KR100266201B1 - Optical pickup apparatus - Google Patents

Abstract

PURPOSE: An optical pickup system is provided to simplify the structure of a beam generating/detecting module and to perform focusing and tracking exactly. CONSTITUTION: LDs(Laser Diode,22a,24a) emit laser beams to an optical disk(40). A first and a second beam generating/detecting modules(22,24) have photodetectors(22b,24b) for detecting the laser beams reflected from the optical disk and generate laser beams having different polarization characteristics. An objective lens(38) focuses the laser beams on the recording face of the optical disk. A DBS(Dichroic Beam Splitter,26) integrates the paths of the laser beams emitted toward the objective. A quarter wave plate(32) changes the polarization characteristics of the laser beams. A selective diffraction grating(34) reduces linear velocity by diffracting a part of the laser beams of the objective lens depending on the polarization characteristics and focuses the laser beam on the photodetectors by diffracting the laser beams of the DBS. Thereby, an optical disk system accesses two kinds of disks by using the DBS and the selective diffraction grating.

Description

Optical pickup device

The present invention relates to an optical pickup device, and more particularly, to a heterogeneous optical pickup device using a selective diffraction grating.

In recent years, optical discs have a larger recording capacity than conventional compact discs (hereinafter referred to as "CD") and rewritable compact discs (hereinafter referred to as "CD-R") due to continuous development efforts to increase recording capacity. Digital Versatile Disk (hereinafter referred to as "DVD") has been developed. A DVD has a higher recording density (i.e. track density) than a CD and a shorter distance from the surface of the disc to the information recording surface. In fact, the DVD has a short distance from the surface of the disc to the information recording surface. In fact, DVD has a distance of 0.6 mm from the surface of the disc to the information recording surface, while CD and CD-R are 1.2 mm. As a result, the wavelength?, The beam size BS, and the numerical aperture NA of the objective lens of the optical beam used in the DVD optical pickup device and the CD and CD-R optical pickup device are different. For example, the wavelength [lambda] c and the beam size BSc of the light beam used in the optical pickup apparatus for CD-R and CD should have 780 nm and 1.4 mu m, respectively, and the numerical aperture NAc of the objective lens is 0.35 ~ 0.45 should be maintained. On the other hand, the wavelength λ _D and beamsite BS _D of the light beam used in the optical pickup device for DVD should have 635 to 650 nm and 0.9 μm, respectively, and the numerical aperture NA _D of the objective lens is 0.6. Should be maintained.

An optical pickup apparatus for heterogeneous optical disks according to the prior art will be described with reference to FIG. 1. 1 shows a conventional optical pickup apparatus for heterogeneous optical disks. The optical pickup apparatus for the heterogeneous optical disc shown in FIG. 1 generates first and second optical beams to be irradiated onto the optical disc 12, respectively, and first and second for converting the optical beams reflected from the optical disc 12 into electrical signals, respectively. The light generation / detection module 2 and 4, the objective lens 10 located between the first light generation / detection module 2 and the optical disc 12, the first light generation / detection module 2 and the objective lens And a beam splitter 6 located between 10. The first light generation / detection module 2 is configured to electrically signal a first light source 2a for generating a first light beam having a wavelength of 650 nm, and a light beam that is arranged in parallel with the first light source and reflected from the optical disk 12. And a hologram 2c which is positioned above the first light source 2a and the first light detector 2b and diffracts the light beam. The second light generation / detection module 4 is arranged to be in parallel with the second light source 4a for generating a second light beam having a wavelength of 780 nm and the light beam reflected from the optical disk 12 as an electrical signal. For CD and CD-R recording / reproduction comprising a second photodetector 4b for conversion, and a hologram 4c positioned above the second light source 4a and the second photodetector 4b for diffracting the light beam Module. On the other hand, the objective lens 10 focuses the light beam from the first or second light source 2a or 4a on the recording surface of the optical disk 12 and passes the light beam reflected from the optical disk 12 toward the beam splitter 6. Let's do it.

In addition, the beam splitter 6 propagates the light beam from the first or second light source 2a or 4a toward the objective lens 10, and transmits the light beam incident from the objective lens 10 to the first photodetector 2b. Pass to the side) or reflect toward the second photodetector 4b.

The recording / reproducing apparatus for the heterogeneous optical disc further includes a collimating lens 8, a λ / 4 plate 14 and a polarizing plate 16 arranged between the objective lens 10 and the beam splitter 6. The collimating lens 8 causes the light beam from the first or second light source 2a or 2b to travel parallel to the objective lens 10 and converges the light beam reflected from the optical disk 12 toward the beam splitter 6. Let's proceed in the form. The λ / 4 plate 14 changes the polarization characteristics of the light beam traveling from the collimating lens 8 toward the polarizing plate 16. The platen plate 16 reduces the beam diameter of the light beam incident on the objective lens 12 when the second light beam is generated from the second light source 4b so that the second light beam is applied to the second information recording surface of the optical disc 14. By focusing in the form of focus, the CD and CD-R are accessed. For this purpose, the polarizing plate 16 has a circular non-polarization part having a predetermined diameter at the center and a polarization part formed around the non-polarization part. The polarizing portion causes the light beam passing through the phase to retard the phase of the light beam passing through the non-polarization portion, that is, the optical path difference is generated.

As a result, the distribution of the light beams incident on the photodetector is not only uniform but also the light beams are asymmetrical. As a result, focusing and tracking cannot be performed correctly. In addition, the light generation / detection module has a disadvantage in that the structure is complicated because it is configured as a package including a hologram.

Accordingly, it is an object of the present invention to simplify the structure of the light generation / detection module and to provide an optical pickup device for heterogeneous optical discs suitable for accurately performing focus and tracking.

1 is a diagram showing the structure of an optical pickup apparatus according to the prior art.

2 is a diagram showing the structure of an optical pickup apparatus according to the present invention.

* Explanation of symbols for the main parts of the drawings

2, 22: first light generation / detection module 4, 24: second light generation / detection module

6, 26: beam splitter 8, 28: collimation lens

10, 38: objective lens 12, 40: optical disk

14: polarizing plate 16, 32: λ / 4 plate

30: actuator 34: selective diffraction grating

36: right angle prism

In order to achieve the above object, the optical pickup apparatus according to the present invention has a light source for generating a light beam to be irradiated on the optical disk, and a light detector for detecting the light beam reflected from the optical disk and disposed on a plane with the light source. First and second light generation / detection modules for generating light beams having different polarization characteristics; An objective lens for focusing the light beams generated by the light generation / detection modules on the recording surface of the optical disc; Beam path integrating means disposed between the light generation / detection modules and the objective lens to match a path of the light beams traveling from the light generation / detection modules toward the objective lens; A λ / 4 plate positioned between the beam path integration means and the objective lens to change the polarization characteristic of the light beam; A portion of the light beam positioned between the beam path integration means and the λ / 4 / plate and traveling from the beam path integration means toward the objective lens is selectively diffracted according to its polarization characteristic to reduce the beam diameter, and also the beam from the λ / 4 plate. And a selective diffraction grating for diffracting the light beam traveling toward the path integration means by an angle from the optical axis to be focused on the photodetectors.

Other objects and features of the present invention in addition to the above objects will become apparent from the description of the embodiments with reference to the accompanying drawings.

Hereinafter, an embodiment of the present invention will be described in detail with reference to FIG. 2.

2 schematically illustrates an optical pickup apparatus for heterogeneous optical disks according to an embodiment of the present invention. The optical pickup apparatus of FIG. 2 generates first and second light beams to be irradiated onto the optical disc 40, and first and second light generation / detection modules 22 for detecting the light beams reflected from the optical disc 40. 24). The first light generation / detection module 22 includes a first light source 22a provided on the planar substrate and a second light source 24a provided on the planar substrate of the second light generation / detection module 24. The first light source 22a generates a first light beam (ie, TM wave) having a wavelength of 650 nm and vertical linear polarization characteristics. The second light source 24a generates a second light beam (ie TE wave) having a wavelength of 780 nm and a horizontal linear polarization characteristic. These first and second light sources 22a and 24a are selectively driven according to the type of the optical disc 40. In detail, the first light source 22a is driven when the optical disk 40 is a DVD having a relatively short distance between the surface and the information recording surface of 0.6 mm, while the second light source 24a is used when the optical disk 40 is surfaced. And the distance between the information recording surface and the information recording surface is 1.2 mm, which is driven when the CD or CD-R is relatively long.

The optical pickup device for the heterogeneous optical disc is arranged on the same axis as the first light generation / detection module 22 and has a dichroic beam splitter (hereinafter referred to as "DBS") 26 and a right angle prism 36. And an objective lens 38 positioned between the right angle prism 36 and the optical disk 40. The DVS 26 passes the first light beam from the first light source 22a as it is, while the light beam from the second light source 24a is reflected at right angles such that the first and second light beams pass through the right angle prism 36. To advance toward the objective lens 38. In other words, the DBS 26 functions to match the paths of the first and second light beams. In addition, the DBS 26 is reflected by the optical disk 40 to pass the reflected light beam through the objective lens 38 and the right angle prism 36 toward the first light generation / detection module 22 or the second light. Reflect toward the generation / detection module 24. The right prism 36 reflects the light beam transmitted between the DBS 26 and the objective lens at right angles. The objective lens 38 focuses the light beam from the rectangular prism 36 in the form of spots on the surface of the optical disc 40.

In addition, the optical pickup device for the heterogeneous optical disk is arranged between the right angle prism 36 and the objective lens 38, the selective diffraction grating 32 for selectively and partially passing the linearly polarized light in a specific direction, and the objective lens 38 And a λ / 4 plate 34 arranged between the selective diffraction gratings 32. The selective diffraction grating 32 passes all of the first light beams of the vertical linearly polarized light from the right angle prism 36 toward the λ / 4 plate 34, while the second light beam of the horizontal linearly polarized light from the right angle prism 36 receives only the light at the center portion. By transmitting, the first light beam can be irradiated in the form of spots to the information recording surface of the DVD and the second light beam to the information recording surface of the CD and the CD-R. In other words, the selective diffraction grating 32 adjusts the beam diameter of the light beam by selectively blocking a part of the light beam traveling toward the objective lens 38 according to the polarization characteristic of the light beam. For this purpose, the selective diffraction grating 32 has a selective diffraction region located around the center of the predetermined diameter. This selective diffraction region diffracts the light beam of horizontal linearly flat light to disperse it out of the objective lens 38, while allowing the light beam of vertical linearly polarized light to travel toward the objective lens 38 as it is. In addition, the selective diffraction grating 32 causes the linearly polarized beam from the λ / 4 plate 34 to be diffracted by an arbitrary angle from the optical axis and reflected by the right angle prism 36 so as to be twisted by an arbitrary angle. Through or reflected by the DBS 26, it is focused on the first and second photodetectors 22b, 24b. Therefore, the distribution of the light beams focused on the first and second photodetectors 22b and 24b is uniformly symmetrical. As a result, focus and tracking can be performed correctly. The λ / 4 plate 34 changes the polarization characteristics of the light beam traveling from the selective diffraction grating 32 toward the objective lens 38.

In detail, the λ / 4 plate 34 converts linearly polarized light traveling from the selective diffraction grating 32 toward the objective lens 40 to circularly polarized light, and proceeds from the objective lens 40 toward the selective diffraction grating 32. The circularly polarized light is converted into linearly polarized light. Further, the λ / 4 plate 34 and the objective lens 38 of the selective diffraction grating 32 are fixedly movable together by the actuator 30 so that they are simultaneously driven by the actuator 30 during servo adjustment. It is being edited.

In addition, the optical pickup device for the heterogeneous optical disk includes a collimating lens 28 positioned between the DBS 26 and the right-angle prism 36 and each plane included in each of the first and second light generation / detection modules 22 and 24. First and second photodetectors 22b and 24b disposed above, below, left, and right of the first and second light sources 22a and 24a on the substrate to convert light beams reflected from the optical disk 40 into electrical signals. It is provided. The reflected light beam split into two by the selective diffraction grating 32 causes the optical path to be changed at right angles at the right angle prism 36. The reflected light beam whose optical path is changed at right angles by the right prism 36 is focused on the surface of the first light detector 22b via the collimating lens 28 and the DBS 26 or via the collimating lens 28. Reflected by the DBS 26, the light beam is focused on the surface of the second photodetector 24b. At this time, the collimating lens 28 causes the divergent light beam from the DBS 26 to run parallel to the right angle prism 36, and the parallel light beam from the right angle prism 36 is converged toward the DBS 26. Let's proceed.

As described above, the optical pickup device for a heterogeneous optical disc according to the present invention uses a dichroic beam splitter to integrate the paths of the light beams and to adjust the beam diameter of the light beam by a selective diffraction grating. To be accessible. In addition, the optical pickup device for a heterogeneous optical disk according to the present invention causes the light beam to be irradiated to the photodetector to be diffracted by the selective diffraction grating to make the distribution of the light beam focused on the photodetector uniform, and also to reflect the reflected light beam directly to the photodetector To be. As a result, the optical pickup apparatus for heterogeneous optical discs according to the present invention enables the focus and tracking to be performed smoothly and the structure of the light generation / detection module is simplified.

Claims (3)

A light source for generating a light beam to be irradiated to the optical disc, and a light detector for detecting the light beam reflected from the optical disc, each having a light detection unit for generating light beams having different polarization characteristics; 2 light generation / detection module; An objective lens for focusing light beams generated by the light generation / detection modules onto a recording surface of the optical disc; Beam path integrating means disposed between the light generation / detection modules and the objective lens to match a path of light beams traveling from the light generation / detection modules toward the objective lens; A λ / 4 plate positioned between the beam path integration means and the objective lens to change the polarization characteristic of the light beam; A portion of the light beam positioned between the beam path integration means and the λ / 4 / plate and traveling from the beam path integration means toward the objective lens is selectively diffracted according to its polarization characteristic to reduce the beam diameter, and And a selective diffraction grating for diffracting a light beam traveling from the plate toward the beam path integrating means by an angle from the optical axis to be focused on the photodetectors. The optical pickup according to claim 1, wherein the light source included in the first light generating / detecting module generates a light beam having a wavelength of 780 nm to enable data recording / reproducing of the compact disc (CD). Device. The optical pickup according to claim 1, wherein the light source included in the second light generation / detection module generates a light beam having a wavelength of 650 nm to enable data recording / reproducing of a digital video disc (DVD). Device.

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