KR0144510B1 - Multi-focusing optical pick-up device - Google Patents

Abstract

The present invention relates to an optical pick-up apparatus capable of multiple focusing, which enables data of two discs having different thicknesses to be read using two focus points.

The present invention provides a parallel light processing unit for converting a beam incident from a laser scanning means into parallel light, a first beam separation unit for converting a beam obtained from the parallel light processing unit into the same amount of parallel beams and diverging beams, and a first beam separation unit. An objective lens for condensing on discs having different thicknesses by means of parallel and divergent beams converted by a negative portion, and a second beam separation unit for converting beams incident through the objective lens into the same amount of parallel beams and diverging beams; A photodetector for detecting a beam in the two beam splitter is provided.

Description

Optical pickup with multiple focusing

1 is a block diagram of a conventional optical pickup device.

FIG. 2 is a diagram of a grape diode for outputting the servo signal shown in FIG.

3 is a block diagram showing a data reading method according to FIG.

4 is a diagram of beam intensity distribution by disk thickness in the prior art.

5 is a state diagram showing the inclination of the disk according to the beam scanned from the objective lens.

6 is a beam intensity distribution diagram according to the tilt of the disk.

7 is a block diagram of an optical pickup apparatus capable of multiple focusing of the present invention.

8 is a detailed block diagram of the first beam splitter of FIG.

9 is a configuration diagram of the first plate in FIG.

10 is a configuration diagram of the second and third plates in FIG.

11 is a position view of two focusing on the disk according to the present invention.

12 is a state in which two focus is generated according to FIG.

(A) and (b) of FIG. 13 are beam intensity distribution diagrams according to a disk tilt in accordance with the present invention.

14 is a first embodiment of the present invention.

15 is a block diagram of a state in which FIG. 14 is applied to the present invention.

16 is a second embodiment of the present invention.

Figure 17 (a) and (b) is a third embodiment of the present invention.

* Explanation of symbols for the main parts of the drawings

11: laser scanning means 12: diffraction grating

13: second beam splitter 14: cylindrical lens

15: light detection means 16: collimation lens

20: objective lens 21: first disc

22: second disc 23: parabolic mirror

24: Aspherical convex mirror 25, 31d: Polarizing beam splitter

30: first beam splitter 31: beam splitter

31a-31c: first to third plates 32, 33: first and second reflectors

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup apparatus, and more particularly, to an optical pickup apparatus capable of multiple focusing, which enables data of two disks having different thicknesses to be read using two focus points.

Recently, the compact disk of 12cm diameter is composed of a conventional CD of 1.2mm in thickness and 4 times higher density disk of 0.6mm in thickness, which is four times thinner than the conventional high density disk, so that two disks having different thicknesses at the same time by optical pickup The correct data could not be read due to the occurrence of optical aberration.

The optical pickup device of the prior art, as shown in FIG. 1, tracks a laser diode (1) for scanning a laser beam (Beam), and a tracking servo for the laser beam scanned from the laser diode (1). A diffraction grating 2 made of a main beam and two sub-beams (three beams), a collimating lens 3 making the beam through the diffraction grating 2 into parallel light, and the collimating lens 3 The objective lens 5 for condensing parallel light through the disk 6 onto the disk 6 and the beam reflected by the presence or absence of information recorded on the disk 6 are again paralleled through the objective lens 5. A prism 4 for making light and reflecting the beam, a condenser lens 7 for condensing the beams reflected through the prism 4, and a flared angle of the beams passing through the condenser lens 7; Cylindrical lens 8 for generating astigmation in the main beam for servo, and the cylindrical It consists of a six-segmented photodiode 9 which detects the focusing servo, the tracking servo and the information of the optical signal by the beams incident through the lens 8.

In the above, the configuration and servo type of the six-segmented photodiode 9 for detecting the information of the focusing servo, the tracking servo and the optical signal are shown in FIG. 2, among the beams through the cylindrical lens 8, as shown in FIG. Tracking servo according to the signal comparison difference between the first and second regions 9a and 9b for detecting a tracking error with the signal difference between the two sub-beams and the main beams focused in the first and second regions 9a and 9b. A first comparator 10a for outputting a signal for a second comparator, and a second comparator 10b for summing each signal of the main beams focused on the third region 9c and the sixth region 9f to detect a focus error; And a third comparator 10c that sums the signals of the main beams focused on the fifth region 9e and the sixth region 9f, and through the second comparator 10b and the third comparator 10c. A fourth comparator 10d for outputting a signal for focusing servo according to a comparison difference between the respective signals, and each signal input to the fourth comparator 10d Comparison consists of a fifth comparator (10e) for outputting optical information signals.

According to such a configuration, the wavelength λ of the laser diode 1 should be reduced and the numerical aperture NA of the objective lens 5 should be increased for the high-density disk, because the following equation (1),

It is because

If the numerical aperture (NA) of the objective lens (5) and the disk (6) are increased in the above formula (1), the spherical aberration generated by the objective lens 5 increases by the following formula (2).

{n: disc refractive index, NA: objective numerical aperture, Δd: disc thickness}

As described above, a method of reading data on the disk 6 having a thickness of 1.2 mm of a conventional CD simultaneously with a conventional high density optical pickup having a conventional optical pickup and increasing the numerical aperture NA to read a thickness of 0.6 mm of a high density optical disk. (See FIG. 3) shows a significant difference in the beam intensity distribution due to the change in the disk thickness due to the large numerical aperture NA, as shown in FIG.

As a result, it is impossible to correct spherical aberration due to the change in the disk thickness.

In the prior art, in order to read data on a high-density disk, optical pickup increases the numerical aperture (NA) of the objective lens (5), shortens the wavelength of the laser diode (1), and forms a small beam on the optical disk. I read.

That is, in order to reduce the size of the beam formed on the disk, the high density optical pickup capable of reading data of the high density disk has a small wavelength? Of the laser diode 1 and the numerical aperture () of the objective lens 5. NA) should be increased.

Accordingly, in the optical pickup having the large numerical aperture NA, aberration occurs due to the tilt of the disk, which greatly affects coma and astigmatism, which are main aberrations (see FIG. 5). ).

That is, coma aberration

astigmatism

(d: disk thickness, θ: disk tilt, NA: objective numerical aperture)

Therefore, in order to reduce the influence of the inclination of the disk 6 caused by the objective lens 5 having a large numerical aperture NA, it is necessary to reduce the disk thickness and increase the beam intensity as shown in FIG.

In other words, it shows that the high density compact disk (thickness 0.6mm) is insensitive to the inclination with respect to the numerical aperture NA larger than the conventional compact disk (thickness 1.2mm).

Therefore, the high-density disc needs to be standardized to 0.6 mm, which is thinner than the thickness of 1.2 mm of the conventional compact disc in a way to reduce the influence of the inclination of the disc due to the high density.

Such a high-density disc can be manufactured from 1.2 mm to 0.6 mm in thickness for correction of the inclination due to the numerical aperture (NA). In this case, a disc having a different thickness cannot be read simultaneously with a conventional optical pickup. There was a problem.

Accordingly, an object of the present invention is to provide an optical pickup apparatus capable of multiple focusing to simultaneously read discs having different thicknesses in order to solve the above problem.

Technical means of the present invention for achieving the above object is a device for recording information on a disk having a different thickness, the parallel light processing unit for making a beam incident from the laser scanning means into parallel light, and obtained in the parallel light processing unit A beam splitter for converting the beam into the same amount of parallel beams and diverging beams, and an objective lens for condensing seek on a disk having a different thickness by the parallel beam and divergent beams converted by the beam splitter.

According to another aspect of the present invention, there is provided an apparatus for reproducing a disc having a different thickness, wherein an objective lens for reading and condensing a beam recorded on the disc, and a beam incident through the objective lens are the same. A beam splitter converts the positive parallel beam and the divergent beam, and a photodetector for detecting the beam obtained by the beam splitter.

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

First, the configuration of the present invention, as shown in Figure 7, the laser scanning means 11 for scanning a linearly polarized laser beam, and the laser scanning means 11 to diffract the beam scanned by the laser scanning means 11 to make parallel light The diffraction grating 12 and the collimating lens 16, and the parallel beams through the collimating lens 16, the first disk (high density disk) 21 and the second disk (existing CD) 22 having different thicknesses from each other. The first beam splitter 30 converting the data into a beam having multiple focuses for reading data simultaneously, and the first and second beams having different thicknesses from the beam having multiple focuses converted from the first beam splitter 30 are different from each other. An objective lens 20 for condensing on the discs 21 and 22, a second beam separation unit 13 for converting beams reflected from the first and second discs 21 and 22 having different thicknesses, and Cylindrical lens 14 for condensing the beam reflected by the second beam splitter 13 at a fixed position, and through the cylindrical lens 14 It consists of a light detecting means 15 for detecting data contained in the focused beam and outputting a necessary operation signal.

The operation and effect of the optical pickup apparatus capable of multiple focusing according to the present invention configured as described above will be described with reference to FIGS. 8 to 17 as follows.

First, prior to explaining the present invention, the P-wave to be emitted in the present invention indicates polarization in a direction perpendicular to the X axis and perpendicular to the direction of the laser beam when the direction in which the laser beam protrudes perpendicularly to the ground is the X axis, S-waves show polarization parallel to the X axis.

Accordingly, as shown in the figure, the configuration of the first beam splitter 30, the beam splitter for converting the beam through the collimating lens 16 into a parallel beam (P wave) and diverging beam (S wave) 31 and first and second reflecting portions 32 and 33 reflecting the parallel beam and the diverging beam converted through the beam splitter 31, respectively.

The beam splitter 31 rotates (about 22.5 °) the optical axis 31a 'with a parallel beam through the collimating lens 16 to separate the parallel beam and the diverging beam by a predetermined ratio (50:50). A polarizing beam splitter 31d having a boundary surface 31d 'for dividing a predetermined polarized beam transmitted or reflected, the first plate 31a having a wavelength, and the first plate 31a and the boundary surface 31d'. A quarter-wavelength product for converting the diverging beam reflected through the first beam 21 and the parallel beam reflected from the first disk 21 into the parallel beam and the diverging beam through the first reflecting unit (eg, flat mirror) 32. The second reflecting part (for example, a convex mirror) includes the second plate 31b, the parallel beam transmitted through the first plate 31a, and the interface 31d ', and the diverging beam reflected from the second disk 22. A third plate 31c having a quarter-wavelength is respectively converted into a diverging beam and a parallel beam through the 33.

Prior to the description of the operation of the present invention, the position where two focuses are formed on the first and second disks 21 and 22 will be described. As shown in (a) and (b) of FIG. The numerical aperture (NA = 0.6) of the objective lens 20 is increased by the parallel beam reflected through the first reflecting portion 32, focusing on the first disk 21, which is a high density disk, and the second reflecting portion. The numerical aperture (NA = 0.5) of the objective lens 20 is reduced by the diverging beam reflected through 33, thereby focusing the second disk 22 (the reference numeral 'F' is the second reflection). The virtual focus of the part 33, 'C' is the center point, 'fK' is the distance between the virtual focus and the objective lens 20, 'L' is between the surface of the second reflecting portion 33 and the objective lens 20 Indicates the distance of).

According to this operation, the linearly polarized divergent laser beam in the laser scanning means 11 generates three beams by the diffraction grating 12 and becomes a straight beam by the collimating lens 16, and the parallel beam is a beam. The optical axis 31a 'on the first plate 31a of the separator 31 is rotated to separate the P wave and the S wave at a predetermined ratio, and among the separated beams, the S wave is the boundary surface 31d' of the polarization beam splitter 31d. B) is converted into a circular wave through the second plate 31b, and is reflected by the first reflecting unit 32 to be converted into a P wave while passing through the second plate 31b.

After the change to the P wave, the light is incident on the objective lens 20 as a parallel beam and is focused on the first disk 21.

In addition, the parallel beam generated from the first plate 31a is sequentially converted into the transmission circular wave by the boundary surface 31d 'and the third plate 31c, and is reflected by the second reflector 33 to be diverged. At this time, the diverging beam is converted into a diverging beam through the third plate 31c and reflected through the boundary surface 31d ', and the reflected diverging beam passes through the objective lens 20 to condense on the second disk 22. do.

Contrary to the above operation, the parallel beam reflected from the first disk 21 passes through the boundary surface 31d 'and is reflected by the first reflecting portion 320, and is converted into a diverging beam through the second plate 31b to make the boundary surface. 31d ', the collimating lens 16, the second beam separation unit 13, and the cylindrical lens 14 are sequentially condensed by the light detecting means 15.

On the other hand, the diverging beam reflected from the second disk 22 is reflected by the boundary surface 31d 'and reflected back through the second reflecting portion 33, and is changed into a parallel beam by the third plate 31c, thereby changing the boundary surface 31d. ′), The collimating lens 16, the second beam splitter 13, and the cylindrical lens 14 are sequentially collected by the light detecting means 15.

As described above, the diverging beam and the parallel beam reflected from the first and second disks 21 and 22 having different thicknesses are focused on the light detecting means 15 so that the data of the disk can be simultaneously read and tracking servo and focusing servo can be performed. .

Meanwhile, two focuses generated by parallel beams and divergence based on FIG. 11 are as shown in FIG. 12, and the focus relationship of the lens is shown in Equation 5 below.

According to Equation (5), the spherical value (r value) of the second reflecting portion (for example, the convex mirror) 33 can be obtained.

For example, using an infinity objective lens having a numerical aperture (NA) = 0.6 and f ₁ = 3.4 mm, and a focal length error (△) of 0.6 mm, f ₂ is calculated to be about 22.7 mm, where In the fin objective system, when the numerical aperture NA has about 0.5 and L = 12.7 in FIG. 11, the spherical mirror surface r becomes about 20 mm.

In this way, the numerical aperture (NA = 0.6) of the infinity-based objective lens can reduce the influence of spherical aberration and inclination by the thickness of the first disk 21, which is a high density disk (see FIG. 13 (a)). The second disk 22, which is a conventional disk, has a spherical aberration and inclination generated at a thickness of 1.2 mm by the numerical aperture (NA = 0.5) of the finite objective lens. This can be corrected by decreasing the value of NA (see FIG. 13A).

In addition, FIG. 13 (b) shows that when the numerical aperture (NA) = 0.5, the existing disk thickness of 1.2 mm is insensitive to the angle when the NA is 0.5.

That is, when the numerical aperture NA made by parallel light is 0.6 and the numerical aperture by adjusting the divergent beam is 0.5, as shown in FIG. 13, the first density is high when the numerical aperture NA is 0.6. The disc 21 is insensitive to angle than the thickness of the second disc 22 (1.2 mm).

As a first embodiment according to the present invention, by using a parabolic mirror 23, a parallel beam incident through the collimating lens 16 is formed as shown in FIG. 14 focusing on one point.

In accordance with the principle of the parabolic mirror 23, the first beam splitter 30 and the second reflector (for example, a convex mirror) 33 are configured as shown in FIG. 15, which includes incident parallel light. It rotates 45 degrees by the water mirror 23 to simultaneously focus the first and second disks 21 and 22 with the beam by the parabolic mirror 23 and the parallel beam.

In addition, as a second embodiment of the present invention, the aspherical convex mirror 24 is formed as shown in FIG. 16 in place of the first beam separation part 30 and the second reflection part 33 to have various thicknesses. Optical pickup with multiple focus on different disks, which causes the linearly polarized beam to be scanned by the laser scanning means 11 to be 45 degrees, and the beam which enters 45 degrees through the polarizing beam splitter 25 (linear beam) ) Is separated into P wave and S wave (50:50), P wave reflects and enters objective lens 20 with parallel light, S wave passes through and enters objective lens 20 through aspherical convex mirror surface It can be configured to focus.

As in the above embodiment, the mirror surface may be configured differently to change the position where the focus is formed.

Further, in the third embodiment of the present invention, as shown in FIG. 17A, the beam through the objective lens 20 is a conventional disk by increasing the size of the reflecting surface 33a of the second reflecting portion 33. The objective lens is focused on the second disk 22 (not shown), and the size of the reflecting surface 33b of the second reflecting portion 33 is made relatively small as described above as shown in FIG. 17 (b). The beam through 20 is focused on a first disk 21 (not shown) which is a high density disk.

In other words, when a becomes small in the following relation NA = a (beam radius) / f (focal distance between the objective lens and the disk), NA becomes small.

Therefore, multiple focusing is possible by adjusting the size of the reflecting surface of the second reflector 33.

As described above, the present invention can read data by simultaneously performing aberration correction on a high-density disk thickness of 0.6 mm and a conventional compact disk thickness of 1.2 mm, and using a high-density optical disk and a conventional compact disk in parallel. , DVD (Digital Video Disc), CD-R, MD, MODD, etc., have the effect of recording and playing back data on discs of different thicknesses with multiple focuses.

Claims (9)

An apparatus for recording information on disks having different thicknesses, the apparatus comprising: a parallel light processing unit for converting a beam incident from a laser scanning means into parallel light, and a beam obtained from the parallel light processing unit for converting the same amount of parallel beams and diverging beams; And a first lens splitter, and an objective lens for focusing the disks having different thicknesses by the parallel beam and the divergent beam converted by the first beam splitter. The method of claim 1, wherein the first beam splitter comprises: a beam splitter 31 for converting the beam through the collimating lens 16 into a parallel beam and a diverging beam; and the parallel beam converted through the beam splitter 31; An optical pickup apparatus capable of multiple focusing, comprising: first and second reflecting portions (32, 33) for reflecting diverging beams, respectively. 3. The beam splitter (31) according to claim 2, wherein the beam splitter (31) rotates the optical axis with the parallel beam through the collimating lens (16) to separate the parallel beam and the diverging beam at a predetermined ratio, and is transmitted or reflected. A polarizing beam splitter 31d having an interface for dividing the predetermined constant polarization beam, a diverging beam reflected through the first plate 31a and the interface, and a parallel beam reflected from the high-density disk 21; A second plate 31b which is converted into a parallel beam and a diverging beam through a first reflecting portion 32, a parallel beam transmitted through the first plate 31a and an interface, and a diverging beam reflected from the disk 22; The optical pickup device capable of multiple focusing, characterized in that consisting of a third plate (31c) for converting each of the outgoing beam and the parallel beam through the second reflector (33). 3. The optical pickup apparatus of claim 2, wherein the first reflector (32) comprises a flat mirror. The optical pickup apparatus of claim 2, wherein the second reflector (33) comprises a convex mirror. The optical pickup apparatus of claim 1, wherein the first beam splitter comprises a parabolic mirror. The optical pickup apparatus of claim 1, wherein the first beam splitter comprises an aspherical convex mirror. 3. The optical pickup apparatus of claim 2, wherein the second reflector (33) makes multiple focuses by adjusting the size of the reflecting surface. An apparatus for reproducing a disc having a different thickness, the apparatus comprising: an objective lens for reading and condensing a beam recorded on the disc, and a second beam for converting a beam incident through the objective lens into the same amount of parallel beam and diverging beam And a photo detector for detecting a beam in the second beam splitter.