KR0160204B1 - Multi-focusing optical pickup - Google Patents

Abstract

The present invention relates to an optical pickup apparatus capable of multiple focusing, comprising a laser diode scanning a linearly polarized laser beam and a laser beam scanned from the laser diode in order to solve the problem that a conventional CD and a high-density disk cannot be read simultaneously. A diffraction grating made of a main beam and a sub beam, a collimating lens making a beam through the diffraction grating into parallel beams, and a parallel beam through the collimating lens are separated into beams for simultaneously reading first and second discs having different thicknesses. A first beam splitting means, an objective lens for focusing the beam separated by the first beam splitting means onto the first and second disks having different thicknesses, and a beam reflected from the first and second disks having different thicknesses Second beam separation means for separating the light beams, and light detection for detecting the beam separated by the second beam separation means and outputting the signal as an electrical signal for determining the disc type By providing the optical pickup device configured as a stage can be applied, etc. CD-ROM, MD, MODD.

Description

Optical pickup device capable of multiple focusing

1 is a graph showing peak intensities of discs of different thickness when the numerical aperture is constant.

2 is a schematic configuration diagram of a conventional optical pickup apparatus.

3 (a) and 3 (b) are cross-sectional views of existing CDs and digital video discs (DVDs).

4 is a relationship between tilt and beam intensity due to disk thickness.

5 is a relationship diagram between tilt and beam intensity caused by the objective lens numerical aperture NA.

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

FIG. 7 is a detailed configuration diagram of the first beam separating means in FIG.

(A) and (b) of FIG. 8 are state diagrams in which a disk focuses on a numerical aperture change caused by an incident beam size.

9 is a light detecting means and its peripheral configuration in FIG.

10 is an operation flowchart for selecting the light detecting means.

11 is another embodiment of the present invention.

* Explanation of symbols for main parts of the drawings

11 laser diode 12 diffraction grating

13: collimating lens 14: first plate

20,30,50: first to third beam separation means

21, 31, 33, 51: first to fourth polarizing beam splitter

22,23: 2nd, 3rd plate 24, 25: 1st, 2nd reflector

32: sensor lens 35: objective lens

36,37: first and second disks 40: light detecting means

41,42: first and second photodetectors 43,44: first and second comparators

45: integrating circuit 52: total reflection part

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pick-up device, and more particularly, to an optical pickup device capable of multiple focusing by focusing on discs having different thicknesses.

Conventional optical pickups can only read optical discs with a constant thickness (conventional CD thickness of 1.2mm), and for high density, the numerical aperture of the objective lens (NA) is compensated for the disc tilt with a disc thickness of 0.6mm. The optical pickup with a value of 0.6 was unable to read the existing disk thickness because of the spherical aberration due to the thickness on the disk.

That is, it is equal to spherical aberration ∝ d (NA) ⁴ (d: disk thickness, NA: objective lens numerical aperture).

Accordingly, when the numerical aperture (NA = 0.6) is constant, the peak intensities of the disk thicknesses d = 1.2 mm and 0.6 mm are 0.6 mm thicker than the 1.2 mm thick discs as shown in FIG.

Therefore, when the numerical aperture value is increased (NA = 0.6) for the high density and the optical pickup is made with the disk thickness of 0.6 mm, there is a problem that it is impossible to read the thickness of the existing CD 1.2 mm.

As shown in FIG. 2, the conventional optical pickup apparatus has a laser diode (1) for scanning a linear P-polarized laser 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 4 making the beam through the diffraction grating 2 into parallel light, and the collimating lens 4 Objective lens 5 for condensing parallel light through the optical disk 6, the beam reflected by the presence or absence of information recorded on the optical disk 6, and incident through the diffraction grating 2 A beam splitting prism 3 for transmitting or reflecting a beam at a predetermined ratio, a sensor lens 7 for sensing beams reflected through the beam splitting freeze 3, and a signal of beams through the sensor lens 7 It consists of a photodetector 8 which detects a.

In the prior art operation by the above configuration, a linear P-polarized beam (E vector plane of the figure) is scanned at a radiation angle in the laser diode 1 to be made into three beams through the diffraction grating 2, The three beams are parallel beams by the collimating lens 4 and pass through the objective lens 5 to focus on the optical disk 6.

The focal point formed on the optical disc 6 is reflected after reading the information of the optical disc 6 and separated by the beam splitting prism 3, and the three split beams are separated by a six-segment photodetector through the sensor lens 7. 8).

Of the three beams, the sub-beams (+1, -1st order beams) are tracking servos for controlling the misalignment of the beam centers on the disc, and the main beams (0th order beams) are focused on servos for focusing the beam centers. Read high frequency signal for reading information.

For reference, the specification of the conventional CD of the optical disc is 120mm in diameter, 1.2mm in thickness, track pitch (1.6 pitch), digital video disc (DVD) specifications are 120mm in diameter, thickness 0.6mm (double-sided recording), track pitch 0.725 μm, and each cross-sectional view is as shown in (a) and (b) of FIG. 3.

Accordingly, an object of the present invention is to provide an optical pickup apparatus capable of multiple focusing for achieving multiple focuses on discs having different thicknesses by adjusting the numerical aperture by the size of the incident beam in order to solve the above problems.

Technical means of the present invention for achieving the above object is a laser diode for scanning a linearly polarized laser beam, a diffraction grating for making the laser beam scanned from the laser diode into a main beam and a sub-beam, and through the diffraction grating A collimating lens for making the beam into a parallel beam, a first beam separating means for separating the parallel beam through the collimating lens into a beam for simultaneously reading discs having different thicknesses, and a beam separated through the first beam separating means. An objective lens for condensing the disks having different thicknesses, second beam separating means for separating beams reflected from the disks having different thicknesses, and a beam separated by the second beam separating means for detecting a disc type. It consists of a light detection means for outputting an electrical signal for the determination of.

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

First, as an example of the present invention having multiple focuses, an optical pickup apparatus having a dual focus is used to read a high density disk (0.6 mm thick) and an existing CD (thickness 1.2 mm) at the same time. For the mm, the numerical aperture NA is set to 0.6 to eliminate the instability caused by the inclination (see FIG. 4). In addition, the instability due to the inclination of the disc at 1.2 mm thickness is determined by the numerical aperture NA of the objective lens 0.3. This eliminates instability caused by (see Figure 5).

That is, the present invention reads the disc 0.6mm at NA = 0.6 in the high-density disc, and reads the disc 1.2mm at NA = 0.3 to make the disc insensitive to the NA value and the disc thickness due to the disc tilt.

Accordingly, the configuration of the present invention, as shown in Figure 6, the laser diode 11 for scanning a linearly polarized laser beam, and the laser beam scanned from the laser diode 11 as a main beam and a sub beam First and second discs having different thicknesses from the diffraction grating 12 to be made, the collimating lens 13 to make the beam through the diffraction grating 12 into parallel beams, and the parallel beam through the collimating lens 13 to each other. The first beam splitting means 20 for separating the beams 36 and 37 into beams for reading at the same time, and the first and second discs having different thicknesses from the beams separated through the first beam splitting means 20 ( An objective lens 35 for condensing on 36 and 37, second beam separation means 30 for detecting and separating beams reflected from the first and second disks 36 and 37 having different thicknesses; The beam split by the second beam splitting means 30 is detected to output an electrical signal for determining the disc type. Is composed of the light detecting means 40.

As shown in FIG. 7, the first beam splitter 20 includes a first disc (previous CD) having different thicknesses from P waves and S waves included in the parallel beams through the collimating lens 13. The first polarized beam splitter 21 and the first polarized beam splitter 21 separated by transmission and reflection to read the 36 and the second disk (high density disk) 37 at the same time. S-waves separated by a quarter wavelength second plate 22 and the first polarization beam splitter 21, which polarize P-waves and convert them into a first disc reading beam (S wave; for conventional CDs). The third plate 23 of 1/4 wavelength and the radius of the P wave polarized through the second plate 22 are reduced. Radius of the first reflection portion 24 completely reflected on the first disk 36 and the S-wave polarized through the third plate 23 is reflected by the first reflection portion 24.The second reflector 25 is made larger relative to the second disk 37 so as to be completely reflected.

The first and second beams reflected from the first and second reflectors 24 and 25 and incident through the objective lens 35 (that is, the former denotes an S wave and the latter denotes a P wave) are the first and the second. In order to be simultaneously formed on the discs 36 and 37, as shown in FIGS. 8A and 8B, when the focal length f of the objective lens is constant (for example, 3.4), the following relation NA Aperture of the objective lens 35 in proportion to the radius (a '= 1mm) of the beam reflected through the first reflecting portion 24 by ≒ a (or a': radius of the beam incident on the objective lens) / f The number NA is changed from 0.6 to 0.3 to focus on the first disk 36. At this time, the aberration correction by changing the numerical aperture is corrected by moving the objective lens 35 in the disk direction by △. .

In addition, the numerical aperture of the objective lens 35 becomes 0.6 in proportion to the radius (a = 2.075mm) of the beam reflected through the second reflecting portion 25 to focus on the second disk 37.

That is, the numerical aperture of the objective lens 35 can be adjusted by the fully reflective mirror to read the information of the first and second disks 36 and 37 simultaneously.

Accordingly, the beam reflected after the focus is formed on the first and second disks 36 and 37 is separated by the second beam separating means 30, and the configuration thereof is configured by the first beam separating means 20. A second polarization beam splitter 31 for splitting the beams returned through the P-wave and the reflection (S wave) and a sensor for detecting and radiating beams separated from the second polarization load divider 31. A lens 32 and a third polarization beam splitter 33 for separating the first disk reading beam and the second disk reading beam from the beams detected by the sensor lens 32.

In addition, the configuration of the light detecting means 40 is an information signal of the first disk 36 in the beams separated by the third polarization beam splitter 33, as shown in FIGS. The first disk detector 41 detects a first disk reading beam corresponding to the first disk reading beam and converts the signal into an electrical signal, and the second disk 37 is separated from the beams separated by the third polarization beam splitter 33. And a second photodetector 42 which detects the corresponding second disc reading beam and converts it into an electrical signal.

The first and second photodetectors 41 and 42 configured as described above are divided into six, and the first comparator 43 includes the first region 41a and the second region 41b of the first photodetector 41. ) Compares the detected E signal with the F signal, and outputs the difference signal (that is, the track signal of the first disk 36 (existing disk)), and the second comparator 44 outputs the second photodetector 42. Compares the E signal and the F signal detected in the third area 42a and the fourth area 42b of the " The integrating circuit 45 integrates the difference signals output from the first and second comparators 43 and 44 to output a high signal when the first disk 36 is used, and conversely, the second disk 37. Outputs a low signal.

The four regions 41c and 42c of the first and second photodetectors 41 and 42 are for reading a focusing servo and a high frequency signal.

Meanwhile, in the method of reading an existing CD when the numerical aperture NA of the objective lens 35 is 0.3 and the method of reading a high density disc when the numerical aperture NA is 0.6, the track pitch of the conventional CD is 1.6. And the track pitch of the high density disk is 0.725 탆.

Here, when the wavelength (λ = 635 nm) of the laser diode 1 is used, the size of the beam passing through the objective lens 35 and formed on the disk is as follows.

Spot size of the beam = λ / NA

As above, when NA = 0.3, the beam size is 1.5 µm or more, so that the track of a conventional CD comes out as a large signal, but the density of a high-density disc is reduced by crosstalk (see FIG. 9).

The flow of the operation of selecting the light detecting means 40 using this is shown in FIG. 10, when the unknown disk is inserted in a state where it is not known whether it is an existing CD or a high-density CD. Using the first photodetector 41 reflected from the lens 35, the track pitch is read by the focusing servo on the disk and the magnitude of the signal is determined by the integrating circuit 45.

At this time, when the determined signal is high (the existing CD is entered), the signal is continuously read by the first photodetector 41 while the signal is read. On the contrary, when the signal is low (the high density disk is inserted), the second photodetector 42 is read. ), The disc is selected by the objective lens having a different numerical aperture depending on the disc.

Accordingly, the overall operation of the present invention will be described with reference to FIG.

First, the linearly polarized beam is rotated in the laser diode 11 to be separated into a P wave and an S wave so that the second polarization beam splitter 31 and collimating lens 13 sequentially perform diffraction gratings 12, partial reflection and transmission. Through it, it becomes a parallel beam.

Here, the linearly polarized beam may be separated into P waves and S waves by rotating the first plate 14 without rotating the laser diode 11.

P-waves of the polarized beams separated into P-waves and S-waves are transmitted through the first polarization beam splitter 921 of the first beam separation means 20 to read the first disk 36 and are circular through the second plate 22. Polarized, reflected by the first reflecting portion 24 (e.g., total reflecting mirror) having a smaller diameter than the second reflecting portion 25 (e.g., total reflecting mirror) to be described later, and passing through the second plate 22. It turns into a wave and is incident on the objective lens 35.

The S-wave incident on the objective lens 35 reads information from the first disk 36 and sequentially passes through the first polarizing beam splitter 21, the second plate 22, and the first reflector 24. Is converted into a wave and passes through the first polarization beam splitter 21, and the disk information read above is reflected back to the second collimation beam splitter 31 of the collimation lens 13 and the second beam splitting means 30 to form a sensor lens ( 32) and the third polarization beam splitter 33 are transmitted to the P wave to form the first photodetector 41.

On the other hand, in order to read the second disk 37, which is a high-density disk, the S-wave is reflected by the first polarization beam splitter 21 and is circularly polarized through the third plate 23 so that the second reflector 25 having a large diameter The reflected beam is reflected back to the P wave through the third plate 23 and is incident on the objective lens 35 to read the disc information from the second disc 37, and then to the third plate 23 and the first plate. The polarized beam splitter 21, the collimating lens 13, the second polarization beam splitter 31, the sensor lens 32, and the third polarization beam splitter 33 are polarized by S-waves to the second photodetector 42. Will come in).

Accordingly, in accordance with the information detected by the first and second photodetectors 41 and 42, the tracking servo signal is output as a ± first order beam (subbeam) of the three beams by the diffraction grating 12, and the zero order The beam outputs a focusing servo and a high frequency signal together with the sensor lens 32.

In accordance with the output servo signal and the high frequency signal, it is operated as described above with reference to FIG.

As an embodiment of the present invention different from the above, the configuration and operation will be described as shown in FIG.

First, the configuration is a configuration in which the third beam separation means 50 is provided in place of the first beam separation means 20 in FIG. 6, and the third beam separation means 50 is a high density disk. 37, a boundary surface for transmitting the second disk reading beam P wave for reading information, and reflecting the first disk reading beam S wave for reading information to the first disk 36, which is an existing CD. A radius of the first disk reading beam reflected through the interface and a radius of the second disk reading beam transmitted through the boundary surface of the fourth polarization beam splitter 51 and the fourth polarization beam splitter 51. It is composed of a third reflecting portion 52 attached to the rear surface of the fourth polarization beam splitter 51 to make it relatively smaller and reflect the first disk 36.

With this configuration, the numerical aperture of the objective lens is adjusted by adjusting the radius of the beam incident on the objective lens 35, so that the information of the first and second disks 36 and 37 can be read in the same manner as in the above operation.

At this time, since the size of the radius incident on the first disk 36 is reduced, the aberration should be corrected by adjusting the focal length of the objective lens 35 by Δ.

As described above, the present invention can simultaneously read information on disks having different thicknesses by adjusting the numerical aperture of the objective lens, and by using this, it can be used for optical pickup in optical disks such as CD-ROM, MD, MODD, etc. have.

Claims (5)

A laser diode 11 for scanning a linearly polarized laser beam, a diffraction grating 12 for making the laser beam scanned by the laser diode 11 into a main beam and a sub-beam, and the diffraction grating 12 A first beam for separating the collimating lens 13 and the parallel beam through the collimating lens 13 into beams for simultaneously reading the first and second disks 36 and 37 having different thicknesses. An objective lens 35 for condensing the beam separated by the separating means 20 and the first beam separating means 20 to the first and second disks 36 and 37 having different thicknesses; Second beam splitting means 30 and a plurality of second beam splitting means 30 including a plurality of reflecting means for adjusting the beam aperture of the beam reflected from the first and second disks 36 and 37 which are different from each other. By detecting the beam separated by the light detection means 40 for outputting an electrical signal for the disc type determination Focusing the generated multi-optical pickup device as possible. The method of claim 1, wherein the first beam separation means 20 is used for the P and S waves included in the parallel beam through the collimating lens 13, the first and second disks 36 and 37 having different thicknesses. A second plate for polarizing and converting the P-waves separated by the first polarization beam splitter 21 and the first polarization beam splitter 21 to be read by the first disk reading beam at the same time. 22) and a third plate 23 for converting the S-waves separated by the first polarization beam splitter 21 into a second disc reading beam, and a polarization through the second plate 22. The first reflecting portion 24 reflects the radius of the S-wave polarized through the first reflecting portion 24 and the third plate 23 to completely reflect the first disk 36 by reducing the radius of the P wave. The second reflector 25 is characterized by consisting of a second reflecting portion 25 that is completely larger than the radius reflected by the second reflection on the second disk (37) Cushing The optical pickup device as possible. The second polarization beam of claim 1, wherein the second beam separation means 30 separates the beams returned through the first beam separation means 20 by partial transmission (P wave) and reflection (S wave). A sensor lens 32 for detecting and radiating beams separated by the splitter 31, the second polarization beam splitter 31, and a first disk reading beam from the beams detected through the sensor lens 32; And a third polarizing beam splitter (33) for separating the second disc reading beam. 4. The first disc dock according to claim 1 or 3, wherein the light detecting means (40) corresponds to an information signal of the first disc (36) in beams separated by the third polarization beam splitter (33). For reading the second disk corresponding to the second disk 37 from the beams separated by the first photodetector 41 and the beam split through the third polarization beam splitter 33 to detect the beam for the conversion to an electrical signal. And a second photodetector (42) for detecting a beam and converting the beam into an electrical signal. The method of claim 1, wherein the second disk reading beam for reading information on the second disk (37) instead of the first beam separating means (20) is transmitted, and information is transmitted to the first disk (36). The first disk reading beam for reading is reflected by the fourth polarization beam splitter 51 and the radius of the second disk reading beam transmitted through the fourth polarization beam splitter 51 to the fourth polarization beam splitter ( Third reflecting portion 52 attached to the rear surface of the fourth polarizing beam splitter 51 to reflect the first disk 36 to be smaller than the radius of the first disk reading beam reflected through the 51) Optical focusing apparatus capable of multiple focusing, characterized in that it comprises a third beam separation means (50) consisting of.