WO1999013464A1 - Dispositif optique - Google Patents
Dispositif optique Download PDFInfo
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- WO1999013464A1 WO1999013464A1 PCT/JP1998/004089 JP9804089W WO9913464A1 WO 1999013464 A1 WO1999013464 A1 WO 1999013464A1 JP 9804089 W JP9804089 W JP 9804089W WO 9913464 A1 WO9913464 A1 WO 9913464A1
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- Prior art keywords
- optical
- light
- region
- linearly polarized
- polarized light
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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
- G11B7/1369—Active plates, e.g. liquid crystal panels or electrostrictive elements
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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
- G11B7/1381—Non-lens elements for altering the properties of the beam, e.g. knife edges, slits, filters or stops
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B2007/0003—Recording, reproducing or erasing systems characterised by the structure or type of the carrier
- G11B2007/0006—Recording, reproducing or erasing systems characterised by the structure or type of the carrier adapted for scanning different types of carrier, e.g. CD & DVD
Definitions
- the present invention is applicable to a super-resolution optical device applicable to an optical disk device, and an optical disk such as a DVD (digital versatile disk) or a CD (compact disk) having an appropriate numerical aperture for imaging.
- the present invention relates to an optical device having a high light utilization factor and capable of easily changing the numerical aperture electrically.
- the focal point of light should be an infinitely small spot.
- the image point has a finite spread due to the diffraction effect due to the wave nature of light.
- the spread of the image formation point is physically defined by the following equation.
- ⁇ is the wavelength of light
- k is a constant determined by the optical system and usually takes a value of about 1 to 2.
- the numerical aperture N A is proportional to the ratio D / f between the effective entrance pupil diameter D of the optical system (generally, the effective light beam diameter) and the focal length f.
- the spread of the imaging point expressed by the above equation becomes the theoretical resolution limit of the optical system, and this is called the diffraction limit.
- a general optical disk device uses a semiconductor laser that emits a light beam having a wavelength of about 70 O nm as a light source and a condensing optical system having a numerical aperture NA of about 0.5. .
- the shielding plate blocking the effective luminous flux of the condensing optical system with the shielding plate reduces the light use efficiency.
- the central area of the light including the optical axis is shielded by the shielding plate.
- the central area of the light has a strong light intensity distribution, and therefore the light use efficiency is reduced. Has become even more remarkable.
- Such low light use efficiency necessitates the use of a high-output light source, but such a high-output light source is expensive, which makes the optical device costly. .
- a high-cost semiconductor laser light source is used even if it has a low output, so that a high-power device cannot be used in cost.
- the configuration becomes complicated because the number of components of the optical system also increases.
- a slit shift occurs, not only the sidelobe but also the light-collecting spot will be shielded, so that the slit must be finely aligned.
- dust and the like adhere to gaps in the slit. .
- the present invention has been made in view of such circumstances, and realizes detection of reflected signal light by a super-resolution focusing spot without reducing the light use efficiency and eliminating the problem of sidelobes.
- the primary purpose is to
- the theoretical resolution of the optical system is greatly affected by the numerical aperture.
- the numerical aperture of the focusing (object) lens of an optical pickup used in an optical disk device is about 0.45 for CDs and CD-ROMs, and about 0.55 for DVDs (digital versatile discs).
- the thickness of the optical disc substrate is about 1.2 mm for CD and about 0.6 mm for 00.
- the focusing lens of the optical pickup that needs to focus light to the diffraction limit is designed taking into account the thickness of the optical disk substrate. Therefore, it is impossible to share optical pickups for CD-ROMs because the appropriate numerical apertures differ for CD-ROM and DVD.
- a method of installing two pickups in one device a method of engraving a hologram on the focusing lens of an optical pickup to make it a two-focus, or a liquid crystal shutter
- a method of switching the effective entrance pupil diameter by using a method is used.
- the present invention also solves such a problem, and enables a common optical device (optical pickup) to be used for an optical disk such as a DVD or a CD having an appropriate numerical aperture for image formation.
- the second object is to make it possible to switch the numerical aperture easily and electrically without significantly lowering the utilization factor. Disclosure of the invention
- the present invention achieves the first and second objects by means that are substantially common.
- the present invention provides a condensing optical system for condensing linearly polarized incident light, and a light reflecting member disposed near a focal plane of the condensing optical system.
- An optical device including a light separating element that separates the reflected light reflected from the incident light from the incident light, and a light detecting element that detects the separated light beam separated by the light separating element.
- a linear polarization detecting element is provided in the optical path of the separated light beam.
- the optical rotation optical element whose optical rotation is controlled by an electric signal is installed in the middle of the linearly polarized incident optical path, and the effective light beam of the linearly polarized light is divided into regions where the polarization axes are orthogonal to each other.
- a super-resolution optical system is realized without interrupting the light beam.
- a linear polarization detector on the optical path after the super-resolution focusing spot is reflected by the light reflecting member, it can be reflected without using a slit-focusing lens. Cycloids can be removed from the signal light.
- the linear polarization detector has a detection axis whose orientation is minus 85 degrees or more and minus 5 degrees or 5 degrees or more and 85 degrees or less with respect to the direction of the polarization axis of linearly polarized light incident on the optical rotation optical element. It is desirable to set the range, that is, the range excluding minus 90 degrees, 0 degrees, and around 90 degrees.
- the optical rotatory optical element a region having a function of rotating the polarization axis of linearly polarized light by 90 degrees by applying a voltage to the liquid crystal in a part of the light transmitting region and a region not having the optical rotation function It is preferable to use a liquid crystal element that generates the following, and arrange the liquid crystal element such that the alignment direction of the liquid crystal molecules on the side where the linearly polarized light is incident coincides with or orthogonal to the direction of the polarization axis of the linearly polarized light.
- liquid crystal element a 90-degree twisted nematic liquid crystal element having a transparent electrode for applying a voltage to the liquid crystal in a part of the light transmitting area is used, and a voltage is applied through the transparent electrode.
- the liquid crystal molecules at the site where the liquid crystal molecules have become homeotropically aligned can lose the 90-degree optical rotation function.
- a part of the area where the polarization axis of the linearly polarized light is rotated by approximately 90 degrees by the optical rotation optical element is converted into a substantially circular ⁇ centered on the optical axis in the effective light beam used by the condensing optical system of the linearly polarized light. It may be a region or a region other than the circular region.
- a part of the area where the polarization axis of the linearly polarized light is rotated by approximately 90 degrees by the optical rotation optical element is formed into a substantially rectangular shape centered on the optical axis in the effective light beam used by the condensing optical system of the linearly polarized light.
- the area may be an area or an area other than the rectangular area.
- the area occupied by the substantially circular region in the effective light beam is preferably 1% or more and 20% or less of the area of the effective light beam on a plane perpendicular to the optical axis.
- the area occupied in the effective light flux in the case of a substantially rectangular area is set to 10% or more and 40% or less (particularly preferably about 20%) of the area of the effective light flux on a plane orthogonal to the optical axis. It's good.
- a part of the area where the polarization axis of the linearly polarized light is rotated by about 90 degrees by the optical rotation optical element is centered on the optical axis in the effective light beam used by the linearly polarized light condensing optical system.
- the super-resolution focusing spot is reflected by the light reflecting member and separated from the incident light by the light separating element.
- the second object can be achieved by installing a linearly polarized light detecting element in which the direction of the detection axis substantially coincides with or orthogonal to the direction of the polarization axis of the incident linearly polarized light in the optical path of the light beam.
- this optical device can be used as a common optical pickup for optical disks such as DVDs and CDs having different numerical apertures suitable for imaging, and the optical rotation of the optical rotation optical element can be increased by electric signals.
- the actual numerical aperture can be switched without lowering the light utilization factor.
- side lobes can be removed from the reflected signal light by the linear polarization detection element.
- the area occupied by the substantially circular region in the effective light flux is 50% or more and 80% or less (particularly preferably about 70%) of the area of the effective light flux on a plane orthogonal to the optical axis. Good to do.
- FIG. 1 is a configuration diagram of an optical system showing a first embodiment of the optical device according to the present invention.
- FIG. 2 is a configuration diagram of an optical system showing a second embodiment of the optical device according to the present invention.
- FIG. 3 is a configuration diagram of an optical system showing a third embodiment of the optical device according to the present invention.
- FIG. 4A and FIG. 4B are diagrams schematically showing the optical rotation function in a general, swiss-nematic liquid crystal element that can be electrically controlled.
- FIG. 5 is a diagram showing a configuration of a twisted nematic liquid crystal element prototyped by the inventor for use as the optical rotation element in the present invention.
- Fig. 6A is a cross-sectional view of the focusing spot P obtained by the optical system shown in Fig. 3 in the X-axis direction. It is a figure showing the profile in 99/13464 side.
- FIG. 6B is a diagram showing a profile in a cross section in the X-axis direction of the light condensing spot P obtained by the optical system from which the liquid crystal element 303 has been removed.
- FIG. 7A is a diagram showing a profile of a light collecting spot Q detected by the photodetector 704 of the optical system shown in FIG.
- Figure 7B shows a photodetector of the optical system with the linear polarization detector 703 removed.
- FIG. 7 is a diagram showing a profile of a light collecting spot Q detected by 704.
- FIG. 8 is a diagram showing the direction of the detection axis of the linearly polarized light detection element 703 in FIG.
- FIG. 9 is a block diagram of an optical system showing a fourth embodiment of the optical device according to the present invention.
- FIG. 10 is a configuration diagram of an optical system showing a fifth embodiment of the optical device according to the present invention.
- FIG. 11 is a diagram showing a configuration of a swiss nematic liquid crystal element prototyped by the inventor for use as an optical rotation element in the fourth and fifth embodiments of the present invention.
- FIG. 1 is a configuration diagram of an optical system showing a first embodiment of an optical device according to the present invention, and is premised on application to an optical disk device.
- the optical device of this embodiment includes a linearly polarized laser light source 101, a collimating lens 102, a rotation optical element 103, a condensing optical system 104, a light separating element 701, a condensing optical system 7
- the optical system of the optical disk device is composed of the linearly polarized light detecting element 703 and the light detecting element 704.
- Linearly polarized light 10 emitted from the linearly polarized laser light source 101 becomes a plane wave by the collimating lens 102.
- linearly polarized light 10 has its polarization axis 10 y in the Y-axis direction. 99/13464
- the optical rotation optical element 103 rotates the incident linearly polarized light 10 in the X-axis direction orthogonal to the Y-axis by 0 degrees (no rotation) and a part 103 a that rotates 90 degrees. 3b.
- the part 103 a that rotates (does not rotate) the 0-degree optical rotation of the optical rotation optical element 103 is formed in a rectangular shape centered on the optical axis as shown by hatching. Therefore, the linearly polarized light 10a transmitted through the 0 ° optically rotated portion 103a enters the substantially rectangular region 104a centered on the optical axis O of the condensing optical system 104. I do.
- This rectangular area 104 a is a part of the effective light beam 11 incident on the condensing optical system 104.
- the effective light beam 11 is equal to the light beam of the linearly polarized light 10 transmitted through the optical rotation optical element 103. I do.
- the linearly polarized light 10 b transmitted through the 90-degree optically rotating portion 103 b of the optical rotation optical element 103 enters the region 104 b of the condensing optical system 104 other than the rectangular region. .
- the polarization axes of the linearly polarized light incident on the rectangular region 104a and the linearly polarized light incident on the region 104b other than the rectangular region are orthogonal to each other. Since the orthogonal light beams do not interfere with each other, they behave as if they are shielded from each other. Therefore, super-resolution occurs.
- the optical rotation function of the optical rotation element 103 of the optical rotation element 103 is controlled by an electrical signal, and the optical rotation function is changed to the area of optical rotation of 90 degrees, the rectangular area of the condensing optical system 104 can be obtained.
- the orthogonal relationship between 4a and the polarization axis of the linearly polarized light in the region 104b other than the rectangular region disappears. As a result, the super-resolution effect is lost and normal resolution is achieved.
- the part 103 b that rotates 90 degrees in the optical rotation optical element 103 is changed to a part that rotates 90 degrees.
- the condensing spot P formed by the condensing optical system 104 is the X-axis.
- the optical disk 105 when recording information on the optical disk 105, the optical disk 105 is arranged at the position of the light collecting spot P on the focal plane of the light collecting optical system 1 • 4, and the optical disk 105 is also recorded.
- the track pitch which is the interval between the spiral recording grooves 105a, can be made smaller and the recording density can be improved.
- the portion 103 a that rotates by 0 degrees in the optical rotation optical element 103 is formed in a rectangular shape, but it may be formed in a circular shape around the optical axis. Good. In this case, super-resolution occurs in both the X-axis and Y-axis components.
- the region where the 0-degree rotation is performed does not have to be a strict rectangular or circular shape, and the same super-resolution can be obtained even if there is some notch or distortion. Further, even if the center of the region is slightly shifted from the optical axis of the optical system, a sufficient super-resolution can be obtained similarly.
- the light beam reflected from the condensing spot P of the optical disc 105 returns almost the same optical path as the incident light path, passes through the condensing optical system 104, and is separated by the light separating element 701. You.
- the separated light flux 12 is condensed again by the condensing optical system 702, and the condensed spot Q is detected by the light detecting element 704.
- a straight-line photodetector 703 is provided in the optical path of the separated light flux 12.
- the linear polarization detector 703 Since the linear polarization detector 703 has its orientation set between the X-axis direction and the ⁇ -axis direction, the orthogonal relationship between the X-axis direction and the ⁇ -axis direction is eliminated, thereby condensing the spotlight. It has a function to remove side lobes from Q. Therefore, it is possible to remove the cyclone from the focusing spot Q without using a slit or the like.
- FIG. 2 is a configuration diagram of an optical system showing a second embodiment of the optical device according to the present invention. This is a modified example of the above-described first embodiment, and the same reference numerals in FIG. 2 denote parts corresponding to those in FIG. 99/13464
- the light separating element is not used, and instead, the optical disc 105 is arranged at an angle to serve the function of the light separating element.
- the light condensing spot P on the optical disc 105 can be reflected in an arbitrary angle direction different from the incident direction.
- the condensing spot Q is detected by the light detecting element 704. It becomes possible.
- FIG. 3 is a configuration diagram of the optical system of the optical device, and the same reference numerals are given to portions corresponding to FIG.
- the twisted nematic liquid crystal element 303 is used as an optical rotation element.
- Figs. 4A and 4B schematically show the optical rotation function of a general twisted nematic liquid crystal device that can be electrically controlled.
- the twisted nematic liquid crystal element has a configuration in which liquid crystal molecules 3 are sealed between glass substrates 1 and 2 on which transparent electrodes are coated.
- the glass substrate 1 on the incident side has the orientation axis direction 1a as the Y-axis direction.
- the orientation axis direction is, for example, the Y-axis direction 2a in the upper half region and the Y axis direction in the lower half region. It is set as 2b in the X-axis direction orthogonal to the axis.
- the liquid crystal molecules 3 have the property of aligning the major axis direction with the orientation axis direction and the property of behaving as a continuum. Due to this property, as shown in FIG. 4A, liquid crystal molecules 3 are arranged in parallel in the upper half region. This is called “homogeneous”. On the other hand, in the lower half region, the liquid crystal molecules 3 gradually and smoothly rotate 90 degrees. This is referred to as "90 degree swiss tone mate".
- the polarization axis 4 of the incident linearly polarized light consequently has the length of the liquid crystal molecule 3 due to the dielectric anisotropy of the liquid crystal molecules. Propagation along the axial direction. That is, the polarization axes of the output linearly polarized light are orthogonal to each other, with the upper half region being in the Y-axis direction 4a and the lower half region being in the X-axis direction 4b.
- the optical path length of the incident linearly polarized light traveling in the liquid crystal layer is generally both upper and lower. Is represented by nl X d.
- the polarization axis 4 of the incident linearly polarized light coincides with the direction of the orientation axis 1a on the incident side (that is, the long axis of the liquid crystal molecule), and the following equation is 3, 15 or 35, etc.
- the incident linearly polarized light is emitted as linearly polarized light.
- ⁇ is the wavelength of the incident light.
- an electric field in the Z-axis direction (light traveling direction) is applied to the liquid crystal device via transparent electrodes (not shown) coated on the glass substrates 1 and 2, as shown in Fig. 4B.
- transparent electrodes not shown
- the major axes of the liquid crystal molecules 3 stand still along the Z-axis direction, which is the direction of the electric field. This state It is called “home mouth pick”.
- the direction of the polarization axis 4c of the output linearly polarized light is the same as the Y axis direction as the polarization axis 4 of the incident linearly polarized light. That is, the optical rotation is lost.
- the optical path length of the incident linearly polarized light traveling in the liquid crystal layer is n2 ⁇ d.
- This optical system is for confirming the principle of the present invention, and is different in scale from the optical system of a pickup of a generally used optical disk device.
- the optical system of this embodiment also has basically the same configuration as the optical system of the first embodiment shown in FIG. 1, except that a 90 ° twisted nematic liquid crystal element 303 is used as an optical rotation element. Used.
- the general optical rotation function of the twisted nematic liquid crystal element is as described above with reference to FIGS. 4A and 4B, but in this embodiment, no homogenous alignment is used.
- the linearly polarized light 30 emitted from the linearly polarized laser light source 101 and converted into a plane wave by the collimating lens 102 is converted into a liquid crystal element whose polarization axis 30 y is in the Y-axis direction parallel to the paper surface. It is incident on 303.
- the liquid crystal element 303 is of a twisted nematic type, but its optical rotation is partially controlled by an electric signal, so that the homeotropic aperture pick region 303 a and the 90 ° twisted nematic region 303 b. That is, a sufficient electric field is applied to the liquid crystal molecules by the electric signal through the transparent electrode in the home opening area 303 a.
- the home aperture pick region 303a is formed in a rectangular shape centered on the optical axis.
- the length in the Y-axis direction of the home aperture pick region 303 a is linearly polarized light 3 99/13464
- the dimensions are set to cover the luminous flux area of zero.
- the width in the X-axis direction is set to a size that covers a part of the light beam region of the linearly polarized light 30.
- the area of the rectangular area occupied by the effective luminous flux is in the range of 10% to 40% of the area of the effective luminous flux on the plane orthogonal to the optical axis.
- the linearly polarized light 30 incident on the home aperture pick region 303 a of the liquid crystal element 303 is transmitted without rotation. Subsequently, the linearly polarized light 30a transmitted through the region enters a substantially rectangular region 104a centered on the optical axis O of the condensing optical system 104.
- the rectangular area 104 a is a part of the effective light flux 31 incident on the condensing optical system 104.
- the effective light beam 31 is a linearly polarized light beam 30 transmitted through the liquid crystal element 303. Matches. Therefore, there is no decrease in light quantity. Then, the effective light beam 31 that has passed through the condensing optical system 104 is condensed, and forms a beam spot P.
- the 90-degree swiss tonematic region 30 3b has transmitted 90 degrees of linearly polarized light 30a, and is incident on the region 104 of the focusing optics 104 other than the rectangular region. I do.
- the linearly polarized light in the rectangular region 104a and the region 104b other than the rectangular region has polarization axes orthogonal to each other, so the beam spot P created by the condensing optical system 104 is Super-resolution occurs for the X-axis component.
- the area occupied by the rectangular area 104a in the effective light flux 31 is preferably in the range of 10% to 40% of the area of the effective light flux 31 on a plane perpendicular to the optical axis. It is a target.
- FIG. 5 is a diagram showing a configuration of a twist nematic liquid crystal element prototyped by the inventor for use in this embodiment.
- the liquid crystal element 310 shown in the figure is, for example, a square having an outer shape of about 15 mm, and has a light transmitting region 311 in which liquid crystal having a diameter of 10 mm is sealed in the center.
- Light transmission area 3 In the center of 1 1, a transparent electrode to which a voltage is applied by an electric signal from the electrode section 3 1 4, 3 1 4 is formed, and a 1 mm wide, almost rectangular home opening pick area 3 1 2 a is formed.
- the other region forms a 90 ° twisted nematic region 312b.
- the orientation axis direction 3 13 of the liquid crystal molecules on the light incident side coincides with the direction of the long side of the rectangular homeotropic region 312 a, which is defined as the Y-axis direction.
- the optical axis extends in the Z-axis direction perpendicular to the paper.
- This liquid crystal element almost satisfies the square root of 15 with respect to the expression (2) described above for light having a wavelength of 633 nm.
- this twisted nematic liquid crystal element 31 1 ⁇ is used as the liquid crystal element 303 as the optical rotation optical element in FIG. 3, the home port pick area 3 12 a becomes the home port pick area 303 a, 90 degree twist nematic area 3 1 2b force; 90 degree twist nematic area 3 03 b.
- the linearly polarized light beam is a circular shape with a diameter of about 5nim.
- a lens with a focal length of 50 Otnm is installed about 5cm away from the liquid crystal element 303. I have.
- FIG. 6A shows a profile of a cross section in the X-axis direction of the light collecting spot P by the optical system shown in FIG.
- FIG. 6B shows a profile in the X-axis direction of the light collecting spot P obtained by removing the liquid crystal element 303 from the optical system shown in FIG.
- the profile BSP of the focusing spot shown in Fig. 6A is about 15% smaller than the profile BSP of the focusing spot shown in Fig. 6B. It can be seen that super-resolution has occurred.
- profile BSP in Fig. 6A side lobes SP are generated on both sides of the peak profile PP generated in the center. 99/13464
- a rectangular part having a width of l mm in the X direction and a length of 10 mm in the Y direction is formed at the center of the condensing optical system 104.
- the profile of the cross section in the X-axis direction of the light collecting spot P obtained with the configuration with the shielding plate (conventional device configuration) was almost the same as the profile shown in Fig. 6A.
- the effect of super-resolution was enhanced by applying an appropriate bias voltage to the 90 ° twist nematic region 303 b. This is because, as is the case with ordinary twisted nematic liquid crystals, when a bias voltage near the liquid crystal starts to operate is applied, the birefringence decreases and the optical rotation phenomenon occurs efficiently. Examination of the light use efficiency revealed that in this embodiment, the liquid crystal element 303 reduced the light intensity by about 15% (see FIGS. 6A and 6B). However, if a non-reflective coating is applied to the glass substrate of the liquid crystal element, the attenuation of light intensity can be reduced to 10% or less.
- the homeotropic region 303 a of the liquid crystal element 303 is changed to a 0 ° twisted nematic liquid crystal region, and a 90 ° twisted nematic region 303 b Even if is changed to a home port pick region, super-resolution can be obtained because the polarization axes of the linearly polarized light passing through both regions are orthogonal to each other.
- a reflection type optical disc 105 which is a light reflecting member is arranged almost perpendicular to the optical axis O. Have been. Therefore, the light beam condensed on the light condensing spot P is reflected in the direction of the optical axis O on the surface of the reverse optical disk 105.
- the light beam reflected in this way passes through the condensing optical system 104 again, and is separated by the light separating element 71.
- the light separating element 701 is provided at an intermediate position between the liquid crystal element 303 and the condensing optical system 104 on the optical axis ⁇ .
- the light beam 32 separated by the light separating element 71 is condensed by another condensing optical system 702 to form a condensing spot Q.
- the condensing spot Q is detected by the photodetector 704.
- a linear polarization detecting element 703 is provided in the optical path of the separated light flux 32.
- the linearly polarized light detecting element 703 has a function of removing side lobes from the converging spot Q.
- a prism beam splitter is used as the light separating element 701
- a lens with a focal length of 50 O mm is used as the condensing optical system 702
- a polarizing plate is used as the linear polarization detecting element 73.
- the linearly polarized light detecting element 703 sets the direction of the detection axis thereof to a negative value based on the azimuth of the polarization axis of the linearly polarized light 30 incident on the liquid crystal element 303 as the optical rotation optical element. It is desirable to set it in the range of 5 degrees or more and minus 5 degrees or less, or 5 degrees or more and 85 degrees or less.
- FIG. 7A is a profile BSP of the condensed spot Q detected by the photodetector 704 in the optical system of the third embodiment shown in FIG. 3, and the half width d Z of this profile BSP is shown. 2 is widened, but sidelobes have been removed. In detecting information recorded on the optical disk 105, the spread of the half width of the profile of the focusing spot has almost no effect.
- FIG. 7B is a profile BSP of the light collection spot Q detected by the light detecting element 704 in the configuration in which the linear polarization detecting element 703 in FIG. 3 is removed.
- a sidelobe SP was generated in the profile BST of the light collection spot.
- the side lobe SP becomes a signal noise source when reproducing information recorded on the optical disk 105.
- FIG. 8 shows the orientation 703 a of the linear polarization detecting element 703 used in this embodiment, that is, the orientation of the transmission axis of the linearly polarized light.
- the light beam transmitted through the linearly polarized light detecting element 703 includes linearly polarized light 30b rotated by 90 degrees and linearly polarized light 30a that does not rotate.
- the linear polarization detection element 703 sets the direction of the detection axis to minus 85 degrees with reference to the direction of the polarization axis of the linearly polarized light 30 incident on the liquid crystal element 303 as the optical rotation element. It is desirable to set it in the range of less than or equal to minus 5 degrees or less than 5 degrees or less than 85 degrees.
- the super-resolution optical device using the optical rotatory optical element according to the present invention has higher light use efficiency than the conventional super-resolution optical device using a light shielding plate. And reduce the problems of the cyclone associated with super-resolution. It can be easily removed without adding slits.
- the liquid crystal element used in the present invention has a very simple structure that is smaller in size and does not require mask rubbing, etc., compared to the liquid crystal display panel for a personal computer or the like having the current complicated structure. It does not add cost.
- the inexpensive polarizing plate used in commercially available liquid crystal devices as it is, and as shown in the conventional technology, only the light spot of the light spot is located at the light spot. Positioning is much easier than inserting a light-blocking slit. Further, the present invention can obtain the same effect even in the case of a transmission type optical disk.
- FIG. 9 is a diagram showing the configuration of the optical system. This optical device is such that the substantial aperture of the condensing optical system can be switched between for CVD and for CD 'by an electric signal.
- a linearly polarized laser light source 101 a collimating lens 102, a liquid crystal element 803 as an optical rotation element, a condensing optical system 104, a light separating element 701, a condensed light
- the optical system of the optical disk device is constituted by the scientific system 702, the linear polarization detector 703, and the photodetector 704.
- the linearly polarized light 80 emitted from the linearly polarized laser light source 101 becomes a plane wave by the collimating lens 102.
- the polarization axis 80 y of the linearly polarized light 80 is oriented in the Y-axis direction.
- the direction of the polarization axis 80y is partially rotated by the optical rotation function. That is, the liquid crystal element 803 has a region 803 a that rotates (does not rotate) 0 degrees in the direction of the incident linearly polarized light • 80 in the X-axis direction orthogonal to the Y-axis, and a region 803 that rotates 90 degrees. 3 b.
- the liquid crystal element 803 is a twisted nematic liquid crystal element, and switches between a 90 degree swiste nematic state and a home port pick state by an electric signal as described with reference to FIGS. 4A and 4B. It is possible.
- the optical rotation can be independently switched between a circular region around the optical axis and a region outside the circular shape.
- the liquid crystal element 910 shown in FIG. 11 has a light transmitting region 911 enclosing the liquid crystal, a home port picking region 911 a and a 90 degree swiss nematic region 911 b by an electric signal. Is divided into functions. That is, a sufficient electric field is applied to the liquid crystal molecules by applying a voltage through the transparent electrode in accordance with an electric signal to the home opening area 912a.
- the home port pick area 912a is a circular area centered on the optical axis.
- the transparent electrode is also patterned in the same circle as the circular home opening pick area 912a.
- the home port pick area 912a of the liquid crystal element 803 becomes the home port pick of the liquid crystal element 803.
- the region 803 becomes the 90-degree swiss nematic region 912 b, and the 90-degree swiss nematic region 803 b of the liquid crystal element 803 becomes.
- the linearly polarized light 800 a transmitted through the home pick-up area 803 a of the liquid crystal element 803 is centered on the optical axis 0 of the condensing optical system 104. It is incident on the almost circular area 104a.
- This circular area 104 a is a part of the effective light beam 81 entering the condensing optical system 104 and has a smaller numerical aperture than the effective light beam 81.
- the opening by the effective light beam 81 is set for DVD, and the opening by the circular area 80a is set for CD. Also, in FIG.
- the effective light beam 81 is a linearly polarized light transmitted through the liquid crystal element 803 which is an optical rotation optical element. It is coincident with the luminous flux of 80.
- the linearly polarized light 80 b transmitted through the 90 ° tones nematic region 803 b of the liquid crystal element 803 enters the region 104 b of the condensing optical system 104 other than the circular region.
- the polarization axes of the linearly polarized light incident on the circular region 104a and the linearly polarized light incident on the region 104b other than the circular region are orthogonal to each other.
- the light beam that has entered the optical disc 105 returns along the substantially same optical path as the incident optical path, passes through the condensing optical system 104 again, and is separated by the light separating element 701. At this time, the polarization state of the separated luminous flux 82 retains the original polarization state unless the optical disc 105 has strong birefringence or polarization dependence of diffraction. In ordinary optical disks, the birefringence is as small as 2 O nm or less, and there is almost no polarization dependence due to diffraction.
- the separated light flux 82 is condensed again by the condensing optical system 72 to form a condensing spot Q.
- the light detecting element 704 is disposed on the light collecting spot Q.
- a linearly polarized light detecting element 703 On the optical path of the separated light beam 82, a linearly polarized light detecting element 703 is provided.
- the azimuth of this linearly polarized light detecting element 703 (the direction of the detection axis for transmitting the linearly polarized light) is adjusted, the polarization axis of the linearly polarized light 80 b rotated by 90 degrees becomes the azimuth of the linearly polarized light detecting element 703. Will almost coincide with or be orthogonal to As a result, the component of the linearly polarized light 80b rotated by 90 degrees is shielded.
- the linearly polarized light 80 b having a 90-degree rotation is a light flux that passes through the outer peripheral portion of the condensing optical system 104 having a large numerical aperture, and is originally a part of the light flux used for DVD. Therefore, if it is used for a CD or the like with a different thickness from the DVD disk substrate, the reflected light will have a large aberration. This reflected light beam breaks the shape of the condensing spot Q, and is detected by the photodetector 704. Output accuracy decreases. In this way, by blocking the component of the linearly polarized light 80b rotated by 90 degrees that adversely affects the reproduction of a CD or the like, the reproduction accuracy of a CD or a CD-ROM can be improved.
- the home aperture area 803a of the liquid crystal element 803 is also switched to a 90 ° swiste nematic area so that linearly polarized light is rotated by 90 ° over the entire area of the liquid crystal element 803. What should I do? As a result, all the components of the effective light beam 81 pass through the linearly polarized light detection element 703 to form the converging spot Q.
- This twisted nematic type liquid crystal element 9 10 has a square shape with an outer shape of about 15 mm, and a light transmitting area 911 enclosing a liquid crystal with a diameter of 10 mm at the center, and the entire area is 90 ° twisted nematic. Oriented.
- the light transmitting region 911 is electrically divided into a central circular region 912a having a diameter of 3 mm and a region 912b outside the circular region. That is, the transparent electrodes are independently coated on the regions 912a and 912b. Then, the circular region 912a becomes a homeotropic region by an electric signal from the electrode portion 914, and the region 912b outside the circular region to which no electric signal is applied becomes a 90 ° twisted nematic region.
- the orientation axis direction 913 of the liquid crystal molecules on the side where the light of the liquid crystal element 910 is incident is the Y-axis direction.
- the optical axis Z is a direction that travels perpendicular to the paper.
- the liquid crystal element 910 almost satisfies the above-mentioned square root of 15 with respect to light having a wavelength of 633 nm.
- the area of the substantially circular region 80a occupying in the effective light beam 81 of linearly polarized light in FIG. 9 is the area on a plane orthogonal to the optical axis of the effective light beam 81. It is desirable that the content be 50% or more and 80% or less, and about 70% is optimal.
- FIG. 10 shows a fourth embodiment of the optical device according to the present invention.
- This embodiment has almost the same configuration as the fourth embodiment described with reference to FIG. 9, and shows a case where a CD is arranged as the light reflecting member 105.
- FIG. 10 the same parts as those in FIG. 9 are denoted by the same reference numerals.
- a twist nematic liquid crystal element 903 is used as the optical rotatory optical element.
- the direction of the alignment axis of the liquid crystal element 903 on the side where the linearly polarized light 90 is incident substantially matches the direction of the polarization axis 90y of the linearly polarized light 90. Both are in the Y-axis direction.
- the liquid crystal element 903 can switch between 90 degree twist nematic and home port pick by an electric signal, and can independently switch the optical rotation between a circular area around the optical axis and a non-circular area.
- the liquid crystal element 903 in FIG. 10 has a homeotropic region 903 a by applying a sufficient electric field to a circular region indicated by diagonal lines, and a region outside the circle 90 degrees tonematic region 903 b. And split the function.
- the linearly polarized light 90 that has entered the home aperture pick region 903 a of the liquid crystal element 903 is transmitted without rotation. Subsequently, the linearly polarized light 90 a transmitted through the same region 90 3 a becomes The light is incident on a substantially circular area 104a centered on the optical axis O of the condensing optical system 104.
- the circular area 104 a is a part of the effective light flux 91 incident on the condensing optical system 104, and has a smaller numerical aperture than the effective light flux 91.
- the numerical aperture of the effective light flux 91 is set for DVD, and the numerical aperture of the circular area 104a is set for CD.
- the effective light beam 91 matches the light beam of linearly polarized light transmitted through the liquid crystal element 93. Therefore, there is no decrease in light quantity. Then, the effective light beam having passed through the condensing optical system 104 is condensed to form a condensing spot P.
- the linearly polarized light 90b transmitted through the 90 ° twisted nematic region 903b of the liquid crystal element 903 is rotated 90 °, and is outside the circular region in the condensing optical system 104. It is incident on region 104b.
- the configuration of the twisted nematic liquid crystal element used in this embodiment may be the same as the liquid crystal element 910 described with reference to FIG.
- An optical disk 105 is arranged on the same plane as the light collecting spot P, orthogonal to the optical axis O.
- the light beam condensed on the condensing spot P is reflected by the optical disk 105, returns almost the same optical path as the incident optical path, passes through the condensing optical system 104 again, and then is separated by the light separating element 70.1. Separated by.
- the separated light flux 92 is condensed by the condensing optical system 72 and forms a condensed spot Q.
- the light collecting spot Q is detected by the light detecting element 704.
- a linear polarization detection element 703 is provided at an intermediate portion between the light separation element 701 and the light detection element 704.
- the linear polarization detector 703 has its azimuth (the azimuth for transmitting linearly polarized light) set to the Y-axis direction, and is adjusted so as to extract only the component transmitted through the circular region 104a.
- a component passing through the outer peripheral portion of the condensing optical system 104 having a large numerical aperture can be shielded from light, and CD can be reproduced.
- the DVD or the like can be used because the entire component of the effective luminous flux 91 can be extracted.
- a polarizing plate was used as the linear polarization detecting element 703, and the diameter of the effective light flux 91 was 5 mm.
- the center portion of the polarizing plate may be hollowed out in a circular shape, and only the component transmitted through the circular region 104a may be passed through. Since the polarizing plate absorbs light, this improves light utilization. However, photodiodes that are frequently used as the photodetector 704 have relatively high sensitivity, so that light utilization efficiency does not matter much here.
- an element in which the entire area is a 90-degree twisted nematic liquid crystal is used as the liquid crystal element 903, and even if the area outside the circle for CD is picked up by the electric field due to the electric field, the circular area and its outer peripheral area Since the linearly polarized light is orthogonal at, the same effect can be obtained.
- the liquid crystal element 903 is used as an optical rotatory optical element, and does not use a polarizing plate or the like in the incident optical path, so that in principle, no light amount loss occurs. In the actual measurement, the light loss was about 15%, but it can be reduced to 10% or less if a non-reflective coating is applied to the liquid crystal glass substrate. '
- the area of the substantially circular region 90a occupying in the effective light beam 91 of the linearly polarized light in FIG. 10 is the area of the effective light beam 91 on a plane orthogonal to the optical axis. It is desirable to be 50% or more and 80% or less, and about 70% is optimal.
- the optical device using the optical rotation optical element and the linearly polarized light detecting element according to the present invention when the optical device using the optical rotation optical element and the linearly polarized light detecting element according to the present invention is applied to an optical disk device, the writing (or reading) of data is performed in principle.
- the numerical aperture can be easily and electrically switched without losing the amount of light required.
- DVD-RAM a writable or rewritable digital versatile disc.
- This is very effective as an optical system that combines the reproduction of CDs in the optical system of a disk drive. This is because increasing the light output of a semiconductor laser as a light source is a difficult problem.
- the present invention can be applied to various optical devices using super-resolution technology, such as an optical disk device and a mask exposure device for manufacturing a semiconductor.
- an optical pickup in an optical disk device one optical pickup can be used for both DVD and CD, and the effective switching of the aperture can be easily performed without lowering the light use efficiency. Can be performed.
Landscapes
- Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Chemical & Material Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Optical Head (AREA)
- Liquid Crystal (AREA)
- Optical Recording Or Reproduction (AREA)
- Automatic Focus Adjustment (AREA)
Description
Claims
Priority Applications (6)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP51536699A JP3830537B2 (ja) | 1997-09-10 | 1998-09-10 | 光学装置 |
US09/508,173 US6437319B1 (en) | 1997-09-10 | 1998-09-10 | Optical device |
AU90020/98A AU9002098A (en) | 1997-09-10 | 1998-09-10 | Optical device |
EP98941821A EP1028419B1 (en) | 1997-09-10 | 1998-09-10 | Optical device |
DE69804993T DE69804993T2 (de) | 1997-09-10 | 1998-09-10 | Optisches gerät |
TW088102252A TW455851B (en) | 1998-09-10 | 1999-02-12 | Optical apparatus |
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP24527497 | 1997-09-10 | ||
JP9/245274 | 1997-09-10 | ||
JP9/248547 | 1997-09-12 | ||
JP24854797 | 1997-09-12 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1999013464A1 true WO1999013464A1 (fr) | 1999-03-18 |
Family
ID=26537142
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/JP1998/004089 WO1999013464A1 (fr) | 1997-09-10 | 1998-09-10 | Dispositif optique |
Country Status (7)
Country | Link |
---|---|
US (1) | US6437319B1 (ja) |
EP (1) | EP1028419B1 (ja) |
JP (1) | JP3830537B2 (ja) |
KR (1) | KR100336682B1 (ja) |
AU (1) | AU9002098A (ja) |
DE (1) | DE69804993T2 (ja) |
WO (1) | WO1999013464A1 (ja) |
Families Citing this family (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE102013218231A1 (de) * | 2013-09-11 | 2015-03-12 | Sirona Dental Systems Gmbh | Optisches System zur Erzeugung eines sich zeitlich ändernden Musters für ein Konfokalmikroskop |
CN112803994B (zh) * | 2021-02-03 | 2022-04-19 | 中航海信光电技术有限公司 | 一种用于光模块的光回波容限测试装置 |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH06124477A (ja) * | 1992-10-08 | 1994-05-06 | Sanyo Electric Co Ltd | 光学ヘッド |
JPH09106566A (ja) * | 1995-08-04 | 1997-04-22 | Pioneer Electron Corp | 光ピックアップ |
JPH09198702A (ja) * | 1995-12-29 | 1997-07-31 | Lg Electron Inc | 光ピックアップ装置 |
JPH09223324A (ja) * | 1995-06-12 | 1997-08-26 | Sanyo Electric Co Ltd | 光記録又は光再生装置 |
Family Cites Families (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE69330735T2 (de) * | 1992-07-30 | 2002-07-04 | Hamamatsu Photonics Kk | Optisch adressierter räumlicher Lichtmodulator |
CA2164384C (en) | 1995-03-04 | 1999-08-17 | Jin-Yong Kim | Optical pick-up apparatus capable of reading data irrespective of disc type |
US5787061A (en) * | 1995-08-31 | 1998-07-28 | Sanyo Electric Co., Ltd. | Optical disc recording reproducing apparatus recording/reproducing information to/from optical discs according to different standards |
JP3062099B2 (ja) * | 1996-02-06 | 2000-07-10 | 日本電気株式会社 | 光ヘッド装置 |
US5745465A (en) | 1997-01-23 | 1998-04-28 | Industrial Technology Research Institute | Digital video disc pick-up head system |
-
1998
- 1998-09-10 AU AU90020/98A patent/AU9002098A/en not_active Abandoned
- 1998-09-10 JP JP51536699A patent/JP3830537B2/ja not_active Expired - Fee Related
- 1998-09-10 KR KR1019997008479A patent/KR100336682B1/ko not_active IP Right Cessation
- 1998-09-10 DE DE69804993T patent/DE69804993T2/de not_active Expired - Fee Related
- 1998-09-10 EP EP98941821A patent/EP1028419B1/en not_active Expired - Lifetime
- 1998-09-10 WO PCT/JP1998/004089 patent/WO1999013464A1/ja active IP Right Grant
- 1998-09-10 US US09/508,173 patent/US6437319B1/en not_active Expired - Fee Related
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH06124477A (ja) * | 1992-10-08 | 1994-05-06 | Sanyo Electric Co Ltd | 光学ヘッド |
JPH09223324A (ja) * | 1995-06-12 | 1997-08-26 | Sanyo Electric Co Ltd | 光記録又は光再生装置 |
JPH09106566A (ja) * | 1995-08-04 | 1997-04-22 | Pioneer Electron Corp | 光ピックアップ |
JPH09198702A (ja) * | 1995-12-29 | 1997-07-31 | Lg Electron Inc | 光ピックアップ装置 |
Non-Patent Citations (1)
Title |
---|
See also references of EP1028419A4 * |
Also Published As
Publication number | Publication date |
---|---|
KR100336682B1 (ko) | 2002-05-13 |
DE69804993D1 (de) | 2002-05-23 |
DE69804993T2 (de) | 2002-10-31 |
EP1028419B1 (en) | 2002-04-17 |
EP1028419A1 (en) | 2000-08-16 |
EP1028419A4 (en) | 2000-10-18 |
AU9002098A (en) | 1999-03-29 |
JP3830537B2 (ja) | 2006-10-04 |
KR20000076377A (ko) | 2000-12-26 |
US6437319B1 (en) | 2002-08-20 |
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