KR980011152A - 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 two-wavelength laser diode for emitting laser beams of first and second wavelengths having different wavelengths; a prism disposed on the upper side of the two-wavelength laser diode and having a plurality of optical elements formed integrally and transmitting a beam; A beam splitter formed at a central portion of the prism so as to diagonally reflect a laser beam incident thereon at a predetermined ratio, a beam splitter formed on both sides of the prism, First and second photodetectors formed on a central portion of the prism and converting and returning optical information reflected from the disk into a current and outputting the current; a first wavelength transmitting portion formed on the prism and having a first wavelength only of the incident beam, And a second wavelength transmitting portion formed on an outer circumferential surface of the wavelength transmitting portion and transmitting only the second wavelength of the incident beam, It is comprised of ever-beam transmitting portions.

Description

Optical pick-up device

In order to solve the above-described problems, the present invention has a two-wavelength laser diode that emits beams of first and second wavelengths having different wavelengths, and includes a beam splitter for a prism, an optional beam transmitting unit for adjusting a beam spot size, Two photodetectors and diffraction gratings are integrally formed so as to eliminate mechanical errors generated during the assembly process, and at the same time, a beam focus of diameters of 1.6 mu m and 0.8 mu m is formed on the disk, It is an object of the present invention to make it 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 width of the pit is remarkably narrow, thereby contributing to the improvement of the reliability of the optical pickup.

That is, the present invention relates to a two-wavelength laser diode which emits a laser beam of first and second wavelengths having different wavelengths, a prism which is disposed on the upper side of the two-wavelength laser diode and in which a plurality of optical elements are integrally formed, A diffraction grating formed on the lower surface of the prism for separating the incident beam into three beams to generate a tracking error, a beam splitter formed diagonally at the center of the prism for reflecting and transmitting a laser beam incident thereon at a predetermined ratio, First and second photodetectors formed on the central portions of both sides of the prism to convert optical information reflected from the disk into electrical current and outputting the electrical currents, and a first and a second photodetector formed on the prism, And a second wavelength transmitting portion formed on the outer peripheral surface of the first wavelength transmitting portion and transmitting only the second wavelength of the incident beam, And an optional beam transmitting portion.

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: 2 wavelength laser diode 32: prism

33: beam splitter 34: first photodetector

35: second optical detector 39: diffraction grating

70: selective beam transmitting portion 71: first wavelength transmitting portion

72: second wavelength transmitting portion

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 several times larger than that of the digital audio disk, and the width of the pit is narrowed to about half of that of the digital audio disk, so that the spot size is also small .

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.

Fig. 2 is a schematic view of the optical pick-up apparatus according to the present invention. On the upper side of a two-wavelength laser diode 31 for emitting beams of first and second wavelengths lambda 1 and lambda 2 having different wavelengths, An objective lens 54 for collecting a beam incident on the prism 32 and forming a beam focus on the disk surface 55 is provided on the prism 32. The prism 32 is formed integrally with the optical element, Respectively.

A diffraction grating 39 for generating a tracking error by separating the laser beam emitted from the two-wavelength laser diode 31 into three beams of zero-order light and ± first-order light is formed on the lower surface of the prism 32, 32 are formed in a diagonal direction at a central portion thereof with a beam splitter 33 for reflecting and transmitting beams separated by three beams at a constant ratio.

The first and second photodetectors 34 and 35 are integrally formed at both sides of the prism 32 at opposite sides of the prism 32 so as to face each other and convert the optical information reflected by the disk 55 into current and output the current. A surface of the first photodetector 34 is coated with a reflective film for absorbing and reflecting the incident beam.

An optional beam transmitting portion 70 is provided on the upper surface of the prism 32 to selectively transmit only a laser beam of a specific wavelength and to reflect the laser beam of other wavelengths to adjust the beam spot size due to the numerical aperture and the chromatic difference Respectively.

The selective beam transmitting portion 70 includes a first wavelength transmitting portion 71 that transmits only the first wavelength? 1 emitted from the two-wavelength laser diode 31 and reflects a beam of another wavelength, The second wavelength transmission portion 71 is formed to have a predetermined size on the outer circumferential surface of the first wavelength transmission portion 71. The second wavelength transmission portion 71 transmits only the second wavelength? 2 emitted from the two-wavelength laser diode 31, (72).

In the present invention as described above, first, a laser beam of first and second wavelengths lambda 1 and lambda 2 having different wavelengths is emitted from the two-wavelength laser diode 31, The light beam is diffracted by the diffraction grating 39 formed on the prism 32 to divide the incident beam into three beams of zero-order light and ± first-order light, thereby generating a tracking error, (33) to reflect and transmit the incident beam at a constant rate.

At this time, the laser beam transmitted through the beam splitter 33 is irradiated to the selective beam transmitting portion 70, thereby forming two kinds of beam paths by the first and second wavelength transmitting portions 71 and 72, And reads information recorded on a digital audio disk (DAD) or a digital video disk (DVD) according to a path.

That is, the laser beam of the first wavelength? 1 transmitted through the beam splitter 33 is converged to the angle of? 1 as it is irradiated to the objective lens 54 via only the first wavelength transmitting portion 71, The laser beam of the second wavelength lambda 2 transmitted through the beam splitter 53 is irradiated to the objective lens 54 only through the second wavelength transmitting portion 72, 2 and forms a beam focus on the disk 55. [0064]

Therefore, the first and second wavelength transmitting portions 71 and 72 of the selective beam transmitting portion 70 are divided into two first and second numerical apertures NA1 and NA2, The size of the beam formed on the disk 55 is changed by the light amount of the light beam.

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 first wavelength transmitting portion 71 of the selective beam transmitting portion 70 and converged at the angle of? 1, are the same as the beam size passing through the second wavelength transmitting portion 72, (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 first wavelength transmitting portion 71 of the selective beam transmitting portion 70 and converged at the angle of? 1 by the objective lens 54 is formed on the disk 55 with a beam spot having a size of 1.6 μm The data recorded on the digital audio disk DAD having a longer length of the pit 55a is read and transmitted through the second wavelength transmitting portion 72 of the selective beam transmitting portion 70 so that the angle? The laser beam focused on the disk 55 is formed with a beam spot having a size of 0.8 mu m on the disk 55 so that the data recorded on the digital video disk (DVD) having a smaller length of the pit 55a is read.

That is to say, the light is condensed in the form of air of 1.6 μm and 0.8 μm converged at the angles of θ1 and θ2 by the first and second wavelength transmitting portions 71 and 72 and the objective lens 54 of the selective beam transmitting portion 70, Video disk or the digital audio disk 55. This light is almost returned when there is no pit 55a in which 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.

In this state, assuming that the disc 55 is a digital audio disc, the optical information of the digital audio disc, which is converged at the angle of? 1, returns to the angle of? 1 with the angle of the objective lens 54 and the selective beam transmitting portion 70 Is irradiated to the beam splitter (33) via the first wavelength transmitting portion (71).

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 reflected by the beam splitter 33 to be opposed to the other side of the prism 32 And is irradiated to the second photodetector 35 so that the optical information is output to the electrical signal.

On the other hand, assuming that the disk 55 is a digital video disk, the optical information of the digital video disk which is converged at the angle of 2 is again incident on the objective lens 54 and the second And is irradiated to the beam splitter 33 via only the wavelength transmitting portion 72.

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 performed by the beam size method by the first and second photodetectors 34 and 35, and the tracking error detection is performed by the three beams ) Method.

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

The present invention has a two-wavelength laser diode for emitting beams of first and second wavelengths having different wavelengths, and includes a beam splitter for a prism, a selective beam transmitting portion for adjusting a beam spot size, two photodetectors, a diffraction grating And a beam focus of diameter of 1.6 mu m and 0.8 mu m is formed on the disk at the same time so that the data recording capacity of the digital audio disk is higher than that of the audio disk It is possible to reproduce a digital video disk in which the width of the pit is remarkably narrow, thereby contributing to the improvement of the reliability of the optical pick-up apparatus.

Claims (1)

1. An optical pick-up apparatus for condensing a beam of laser beams as an objective lens to record a signal on a disk and reproduce the recorded information as an electric signal, comprising: a first and a second laser beams having different wavelengths, Wavelength laser diode 31, a prism 32 disposed on the upper side of the two-wavelength laser diode 31 and having a plurality of optical elements formed integrally therethrough and transmitting a beam, A beam splitter 33 formed diagonally at the center of the prism 32 to reflect and transmit a laser beam incident thereon at a predetermined ratio, and a diffraction grating 39 that separates the incident beam into three beams to generate a tracking error. First and second photodetectors 34 and 35 formed on the central portions of both sides of the prism 32 to convert optical information reflected from the disk into current and outputting the current, And only the first wavelength of the incident beam A first wavelength transmitting portion 72 and a second wavelength transmitting portion 72 formed on the outer peripheral surface of the first wavelength transmitting portion 71 and transmitting only a second wavelength of the incident beam, And a transmissive portion (70). ※ Note: It is disclosed by the contents of the first application.