=-0.036,CM3*=-0.085、CM5*=0.023である。
表23に実施例12のレンズデータを示す。表24に、実施例12の対物レンズに対して半画角1度の斜め光束を入射させた場合におけるスポットに生じる3次球面収差CM3及び5次球面収差CM5と、同対物レンズを1度傾けた場合にカバーガラス厚Tを介して集光したスポットに生じる3次球面収差CM3*及び5次球面収差CM5*を示す。更に、図31に、本実施例にかかる対物レンズの光ディスク側の光学面形状を示す。本実施例は3層以上の多層BD(TMAX=0.1mm、TMIN=0.05mm)に対応したガラス製の対物レンズであり、T=0.08mmとした。図16に実施例12の正弦条件違反量カーブを示す。本実施例においては、f=1.27、H1=0.405,H2=0.815,δF/f=0.0035、OSCmax/f=0.0020,OSCmin/f=-0.0015、CM3=0.008、CM5=-0.019,CM3*=-0.093、CM5*=0.006である。
表25に実施例13のレンズデータを示す。表26に、実施例13の対物レンズに対して半画角1度の斜め光束を入射させた場合におけるスポットに生じる3次球面収差CM3及び5次球面収差CM5と、同対物レンズを1度傾けた場合にカバーガラス厚Tを介して集光したスポットに生じる3次球面収差CM3*及び5次球面収差CM5*を示す。更に、図32に、本実施例にかかる対物レンズの光ディスク側の光学面形状を示す。本実施例は3層以上の多層BD(TMAX=0.1mm、TMIN=0.05mm)に対応したガラス製の対物レンズであり、T=0.08mmとした。図17に実施例13の正弦条件違反量カーブを示す。本実施例においては、f=1.27、H1=0.385,H2=0.82,δF/f=0.0044、OSCmax/f=0.0032,OSCmin/f=-0.0013、CM3=0.009、CM5=-0.025,CM3*=-0.094、CM5*=0.012である。
表27に実施例14のレンズデータを示す。表28に、実施例14の対物レンズに対して半画角1度の斜め光束を入射させた場合におけるスポットに生じる3次球面収差CM3及び5次球面収差CM5と、同対物レンズを1度傾けた場合にカバーガラス厚Tを介して集光したスポットに生じる3次球面収差CM3*及び5次球面収差CM5*を示す。更に、図33に、本実施例にかかる対物レンズの光ディスク側の光学面形状を示す。本実施例は3層以上の多層BD(TMAX=0.1mm、TMIN=0.05mm)に対応したガラス製の対物レンズであり、T=0.08mmとした。図18に実施例14の正弦条件違反量カーブを示す。本実施例においては、f=1.27、H1=0.305,H2=0.815,δF/f=0.0061、OSCmax/f=0.0054,OSCmin/f=-0.0007、CM3=0.004、CM5=-0.039,CM3*=-0.089、CM5*=-0.025である。
PU1 光ピックアップ装置
LD 青紫色半導体レーザ
AC1 1軸アクチュエータ
AC2 3軸アクチュエータ
PBS 偏光プリズム
CL カップリングレンズ
L2 正レンズ群
L3 負レンズ群
PL1 第1の透明基板
PL2 第2の透明基板
PL3 第3の透明基板
RL1 第1の情報記録面
RL2 第2の情報記録面
RL3 第3の情報記録面
QWP λ/4波長板
Claims (16)
- 波長λ1(390nm<λ1<415nm)の光束を出射する光源と対物レンズとを有し、光束入射面からの距離(透明基板厚)が互いに異なる情報記録面を厚さ方向に3つ以上有する光ディスクにおけるいずれかの情報記録面を選択して、前記光源から出射された波長λ1の光束を前記対物レンズにより前記選択された情報記録面に集光することによって、情報の記録及び/または再生を行う光ピックアップ装置用の対物レンズであって、
前記対物レンズは、単玉レンズであり、
像側開口数(NA)は0.8以上、0.95以下であり、
常温(25±3℃)環境下において、(1)式を満たす倍率Mでの正弦条件違反量が瞳半径H1で第1極大値を、瞳半径H2で第2極大値をそれぞれとり、瞳半径H3を0.9以上としたときに(2)式を満たし、更に正弦条件違反量の導関数Φ(h)が(3)~(5)式を満たすことを特徴とする対物レンズ。
-0.003≦M≦0.003 (1)
H1<H2<H3 (2)
Φ(h) <0.0(h<H1) (3)
Φ(h) >0.0(H1<h<H2) (4)
Φ(h) <0.0(H2<h<H3) (5)
ただし、前記瞳半径H1、H2、H3は前記対物レンズの有効半径を1としたときの相対値とする。 - 以下の式を満たすことを特徴とする請求項1に記載の対物レンズ。
0.19≦H1≦0.62 (6)
0.74≦H2≦0.88 (7)
0.0013≦δF/f≦0.0064 (8)
但し、fは常温(25±3℃)環境下での前記波長λ1における前記対物レンズの焦点距離であり、またδF(mm)は、正弦条件違反量のPV値として、前記瞳半径H1、H2における正弦条件違反量をそれぞれOSCmin(mm)、OSCmax(mm)とした場合に、以下の(9)式で表わされるものとする。
δF=|OSCmin-OSCmax| (9) - 正弦条件違反量の前記第1極大値をOSCmin(mm)、常温(25±3℃)環境下での前記波長λ1における焦点距離をf(mm)としたとき、(10)式を満たすことを特徴とする請求項1又は2に記載の対物レンズ。
-0.0021≦OSCmin/f≦-0.0001 (10) - 正弦条件違反量の前記第2極大値をOSCmax(mm)、常温(25±3℃)環境下での前記波長λ1における焦点距離をf(mm)としたとき、(11)式を満たすことを特徴とする請求項1又は2に記載の対物レンズ。
-0.0001≦OSCmax/f≦0.0062 (11) - 波長λ1(390nm<λ1<415nm)の光束を出射する光源と対物レンズとを有し、光束入射面からの距離(透明基板厚)が互いに異なる情報記録面を厚さ方向に3つ以上有する光ディスクにおけるいずれかの情報記録面を選択して、前記光源から出射された波長λ1の光束を前記対物レンズにより前記選択された情報記録面に集光することによって、情報の記録及び/または再生を行う光ピックアップ装置用の対物レンズであって、
前記対物レンズは、単玉レンズであり、
像側開口数(NA)は0.8以上、0.95以下であり、
常温(25±3℃)環境下において、(1)式を満たす倍率Mでの球面収差が最小となるカバーガラス厚をT(mm)としたとき、前記対物レンズに対して半画角1度の斜め光束を入射させた場合における、前記カバーガラス厚Tを介して集光したスポットの3次コマ収差CM3(λrms)が(12)式を満たし、前記カバーガラス厚Tを介して集光したスポットの5次コマ収差CM5(λrms)が(13)式を満たし、前記3次コマ収差CM3と前記5次コマ収差CM5の符号が異なることを特徴とする対物レンズ。
-0.003≦M≦0.003 (1)
0<|CM3|≦0.026 (12)
0.002≦|CM5|≦0.039 (13) - 波長λ1(390nm<λ1<415nm)の光束を出射する光源と対物レンズとを有し、光束入射面からの距離(透明基板厚)が互いに異なる情報記録面を厚さ方向に3つ以上有する光ディスクにおけるいずれかの情報記録面を選択して、前記光源から出射された波長λ1の光束を前記対物レンズにより前記選択された情報記録面に集光することによって、情報の記録及び/または再生を行う光ピックアップ装置用の対物レンズであって、
前記対物レンズは、単玉レンズであり、
像側開口数(NA)は0.8以上、0.95以下であり、
常温(25±3℃)環境下において、(1)式を満たす倍率Mでの球面収差が最小となるカバーガラス厚をT(mm)としたとき、前記対物レンズを1度傾けた場合に前記カバーガラス厚Tを介して集光したスポットの3次コマ収差CM3*(λrms)と5次コマ収差CM5*(λrms)が(14)式を満たすことを特徴とする対物レンズ。
-0.003≦M≦0.003 (1)
0.145≦|CM3*-CM5*|≦0.229 (14) - 波長λ1(390nm<λ1<415nm)の光束を出射する光源と対物レンズとを有し、光束入射面からの距離(透明基板厚)が互いに異なる情報記録面を厚さ方向に3つ以上有する光ディスクにおけるいずれかの情報記録面を選択して、前記光源から出射された波長λ1の光束を前記対物レンズにより前記選択された情報記録面に集光することによって、情報の記録及び/または再生を行う光ピックアップ装置用の対物レンズであって、
前記対物レンズは、単玉レンズであり、
像側開口数(NA)は0.8以上、0.95以下であり、
像側の光学面の非球面形状X(h)は、有効半径内に変極点を2つ有するとともに、(15)~(18)式を満たすことを特徴とする対物レンズ。
0.524≦PV≦0.855 (15)
0.270≦D1≦0.340 (16)
0.780≦D2≦0.930 (17)
0.530≦D3≦0.640 (18)
但し、
D1(mm):前記対物レンズの有効半径に対する、像側の光学面の非球面形状X(h)が第1変曲点をとる半径高さの比
D2(mm):前記対物レンズの有効半径に対する、像側の光学面の非球面形状X(h)が第2変曲点をとる半径高さの比
D3(mm):前記対物レンズの有効半径に対する、像側の光学面の非球面形状X(h)の2階の導関数が極大値をとる半径高さの比
PV:像側の光学面の非球面形状X(h)の2階の導関数の最大値と最小値の差の絶対値 - 前記透明基板厚のうち最小の透明基板厚をTMIN(mm)とし、前記透明基板厚のうち最大の透明基板厚をTMAX(mm)としたとき、常温(25±3℃)環境下において、前記倍率Mでの球面収差が最小となるカバーガラス厚T(mm)が(19)式を満たすとともに、前記対物レンズはプラスチック材料からなることを特徴とする請求項1から7までのいずれか一項に記載の対物レンズ。
TMAX×0.85≦T≦TMAX×1.1 (19) - 以下の(20)式を満たすことを特徴とする請求項8に記載の対物レンズ。
TMAX×0.85≦T≦TMAX×1.0 (20) - 前記透明基板厚のうち最小の透明基板厚をTMIN(mm)とし、前記透明基板厚のうち最大の透明基板厚をTMAX(mm)としたとき、常温(25±3℃)環境下において、前記倍率Mでの球面収差が最小となるカバーガラス厚T(mm)が(21)式を満たすとともに、前記対物レンズはガラス材料からなることを特徴とする請求項1から7までのいずれか一項に記載の対物レンズ。
TMAX×0.75≦T≦TMAX×1.0 (21) - 以下の(22)式を満たすことを特徴とする請求項10に記載の対物レンズ。
TMAX×0.8≦T≦TMAX×0.95 (22) - 常温(25±3℃)環境下における、前記波長λ1の屈折率Nと、物体側の光学面の有効径最周辺における傾斜角θ(度)が(23)式を満たすことを特徴とする請求項1から11までのいずれか一項に記載の対物レンズ。
-59.8×N+158<θ<-59.8×N+166 (23) - 前記透明基板厚のうち最小の透明基板厚をTMIN(mm)とし、前記透明基板厚のうち最大の透明基板厚をTMAX(mm)としたとき、(24)式を満たすことを特徴とする請求項1から12までのいずれか一項に記載の対物レンズ。
0.03(mm)<TMAX-TMIN<0.06(mm) (24) - 請求項1から13までのいずれか一項に記載の対物レンズと、光軸方向に移動可能なカップリングレンズとを有し、前記カップリングレンズを光軸方向に移動させることによって、光ディスクにおけるいずれかの情報記録面を選択することを特徴とする光ピックアップ装置。
- 前記カップリングレンズは単玉レンズからなることを特徴とする請求項14に記載の光ピックアップ装置。
- 前記カップリングレンズは正のレンズ群及び負のレンズ群の2群構成からなり、前記正のレンズ群の少なくとも1枚のレンズを移動させることによって、光ディスクにおけるいずれかの情報記録面を選択することを特徴とする請求項14に記載の光ピックアップ装置。
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JP2007133967A (ja) * | 2005-11-10 | 2007-05-31 | Canon Inc | 光学式情報記録再生装置 |
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