JP2008299996A - Optical pickup and diffraction grating used for optical pickup - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup correcting astigmatic difference of laser diode LD without increasing the number of components and an installation space, and reducing manufacturing cost, and also to provide a diffraction grating used for an optical pickup. <P>SOLUTION: The diffraction grating GRT has a convex cylindrical surface 2 for astigmatic difference correction, which extends in a vertical direction (Y-axis direction) to the extending direction of an active layer 1 of the laser diode LD on a surface confronting the laser diode LD, and has a diffraction grating part 3 on the opposite side of a plane where the cylindrical surface 2 is formed, wherein an apparent focal length of a laser beam in a parallel direction is made shorter by the cylindrical surface 2 to eliminate the astigmatic difference AS. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical pickup for recording or reproducing an optical recording medium (optical disc) and a diffraction grating having an astigmatic difference correction function used for the optical pickup.

  An optical pickup is a device that performs recording or reproduction of an optical disk. Examples of the optical disk include DVD, CD, CD-R, CD-RW, DVD-R, and DVD-RW. In this type of optical pip-up, a laser beam emitted from a laser diode as a light source is irradiated onto a track of an optical disc, data is recorded on the optical disc, or data recorded on the optical disc is reproduced.

  FIG. 8 is a conceptual diagram for explaining the intensity distribution of emitted light from a general laser diode LD. The laser diode LD has an active layer that emits laser light, and the emitted light from the laser diode LD is distributed in a parallel direction (X-axis direction in FIG. 8) with respect to the active layer. And vertical laser light distributed in a direction perpendicular to the active layer (Y-axis direction in FIG. 8). The apparent focal points of the parallel laser beam and the vertical laser beam are shown as a focal point x and a focal point y, respectively, in FIG. Since the apparent focal point x of the parallel laser beam is located in the depth direction of the laser diode LD with respect to the apparent focal point y of the vertical laser beam, the focal positions of the focal point x and the focal point y are different. Yes. This position difference between the focal point x and the focal point y is called astigmatism AS.

  The laser light emitted from the laser diode LD is diffracted by the diffraction grating and split into three beams of zero-order diffracted light and a pair of first-order diffracted light (−1st-order diffracted light and + 1st-order diffracted light). Here, the zero-order diffracted light is called a main beam, and the pair of first-order diffracted lights is called a sub beam. Of the pair of first-order diffracted beams, the one that first crosses the track is called a preceding sub-beam, and the one that crosses later is called a trailing sub-beam.

  When the astigmatic difference AS in the laser diode LD is large, the spot positions of the preceding sub-beam and the succeeding sub-beam on the optical disk are shifted from the proper positions, and accurate tracking servo cannot be realized. For this reason, conventionally, a laser diode unit that also houses an astigmatism correction plate on the outgoing light side of the laser diode LD is used inside the laser diode unit that houses the laser diode LD. This astigmatic difference correction plate is a small flat glass, and is provided, for example, so as to be inclined in the vertical direction of the active layer of the laser diode LD. In this case, the vertical laser beam in the active layer of the laser diode LD is refracted by the astigmatism correction plate, and the apparent focal length extends in the direction toward the back of the laser diode LD. For this reason, the focal point x and the focal point y coincide with each other, and the astigmatic difference AS is eliminated.

  Since the conventional laser diode unit having an astigmatic difference correction plate incorporates an astigmatic difference correction plate, its manufacturing cost increases.

  In order to solve this problem, it is also possible to use a laser diode unit that does not have an astigmatism correction plate and to provide an astigmatism correction plate independently in the vicinity of the laser light exit of the laser diode LD. . However, with this method, it is necessary to provide an astigmatism correction plate separately from the laser diode unit, which increases the number of parts of the optical pickup and increases the manufacturing cost, and requires an installation space for the astigmatism correction plate. A new problem arises.

  In view of the above problems, the present invention is used for an optical pickup and an optical pickup that can correct the astigmatic difference of the laser diode LD without increasing the number of components and the installation space, and can reduce the manufacturing cost. An object is to provide a diffraction grating.

  An optical pickup according to the present invention includes a laser diode having an active layer for irradiating a laser beam, and guides the laser beam irradiated from the laser diode to an optical disc and reflects the laser beam reflected from the optical disc in a predetermined direction. An optical pickup having an optical system composed of a plurality of optical system members for guiding, and a photodetector for receiving laser light reflected from the optical disk and guided by the optical system, A convex cylindrical surface for correcting astigmatism extending in a direction perpendicular to the extending direction of the active layer is provided on a surface facing the laser diode, and is opposite to the surface on which the cylindrical surface is formed. And a diffraction grating having a diffraction grating portion on the surface.

  An optical pickup according to the present invention includes a laser diode having an active layer for irradiating a laser beam, and guides the laser beam irradiated from the laser diode to an optical disc and reflects the laser beam reflected from the optical disc in a predetermined direction. An optical pickup having an optical system composed of a plurality of optical system members for guiding, and a photodetector for receiving laser light reflected from the optical disk and guided by the optical system, A concave cylindrical surface for correcting astigmatism extending in a horizontal direction with respect to the extending direction of the active layer is provided on a surface facing the laser diode, and is opposite to the surface on which the cylindrical surface is formed. A diffraction grating having a diffraction grating portion on the surface is provided.

  In order to irradiate a laser beam, the diffraction grating according to the present invention guides a laser diode having an active layer and a laser beam irradiated from the laser diode to an optical disc and reflects the laser beam reflected from the optical disc in a predetermined direction A diffraction grating used for an optical pickup having an optical system composed of a plurality of optical system members for guiding and a photodetector for receiving laser light reflected from the optical disc and guided by the optical system, The diffraction grating has a convex cylindrical surface for correcting astigmatism extending in a direction perpendicular to the extending direction of the active layer of the laser diode on a surface facing the laser diode, and the cylindrical It has a diffraction grating part on the surface opposite to the surface on which the surface is formed.

  In order to irradiate a laser beam, the diffraction grating according to the present invention guides a laser diode having an active layer and a laser beam irradiated from the laser diode to an optical disc and reflects the laser beam reflected from the optical disc in a predetermined direction. A diffraction grating used for an optical pickup having an optical system composed of a plurality of optical system members for guiding and a photodetector for receiving laser light reflected from the optical disc and guided by the optical system, The laser diode has a concave cylindrical surface for correcting astigmatism extending in the horizontal direction with respect to the extending direction of the active layer of the laser diode on the surface facing the laser diode, and the cylindrical surface is formed. A diffraction grating portion is provided on the surface opposite to the surface.

  The optical pickup according to the present invention has a convex cylindrical surface for correcting astigmatism extending in a direction perpendicular to the extending direction of the active layer of the laser diode on the surface facing the laser diode, and the cylindrical surface is A diffraction grating having a diffraction grating portion is provided on a surface opposite to the formed surface. Therefore, since it is not necessary to provide an astigmatic difference correction plate integrally as in the conventional laser diode unit, the manufacturing cost of the laser diode unit can be reduced, and the astigmatism correction plate is provided inside the laser diode unit. There is no need to secure installation space. Furthermore, since the cylindrical surface is provided on a part of the diffraction grating, it is possible to prevent the number of parts of the optical pickup from increasing.

  Furthermore, the optical pickup according to the present invention has a concave cylindrical surface for correcting astigmatism extending in the horizontal direction with respect to the extending direction of the active layer of the laser diode on the surface facing the laser diode, and the cylindrical surface A diffraction grating having a diffraction grating portion is provided on the surface opposite to the surface on which is formed. In the present invention, in addition to the advantages of the present invention described above, even when a two-wavelength laser diode is used, the spot position of the laser beam from the light emitting portion arranged at a position off the central axis of the diffraction grating is not shifted. There are advantages.

  Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings. The optical pickup according to the present embodiment is configured to irradiate laser light with a laser diode LD having an active layer 1 and to guide the laser light emitted from the laser diode LD to the optical disc and to reflect the laser light reflected from the optical disc. An optical pickup having an optical system composed of a plurality of optical system members for guiding in a predetermined direction, and a photodetector DET that receives laser light reflected from the optical disk and guided by the optical system, A convex cylindrical surface 2 for correcting astigmatism extending in a direction perpendicular to the extending direction of the active layer 1 of the laser diode LD (Y-axis direction) is provided on a surface facing the laser diode LD. And a diffraction grating GRT having a diffraction grating portion 3 on a surface opposite to the surface on which the cylindrical surface 2 is formed. And wherein the are.

  FIG. 3 shows a system configuration diagram of an optical system of the optical pickup. This optical pickup includes a laser diode LD as a light source, a diffraction grating GRT, a collimator lens CL, a half mirror HM, an objective lens OL, and a condenser lens SL as optical members, and a photo detector DET as a photodetector. . The diffraction grating GRT eliminates the astigmatic difference AS by a convex cylindrical surface 2 described later, and divides one laser beam from the laser diode LD into three beams by a diffraction grating section 3 described later. . Of these three beams, the central beam is the main beam, and the two beams on both sides thereof are the preceding sub beam and the trailing sub beam. The collimator lens CL converts the three beams from the diffraction grating GRT into parallel beams. The half mirror HM transmits a parallel beam from the collimator lens CL and reflects a return beam (a reflected beam from the optical disc DISC) described later. The objective lens OL focuses the laser beam transmitted through the half mirror HM on the information recording surface of the optical disc DISC. The reflected beam reflected by the optical disc DISC is incident on the half mirror HM as a return beam through the objective lens OL. The return light reflected by the half mirror HM is focused and astigmatized by the condensing lens SL and guided to the photodetector DET, which generates an electrical signal corresponding to the light intensity.

  As shown in FIG. 1, the diffraction grating GRT has a convex cylindrical shape for correcting astigmatism extending in a direction perpendicular to the extending direction of the active layer 1 of the laser diode LD (Y-axis direction in FIG. 1). The surface 2 is provided on the surface facing the laser diode LD. The emitted light of the laser diode LD is parallel laser light distributed in a direction parallel to the active layer 1 (X-axis direction in FIG. 1) and a direction perpendicular to the active layer (Y-axis direction in FIG. 1). The vertical direction laser beam is distributed.

  In FIG. 1, the apparent focal point of the parallel laser beam of the laser diode LD becomes the focal point x when the cylindrical surface 2 does not exist. The apparent focus of the vertical laser beam of the laser diode LD is the focus y. Therefore, when the cylindrical surface 2 does not exist, the difference in position between the focal point x and the focal point y becomes an astigmatic difference AS.

  The cylindrical surface 2 is designed so that the apparent focal position of the parallel laser beam of the laser diode LD becomes the position of the focal point y. For this reason, in this embodiment, the apparent focal length of the parallel laser beam is shortened by the cylindrical surface 2, and the astigmatic difference AS is completely eliminated.

  The diffraction grating GRT has a diffraction grating portion 3 on the surface opposite to the surface on which the cylindrical surface 2 is formed. As described above, the diffraction grating portion 3 is provided to divide one laser beam from the laser diode LD into three beams. In FIG. 1, the formation direction of the plurality of grooves in the diffraction grating portion 3 is perpendicular to the extending direction of the active layer 1, but the formation direction of the plurality of grooves in the diffraction grating portion 3 is It can be appropriately changed according to the optical system member of the optical pickup.

  Next, the diffraction grating GRT 'according to the second embodiment will be described with reference to FIG. This diffraction grating GRT ′ has a concave cylindrical surface 2 ′ for correcting astigmatism extending in the horizontal direction (X-axis direction in FIG. 2) with respect to the extending direction of the active layer 1 of the laser diode LD. The diffraction grating portion 3 is provided on the surface opposite to the surface on which the cylindrical surface 2 ′ is formed.

  In FIG. 2, the apparent focus of the laser light distributed in the vertical direction of the laser diode LD (Y-axis direction in FIG. 2) is the focus y when the cylindrical surface 2 'does not exist. The apparent focus of the laser light distributed in the parallel direction of the laser diode LD (X-axis direction in FIG. 2) is the focus x. Therefore, when the cylindrical surface 2 ′ does not exist, the difference in position between the focal point x and the focal point y becomes an astigmatic difference AS.

  The surface shape of the cylindrical surface 2 'is designed so that the apparent focal position of the laser beam in the vertical direction of the laser diode LD becomes the position of the focal point x. For this reason, in this embodiment, the apparent focal length of the vertical laser beam is extended by the cylindrical surface 2 ′, and the astigmatism AS is completely eliminated.

  Next, the mounting state of the laser diode LD and the diffraction grating GRT in the optical pickup of this embodiment will be described with reference to FIGS. The laser diode LD is provided inside the laser diode unit 4, and the diffraction grating GRT is configured as a component separate from the laser diode unit 4.

  The diffraction grating GRT is a cylindrical member made of a transparent synthetic resin such as ZEONEX (trademark), for example, and is provided with a laser diode unit 4 of an optical pickup, a plurality of optical system members, a photodetector DET, and the like. The optical base 5 is attached to the inside of a cylindrical hole 51 so as to be rotatable. The diffraction grating GRT has a cylindrical surface 2 on the opposite side of the laser diode unit 4 and a diffraction grating portion 3 on the opposite side.

  The diffraction grating GRT can be rotated about a rotation axis along the extending direction of the cylindrical hole 51. This makes it possible to adjust the diffraction direction of the diffraction grating portion 3 of the diffraction grating GRT. This adjustment of the diffraction direction is performed by inserting the tip of a jig (not shown) into the square hole 23 formed in the upper part of the diffraction grating GRT. As shown in FIG. 3, a communication hole 54 is formed in the upper part of the cylindrical hole 51 of the optical base 5. Through this communication hole 54, the tip of a jig can be inserted into the square hole 23 of the diffraction grating GRT, and the diffraction grating GRT can be rotated in the direction of the arrow shown in FIG.

  In order to rotatably support the diffraction grating GRT, a coil spring 6 is provided inside the cylindrical hole 51. One end of the coil spring 6 biases the periphery 22 on the cylindrical surface 2 side of the diffraction grating GRT. Due to the urging force of the coil spring 6, the periphery 21 on the diffraction grating part 3 side of the diffraction grating GRT is applied to the first flange surface 52 that protrudes toward the inside of the cylindrical hole 51 at one end of the cylindrical hole 51. It is pressed.

  The other end of the coil spring 6 is supported by an inner portion of the flange surface 41 of the laser diode unit 4. The outer portion of the flange surface 41 of the laser diode unit 4 is bonded to the second flange surface 53 that extends toward the outside of the cylindrical hole 51 at the other end of the cylindrical hole 51.

  Note that the adjustment of the diffraction direction of the diffraction grating portion 3 of the diffraction grating GRT as described above may cause the vertical direction of the cylindrical surface 2 to slightly deviate from the extending direction of the active layer 1 of the laser diode LD. The shift does not have a great effect on the elimination of the astigmatic difference AS. Therefore, in the present specification, the terms “vertical direction” and “horizontal direction” in the cylindrical surfaces 2, 2 ′ include such a slight shift.

  Also, the diffraction grating GRT ′ of the second embodiment can be attached to the optical pickup by adopting the same configuration as that of the first embodiment.

  Hereinafter, the operation and effect of the first embodiment will be described. In this embodiment, since it is not necessary to provide an astigmatic difference correction plate integrally as in the conventional laser diode unit, the manufacturing cost of the laser diode unit can be reduced, and there is no non-inclination inside the laser diode unit. There is no need to secure installation space for the point difference correction plate. Furthermore, since the cylindrical surface 2 is provided in a part of the diffraction grating GRT, it is possible to prevent the number of parts of the optical pickup from increasing.

  The operational effects of the second embodiment are substantially the same as those of the first embodiment. However, in the second embodiment, when the two-wavelength laser diode LD ′ is used, the spot position of the laser beam on the photodetector DET ′ is not shifted. There is an advantage. FIG. 7 shows a spot position of the laser beam in a plan view when a two-wavelength laser diode LD 'is used instead of the laser diode LD of the first embodiment shown in FIG. When the DVD light emitting part is arranged on the central axis of the diffraction grating GRT, the CD light emitting part must be arranged at a position off the axis. As shown in FIG. 7, the laser light emitted from the light emitting unit for CD is slightly refracted by the convex cylindrical surface 2 for correcting the astigmatism of the diffraction grating GRT, so that it is provided on the photodetector DET ′. In the PD-IC, the spot position of the laser beam is shifted.

  On the other hand, FIG. 6 shows the spot position of the laser beam in a plan view when a two-wavelength laser diode LD ′ is used instead of the laser diode LD of the second embodiment shown in FIG. Similarly to FIG. 7, when the light emitting part for DVD is arranged on the central axis of the diffraction grating GRT and the light emitting part for CD is arranged at a position off the axis, the light emitting part for CD is emitted from the light emitting part. The laser beam is incident on a position shifted from the central axis in the horizontal direction of the concave cylindrical surface 2 ′ for correcting the astigmatism of the diffraction grating GRT ′, but is incident on the concave cylindrical surface 2 ′ of the diffraction grating GRT ′. There is no refraction. Therefore, the laser light emitted from the light emitting unit for CD has an advantage that the spot position of the laser light does not shift in the PD-IC provided on the photodetector DET ′.

It is a conceptual explanatory view about the astigmatic difference AS in the first embodiment according to the present invention. It is a conceptual explanatory view about the astigmatic difference AS in the second embodiment according to the present invention. 1 is a system configuration diagram of an optical pickup according to the present invention. FIG. It is a partial horizontal sectional view of the optical pickup of the first embodiment according to the present invention. It is the sectional view on the AA line shown in FIG. It is explanatory drawing which illustrated the spot position of the laser beam by planar view at the time of using 2 wavelength laser diode LD 'instead of the laser diode LD of 2nd Embodiment shown in FIG. It is explanatory drawing which illustrated the spot position of the laser beam by planar view at the time of using 2 wavelength laser diode LD 'instead of the laser diode LD of 1st Embodiment shown in FIG. It is a conceptual explanatory view about the astigmatic difference AS.

Explanation of symbols

AS Astigmatic LD LD Laser diode LD 'Two-wavelength laser diode GRT, GRT' Diffraction grating CL Collimator lens HM Half mirror OL Objective lens SL Condensing lens DET Photo detector DET 'Photo detector DISC Optical disc 1 Active layer 2, 2' Cylindrical surface 21, 22 Perimeter 23 Square hole 3 Diffraction grating part 4 Laser diode unit 41 Flange surface 5 Optical base 51 Cylindrical hole 52 First flange surface 53 Second flange surface 54 Communication hole 6 Coil spring

Claims (4)

A laser diode having an active layer for irradiating the laser beam;
An optical system composed of a plurality of optical system members for guiding laser light emitted from the laser diode to the optical disc and guiding laser light reflected from the optical disc in a predetermined direction;
An optical pickup having a photodetector that receives laser light reflected from the optical disk and guided by the optical system;
A convex cylindrical surface for correcting astigmatism extending in a direction perpendicular to the extending direction of the active layer of the laser diode is provided on a surface facing the laser diode;
An optical pickup comprising a diffraction grating having a diffraction grating portion on a surface opposite to a surface on which the cylindrical surface is formed. A laser diode having an active layer for irradiating the laser beam;
An optical system composed of a plurality of optical system members for guiding laser light emitted from the laser diode to the optical disc and guiding laser light reflected from the optical disc in a predetermined direction;
An optical pickup having a photodetector that receives laser light reflected from the optical disk and guided by the optical system;
A concave cylindrical surface for correcting astigmatism extending in a horizontal direction with respect to the extending direction of the active layer of the laser diode is provided on a surface facing the laser diode;
An optical pickup comprising a diffraction grating having a diffraction grating portion on a surface opposite to a surface on which the cylindrical surface is formed. A laser diode having an active layer for irradiating the laser beam;
An optical system composed of a plurality of optical system members for guiding laser light emitted from the laser diode to the optical disc and guiding laser light reflected from the optical disc in a predetermined direction;
A diffraction grating used in an optical pickup having a photodetector that receives a laser beam reflected from the optical disc and guided by the optical system;
The diffraction grating has a convex cylindrical surface for correcting astigmatism extending in a direction perpendicular to the extending direction of the active layer of the laser diode on a surface facing the laser diode,
A diffraction grating having a diffraction grating portion on a surface opposite to a surface on which the cylindrical surface is formed. A laser diode having an active layer for irradiating the laser beam;
An optical system composed of a plurality of optical system members for guiding laser light emitted from the laser diode to the optical disc and guiding laser light reflected from the optical disc in a predetermined direction;
A diffraction grating used in an optical pickup having a photodetector that receives a laser beam reflected from the optical disc and guided by the optical system;
A concave cylindrical surface for correcting astigmatism extending in a horizontal direction with respect to the extending direction of the active layer of the laser diode is provided on a surface facing the laser diode;
A diffraction grating having a diffraction grating portion on a surface opposite to a surface on which the cylindrical surface is formed.

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