KR100244223B1 - Manufacturing method of the polarizing liquid crystal hologram and optical pickup device thereof - Google Patents

Abstract

In particular, the present invention relates to a method of manufacturing a polarizing liquid crystal hologram (hereinafter referred to as PLCH) for etching a glass substrate into a predetermined pattern and having a grating effect by liquid crystal injection and polarized light irradiation, and particularly, an optical pickup device using the same. It is not necessary to fabricate the electrode by bonding the upper glass substrate of the flat plate pattern and the lower glass substrate etched directly into a predetermined pattern and irradiating the 0 wave and the E wave after the liquid crystal injection and living process to have a graffiti effect due to refractive power without supplying power. In addition, there is no need to supply power, which shortens and simplifies the number of PLCH manufacturing processes and lowers the manufacturing process costs. In addition, since there is no optical path difference because the optical path is the same at any position, performance is not degraded, and since the glass substrate is directly etched without using a polymer, the temperature range of which is high in reliability is almost unaffected by temperature change. The polarized liquid crystal hologram applied to the optical pickup device diffracts a part of the light according to the polarization characteristic of the light beam, thereby maintaining different numerical apertures according to the straight light that is not diffracted and the diffracted light that is deflected by refraction. Since the light beam can be accurately focused on the surface of the field, heterogeneous optical disks can be played simultaneously.

Description

Manufacturing method of polarizing liquid crystal hologram and optical pickup device using same

The present invention is a method for manufacturing a polarizing liquid crystal hologram (hereinafter referred to as PLCH) to have a grating effect by liquid crystal injection and polarization irradiation after directly etching the glass substrate. An optical pickup apparatus which applies PLCH to an optical pickup apparatus so that heterogeneous optical disks can be reproduced simultaneously.

In general, optical disk memory systems have been expanded in application, and research for high density and large data recording is continued.

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

This research has led to the development of Digital Video Discs (DVDs) with a larger recording capacity than Compact Discs (CDs).

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.

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 such DVDs, effective use of laser output power is strongly required for writeable functions and high density.

To this end, polarized beam splitters using birefringence materials have recently been actively developed.

One of them is a grating type polarized beam splitter (GPBS) using fine-patterned photo-polymerized liquid crystal, which is an international Symposium on Optical Memory and Optical Data. Storage, July 8-12, 1996).

1A to 1C are side cross-sectional views illustrating a manufacturing process of the GPBS, and as shown in FIG. 1A, a phase-transparent electrode (ITO) 13 and a phase alignment film (stripe pattern) are formed on the upper glass substrate 11. Not shown) in turn.

In addition, a lower transparent electrode 14 and a lower alignment layer of a flat plate pattern are sequentially formed on the lower glass substrate 12.

The upper and lower glass substrates 11 and 12 formed as described above are bonded to the upper and lower glass substrates 11 and 12 with an epoxy seal material 15 such that the upper and lower glass substrates 11 and 12 have a predetermined space and face each other. The liquid crystal molecules 16 are injected into the formed space.

In addition, a normal rubbing process is performed on the upper alignment layer so that the upper alignment layer is rubbed in a predetermined direction, and a rubbing process is also performed on the lower alignment layer so that the lower alignment layer is rubbed in the opposite direction to the upper alignment layer.

When the alternating voltage of the square wave is applied to the upper and lower transparent electrodes 13 and 14 of the GPBS prepared as shown in FIG. 1B and irradiated with ultraviolet light having an energy density of 10 mW / cm 2 while the alternating voltage is applied. The liquid crystal molecules 16 between the facing electrodes are aligned parallel to the electric field.

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

At this time, the orientation is frozen by photopolymerization so that the grating properties remain unchanged even after the power source is removed as shown in FIG.

However, the conventional GPBS described above has to align the electrode pattern in a specific direction while making the electrodes of the upper glass substrate into a stripe shape, so that the electrode making process is difficult and complicated, thereby increasing the cost.

In addition, since there are portions with and without electrodes in the upper glass substrate, optical path differences occur and performance decreases.

In addition, since the use of photo-polymerized liquid crystal molecules (photo-polymerized liquid crystal molecules) has a large effect on the temperature, there is a lack of reliability for the temperature, thereby causing performance degradation.

In addition, since the temperature range is limited in this manner, there is a problem even in the application of the product.

The present invention is to solve the above problems, the object of the present invention is to etch by diffraction by directly irradiating O and E waves after bonding to a glass substrate and then etched with a non-etched glass substrate after direct etching on the glass substrate By providing an effect, it provides a PLCH manufacturing method which is short and simple, and is hardly influenced by temperature change.

Another object of the present invention is to apply the PLCH to a light pickup device instead of a polarizing plate that selectively transmits light to diffract a portion of the light by refractive power, so that the light is different from the straight light that is not diffracted and the diffracted light that is deflected by diffraction. SUMMARY OF THE INVENTION An optical pickup apparatus using a polarization liquid crystal hologram that simultaneously maintains a numerical aperture and enables reproduction of heterogeneous optical disks having different thicknesses and recording densities.

A polarizing liquid crystal hologram manufacturing method according to the present invention for achieving the above object is a step of forming a first alignment layer on the first glass substrate, and the second alignment layer after etching the second glass substrate in a predetermined pattern Forming the first and second glass substrates so that the first and second glass substrates face each other and the first and second alignment layers face each other, and injecting liquid crystal molecules into the spaces; And rubbing the first and second alignment films in a predetermined direction, and irradiating a light beam whose polarization direction changes according to polarization characteristics.

An optical pickup apparatus using a polarization liquid crystal hologram according to the present invention is characterized in that the light source for generating a light beam to be irradiated on the surface of the optical disk, and the polarization direction of the light beam positioned between the light source and the optical disk to be incident toward the optical disk The liquid crystal shutter selectively varies depending on the type of optical disk, the polarization liquid crystal hologram diffracting a part of the light according to the polarization direction of the light beam incident from the liquid crystal shutter, and the linear and diffracted light of the polarization liquid crystal hologram. And an objective lens for accurately condensing a light beam on the surface of heterogeneous optical disks having different numerical values and recording density and thickness.

1A to 1C are side cross-sectional views illustrating a manufacturing process of a grating polarizing beam splitter.

2a to 2d is a side cross-sectional view showing the manufacturing process of the planar liquid crystal hologram according to the present invention.

3 is a cross-sectional view showing an embodiment of an etching pattern of the glass substrate of FIG.

4 is a block diagram of an optical pickup apparatus using the polarization liquid crystal hologram manufactured in FIG.

* Explanation of symbols for main parts of the drawings

21: upper glass substrate 22: upper alignment film

23: lower glass substrate 24: lower alignment film

25 liquid crystal molecule 41 light source

42 liquid crystal shutter 43 collimating lens

44: beam splitter 45: actuator

46: polarization liquid crystal hologram 47: objective lens

48: optical disk 49: sensor lens

50: light detector

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

2A to 2B are side cross-sectional views showing a PLCH manufacturing process according to the present invention, in which the upper alignment layer 22 is formed on the upper glass substrate 21 of the flat plate pattern as shown in FIG. 2A.

In addition, the lower glass substrate 23 is directly etched as shown in FIG. 2B, and then the lower alignment layer 24 is formed as shown in FIG. 2C.

The upper and lower glass substrates 21 and 23 formed as described above have a predetermined space, and the upper and lower glass substrates 21 and 23 are sealed (not shown) so that the upper and lower alignment layers 22 and 24 face each other. ) Is bonded and the liquid crystal molecules 25 are injected into the space and sealed.

Then, the formed upper alignment layer 22 is subjected to a normal rubbing process, and the upper alignment layer 22 is rubbed in a predetermined direction, and the lower alignment layer 24 is also subjected to a rubbing process so that the lower alignment layer 24 is the upper alignment layer 22. Rubbing in the opposite direction).

When rubbing is performed, the liquid crystal molecules 25 are aligned in the horizontal direction.

In this case, polyimide-based materials are widely used as the polymer material used as the vertical alignment layers 22 and 24.

Then, rubbing is performed on the substrate on which the upper and lower alignment films 22 and 24 are formed in order to obtain a uniform and controllable effect of the liquid crystal molecules.

The rubbing process attaches a fiber of rayon or nylon to a roll to make a rubbing cloth, and then bends the surface of the alignment film in a direction determined with respect to the upper and lower glass substrates 21 and 23 on which the alignment films 22 and 24 are formed. Is formed to determine the alignment direction of the liquid crystal molecules.

At this time, the etching pattern of the lower glass substrate 23 is etched in a stripe pattern as shown in FIG. 3, but the non-diffraction region which does not diffract the light beam irrespective of the polarization direction is placed in the form of an ellipse in the center.

In addition, the direct etching on the glass substrate is preferably formed only on one of the upper and lower glass substrates 21 and 23, and in the present invention, the etching is performed on the lower glass substrate.

Meanwhile, the upper and lower glass substrates 21 and 23 have the same isotropy (n _o = n _e ) having the same refractive index n _o in the normal ray direction and the refractive index n _{e in} the extra ordinary ray direction. Since the refractive index n _g of the glass substrate is constant at any position, the liquid crystal is an anisotropy n _o ≠ n _{e in which} the refractive index n _o in the normal light direction and the refractive index n _{e in the} abnormal light direction are different.

Therefore, when the refractive index (for example, n _o ) of the liquid crystal having the same refractive index as the refractive index n _g of the glass substrate is selected, n _g = n _o ≠ n _e .

When the O wave having the refractive index n _o in the normal ray direction enters the PLCH, the O wave has the same refractive index (n _g = n _o ) as that of the glass substrate as shown in FIG. Permeate.

However, when the E wave having the refractive index n _e in the extraordinary ray direction is incident on the PLCH, the E wave is diffracted because the refractive index difference is generated by the combination of the glass substrate and the liquid crystal as shown in FIG.

That is, graying occurs because the refractive index n _e of the abnormal light direction on the glass substrate and the refractive index n _e of the abnormal light direction at the position where the liquid crystal is injected are different.

Here, the O wave or the E wave is generated by the liquid crystal shutter that changes the polarization direction of the incident light beam according to the type of the optical disk, that is, whether or not the power is supplied to the PLCH.

The incident light and the reflected light and the transmitted light are on one plane, which is called the incident surface. If the electric field direction is perpendicular to the incident surface, it is called O wave. If the electric field direction is the same horizontal direction as the incident surface, it is called E wave. .

O wave is also called S wave, and E wave is also called P wave.

Therefore, as shown in FIG. 3, when the etching pattern of the lower glass substrate is etched into a pattern having a desired shape, the spatial distribution of the refractive index can be changed into a desired shape, thereby making it possible to manufacture a PLCH having a grating function.

At this time, the linear light without diffraction is called 0th order light, and the light diffracted is called +1 order light, + 2nd light order, ... in order from the smallest deflection angle, and the light diffracted in the opposite direction is smaller side In order, it is called -first shading, -second shading, ...

Therefore, the O wave generates 0th order light, and the E wave generates ± 1st order light, ± 2nd order light, ...

As described above, the PLCH does not need to make an electrode and thus does not need to supply power, thereby shortening and simplifying the number of manufacturing processes, and directly etching a glass substrate having a wide range of temperature reliability without using a polymer. You will rarely receive.

4 is a block diagram of an optical pickup device for a dual optical disk of the present invention in which a PLCH manufactured as in FIG. 2 is applied to an optical pickup device.

Referring to FIG. 4, the light source 41 which generates the light beam to be irradiated to the optical disk 48 and the LC shutter 42 which changes the polarization direction of the light beam incident from the light source 41 according to on / off of an electrode. And a collimator lens 43 for allowing the light beam incident through the LC shutter 42 to proceed in parallel in a predetermined direction, a beam splitter 44 for dispersing the incident light beam, and a beam splitter 44. An objective lens 47 for condensing the light beam passing through at one point on the surface of the optical disk 48, and an optical detector 50 for detecting the vacant light beam from the beam splitter 44 and converting it into an electrical signal.

A sensor lens 49 is provided between the beam splitter 44 and the photo detector 50, and a polarization liquid crystal hologram 46 is provided between the beam splitter 44 and the objective lens 47. An actuator 45 for moving the 47 in the horizontal and vertical directions is provided.

Here, the photodetector 50 is reflected by the information recording surfaces 48a and 48b of the optical disk 48 to cover the objective lens 47, the polarization liquid crystal hologram 46, the beam splitter 44 and the sensor lens 49. Converts the reflected light beam incident via the signal into an electrical signal.

The collimating lens 43 causes the light beam passing through the LC shutter 42 to be directed toward the beam splitter 44 in parallel.

The beam splitter 44 passes the light beam from the collimation lens 43 toward the polarization liquid crystal hologram 46 and the objective lens 47, and reflects the reflected light beam incident from the objective lens 47 toward the sensor lens 49. Let's do it.

The sensor lens 49 focuses the reflected light beam from the beam splitter 44 on the surface of the light detector 50.

The collimating lens 43 and the sensor lens 49 improve the sensitivity of the reflected light beam which decreases as the objective lens 47 moves in the horizontal and vertical directions due to the focusing and tracking servo.

The LC shutter 42 changes the polarization direction of the light beam incident from the light source 41 according to the on / off of the power source, that is, the type of the optical disk (for example, CD or DVD) to O wave or E wave.

That is, when the O-wave light beam is incident on the LC shutter 32 when the DVD is reproduced, the supply of driving power to the LC shutter 32 is cut off so that the O-wave light beam is passed as it is, and the E-wave light beam is incident. In this case, the driving power is supplied to the LC shutter 32 so that the polarization direction is converted to 90 degrees and becomes an O wave.

On the other hand, when the O-beam light beam is incident on the LC shutter 32 when the CD is reproduced, the drive power is supplied to the LC shutter 32 to be changed to the E-wave, and when the E-wave light beam is incident, the LC shutter ( The driving power supply of 32 is cut off so that the E-wave passes as it is, and is sent to the polarized liquid crystal holograms 36 installed at the rear ends thereof, so that the numerical aperture of the objective lens 37 is adjusted as described later.

The PLCH 46 diffracts or passes the light toward the objective lens 47 without diffraction according to the polarization direction of the light beam incident from the LC shutter 42 via the collimating lens 43 and the beam splitter 44. By this, the spot of the light beam incident on the objective lens 47 is adjusted.

The PLCH 46 is manufactured to have a grating effect by refractive power without supplying power by irradiating O and E waves after joining and living the upper glass substrate of the flat pattern and the lower glass substrate etched into a predetermined pattern as shown in FIG. do.

As described above, the PLCH 46 generates O-shielded light that is not diffracted when the O-wave is incident from the LC shutter 42. When the E-wave enters, the PLC-H 46 is diffracted by the refractive power and deflected. By generating?, The effect of adjusting the numerical aperture of the objective lens 47 is obtained.

The objective lens 47 focuses the light beam from the light source 41 on the first or second information recording surface 48a or 48b of the optical disk 48 in accordance with the diffracted light in the polarization direction.

Here, the first information recording surface 48a is an information recording surface of a DVD, the second information recording surface 48b is an information recording surface of a CD, and the second information recording surface 48b is an optical disc 48 than the first information recording surface 48a. ) 0.6 mm away from the surface of the

That is, the objective lens 47 maintains a numerical aperture of 0.35 by O-blocking light that is not diffracted in the PLCH 46 so that the light beam is focused on the second information recording surface 48b of the optical disk 48.

On the other hand, by the diffracted light deflected by the polarization liquid crystal hologram 46, the objective lens 47 maintains the numerical aperture of 0.6 so that the light beam is focused on the first information recording surface 48a of the optical disk 48. do.

The actuator 45 moves the PLCH 46 and the objective lens 47 in the vertical and horizontal directions so that the focus of the light beam is formed on the information recording surface 48a or 48b of the optical disk 48 and the light beam Follow the information recording surface 48a or 48b precisely.

As described above, according to the polarizing liquid crystal hologram manufacturing method and the optical pickup apparatus using the same, an upper glass substrate of a flat pattern and a lower glass substrate directly etched into a predetermined pattern are bonded to each other, and O and E waves are applied after the liquid crystal injection and living process. By having the grating effect by diffraction without the power supply by irradiating, it is not necessary to manufacture an electrode and also to supply power, shortening and simplifying the number of PLCH manufacturing processes, and making manufacturing process cost low.

In addition, since the optical path is not the same in any position, the optical path difference does not occur, and thus the performance degradation does not occur, and since the glass substrate is directly etched without using a polymer, the temperature range of the reliability of the temperature is largely unaffected by the temperature change.

In addition, by applying the polarization liquid crystal hologram prepared as described above to the optical pickup device to diffract part of the light according to the polarization characteristics of the light beam, a different numerical aperture according to the straight light is not diffracted and diffracted light deflected by diffraction This makes it possible to precisely focus the light beam on the surface of the heterogeneous optical discs and thus to simultaneously reproduce the heterogeneous optical discs.

Claims (8)

Forming a first alignment layer on the first glass substrate; Etching the second glass substrate onto a predetermined pattern to form a second alignment layer; Bonding the first and second glass substrates so that the first and second glass substrates have a predetermined space and the first and second alignment layers face each other, and injecting liquid crystal molecules into the space; Rubbing the first and second alignment films in a predetermined direction; Polarizing liquid crystal hologram manufacturing method comprising the step of irradiating a light beam in which the polarization direction is changed in accordance with the polarization characteristics. The method of claim 1, wherein the etching of the second glass substrate is performed by etching a stripe pattern, but forming a non-diffraction region that does not diffract the light beam in the form of an ellipse in the center thereof. The method of claim 1, wherein the second glass substrate is any one of upper and lower glass substrates. The method of claim 1, wherein the liquid crystal refractive index having the same refractive index as that of the glass substrate is selected. The method of claim 1, wherein when the O-wave perpendicular to the plane of incidence is incident, the light is transmitted without being diffracted, and when E-waves in which the field is in the same direction as the plane of incidence are incident, part of the light is diffracted due to the difference in refractive power. Polarizing liquid crystal hologram manufacturing method characterized in that. A light source 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 disk to selectively change the polarization direction of the light beam incident on the optical disk according to the type of the optical disk, and the liquid crystal shutter Surfaces of heterogeneous optical disks having different recording densities and thicknesses by maintaining polarization liquid crystal holograms diffracting part of light in accordance with the polarization direction of the light beam incident from Optical pickup device using a polarizing liquid crystal hologram, characterized in that it comprises an objective lens for accurately condensing a light beam. The polarization liquid crystal hologram of claim 6, wherein the polarization liquid crystal hologram bonds the first glass substrate of the flat plate pattern and the second glass substrate directly etched into the predetermined pattern, and has a refractive index of O wave and abnormal light having a refractive index of ordinary light after liquid crystal injection and living process. Optical pickup device using a polarizing liquid crystal hologram, characterized in that formed by irradiating E-wave. The light using the polarization liquid crystal hologram according to claim 6, wherein the polarization liquid crystal hologram is transmitted as it is without diffraction when the O wave is incident from the liquid crystal shutter, and part of the light is diffracted due to the difference in refractive power when the E wave is incident. Pickup device.