KR100828369B1 - Optical pickup apparatus - Google Patents

Abstract

An optical pickup apparatus having a compatibility system combining a BD / CD optical system having an objective lens having an NA of 0.85 and an HD DVD / DVD optical system having an objective lens having an NA of about 0.6 is disclosed.

The disclosed optical pickup apparatus includes: a first optical disk for reproducing a first optical disk having a cover layer thickness of 0.1 mm and a second optical disk having a cover layer thickness of 1.2 mm; A second optical system for reproducing each of the third and fourth optical disks having a cover layer thickness of 0.6 mm; A first semiconductor laser having a wavelength in a range of about 405 nm for irradiating a beam to the first optical disk via the first optical system or for irradiating the beam to the third optical disk via the second optical system; A second semiconductor laser having a wavelength in the range of about 780 nm for irradiating a beam onto the second optical disk via the first optical system; And a third semiconductor laser having a wavelength of about 650 nm for irradiating a beam to the fourth optical disk via the second optical system.

Description

Optical pickup apparatus

1 is a view showing an optical arrangement of an optical pickup device consisting of a HD DVD / DVD compatible optical system and a BD / CD compatible optical system according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a polarization state of light incident on an objective lens, FIG. 2A is a schematic diagram focused on a low NA, and FIG. 2B is a schematic diagram focused on a high NA.

3 is a schematic diagram showing a spot in a direction orthogonal to the vibration direction in the polarization state of FIG. 2, FIG. 3A is a schematic diagram focused on a low NA, and FIG. 3B is a schematic diagram focused on a high NA.

FIG. 4 is a graph showing the relationship between the half-width of the spot diameter in the polarization state and the NA of the objective lens in the case where the far field pattern is not considered.

FIG. 5 is a graph showing the relationship between the spot diameter half-width ratio and the NA of the objective lens in the polarization state of FIG.

Fig. 6 is a graph showing the relation between the spot diameter half width in the polarization state and the NA of the objective lens in the case of considering the farfield pattern.

FIG. 7 is a graph showing a relationship between the spot diameter half-width ratio in the polarization state of FIG. 6 and the NA of the objective lens. FIG.

8 is a view showing an optical arrangement of a conventional optical pickup apparatus having a compatible optical system.

Explanation of symbols on the main parts of the drawings

4 ... BD / CD compatible optics

8 ... HD DVD / DVD compatible optics

10 ... Blue Purple Laser Element

15 ... Dragonist

45a, 45b ... 1/4 wave plate

50 ... polarization hologram element

55 ... BD / CD compatible objective unit

60 ... hologram unit for CD

70 ... DVD hologram unit

85 ... HD DVD / DVD / CD compatible objective unit

The present invention relates to an optical pickup device, and more particularly, to an optical pickup device having a compatible optical system.

Generally, an optical disc system using a blue-violet laser diode (LD) for recording large data of 15 GB or more on a small and portable recording medium, Blu-ray Disc (hereinafter abbreviated as "BD") or HD DVD (trade name) is developed.

The optical pickup apparatus applied to these systems is not only compatible with compact discs (CDs) and digital versatile discs (DVDs), which are typical recording media, but also with BD and HD DVDs.

In general, an optical pickup device for reproducing CD has a laser diode (hereinafter referred to as LD) for irradiating laser light having a wavelength of about 780 nm and an objective lens having a numerical aperture (hereinafter referred to as NA) of 0.45. Use The optical pickup device for DVD uses LD and NA of 0.6 for irradiating laser light with wavelength of about 650 nm. The optical pickup apparatus for recording and reproducing HD DVD uses an objective lens having a NA of 0.65.

The thickness of the optical disc cover layer is 0.1 mm for BD, 0.6 mm for HD DVD, 0.6 mm for DVD, and 1.2 mm for CD. Therefore, there is a possibility that the compatibility between the optical pickup device for HD DVD and the optical pickup device for DVD can be secured relatively easily. However, since an objective lens having a NA of 0.85 is used for BD, it is difficult to be compatible with other optical systems.

Accordingly, there has been proposed an optical pickup apparatus having two optical systems that distinguishes the BD optical system from other optical systems.

FIG. 8 is a view showing an optical arrangement of an optical pickup apparatus having a conventional HD DVD / DVD / CD compatible optical system 108 and a BD optical system 104. As shown in FIG.

Referring to FIG. 8, in the conventional compatible optical pickup apparatus, since the optical component used in the HD DVD / DVD / CD compatible optical system 108 corresponds to three wavelengths, the following problem may occur.

For example, the hologram element is difficult to improve the light utilization efficiency for all wavelengths, and a high output LD for recording must be used even when playing a DVD or a CD. Therefore, when high output of the LD for DVD and the LD for CD is performed, high frequency (HF) modulation of LD may become difficult during reproduction. The low light utilization efficiency of the hologram element means that there is a lot of unnecessary light. For example, an offset signal included in a focusing error (FE) signal increases. In addition, since a dichroic filter (DF) mirror corresponding to three wavelengths has a large film thickness, a problem arises in that distortion is large.

Accordingly, the present invention has been made in view of the above problems, and includes a compatible optical system in which a BD / CD optical system having an objective lens having a NA of 0.85 and an HD DVD / DVD optical system having an objective lens having a NA of about 0.6 are combined. Its purpose is to provide an optical pickup apparatus having a.

In order to achieve the above object, the present invention includes a first optical system for reproducing a first optical disk having a cover layer thickness of 0.1 mm, and a second optical disk having a cover layer thickness of 1.2 mm; A second optical system for reproducing each of the third and fourth optical disks having a cover layer thickness of 0.6 mm; A first semiconductor laser having a wavelength of about 405 nm for irradiating a beam to said first optical disk via said first optical system or to irradiate a beam to said third optical disk via said second optical system; A second semiconductor laser having a wavelength in the range of about 780 nm for irradiating a beam to the second optical disk via the first optical system; And a third semiconductor laser having a wavelength of about 650 nm for irradiating a beam to the fourth optical disk via the second optical system. Here, the first optical system includes a first objective lens having a numerical aperture of 0.85, and the second optical system includes a second objective lens having a numerical aperture of 0.65.

In addition, the present invention includes a plurality of optical systems having an objective lens having a numerical aperture different from each other so as to reproduce or reproduce recording of a plurality of different standard optical discs, the optical system is characterized in that the circularly polarized light of the optical system Characterized in that the numerical aperture of the objective lens to be incident on the largest objective lens. Herein, the optical discs of the different standards include an optical disc standard using blue violet light.

Hereinafter, an optical pickup apparatus according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals are used for substantially the same components, and repeated description thereof will be omitted.

1 is a schematic diagram showing an optical arrangement of an optical pickup apparatus according to an embodiment of the present invention.

This optical pickup device consists of a BD / CD compatible optical system 4 and an HD DVD / DVD compatible optical system 8. To this end, the optical pickup apparatus according to the present invention comprises a DVD hologram unit 70 having a LD for DVD constituting the compatible optical system 4 and 8 and a CD hologram unit 60 having a CD for LD. And a blue violet LD (10), a compatible objective lens unit (85) for HD DVD / DVD, and a BD / CD compatible objective lens unit (55). The blue violet LD 10 is common to the HD DVD optical system and the BD optical system.

The optical paths of the HD DVD optical system and the DVD optical system are generally common, and the HD DVD / DVD compatible objective unit 85 has a center wavelength of 405 nm due to the blue LD 10 and 650 nm due to the DVD hologram unit 70. Laser light of a large wavelength is focused on the optical disk. On the other hand, a part of the optical path of the BD optical system is common to the CD optical system, and the BD / CD compatible objective unit 55 has a center wavelength of 405 nm due to the blue LD 10 and a hologram unit 60 for the CD. It serves to condense laser light of 780nm band on the optical disk.

Hereinafter, an optical path of an optical pickup apparatus having a compatible optical system according to the present embodiment will be described.

First, the optical path of the HD DVD / DVD compatible optical system 8 is as follows.

The divergent light in the 405 nm band, which is linearly polarized light (hereinafter abbreviated as "P wave") of the P-polarized light emitted from the blue violet LD 10, passes through the diffraction grating 15 and then polarized in the polarization conversion element 20a. Is converted. That is, the P wave incident on the polarization conversion element 20a is converted into linearly polarized light (hereinafter, abbreviated as "S wave") of the S polarization component. This converted S-wave is reflected by the polarization prism 25a and then by the dichroic filter (DF) 25b having wavelength selectivity. Then, the collimated lens 30a is converted into the parallel light beam. Thereafter, the phase is delayed by 90 ° in the half wave plate 80 and converted into P waves again, and is separated into two paths in the DF mirror 40b. That is, the light transmitted through the DF mirror 40b is incident on the monitor light receiving element 95b via the detection lens 90b. On the other hand, the light reflected by the DF mirror 40b is 45 degrees out of phase with the quarter wave plate 45b and becomes circularly polarized light, and is condensed by the HD DVD / DVD compatible objective lens unit 85 to record the signal of the optical disk. Converges into layers. Further, the light reflected from the optical disc is incident again to the HD DVD / DVD compatible objective lens unit 85, and after passing through the objective lens unit 85, the S wave is generated at the quarter wave plate 45b. And converted into P waves at the 1/2 wave plate 80. After being reflected by the DF 25b, the light is transmitted through the polarizing prism 25a and received by the light receiving element 96 via the detection lens 90c.

Next, the optical path of the DVD optical system will be described.

The 650-nm divergent light emitted from the DVD hologram unit 70 is reflected by the mirror 75 and is incident on the DF 25b having wavelength selectivity. The P wave passing through the DF 25b is incident on the optical disc through the same optical path as that of the HD DVD.

The light reflected from the optical disc proceeds in the reverse order of the same optical path as that directed to the optical disc, and is received by the DVD hologram unit 70. Here, the polarization state of the DVD optical system may be any one because the difference in performance between linearly polarized light and circularly polarized light is small.

Next, in the BD / CD compatible optical system 4, the optical path of the BD optical system will be described.

The divergent light of about 405 nm band which is P wave irradiated from the blue violet LD 10 is transmitted by the polarization conversion element 20a without polarization conversion. Then, the transmitted light passes through the polarizing prism 25a and is then focused at the collimated lens 30a at the parallel luminous flux. Then, after passing through the second DF 27, it is separated into two paths in the DF mirror 40a. That is, the light transmitted through the DF mirror 40a is incident to the monitor light receiving element 95a via the detection lens 90a. On the other hand, the light reflected by the DF mirror 40a is circularly polarized due to a 45 degree phase delay at the quarter wave plate 45a, and is converged by the BD objective lens unit 55 to converge to the signal recording layer of the optical disk. do. The light reflected from the optical disk is sequentially returned to the S-wave by the quarter wave plate 45a, and is reflected by the polarization prism 25a and received by the light receiving element 96 through the detection lens 90c. .

On the other hand, the optical path of the CD optical system is as follows.

About 780 nm of divergent light emitted from the hologram unit 60 for CD is focused through the collimating lens 30c. This focused light is reflected by the second DF 27 and converges to the signal recording layer of the optical disc in the same optical path as that of the light irradiated from the BD optical system. The light reflected from the optical disc is returned to the incident light path and received by the CD hologram unit 60. Here, the polarization state of the CD optical system may be any one because the difference in performance between linearly polarized light and circularly polarized light is small.

As described above, according to the embodiment of the present invention, each optical element corresponds to two wavelengths, for example, to improve the light utilization efficiency of the hologram and to reduce the thickness of the DF mirror. Therefore, the focus error signal generated when playing the CD can be suppressed. In addition, low output LD can be used in DVD playback or CD playback, and furthermore, distortion of the DF mirror can be suppressed.

On the other hand, when an objective lens having a NA larger than 0.65 is used, the influence of the polarization state of the light on the spot diameter cannot be ignored. In the specific embodiment illustrated in FIG. 1, linearly polarized light is converted into circularly polarized light using quarter wave plates 45a and 45b. However, when linearly polarized light is incident on the objective lens, the spot shape is ellipsized. The phenomenon that the spot intensity is also lowered appears.

On the other hand, in the conventional optical pickup device for CD or DVD, the above-mentioned phenomenon was not a problem because the NA had an objective lens of 0.65 or less. On the other hand, as the number of objective lenses is increased due to the higher density of the recording medium, such a phenomenon becomes remarkable as the NA of the objective lens becomes larger than 0.65. In other words, when the spot diameter is ellipsized or the intensity is reduced, the modulation degree or the intensity of each reproduction signal becomes small.

For example, FIG. 2 is a schematic diagram showing a polarization state of light incident on an objective lens, and FIG. 2A is a schematic diagram focused on a low NA, and FIG. 2B is a schematic diagram focused on a high NA.

Here, the optical axis direction is the z axis, the planes of the objective lenses are the x axis and the y axis, and the light incident on the objective lens vibrates in the x direction. This vibration direction is represented by a vector and a 'vector (a = a') in FIG. 2A, and is shown by a t vector and t 'vector (t = t') in FIG. 2B.

The vector of the light beam passing through the objective lens and converging light becomes a vector and a 'vector in FIG. 2 (a), respectively. This ｂ vector is represented by the sum of the d vector (x direction component) and the e vector (z direction component) (b = d + e), and the c vector is represented by the f vector (x direction component) and the g vector (z direction component). Expressed as sum (c = f + g). In FIG. 2B, the t vector and the t 'vector become h and i vectors, respectively. The h vector is represented by the sum of the j vector (x direction component) and the k vector (z direction component) (h = j + k), and the i vector is represented by the l vector (x direction component) and the m vector (z direction component). It is represented by the sum (i = l + m).

3 is a schematic diagram showing spots in a direction orthogonal to the vibration direction in the polarization state of FIG. 2, and FIG. 3A is a schematic diagram focused on a low NA, and FIG. 3B is a schematic diagram focused on a high NA.

Here, the optical axis direction is the z axis, and the plane of the objective lens OL is the x axis and the y axis, and vibrates in the y direction. That is, as shown in Fig. 2, when vibrating in the x direction, the y and g vectors, and the k and m vectors, which are the z-direction components irrespective of NA, are opposite directions and are the same size, respectively. At the time of spot formation, this component direction cancels out. However, when NA is large, the z-direction component is large, so that the component to be canceled is large, and the influence on the spot diameter becomes large.

On the other hand, as shown in Fig. 3, the polarized light oscillating in the y direction is not affected even if it passes through the objective lens. Therefore, in the case of condensing linearly polarized light, if the vibration direction and the direction component are the same, the light weakens each other and the intensity of the light decreases. However, the light weakening component does not occur in the direction orthogonal to the vibration direction. As a result, the phenomenon that the spot diameter is elliptical occurs, and as the NA is increased, the ellipsation becomes remarkable.

FIG. 4 is a graph showing the relationship between the half-width of the spot diameter in the polarization state and the NA of the objective lens in the case where the Far Field Pattern (hereinafter referred to as FFP) of LD is not taken into consideration. Here, the horizontal axis represents the NA of the objective lens, and the vertical axis represents the spot diameter half width (占 퐉), respectively. Moreover, FFP of LD is set to (theta) 20 degrees (parallel to the layer direction of LD) and (theta) 20 degrees (perpendicular to the layer direction of LD), and linearly polarized light vibrates only in the x direction. At this time, light having a wavelength of about 405 nm is incident on the objective lens with NA of 0.85, the intensity distribution is formed by an isotropic Gaussian distribution, and the aperture diameter of the objective lens is about 3.0 mm.

5 is a graph showing the relationship between the spot diameter half-width ratio in the polarization state of FIG. 4 and the NA of the objective lens. Here, the spot diameter half value width ratio is a value obtained by dividing the spot diameter half value width of the x-direction component by the y-direction component in the polarization state oscillated in the same direction.

As shown in FIG. 4, it can be seen that the spot diameter half width becomes smaller with increasing NA of the objective lens. Further, since the direction components orthogonal to the vibration direction of the linearly polarized light strengthen each other, the spot diameter half width is smaller than the curve of the circularly polarized light, and larger than the circularly polarized light because the component weakens each other in the direction components parallel to the vibration direction of the linearly polarized light. Therefore, it can be seen that the difference between the orthogonal component and the parallel component in the vibration direction of the linearly polarized light increases with increasing NA.

In addition, as shown in FIG. 5, since the direction component parallel to the vibration direction is weakened as the NA of the objective lens increases, the spot diameter half-width ratio can be confirmed to increase and ellipse. For example, the spot diameter half value width ratio of linearly polarized light vibrated in the x direction when NA is 0.35 is 1.03, and the spot diameter half value width ratio is 1.28 when NA is 0.85. Here, this long axis direction coincides with the vibration direction of linearly polarized light. On the other hand, when the polarization state is circularly polarized light, it can be confirmed that the spot diameter half-width width ratio is equiaxed with 1.0, for example.

Fig. 6 is a graph showing the relationship between the half-width of the spot diameter in the polarization state and the NA of the objective lens in the case of considering the FFP. 7 is a graph showing the relationship between the spot diameter half-width ratio in the polarization state of FIG. 6 and the NA of the objective lens.

Here, the FFP of LD is considered as θ 8 .5 ° and θ 20 °, and linearly polarized light vibrates in the x direction and the y direction. At this time, the intensity distribution incident on the objective lens forms an anisotropic Gaussian distribution.

As shown in FIG. 6, as the NA increases, the spot diameter half width becomes smaller as shown in FIG. 4. In addition, even when considering FFP, the direction components orthogonal to the vibration direction of linearly polarized light are strengthened. Therefore, the spot diameter half width is smaller than the curve of circular polarization. In addition, in the direction components parallel to the oscillation direction of linearly polarized light, the spot components are half-width wider than the circularly polarized light.

7, the same tendency as in FIG. 5 is seen. For example, when the NA of an objective lens is 0.35, the half width ratio of the spot diameter oscillated in the x direction is 1.075, the y direction is 1.020, and when NA is 0.85, the half width ratio of the spot diameter oscillated in the x direction is 1.310, the y direction is 0.811. Here, this long axis direction coincides with the vibration direction of linearly polarized light.

In this way, when the linearly polarized light is incident on the optical disk, the spot shape is ellipsized according to the increase of NA, and the optical frequency characteristics in the circumferential direction and the radial direction are different at the time of vibration reproduction, and problems such as cross talk and signal degradation occur.

On the other hand, if the polarization state is circularly polarized light, as shown in Fig. 7, the spot diameter half width ratio can be made to be equal to 1.05, for example, regardless of the increase of NA.

In addition, when NA increases from 0.35 to 0.85, the spot diameter shrinkage ratio is about 50% when the direction of vibration of the linearly polarized light and the direction component are the same, and about 40% in the direction perpendicular to the direction of vibration. On the other hand, in circularly polarized light, it can contract uniformly at 44%.

As described above, in the BD / CD compatible optical system 4 of the optical pickup apparatus according to the present embodiment, cross talk, signal degradation, and the like can be suppressed by injecting circular polarized light into the objective lens having NA of 0.85. . Further, when circularly polarized light is used for the HD DVD / DVD compatible optical system 8, better signal characteristics can be obtained. Therefore, it becomes possible to design an optical pickup apparatus having compatible optics in consideration of light utilization efficiency.

6, it is generally known that the spot diameter of the optical disc becomes elliptical under the influence of the FFP of LD. On the other hand, when the linearly polarized light is incident on the objective lens as described above, the spot becomes elliptical. Therefore, the spot diameter on the optical disk can be made circular by setting the direction of linearly polarized light in the direction orthogonal to the layer direction of LD. This may form a 1/2 wave plate in the cap layer of LD, for example. This spot shape can be visually confirmed.

However, since the influence of FFP on the spot shape varies depending on the size of the LD FFP and the focal length of the collimated lens, the spot shape can be adjusted to a circular shape by making the linearly polarized light somewhat elliptical. Further, for example, the same effect can be obtained even if the polarization state of LD having a center wavelength of 405 nm band is linearly polarized in a direction orthogonal to the layer direction of the laser.

In an optical pickup apparatus having a compatible optical system composed of an HD DVD / DVD compatible optical system 8 and a BD / CD compatible optical system 4 according to the present invention configured as described above, an optical element corresponds to two wavelengths, for example, a component An optical pickup apparatus having a compatible optical system that is easy to design and manufacture and has high hologram efficiency can be obtained.

The above embodiments are merely exemplary, and those skilled in the art may have various modifications and equivalent other embodiments.

For example, various design changes made by those skilled in the art regarding the configuration of the apparatus constituting the optical information recording and reproducing apparatus, the size, shape, arrangement, and the like of components such as optical components, light receiving elements, and the like may be used without departing from the spirit of the present invention. It is included in the invention.

Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the invention described in the claims below.

Claims (8)

A first optical system for reproducing a first optical disk having a cover layer thickness of 0.1 mm and a second optical disk having a cover layer thickness of 1.2 mm; A second optical system for reproducing each of the third and fourth optical disks having a cover layer thickness of 0.6 mm; A first semiconductor laser having a wavelength in the bluish violet band by irradiating a beam to the first optical disk via the first optical system or to the third optical disk via the second optical system; A second semiconductor laser for CD for irradiating a beam to said second optical disk via said first optical system; And a third semiconductor laser for DVD for irradiating a beam to the fourth optical disk via the second optical system. The method of claim 1, The first optical system includes a first objective lens having a numerical aperture of 0.85. And the second optical system comprises a second objective lens having a numerical aperture of 0.65. The method of claim 2, And a circular polarization of light incident on the first objective lens. The method of claim 2, And a polarization state of the laser light from the first semiconductor laser incident on the first and second objective lenses is linearly polarized light in a direction orthogonal to the layer direction of the first semiconductor laser. The method of claim 2, The polarization state of the laser light from the first semiconductor laser incident on the first and second objective lenses is an elliptical polarization having a long axis in a direction orthogonal to the layer direction of the first semiconductor laser, The ellipticity is set so that the spot shape in the optical disk of the laser light from the said 1st semiconductor laser will be circular. The method according to any one of claims 1 to 5, And the first semiconductor laser emits laser light that is linearly polarized in a direction orthogonal to the stacking direction thereof. An optical pickup apparatus comprising a plurality of optical systems each having an objective lens having a numerical aperture different from each other so as to reproduce or reproduce and record an optical disc of a plurality of different standards. The optical system, An optical pickup apparatus, wherein light of circular polarization is incident on an objective lens having the largest numerical aperture among the objective lenses of the optical system. The method of claim 7, wherein And said optical disc of said plurality of different standards comprises an optical disc standard using bluish violet light.

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