JP4248597B2 - Objective lens - Google Patents

Description

The present invention relates to an optical disc apparatus for recording or reproducing information signals using two types of optical discs having different substrate thicknesses.

An optical disk apparatus is an information signal recording / reproducing apparatus characterized by a large capacity and high-speed access, and has been widely used as a reproducing apparatus for digital audio signals and an external storage apparatus for computers utilizing the characteristics. 2. Description of the Related Art In recent years, with the increase in capacity of computer data and the practical use of recording and reproduction of digital moving image information, it is necessary to increase the recording capacity of an optical disc apparatus. The size of the light spot condensed on the recording surface of the optical disc is determined by the wavelength of the laser light source and the numerical aperture (hereinafter referred to as NA) of the objective lens. By increasing the NA and reducing the diameter of the light spot, the recording capacity can be increased. However, when the NA is increased, coma generated by the tilt of the disk increases, and there is no margin for the tilt of the disk and the disc thickness error. In order to solve this problem, it is considered to use a thin disk substrate of 0.6 mm or the like instead of the conventional 1.2 mm thick disk substrate. The problem here is the compatibility of a conventional substrate-thickness disc with a thin disc. That is, in the optical disc apparatus, the recording lens is irradiated with a laser beam through the disc substrate, so that the objective lens is designed according to the disc thickness. Since a large spherical aberration occurs in a disc having a thickness different from the design value, it becomes impossible to record or reproduce a signal at all.

  On the other hand, in the prior art described in Japanese Patent Laid-Open No. 7-182690 shown in FIG. 9, the conversion lens 52 is detachably provided in the optical path connecting the semiconductor laser 1 as the light source and the objective lens 19. I'm taking it. Then, by detecting the thickness of the disk substrate and inserting / removing the conversion lens 52 based on the detected signal, aberration due to the difference in the disk thickness is suppressed and a good recording or reproduction signal is obtained.

JP-A-7-182690

  However, the above configuration has a problem that a mechanism for inserting and removing the conversion lens 52 is necessary. Furthermore, since the positional accuracy and inclination when the conversion lens 52 is inserted directly affect the optical performance, the mechanism for the insertion / removal is required to have a high accuracy, and the apparatus becomes large and expensive. Had.

  Also, it is assumed that high-density discs are reproduced using laser light having a shorter wavelength than conventional optical discs in order to increase recording density. For example, a laser having a wavelength of 650 nm or 635 nm is used for a high-density disk with respect to a wavelength of 780 nm of the conventional method. In the configuration of the above prior art, a short wavelength laser for a high density disk is used as the semiconductor laser 1, and the wavelength for the high density disk is also used when recording or reproducing a conventional disk. Here, recording / reproduction of a disk having a wavelength dependency of characteristics such as reflectance among conventional optical disks becomes a problem. For example, a so-called write-once type optical disc that uses an organic dye recording film and can be recorded only once and can be reproduced by a reproduction-only device after recording has already been put into practical use. The reflectance of the film varies greatly depending on the wavelength. Therefore, it is not possible to reproduce a disk for a wavelength of 780 nm using a wavelength of 650 nm or 635 nm. In the configuration of the above prior art, a conventional optical disc must be reproduced using a light source having a wavelength for a high-density disc, so that a disc having such wavelength dependency among conventional optical discs is reproduced. There is a problem that cannot be done.

In view of the above problems, an object of the present invention is to provide an objective lens capable of reproducing two or more types of discs having different thicknesses .

The above object can be solved by the configuration of the claims as an example.

According to the present invention, it is possible to provide an objective lens capable of reproducing two or more types of discs having different thicknesses .

The configuration and operation of the optical pickup as the first embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a configuration diagram of an optical pickup according to the present embodiment . In FIG. 1, a light emitting element 1 and a light emitting element 11 which are light sources of an optical pickup are, for example, semiconductor laser elements. In the present embodiment, the light emitting element 1 and the light emitting element 11 are elements having different wavelengths. Hereinafter, the wavelengths of the output light of the light emitting element 1 and the light emitting element 11 are λ1 and λ2, respectively. The light-emitting element 1 is used for recording or reproduction on a high-density disk 20 having a thin disk substrate thickness, and the light-emitting element 11 is used for recording or reproduction on a conventional disk (not shown) having a large disk substrate thickness. Use. Desirably, λ1 may be a short wavelength such as 650 nm or 635 nm suitable for a high-density disk, and λ2 may be a wavelength such as 780 nm that is used in the conventional method. In addition, the emission wavelength of an actual laser element has a product variation, and the wavelength value here is a nominal value.

  The objective lens 19 is designed to collect a light spot having a predetermined aberration amount or less through the substrate 20a of the high-density disk 20 when a parallel light beam is incident.

  The light beam 2 emitted from the light emitting element 1 as the first light source passes through the first light beam separation element 3 and is converted into a parallel light beam by the collimator lens 7.

  The light beam separating element 3 allows the light beam 2 to pass therethrough and guide it to the subsequent optical system, and also separates the reflected light beam 4 from the high density disk 20 from the optical path connecting the light emitting element 1 and the high density disk 20 to a photodetector. 5 is an optical element. For example, by using a diffraction grating or a hologram as the light beam separation element 3, the light beam 2 is guided to the collimating lens 7 as 0th order diffracted light, that is, directly transmitted light, and the reflected light from the high density disk 20 is used as the first order diffracted light. Lead to 5.

  The light beam separating element 3 can be configured using an optical element such as a prism, a half mirror, and a waveguide in addition to a diffraction grating or a hologram. Further, a diffraction grating for performing tracking error detection by the three-spot method may be installed between the light emitting element 1 and the light beam separating element 3. The collimating lens 7 can also be disposed between the light emitting element 1 and the light beam separating element 3. Further, the light emitting element 1, the light beam separating element 3, and the photodetector 5 may be integrally mounted as the first optical block 6. By integrally mounting them, the optical pickup can be reduced in size.

  The light beam 8 emitted from the collimating lens 7 is incident on the objective lens 19 as a parallel light beam 17 through the light beam combining / separating element 9, and is condensed as a light spot on the recording surface 20b through the substrate 20a of the high-density disk 20.

  Reflected light from the recording surface 20 b enters the photodetector 5 as a light beam 4 through the objective lens 19, the light beam combining / separating element 9, the collimating lens 7, and the light beam separating element 3.

  On the other hand, the laser light beam 12 emitted from the light emitting element 11 as the second light source passes through the second light beam separating element 13 and enters the light beam combining / separating element 9.

  The light beam combining / separating element 9 is a kind of prism and has a wavelength filter 10 therein. The wavelength filter 10 functions as a transmission film at λ1 and a reflection film at λ2. Therefore, the light beam that has passed through the light beam separating element 13 and entered the light beam combining / separating element 9 is reflected by the wavelength filter 10, enters the objective lens 19 as a divergent light beam 18, and is condensed as a light spot 22.

  Here, as described above, the objective lens 19 is designed to collect the parallel light beam 17 through a thin disk substrate of 0.6 mm or the like, for example. A divergent light beam 18 is incident on such an objective lens at a predetermined divergence angle, and is condensed through a thick disk substrate such as 1.2 mm. With such a configuration, the light spot 22 is focused on the recording surface of a conventional disk having a large substrate thickness as a good light spot with less aberration. Note that the disk recorded or reproduced by the light spot 22 is not shown for simplicity.

  The reflected light beam from the disk of the light spot 22 enters the second photodetector 15 as the light beam 14 through the objective lens 19, the light beam combining / separating element 9, and the second light beam separating element 13. The light emitting element 11, the light beam separating element 13, and the photodetector 15 may be integrally mounted as the optical block 16. Hereinafter, the divergence angle of the divergent light beam 18 incident on the objective lens 19 will be described. Here, the divergence angle is an angle of the light beam passing through the outermost side of the divergent light beam 18, that is, the peripheral light beam, with respect to the optical axis. In the design by the inventor, for example, when an aspherical lens having a focal length of 3.4 mm is used as the objective lens 19 and the substrate thickness of the high-density disc is 0.6 mm and the substrate thickness of the conventional disc is 1.2 mm, When NA on the disk side of the objective lens 19 is 0.6, 1.87 degrees, or 1.29 degrees when NA is 0.4, the spherical aberration due to the disc thickness difference is effective. It was found that it can be corrected automatically. Optimum divergence angle differs if the objective lens 19 has a different design such as focal length or aspherical coefficient. However, spherical aberration can be effectively reduced by setting it to 1 degree or more and 3 degrees or less, preferably 1 degree or more and 2 degrees or less. Can be corrected. According to the present embodiment, both a high-density disk and a conventional disk can be recorded with a good light spot without using a mechanical switching mechanism such as insertion and removal of a correction lens or switching between two types of objective lenses. Can play. Further, a high-density disk and a conventional disk can be recorded or reproduced using a light source having an optimum wavelength.

In addition, since the structure of this embodiment includes two light emitting elements, elements having wavelengths suitable for a high density disk and a conventional disk can be used for the first light emitting element and the second light emitting element, respectively. . Therefore, for example, by using a semiconductor laser having a wavelength of 650 nm band or 635 nm band as the first light emitting element and using a semiconductor laser having a wavelength of 780 nm band as the second light emitting element, it is possible to cope with a high density disk and to add an organic dye. Recording or reproduction can also be performed on an optical disc having a remarkable wavelength dependency such as the write-once type used.

  In the present embodiment, the light emitting element 1 and the light emitting element 11 are installed so that the polarization directions of the output light are different from each other. For example, as shown in the figure, the polarization directions of the output light of the light emitting element 1 and the light emitting element 11 are set to a direction parallel to the paper surface and a direction perpendicular to the paper surface, respectively. The wavelengths of the light emitting element 1 and the light emitting element 11 may be different from each other, or the same wavelength may be used.

  The light beam combining / separating element 9 according to the present embodiment is a polarizing prism, and has a polarizing film 30 therein. The polarizing film 30 functions as a transmissive film for polarized light parallel to the paper surface and as a reflective film for polarized light perpendicular to the paper surface. Therefore, similarly to the wavelength filter 10 in the first embodiment, the light beams emitted from the light emitting element 1 and the light emitting element 11 can be respectively guided to the objective lens 19. Since other configurations and operations are the same as those in the first embodiment, description thereof will be omitted.

  Also according to this embodiment, it is possible to record or reproduce both a high-density disk and a conventional disk with a good light spot without using a mechanical switching mechanism.

  Next, the configuration and operation of the optical pickup as the third embodiment of the present invention will be described with reference to FIG.

  In the present embodiment, the limiting opening 23 is inserted into the optical path connecting the light emitting element 11 and the light beam combining / separating element 9. The limiting aperture 23 determines the NA on the disk side of the conventional disk recording or reproducing light beam emitted from the light emitting element 11 and condensed on the disk by the objective lens 19. Other configurations and operations are the same as those in the first embodiment. Further, instead of the light beam combining / separating element 9 having the wavelength filter 10, the polarizing prism described in the second embodiment may be used.

  Generally, when reproducing a high-density disk, since the disk substrate thickness is thin, a large NA such as 0.6 can be used to reduce the diameter of the light spot 21 on the disk and increase the density. . However, in the conventional disk, since the substrate is thick, it is desirable to set the NA to a value such as 0.4 or 0.5 to prevent the aberration from being deteriorated due to the disk tilt or the like. The restriction aperture 23 is inserted into the optical path connecting the light emitting element 11 and the beam combining / separating element 9 as in the present embodiment, so that a high-density disk and a conventional disk can be recorded using optimum NAs. Or you can play.

  Next, the configuration of the light beam combining / separating element 9 and the limiting aperture 23 as the fourth embodiment of the present invention will be described with reference to FIG.

  4A, 4B, 4C, and 4D are configuration diagrams showing the light beam combining / separating element 9. FIG. The light beam combining / separating element 9 and the restriction opening 23 can be integrated as shown in FIG. Further, as shown in (b), if the wavelength filter 10 is provided only in a part of the prism constituting the light beam combining / separating element 9 instead of installing the limiting aperture 23, the same effect as the limiting aperture can be obtained. There is an advantage that the number of parts can be reduced.

  Furthermore, as shown in (c), a plate-shaped light beam combining / separating element 9 may be used in place of the prism-shaped light beam combining / separating element, which is advantageous in that it is less expensive than the prism-shaped element. Further, by providing the wavelength filter 10 only in a part of the flat light beam combining / separating element 9 as shown in FIG.

  In the present embodiment, the polarizing film shown in the second embodiment can be used in place of the wavelength filter 10. Further, when the loss of light quantity does not become a problem, a half mirror film is used in place of the wavelength filter or polarizing film of the light beam combining / separating element 9 of the first, second, and third embodiments and the present embodiment. May be. Further, the light beam combining / separating element 9 is not limited to the shape shown above, and any element having a function of guiding the light beams emitted from the first and second light emitting elements to the objective lens can be used.

  Next, the configuration of the limiting aperture and the objective lens as the fifth and sixth embodiments of the present invention will be described with reference to FIG.

  FIG. 5A is a configuration diagram showing the objective lens 19 and the wavelength selectivity limiting aperture 26 as a fifth embodiment of the present invention, and FIG. 5B is a wavelength selectivity limiting aperture 26. It is the top view which looked at from the direction of the optical axis. The objective lens 19 and the wavelength selectivity limiting opening 26 are connected via a support member 25. The wavelength selectivity limiting aperture 26 is divided into a wavelength filter 27 and a central portion 28 provided in the peripheral portion as shown in FIG.

  The wavelength filter 27 transmits the light beam having the wavelength λ1 in the first embodiment of the present invention, and reflects, absorbs, or scatters the light beam having the wavelength λ2 without transmitting the light beam. The central portion 28 transmits both wavelengths. Desirably, the central portion 28 may be provided with an antireflection film for the wavelengths λ1 and λ2. In the present embodiment, the wavelength selectivity limiting aperture 26 functions as a limiting aperture only for the light flux having the wavelength λ2.

  FIG. 5C is a configuration diagram showing an objective lens 19 as a sixth embodiment of the present invention, and FIG. 5D is a plan view of the objective lens 19 viewed from the direction of the optical axis. is there. The objective lens 19 is provided with a wavelength filter 27. The wavelength filter 27 transmits the light beam having the wavelength λ1 and reflects, absorbs, or scatters the light beam having the wavelength λ2 without transmitting the light beam. The central portion 28 transmits both wavelengths. Desirably, the central portion 28 may be provided with an antireflection film for the wavelengths λ1 and λ2. The wavelength filter 27 may be provided on the light source side surface of the objective lens 19 or on the disk side. In the present embodiment, the objective lens 19 functions as a limiting aperture only for the light flux having the wavelength λ2. In the fifth and sixth embodiments, a polarizing filter may be used in place of the wavelength filter 27 and applied to the configuration described in the second embodiment. The fifth and sixth embodiments can be applied to all configurations of the present invention. In the fifth and sixth embodiments, the limiting aperture means is integrated with the objective lens. However, the limiting aperture means may be provided in the optical path connecting the light beam combining / separating element, the objective lens, and the disk.

  According to the fifth and sixth embodiments, as in the third embodiment of the present invention, a high-density disk and a conventional disk can be recorded or reproduced using an optimum NA. Furthermore, according to the fifth and sixth embodiments, since the limiting aperture is provided integrally with the objective lens, even if the objective lens is moved by the tracking operation, the reflected light beam from the disk is limited by the limiting aperture. There is an effect that a partly missing problem does not occur.

  Next, a seventh embodiment of the present invention will be described with reference to FIG.

  FIG. 6 is a configuration diagram illustrating the configuration of the seventh embodiment. In FIG. 6, the optical path of the light beam emitted from the light emitting element 1 is the same as that of the embodiment described so far. In the present embodiment, the intermediate lens 24 is inserted into an optical path connecting the light emitting element 11 and the light beam combining / separating element 9.

  The intermediate lens 24 changes the divergence angle of the light beam 12 emitted from the light emitting element 11 and makes it incident on the objective lens 19 as the light beam 18. The purpose of this configuration is to make the light beam emitted from the light emitting element 11 and incident on the objective lens different in the divergence state on the light emitting element 11 side and the objective lens 19 side, so that the aberration on the divergence state on the objective lens 19 side is the best. And the light emitting element 11 side is designed so as to obtain the required light utilization efficiency. That is, the divergence angle on the objective lens 19 side is set to, for example, 1 degree to 3 degrees, or 1 degree to 2 degrees as described in the first embodiment. At this time, by setting the divergence angle on the light emitting element 11 side to a larger value, the light beam emitted from the light emitting element 11 can be used effectively, and the optical path length from the light emitting element 11 to the objective lens 19 is further increased. It can be shortened and the apparatus can be miniaturized. Note that the intermediate lens 24 may be a convex lens, a concave lens or the like as long as it meets the purpose of the present embodiment. Further, the intermediate lens 24 can be applied to any configuration of the present invention. Further, by forming the intermediate lens 24 integrally with the light beam combining / separating element 9, the light beam separating element 13, or the optical block 16, it is possible to reduce the size of the optical pickup and the number of parts.

  Next, an eighth embodiment of the present invention will be described with reference to FIG.

  FIG. 7 is a configuration diagram illustrating the configuration of the eighth embodiment of the present invention. In FIG. 7, light beams emitted from the light emitting element 1 and the light emitting element 11 are incident on the objective lens 19 as divergent light beams, respectively. Also in the configuration of the present embodiment, the light spots 21 and 22 formed by the light flux 17 and the light flux 18 can perform recording or reproduction of a high-density disc and a conventional disc, respectively.

  Next, an embodiment of the optical disk apparatus of the present invention will be described with reference to FIG.

FIG. 8 is a configuration diagram showing the configuration of the optical disc apparatus of the present embodiment . In FIG. 8, the optical pickups of the embodiments described so far can be used as the optical pickup 30.
Further, it is possible to determine the type of the optical disk mounted on the optical disk device, and to electrically switch between the light source and the signal processing according to the determination result.
Furthermore, the above effects can be realized without providing a mechanical switching mechanism such as a correction lens, and a small and highly reliable optical pickup and optical disc apparatus can be provided.
Furthermore, by using an element having the optimum wavelength for each of the two light emitting elements as a high-density disk and a conventional disk, a disk whose reflectivity varies greatly depending on the wavelength of an organic dye system or the like can be recorded without any problem. Can be played.

  The light emitting element 1 and the light emitting element 11 of the optical pickup 30 are turned on / off of light emission and controlled of light emission output by a laser driving circuit 31 and a laser driving circuit 36, respectively. Outputs of the photodetectors 5 and 15 are supplied to signal processing circuits 33 and 38 through current-voltage conversion circuits 32 and 37, respectively, and signals such as a focus error signal, a tracking error signal, and a main signal are generated. These signals are supplied to the system control circuit 34.

  In FIG. 8, the disc type discriminating means 35 discriminates the type of disc loaded in the optical disc apparatus and outputs the result to the system control circuit 34. As the disc type discriminating means 35, a method of detecting the substrate thickness of the disc by an optical or mechanical method, a method of detecting an identification mark recorded in advance on the disc or the cartridge of the disc, and the like can be considered. Alternatively, a method may be used in which a disc signal is reproduced assuming a disc type, and if a normal signal is not obtained, it is determined that the disc is of another type.

  The system control circuit 34 turns on the light emitting element 1 or the light emitting element 11 based on the determination result received from the disk type determining means 35, and forms a light spot suitable for recording or reproduction of the loaded disk. At the same time, an appropriate output of the signal processing circuit 33 or the signal processing circuit 38 is selected, and the focus error signal and the tracking error signal are supplied to the focus actuator driving circuit 39 and the tracking actuator driving circuit 40, respectively. The outputs of the focus actuator drive circuit 39 and the tracking actuator drive circuit 40 are respectively supplied to the focus coil 41 and the tracking coil 42 of the objective lens actuator in the optical pickup 30, and the focus and tracking servo operations are performed to record or reproduce the disk 20. Is executed.

  According to the present embodiment, the optical pickup of the present invention is used to select a light emitting element, a photodetector, and a signal processing circuit suitable for the type of the optical disk mounted on the optical disk apparatus, and a mechanical lens such as a correction lens. Recording or reproduction of at least two types of optical discs can be performed without switching. By not performing mechanical switching, it is possible to realize an optical disc apparatus having a small size, high reliability, and a simple configuration.

1 is a configuration diagram of an optical pickup as a first embodiment of the present invention. FIG. It is a block diagram of the optical pick-up as the 2nd Embodiment of this invention. It is a block diagram of the optical pick-up as the 3rd Embodiment of this invention. It is a block diagram which shows the structure of the light beam combining / separating element as the 4th Embodiment of this invention. It is the block diagram and the top view which showed the objective lens and restriction | limiting aperture as 5th and 6th embodiment of this invention. It is a block diagram explaining the structure of the 7th Embodiment of this invention. It is a block diagram explaining the structure of the 8th Embodiment of this invention. It is a block diagram which shows embodiment of the optical disk apparatus of this invention. It is a block diagram which shows the structure of a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Light emitting element, 5 ... Photodetector, 6 ... Optical block, 7 ... Collimating lens, 9 ... Light beam synthetic | combination separation element, 11 ... Light emitting element, 15 ... Photodetector, 16 ... Optical block, 19 ... Objective lens, 23 Reference aperture, 24: Intermediate lens, 26: Wavelength selectivity limiting aperture, 27: Wavelength filter, 30: Optical pickup, 35: Disc type discriminating means

Claims (4)

A first incident light beam having a first wavelength is incident at a first incident angle and condensed on the recording surface of the first disk for recording or reproduction, and a second longer than the first wavelength. An objective lens that makes a second incident light beam having a wavelength incident at a second incident angle and collects it on a recording surface of a second disk for recording or reproduction,
When the convergence direction is defined as plus and the divergence direction is defined as minus with respect to the objective lens, the first incident angle is larger than the second incident angle,
In the central part, the first incident light beam and the second incident light beam are transmitted, and in the peripheral part, the first incident light beam does not function as a restriction opening, but the restriction opening functions as a restriction opening for the second light beam. Means are integrally provided on the incident surface side,
The objective lens according to claim 1, further comprising an antireflection film for the light fluxes having the first wavelength and the second wavelength at the central portion. 2. The objective lens according to claim 1, wherein the limiting aperture means is a polarizing filter .   2. The objective lens according to claim 1, wherein the limiting aperture means and the objective lens are connected to each other by a support member.   The objective lens according to claim 1, wherein the limiting aperture means is provided on the objective lens surface.

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