KR100194341B1 - Dual Focus Optical Pick-Up Unit - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dual focus optical pick-up apparatus, comprising: a hologram element in which a plurality of optical elements are integrally formed; and a bobbin for forming an objective lens by forming a through-hole in the center at a predetermined position on the upper side of the hologram element. And an aspherical circular lens which is formed at a predetermined position between the bobbin and the objective lens and adjusts the beam width according to the angle of incidence to easily form a dual focus, thereby making the dual focus optical pick-up device thin and short, as well as the mechanism of several optical elements. The reliability of the product can be improved by drastically reducing the error.

Description

Dual Focus Optical Pick-Up Unit

The present invention relates to a dual focus optical pick-up device, and more particularly, to a dual focus optical pick-up device capable of simultaneously playing a digital audio disc having a thickness of 1.2 mm and a digital video disc having a thickness of 0.6 mm.

In general, a device for picking up recorded information includes a method of detecting information of a disk surface by a mechanical change amount using a contact needle, and a method of detecting information by a change of capacitance of a fine groove in a disk. , A digital audio disc (DAD) with a spot size of 1.6 μm or a digital with a spot size of 0.8 μm, using an optical pick-up device with individual components such as beam splitters, diffraction gratings, laser diodes, and photodetectors Background Art A method of reproducing electric signals from information recorded on a video disc (DVD) has been widely used.

As shown in FIGS. 1A and 1B, such a digital audio disc and a digital video disc record data in two layers on a 1.2 mm thick digital audio disc, and a 0.6 mm thick digital video disc records data in a double layer in the middle. It records so that a large amount of data is recorded on one disk. Therefore, the optical pick-up device for reading the data recorded on these two types of discs can read only the information recorded on either the 0.6mm or 1.2mm discs to selectively read the information recorded on the two types of discs. It is not intended.

The reason is that when the information recorded on the 0.6mm disk is read compared to the 1.2mm disk, the thickness difference of 0.6mm occurs and the optical aberration increases, so that the noise increases. You can't read it correctly. Therefore, in recent years, the laser beam is formed at different positions by the optical path difference (0th order and 1st order diffracted light) of the beam incident on the objective lens according to the diffraction degree of the beam passing through the diffraction grating. Dual-focus optical pick-up devices are being developed to selectively read information recorded on discs and 0.6mm discs.

The structure of the conventional dual focus optical pick-up apparatus includes a laser diode 71 that generates a constant laser beam as shown in FIG. 2, and a laser beam that is formed at a predetermined distance from the laser diode 71 and is incident. And a diffraction grating 72 for dividing the light into 0th order light and ± 1th order light and a predetermined inclination at a predetermined distance from the diffraction grating 72 to have a constant ratio of reflectance and transmittance to separate incident light into reflected light and transmitted light. A beam splitter 73, a collimated lens 74 formed at an upper predetermined position of the beam splitter 73 so that the refracted light has a straightness, and a holographic optical lens 76 and an objective lens 77 A composite video disk (hereinafter referred to as a first disk) 78 mm and a 1.2 mm digital audio disk (hereinafter referred to as a second disk) are condensed to collect light incident straightly by the collimated lens 74. (79) on It is made of a dual-focus lens 75 to read the recorded information by focusing.

In addition, the first disk 78 and the second disk 79 that are incident on the lower predetermined position of the beam splitter 73 via the dual focus lens 75, the collimated lens 74, and the beam splitter 73. An astigmatism generating lens 80 for generating astigmatism using optical information recorded thereon is formed, and at the lower predetermined position of the astigmatism generating lens 80, an optical signal for outputting an electrical signal is generated. The detector 81 is formed. Meanwhile, as shown in FIG. 3, a bobbin through-hole 83 is formed in the center of the bobbin 82 in which the objective lens 77 is placed, and is wound around the bobbin 82 at a constant turns ratio. The focusing coil 84 and the tracking coil 85 are formed.

The conventional optical pick-up apparatus having such a structure first emits a laser beam of about 780 nm, which is a predetermined oscillation wavelength, in the laser diode 71, and the laser beam passes through the diffraction grating 72 to zero. It is separated into differential and ± first order light. In this case, the separated 0th order light is used for focusing, and ± 1st order light is used for tracking, and is commonly referred to as a three beam. Accordingly, the light split into three beams by the diffraction grating 72 is incident on the beam splitter 73 having a constant ratio of reflectance and transmittance so that the light is separated into reflected light and transmitted light, and the double reflected light is collimated lens 74. ) Is kept straight and enters into the dual focus lens 75 placed on the upper surface of the bobbin through hole 83 of the bobbin 82. At this time, the beam incident on the dual focus lens 75 is divided into 0th order and ± 1st order light via the holographic optical lens 76, and the separated beam is sent to the objective lens 77 at a constant diffraction limit. It focuses about 1.6 μm on the first disk 78 that is condensed and the second disk 79 that is 0.6 mm, and reads the information recorded on the disk.

That is, the light incident on the objective lens 77 is collected in an area of about 1.6 μm and irradiated onto a signal surface that is a pit 78a or 79a of the first disk 78 and the second disk 79. At this time, the light is returned as it is when there is no pit 78a (79a) in which data is recorded, but where the pit 78a (79a) exists, the light is diffracted by the pit 78a (79a). The out of range of the lens 77, so that only a part of the incident light is returned, so that the modulated light information reflected from the first disk 78 and the second disk 79 is returned to the dual focus lens 75. ) And the collimator lens 74 and the beam splitter 73 are sent to the astigmatism generating lens 80 to generate astigmatism by detecting a focus error.

At this time, the light information via the astigmatism generating lens 80 is sent to the photodetector 81 and converted into a constant electrical signal. Therefore, this converted electrical signal is demodulated by the digital signal processing unit (not shown) to the original signal so that the audio signal recorded on the disc is output. In addition, the focus signal and the tracking signal, which are error detection signals input to the photodetector 81, are converted into a predetermined amount of electrical signals and applied to the focus coil 84 and the tracking coil 85, respectively.

However, such a conventional dual focus optical pick-up apparatus includes a dual focus lens for forming a focus according to a thickness of a disk, a collimating lens for maintaining a laser beam in a straight line, a beam splitter for separating incident light into reflected light and transmitted light, As astigmatism generating lenses for detecting aberration aberration are generated independently of each other, and optical pick-up devices are constructed by assembling, the error occurrence rate during operation is high due to mechanical errors generated during assembly. The size and installation of individual parts are limited by the accuracy of positioning, which makes it difficult to miniaturize. In particular, in accordance with the recent trend of miniaturization of optical disc players, the optical pick-up device has to be miniaturized in proportion. It is not easy.

The present invention has been made to solve the above problems, as well as forming a bobbin so that the laser beam radiated from the hologram element is incident to a different width, as well as adjusting the width of the beam incident between the bobbin and the objective lens The purpose of the present invention is to provide a dual-focus optical pick-up apparatus that enables the formation of beam spots of 1.6 μm and 0.8 μm in diameter on the disc at the same time, thereby enabling the reproduction of digital audio discs and digital video discs. .

In order to achieve the above object, the present invention provides an optical pick-up apparatus for condensing a laser beam with an objective lens, recording a signal on a disk, and reproducing the recorded optical information, wherein the laser diode and the photodetector are integrally formed. A formed hologram element, a bobbin in which a rectangular through-hole is formed in the center of a predetermined position on the upper side of the hologram element so that different beam widths are incident, and an aspherical circular shape for adjusting the width of the incident beam formed between the bobbin and the objective lens A lens is further provided.

1 is a data recording state diagram according to the type of a conventional disk;

2 is a conventional dual focus optical pick-up device,

3 is a perspective view of a bobbin in which a conventional objective lens is placed;

4 is a block diagram of a dual focus optical pick-up apparatus according to the present invention;

5 is a perspective view of a bobbin in which an objective lens according to the present invention is placed.

Explanation of symbols on the main parts of the drawing

1: hologram element 2: laser diode

3: photodetector 4: hologram optical element

5: 1st bobbin surface 6: 2nd bobbin surface

7: bobbin 8: bobbin through hole

9: first lens surface 10: second lens surface

11: Aspherical circular lens 12: Objective lens

13: first disk 14: second disk

The configuration of the dual focus optical pick-up apparatus according to the present invention includes a laser diode 2 for generating a beam of a constant wavelength, a photo detector 3 for outputting optical information as an electric signal, and a hologram as shown in FIG. 4. Hologram element 1 incorporating optical element 4, and bobbin which is formed while maintaining a constant distance from the upper part of the hologram element 1, and the objective lens 11 is settled while focusing coil and tracking coil are wound. (7), a bobbin through hole (8) through which a rectangular portion penetrates into the center of the bobbin (7) so that the width of the beam radiated from the hologram element (1) is different; and the bobbin (7) and the objective lens An aspherical circular lens 11 irradiated differently according to the angle of incidence, and a beam having a specific wavelength formed at a predetermined position on the upper side of the aspherical circular lens 11 and selectively transmitted therebetween; Focusing on the disk 13 to form a beam spot It made of a water lens 12.

Here, when the y-axis and the y-axis are set with respect to the bobbin 7 as shown in FIG. 5, the diameter of the x-axis (the second bobbin plane distance (ie, the distance between 6a and 6b); Larger than the aperture (distance of the first bobbin surface (ie, the distance between 5a and 5b); β). In addition, the aspherical circular lens 11 is formed of a first lens surface 9 and a second lens 10 surface, and the vertical direction (ie, y-axis direction) and the left and right directions with respect to the beam passing through the bobbin 7. The beam spot angles (ie, θ _{1 and} θ ₂ ) in the (x-axis direction) are adjusted.

Next, the operation of the present invention made as described above will be described.

First, a laser beam having a predetermined oscillation wavelength is transmitted from the laser diode 2 of the hologram element 1, and the laser beam passes through the hologram optical element 4 formed on one side of the hologram element 1. It is separated into zero order light and ± first order light, and the separated light is diffracted at a constant wavelength. The diffracted beam then enters the aspherical circular lens 11 formed at the upper side of the bobbin 7 by setting a predetermined beam width via the bobbin through-hole 8 formed in the center of the bobbin 7. . That is, when the incident beam passes through the bobbin through hole 8 and the beam width is uniformly formed in accordance with the angle of incidence and irradiated with the aspherical circular lens 11, the aspherical circular lens 11 enters the first lens surface 9. Two types of beam paths are formed, namely, a beam size and a beam size incident on the second lens surface 10, and information recorded on a digital audio disc (DAD) or a digital video disc (DVD) according to the beam path difference is formed. Will be read selectively.

In other words, the laser beam incident from the hologram element 1 is incident on the first bobbin surface 5 of the bobbin through hole 8 so that a constant beam width is adjusted in the aspherical circular lens 11 to the objective at an angle of θ ₁ . By focusing through the lens 12 to form a beam focus on the disk 13, a focus of about 1 [mu] m is made on the first disk 13 having a thickness of 0.6 mm to read the information recorded on the disk. . At the same time, the laser beam incident from the hologram element 1 is incident in the direction of the second bobbin surface 6 of the bobbin through-hole 8 and passes through the aspherical circular lens 11 at an angle of θ ₂ . The beam focus is focused on the disk 8 to form a beam focus, so that a focus of about 1 [mu] m is made on the second disk 14 having a thickness of 1.2 mm to read the information recorded on the disk.

Therefore, the modulated light information reflected from the first disk 13 and the second disk 14 is returned to the photodetector 3 of the hologram element 1 through the objective lens 12 and the aspherical circular lens 11. The signal is output to the corresponding electrical signal, which is demodulated and reproduced by the signal processing circuit (not shown).

As described above, in the present invention, the laser beam radiated from the laser diode forms a beam focus at different positions as it passes through a rectangular bobbin and an aspherical circular lens, thereby recording on a 1.2 mm disk and a 0.6 mm disk. The information can be easily and selectively read out, making the dual focus optical pick-up device light and small, and significantly reducing the mechanical errors of various optical elements, thereby increasing the reliability of the product.

Claims (1)

A laser diode 2 emitting a constant wavelength and an optical pick-up for condensing a beam emitted from the laser diode 2 with an objective lens 12 to record a signal on a disk and to reproduce the recorded optical information. In the apparatus, The hologram element 1 in which a plurality of optical elements including the laser diode 2 are integrally formed, and the bobbin through holes 8 having different apertures in the x-axis and the y-axis at a predetermined distance from the hologram element 1 are provided. The x-axis of the bobbin (7) formed in the center portion and provided between the bobbin (7) and the objective lens (12) and the beam passed through the bobbin through hole (8) to allow different beam widths to be incident by the angle of incidence And an aspherical circular lens (11) for adjusting the y-axis beam spot angle (θ _1, θ ₂ ) to the objective lens (12) side.