KR980011141A - 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.

A laser diode disposed on the upper side of the laser diode and integrally formed with a plurality of optical elements and transmitting a beam; a laser beam formed diagonally at a central portion of the prism and incident on the laser diode; First and second photodetectors formed on the central portions of both sides of the prism for converting and returning optical information reflected from the disk to a current and outputting the current; And a spot size adjusting plate for adjusting the size of the beam spot on the disk, the beam size adjusting plate being composed of a combat light portion transmitting the entire beam and a semi-light projecting portion formed inside the combat light portion to reflect and transmit the incident beam at a predetermined ratio.

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, the structure of the optical pick-up device used in a digital audio disc generally includes a laser diode 51 for generating a laser beam as shown in FIG. 1, And diffraction gratings 52 for separating light into light for error detection 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, and two photodetectors are integrally formed by integrally forming a beam splitter on a prism to eliminate mechanical errors generated in the assembly process, and a beam focus of diameters of 1.6 μm and 0.8 μm So that it is possible to reproduce a digital video disk in which the data recording capacity is several times larger than that of the audio disk and the pit width is significantly narrower than that of the digital audio disk so as to contribute to the improvement of the reliability of the optical pick- There is a purpose of.

That is, the present invention provides a laser diode having a laser diode emitting a laser beam of a predetermined wavelength, a prism disposed on the upper side of the laser diode and having a plurality of optical elements formed integrally therethrough and transmitting a beam, A beam splitter for reflecting and transmitting the laser beam at a predetermined ratio, first and second photodetectors formed on both sides of the prism for converting and returning optical information reflected from the disk to a current, And a spot size regulating plate formed on the inside of the combat light portion and configured to regulate the size of the beam spot on the disc, the reflector being formed of a semi-light-projecting portion for reflecting and transmitting the incident beam at a predetermined ratio.

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.

FIG. 3 is a view of a beamforming in focus error detection of the optical pick-up apparatus according to the present invention. FIG.

DESCRIPTION OF THE REFERENCE NUMERALS

31: laser diode 32: prism

33: beam splitter 34: first photodetector

35: second optical detector 36: spot size adjusting plate

38: Translucent Miner 37: Combat Miner

54: objective lens 55: disk

FIG. 2 is a schematic view of an optical pick-up apparatus according to the present invention. In the optical pick-up apparatus according to the present invention, a plurality of optical elements are integrally formed on a laser diode 31 for emitting a laser beam of a predetermined wavelength, And an objective lens 54 for focusing a beam incident thereon and forming a beam focus on the disk surface 55 is disposed on the upper side of the prism 32.

A beam splitter 33 for reflecting and transmitting a laser beam radiated from the laser diode 31 at a predetermined ratio is formed in a diagonal direction at the central portion of the prism 32, The first and second photodetectors 34 and 35 are integrally formed to convert the optical information reflected by the first photodetector 55 into a current and output the converted current. And a reflective film which is absorbed and reflected is coated.

The prism 32 has a combed light portion 37 for transmitting the entire amount of the incident beam and a semitransparent portion 38 formed inside the combed light portion 37 for reflecting and transmitting the incident beam at a constant ratio, And a spot size regulating plate 36 for controlling the size of the beam spot on the disk 55 is integrally formed.

In the present invention as described above, a laser beam of a predetermined wavelength is first radiated from the laser diode 31. The laser beam is transmitted through a prism 32 to the prism 32 in the diagonal direction, So that the incident beam is reflected and transmitted at a constant rate.

At this time, as the laser beam transmitted through the beam splitter 33 is irradiated on the spot size regulating plate 36, two kinds of beam paths are formed. The spot size is formed differently according to the beam path, and a digital audio disk DAD ) Or a digital video disk (DVD).

That is, the laser beam reflected through the beam splitter 33 is half-reflected by the translucent portion 38 of the spot-size adjusting plate 36, 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 33 is totally transmitted by the combed light portion 37 of the spot size regulating plate 36 and is irradiated to 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 of the spot size regulating plate 36 are divided by the light converting portion 37 and the translucent portion 38, 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 38 of the spot size regulating plate 36 and converged at the angle of? 1, are smaller than the beam size and depth of focus converged at the angle of? 2 through the comb- (Because the beam size is inversely proportional to NA and the depth of focus is inversely proportional to (NA) 2)

Therefore, the laser beam that has been transmitted through the semi-transparent portion 38 of the spot size regulating plate 36 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 mu m, The laser beam is converged by the objective lens 54 at the angle of? 2 and the laser beam is converged by the objective lens 54 at the angle of? 2, 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.

That is, the light is condensed in the airy form of 1.6 占 퐉 and 0.8 占 퐉 converged at the angles? 1 and? 2 by the combinational light portion 37, the translucent portion 38 and the objective lens 54 of the spot size regulating plate 36, 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? 1 at the angle of? 1 with respect to the objective lens 54 and the spot size regulating plate 36 Is irradiated to the beam splitter (33) via the translucent portion (38).

Therefore, the beam splitter 33 reflects and transmits the optical information returned through the disk 55 at a predetermined ratio, and the reflected beam is formed on one side of the prism 32 and has a reflective film formed on the surface thereof 1 photodetector 34 to output the optical information to the electrical signal.

At this time, the incident light information is reflected by the reflection film formed on the surface of the first photodetector 34, and the reflected light information is transmitted through the beam splitter 33 2 photodetector 35, thereby outputting the optical information to the electrical signal.

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- The beam splitter 33 is irradiated via both the beam splitter 37 and the semi-transparent portion 38.

Therefore, as described above, the beam splitter 33 reflects and transmits the light information returned through the disk 55 at a predetermined ratio, and the reflected beam is irradiated to the first photodetector 34, And the optical information is outputted to the second photodetector 35 by the reflection film formed on the surface of the first photodetector 34 so that the optical information is output to the electrical signal.

Accordingly, the current corresponding to the optical information of the disk output from the first and second photodetectors 34 and 35 is converted into an RF signal, a focus signal, and a tracking signal by a digital signal processing unit And reproduces the audio signal recorded on the digital audio and video disk by demodulating the audio signal into the original signal.

In the structure of the present invention, the focus error detection is detected by the beam size method by the first and second photodetectors 34 and 35 and the push-pull method by the tracking error detection.

That is, in the focus error detection by the beam size method, when the focus is in the optimum state as in FIG. 3, the beam sizes of the first and second photodetectors 34 and 35 are matched as shown in (B) The beam size of the first photodetector 34 is formed to be larger than that of the second photodetector 35 as shown in (A), and when the focus is far away, as shown in (A) The focus of the first photodetector 35 is formed to be larger than that of the first photodetector 34 so that the focus error can be accurately detected by the difference of the beam sizes detected by the first and second photodetectors 34 and 35.

In the present invention, a beam splitter, a spot size regulating plate, two photodetectors, and the like are integrally formed by integrally forming a beam splitter on a prism, thereby eliminating a mechanical error generated in the assembling process. At the same time, Focus can be 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, thereby contributing to the improvement of the reliability of the optical pick- .

Claims (1)

1. An optical pick-up apparatus for condensing a beam with a laser beam as an objective lens to record a signal on a disk and reproduce the recorded information as an electrical signal, comprising: a laser diode (31) for emitting a laser beam of a predetermined wavelength; A prism 32 disposed on the upper side of the laser diode 31 and having a plurality of optical elements formed integrally therethrough and transmitting a beam; a prism 32 formed diagonally at a central portion of the prism 32 to reflect the incident laser beam at a predetermined ratio First and second photodetectors 34 and 35 formed at both sides of the prism 32 to convert the optical information reflected from the disk into a current and output the current, A combed light portion 37 formed on the upper surface of the prism 32 to transmit the entire incident beam and a translucent portion 38 formed at the central portion of the combed light portion 37 to reflect and transmit the incident beam at a predetermined ratio On the disk Optical pick, characterized in that consists of spot size control panel 36 to control the spot size-up device. ※ Note: It is disclosed by the contents of the first application.