WO2004012188A1 - 位相補正素子および光ヘッド装置 - Google Patents
位相補正素子および光ヘッド装置 Download PDFInfo
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- WO2004012188A1 WO2004012188A1 PCT/JP2003/009746 JP0309746W WO2004012188A1 WO 2004012188 A1 WO2004012188 A1 WO 2004012188A1 JP 0309746 W JP0309746 W JP 0309746W WO 2004012188 A1 WO2004012188 A1 WO 2004012188A1
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- wavelength
- light
- phase
- phase correction
- refractive index
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Classifications
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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
- G11B7/1365—Separate or integrated refractive elements, e.g. wave plates
- G11B7/1367—Stepped phase plates
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/0025—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for optical correction, e.g. distorsion, aberration
- G02B27/0037—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for optical correction, e.g. distorsion, aberration with diffracting elements
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/42—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect
- G02B27/4233—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect having a diffractive element [DOE] contributing to a non-imaging application
- G02B27/4238—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect having a diffractive element [DOE] contributing to a non-imaging application in optical recording or readout devices
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/42—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect
- G02B27/4261—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect having a diffractive element with major polarization dependent properties
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/30—Polarising elements
-
- 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
- G11B7/125—Optical beam sources therefor, e.g. laser control circuitry specially adapted for optical storage devices; Modulators, e.g. means for controlling the size or intensity of optical spots or optical traces
- G11B7/127—Lasers; Multiple laser arrays
- G11B7/1275—Two or more lasers having different wavelengths
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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
-
- 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
- G11B7/1392—Means for controlling the beam wavefront, e.g. for correction of aberration
- G11B7/13922—Means for controlling the beam wavefront, e.g. for correction of aberration passive
-
- 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 a phase correction element and an optical head device, and more particularly to a phase correction element mounted on an optical head device used for recording and Z or reproduction of information on three types of optical recording media having different wavelengths used, and a phase correction element for the same.
- the present invention relates to an optical head device. Background art
- optical recording media for recording and Z or reproducing information
- optical head devices capable of recording and Z or reproducing information on and from this optical recording medium
- optical recording media for CDs are optical discs with a cover thickness of 1.2 mm for protecting the information recording surface, and are used as light sources for information recording and Z or playback.
- a semiconductor laser with a 780 nm wavelength band and an objective lens with NA (numerical aperture) of 0.44 to 0.51 are used.
- optical discs for DVDs are optical discs with a cover thickness of 0.6 mm, and a semiconductor laser with a 650 nm wavelength band and a NA of 0.60 to 0.65 as a light source for recording and / or reproducing information. Are used.
- an optical disk with a cover thickness of 0.1 mm using a semiconductor laser in the 41 Onm wavelength band and an objective lens with a NA of 0.85 as a light source has been proposed.
- the optical disk used for the semiconductor laser in the 41 Onm wavelength band is referred to as an HD optical disk in particular.
- ⁇ light in the wavelength band of 410 nm is light with a wavelength of approximately 390 nm to approximately 430 ⁇ m
- the numerical aperture N of the objective lens used for HD, DVD and CD The A and NA have NA 2, NA 3, respectively, NA i zeros. 8 5 about, NA 2 0s. 6 0 at 0. 6 5 approximately, NA 3 0s. 4 4 at 0. 5 1 value of about Is used.
- phase difference caused by the difference between the ordinary refractive index and the extraordinary refractive index of the birefringent material with respect to the ordinary polarized light and the extraordinary polarized light
- birefringent phase difference does not depend on the polarization dependence of the refractive index.
- the term is used to distinguish the term from the ordinary phase difference corresponding to the optical path length difference.
- phase difference is described in radians (rad), but when expressed in wavelength units, it is called “wavelength phase difference”.
- the three types of optical disks for CD, DVD and HD have different cover thicknesses and wavelengths.
- an objective lens designed for one type of optical disk is temporarily attached, and information is recorded and recorded on the optical disk by using these optical disks interchangeably.
- Z or reproduction for example, when this optical head device is used for recording and Z or reproduction on another type of optical disk than the above-mentioned optical disk, a large spherical aberration occurs, and information recording and There was a problem with Z or playback not possible.
- Patent Literature 1 Patent No. 27131325
- Patent Literature 2 Patent No. 2725653
- Patent Document 1 proposes an aperture limiting element that switches NA by diffraction.
- the phase of the transmitted light of the wavelength ⁇ 2 is aligned so that the multilayer filter 1 2 0 in the circular region is used.
- a phase compensation film 1300 for phase adjustment is formed.
- An optical head device that can reduce the spherical aberration generated due to the difference in the cover thickness of the optical disk can be configured.
- the residual spherical aberration is reduced by making divergent light the incident light of wavelength ⁇ 3 with respect to the objective lens.
- Patent Document 2 proposes a phase correction element that generates a spherical aberration by diffracting light having a second wavelength different from that, and cancels the spherical aberration of the objective lens.
- an optical head device that records and / or reproduces information on an optical recording medium on an optical disk such as a CD or DVD
- the light emitted from a semiconductor laser as a light source is focused on the optical recording medium by an objective lens.
- the return light reflected by the optical recording medium is guided by a beam splitter to a light receiving element, which is a photodetector, and the information on the optical recording medium is converted into an electric signal.
- the polarization beam splitter transmits linearly polarized light of a polarization plane in a specific direction emitted from a light source on the outward path, reflects or diffracts on the return path linearly polarized light that has been reflected by the optical recording medium and has become a plane of polarization orthogonal to the outward path.
- the direction of light can be switched to a photodetector.
- a phase plate (1Z4 wavelength plate) having a birefringence phase difference of 2 with respect to the wavelength of the incident light is used in order to set the polarization plane of the return path to linearly polarized light orthogonal to the outward path. It is located in the optical path of the evening and optical recording media.
- the HD since there is no phase compensator for three wavelengths that can record and / or reproduce information on the three types of optical discs, DVD and CD, a single objective lens can be used to collect information on these three types of optical discs. Recording and / or playback was difficult.
- the aperture limiting element 100000 shown in FIG. The first annular region obtained by subtracting the circular region of the numerical aperture of DVD NA 2 (where NA X > NA 2 ) from the circular region of the numerical aperture of It was not wavelength selective fill evening function transmits 2 and wavelength lambda 3 of the incident light has to be added.
- D VD aperture Nyuarufa 2 circular area or al aperture Nyuarufa 3 of CD (but, ⁇ 2> ⁇ 3) to the second annular region that obtained by subtracting the circular area, the wavelength ⁇ it is necessary to add a wavelength selective fill evening function which does not transmit through the i and wavelength lambda 2 of the incident light incident light having a wavelength lambda 3.
- a multilayer film having a different spectral transmittance is formed in each of the first annular region and the second annular region by dividing the region. It must be an extremely complex process and the numerical aperture ⁇ ! The it is difficult to stably produce a degraded without aperture limiting element of the transmitted wavefront aberration for incident light of wavelength lambda chi in the entire surface.
- the transmitted wavefront means a wavefront of light transmitted through an optical element such as a phase correction element.
- the birefringence phase difference of Paizeta 2 with respect to the wavelength E, the wavelength lambda 2 Contact and wavelength lambda 3 of phases that no position phase plate causing deterioration of the characteristics of the phase correction device is integrated with respect to the wavelength A correction element has been required.
- the present invention has been made in order to solve the above-mentioned drawbacks, and is intended to record and / or reproduce information on three types of optical disks, HD, DVD and CD, using a single objective lens for HD. It is intended to provide a phase correction element and an optical head device that can be used. Disclosure of the invention
- the present invention relates to a phase complementary element that transmits light of three wavelengths ⁇ 2 and ⁇ 3 ( ⁇ ⁇ 2 ⁇ 3 ), wherein the numerical aperture is within the plane of the phase correction element where the light is incident.
- eight second realm and numerical aperture ⁇ numerical aperture comprising a second region and a region of (NA 1> NA 2), in the region of the aperture NA 2, serrated or saw-tooth of the projections is the cross-sectional shape
- a first phase correction layer formed of a saw-toothed or approximated saw-toothed uneven portion whose portion is approximated by a staircase shape and has rotational symmetry with respect to the optical axis of the incident light;
- the correction layer and the first phase plate that generates an odd-numbered birefringence phase difference of 7tZ2 with respect to the incident light of the linearly polarized light having the wavelength ⁇ and converts it into circularly polarized light are integrally formed.
- Wavelength incident on the numerical aperture NA i! Function of the transmitted wavefront of light is a regardless invariant involved in its polarization state, the wavelength lambda 2 of the light incident on the area of the numerical aperture NA 2 or transmitted wavefront of light of wavelength lambda 2 and wavelength lambda 3, the changing A phase correction element characterized by having:
- the first phase correction layer includes a first translucent material and a second translucent material having different refractive indices and wavelength dispersions, and the refractive index difference ⁇ ⁇
- the refractive index difference ⁇ ⁇ shall apply at wavelengths's 2 and wavelength lambda 3 in finite value with a zero at a wavelength of said first light-transmissive material, the approximate cross-section shape of the serrated or sawtooth respective protrusions stepped shape And a sawtooth-shaped uneven portion having rotational symmetry with respect to the optical axis of the incident light, at least a concave portion of the uneven portion is filled with the second light-transmitting material, and a refractive index at a wavelength ⁇ 2
- a second phase correction element is provided in which the height d of each of the saw-tooth-shaped convex portions satisfies the following equation: ⁇ 2 ⁇ 2 ⁇ !
- the first phase correction layer is A third phase correction element in which each tooth-like convex portion is approximated by a staircase shape, and the phase difference of transmitted light of wavelength ⁇ , with respect to the convex and concave portions of each step of the staircase shape, is a natural number multiple of 47 °. I will provide a.
- + ⁇ 2 ) / 2 is composed of two phase plates with a birefringence phase difference of Tt and ⁇ 2 stacked so that the angle between their optical axes is 57 ⁇ 5 °.
- a fourth phase correction element for generating a birefringent phase difference of an odd multiple of ⁇ / 2 with respect to the linearly polarized incident light in the wavelength band of ⁇ 2 to convert the light into circularly polarized light.
- a second phase correction layer is formed in a region of a numerical aperture ⁇ 3 ( ⁇ 2 > 3 ) in a plane thereof;
- the phase correction layer has an ordinary refractive index ⁇ .
- a birefringent material layer in which the optical axis of the refractive index ellipsoid is aligned in one direction with an extraordinary refractive index ne (n e ⁇ n.).
- the portion is approximated by a step-like shape, and is composed of a saw-toothed uneven portion having rotational symmetry with respect to the optical axis of the incident light, and at least the concave portion of the uneven portion has an ordinary light refractive index n.
- a transparent material is filled with a refractive index n s that is substantially equal to the extraordinary light refractive index n e, and transmitted light of extraordinary polarized light or ordinary polarized light of wavelength ⁇ i with respect to the convex portions and concave portions of each step of the step-shaped grating.
- a fifth complementary element whose phase difference is an odd multiple of 27T.
- the first phase plate generates a birefringent phase difference of an odd multiple of ⁇ / 2 with respect to the linearly polarized incident light having the wavelength ⁇ and converts the linearly polarized incident light into circularly polarized light.
- a sixth phase correction element having a function of rotating the polarization plane by generating birefringence position phase difference of an odd multiple of ⁇ with respect to linearly polarized incident light having a wavelength of lambda 2 and wavelength lambda 3, the first In the phase compensating element of 6, the first phase plate has an angle of 45 ⁇ 5 ° between two optical phase plates whose birefringence phase difference with respect to wavelength is 7 ° / 2 and 7C.
- a seventh phase correction element having a configuration stacked as follows. Further, in the first phase correction element, the first phase correction layer has an ordinary light refractive index n. And a birefringent material layer having an extraordinary refractive index n e (n. ⁇ n e ) and an optical axis of a refractive index ellipsoid aligned in one direction, wherein the birefringent material layer has a sawtooth or sawtooth cross-sectional shape.
- Each of the convex portions is approximated by a step-like shape, and has a saw-tooth-shaped uneven portion having rotational symmetry with respect to the optical axis of the incident light.
- At least the concave portion of the uneven portion has an ordinary refractive index n. Or the extraordinary light refractive index n.
- a first polarization phase correction layer and a second polarization phase correction layer having a structure filled with a homogeneous refractive index transparent material having a refractive index n s substantially equal to the first phase plate.
- the second phase plate has a function of rotating the plane of polarization by generating a birefringent phase difference that is an odd multiple of the linearly polarized incident light, and the second phase plate includes:
- the present invention provides an eighth compensating element which is arranged and integrated in the order of a phase plate and a second polarizing phase correcting layer.
- a ninth phase correction element in which a diffraction grating having a phase difference of 10 ⁇ is formed.
- a tenth phase correction element, wherein a diffraction grating of ⁇ is formed
- the annular region in the ninth phase correction element in which the diffraction grating or the multilayer filter is formed or the first and the tenth phase correction elements in the tenth phase correction element for the second pre-Symbol circular area of each annular area and numerical aperture ⁇ 3, providing a first first phase correcting element according to feature the phase difference of incident light having a wavelength lambda i is an integer multiple of 27T I do.
- a light source that emits light of three wavelengths in the 5 O nm wavelength band and ⁇ 3 780 nm wavelength band, an objective lens that focuses the emitted light of three wavelengths on the optical recording medium, and optical recording that is focused
- a light head device comprising at least a light detector that detects light reflected by a medium, wherein the light source that emits the three wavelengths of light and an optical path leading to an optical recording medium include:
- An optical head device provided with the phase correction element according to the eleventh aspect is provided.
- FIG. 1 is a cross-sectional view showing a configuration of the phase correction element according to the first and second embodiments of the present invention.
- FIG. 2 is a plan view showing a configuration of the phase correction element according to the first and second embodiments of the present invention.
- Figure 3 shows the wavefront aberration of the transmitted light in a DVD or CD optical disc.
- 5A is a graph, in which (A) shows a wavefront aberration generated by the phase correction element of the present invention, and (B) shows a wavefront aberration of transmitted light in an optical disk for DVD or CD.
- FIG. 4 is a cross-sectional view illustrating a configuration of a phase correction element according to the third embodiment of the present invention.
- FIG. 5 is a partially enlarged view of a wavefront aberration showing a wavefront aberration correction action of a first phase correction layer of the phase correction element according to the third embodiment.
- FIG. 6 is a cross-sectional view illustrating a configuration of a phase correction element according to the fourth embodiment of the present invention.
- FIG. 7 is a cross-sectional view illustrating a configuration of a phase correction element according to a fifth embodiment of the present invention.
- FIG. 8 is a plan view showing the configuration of the phase correction element according to the fifth embodiment of the present invention.
- FIG. 9 is a partially enlarged view of a wavefront aberration showing a wavefront aberration correction action of a second phase correction layer of the phase correction element according to the fifth embodiment.
- FIG. 10 is a cross-sectional view illustrating a configuration of a phase correction element according to the sixth embodiment of the present invention.
- FIG. 11 is a cross-sectional view illustrating a configuration of a phase correction element according to a seventh embodiment of the present invention.
- FIG. 12 is a plan view showing the configuration of the phase correction element according to the seventh embodiment of the present invention.
- FIG. 13 is an enlarged cross-sectional view showing the positional relationship between the processing surfaces of the aperture limiting substrate of the seventh phase correction element shown in FIGS. 11 and 12.
- FIG. 14 is a cross-sectional view illustrating a configuration of a phase correction element according to a modification of the seventh embodiment of the present invention.
- FIG. 15 is a configuration diagram showing an optical head device equipped with the phase correction element according to the eighth embodiment.
- FIGS. 16A and 16B are cross-sectional views showing a light beam and a wavefront when light of three different wavelengths enters the phase correction element according to the eighth embodiment, where FIG. 16A is light having a wavelength and FIG. Wavelength ⁇ (C) is light of wavelength ⁇ 3 .
- FIGS. 17A and 17B are cross-sectional views showing a light beam and a wavefront when light of three wavelengths is incident on the phase correction element according to the eighth embodiment.
- FIG. 17A is light having a long wavelength
- (c) is light of wavelength ⁇ 3 .
- FIGS. 18A and 18B are cross-sectional views illustrating a light beam and a wavefront when light of three wavelengths enters the phase correction element according to the eighth embodiment, where FIG. the wavelength lambda 2 of light, (c) the light of the wavelength lambda 3.
- FIG. 19 shows the spectral transmittance of each area of the aperture limiting substrate shown in FIG. 12, wherein (a) is the first annular area (A, (b) is the second annular area (A 2 ), (C) is a graph showing the spectral transmittance in the circular region (A 3 ).
- FIG. 20 is a cross-sectional view showing a configuration of a conventional aperture limiting element.
- FIG. 1 is a cross-sectional view and FIG. 2 is a plan view of a configuration example of a first phase correction element according to a first embodiment of the present invention.
- First phase correction element 100 in accordance with the present embodiment is configured to include a first phase correction layer 1 ratio A and the first phase plate 3 OA which is formed in a region of numerical aperture NA 2.
- the first phase correction layer 10 A the effective diameter of the opening number of units NA i of the phase correction elements corresponding to the optical disc for HD, be formed in a region of numerical aperture NA 2 corresponding to an optical disk for DVD,
- the cross-sectional shape is a saw-tooth shape (so-called blazed diffraction grating type) or a saw-tooth uneven portion in which each protruding portion is approximated by a step-shaped grating and has rotational symmetry with respect to the optical axis of incident light.
- a configuration may be adopted in which the recess is formed on the surface of the light-transmitting substrate 5 and the concave portion has no filler.
- This first phase correction layer 1 OA has the same wavelength as that of the wavelength ⁇ 2 , or the wavelength ⁇ 2 and the wavelength ⁇ 3 , although the transmitted wavefront of light having a wavelength incident on the area of the numerical aperture NA 1 in the plane of the phase correction element is unchanged.
- a transmitted wavefront change can be generated in accordance with the spatial shape distribution of the blazed diffraction grating.
- the wavelength selectivity function of the phase correction layer is based on the difference in the refractive index wavelength dependence and the difference in the refractive index polarization between the translucent material 1 ⁇ and the translucent material 1B, or the phase difference of the processing step of the step grating. It is expressed by utilizing the wavelength dependence and the like.
- the first phase correction element 100 has a first phase plate 3 OA having a birefringence phase difference that is an odd multiple of ⁇ 2 with respect to the wavelength, and the light transmitting substrate 5 and the light transmitting substrate 6. It is sandwiched and integrated.
- the first phase plate 3OA any material may be used as long as the material has birefringence.
- it may be an optical crystal such as a polymer liquid crystal or quartz, or a polycarbonate which exhibits birefringence by uniaxial stretching.
- a polymer liquid crystal is preferable as a phase plate because it has a relatively large value of birefringence, can hold a thin film of 5 or less on a light-transmitting substrate such as glass having excellent flatness, and can be uniformly formed over a large area.
- the linearly polarized light having the wavelength ⁇ i is incident on the polarization plane that forms an angle of 45 ° with the optical axis of the first phase plate 30 A, and the polarization planes are orthogonalized by reciprocating through the first phase plate 3 OA. Converted to linearly polarized light.
- the first phase plate 3OA may be a single layer of a birefringent material, a configuration in which two or more layers are laminated, or a configuration in which two or more translucent substrates are used and a polymer liquid crystal film is sandwiched between them.
- the wavelength dependence of the birefringence phase difference can be controlled by controlling the birefringence wavelength dependence with a birefringent material or by laminating a phase plate.
- wavelength lambda lambda 2 For example, three wavelengths lambda lambda 2, the phase plate and that acts as a 1 Z 4-wave plate with respect to lambda 3 of the incident light, the wavelength lambda 2 as well as act as a by pairs wavelength lambda, of the incident light 1/4-wave plate And a phase plate that acts as a half-wave plate for incident light of wavelength ⁇ 3.
- the phase correction element of the present embodiment the wavefront aberration generated when the HD objective lens is used for DVD or CD can be corrected. Also the waves By using it as a phase correction element in an optical head device equipped with a polarizing beam splitter (PBS) that transmits linearly polarized incident light with a long polarization and reflects or diffracts linearly polarized incident light with a plane of polarization orthogonal to it.
- PBS polarizing beam splitter
- An optical system with high light utilization efficiency and stable oscillation of the semiconductor laser light source make it a highly reliable optical head device for recording and Z or reproduction.
- a light-transmitting material having different refractive index wavelength dispersions that is, a first light-transmitting material 1A and a second light-transmitting material 1B, is used.
- the second phase correction element 200 will be described below.
- the first phase plate 300 has the same configuration as the first phase plate 3OA in the first phase correction element 100.
- the translucent material 1A and the translucent material 1B are two types of materials having a large difference in the refractive index chromatic dispersion in the visible wavelength range, and have the same refractive index value in the wavelength range and the wavelength ⁇ or ⁇ . if transparent at 2 and lambda 3, it may be filed light absorption at other wavelengths.
- the translucent material 1 1 and the translucent material 1B may be an inorganic material such as glass or an organic material used as a plastic lens or an optical resin.
- a composite material in which fine particles are dispersed in an inorganic material or an organic material to adjust the wavelength dispersion of the refractive index may be used.
- Fig. 3 is a graph showing the wavefront aberration of transmitted light in a DVD or CD optical disc.
- (A) shows the wavefront aberration generated by the second phase correction element 200 when the second phase correction element 200 of the present embodiment is used
- (B) shows the second phase correction element 200. The wavefront aberration that occurs when not used is shown.
- the wavefront aberration in which the power (magnification) component is added to the spherical aberration is shown
- the horizontal axis is the numerical aperture NA corresponding to the aperture diameter
- the cross-section of the wavelength phase difference indicates the optical distance difference of the light beam at each NA value in the unit of used wavelength.
- This wavefront aberration actually has a substantially axisymmetric three-dimensional shape and a substantially parabolic distribution.
- a plurality of dotted horizontal indicates equiphase wavefront integer multiple of the wavelength lambda 2, the spacing of the horizontal lines has a wavelength lambda 2.
- lambda 2 or less of the wavefront aberration is wavefront aberration to be corrected.
- Figure 3 (Alpha) is wavefronts generated using a first phase correction layer 1 0 beta in the second phase correction element 2 0 0 of the onset bright so as to correct the lambda 2 or less wavefront aberration This shows the aberration, and the concentric shape is such that the width of the bottom surface of the sawtooth becomes narrower from the center to the outer periphery.
- the translucent material 1 ⁇ processed into the cross-sectional shape of the sawtooth-shaped uneven portion in the first phase correction layer 10 ⁇ ⁇ ⁇ has a Fresnel lens shape having a sawtooth cross-section shown in FIGS. 1 and 2. This shape is determined as follows.
- the cross-sectional shape shown in FIG. 3 (B) is substantially parabolic, and the three-dimensionally substantially parabolic wavefront aberration is sliced at intervals of a wavelength ⁇ 2 in a circular region with a numerical aperture NA 2.
- the annular zone radius of each convex portion of the translucent material 1 1 is determined.
- the height of these zones are all lambda 2 Become. That is, the translucent material 1 1 is processed so that the difference in optical path length between the concave and convex portions of the translucent material 1A and the translucent material 1B at the wavelength ⁇ 2 is ⁇ 2 .
- the cross-sectional shape of the light-transmitting material 1 A is processed to a sawtooth corresponding to 1 A in FIG.
- the cross-sectional shape corresponding to the Figure 3 to the plane perpendicular to the plane is a plane-symmetric shape (A), it may be processed to translucent material 1 A .
- the height d may be within the range of the height d.
- the height d may be within the range of the height d.
- the height d that satisfies is more preferable.
- the transmitted wavefront becomes zero because the refractive index difference ⁇ between the translucent material 1 ⁇ and the translucent material 1 ⁇ ⁇ ⁇ ⁇ at the wavelength input is zero. It does not change.
- the refractive index difference ⁇ is finite for the incident light of wavelength ⁇ 2
- a phase difference ⁇ X dZA 2 in wavelength units is generated according to the height d of each of the saw-tooth-shaped protrusions, and FIG.
- the transmitted wavefront change shown in Fig. 3A that corrects the wavefront aberration shown in Fig. 3) occurs.
- the refractive index difference ⁇ is finite for incident light of wavelength ⁇ 3
- a phase difference AnXd / A 3 is generated in wavelength units according to the height d of each of the sawtooth-shaped protrusions.
- a transmitted wavefront change similar to A) occurs. That is, the transmitted wavefront has a power corresponding to that of the concave lens.
- the this phase correcting element has the effect of a concave lens, it is possible to enlarge the distance between the optical disk and the objective lens, the stability of recording and ⁇ or head device to light in reproduction Is improved.
- the first phase complementary layer 10 ⁇ is processed so as to correct the wavefront aberration of the wavelength ⁇ 2 and the wavelength ⁇ 3 generated when the incident light of the wavelength ⁇ 2 and the wavelength ⁇ 3 are both slightly divergent light.
- a semiconductor laser that emits light with wavelengths ⁇ 2 and ⁇ 3 In a light head device that uses a two-wavelength laser integrated in one package as a light source and uses a common collimating lens to make two wavelengths of light incident on the objective lens as approximately the same divergent light, It is effective to use a phase correction element 200 having excellent performance.
- the second phase correction element 2 0 0, the wavelength lambda 2 and wavelength; since it is the aberration compensation only difference in wavelength between the wavelength lambda E regardless of the polarization state of the incident light 1 3, There are few restrictions on the first phase plate 30 ⁇ ⁇ ⁇ ⁇ for the wavelengths ⁇ 2 and ⁇ 3.
- FIG. 4 is a cross-sectional view showing a configuration of a third phase correction element 300 according to another embodiment of the present invention.
- the plan view is the same as FIG.
- Phase correction element 3 0 0 according to this embodiment, light transmissive, such as the first phase correction layer 1 0 C and the glass that is formed in a region of numerical aperture Nyuarufa 2 on the surface of the transparent substrate 5 such as a glass And a first phase plate 30 C formed on one side of the conductive substrate 6.
- the first phase plate 300 has the same configuration as the first phase plate 300 of the first phase correction element 100.
- the first phase correction layer 1 0 C is shown in FIG. 3 with respect to the incident light of wavelength lambda 2 (Alpha)
- the third embodiment corrects the wavefront aberration shown in ( ⁇ ) of FIG. 3 that occurs when the third phase correction element 300 is not used.
- the first phase correction layer 1 0 C is the light-transmission area of the numerical aperture Nyuarufa 2 on the surface of the substrate 5 such as glass, which cross section is formed in a sawtooth shape (a so-called blazed diffraction grating type)
- Each of the saw-tooth-shaped convex portions is composed of a multi-step blazed diffraction grating made of a homogeneous material approximated by a step-shaped grating.
- the uneven portion is formed in a shape having rotational symmetry with respect to the optical axis.
- the phase difference between the transmitted light of the homogeneous material having the refractive index ⁇ and the transmitted light of the air in each step of the step-shaped grating is set to a natural number multiple of about 47 ° with respect to the wavelength ⁇ .
- the phase difference is a natural number multiple of approximately 2 [pi for the wavelength lambda 3 if the natural number multiple of approximately 4 [pi with respect to the wavelength e E.
- the shape of the saw-toothed uneven portion in the first phase correction layer 10C is a Fresnel lens shape composed of a step-shaped lattice shown in FIGS. 2 and 4, and this shape is the same as that of the first phase correction layer 10C. Is determined in the same manner as.
- X d N1 A 3
- the first phase correction layer 10C which is processed into a stepped shape, a case where light of wavelength lambda 2 is incident.
- the phase of the transmitted light wavefront is
- FIG. 5 is a partially enlarged view of the wavefront aberration showing the wavefront aberration correction action of the first phase correction layer 10C.
- the corrected optical path difference a corresponding to the height d N1 of one step of the staircase-shaped grating, that is,
- the units have a wavefront aberration of the wavelength lambda 2 minutes corrected approximately wavefront aberration by dividing by a.
- FIG. 5 shows an example of aberration correction using a five-level (four-step) step-shaped grating.
- the surface of the translucent substrate 5 may be directly finely processed into a step-shaped lattice, or a layer formed to a desired film thickness may be processed. Therefore, in the third phase correction element 300, the material used for the first phase correction layer 10C is less restricted, and the processing amount is relatively small due to a large refractive index difference from air. There are strong points.
- FIG. 6 is a sectional view showing a configuration example of a fourth phase correction element 400 according to the fourth embodiment of the present invention.
- the plan view is the same as FIG.
- phase correction element 400 of this embodiment two types of phase plates 3A and 3B made of birefringent materials having different retardation values are stacked as a first phase plate so that their optical axes form a predetermined angle.
- the first phase plate 30D is used. Note that, in FIG. 6, the same phase correction layer as the first phase correction layer 10B in the second phase correction element 200 of FIG. 1 showing the second embodiment is used as the first phase correction layer 10D. However, the first phase correction layer 10C used in the third phase correction element 300 of the third embodiment may be used.
- the phase plates 3A and 3B constituting the first phase plate 30D are made of a birefringent material such as a polymer liquid crystal, an optical crystal such as a crystal, or a polycarbonate which exhibits birefringence by uniaxial stretching. Is formed from.
- the phase plates 3 A and 3 B are formed by laminating polymer liquid crystal films having different optical axes and retardation values on the light transmitting substrate 6, or by forming the polymer liquid crystal films formed on the light transmitting substrate 6.
- the phase plate 3A made of polycarbonate may be bonded to the phase plate 3B made of a film using an adhesive. Further, a phase plate 3B made of quartz may be used instead of the translucent substrate 6, and a phase plate 3A made of a polymer liquid crystal film may be formed thereon.
- phase plate 3A and the phase plate 3B are arranged in this order from the phase correction layer 10D side, and the angles of the fast axes of the phase plates 3 ⁇ and 3 ⁇ with respect to the polarization plane of the linearly polarized incident light of wavelength ⁇ are 0 ° and 0 °. If the respective retardation values are R A and R B , S 3 of the Stokes matrix component representing the polarization state of the transmitted light of the laminated phase plate is described by the following equation (1).
- ellipticity represents the linear polarization of the transmitted light / c (the ratio of the minor axis amplitude with respect to the long axis amplitude of elliptically polarized light) by using the S 3, the following equation,
- the phase in which the birefringence phase difference is an odd multiple of approximately 2 so that the first phase plate 30D acts as a quarter-wave plate with respect to, for example, incident light of three wavelengths ⁇ 2 and ⁇ 3.
- 0 A , 0 B , R A , and RB should be determined so that ⁇ is 1 for three wavelengths, that is, S 3 is close to 1.
- the laminated structure of the phase plate 3 ⁇ and the phase plate 3 ⁇ constituting the first phase plate 30 D is merely an example, and the numerical ranges of 0 A , 0 B , R A , and R B are not necessarily required. It is not limited to. Since the wavelength dependence of the amount of birefringence varies depending on the birefringent material used, the desired S3 described by equation (1) is obtained according to the purpose of polarization conversion for each wavelength. Cormorants, ⁇ , ⁇ ⁇ , R A , may be adjusted R B.
- phase correcting element 4 00 of the present invention that such a first phase plate 30 D is integrated, even against the incident light of wavelength lambda 2 and wavelength lambda 3 not Wavelength ⁇ only Functions as a quarter-wave plate.
- the fourth phase correction element 400 when the fourth phase correction element 400 is mounted on an optical head device used for recording and / or reproducing information on three types of optical recording media having different wavelengths, it can be used together with a polarization beam splitter. As a result, it is possible to perform recording and / or reproduction on an optical recording medium having high light use efficiency. Even when a polarization beam splitter is not used, the reflected return light from the optical recording medium reciprocates through the first phase plate 30D to become linearly polarized light orthogonal to the polarization plane of the light emitted from the semiconductor laser light source. Since the light is incident on the light emitting point, stable emission light intensity is obtained without affecting the oscillation of the semiconductor laser, and highly reliable and stable recording and reading or reproduction are realized.
- FIG. 7 shows a cross-sectional view
- FIG. 8 shows a plan view of a configuration example of a fifth phase correction element 500 according to a fifth embodiment of the present invention.
- FIG. 8 (a) shows the appearance as seen from the side where the first complementary layer 10E is formed
- FIG. 8 (b) shows the appearance as seen from the opposite side.
- Phase correction element 500 according to this embodiment the first phase correction layer 10 E is formed in a region of numerical aperture NA 2 in the third phase correction element 300 similarly to the surface of the transparent substrate 5, further Toru second phase correction layer 20 E is formed in a region of numerical aperture NA 3 on the other surface of the optical substrate 5, the first phase plate 30 E are integrated.
- the first phase correction layer 10E has the same configuration as the first phase correction layer 10C of the third embodiment.
- the second phase correction layer 20E will be described in detail below.
- the numerical aperture HD objective lens, ⁇ 3 780 nm Pas Wa component to the spherical aberration generated when used at a wavelength in the cover IchiAtsu 1.
- aperture NA 3 to an optical disk for the 2 mm CD is added
- Wavefront aberration corresponds to (B) in Fig. 3.
- the method of correcting this wavefront aberration using the second phase correction layer 20E is the same as the procedure described above for the first phase correction layers 1OA and 10C.
- Second phase correction layer 20 E the area of the numerical aperture NA 3 of the transparent substrate 5 such as a glass The ordinary refractive index n.
- a polymer liquid crystal layer as a birefringent material layer having an extraordinary refractive index ne ( ne > n).
- a liquid crystal monomer solution is applied on an alignment film on a translucent substrate that has been subjected to an alignment treatment, and the alignment vector (molecular alignment axis) of the liquid crystal molecules is aligned in a specific direction in a plane parallel to the substrate.
- the polymer liquid crystal layer is formed by polymerizing and curing by irradiating light such as ultraviolet rays.
- the polymer liquid crystal layer is a multi-step blazed diffraction grating in which the cross-sectional shape is a sawtooth shape (so-called blazed diffraction grating type), and each of the sawtooth-shaped protrusions is approximated by a step-shaped grating. Then, it is processed so as to form an uneven portion having a shape having rotational symmetry with respect to the optical axis. That is, concavo-convex portions are formed concentrically so that the width of the bottom surface of the sawtooth becomes narrower from the center toward the outer periphery.
- the ordinary light refractive index n is provided in at least the concave portion of the uneven portion of the formed polymer liquid crystal layer.
- the second phase correction layer 20E is filled with a homogeneous refractive index transparent material 2B having a refractive index n s substantially equal to. That is, between the translucent substrate 5 on which the stepped blazed diffraction grating 2 A formed of concave and convex portions of the polymer liquid crystal is formed and the first phase plate 30 E, the homogeneous refractive index transparent material 2 B is filled. Fill the material.
- the second phase correction layer 2 0 E is the wavelength and the wavelength lambda 2 and the light incident ordinarily polarized light, using a wavelength lambda 3 as an incident light of extraordinarily polarized light. By doing so, a transmission wavefront is invariant with respect to wavelength and the wavelength lambda 2, the second phase correction layer 2 0 transmitted wavefront change to correct the wavefront aberration arises, which occurs only for the wavelength lambda 3 ⁇ is obtained.
- the wavelength is an odd multiple of approximately 27T.
- the transmitted wavefront is transmitted without change even for extraordinary light polarization of wavelength ⁇ i, but it is transmitted for extraordinary light polarization of wavelength ⁇ 3.
- the second phase correction layer 20 has a wavelength selectivity function in which the transmitted wavefront changes.
- the sectional shape of the serrated concavo-convex portion in the second phase correction layer 2 0 E is, n e> n.
- n e the Fureneruren's shape composed of step-like grating shown in FIGS. 7 and FIG. 8 (b)
- n e ⁇ n.
- This shape is determined as follows. That, sliced cross section shape is a Ryakuho paraboloid shape of the wavefront aberration in 3 dimensions in a substantially parabolic shown, at each interval of the wavelength lambda 3 in a circular area of the numerical aperture NA 3 (B) in FIG.
- the orbicular zone radius of each convex portion of the blazed diffraction grating 2 ⁇ is determined from the plurality of orbicular zones obtained by the above.
- Flat surfaces of the annular a wavefront aberration zero (plane perpendicular to the paper surface in FIG. 3) on, if Ru arranged concentrically about the axis of NA 0, the height of these zones at all lambda 3 Yes, the cross-sectional shape is serrated.
- the transmitted wavefront is effectively delayed by 0.52 wavelength for one step of the step-shaped grating.
- the ordinary light refractive index ⁇ of the polymer liquid crystal is obtained by converting incident light of wavelength ⁇ 2 into ordinary light polarization.
- the refractive index n s of the homogeneous refractive index transparent material are substantially the same, so that the light is transmitted by the second phase correction layer 20E without being affected by the transmitted wavefront change.
- Figure 9 is a partially enlarged view of the wavefront aberration shows the wavefront aberration correction action of the second phase correction layer 20 ⁇ respect to the wavelength lambda 3.
- the corrected optical path difference b corresponding to the height d M1 of one step of the staircase-shaped grid, that is,
- Fig. 9 shows an example of aberration correction using a three-level (two-stage) step-shaped grating.
- the ordinary light refractive index n of the polymer liquid crystal layer which is a birefringent material layer. Is equal to the homogeneous refractive index n s of the transparent material, but if the extraordinary refractive index ne and n s are equal, the extraordinary polarization and the ordinary polarization are interchanged, and a staircase-shaped lattice of the polymer liquid crystal layer is also generated. A similar function can be obtained by processing so as to correct the wavefront aberration.
- any material having birefringence may be used.
- it may be an optical crystal such as quartz or lithium niobate, or an organic material such as polycarbonate which exhibits birefringence by uniaxial stretching.
- the optical axes of the refractive index ellipsoids are aligned in one direction.
- the molecular orientation axis corresponds to this.
- this fifth phase correction element 5 0 0 not give wavefront aberration change to the transmitted light through the wavelength lambda [and wavelength lambda 3, wavelength: wavefront aberration change wavefront aberration correcting only the transmitted light of the L 2
- a first phase correction layer 10 # to be applied is also formed.
- the wavefront aberration generated when the HD objective lens is used for an optical disc for DVD at the wavelength ⁇ 2 and the numerical aperture NA 2 is reduced by the first phase correction layer 10 E, and the wavelength ⁇ 3 and the numerical aperture NA
- the wavefront aberration generated when the optical disk is used for a CD optical disc in step 3 can be independently corrected by the second phase correction layer 20E.
- the second phase correction layer 20 E used in the fifth phase correction element 500 does not change the transmitted wavefront with respect to the wavelength irrespective of its polarization state.
- the transmitted wavefront of ordinary polarized light does not change, but the transmitted wavefront of extraordinary polarized light changes according to the shape of the staircase-shaped preserved diffraction grating 2 2. .
- the fifth phase correction element 500 when the fifth phase correction element 500 is mounted on an optical head device integrally with the objective lens, the incident light having the wavelengths ⁇ 2 and ⁇ 3 on the outward path that propagates light from the light source to the optical disk is used.
- the polarization of the light is changed to the ordinary light polarization and the extraordinary light polarization, respectively, the desired wavefront aberration can be corrected only in the incident light of wavelength ⁇ 3 in the second phase correction layer 20 ⁇ .
- the transmitted wavefront changes.
- the light reflected on the optical disk and incident on the phase correction element 500 on the return path reciprocates through the first phase plate 30E, and therefore, usually has a different polarization state from the forward path.
- the transmitted wavefront of the second phase correction layer 2 0 E generates the changed wavefront aberration.
- ordinarily polarized light component of the wavelength lambda 3 since the transmitted wavefront change to correct the wavefront aberration does not occur in the second phase correction layer 2 0 E, original wavefront yield difference remains.
- the signal light cannot be sufficiently focused on the light receiving surface of the photodetector on the return path.
- the first phase plate 30 of the present embodiment generates a birefringent phase difference of an odd multiple of substantially ⁇ to rotate the plane of polarization.
- Use ⁇ An example of the configuration will be described with reference to a cross-sectional view shown in FIG.
- the first phase plate 30 ⁇ is composed of two types of birefringent materials having different values of the retardation values in the order of the phase plate 3 C and the phase plate 3 D from the second phase correction layer 20 ⁇ side.
- the angles of the optical axes of the phase plates 3 C and 3 D with respect to the plane of polarization of the linearly polarized incident light of wavelength ⁇ are 0 C and 0 D , respectively.
- the ellipticity ⁇ calculated from S 3, which is the Stokes matrix component of the transmitted light of the laminated wave plate described in equation (1), is Is approximately 1, and 6 C , SD , R c , and RD may be determined so as to be 0.1 or less for the wavelength ⁇ 2 and the wavelength ⁇ 3 .
- a birefringent phase difference [delta] a birefringent phase difference [delta].
- the optical axis angle of the phase plate 3 C is Sc 45 ⁇ 5 °. like this
- the ordinary light polarization of the wavelength ⁇ becomes the extraordinary light polarization
- the ordinary light polarization of the wavelength ⁇ 2 becomes the ordinary light polarization.
- the extraordinary light polarization of wavelength ⁇ 3 remains extraordinary light polarization. Consequently, in the backward and you forward, the wavelength lambda 1 transmitted wavefront are immutable, transmission wavefront of Hachoe 2 is corrected only by the first phase correction layer 1 0 E, transmitted wavefront of the wavelength lambda 3 is the second The phase is corrected only by the phase correction layer 20 #.
- FIG. 10 shows a cross-sectional view of a configuration example of a sixth phase correction element 600 according to the sixth embodiment of the present invention.
- a first phase plate that rotates the plane of polarization by generating a birefringent phase difference that is almost an odd multiple of the vertex 3 0 F and, ⁇ !
- Reference numerals 51 and 52 denote translucent substrates on which the polarizing phase correction layers 10 F 2 and 10 F are formed.
- the ordinary refractive index n In the region of numerical aperture NA 2 of a light-transmitting substrate 52 such as glass and 51, the ordinary refractive index n.
- Polymer liquid crystal layer is formed optical axis is unidirectional two assortment ivy birefringent material and the extraordinary refractive index n e.
- This polymer liquid crystal layer has a saw-tooth cross-section or each of the saw-tooth-shaped protrusions is approximated by a step-shaped lattice, and is formed of saw-tooth-shaped uneven portions having rotational symmetry with respect to force and optical axis.
- At least the concave portion of the concave and convex portion of the polymer liquid crystal layer has an ordinary refractive index n.
- a second polarizing phase correction layer 10 F 2 is constituted by the sawtooth grating 1 F and the homogeneous refractive index transparent material 1 G.
- the sawtoothed lattice 1F has the serrated slopes facing, and the sawtoothed lattice 1D has the serrated vertical surfaces facing. Therefore, n e > n.
- the transmitted wavefront of the sawtooth grating 1F becomes a divergent spherical wave
- the transmitted wavefront of the sawtooth grating 1D becomes a convergent spherical wave, which has the functions of a concave lens and a convex lens, respectively. .
- the alignment directions of the polymer liquid crystals processed into the sawtooth gratings 1 D and 1 F are aligned, and the transmitted wavefront does not change with respect to ordinary light polarization, but the extraordinary light For polarized light, the transmitted wavefront changes according to the sawtooth-shaped unevenness distribution.
- n e n.
- the irregularities of the saw-toothed gratings 1F and 1D may be processed in reverse.
- n e n s
- sawtooth grating 1 F and 1D of irregularities n e ⁇ n.
- n e n s
- Figure for generating an objective lens for HD either when used in an optical disk for DVD the wavelength lambda 2 and the numerical aperture NA 2, or used in a wavelength lambda 3 and the numerical aperture NA 3 in the optical disk for CD
- the wavefront aberration shown in (B) of FIG. 3 shows that the wavefront aberration generated in the transmitted light of the polarizing phase correction layer 10 F 2 with respect to the incident light of the extraordinary polarized light having the wavelengths ⁇ 2 and ⁇ 3 is shown in FIG.
- the correction can be made by processing the polymer liquid crystal layer 1F so as to correspond to the above ( ⁇ ). This is the same as the case where the correction is performed by the first phase correction layer 10 in the second phase correction element 200 shown in FIG.
- the first phase plate 3OF has the same configuration and function as the first phase plate 30E used for the fifth phase correction element 500, and has a function of 1 for linearly polarized light of wavelength ⁇ . It acts as a Z4 wave plate and converts it to circularly polarized light. For linearly polarized light of wavelengths ⁇ 2 and ⁇ 3 , it acts as a 1 ⁇ 2 wave plate to rotate the plane of polarization.
- the second phase plate 4 OF is emitted while maintaining a knitting state of the incident light with respect to wavelength At, approximately 90 ° to the polarization plane for linearly polarized light of wavelength lambda 2 and wavelength lambda 3 Acts as a rotating half-wave plate.
- the specific configuration of the second phase plate 40F is the wavelength ⁇ !
- a phase plate 3 ⁇ and a phase plate 3F each having a birefringence phase difference of about 2 ⁇ corresponding to about one wavelength are stacked such that their optical axes make an angle of about 45 °. That is, if the birefringent phase differences of the phase plates 3 ⁇ and 3 with respect to the wavelength input 1 are ⁇ ⁇ and 5 F, and the angles of the fast axis with respect to the plane of polarization of the incident light are ⁇ E and 0 F ,
- the light passes through F to become ordinary light polarized light, passes straight through without being diffracted by the first polarizing phase correction layer 10 F, and transmits through the first phase plate 30 F with its polarization plane rotated.
- blazed diffraction grating formed on the second polarizing phase correction layer 10 F 2 to the extraordinarily polarized light having a wavelength of lambda 2 and wavelength lambda 3, 1 so that a high diffraction efficiency of diffracted light, the grating it is preferred that the cross-section phase difference of the transmitted wave surface grating uneven portion in sawtooth blazed grating shape and about one wavelength of the wavelength lambda 2 and wavelength lambda 3. Furthermore, this blazed diffraction grating reduces the spherical aberration in which the first-order diffracted light occurs in the optical head device. A concentric annular band-shaped lattice pattern is formed so as to make correction.
- the linearly polarized light having the wavelength reciprocates through the first phase plate 3OF and becomes extraordinary light polarized light, thereby performing the first polarization phase correction.
- the extraordinary light is transmitted through the second phase plate 40 F with the extraordinary polarization, and diffracted again by the second polarizing phase correction layer 10 F 2 .
- the light of wavelengths ⁇ 2 and ⁇ 3 is transmitted through the first phase plate 3 OF without being diffracted by the first polarizing phase correction layer 1 without being diffracted by the first polarization plate 1 OF and the polarization plane is rotated back to the original ordinary light polarization. Then, the light passes through the second phase plate 40 F and becomes extraordinary light polarization, and is diffracted by the second polarizing phase correction layer 10 F 2 in the same way as the forward path.
- the second polarization phase correction layer 10 F 2 is formed so that the first-order diffraction efficiency is increased with respect to the extraordinary light polarization of the wavelengths ⁇ 2 and ⁇ 3 , so that the wavelength ⁇ Second-order diffracted light is mainly generated for light polarization.
- the diffracted light of the convergent transmission wavefront generated in the first polarization phase correction layer 10 with respect to the extraordinary light polarization of the wavelength ⁇ on the return path, and the divergent transmission generated by the second polarization phase correction layer 10 F 2 The multiplexed diffraction of the wavefront with the second-order diffracted light forms the blazed diffraction grating pattern of the first polarization phase correction layer 1 OF so that the wavefront state becomes the same as that of the incident light of the phase correction element 600 in the forward path. ing.
- the diffraction order of the diffracted light of the wavelength ⁇ by the first polarization phase correction layer 10 F may be the first or second order, but the diffraction direction with respect to the central axis of the concentric grating pattern is the second polarization phase correction. Opposite to layer 10 F 2 .
- the transmitted wavefront is invariant on the outward path and the return path for the incident light of the ordinary polarization of the wavelength ⁇ i, and is orthogonal to the incident light after the forward and backward.
- extraordinary light polarization Into extraordinary light polarization.
- the wavelength; the ability to change the transmitted wavefront so as to correct the wavefront aberration in the forward path and the backward path is obtained for the 2 and wavelength lambda 3 of the extraordinarily polarized light of the incident light. That is, the combination of the second polarization phase correction layer 10 F 2 , the second phase plate 40 F, and the first polarization phase correction layer 10 F allows the second phase correction element 20 F The same function as the first complementary layer at 0 is obtained.
- the above-described first to sixth phase correction elements 100 to 600 of the present invention are mounted on an optical head device as compatible elements corresponding to three types of optical disks, HD, DVD and CD.
- aperture limiting element for limiting a wavelength ei lambda 2 and lambda 3, respectively of the incident light beam to the open talkative Nyuarufa There Nyuarufa 2 and ⁇ 3.
- This aperture limiting element may be arranged separately from the phase correction element of the present invention. However, since the aperture correction function is integrated with the phase correction element, the size and weight can be reduced, and mounting position adjustment is not required. .
- the first light flux with wavelength lambda 2 that has transmitted wavefront varies with phase correction layer formed in a region corresponding to the numerical aperture Nyuarufa 2 of D VD is the spherical surface aberration correction component in addition large power component is the granted to the transmitted wavefront, the light flux of the outer circumferential region than the numerical aperture NA 2 is focused on the focal plane of a different objective.
- the first phase correction layer has the aperture limiting function of the numerical aperture NA 2 for the incident light of wavelength ⁇ 2 .
- the wavelength ⁇ 3 at which the transmitted wavefront changes due to the second phase correction layer 20 E formed in the area corresponding to the numerical aperture NA 3 of the CD. light beam, when large power component is applied to the transmission wavefront is converged on the focal plane of a different objective to the light flux of the outer peripheral region than a numerical aperture of New a 3.
- the aperture limiting function of the numerical aperture NA 3 second phase correction layer 2 0 E is the incident light of wavelength lambda 3 You will have.
- phase correction element When the first phase correction layer and the second phase correction layer have a function of generating a large power component, it is not necessary to add a new aperture limiting function to the phase correction element.
- the power component given by the phase correction layer to the transmitted wavefront is small and the light flux in the outer peripheral region enters the photodetector as stray light with a predetermined numerical aperture, stable recording and / or reproduction cannot be performed.
- the light flux of a CD having a wavelength of 3 is used as the numerical aperture. It is preferable to provide an aperture limiting function of limiting the NA 3.
- FIG. 11 is a cross-sectional view of a seventh phase correction element 700 according to the seventh embodiment of the present invention
- FIG. 12 is a plan view thereof.
- the diffraction grating 91 has a length ratio of 1: 1 and a wavelength phase difference corresponding to the wavelength difference.
- the wavelength retardation of the concave and convex portions is substantially 1 Z 2 wavelength lambda 2 and wavelength lambda 3
- the incident light of wavelength lambda E is straightly transmitted
- incident light of wavelength lambda 2 and wavelength lambda 3 is An aperture limiting function is realized in which the transmitted light that is diffracted is 30% or less.
- a similar wavelength selection function is that the wavelength phase difference between the concave portion and the convex portion is substantially an integer multiple of the wavelength ⁇ , and is a non-integer multiple of the wavelength ⁇ 2 and the wavelength ⁇ 3 and preferably close to an odd multiple of 1/2. If the value is expressed.
- the second annular region consisting of the difference between the circular region and Nyuarufa 3 circular region of numerical aperture Nyuarufa second surface of the transparent substrate 5 (Alpha 2), a transparent dielectric having a relatively high refractive index
- a multilayer filter 92 having a structure in which a transparent dielectric film (not shown) having a relatively low refractive index and a body film (not shown) are laminated alternately in the order of the wavelength of the optical film thickness of each film.
- the multilayer filter 4 Alpha formed transmitted through the wavelength and the wavelength lambda 2 of the light 90% or more, to reflect 70% or more light of wavelength lambda 3, the refraction of the two transparent dielectric
- the ratio, the number of layers, and the thickness of each layer are set by a conventional multilayer filter design method.
- the transparent dielectric film having a high refractive index T i 0 2, T a 2 0 5, N b 2 0 5, Z R_ ⁇ 2 and used as the transparent dielectric film having a low refractive index S i 0 2 and M g F 2 is used.
- the incident light Hachoe is straightly transmitted a region of numerical aperture NA i
- the incident light of wavelength lambda 2 is straightly transmitted a region of numerical aperture Nyuarufa 2
- the incident light of wavelength lambda 3 is opened wavelength selectivity which straightly transmitted a region of numerical aperture Nyuarufa 3 A mouth-restricted board 5 A is obtained.
- the configuration other than the aperture limiting substrate 5A may be any one of the first force to the sixth phase correction element.
- FIG. 11 shows a case where the configuration of the fourth phase correction element 400 is used.
- the wavefront of the light of wavelength At that has passed through the numerical aperture area of the numerical aperture limiting substrate 5A (including the inside) does not change, and the numerical aperture NA 2 area (including the entire inside).
- the first annular region ( ⁇ ⁇ and the second annular region (A 2 ) and the circular region (A 3 ) It is preferable that at least one of the regions has a step for phase adjustment.
- the step for adjusting the phase may be processed directly on the light-transmitting substrate 5 or may be formed after forming the light-transmitting dielectric film on the surface of the light-transmitting substrate 5. Both are circular areas
- (A 3 ) is preferably provided with an anti-reflection function by forming an anti-reflection film 8 or the like so as to transmit incident light having wavelengths of ⁇ 2 and ⁇ 3 .
- FIG. 11 Next, the aperture limiting substrate 5 in FIG. 11 will be specifically described with reference to FIG. 13 in which a cross-sectional view is partially enlarged.
- a diffraction grating 91 having an uneven cross-sectional shape is formed in the annular region (A.
- the surface of the concave portion is denoted by S ⁇
- the interval between S. and Si is denoted by: the surface of the convex portion of the diffraction grating 9 1 and S 4, the distance between the S. and S 4 and d 4.
- the in an annular region (a 2) multilayer filter 9 2 is formed the multilayer film fill evening 9 2 surface and S 2 surface, the spacing or thickness of the multilayer filter 9 2 S., S 2 and d 2.
- the annular region and the annular region ( ⁇ 2 ) The wavelength phase difference of transmitted light of wavelength ⁇ passing through each area of the circular area ( ⁇ 3 ) is set to be an integer multiple of wavelength ⁇ .
- the annular region (Alpha 2) and the circular area (Alpha) is set to be an integral multiple of the wavelength ⁇ 2 .
- the wavelength phase difference of the transmitted light may be an integral multiple of the wavelength ⁇ .
- the multilayer filter 92 having a total thickness d 2 of the annular region ( ⁇ 2 ) is regarded as a uniform layer having an average refractive index ⁇ ⁇ , and the optical path length associated with multiple reflection at a film interface having a different refractive index inside the multilayer filter 92.
- n 3 S including the antireflection film 8 in the circular area (A 3 ). Shows the average refractive index between the surface and the S 3 surface.
- the configuration of the multilayer filter 92 (total film thickness d 2 and average refractive index n M ) is such that the wavelength phase difference of (L 2 ⁇ L 3 ) is substantially an integral multiple of wavelength ⁇ and approximately an integral multiple of wavelength ⁇ 2.
- Oyo wavelength ⁇ E in NA 2 region Transmitted wavefront fine wavelength lambda 2 of the light no longer be changed, the wave front aberration by the aperture limiting substrate 5 Alpha does not occur.
- the seventh phase correction element 700 is used integrally with the objective lens of the optical head device, incident light can be efficiently converged on the information recording surface of the HD and DVD optical discs.
- the diffraction grating 91 may be processed only in the annular region (A).
- the step for adjusting the phase is formed by processing the surface of the annular region (A 2 ) of the translucent substrate 5.
- the annular region (A and A) of the surface of the translucent substrate 5 is formed. Only in the circular area (A 3 ) A translucent dielectric film may be formed to provide a step for phase adjustment.
- a translucent dielectric film for phase adjustment is formed in the circular region (A 3 )
- a single-layer intermediate refractive index dielectric made of a mixture or compound of a low refractive index dielectric and a high refractive index dielectric is used. It is preferred to use a body.
- the plane pattern of the diffraction grating 91 is designed so that there is no rotational symmetry twice about the optical axis of the transmitted light.
- the Y-axis symmetric two-division grating pattern is used, and does not have twice rotational symmetry about the optical axis.
- the two-divided grid pattern may have a concentric shape or a grid pitch distributed.
- the light diffracted by the diffraction grating 91 on the outward path is reflected by the information recording surface of the optical disk, and then diffracted again by the diffraction grating 91 on the return path, and the information recorded on the optical disk is obtained. It can be prevented from entering the light receiving surface of the photodetector through the same optical path as the signal light. As a result, a substantial annular region (A ⁇ wavelength selective aperture limiting function is obtained).
- FIG. 14 is a cross-sectional view of a phase correction element 800 according to a modification of the seventh embodiment using the formed aperture limiting substrate 5B.
- the length ratio of the concave portion to the convex portion is 1: 1 and the wavelength phase difference is approximately five times the wavelength, the wavelength phase difference is reduced. Since the wavelength is approximately three times the wavelength ⁇ 2 and approximately 2.5 times the wavelength ⁇ 3 , the incident light of the wavelength and the wavelength ⁇ 2 is transmitted straight ahead, and the incident light of the wavelength ⁇ 3 is diffracted and the straight transmitted light becomes 30%. % Or less.
- wavelength phase difference between the concave portion and the convex portion is substantially an integer multiple of the wavelength ⁇ and the wavelength ⁇ 2 and a non-integer multiple of the wavelength ⁇ 3, preferably an odd multiple of 1 ⁇ 2. If present, it is expressed.
- the diffraction grating 91 is formed in the ring region and the diffraction grating 93 is formed in the ring region ( ⁇ 2 ).
- the surface of the translucent substrate 5 is directly processed so that the surfaces of the grating projections are aligned.
- the example of forming the two different aperture limiting function of wavelength selectivity in the annular region (Alpha an annular region (Alpha 2) first when having a functional phase correction layer is to limit the numerical aperture with respect to the wavelength e 2 Nyuarufa 2, the annular region (Alpha 2) or only the annular region (Alpha and annular region (Alpha 2), multilayer film
- the filter 92 or the diffraction grating 93 may be formed.Although the example in which the aperture limiting function is formed on the surface of the light-transmitting substrate 5 has been described, the surface of the light-transmitting substrate 6 or the inside of the phase correction element is shown. May be formed.
- the cross section is rectangular by using the same translucent material 1 ⁇ as the first phase correction layer 100 ⁇ formed in the annular region (also in the region of the numerical aperture ⁇ 2 ).
- An aperture limiting function can be obtained by forming a rectangular diffraction grating with a fine grating pitch and diffracting incident light of wavelengths ⁇ 2 and ⁇ 3.
- the height of the convex portion of the rectangular diffraction grating is determined by the phase.
- Approximately half of the translucent material of the sawtooth grating in the correction layer Just do it.
- the first phase correction layer 10C formed in the region of the aperture NA 2, like 10E, cross section Form a rectangular diffraction grating with a rectangular and fine grating pitch
- An aperture limiting function can be obtained by diffracting incident light of wavelengths ⁇ 2 and ⁇ 3.
- the height of the convex portion of the rectangular diffraction grating is a phase correction layer that is a step-shaped grating.
- One step height d N1 of 10 C and 10 E may be used.
- phase correction element 500 using the same liquid crystal polymer as the second phase correction layer 20E to the annular region (A ⁇ and the annular region (A 2) which is formed in a region of numerical aperture NA 3 section Forms a rectangular diffraction grating having a rectangular shape with a fine grating pitch, and diffracts incident light of an abnormally polarized light having a wavelength of ⁇ 3 to obtain an aperture limiting function.
- the height may be the height d M1 of one step of the phase correction layer 20, which is a step-shaped grating.
- FIG. 15 is a configuration diagram showing an optical head device equipped with the first phase correction element 100 according to the first embodiment.
- the phase correction element 100 is not limited to the first phase correction element 100 described above, but may be any of the first to seventh phase correction elements.
- (a), (b), and (c) in FIGS. 16 to 18 show the luminous flux and wavefront when light of three different wavelengths ⁇ 2 and ⁇ 3 enter the phase correction element, respectively.
- It is sectional drawing. 16 shows a case of the seventh phase correction element 700
- FIG. 17 shows a case of the fifth phase correction element 500
- FIG. 18 shows a ring region ( ⁇ and a ring region ( ⁇ ⁇ ⁇ ⁇ 2 )) of the sixth phase correction element 600.
- FIG. 9 shows a case of a phase correction element 900 in which a multilayer filter (not shown) for transmitting light of wavelength ⁇ 2 and reflecting light of wavelength ⁇ 3 is formed.
- Semiconductor laser 14B which emits light in the wavelength band
- a polarization beam splitter 19 a multiplexing prism 17, a collimating lens 13 and the above-described phase correction element are provided in the optical path of the light having the wavelength ⁇ . 100 and an objective lens 12 are provided.
- the optical path of the wavelength lambda 2 of the light, and the hologram beam splitter 1 6 beta, is provided and the multiplexing prism 1 8, is by Uni configured reaches the multiplexing prism 1 7 together are, in the optical path of the wavelength lambda 3 of the light, the hologram-bi one Mus Puritsu evening 1 6 C is provided, and is configured to reach the multiplexing prism 1 8.
- the light is reflected by the polarization beam splitter 19, passes through the multiplexing prism 17, becomes parallel light by the collimator lens 13, and enters the phase correction element 100 as ordinary light polarization. Further, the light is converted into circularly polarized light by the first phase plate in the phase correction element 100 acting as a 1/4 wavelength plate with respect to the wavelength, and as shown in (a) of FIGS. 16 to 18, The light passes straight through the phase correction element 100. Then, a light beam corresponding to a numerical aperture of 85 is focused on the information recording surface of the optical disk 13 (HD optical disk) by the objective lens 12 designed for the HD optical disk.
- the signal light of wavelength ⁇ i reflected on the information recording surface of the optical disc D i is converted into extraordinary light polarization by the first phase plate in the phase correction bare hand 100 0 via the original path, and the phase correction element 10 0
- the light passes straight through 0, passes through the multiplexing prism 17 and the polarizing beam splitter 19, is efficiently condensed on the light receiving surface of the photodetector 15A, and is converted into an electric signal.
- the phase correction layer corrects the wavefront aberration generated due to the difference in the cover thickness of the optical disk, and changes the transmitted wavefront from Fig. 16 to Fig. 18 (b) so that it has the power equivalent to the concave lens. Is converted as shown.
- the light beam transmitted through the phase correction element 100 is condensed by the objective lens 12 on the information recording surface of the optical disk D 2 (in this case, an optical disk for DVD).
- Signal light having a wavelength lambda 2 reflected on the information recording surface of the optical disc D 2 is condensed through the original path, a part is diffracted by the hologram-bi one Musupuri' evening 1 6 beta to the light receiving surface of the photodetector 1 5 beta It is lighted and converted to electrical signals.
- the light beam transmitted through the phase correction element 100 is condensed by the objective lens 12 onto the information recording surface of the optical disc D 3 (in this case, an optical disc for CD).
- the signal light of wavelength 3 reflected on the information recording surface of the optical disc D 3 is partially diffracted by the hologram beam splitter 16 C through the original path and condensed on the light receiving surface of the photo detector 15. Is converted into an electrical signal.
- the use of the first phase correction layer 1 0 G has no polarization dependence, it is aberration corrected irrespective of the polarization state of the incident light of wavelength lambda 2.
- the first phase plate 30 D functioning as a 1Z4 wavelength plate for the incident light having the wavelength ⁇ 2 and the wavelength ⁇ 3 , the light reciprocating through the phase plate is used. Can be converted into linearly polarized light whose incident light and polarization plane are orthogonal to each other.
- the hologram beam splitter 16 1 or 16C if a hologram beam splitter that transmits ordinary polarized light and diffracts extraordinary polarized light is used as the hologram beam splitter 16 1 or 16C, the hologram beam splitter will be more efficient. Use efficiency is improved. Alternatively, since the light having the same polarization plane as the oscillating light does not return to the light emitting point of the semiconductor laser, the laser oscillation is stabilized, and highly reliable recording and / or reproduction can be performed.
- the first phase correction layer 10 ⁇ achieves wavefront aberration correction for incident light of wavelength ⁇ 2. it can.
- phase correction element 900 shown in FIG. 18 when the wavelength ⁇ 2 is regarded as extraordinary light polarization in the forward path and the return path, the wavelength is determined by the second polarization phase correction layer 10 F 2 (see FIG. 10). wavefront aberration correction can be achieved for example 2 of the incident light.
- phase correcting element 5 0 0 shown in FIG. 7 when the wavelength example 3 in the forward and backward and extraordinarily polarized light, the second phase correction layer 2 0 E, wavefront yield difference correction with respect to incident light of wavelength lambda 3 Can be achieved.
- the first phase correction layer 10 G or the second polarizing phase correction layer 10 F 2 (the 1 0 reference), but the aberration correction function in the forward and backward with respect to incident light of wavelength lambda 3 is arising, the spherical aberration remains, the incident wavelength lambda 3 with respect to the phase correction device and the objective lens
- the incident light of wavelength ⁇ 2 and wavelength ⁇ 3 is made to be the same divergent light for the phase correction element and the objective lens, and the phase correction layer is formed so that the wavefront aberration can be corrected for both wavelengths. You can also.
- the incident light of wavelength lambda 3 as the aberration correction by the phase the correction element 9 0 0 second polarization position complementary Tadashiso 1 0 F 2 is the same extraordinarily polarized light and the wavelength lambda 2.
- the diffraction grating 91 has an incident wavelength of ⁇ 2 .
- the objective lens 12 designed for an HD optical disk having a cover thickness of 0.1 mm can be covered with the cover thickness. It can correct the wavefront aberration that occurs when used for recording, Z or playback on an optical disc for DVD with a thickness of 0.6 mm and an optical disc for CD with a thickness of 1.2 mm. Therefore, the light emitted from the semiconductor laser can be stably focused on the information recording surface of the optical disc, and recording and / or reproduction on three types of optical discs, HD, DVD, and CD can be realized.
- the optical path indicated by the dotted line in FIG. By increasing the working distance, the stability when the focus lens is activated by mounting the objective lens 12 and the phase correction element (100 to 900) on an actuator (not shown) is improved.
- the optical disk DD 2 for the HD and DVD, the numerical aperture of the cover thickness and the objective lens for the same degree, as the refractive index wavelength dispersion of the optical material due to the difference of the wavelength used (especially the objective lens) occurs Should be corrected.
- the phase correction element does not need a concave lens function of converting a transmitted wavefront having a large power component, and the spherical aberration component may be corrected.
- the phase correction element 300 has a Fresnel lens shape composed of a blazed diffraction grating having a multi-step stair-shaped cross section. Even when the wavefront aberration to be performed is only spherical aberration and the magnitude is within one wavelength, the pattern of the multi-step staircase shape may be determined by the wavefront aberration correction method shown in FIG.
- the wavelength dispersion material of the refractive index constituting the first phase correction layer 10 B used in the second phase correction element 200 is made to have a high quality. What is necessary is just to process it into a shape in which the next wavefront aberration is corrected, and use it together with the first phase correction layer 10 C (see FIG. 4). Further, the polymer liquid crystal constituting the polarizing phase correction layer used in the sixth phase correction element 600 shown in FIG. 10 is processed into a shape in which high-order wavefront aberration is corrected, and the first phase is corrected. You may use together with 10 C of correction layers.
- the above-mentioned numerical aperture NA-O.65 HD objective lens is inserted into CD optical disc D How to correct the spherical aberration generated when used with 3 to the wavelength lambda 3, and the numerical aperture NA 3 is incident light to the objective lens is diverging light, or in the fifth phase correction element 500 shown in FIG. 7
- a phase correction layer similar to the second phase correction layer 20E to be used may be used.
- the multilayer filter 92 used in the seventh phase correction element 700 shown in FIG. 11 or the eighth phase correction element 800 shown in FIG. a diffraction grating 93 used may be formed on the outer circumferential region of the aperture NA 3.
- FIG. 11 cross-sectional view
- FIG. 12 plane view
- the deposition Suruga shows the structure in Table 1.
- the optical path length of the anti-reflection film 8 (refractive index X thickness) of, 331 nm in wavelength lambda, is 322 nm at a wavelength lambda 2.
- an annular region (A) obtained by subtracting the circular region with the numerical aperture NA 3 from the circular region with the numerical aperture NA 2 0.60. 2), and transmits light of Hachoe and wavelength lambda 2 90% or more, the multilayer film as a filter 92, a transparent dielectric film T a 2 0 5 having a high refractive index which the light of the wavelength lambda 3 to reflection 70% And 12 transparent dielectric films S i 0 2 having a low refractive index are alternately laminated, and the configuration is shown in Table 2.
- the total thickness d 2 of the multilayer film fill evening 92 is 1364Nm
- the optical path length is 2420 nm, 2373 nm in wavelength lambda 2 at a wavelength lambda ⁇ .
- FIG. 19 shows the thus obtained spectral transmittance of the aperture limiting substrate 5 of the present example.
- the spectral transmittance of the diffraction grating 91 formed in the annular region is (a), and the spectral transmittance of the multilayer film 92 formed in the annular region (A 2 ) is (b). formed 3) the spectral transmittance of the antireflection film 8 shown in (c).
- S i ON film composed of a mixed composition of S i N and S i 0 2 as the translucent material having a refractive index n A Is formed to a film thickness of 32 m. And it has a sawtooth cross section as shown in Fig. 11. It is processed into a Fresnel lens shape to obtain a light-transmitting material 1A constituting the first phase correction layer 10G.
- a first phase correction layer 10G is filled and solidified, transparent material 1 A ( refractive index of the S i ON) and translucent material IB (high refractive index Purasute worship material), substantially equal in Hachoe, refraction index difference of a wavelength lambda 2 in 0.020 occurs, the wavelength lambda 3 0. A refractive index difference of 023 occurs. Therefore, the first phase correction layer 10 G is transmitted wavefront is immutable with respect to the incident light wavelength, it is transmitted wavefront changes with respect to incident light of wavelength lambda 2 and wavelength lambda 3. Since the step of serrated concavo-convex portion corresponding to the phase difference of about one wavelength with respect to the intermediate wavelength of lambda 2 and wavelength lambda 3, the wavelength lambda 2 and wavelength lambda 3 1-order diffracted light is maximized.
- the first phase correction layer 10 G because the wavelength lambda 2 and wavelength lambda 3 translucent material 1 A is larger refractive index than the transparent material 1 B, a Kymene shape shown in FIG. 11 ing.
- a solution of an acryl-based liquid crystal monomer is applied, and ultraviolet light is applied. Irradiation is carried out to polymerize and cure to form a phase plate 3B made of a polymer liquid crystal film of a birefringent material whose fast axis is aligned with the X axis at an angle of 73 °.
- Ritade one Chillon value of the phase plate 3 B for the wavelength 52 onm corresponding to the middle wavelength of lambda 2 and wavelength lambda 3 corresponds substantially 1Z4 wavelength 130 nm.
- the positive direction is the counterclockwise direction in FIG.
- phase plate 3A an organic thin film made of polycarbonate, which has developed birefringence by stretching, is used as the phase plate 3A, laminated on the phase plate 3B using an adhesive, and bonded and fixed to the phase correction layer 1.
- the retardation value of the phase plate 3A for a wavelength of 520 nm is 260 nm, which is equivalent to approximately 1Z2 wavelength, and its fast axis is set to a direction forming an angle of 17 ° with the X axis. That is, the fast axes of the phase plates 3A and 3B form an angle of 56 °.
- a first phase plate 30G in which the phase plate 3A and the phase plate 3B are laminated is manufactured.
- the seventh phase correction element 700 manufactured in this manner the light having wavelengths ⁇ 2 and ⁇ 3 having a plane of polarization in the X-axis direction is applied to the first phase plate 30G on the side of the aperture limiting substrate 5A.
- they When they are incident from different wavelengths, they all emit circularly polarized light with an ellipticity ⁇ of 0.9 or more, and a function equivalent to a 1Z 4 wavelength plate with 3 wavelengths is obtained.
- FIG. 7 cross-sectional view
- FIG. 8 plane view
- a first phase correction layer 10E composed of a step-like blazed diffraction grating approximated by a (four-step) step-like grating is formed.
- the height d N1 of one step of the staircase-shaped grating is set to 1.723 / m, and the optical path difference from air is 2 2 ⁇ ⁇ with respect to the wavelength ⁇ .
- 1. 2 ⁇ 2 i.e. becomes 0. 2 ⁇ 2 equivalent for the wavelength lambda 2
- the fast axis was set in the X-axis direction by the same preparation method as the phase plate 3 ⁇ of Example 1.
- the ordinary index of refraction ⁇ in line with.
- a blazed diffraction grating 2A having a sawtooth cross-section and approximated by a three-level (two-step) stair-step grating is machined, and the concave part has an ordinary refractive index n.
- the second phase correction layer 20E is filled with a homogeneous refractive index transparent material 2B having a refractive index n s substantially equal to the following.
- the refractive index differences (n e — n s ) for three wavelengths ⁇ 2 and ⁇ 3 are 0.277, 0.213 and 0.200, and the height d M1 of one step of the staircase-shaped grating To 1. 62 m.
- the optical path length difference between the step-shaped blazed diffraction grating 2 A composed of the polymer liquid crystal layer and the one-step homogeneous refractive index transparent material 2 B is ⁇ ⁇ for the wavelength. next, it has become 0. 37 ⁇ 3 for the wavelength lambda 3.
- the transmitted wavefront of the ordinary polarized light incident on the second phase correction layer 20 ° does not change regardless of the wavelength, and the transmitted wavefront of the wavelength change does not change regardless of the incident polarization.
- the transmitted wavefront of the extraordinary polarized light of wavelength 3 changes according to the annular distribution of the step-shaped grating.
- phase plate 3D made of a polymer liquid crystal film whose fast axes are aligned in the X-axis direction is formed in the same manner as the phase plate 3B of Example 1.
- the retardation value of the phase plate 3D with respect to the wavelength is 203 nm, which is equivalent to substantially a half wavelength.
- an organic thin film made of polycarbonate is used as the phase plate 3C, laminated on the phase plate 3D using an adhesive, and bonded to the phase correction layer 20E. Fix it.
- the light having the wavelength ⁇ 1 having a plane of polarization in the X-axis direction enters the first phase plate 30 E from the light transmitting substrate 5 side. Then, the light is emitted as circularly polarized light having an ellipticity ⁇ of 0.9 or more, and a function equivalent to a quarter-wave plate is obtained.
- each plane of polarization is converted into rotated linearly polarized light, and a function equivalent to a 1Z2 wave plate is obtained.
- the ordinary polarization incident light having the wavelength ⁇ 2 reciprocates through the first phase plate 30 ° and becomes the original ordinary polarization, and also travels straight through the second phase correction layer 20 ° without change in the transmitted wavefront on the return path.
- the extraordinary polarized light of wavelength ⁇ 3 travels back and forth through the first phase plate 30 °, it becomes the original extraordinary polarized light, and also on the return path, the transmitted wavefront changes in the second phase correction layer 20 ° and the wavefront aberration is corrected. The action appears.
- FIG. 10 cross-sectional view
- the same multilayer filter (not shown) as the multilayer filter 92 of the first embodiment is formed in the annular region (A and the annular region (A 2 )) of the glass substrate 51 (translucent substrate).
- the first phase plate 3OF formed by laminating the phase plate 3D and the phase plate 3C formed on one surface of the glass substrate 6 (translucent substrate) is the first phase plate 3OF used in the second embodiment.
- the description is omitted because it is the same as 30E (FIG. 7).
- phase plate made of a polymer liquid crystal film having a fast axis aligned in a direction forming an angle of 70 ° with the X axis by the same preparation method as the phase plate 3B of the first embodiment.
- the retardation value of the phase plate 3F with respect to the wavelength Ii is 405 nm, which corresponds to approximately one wavelength.
- an organic thin film made of polycarbonate is used as the phase plate 3E, and the homogeneous refractive index transparent material 1G is laminated on the phase plate 3F using an adhesive as an adhesive.
- Second polarizing phase correction layer 10 It was filled into the recess of the blazed diffraction grating 1 F consisting of polymer liquid crystal F 2, you bonded.
- the retardation value of the phase plate 3 ⁇ with respect to the wavelength ⁇ is 405 nm, which is equivalent to approximately one wavelength, and the fast axis is defined as a direction that forms an angle of 25 ° with the X axis. That is, the fast axes of the phase plates 3E and 3F make an angle of 45 °.
- a second phase plate 40F in which the phase plate 3E and the phase plate 3F are laminated is manufactured.
- each plane of polarization is converted into linearly polarized light in the X-axis direction rotated by approximately 90 °, equivalent to a half-wave plate. The function is obtained.
- Each of the second polarizing phase correcting layer 10 F 2 and the first polarizing phase correcting layer 10 F in the sixth phase correcting element 600 is the same as the second phase correcting layer 20 ⁇ of the second embodiment.
- the ordinary light refractive index ⁇ in which the fast axis is aligned with the X-axis direction on one surface of the glass substrates 51 and 52 is obtained.
- the ordinary refractive index n in the recess Filled with the homogeneous refractive index transparent materials 1 G and 1 E having a refractive index n s substantially equal to the second polarizing phase correcting layer 10 F 2 and the first polarizing phase correcting layer 10 F.
- the slope of the sawtooth cross section is machined in the opposite direction to the center axis of the concentric grating pattern.
- the transmitted wavefront does not change because there is no difference in the refractive index between the polymer liquid crystal and the transparent material having a uniform refractive index.
- a refractive index difference of about 0.15 between the polymer liquid crystal and the homogeneous refractive index transparent material occurs, and the transmitted wavefront changes according to the shape of the sawtooth blazed diffraction grating.
- a three-level (two-step) stepped blazed diffraction grating 2 A was used.
- the unevenness of the entire sawtooth was increased. There point that the thickness of the polymer liquid crystal corresponding to the phase difference of about one wavelength to the wavelength lambda 2 and wavelength example 3 of abnormal light is different. As a result, the first-order diffracted light becomes maximum at the wavelength ⁇ 2 and the wavelength 3 . At this time, the second-order diffracted light becomes the maximum for the extraordinary light of the wavelength.
- phase correction element manufactured in this way for example, the sixth phase correction element 600 and the objective lens 12 are integrated into an actuator (not shown), and the optical head device shown in FIG. Mount.
- this optical head device When this optical head device is used for recording and / or reproduction of an optical disk for DVD and CD, the wavefront aberration generated by the objective lens alone must be corrected, and the distance between the objective lens and the optical disk must be ensured. Can be. As a result, it is possible to stably record and / or reproduce three types of optical discs for HD, DVD, and CD.
- the ordinary polarization incident light having the wavelength ⁇ reciprocates through the phase correction element, for example, the sixth phase correction element 600, so that extraordinary light polarization in the polarization direction orthogonally shifted by the phase plate 30F is output. Since the light is converted into the emitted light, the signal light can be efficiently detected by the photodetector 15A when used in combination with the polarizing beam splitter 19.
- the transmitted wavefront of wavelength ⁇ remains unchanged.
- Transmitted wavefront peel length lambda 2 or wavelength lambda 3 can be corrected.
- the first phase plate having the function of a 1Z4 wavelength plate at the wavelength At is integrated, the linearly polarized light having the wavelength ⁇ that has reciprocated through the phase correction element is converted into orthogonal linearly polarized light.
- the phase correction element is mounted on the optical head device together with the HD objective lens, which is optimally designed for the HD optical disc in terms of wavelength. Stable information recording and recording on VD and CD optical discs And z or play.
- the optical head device of the present invention equipped with a polarizing beam splitter, the light use efficiency of the forward path and the return path with respect to the wavelength light is improved, and the power consumption of the semiconductor laser light source is reduced. High speed recording and Z or playback. Also
- the wavefront aberration of the wavelength ⁇ 2 can be corrected independently.
- a material having a different birefringence is used for the second phase correction layer in the phase correction element, and the one-stage phase difference with respect to the abnormal light polarization has a wavelength; And the corresponding step-like grating, by defining the incident polarized light of three wavelengths can be corrected independently wavefront aberration of the wavelength lambda 3.
- a first phase correction layer capable of correcting the wavefront aberration of the wavelength lambda 2 independently has the function of a wavelength input 1 Z4 wave plate and a 1 Z 2 wave plate at wavelength lambda 2 and wavelength lambda 3
- the opening limit in an annular area obtained by subtracting the numerical aperture NA 3 of the numerical aperture, for the light flux with wavelength lambda 3 for CD by forming the multilayer filter or a diffraction grating to linearly transmit only light of the wavelength and the wavelength lambda 2 By doing so, stable wavefront aberration correction of CD can be performed.
- a diffraction grating is formed in the first annular region obtained by subtracting the numerical aperture ⁇ 2 from the numerical aperture to transmit only the light having the wavelength ⁇ in a straight line, thereby limiting the aperture for the luminous flux of the wavelength ⁇ 2 for DVD.
Description
Claims
Priority Applications (3)
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AU2003252288A AU2003252288A1 (en) | 2002-07-31 | 2003-07-31 | Phase correction element and optical head device |
KR1020057000568A KR100985420B1 (ko) | 2002-07-31 | 2003-07-31 | 위상 보정 소자 및 광헤드 장치 |
US11/045,088 US7688700B2 (en) | 2002-07-31 | 2005-01-31 | Phase correction element and optical head device |
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JP2002-251911 | 2002-08-29 | ||
JP2002251911 | 2002-08-29 | ||
JP2002-295731 | 2002-10-09 | ||
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Also Published As
Publication number | Publication date |
---|---|
US20050226122A1 (en) | 2005-10-13 |
JP4341332B2 (ja) | 2009-10-07 |
KR100985420B1 (ko) | 2010-10-05 |
AU2003252288A1 (en) | 2004-02-16 |
JP2004219977A (ja) | 2004-08-05 |
US20100020671A9 (en) | 2010-01-28 |
KR20050021462A (ko) | 2005-03-07 |
US7688700B2 (en) | 2010-03-30 |
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