KR19980021640A - Liquid crystal plate and optical pickup device using same - Google Patents

Abstract

The cholesteric liquid crystal molecules are arranged in a spiral to the pitch (P) / 2 thickness of the liquid crystal layer to prepare a liquid crystal plate, and the cholesteric liquid crystal (CLC) plates thus prepared are applied to an optical pickup device to thereby be compatible with heterogeneous optical disks. The present invention relates to a liquid crystal plate capable of recording / reproducing and an optical pickup device using the same, and particularly, to cholesteric liquid crystal molecules arranged in a spiral structure up to a liquid crystal layer having a pitch / 2 thickness to form a liquid crystal plate, and supplying reflection conditions or voltage. By selectively passing or reflecting part of the light depending on whether it is present or not, compatibility with light reflection and transmission is realized so that there is no deformation of the plate to accurately record and read information on the optical disc, and there is no hysteresis, so that the optical disc is inserted. The warm-up time is shortened and no heat is generated by the light reflection, which extends the life of the pick-up unit. , And the objective lens has the compatibility between the disk that can be played on both the two kinds of the optical disc by maintaining a different numerical aperture can be accurately converging a light beam on the surface of the optical disk according to a heterogeneous reflection or passage of the light.

Description

Liquid crystal plate and optical pickup device using same

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device for heterogeneous optical disks. In particular, a cholesteric liquid crystal molecule is spirally arranged to a pitch (P) / 2 liquid crystal layer thickness to produce a liquid crystal plate, and the cholester thus produced. The present invention relates to a liquid crystal plate and an optical pickup device using the same, by applying a liquid crystal plate (CLC) plate to an optical pickup device to enable compatible recording / playback between different optical discs.

In recent years, optical discs have been recorded by digital video discs having a larger recording capacity than conventional compact discs (hereinafter referred to as CDs) due to continuous development efforts to increase recording capacity. Has been developed.

A DVD has a higher recording density than a CD and a shorter distance from the surface of the disc to the information recording surface. In fact, a DVD has a distance of 0.6 mm from the surface of the disc to the information recording surface, while a CD has 1.2 mm.

The CD has a track pitch of 1.6 µm, a pit length of 0.834 µm, a light source of 780 nm, an objective lens of 0.45, while a DVD has a track pitch of 0.74 µm, a pit length of 0.4 µm, and a wavelength of light source. The numerical aperture of the objective lens is 650 nm and 0.60.

That is, the recording capacity of a DVD is 6 to 8 times that of a CD, and video and audio data compression is used, and one film of the same image quality as that of the current TV broadcast is recorded on a disc having a diameter of 120 mm.

At this time, the data may be recorded on both sides of the disc or the recording surface may be formed in two layers to increase the recording capacity.

In addition, considering that a large amount of software in a CD format is used, a DVD needs to be able to play a CD. In other words, higher regeneration compatibility must be ensured.

In order to have such high compatibility, an electric control device (ECD) has been conventionally used for the optical pickup apparatus.

That is, the ECD was manufactured by forming a transparent electrode between two substrates and inserting an electrolyte between the formed transparent electrodes.

The ECD manufactured in this way is colored by applying a direct current to the transparent electrode, absorbs light, and then decolorized by passing a direct current in the opposite direction to the ECD and passes through the light, thereby adjusting the beam diameter incident on the objective lens to control the numerical aperture of the objective lens. Was adjusted.

Therefore, all of the optical disks having different thicknesses and recording densities of the substrate could be accessed.

However, the conventional ECD has a problem in that deformation of the plate occurs due to light absorption, and thus the beam quality is deteriorated, so that the recording to the optical disc and the reproduction from the optical disc are not accurately performed.

In addition, hysteresis occurs in light absorption and transmission, that is, the response time is slow, the time difference between the time of coloring and discoloration is about 10 times, there was a problem that the time to warm up when the disc is inserted.

In addition, heat is generated due to light absorption, which shortens the life of the pickup apparatus.

The present invention is to solve the above problems, an object of the present invention is to prepare a liquid crystal plate by arranging the cholesteric liquid crystal molecules of each side in a spiral structure to the pitch (P) / 2 liquid crystal layer thickness as an objective lens By adjusting the beam diameter of the incident light beam, there is no deformation of the plate, no hysteresis, and no heat is generated by the light reflection, thereby providing a CLC plate extending the life of the pick-up apparatus.

Another object of the present invention is to apply heterogeneous optical disks having different thicknesses and recording densities by applying the CLC plate to an optical pickup device instead of ECD and maintaining different numerical apertures by reflecting or transmitting a part of light depending on the reflecting conditions. An optical pickup device using a CLC plate capable of reproducing all is provided.

Another object of the present invention is to apply the CLC plate to an optical pickup device instead of ECD and to maintain a different numerical aperture by reflecting or transmitting a part of light depending on whether the CLC plate is supplied with power to the transparent electrode. An optical pickup apparatus using a CLC plate capable of reproducing all kinds of optical discs having different recording densities.

Features of the liquid crystal plate according to the present invention for achieving the above object, the process of forming the upper and lower transparent electrodes between the upper and lower glass substrates, and the cholesteric liquid crystal molecules to the predetermined liquid crystal layer between the upper and lower transparent electrodes in a spiral structure CLC plate is formed including the process of arranging, and it reflects or passes a part of incident light according to a reflection condition.

Another feature of the CLC plate according to the present invention includes a process of forming a vertical transparent electrode between upper and lower glass substrates, and a process of arranging cholesteric liquid crystal molecules in a spiral structure to a predetermined liquid crystal layer between the upper and lower transparent electrodes. It forms a plate and reflects or passes a part of the incident light depending on the presence or absence of voltage supply to the upper and lower transparent electrodes.

A feature of the optical pickup device according to the present invention is that a polarization direction of a light source for generating a light beam to be irradiated on the surface of the optical disk, and a light beam positioned between the light source and the optical disk to be incident toward the optical disk, depends on the type of optical disk. A liquid crystal shutter that selectively changes according to the polarization, a polarizer that converts linearly polarized beams incident from the liquid crystal shutters into circularly polarized beams, and cholesteric liquid crystal molecules are arranged in a spiral structure up to a predetermined liquid crystal layer, CLC plate that reflects or passes a part of incident light, and an object that accurately condenses a light beam on the surface of heterogeneous optical discs having different recording densities and thicknesses by maintaining different numerical apertures according to the amount of light selectively passing through the CLC plate. It is configured to include a lens.

Another feature of the optical pickup device according to the present invention is a light source for generating a light beam to be irradiated on the outer surface of the optical disk, a collimating lens for allowing the light beam generated from the light source to proceed in parallel in a predetermined direction, and incident from the collimating lens A beam splitter for dispersing the light beams, a top and bottom substrate, and a top and bottom transparent electrode are formed in this order, and cholesteric liquid crystal molecules are arranged in a spiral structure up to a predetermined liquid crystal layer thickness between the top and bottom transparent electrodes, depending on whether a voltage is supplied to the transparent electrode. The CLC plate reflects or passes a part of the light incident from the beam splitter, and maintains the numerical aperture according to the amount of light selectively passing through the CLC plate, so that the optical beam is accurately reflected on the surface of the heterogeneous optical discs having different recording densities and thicknesses. It is comprised including the objective lens which condenses.

1A to 1C are cross-sectional views illustrating a manufacturing process of a liquid crystal plate according to the present invention.

FIG. 2 is a block diagram of an optical pickup apparatus according to a first embodiment of the present invention using the liquid crystal plate manufactured in FIG.

3 is a block diagram of an optical pickup apparatus according to a second embodiment of the present invention using the liquid crystal plate manufactured in FIG.

Explanation of symbols for main parts of the drawings

21: light source 22: liquid crystal shutter

23 collimating lens 24 beam splitter

25 polarization converter 26 cholesteric liquid crystal plate

27: actuator 28: objective lens

29: optical disc 29a: first information recording surface

29b: second information recording surface 30: sensor lens

31: light detector

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

Fig. 1A shows the cell structure of the CLC plate, which shows whether the non-liquid crystal region 10 in the center passes light beams unconditionally and whether the power is supplied to the reflective condition or the transparent electrode regardless of the reflection condition or the power supply to the transparent electrode. Thus, it is divided into an edged hatched liquid crystal region 12 that reflects or transmits a light beam.

Unexplained reference numeral 26 is a CLC plate, and 13 is a laser beam which is a light source.

FIG. 1B is a cross-sectional view showing the arrangement structure of the cholesteric liquid crystal molecules of the liquid crystal region 12 of FIG. 1A, wherein the liquid crystal molecules 14 on each side have a spiral structure up to the pitch P / 2 liquid crystal layer thickness. .

That is, the direction of the CLC array varies for each liquid crystal plane, and as the depth of the liquid crystal plane increases, the alignment direction of the liquid crystal molecules is rotated to the left.

Here, the pitch P represents the thickness of the liquid crystal layer until the spiral arrangement of the liquid crystal molecules is rotated 360 °, so P / 2 is the half-pitch, that is, the thickness of the liquid crystal layer until the spiral arrangement of the liquid crystal molecules is rotated 180 °. Indicates.

In other words, the liquid crystal array direction on the lowermost side and the liquid crystal array direction on the uppermost side are 180 degrees different.

And a wavelength λ _C = _a n × p of the CLC.

Here n _a is the average refractive index of CLC.

Figure 1c is a side cross-sectional view of the CLC plate according to the present invention, the cholesteric liquid crystal molecules arranged in the upper and lower transparent electrodes 16 between the upper and lower glass or plastic substrate 15, and arranged as shown in Figure 2b between the upper and lower transparent electrodes It is made by injecting the field (14).

The state of the cholesteric liquid crystal molecules of FIG. 1c shows a 180 ° rotation without applying voltage to the transparent electrode 16.

Since the CLC plate 26 manufactured as described above does not pass through the cholesteric liquid crystal molecules when the reflection condition is satisfied in the state where no voltage is applied to the transparent electrode, the light reflects all the light and the light is reflected when the reflection condition is not satisfied. Permeate everything.

That is, the wavelength λ _C = n _a × p of the wavelength λ _LD = CLC of the light source,

If the circular polarization rotational direction incident on the CLC and the rotational direction of the CLC are the same, the reflection condition is satisfied.

On the other hand, if there is no liquid crystal shutter (LCS) for converting the polarization direction of the light and the polarization converter for converting the linearly polarized light or the circularly polarized light into the linearly polarized light, power is supplied to the transparent electrode 16 of the CLC plate 26. It is supplied or blocked to reflect or transmit incident light.

That is, when no voltage is applied to the transparent electrode 16 of the CLC plate 26 in the absence of the LCS and the polarization converter, the array of cholesteric liquid crystal molecules is rotated to the left as shown in FIG. When all the light is reflected and voltage is applied to the transparent electrode 16, the array of liquid crystal molecules is aligned in the direction of the electrode, thereby transmitting all incident light.

Fig. 2 is a block diagram of the optical pickup device using the LCS, the polarization converter, and the CLC plate as the first embodiment of the present invention.

2, a light source 21 for generating a light beam to be irradiated on the optical disk 29, and an LC shutter 22 for changing the polarization direction of the light beam incident from the light source 21 according to on / off of the electrode. And a collimator lens 23 for allowing the light beam incident through the LC shutter 22 to proceed in parallel in a predetermined direction, a beam splitter 24 for dispersing the incident light beam, and a beam splitter 24. A polarization transducer 25 for converting the linearly polarized beam passing through the circularly polarized beam, a CLC plate 26 for selectively reflecting or transmitting a part of light, and an optical beam passing through the CLC plate 26 for the optical disk 29 And an objective lens 28 for condensing at one point on the surface of the X-ray and a photodetector 31 for detecting the reflected light beam from the beam splitter 24 and converting it into an electrical signal.

A sensor lens 30 is provided between the beam splitter 24 and the photo detector 31, and an actuator 27 is provided to move the objective lens 28 in the horizontal and vertical directions.

The polarization transducer 25 uses a λ / 4 plate.

The LC shutter 23 changes the polarization direction of the light beam incident from the light source 21 according to on / off of the power source, that is, according to the type of the optical disk (for example, CD or DVD).

The first information recording surface 29a of the optical disc 29 is an information recording surface of a DVD, the second information recording surface 29b is an information recording surface of a CD, and the second information recording surface 29b is a first information recording surface ( Is positioned 0.6 mm further from the surface of the optical disk 29 than 29a).

In the first embodiment of the present invention configured as described above, for the convenience of description, a P-wave light beam is generated from the light source 21 and incident on the LC shutter 23, and when power is not supplied to the LC shutter 23, the S-wave is converted. It is assumed that the P wave is incident to the beam splitter 24 as it is when the light is incident on the beam splitter 24 and power is supplied.

The direction of polarization converted according to the polarization direction of the light beam generated from the light source 21 and whether or not power is supplied to the LC shutter 23 may vary depending on the design.

That is, when a P-wave light beam is generated from the light source 21 and incident on the collimating lens 22, the collimating lens 22 causes the light beam passing through the LC shutter 23 to travel in parallel to the beam splitter 24. .

At this time, if power is not supplied to the LC shutter 23, the P-wave, which is a linearly polarized beam, is converted into an S-wave and is incident to the beam splitter 24.

The S-wave is incident to the [lambda] / 4 plate which is the polarization transducer 25 through the beam splitter 24, and when the S-wave passes through the polarization transducer 25, it is converted into the left rotating circularly polarized light.

The left rotating circularly polarized light converted by the polarization transducer 25 is incident on the CLC plate 26.

At this time, since the circularly polarized light incident on the CLC plate 26 is the left rotating circularly polarized light and the rotation direction of the cholesteric liquid crystal molecules of the CLC plate 26 is the left rotating direction, the wavelength λ _LD of the light source λ _C = n _a × If p is left, the left circularly polarized light incident on the CLC plate 26 satisfies the reflection condition and thus cannot be passed through the cholesteric liquid crystal molecules of the liquid crystal molecule region 12.

Therefore, the left-rotating circularly polarized beam passes through only the non-liquid crystal region 10 of the CLC plate 26 without the arrangement of the cholesteric liquid crystal molecules and enters the objective lens 28, thereby reducing the beam diameter of the light beam.

When the beam diameter of the light beam is reduced, the objective lens 28 reduces the numerical aperture (i.e. 0.45) so that the left rotating circularly polarized light beam incident through the CLC plate 26 receives the second information recording surface 29b of the optical disc 29. In other words, the information is condensed on the information recording surface of the CD so that the information can be accurately recorded on the CD or the recorded information can be accessed accurately.

This is due to the light beam being irradiated only to the center portion of the objective lens 28.

On the other hand, when power is supplied to the LC shutter 23, the light beam of P wave generated from the light source 21 is incident on the beam splitter 24 as it is through the collimating lens 22 and the LC shutter 23.

The P-wave, which is the linearly polarized beam, is incident on the λ / 4 plate, which is the polarization converter 25, through the beam splitter 24, and is converted to right-circular circular polarization when the P-wave passes through the polarization converter 25.

The right-handed circularly polarized light converted by the polarization transducer 25 is incident on the CLC plate 26.

At this time, since the circularly polarized light incident on the CLC plate is the right rotating circularly polarized light and the rotation direction of the cholesteric liquid crystal molecules of the CLC plate 26 is the left rotating direction, the wavelength of the light source λ _LD = the wavelength of the CLC λc = n _a × p is satisfied. Irrespective of the reflection condition, it is not satisfied.

Accordingly, the right-handed circularly polarized light incident on the CLC plate 26 passes through both the liquid crystal molecule region 12 in which the cholesteric liquid crystal molecules are arranged and the non-liquid crystal region 10 having no cholesteric liquid crystal molecules to the objective lens 28. Since it is incident on the beam beam, the beam diameter of the light beam is not reduced.

When the beam diameter of the light beam is not reduced, the objective lens 28 maintains the original numerical aperture (i.e., 0.6) so that the right-turning circularly polarized beam incident through the CLC plate 26 is supplied with the first information recording surface of the optical disk 29. (29a) That is, the information is condensed on the information recording surface of the DVD so that the information can be recorded accurately on the DVD or the recorded information can be accessed correctly.

This is due to the light beam being irradiated to the edge as well as the center portion of the objective lens 28.

The collimating lens 23 causes the light beam passing through the LC shutter 22 to travel in parallel to the beam splitter 24.

The beam splitter 24 passes the light beam from the collimation lens 23 toward the polarization converter 25, the CLC plate 26, and the objective lens 28, and senses the reflected light beam incident from the objective lens 28. Reflect toward the lens 30.

The sensor lens 30 focuses the reflected light beam from the beam splitter 24 on the surface of the photo detector 31.

The collimating lens 23 and the sensor lens 30 improve the sensitivity of the reflected light beam that decreases as the objective lens 28 moves in the horizontal and vertical directions due to the focusing and tracking servo.

The actuator 27 moves the pickup device up, down, left, and right so that the focus of the light beam is accurately formed on the first or second information recording surface 29a or 29b, and the light beam is formed on the first or second information recording surface 29a or 29b. Follow the information on the page correctly.

The photo detector 31 converts the reflected light beam incident through the sensor lens 30 into an electrical signal to obtain a high frequency signal, a focus error signal, and a tracking error signal.

3 is a block diagram of an optical pickup apparatus using a CLC plate in a state in which there is no LCS and a polarization converter as a second embodiment according to the present invention.

3, a light source 41 for generating a light beam to be irradiated to the optical disk 47, a collimating lens 42 for allowing the light beam generated from the light source 41 to travel in parallel in a predetermined direction, and an incident light beam A beam splitter 43 for dispersing the light beam, a CLC plate 45 for selectively reflecting or transmitting a portion of the light passing through the beam splitter 43 according to the presence or absence of power, and a light beam passing through the CLC plate 45. An objective lens 46 for condensing at one point on the surface of the optical disk 47, and a photo detector 49 for detecting the reflected light beam from the beam splitter 43 and converting it into an electrical signal.

A sensor lens 48 is provided between the beam splitter 43 and the photo detector 49, and an actuator 44 for moving the objective lens 46 in the horizontal and vertical directions.

The first information recording surface 47a of the optical disc 47 is an information recording surface of a DVD, the second information recording surface 47b is an information recording surface of a CD, and the second information recording surface 47b is a first information recording surface 47a. More than 0.6 mm away from the surface of the optical disk 47.

In the second embodiment of the present invention configured as described above, when a light beam is generated from the light source 41 and incident on the collimating lens 42, the collimating lens 42 causes the light beam to travel toward the beam splitter 43 in parallel.

The light beam passing through the beam splitter 43 is incident on the CLC plate 45.

At this time, if the voltage is not applied to the transparent electrode 16 of the CLC plate 45, since the arrangement of the cholesteric liquid crystal molecules is rotated to the left direction, the incident light beam is the cholesteric liquid crystal molecules of the liquid crystal molecule region 12. It does not pass through them and is totally reflected.

Therefore, since the incident light beam passes through only the non-liquid crystal region 10 of the CLC plate 45 and enters the objective lens 46, the beam diameter of the light beam is reduced.

When the beam diameter of the light beam is reduced, the objective lens 46 decreases the numerical aperture (i.e. 0.45), so that the light beam incident through the CLC plate 45 is transferred to the second information recording surface 47b of the optical disc 47, that is, CD. The information is recorded on the CD's information recording surface to accurately record the information on the CD or to access the recorded information correctly.

This is due to the light beam being irradiated only to the center portion of the objective lens 46.

On the other hand, when power is supplied to the CLC plate 45, the array of cholesteric liquid crystal molecules is aligned in the direction of the electrode.

Therefore, since the light beam incident on the CLC plate 45 passes through both the liquid crystal molecule region 12 and the non-liquid crystal region 10 in which the cholesteric liquid crystal molecules are arranged and enters the objective lens 46, the beam beam diameter of the light beam is decreased. Not reduced.

When the beam diameter of the light beam is not reduced, the objective lens 46 maintains the original numerical aperture (i.e., 0.6) and transmits the light beam incident through the CLC plate 45 to the first information recording surface 47a of the optical disc 47. In other words, the information is condensed on the information recording surface of the DVD so that the information can be recorded accurately on the DVD or the recorded information can be accessed accurately.

This is due to the light beam being irradiated to the edge as well as the center portion of the objective lens 46.

The beam splitter 43 passes the light beam from the collimation lens 42 toward the CLC plate 45 and the objective lens 46, and reflects the reflected light beam incident from the objective lens 46 toward the sensor lens 48. Let's do it.

The sensor lens 48 condenses the reflected light beam from the beam splitter 43 on the surface of the photo detector 49.

The collimating lens 42 and the sensor lens 48 improve the sensitivity of the reflected light beam that decreases as the objective lens 46 moves in the horizontal and vertical directions due to the focusing and tracking servo.

The actuator 44 moves the pickup apparatus up, down, left, and right so that the focus of the light beam is accurately formed on the first or second information recording surface 47a or 47b, and the light beam is formed on the first or second information recording surface 47a or 47b. Follow the information on the page correctly.

The photo detector 49 converts the reflected light beam incident through the sensor lens 48 into an electrical signal to obtain a high frequency signal, a focus error signal, and a tracking error signal.

As described above, according to the liquid crystal plate and the optical pickup device using the same, the cholesteric liquid crystal molecules are arranged in a helical structure up to the pitch / 2 liquid crystal layer to form a CLC plate, depending on the reflection condition or the supply of voltage. By selectively passing or reflecting a part of the light, compatibility with light reflection and transmission is realized so that there is no deformation of the plate, and thus no degradation of the beam occurs, thereby accurately recording and reading information onto the optical disc. .

In addition, since there is no hysteresis, the warm-up time when the optical disk is inserted is shortened and heat is not generated due to light reflection, thereby extending the life of the pickup apparatus.

In addition, by applying such a CLC plate to the optical pickup device by reflecting or passing a part of the light according to the reflecting conditions or the presence or absence of power supply, the objective lens maintains a different numerical aperture in accordance with the reflection or passage of light, the heterogeneous optical disk Since the light beam can be accurately focused on the surface of the field, it is compatible with each other that can reproduce all kinds of optical discs.

Claims (22)

Forming a cholesteric liquid crystal plate by forming a vertical transparent electrode between the upper and lower glass substrates, and arranging cholesteric liquid crystal molecules in a spiral structure between the upper and lower transparent electrodes to a predetermined liquid crystal layer thickness, and A liquid crystal plate, characterized in that for reflecting or passing a portion of the incident light according to the reflection conditions in the state that the voltage is not supplied to the electrode. The cholesteric liquid crystal plate of claim 1, wherein the cholesteric liquid crystal plate is formed at a central portion to pass light beams unconditionally regardless of reflection conditions, and the cholesteric liquid crystal molecules are arranged in a spiral structure around the non-liquid crystal region. And divided into liquid crystal regions for reflecting or passing light beams according to reflection conditions. The liquid crystal plate of claim 1, wherein the liquid crystal layer has a thickness until the array of cholesteric liquid crystal molecules is rotated 180 °. The method of claim 1, wherein the cholesteric liquid crystal plate has a wavelength λ _LD of a light source and a wavelength λ _C of a cholesteric liquid crystal, and the rotation direction of the incident circularly polarized light and the cholesteric liquid crystal molecules are the same. A liquid crystal plate characterized by reflecting circularly polarized beams incident upon satisfying reflection conditions. The wavelength λ _C of the cholesteric liquid crystal is a thickness p until the refractive index n _a of the cholesteric liquid crystal and the spiral arrangement of the cholesteric liquid crystal molecules rotate 180 °. Liquid crystal panel characterized in that the multiplied value. The cholesteric liquid crystal panel of claim 1, wherein the cholesteric liquid crystal plate has a wavelength λ _LD of the light source and a wavelength λc of the cholesteric liquid crystal plate that are not equal to each other, or that the circular polarization rotation direction and the rotation direction of the cholesteric liquid crystal molecules are incident. If it is not equal to the liquid crystal plate characterized in that it passes through the circularly polarized beam that is not satisfied the reflection conditions. Forming a cholesteric liquid crystal plate, including forming a vertical transparent electrode between the upper and lower glass substrates, and arranging the cholesteric liquid crystal molecules in a spiral structure between the upper and lower transparent electrodes to a predetermined liquid crystal layer thickness. A liquid crystal plate characterized by reflecting or passing part of the incident light depending on whether or not a voltage is supplied to the transparent electrode. The non-liquid crystal region of claim 7, wherein the cholesteric liquid crystal plate is formed at a central portion to pass light beams unconditionally regardless of the voltage supply, and the cholesteric liquid crystal molecules have a spiral structure around the non-liquid crystal region. And a liquid crystal region arranged to reflect or pass an incident light beam according to whether a voltage is supplied to the transparent electrode. The liquid crystal plate of claim 7, wherein the liquid crystal layer has a thickness until the spiral arrangement of the clesteric liquid crystal molecules is rotated 180 °. The liquid crystal panel of claim 7, wherein the cholesteric liquid crystal plate reflects light incident upon being arranged in a helical structure when voltage is not applied to the upper and lower transparent electrodes. The liquid crystal panel of claim 7, wherein the cholesteric liquid crystal plate is configured to pass an incident light by aligning an array of liquid crystal molecules when the voltage is applied to the upper and lower transparent electrodes. A light source generating a light beam to be irradiated to the surface of the optical disk, a liquid crystal shutter positioned between the light source and the optical disk to selectively change the polarization direction of the light beam incident on the optical disk according to the type of the optical disk; A polarization transducer that converts the linearly polarized beam incident from the shutter into a circularly polarized beam, and cholesteric liquid crystal molecules are arranged in a spiral structure up to a predetermined liquid crystal layer thickness to reflect or pass a part of the light incident from the polarization transducer according to the reflecting conditions. A cholesteric liquid crystal plate, and an objective lens for accurately condensing a light beam on the surface of heterogeneous optical discs having different recording densities and thicknesses by maintaining different numerical apertures according to the amount of light selectively passing through the cholesteric liquid crystal plate. Optical pickup device, characterized in that configured by. The non-liquid crystal region of claim 12, wherein the cholesteric liquid crystal plate is formed at a central portion to pass the light beam unconditionally regardless of reflection conditions, and the cholesteric liquid crystal molecules are arranged in a spiral structure around the non-liquid crystal region. And divided into liquid crystal regions for reflecting or passing light beams according to reflecting conditions. The optical pickup apparatus of claim 12, wherein the liquid crystal layer of the cholesteric liquid crystal plate has a thickness until the spiral arrangement of the cholesteric liquid crystal molecules is rotated 180 degrees. The cholesteric liquid crystal plate of claim 12, wherein the cholesteric liquid crystal plate reflects light when the wavelength λ _LD of the light source and the wavelength λc of the cholesteric liquid crystal are the same and the rotation direction of the incident circularly polarized light and the rotation direction of the cholesteric liquid crystal molecules are the same. An optical pickup apparatus characterized by reflecting an incident circularly polarized beam satisfying a condition. The wavelength λc of the cholesteric liquid crystal is obtained by multiplying the refractive index n _a of the cholesteric liquid crystal by the thickness p until the spiral arrangement of the cholesteric liquid crystal molecules is rotated 180 °. Optical pickup device, characterized in that the value. 13. The method of claim 12, wherein the cholesteric liquid crystal plate has a wavelength λ _LD of a light source and a wavelength λc of a cholesteric liquid crystal plate not equal to each other, or a circular polarization rotation direction and a rotation direction of cholesteric liquid crystal molecules incident thereto. If not equal to the optical pickup device characterized in that passing through the incident circularly polarized beam does not satisfy the reflection conditions. A light source for generating a light beam to be irradiated on the surface of the optical disk, a collimating lens for allowing the light beam generated from the light source to proceed in parallel in a predetermined direction, a beam splitter for dispersing the light beam incident from the collimating lens, the upper and lower substrates and the vertical substrate Transparent electrodes are formed in sequence and cholesteric liquid crystal molecules are arranged in a spiral structure to a predetermined liquid crystal layer thickness between upper and lower transparent electrodes, thereby reflecting or passing a part of the light incident from the beam splitter depending on whether or not voltage is supplied to the transparent electrodes. A cholesteric liquid crystal plate and an objective lens for accurately concentrating a light beam on the surface of heterogeneous optical discs having different recording densities and thicknesses by maintaining different numerical apertures according to the amount of light selectively passing through the cholesteric liquid crystal plate. Optical pickup device, characterized in that configured. 19. The non-liquid crystal liquid crystal panel of claim 18, wherein the cholesteric liquid crystal plate is formed at a central portion to pass light beams unconditionally regardless of the voltage supply, and the cholesteric liquid crystal molecules have a spiral structure around the non-liquid crystal region. And an optical pickup device arranged in a liquid crystal region arranged to reflect or pass an incident light beam depending on whether a voltage is supplied to the transparent electrode. 19. The optical pickup apparatus according to claim 18, wherein the liquid crystal layer of the cholesteric liquid crystal plate has a thickness until the spiral arrangement of the cholesteric liquid crystal molecules is rotated 180 degrees. 19. The optical pickup apparatus of claim 18, wherein the cholesteric liquid crystal plate reflects the incident light by forming liquid crystal molecules in a helical structure when voltage is not applied to the upper and lower transparent electrodes. 19. The optical pickup apparatus of claim 18, wherein the cholesteric liquid crystal plate applies voltage to the upper and lower transparent electrodes so that an array of liquid crystal molecules is aligned in an electrode direction and passes through incident light.