KR19980014883A - Polarizing liquid crystal hologram manufacturing method and optical pick-up apparatus using the same - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing liquid crystal hologram (hereinafter, referred to as PLCH) manufacturing method having a grating effect using a liquid crystal, and an optical pickup apparatus using the polarizing liquid crystal hologram A polarizing liquid crystal hologram having a diffraction function is manufactured even after the power is removed by removing the mask after the upper and lower transparent electrodes are formed and the ultraviolet rays are irradiated through the mask so that the optical path difference does not occur at any position and the optical path does not occur, Since the upper and lower transparent electrodes are formed in a flat pattern, there is no need to align them in a specific direction, the number of processes is shortened, the electrode making process is simplified, and the manufacturing process cost can be reduced. Further, by applying the polarizing liquid crystal hologram produced as described above to an optical pickup device, a part of light is excited by diffraction, whereby a linearly polarized light which is not diffracted, and a diffracted light which is diffracted by diffraction, It is possible to simultaneously reproduce different types of optical discs having different thicknesses and recording densities.

Description

Polarizing liquid crystal hologram manufacturing method and optical pick-up apparatus using the same

The present invention relates to a method for manufacturing a PLCH (Polarizing Liquid Crystal Hologram, hereinafter referred to as PLCH) having a grating effect by using a polymer liquid crystal and for reproducing a heterogeneous optical disc using the polymerized liquid crystal hologram And an optical pickup apparatus using the same.

In general, optical disc memory systems have been applied to a wide range of applications for high density and large capacity data recording.

In order to increase the densification, a short wavelength of a light source and a high numerical aperture (NA) of an objective lens for recording / reproducing have been studied.

With these research efforts, a digital video disc (DVD) having a recording capacity of a larger capacity than that of a compact disc (CD) has been developed.

DVDs are not only dense in recording density as compared with CDs, but also have a short distance from the surface of the disc to the information recording surface.

In reality, the distance from the surface of the disc to the information recording surface is 0.6 mm, whereas the CD is 1.2 mm.

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

At this time, the data may be recorded on both sides of the disk, or the recording capacity may be increased by forming the recording surface in two layers.

In these DVDs, effective use of the laser output power is strongly required for a writeable function and a high density.

Recently, polarized beam splitter using a birefringence material has been actively developed.

One of them is a Grating Type Polarized Beam Splitter (GPBS) using a fine-patterned photo-polymerized liquid crystal, and is described in International Symposium on Optical Memory and Optical Data Storage, July 8-12, 1996).

1A to 1C are cross-sectional side views showing a manufacturing process of the GPBS. As shown in FIG. 1A, a top transparent electrode (ITO) 13 of a stripe pattern and a top orientation film (not shown) are formed on a glass substrate 11, And a normal rubbing process is performed on the formed upper alignment film so that the upper alignment film is rubbed in a predetermined direction.

In addition, the lower transparent electrode 14 and the lower alignment film are formed on the lower glass substrate 12, and the lower alignment film formed is subjected to a rubbing process so that the lower alignment film rubs in a direction opposite to the upper alignment film.

The upper and lower glass substrates 11 and 12 are attached to each other by an epoxy seal material 15 such that the upper and lower glass substrates 11 and 12 have a predetermined space and the upper and lower oriented films face each other, Liquid crystal molecules 16 are injected into the space and sealed to form GPBS. When an AC voltage of a square wave is applied to the upper and lower transparent electrodes 13 and 14 of the GPBS thus manufactured and the UV light having an energy density of 10 mW / cm 2 is applied while the AC voltage is applied, The liquid crystal molecules 16 between the facing electrodes are aligned in parallel with the electric field.

Thus, the grating by the refractive index is formed due to the periodic orientation of the liquid crystal molecules 16. [

At this time, since the orientation is frozen by photopolymerization, the grating property is maintained unchanged even after the power source is removed as shown in FIG. 1C.

However, the above-described conventional GPBS requires the alignment of the electrode pattern in a specific direction while making the electrodes of the glass substrate in a stripe shape, so that the electrode making process is difficult and complicated and the cost is increased.

In addition, since there is a portion where the electrode is present and a portion where there is no electrode on the glass substrate, the optical path difference occurs and the performance deteriorates.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to provide a plasma display panel in which upper and lower transparent electrodes are formed in a flat plate shape between upper and lower glass substrates and ultraviolet rays are irradiated through a mask, So that the optical path is constant and does not need to be aligned in a specific direction, and the number of electrode manufacturing processes is shortened.

Another object of the present invention is to provide a polarizing-type liquid-crystal hologram, which is applied to an optical pick-up apparatus, by separating a part of light by diffraction so as to maintain a different numerical aperture according to diffracted light, The present invention provides an optical pickup apparatus using a polarized light liquid crystal hologram capable of accurately condensing a light beam on the surface of optical disks to simultaneously reproduce different types of optical disks.

According to another aspect of the present invention, there is provided a method of fabricating a polarized light hologram, including: sequentially forming an upper transparent electrode and an upper oriented film on a glass substrate, sequentially forming a lower transparent electrode and a lower oriented film on the glass substrate, A step of actually bonding the upper and lower glass substrates so that the upper and lower glass substrates have a certain space and the upper and lower alignment films facing each other and injecting liquid crystal molecules into the space, a step of rubbing the upper and lower glass substrates, A step of disposing a mask pattern on the upper surface of the glass substrate; a step of applying an alternating voltage to the upper and lower transparent electrodes to irradiate a resistive line; and a step of removing the power source and the mask.

An optical pickup apparatus using a polarized light liquid crystal hologram according to the present invention is characterized by including a light source for generating a light beam to be irradiated on a surface of an optical disk and a light source for generating a light beam having a polarization direction of a light beam to be incident on the optical disk, A polarization liquid crystal hologram for diffracting a part of light according to a polarization direction and a mask pattern of a light beam incident from the liquid crystal shutter; And an objective lens for accurately focusing a light beam on the surface of different types of optical disks having different recording densities and thicknesses.

1A to 1C are side sectional views showing a manufacturing process of a conventional grating polarizing beam splitter

2A to 2C are cross-sectional side views showing a manufacturing process of the polarizing-type liquid crystal hologram according to the present invention

3 is a block diagram of an optical pick-up apparatus using the polarization liquid crystal hologram manufactured in FIG.

Description of the Related Art [0002]

21: glass substrate 22: glass substrate

23: Upper transparent electrode 24: Lower transparent electrode

25: Upward alignment film 26: Lower alignment film

27: liquid crystal molecule 28: mask

31: light source 32: liquid crystal shutter

33: collimating lens 34: beam splitter

35: Actuator 36: Polarizing liquid crystal hologram

37: objective lens 38: optical disk

39: sensor lens 40: photodetector

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

2A to 2C are side cross-sectional views illustrating a manufacturing process of a polarizing hologram according to the present invention. As shown in FIG. 2A, an upper transparent electrode 23 and an upper orientation film 25 are sequentially formed in a planar pattern on a glass substrate 21 .

In addition, a lower transparent electrode 24 and a lower orientation film 26 of a flat plate pattern are sequentially formed on the lower glass substrate 22.

At this time, polyimide-based materials are widely used as the polymer materials used for the upper and lower alignment films 25 and 26.

Then, rubbing is performed on the substrate on which the alignment film is formed in order to obtain a uniform and controllable effect of the liquid crystal molecules.

In the rubbing process, a rubbing cloth is formed by attaching rayon or nylon-based fibers to a roll, and then the surface of the alignment film is scratched with respect to a glass substrate on which the alignment film is formed, thereby forming a bend on the surface of the alignment film to determine the alignment direction of the liquid crystal molecules.

The upper and lower glass substrates 21 and 22 are adhered to each other with a sealing material (not shown) so that the upper and lower glass substrates 21 and 22 formed as described above have a certain space and the upper and lower orientation films 25 and 26 face each other, Liquid crystal molecules 27 are injected and sealed.

Then, as shown in FIG. 2B, a mask pattern 28 is placed on the upper surface of the upper glass substrate 21 at predetermined intervals.

Then, when AC voltage is applied to the upper and lower transparent electrodes 23 and 24 as shown in FIG. 2B, the liquid crystal molecules 27 are aligned in parallel with the electric field.

At this time, UV light having an energy density of 10 mW / cm < 2 > is irradiated.

Then, when the power source is removed, as shown in FIG. 2C, there is no mask pattern and the liquid crystal of the UV cured portion is maintained in the aligned state, and the liquid crystal of the portion not UV cured by the mask pattern is returned to the original state.

Then, the mask 28 is removed.

Here, when ultraviolet rays are irradiated to the liquid crystal molecules 27 through the unmasked portion, a part of the ultraviolet rays is diffracted by the mask 28.

That is, the ultraviolet rays are separated into the light that goes straight as it is, and the plurality of diffracted lights which are deflected by the diffraction.

Light that is not diffracted is referred to as zero-order light, diffracted light is referred to as + first-order light, + second-order light, ... in order from the side having a small deflection angle, and light diffracted in the opposite direction -1 st, 2 st, and so on.

Each of the liquid crystal molecules 27 is polymerized by receiving 0-order light and diffracted left and right diffracted light of ± 1st order light.

Therefore, the polarizing liquid crystal hologram is maintained without changing the grating characteristic even after the power source and the mask are removed.

FIG. 3 is a block diagram of an optical pickup device for a heterogeneous optical disc of the present invention in which the polarized-light liquid crystal hologram manufactured in FIG. 2 is applied to an optical pickup device.

3, a light source 31 for generating a light beam to be irradiated to the optical disk 38, an LC shutter 32 for changing the polarization direction of a light beam incident from the light source 31 according to ON / OFF of the electrode, A collimator lens 33 for allowing the light beam incident through the LC shutter 32 to travel in parallel in a predetermined direction, a beam splitter 34 for dispersing the incident light beam, a beam splitter 34 An objective lens 37 for condensing a light beam at a point on the surface of the optical disk 38 and a photodetector 40 for detecting a reflected light beam from the beam splitter 34 and converting the electrical signal.

A sensor lens 39 is provided between the beam splitter 34 and the photodetector 40 and a polarizing liquid crystal hologram 36 is provided between the beam splitter 34 and the objective lens 37, And an actuator 35 for moving the actuator 37 in the horizontal and vertical directions.

Here, the photodetector 40 is an information recording layer 38a and 38b of the optical disk 38, and is reflected by the objective lens 37, the polarization liquid crystal hologram 36, the beam splitter 34, and the sensor lens 39, And converts the reflected light beam into an electrical signal.

The collimator lens 33 allows the light beam passed through the LC shutter 32 to travel in parallel to the beam splitter 34. [

The beam splitter 34 passes the light beam from the collimator lens 33 to the polarization liquid crystal hologram 36 and the objective lens 37 and reflects the reflected light beam incident from the objective lens 37 toward the sensor lens 39 .

The sensor lens 39 condenses the reflected light beam from the beam splitter 34 onto the surface of the photodetector 40.

The collimator lens 33 and the sensor lens 39 improve the sensitivity of the reflected light beam which is lowered as the objective lens 37 moves in the horizontal and vertical directions due to the focus and tracking servo to a certain level.

The LC shutter 32 changes the polarization direction of a light beam incident from the light source 31 in accordance with the type of the optical disc (for example, CD or DVD) in accordance with the power ON / OFF.

The polarizing liquid crystal hologram 36 diffracts a part of light according to the polarization direction of the light beam incident from the LC shutter 32 via the collimator lens 33 and the beam splitter 34 and passes the light to the objective lens 17, Thereby adjusting the diameter of the light beam incident on the lens 17. [

The polarizing liquid crystal hologram 36 is fabricated by forming upper and lower transparent electrodes of a flat plate pattern between the upper and lower glass substrates as shown in FIG. 2, applying power while applying a mask with a predetermined period, and irradiating ultraviolet rays.

Therefore, since the liquid crystal molecules are polymerized by the 0th-order light and the ± 1st-order diffracted light on the right and left, the grating characteristics are maintained even when the mask and the power source are removed.

Thus, the polarizing liquid crystal hologram 36 generates the light beam from the LC shutter 32 as ± first-order light, ± second-order light, and the like which are deflected by zero-order light and diffraction which are not subjected to diffraction, The effect of adjusting the numerical aperture can be obtained.

The objective lens 37 condenses the light beam from the light source 31 onto the first or second information recording surface 38a or 38b of the optical disc 38 in accordance with the diffracted light of that piece and the incident light.

Here, the first information recording surface 38a is the information recording surface of the DVD, the second information recording surface 38b is the information recording surface of the CD, and the second information recording surface 38b is the optical disc 38 ) By a distance of 0.6 mm from the surface.

That is, the objective lens 37 maintains the numerical aperture of 0.35 by zero-order light which is not rotated in the polarization liquid crystal hologram 36, so that the light beam is focused on the second information recording surface 38b of the optical disk 38. [

On the other hand, the objective lens 37 maintains the numerical aperture of 0.6 by the diffracted light which is diffracted and deflected in the polarization liquid crystal hologram 36 so that the light beam is condensed on the first information recording surface 38a of the optical disk 38 do.

As described above, according to the method of manufacturing a polarized light liquid crystal hologram according to the present invention and the optical pickup device using the same, upper and lower transparent electrodes are formed in a flat plate shape between upper and lower glass substrates, ultraviolet rays are irradiated through a mask, The polarized light hologram having the diffraction function can be manufactured so that the optical path difference does not occur at any position and the optical path difference does not occur so that the performance is not deteriorated and the upper and lower transparent electrodes are formed in the flat plate pattern, Thereby reducing the number of processes and simplifying the electrode manufacturing process and reducing the manufacturing process cost.

Further, by applying the polarizing-type liquid crystal hologram produced as described above to the optical pickup apparatus, a part of the light is refracted by diffraction, whereby a different numerical aperture is maintained in accordance with diffracted light which is deflected by diffraction, It is possible to simultaneously reproduce different types of optical disks having different thicknesses and recording densities.

Claims (6)

Forming an upper transparent electrode and an upper oriented film on the glass substrate in order; Forming a lower transparent electrode and a lower orientation film on the lower glass substrate in order; A step of injecting liquid crystal molecules into the space by vertically bonding the upper and lower glass substrates so that the upper and lower glass substrates have a certain space and the upper and lower alignment films face each other; A step of rubbing the upper and lower glass substrates; Placing the mask pattern on the upper surface of the upper glass substrate at predetermined intervals; Applying an alternating voltage to the upper and lower transparent electrodes and irradiating ultraviolet rays; And removing the power source and the mask. The method of claim 1, wherein the upper and lower transparent electrodes are formed in a flat plate pattern. A light source for generating a light beam to be irradiated onto the surface of the optical disk; A liquid crystal shutter positioned between the light source and the optical disc and selectively changing the polarization direction of a light beam to be incident on the optical disc according to the type of the optical disc; A polarization liquid crystal hologram for diffracting a part of light according to a polarization direction of a light beam incident from the liquid crystal shutter and a mask pattern; And an objective lens for holding a different numerical aperture according to the diffracted light to accurately condense a light beam on a surface of a different type of optical disk having different recording densities and thicknesses. The polarizing liquid crystal hologram according to claim 3, wherein the polarizing liquid crystal hologram is formed by forming upper and lower transparent electrodes of a flat plate pattern between upper and lower glass substrates, applying power while applying a mask with a predetermined period, and irradiating ultraviolet rays. Pickup device. [4] The optical pickup apparatus of claim 3, wherein the polarizing liquid crystal hologram is polymerized by liquid crystal molecules by zero order light and ± first order diffracted light. 6. The optical pick-up apparatus according to claim 5, wherein the grating characteristic of the polarization liquid crystal hologram is maintained unchanged even after power is removed.