KR19990050022A - Dual Focus Optical Pickup Device Using Optical Control Liquid Crystal Panel - Google Patents

Abstract

The present invention relates to a dual focus optical pickup apparatus using a light control liquid crystal plate. The liquid crystal device 20 is installed horizontally below the optical disks 50 and 60 to transmit and reflect the laser light at different refractive indices to convert polarization by diffusing the reflected light according to the application of voltage, and the liquid crystal device is diffracted. A first laser diode 10 emitting a laser beam having a predetermined wavelength from below 20, and installed perpendicular to the first laser diode 10 and opposed to an installation vertical surface of the liquid crystal element 20; Between the second laser diode 15, the plurality of photodetectors 12 and 14 which receive reflected light from both sides of the first laser diode 10, and between the liquid crystal element 20 and the optical disks 50 and 60. It comprises an objective lens 40 for condensing laser light. Thus, since the spherical aberration generated by the thickness of the optical disk and the recording surface difference of the signal information varies the refractive index of the light beam incident on the objective lens, the numerical aperture (NA) of the objective lens is actively converted so that the spherical aberration significantly decreases. It has the effect of playing compatible audio and digital video discs.

Description

Dual Focus Optical Pickup Device Using Optical Control Liquid Crystal Panel

The present invention relates to a dual focus optical pickup apparatus using an optical control liquid crystal plate. In particular, the spherical aberration caused by the difference in the thickness of the optical disk and the recording surface of the signal information varies the refractive index of the luminous flux incident on the objective lens. The present invention relates to a dual focus optical pickup apparatus using an optical control liquid crystal panel capable of compatible reproduction of digital audio and digital video discs since the number NA is actively converted and spherical aberration is significantly reduced.

In general, an optical data recording medium, that is, an optical disk, is divided into a digital audio disk (DAD) for music playback having a thickness of 1.2 mm and a digital video disk (DVD) having a thickness of 0.6 mm. A thick digital audio disc records data in multiple layers on one side, and a 0.6 mm thick digital video disc records data in multiple layers in the middle to record a large amount of data on a single disc.

An optical pickup apparatus for reproducing data recorded on the above two types of discs reads information recorded on a 1.2 mm thick digital audio disc and a 0.6 mm thick digital video disc. Since the track pitch of the image is 0.74 µm and the shortest length between the pit, which is the recording signal, is 0.4 µm, the diameter of the optical spot must be different during playback because the track pitch is different from that of a digital audio disc having 1.6 µm and the shortest length between the feet is 0.834 µm. Because spherical aberrations do not match, simultaneous playback is impossible, and optical aberration is increased due to the difference of 0.6mm thickness of the discs. Only the recorded information on one of the 1.2mm discs could be read.

Therefore, an objective lens having a numerical aperture NA of 0.6 designed for a 0.6 mm disk as shown in the detailed view of FIG. 1 to selectively read out information recorded on a 1.2 mm disk and a 0.6 mm disk in recent years. 1130 and a holographic optical element 1120 having a multi-stage diffraction layer w1, w2, h0 formed by etching, adopt a dual focus lens in which a composite array is arranged, and the holographic optical element 1120 The zero-diffracted light is linearly diverged and the first-diffracted laser light is divergent light. Therefore, a dual-focus optical pickup device for controlling the diffraction efficiency and appropriately distributing the amount of light has been developed.

As shown in FIG. 1, the dual focus optical pickup device employing the holographic optical device 1120 includes a laser diode 1100 that scans laser light having a linearly polarized constant wavelength, and the laser diode 1100. A diffraction grating 1105 which separates the laser beam scanned by the laser beam into a zero-order diffraction light and a ± first-order diffraction light for detecting a tracking error signal, that is, a three beam, and at one side of the diffraction grating 1105 A beam splitter 1110 which reflects and transmits the scanned laser light at a predetermined ratio with a predetermined slope, and a collimator lens 1115 which converts the laser light via the beam splitter 1110 into parallel light; The holographic optical element 1120 for distributing the amount of light by adjusting the diffraction efficiency of the parallel light via the collimator lens 1115 and the laser light via the holographic optical element 1120 for 0.6 mm digital discs. An objective lens 1130 that reads the recorded information by focusing on a disk 1150 (hereinafter referred to as "first disk") and a 1.2 mm disk (hereinafter referred to as "second disk") that is a digital audio disk; Astigmatism generating lens 1140 for generating a focusing error signal by the astigmatism method for detecting an error signal in the laser light with recorded information, and detecting the optical information passing through the astigmatism generating lens 1140 And a photodetector 1145 for converting the signal into a current signal.

In operation of the conventional optical pickup apparatus having such a configuration, first, the laser light having a predetermined oscillation wavelength is scanned by the laser diode 1100 and incident on the diffraction grating 1105, and the incident laser light is incident on the diffraction grating 1105. ) And radiated into 0th and ± 1st light, that is, three beams. The three beams are used for tracking errors. The three beams penetrate the diffraction grating 1105 and enter the beam splitter 1110. The three beams are reflected and transmitted at a constant rate by the beam splitter 1110. The laser light reflected from the reflected and transmitted laser light is incident from the beam splitter 1110 to the collimator lens 1115, and the laser light passes through the collimator lens 1115, thereby providing linearity. The laser light, which is thus provided with linearity and becomes parallel light, is incident from the collimator lens 1115 into the holographic optical element 1120, and the laser light is diffracted by the holographic optical lens 1120. Since the zero diffraction light goes straight among the diffracted laser beams, the light is collected in a spot having a diameter of 1.6 μm on the first disc 1150 having a diameter of 0.6 mm through the aperture of the objective lens 1130 having a numerical aperture of 0.6, Since the light is converted into divergent light and condensed narrowly by the objective lens, the light is condensed on the second disk 1155 in an airy shape having a diameter of 0.8 μm, so that the laser light is reflected almost as it is in the absence of the pit 1155 on the disk. To return to the objective lens 1130, but where the pit 1155 is present, the laser light is diffracted by the pit 1155 and emitted outside the range of the objective lens 1130, thereby causing only a part of the incident light to return. Thereby generating a light quantity difference in the photodetector 1145. This is because the depth of the pit 1155 is set to λ / 4 of the wavelength, and the reflected light is canceled by interference due to different half wavelengths above and below the pit 1155, thereby reducing the amount of light returned to the photodetector 1145.

The modulated reflected light reflected by the first disk 1150 or the second disk 1160 is returned to the beam splitter 1110 via the holographic optical device 1120 and the collimator lens 1115. The reflected light is reflected and transmitted again at a constant rate, and the laser light transmitted by the beam splitter 1110 is moved straight toward the photodetector 1145. The modulated reflected light is irradiated from the beam splitter 1110 to the astigmatism generating lens 1140, and the reflected light is generated by the astigmatism generating lens 1140 to detect a focus error, and thus the photodetector 1145. The reflected light, which is modulated by the disk, is converted into RF (RF), focus error detection, tracking control, and information into a current by a photodetector, which is converted into an original signal by a control circuit (not shown). Demodulation is performed.

Therefore, as described above, the laser light emitted from the laser diode 1100 is collected in different airy shapes on the disk via the holographic optical device 1120, so that the beam focus is formed at different positions so that the thickness is 1.2 mm. The disc and the information recorded on the 0.6 mm disc can be selectively read.

However, such a conventional dual focus optical pickup device has a processing effect due to the complex arrangement of the holographic optical element 1120 and the objective lens 1130 using diffraction of light in order to focus the optical disk with a double focus according to the thickness of the disk. Since a high level of technical skill is required, manufacturing is difficult and at the same time, the holographic optical device 1120 is fixed to the mover 1125 and thus adversely affects the dynamic characteristics of the actuator, and from the first disk 1150 to the second disk 1160. In the case of change, there is a problem that the obstacle of miniaturization of the optical pickup due to the enlargement of the objective lens by increasing the focal length of the objective lens due to the aberration change and the increase of the design dimension due to maintaining a predetermined distance between the optical elements.

The present invention has been made in view of the above problems, and improves the dynamic characteristics of the actuator by eliminating the complexity of the shape due to the manufacturing difficulties and aberration changes due to the precise interlayer alignment of the holographic optical element by etching, Dual focus using an optical control liquid crystal panel that can reduce the size of the optical pickup device by eliminating the problem of adjusting the focal length of the objective lens due to aberration change during playback caused by a plurality of disc thickness differences. The object is to provide an optical pickup device.

The present invention to achieve the above object,

A phase hologram lattice provided horizontally with the recording surface on the optical disc and selectively diffracting according to the polarization of the laser light,

A transparent substrate formed on the phase hologram lattice and opposed to the plurality of transparent substrates, and a laser light polarized in the voltage application direction when voltage is applied between the transparent substrates is larger than a laser light polarized in the direction perpendicular to the voltage application direction. A light adjusting liquid crystal panel comprising a liquid crystal layer to which a voltage is applied at a central portion and one side of the liquid crystal layer to transmit at different refractive indices according to the polarization of the laser light;

A wavelength plate for converting a phase of a laser beam above the light control liquid crystal plate,

A liquid crystal element in which the wave plate, the light control liquid crystal plate and the phase hologram grid are integrally formed;

A first laser diode which emits laser light of a constant wavelength under the liquid crystal element;

A second laser diode which is installed perpendicular to the first laser diode and installed to face the mounting vertical surface of the liquid crystal element;

A plurality of photodetectors for receiving reflected light from both sides of the first laser diode;

An objective lens for condensing laser light between the liquid crystal element and the optical disk;

Provided is a dual focus optical pickup apparatus using a light control liquid crystal panel including the above components.

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

2 is a block diagram of the present invention,

3 is a partial detailed view of the present invention;

4 is an operating state in which the present invention shows a digital video disc playback;

5 is an operational state in which the present invention shows digital audio disc playback;

<Explanation of symbols for main parts of drawing>

10, 15: laser diode 20: liquid crystal device

22: phase hologram lattice 24: beam splitter surface

28: wave plate 30: light control liquid crystal plate

40: objective lens 12, 14: photodetector

50, 60: optical disc

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

As shown in FIG. 2, the liquid crystal is installed horizontally under the optical disks 50 and 60 to transmit and reflect laser light at different refractive indices according to whether voltage is applied to convert polarization and diffracted reflected light. An element 20, a first laser diode 10 that emits a laser beam of a constant wavelength from below the liquid crystal element 20, and a first laser diode 10 perpendicular to the first laser diode 10 and disposed above the liquid crystal element 20 A second laser diode 15 which is installed to face a vertical surface of the panel, a plurality of photo detectors 12 and 14 that receive reflected light from both sides of the first laser diode 10, and the liquid crystal device 20 And an objective lens 40 for condensing laser light between the optical discs 50 and 60.

On the bottom of the liquid crystal device 20, a first laser diode 10 and a second laser diode installed perpendicularly to the first laser diode 10 and installed opposite to an installation vertical surface of the liquid crystal device 20 ( 15) is installed to emit a laser light of a constant wavelength phase shifted to a constant polarization component, that is, the S-wave which is a component perpendicular to the direction of light travel.

On both sides of the first laser diode 10, there are provided photo detectors 12, 14 for receiving reflected light reflected on the optical disk and reading the optical information. Each photo detector 12, 14 has a focusing error. A four-segment photodetector is installed to detect the light. Two photodetectors are provided on both sides of the first laser diode 10 to detect tracking errors according to the intensity distribution of the reflected light. The photodetectors 12 and 14 on both sides are spaced apart from each other. Since an image is formed at an arbitrary point between the light receiving sections, an optical signal is condensed on each of the photodetectors 12 and 14 and output as an electrical signal.

The liquid crystal element 20 is formed of a prism of a cube, and a beam splitter surface 24 for transmitting and reflecting a laser beam at a predetermined ratio is formed on a splined surface, and an upper portion of the beam splitter surface 24 is formed of a laser beam splitter. A phase hologram lattice 22 that selectively diffracts in accordance with polarization is provided, and a light adjusting liquid crystal plate 30 for transmitting laser light at different refractive indices is provided on the upper side of the phase hologram lattice 22. On the upper side of the liquid crystal plate 30, a wave plate 28 for converting the phase of the laser light is formed.

As shown in FIG. 4, the light control liquid crystal plate 30 includes a plurality of transparent substrates 32 formed to face each other, a liquid crystal layer 38 formed between the transparent substrates 32, and the liquid crystal layer ( 38 is composed of a transparent electrode 34 to which a voltage is applied at one side of the center and the liquid crystal layer 38 transmits at a different refractive index according to the polarization direction of the laser light when voltage is applied, which is applied in the voltage application direction (Y). The polarized laser light is refracted larger than the laser light polarized in the direction X perpendicular to the voltage application direction.

Since the different refractive indices (ηs, ηℓ) are proportional to the numerical aperture, the amount of light is controlled by the transmittance according to the width, so that the numerical aperture (NA: Numerical Aperture) can be adjusted when the refractive index is focused on the optical discs 50 and 60 at different refractive indices. .

The numerical aperture N.A. adjusted in the liquid crystal element 20 is arranged as follows.

According to the present invention, the diameters of the light spots focused on the optical discs 50 and 60 are differently determined according to the refractive indices η s and η ℓ. The refractive index transmitted during reproduction of the digital video disc 52 having a thickness of 0.6 mm is η s and the refractive index transmitted during reproduction of the digital audio disc 54 having a thickness of 1.2 mm is η ℓ on the optical discs 50 and 60. Assuming that the outermost incident angle of the light to be focused is θ, the determination of the numerical aperture NA for this is determined by the following equation (1).

N.A.1 = ηS sinθ N.A.2 = ηℓ sinθ

According to Equation 1, when the outermost incidence angles are the same, the numerical aperture is proportional to the refractive indexes η s and η ℓ.

Then, the size of the light spots due to the different numerical apertures is determined by the following expression (2). The radius W of the beam (K is a constant determined by the intensity distribution of the light),

Therefore, the diameter of the light spot is in inverse proportion to the numerical aperture.

Therefore, in the case of the optical disc 50 having a thickness of 0.6 mm, since the track interval and the size of the pit which is the signal surface are small, a small optical spot diameter is required, and an object having a numerical aperture larger than the optical disc 60 having a thickness of 1.2 mm is required. You need a lens. At this time, the beam spot diameter can read the optical signal even if the beam spot diameter is somewhat larger on the optical disk 60 having a thickness of 1.2 mm, so that the objective lens 40 having the numerical aperture (NA = 0.6) dedicated to the digital video disk 50 can be obtained. It will try to play compatible.

On the other hand, the relationship between the numerical aperture and the incident angle incident on the objective lens is determined by the following equation (3). If D and f are the focal lengths of the objective lenses,

D = 2 × f × (N.A.)

That is, by controlling the incident light width to the objective lens having the same focal length in Equation 3, it is possible to adjust the effective N.A.

In the present invention, since a single objective lens, i.e., an objective lens 40 dedicated to a digital video disc, is adopted on the basis of the same focal length, the optical signal is read out on the optical disc 50 having a thickness of 0.6 mm without the occurrence of spherical aberration.

However, in this case, when the optical disc 60 having a thickness of 1.2 mm is read out, first, when focus compensation is not performed, the focusing accuracy is not accurate due to defocus, and thus the error occurrence width becomes large. Second, the disc thickness difference The spherical aberration causes the increase in the distribution light intensity of the side lobe of the laser beam and the decrease in the central intensity distribution, thereby increasing the crosstalk between adjacent signals and decreasing the signal-to-noise ratio (S / N ratio). The optical performance is significantly lowered, making it impossible to read optical information. Therefore, the effective N.A. must be adjusted by Equation 3 above. The range of these effective openings is determined as follows.

First, the amount of spherical aberration caused by the difference in disk thickness is determined by the following equation (4). If the refractive index is η and the disk thickness change is Δd,

On the other hand, if the amount of aberration generated by defocus is ΔZ, Equation 4 is modified as follows.

The cumulative wave front aberration of the optical system of the present invention can be expressed by the aberration system from the relationship between the center intensity distribution and the wave aberration by matching the spherical aberration by equating the aberration generation amount of Equation 4 to a value compensated for defocusing. According to marechal's criterion that should be less than 0.07λ, the effect on the defocus can be eliminated, thus approaching the anhydrometer.

Therefore, when the outermost incident angle is adjusted by Equations 4 and 5 or the refractive index is adjusted by Equations 1 to 3 to compensate for the numerical aperture, the maximum value of spherical aberration value 0.5 is obtained. That is, the effective number of openings should be 0.5 or less, and the minimum value is limited to Equation 2, thereby increasing the diameter of the light spot. The increase in the light spot diameter causes a crosstalk caused by an increase in the light spot size rather than the crosstalk due to the change in the intensity distribution due to the generated aberration, thereby lowering the signal-to-noise ratio. Therefore, since the minimum value is limited to the intensity distribution of the generated aberration, when the optical disk having a thickness of 0.6 mm is read out by the objective lens having a numerical aperture of 0.6 used in this embodiment, the effective number of openings is summarized as follows.

0.27 <N.A.≤0.5

In this way, the numerical aperture can be determined by selecting an appropriate numerical value from among the values calculated for the change of the crosstalk according to the numerical aperture change and the sensitivity size of the reproduction signal. In the present invention, the numerical aperture is determined to be 0.3.

Therefore, when the outermost incident angle and the refractive index (ηs, ηℓ) from the liquid crystal element 20 onto the optical disc 50 are adjusted by Equations 1 to 6, the numerical aperture is adjusted, so that only the optical disc 50 having a thickness of 0.6 mm can be used. The objective lens 40 can reproduce the optical disc 60 having a thickness of 1.2 mm, and the spherical aberration generated during the compatible reproduction is reproduced by refracting and transmitting the laser light at different refractive indices, so that the effective number of apertures can be controlled and the compatible reproduction is excellent. It can be.

Next, a description will be given of the operation of the present invention in which the liquid crystal device 20 capable of adjusting the numerical aperture is adopted as described above.

First, when reproducing the digital video disk 50 having a thickness of 0.6 mm among the optical disks 50 and 60, when a reproduction signal of the optical disks 50 and 60 is generated by a controller (not shown) as shown in FIG. The control unit applies a constant voltage to the light control liquid crystal panel 30 of the liquid crystal device 20 and emits a laser light having a predetermined wavelength λ 2 from the first laser diode 10. The first laser diode 10 ) Is a light perpendicular to the plane of incidence with respect to the advancing direction of the laser light, for example, polarization is adjusted so that S-polarized light is emitted to emit laser light. The polarized laser light is irradiated from the laser diode 10 to the liquid crystal element 20, and the laser light is partially reflected and transmitted while passing through the beam splitter surface 24. Therefore, the transmitted laser light is a phase hologram lattice ( 22). The laser beam thus transmitted is not diffracted via the phase hologram lattice 22. This does not diffract the S-polarized laser light, but rather diffracts only the laser light parallel to the optical axis direction, that is, the P-polarized laser light, so that incident light is transmitted without diffraction.

Thus, the laser light passing through the phase hologram lattice 22 is irradiated to the light adjusting liquid crystal plate 30 of the liquid crystal element 20, and the laser light is adjusted by the light adjusting liquid crystal plate 30 to adjust the refractive index. The refractive index is adjusted by varying the light intensity distribution of the incident light intensity. When voltage is applied, laser light polarized in the voltage application direction (Y) is lower than laser light polarized in the direction (X) perpendicular to the voltage application direction. Since the refractive index (ηs) in the vertical direction (Y) and the refractive index (ηℓ) in the horizontal direction (X) are formed differently so that the refractive is greatly refracted, the laser beam transmitted at different refractive indices is made because the refractive in the horizontal direction is larger than that in the standing direction. The light passes through the wave plate 28 at the same time by different numerical apertures NA according to the above-described equations (1) through (6). The laser light polarized by circularly polarized light through the wave plate 28 and whose light amount is adjusted is irradiated onto the objective lens 40 and focused onto the optical disk 50.

By the way, the laser light focused by the objective lens 40 via the light control liquid crystal plate 30 at different numerical apertures is different in refractive index (ηs, ηℓ) of the laser light when it is incident on the optical disks 50 and 60. The difference in the diameter of the light spot due to is as described above.

Thus, in the case of reproducing each of the optical discs 50 and 60, for example, the digital video disc 50 having a thickness of 0.6 mm, the refractive index ηℓ in the horizontal direction X and the objective lens 40 are applied due to the application of voltage. As a result, a numerical aperture of about 0.6 mu m is formed on the optical disc 50 at a numerical aperture of 0.6, which interferes with diffraction on the recording surface, thereby reading optical information with an amount of light and the presence or absence of light. At this time, since the objective lens 40 dedicated to the digital video disc 50 is used in the present invention, the recording surface is accurately focused without generating spherical aberration.

When the digital audio disc 60 having a thickness of 1.2 mm is reproduced, as shown in FIG. 5, the control unit cuts off the voltage from the light adjusting liquid crystal plate 30 and is provided on one side of the liquid crystal element 20. The laser light of a predetermined wavelength λ1 is emitted from the second laser diode 15, and the second laser diode 15 also has the same polarization as the first laser diode 10 so that the polarization is adjusted so that the laser light is emitted. Emits light. The polarized laser light is a laser light having a wavelength larger than a predetermined wavelength λ 2 of the first laser diode 10, and is irradiated from the second laser diode 15 to the liquid crystal element 20, and the laser light is a liquid crystal. Partially reflected and transmitted at the beam splitter surface 24 of the element 20, the double reflected laser light is irradiated to the phase hologram lattice 22 and transmitted without diffraction. This is because the phase hologram lattice 22 diffracts only the P-polarized laser light, the incident light is transmitted without diffraction, and the transmitted laser light is not applied while passing through the light control liquid crystal panel 30, so the vertical direction (Y) It is transmitted by the refractive index η s and is collected by the objective lens 40 on the optical disk 60 with a numerical aperture of 0.3.

Thus, the laser light, which reads the optical information on each of the optical disks 50 and 60 in the above-described process, is irradiated to the liquid crystal element 20 via the objective lens 40.

In the laser beam, circularly polarized light is polarized by linearly polarized light when the wavelength plate 28 of the liquid crystal element 20 is transmitted. At this time, since the linearly polarized laser light is incident on the wavelength plate 28 when the inverted circular polarized light is reflected on the optical disks 50 and 60, the linearly polarized light having the polarization direction orthogonal to the time of incidence upon the initial wavelength plate 28. Becomes The laser light of the inverted linearly polarized light is incident on the phase hologram lattice 22 via the light control liquid crystal plate 30.

Thus, the reflected light is irradiated onto the phase hologram lattice 22 with the phase of the linearly polarized light being delayed, wherein the laser light reflected on the digital video disc 50 is diffracted from the phase hologram lattice 22.

Thus, the diffracted laser light is irradiated from the phase hologram lattice 22 to the photodetectors 12 and 14, and the reflected light is diffracted to cause the focus error to be detected in the photodetectors 12 and 14 and to be diffracted to both photodetectors 12 Tracking error is detected by calculating the amount of light to be formed.

In this way, the laser light, which reads the optical information via the respective paths, is diffracted, interfered and reflected and transmitted, and outputs the digital audio signal and the digital video signal as original electrical signals, and the output optical signal is a digital signal processor (not shown). Demodulated to the original signal to output an RF (RF) signal which is an audio signal recorded on the optical disc, a focus signal which is an error detection signal, and a tracking signal.

As described above, according to the present invention, since the light control liquid crystal plate 30 has a different transmittance, the laser light is passed through the objective lens 40 by transmitting the light control liquid crystal plate 30 with a transmittance η 1 at the time of reproduction of the digital video disc. Since light is condensed at the optical disc 50, a light spot having a diameter of about 0.8 μm is formed and received by the photodetectors 12 and 14, so that the digital video disc is reproduced. Since the light is transmitted from the plate 30 with the refractive index ηs and is collected on the optical disk 60 by the objective lens 40, it is received by the photodetectors 12 and 14, which is caused by the thickness difference between the optical disks 50 and 60. The spherical aberration is greatly reduced and each optical information is received by a different photodetector, so that compatible reproduction can be performed without interference of light.

The dual focus optical pickup apparatus of the optical control liquid crystal panel of the present invention changes the spherical aberration caused by the difference in the thickness of the optical disk and the recording surface of the signal information, thereby varying the incident light intensity distribution of the light beam incident on the objective lens. Since the NA) is actively converted, the spherical aberration is significantly reduced, so that digital audio and digital video discs can be interchangeably played.

Claims (2)

A liquid crystal device 20 horizontally disposed below the optical discs 50 and 60 to transmit and reflect the laser light at different refractive indices to convert polarization and diffract the reflected light according to whether voltage is applied; The first laser diode 10 and the first laser diode 10 which emit a laser beam having a predetermined wavelength below the liquid crystal element 20 are installed perpendicularly to each other and face the mounting vertical surface of the liquid crystal element 20. A second laser diode 15 installed; A plurality of photodetectors (12, 14) for receiving reflected light from both sides of the first laser diode (10); An objective lens 40 for condensing laser light between the liquid crystal element 20 and the optical disks 50 and 60; Dual focus optical pickup apparatus using a light control liquid crystal panel comprising the component. 2. The liquid crystal device (20) according to claim 1, wherein the liquid crystal element (20) is selectively in accordance with a beam splitter surface (24) for partially reflecting and transmitting a laser beam on a splined surface and in accordance with the polarization of the laser light on the beam splitter surface (24). A phase hologram lattice 22 to be diffracted, a transparent substrate 32 formed integrally on the upper side of the phase hologram lattice 22 so as to face each other, and a voltage formed when the voltage is applied A liquid crystal layer 38 that refracts the laser light polarized in the application direction Y more than the laser light polarized in the direction X perpendicular to the voltage application direction, and a voltage at the central portion and one side of the liquid crystal layer 38. Light comprising a light control liquid crystal plate 30 composed of the transparent electrode 34 to be applied, and a wavelength plate 28 for converting the phase of the laser light integrally on the upper side of the light control liquid crystal plate 30. Dual focus light using adjustable liquid crystal panel Up device.