KR980011140A - Optical pick-up device - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pick-up apparatus for recording a signal on an optical data recording medium and reproducing the recorded information as an electric signal, And a video disk (DVD) can be played back at the same time.

For this purpose, a laser diode for emitting a laser beam of a predetermined wavelength, a prism for arranging a plurality of optical elements integrally on the upper side of the laser diode and transmitting a beam, a tracking error of three beams formed on the lower surface of the prism A beam splitter formed at a central portion of the prism so as to diagonally reflect and transmit a laser beam incident thereon at a predetermined ratio, optical information formed on one side of the prism and reflected from the disk and converted into a current A reflection type holographic grating formed on the other side of the prism for reflecting and focusing optical information reflected and returned to the photodetector, a comb-shaped hologram grating formed on the prism for transmitting the entire amount of the incident beam, And a translucent portion formed inside the comb-shaped light portion to reflect and transmit the incident beam at a predetermined ratio, It is made consisting of a spot size control panel for adjusting the beam spot size on the disk.

Description

Optical pick-up device

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pick-up apparatus for recording a signal on an optical data recording medium and reproducing the recorded information as an electric signal, And a video disk (DVD) can be played back at the same time.

2. Description of the Related Art In general, an optical pick-up apparatus for reproducing electric signals from information recorded on a digital audio disk (DAD) or a digital video disk (DVD) is provided with individual components such as an objective lens, a beam splitter, a diffraction grating, a laser diode, .

That is, as shown in FIG. 1, a structure of an optical pick-up device used in a digital audio disc generally includes a laser diode 51 for generating a laser beam, And diffraction gratings 52 for separating light into tracking error detection light are provided at predetermined intervals.

A beam splitter 53 is disposed on one side of the diffraction grating 52 and has a predetermined slope so as to separate the incident light into the reflected light and the transmitted light having a constant reflectance and transmittance.

An objective lens 54 having a diffraction limit performance of a predetermined wavelength or less and condensing the separated light to focus information on the disk 55 and reading information recorded thereon is disposed at a predetermined interval on the beam splitter 53 And a photodetector 56 for converting the optical information recorded on the audio and video disk 55 into an electric current through an objective lens 54 at a lower portion of the beam splitter 53 is installed at a predetermined interval .

In the conventional optical pick-up apparatus having such a structure, first, a laser beam having a predetermined oscillation wavelength is emitted from the laser diode 51. As the laser beam passes through the diffraction grating 52, the focus and tracking error Three beams for detection (THREE BEAM: zero-order light and ± one-order light) are separated and emitted.

Therefore, the light separated by the diffraction grating 52 is emitted to the beam splitter 53 having a constant reflectance and transmittance, thereby separating the incident light into the reflected light and the transmitted light, and the reflected light is transmitted to the objective lens 54 The beam is focused on the audio or video disk 55 to focus on the disk 55 and read the information recorded on the disk 55. [

In other words, the objective lens 54 condenses light onto the signal surface of the disk 55 in the form of air having a size of several micrometers. The light is returned almost as it is without the pit 55a on which the data is recorded, The light is diffracted by the pit 55a and is emitted outside the range of the objective lens 54. As a result, only a part of the incident light is returned, thereby causing a light amount difference in the photodetector 56. [

On the other hand, the intensity of the light reflected from the audio or video disk 55 is modulated by the pit 55a, and the modulated light information is transmitted through the objective lens 54 and the beam splitter 53 to the photodetector 56 To convert the optical information into a current and demodulate the converted current into an original signal by a digital signal processing unit (not shown) to reproduce the audio signal recorded on the disk 55. [

Such a conventional optical pick-up apparatus is disadvantageous in that a plurality of individual optical elements are assembled and constituted, thereby causing a mechanical error in the assembling process. Further, the conventional optical pick-up apparatus is also capable of recording on one of a digital audio disk (DAD) It is impossible to selectively read the data recorded on the two types of discs.

The reason is that the data recording capacity of the digital video disk is four times as large as that of the digital audio disk, and the width of the pit is reduced to about half that of the digital audio disk, so that the spot size is also small Should be formed.

That is, when the spot size in the digital audio disk is 1.6 mu m in diameter and the spot size in the digital video disk is 0.8 mu m in diameter, audio and video data recorded on the disk can be accurately reproduced.

Therefore, since the conventional optical pick-up apparatus shown in FIG. 1 can form a spot size of only one of a diameter of 1.6 μm and a diameter of 0.8 μm, it is possible to selectively reproduce audio and digital video disks having different data recording systems A problem that can not be solved occurs.

In the present invention, a beam splitter, a spot size regulating plate, a photodetector, a reflection type holographic grating, and a diffraction grating are integrally formed and integrated in a prism to remove a mechanical error generated in the assembly process, A beam focus of 0.8 mu m is formed at the same time, so that it is possible to reproduce a digital video disk not only a digital audio disk but also a digital video disk whose data recording capacity is several times larger than that of the audio disk so that the pit width is remarkably narrow. The present invention has been made to solve the above problems.

That is, the present invention provides a laser diode device comprising: a laser diode that emits a laser beam of a predetermined wavelength; a prism that is disposed on the upper side of the laser diode and includes a plurality of optical elements integrally formed and transmits a beam; A beam splitter formed at a central portion of the prism for generating an error; a beam splitter formed diagonally at a central portion of the prism to reflect and transmit the incident laser beam at a predetermined ratio; optical information formed at the center of one side of the prism, A reflection type holographic grating formed on the other side of the prism for reflecting and focusing optical information reflected and returned to the photodetector; a reflection type holographic grating formed on the prism for transmitting the entire amount of the incident beam; And a translucent portion formed inside the combat light portion to reflect and transmit the incident beam at a predetermined ratio, And a spot size adjustment plate for adjusting the beam spot size on the disc.

FIG. 1 is a block diagram of a conventional optical pick-up apparatus. FIG.

FIG. 2 is a configuration diagram of an optical pick-up apparatus according to the present invention; FIG.

DESCRIPTION OF THE REFERENCE NUMERALS

21: laser diode 22: prism

23: beam splitting 24: photodetector

25: reflection type holographic grating 26: translucent part

27: Combat Miner 28: Spot size control plate

29: diffraction grating 54: objective lens

55: disk

FIG. 2 is a schematic view of the optical pick-up apparatus according to the present invention. In FIG. 2, a prism 22 having a plurality of optical elements integrally formed on a laser diode 21 for emitting a laser beam of a predetermined wavelength, And an objective lens 54 for focusing the incident beam and forming a beam focus on the disk surface 55 is disposed above the prism 22.

A diffraction grating 29 is formed on the lower surface of the prism 22 for separating the laser beam emitted from the laser diode 21 into three beams of zero-order light and ± first-order light to generate a tracking error.

A beam splitter 23 for reflecting and transmitting a beam separated by the diffraction grating 29 at a predetermined ratio is formed in a diagonal direction at the central portion of the prism 22, And a photodetector 24 for converting the optical information reflected by the photodetector 55 into a current and outputting the current is integrally formed.

A reflective hologram grating 25 is formed on the other side of the prism 22 for reflecting and focusing optical information reflected from the disk 55 and irradiating the light to the photodetector 24. The prism 22 has a A combinational light portion 27 for transmitting the entire amount of the incident beam and a semi-transparent portion 26 formed inside the combinational light portion 27 for reflecting and transmitting the incident beam at a constant ratio are mixed and formed on the disk 55, And a spot size regulating plate 28 for regulating the beam spot size are integrally formed.

The laser beam emitted from the laser diode 21 is irradiated to the diffraction grating 29 formed on the lower surface of the prism 22, Shading and ± first-order light beams to generate a tracking error. Then, the beam splitter 23 is irradiated to the central portion of the prism 22 in a diagonal direction to reflect and transmit the incident beam at a predetermined ratio.

At this time, the laser beam transmitted through the beam splitter 23 is irradiated on the spot size regulating plate 28 to form two kinds of beam paths, and the spot size is formed differently according to the beam path, ) Or a digital video disk (DVD).

That is, the laser beam reflected through the beam splitter 23 is half-reflected by the translucent portion 26 of the spot size regulating plate 28, and the other half is transmitted, and the transmitted beam passes through the objective lens 54 And is focused at an angle of &thetas; 1 to form a beam focus on the disk 55. [

At the same time, the laser beam reflected by the beam splitter 23 is entirely transmitted by the comb-shaped beam portion 27 of the spot size regulating plate 28 and irradiated onto the objective lens 54, The beam focus is formed on the disk 55 at an angle of &thetas;

Therefore, the first and second numerical apertures NA1 and NA2 are divided into two parts by the combed light portion 27 and the translucent portion 26 of the spot size regulating plate 28. By the difference between these two numerical apertures The size of the beam formed on the disk 55 is changed, resulting in a difference in the amount of light.

Here, the numerical expression of the numerical aperture is as follows.

NA1 =? Sin? 1 (1)

, And NA2 =? Sin? 2.

(Where eta is the refractive index and eta in the air is 1.)

NA1 = Sin? 1 (2)

, And NA2 = Sin &thetas; 2.

D = K x lambda / NA, H = R x lambda / (NA) 2 (3)

(Where D is the beam size, H is the depth of focus, and K and R are constants, respectively, the beam size and depth of focus change as the NA changes).

Therefore, the beam size and the depth of focus, which are transmitted through the translucent portion 26 of the spot size regulating plate 28 and converged at the angle of? 1, are smaller than the beam size and depth of focus converged at the angle? (Because the beam size is inversely proportional to NA and the depth of focus is inversely proportional to (NA) 2)

Thus, the laser beam that has been transmitted through the semi-transparent portion 26 of the spot size regulating plate 28 and focused by the objective lens 54 at the angle of? 1 is formed on the disk 55 with a beam spot having a size of 1.6 m, 55a of the spot size regulating plate 28 and transmitted through the combed light portion 27 of the spot size regulating plate 28 and is converged by the objective lens 54 at an angle of? The beam is formed with a beam spot having a size of 0.8 mu m on the disk 55, thereby reading the recorded data on the digital video disk (DVD) having a narrower length of the pit 55a.

In other words, the light is condensed in the airy form of 1.6 袖 m and 0.8 袖 m converged at the angles of 慮 1 and 慮 2 by the combed light portion 27, the translucent portion 26 and the objective lens 54 of the spot size regulating plate 28, Or the signal surface of the digital audio disk 55. This light is returned almost as it is in the absence of the pit 55a in which the data is recorded but in the place where the pit 55a is located, Diffracted by the objective lens 54 and emitted out of the range of the objective lens 54. As a result, only a part of the incident light is returned, resulting in a light amount difference in the photodetector.

Assuming that the disc 55 is a digital audio disc in this state, the optical information of the digital audio disc, which is converged at the angle of? 1, returns again to the angle of? 1 with respect to the objective lens 54 and the spot size regulating plate 28 And is irradiated to the beam splitter 23 via the translucent portion 26.

Therefore, the beam splitter 23 reflects and transmits the optical information returned through the disk 55 at a predetermined ratio, and the reflected beam is reflected by the reflective hologram grating 25 formed on one side of the prism 22, And is irradiated to the photodetector 24 formed on the other side of the prism 22. [

On the other hand, assuming that the disk 55 is a digital audio disk, the optical information of the digital audio disk, which is converged at the angle of 2, is again incident on the objective lens 54 and the comb- Is irradiated to the beam splitter (23) via the beam splitter (27).

Therefore, as described above, the beam splitter 23 reflects and transmits the light information returned through the disk 55 at a predetermined ratio, and the reflected beam is reflected by the reflective hologram 22 formed on one side of the prism 22 Is reflected and focused by a grating (25) and is irradiated to a photodetector (24) formed on the other side of the prism (22).

The photodetector 24 converts the optical information of the disk into a current and outputs an RF signal, a focus signal, and an RF signal by a digital signal processing unit (not shown) The audio signal recorded on the digital audio and video disc is reproduced by detecting and demodulating the tracking signal into the original signal.

In the structure of the present invention, the focus error detection is detected by the Foucault method, and the tracking error detection is detected by the three beam method by the diffraction grating 29.

In the present invention, a beam splitter, a spot size regulating plate, a photodetector, a reflection type holographic grating, and a diffraction grating are integrally formed and integrated in a prism to remove a mechanical error generated in the assembly process, A beam focus of 0.8 mu m is formed at the same time, so that it is possible to reproduce a digital video disk not only a digital audio disk but also a digital video disk whose data recording capacity is several times larger than that of the audio disk so that the pit width is remarkably narrow. It can contribute.

Claims (1)

A optical pick-up apparatus for condensing a beam with an objective lens and recording a signal on a disc and reproducing the recorded information by an electric signal, comprising: a laser diode (21) for emitting a laser beam of a predetermined wavelength; A prism 22 disposed on the upper side of the laser diode 21 and having a plurality of optical elements formed integrally therethrough and transmitting a beam, a diffraction grating (not shown) formed on the lower surface of the prism 22 for generating a tracking error of three beams 29, a beam splitter 23 diagonally formed at the center of the prism 22 for reflecting and transmitting the incident laser beam at a predetermined ratio, a reflector 23 formed at the center of one side of the prism 22, A reflection type hologram formed on the other side surface of the prism 22 for reflecting and focusing optical information reflected and reflected by the photodetector 24, A prism 22 formed on the upper surface of the prism 22 and having a combinational light portion 27 for transmitting the entire amount of the incident beam 27 and a half- And a spot size regulating plate (28) composed of a light part (26) and controlling a beam spot size on the disk. ※ Note: It is disclosed by the contents of the first application.