WO2007040147A1

WO2007040147A1 - Optical head, optical disc device, computer, and optical disc recorder

Info

Publication number: WO2007040147A1
Application number: PCT/JP2006/319347
Authority: WO
Inventors: Sadao Mizuno
Original assignee: Matsushita Electric Industrial Co., Ltd.
Priority date: 2005-09-30
Filing date: 2006-09-28
Publication date: 2007-04-12
Also published as: JP2008310838A

Abstract

It is possible to simplify configuration of an optical head by receiving light corresponding to a plurality of wavelengths by a single photo-detector. A blue laser (1) emits light of wavelength λ1, a red laser (2) emits light of wavelength λ2, and an infrared laser (3) emits light of wavelength λ3. A collimator lens (13) collects the lights of wavelengths λ1, λ2, and λ3. An objective lens (16) causes optical discs (51, 52, 53) to converge the lights of wavelengths λ1, λ2, and λ3. A photo-detector (20) receives reflected lights from the optical discs (51, 52, 53) converged by the collimator lens (13). A stepping motor (22) moves the collimator lens (13) in the optical axis direction and records information in the optical discs (51, 52, 53). Alternatively, when reproducing the information from the optical discs (51, 52, 53), the stepping motor (22) selectively changes the position of the collimator lens (13) according to the respective wavelengths of the lights emitted from the lasers (1, 2, 3).

Description

Specification

Optical head, optical disc apparatus, computer and optical disc recorder

Technical field

[0001] The present invention relates to an optical head for recording, reproducing, or erasing information on an optical information medium such as an optical disc, an optical disc apparatus using the optical head, a personal computer to which the apparatus is applied, It relates to systems such as optical disc recorders that record video 'audio signals.

Background art

[0002] In compact discs (hereinafter referred to as CDs) that can be said to be the first generation of optical discs, the numerical aperture of the objective lens is in the range of 0.45 to 0.5, and infrared light with a wavelength of 780 nm is used. Protective layer thickness 1. Information is recorded or played back on an optical disk with a thickness of 2 mm (hereinafter referred to as recording Z playback). In this specification, the protective layer refers to a transparent medium from the surface where the light beam is incident on the optical disk to the information recording surface. In the second-generation digital versatile disc (hereinafter referred to as DVD), the objective lens has a numerical aperture of 0.6 and red light with a wavelength of 655 nm is used to record information on an optical disc with a protective layer thickness of 0.6 mm. Recording Z Playback is in progress. In a third-generation Blu-ray disc (hereinafter referred to as BD), information is recorded on an optical disc with a protective layer thickness of 0.1 mm using blue light with a wavelength of 405 nm, with a numerical aperture of the objective lens of 0.85. Playing.

[0003] In this way, the third generation optical disc has a short wavelength, a blue laser, and a large numerical aperture! /, The optical system is used to achieve higher density than before, and future market expansion is expected. However, even for BD, which is a high-density optical disc, succession of assets stored in DVDs and CDs is desired, and a compact and inexpensive optical disc apparatus is required. For this purpose, the optical head, which is a key device of the optical disk apparatus, needs to be a streamlined and simple optical system.

[0004] Conventionally, there has been disclosed a configuration for recording and reproducing information on different types of optical disks by using light beams having a plurality of wavelengths. Here, a first conventional example of an optical head will be described with reference to FIG. Figure 15 shows the schematic configuration of the optical head of the first conventional example. It is a figure.

In FIG. 15, the light having a wavelength of 405 nm emitted from the blue laser 61 has its light intensity distribution corrected by the beam shaper 64, transmitted through the beam splitters 65 and 66, and converted into parallel light by the collimator lens 67. . Thereafter, the light passes through the beam splitter 68 and is converged on the information recording surface of the optical disc 51 by the objective lens 70 through the protective layer having a thickness of 0.1 mm. The object lens 70 has a diffractive element formed on its surface, and can record information on an optical disk 52 with a protective layer thickness of 0.6 mm and an optical disk 53 with a protective layer thickness of 1.2 mm. It is configured as follows. The light reflected from the optical disc 51 follows the original optical path in the reverse direction, is narrowed down by the collimating lens 67, and is reflected by the beam splitter 65. The reflected light is given astigmatism by the cylindrical lens 73, the focal length is extended by the detection lens 74, and enters the photodetector 75. Then, the optical head uses the output signal of the photodetector 75 to obtain a focus signal, a tracking signal, and an information signal.

On the other hand, the light emitted from the red laser 62 has its light intensity distribution corrected by the beam shaper 71, transmitted through the beam splitter 72, reflected from the beam splitter 66, and converted into a weakly divergent light beam by the collimator lens 67. The Thereafter, the light passes through the beam splitter 68 and is converged on the information recording surface of the optical disc 52 by the objective lens 70 through the protective layer having a thickness of 0.6 mm. The light reflected from the optical disc 52 follows the original optical path in the reverse direction, is narrowed down by the collimating lens 67, and is reflected by the beam splitters 66 and 72. The reflected light is given astigmatism by the cylindrical lens 76, the focal length is extended by the detection lens 77, and enters the photodetector 78. Then, the optical head uses the output signal of the photodetector 78 to obtain a focus signal, tracking signal, and information signal.

[0007] The light emitted from the infrared laser 63 is divergent light, and this light passes through the hologram element 79, reflects off the beam splitter 68, and is protected to a thickness of 1.2 mm by the objective lens 70. It converges on the information recording surface of the optical disc 53 through the layers. The reflected light from the optical disk 53 is reflected by the beam splitter 68, is branched by the hologram element 79, and enters the photodetector 80. Then, the optical head uses the output signal of the photodetector 80 to obtain a focus signal, a tracking signal, and an information signal (see, for example, Patent Document 1).

[0008] As a second conventional example, there are an optical disc having a protective layer thickness of 0.1 mm and an optical disc having a protective layer thickness of 0.6 mm. A configuration of a compatible optical head that records and reproduces information on a disk is disclosed. FIG. 16 is a diagram showing a schematic configuration of the optical head of the second conventional example.

In FIG. 16, light having a wavelength of 405 nm emitted from the blue laser 81 has its light intensity distribution corrected by the beam shaping element 83, reflected by the beam splitter 84, and converted into circularly polarized light by the wave plate 85. Thereafter, the light is condensed into collimated light by the collimating lens 86, reflected by the mirror 87, and reflected by the diffraction element 88 and the objective lens 89 through the protective layer having a thickness of 0.1 mm. Converge to. In combination with the objective lens 89, the diffractive element 88 is configured to converge light with a wavelength of 405 nm onto an optical disk with a protective layer thickness of 0.1 mm, and focus light with a wavelength of 655 ηm onto an optical disk with a protective layer thickness of 0.6 mm. Yes. The light reflected from the optical disc 51 follows the original optical path in reverse, is converted into linearly polarized light in a direction perpendicular to the forward path by the wave plate 85, and is reflected by the beam splitter 90. Thereafter, the reflected light is diffracted by the detection hologram 91, the focal length is extended by the detection lens 92, and enters the photodetector 93. The optical head obtains a focus signal, a tracking signal, and an information signal by calculating the output of the photodetector 93.

Next, light having a wavelength of 655 nm emitted from the red laser 82 passes through the beam splitter 90 and the beam splitter 84 and is condensed into parallel light by the collimator lens 86. Thereafter, the light is reflected by the mirror 87 and converged on the information recording surface of the optical disc 52 by the diffraction element 88 and the objective lens 89 through the protective layer having a thickness of 0.6 mm. The light reflected from the optical disk 52 follows the original optical path in the opposite direction, is reflected by the beam splitter 90, is diffracted by the detection hologram 91, and is further extended in focal length by the detection lens 92. Incident in 93. The optical head obtains a servo signal, a tracking signal, and an information signal by calculating the output of the photodetector 93 (see, for example, Patent Document 2).

[0011] In the first conventional example, recording Z reproduction of BD, DVD, and CD is performed by one objective lens. Although there is no detailed explanation of the compatibility method, the detection optical system is complicated because it uses parallel light and divergent light. The divergent light from the blue laser 61 is condensed into parallel light by the collimating lens 67, the divergent light from the red laser 62 is condensed into weakly divergent light by the collimating lens 67, and the divergent light from the infrared laser 63 remains as it is. The light is incident on the objective lens 70 without being condensed. For this reason, the light reflected from the optical disk is detected by a single photodetector. It is difficult to emit, and three photodetectors 75, 78, and 80 are provided for each laser. By providing three photodetectors, the force detection optical system that can set the positional relationship between the laser and the photodetector independently for each wavelength of light consists of two sets of cylindrical lenses, a detection lens, and one It is necessary to provide a hologram element. This complicates the configuration of the optical head, which is not only difficult to reduce in size but also disadvantageous in terms of cost.

[0012] In the second conventional example, recording Z playback of BD and DVD is performed by one objective lens. Light with a wavelength of 405 nm uses the second-order diffracted light of diffraction element 88, and light with a wavelength of 655 nm uses the first-order diffracted light of diffraction element 88 to correct spherical aberration due to the difference in protective layer thickness between BD and DVD. ing. In this case, light with a wavelength of 780 nm cannot be optimized for the protective layer of the CD, so the CD cannot be recorded and played back. The reflected light of the optical disc 51, which is a BD, and the reflected light of the optical disc 52, which is a DVD, are received by a common photodetector 93, and a servo signal is obtained. For this reason, the blue laser 81 and the red laser 82 are arranged so that their respective emission points are in an imaging relationship with respect to a common position on the objective lens side. This is to set a laser emission point at a convergence position when light having a wavelength of 405 nm and light having a wavelength of 655 nm are incident as parallel light from the optical disk side. In this case, the two lights cannot be converged in the same manner on the photodetector 93 due to the chromatic aberration of the collimating lens 86. For example, when focus detection is performed by the astigmatism method, the position of the minimum circle of confusion is shifted between the wavelength of 405 nm and the wavelength of 655 nm, so that a constant offset occurs in the focus signal. For this reason, the range in which focus control can be performed becomes narrow, and force control becomes difficult depending on the configuration.

Patent Document 1: Japanese Unexamined Patent Publication No. 2005-209325 (pages 17-19, Fig. 6)

Patent Document 2: Japanese Patent Application Laid-Open No. 2004-192783 (Page 12-18, Fig. 1)

Disclosure of the invention

[0013] The present invention has been made to solve the above-described problem. A single photodetector can receive light corresponding to a plurality of wavelengths, and the configuration of the optical head can be simplified. An object of the present invention is to provide an optical head, an optical disk device, a computer, and an optical disk recorder that can perform recording.

[0014] An optical head according to one aspect of the present invention includes a first light source that emits light of a first wavelength, A second light source that emits light of a second wavelength that is longer than the first wavelength; a third light source that emits light of a third wavelength that is longer than the second wavelength; and A collimating lens that collects the light of the first wavelength, the second wavelength, and the third wavelength; and the light of the first wavelength that is collected by the collimating lens is converged on the first optical disc. The second wavelength light collected by the collimating lens is converged on a second optical disc having a protective layer thickness different from that of the first optical disc, and is collected by the collimating lens. An objective lens for converging light having a wavelength of 3 to a third optical disc having a protective layer thickness different from that of the first optical disc and the second optical disc, the first optical disc bundled by the collimator lens, and the first optical disc 2 optical discs and The photodetector that receives the reflected light from the third optical disc and the collimating lens are moved in the optical axis direction, and information is recorded on the first optical disc, the second optical disc, and the third optical disc. Or each of the light emitted from the first light source, the second light source, and the third light source when reproducing information from the first optical disc, the second optical disc, and the third optical disc. A collimating lens moving unit that selectively changes the position of the collimating lens in accordance with the wavelength of light.

Accordingly, the position of the collimating lens is selectively changed corresponding to the wavelength of each light emitted from the first light source, the second light source, and the third light source, and light detection that occurs due to a difference in wavelength is detected. Since the deviation of the convergence position of the system can be corrected, light corresponding to a plurality of wavelengths can be received by one photodetector, and the configuration of the optical head can be simplified.

Brief Description of Drawings

FIG. 1 is a diagram showing a basic configuration of an optical head and a state of light propagation in Embodiment 1 of the present invention.

FIG. 2 is a cross-sectional view of an objective lens according to Embodiment 1 of the present invention.

FIG. 3 is a plan view of the diffraction element according to the first embodiment of the present invention.

FIG. 4A is a cross-sectional view of the detection optical system according to Embodiment 1 of the present invention, showing a state of propagation of convergent light, and FIG. 4B is a detection optical system shown in FIG. 4A. It is sectional drawing of the orthogonal direction of these.

FIG. 5A shows a pattern of a light receiving element and a focus signal in Embodiment 1 of the present invention. FIG. 5B is a diagram for explaining the pattern of the light receiving element and the tracking signal detection.

FIG. 6 is a diagram showing a focus signal in the first embodiment of the present invention.

FIG. 7A is a diagram showing a collimating lens position when detecting light of wavelength λ 1 in Embodiment 1 of the present invention, and FIG. 7A is a diagram of detecting light of wavelength 2 FIG. 7C is a diagram showing a collimating lens position, and FIG. 7C is a diagram showing a collimating lens position when detecting light of wavelength 3. FIG.

FIG. 8 is an enlarged view of the beam splitter in the first embodiment of the present invention.

[Fig. 9] Fig. 9 (b) is a graph showing the relationship between the wavelength and transmittance characteristics in the optical multilayer film.

Fig. 9 is a diagram showing the relationship between the incident angle of the light beam with wavelength λ 1 and the transmittance characteristics, and Fig. 9C is a diagram showing the relationship between the incident angle of the light beam with wavelength 2 and the transmittance characteristics. FIG. 9D is a diagram showing the relationship between the incident angle of the light beam having the wavelength λ 3 and the transmittance characteristic.

FIG. 10 is a diagram showing a basic configuration of an optical head and a state of light propagation in Embodiment 2 of the present invention.

FIG. 11 is a diagram showing a pattern of a light receiving element in the second embodiment of the present invention.

FIG. 12 is a schematic configuration diagram of an optical disc device in a third embodiment of the present invention.

FIG. 13 is a schematic perspective view of a computer according to Embodiment 4 of the present invention.

FIG. 14 is a schematic perspective view of an optical disc recorder according to Embodiment 5 of the present invention.

FIG. 15 is a diagram showing a schematic configuration of a first conventional example of an optical head.

FIG. 16 is a diagram showing a schematic configuration of a second conventional example of an optical head.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0018] (Embodiment 1)

FIG. 1 is a diagram showing the configuration of the optical head according to Embodiment 1 of the present invention. In Fig. 1, the optical head consists of blue laser 1, red laser 2, infrared laser 3, diffraction gratings 7, 8, 9, dichroic prisms 10, 11, beam splitter 12, collimating lens 13, and wave plate. 14, mirror 1, objective lens 16, detection lens 19 and photodetector 20.

The blue laser 1 emits light having a wavelength λ 1 (approximately 405 nm). Red laser 2 has wavelength 2 Light (approximately 655nm) is emitted. The infrared laser 3 emits light having a wavelength of 3 (approximately 780 nm).

The optical disc 51 is an optical disc having a protective layer thickness tl of about 0.1 mm, and is an optical information medium that is recorded and reproduced by an optical beam having a wavelength λ1, for example, an optical disc for BD. The optical disk 52 is an optical disk having a protective layer thickness t2 of about 0.6 mm, and is an optical information medium that is recorded and reproduced by a light beam having a wavelength of 2, for example, an optical disk for DVD. The optical disc 53 is an optical disc having a protective layer thickness t3 of about 1.2 mm, and is an optical information medium that is recorded and reproduced by a light beam having a wavelength of 3, for example, an optical disc for CD. In FIG. 1, the optical disc 51 is indicated by a solid line, the optical disc 52 is indicated by a dotted line, the optical disc 53 is indicated by a one-dot chain line, and the surface force on which the light beam is incident also indicates only the protective layer up to the information recording surface. Actually, the optical disks 51, 52, and 53 are bonded to each other in order to ensure the mechanical strength and to make the outer shape the same as that of CD, 1.2 mm. The optical disc 52 has a thickness of 0.6 mm, and the optical disc 51 has a thickness of 1.1 mm. The substrate is omitted in the drawings of the present invention for simplicity. .

The objective lens 16 converges the light beam on the information recording surface of the optical discs 51, 52, and 53 in order to record and reproduce information on the optical discs 51, 52, and 53. The objective lens 16 has a diffractive element 16a on the lens surface, and corrects spherical aberration due to the difference in the protective layer thickness of the optical disks 51, 52, and 53 by utilizing the wavelength dependence of diffraction generated by the diffractive element 16a. .

[0022] The operation of the thus configured optical head will be described. When recording and reproducing information on a high-density optical disk 51, the blue laser 1 emits a light beam 4 of wavelength λ1. The light beam 4 having a wavelength λ 1 emitted from the blue laser 1 is divided into a main beam and two sub beams by the diffraction grating 7, passes through the dichroic prism 10 and the dichroic prism 11, and is transmitted to the beam splitter. Incident on 12

The dichroic prism 10 is configured to transmit light having a wavelength λ 1 and reflect light having a wavelength λ 2. The dichroic prism 11 transmits light having a wavelength λ 1 and light having a wavelength λ 2. It is configured to transmit and reflect light of wavelength λ3. In addition, the beam splitter 12 reflects the linearly polarized light in the horizontal direction (hereinafter referred to as S-polarized light) on the incident surface for the light of wavelengths λ1 and λ2, and the straight line in the direction orthogonal thereto. Polarized light separation characteristic that transmits polarized light (hereinafter referred to as `` polarized light '') This is an optical path branching element that has the property of reflecting part of S-polarized light and transmitting part of S-polarized light for wavelength 3 light. The light beam 4 emitted from the blue laser 1 is set so as to be incident on the beam splitter 12 as S-polarized light. The light beam 4 is reflected and condensed by the collimator lens 13 to become substantially parallel light. Converted from linearly polarized light to circularly polarized light.

The collimating lens 13 is attached to a transfer table 24 that moves along the guide shafts 25 and 26. The transfer table 24 is configured to be moved in the direction of the arrow by the feed screw 23 directly connected by the rotation of the stepping motor 22. The wave plate 14 is designed to act as a 1Z4 wave plate for light of wavelengths λ 1 and λ 2 and not as a wave plate for light of wavelength 3.

Furthermore, the light beam 4 is reflected by the mirror 15 and enters the objective lens 16. Here, the light beam 4 is diffracted by the diffraction element 16a formed on the lens surface of the objective lens 16, is refracted by the object lens 16, and passes through the protective layer having the protective layer thickness tl to the information recording surface of the optical disc 51. Convergence with numerical aperture NA1.

The light beam 4 reflected on the information recording surface of the optical disc 51 becomes circularly polarized light opposite to the forward path, and is converted into P-polarized light by following the original optical path in reverse. The light beam 4 converted to P-polarized light is narrowed by the collimating lens 13 and passes through the beam splitter 12. The converged light beam 4 is given astigmatism by the detection lens 19, enters the photodetector 20, and is photoelectrically converted by the light receiving element 20a. The detection lens 19 is constituted by a cylindrical lens having a lens action in a direction inclined by 45 ° with respect to the incident surface of the beam splitter 12. The optical head can obtain a focus signal by the astigmatism method by giving astigmatism to the light beam 4. Further, the optical head can obtain a tracking signal based on the three beams formed by the diffraction grating 7 by a differential push-pull method (hereinafter referred to as DPP). Further, the optical head can obtain an information signal from the output of the photodetector 20.

Next, when recording information on the optical disc 52 and reproducing it, the red laser 2 emits the light beam 5 having the wavelength λ 2. The light beam 5 of wavelength 2 emitted from the red laser 2 is divided into a main beam and two sub beams by the diffraction grating 8, and is reflected by the dichroic prism 10. Then, the light passes through the dichroic prism 11 and enters the beam splitter 12. The light beam 5 from which the red laser 2 has also been emitted is set to be incident on the beam splitter 12 as S-polarized light. The light beam 5 is reflected and condensed by the collimating lens 13 to become substantially parallel light. Is converted from linearly polarized light to circularly polarized light. Further, the light beam 5 is reflected by the mirror 15 and enters the objective lens 16. Here, the light beam 5 is diffracted by the diffractive element 16a formed on the surface of the objective lens 16, is refracted by the objective lens 16, and opens on the information recording surface of the optical disc 52 through the protective layer having the protective layer thickness t2. Convergence with number NA2.

[0028] The light beam 5 reflected by the information recording surface of the optical disc 52 becomes circularly polarized light opposite to the forward path, and is converted into P-polarized light by following the original optical path in reverse. The light beam 5 converted to P-polarized light is narrowed by the collimating lens 13 and passes through the beam splitter 12. The converged light beam 5 is given astigmatism by the detection lens 19, enters the photodetector 20, and is photoelectrically converted by the light receiving element 20a. The optical head obtains a focus signal, tracking signal, and information signal in the same manner as described above by calculating the output of the photodetector 20.

In addition, when recording information on the optical disk 53 and reproducing it, the light beam 6 having the wavelength λ 3 is emitted from the infrared laser 3. The light beam 6 having a wavelength of 3 emitted from the infrared laser 3 is divided into a main beam and two sub beams by a diffraction grating 9, reflected by a dichroic prism 11, and incident on a beam splitter 12. The light beam 6 emitted from the infrared laser 3 is set so as to be incident on the beam splitter 12 as S-polarized light, and a part of the S-polarized light is reflected here and is condensed by the collimating lens 13 to be substantially parallel light. become. Further, the light beam 6 passes through the wave plate 14, is reflected by the mirror 15, and enters the objective lens 16. Here, the light beam 6 is diffracted by the diffraction element 16a, refracted by the objective lens 16, and converges on the information recording surface of the optical disc 53 with a numerical aperture NA3 through the protective layer having the protective layer thickness t3.

[0030] The light beam 6 reflected by the information recording surface of the optical disc 53 follows the original optical path in reverse, passes through the wave plate 14, is narrowed down by the collimator lens 13, and enters the beam splitter 12 with S-polarized light. To do. A part of the S-polarized light of the light beam 6 passes therethrough, is given astigmatism by the detection lens 19, enters the photodetector 20, and is photoelectrically converted by the light receiving element 20a. As described above, the optical head calculates the output of the light detector 20 to produce a focus signal, A tracking signal and an information signal are obtained. Some optical discs for CDs have large birefringence, and if the optical path is branched by polarization separation as in the case of the light beams 4 and 5, light may not propagate to the photodetector 20. For this reason, it is desirable that the beam splitter 12 branch the optical path so as to reflect constant light and transmit constant light regardless of the polarization direction of the light beam 6.

Note that the wavelength λ 1 corresponds to an example of the first wavelength, the blue laser 1 corresponds to an example of the first light source, the wavelength 2 corresponds to an example of the second wavelength, and the red laser 2 Is equivalent to an example of the second light source, wavelength 3 is equivalent to an example of the third wavelength, infrared laser 3 is equivalent to an example of the third light source, and optical disc 51 is an example of the first optical disc. The optical disk 52 corresponds to an example of the second optical disk, the optical disk 53 corresponds to an example of the third optical disk, the stepping motor 22 corresponds to an example of the collimating lens moving unit, and the beam splitter 12 branches the optical path. It corresponds to an example of a member.

Next, the function and configuration of the objective lens 16 and the diffraction element 16a will be described with reference to FIGS. 2 and 3. FIG. FIG. 2 is a cross-sectional view of the objective lens 16 and shows the propagation of light that converges on the optical disk. FIG. 3 is a front view of the diffraction element 16a. As shown in FIG. 3, the diffraction grating of the diffraction element 16a has a concentric shape, and the inner peripheral portion 16al, the intermediate peripheral portion 16a2, and the outer peripheral portion 16a3 have different configurations.

[0033] The inner peripheral portion 16al is a portion having a numerical aperture equivalent to NA3, and generates the third-order diffracted light most strongly with respect to the light beam 4 with the wavelength λ1, and with respect to the light beam 5 with the wavelength 2 It is designed to generate the second-order diffracted light most strongly, and to generate the second-order diffracted light most strongly for the light beam 6 of wavelength 3. Then, the objective lens 16 converges the third-order diffracted light of the light beam 4 onto the optical disc 51, converges the second-order diffracted light of the light beam 5 onto the optical disc 52, and converges the second-order diffracted light of the light beam 6 onto the optical disc 53.

[0034] The middle peripheral portion 16a2 is a portion corresponding to a numerical aperture of NA3 to NA2, and the 6th-order diffracted light is most strongly generated in the light beam 4 having the wavelength λ1, and the light beam having the wavelength 2 It is designed so that the fourth-order diffracted light is generated most strongly for 5, and the third-order diffracted light is generated most strongly for the light beam 6 of wavelength λ3 and the fourth-order diffracted light is hardly generated. Then, the objective lens 16 converges the 6th-order diffracted light of the light beam 4 in the same Cf position as the 3rd-order diffracted light of the inner peripheral portion 16al, so that the fourth-order diffracted light of the light beam 5 becomes the second-order diffracted light of the inner peripheral portion 16al. And converge to the same position as the light The third-order diffracted light of the beam 6 is not converged to the same position as the second-order diffracted light of the inner peripheral portion 16al, and the numerical aperture of the optical beam 6 can be restricted to NA3.

[0035] The outer peripheral portion 16a3 is a portion having a numerical aperture corresponding to NA2 to NA1, and is designed to generate the second-order diffracted light most strongly with respect to the light beam 4 having the wavelength λ1. The objective lens 16 converges the second-order diffracted light of the light beam 4 to the same position as the third-order diffracted light of the inner peripheral portion 16al, so that the light beams 5 and 6 are the same as the second-order diffracted light of the inner peripheral portion 16al. There is no diffracted light converging at the position, the numerical aperture of the light beam 5 is restricted to NA2, and the light beam 6 can be restricted with the middle portion 16a2. Therefore, the light beam 4 is converged on the optical disc 51 with the numerical aperture N A1 by the third order diffracted light of the inner peripheral portion 16al, the sixth order diffracted light of the inner peripheral portion 16a2, and the second order diffracted light power of the outer peripheral portion 16a3. Second-order diffracted light of peripheral part 16al and fourth-order diffracted light of middle part 16a2 Optical power Converged to optical disk 52 with numerical aperture NA2, and light beam 6 converged to inner peripheral part 16al 2 diffracted light 1S optical disk 53 with numerical aperture NA3 To do.

Next, the propagation of light to the photodetector 20 will be described with reference to FIGS. 4 to 7. FIG. 4 is a diagram showing how reflected light from an optical disk is converged by the collimating lens 13. The collimating lens 13 is made of glass or resin, and the refractive index has wavelength dependence (dispersion). When the wavelength changes, the focal length of the collimating lens 13 changes. Further, the detection lens 19 is constituted by a cylindrical concave lens, and the convergence position is different between a direction having a lens action and a direction having no lens action. Figure 4A shows the propagation of light in a direction that has a lens effect. When the reflected light from the optical disk force enters the collimating lens 13 as a parallel light beam, the light beam 4 with the wavelength λ 1 converges at the position PI, and the light beam 5 with the wavelength λ 2 converges at the position Ρ2, and the wavelength 3 The light beam 6 converges to position Ρ3. Figure 4 (b) shows the propagation of light in the direction without the concave lens action. In Fig. 4 (b), light beam 4 with wavelength λ 1 converges at position P1 ', light beam 5 with wavelength λ 2 converges at position P2', and light beam 6 with wavelength λ 3 converges at position P3 '. Here, the distance between the position P1 and the position P1 ′, the distance between the position Ρ2 and the position P2 ′, and the distance force between the position Ρ3 and the position P3 ′ are the astigmatic differences between the light beams 4, 5, and 6, respectively. This is the detection range of a single signal.

FIG. 5B is a diagram for explaining the pattern of the light receiving element 20a and the focus signal detection method. This detection method is a so-called astigmatism method, which is caused by a focus shift. The deformation of the generated light spot is detected by the four-divided element 20a2. FIG. 5B is a diagram for explaining the pattern of the light receiving element 20a and the tracking signal detection method. This detection method is a so-called DPP method, in which the element 20a2 detects the push-pull signal of the main beam and the elements 20al and 20a3 detect the push-pull signal of the sub beam. Push-pull signal force of the secondary beam The secondary beam is arranged with respect to the recording track so that it has the opposite phase to the primary beam, and the tracking signal is obtained by taking the difference between the push-pull signals of the primary beam and the secondary beam.

[0038] In order to obtain a focus signal, the light beam is set so as to form a minimum circle of confusion on the light receiving element 20a. The light spot 4a in Fig. 5A is the minimum circle of confusion formed by the light beam 4, and when it is out of focus, it becomes an ellipse in the 45 ° direction with respect to the dividing line of the element 20a2. A focus signal can be obtained. For this reason, the optical spot 4a is received by the four-divided element 20a2, and the output of the element is configured as shown. In order to make the light spot of the optical beam 4 into the minimum circle of confusion on the light receiving element 21a, it is desirable that the light receiving element 21a is set at the approximate center between the position P1 and the position P1 ′. Further, in order to make the light spot of the light beam 5 have a minimum circle of confusion on the light receiving element 21a, it is desirable that the light receiving element 21a is set at a substantially center between the position P2 and the position P2 ′. Further, in order to make the light spot of the light beam 6 have a minimum circle of confusion on the light receiving element 21a, it is desirable that the light receiving element 21a is set at substantially the center between the position P3 and the position P3 ′. However, since the position where the light beam converges changes according to the wavelength due to the dispersion of the collimating lens 13 as described above, if the light receiving element 21a is set to be the minimum circle of confusion for light of one wavelength. For light of other wavelengths, the position of the minimum circle of confusion shifts.

On the other hand, the focal length of the collimating lens 13 is determined by the light uptake rate of each of the light beams 4, 5, 6, and the light uptake rate ensures the necessary light amount and the central portion of the light converged by the objective lens 16. The ratio of the light intensity at the periphery to the light intensity of the optical disc is designed to be within the range of values standardized as the evaluation criteria for optical discs. The light capture rate is a light amount ratio between light emitted from the light source and light converged on the optical disc through the objective lens 16. Also, the astigmatic difference is determined by the focus control range and focus sensitivity (output for focus deviation). [0040] As an example, when the focal length of the objective lens 16 is 1.3 mm, the focal length of the collimating lens 13 is 17 mm, and the astigmatic difference is 1.3 mm, the collimating lens 13 Even if BK7 glass with relatively small dispersion is used, the focal length of the light beam 5 with the wavelength 2 is 17.53 mm, and the focal length of the light beam 6 with the wavelength 3 is 17.64 mm. Even if BK7 glass with relatively small dispersion is used for the detection lens 19, the astigmatic difference of the light beam 5 with a wavelength of 2 is 1.4 mm, and the astigmatic difference of the light beam 6 with a wavelength of 3 is 1.42 mm. It becomes. Therefore, the distance from the collimating lens 13 to the minimum circle of confusion of the light beam 4 is 17.65 mm, the distance from the collimating lens 13 to the minimum circle of confusion of the light beam 5 is 18. 23 mm, and the force of the collimating lens 13 is also the light beam 6 The distance to the minimum circle of confusion is 18.35mm. For this reason, even if the position of the light receiving element 20a is set to be the minimum circle of confusion with respect to the light beam 4, the positions of the light beam 5 and the light beam 6 are each 0.5 mm from the position of the minimum circle of confusion. And 0.70 mm. Focus by the astigmatism difference of the light beam 4 1.3 mm and the vertical magnification of the light beam 4 detection system (the square of the ratio of the distance from the collimating lens 13 to the minimum circle of confusion and the focal length of the objective lens 16) The possible detection range is ± 1.76 m as shown in Fig. 6. Since the focus ranges of the light beam 5 and the light beam 6 are almost the same, if the position of the minimum circle of confusion is shifted by 0.70 mm as in the light beam 6, the focus is shifted by 1.89 m, and the force detection range is reduced. This will exceed the focus control.

[0041] To cope with this, there is a method of correcting chromatic aberration by using a collimating lens 13 as an achromatic lens in which a concave lens and a convex lens are cemented. If a color-corrected collimating lens is used, the light from the light source can be condensed into parallel light, and the parallel light beam reflected from the optical disk can be converged at the same position. However, cemented lenses are not suitable for expensive and inexpensive optical heads.

Therefore, as shown in FIG. 7, the collimator lens 13 is moved in the optical axis direction so that the minimum circle of confusion of the light beams 4, 5, 6 is formed on the light receiving element 20a of the photodetector 20. . In other words, for the light beam 4 with the wavelength λ 1, the collimator lens 13 is set at a distance S1 from the light receiving element 20a as shown in FIG. As shown in Fig. 7B, the collimating lens 13 is set at a distance S2 from the light receiving element 20a, and for the light beam 6 of wavelength 3, the distance from the light receiving element 20a is shown in Fig. 7C. Collimate at position S3 Set lens 13. The distances SI, S2, and S3 are distances for forming a light spot having a minimum circle of confusion on the light beams 4, 5, and 6 light receiving element 20a, respectively. In the present embodiment, the exemptions are a separation S1 force of 17.65 mm, a separation S2 force of 18.23 mm, and a separation S3 force of 18.35 mm. As a result, substantially parallel light is incident on the objective lens 16, and reflected light of each wavelength from the optical disk is also incident on the collimator lens 13 as substantially parallel light, thereby creating a light spot with the least circle of confusion at the same position. it can.

[0043] Further, the optical disc 51 has a standard with two information recording surfaces, and the protective layer thicknesses are tl and tl-Atl. In order to converge the light beam 4 having the wavelength λ1 on the information recording surface having the protective layer thickness tl, the collimating lens 13 is moved in the direction approaching the light emitting point and set to a position where the spherical aberration is reduced. In addition, in order to focus the light beam 4 having the wavelength λ 1 on the information recording surface with the protective layer thickness of tl A tl, the collimating lens 13 is moved in the direction in which the light emitting point force is also moved away, and the spherical aberration is reduced. Set to position. Thereby, it is possible to deal with the two-layer optical disc 51. Therefore, as described above, a mechanism for correcting the position of the minimum circle of confusion of each light beam generated by the dispersion of the collimating lens 13 by the movement of the collimating lens 13 is provided for the two-layer optical disc 51. Therefore, the optical head price will not increase.

In the present embodiment, the light emitted from the collimating lens 13 has been described as substantially parallel light, but naturally the light emitted from the collimating lens 13 is weakly diverging light as in the conventional example. Even so, the same function can be achieved by moving the position of the collimating lens 13 in the optical axis direction.

[0045] Further, as a mechanism for moving the position of the collimating lens 13 in the optical axis direction, a force using a stepping motor and a feed screw or another driving unit may be used. For example, the collimating train 13 can be supported by four wires and moved in the optical axis direction by electromagnetic drive.

Next, the configuration of the beam splitter 12 will be described with reference to FIG. 8 and FIG. FIG. 8 is an enlarged view of the beam splitter 12. As shown in FIG. 8, the beam splitter 12 has an optical multilayer film 12a formed between two prisms. The optical multilayer film 12a is formed by alternately laminating high-refractive index dielectrics and low-refractive index dielectrics, and for the wavelengths λ1 and λ2, the polarization separation characteristic that reflects S-polarized light and transmits Ρ-polarized light. For wavelength 3, one of the light It has a half mirror characteristic of reflecting a part and transmitting a part thereof. The conventional polarizing beam splitter mirror has a limited wavelength band, but in this embodiment, in order to simplify the optical system, it supports a relatively wide wavelength band up to 400 nm and 800 nm, and further diverges. It was necessary to branch the optical path with light, and it was difficult to realize.

In the case of the optical system described above, first, the refractive index of the prism of the beam splitter 12 is set to 1.64 (for example, FD2 of HOYA) at a wavelength of 655 ηm, and the range in which the objective lens 16 moves by tracking control is 0.15 mm. Then, the incident angle of the effective light beam to the optical multilayer film 12a is the light beam 4 force S45 ± 2.6 °, the light beam 5 force 45 ± 1.9 °, and the light beam 6 force 45 ± 1. 7 °. In order to make the divergent light of wavelengths λ 1 and λ 2 have polarization separation characteristics and the divergent light of wavelength λ 3 to be uniform, it is simply laminated with a high refractive index dielectric and a low refractive index dielectric. Doing so will not satisfy the characteristics. Therefore, for the light beam 6 of wavelength 3, the polarization direction of the light beam 6 is set to the radial direction of the optical disk 53 or the orthogonal direction thereof as a half mirror characteristic of only S-polarized light, and is affected by the birefringence of the optical disk. Do not. The light beam 6 emitted from the beam splitter 12 with S polarization is reflected by the optical disk 53 and is incident on the beam splitter 12 with S polarization. This is because, when the optical disk 53 has birefringence, its optical axis is formed along the flow of the resin during molding, and therefore linearly polarized light in a direction parallel or orthogonal to this is not affected by birefringence. Therefore, the light beam 6 can satisfy the characteristics even if it is a half mirror that transmits or reflects part of the S-polarized light.

[0048] The optical multilayer film 12a having such characteristics is a TaO having a refractive index of 2.25 as a high refractive index film.

2 5 and using SiO with a refractive index of 1.46 as the low refractive index film,

2

A multilayer film can be used. As the two groups of multilayer films, the first central wavelength is assumed to be m, the alternating film of the high refractive index film and the low refractive index film having an optical thickness of 1Z4, and the second central wavelength is assumed to be λ η, It consists of alternating films of high and low refractive index films with an optical thickness of 1Z4. The central wavelength is a reference wavelength when the film is formed, and the optical film thickness is a product of the physical film thickness and the refractive index. As a specific optical multilayer film, the first central wavelength m is 635 nm, the second central wavelength λ η is 1.2 times m, and the optical thickness of the first layer is λ mZ8. For the second layer, the optical film thickness of the 33rd layer is λ mZ4, and the optical film thickness of the 34th to 50th layers is λ η / 4. Obtainable. FIG. 9A is a diagram showing the relationship between the wavelength and the transmittance characteristic in the optical multilayer film 12a, and FIG. 9B is a diagram showing the relationship between the incident angle of the light beam 4 and the transmittance characteristic. 9C is a diagram showing the relationship between the incident angle of the optical beam 5 and the transmittance characteristic, and FIG. 9D is a diagram showing the relationship between the incident angle of the light beam 6 and the transmittance characteristic. In FIG. 8, the optical multilayer film 12a is a dielectric, and the reflectance is a value obtained by subtracting the transmittance from 100. In other words, a transmittance of 0% means a reflectance of 100%. If the transmittance of P-polarized light is 90% or more, the light beam 4 has a polarization splitting characteristic from 37 ° to 54 °, and the light beam 5 has an incident angle of 38 °. ° Force also has polarization separation characteristics of 55 ° or more. Also, assuming that the transmittance of S-polarized light is 60 ± 5%, the light beam 6 has noise mirror characteristics up to an incident angle of 39 ° and a force of 50 °. Therefore, with this optical multilayer film configuration, necessary characteristics can be obtained in an angle range sufficiently larger than the angle at which the light beams 4, 5, and 6 are incident on the optical multilayer film 12a as diverging light. This optical multilayer film is an example, and the number of layers can be further increased or decreased. In addition, TaO is used for the high refractive index film, but the same can be achieved using TiO.

2 5 2

The following results are obtained. Furthermore, the second optical film thickness can be designed from 1.1 to 1.3 times the first optical film thickness, and the total number of layers corresponding to the first central wavelength is 50 layers. In this case, it is possible to design from 25 to 38 layers.

[0050] In the present embodiment, the power when the light from the light source is incident on the beam splitter 12 as S-polarized light is described as the light having the wavelengths λ1 and λ2 from the light source as the polarized light. The light of λ 3 is converted to S-polarized light, the side force of the photodetector 20 in FIG. 1 is also incident, the reflected light from the optical disk is converted to S-polarized light, reflected by the beam splitter 12, The same function can be achieved even in a configuration with a photodetector.

[0051] Although the astigmatism method has been described as an example of focus detection and the DPP method has been described as an example of tracking detection, it is a matter of course that other methods can similarly set collimating lenses to solve the chromatic aberration problem. I can do it.

[0052] As described above, according to the present embodiment, one optical detector is configured in an optical head that records and reproduces information on a plurality of optical disks using a plurality of light beams having different wavelengths. A collimating lens that collects the light from the light source by splitting the light path of the multiple light beams with diverging light, and a lens that converges the reflected light from the optical disk onto the photodetector. Can also be used. As a result, an inexpensive and practical optical head can be supplied.

[0053] (Embodiment 2)

Next, Embodiment 2 of the present invention will be described with reference to the drawings. The present embodiment is different from the first embodiment in the light source, the coupling lens, the detection lens, and the photodetector, and the other configurations are the same as those in the first embodiment. Therefore, in the present embodiment, the structural members given the same reference numerals as those in the first embodiment have the same functions as those in the first embodiment unless otherwise specified.

FIG. 10 is a diagram showing a configuration of the optical head in the second embodiment of the present invention. In FIG. 10, the dual wavelength laser 30 emits light of wavelength λ 2 and light of wavelength λ 3, the coupling lens 34 has a convex lens action, and the detection lens 36 converts the detection magnification to astigmatism. give. The operation of the thus configured optical head will be described.

When recording / reproducing information on / from the optical disc 51 having a high recording density, a light beam 4 having a wavelength λ 1 is emitted from the blue laser 1. The light beam 4 having the wavelength λ 1 emitted from the blue laser 1 is divided into three beams by the diffraction grating 7, passes through the dichroic prism 35, and enters the beam splitter 12 with S polarization. The dichroic prism 35 is configured to transmit light having a wavelength of λ 1 and reflect light having a wavelength of 2, λ 3. The light beam 4 is reflected by the beam splitter 12, condensed by the collimator lens 13, becomes substantially parallel light, and is converted from linearly polarized light to circularly polarized light by the wave plate 14. The light beam 4 converted to circularly polarized light is reflected by the mirror 15 and enters the objective lens 16. Here, the light beam 4 is diffracted by the diffraction element 16a, refracted by the objective lens 16, and converges on the information recording surface of the optical disk 51 with a numerical aperture NA1 through the protective layer having the protective layer thickness tl.

The light beam 4 reflected by the information recording surface of the optical disc 51 becomes circularly polarized light opposite to the forward path, and is converted into P-polarized light by following the original optical path in reverse. The light beam 4 converted to P-polarized light is narrowed by the collimating lens 13 and passes through the beam splitter 12. The converged light beam 4 is extended in focal length and given astigmatism by a detection lens 36 consisting of a cylindrical concave lens on one side and an aspherical lens on the other side. Then, photoelectric conversion is performed by the light receiving element 37a. The cylindrical surface of the detection lens 36 is rotated 45 ° with respect to the incident surface of the beam splitter 12 as in the first embodiment. It is rolling. The optical head obtains a focus signal, a tracking signal, and an information signal by calculating the output of the photodetector 37.

Next, when information is recorded on the optical disk 52 and reproduced, the light beam 31 having the wavelength λ 2 is emitted from the two-wavelength laser 30. The light beam 31 having a wavelength of 2 emitted from the two-wavelength laser 30 is divided into a main beam and two sub-beams by the diffraction grating 33, receives a convex lens action by the coupling lens 34, and is reflected by the dichroic prism 35. Then, it enters the beam splitter 12 with S polarization. The coupling lens 34 is a lens for increasing the light capture rate of the light beam 31 and the light beam 32. The emission point of the two-wavelength laser 30 is provided inside the focal length of the collimating lens 13, and the two-wavelength laser 30 is provided. The degree of divergence of the light emitted from the light beam is converted, and the collimator lens 13 is configured to be substantially parallel light. The light beam 31 reflected from the beam splitter 12 is condensed by the collimating lens 13 to become substantially parallel light, and the linear polarization power is also converted into circularly polarized light by the wave plate 14. The light beam 31 converted into circularly polarized light is reflected by the mirror 15 and enters the objective lens 16. Here, the light beam 31 is diffracted by the diffraction element 16a, refracted by the objective lens 16, and converges on the information recording surface of the optical disc 52 with a numerical aperture NA2 through the protective layer having the protective layer thickness t2.

The light beam 31 reflected by the information recording surface of the optical disk 52 follows the original optical path and is converted to P-polarized light by the wave plate 14. The light beam 31 converted to P-polarized light is narrowed down by the collimating lens 13 and transmitted through the beam splitter 12. Furthermore, the focal length of the light beam 31 is extended by the detection lens 36, astigmatism is given, the light beam 31 enters the photodetector 37, and is photoelectrically converted by the light receiving element 37a. The optical head obtains a focus signal, a tracking signal, and an information signal by calculating the output of the photodetector 37.

In addition, when information is recorded on the optical disc 53 and reproduced, the light beam 32 having the wavelength λ 3 is emitted from the two-wavelength laser 30. The light beam 32 having a wavelength of 3 emitted from the two-wavelength laser 30 is divided into three beams by the diffraction grating 33, is subjected to a convex lens action by the coupling lens 34, is reflected by the dichroic prism 35, and is reflected to the beam splitter 12 by S. Incident with polarized light. A part of the S-polarized light is reflected by the beam splitter 12, condensed by the collimating lens 13, becomes substantially parallel light, and passes through the wave plate 14. The light beam 32 transmitted through the wave plate 14 is reflected by the mirror 15 and enters the objective lens 16. Here, the light beam 32 is diffracted by the diffraction element 16a, It is refracted by the objective lens 16 and converges on the information recording surface of the optical disc 53 with a numerical aperture NA3 through a protective layer with a protective layer thickness t3.

[0060] The light beam 32 reflected by the information recording surface of the optical disc 53 follows the original optical path in reverse, passes through the wave plate 14, is narrowed by the collimator lens 13, and enters the beam splitter 12 with S-polarized light. . Part of the S-polarized light passes through the beam splitter 12. Further, the focal length of the light beam 32 is extended by the detection lens 36, astigmatism is given, the light beam 32 enters the photodetector 37, and is photoelectrically converted by the light receiving element 37a. The optical head obtains a focus signal, a tracking signal, and an information signal by calculating the output of the photodetector 37.

[0061] For ease of explanation, the force light-emitting element in which the light source having the wavelength λ 2 and the light source having the wavelength λ 3 of the two-wavelength laser 30 are arranged in parallel to the incident surface of the beam splitter 12 is monolithic. In this arrangement, the light beams 31 and 32 are incident on the beam splitter 12 with negative polarization. In this case, the light source force is also the force to provide a 1Z2 wavelength plate between the dichroic prism 35, and the two-wavelength laser is rotated 90 ° to place the two light sources perpendicularly to the incident surface of the beam splitter 12 It can respond by.

[0062] In the present embodiment, the focus sensitivity of the collimating lens 13 is changed by changing the focal length of the detection system in which the collimating lens 13 and the detection lens 36 are combined with the focal length of the collimating lens 13. It can be set arbitrarily. However, both the detection lens 36 and the collimating lens 13 have dispersion, and the refractive index changes depending on the wavelength. For this reason, when the wavelength changes, the focal length of the detection system changes, and as in the first embodiment, the light beam 4 of wavelength λ1, the light beam 31 of wavelength λ2, and the light beam 32 of wavelength λ3 converge. The position will shift. Although a slight chromatic aberration can be corrected by providing the detection lens 36 with a concave lens action, a practical improvement cannot be expected.

[0063] For example, by combining the detection lens 36 and the collimating lens 13, the focal length of the light beam 4 having the wavelength λ 1 is extended to 22 mm, and the Abbe number 20. Use 88 FDSl (HOYA). However, in this case, the focal length of the light beam 31 with the wavelength λ 2 is 22.52 mm, and the focal length of the light beam 32 with the wavelength λ 3 is 22.65 mm. Control becomes difficult. Therefore, as in the first embodiment, the collimating lens corresponds to the wavelength. By moving 13 in the direction of the optical axis and setting the reflected light from the optical disc to form a circle of minimal confusion on the light receiving element 37a, optimal focus control can be applied to the three-wavelength light beam. it can.

Next, the configuration of the photodetector 37 will be described with reference to FIG. FIG. 11 is a diagram showing a pattern of the light receiving element 37a of the photodetector 37. As shown in FIG. In the second embodiment, as in the first embodiment, the element 37a2 detects the focus signals of the light beam 4 and the light beam 31, and the element 37a5 detects the focus signal of the light beam 32. In addition, the tracking signals of the element 37al, 37a2, 37a3 force light beam 4 and the light beam 31 are detected, and the tracking signal of the element 37a4, 37a5, 37a6 force light beam 32 is detected. In an optical system using a two-wavelength laser, the emission point at wavelength 2 and the emission point at wavelength 3 are shifted by about 100 to 120 m. For this reason, the light spot on the light receiving element 37a is also shifted, and it becomes difficult to also use the light receiving element. However, the collimating lens 13 in the present embodiment can match the convergence position of the light beam 4 having the wavelength λ 1 with the convergence position of the light beam 31 or the light beam 32. Therefore, for example, the focus signal, tracking signal, and information signal of the light beam 4 and the light beam 31 are detected by the elements 37al, 37a2, and 37a3, and the focus signal and tracking of the optical beam 32 are detected by the elements 37a4, 37a5, and 37a6. Signals and information signals are detected. In this way, the number of light receiving elements 37a can be reduced, and the number of amplifiers that amplify the signals obtained here can be reduced.

[0065] The numerical aperture for each optical disk is NA1>NA2> NA3, and the effective diameter of the light beam converged on each optical disk is light beam 4> light beam 31> light beam 32. In this case, if no coupling lens is provided as in the first embodiment and the focal length of the collimating lens 13 is designed in accordance with the light beam 4, the light capture rate of the light beams 5 and 6 is reduced. The coupling lens 34 is a lens for increasing the light capture rate, and converts the wavefront of divergent light from the two-wavelength laser 30. However, when the numerical apertures of the three light beams are different as in the present embodiment, the light capture rates of all the light beams 4, 31, 32 cannot be adjusted simultaneously. Therefore, the focal length of the collimating lens 13 is designed according to the optimum light capture rate for the light beam 4, and the focal length of the optical system combining the coupling lens 34 and the collimating lens 13 is optimized for the light beam 31. Light uptake rate And a numerical aperture of 3 wavelengths by adjusting to the midpoint between the optimal light capture rate for the light beam 32.

Specifically, the divergence angles of blue laser, red laser, and infrared laser are the same, the focal length of each wavelength of the object lens 16 is also equivalent, the focal length of the collimating lens 13 is fcl, If the focal length of the optical system combining the collimating lens 13 and the coupling lens 34 is fc2, it is desirable that the specific power of fcl and fc2 is equal to the ratio of NA1 and (NA2 + NA3) Z2. However, the ratio of the light intensity at the center of the aperture to the light intensity at the periphery differs by about 10% for the optical disks 51, 52, and 53, and the difference in the divergence angles of the blue, red, and infrared lasers, the objective Since the difference in the focal length of the lens 16 depending on the wavelength is about 10%, it includes a variation of about 30% practically. Therefore, if α is set to 1 ± 0.3, the three-wavelength optical system can be optimized by designing the coupling lens 34 so that fcl / fc2 = α X 2 X NA1Z (NA2 + NA2) is satisfied. .

[0067] In the present embodiment, the force described with the astigmatism method as the focus detection and the DPP method as the tracking detection has been described as an example. The problem of chromatic aberration can be solved.

[0068] In the present embodiment, the force when the light from the light source is incident on the beam splitter 12 as S-polarized light is converted into light having wavelengths λ1 and λ2 from the light source as polarized light. The light of λ 3 is changed to S-polarized light, and the side force of the photo detector shown in FIG. 10 is also incident. The same function can be achieved even with a structure provided with a vessel. In that case, since the polarization direction of the light of wavelength 2 is orthogonal to the polarization direction of the light of wavelength λ3, it is necessary to provide a 1 × 2 wavelength plate that acts only on the light of one wavelength.

[0069] As described above, according to the second embodiment, a plurality of light beams are diverged from an optical head that records and reproduces information on a plurality of optical disks using a plurality of light beams having different wavelengths. The collimating lens that condenses the light from the light source is also used as a lens that converges the reflected light from the optical disk to the photodetector, and suppresses the decrease in the light capture rate due to the difference in numerical aperture. It is possible to set the light capture rate suitable for 3 wavelengths. As a result, an inexpensive and practical optical head can be supplied. [Embodiment 3]

FIG. 12 is a schematic configuration diagram of an optical disc apparatus using the optical head of the first embodiment or the second embodiment. The optical disk device 107 includes a drive device 101, an optical head 102, an electric circuit 103, a motor 104, and a turntable 105. In FIG. 12, an optical disc 100 is mounted on a turn table 105 and rotated by a motor 104. The optical head 102 shown in the first and second embodiments is transported by the driving device 101 to the track on the optical disc 100 where desired information exists.

The optical head 102 sends a focus error signal and a tracking error signal to the electric circuit 103 in accordance with the positional relationship with the optical disc 100. In response to this signal, the electric circuit 103 sends a signal for driving the objective lens to the optical head 102. With this signal, the optical head 102 performs focus control and tracking control on the optical disc 100, and reads, writes, or erases information.

In the above description, the optical disc 100 mounted on the optical disc apparatus 107 is an optical disc having any one of the protective layer thicknesses Stl, t2, and t3. Since the optical disk device 107 according to the present embodiment uses the optical head according to the first embodiment or the second embodiment, the single optical head can support a plurality of optical disks having different recording densities.

[0073] (Embodiment 4)

The present embodiment is an embodiment of a computer provided with the optical disk device 107 according to the third embodiment. FIG. 13 is a schematic perspective view of a computer according to the present embodiment. A computer 109 shown in FIG. 13 includes an optical disc device 107 according to the third embodiment, an input device 116 such as a keyboard 111 and a mouse 112 for inputting information, and information input from the input device 116. , An arithmetic unit 108 such as a CPU that performs calculations based on information read from the optical disc device 107, and an output unit 110 such as a cathode ray tube or a liquid crystal display unit that displays information on the results calculated by the arithmetic unit 108. And

Note that the computer 109 may be configured to include only the optical disk device 107 and the arithmetic device 108 without including the input device 116 and the output device 110. Further, the computer 109 may be equipped with a wired or wireless input / output terminal that takes in information to be recorded on the optical disc device 107 or outputs information read out by the optical disc device 107 to the outside. The computer 109 according to the present embodiment includes the optical disc device 107 according to the third embodiment, and can record or reproduce different types of optical discs stably, so that it can be used for a wide range of purposes.

[Embodiment 5]

The present embodiment is an embodiment of an optical disc recorder provided with the optical disc device 107 according to the third embodiment. FIG. 14 is a schematic perspective view of the optical disc recorder according to the present embodiment. An optical disk recorder 115 shown in FIG. 14 includes an optical disk device 107 according to Embodiment 3, and a recording signal processing circuit 113 that converts an image signal into an information signal to be recorded on an optical disk by the optical disk device 107. ing.

[0077] It is desirable that the optical disc recorder 115 also includes a reproduction signal processing circuit 114 that converts an information signal obtained from the optical disc device 107 into an image signal. According to this configuration, it is possible to reproduce the already recorded portion. Furthermore, the optical disk recorder 115 may include an output device 110 such as a cathode ray tube or a liquid crystal display device for displaying information.

The optical disc recorder 115 according to the present embodiment includes the optical disc device 107 according to the third embodiment, and can record or play back different types of optical discs stably, so that it can be used for a wide range of applications.

[0079] The specific embodiments described above mainly include inventions having the following configurations.

An optical head according to one aspect of the present invention includes a first light source that emits light having a first wavelength, and a second light that emits light having a second wavelength that is longer than the first wavelength. The light source, the third light source that emits light having a third wavelength longer than the second wavelength, the light having the first wavelength, the second wavelength, and the third wavelength. The collimating lens for condensing the light having the first wavelength condensed by the collimating lens is converged on the first optical disc, and the light having the second wavelength condensed by the collimating lens is The first optical disc is converged on a second optical disc having a different protective layer thickness, and the light of the third wavelength condensed by the collimating lens is a protective layer between the first optical disc and the second optical disc. Thickness An objective lens that converges on a different third optical disc, a photodetector that receives reflected light from the first optical disc, the second optical disc, and the third optical disc bundled by the collimating lens; The collimating lens is moved in the optical axis direction, and information is recorded on the first optical disc, the second optical disc, and the third optical disc, or the first optical disc, the second optical disc, and the third optical disc. When reproducing information from the optical disc, the position of the collimating lens is selectively changed according to the wavelength of each light emitted from the first light source, the second light source, and the third light source. A collimating lens moving unit.

[0081] According to this configuration, the first light source power of the first wavelength is emitted, the second light source power of the second wavelength longer than the first wavelength is emitted, and the third light source power The light source power of the third wavelength light having a wavelength longer than the second wavelength is emitted. Then, the collimating lens has the first wavelength light emitted from the first light source, the second wavelength light emitted from the second light source, and the third wavelength light emitted from the third light source. Collect the light. Subsequently, the objective lens converges the light having the first wavelength collected by the collimating lens onto the first optical disc, and the light having the second wavelength collected by the collimating lens is converged on the first optical disc. Is converged on a second optical disc having a different protective layer thickness, and the light of the third wavelength condensed by the collimating lens is applied to the third optical disc having a different protective layer thickness from the first optical disc and the second optical disc. Converge. The photodetector receives the reflected light from the first optical disk, the second optical disk, and the third optical disk converged by the collimating lens. The collimating lens moving unit moves the collimating lens in the optical axis direction and records information on the first optical disc, the second optical disc, and the third optical disc, or the first optical disc, the second optical disc, and When reproducing information from the third optical disk, the position of the collimating lens is selectively changed according to the wavelength of each light emitted from the first light source, the second light source, and the third light source.

Accordingly, the position of the collimating lens is selectively changed corresponding to the wavelength of each light emitted from the first light source, the second light source, and the third light source, and light detection that occurs due to the difference in wavelength. Since the deviation of the convergence position of the system can be corrected, light corresponding to a plurality of wavelengths can be received by one photodetector, and the configuration of the optical head can be simplified.

[0083] In the optical head described above, the collimating lens moving unit may include the first optical device. When information is recorded on the disk or when information is reproduced from the first optical disk, the light from the first light source converges on the first optical disk, and the reflected light is focused on the photodetector. When the position of the collimating lens is set so as to form a light spot suitable for detection and information is recorded on the second optical disc or information is reproduced from the second optical disc, the second light source The position of the collimating lens is set so that the light from the light beam converges on the second optical disk and the reflected light forms a light spot suitable for focus detection on the photodetector, and the third optical disk When recording information or reproducing information from the third optical disc, the light from the third light source converges on the third optical disc, and the reflected light is used for focus detection on the photodetector. Suitable It preferred to set the position of the collimating lens to form a light spot.

[0084] According to this configuration, when recording information on the first optical disc or reproducing information from the first optical disc, the light from the first light source converges on the first optical disc and the reflected light thereof The position of the collimating lens is set so that a light spot suitable for focus detection is formed on the photodetector. In addition, when recording information on the second optical disk or reproducing information from the second optical disk, the light of the second light source power converges on the second optical disk, and the reflected light is focused on the photodetector. The collimating lens position is set so as to form a light spot suitable for detection. Furthermore, when recording information on the third optical disk or reproducing information from the third optical disk, the light from the third light source converges on the third optical disk, and the reflected light is reflected on the photodetector. The collimating lens position is set to form a light spot suitable for focus detection.

Accordingly, the position of the collimating lens is set so that the light from each light source converges on the optical disc and the reflected light forms a light spot suitable for focus detection on the photodetector. And the light receiving position of the photodetector can be arranged in an imaging relationship

[0086] In the above optical head, the light emitted from the first light source, the second light source, and the third light source, the first optical disc, the second optical disc, and the third optical source. An optical path branching member for branching the reflected light reflected by the optical disc, wherein the collimating lens has the first wavelength branched by the optical path branching member The first and second optical disks, which collect the light of the second wavelength and the third wavelength, and are converged by the collimating lens and branched by the optical path branching member, The reflected light from the second optical disk and the third optical disk is received, and the optical path branching member is perpendicular to the incident surface when light having the first wavelength and the second wavelength is incident. Transmits light, reflects light in the horizontal direction on the incident surface, and when light of the third wavelength is incident, reflects part of the light in the horizontal direction on the incident surface, and reflects light in the horizontal direction on the incident surface. Preferable to penetrate part.

According to this configuration, the light emitted from the first light source, the second light source, and the third light source by the optical path branching member, and the first optical disc, the second optical disc, and the third optical disc. The reflected light reflected by is branched. The collimating lens condenses light having the first wavelength, the second wavelength, and the third wavelength branched by the optical path branching member. The optical detector receives the reflected light of the first optical disk, the second optical disk, and the third optical disk, which is converged by the collimating lens and branched by the optical path branching member. When light having the first wavelength and the second wavelength is incident, the optical path branching member transmits light in the vertical direction to the incident surface and reflects light in the horizontal direction on the incident surface. In addition, when light having the third wavelength is incident, the optical path branching member reflects a part of the light in the horizontal direction on the incident surface and transmits a part of the light in the horizontal direction on the incident surface.

[0088] Accordingly, light of three wavelengths from each light source can be branched, a collimating lens that collects light of three wavelengths, and light that receives light reflected by the optical disk of light of three wavelengths It can also be used as a stop lens for the detection system, and a compact and inexpensive optical head can be realized. In addition, the light of the first wavelength and the light of the second wavelength have polarization separation characteristics, and the light of the third wavelength that easily generates birefringence has a half mirror characteristic. An optical path branching member corresponding to each of the three wavelengths of light is not necessary, and even one optical path branching member can support three wavelengths of light.

[0089] An optical head according to another aspect of the present invention emits light of a first light source that emits light of a first wavelength and light of a second wavelength that is longer than the first wavelength. A second light source, a third light source that emits light having a third wavelength longer than the second wavelength, the first wavelength, the second wavelength, and the third wavelength. A collimating lens that collects the light, and the collimator lens The light of the first wavelength collected by the laser beam is converged on the first optical disk, and the light of the second wavelength collected by the collimator lens is the protective layer thickness of the first optical disk. Converging to a different second optical disc, and converging the light of the third wavelength condensed by the collimating lens to a third optical disc having a protective layer thickness different from that of the first optical disc and the second optical disc Reflected by the objective lens, the light emitted by the first light source, the second light source, and the third light source, and the first optical disc, the second optical disc, and the third optical disc An optical path branching member for branching the reflected light, and the first optical disc and the second optical disc converged by the collimating lens and branched by the optical path branching member And a photodetector for receiving the reflected light from the third optical disc, and the optical path branching member is perpendicular to the incident surface when the light of the first wavelength and the second wavelength is incident. When light is transmitted, reflects light in the horizontal direction on the incident surface, and light of the third wavelength is incident, part of the light in the horizontal direction is reflected on the incident surface, and light in the horizontal direction is reflected on the incident surface. Part of.

According to this configuration, the first light source power emits light of the first wavelength, the second light source power emits light of the second wavelength longer than the first wavelength, and the third light source power. Light with a third wavelength that is longer than the second wavelength is emitted. Then, the collimating lens has the first wavelength light emitted from the first light source, the second wavelength light emitted from the second light source, and the third wavelength light emitted from the third light source. Collect the light. Subsequently, the objective lens converges the light having the first wavelength collected by the collimating lens onto the first optical disc, and the light having the second wavelength collected by the collimating lens is converged on the first optical disc. Is converged on a second optical disc having a different protective layer thickness, and the light of the third wavelength condensed by the collimating lens is applied to the third optical disc having a different protective layer thickness from the first optical disc and the second optical disc. Converge. The optical path branching member branches the light emitted from the first light source, the second light source, and the third light source, and the reflected light reflected by the first optical disc, the second optical disc, and the third optical disc. . The photodetector receives the reflected light from the first optical disc, the second optical disc, and the third optical disc that is converged by the collimating lens and branched by the optical path branching member. In addition, when light of the first wavelength and the second wavelength is incident, the optical path branching member transmits light in the vertical direction to the incident surface, reflects light in the horizontal direction to the incident surface, and When light having a wavelength of is incident, part of the light in the horizontal direction is reflected on the incident surface and part of the light in the horizontal direction is transmitted to the incident surface.

[0091] Accordingly, light of three wavelengths from each light source can be branched, a collimating lens that collects light of three wavelengths, and light that receives light reflected by the optical disk of light of three wavelengths It can also be used as a stop lens for the detection system, and a compact and inexpensive optical head can be realized. In addition, the light of the first wavelength and the light of the second wavelength have polarization separation characteristics, and the light of the third wavelength that easily generates birefringence has a half mirror characteristic. An optical path branching member corresponding to each of the three wavelengths of light is not necessary, and even one optical path branching member can support three wavelengths of light.

[0092] In the above optical head, the optical path branching member includes an optical multilayer film and two prisms having a predetermined refractive index sandwiching the optical multilayer film, and the optical multilayer film includes: It consists of an alternating film of a high refractive index film with a refractive index of 2.25 ± 0.1 and a low refractive index film with a refractive index of 1.46 ± 0.1, where the first central wavelength is λm. When the second central wavelength is λη, the optical thickness of the first layer is λmZ4 to λmZlO, the optical thickness of the second to jth layers is λmZ4, and j + The optical thickness of the first to j + k layers is λ ηΖ4, the second center wavelength λ η is 1.1 to 1.3 times the first center wavelength m, and the number of layers j is preferably larger than the number of layers k.

According to this configuration, the optical path branching member includes the optical multilayer film and the two prisms having a predetermined refractive index sandwiching the optical multilayer film. The optical multilayer film is composed of alternating films of a high refractive index film having a refractive index of 2.25 ± 0.1 and a low refractive index film having a refractive index of 1.46 ± 0.1. When the first central wavelength of the optical multilayer film is m and the second central wavelength is λη, the optical thickness of the first layer is λmZ4 to λmZlO, and the second layer is j layer The optical film thickness of the eye is λ m / 4, the optical film thickness of the j + 1 to j + k layers is λ ηΖ4, and the second center wavelength λ η is the first center wavelength. From 1.1 times to 1.3 times m, the number of layers j is larger than the number of layers k.

Therefore, when light having the first wavelength and the second wavelength is incident, the optical path branching member transmits light in the vertical direction to the incident surface and reflects light in the horizontal direction on the incident surface. When light of wavelength 3 is incident, it is possible to obtain a characteristic that a part of the horizontal light is reflected on the incident surface and a part of the horizontal light is transmitted to the incident surface. In the optical head described above, it is preferable that the refractive index of the prism is 1.65 ± 0.1, and the first central wavelength m is 635 ± 10 nm. According to this configuration, when the refractive index of the prism of the optical path branching member is 1.65 ± 0.1 and the first central wavelength m is 635 ± 10 nm, the first wavelength and the second wavelength This light has polarization separation characteristics, and the third light has half mirror characteristics.

[0096] Further, in the above optical head, the second light source and the third light source are integrally configured, and the photodetector has a plurality of light receiving elements for detecting a focus signal, and Among the plurality of light receiving elements, the light receiving element for detecting the reflected light force force signal reflected by the first optical disk includes a light receiving element for detecting a focus signal from the reflected light reflected by the second optical disk, and The reflected light reflected by the third optical disk is preferably used also as one of the light receiving elements for detecting the focus signal.

According to this configuration, the second light source and the third light source are configured as a single body, and the photodetector has a plurality of light receiving elements for detecting a focus signal. Among the plurality of light receiving elements, the light receiving element that detects the focus signal from the reflected light reflected by the first optical disk includes the light receiving element that detects the reflected light force focus signal reflected by the second optical disk, and Reflected light force reflected by the third optical disk Also serves as one of the light receiving elements that detect the focus signal. Therefore, in the photodetector, the number of light receiving elements that detect the force signal can be reduced, and the number of amplifiers that amplify the signal that can also obtain the light receiving element force can be reduced.

[0098] Further, in the above optical head, the second light source and the third light source are integrally formed, and the photodetector includes a plurality of light receiving elements for detecting a tracking signal, and Among the plurality of light receiving elements, the light receiving element that detects the tracking signal from the reflected light reflected by the first optical disk includes: a light receiving element that detects a tracking signal from the reflected light reflected by the second optical disk; and It is preferable to also use one of the light receiving elements for detecting the tracking signal from the reflected light reflected by the third optical disk.

[0099] According to this configuration, the second light source and the third light source are configured in a single body, and the photodetector is a It has a plurality of light receiving elements for detecting a knocking signal. Among the plurality of light receiving elements, the light receiving element that detects the tracking signal from the reflected light reflected by the first optical disk has the reflected light power reflected by the second optical disk that also detects the tracking signal. It is also used as one of the light receiving elements that detect the tracking signal from the reflected light reflected by the optical disk. Therefore, in the photodetector, the number of light receiving elements for detecting the tracking signal can be reduced, and a small and inexpensive optical head can be realized.

[0100] In the optical head, the objective lens converges the light of the first wavelength with respect to the first optical disc with a numerical aperture NA1, and causes the light of the second wavelength to converge to the second optical disk. The third optical disc is converged with a numerical aperture NA3 larger than the numerical aperture NA2 with respect to the third optical disc. Is preferred.

[0101] According to this configuration, the objective lens converges the light of the first wavelength with respect to the first optical disc with the numerical aperture NA1, and opens the light of the second wavelength with respect to the second optical disc. Convergence is performed with a numerical aperture NA2 larger than the numerical aperture NA1, and light of the third wavelength is converged with respect to the third optical disc with a numerical aperture NA3 larger than the numerical aperture NA2. Therefore, the numerical apertures NA1, NA2, and NA3 of the first light, the second light, and the third light are NA1> NA2> NA3, and the effective diameter of the light that converges on each optical disk is set to the first light> The second light can be the third light.

[0102] Further, in the above optical head, the optical head further includes a coupling lens that converts a divergence degree of the light of the second wavelength and the light of the third wavelength, and the collimating lens includes the first collimating lens. Condensing the light of the wavelength, the light of the second wavelength and the light of the third wavelength whose degree of divergence is converted by the coupling lens, and the focal length of the collimating lens is f cl, When the focal length of the optical system combining the ring lens and the collimating lens is fc2 and α is 0.7 force and 1.3, the relationship fclZfc2 = α Χ 2 Χ Ζ1Ζ (ΝΑ2 + ΝΑ3) is satisfied. U prefer that.

[0103] According to this configuration, the degree of divergence between the second wavelength light and the third wavelength light is converted by the coupling lens, and the first wavelength light and the coupling lens are converted by the collimating lens. The light of the second wavelength and the light of the third wavelength whose degree of divergence is converted by It is. When the focal length of the collimating lens is fcl, the focal length of the optical system combining the coupling lens and the collimating lens is fc2, and α is 0.7 to 1.3, fc l / fc2 = The relationship of α X 2 X NA1Z (NA2 + NA3) is satisfied. Therefore, the position of the collimating lens is moved so as to satisfy this relationship, so the efficiency of light capture due to the difference between the numerical apertures NA1, NA2, and NA3 of the first light, the second light, and the third light. The difference can be corrected.

In the optical head, the numerical aperture NA1 is 0.85, the numerical aperture NA2 is 0.6 force and 0.65, and the numerical aperture NA3 is 0.45 force and 0. A power of 5 is preferred. According to this configuration, the numerical aperture NA1 is 0.85, the numerical aperture NA2 is 0.6 force to 0.65, and the numerical aperture NA3 is 0.45 force to 0.5. The difference in light capture efficiency due to the difference between the numbers NA1, NA2 and NA3 can be corrected.

[0105] In the optical head, the protective layer thickness tl of the first optical disc is smaller than the protective layer thickness t2 of the second optical disc. The protective layer thickness t2 of the second optical disc is It is preferable that the protective layer thickness t3 of the third optical disk is smaller.

According to this configuration, the protective layer thickness tl of the first optical disc is smaller than the protective layer thickness t2 of the second optical disc. The protective layer thickness t2 of the second optical disc is the protective layer of the third optical disc. Since the thickness is smaller than t3, information can be recorded and reproduced on optical disks having different protective layer thicknesses.

[0107] In the above optical head, the protective layer thickness tl is approximately 0.1 mm, the protective layer thickness t2 is approximately 0.6 mm, and the protective layer thickness t3 is approximately 1.2 mm. Is preferred. According to this configuration, the protective layer thickness tl is approximately 0.1 mm, the protective layer thickness t2 is approximately 0.6 mm, and the protective layer thickness t3 is approximately 1.2 mm. Information can be recorded and played back on DVD and CD optical discs.

In the optical head described above, it is preferable that the first wavelength is near 405 nm, the second wavelength is around 655 nm, and the third wavelength is around 780 nm.

[0109] According to this configuration, the first wavelength is around 405 nm, the second wavelength is around 655 nm, and the third wavelength is around 780 nm. Therefore, for BD, DVD, and CD having different wavelengths, Information can be recorded on an optical disk and played back.

[0110] An optical disc device according to another aspect of the present invention includes an optical head according to any one of the above, A motor for rotating the first optical disc, the second optical disc, and the third optical disc; an optical lens used for the optical head; and the optical head based on a signal obtained from the optical head And an electric circuit for controlling and driving at least one of the light sources used in the above.

[0111] According to this configuration, the first optical disc, the second optical disc, and the third optical disc are rotated by the motor, and the motor, the optical head based on the signal obtained from the optical head by the electric circuit Since at least one of the optical lens used in the above and the light source used in the optical head is controlled and driven, the above optical head can be applied to an optical disc apparatus.

[0112] A computer according to another aspect of the present invention provides the above optical disc device, an input device or an input terminal for inputting information, information input from the input device or the input terminal, and the optical disc. Device power An arithmetic device that performs an operation based on at least one of the reproduced information, information input from the input device or the input terminal, information reproduced from the optical disk device, and an arithmetic device. An output device or an output terminal for outputting at least one of the results.

[0113] According to this configuration, the arithmetic device performs an operation based on at least a deviation between the information input from the input device or the input terminal and the information reproduced from the optical disc device, and the output device or Since the output terminal outputs at least one of the information input from the input device or the input terminal, the information reproduced from the optical disk device, and the result calculated by the arithmetic device, the optical disk device including the optical head is configured. It can be applied to computers.

[0114] An optical disc recorder according to another aspect of the present invention includes the above optical disc device, a recording signal processing circuit for converting image information into a signal to be recorded on the optical disc device, and a signal obtained by the optical disc device power. And a reproduction signal processing circuit for converting the image data into image information.

According to this configuration, the recording signal processing circuit converts the image information into a signal to be recorded on the optical disc apparatus, and the reproduction signal processing circuit converts the signal obtained from the optical disc apparatus into the image information. Therefore, the optical disk device provided with the above optical head can be applied to the optical disk recorder. Industrial applicability

The optical head according to the present invention realizes compatible reproduction and compatible recording of different types of optical discs by using one objective lens, and can ensure light transmission efficiency even when the optical discs are different, and can stably reproduce or record information. It is useful as an optical head for recording, reproducing, or erasing information on an optical information medium such as an optical disk. Further, the present invention is also useful as an optical disk device equipped with such an optical head, a computer equipped with this optical disk device, and an optical disk recorder.

Claims

The scope of the claims

[1] a first light source that emits light of a first wavelength;

A second light source that emits light of a second wavelength that is longer than the first wavelength; a third light source that emits light of a third wavelength that is longer than the second wavelength; A collimating lens for condensing the light of the first wavelength, the second wavelength, and the third wavelength;

The light of the first wavelength condensed by the collimating lens is converged on a first optical disc, and the light of the second wavelength condensed by the collimating lens is a protective layer thickness. The third wavelength light focused by the collimating lens is converged on a second optical disc having a different protective layer thickness from that of the first optical disc and the second optical disc. An objective lens for focusing on the optical disc;

A photodetector for receiving reflected light from the first optical disc, the second optical disc, and the third optical disc converged by the collimating lens;

The collimating lens is moved in the optical axis direction to record information on the first optical disc, the second optical disc, and the third optical disc, or the first optical disc, the second optical disc, and the When reproducing information from the third optical disc, the position of the collimating lens is selectively selected according to the wavelength of each light emitted from the first light source, the second light source, and the third light source. An optical head characterized by comprising a collimating lens moving part for changing the position.

[2] The collimating lens moving unit is

When information is recorded on the first optical disc or when the first optical disc force information is reproduced, light from the first light source converges on the first optical disc, and reflected light thereof is detected by the light detection. Set the position of the collimating lens to form a light spot suitable for focus detection on the instrument,

When recording information on the second optical disc or reproducing the second optical disc force information, the light from the second light source converges on the second optical disc, and the reflected light becomes the light detection Set the position of the collimating lens to form a light spot suitable for focus detection on the instrument, When recording information on the third optical disc or reproducing the third optical disc force information, the light from the third light source converges on the third optical disc, and the reflected light is the light detection 2. The optical head according to claim 1, wherein a position of the collimating lens is set so as to form a light spot suitable for focus detection on the vessel.

[3] Light emitted by the first light source, the second light source, and the third light source, and reflected by the first optical disc, the second optical disc, and the third optical disc It further comprises an optical path branching member that branches the reflected light,

The collimating lens condenses the light of the first wavelength, the second wavelength, and the third wavelength branched by the optical path branching member;

The photodetector receives reflected light from the first optical disc, the second optical disc, and the third optical disc that is converged by the collimating lens and branched by the optical path branching member;

When the light having the first wavelength and the second wavelength is incident, the optical path branching member transmits light in a vertical direction to the incident surface, reflects light in the horizontal direction on the incident surface, and transmits the third light. 3. The optical head according to claim 1, wherein when light having a wavelength is incident, a part of the horizontal light is reflected on the incident surface and a part of the horizontal light is transmitted to the incident surface.

[4] The optical path branching member includes an optical multilayer film and two prisms having a predetermined refractive index sandwiching the optical multilayer film,

The optical multilayer film is composed of alternating films of a high refractive index film having a refractive index of 2.25 ± 0.1 and a low refractive index film having a refractive index of 1.46 ± 0.1.

When the first central wavelength is λ m and the second central wavelength is λ η, the optical thickness of the first layer is λ mZ4 to λ mZlO, and the optical film of the second to jth layers The thickness is λ mZ4, the optical thickness of the j + 1 to j + k layers is λ ηΖ4, and the second central wavelength λ η is 1.1 times the first center wavelength m 1. The optical head according to claim 3, wherein the optical head is 1.3 times and the number of layers j is larger than the number of layers k.

5. The optical head according to claim 4, wherein the refractive index of the prism is 1.65 ± 0.1, and the first central wavelength m is 635 ± 10 nm.

[6] The second light source and the third light source are configured integrally, The photodetector has a plurality of light receiving elements for detecting a focus signal, and the light receiving element for detecting a focus signal from reflected light reflected by the first optical disc is the first light receiving element. The reflected light force reflected by the optical disk of No. 2 and the reflected light force reflected by the third optical disk and the light receiving element that detects the focus signal are combined. The optical head according to any one of claims 1 to 5.

[7] The second light source and the third light source are integrally formed,

The photodetector has a plurality of light receiving elements for detecting a tracking signal,

Among the plurality of light receiving elements, a light receiving element that detects a tracking signal from reflected light reflected by the first optical disk includes a light receiving element that detects a reflected light tracking signal reflected by the second optical disk, and 7. The optical head according to claim 1, wherein the optical head is also used as one of light receiving elements that detect a tracking signal from reflected light reflected by the third optical disk.

[8] The objective lens converges the light having the first wavelength with respect to the first optical disc with a numerical aperture NA1, and the light having the second wavelength with respect to the second optical disc. The light beam having the third wavelength is converged with a numerical aperture NA3 larger than the numerical aperture NA2 with respect to the third optical disk, and converged with a numerical aperture NA2 larger than the numerical value NA1. Item 8. The optical head according to any one of Items 1 to 7.

[9] a coupling lens that converts a divergence degree between the light of the second wavelength and the light of the third wavelength;

The collimating lens condenses the light of the first wavelength, the light of the second wavelength and the light of the third wavelength whose degree of divergence has been converted by the coupling lens, and the collimating lens Fcl / fc2 = α X 2 X where fcl is the focal length of the optical system combining the coupling lens and the collimating lens, and fc2 is α. 9. The optical head according to claim 8, wherein the relationship NA1Z (NA2 + NA3) is satisfied.

[10] The numerical aperture NA1 is 0.85, the numerical aperture NA2 is 0.6 to 0.65, and the numerical aperture NA3 is 0.45 to 0.5. 8 or 9 optical head

[11] The protective layer thickness tl of the first optical disc is smaller than the protective layer thickness t2 of the second optical disc. The protective layer thickness t2 of the second optical disc is the protective layer thickness of the third optical disc. 11. The optical head according to claim 1, wherein the optical head is smaller than t3.

12. The protective layer thickness tl is about 0.1 mm, the protective layer thickness t2 is about 0.6 mm, and the protective layer thickness t3 is about 1.2 mm. Light head.

13. The first wavelength according to any one of claims 1 to 12, wherein the first wavelength is near 405 nm, the second wavelength is near 655 nm, and the third wavelength is near 780 nm. The light head.

[14] The optical head according to any one of claims 1 to 13,

A motor for rotating the first optical disc, the second optical disc, and the third optical disc;

And an electric circuit that controls and drives at least one of the motor, an optical lens used in the optical head, and the light source used in the optical head based on a signal obtained from the optical head. An optical disk device.

[15] The optical disc device according to claim 14,

An input device or input terminal for inputting information;

An arithmetic device that performs an operation based on at least one of information input from the input device or the input terminal and information reproduced from the optical disc device;

And an output device or an output terminal for outputting at least one of information input from the input device or the input terminal, information reproduced from the optical disc device, and a result calculated by the arithmetic device. And computer.

[16] The optical disc device according to claim 14,

An optical disc recorder comprising: a recording signal processing circuit for converting image information into a signal to be recorded on the optical disc device; and a reproduction signal processing circuit for converting a signal obtained by the optical disc device power into image information.