KR100754520B1 - Pick-up apparatus for multi-layer type disc - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup apparatus for a multilayer optical recording medium, comprising: a laser generator for generating a laser light, and a laser generator arranged on a path of the laser light and controlling the concentration of the laser light to project the optical recording medium having at least two layers. A plurality of lenses, a HOE for dividing the laser light reflected by the optical recording medium into a plurality of spots, a photodetector for detecting the light intensity between the center region and the external region of the laser light divided by the HOE, and at least a laser light incident on the optical recording medium And a controller for controlling the operation of the spherical aberration corrector by calculating the spherical aberration between the central region and the external region of the laser light according to a detection result of the photodetector. As a result, the spherical aberration caused by the change of the optical path in the dual-layer or multilayer optical recording medium can be eliminated, so that the reproduction and recording of the multilayer optical recording medium can be performed more accurately.

Multi-Layer, Dual-Layer, DVD, Spherical Aberration, Liquid Crystal Panel

Description

Optical pickup device for multilayer optical recording media {PICK-UP APPARATUS FOR MULTI-LAYER TYPE DISC}

1 is a schematic configuration diagram of a conventional optical pickup device;

2 is a plan view of the structure of the PDIC and the shape of the spot of FIG.

3 is a schematic structural diagram of an optical pickup apparatus according to the present invention;

4 is a plan view of the structure of the PDIC and the shape of the spot of FIG.

5 is a distribution diagram of laser light in the absence of spherical aberration,

6 is a distribution diagram of laser light when there is spherical aberration;

7 is a cross-sectional view when spherical aberration occurs;

8 is a wavefront diagram generated in the LCP for correction of spherical aberration,

9 is a flowchart illustrating a spherical aberration correction process according to the present invention.

Explanation of symbols on the main parts of the drawings

110: laser diode 120: beam split

130: CL 135: HOE

140; OL 150; PDIC

160: control unit 165: memory

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device for a multilayer optical recording medium. More specifically, in an optical recording medium having a plurality of layers, spherical aberration caused by the optical path difference of laser light between each layer is detected, and a detection result is obtained. The optical pickup device for a multilayer optical recording medium which makes it possible to correct spherical aberration by adjusting the angle of incidence of laser light according to the above.

Currently, optical recording media mainly used include CDs and DVDs, and recently BDs using blue-rays have been released. Among such optical recording media, there are various types of DVDs depending on whether data is recorded or played back, such as DVD RAM, DVD-R, DVD + R, DVD-RW, DVD + RW, and standards. A DVD is formed by combining two discs of the same thickness, one disc being called a side, and a layer for recording data on each side. More than one layer can be formed on each side. Currently, DVD-R, DVD + R, DVD-RW, and DVD + RW are available in dual layer DVD products.

As shown in FIG. 1, an optical pickup apparatus for recording or reproducing data on a DVD includes a laser diode 10, a beam splitter 20, an optical conversion mirror 25, and a CL 30 (collimating lens). , OL 40 (Object Lens), HOE 35, Yo Lens 45, photodetector 50, and the like.

The laser diode 10 generates a laser light having a wavelength of 650 nm used for recording and reproducing the DVD 70, and the half wave plate (HWP 15) changes the polarization direction of the laser light by half wavelength. The beam splitter 20 changes the path of the laser light toward the light conversion mirror 25, and the CL 30 converges the laser light into parallel light. The HOE 35 circularly polarizes the laser light, and the circularly polarized laser light is focused on the OL 40 and reaches the DVD 70.

The laser light reflected by the DVD 70 passes through the OL 40, the HOE 35, and the CL 30 and is reflected by the light conversion mirror 25, as opposed to when it is incident, and then the beam splitter 20 is moved. To pass. Then, the laser beam is adjusted in focus at the Yo lens 45 and is incident on the photodetector PDIC 50 (Photo Diode IC).

The laser light incident on the PDIC 50 is divided into 12 spots and is incident as shown in FIG. 2. The four spots incident on the right side of the PDIC 50 are the focusing parts (B) to determine whether the focus of the laser beam is properly focused, and the four spots incident on the left side indicate that the laser beam properly tracks the track of the DVD 70. It is a tracking part (A) for determining whether it is following.

Such an optical pickup apparatus is used not only for a DVD having a single layer but also for reproduction and recording of a DVD having a dual layer. In general, the dual-layer DVD 70 has a distance of about 55 ± 15 μm between the first layer and the second layer. In order to record and reproduce data in each layer, the focus of the laser beam is focused on the recording or reproducing layer. It must be made. There are many ways to adjust the focus, and among these, the method of adjusting the focal length of the laser beam is most frequently performed by changing the position of the CL 30 so that the distance between the OL 40 and the CL 30 is adjusted. Used.

By the way, in the case of such a dual-layer DVD 70, the lengths of the optical paths through which the laser light enters the DVD 70 to reach each layer are different. Therefore, in the case of the dual-layer DVD 70, it is necessary to correct the spherical aberration as the range of the spherical aberration is much larger than the spherical aberration within the predetermined error range generated in the conventional single-layer DVD 70. This phenomenon is expected to occur not only in DVDs having dual layers, but also in multilayer DVDs having more layers. Accordingly, a method of detecting spherical aberration of the multilayer DVD 70 and correcting spherical aberration according to the detection result should be found.

Accordingly, it is an object of the present invention to provide an optical pickup apparatus for a multilayer optical recording medium which makes it possible to detect and correct spherical aberration caused by a change in optical path length.

The configuration of the present invention for achieving this object, the laser generator for generating a laser light; A plurality of lenses disposed on a path of the laser light and projecting onto a optical recording medium having at least two layers by adjusting the concentration of the laser light; A HOE for dividing the laser light reflected by the optical recording medium into a plurality of spots; A photodetector for detecting the light intensity between the center region and the outer region of the laser light divided by the HOE; A spherical aberration corrector for adjusting a wavefront of at least a portion of the laser light incident on the optical recording medium; And a controller for controlling the operation of the spherical aberration corrector by calculating the spherical aberration between the central region and the external region of the laser light according to the detection result of the photodetector.

Preferably, the photodetector is equipped with a plurality of photodetector sensors that separate the spots into a central region and an external region with respect to the laser beam and detect the intensity of the laser light incident on the respective central and external regions. Do.

The controller may be configured to calculate a spherical aberration value, which is a difference of laser light intensities between the center region and the external region of each spot, by receiving the intensity of the laser light detected by each photodetection sensor, and determine the spherical aberration value based on the spherical aberration value. Can be.

The spherical aberration corrector is formed of a liquid crystal panel composed of a liquid crystal element divided into a plurality of correction areas capable of separate power control, and the wavefront of the laser light may be changed according to voltage values supplied to the correction areas. Can be.

Preferably, the controller controls the power of each of the correction areas according to the spherical aberration value to at least partially change the wavefront of the laser light.

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

3 is a block diagram of an optical pickup apparatus for a dual layer type DVD according to the present invention. The optical pickup device includes a laser diode laser diode 110, a HWP 115 (Half Wave Plate), a beam splitter 120, a light conversion mirror 125, a CL 130 (Collimating Lens), and an OL 140. (Object Lens), HOE (135), Yo lens (145), PDIC (150) as a photodetector, LCP (155) as a spherical aberration corrector (Liquid Crystal Panal), memory 165, controller 160 do.

The laser diode 110 generates 650 nm laser light used for recording or reproducing information on the DVD disk 170, at which time the laser light is P-polarized.

The HWP 115 converts the P-polarized laser light generated by the laser diode 110 by half wavelength, that is, 180 °, to S-polarize the laser light.

The beam splitter 120 changes the path by passing the laser beam by reflecting the laser beam according to the polarization direction of the laser beam using a polarizing element. Accordingly, the beam splitter 120 reflects the S-polarized laser light passing through the HWP 115 at right angles to the optical conversion mirror 125 (DF Mirror), while being reflected from the DVD disk 170. P-polarized laser light passes through. The laser light reflected by the beam splitter 120 and reaches the light conversion mirror 125 is reflected at right angles to the CL 130.

The CL 130 converges the laser light in the divergent state so that the laser light travels in parallel toward the HOE 135, and is moved by the actuator to adjust the distance from the OL 140. When the distance between the CL 130 and the OL 140 is adjusted, the focal length of the laser beam is changed to form a focus on the first layer and the second layer of the dual layer DVD disk 170, respectively.

The HOE 135 circularly polarizes the S-polarized laser light and provides it to the OL 140, and the circularly polarized laser light reflected from the DVD disk 170 is P-polarized, and this polarization is a quarter-wave plate QWP. Is done in The HOE 135 splits only the P-polarized laser light reflected from the DVD disk 170 so as to be incident on the photodetector PDIC 150 in the form of a spot as shown in FIG. 4.

The OL 140 focuses the laser light that has passed through the HOE 135 to form a focal point on one of the layers of the DVD disc 170, and the laser light is reflected on the disc.

The laser light reflected by the disk 170 moves along the optical path in the opposite direction as when it is incident, and sequentially passes through the OL 140, the HOE 135, and the CL 130. The circularly polarized laser light passing through the OL 140 is P-polarized while passing through the HOE 135, and the P-polarized laser light is divided into 12 spot shapes as shown in FIG. Then, the divided laser light is reflected at right angles to the beam splitter 120 in the light conversion mirror 125, and the P-polarized laser light passes through the beam splitter 120, unlike the S-polarized laser light. .

The Yo lens 145 causes the laser light passing through the beam splitter 120 to be focused on the PDIC 150.

As illustrated in FIG. 4, the PDIC 150 receives a laser beam divided into 12 spots, converts an optical signal into an electrical signal, and analyzes the detected electrical signal to determine spherical aberration of the DVD. The spots focused on the PDIC 150 are largely divided into four groups. The four spots on the right side are the focusing parts (C) for determining the focus of the laser beam, and the four spots on the left side are used for tracking and spherical aberration. Aberration detection and tracking part (D) for grasping, and two spots located at the top and the bottom are also used for tracking.

Here, the focusing part (C) is equipped with eight light detection sensors for dividing four spots up and down to detect the intensity of the laser light for each, and focus according to the distribution of the intensity of the laser light detected by each light detection sensor. It can be determined whether is formed correctly.

In the aberration detection and tracking part D, four spots are divided diagonally, and two undetected light detection sensors are mounted for each spot. At this time, a diagonal line dividing each spot is formed to divide the center region of the laser beam before the laser beam is divided and the outer region that was the edge of the laser beam. In FIG. 4, the center regions of the laser beam are A1, B1, C1, and D1, respectively. And the outer regions are A2, B2, C2, and D2, respectively. Here, as the light detection sensors are mounted in each of the center area and the outside area, the laser light intensity of the center area and the outside area of each spot may be detected. When the intensity of the laser light is detected by each light detection sensor as described above, the controller 160 calculates a spherical aberration value according to Equation 1 below.

Spherical Aberration = (Light Intensity of Spot Center Area)-(Light Intensity of Spot Outside Area)

           = (A1 + B1 + C1 + D1)-(A2 + B2 + C2 + D2)

According to Equation 1, by subtracting the intensity of the spot external region from the intensity of the spot central region, the difference between the laser light intensity of the spot central region and the external region is calculated. The intensity of the detected laser light is changed into a voltage value by the photodetector, and this voltage difference becomes a reference for determining spherical aberration.

5 and 6 are graphs showing the distribution of the laser light intensity of the spot when there is no spherical aberration and when there is spherical aberration, respectively. As shown in the graph of FIG. 5, since there is no spherical aberration, the spot will be concentrated almost only in the center region, so that the laser light intensity of the center region is much larger than that of the external region. However, when there is spherical aberration, as shown in the graph of FIG. 6, the spot is distributed over a wide area, and it can be seen that the laser light intensity of the central area is significantly reduced compared to the case where there is no spherical aberration. . As described above, when there is spherical aberration, the laser light intensity of the external region increases, so that the voltage difference according to Equation 1 becomes small. That is, as the voltage difference in Equation 1 increases, the actual spherical aberration hardly occurs, and as the voltage difference decreases, the spherical aberration occurs severely.

In order to correct spherical aberration, the LCP 155 is disposed on the laser light path between the HOE 135 and the CL 130. The LCP 155 is a liquid crystal panel. In general, since the arrangement of the liquid crystal elements changes according to the voltage provided, the LCP 155 may change the refractive index of the laser light passing through the LCP 155. The liquid crystal panel of the LCP 155 has a plurality of correction regions divided into concentric circles with a predetermined distance from the center to the outside. Here, each of the correction areas is formed in the form of the laser light is incident, for example circular, each correction area has a separate power supply source to enable a separate power control or is configured to enable control of each power supply. Therefore, each correction region can be supplied with a different level of power, thereby controlling the refractive index of the laser beam passing through each correction region. When the refractive index is changed in this way, the wavefront of the laser light incident on the OL 140 is changed.

On the other hand, in the above-described embodiment, the correction region is divided into several parts. However, the correction region may be divided into two parts corresponding to the center region and the external region of the laser beam, or may be divided into a grid shape or other shapes other than concentric circles. Of course.

On the other hand, if spherical aberration occurs in the outer region of the laser light, and as shown in FIG. 6, when the distribution of light intensity is widely distributed over the spot center region and the outer region, the waveform of spherical aberration as shown in FIG. ) Is formed. However, if there is no spherical aberration, no waveform is formed as shown in II of FIG. Therefore, in order to implement a state without spherical aberration as shown in II of FIG. 7, as shown in FIG. 8, a waveform opposite to I in FIG. 7 must be provided to extinction and interfere with the waveform of I in FIG. 7. To this end, each correction region of the LCP 155 should be supplied with an appropriate voltage for adjusting the refractive index of the laser light so as to eliminate the spherical aberration.

On the other hand, the memory 165 stores the spherical aberration value and the information on the voltage value supplied to each correction region of the LCP 155 in order to remove the spherical aberration according to the spherical aberration value in a table form.

When the spherical aberration value is calculated according to the aberration detection and the detection part of the tracking part D of the PDIC 150, the controller 160 stores information about the voltage of each correction area corresponding to the calculated spherical aberration value in the memory ( 165, and controls the voltage provided to each correction region of the LCP 155 according to the corresponding voltage.

A spherical aberration correction process in the optical pickup device having such a configuration will be described with reference to FIG.

When power is supplied to the optical pickup apparatus and recording or reproduction of an optical recording medium such as a DVD disk 170 is selected (S200), the controller 160 operates the laser diode 110 to generate P-polarized laser light. (S210). The P-polarized laser light is S-polarized while passing through the HWP 115 to be incident on the beam splitter 120, and then reflected toward the light conversion mirror 125. The light conversion mirror 125 again reflects the laser light toward the CL 130, and the CL 130 converges the laser light to convert it into parallel light. Then, the LCP 155 and the HOE 135 are sequentially passed. At this time, since the power is not supplied to the LCP 155, the laser light passes through the LCP 155 as it is. In the HOE 135, the laser light is converted from S-polarized light to circularly polarized light, and the circularly polarized laser light converges while passing through the OL 140 to form a focus on the disk (S220). The laser light incident on the disk is reflected and travels back to the incident optical path.

The reflected laser light is again incident to the HOE 135 via the OL 140, and the circularly-polarized laser light is divided into spots that are P-polarized at the HOE 135 and then incident to the PDIC 150 (S230). . The split laser light passes through the LCP 155 and the CL 130, is reflected by the light changing mirror 125, and then incident to the beam splitter 120. The beam splitter 120 passes the P-polarized laser light, and the laser light passing through the Yo lens 145 is incident on the PDIC 150 in the form as shown in FIG. 4 (S240). The PDIC 150 converts the incident laser light into an electrical signal, and the aberration detection and tracking part D detects the light intensity of each spot by a total of eight light detection sensors (S250). The intensity of the laser light detected by each light detecting sensor is provided to the controller 160, and the controller 160 calculates spherical aberration value by Equation 1 (S260). When the spherical aberration value is calculated, the controller 160 determines whether the spherical aberration is in accordance with the spherical aberration value, and when the spherical aberration occurs, the voltage value of each correction region corresponding to the spherical aberration value is withdrawn from the memory 165. (S270). Then, the controller 160 adjusts the voltage provided to each correction region of the LCP 155 according to the corresponding voltage value.

When different voltages are supplied to each correction region of the LCP 155, the arrangement of the liquid crystal elements is changed according to the voltage, and the incident angle of the laser light passing through the LCP 155 is changed according to the correction region (S280). Accordingly, since the laser beam focuses on the same position regardless of whether the laser beam passes through the center region or the external region of the OL 140, spherical aberration can be corrected. When the voltage value supplied to each correction region of the LCP 155 is set such that the spherical aberration is corrected, the process of recording or reproducing data by driving the DVD is performed (S290).

As described above, the optical pickup apparatus detects spherical aberration in the preparation step for driving the DVD 170 by supplying power, and then provides an appropriate voltage to each correction region of the LCP 155 so as to adjust the incident angle of the laser light. At this point, the focus is precisely on each layer. As a result, spherical aberration caused by the change of the optical path in the dual layer or the multilayer optical recording medium can be eliminated, so that the reproduction and recording of the multilayer optical recording medium can be performed more accurately.

As described above, according to the present invention, since the spherical aberration caused by the change of the optical path in the dual-layer or multilayer optical recording medium can be eliminated, the reproduction and recording of the multilayer optical recording medium can be performed more accurately. Can be.

In addition, the detailed description of the present invention has been described with respect to specific embodiments, which should be taken as exemplary, and various modifications may be made without departing from the technical spirit of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined not only by the claims below, but also by the equivalents of the claims.

Claims (5)

A laser generator for generating laser light; A plurality of lenses disposed on a path of the laser light and projecting onto a optical recording medium having at least two layers by adjusting the concentration of the laser light; A HOE for dividing the laser light reflected by the optical recording medium into a plurality of spots; A photodetector for detecting the light intensity between the center region and the outer region of the laser light divided by the HOE; A spherical aberration corrector for adjusting a wavefront of at least a portion of the laser light incident on the optical recording medium; A control unit for controlling the operation of the spherical aberration corrector by calculating the spherical aberration between the central region and the external region of the laser light according to the detection result of the photodetector; The spherical aberration corrector is formed of a liquid crystal panel composed of liquid crystal elements divided into a plurality of correction regions capable of separate power control, and the incident angle of the laser light is changed according to voltage values supplied to the correction regions. Optical pickup device for a multilayer optical recording medium. The method of claim 1, The photodetector is equipped with a plurality of photodetector sensors for detecting the intensity of the laser beam incident on each of the center region and the external region by separating each spot into a central region and an external region with respect to the laser light. An optical pickup apparatus for a multilayer optical recording medium. The method according to claim 1 or 2, The controller may be configured to calculate a spherical aberration value, which is a difference between the laser light intensities between the center region and the external region of each spot by receiving the intensity of the laser light detected by each light detection sensor, and determine the spherical aberration based on the spherical aberration value. Optical pickup apparatus for a multilayer optical recording medium, characterized in that. The method of claim 3, wherein And the controller controls the power of each of the correction areas according to the spherical aberration value to at least partially change the wavefront of the laser light. delete

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