KR20010036812A - Compatible optical pickup apparatus - Google Patents

Abstract

PURPOSE: A compatible optical pick-up device is provided to compatibly use a CD-RW(rewritable) and a DVD, etc., by improving a configuration of an optical system to minimize aberration generated in an optical pick-up device. CONSTITUTION: The first optical source(51) emits an optical of first wavelength. The second optical source emits an optical of second wavelength shorter than the first wavelength. An optical track converting unit converts a rout of an incident optical. An object lens(83) focuses the incident optical, which is emitted by the first and second optical sources and passed through the optical tract converting unit, on an optical disk(30). An optical detector(75) receives the optical, which is emitted by the first and second optical sources and reflected on the optical disk(30), and detects an information signal and an error signal. The first beam splitter(57) shifts a track of the optical emitted by the first optical source(51). The second beam splitter(63) shifts a track of the optical emitted by the second optical source. The first collimating lens(54) is disposed on an optical route between the first optical source(51) and the first beam splitter(57), and enables the optical emitted by the first optical source(51) to be focused and thus to be a parallel optical. A grating(55) is disposed on an optical route between the first collimating lens(54) and the first beam splitter(57), and diffracts the incident parallel optical into a 0 optical +- optical. The second collimating lens(63) is disposed on an optical route between the second optical source(61) and the first beam splitter(57), and enables the optical emitted by the second optical source to be focused and thus to be a parallel optical.

Description

Compatible optical pickup apparatus

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compatible optical pickup apparatus capable of interchangeably employing optical discs having different thicknesses, and more particularly, to a compatible optical pickup apparatus capable of interchangeably employing CD-RW (rewritable), DVD, or the like. will be.

In general, an optical pickup apparatus is a device that records information on a disc or reproduces recorded information in a non-contact manner. There is a demand for an optical pickup apparatus employing an objective lens having a short wavelength and using a high aperture number due to the higher density of the disc. In addition, the high-density optical pickup device needs to adopt compatible disks such as CD, CD-R, CD-RW, CD-I and the like.

Referring to FIG. 1, a conventional compatible optical pickup apparatus includes first and second light sources 11 and 21, a grating 13 diffractively transmitting incident light, optical path changing means for converting a path of incident light, and collimating. The lens 17, the objective lens 19 for focusing incident light to form an optical spot on the optical disk 1, and the light reflected from the optical disk 1 and received through the light receiving lens 25 to receive an information signal and And a photodetector 27 for detecting an error signal.

The first light source 11 is a light source for an optical disk having a thickness of 1.2 mm, such as CD, and emits light having a wavelength of approximately 780 nm. The second light source 21 irradiates light having a wavelength of approximately 650 nm with an optical disk light source having a cross-sectional thickness of 0.6 mm such as a DVD. Here, the light irradiated from the first and second light sources 11 and 21 is focused by the collimating lens 17 as divergent light to become parallel light.

The grating 13 is disposed on an optical path between the first light source 11 and the optical path changing means to diffract and transmit divergent incident light irradiated from the first light source 11 to zero order light, ± 1 order light, or the like. . The +1 order light and the -1 order light that are diffracted through the grating 13 are used to detect the track error signal of the optical disc 1.

The optical path converting means includes a first beam splitter 15 for converting a traveling path of the light irradiated from the first light source 11 and a second path for converting a traveling path of the light irradiated from the second light source 21. And a beam splitter 23.

The collimating lens 17 is disposed on an optical path between the first beam splitter 17 and the objective lens 19 to focus and transmit incident light. That is, the collimating lens 17 focuses divergent light incident on the first and second light sources 11 and 21 to be parallel light.

In the optical pickup apparatus configured as described above, since the grating is disposed on a path between the first light source and the first beam splitter, incident light diverges and passes through the grating. As a result, aberration occurs in a portion located far from the optical axis of the incident light, which affects the detection of the track error signal using the ± first order diffracted light. In addition, when the assembly tolerance of the grating about the optical axis occurs, the interval between the 0th order light and ± 1st order light on the optical disk and the photodetector is different, there is a disadvantage that the detection signal offset (offset) is present, the degree of the error signal falls. Due to such a disadvantage, it is impossible to employ a conventional compatible optical pickup apparatus that is compatible with CD-RW (rewritable) and DVD as an optical disk.

The present invention has been made in view of the above points, and by improving the arrangement of the optical system to minimize the aberration generated in the optical pickup device, it is possible to use a compatible CD-RW (rewritable), DVD, etc. It is an object of the present invention to provide a compatible optical pickup device.

1 is a schematic view showing an optical arrangement of a conventional compatible optical pickup device.

2 is a schematic view showing an optical arrangement of a compatible optical pickup device according to an embodiment of the present invention.

FIG. 3 is a view showing the light source of FIG. 2 and the beam shape irradiated from the light source. FIG.

4 is a view showing the shape of an optical spot formed on an optical disc.

5 is a schematic view showing a photodetector according to an embodiment of the present invention.

<Explanation of symbols for main parts of drawing>

30 Optical disc 50 Fixed optics 51 First light source

54 First collimating lens 55 Grating 57 First beam splitter

61 ... 2nd light source 63 ... 2nd beam splitter 71 ... 2nd collimating lens

73.Receiving lens 75.Photodetector 77.Monitor photodetector

80.Operating optical system 81.Reflective member 83.Objective lens

In order to achieve the above object, the present invention comprises a first light source for irradiating light of a first wavelength; A second light source for irradiating light of a second wavelength shorter than the first wavelength; Optical path converting means for converting a traveling path of the incident light; An objective lens irradiated from the first and second light sources and focuses the light incident on the optical disk via the optical path changing means; And a light detector for detecting the information signal and the error signal by receiving the light reflected from the first and second light sources and receiving the light reflected from the optical disk. A first beam splitter for converting a traveling path of the light irradiated from the light source, and a second beam splitter for converting a traveling path of the light irradiated from the second light source,

A first collimating lens disposed on an optical path between the first light source and the first beam splitter, focusing divergent light emitted from the first light source to be parallel light; A grating disposed on an optical path between the first collimating lens and the first beam splitter to diffract and transmit incident parallel light to at least zero order light and ± 1 order light; And a second collimating lens disposed on an optical path between the second light source and the first beam splitter to focus divergent light emitted from the second light source so as to be parallel light.

Hereinafter, a compatible optical pickup apparatus according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Referring to FIG. 2, the compatible optical pickup apparatus according to the present invention focuses a fixed optical system 50 fixedly disposed on an optical path by irradiating and receiving light, and parallel light incident from the fixed optical system 50. The optical disk 30 is configured to include a movable optical system 80 installed to reciprocate in the radial direction of the optical disk 30.

The fixed optical system 50 includes a second light source (61 for irradiating the first light a first light source 51, the first light (L ₁₎ than the short wavelength of the second light (L ₂₎ for irradiating (L ₁₎ ), An optical path converting means, and a photodetector 75 for receiving the first and second light beams L ₁ and L ₂ reflected by the optical disk 30 to detect an information signal and an error signal. Grating 55 for diffracting and transmitting collimating lenses 54 and 71 and first light L ₁ incident in parallel on a path between the first collimating lens 54 and the optical path changing means. It is configured to include).

In addition, the movable optical system 80 focuses the first and second lights L ₁ and L ₂ incident in parallel from the fixed optical system 50 onto each of the optical discs 33 and 31. And a lens 83. In addition, the movable optical system 80 further includes a reflecting member 81 provided on the optical path between the optical path changing means and the objective lens 83 to change the incident light in parallel in the horizontal direction to the vertical direction. As described above, the configured optical optical system 80 is transferred in the radial direction of the optical disk 30 when recording / reproducing information on the optical disk 30, so that the optical spot irradiated from the fixed optical system 50 is transmitted to the optical disk 30. )

The first and second light sources 51 and 61 are usually composed of semiconductor lasers, and irradiate laser light having a predetermined divergence angle, respectively. That is, the first light L ₁ irradiated from the first light source 51 is suitable for employing a relatively thick disk 33, for example, a compact disk, and has a wavelength of approximately 780 nm. The second light L ₂ irradiated to the second light source 61 is suitable for adopting a relatively thin disk 31, for example, a DVD, and has a wavelength of approximately 650 nm.

As illustrated in FIG. 3, the first light source 51 includes a corner light emitting laser diode 52 installed on the substrate 53 and irradiating laser light in a lateral direction. The laser diode 52 has a structure in which semiconductor material layers are stacked on the substrate 53, and irradiates laser light L to a side surface thereof (z-axis direction). The laser diode 52 irradiates light of TE polarization mode, that is, light of S polarization. This is the electric field of the irradiated light It means that the components are parallel to the boundaries of the stacked portions of the semiconductor material layer. In addition, the laser diode 52 has a longitudinal direction and a transverse direction difference at the start point of the irradiated light. Accordingly, the irradiation light has an elliptical beam cross-sectional shape in which a long diameter is arranged in the stacking direction. That is, the light irradiated from the laser diode 52 is a magnetic field The component is arranged in the longitudinal direction of the cross section, and the electric field The components are arranged in the short diameter direction. Meanwhile, as shown in FIG. 4, the light spot irradiated from the first light source 51 and formed on the optical disc has a long radius in the radial direction R of the optical disc 30, and a short radius in the tangential direction T. It is preferable to be located. The first light source 51 is disposed in view of the above points.

The first collimating lens 54 is disposed between the first light source 51 and the grating 55 so that the first light L ₁ irradiated and emitted from the first light source 51 is parallel light. To be Therefore, since the light incident on the grating 55 maintains parallel light, the optical aberration of the light transmitted through the grating 55 and diffracted is reduced. In addition, in the optical arrangement of the grating 55, even if an optical axis assembly tolerance occurs, there is an advantage that the spacing between the three beams including the diffracted zeroth order light and the ± first order light is constant.

The second collimating lens 71 allows incident light to be parallel light and incident parallel light to be focused light. That is, the second light L ₂ irradiated from the second light source 61 becomes parallel light, and the first and second light L ₁ incident in parallel reflected by the optical disk 30 and incident thereto ( L ₂ ) is focused light.

The optical path converting means includes a first beam splitter 57 for converting a traveling path of the light irradiated from the first light source 51 and a second beam splitter 63 for converting a traveling path of the light irradiated from the second light source. It is configured to include. The first beam splitter 57 is disposed on an optical path between the grating 55, the second collimating lens 71, and the reflective member 81 so that the light incident from the first light source 51 is incident. The light is directed toward the disk 33, and the light incident from the disk 33 is directed toward the photodetector 75. The first beam splitter 57 is a polarizing beam splitter for splitting incident light according to a polarization component, a normal beam splitter for splitting incident light in a predetermined light quantity ratio, or a straight beam of light incident in one direction. The light incident in the direction is composed of a hologram element or the like for diffraction transmission. Here, the first beam splitter 57 reflects most of the light irradiated from the first light source 51 toward the optical disc 33, but transmits a portion of the first beam splitter 57 to the first and second light sources 51 ( The light is detected by the monitor photodetector 77 which detects the light output degree of the light. Light directed to the monitor photodetector 77 is incident in parallel via the first and second collimating lenses 54 and 71. Accordingly, the optical output receiving efficiency of the monitor photodetector 77 may be improved, as compared to an optical pickup apparatus including an optical arrangement as shown in FIG. 1, in which light directed to the monitor photodetector becomes divergent light. .

The second beam splitter 63 is disposed on an optical path between the second light source 61, the collimity lens 71, and the light receiving lens 73, and is incident from the second light source 61. Light is directed toward the optical disc 31 and light reflected by the optical disc 31 is directed toward the photodetector 75.

2 and 5, the photodetector 75 receives a first photodetector for receiving zero order diffracted light reflected from the optical disk 30, a first order diffracted light, and a -first order diffracted light, respectively. And second and third photodetectors.

The first photodetector independently photoelectrically converts the received light, and includes split plates A, B, C and D having a 2 × 2 arrangement. The second photodetector is disposed on one side of the first photodetector to receive the + 1st order diffracted light diffracted by the grating 55, and includes split plates E1 and E2 that independently photoelectrically convert. The third photodetector is disposed on the other side of the first photodetector to receive -first-order diffracted light diffracted by the grating 55, and includes split plates F1 and F2 that independently photoelectrically convert. do.

The reason why the first to third photodetectors having such a configuration is provided is that, when employing a relatively thick optical disk 33, the track error signal for the optical disk 33 is differential push pull (DPP). To detect using).

That is, the detection of the track error signal TE by the DPP method can be detected by differential and summing as in Equation (1).

As described above, by detecting the track error signal by the DPP method, when detecting information on a correct track of an optical disc, a + 1st diffraction light and a -1st diffraction light are received and a value other than (0) at differential time is received. There is an advantage that the offset problem that is detected can be solved.

The optical axis adjustment of the optical element of the optical pickup apparatus configured as described above is as follows. First, the first light source 51, the objective lens 83, and the photodetector 75 are adjusted based on the relatively thick optical disk 33, and then the second light source suitable for the relatively thin optical disk 31 is used. Adjust 61 to the x, y, and z axes.

The compatible optical pickup apparatus according to the present invention configured as described above changes the positions of the first and second collimating lenses so that the light transmitted between the fixed optical system 50 and the movable optical system 80 becomes parallel light. As a result, the width of the light directed toward the photodetector 75 can be constant regardless of the movable position of the movable optical system 80. In addition, by arranging the grating on the path through which the parallel light travels, the light incident on the grating is maintained to maintain parallel light, thereby reducing the optical aberration of the light diffracted through the grating. Even if it occurs, there is an advantage that the interval between the three beams including the diffracted zeroth order light and the ± first order light is constant. In addition, by detecting the track error signal by the DPP method, the first to third photodetectors having a plurality of dividers having a photodetector can reduce the offset at the time of detecting the track error signal.

The compatible optical pickup apparatus according to the present invention having the advantages as described above can employ a recordable CD-RW (rewritable) in addition to the conventional CD and DVD compatible adoption.

Claims (3)

A first light source for irradiating light of a first wavelength; A second light source for irradiating light of a second wavelength shorter than the first wavelength; Optical path converting means for converting a traveling path of the incident light; An objective lens irradiated from the first and second light sources and focuses the light incident on the optical disk via the optical path changing means; The optical pickup apparatus of claim 1 or 2, comprising: a photodetector irradiated from the first and second light sources and receiving the light reflected from the optical disk to detect an information signal and an error signal; The optical path converting means includes a first beam splitter for converting a traveling path of light irradiated from the first light source, and a second beam splitter for converting a traveling path of light irradiated from the second light source, A first collimating lens disposed on an optical path between the first light source and the first beam splitter, focusing divergent light emitted from the first light source to be parallel light; A grating disposed on an optical path between the first collimating lens and the first beam splitter to diffract and transmit incident parallel light to at least zero order light and ± 1 order light; A second collimating lens disposed on an optical path between the second light source and the first beam splitter to focus divergent light emitted from the second light source so as to be parallel light; Fluorescent pickup device. The optical lens of claim 1, wherein the objective lens focuses incident parallel light and is movable in a radial direction of the optical disk. And the first and second light sources, the optical path changing means, the first and second collimating lenses, the grating, and the photodetector are fixedly arranged. The method according to claim 1 or 2, wherein the photodetector, A first photodetector, each independently photoelectrically converting the received light, comprising split plates A, B, C and D having a 2 × 2 array; A second photodetector disposed on one side of the first photodetector to receive one diffracted light diffracted by the grating, and including split plates E1 and E2 independently photoelectrically converted; And a third photodetector disposed on the other side of the first photodetector to receive other diffracted light diffracted by the grating, and including split plates F1 and F2 independently photoelectrically converted. Compatible optical pickup device.