JP2005174529A - Optical head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical head which allows to enter lights of three types of wavelengths approximately matching an optical axis of an objective lens with simple configuration and realizes good recording and reproducing performance for various recording media with different substrate thickness. <P>SOLUTION: A first light, a second light, and a third light are specified in order of increasing wavelength. A first light emitting element 74 emitting the first light and a second light emitting element 73 emitting the second light are configured with a hybrid semiconductor laser 70 and the second light emitting element 73 is arranged matching an optical axis of an objective lens 1. A third light emitting element 33 emitting the third light is arranged matching the optical axis of the objective lens 1. The first, second, and third lights output such that the optical axes of the second and third lights approximately match in the same direction due to a first wavelength selective prism 50 and the first light matches the optical axes of the second and third lights due to a second wavelength selective prism 60. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical head provided in an optical disk drive device of an optical recording / reproducing apparatus for optically recording / reproducing information.

  The optical recording / reproducing apparatus generates a DVD having a substrate thickness of 0.6 mm using a laser beam having a wavelength of about 650 nm and a laser beam having a wavelength of about 405 nm from a CD having a substrate thickness of 1.2 mm using a laser beam having a wavelength of about 780 nm. Adoption of an optical disk having a substrate thickness of 0.1 mm used and higher density by shortening the wavelength are being promoted. For this reason, in the optical disk drive device, not only a new type of optical disk but also an optical head corresponding to a conventional optical disk is required in order to make use of past assets.

  In order to cope with three types of wavelengths, a total of three optical heads corresponding to the respective wavelengths are provided, or a total of two optical heads including an optical head corresponding to two wavelengths and an optical head corresponding to one wavelength. Although there is a method with a head, in terms of size and price, it is ideal that one optical head supports three types of wavelengths.

  As such a single optical head corresponding to three types of wavelengths, for example, a hybrid type semiconductor laser in which laser chips emitting light of three types of wavelengths are accommodated in the same package is used (for example, Patent Documents). 1), or one using a monolithic multi-beam semiconductor laser that emits light of three types of wavelengths (for example, see Patent Document 2). In addition, since a hybrid semiconductor laser in which laser chips that emit light of two types of wavelengths are housed in the same package is well known (see, for example, Patent Document 3), a hybrid semiconductor laser corresponding to these two wavelengths, It is also conceivable to configure the optical head using a semiconductor laser corresponding to another one wavelength.

JP 2003-187492 A JP 2002-133696 A JP 2002-123971 A

  However, as disclosed in Patent Document 1 and Patent Document 2, when a semiconductor laser that emits light of three types of wavelengths is used, the emission points of the respective wavelengths are arranged apart from each other in the package. For example, when a semiconductor laser is installed by aligning the optical axis of light emitted from one of the light emitting points with the optical axis of the objective lens, the light emitted from the other two light emitting points is emitted from the optical axis of the objective lens. This causes a problem that the recording / reproducing performance deteriorates.

  Such a problem also occurs when a hybrid semiconductor laser that emits light of two types of wavelengths as disclosed in Patent Document 3 is used.

  Accordingly, an object of the present invention made in view of such a point is that light of three kinds of wavelengths can be incident substantially coincident with the optical axis of the objective lens with a simple configuration and can be applied to various recording media having different substrate thicknesses. An object of the present invention is to provide an optical head capable of obtaining good recording / reproducing performance.

The invention according to claim 1, which achieves the above object, comprises a single objective lens for condensing light onto a plurality of recording media having different substrate thicknesses, and a lens actuator for driving the objective lens, and tracks the recording medium. In an optical head having a carriage supported so as to be movable in a transverse direction, and three light emitting elements for emitting three lights having different wavelengths irradiated to a recording medium through the objective lens,
The three lights having different wavelengths are set as the first light, the second light, and the third light from the shorter wavelength, and the light emitting elements that emit the first light are the first light emitting element and the second light emitting element. The light emitting element that emits the light of the second light emitting element, the light emitting element that emits the third light as the third light emitting element,
The first light-emitting element and the second light-emitting element each include a hybrid semiconductor laser in which the first light-emitting element and the second light-emitting element are housed in one package, and the hybrid semiconductor laser is used as the objective for the second light-emitting element. Arrange it in line with the optical axis of the lens,
The third light emitting element is disposed so as to coincide with the optical axis of the objective lens,
In the optical path between the hybrid semiconductor laser and the third light emitting element and the objective lens,
The first light and the second light from the hybrid type semiconductor laser are transmitted or reflected, and the third light from the third light emitting element is reflected or transmitted, so that the first light, A first wavelength-selective prism that emits the second light and the third light in substantially the same direction by matching the optical axes of the second light and the third light;
A second wavelength-selective prism that emits the first light from the first wavelength-selective prism with its optical axis aligned with the optical axes of the second light and the third light;
It is characterized by having arranged.

According to a second aspect of the present invention, in the optical head according to the first aspect, the second wavelength selective prism has an incident surface on which the first light, the second light, and the third light are incident. And a second prism joined to a surface that is non-parallel to the incident surface of the first prism,
A wavelength selection film that reflects the second light and the third light and refracts and transmits the first light is formed on the incident surface,
A reflective film that reflects the first light is formed on the bonding surface,
The first light is refracted and transmitted through the wavelength selective film and reflected by the reflective film, and then refracted and transmitted through the wavelength selective film, and the optical axis of the first light is reflected by the wavelength selective film. The second light and the third light are configured to coincide with the optical axes of the third light and the third light.

  According to a third aspect of the present invention, in the optical head according to the first or second aspect, the hybrid semiconductor laser includes the first light emitting element, the second light emitting element, the first light emitting element, and the above A diffraction grating that diffracts the first light and the second light from the second light emitting element to generate a plurality of light beams, and a first that diffracts the return light of the first light from the recording medium A hologram, a second hologram that diffracts the return light of the second light from the recording medium, a first photodetector that receives the diffracted light from the first hologram, and diffraction by the second hologram It is characterized by comprising a hybrid hologram unit having a second photodetector for receiving light.

According to a fourth aspect of the present invention, in the optical head according to the third aspect, the first hologram is a circle divided into a plurality of regions in the concave portion of the first transparent substrate in order to detect a focus error by a double knife edge method. Formed into
The second hologram is formed in the concave portion of the second transparent substrate in a circular shape divided into a plurality of regions in order to detect a focus error by a double knife edge method.
The first transparent substrate and the second transparent substrate are arranged such that the first hologram and the second hologram are inside, and the distance between the light emitting points of the first light emitting element and the second light emitting element is the center thereof. It is characterized by being joined in a shifted manner according to the above.

  The invention according to claim 5 is the optical head according to any one of claims 1 to 4, wherein the third light emitting element includes the third light emitting element and the third light emitting element. A diffraction grating that diffracts the third light to generate a plurality of light beams, a hologram that diffracts the return light of the third light from the recording medium, and a photodetector that receives the diffracted light from the hologram; It is characterized by comprising a hologram unit having

Furthermore, in order to achieve the above object, the invention according to claim 6 includes a single objective lens for focusing on a plurality of recording media having different substrate thicknesses, and a lens actuator for driving the objective lens. In an optical head having a carriage supported so as to be movable in a direction crossing a track of the medium, and three light emitting elements for emitting three lights having different wavelengths irradiated to the recording medium through the objective lens,
The three light beams having different wavelengths are used as the first light, the second light, and the third light from the shortest wavelength, and the multi-beam semiconductor laser is configured such that the three light emitting elements are housed in one package.
In the optical path between the multi-beam semiconductor laser and the objective lens, the first light, the second light, and the third light from the multi-beam semiconductor laser have their optical axes on the objective. A wavelength-selective element that emits light substantially coincides with the optical axis of the lens is arranged.

  According to a seventh aspect of the present invention, in the optical head according to the sixth aspect, the wavelength selective element comprises a wavelength selective prism.

According to an eighth aspect of the present invention, in the optical head according to the seventh aspect, the wavelength selective prism has a first incident surface on which the first light, the second light, and the third light are incident. 1 prism, and a second prism joined to a surface non-parallel to the incident surface of the first prism,
A first wavelength selection film that reflects one of the first light, the second light, and the third light and refracts and transmits the other two light is formed on the incident surface. And
On the bonding surface, a second wavelength selection film is formed that reflects one of the other two lights and refracts and transmits the other light.
The second prism is characterized in that a reflection film for reflecting the other light is formed on a surface non-parallel to the joint surface.

  The invention according to claim 9 is the optical head according to claim 6, 7 or 8, wherein the multi-beam semiconductor laser is a hybrid semiconductor laser.

  According to the first aspect of the present invention, the first light and the second light are emitted as the first light, the second light, and the third light from the shortest wavelength. The first light emitting element and the second light emitting element are configured to have a hybrid semiconductor laser, and the second light emitting element is arranged so as to coincide with the optical axis of the objective lens to emit the third light. The third light emitting element is arranged so as to coincide with the optical axis of the objective lens, and the optical axis of the second light and the optical axis of the third light are made coincident with each other by the first wavelength selective prism. Since the optical axis of the first light is made to coincide with the optical axes of the second light and the third light by the wavelength selective prism, the light axes of the three types of wavelengths can be obtained with a simple configuration. Therefore, good recording / reproducing performance can be obtained for various recording media having different substrate thicknesses.

  According to the invention of claim 2, the second wavelength selective prism can be easily manufactured.

  According to the invention of claim 3, the hybrid type semiconductor laser comprises a diffraction grating common to the first light and the second light, a first hologram for return light with respect to the first light, and a first photodetector, Since the hybrid hologram unit is configured with the second hologram for return light with respect to the second light and the second photodetector, the number of parts can be reduced, the configuration can be further simplified, and the size and cost can be reduced. .

  According to the invention of claim 4, since the first hologram and the second hologram have a sealed structure and are not affected by scratches, dust, etc., good recording / reproducing performance can be stably maintained over a long period of time. And reliability can be improved.

  According to the invention of claim 5, since the third light emitting element is configured with the hologram unit together with the diffraction grating, the hologram and the photodetector, the configuration can be further simplified, and the size and cost can be further reduced.

  According to the invention of claim 6, as a multi-beam semiconductor laser in which three light emitting elements emitting the first light, the second light, and the third light from the shorter wavelength are accommodated in one package, Light of three types of wavelengths from the beam semiconductor laser is made to substantially coincide with the optical axis of the objective lens by means of the wavelength selective element, so that good recording and reproduction can be performed on various recording media with different substrate thicknesses with a simple configuration. Performance can be obtained.

  According to the invention of claim 7, it becomes possible to easily manufacture the wavelength selective element.

  According to the invention of claim 8, it becomes possible to match the light of three kinds of wavelengths with high accuracy by the optical axis of the objective lens.

  According to the invention of claim 9, a multi-beam semiconductor laser can be easily manufactured.

  Embodiments of an optical head according to the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 and FIG. 2 show a first embodiment. FIG. 1 is a cross-sectional view of the main part of the optical head, and FIG. 2 is a diagram showing the configuration of the optical system. In FIG. 1, parts and the like that are not necessary for the description are omitted, and hatching is partially omitted because the drawing is complicated.

  In FIG. 1, the objective lens 1 is mounted on a holder 2, and a focus coil 3 and tracking coils 4 a and 4 b are bonded to the holder 2. One end of four wire springs 5a to 5d (5c and 5d are not shown) made of beryllium copper is attached to the holder 2, and terminals of the focus coil 3 and tracking coils 4a and 4b are attached to the wire springs 5a to 5d. It is connected. The other ends of the wire springs 5a to 5d are bonded to the spring spacer 6, whereby the holder 2 is perpendicular to the disk-shaped recording medium 11 (see FIG. 2) (Z direction) and radial direction (X direction) via the wire springs 5a to 5d. ) Is movably supported. The wire springs 5a to 5d are further connected to an external electric circuit via a flexible substrate (not shown). The spring spring 6 is fixed to an iron base 7. Magnets 9a and 9b for generating a magnetic field are also fixed to the bent rising portions 8a and 8b of the base 7. A mechanism for driving the objective lens 1 assembled on the base 7 is referred to as a lens actuator 10.

  The lens actuator 10 is fixed to the carriage 21. The carriage 21 is supported by shafts 23a and 23b via bearing portions 22a, 22b, and 22c. Thus, the carriage 21 is supported so as to be movable in the radial direction (X direction) of the recording medium 11. When the carriage 21 moves to the innermost periphery of the recording medium 11, an arcuate shape 25 is formed at the X (−) end so as not to interfere with a motor 24 (the outer shape is indicated by a two-dot chain line) that rotates the recording medium 11. have.

  A hologram unit 30 is attached to the carriage 21 via an ita 32. The hologram unit 30 includes a laser chip 33 (third light emitting element) that emits laser light (third light) having a wavelength of around 780 nm, a diffraction grating 34 for generating three beams, a hologram 35, and a photodetector 36 (photodetector). ) Are housed in the same package, and the laser chip 33 is arranged so as to coincide with the optical axis of the objective lens 1. The reason for using the ita 32 is that the position of the laser chip 33 can be adjusted in the plane of the ita 32 (in a plane perpendicular to the optical axis). The ita 32 is fixed to the carriage 21 by screws 37a and 37b.

  As clearly shown in FIG. 2, the collimator lens 40, the first wavelength selective prism 50, the second wavelength selective prism 60, and the reflection mirror 14 are arranged in this order on the optical path from the hologram unit 30 to the objective lens 1. Is arranged in. In FIG. 2, for convenience of explanation, the reflecting mirror 14, the objective lens 1, and the recording medium 11 are shown rotated by 90 degrees.

  As shown in FIG. 1, the collimator lens 40 is fixed to the carriage 21 via a lens barrel 41 so that the position in the optical axis direction can be adjusted, and includes a first wavelength selective prism 50 and a second wavelength selective prism 60. The reflecting mirror 14 is directly fixed to the carriage 21. The reflection mirror 14 is disposed at a position in the Z (−) direction of the objective lens 1.

  Further, a hybrid semiconductor laser 70 that emits laser light (second light) having a wavelength of about 650 nm and laser light (first light) having a wavelength of about 405 nm is attached to the carriage 21 via an ita 72. ing. As shown in FIG. 2, the hybrid semiconductor laser 70 includes a laser chip 73 (second light emitting element) that emits second light arranged in a single package with a light emitting point slightly shifted, and a first light emitting element. And a laser chip 74 (first light emitting element) that emits the light, and the laser chip 73 is attached so as to coincide with the optical axis of the objective lens 1. The ita 72 is used for adjusting the position of the hybrid type semiconductor laser 70 as with the ita 32 and is fixed to the carriage 21 by screws 75a and 75b.

  As shown in FIG. 2, the optical path from the hybrid semiconductor laser 70 to the objective lens 1 includes a diffraction grating 80, a collimator lens 85, a polarizing beam splitter 90, a quarter wavelength plate 95, and a first wavelength selective prism 50. The second wavelength-selective prism 60 and the reflection mirror 14 are arranged in this order, and the optical components in the optical path from the first wavelength-selective prism 50 to the objective lens 1 are common to the hologram unit 30. ing.

  As shown in FIG. 1, the diffraction grating 80 is fixed to the carriage 21 via a holder 81, the collimator lens 85 is fixed to the carriage 21 via a lens barrel 86, and the polarization beam splitter 90 is directly fixed to the carriage 21. The quarter wavelength plate 95 is joined to the polarization beam splitter 90.

  Here, the first wavelength-selective prism 50 is configured by joining two triangular prisms 51 and 52 via a wavelength-selective film 53, and the wavelength-selective film 53 substantially transmits the third light. It is configured to transmit 90% and reflect the remaining approximately 10%, and reflect the first light and the second light approximately 100%.

  The second wavelength selective prism 60 has a first prism 61 and a second prism 62 which are joined, and the first prism into which the first light, the second light and the third light are incident. A wavelength selection film 63 that reflects the second light and the third light and refracts and transmits the first light is formed on the incident surface of 61, and is formed on the joint surface between the first prism 61 and the second prism 62. Is formed with a reflective film 64 for reflecting the first light. Note that the incident surface of the first prism 61 and the joint surface of the first prism 61 and the second prism 62 are non-parallel in FIG. 2 such that the angles θ1 and θ2 are θ1 <θ2.

  Further, the polarization beam splitter 90 includes a polarizing film 91 that transmits 80% for P-polarized light, reflects the remaining 20%, and reflects 100% for S-polarized light. .

  In FIG. 1, the third light emitted from the laser chip 33 of the hologram unit 30 is made into three beams by the diffraction grating 34, enters the collimator lens 40 through the hologram 35, and is converted into parallel light here. Is incident on the wavelength selective prism 50, and approximately 10% is reflected by the wavelength selective film 53, and the remaining 90% is transmitted. The third light transmitted through the wavelength selective film 53 of the first wavelength selective prism 50 is reflected by the wavelength selective film 63 of the second wavelength selective prism 60 and beam-shaped, and then is reflected on the reflection mirror 14. Then, the objective lens 1 irradiates the recording medium 11. Note that the third light reflected by the wavelength selection film 53 of the first wavelength selective prism 50 is received by a photodetector 55 fixed to the carriage 21.

  The return light of the third light reflected by the recording medium 11 enters the hologram unit 30 along a path opposite to the forward path, is diffracted by the hologram 35, and is received by the photodetector 36. ing.

  The lens barrel 41 that holds the collimator lens 40 is fixed to the wall surface of the carriage 21 so as to be slidable in the optical axis direction, so that a predetermined signal can be obtained in the photodetector 36. The position 40 can be adjusted in the optical axis direction.

  On the other hand, the second light emitted from the laser chip 73 of the hybrid semiconductor laser 70 enters the polarization beam splitter 90 as P-polarized light through the diffraction grating 80 and the collimator lens 85, and 20% is reflected by the polarization film 91. 80% is transmitted, and the transmitted light is reflected by the wavelength selection film 53 of the first wavelength selective prism 50 through the quarter wavelength plate 95, and the optical axis of the second light is the third. So as to coincide with the optical axis of the light, and after being reflected by the wavelength selection film 63 of the second wavelength selective prism 60 and beam-shaped, the recording medium 11 is irradiated by the objective lens 1 through the reflection mirror 14. It has become. The second light reflected by the polarizing film 91 of the polarizing beam splitter 90 is received by the photodetector 93 fixed to the carriage 21.

  The return light of the second light reflected by the recording medium 11 follows the path opposite to the forward path and is reflected by the polarizing film 91 of the polarizing beam splitter 90. In the optical path of the return light reflected by the polarizing film 91, a condenser lens 94 is fixed to the carriage 21 via a lens barrel 95, and photo detectors 96 and 97 and a third wavelength selective prism 98 are provided. It is fixed to the carriage 21 via 110.

  The third wavelength selective prism 98 is configured by joining a triangular prism 99 and a parallel prism 100 via a wavelength selective film 101, and the wavelength selective film 101 transmits the first light and the second light. The return light of the second light reflected by the polarizing film 91 is incident on the third wavelength selective prism 98 through the condenser lens 94, and is reflected by the wavelength selective film 101. After being reflected, it is reflected in the parallel prism 100 and received by the photodetector 96.

  The first light emitted from the laser chip 74 of the hybrid semiconductor laser 70 enters the polarization beam splitter 90 as P-polarized light through the diffraction grating 80 and the collimator lens 85, and 20% is reflected by the polarization film 91. Then, 80% of the light is transmitted, and the transmitted light is reflected by the wavelength selective film 53 of the first wavelength selective prism 50 through the quarter wavelength plate 95 and enters the second wavelength selective prism 60. Here, since the first light emitted from the laser chip 74 is shifted from the optical axis of the objective lens 1, the optical axis of the first light incident on the second wavelength selective prism 60 is second. And the optical axis of the third light do not coincide with each other.

  The first light incident on the second wavelength selective prism 60 is refracted and transmitted through the wavelength selective film 63, then reflected by the reflective film 64, and further refracted and transmitted through the wavelength selective film 63. The optical axis of the light and the third light, that is, the optical axis of the objective lens 1 is matched, and the beam is shaped and irradiated onto the recording medium 11 by the objective lens 1 via the reflection mirror 14.

  The return light of the first light reflected by the recording medium 11 follows the path opposite to the forward path, is reflected by the polarizing film 91 of the polarization beam splitter 90, and further passes through the condenser lens 94 to have the third wavelength selectivity. The light enters the prism 98, passes through the wavelength selection film 101, and is received by the photodetector 97. The ita 110 is for adjusting the photodetectors 96 and 97, and is fixed to the carriage 21 after the adjustment.

  The holder 81 for holding the diffraction grating 80 is formed in an outer cylindrical shape, and is loaded in a cylindrical hole formed in the carriage 21 so as to be rotatable around the optical axis. The rotation adjustment is possible with respect to the optical axis of the light. Further, the lens barrel 86 holding the collimator lens 85 is fixed to the wall surface of the carriage 21 so as to be slidable in the optical axis direction, so that the position of the collimator lens 85 can be adjusted in the optical axis direction. Yes. Similarly, the lens barrel 95 holding the condenser lens 94 is also fixed in such a manner that it can be slidably pressed against different wall surfaces of the carriage 21 in the optical axis direction, thereby adjusting the position of the condenser lens 94 in the optical axis direction. It is possible. With these adjustment functions, the photodetectors 96 and 97 can obtain predetermined signals.

  Next, the operation of the present embodiment configured as described above will be described.

  When the recording medium 11 corresponding to the first light having a wavelength of around 405 nm is set in the apparatus, the laser chip 74 of the hybrid semiconductor laser 70 is caused to emit light. The first light emitted from the laser chip 74 is incident on the diffraction grating 80 and is divided into zero-order light and ± first-order light in order to perform tracking signal detection by the differential push-pull method. Next, after being collimated by the collimator lens 85, the light is transmitted through the polarization film 91 of the polarization beam splitter 90 as P-polarized light, and passes through the quarter-wave plate 95 to be the wavelength of the first wavelength-selective prism 50. The light is reflected by the selective film 53 and enters the second wavelength selective prism 60.

  The first light incident on the second wavelength selective prism 60 is refracted and transmitted through the wavelength selective film 63, reflected by the reflective film 64, and further refracted and transmitted through the wavelength selective film 63. And the beam is shaped, the optical path is directed in the Z direction by the reflecting mirror 14, and the recording medium 11 is irradiated by the objective lens 1 to form a spot.

  A part of the first light incident on the polarization beam splitter 90 is reflected by the polarizing film 91 and received by the photodetector 93, and the light emission amount of the laser chip 74 is adjusted based on the output.

  On the other hand, the return light of the first light reflected by the recording medium 11 follows the path opposite to the forward path, is reflected by the polarizing film 91 of the polarization beam splitter 90, and further passes through the condenser lens 94 to the third wavelength. The light enters the selective prism 98, passes through the wavelength selective film 101, is received by the photodetector 97, and a focus error, tracking error, and recording signal are detected based on the output.

  When a focus error is detected, a current is passed through the focus coil 3 to drive the holder 2 in a direction perpendicular to the recording medium. When a tracking error is detected, the holder 2 is driven in the radial direction of the recording medium by passing a current through the tracking coils 4a and 4b. When accessing different tracks, the holder 2 and the carriage 21 are driven in the radial direction of the recording medium by a driving means (not shown). As described above, the holder 2 and the objective lens 1 fixed thereto are subjected to focus control, tracking control, and access control.

  When the recording medium 11 corresponding to the second light having a wavelength of about 650 nm is set in the apparatus, the laser chip 73 of the hybrid semiconductor laser 70 is caused to emit light. The first light emitted from the laser chip 73 is incident on the diffraction grating 80, and is divided into zero-order light and ± first-order light in order to perform tracking signal detection by the differential push-pull method or the three-beam method. It is done. Next, after being collimated by the collimator lens 85, the light is transmitted through the polarization film 91 of the polarization beam splitter 90 as P-polarized light, and passes through the quarter-wave plate 95 to be the wavelength of the first wavelength-selective prism 50. The light is reflected by the selective film 53 and enters the second wavelength selective prism 60.

  The first light incident on the second wavelength selective prism 60 is reflected by the wavelength selective film 63 and beam-shaped, and then the optical path is directed in the Z direction by the reflection mirror 14 and is recorded by the objective lens 1. Irradiation onto the medium 11 forms a spot.

  A part of the second light incident on the polarization beam splitter 90 is reflected by the polarizing film 91 and received by the photodetector 93, and the light emission amount of the laser chip 73 is adjusted based on the output.

  On the other hand, the return light of the second light reflected by the recording medium 11 follows the path opposite to the forward path, is reflected by the polarizing film 91 of the polarizing beam splitter 90, and further passes through the condenser lens 94 to the third wavelength. The light enters the selective prism 98, is reflected by the wavelength selective film 101, is reflected by the parallel prism 100, is received by the photodetector 96, and a focus error, tracking error, and recording signal are detected based on the output. Is called. The operation when a focus error or tracking error is detected is the same as in the case of the first light described above.

  When the recording medium 11 corresponding to the third light near the wavelength of 780 nm is set in the apparatus, the laser chip 33 of the hologram unit 30 is driven. The third light emitted from the laser chip 33 is divided into zero-order light and ± first-order light in order to perform tracking signal detection by the diffraction grating 34 by the dereference push-pull method or the three-beam method. Then, the three beams that pass through the zero-order light are converted into parallel light by the collimator lens 40 and enter the first wavelength selective prism 50.

  The third light that has passed through the wavelength selective film 53 of the first wavelength selective prism 50 is reflected by the wavelength selective film 63 of the second wavelength selective prism 60 and is shaped by the beam. Are directed onto the recording medium 11 by the objective lens 1 to form spots.

  Further, a part of the third light incident on the first wavelength selective prism 50 is reflected by the wavelength selective film 53 and received by the photodetector 55, and the light emission amount of the laser chip 33 is adjusted based on the output. Is done.

  On the other hand, the return light of the third light reflected by the recording medium 11 passes through the objective lens 1 again, follows the path opposite to the outward path, enters the hologram unit 30, is diffracted by the hologram 35, and is detected by the photodetector 36. And a focus error, tracking error, and recording signal are detected based on the output. The operation when a focus error or tracking error is detected is the same as in the case of the first light and the second light described above.

  According to the present embodiment, the first light emitting element that emits the first light as the first light, the second light, and the third light from the shorter wavelength is used as the three light beams having different wavelengths, and The second light-emitting element that emits the second light is configured by the hybrid semiconductor laser 70, and the second light-emitting element is arranged so that the optical axis of the objective lens 1 coincides with the third light. The third light emitting element that emits light is disposed so as to coincide with the optical axis of the objective lens 1, and the optical axis of the second light and the optical axis of the third light are caused to coincide with each other by the first wavelength selective prism 50. Since the optical axis of the first light coincides with the optical axes of the second light and the third light by the second wavelength selective prism 60, the light of three types of wavelengths can be obtained with a simple configuration. Good recording / reproducing performance can be obtained for various recording media 11 having different substrate thicknesses, which can be incident on the optical axis of the lens It is possible.

  The second wavelength-selective prism 60 is joined to the first prism 61 and the second prism 62 having non-parallel surfaces, and the first light, the second light, and the third light are incident thereon. A wavelength selection film 63 that reflects the second light and the third light and refracts and transmits the first light is formed on the incident surface of the first prism 61, and the first prism 61 and the second prism 62 are joined to each other. Since the reflection film 64 for reflecting the first light is formed on the surface, it can be easily manufactured.

  Further, the light emitting element that emits the third light is configured by the hologram unit 30 having the laser chip 33, the diffraction grating 34, the hologram 35, and the photodetector 36, and the second wavelength selective prism 60 also has a beam shaping function. Therefore, the number of parts can be reduced, the configuration can be further simplified, and the size and cost can be reduced.

(Second Embodiment)
FIG. 3 shows the main configuration of the optical system of the optical head according to the second embodiment of the present invention.

  In this embodiment, the hybrid semiconductor laser 70 is configured with the hybrid hologram unit 120 in the first embodiment, and the diffraction grating 80, the polarization beam splitter 90, the photodetector 93, the condensing lens 94, and the quarter wavelength. The plate 95, the photodetectors 96 and 97, and the third wavelength selective prism 98 are omitted.

  The hybrid hologram unit 120 generates three beams by diffracting the first light and the second light in the forward path with the laser chip 73 that emits the second light and the laser chip 74 that emits the first light. A diffraction grating 121, a first hologram 122 that diffracts the return light of the first light from the recording medium, a second hologram 123 that diffracts the return light of the second light from the recording medium, and the first hologram 122 The first photo detector 124 (first photo detector) that receives the diffracted light of the second photo detector and the second photo detector 125 (second photo detector) that receives the diffracted light from the second hologram 123 are included.

  The first hologram 122 is formed in the concave portion 131a of the first transparent substrate 131, and the second hologram 123 is formed in the concave portion 132a of the second transparent substrate 132, and the first transparent substrate 131 and the second transparent substrate 132 are formed. The first hologram 122 and the second hologram 123 are joined inside.

  In the present embodiment, since the focus error is detected by the double knife edge method, each of the first hologram 122 and the second hologram 123 is circular and passes through the center and is divided into a plurality of regions (for example, two divisions, three divisions). In addition, the centers thereof are formed while being shifted in accordance with the distance between the light emitting points of the laser chips 73 and 74.

  Thus, when a recording medium corresponding to the first light having a wavelength of about 405 nm is set in the apparatus, the laser chip 74 is driven to emit the first light, and the first light is emitted from the diffraction grating. The first-order light and the first-order light are diffracted by the first-order light 121, these light beams are transmitted through the second hologram 123 and the first hologram 122 with the 0th-order light, and converted into parallel light beams by the collimator lens 85. The light is reflected by the wavelength selective prism 50, and then irradiated onto the recording medium 11 in a spot shape by the objective lens 1 through the second wavelength selective prism 60 and the reflection mirror 14 in the same manner as in the first embodiment.

  The return light of the first light reflected by the recording medium 11 enters the hybrid hologram unit 120 along a path opposite to the forward path, is diffracted by the first hologram 122, and is received by the first photodetector 124. Then, a focus error, a tracking error, and a recording signal are detected based on the output.

  When a recording medium corresponding to the second light having a wavelength of about 650 nm is set in the apparatus, the laser chip 73 is driven to emit the second light, and the second light is emitted from the first light. Similarly to the case, it is diffracted by the diffraction grating 121 to obtain 0th order light and ± 1st order light, and these light beams are transmitted through the second hologram 123 and the first hologram 122 with the 0th order light. A parallel light beam is reflected by the first wavelength-selective prism 50, and then on the recording medium 11 by the objective lens 1 via the second wavelength-selective prism 60 and the reflection mirror 14, as in the first embodiment. Irradiate to the spot.

  The return light of the second light reflected by the recording medium 11 enters the hybrid hologram unit 120 along a path opposite to the forward path, is diffracted by the second hologram 123, and is received by the second photodetector 125. Then, a focus error, a tracking error, and a recording signal are detected based on the output.

  Note that the light emission amount control of the laser chips 73 and 74 is performed by, for example, configuring the wavelength selection film 53 of the first wavelength selective prism 50 to partially transmit the first light and the second light. The transmitted light is received by the photo detector 55. Other configurations and operations are the same as those of the first embodiment, and thus description thereof is omitted here.

  Thus, in this embodiment, since the hybrid semiconductor laser 70 in the first embodiment is configured with the hybrid hologram unit 120, the number of components can be further reduced than in the first embodiment. The configuration can be further simplified, and the size and cost can be reduced.

(Third embodiment)
FIG. 4 shows the main configuration of the optical system of the optical head according to the third embodiment of the present invention.

  In the present embodiment, a laser chip 141 that emits first light near a wavelength of 405 nm, a laser chip 142 that emits second light near a wavelength of 650 nm, and a laser that emits third light near a wavelength of 780 nm. A hybrid semiconductor laser 145 that is a multi-beam semiconductor laser in which a laser chip 142 that emits second light and a laser chip 142 that emits second light is positioned in the center and is housed in one package is used as the chip 143. To be aligned with the optical axis.

  The first light emitted from the laser chip 141 is incident on the polarization beam splitter 146 as P-polarized light. The polarizing beam splitter 146 is configured such that the polarizing film 147 has, for example, a P-polarized light transmittance of 80%, a P-polarized light reflectance of 20%, and an S-polarized light reflectance of 100%. The first light reflected by the polarizing film 147 of the polarizing beam splitter 146 is received by the photodetector 148, the light emission amount of the laser chip 141 is controlled based on the output, and the first light transmitted through the polarizing film 147 is transmitted. The light is collimated by the collimator lens 149, passes through the quarter-wave plate 150, is reflected by the mirror 151, and enters the wavelength selective prism 152.

  The wavelength-selective prism 152 includes a first prism 153 and a second prism 154 that are joined, and the incident surface of the first prism 153 on which the first light, the second light, and the third light are incident, A first wavelength selection film 155 that reflects the third light and refracts and transmits the first light and the second light is formed, and the second prism 154 has a second surface on the joint surface. A second wavelength selection film 156 that reflects the first light and refracts and transmits the first light is formed, and a reflection film 157 that reflects the first light is formed on the back surface of the second prism 154. The incident surface of the first prism 153, the joint surface of the first prism 153 and the second prism 154, and the back surface of the second prism are not parallel to each other.

  The first light incident on the wavelength selective prism 152 is sequentially refracted and transmitted through the first wavelength selective film 155 and the second wavelength selective film 156, then reflected by the reflective film 157, and then the second wavelength selected. By sequentially refracting and transmitting the film 156 and the first wavelength selection film 155, the film is aligned with the optical axis of the objective lens 1, and passes through the reflection mirror 14 to the recording medium 11 corresponding to the first light by the objective lens 1. Irradiate in a spot shape. In FIG. 4, for convenience of explanation, the reflection mirror 14, the objective lens 1, and the recording medium 11 are shown rotated by 90 degrees.

  The return light of the first light reflected by the recording medium 11 is incident on the polarization beam splitter 146 along a path opposite to the forward path, and the return light reflected by the polarization film 147 passes through the multi lens 158 and enters the first light. The light is received by one photo detector 161, and a focus error, tracking error and recording signal are detected based on the output. The multi-lens 158 is made of, for example, a petit material, and the incident surface is formed into a cylindrical surface and the output surface is formed into a concave surface. To be configured.

  Similarly, the second light emitted from the laser chip 142 is incident on the polarization beam splitter 146 as P-polarized light, and the second light reflected by the polarizing film 147 is received by the photodetector 148. The amount of light emitted from the laser chip 142 is controlled based on the output, and the second light transmitted through the polarizing film 147 is converted into parallel light by the collimator lens 149 and then reflected by the mirror 151 through the quarter-wave plate 150. Then, the light is incident on the wavelength selective prism 152.

  The second light incident on the wavelength selective prism 152 is refracted and transmitted through the first wavelength selective film 155, then reflected by the second wavelength selective film 156, and further refracted and transmitted through the first wavelength selective film 155. Then, the recording medium 11 corresponding to the second light is irradiated in a spot shape by the objective lens 1 through the reflection mirror 14.

  The return light of the second light reflected by the recording medium 11 follows the path opposite to the forward path and enters the polarization beam splitter 146, and the return light reflected by the polarizing film 147 passes through the multilens 158 and passes through the multilens 158. The light is received by the two-photodetector 162, and a focus error, a tracking error, and a recording signal are detected based on the output.

  Similarly, the third light emitted from the laser chip 143 is incident on the polarization beam splitter 146 as P-polarized light, and the third light reflected by the polarizing film 147 is received by the photodetector 148. The amount of light emitted from the laser chip 143 is controlled based on the output, and the third light transmitted through the polarizing film 147 is converted into parallel light by the collimator lens 149 and then reflected by the mirror 151 through the quarter-wave plate 150. Then, the light is incident on the wavelength selective prism 152.

  The third light incident on the wavelength selective prism 152 is reflected by the first wavelength selective film 155 so as to coincide with the optical axis of the objective lens 1, passes through the reflection mirror 14, and is reflected by the objective lens 1. The recording medium 11 corresponding to the light is irradiated in a spot shape.

  The return light of the third light reflected by the recording medium 11 enters the polarization beam splitter 146 through a path opposite to the forward path, and the return light reflected by the polarization film 147 passes through the multilens 158 and passes through the multilens 158. The light is received by the two-photodetector 163, and a focus error, a tracking error, and a recording signal are detected based on the output.

  According to the present embodiment, the three laser chips 141, 142, and 143 that emit the first light, the second light, and the third light from the shorter wavelength are used for the laser that emits the second light. A hybrid type semiconductor laser 145 having the chip 142 positioned at the center and housed in the same package is used, and the laser chip 142 is arranged so as to coincide with the optical axis of the objective lens 1 so that the first light and the third Since the light is made to coincide with the optical axis of the second light by the wavelength selective prism 152, light of three types of wavelengths can be made coincident with the optical axis of the objective lens 1 with a simple configuration. Good recording and reproducing performance can be obtained for various different recording media.

  Further, the wavelength selective prism 152 is joined to the first prism 153 and the second prism 154 each having non-parallel surfaces, and the first prism 153 on which the first light, the second light, and the third light are incident. A first wavelength selection film 155 that reflects the third light and refracts and transmits the first light and the second light is formed on the incident surface of the first prism 153 and the second prism 154. A second wavelength selection film 156 that reflects the second light and refracts and transmits the first light is formed on the surface, and a reflection film 157 that reflects the first light is formed on the back surface of the second prism 154. Can be manufactured easily.

(Fourth embodiment)
FIGS. 5 and 6 show a fourth embodiment of the present invention. FIG. 5 is a diagram showing the configuration of the main part of the optical system. FIG. 6 is a schematic plan view of the hybrid semiconductor laser shown in FIG. It is.

  In this embodiment, in the third embodiment, the laser chip 141 and the laser chip 142 of the hybrid type semiconductor laser 145 that is a multi-beam semiconductor laser are stacked in the active layer in the Z direction in FIG. 6 and emitted in the Y direction. The laser chip 143 is configured so as to be separated from the laser chips 141 and 142 so that the light emission points thereof coincide with the laser chips 141 and 142 in the Y direction. . In the hybrid semiconductor laser 145, the first light and the second light incident on the wavelength selective prism 152 are shown in FIG. 4 so that the emission point of the laser chip 141 coincides with the optical axis of the objective lens 1. Arrange them so that they are interchangeable.

  Further, the wavelength selective prism 152 forms a first wavelength selective film 155 similar to that of the third embodiment on the incident surface of the first prism 153, and a joint surface between the first prism 153 and the second prism 154. The second wavelength selection film 171 that reflects the first light and refracts and transmits the second light is formed, and the reflection film 172 that reflects the second light is formed on the back surface of the second prism 154. To do.

  Further, in the optical path between the reflection mirror 14 and the objective lens 1, the first light is transmitted as it is while being held in the lens barrel 175 of the objective lens 1, and the second light and the third light are transmitted. In this case, a hologram element 176 having a convergence function is arranged.

  In addition, a wavelength selective prism 180 is disposed in the optical path of the return light reflected by the polarization beam splitter 146. This wavelength selective prism 180 is joined to the first prism 181 and the second prism 182 via a wavelength selective film 183 that reflects the first light and transmits the second light and the third light. The first light detector 161 receives the return light of the first light reflected from the wavelength selection film 183 and emitted from the first prism 181, passes through the wavelength selection film 183, and is emitted from the second prism 182. The return light of the second light and the return light of the third light are received by the corresponding second photo detector 162 and third photo detector 163, respectively.

  Since other configurations are the same as those of the third embodiment shown in FIG. 4, the same components are denoted by the same reference numerals, and description thereof is omitted.

  In FIG. 5, the first light incident on the wavelength selective prism 152 is refracted and transmitted through the first wavelength selective film 155, then reflected by the second wavelength selective film 171, and further the first wavelength selective film. By refracting and transmitting 155, the recording medium 11 corresponding to the first light is irradiated in a spot shape by the objective lens 1 through the reflection mirror 14 and the hologram element 176 so as to coincide with the optical axis of the objective lens 1.

  The return light of the first light reflected by the recording medium 11 enters the polarization beam splitter 146 along a path opposite to the forward path, and the return light reflected by the polarizing film 147 is converted into the wavelength selective prism 180. Are reflected by the wavelength selection film 183 and received by the first photodetector 161, and a focus error, tracking error, and recording signal are detected based on the output.

  The second light incident on the wavelength selective prism 152 is refracted and transmitted sequentially through the first wavelength selective film 155 and the second wavelength selective film 171, and then reflected by the reflective film 172. By sequentially refracting and transmitting the wavelength selection film 171 and the first wavelength selection film 155, the second light is transmitted by the objective lens 1 through the reflection mirror 14 and the hologram element 176 so as to substantially coincide with the optical axis of the objective lens 1. The recording medium 11 corresponding to is irradiated in a spot shape.

  The return light of the second light reflected by the recording medium 11 follows the path opposite to the forward path and enters the polarization beam splitter 146, and the return light reflected by the polarizing film 147 is converted into the wavelength selective prism 180. The wavelength selection film 183 is transmitted and received by the second photodetector 162, and a focus error, tracking error, and recording signal are detected based on the output.

  Further, the third light incident on the wavelength selective prism 152 is reflected by the first wavelength selective film 155 so as to substantially coincide with the optical axis of the objective lens 1, and passes through the reflection mirror 14 and the hologram element 176. The objective lens 1 irradiates the recording medium 11 corresponding to the third light in a spot shape.

  The return light of the third light reflected by the recording medium 11 enters the polarization beam splitter 146 through a path opposite to the forward path, and the return light reflected by the polarization film 147 is converted into the wavelength selective prism 180. Is transmitted through the wavelength selective film 183 and received by the third photodetector 163, and a focus error, tracking error and recording signal are detected based on the output.

  According to the present embodiment, similarly to the third embodiment, by using the hybrid semiconductor laser 145 that emits light of three types of wavelengths, light of three types of wavelengths can be obtained with a simple configuration. Therefore, good recording / reproducing performance can be obtained for various recording media having different substrate thicknesses.

  In addition, this invention is not limited only to the said embodiment, Many deformation | transformation or a change is possible. For example, the diffraction gratings 34 and 80 in the first embodiment and the diffraction gratings 34 and 121 in the second embodiment can be omitted depending on the tracking error detection method, and conversely, the third embodiment and the third embodiment. In the fourth embodiment, a plurality of light beams can be generated by arranging a diffraction grating between the hybrid semiconductor laser 145 and the polarization beam splitter 146, for example, according to the tracking error detection method.

  In the fourth embodiment, the first light is made to coincide with the optical axis of the objective lens 1, and the second light and the third light are made to substantially coincide with the optical axis of the objective lens 1. It is also possible to make the second light and the third light coincide with the optical axis of the objective lens 1 and make the first light substantially coincide with the optical axis of the objective lens 1.

  Furthermore, in the fourth embodiment, instead of the wavelength selective prism 152, a wavelength selective prism 185 including one non-parallel prism as shown in FIG. 7 is used, and the first light and the second light are used. Is reflected by the front surface 186 and guided to the reflection mirror 14, and the third light is refracted and transmitted through the surface 186, reflected by the back surface 187 not parallel to the surface 186, and then refracted and transmitted through the surface 186. 14 can also be configured. In this way, the wavelength selective prism 185 can be made simpler and less expensive than the wavelength selective prism 152, so that the cost can be reduced.

Appendix 1. One objective lens for condensing light onto a plurality of recording media having different substrate thicknesses, a carriage provided with a lens actuator for driving the objective lens and supported so as to be movable in a direction crossing a track of the recording medium; In an optical head having three light emitting elements for emitting three lights having different wavelengths that are irradiated onto a recording medium through an objective lens,
The three lights having different wavelengths are designated as the first light, the second light, and the third light from the shorter wavelength.
The three light emitting elements include a hybrid semiconductor laser in which the light emitting element for emitting the second light is located in the center and accommodated in one package, and the hybrid semiconductor laser is A light emitting element that emits the light of 2 is arranged so as to coincide with the optical axis of the objective lens;
In the optical path between the hybrid type semiconductor laser and the objective lens, the first light and the third light from the hybrid type semiconductor laser are used, and the optical axes thereof are the light of the second light. An optical head comprising a wavelength-selective prism that emits light in alignment with an axis.
Appendix 2. The wavelength selective prism includes a first prism having an incident surface on which the first light, the second light, and the third light are incident, and a surface that is not parallel to the incident surface of the first prism. A second prism joined to
Forming a first wavelength selection film on the incident surface that reflects the third light and refracts and transmits the first light and the second light;
Forming a second wavelength selection film on the bonding surface that reflects the second light and refracts and transmits the first light;
The second prism is formed with a reflective film that reflects the first light on a surface that is not parallel to the joint surface,
The first light is sequentially refracted and transmitted through the first wavelength selection film and the second wavelength selection film and reflected by the reflection film, and then the second wavelength selection film and the first wavelength. The selective film is sequentially refracted and transmitted so that the optical axis of the first light coincides with the optical axis of the objective lens,
The second light is refracted and transmitted through the first wavelength selective film and reflected by the second wavelength selective film, and is then refracted and transmitted through the first wavelength selective film. Is aligned with the optical axis of the objective lens,
The supplementary note 1 is characterized in that the third light is reflected by the first wavelength selection film so that the optical axis of the third light coincides with the optical axis of the objective lens. Optical head.

It is principal part sectional drawing of the optical head in 1st Embodiment of this invention. Similarly, it is a figure which shows the structure of an optical system. It is a principal part block diagram of the optical system of the optical head in 2nd Embodiment of this invention. Similarly, it is a principal part block diagram of the optical system of the optical head in 3rd Embodiment. Similarly, it is a principal part block diagram of the optical system of the optical head in 4th Embodiment. FIG. 6 is a schematic plan view of the hybrid semiconductor laser shown in FIG. 5. It is a figure which shows the wavelength selective prism used in the modification of 4th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Objective lens 10 Lens actuator 11 Recording medium 21 Carriage 30 Hologram unit 33 Laser chip (3rd light emitting element)
34 Diffraction grating 35 Hologram 36 Photo detector (photodetector)
DESCRIPTION OF SYMBOLS 50 1st wavelength selective prism 60 2nd wavelength selective prism 61 1st prism 62 2nd prism 63 Wavelength selective film 64 Reflective film 70 Hybrid type semiconductor laser 73 Laser chip (2nd light emitting element)
74 Laser chip (first light emitting element)
121 Diffraction grating 122 First hologram 123 Second hologram 124 Photodetector (first photodetector)
125 photodetector (second photodetector)
131 First transparent substrate 131a Concave portion 132 Second transparent substrate 132a Concave portion 141, 142, 143 Laser chip 152 Wavelength selective prism 153 First prism 154 Second prism 155 First wavelength selective film 156, 171 Second wavelength selective film 157, 172 Reflective film 175 Lens barrel 176 Hologram element 180 Wavelength selective prism 183 Wavelength selective film 185 Wavelength selective prism

Claims (9)

One objective lens for condensing light onto a plurality of recording media having different substrate thicknesses, a carriage provided with a lens actuator for driving the objective lens and supported so as to be movable in a direction crossing a track of the recording medium; In an optical head having three light emitting elements for emitting three lights having different wavelengths that are irradiated onto a recording medium through an objective lens,
The three lights having different wavelengths are set as the first light, the second light, and the third light from the shorter wavelength, and the light emitting elements that emit the first light are the first light emitting element and the second light emitting element. The light emitting element that emits the light of the second light emitting element, the light emitting element that emits the third light as the third light emitting element,
The first light-emitting element and the second light-emitting element each include a hybrid semiconductor laser in which the first light-emitting element and the second light-emitting element are housed in one package, and the hybrid semiconductor laser is used as the objective for the second light-emitting element. Arrange it in line with the optical axis of the lens,
The third light emitting element is disposed so as to coincide with the optical axis of the objective lens,
In the optical path between the hybrid semiconductor laser and the third light emitting element and the objective lens,
The first light and the second light from the hybrid type semiconductor laser are transmitted or reflected, and the third light from the third light emitting element is reflected or transmitted, so that the first light, A first wavelength-selective prism that emits the second light and the third light in substantially the same direction by matching the optical axes of the second light and the third light;
A second wavelength-selective prism that emits the first light from the first wavelength-selective prism with its optical axis aligned with the optical axes of the second light and the third light;
An optical head characterized by the arrangement. The second wavelength selective prism includes a first prism having an incident surface on which the first light, the second light, and the third light are incident, and the incident surface of the first prism is not A second prism joined to a parallel surface;
A wavelength selection film that reflects the second light and the third light and refracts and transmits the first light is formed on the incident surface,
A reflective film that reflects the first light is formed on the bonding surface,
The first light is refracted and transmitted through the wavelength selective film and reflected by the reflective film, and then refracted and transmitted through the wavelength selective film, and the optical axis of the first light is reflected by the wavelength selective film. The optical head according to claim 1, wherein the optical head is configured to coincide with optical axes of the second light and the third light.   The hybrid semiconductor laser diffracts the first light and the second light emitting element, and the first light and the second light from the first light emitting element and the second light emitting element. A diffraction grating that generates a plurality of light beams, a first hologram that diffracts the return light of the first light from the recording medium, and a first diffraction that diffracts the return light of the second light from the recording medium. And a hybrid hologram unit having two holograms, a first photodetector for receiving diffracted light from the first hologram, and a second photodetector for receiving diffracted light from the second hologram. The optical head according to claim 1, wherein: The first hologram is formed in a concave portion of the first transparent substrate in a circular shape divided into a plurality of regions in order to detect a focus error by a double knife edge method.
The second hologram is formed in the concave portion of the second transparent substrate in a circular shape divided into a plurality of regions in order to detect a focus error by a double knife edge method.
The first transparent substrate and the second transparent substrate are arranged such that the first hologram and the second hologram are inside, and the distance between the light emitting points of the first light emitting element and the second light emitting element is the center thereof. The optical head according to claim 3, wherein the optical head is shifted and bonded in accordance with the optical head.   The third light emitting element includes the third light emitting element, a diffraction grating that diffracts the third light from the third light emitting element to generate a plurality of light beams, and the third light emitting element from the recording medium. 5. It comprises a hologram unit having a hologram that diffracts the return light of the light 3 and a photodetector that receives the diffracted light at the hologram. Optical head. One objective lens for condensing light onto a plurality of recording media having different substrate thicknesses, a carriage provided with a lens actuator for driving the objective lens and supported so as to be movable in a direction crossing a track of the recording medium; In an optical head having three light emitting elements for emitting three lights having different wavelengths that are irradiated onto a recording medium through an objective lens,
The three light beams having different wavelengths are used as the first light, the second light, and the third light from the shortest wavelength, and the multi-beam semiconductor laser is configured such that the three light emitting elements are housed in one package.
In the optical path between the multi-beam semiconductor laser and the objective lens, the first light, the second light, and the third light from the multi-beam semiconductor laser have their optical axes on the objective. An optical head comprising a wavelength-selective element that emits light so as to substantially coincide with an optical axis of a lens.   The optical head according to claim 6, wherein the wavelength selective element comprises a wavelength selective prism. The wavelength selective prism includes a first prism having an incident surface on which the first light, the second light, and the third light are incident, and a surface that is not parallel to the incident surface of the first prism. A second prism joined to
A first wavelength selection film that reflects one of the first light, the second light, and the third light and refracts and transmits the other two light is formed on the incident surface. And
On the bonding surface, a second wavelength selection film is formed that reflects one of the other two lights and refracts and transmits the other light.
8. The optical head according to claim 7, wherein the second prism is formed with a reflective film that reflects the other light on a surface that is not parallel to the joint surface.   9. The optical head according to claim 6, 7 or 8, wherein the multi-beam semiconductor laser is a hybrid semiconductor laser.

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