KR100190576B1 - Optical pickup 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. An optical pick-up device for simultaneously playing a video disc (DVD).

To this end, a two-wavelength laser diode which simultaneously emits beams of first and second wavelengths having different wavelengths, a prism disposed on the upper side of the two-wavelength laser diode, in which a plurality of optical elements are integrally formed and transmitting the beam, the prism A beam split that is diagonally formed at a central portion of the beam to reflect and transmit an incident laser beam at a predetermined ratio, and is formed to face the central portions of both sides of the prism, and converts and outputs optical information reflected from the disk to current And a second photodetector and an optional beam transmitter formed on the upper surface of the prism to selectively transmit only a beam having a specific wavelength and to adjust a 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. An optical pick-up device for simultaneously playing a video disc (DVD).

In general, optical pick-up devices for reproducing an electric signal from information recorded on a digital audio disc (DAD) or a digital video disc (DVD) include individual parts such as an objective lens, a beam split, a diffraction grating, a laser diode, and a photodetector. Assemble using

That is, the structure of the optical pick-up device, which is generally used for digital audio discs, focuses and tracks the laser beam on one side of the laser diode 51 that generates the laser beam as shown in FIG. A diffraction grating 52 for separating the light for error detection is provided at a predetermined interval.

In addition, a beam split 53 is installed at one side of the diffraction grating 52 to have a predetermined inclination and to separate incident light into reflected light and transmitted light with a predetermined ratio of reflectance and transmittance.

In addition, the objective lens 54 having a diffraction limit performance of a predetermined wavelength or less on the upper portion of the beam split 53 and focusing the separated light on the disk 55 reads the recorded information. In the lower portion of the beam split 53, a photodetector 56 for converting optical information recorded on the audio and video disk 55 into current through the objective lens 54 is installed at a predetermined interval. It is.

The conventional optical pick-up apparatus having such a structure first transmits a laser beam having a predetermined oscillation wavelength from the laser diode 51, and the laser beam passes through the diffraction grating 52, thereby causing a focusing and tracking error. It is separated and radiated into 3 beams (THREE BEAM: 0th order, ± 1st order) for detection.

Accordingly, the light separated by the diffraction grating 52 is emitted to the beam split 53 having a constant ratio of reflectance and transmittance, thereby separating incident light into reflected light and transmitted light, and the reflected light is applied to the objective lens 54. By condensing the beam with a diffraction limit performance of less than a predetermined wavelength, the beam is focused on the audio or video disc 55 and focused on the disc 55 to read the information recorded on the disc 55.

In other words, the objective lens 54 collects light in the form of Airy on the order of several micrometers and irradiates the signal surface of the disk 55. The light is returned almost as it is when there is no pit 55a in which data is recorded. Where there is a pit 55a, light is diffracted by the pit 55a and emitted outside the range of the objective lens 54, thereby causing only part of the incident light to be returned, thereby generating a light quantity difference in the photodetector 56.

On the other hand, the intensity of the light reflected back from the audio or video disc 55 is modulated by the pit 55a, and the modulated light information is transmitted to the photodetector 56 through the objective lens 54 and the beam split 53. And converts the optical information into a current, and by demodulating the converted current into an original signal by a digital signal processor (not shown), the audio signal recorded on the disc 55 can be reproduced.

In the conventional optical pick-up device, a mechanical error occurs during the assembly process by assembling a plurality of individual optical elements, and recording on one of a digital audio disc (DAD) or a digital video disc (DVD). It only reads the information that has been read, and it cannot selectively read the data recorded on both types of disks.

The reason for this is that digital video discs have many times more data recording capacity than digital audio discs, and the width of the pit is about half as narrow as that of digital audio discs. Should be.

In other words, the spot size of the digital audio disc is 1.6 μm in diameter and the spot size of the digital video disc is 0.8 μm in diameter so that the audio and video data recorded on the disc can be accurately reproduced.

Accordingly, the conventional optical pick-up apparatus shown in FIG. 1 can form a spot size of only 1.6 μm in diameter or 0.8 μm in diameter, and thus can selectively reproduce audio and digital video discs having different data recording methods. There will be no problems.

The present invention includes a two-wavelength laser diode that simultaneously emits beams of first and second wavelengths having different wavelengths, and integrates a beam split, an optional beam projector for adjusting spot size, two photodetectors, and the like into a prism. It eliminates the mechanical errors generated during the assembly process and simultaneously forms the beam focus of 1.6μm and 0.8μm on the disc, and the data recording capacity is many times higher than that of the audio disc. It is an object of the present invention to enable the reproduction of digital video discs with a significantly narrow pit width, thereby contributing to improved reliability of the optical pick-up device.

That is, the present invention is a two-wavelength laser diode which simultaneously emits beams of the first and second wavelengths having different wavelengths, and a prism disposed on the upper side of the two-wavelength laser diode, in which a plurality of optical elements are integrally formed and transmitted through the beam. And a beam split that is formed diagonally at the center of the prism to reflect and transmit an incident laser beam at a predetermined ratio, and is formed to be opposite to the center of both sides of the prism to convert the optical information reflected from the disk and returned to a current. The first and second photodetectors and the first and second wavelength transmitters are formed on the upper surface of the prism, and selectively transmit only beams of a specific wavelength to selectively adjust the beam spot size on the disk.

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

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

3 is a view illustrating beamforming when detecting a focus error of an optical pick-up apparatus according to the present invention;

〈Description of the symbols for the main parts of the drawings〉

31 laser diode 32 prism

33: beam split 34: first photodetector

35: second photodetector 36: selective beam projector

38: first wavelength light emitting portion 37: second wavelength light emitting portion

54 objective lens 55 disc

FIG. 2 is a block diagram of an optical pick-up apparatus according to the present invention, and a plurality of upper wavelengths of two-wavelength laser diodes 31 simultaneously emitting beams of first and second wavelengths λ1 and λ2 having different wavelengths. An optical element of which is integrally formed and a prism 32 for transmitting a beam is disposed, and an objective lens 54 for converging an incident beam to form a beam focus on the disk 55 above the prism 32. Is arranged.

In addition, beam splits 33 for reflecting and transmitting the laser beam radiated from the two-wavelength laser diode 31 at a constant rate are formed in a diagonal direction at the center of the prism 32, and at both centers of the prism 32. The first and second photodetectors 34 and 35 for converting and outputting optical information reflected by the disk 55 to be returned to a current are integrally formed so as to face each other, and the surface of the first photodetector 34 A reflective film is coated to absorb and reflect the incident beam.

In addition, an optional beam transmitting unit 36 may selectively transmit only a laser beam having a specific wavelength on the upper surface of the prism 32, and reflect a laser beam having a wavelength other than that, and adjust the beam spot size on the disk 55. Formed.

Here, the configuration of the selective beam projector 36 transmits only the first wavelength λ1 emitted from the two-wavelength laser diode 31, and reflects the laser beam having a wavelength other than that. And a second wavelength λ2 formed on the outer circumferential surface of the first wavelength transmitting part 38 to be emitted at the predetermined wavelength, and the laser beam having a wavelength other than that is reflected. It consists of a second wavelength light emitting portion 37.

According to the present invention, the laser beams of the first and second wavelengths λ1 and λ2 having different wavelengths are simultaneously radiated from the two-wavelength laser diode 31, and the laser beams are respectively radiated through the prism 32. Irradiated to the beam split 33 formed diagonally in the central portion of the prism 32 to reflect and transmit the incident beam at a constant ratio.

In this case, the laser beam transmitted through the beam split 33 is irradiated to the selective beam projector 36 to form two types of beam paths by the first and second wavelength transmitters 38 and 37. According to this beam path, information recorded on a digital audio disc (DAD) or a digital video disc (DVD) is read.

That is, the laser beam of the first wavelength λ1 reflected through the beam split 33 is focused at an angle of θ1 as it is irradiated to the objective lens 54 via only the first wavelength light transmitting portion 38, and thus the disk ( 55 to form a beam focus, and at the same time, the laser beam of the second wavelength λ2 reflected through the beam split 33 is irradiated to the objective lens 54 via only the second wavelength light transmitting part 37. As a result, the light is focused at an angle θ2 to form a beam focus on the disk 55.

Therefore, the first and second numerical apertures NA1 and NA2 are divided by the first wavelength transmitter 38 and the second wavelength transmitter 37 of the selective beam projector 36. The size of the beam formed on the disk 55 is changed by the difference in numerical aperture, which causes a difference in the amount of light.

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

[Equation 1]

NA1 = ηSinθ1, and NA2 = ηSinθ2.

(Where η is the refractive index and η is 1 in air)

[Formula 2]

NA1 = Sinθ1, and NA2 = Sinθ2.

[Equation 3]

D = K × λ / NA, H = R × λ / (NA) ²

(Where D is the beam size, H is the depth of focus, and K and R are constants, respectively, so that the NA changes in beam size and depth of focus.

Therefore, the beam size and focus depth transmitted through the first wavelength transmitter 38 of the selective beam projector 36 and focused at an angle of θ1 are transmitted through the second wavelength transmitter 37 and focused at an angle of θ2. It is formed larger than the beam size and the depth of focus (because the beam size is inversely proportional to NA and the depth of focus is inversely proportional to (NA) ² ).

Accordingly, the laser beam transmitted through the first wavelength transmitting portion 38 of the selective beam transmitting portion 36 and focused at an angle of θ1 by the objective lens 54 has a beam spot of 1.6 μm on the disk 55. As a result, the data recorded on the digital audio disc (DAD) having a longer length of the pit 55a is read, and the light is transmitted through the second wavelength transmitting portion 37 of the selective beam transmitting portion 36 to the objective lens 54. The laser beam focused at an angle of? 2 forms a beam spot having a size of 0.8 mu m on the disc 55, thereby reading data contained in a digital video disc DVD having a narrower length of the pit 55a.

That is, 1.6 μm and 0.8 μm of airy focused at the angles of θ1 and θ2 by the second wavelength transmitting part 37, the first wavelength transmitting part 38, and the objective lens 54 of the selective beam transmitting part 36. Condensed into a shape and irradiated to the signal surface of the digital video disc or the digital audio disc 55, and the light is returned almost as it is in the absence of the pit 55a in which the data is recorded, but where the pit 55a is present. The light is diffracted by the pit 55a and emitted outside the range of the objective lens 54, thereby causing only a part of the incident light to be returned, thereby causing a light quantity 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 that is focused and returned at an angle of θ1 is again returned to the objective lens 54 and the selective beam projector 36 at an angle of θ1. The beam split 33 is irradiated via the first wavelength light-transmitting portion 38.

Accordingly, the beam split 33 reflects and transmits the optical information returned through the disk 55 at a constant rate, and the reflected beam is formed on one side of the prism 32 and a reflective film is formed on the surface thereof. 1 is irradiated to the photodetector 34 to output the optical information as an electrical signal.

At this time, the incident light information is reflected by a reflective film formed on the surface of the first photodetector 34, and the reflected light information is formed on the other side of the prism 32 through the beam split 33. 2 is irradiated to the photodetector 35 to output the optical information as an electrical signal.

On the other hand, assuming that the disk 55 is a digital video disk, the optical information of the digital video disk that is focused and returned at an angle of θ2 is again generated by the objective lens 54 and the selective beam projector 36 at an angle of θ2. It is irradiated to the beam split 33 via the 2 wavelength light transmission part 37.

Therefore, as described above, the beam split 33 reflects and transmits the optical information returned through the disk 55 at a constant rate, and the reflected beam is irradiated to the first photodetector 34 to thereby receive the optical information. While outputting as an electrical signal, the optical information is irradiated to the second photodetector 35 by a reflecting film formed on the surface of the first photodetector 34 to output the optical information as an electrical signal.

Therefore, the digital signal processor (not shown) receives current corresponding to the optical information of the disk output from the first and second photodetectors 34 and 35 to output the RF signal, the focus signal, and the tracking signal. By detecting and demodulating the original signal, audio signals recorded on digital audio and video discs are reproduced.

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 tracking error detection by the push-pull method.

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

The present invention includes a two-wavelength laser diode that simultaneously emits beams of first and second wavelengths having different wavelengths, and integrates a beam split, an optional beam projector for adjusting spot size, two photodetectors, and the like into a prism. It eliminates the mechanical errors generated during the assembly process and simultaneously forms the beam focus of 1.6μm and 0.8μm on the disc, and the data recording capacity is many times higher than that of the audio disc. It is possible to play digital video discs with a significantly narrow pit width, thereby contributing to improved reliability of the optical pick-up device.

Claims (1)

An optical pick-up apparatus for condensing a beam using a laser beam as an objective lens to record a signal on a disk, and reproducing the recorded information as an electric signal. The two-wavelength laser diode 31 which simultaneously emits beams of the first and second wavelengths λ1 and λ2 having different wavelengths, and is disposed above the two-wavelength laser diode 31 so that a plurality of optical elements are integrated. A prism 32 which is formed and transmits the beam, a beam split 33 which reflects and transmits a laser beam that is formed diagonally at a central portion of the prism 32 at a predetermined ratio, and both central portions of the prism 32 First and second photodetectors 34 and 35 and opposing first and second wavelength light emitters formed on the upper surface of the prism 33 to convert the optical information reflected by the disk and returned from the disk into current. (38) An optical pick-up apparatus, comprising: an optional beam transmitting unit (36) formed by (37) to selectively transmit only a beam of a specific wavelength to adjust a beam spot size on a disk.