KR980011149A - 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 beams of first and second wavelengths having different wavelengths at the same time, a prism disposed on the upper side of the two-wavelength laser diode and integrally formed with a plurality of optical elements and transmitting a beam, A beam splitter formed diagonally at a central portion of the prism to reflect and transmit the incident laser beam at a predetermined ratio, a photodetector formed at the center of one side of the prism, A reflection type hologram grating formed on the other side of the prism for reflecting and focusing optical information reflected and returned to the photodetector, and a reflection type hologram grating formed on the prism for forming the first and second wavelength light- And the beam spot size of the beam spot can be adjusted on the disc.

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 apparatus used in a digital audio disk generally includes a laser diode 51 for emitting a laser beam, And diffraction gratings 52 for separating light into light for focus and tracking 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 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.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a holographic optical system and a holographic optical system which are equipped with an optic prism, a beam splitter for adjusting a spot size, a selective beam transmitting unit for adjusting a spot size, a photodetector and a reflection type holographic grating. And a beam focus of diameters of 1.6 mu m and 0.8 mu m is formed on the disk at the same time, so that a digital video disk can be reproduced which has a data recording capacity of several times larger than that of the above-mentioned audio disk, So that it is possible to contribute to the improvement of the reliability of the optical pick-up apparatus.

That is, the present invention relates to a two-wavelength laser diode which emits a beam of first and second wavelengths having different wavelengths at the same time, 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 beam splitter formed diagonally at a central portion of the prism and adapted to reflect and transmit an incident laser beam at a predetermined ratio, and a light splitter formed at one side of the prism, A reflection type hologram grating formed on the other side of the prism for reflecting and focusing optical information reflected and returned to the photodetector, and a reflection type holographic grating formed on the prism surface by first and second wavelength light- And a selective beam light-transmitting portion capable of selectively transmitting only the beam to adjust the beam spot size on the disk.

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: first wavelength transmitting portion

27: second wavelength light-projecting unit 28: selective beam-transmitting unit

54: objective lens 55: disk

FIG. 2 is a block diagram of an optical pick-up apparatus according to the present invention. In FIG. 2, a plurality (two or more) of two-wavelength laser diodes 21 for simultaneously emitting beams of first and second wavelengths? 1 An objective lens 54 for collecting a beam incident on the prism 22 and forming a beam focus on the disk 55 is provided on the prism 22, Respectively.

A beam splitter 23 for reflecting and transmitting a laser beam emitted from the laser diode 21 at a predetermined ratio is formed in a diagonal direction at the center of the prism 22, And a photodetector 24 for converting the optical information returned from the light source 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 reflects, An optional beam transmitting portion 28 is formed on the top surface of the disk 55 so as to selectively transmit only a laser beam of a specific wavelength and reflect the laser beam of other wavelengths to adjust the beam spot size on the disk 55. [

Here, the configuration of the selective beam transmitting portion 28 includes a first wavelength transmitting portion 26 for transmitting only the first wavelength? 1 emitted from the two-wavelength laser diode 21 and for reflecting the laser beam having the other wavelengths ) And a second wavelength? 2 emitted from the two-wavelength laser diode (21) formed at a predetermined size on the outer circumferential surface of the first wavelength transmitting portion (26), and the laser beam of the other wavelength is reflected And a second wavelength light projecting part 27 for projecting the light.

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 radiated from the laser diode 21 at the same time, and the laser beam is transmitted through the prism 22, The beam splitter 23 formed in a diagonal direction in the central portion of the beam splitter 22 reflects and transmits the incident beam at a predetermined ratio and irradiates the beam to the selective beam transmitting portion 28.

At this time, the laser beams of the first and second wavelength lambda 1 (lambda 2) irradiated to the selective beam transmitting portion 28 are split by the first and second wavelength light projecting portions 26 and 27 into two types of beam paths And reads information recorded in a digital audio disk (DAD) or a digital video disk (DVD) according to the beam path.

That is, the laser beam of the first wavelength? 1 reflected through the beam splitter 23 is converged to the angle of? 1 as it is irradiated to the objective lens 54 via only the first wavelength transmitting portion 26, The laser beam of the second wavelength lambda 2 reflected through the beam splitter 23 is irradiated to the objective lens 54 via the second wavelength light transmitting portion 27 only, The beam 55 is focused at an angle of? 2 to form a beam focus.

The first and the second numerical apertures NA1 and NA2 are divided by the first and second wavelength light transmitting portions 26 and 27 of the selective beam transmitting portion 28, The size of the beam formed on the disk 55 is changed due to the difference between the numerical apertures, 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 first wavelength transmitting portion 26 of the selective beam transmitting portion 28 and converged at the angle of? 1, are transmitted through the second wavelength transmitting portion 27 and converged at an angle of? 2 (Because the beam size is inversely proportional to NA and the depth of focus is inversely proportional to (NA) 2)

Therefore, the laser beam transmitted through the first wavelength transmitting portion 26 of the selective beam transmitting portion 28 and converged by the objective lens 54 at the angle of? 1 is irradiated onto the disk 55 with a beam spot having a size of 1.6 μm The data stored in the digital audio disk DAD having a longer length of the pit 55a is read and the data is transmitted to the objective lens 54 through the second wavelength light transmitting portion 27 of the selective beam transmitting portion 28 The laser beam focused at the angle of? 2 is formed with a beam spot having a size of 0.8 mu m on the disk 55, thereby reading the data recorded on the digital video disk (DVD) having a narrower length of the pit 55a.

That is, the first wavelength transmitting portion 26 and the second wavelength transmitting portion 27 of the selective beam transmitting portion 28 and the objective lens 54 are arranged at angles of? 1 and? 2, And is irradiated onto the signal surface of the digital video disk or the digital audio disk 55. This light returns almost as it is without the pit 55a in 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.

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 objective lens 54 and the selective beam transmitting portion 28 at an angle of? And the reflected beam is reflected and transmitted at a constant ratio, and the reflected beam is reflected by the beam splitter 23 formed on one side of the prism 22 Type hologram grating 25 and is then irradiated onto 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 that is converged at the angle of? 2 and returns to the angle? 1 and the second wave-radiating portions 26 and 27, and the irradiated beam is reflected and transmitted at a constant ratio, and the reflected beam is reflected on one side of the prism 22 And is reflected and focused by the reflective hologram grating 25 formed thereon and is irradiated to the 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, focus error detection is detected by a Foucault method, and tracking error detection is detected by a push-pull method by a one-beam method.

The present invention includes a two-wavelength laser diode that emits two different wavelengths, and integrally forms a beam splitter, a selective beam transmitting portion, a photodetector, and a reflective holographic grating for adjusting a spot size on a prism And a beam focus of diameters of 1.6 mu m and 0.8 mu m are formed on the disk at the same time, so that the data recording capacity is larger than that of the digital audio disk, It is possible to reproduce a remarkably narrow digital video disk, contributing to the improvement of the reliability of the optical pick-up apparatus.

Claims (1)

1. An optical pick-up apparatus for condensing a laser beam as an objective lens to record a signal on a disk and reproduce the recorded information as an electric signal, characterized in that the first and second wavelengths lambda 1 and lambda 2, A prism 22 disposed on the upper side of the two-wavelength laser diode 21 and having a plurality of optical elements formed integrally therethrough and transmitting a beam, a prism 22 disposed on the prism 22, A beam splitter 23 formed diagonally at the center of the prism 22 to reflect and transmit the incident laser beam at a predetermined ratio, and a beam splitter 23 formed at one side of the prism 22, A reflection type holographic grating 25 formed on the other side of the prism 22 for reflecting and focusing optical information reflected and returned to the photodetector 24, 23, the first and second Jangtu is formed of a portion (26, 27), characterized in that the optical pick-to selectively transmit only the beam of a particular wavelength selective beam consisting of light-transmitting portion 28, which can control the beam spot size on the disc-up device. ※ Note: It is disclosed by the contents of the first application.