KR100214591B1 - Apparatus for optic pickup double using cd and dvd - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CD / DVD combined optical pickup apparatus, and more particularly, to an optical pickup apparatus which increases contrast ratio and suppresses the generation of jitter. The present invention is constructed by installing a liquid crystal shutter 30 having a PSCT (Polymer Stablized Cholisteric Texture) liquid crystal on an optical path scanned by a laser diode 21 and transmitted to an optical disc D. Stablized Cholisteric Texture The liquid crystal is doped with a dichroic die to increase the light absorption and decrease the scattering rate to improve the contrast ratio.

Description

CD / DVD combined optical pickup

1 is a block diagram of a general optical pickup apparatus according to the prior art.

2 is an intensity distribution diagram of beams distributed on optical disks having different thicknesses in a general optical pickup apparatus.

3 is an overall configuration diagram of an optical pickup apparatus having a conventional general liquid crystal shutter.

4 is a view for explaining the operation for the numerical aperture conversion of the conventional optical pickup apparatus having a conventional liquid crystal shutter,

a is an operation diagram showing a state where no power is applied to the transparent electrode of the liquid crystal shutter.

b is an operation diagram showing a state in which power is applied to the transparent electrode of the liquid crystal shutter.

5 is an overall configuration diagram of a CD / DVD combined optical pickup device according to the present invention.

6 is a block diagram showing the configuration of a liquid crystal shutter of the optical pickup apparatus according to the present invention.

7 is a view for explaining that the liquid crystal shutter of the optical pickup apparatus according to the present invention is driven,

a is an operating state diagram showing a state in which a voltage is applied to the transparent electrode;

b is an operating state diagram showing a state in which no voltage is applied to the transparent electrode.

8 is a schematic view showing the shape of a transparent electrode formed on the glass substrate of one embodiment of the optical pickup apparatus according to the present invention.

9 is a state diagram showing light absorption and scattering states in a state where no voltage is applied to the transparent electrode of the liquid crystal shutter in the optical pickup apparatus according to the present invention.

FIG. 10 is a graph illustrating an operation characteristic by doping a dichroic die in the optical pickup apparatus according to the present invention.

a is a graph showing the light transmittance at the time of voltage application according to the diconcentration,

b is a graph showing the contrast ratio of the liquid crystal shutter according to the polymer concentration;

c is a graph showing contrast ratio according to collection angle.

* Explanation of symbols for main parts of the drawings

21: laser diode 22: beam splitter

23: collimating lens 25: objective lens

26: photodetector 30: liquid crystal shutter

31: first transparent substrate 32: second transparent substrate

33,34: transparent electrode 35: liquid crystal layer

B: beam D: optical disc

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an optical pickup device for a CD / DVD device. In particular, each optical disk having a different recording density and thickness is recorded in one unit by using a PSCT (Polymer Stablized Cholesteric Texture) liquid crystal as a liquid crystal material in a liquid crystal shutter. And it relates to a CD / DVD combined optical pickup device that can be read.

As shown in FIG. 1, the optical pickup apparatus according to the prior art has a laser diode 1 for scanning a laser beam and a laser beam scanned from the laser diode 1 for main purpose of tracking servo. A diffraction grating 2 made of a beam and two sub-beams, a collimating lens 3 which makes the beam through the diffraction grating 2 parallel light, and a parallel light through the collimating lens 3 An objective lens 4 for condensing on the optical disk D, a beam which is installed on the path of the parallel light and reflected by the presence or absence of information recorded on the optical disk D, and through the diffraction grating 2 A beam splitting prism 5 for transmitting or reflecting an incident beam at a predetermined ratio, a sensor lens 6 for focusing beams reflected through the beam splitting prism 5, and a beam through the sensor lens 6 It consists of the photodetector 7 which detects these data signals.

In the general optical pickup device as described above, after the beam emitted from the laser diode 1 is converted into parallel light by the collimating lens 3 through the diffraction grating 2 and the beam splitting prism 5, the objective lens 4 Is focused through the light and reflected or rotated by the information recorded on the surface of the optical disc D. Thereafter, the beam reflected from the surface of the optical disc D is reflected by the beam splitting prism 5 after returning the same path, and is detected by the photodetector 7 past the sensor lens 6.

On the other hand, high-density optical discs (hereinafter referred to as 'DVD'), such as DVD (Digital Video Disk), have a recording density of 6-8 times more than conventional CD-based optical discs (hereinafter referred to as CDs). Regeneration is possible only when the numerical aperture (NA: Numerical Aperture) has a high value of about 0.6. In this case, the aberration due to the tilt increases as the thickness of the optical disc D increases. To prevent this, the thickness of the DVD optical disc D is 0.6 mm.

At this time, when one unit having the configuration as shown in FIG. 1 plays a high density optical disk D for a DVD having a thickness of 0.6 mm and an optical disk D having a CD series having a thickness of 1.2 mm, the following problems occur. .

That is, the beam intensity distribution in the state in which the focus of the surface of the optical disk D is focused with the objective lens 4 having the aperture NA NA of 0.6, which is optimally designed for the optical disk D having a thickness of 0.6 mm, is shown in FIG. It is displayed as a solid line.

At this time, when the beam is focused on the optical disk D having a thickness of 1.2 mm through the objective lens 4, spherical aberration of the objective lens 4 is displayed as a dotted line in FIG.

That is, not only the beam intensity of the main lobe is significantly reduced, but also the beam intensity of the side lobes is relatively increased, so that crosstalk from signals recorded in adjacent tracks becomes large.

This crosstalk value is calculated to be worse than -20dB when reading the CD series (thickness 1.2mm, track pitch 1.6μm) of the optical lens D with NA = 0.6.

As a result, the spherical aberration for the optical disk D is too large to reproduce the 1.2 mm thick optical disk D with the objective lens 4 having NA = 0.6, and as a conventional optical pickup apparatus, a 1.2 mm optical disk D for CD is used. And 0.6 mm optical disc D for DVD cannot be reproduced in one unit.

In order to solve this problem, optical pickups having the configuration as shown in FIG. 3 have been developed, which have a numerical aperture adjusting means capable of adjusting the numerical aperture of the objective lens 4. An example of such numerical aperture adjusting means includes a liquid crystal shutter 10, and the principle of controlling the numerical aperture using the liquid crystal shutter 10 is as follows. In FIG. 3, reference numeral 11 denotes a polarization hologram and 8 denotes a rectangular prism.

In other words, by using the principle that the spherical aberration is proportional to the quadratic power of the aperture (NA), the objective lens (when recording or reading on the CD optical disk (D) and when recording or reading on the optical disk (D) for DVD) By changing the aperture ratio of 4), it is possible to record or read on the optical disc D for CD and DVD in one unit.

Here, the operation of changing the aperture ratio of the objective lens 4 is as follows. That is, when the beam incident on the liquid crystal shutter 10 is P-file, if no voltage is applied to the liquid crystal shutter 10, the P wave is converted into an S wave by converting the polarization direction by 90 ° while passing through the liquid crystal shutter 10. The polarization hologram 11 whose diffraction efficiency with respect to the S-wave is zero is passed through the objective lens 4 without any change and is focused on the optical disc D for DVD. (See Figure 4 a)

On the other hand, when a voltage is applied to the liquid crystal shutter 10, the P wave incident on the liquid crystal shutter 10 passes through the polarization hologram 11 having a high diffraction efficiency with respect to the P wave as it passes through without changing the polarization direction. The beam of eye is diffracted out of the objective lens 4. By diffracting a certain portion of the beam out of the objective lens 4 as described above, the aperture ratio is reduced so as to be focused on the optical disc D for CD (see FIG. 4B).

However, in the optical pickup device having the liquid crystal shutter 10 having the above-described configuration, the polarization hologram 11 should be used, so that the loss of the beam emitted from the laser diode 1 may occur, resulting in a decrease in contrast ratio. There is another problem of jitter, and the polarization hologram 11 is used, and thus the configuration of the redundant optical pickup device is complicated and manufacturing costs are increased.

In order to solve such a problem, a method of using a PDLC (Polymer Dispersion Liquid Crystal) has been proposed. However, when the liquid crystal layer is actually applied, there is a problem in that the effect is not good, such as a low contrast ratio.

Accordingly, it is an object of the present invention to provide a CD / DVD combined optical pickup device for recording / reading CDs and DVDs in one unit, and at the same time, the liquid crystal shutter is configured to increase the absorption rate of the light scanned from the light source and reduce the scattering rate. By improving the contrast ratio of the shutter, the performance of the CD / DVD combined optical pickup device is improved.

Another object of the present invention is to simplify the configuration of the optical pickup device to reduce the manufacturing cost of the device.

The object of the present invention is a dichro to increase the absorption rate of the beam and reduce the scattering rate between the first and second transparent substrates and the transparent substrates through which the beam is transmitted on the path of the beam emitted from the light source and transmitted to the optical disk. Combined with CD / DVD, characterized in that the liquid crystal shutter is driven to penetrate or absorb a portion of the beam transmitted to the optical disc through a PSCT (Polymer Stablized Cholisteric Texture) liquid crystal doped with a dichroic dye. Achieved by an optical pickup device.

When described in detail with reference to the embodiment shown in the accompanying drawings of the CD / DVD combined optical pickup device according to the present invention as described above.

5 is an overall configuration diagram of a CD / DVD-use optical pickup apparatus according to the present invention, and FIG. 6 is a configuration diagram showing the configuration of a liquid crystal shutter of the optical pickup apparatus according to the present invention.

As shown in the drawing, one embodiment of the CD / DVD-using optical pickup apparatus according to the present invention includes a laser beam 21 having a specific polarization (B) among the laser diode 21 and the beam B emitted from the laser diode 21. ), A beam splitter 22 which transmits the beam B of other specific polarization and reflects it, a collimation lens 23 which makes the beam B reflected by the beam splitter 22 into a parallel beam B, Orthogonal prism 24 for reflecting the parallel beam passing through the collimating lens 23 in a predetermined path, and the liquid crystal shutter 30 for adjusting the aperture ratio (NA) while passing through the parallel beam reflected from the rectangular prism 24 ), The objective lens 25 for condensing the parallel beam B passing through the liquid crystal shutter 30 on the optical disk D, and the beam splitter 22 is reflected by the optical disk D, and proceeds in the reverse order. It consists of a photodetector 26 for detecting the beam passed. Reference numeral 27 is an actuator.

The liquid crystal shutter 30 is used to adjust the aperture ratio NA, and is provided between the first and second transparent substrates 31 and 32 and the first and second transparent substrates 31 and 32. It is composed of a layer 35, the transparent electrode 33, 34 is formed in a predetermined shape on the first and second transparent substrates 31, 32, respectively.

The transparent electrode 33 formed on the first transparent substrate 31 has a circular electrode 33C formed at the center of the first transparent substrate 31 and an annular electrode surrounding the circular electrode 33C. 33R), one example of which is shown in FIG. The size and shape of the circular electrode 33C and the annular electrode 33R may be formed to suit the opening ratio to be obtained.

The liquid crystal material provided in the liquid crystal layer 35 is a PSCT (Polymer Stablized Cholisteric Texture) liquid crystal.

On the other hand, the PSCT (Polymer Stablized Cholisteric Texture) is preferably doped with a dichroic die (Dichroic Dye) to increase the absorption of the beam and to reduce the scattering rate (Contrast Ratio) to improve the contrast ratio (Contrast Dye).

Such a dichroic die is preferably doped at least 2% or more, and in the embodiment of the present invention it can be seen that most preferably doped 3%.

Hereinafter, the effect of the CD / DVD combined optical pickup device according to the present invention configured as described above will be described.

The characteristic of the PSCT (Polymer Stablized Cholisteric Texture) liquid crystal is that when no voltage is applied, the incident beam is mainly absorbed and partially scattered regardless of the polarization state. Therefore, the circular electrode 33C is formed to have a diameter as much as a desired beam bundle, and the annular electrode 33R is also formed accordingly so that an appropriate voltage is applied to the electrodes 33 and 34. The diameter of the beam B bundle incident on the lens 25 may vary depending on the type of the optical disc D.

Adjusting the aperture ratio of the objective lens 25 using this principle will be described in more detail with reference to FIG. 7 below.

First, as shown in FIG. 7A, when the voltages are applied to the transparent electrodes 33 and 34 of the first and second transparent substrates 31 and 32, the laser diode 21 The light beam B incident on the liquid crystal shutter 30 is transmitted through the liquid crystal layer 35 provided between the first and second transparent substrates 31 and 32. In this case, the amount of beam B transmitted is about 89% or more of the incident beam B. (The lost beam B is due to the reflection of the cover glass 31 and 32.) As such, the beam B passing through the liquid crystal shutter 30 is transferred to the objective lens 25 to the optical disk D. The light is collected and reflected and transmitted to the photodetector 26 through the same path as the incident light.

As shown in FIG. 7B, a voltage is applied to the circular electrode 33C of the first transparent substrate 31 and the transparent electrode 34 of the second transparent substrate 32 and the first transparent substrate. When no voltage is applied to the annular electrode 33R of (31), the beam B emitted from the laser diode 21 passes through the portion of the liquid crystal layer 35 corresponding to the circular electrode 33C, Most of the portion corresponding to the annular electrode 33R is absorbed or scattered so that it is not transmitted to the objective lens 25. Therefore, the size of the beam B bundle delivered to the objective lens 25 is equal to the diameter of the circular electrode 33C, and the beam delivered to the objective lens 25 passes through the objective lens 25. The light is condensed and reflected on the surface of the optical disc D (here, CD) and transmitted to the photodetector 26 through the same path as the incident.

Meanwhile, the polymer stablized cholisteric texture (PSCT) liquid crystal is doped with a dichroic die to increase light absorption and reduce scattering to improve contrast ratio. As described above, the dichroic die is doped. ), It has an effect, as shown in FIG.

That is, a degree in FIG. 10 is a graph showing light transmittance when voltage is applied according to die concentration, and b degree in FIG. 10 is 3%, 2%, and 1% when the collection angle is 5 °. The contrast ratio of the liquid crystal shutter 30 having the PSCT liquid crystal according to the polymer condensation is shown. As can be seen from this graph, the contrast ratio is best when the die is 3% doped.

In addition, the graph shown in FIG. 10C illustrates the contrast ratio according to the collection angle, and it can be seen that the contrast ratio is better at a constant collection angle that is 3% doped than the die is not doped. In particular, it can be seen that the contrast ratio is improved by 2 times or more when the collection angle is more than 0% die doping when 16% or more.

In the CD / DVD combined optical pickup apparatus according to the present invention as described in detail above, a PSCT (Polymer) has a characteristic of passing a beam regardless of the polarization direction of the beam when a voltage is applied and absorbing or scattering the beam if a voltage is not applied. Stablized Cholisteric Texture) Since the liquid crystal shutter with the liquid crystal is installed on the optical path, it is not necessary to use an expensive polarizing plate or a polarizing hologram replacing the polarizing plate, thereby simplifying the optical system of the optical pickup and reducing the manufacturing cost. The PSCT (Polymer Stablized Cholisteric Texture) liquid crystal doping the die of the dichro to increase the absorption of the beam and to reduce the scattering rate can significantly improve the contrast ratio has the effect of significantly improving the performance of the optical pickup device.

Claims (2)

On the path of the beam emitted from the light source to the optical disk, PSCT liquid crystal doped with a dichroic die between the first and second transparent substrates through which the beam passes and these transparent substrates to increase the absorption of the beam and reduce the scattering rate. And a liquid crystal shutter which is driven to transmit or absorb a portion of the beam transmitted to the optical disk via the CD / DVD device. The apparatus of claim 1, wherein the dichroic die is doped at least 2% or more.