KR100607937B1 - Apparatus for compensating tilt of optical disk and optical pickup apparatus adopting thereof - Google Patents

Abstract

To drive the second objective lens in a direction perpendicular to the optical axis to correct the inclination

Disclosed are an optical disk tilt correction device and an optical pickup device employing the same.

The disclosed optical disc tilt correction device includes a tilt detection sensor detecting a tilt of an optical disc; It is disposed between the first objective lens and the optical disk for focusing the incident light to be formed on the optical disk, and focuses again the light focused by the first objective lens and perpendicular to the optical axis according to the inclination of the optical disk detected by the tilt detection sensor A second objective lens driven in one direction and generating inverse coma aberration with respect to coma aberration generated by the inclination of the optical disk; And second objective lens driving means for driving the second objective lens, wherein the inclination of the optical disk can be corrected.

In addition, the optical pickup device and a light source; A first objective lens for focusing the light irradiated from the light source on the optical disk primarily; Optical path converting means disposed on an optical path between the light source and the first objective lens to convert a traveling path of the incident light; A photodetector for reflecting the optical disk and receiving the incident light via the optical path changing means; And an optical disk tilt correction device.

Description

Apparatus for compensating tilt of optical disk and optical pickup apparatus adopting

1 is a view showing an optical disk tilt correction device of a conventional optical pickup.

2 is a view for explaining the operation of the optical disk tilt correction device of FIG.

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

4 is a view showing an optical arrangement of the first and second objective lenses according to an embodiment of the present invention.

5 is a view showing optical arrangement of first and second objective lenses according to another embodiment of the present invention;

6 is a schematic perspective view showing an embodiment of a second objective lens driving means according to the present invention;

7 is a view showing the optical arrangement and the optical path when there is no optical disk tilt of the optical disk tilt correction device according to the present invention.

Fig. 8 is a diagram showing an optical path when there is an optical disc tilt when no optical disc tilt correction is performed.

9 is a view showing the optical arrangement and the optical path when there is an optical disk tilt of the optical disk tilt correction device according to the present invention.

10 is a graph showing the decenter amount of the second objective lens required for tilt correction according to the tilt of the optical disk;

를 보인 그래프.Fig. 11 shows the optical disc tilt angles for the case where the optical disc tilt is corrected and when the optical disk tilt is not corrected.

Shows the graph.

<Explanation of symbols for the main parts of the drawings>

1 ... optical disk 10 ... incline detection sensor 20 ... light source

31 ... collimating lens 33 ... focusing lens 40 ... optical path changing means

41.Polarization beam splitter 43 ... 1/4 wavelength plate 51 ... 1st objective lens

53 Second objective lens 60 Second objective lens driving means 61 Lens holder

62 ... 1st slider 63 ... 1st driver 64 ... 2nd slider

65.2nd driver 71 ... photodetector

The present invention relates to an optical disk tilt correction device capable of correcting coma aberration caused by tilting of an optical disk, and an optical pickup device employing the optical disk tilting device. The present invention relates to an optical disk tilt correction device capable of correcting the error and an optical pickup device employing the same.

In general, the optical pickup apparatus is capable of recording information on the optical disk or playing the recorded information. As the optical disk becomes dense, the light irradiated from the light source is shortened, and the numerical aperture NA of the light increases to a high number of apertures. Therefore, in the case where information is to be recorded / reproduced on the optical disc through this optical pickup apparatus, when the optical disc is arranged inclined, that is, when the information surface of the optical disc is arranged inclined instead of being located in the direction perpendicular to the optical axis. There is a problem that coma aberration occurs due to the inclination.

Here, since the coma aberration W ₃₁ has a proportional relationship as shown in Equation 1, the coma aberration due to the optical disk inclination increases rapidly in the optical pickup with a high numerical aperture compared to the relatively low numerical aperture for the same optical disk inclination.

Referring to FIG. 1, a conventional optical disk tilt correction device for correcting coma aberration as described above is provided on an optical path between an optical disk 1 and an objective lens 3 that focuses incident light and forms an optical disk 1. And flat glass 5 arranged inclinedly. Therefore, when the optical disc 1 is inclined in one direction, the flat glass 5 is inclined in a direction opposite to the inclination direction of the optical disc 1 to correct coma aberration.

In particular, when the thickness of the flat glass 5 is the same as the substrate thickness of the optical disk 1, as shown in FIG. 2, when the optical disk 1 is inclined by an angle θ in one direction, the flat glass ( 5) is arranged inclined by the angle θ in the opposite direction.

As described above, in the case where the flat glass is provided between the one objective lens and the optical disc to correct the inclination of the optical disc, the numerical aperture of the optical pickup is determined by the objective lens described above. On the other hand, due to limitations in the die processing and molding technology of the objective lens, one objective lens cannot realize a high numerical aperture of 0.65 or more, and thus it is difficult to construct a high-density recording / reproducing optical pickup requiring a high numerical aperture. There is this. In addition, when a separate objective lens is provided in consideration of the numerical aperture, a separate objective lens and a flat plate lens are provided, respectively.

Accordingly, the present invention has been made in view of the above problems, and includes a second objective lens driven in a direction perpendicular to the optical axis to increase the numerical aperture of the optical pickup and to correct the inclination of the optical disk. An object of the present invention is to provide an optical disk tilt correction device and an optical pickup device employing the same.

In order to achieve the above object, the optical disk tilt correction apparatus according to the present invention, the tilt detection sensor for detecting the tilt of the optical disk; Disposed between the first objective lens and the optical disk for focusing incident light on the optical disk, focusing the light focused by the first objective lens again, and at an inclination of the optical disk detected by the tilt detection sensor; A second objective lens driven in a direction perpendicular to the optical axis to generate inverse coma aberration with respect to coma aberration generated by the inclination of the optical disk; And a second objective lens driving means for driving the second objective lens. The inclination of the optical disc may be corrected.

In addition, the optical pickup device according to the present invention for achieving the above object, the inclination detection sensor for detecting the inclination of the optical disk; A light source for irradiating light to the optical disk; A first objective lens for focusing the light irradiated from the light source onto the optical disk; Disposed between the first objective lens and the optical disk, focusing the light focused by the first objective lens again, and driving in a direction perpendicular to the optical axis according to the inclination of the optical disk detected by the tilt detection sensor; A second objective lens configured to generate inverse coma aberration with respect to coma aberration generated by the inclination of the optical disk; Second objective lens driving means for driving the second objective lens; Optical path converting means disposed on an optical path between the light source and the first objective lens to convert an advancing path of incident light; And a photodetector configured to receive light incident through the optical path changing means after being reflected by the optical disk.

Hereinafter, an optical disk tilt correction apparatus and an optical pickup employing the optical pickup according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Referring to FIG. 3, an optical pickup apparatus according to an exemplary embodiment of the present invention includes a light source 20, an optical path converting means 40 for converting an advancing path of incident light, and light emitted from the light source 20 to the optical disc. A first objective lens 51 focused primarily at (1), a photodetector (71) for receiving light reflected from the optical disc (1) and received through the optical path changing means (40), and the first objective lens (51) And an optical disk tilt correction device for detecting and correcting the tilt of the optical disk 1 while focusing the light focused by the single objective lens 51 again.

The light source 20 generates and irradiates laser light having a predetermined wavelength, and the use wavelength is determined in consideration of the diameter of the light spot formed on the optical disc 1, which is an element that determines the recording density of the optical disc 1. It is disposed on the optical path between the light source 20, the first objective lens 51 and the photodetector 71, the light incident from the light source 20 is directed toward the objective lens 51 and the objective The light incident from the lens 51 side changes the traveling path of the incident light so as to be directed toward the photodetector 71. The optical path converting means 40 includes a polarizing beam splitter 41 for selectively transmitting or reflecting incident light according to polarization, and a quarter wave plate 43 for changing the phase of the incident light, as shown. Can be. In addition, a well-known optical element such as a beam splitter for dividing the incident light by the light quantity ratio and transmitting / reflecting the light path conversion means 40 or a hologram element for converting the incident light through a straight line or diffraction line may be employed.

Here, preferably, a collimating lens 31 is further provided on the optical path between the light source 20 and the optical path converting means 40 to focus the divergent light emitted from the light source 20 to become parallel light. A focusing lens 33 is further provided between the optical path changing means 40 and the photodetector 71.

The optical disk tilt correction apparatus includes a tilt detection sensor 10 for detecting the tilt of the optical disk 1, a second objective lens 53 disposed between the first objective lens and the optical disk, and the second objective lens ( And a second objective lens driving means 60 for driving 53. The second objective lens 53 focuses the light focused by the first objective lens 51 again, and according to the degree of inclination of the optical disc 1 detected by the tilt detection sensor 10. It is driven by the two objective lens driving means 60 in a direction perpendicular to the optical axis to compensate for the coma aberration generated by the coma aberration generated by the inclination of the optical disc 1.

In the optical pickup apparatus configured as described above, the effective numerical aperture of the objective lens is determined by the refractive power of the first objective lens 51 and the second objective lens 53, so that the numerical aperture is determined by one lens. As compared with increasing the ratio, a relatively high numerical aperture can be realized.

An embodiment of the optical data and the optical arrangement of the first objective lens 51 and the second objective lens 53 will now be described in detail.

4, Table 1, and Table 2, optical data and optical arrangement of the first and second objective lenses 51a and 53a according to an embodiment of the present invention are as follows. Here, the first objective lens 51a is composed of biconvex lenses each having an aspherical surface on both sides, and the second objective lens 53a is composed of a flat convex lens whose one surface is spherical.

division Bending Radius [mm] Thickness or thickness [mm] Refractive index First objective lens 51a S ₁ = 2.081564 [Aspherical surface 1] d ₁ = 1.800000 n1 = 1.623893 S ₂ = 13.937485 [Aspherical surface 2] d ₂ = 0.100000 Second objective lens 53a S ₃ = 3.803052 d ₃ = 0.600000 n2 = 1.623893

S ₄ =

 d4 = 0.970124 Optical disc S ₅ =

 d5 = 0.600000 n3 = 1.623343 S ₆ =

In expressing the aspherical surfaces 1 and 2, when the height from the vertex of the aspherical surface is z, the height z of the aspherical surface can be expressed as in Equation (2).

Where h is the height from the optical axis, c is the curvature, K is the conical constant, and A to F are aspherical coefficients.

Table 2 shows the conical constants and aspheric coefficients of the aspherical surface ₁ of the curvature S _{1 and} the aspherical surface ₂ of the S ₂ of the first objective lens 51a.

 Cone Constant (K) Aspheric modulus Aspheric surface 1 -0.765142 A = 0.342804E-02, B = 0.353767E-03, C = -0.156847E-03 D = 0.425110E-04, E = 0.374524E-04, F = -0.348165E-06 Aspheric surface 2  32.559218 A = 0.567216E-02, B = -0.142520E-03, C = -0.595222E-03 D = -0.625598E-04, E = 0.214939E-04, F = -0.432031E-06

As described above, in the case where the first and second objective lenses 51a and 53a are configured, the incident pupil diameter of light incident in parallel through the first objective lens 51a described above is 4.0 mm, and the light source 20 The wavelength of light irradiated at) is 400 nm. Further, the total focal length is 2.667 mm, the incident side focal length is 3.706 mm, and the optical disc side focal length is 6.096 mm.

5, Table 3, and Table 4, optical data and optical arrangement of the first and second objective lenses 51b and 53b according to another embodiment of the present invention are as follows. Here, the first objective lens 51b is composed of biconvex lenses each having aspherical surfaces on both sides thereof, and the second objective lens 53b is a hologram element having a hologram pattern formed on a surface facing the first objective lens 51b. Configured.

division Bending Radius [mm] Thickness or thickness [mm] Refractive index First objective lens 51b S1 '= 2.070010 [Aspherical surface 1]  d1 '= 1.800000 n1 '= 1.606048 S2 '= -39.706457 [Aspherical surface 2]  d2 '= 0.300000 Second objective lens 53b

[홀로그램]S3 '=

[hologram]  d3 '= 0.600000 n2 '= 1.530826 S4 '=

 d4 '= 0.789337 Optical disc S5 =

 d5 = 0.600000 n3 = 1.623343 S6 =

When the height from the vertex of the aspherical surface is z ', it can be expressed as Equation 3.

Where h is the height from the optical axis, c is the curvature, K is the conical constant, and A to J are aspherical coefficients.

In addition, when the phase of the hologram element φ, it can be expressed as shown in equation (4).

는 홀로그램소자의 해석파장(construction wavelength)이고, m과 n은 정수이며, N은 65이하의 정수로 수학식 5의 관계를 가지며, x와 y 각각은 면의 정점으로부터의 광축에 수직한 면의 직각좌표이다.here,

Is the construction wavelength of the hologram element, m and n are integers, N is an integer less than or equal to 65, and has a relationship of Equation 5, where x and y are each perpendicular to the optical axis from the vertex of the plane. Rectangular coordinates.

Table 4 shows the conical constants and aspheric coefficients of the aspherical surface 1 of the curvature S1 'of the first objective lens and the aspherical surface 2 of the S2'.

 Cone Constant (K) Aspheric coefficient, hologram constant Aspheric surface 1  -0.884048  A = 0.567870E-02, B = 0.185621E-03, C = 0.163511E-03 D = -0.904530E-04, E = 0.675133E-04, F = -0.353761E-04 G = 0.946803E-05, H = -0.121402E-05, J = 0.423455E-07 Aspheric surface 2  -142.582396  A = 0.111420E-01, B = -0.140872E-02, C = 0.114279E-03 D = -0.486409E-04, E = -0.804363E-05, F = -0.759926E-06 G = -0.241673E- 07, H = 0.222155E-07, J = 0.102113E-07 hologram  C3 = 6.1538E-02, C5 = 6.1538E-02

As described above, when the first and second objective lenses 51a and 53b are configured, the incident pupil diameter of light incident in parallel through the first objective lens 51a is 4.0 mm, and the light source 20 The wavelength of light irradiated at) is 400 nm. Further, the total focal length is 2.67 mm, the incident side focal length is 3.300 mm, and the optical disc side focal length is 8.125 mm.

As described above, by constructing each of the first and second objective lenses 51 and 53, and determining the numerical aperture through these two objective lenses, it is desired within the limits of the mold processing and molding technology of the objective lens. A numerical aperture suitable for an optical pickup apparatus requiring a high numerical aperture can be obtained.

Referring to FIG. 3, the first and second objective lenses 51 and 53 may be actuators in a direction in which an error signal is compensated according to a focus error signal and a track error signal detected by the photodetector 71. It is driven by). Since such a driving method is widely known, its detailed description is omitted. On the other hand, as described above, the second objective lens is driven by the second objective lens driving means in a direction perpendicular to the optical axis to correct wavefront aberration.

The objective lens driving means is installed in the actuator (not shown) to allow the second objective lens 53 to move relative to the first objective lens 51, as shown in FIG. 6. The first and second sliders 62 and 64 slidably installed in the lens holder 61 supporting the first objective lens 51 and the first and second sliders 62 and 64 are respectively driven. It comprises a first and second drivers (63, 65).

The first slider 62 is installed in the lens holder 61 so as to be slidable in the X-axis direction perpendicular to the optical axis, and is slidably driven in the X direction by the first driver 63. The first driver 63 is installed between the lens holder 61 and the first slider 62 and is expanded and contracted according to an input electric signal to drive the first slider 62. It consists of.

The second slider 64 is installed in the first slider 62 so as to be slidable in the Y axis direction perpendicular to the optical axis and the X axis, and is driven in the Y direction by the second driver 64. The second driver 64 is installed between the first slider 62 and the second slider 64 and is expanded and contracted according to an input electric signal to drive the second slider 64. It consists of.

As described above, the operation of the configured optical disk tilt adjusting device will be described with reference to Figs.

When there is no inclination of the optical disc 1, the second objective lens 53 is disposed so that the center thereof is located on the optical axis as shown in FIG. Fig. 8 shows a case in which the inclination correction is not performed despite the inclination of the optical disc. In this case, the inclination of the optical disc 1 causes the optical spot to deviate from the optical axis.

9 shows the optical arrangement of the second objective lens 53 for correcting the inclination when the inclination of the optical disc 1 occurs. In this case, the second objective lens 53 is displaced by a predetermined amount in the direction perpendicular to the optical axis according to the inclination direction and the degree of inclination of the optical disc 1, thereby forming an optical spot on the optical axis. Here, the inclination direction and the degree of inclination of the optical disc 1 are detected by the inclination detection sensor 10. Thus, the decenter amount of the second objective lens 53 required from the value detected by the tilt detection sensor 10 is determined by the tilt of the second objective lens 53 required for tilt correction according to the optical disk tilt as shown in FIG. 10. This can be known using the relation of the decenter amount. For example, when the optical disc 1 is inclined by one degree, the inclination can be corrected by moving the second objective lens 53 by about 27 m in the inclined direction.

를 보인 그래프이다.FIG. 11 is a root mean square root of an optical path difference (OPD) at a wavefront according to the inclination angle of the optical disc 1 for the case where the optical disc inclination is corrected and when the optical disc inclination is not corrected.

This graph shows

값이 크게 증가함을 알 수 있다. 반면, 경사보정시에는 광디스크 경사각도가 증가하여도

값의 증가 기울기가 완만하여 크게 증가하지 않음을 알 수 있다. 예를 들어, 광디스크 경사각도가 1도인 경우를 살펴보면, 경사 미보정시에는

값이 대략 0.4λ로 파면수차가 크게 발생하는 반면, 경사보정시에는

값이 대략 0.03λ로 파면수차가 거의 없음을 알 수 있다.As shown in the figure, the larger the inclination angle of the optical disc 1 is,

It can be seen that the value increases significantly. On the other hand, even if the tilt angle of the optical disc increases

It can be seen that the increasing slope of the value is gentle and does not increase significantly. For example, in the case where the optical disk tilt angle is 1 degree, when the tilt is not corrected

When the value is approximately 0.4λ, the wavefront aberration is large, while the slope correction

The value is approximately 0.03λ, indicating little wavefront aberration.

The optical disk compensator according to the present invention configured as described above and the optical pickup device employing the same have a second objective lens to design the first objective lens to have a numerical aperture within the range that can be manufactured by the current mold processing and molding technology. In addition, the optical pickup device requiring a high number of apertures can be easily implemented by using a second objective lens to compensate for the insufficient numerical aperture. Further, by shifting the second objective lens in a direction perpendicular to the optical axis according to the degree of inclination of the optical disk, coma aberration due to the inclination of the disk can be corrected so that the center of the second objective lens does not deviate in the direction perpendicular to the optical axis. .

Claims (6)

An inclination detection sensor for detecting inclination of the optical disk; Disposed between the first objective lens and the optical disk for focusing incident light on the optical disk, focusing the light focused by the first objective lens again, and at an inclination of the optical disk detected by the tilt detection sensor; A second objective lens driven in a direction perpendicular to the optical axis to generate inverse coma aberration with respect to coma aberration generated by the inclination of the optical disk; And a second objective lens driving means for driving the second objective lens, wherein the inclination of the optical disk can be corrected. The method of claim 1, wherein the second objective lens driving means, A first slider slidably mounted on one axis perpendicular to the optical axis to a lens holder supporting the first objective lens; A first driver installed between the lens holder and the first slider to drive the first slider; A second slider slidably installed on another axis perpendicular to the optical axis and supporting the second objective lens; And a second driver installed between the first slider and the second slider to drive the second slider. The method of claim 2, wherein each of the first and second drivers, And a piezo driver, which expands and contracts according to an input electric signal to drive each of the first and second sliders. An inclination detection sensor for detecting inclination of the optical disk; A light source for irradiating light to the optical disk; A first objective lens for focusing the light irradiated from the light source onto the optical disk; Disposed between the first objective lens and the optical disk, focusing the light focused by the first objective lens again, and driving in a direction perpendicular to the optical axis according to the inclination of the optical disk detected by the tilt detection sensor; A second objective lens configured to generate inverse coma aberration with respect to coma aberration generated by the inclination of the optical disk; Second objective lens driving means for driving the second objective lens; Optical path converting means disposed on an optical path between the light source and the first objective lens to convert an advancing path of incident light; And a light detector for reflecting the light incident through the optical path converting means after being reflected from the optical disk. The method of claim 4, wherein the second objective lens driving means, A first slider slidably mounted to a lens holder supporting the first objective lens; A first driver disposed between the lens holder and the first slider to drive the first slider; A second slider slidably mounted to the first slider and supporting the second objective lens; And a second driver installed between the first slider and the second slider to drive the second slider. The method of claim 5, wherein each of the first and second drivers, And a piezo driver, which expands and contracts according to an input electric signal to finely drive each of the first and second sliders.

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