KR19990050016A - Reflective Dual Focus Optical Pickup Device - Google Patents

Abstract

The present invention relates to a light control reflective dual focus optical pickup device. This is because the silicon substrate 1 is installed in parallel with the recording surface 65 of the optical disks 60 and 70, and the polarization separation is provided at an acute angle on the upper surface of the silicon substrate 1 to selectively transmit and reflect the laser light. A portion 12, a reflecting portion 18 for totally reflecting the laser light on the lower slope of the polarization separating portion 12, a laser diode 5 spaced apart from the polarization separating portion 12, and the laser A plurality of photodetectors 80, 80 ', 90, 90' installed on both sides of the mounting surface of the diode 5 and selectively diffracted laser light integrally on the upper surface of the polarization splitter 12 A phase hologram lattice 20, a light regulating liquid crystal plate 30 which is formed integrally on the upper surface of the phase hologram lattice 20 and separates and transmits the laser light at different transmittances depending on the width of the phase hologram lattice; Wavelength plate 40 for converting the phase of the laser beam integrally on the upper surface of And an objective lens 50 for condensing laser light via the plate 40. As a result, the spherical aberration caused by the thickness of the optical disk and the recording surface difference of the signal information is varied by varying the incident light intensity distribution of the light beam incident on the objective lens. Therefore, the numerical aperture (NA) of the objective lens is actively converted to reduce spherical aberration. As a result, the digital audio and digital video discs can be interchangeably played.

Description

Reflective Dual Focus Optical Pickup Device

The present invention relates to an optically controlled reflective dual focus optical pickup device. 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 incident light intensity distribution of the light beam incident on the objective lens using the liquid crystal plate. Since the numerical aperture (NA) of the objective lens is actively converted, the spherical aberration is significantly reduced, and the present invention relates to a light control reflective dual focus optical pickup device capable of compatible reproduction of digital audio and digital video discs.

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, Light control reflective dual focus optical pickup that can reduce the size of the optical pickup device by reducing the design dimension by eliminating the problem of adjusting the focal length of the objective lens due to aberration change during reproducing caused by a plurality of disc thickness differences The object is to provide a device.

The present invention to achieve the above object,

A silicon substrate installed in parallel with the recording surface of the optical disc and having an optical element thereon;

A polarization separator installed at an acute angle on the upper surface of the silicon substrate to transmit laser light having a component parallel to the incident surface and to reflect the laser light having a component perpendicular to the incident surface;

A reflector integrally formed at the lower slope of the polarization separator to totally reflect the laser light;

A laser diode spaced apart from the polarization separator and disposed on the silicon substrate, the laser diode emitting polarized laser light with a component perpendicular to the traveling direction of the light;

A first photodetector provided on both sides from above the mounting surface of the laser diode to receive the laser light reflected from the digital video disk, and a laser beam reflected from the digital audio disk to be spaced apart from the first photodetector to receive the light; A second photodetector;

A phase hologram grating integrally formed on an upper surface of the polarization separator to selectively diffract laser light;

Transparent substrates which are formed integrally on the upper surface of the phase hologram grating so as to be opposed to the upper and lower sides of the laser beam focused on the optical disc, and which are installed opposite to the upper and lower sides, and which are provided inside the transparent substrate and to which power is applied. And a light control liquid crystal plate disposed between the transparent electrodes and comprising a hollow liquid crystal plate configured to transmit laser light at different widths depending on whether power is applied thereto;

A wavelength plate integrally disposed on an upper surface of the light control liquid crystal plate and horizontally aligned with the optical disk surface to delay the phase difference of the laser light to convert polarization;

Provided is a light control reflective dual focus optical pickup apparatus comprising an objective lens for focusing laser light via a wave plate onto an optical disk.

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

2 is a block diagram of the present invention,

3 is a view showing in detail the light control liquid crystal panel according to the present invention;

4 is a schematic diagram of an operating state in which the optical system according to the present invention plays a digital video disc;

5 is a schematic diagram of an operating state in which the optical system according to the present invention plays a digital audio disc;

<Explanation of symbols for main parts of drawing>

5: laser diode 12: polarization diffraction portion

18 reflector 20 phase hologram lattice

30: light control liquid crystal plate 32: transparent substrate

34 transparent electrode 36 hollow liquid crystal plate

37: hollow park portion 38: liquid crystal layer

40: wave plate 50: objective lens

60, 70: optical disk 80, 80 ', 90, 90': photodetector

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

As shown in FIG. 2, the present invention provides a silicon substrate 1 installed in parallel with the recording surfaces 65 of the optical discs 60 and 70 and having an optical element thereon, and an upper surface of the silicon substrate 1. A polarization splitter 12 installed at an acute angle to selectively transmit and reflect the laser beam, a reflector 18 totally reflecting the laser beam from the lower side of the polarizer splitter 12, and the polarization splitter ( 12 and a laser diode 5 which is installed on the silicon substrate 1 and spaced apart from the laser diode 5 to emit a laser beam of a predetermined wavelength, and is installed on both sides of the laser diode 5 above the mounting surface. The first light detectors 80 and 80 ', which receive the laser light reflected by the light beams), and the laser light reflected from the digital audio disc 70, are installed inside the first light detectors 80 and 80'. The second photodetectors 90 and 90 'and the upper side of the polarization separator 12 The phase hologram grating 20 is installed horizontally with the optical disks 60 and 70 and selectively diffracts the laser light, and is integrally formed on the upper surface of the phase hologram grating 20 to transmit the laser light at different transmittances depending on the width thereof. The light control liquid crystal plate 30 to be separated and transmitted, the wavelength plate 40 which converts the phase of the laser light integrally on the upper surface of the light control liquid crystal plate 30, and the laser light passing through the wave plate 40 It includes an objective lens 50 to focus on the optical disk (60, 70).

The laser diode 5 emits laser light polarized in a component perpendicular to the traveling direction of the light, for example, S-polarized laser light.

The polarization splitter 12 transmits the laser light having a component parallel to the incident surface and reflects the laser light having a component perpendicular to the incident surface, whereby the S-polarized light emitted from the laser diode 5 It reflects the laser light.

In addition, the light control liquid crystal plate 30 adjusts the outermost incident angles θ1 and θ2 of the laser light focused on the optical discs 60 and 70, and is installed to face the upper and lower sides as shown in FIG. 3. A transparent substrate 32, a transparent electrode 34 provided inside the transparent substrate 32 to which power is applied, and a hollow liquid crystal plate 36 provided between the transparent electrodes 34, The double hollow liquid crystal plate 36 includes a hollow cone-shaped portion 37 formed at a predetermined radius inside thereof, and a liquid crystal layer 38 formed outside of the hollow cone-shaped portion 37 to transmit laser light when voltage is applied thereto.

Therefore, the light control liquid crystal plate 30 adjusts the outermost incident angles θ1 and θ2 of the laser light focused on the optical discs 60 and 70.

Since the outermost incident angles θ1 and θ2 are proportional to the numerical aperture, the amount of light is controlled by the transmittance according to the width, and when the light is focused at different incidence angles on the optical discs 60 and 70, the numerical aperture NA may be adjusted. will be.

The numerical aperture (N.A.) adjusted by this light control liquid crystal plate 30 is arranged as follows.

According to the present invention, the diameters of the light spots focused on the optical discs 60 and 70 are differently determined according to the outermost incident angles θ1 and θ2. When the outermost incident angle irradiated to the digital video disk 60 having a thickness of 0.6 mm is θ2, and the outermost incident angle irradiated to the digital audio disk 70 having a thickness of 1.2 mm is θ1, and the refractive index of the medium is η, The determination of the numerical aperture (NA) is determined by the following equation.

N.A.1 = ηsinθ1 N.A.2 = ηsinθ2

When the refractive index is the same according to Equation 1, the numerical aperture is proportional to the outermost incidence angles θ1 and θ2. When θ2> θ1, the numerical aperture is determined to be N.A.2> N.A.1.

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 60 having a thickness of 0.6 mm, since the track interval and the size of the pit 65 as the signal surface are small, a small optical spot diameter is required, and thus an opening larger than the optical disc 70 having a thickness of 1.2 mm. You will need a number of objectives. At this time, the beam spot diameter can read an optical signal even if it is somewhat larger on the optical disk 70 having a thickness of 1.2 mm, so that the objective lens 50 having a numerical aperture (NA = 0.6) dedicated to the digital video disk 60 can be obtained. As a result, compatible playback will be attempted.

The relationship between the numerical aperture and the light width incident on the objective lens is determined by the following equation. 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, a single objective lens, that is, an objective lens 50 dedicated to a digital video disc, is adopted based on the same focal length, so that the optical signal can be read out without generating spherical aberration on the optical disc 60 having a thickness of 0.6 mm.

However, in this case, when the optical disc 70 having a thickness of 1.2 mm is read out, first, when the focus compensation is not performed, the focusing accuracy is not accurate due to defocus, and 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 numerical aperture is compensated for in the above equations, 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 angles θ1 and θ2 from the light control liquid crystal plate 30 to the optical discs 60 and 70 are adjusted by Equations 1 to 6, the numerical aperture is adjusted so that the optical disc 60 is only 0.6 mm thick. ) The dedicated objective lens 50 can reproduce the optical disk 70 having a thickness of 1.2 mm, and the spherical aberration generated during the compatible playback is reproduced by fighting the narrow laser light, that is, the laser light around the optical axis, so that the effective number of apertures can be adjusted. And compatible playback can be excellent.

Next, a description will be given of the operation of the present invention in which the light control liquid crystal plate 30 capable of adjusting the numerical aperture is adopted as described above.

First, as shown in FIG. 4, a laser beam having a constant wavelength is emitted from the laser diode 5, and the light, which is a component perpendicular to the incident surface with respect to the traveling direction of the laser light, is emitted from the laser diode 5, for example, S polarization is emitted. The phase of the laser light is adjusted so that the laser light is emitted. The polarized laser light is irradiated from the laser diode 5 to the polarization splitter 12. Since the polarization splitter 12 is polarized split coating, the polarized laser beam reflects the S-polarized light which is a vertical component with respect to the incident surface. P-polarized light, which is a horizontal component, is transmitted to the incident surface. Therefore, the laser light incident by the polarization separator 12 is reflected and the optical path is irradiated to the phase hologram grid 20 side. The laser light irradiated in this way is not diffracted via the phase hologram grating 20. This is because the phase hologram grating 20 is grating to diffract only the P-polarized laser light, so that the laser light of S-polarized light, which is incident light, is transmitted without diffraction. Thus, the laser light is irradiated from the phase hologram lattice 20 to the light control liquid crystal plate 30, and the laser light is separately transmitted by the light control liquid crystal plate 30.

At this time, the laser beam passing through the hollow liquid crystal plate 36 of the light control liquid crystal plate 30 is controlled by the hollow liquid crystal plate 36. The transmission is controlled by selectively varying the light intensity distribution of the incident light intensity. When power is applied to the light control liquid crystal panel 30, the liquid crystal layer 38 is separated from the transparent electrode 36 of the light control liquid crystal panel 30. Since the liquid crystal molecules of the liquid crystal layer 38 are arranged in the vertical direction in the electric field direction, the laser light of S polarization can be transmitted, and power is applied to the light control liquid crystal plate 30. If not, since the voltage is not applied to the liquid crystal layer 38 from the transparent electrode 34 of the light control liquid crystal plate 30, the liquid crystal molecules are twisted and oriented in the same direction as the polarization plane of the laser light. It will not be transmitted.

Therefore, the laser beam is separately transmitted from the liquid crystal layer 38 of the hollow liquid crystal plate 36 depending on whether voltage is applied, and the liquid crystal layer 38 and the hollow cone part 37 of the hollow liquid crystal plate 36 are applied when voltage is applied. The laser beam having passed through) is irradiated to the wave plate 40 side, and the linear wave is polarized by the wave plate 40 into circularly polarized light. The laser light polarized by circularly polarized light is the outermost incident angle of the optical plate on the optical axis of the wavelength plate 40 via the objective lens 50, and no voltage is applied to the light control liquid crystal plate 30. If not, the laser beam that does not penetrate the liquid crystal layer 38 and passes only the hollow cone-shaped portion 37 is focused to the outermost incident angle θ1 with respect to the optical axis via the objective lens 50. That is, the laser beams passing through the light control liquid crystal plate 30 have different outermost incident angles θ1 and θ2, respectively, and the wavelength plate 40 has different numerical apertures NA according to Equations 1 to 6 described above. Will pass through at the same time. Thus, the laser light polarized by circularly polarized light through the wavelength plate 40 and the light control liquid crystal plate 30 at the same time and the amount of light is adjusted is irradiated onto the objective lens 50 and focused onto the optical discs 60 and 70.

By the way, the laser light focused by the objective lens 50 via the light control liquid crystal plate 30 with the numerical apertures different from each other when the incident light on the optical disks 60 and 70 is incident to the outermost incident angles θ1 and θ2 of the laser light. The difference in the diameter of the light spot due to the difference of the light is transmitted through the liquid crystal layer 38 is more concentrated than the light is transmitted through the hollow cone-shaped portion 37 of the light control liquid crystal panel 30, the light is focused Becomes small.

Thus, in the case of reproducing each of the optical discs 60 and 70, for example, a 0.6 mm thick digital video disc 60, the optical lens 60 penetrates the liquid crystal layer 38 and has a numerical aperture of 0.6 by the objective lens 50 in the optical axis. With respect to θ2, an optical spot having a size of about 0.8 占 퐉 is formed on the optical disc 60, which interferes with diffraction on the recording surface, thereby reading optical information with the amount of light and the presence or absence of light. At this time, since the objective lens 50 dedicated to the digital video disc 60 is used in the present invention, it is condensed accurately without generating spherical aberration in the recording surface.

When the digital audio disc 70 having a thickness of 1.2 mm is reproduced, as shown in FIG. 5, since no voltage is applied to the light control liquid crystal panel 30, the liquid crystal molecules are arranged to be deflected so that the hollow liquid crystal plate 36 is disposed. The laser beam, which does not transmit the liquid crystal layer 38 of the light source and passes only the hollow cone-shaped portion 37, is polarized by the wavelength plate 40, is focused by the objective lens 50 at a numerical aperture of 0.3, and the optical disk is at θ1 with respect to the optical axis. It is condensed on (60).

Thus, the laser light that reads the optical information on each of the optical disks 60 and 70 in the above-described process is circularly polarized by linearly polarized light while passing through the objective lens 50 and via the wave plate 40. do. At this time, since the linearly polarized laser light is incident on the wavelength plate 40 when the circularly polarized light is reflected on the optical disks 60 and 70, the P wave having the polarization direction perpendicular to the initial wavelength plate 40 is incident. Linearly polarized light. The inverted linearly polarized laser light is irradiated from the wave plate 40 to the phase hologram grating 20 via the light control liquid crystal plate 30, and the phase hologram grating 20 diffracts the laser light of P polarized light. Therefore, the reflected light is diffracted and irradiated to the polarization separator 12. Thus, the laser light of this linearly polarized light is transmitted by the polarization separator 12. Since the transmission is polarized split coating so that the polarization splitter 12 is transmitted to the P wave, the laser beam is transmitted through the polarization splitter 12. Thus, the laser beam transmitted through the polarization separator 12 is irradiated to the reflector 18. Since the path of the laser light is reflected by the reflector 18 and is diffracted by the phase hologram grating 20, the reflected light is induced differently from the optical path different from when it is emitted from the initial laser diode 5. The laser light totally reflected by the reflector 18 with a focus error signal, and the totally reflected laser light is provided on both sides of the first photodetector 80. 80 'and the second photodetector 90, which are provided on both sides of the laser diode 5 above the mounting surface. 90 ', the laser light reflected on the digital video disk 60 of the reflected light is detected by the first photodetector 80. 80', and the laser light reflected on the digital audio disk 70 is the second light. It is detected by detectors 90 and 90 '. At this time, each photodetector (80, 80 'or 90, 90') of the photodetector (80, 90) of the one side is disposed in front of the installation vertical plane of the laser diode (5), the other photodetector (80) ', 90') is disposed rearward, the focus error and the tracking error during the photodetection can be detected due to the light amount difference and the spot difference on each detector (80, 80 ', 90, 90'). In other words, the reflected light reflected on the digital video disk can detect the focusing error from the photodetectors 80 and 80 'disposed forward and backward, and the tracking error can be detected from the reflected light arranged on both sides and detected simultaneously. Therefore, the interference between the reflected light due to the thickness difference of the optical disk from the reflected light detected separately at each photodetector 80, 80 ', 90, 90' can be prevented.

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, the present invention is condensed by the objective lens 50 due to the light control liquid crystal plate 30 which transmits the laser light at different transmittances depending on whether the voltage is applied. The digital video disc is reproduced by forming a light spot, and when the digital audio disc is reproduced, the laser light is transmitted to the hollow shaft 37 and the liquid crystal layer 38 so that the light of the optical axis portion is the outermost incident angle of the digital video disc. Since the spherical aberration caused by the difference in the thickness of the optical disks 60 and 70 is greatly reduced due to the incident of the disk, the optical spot having a larger width of the recording surface is formed on the optical disk 70 because an optical spot having a diameter larger than 1.6 µm is formed. Audio discs can also be played accurately without losing light.

The optical control reflective dual focus optical pickup device 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. B) is actively converted to reduce spherical aberration, so that digital audio and digital video discs can be compatible.

Claims (3)

A silicon substrate 1 installed in parallel with the recording surface 65 of the optical discs 60 and 70 and having an optical element thereon; A polarization separator 12 which is provided at an acute angle on the upper surface of the silicon substrate 1 to transmit laser light having a component parallel to the incident surface and reflects the laser light having a component perpendicular to the incident surface; A reflector 18 which totally reflects the laser light on the lower slope of the polarization separator 12; A laser diode (5) spaced apart from the polarization separator (12) and installed on the silicon substrate (1) and emitting laser light polarized with a component perpendicular to the traveling direction of the light; A plurality of first photodetectors 80, 80 'provided on both sides of an installation surface of the laser diode 5 and receiving laser light reflected from the digital video disk 60; A plurality of second photodetectors 90, 90 'installed inside the first photodetectors 80, 80' and receiving laser light reflected from the digital audio disc 70; A phase hologram lattice 20 integrally installed on the upper side of the polarization separator 12 and horizontally arranged with the optical discs 60 and 70 to selectively diffract laser light; A light control liquid crystal plate 30 formed integrally with the phase hologram grating 20 to separate and transmit the laser light at different transmittances depending on the width thereof; A wavelength plate 40 for converting the phase of the laser light integrally on the upper surface of the light control liquid crystal plate 30; An objective lens 50 for focusing the laser light via the wave plate 40 onto the optical discs 60 and 70; Light control reflective dual focus optical pickup device characterized in that it comprises the component. The light control reflection type dual focus optical pickup of claim 1, wherein the light control liquid crystal panel 30 adjusts the outermost incident angles θ1 and θ2 of the laser light focused on the optical discs 60 and 70. Device. The liquid crystal display device of claim 1, wherein the light control liquid crystal plate 30 is provided with a transparent substrate 32 disposed to face the upper and lower sides, a transparent electrode 34 provided inside the transparent substrate 32 to which power is applied, It is formed between the hollow electrode portion 37 provided between the transparent electrode 34 and formed in a predetermined radius inside and the liquid crystal layer 38 that is formed outside the hollow cone portion 37 and transmits laser light when voltage is applied. Light control reflective dual focus optical pickup device, characterized in that consisting of a hollow liquid crystal plate (36).