WO2011114895A1 - 対物レンズ、光ピックアップ装置及び光情報記録再生装置 - Google Patents
対物レンズ、光ピックアップ装置及び光情報記録再生装置 Download PDFInfo
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- WO2011114895A1 WO2011114895A1 PCT/JP2011/054873 JP2011054873W WO2011114895A1 WO 2011114895 A1 WO2011114895 A1 WO 2011114895A1 JP 2011054873 W JP2011054873 W JP 2011054873W WO 2011114895 A1 WO2011114895 A1 WO 2011114895A1
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- path difference
- optical path
- light
- difference providing
- providing structure
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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
- G11B7/1353—Diffractive elements, e.g. holograms or gratings
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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
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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
- G11B2007/0003—Recording, reproducing or erasing systems characterised by the structure or type of the carrier
- G11B2007/0006—Recording, reproducing or erasing systems characterised by the structure or type of the carrier adapted for scanning different types of carrier, e.g. CD & DVD
Definitions
- the present invention relates to an optical pickup device capable of recording and / or reproducing information interchangeably for different types of optical disks, an objective lens for the optical pickup device, and an optical information recording / reproducing device.
- a laser light source used as a light source for reproducing information recorded on an optical disc and recording information on the optical disc has been shortened.
- a wavelength 390 such as a blue-violet semiconductor laser is used.
- a laser light source of ⁇ 420 nm has been put into practical use.
- these blue-violet laser light sources are used, it is possible to record 15 to 20 GB of information on an optical disk having a diameter of 12 cm when an objective lens having the same numerical aperture (NA) as that of a DVD (digital versatile disk) is used.
- NA of the objective optical element is increased to 0.85, 23 to 25 GB of information can be recorded on an optical disk having a diameter of 12 cm.
- BD Blu-ray Disc
- NA 0.85 objective lens As described above.
- NA the protective substrate is designed to be thinner than in the case of DVD (to 0.6 mm of DVD).
- the amount of coma due to skew is reduced by 0.1 mm.
- the value as a product of an optical disc player / recorder is sufficient just to be able to record and / or reproduce information appropriately (hereinafter referred to as recording / reproducing) with respect to the BD. It's not a good thing.
- DVDs and CDs compact discs
- DVDs owned by users it is possible to appropriately record / reproduce information on a CD, which leads to an increase in the commercial value of an optical disc player / recorder for BD.
- the optical pickup device mounted on the BD optical disc player / recorder can record / reproduce information appropriately while maintaining compatibility with any of BD, DVD, and CD. It is desirable to have
- the optical system for BD and the optical system for DVD or CD can be shared. It is preferable to reduce the number of optical components constituting the pickup device as much as possible. And, it is most advantageous to simplify the configuration of the optical pickup device and to reduce the cost to make the objective lens arranged facing the optical disc in common. In order to obtain a common objective lens for a plurality of types of optical disks having different recording / reproducing wavelengths, it is desirable to form a diffractive structure having a wavelength dependency of spherical aberration in the objective lens.
- Patent Document 1 describes an objective lens that has two diffractive structures and can be used in common for three types of optical disks, and an optical pickup device equipped with the objective lens.
- the first diffractive structure generates primary light as the strongest diffracted light in the light beam with the first wavelength ⁇ 1, and the 0th-order light as the strongest diffracted light in the light beam with the second wavelength ⁇ 2.
- the second-order light is generated as the strongest diffracted light by the second diffractive structure, and the second-order light is generated as the strongest diffracted light by the second-diffractive structure.
- the primary light is generated as the strongest diffracted light in the light beam with the second wavelength ⁇ 2, and the primary light is generated as the strongest diffracted light in the light beam with the third wavelength ⁇ 3.
- the first diffractive structure when the DVD / CD is used, the first diffractive structure generates zero-order diffracted light, and therefore does not receive a diffractive action, so that the occurrence of chromatic spherical aberration can be suppressed.
- first-order diffracted light is generated in any of the second diffractive structures, so that it is possible to use a conventionally designed DVD / CD compatible objective lens.
- the value of P2 in the first region is zero with reference to, for example, the numerical value of the optical path difference function (Table 30).
- the second diffractive structure is designed to have no power.
- the second diffractive structure does not have power, for example, in the BD, the second-order diffracted light used has light of other orders superimposed on the position of the longitudinal spherical aberration on the optical axis.
- the efficiency of diffraction of the first-order diffracted light and the third-order diffracted light generated on both sides is extremely low in design, so that an inherently erroneous spot may be detected on the photodetector. Should be low.
- the diffractive structure is a fine structure that requires an accuracy of several tens of nanometers, the diffraction efficiency of first-order diffracted light, third-order diffracted light, or the like may be higher than the theoretical value due to manufacturing errors or the like.
- the light spot such as the first-order diffracted light or the third-order diffracted light may be erroneously detected by the photodetector while being superimposed on the condensing spot of the second-order diffracted light.
- An object of the present invention is to solve the above-described problems.
- an objective lens and an optical pickup device for an optical pickup device capable of suppressing the generation of an error signal and the like and
- An object of the present invention is to provide an optical information recording / reproducing apparatus.
- Information is recorded and / or reproduced, information is recorded and / or reproduced on a second optical disc having a protective substrate having a thickness t2 (t1 ⁇ t2) using the second light flux, and the third light flux is reflected on the third light flux.
- the step d1 (nm) of the second optical path difference providing structure satisfies the following formula when the refractive index of the objective lens material with respect to the first wavelength is n1: (1.8 ⁇ ⁇ 1 / (n1-1)) ⁇ d1 ⁇ (3.0 ⁇ ⁇ 1 / (n1-1)) (1)
- the first optical path difference providing structure and the second optical path difference providing structure both have power.
- the first optical path difference that gives a diffractive action to the first light flux having the first wavelength ⁇ 1 passing therethrough but does not give the diffractive action to the second light flux having the second wavelength ⁇ 2 and the third light flux having the third wavelength ⁇ 3.
- the providing structure and the second optical path difference providing structure having a blaze shape, information can be recorded / reproduced on / from different optical disks using light beams having three different wavelengths.
- both the first optical path difference providing structure and the second optical path difference providing structure have power, for example, the n-th order diffracted light having the highest diffraction efficiency in the first optical path difference providing structure and the second optical path difference structure.
- the paraxial power is given to the paraxial Misdetection can be effectively avoided by shifting the condensing position in the optical axis direction.
- the objective lens according to claim 2 is the following formula in the invention according to claim 1, 0.08 ⁇ P1 / P ⁇ 0.15 (2) 0.02 ⁇
- P1 Power of the first optical path difference providing structure
- P2 Power of the second optical path difference providing structure
- P Power of the entire objective lens, P> 0 It is characterized by satisfying.
- the working distance of the third optical disc with respect to the first disc can be increased, and the nth-order diffracted light with the highest diffraction efficiency emitted from the first optical path difference providing structure.
- the diffraction efficiency of adjacent (n-1) th order diffracted light or (n + 1) th order diffracted light is increased, false detection can be effectively performed by applying a paraxial power and shifting the focusing position in the optical axis direction. Can be avoided.
- the value of the expression (2) exceeds the upper limit value, the pitch of the diffractive structure may be too fine.
- the value of the expression (3) is set to be equal to or higher than the lower limit value, the (m ⁇ 1) th order diffracted light adjacent to the mth order diffracted light having the highest diffraction efficiency emitted from the second optical path difference providing structure or Even when the diffraction efficiency of the (m + 1) th order diffracted light is increased, erroneous detection can be effectively avoided by providing paraxial power and shifting the condensing position in the optical axis direction.
- the value of the expression (3) exceeds the upper limit value, the pitch of the diffractive structure may be too fine.
- the objective lens described in claim 3 is characterized in that, in the invention described in claim 2, P2 / P is positive.
- P2 / P is positive.
- the objective lens described in claim 4 is characterized in that, in the invention described in claim 2, P2 / P is negative. As a result, the working distance of the third optical disc with respect to the first disc can be made longer than when P2 / P is positive.
- the objective lens according to claim 5 is characterized in that, in the invention according to any one of claims 1 to 4, the first optical path difference providing structure has a blaze shape. Thereby, the diffraction efficiency in a reference wavelength can be maintained high.
- the objective lens described in claim 6 is characterized in that, in the invention described in any one of claims 1 to 4, the first optical path difference providing structure has a step shape. Thereby, the change of the diffraction efficiency at the time of wavelength fluctuation can be suppressed small. Moreover, highly efficient unnecessary light can be kept away from the diffracted light used for recording and reproduction.
- the objective lens according to claim 7 is the objective lens according to any one of claims 1 to 6, wherein the first optical path difference providing structure is the first order of the first light flux that has passed through the first optical path difference providing structure.
- the diffracted light quantity is made larger than any other order diffracted light quantity
- the 0th-order diffracted light quantity of the second light flux that has passed through the first optical path difference providing structure is made larger than any other order diffracted light quantity
- the 0th-order diffracted light amount of the third light beam that has passed through the optical path difference providing structure is made larger than any other order diffracted light amount
- the second optical path difference providing structure is the first light beam that has passed through the second optical path difference providing structure.
- the second order diffracted light quantity of the light beam is made larger than any other order diffracted light quantity
- the first order diffracted light quantity of the second light flux that has passed through the second optical path difference providing structure is made larger than any other order diffracted light quantity.
- the third light passing through the second optical path difference providing structure The first order diffracted light, characterized in that larger than the other diffracted light of any order. This makes it possible to effectively record / reproduce information with respect to three different optical discs using light beams having three different wavelengths.
- An objective lens according to an eighth aspect is characterized in that, in the invention according to any one of the first to seventh aspects, the first optical path difference providing structure and the second optical path difference providing structure are superimposed. .
- An optical pickup device includes the objective lens according to any one of the first to eighth aspects.
- An optical information recording / reproducing apparatus has the optical pickup apparatus according to the ninth aspect.
- the optical pickup device has at least three light sources: a first light source, a second light source, and a third light source. Furthermore, the optical pickup device of the present invention condenses the first light flux on the information recording surface of the first optical disc, condenses the second light flux on the information recording surface of the second optical disc, and causes the third light flux to be third. It has a condensing optical system for condensing on the information recording surface of the optical disc.
- the optical pickup device of the present invention includes a light receiving element that receives a reflected light beam from the information recording surface of the first optical disc, the second optical disc, or the third optical disc.
- the first optical disc has a protective substrate having a thickness t1 and an information recording surface.
- the second optical disc has a protective substrate having a thickness t2 (t1 ⁇ t2) and an information recording surface.
- the third optical disc has a protective substrate having a thickness t3 (t2 ⁇ t3) and an information recording surface.
- the first optical disc is preferably a BD
- the second optical disc is a DVD
- the third optical disc is preferably a CD, but is not limited thereto.
- the first optical disc, the second optical disc, or the third optical disc may be a multi-layer optical disc having a plurality of information recording surfaces.
- BD means that information is recorded / reproduced by a light beam having a wavelength of about 390 to 415 nm and an objective lens having an NA of about 0.8 to 0.9, and the thickness of the protective substrate is 0.05 to 0.00 mm.
- It is a generic term for a BD series optical disc of about 125 mm, and includes a BD having only a single information recording layer, a BD having a plurality of information recording layers, and the like.
- DVD is a general term for DVD series optical discs in which information is recorded / reproduced by an objective lens having an NA of about 0.60 to 0.67 and the thickness of the protective substrate is about 0.6 mm.
- CD is a general term for CD series optical discs in which information is recorded / reproduced by an objective lens having an NA of about 0.45 to 0.51 and the thickness of the protective substrate is about 1.2 mm.
- 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 thickness of a protective substrate is the thickness of the protective substrate provided in the optical disk surface. That is, the thickness of the protective substrate from the optical disc surface to the information recording surface closest to the surface.
- 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 defined by the following conditional expressions (7), (8), 1.5 ⁇ ⁇ 1 ⁇ 2 ⁇ 1.7 ⁇ ⁇ 1 (7) 1.8 ⁇ ⁇ 1 ⁇ 3 ⁇ 2.0 ⁇ ⁇ 1 (8) 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, and the third wavelength ⁇ 3 of the third light source is preferably 415 nm or less. It is 750 nm or more and 880 nm or less, More preferably, it is 760 nm or more and 820 nm or less.
- 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 an objective lens.
- the condensing optical system preferably has a coupling lens such as a collimator in addition to the objective lens.
- the coupling lens is a single lens or a lens group that is disposed between the objective lens and the light source and changes the divergence angle of the light beam.
- the collimator is a type of coupling lens, and is a lens that emits incident light as parallel light.
- the objective lens refers to an optical system that is disposed at a position facing the optical disk in the optical pickup device and has a function of condensing the light beam emitted from the light source onto the information recording surface of the optical disk.
- the objective lens may be composed of two or more plural lenses and / or optical elements, may be composed of only a single lens, and is more preferably an objective lens composed of a single convex lens.
- the objective lens may be a glass lens or a plastic lens, or an optical path difference providing structure is provided on the glass lens with a photo-curing resin, a UV-curing resin, or a thermosetting resin.
- a hybrid lens may also be used.
- the objective lens has a plurality of lenses, a glass lens and a plastic lens may be mixed and used.
- the objective lens includes a plurality of lenses, it may be a combination of a flat optical element having an optical path difference providing structure and an aspherical lens (which may or may not have an optical path difference providing structure).
- the objective lens preferably has a refractive surface that is aspheric.
- the base surface on which the optical path difference providing structure is provided is preferably an aspherical surface.
- the objective lens is a glass lens
- a glass material having a glass transition point Tg of 450 ° C. or lower more preferably 400 ° C. or lower.
- a glass material having a glass transition point Tg of 450 ° C. or lower molding at a relatively low temperature becomes possible, so that the life of the mold can be extended.
- Examples of such a glass material having a low glass transition point Tg include K-PG325 and K-PG375 (both product names) manufactured by Sumita Optical Glass Co., Ltd.
- the specific gravity of the glass lens is generally larger than that of the resin lens, if the objective lens is a glass lens, the mass is increased 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.
- cycloolefin resin is preferably used.
- ZEONEX manufactured by Nippon Zeon, APEL manufactured by Mitsui Chemicals, TOPAS ADVANCED, TOPAS manufactured by POLYMERS, ARTON manufactured by JSR, etc. are preferable examples. Can be mentioned.
- the Abbe number of the material constituting the objective lens is preferably 50 or more.
- the objective lens is described below. It is preferable that at least one optical surface of the objective lens has at least a central region, an intermediate region around the central region, and a peripheral region around the intermediate region.
- the central region is preferably a region including the optical axis of the objective lens, but a minute region including the optical axis is used as an unused region or a special purpose region, and the surroundings are defined as a central region (also referred to as a central region). Also good.
- the central region, the intermediate region, and the peripheral region are preferably provided on the same optical surface. As shown in FIG. 1, the central region CN, the intermediate region MD, and the peripheral region OT are preferably provided concentrically around the optical axis on the same optical surface.
- the central region, the intermediate region, and the peripheral region are preferably adjacent to each other, but there may be a slight gap between them.
- the region including the optical axis gives a diffractive action to the first light beam having the first wavelength ⁇ 1 that passes therethrough, but has the second wavelength ⁇ 2 in the first region.
- a first optical path difference providing structure that does not give diffraction action to the two light beams and the third light beam having the third wavelength ⁇ 3, and a second optical path difference providing structure having a blaze shape, Both of the second optical path difference providing structures have power.
- does not give a diffractive action means that the light having the strongest light intensity among the light beams that have passed through the optical path difference providing structure is zero-order diffracted light. Means that the diffracted light of the order other than 0 has the strongest light intensity among the light beams that have passed through the optical path difference providing structure.
- the central area of the objective lens can be said to be a shared area of the first, second, and third optical disks used for recording / reproduction of the first optical disk, the second optical disk, and the third optical disk. That is, the objective lens condenses the first light flux that passes through the central area so that information can be recorded / reproduced on the information recording surface of the first optical disc, and the second light flux that passes through the central area becomes the second light flux. Focusing on the information recording surface of the optical disc so that information can be recorded and / or reproduced, and allowing the third light flux passing through the central area to be recorded / reproduced on the information recording surface of the third optical disc Condensate.
- the optical path difference providing structure provided in the central region has the thickness t1 of the protective substrate of the first optical disc and the protective substrate of the second optical disc with respect to the first light flux and the second light flux passing through the optical path difference providing structure. It is preferable to correct spherical aberration generated due to the difference in thickness t2 / spherical aberration generated due to the difference in wavelength between the first light beam and the second light beam. Further, the optical path difference providing structure is different from the thickness t1 of the protective substrate of the first optical disc and the thickness t3 of the protective substrate of the third optical disc with respect to the first and third light fluxes that have passed through the optical path difference providing structure. It is preferable to correct the spherical aberration caused by the difference in the wavelength of the first light beam and the third light beam.
- the intermediate area of the objective lens is used for recording / reproduction of the first optical disk and the second optical disk, and can be said to be the first and second optical disk shared areas not used for recording / reproduction of the third optical disk. That is, the objective lens condenses the first light flux that passes through the intermediate area so that information can be recorded / reproduced on the information recording surface of the first optical disc, and the second light flux that passes through the intermediate area becomes the second light flux. The light is condensed on the information recording surface of the optical disc so that information can be recorded / reproduced. On the other hand, the third light flux passing through the intermediate region is not condensed so that information can be recorded / reproduced on the information recording surface of the third optical disk.
- the third light flux passing through the intermediate region of the objective lens preferably forms a flare on the information recording surface of the third optical disc.
- the spot center portion having a high light amount density and the light amount density in order from the optical axis side (or the spot center portion) to the outside. It is preferable to have a spot middle part lower than the spot center part and a spot peripheral part whose light intensity is higher than the spot middle part and lower than the spot center part.
- the center portion of the spot is used for recording / reproducing information on the optical disc, and the middle portion of the spot and the peripheral portion of the spot are not used for recording / reproducing information on the optical disc.
- this spot peripheral part is called flare.
- the spot peripheral part may be called a flare.
- the third light flux that has passed through the intermediate region of the objective lens preferably forms a spot peripheral portion on the information recording surface of the third optical disc.
- the peripheral area of the objective lens is used for recording / reproduction of the first optical disk, and can be said to be an area dedicated to the first optical disk that is not used for recording / reproduction of the second optical disk and the third optical disk. That is, the objective lens condenses the first light flux passing through the peripheral region so that information can be recorded / reproduced on the information recording surface of the first optical disc.
- the second light flux that passes through the peripheral area is not condensed so that information can be recorded / reproduced on the information recording surface of the second optical disc, and the third light flux that passes through the peripheral area does not converge. The light is not condensed so that information can be recorded / reproduced on the information recording surface.
- the second light flux and the third light flux that pass through the peripheral area of the objective lens preferably form a flare on the information recording surfaces of the second optical disc and the third optical disc. That is, it is preferable that the second light flux and the third light flux that have passed through the peripheral area of the objective lens form a spot peripheral portion on the information recording surfaces of the second optical disc and the third optical disc.
- the optical path difference providing structure is preferably provided in a region of 70% or more of the area of the central region of the objective lens, and more preferably 90% or more. More preferably, the optical path difference providing structure is provided on the entire surface of the central region. Further, another optical path difference providing structure is preferably provided in a region of 70% or more of the area of the intermediate region of the objective lens, and more preferably 90% or more. More preferably, another optical path difference providing structure is provided on the entire surface of the intermediate region.
- the optical path difference providing structure is preferably provided in a region of 70% or more of the area of the peripheral region of the objective lens, and more preferably 90% or more. More preferably, the optical path difference providing structure is provided on the entire surface of the peripheral region.
- the optical path difference providing structure referred to in this specification is a general term for structures that add an optical path difference to an incident light beam.
- the optical path difference providing structure also includes a phase difference providing structure for providing a phase difference.
- the phase difference providing structure includes a diffractive structure.
- the optical path difference providing structure of the present invention is preferably a diffractive structure.
- the optical path difference providing structure has a step, preferably a plurality of steps. This step adds an optical path difference and / or phase difference to the incident light flux.
- the optical path difference added by the optical path difference providing structure may be an integer multiple of the wavelength of the incident light beam or a non-integer multiple of the wavelength of the incident light beam.
- the steps may be arranged with a periodic interval in the direction perpendicular to the optical axis, or may be arranged with a non-periodic interval in the direction perpendicular to the optical axis.
- the objective lens provided with the optical path difference providing structure is a single aspherical lens
- the incident angle of the light flux to the objective lens differs depending on the height from the optical axis.
- Each will be slightly different.
- the objective lens is a single-lens aspherical convex lens, even if it is an optical path difference providing structure that provides the same optical path difference, generally the distance from the optical axis tends to increase.
- the diffractive structure referred to in this specification is a general term for structures that have a step and have a function of converging or diverging a light beam by diffraction.
- a plurality of unit shapes are arranged around the optical axis, and a light beam is incident on each unit shape, and the wavefront of the transmitted light is shifted between adjacent annular zones, resulting in new It includes a structure that converges or diverges light by forming a simple wavefront.
- the diffractive structure preferably has a plurality of steps, and the steps may be arranged with a periodic interval in the direction perpendicular to the optical axis, or may be arranged with a non-periodic interval in the direction perpendicular to the optical axis.
- the exit angle from the diffractive structure and the optical path length to enter the lens differ depending on the height from the optical axis.
- the amount will vary slightly for each zone.
- the objective lens is a single aspherical convex lens, even if it is a diffractive structure that generates diffracted light of the same diffraction order, generally, the distance from the optical axis tends to increase.
- the optical path difference providing structure has a plurality of concentric annular zones with the optical axis as the center.
- the optical path difference providing structure can generally have various cross-sectional shapes (cross-sectional shapes on the plane including the optical axis), and the cross-sectional shapes including the optical axis are roughly classified into a blazed structure and a staircase structure.
- the blaze-type structure means that the cross-sectional shape including the optical axis of the optical element having the optical path difference providing structure is a sawtooth shape.
- the upper side is the light source side and the lower side is the optical disk side, and the optical path difference providing structure is formed on a plane as a mother aspherical surface.
- the pitch Ph the length of one blaze unit in the direction perpendicular to the optical axis
- the length of the step in the direction parallel to the optical axis of the blaze is referred to as a step amount d (see FIG. 2A).
- the staircase structure has a small staircase shape in cross section including the optical axis of an optical element having an optical path difference providing structure (referred to as a staircase unit).
- V level means a ring-shaped surface (hereinafter also referred to as a terrace surface) corresponding to (or facing) the vertical direction of the optical axis in one step unit of the step structure. In other words, it is divided by V steps and divided into V ring zones.
- a three-level or higher staircase structure has a small step and a large step.
- the optical path difference providing structure illustrated in FIG. 2C is referred to as a five-level step structure
- the optical path difference providing structure illustrated in FIG. 2D is referred to as a two-level step structure (also referred to as a binary structure).
- a two-level staircase structure is described below.
- a plurality of annular zones including a plurality of concentric annular zones around the optical axis, and a plurality of annular zones including the optical axis of the objective lens have a plurality of stepped surfaces Pa and Pb extending in parallel to the optical axis,
- the light source side terrace surface Pc for connecting the light source side ends of the adjacent step surfaces Pa and Pb and the optical disk side terrace surface Pd for connecting the optical disk side ends of the adjacent step surfaces Pa and Pb are formed.
- the surface Pc and the optical disc side terrace surface Pd are alternately arranged along the direction intersecting the optical axis.
- the length of one staircase unit in the direction perpendicular to the optical axis is referred to as the pitch Ph (see FIGS. 2C and 2D).
- the length of the step in the direction parallel to the optical axis of the staircase is referred to as step amounts B1 and B2.
- a large step amount B1 and a small step amount B2 exist (see FIG. 2C).
- the optical path difference providing structure is preferably a structure in which a certain unit shape is periodically repeated.
- unit shape is periodically repeated” naturally includes shapes in which the same shape is repeated in the same cycle.
- the unit shape that is one unit of the cycle has regularity, and the shape in which the cycle gradually increases or decreases gradually is also included in the “unit shape is periodically repeated”.
- the sawtooth shape as a unit shape is repeated.
- the same serrated shape may be repeated, or as shown in FIG. 2 (b), the serrated shape gradually increases as it moves away from the optical axis.
- a shape in which the pitch becomes longer or a shape in which the pitch becomes shorter may be used.
- the blazed structure has a step opposite to the optical axis (center) side, and in other areas, the blazed structure has a step toward the optical axis (center). It is good also as a shape in which the transition area
- mold structure is provided in the meantime.
- the optical path difference providing structure has a staircase structure
- the first optical path difference providing structure and the second optical path difference providing structure may be provided on different optical surfaces of the objective lens, respectively, but are preferably provided on the same optical surface.
- first optical path difference providing structure, the second optical path difference providing structure, and the third optical path difference providing structure are preferably provided on the light source side surface of the objective lens rather than the surface of the objective lens on the optical disk side.
- first optical path difference providing structure, the second optical path difference providing structure, and the third optical path difference providing structure are preferably provided on the optical surface having the smaller absolute value of the radius of curvature of the objective lens.
- the first optical path difference providing structure is a blaze type structure or a staircase type structure. Further, the first optical path difference providing structure makes the first-order diffracted light quantity of the first light flux that has passed through the first optical path difference-providing structure larger than any other order of diffracted light quantity, and passed through the first optical path difference providing structure.
- the 0th-order diffracted light amount of the second light beam is made larger than any other order diffracted light amount
- the 0th-order diffracted light amount of the third light beam that has passed through the first optical path difference providing structure is made higher than any other order diffracted light amount. Larger is preferable.
- the second optical path difference providing structure is a blaze type structure. Further, the second optical path difference providing structure makes the second-order diffracted light amount of the first light beam that has passed through the second optical path difference providing structure larger than any other order diffracted light amount, and passed through the second optical path difference providing structure.
- the first order diffracted light amount of the second light beam is made larger than any other order diffracted light amount
- the first order diffracted light amount of the third light beam that has passed through the second optical path difference providing structure is made higher than any other order diffracted light amount. Larger is preferable.
- the blaze step d1 (nm) in the second optical path difference providing structure satisfies the following expression when the refractive index for the first wavelength ⁇ 1 of the blazed structure is n1: (1.8 ⁇ ⁇ 1 / (n1-1)) ⁇ d1 ⁇ (3.0 ⁇ ⁇ 1 / (n1-1)) (1)
- Both the first optical path difference providing structure and the second optical path difference providing structure have paraxial power.
- P2 / P may be positive or negative.
- the first optical path difference providing structure and the second optical path difference providing structure may be superimposed on one optical surface.
- the thick on-axis objective lens used for compatibility with the three types of optical discs of BD / DVD / CD according to the present invention affects the condensed spot on the information recording surface even if the efficiency of unnecessary diffracted light increases due to manufacturing errors.
- the first optical path difference providing structure and the second optical path difference providing structure have paraxial power with respect to the first light flux (also referred to as power in this specification).
- “having paraxial power” means that C 2 h 2 is not 0 when the optical path difference functions of the first optical path difference providing structure and the second optical path difference providing structure are expressed by the following equation ( 2).
- FIG. 3A is a diagram showing a change in diffraction efficiency with respect to wavelength variation of the blazed diffraction structure and the staircase diffraction structure.
- FIG. 3B is a diagram showing the relationship between the order of diffracted light generated with respect to the wavelength used and the diffraction efficiency.
- the first-order diffracted light amount of the first light beam that has passed through the diffractive structure is made larger than any other order of diffracted light amount
- the zero-order diffracted light amount of the second light beam that has passed through the diffractive structure is set to any other order.
- An example will be described in which the 0th-order diffracted light amount of the third light flux that has passed through the diffractive structure is made larger than any other order diffracted light amount.
- the variation of the diffraction efficiency of the blazed diffraction structure is about 3% as shown in FIG.
- the fluctuation of the diffraction efficiency is about 2%, and the fluctuation of the diffraction efficiency of the staircase type diffraction structure is smaller.
- a blazed diffraction structure if the light source has a small variation in oscillation wavelength, and it is preferable to use a staircase diffraction structure if the light source has a large variation in oscillation wavelength.
- 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 0.75 or more and 0.9 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 boundary between the central region and the intermediate region of the objective lens is 0.9 ⁇ NA 3 or more and 1.2 ⁇ NA 3 or less (more preferably 0.95 ⁇ NA 3 or more, 1.15 ⁇ NA 3) when the third light beam is used. It is preferably formed in a portion corresponding to the following range. More preferably, the boundary between the central region and the intermediate region of the objective lens is formed in a portion corresponding to NA3. Further, the boundary between the intermediate region and the peripheral region of the objective lens is 0.9 ⁇ NA 2 or more and 1.2 ⁇ NA 2 or less (more preferably 0.95 ⁇ NA 2 or more, 1.15) when the second light flux is used. -It is preferably formed in a portion corresponding to the range of NA2 or less. More preferably, the boundary between the intermediate region and the peripheral region of the objective lens is formed in a portion corresponding to NA2.
- the spherical aberration has at least one discontinuous portion.
- the discontinuous portion has a range of 0.9 ⁇ NA 3 or more and 1.2 ⁇ NA 3 or less (more preferably 0.95 ⁇ NA 3 or more and 1.15 ⁇ NA 3 or less) when the third light flux is used. It is preferable that it exists in.
- an objective lens satisfy
- dt represents the thickness (mm) of the objective lens on the optical axis
- f represents the focal length (mm) of the objective lens in the first light flux.
- the objective lens When dealing with an optical disk with a short wavelength and high NA such as BD, the objective lens has a problem that astigmatism is likely to occur and decentration coma is likely to occur, but the conditional expression (11) is satisfied. As a result, it is possible to suppress the generation of astigmatism and decentration coma.
- the objective lens becomes a thick objective lens having a thick on-axis thickness, so that the working distance during CD recording / reproduction tends to be shortened.
- the working distance in CD recording / reproduction can be sufficiently ensured, and the effect of the present invention becomes more remarkable.
- the first light beam, the second light beam, and the third light beam may be incident on the objective lens as parallel light, or may be incident on the objective lens as divergent light or convergent light. Even during tracking, in order to prevent coma from occurring, it is preferable that all of the first light beam, the second light beam, and the third light beam be incident on the objective lens as parallel light or substantially parallel light.
- all of the first light beam, the second light beam, and the third light beam can be incident on the objective lens as parallel light or substantially parallel light. The effect becomes more remarkable.
- the imaging magnification m1 of the objective lens when the first light flux enters the objective lens is expressed by the following equation (12): -0.01 ⁇ m1 ⁇ 0.01 (12) It is preferable to satisfy.
- the imaging magnification m2 of the objective lens when the second light beam is incident on the objective lens is expressed by the following equation (13): -0.01 ⁇ m2 ⁇ 0.01 (13) It is preferable to satisfy.
- the imaging magnification m2 of the objective lens when the second light flux is incident on the objective lens is expressed by the following equation (13) ′, ⁇ 0.025 ⁇ m2 ⁇ ⁇ 0.01 (13) ′ It is preferable to satisfy.
- the imaging magnification m3 of the objective lens when the third light beam is incident on the objective lens is expressed by the following equation (14): -0.01 ⁇ m3 ⁇ 0.01 (14) It is preferable to satisfy.
- the imaging magnification m3 of the objective lens when the third light beam enters the objective lens is expressed by the following equation (14) ′, ⁇ 0.025 ⁇ m3 ⁇ ⁇ 0.01 (14) ′ It is preferable to satisfy.
- the working distance (WD) of the objective optical element when using the third optical disk is preferably 0.15 mm or more and 1.5 mm or less. Preferably, it is 0.3 mm or more and 0.9 mm or less.
- the WD of the objective optical element when using the second optical disc is preferably 0.2 mm or more and 1.3 mm or less.
- the WD of the objective optical element when using the first optical disk is preferably 0.25 mm or more and 1.0 mm or less.
- An optical information recording / reproducing apparatus 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 objective lens for an optical pickup device, an optical pickup device, and an optical information recording / reproducing device that can suppress the occurrence of an error signal or the like when three different optical disks are used interchangeably.
- FIG. 1 It is the figure which looked at the single objective lens OL concerning this Embodiment in the optical axis direction. It is an axial direction sectional view showing an example of an optical path difference grant structure.
- (A) is a figure which shows the change of the diffraction efficiency with respect to the wavelength fluctuation of a blaze
- (b) is the relationship between the order of the diffracted light generate
- FIG. It is a figure which shows schematically the structure of optical pick-up apparatus PU1 of this Embodiment which can record and / or reproduce
- FIG. 4 is a longitudinal spherical aberration diagram of Example 1, and B1 to B5, D1 to D5, and C1 to C5 in the figure respectively correspond to light beams indicated by the same reference numerals on the upper side of Table 4.
- FIG. 4 is a longitudinal spherical aberration diagram of Example 2, and B1 to B5, D1 to D5, and C1 to C5 in the figure respectively correspond to light beams indicated by the same reference numerals on the upper side of Table 4.
- FIG. 6 is a longitudinal spherical aberration diagram of Example 3. B1 to B5, D1 to D5, and C1 to C5 in the figure respectively correspond to light beams indicated by the same reference numerals on the lower side of Table 4.
- FIG. 4 is a diagram schematically showing a configuration of the optical pickup apparatus PU1 of the present embodiment that can appropriately record and / or reproduce information on BD, DVD, and CD, which are different optical disks.
- Such an optical pickup device PU1 can be mounted on an optical information recording / reproducing device.
- the first optical disc is a BD
- the second optical disc is a DVD
- the third optical disc is a CD.
- the present invention is not limited to the present embodiment.
- the optical pickup device PU1 shown in FIG. 4 emits light when recording / reproducing information with respect to the objective lens OL, the ⁇ / 4 wavelength plate QWP, the collimating lens COL, the polarization beam splitter BS, the dichroic prism DP, and BD.
- the first optical path difference providing structure formed on the objective lens OL makes the first light amount of the first light flux that has passed through the first optical path difference providing structure larger than any other order of the diffracted light amount.
- the 0th-order diffracted light amount of the second light beam that has passed through the providing structure is made larger than any other order diffracted light amount, and the 0th-order diffracted light amount of the third light beam that has passed through the first optical path difference providing structure is set to any other order.
- the second optical path difference providing structure formed on the objective lens OL makes the second order diffracted light quantity of the first light beam that has passed through the second optical path difference providing structure larger than any other order diffracted light quantity.
- the first-order diffracted light amount of the second light beam that has passed through the optical path difference providing structure is made larger than any other order of diffracted light amount
- the first-order diffracted light amount of the third light beam that has passed through the second optical path difference providing structure is It is made larger than the diffracted light quantity of any order.
- the following formula 0.08 ⁇ P1 / P ⁇ 0.15 (2) 0.02 ⁇
- P1 Power of the first optical path difference providing structure
- P2 Power of the second optical path difference providing structure
- P Power of the entire objective lens, P> 0 Meet.
- the light beam condensed by the central region, the intermediate region, and the peripheral region of the objective lens OL becomes a spot formed on the information recording surface RL1 of the BD through the protective substrate PL1 having a thickness of 0.1 mm. .
- the reflected light beam modulated by the information pits on the information recording surface RL1 is again transmitted through the objective lens OL and a diaphragm (not shown), and then converted from circularly polarized light to linearly polarized light by the ⁇ / 4 wavelength plate QWP, and by the collimating lens COL.
- a converged light beam is reflected by the polarization beam splitter BS, and converges on the light receiving surface of the light receiving element PD via the sensor lens SEN.
- the information recorded on the BD can be read by using the output signal of the light receiving element PD to focus or track the objective lens OL by the biaxial actuator AC1.
- the spherical aberration generated due to the wavelength fluctuation or different information recording layers is changed in magnification. Correction can be made by changing the divergence angle or convergence angle of the light beam incident on the objective optical element OL by changing the collimating lens COL as means in the optical axis direction.
- the ⁇ / 4 wavelength plate QWP converts the linearly polarized light into circularly polarized light and enters the objective lens OL.
- the light beam condensed by the central region and the intermediate region of the objective lens OL (the light beam that has passed through the peripheral region is flared and forms a spot peripheral part) is passed through the protective substrate PL2 having a thickness of 0.6 mm.
- the spot is formed on the information recording surface RL2 of the DVD and forms the center of the spot.
- the reflected light beam modulated by the information pits on the information recording surface RL2 is transmitted again through the objective lens OL, converted from circularly polarized light to linearly polarized light by the ⁇ / 4 wave plate QWP, and converted into a convergent light beam by the collimating lens COL.
- the light is reflected by the polarization beam splitter BS and converges on the light receiving surface of the light receiving element PD via the sensor lens SEN.
- the information recorded on DVD can be read using the output signal of light receiving element PD.
- the light beam condensed by the central region of the objective lens OL (the light beam that has passed through the intermediate region and the peripheral region is flared to form a spot peripheral portion) is passed through the protective substrate PL3 having a thickness of 1.2 mm.
- the spot is formed on the information recording surface RL3 of the CD.
- the reflected light beam modulated by the information pits on the information recording surface RL3 is transmitted again through the objective lens OL, converted from circularly polarized light to linearly polarized light by the ⁇ / 4 wave plate QWP, and converted into a convergent light beam by the collimating lens COL.
- the light is reflected by the polarization beam splitter BS and converges on the light receiving surface of the light receiving element PD via the sensor lens SEN.
- the information recorded on CD can be read using the output signal of light receiving element PD.
- a power of 10 (for example, 2.5 ⁇ 10 ⁇ 3 ) may be expressed using E (for example, 2.5 ⁇ E ⁇ 3).
- the optical surface of the objective lens is formed as an aspherical surface that is symmetric about the optical axis and is defined by a mathematical formula in which the coefficients shown in Table 1 are substituted into Formula 1.
- X (h) is an axis in the optical axis direction (the light traveling direction is positive)
- ⁇ is a conical coefficient
- Ai is an aspherical coefficient
- h is a height from the optical axis
- r is a paraxial radius of curvature. It is.
- the optical path difference given to the light flux of each wavelength by the diffractive structure is defined by an equation in which the coefficient shown in the table is substituted into the optical path difference function of Formula 2. .
- ⁇ is the wavelength of the incident light beam
- ⁇ B is the design wavelength (also called a blazed wavelength in the case of a blazed diffraction structure)
- dor is the diffraction order
- C 2i is a coefficient of the optical path difference function.
- Example 1 shows lens data of Example 1. Further, FIG. 5 shows a conceptual diagram of the first optical path difference providing structure (diffractive structure 1) that is the step type of the first embodiment (FIG. 5 is a conceptual diagram different from the actual shape of the first embodiment). .
- the second optical path difference providing structure of Example 1 is a blazed diffractive structure.
- the steps d and d1 in the examples indicate the theoretical steps in the optical axis direction when the optical path difference providing structure is formed on the parallel plate, and the on-axis thickness is the thickest as in the present embodiment. If a ring-shaped optical path difference providing structure centered on the optical axis is formed on the aspheric lens, the step tends to increase as the distance from the optical axis increases. However, in the case of an objective lens having an NA of about 0.8, the step d1 hardly exceeds (3.0 ⁇ ⁇ 1 / (n1-1)).
- Example 2 shows lens data of Example 2.
- the first optical path difference providing structure (diffraction structure 1) of the step type of the second embodiment is the same as that shown in FIG.
- the second optical path difference providing structure of Example 2 is a blazed diffractive structure.
- Example 3 shows lens data of Example 3. Further, the first optical path difference providing structure of Example 3 is a blazed diffractive structure, and the second optical path difference providing structure is a blazed diffractive structure.
- Table 4 shows the relationship of the light intensity of the diffracted light of each example.
- a third-order diffracted light is generated as light, and a zeroth-order diffracted light is generated as the third strongest diffracted light.
- 0th order diffracted light is generated as the strongest diffracted light
- 1st order diffracted light is generated as the second strongest diffracted light
- ⁇ 1st order diffracted light is generated as the third strongest diffracted light. Is generated.
- the third order diffracted light is generated as the strongest diffracted light, and the first order diffracted light is generated as the third strongest diffracted light.
- the first-order diffracted light is generated as the strongest diffracted light
- the second-order diffracted light is generated as the second strongest diffracted light
- the zero-order diffracted light is generated as the third strongest diffracted light.
- first-order diffracted light is generated as the strongest diffracted light
- zero-order diffracted light is generated as the second strongest diffracted light
- second-order diffracted light is generated as the third strongest diffracted light.
- a structure in which the diffraction structure 1 and the diffraction structure 2 are superposed by multiplying the diffraction efficiency of each order of diffracted light generated in the diffraction structure 1 and the diffraction efficiency of each order generated in the diffraction structure 2. It can be seen which order of diffraction light is generated most. For example, in a light beam of 405 nm, the diffraction structure 1 generates the most first-order diffracted light, and the diffraction structure 2 generates the most second-order diffracted light. Therefore, naturally, the diffraction order of the diffraction structure 1 and the diffraction structure 2 are diffracted. The combination of order> ⁇ 1,2> is the most frequently generated diffracted light.
- FIG. 6 is a longitudinal spherical aberration diagram of the objective lens of Example 1.
- the second-order diffracted light (B1) is emitted, the amount of light emitted becomes maximum (efficiency 72%), and the third-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure for the second time.
- the amount of light emitted when the folded light (B2) is emitted is the second highest, and the 0th-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and exits the second-order diffracted light (B3).
- the third-order diffracted light is the third highest, and the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference-providing structure and the third-order diffracted light (B4) is emitted.
- the first-order diffracted light emitted from the first optical path difference providing structure is the second optical path difference.
- the amount of light emitted upon exiting the first-order diffracted light (B5) and enters the given structure is high fifth.
- the spherical aberration curves of the light beams B4 and B5 which are unnecessary light are close to the spherical aberration of the light beam B1 used when the BD is used.
- the first optical path difference providing structure and the second optical path difference providing structure are given power so that the unnecessary light beams B4 and B5 are on the optical axis. The condensing position can be shifted from the used light beam B1, thereby suppressing reading errors and the like.
- the 0th-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and the first-order diffracted light ( D1) is emitted in the maximum amount (efficiency 42%)
- the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure to emit the first-order diffracted light (D2).
- the amount of light emitted when the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and is emitted from the first-order diffracted light (D3).
- the third highest light output when the 0th-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and the second-order diffracted light (D4) is emitted is the fourth highest, and the first The zero-order diffracted light emitted from the optical path difference providing structure enters the second optical path difference providing structure. It shines and 0 the amount of light emitted upon exiting order diffracted light (D5) is high fifth.
- the spherical aberration curves of the light beams D4 and D5 that are unnecessary light are close to the spherical aberration of the light beam D1 used when the DVD is used.
- the first optical path difference providing structure and the second optical path difference providing structure are given power so that the unnecessary light beams D4 and D5 are on the optical axis.
- the condensing position can be shifted from the used light beam D1, thereby suppressing reading errors and the like.
- the 0th-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and the first-order diffracted light
- the amount of light emitted when C1) is emitted is maximized (efficiency 60%)
- the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure to emit the first-order diffracted light (C2).
- the amount of light emitted when the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference-providing structure and the first-order diffracted light (not shown) is emitted. Is the third highest, and the amount of emitted light when the 0th-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and exits the 0th-order diffracted light (C4) is the fourth highest, The zero-order diffracted light emitted from the one optical path difference providing structure is converted into the second optical path difference providing structure. Quantity of light emitted when emitted incident to the second-order diffracted light (C5) to a higher fifth.
- the spherical aberration curves of the light beams C4 and C5 which are unnecessary light are close to the spherical aberration of the light beam C1 used when the CD is used.
- the efficiency of the unnecessary light beams C4 and C5 increases due to a manufacturing error or the like, by giving power to the first optical path difference providing structure and the second optical path difference providing structure, the unnecessary light beams C4 and C5 on the optical axis.
- the condensing position can be shifted from the used light beam C1, thereby suppressing reading errors and the like.
- FIG. 7 is a longitudinal spherical aberration diagram of the objective lens of Example 2.
- the second-order diffracted light (B1) is emitted, the amount of light emitted becomes the maximum (efficiency 72%), and the 0th-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and the second-order diffracted light.
- the second-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and exits the second-order diffracted light (B3) Is the third highest, and the first order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and the third order diffracted light (B4) is emitted fourth.
- the first-order diffracted light emitted from the first optical path difference providing structure is high and has the second optical path difference.
- the amount of light emitted upon exiting the first-order diffracted light (B5) is incident on the structure is high fifth.
- the spherical aberration curves of the light beams B4 and B5 that are unnecessary light are close to the spherical aberration of the light beam B1 used when the BD is used.
- the first optical path difference providing structure and the second optical path difference providing structure are given power so that the unnecessary light beams B4 and B5 are on the optical axis. The condensing position can be shifted from the used light beam B1, thereby suppressing reading errors and the like.
- the 0th-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and the first-order diffracted light ( D1) is emitted in the maximum amount (efficiency 42%)
- the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure to emit the first-order diffracted light (D2).
- the amount of light emitted when the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and is emitted from the first-order diffracted light (D3).
- the third highest light output when the 0th-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and the second-order diffracted light (D4) is emitted is the fourth highest, and the first The zero-order diffracted light emitted from the optical path difference providing structure enters the second optical path difference providing structure. It shines and 0 the amount of light emitted upon exiting order diffracted light (D5) is high fifth.
- the spherical aberration curves of the light beams D4 and D5 which are unnecessary light are close to the spherical aberration of the light beam D1 used when the DVD is used.
- the first optical path difference providing structure and the second optical path difference providing structure are given power so that the unnecessary light beams D4 and D5 are on the optical axis.
- the condensing position can be shifted from the used light beam D1, thereby suppressing reading errors and the like.
- the 0th-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and the first-order diffracted light
- the amount of light emitted when C1) is emitted is maximized (efficiency 60%)
- the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure to emit the first-order diffracted light (C2).
- the amount of emitted light is the second highest, and the amount of emitted light when the ⁇ 1st order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and exits the first order diffracted light (C3).
- the third highest light output when the 0th order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and the 0th order diffracted light (C4) is emitted is the fourth highest, and the first The 0th-order diffracted light emitted from the optical path difference providing structure is the second optical path difference providing structure.
- Quantity of light emitted when emitted incident to the second-order diffracted light (C5) is high fifth.
- the spherical aberration curves of the light beams C4 and C5 which are unnecessary light are close to the spherical aberration of the light beam C1 used when the CD is used.
- the efficiency of the unnecessary light beams C4 and C5 increases due to a manufacturing error or the like, by giving power to the first optical path difference providing structure and the second optical path difference providing structure, the unnecessary light beams C4 and C5 on the optical axis.
- the condensing position can be shifted from the used light beam C1, thereby suppressing reading errors and the like.
- FIG. 8 is a longitudinal spherical aberration diagram of the objective lens of Example 3.
- the second-order diffracted light (B1) is emitted, the amount of light emitted becomes maximum (efficiency 72%), and the third-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure for the second time.
- the amount of light emitted when the folded light (B2) is emitted is the second highest, and the 0th-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and emitted the second-order diffracted light (B3).
- the third-order diffracted light is the third highest, and the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference-providing structure and the third-order diffracted light (B4) is emitted.
- the first-order diffracted light emitted from the first optical path difference providing structure is the second optical path difference.
- the amount of light emitted upon exiting the first-order diffracted light (B5) and enters the given structure is high fifth.
- the spherical aberration curves of the light beams B4 and B5 which are unnecessary light are close to the spherical aberration of the light beam B1 used when the BD is used.
- the first optical path difference providing structure and the second optical path difference providing structure are given power so that the unnecessary light beams B4 and B5 are on the optical axis. The condensing position can be shifted from the used light beam B1, thereby suppressing reading errors and the like.
- the 0th-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and the first-order diffracted light ( D1) is emitted in the maximum amount (efficiency 42%)
- the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure to emit the first-order diffracted light (D2).
- the amount of light emitted when the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and is emitted from the first-order diffracted light (D3) is the second highest.
- the third highest light output when the 0th-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and the second-order diffracted light (D4) is emitted is the fourth highest, and the first The zero-order diffracted light emitted from the optical path difference providing structure enters the second optical path difference providing structure. It shines and 0 the amount of light emitted upon exiting order diffracted light (D5) is high fifth.
- the spherical aberration curves of the light beams D4 and D5 that are unnecessary light are close to the spherical aberration of the light beam D1 used when the DVD is used.
- the first optical path difference providing structure and the second optical path difference providing structure are given power so that the unnecessary light beams D4 and D5 are on the optical axis.
- the condensing position can be shifted from the used light beam D1, thereby suppressing reading errors and the like.
- the 0th-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and the first-order diffracted light
- the amount of light emitted when C1) is emitted is maximized (efficiency 60%)
- the first-order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure to emit the first-order diffracted light (C2).
- the amount of emitted light is the second highest, and the amount of emitted light when the ⁇ 1st order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and exits the first order diffracted light (C3).
- the third highest light output when the 0th order diffracted light emitted from the first optical path difference providing structure is incident on the second optical path difference providing structure and the 0th order diffracted light (C4) is emitted is the fourth highest, and the first The 0th-order diffracted light emitted from the optical path difference providing structure is the second optical path difference providing structure.
- Quantity of light emitted when emitted incident to the second-order diffracted light (C5) is high fifth.
- the spherical aberration curves of the light beams C4 and C5 which are unnecessary light are close to the spherical aberration of the light beam C1 used when the CD is used.
- the efficiency of the unnecessary light beams C4 and C5 increases due to a manufacturing error or the like, by giving power to the first optical path difference providing structure and the second optical path difference providing structure, the unnecessary light beams C4 and C5 on the optical axis.
- the condensing position can be shifted from the used light beam C1, thereby suppressing reading errors and the like.
- Table 5 summarizes the numerical values that are characteristic of Examples 1 to 3.
- the light beam emitted from the light source may first pass through the second optical path difference providing structure and then pass through the first optical path difference providing structure.
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Abstract
Description
前記対物レンズは、通過する第1波長λ1の第1光束に回折作用を与えるが、第2波長λ2の第2光束及び第3波長λ3の第3光束に回折作用を与えない第1光路差付与構造と、ブレーズ形状を有する第2光路差付与構造とを有し、
前記第2光路差付与構造の段差d1(nm)は、前記対物レンズの素材の前記第1波長に対する屈折率をn1としたときに、以下の式を満たし、
(1.8×λ1/(n1-1))≦d1≦(3.0×λ1/(n1-1))
(1)
前記第1光路差付与構造と前記第2光路差付与構造は、共にパワーを持つことを特徴とする。
0.08≦P1/P≦0.15 (2)
0.02≦│P2/P│≦0.05 (3)
但し、
P1:前記第1光路差付与構造のパワー
P2:前記第2光路差付与構造のパワー
P :前記対物レンズ全体のパワーであって、P>0
を満たすことを特徴とする。
0.050mm≦t1≦0.125mm (4)
0.5mm≦t2≦0.7mm (5)
1.0mm≦t3≦1.3mm (6)
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 (7)
1.8・λ1<λ3<2.0・λ1 (8)
を満たすことが好ましい。
d=(1×λB)/(n1-1) (9)
但し、λBはブレーズ化波長(220nm≦λB≦330nm)、n1はブレーズ型構造の波長λ1(nm)に対する屈折率である。
(0.54λ1/(n1-1))≦d≦(0.81λ1/(n1-1))
(9)′
で表せる。
(1.8×λ1/(n1-1))≦d1≦(3.0×λ1/(n1-1))
(1)
第1光路差付与構造と前記第2光路差付与構造は、共に近軸パワーを持つ。
0.08≦P1/P≦0.15 (2)
0.02≦│P2/P│≦0.05 (3)
但し、
P1:第1光路差付与構造のパワー
P2:第2光路差付与構造のパワー
P :対物レンズ全体のパワーであって、P>0
を満たすと好ましい。
P=-2×B1×mλ (10)
但し、B1は光路差関数係数であり、mは回折次数であり、λは波長である。
1.0≦dt/f≦1.5 (11)
但し、dt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(mm)を表す。
-0.01<m1<0.01 (12)
を満たすことが好ましい。
-0.01<m2<0.01 (13)
を満たすことが好ましい。
-0.025<m2≦-0.01 (13)′
を満たすことが好ましい。
-0.01<m3<0.01 (14)
を満たすことが好ましい。
-0.025<m3≦-0.01 (14)′
を満たすことが好ましい。
0.08≦P1/P≦0.15 (2)
0.02≦│P2/P│≦0.05 (3)
但し、
P1:第1光路差付与構造のパワー
P2:第2光路差付与構造のパワー
P :対物レンズ全体のパワーであって、P>0
を満たす。
実施例1のレンズデータを表1に示す。又、実施例1の階段型である第1光路差付与構造(回折構造1)の概念図を図5に示す(図5は実施例1の実際の形状とは異なり、あくまでも概念図である)。実施例1の第2光路差付与構造はブレーズ型回折構造である。実施例1の対物レンズは、波長λ1の光束に関してf=2.2mmの焦点距離を有し、P2/Pは負であり、第1光路差付与構造の設計波長λBを0.25×0.405μmとして、第1光路差付与構造の段差d=0.25×0.405μm/(1.525-1)=0.193μmである。又、第1波長λ1を0.405μm(=405nm)として、第2光路差付与構造の段差d1=2×0.405μm/(1.525-1)=1.543μmであるので式(1)を満たしている(但し、対物レンズの素材の屈折率n1=1.525とする)。尚、実施例の段差d、d1は、平行平板上に光路差付与構造を形成した場合の光軸方向の理論的な段差量を示しており、本実施の形態のごとき軸上厚が最も厚くなる非球面のレンズに、光軸を中心とした輪帯状の光路差付与構造を形成すると、光軸から離れるに従って段差は大きくなる傾向がある。但し、NA0.8前後の対物レンズの場合、段差d1は、(3.0×λ1/(n1-1))を超えることは殆どない。
実施例2のレンズデータを表2に示す。又、実施例2の階段型である第1光路差付与構造(回折構造1)は図5に示すものと同じである。実施例2の第2光路差付与構造はブレーズ型回折構造である。実施例2の対物レンズは、波長λ1の光束に関してf=2.2mmの焦点距離を有し、P2/Pは正であり、第1光路差付与構造の設計波長λBを0.25×0.405μmとして、第1光路差付与構造の段差d=0.25×0.405μm/(1.525-1)=0.193μmである。又、第1波長λ1を0.405μm(=405nm)として、第2光路差付与構造の段差d1=2×0.405μm/(1.525-1)=1.543μmであるので式(1)を満たしている(但し、対物レンズの素材の屈折率n1=1.525とする)。
実施例3のレンズデータを表3に示す。又、実施例3の第1光路差付与構造はブレーズ型回折構造であり、第2光路差付与構造はブレーズ型回折構造である。実施例3の対物レンズは、波長λ1の光束に関してf=1.8mmの焦点距離を有し、P2/Pは負であり、ブレーズ化波長λB=0.2847μmとして、第1光路差付与構造の段差d=0.2847μm/(1.525-1)=0.542μmである。又、第1波長λ1を0.405μm(=405nm)として、第2光路差付与構造の段差d1=2×0.405μm/(1.525-1)=1.543μmであるので式(1)を満たしている(但し、対物レンズの素材の屈折率n1=1.525とする)。
BS 偏光ビームスプリッタ
CN 中央領域
COL コリメートレンズ
DP ダイクロイックプリズム
LD1 第1半導体レーザ
LD2 第2半導体レーザ
LD3 第3半導体レーザ
LDP レーザユニット
MD 中間領域
OL 対物レンズ
OT 周辺領域
PD 受光素子
PL1 保護基板
PL2 保護基板
PL3 保護基板
PU1 光ピックアップ装置
QWP λ/4波長板
RL1 情報記録面
RL2 情報記録面
RL3 情報記録面
SEN センサレンズ
Claims (10)
- 第1波長λ1(nm)の第1光束を射出する第1光源と、第2波長λ2(nm)(λ2>λ1)の第2光束を射出する第2光源と、第3波長λ3(nm)(λ3>λ2)の第3光束を射出する第3光源とを有し、前記第1光束を用いて厚さがt1の保護基板を有する第1光ディスクの情報の記録及び/又は再生を行い、前記第2光束を用いて厚さがt2(t1<t2)の保護基板を有する第2光ディスクの情報の記録及び/又は再生を行い、前記第3光束を用いて厚さがt3(t2<t3)の保護基板を有する第3光ディスクの情報の記録及び/又は再生を行う光ピックアップ装置において用いられる対物レンズであって、
前記対物レンズは、通過する第1波長λ1の第1光束に回折作用を与えるが、第2波長λ2の第2光束及び第3波長λ3の第3光束に回折作用を与えない第1光路差付与構造と、ブレーズ形状を有する第2光路差付与構造とを有し、
前記第2光路差付与構造の段差d1(nm)は、前記対物レンズの素材の前記第1波長に対する屈折率をn1としたときに、以下の式を満たし、
(1.8×λ1/(n1-1))≦d1≦(3.0×λ1/(n1-1))
(1)
前記第1光路差付与構造と前記第2光路差付与構造は、共にパワーを持つことを特徴とする対物レンズ。 - 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。
0.08≦P1/P≦0.15 (2)
0.02≦│P2/P│≦0.05 (3)
但し、
P1:前記第1光路差付与構造のパワー
P2:前記第2光路差付与構造のパワー
P:前記対物レンズ全体のパワーであって、P>0 - P2/Pは正であることを特徴とする請求項2に記載の対物レンズ。
- P2/Pは負であることを特徴とする請求項2に記載の対物レンズ。
- 前記第1光路差付与構造は、ブレーズ形状を有することを特徴とする請求項1~4のいずれかに記載の対物レンズ。
- 前記第1光路差付与構造は、階段形状を有することを特徴とする請求項1~4のいずれかに記載の対物レンズ。
- 前記第1光路差付与構造は、前記第1光路差付与構造を通過した第1光束の1次の回折光量を他のいかなる次数の回折光量よりも大きくし、前記第1光路差付与構造を通過した第2光束の0次の回折光量を他のいかなる次数の回折光量よりも大きくし、前記第1光路差付与構造を通過した第3光束の0次の回折光量を他のいかなる次数の回折光量よりも大きくし、
前記第2光路差付与構造は、前記第2光路差付与構造を通過した第1光束の2次の回折光量を他のいかなる次数の回折光量よりも大きくし、前記第2光路差付与構造を通過した第2光束の1次の回折光量を他のいかなる次数の回折光量よりも大きくし、前記第2光路差付与構造を通過した第3光束の1次の回折光量を他のいかなる次数の回折光量よりも大きくすることを特徴とする請求項1~6のいずれかに記載の対物レンズ。 - 前記第1光路差付与構造と前記第2光路差付与構造とが重畳されていることを特徴とする請求項1~7のいずれかに記載の対物レンズ。
- 請求項1~8のいずれかに記載の対物レンズを有することを特徴とする光ピックアップ装置。
- 請求項9に記載の光ピックアップ装置を有することを特徴とする光情報記録再生装置。
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