KR19990041787A - Compatible Optical Pickup Device - Google Patents

Abstract

A compatible optical pickup apparatus capable of interchangeably employing recording media having different thicknesses is disclosed.

The compatible optical pickup apparatus includes first and second light sources for generating and outputting light of different wavelength regions, an objective lens disposed between the first and second light sources and a recording medium to focus incident light, and a first light source. The first optical path converting means disposed on the optical path between the objective lenses and converting the advancing path of the incident light, and the light incident on the optical path between the first optical path converting means and the objective lens and incident from the first light source Second light path converting means for transmitting the light path passing through the second light source, and passing through the objective lens, the second light path converting means, and the first light path converting means. And a photodetector which receives the light and detects the information signal and the error signal.

Description

Compatible Optical Pickup Device

The present invention relates to an optical pickup apparatus, and more particularly, to a compatible optical pickup apparatus capable of interchangeably employing recording media having different thicknesses.

In general, an optical pickup device is employed in a compact disc player (CDP), a digital multifunction disc player (DVDP), or the like to record / reproduce information such as video or sound from a disc-type recording medium. Digital multi-function disc player is attracting attention in the field of video sound as a device capable of high-density recording and playback. The optical pickup device employed in this digital multi-function disc player is not only a digital multi-function disc (DVD) but also a compact disc (CD), CD-R (Recordable), CD-I, CD-G, etc. In the case of adopting the CD family, information should be recorded and / or reproduced.

By the way, the standard thickness of the existing CD family is 1.2mmDLS, while the thickness of the DVD is standardized to 0.6mm due to the disc tilt tolerance and the objective lens numerical aperture. In addition, the wavelengths of the reproduction light sources for DVD and CD are also different, whereas the wavelength of the reproduction light source for CD is approximately 780 nm, while the wavelength of the reproduction light source for DVD is approximately 650 nm.

The conventional compatible optical pickup apparatus capable of recording / reproducing information on discs having different formats as described above includes a single light source that emits light having a wavelength of approximately 650 nm in accordance with the DVD format, and compensates for the difference in thickness of the discs employed. The structure can be improved to enable compatible adoption of the disk-type recording medium. In this case, degradation of about 5% occurs in comparison with an optical pickup apparatus employing a light source that emits light of 780 nm wavelength when the CD family is reproduced, but this is not a big problem since it is within the reproduction tolerance range.

However, when CD-R, which is one of the CD families, is adopted, a sensitivity difference occurs when using a light source that emits light of approximately 650 nm wavelength and a light source that emits light of approximately 780 nm wavelength. That is, since the CD-R has an organic dye film recording layer as is known, the difference in reflectance is large depending on the wavelength of light. Accordingly, when using light of 780 nm wavelength, the reflectance is large, but when using light of approximately 650 nm wavelength, the reflectance is lowered to 10% or less, thereby preventing signal reproduction.

In order to overcome this problem, as shown in FIG. 1, a conventional compatible optical pickup apparatus capable of interchangeably employing a digital multifunction disc and a compact disc includes first and second light sources 1 and 11 and a first one. And first and second polarization beam splitters 3 and 13 for converting the optical paths of the light emitted from the second light sources 1 and 11, variable aperture 30 for limiting the numerical aperture of the incident light, and incident light. First and second photodetectors for collecting the light reflected from the objective lens 35 for focusing the light and the recording medium 40 having different thicknesses and emitted from the first and second light sources 1 and 11. And 7) 17.

The first light source 1 is a semiconductor laser that generates and emits light having a wavelength of 635 nm, and records and reproduces an information signal of a thin recording medium, that is, a DVD 40a. The light emitted from the first light source 1 is converted into parallel light by the collimating lens 2 and is incident on the first polarization beam splitter 3, and only one linearly polarized light is reflected. The reflected light is converted into approximately one circular polarized light while passing through the wave plate 25, and is focused by the objective lens 35 to form a light spot on the recording surface of the DVD 40a. Light reflected from the recording surface of the DVD 40a is detected by the first photodetector 7 via the objective lens 35, the wave plate 25, and the first polarization beam splitter 3. In this case, the objective lens 35 is provided so that the light emitted from the first light source 1 forms a suitable light spot on the recording surface of the DVD 40a.

The second light source 11 is a semiconductor laser that generates and emits light having a wavelength of 780 nm, and records and reproduces an information signal of a thick recording medium, that is, a CD 40b. The light emitted from the second light source 11 is converted into parallel light by the collimating lens 12 and is incident on the second polarization beam splitter 13, and only one linearly polarized light is transmitted. The transmitted light is reflected by the interference filter type prism 20 provided between the first polarization beam splitter 3 and the wave plate 25 and is directed toward the wave plate 25. This light is converted into approximately one circular polarized light while passing through the wave plate 25 and focused by the objective lens 35 to form a light spot on the recording surface of the CD 40b. The light reflected from the recording surface of the CD 40b is reflected by the interference filter prism 20 via the objective lens 35 and the wave plate 25 to thereby pass the second polarization beam splitter 13. The light is reflected by the second polarization beam splitter 13 and detected by the second photodetector 17.

In this case, the interference filter prism 20 reflects light of 780 nm wavelength incident from the second light source 11 and transmits light of 635 nm wavelength incident from the first light source 1. It has two mirror surfaces 20a and 20b. Therefore, the light incident from the second light source 11 side is reflected from the first mirror surface 20a toward the second mirror surface 20b and reflected from the second mirror surface 20b to the objective lens 35. Heads up.

On the other hand, the second polarized beam splitter 13 and the interference filter type prism are formed so as to focus the light emitted from the second light source 11 between two mirror surfaces 20a and 20b of the interference filter type prism 20. A condenser lens 15 is further provided on the optical path between the 20. In this case, the light emitted from the second light source 11 is emitted toward the objective lens 35.

As described above, when a divergent light is incident on the objective lens 35 by employing a finite optical system composed of the interference filter-type prism 20 and the condenser lens 15, the recording / reproducing object is a thick recording medium, that is, the When exchanged with the CD 40b, spherical aberration generated can be eliminated.

Meanwhile, the variable stop 30 is disposed on the optical path between the wavelength plate 25 and the objective lens 35. As shown in FIG. 2, the variable stop 30 allows light of 780 nm wavelength to be incident only to a region corresponding to a numerical aperture 0.45 to the objective lens 35 during recording and reproduction of the CD 40b. The first and second regions 31 and 33 are formed in and out of an area corresponding to the numerical aperture 0.45 of the objective lens 35. The first region 31 is provided so that light of 635 nm and 780 nm wavelengths emitted from the first and second light sources 1 and 11 can be transmitted. The second region 33 reflects all light of 780 nm wavelength and is coated with a dielectric thin film to transmit light of 635 nm wavelength in the region 34 corresponding to the numerical aperture 0.6 of the objective lens 35. Filter. In this case, the first region 31 is made of a quartz thin film to remove the optical path difference generated between the dielectric thin film of the second region 33.

Since the conventional compatible optical pickup apparatus as described above requires an additional interference filter type prism 20 to construct a finite optical system for eliminating spherical aberration generated when the recording medium 40 is compatible with different thicknesses. , The structure is complicated.

In addition, in order to adjust the numerical aperture of the objective lens 35 so as to form an appropriate light spot according to the compatible adoption of recording media 40 having different thicknesses, a variable stop 30 made of a quartz thin film and a dielectric thin film is employed. The manufacturing process of the variable stop 30 is complicated and difficult to mass-produce. Therefore, it is difficult to mass-produce a compatible optical pickup device employing the variable aperture 30 and the manufacturing cost is high.

In addition, since two expensive polarizing beam splitters 3 and 13 are employed and two photodetectors 7 and 17 are employed, the number of parts is high and the manufacturing cost is high overall.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems described above, and an object thereof is to provide a compatible optical pickup apparatus which can reduce the number of parts and manufacturing cost due to its simple structure.

1 is a view schematically showing an optical arrangement of a conventional compatible optical pickup device;

Figure 2 is a plan view schematically showing the variable aperture of Figure 1,

3 is a view schematically showing an optical arrangement of a compatible optical pickup device according to an embodiment of the present invention;

4 is a view schematically showing a reflectance characteristic according to an incident wavelength of the first optical path converting means of FIG.

FIG. 5 is a view schematically showing reflectance characteristic according to an incident wavelength of the second optical path converting means of FIG. 3;

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

<Description of Symbols for Main Parts of Drawings>

51,61 ... 1st and 2nd light source 53 ... beam orthopedic prism

55,65 First and second optical path changing means 55a

57 ... wavelength 67,110 ... objective lens

70 ... recording medium 73 ... photodetector

110a ... light control pattern

In accordance with an aspect of the present invention, a compatible optical pickup apparatus includes: first and second light sources for generating and emitting light having different wavelength regions; An objective lens disposed between the first and second light sources and the recording medium to focus incident light; First optical path converting means disposed on an optical path between the first light source and the objective lens to convert an advancing path of incident light; A second optical path conversion disposed on the optical path between the first optical path conversion means and the objective lens to transmit most of the light incident from the first light source toward a straight line, and convert the traveling path of the light incident from the second light source; Means; And a photodetector which is reflected from the recording medium and receives the light passing through the objective lens, the second optical path converting means and the first optical path converting means to detect an information signal and an error signal.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

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

Referring to the drawings, a compatible optical pickup device includes first and second light sources 51 and 61 for generating and emitting light having different wavelength regions, an objective lens 67 for focusing incident light, and a traveling path of incident light. And first and second optical path converting means (55) (65) for converting the?, And photodetectors (73) for detecting information signals and error signals.

As the first light source 51, a semiconductor laser that generates and emits light having a predetermined wavelength, that is, about 650 nm, is suitable for recording / reproducing information on a relatively thin recording medium 70a such as a DVD or a DVD-RAM. It is provided. In this case, a high output semiconductor laser is employed to enable recording of an information signal on a recording medium by the first light source 51. The light emitted from the first light source 51 is converted into parallel light by the collimating lens 53 and is incident on the first light path converting means 55.

On the other hand, it is preferable to further include a beam shaping prism 53 for shaping the light beam emitted from the first light source 51 on the optical path between the first light source 51 and the first light path converting means 55. Do. In this case, the light emitted from the first light source 51 can be focused on the recording surface of the recording medium with sufficient optical power for recording.

At this time, the optical arrangement of the first light source 51, the collimating lens 52 and the beam shaping prism 53 is converted into parallel light by the collimating lens 52 to the first light path converting means 55 The beam size of the incident light is approximately equal to the numerical aperture 0.6 of the objective lens 67. In this case, the collimating lens 52 and the beam shaping prism 53 form an infinite optical system for allowing parallel light to enter the objective lens 67.

The second light source 61 may be a wavelength longer than that of the first light source 51 so as to be suitable for recording / reproducing information of a CD family, in particular, a relatively thick recording medium 70b such as CD-R. And a semiconductor laser for generating and emitting light having a wavelength of approximately 780 nm. The light emitted from the second light source 61 is converted into parallel light by the collimating lens 62 and is incident on the second light path converting means 65. Here, the first light source 51 and the second light source 61 are disposed on different light paths, and are selectively driven according to the type of the recording medium 70.

At this time, the optical arrangement of the second light source 61 and the collimating lens 62 is converted into parallel light by the collimating lens 62 so that the beam size of the light incident on the second light path converting means 65 is approximately. The aperture lens 67 is disposed to correspond to the numerical aperture 0.45. In this case, the collimating lens 62 forms an infinite optical system that allows parallel light to enter the objective lens 67.

The objective lens 67 is disposed between the first and second light sources 51 and 61 and the recording medium 70 to focus the light emitted from the first and second light sources 51 and 61. Light spots are formed on the recording medium 70. The objective lens 67 is driven by an actuator (not shown) driven in accordance with the focus error signal and the track error signal.

The first optical path converting means 55 is disposed on the optical path between the first light source 51 and the objective lens 67 to convert the traveling path of the incident light. The first optical path converting means 55 is preferably a polarizing beam splitter having a mirror surface 55a which transmits or reflects the light emitted from the first light source 51 according to its linear polarization component.

In this case, as shown in FIG. 4, the mirror surface 55a transmits one linearly polarized light, that is, light of p-polarized light, of at least 80% of light emitted from the first light source 51 (wavelength 650 nm). And other linearly polarized light, ie s-polarized light, is coated to reflect at least 90%, for example at least 99%. In addition, the mirror surface 55a is coated to reflect light (wavelength 780 nm) emitted from the second light source 61 to 80% or more, for example, 90% or more, as shown in FIG. 4.

Here, reference numeral 81 is a graph schematically showing reflectance according to the wavelength of light of p-polarized light incident on the mirror surface 55a. Reference numeral 83 is a graph showing a reflectance according to the wavelength of s-polarized light incident on the mirror surface 55a, and reference numeral 85 is a graph showing an average reflectance according to the wavelength of light incident on the mirror surface 55a. to be.

On the other hand, it is preferable to further include a wavelength plate 57 for converting the polarization of the incident light on the optical path between the first optical path conversion means 55 and the objective lens 67. In this case, the wavelength plate 57 is preferably a quarter wave plate with respect to the light wavelength emitted from the first light source 51, that is, the 650 nm light wavelength.

The second light path converting means 65 is disposed on the light path between the first light path converting means 55 and the objective lens 67. The second light path converting means 65 is disposed to be inclined at a predetermined angle with respect to the first light path converting means 55 to convert the traveling path of the light incident from the second light source 61. That is, as shown in FIG. 5, the second light path converting means 65 partially transmits and reflects light of the 780 nm wavelength emitted from the second light source 61 at a ratio of approximately 50:50. A beam splitter is provided. In this case, as shown in FIG. 5, the beam splitter is preferably provided to transmit approximately 80% or more of light having a wavelength of 650 nm emitted from the first light source 51.

Here, reference numeral 86 is a graph showing the reflectance according to the wavelength when the p-polarized light is incident on the second optical path converting means 65. Reference numeral 87 is a graph showing a reflectance according to a wavelength when light of s-polarized light is incident, and reference numeral 88 schematically shows an average reflectance according to a wavelength of light incident on the second optical path converting means 65. This is the graph shown.

The photodetector 73 reflects light from the recording medium 70 and receives light passing through the objective lens 67, the second optical path converting means 65, and the first optical path converting means 55. Signals and error signals are detected.

On the other hand, it is preferable to further include a focusing lens 71 for focusing the incident light on the optical path between the first optical path conversion means 55 and the photodetector 73. In this case, it is preferable that the focusing lens 71 includes an astigmatism lens causing astigmatism so that the focus error signal can be detected by the astigmatism method.

3 to 5, the operation of the compatible optical pickup apparatus according to an embodiment of the present invention will be described.

First, the first light source 51 is operated at the time of recording / reproducing of a recording medium 70a having a thin thickness such as a DVD or a DVD-RAM. The light emitted from the first light source 51 is converted into parallel light by the collimating lens 52 and is shaped while passing through the beam shaping prism 53 and is incident on the first light path converting means 55. . Of the incident light, p-polarized light is transmitted through the mirror surface 55a, and s-polarized light is reflected on the mirror surface 55a. The light transmitted through the mirror surface 55a is converted into one circularly polarized light while passing through the wavelength plate 57, and passes through the second optical path converting means 65 to be incident on the objective lens 67. The incident light is focused by the objective lens 67 to form light spots on the recording surface of the recording medium 70a.

Light of one circularly polarized light incident on the recording surface of the recording medium 70a is reflected and converted into another circularly polarized light, and the wavelength plate 57 is passed through the objective lens 67 and the second optical path converting means 65. Is incident on. The polarization is converted into s-polarized light at the wavelength plate 57 and incident on the first optical path converting means 55. The s-polarized light incident on the first optical path converting means 55 is reflected by the mirror surface 55a, is focused by the focusing lens 71, and detected by the photodetector 73.

The second light source 61 is operated when recording / reproducing the thick recording medium 70b such as CD, CD-R, or the like. The light emitted from the second light source 61 is converted into parallel light by the collimating lens 62 and is incident on the second light path converting means 65. The incident light is partially reflected by the second light path converting means 65 and is incident on the objective lens 67. The objective lens 67 focuses the light on the recording surface of the recording medium 70b.

The light incident on the recording surface of the recording medium 70b is reflected and passes through the objective lens 67, and then partially passes through the second optical path converting means 65, so that the first optical path converting means 55 Is incident on. The light is reflected by the mirror surface 55a of the first optical path converting means 55, is focused by the focusing lens 71, and detected by the photodetector 73.

The compatible optical pickup device as described above is disposed so that the beam sizes of the light emitted from the first and second light sources 51 and 61 are incident to the objective lens 67 so as to be 0.6 and 0.45, respectively. It is possible to adopt compatible recording media 70a and 70b.

Here, the second light source 61 is used for recording CD, CD-R, etc., but the first light source 51 may be used. As such, when the first light source 51 that generates and emits light having a wavelength of 650 nm is used for recording the information signal on the recording medium 70 having different thicknesses, a high power semiconductor laser suitable for recording is used as one light source. There is an advantage that can be employed only in the first light source 51.

On the other hand, the mirror surface 55a of the first optical path conversion means 55 is described and illustrated to transmit p-polarized light and s-polarized light with respect to light having a wavelength of 650 nm, but is not limited thereto. That is, the mirror surface 55a may be provided to transmit s-polarized light and reflect p-polarized light with respect to light having a wavelength of 650 nm. In addition, the mirror surface 55a may be provided to transmit most of the light of the 780nm wavelength. In this case, the first light source 51 and the photodetector 73 are disposed correspondingly.

6 is a view schematically showing an optical arrangement of a compatible optical pickup device according to another embodiment of the present invention. The compatible optical pickup apparatus of the present exemplary embodiment is the same as the compatible optical pickup apparatus according to the exemplary embodiment of the present invention described with reference to FIGS. 3 to 5, and the objective lens 67 of FIG. 3 is a light control pattern 110a. It is characterized in that it is converted to the objective lens 110 having. Here, the same reference numerals as in FIG. 3 denote the same members.

The light control pattern 110a is formed on at least one surface of the objective lens 110 to control the light incident on the objective lens 110. 6 shows an example in which the light control pattern is an annular groove. Here, the light control pattern 110a is variously modified as described in Korean Patent Application Nos. 95-14928, 96-3605, 96-13918, and 97-4273 proposed by the present applicant. Can be. That is, the light control pattern 110a may have a groove for scattering light or an annular lens surface for the purpose of increasing the numerical aperture.

As described above, when the light control pattern 110a, for example, the annular light control pattern 110a is provided in the objective lens 110, the light control pattern 110a and the light control pattern 110a are emitted from the second light source 61. Light passing through the inner side forms light spots on the recording surface of the thick recording medium 70b. Light emitted from the first light source 51 and passing outside the light control pattern 110a forms a light spot on the recording surface of the thin recording medium 70a.

The compatible optical pickup apparatus according to the present invention as described above is composed of an infinite optical system for allowing parallel light to be incident on the objective lens, and also includes first and second optical path converting means, that is, a polarizing beam splitter and a beam splitter. Since the photodetector is used, its optical arrangement structure is simple. In addition, the number of parts can be reduced, thereby reducing the manufacturing cost.

Claims (10)

First and second light sources for generating and emitting light in different wavelength regions; An objective lens disposed between the first and second light sources and the recording medium to focus incident light; First optical path converting means disposed on an optical path between the first light source and the objective lens to convert an advancing path of incident light; A second optical path conversion disposed on the optical path between the first optical path conversion means and the objective lens to transmit most of the light incident from the first light source toward a straight line, and convert the traveling path of the light incident from the second light source; Means; And a photodetector which is reflected from the recording medium and receives the light through the objective lens, the second optical path converting means, and the first optical path converting means to detect an information signal and an error signal. Optical pickup device. The method of claim 1, The first light source is a semiconductor laser that emits light of a predetermined wavelength, And the second light source is a semiconductor laser that emits light having a relatively longer wavelength than that of the first light source. The method of claim 2, And the first light source emits light having a wavelength of approximately 650 nm, and the second light source emits light having a wavelength of approximately 780 nm. The method according to any one of claims 1 to 3, wherein the first light path converting means transmits or reflects the light emitted from the first light source according to the linearly polarized light component, and the light emitted from the second light source Mostly polarized beam splitters with mirrors adapted to reflect, And a wavelength plate for converting polarized light of incident light on the optical path between the first optical path converting means and the objective lens. The compatible optical pickup apparatus of claim 4, wherein the mirror is configured to reflect at least 80% of light emitted from the second light source. The compatible optical pickup apparatus of claim 4, wherein the mirror is configured to transmit 80% or more of p-polarized light and reflect 90% or more of s-polarized light among the light emitted from the first light source. 5. The compatible optical pickup apparatus of claim 4, wherein the wavelength plate is a quarter wave plate with respect to the light wavelength emitted from the first light source. The method according to any one of claims 1 to 3, wherein the first light path converting means transmits or reflects the light emitted from the first light source according to the linearly polarized light component, and the light emitted from the second light source Mostly polarized beam splitters with mirrors adapted to transmit, And a wavelength plate for converting polarized light of incident light on the optical path between the first optical path converting means and the objective lens. According to any one of claims 1 to 3, wherein the objective lens of the annular for controlling the light incident on the objective lens so that the light irradiated from the first and second light source is compatible with the disk having a different thickness. Compatible optical pickup device, characterized in that the light control pattern is formed. The beam shaping prism according to any one of claims 1 to 3, further comprising: a beam shaping prism for shaping a light beam emitted from the first light source on an optical path between the first light source and the first light path converting means. Compatible optical pickup device characterized in that.