KR19980029889A - 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 capable of simultaneously playing back a general digital audio disc (DAD) for music reproduction and a digital video disc (DVD) for video and audio reproduction.

To this end, a silicon substrate in which a plurality of optical elements are placed, a two-wavelength laser diode which is formed inside the support of the upper surface of one side of the silicon substrate and simultaneously emits beams of λ1 and λ2 having different wavelengths, and is formed on the other surface of the silicon substrate A photodetector for converting and returning optical information reflected by the optical signal to an electrical signal, and a prism formed on a top surface of the silicon substrate on which the photodetector is formed to have a predetermined size to transmit a laser beam, and formed on one side of the prism to be incident A diffraction grating separating the beam into three beams, a beam split formed at a predetermined thickness in the center of the prism at a predetermined thickness to reflect and transmit the incident beam at a constant rate, and to generate astigmatism; first and second surfaces of the prism; It is formed as a second light transmission portion to selectively transmit only a beam of a specific wavelength to adjust the spot size on the disk Consists of a beam size control plate.

Description

Optical pick-up device

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] 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. In particular, a digital audio disc (DAD) for general music reproduction and digital for image and audio reproduction are provided. An optical pick-up device for simultaneously playing a video disc (DVD).

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

That is, the structure of the optical pick-up apparatus generally used for digital audio discs is that one side of the laser diode 51 that generates the laser beam as shown in FIG. 1 has the laser beam as light for focusing and tracking error detection. A diffraction grating 52 to be separated is provided at a predetermined interval.

A polarization beam split 53 is disposed on 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, an objective lens 54 having a diffraction limit performance of a predetermined wavelength or less on the polarizing beam split 53 and focusing the separated light on the disk 55 to read recorded information has a predetermined interval. In the lower portion of the polarization beam split 53, a photodetector 56 for converting optical information recorded on the audio and video disc 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 so that focusing and tracking errors can occur. For detection, it splits into three beams (0th order light and ± 1th order light) and emits them.

Accordingly, the light separated for focusing and tracking 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 an objective lens. By 54, the beam is condensed with diffraction limit performance below a predetermined wavelength and sent onto the audio or video disc 55 to focus on the disc 55 to read the recorded information.

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 from the audio or video disc 55 and returned is modulated by the pit 55a, and the modulated light information is transmitted through the objective lens 54 and the polarization beam split 53. ) Is converted into an R. F (RF) signal, a focus signal, and a tracking signal into a current, which is recorded on the disc 55 by demodulating the converted current into an original signal by a digital signal processor (not shown). The audio signal can be reproduced.

Such a conventional optical pick-up apparatus only reads information recorded on one of a digital audio disc (DAD) or a digital video disc (DVD), and cannot selectively read data recorded on two types of discs. do.

The reason for this is that digital video discs have four times the data recording capacity of digital audio discs, so that the width of the pit is about half as narrow as that of digital audio discs. It must be formed.

That is, the spot size of the digital audio disc is 1.6 μm in diameter and the spot size of the digital video disc is 0.6 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 provides a two-wavelength laser diode that emits two different wavelengths, a beam split that has a constant thickness and reflects and transmits an incident beam at a constant rate to generate astigmatism, and selectively transmits only a laser beam having a specific wavelength, Laser beams of other wavelengths are reflected to integrally form a beam size adjusting plate for adjusting spot size on the disc so that beam focus of 1.6 μm and 0.8 μm in diameter can be simultaneously formed on the disc. The data recording capacity is many times larger, and the digital video disc can be reproduced with a significantly narrower pit width.

That is, a silicon substrate in which a plurality of optical elements are placed, a two-wavelength laser diode which is formed inside the support of the upper surface of the silicon substrate and simultaneously emits beams of λ1 and λ2 having different wavelengths, and is formed on the other surface of the silicon substrate. A photodetector for converting and returning optical information reflected by the optical signal to an electrical signal, and a prism formed on a top surface of the silicon substrate on which the photodetector is formed to have a predetermined size to transmit a laser beam, and formed on one side of the prism to be incident A diffraction grating separating the beam into three beams, a beam split formed at a predetermined thickness in the center of the prism at a predetermined thickness to reflect and transmit the incident beam at a constant rate, and to generate astigmatism; first and second surfaces of the prism; A beam yarn formed by the second light transmitting portion to selectively transmit only a beam of a specific wavelength to adjust spot size on the disk. It has been made by the throttle's.

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.

Explanation of symbols for the main parts of the drawings

54 objective lens 55 disc

60 silicon substrate 61 support

62: photodetector 63: 2 wavelength laser diode

65: beam split 66: prism

67 diffraction grating 68 first floodlight

69: second floodlight 70: beam size control plate

FIG. 2 is a block diagram of an optical pick-up apparatus according to the present invention, and includes beams having first and second wavelengths λ1 and λ2 having different wavelengths in one upper surface support 61 of a silicon substrate 60. A two-wavelength laser diode 63 for emitting light is formed, and a photodetector 62 is formed on the other upper surface of the silicon substrate 60 to convert and output optical information reflected from the disk 55 into an electrical signal. have.

In addition, a prism 66 for transmitting a laser beam is formed on the silicon substrate 60 on which the photodetector 62 is formed to have a predetermined size, and a predetermined thickness t is provided at the center of the prism 66. In order to detect and focus error by reflecting and transmitting the incident beam at a constant rate, a beam split 65 is formed in a diagonal direction to generate astigmatism.

In addition, a diffraction grating 67 is formed on one side of the prism 66 to generate a tracking error by separating the beam incident from the two-wavelength laser diode 63 into three beams of 0 order and ± 1 order light. On the upper surface of the prism 66, a beam size adjusting plate 70 is formed on the disk 55 to selectively transmit only a laser beam of a specific wavelength to adjust the beam focusing size.

The beam size adjusting plate 70 is formed to have a predetermined size on the upper surface of the prism 66 to transmit only the first wavelength λ1 emitted from the two-wavelength laser diode 63, and has a laser beam having a wavelength other than that. A second light-transmitting portion 68 reflecting silver and a second light-transmitting portion formed on an outer circumferential surface of the first light-transmitting portion 68 and transmitting only a second wavelength λ 2 emitted from the two-wavelength laser diode 63 ( 69).

According to the present invention, first and second wavelengths λ1 and λ2 having different wavelengths from the two-wavelength laser diode 63 formed in the support 61 on the upper surface of one side of the silicon substrate 60. Laser beams are emitted at the same time, the laser beam of the wavelength is divided into 0-order light and ± 1-order light, that is, 3 beams via the diffraction grating 67 to generate a tracking error, diagonally in the center of the prism 66 Irradiated with the beam split 65 formed.

Accordingly, the beam split 65 reflects and transmits the laser beam emitted from the two-wavelength laser diode 63 at a constant ratio. That is, the laser beams of the first and second wavelengths λ1 and λ2 emitted from the two-wavelength laser diode 63 are reflected and transmitted by the beam split 65 having a predetermined thickness t. The reflected laser beams of the first and second wavelengths λ1 and λ2 are irradiated to the beam size control plate 70 formed on the upper surface of the prism 66.

In this case, the beam size adjusting plate 70 transmits the laser beams of the first and second wavelengths λ1 and λ2 emitted from the two-wavelength laser diode 63 to the first and second light-transmitting portions 68 and 69. Thus, two types of beam paths are formed, and information recorded on a digital audio disc (DAD) or a digital video disc (DVD) is read according to the beam path.

That is, the laser beam of the first wavelength λ1 reflected through the beam split 65 is focused at an angle of θ1 as it is irradiated to the objective lens 54 via only the first light projecting portion 68, thereby disc 55 ), And at the same time, the laser beam of the second wavelength λ2 reflected through the beam split 65 is irradiated to the objective lens 54 only through the second light transmitting portion 69. The light is focused at an angle of? 2 to form beam focus on the disk 55, respectively.

Accordingly, the first and second numerical apertures 68 and 69 of the beam size adjusting plate 70 are divided into two first and second numerical apertures NA1 and NA2. By changing the amount of light, the beam size is formed differently.

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

[Equation 1]

NA1 = ηSinθ1, NA2 = ηSinθ2

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

[Equation 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 each constant so that the NA changes the beam size and depth of focus.)

Therefore, the beam size and the depth of focus that pass through the first light projecting portion 68 of the beam size adjusting plate 70 and focus at an angle of θ1 and the beam size that pass through the second light projecting portion 69 and focus at an angle of θ2 It is formed larger than the depth of focus (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 light-transmitting portion 68 of the beam size adjusting plate 70 and focused at an angle of θ1 by the objective lens 54 forms a beam spot having a size of 1.6 μm on the disk 55. The data recorded on the digital audio disc (DAD) having a longer length of the pit 55a is read, and the angle of? 2 is transmitted by the objective lens 54 by passing through the second light transmitting portion 69 of the beam size adjusting plate 70. The focused laser beam is formed with a beam spot having a size of 0.8 mu m on the disk 55, thereby reading the data contained in the digital video disk DVD having a narrower length of the pit 55a.

That is, the first and second light-transmitting portions 68 and 69 and the objective lens 54 of the beam size adjusting plate 70 are condensed in an airy form of 1.6 μm and 0.8 μm focused at angles of θ1 and θ2. The signal surface of the video disc or the digital audio disc 55 is irradiated, and the light is returned almost as it is in the absence of the pit 55a in which data is recorded, but the light is returned to the pit 55a in the presence of the pit 55a. By diffraction, the light is emitted outside the range of the objective lens 54, thereby causing only a part of the incident light to be returned, thereby generating 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 which is focused at an angle of θ1 is returned to the beam size control plate 70 through the objective lens 54 at an angle of θ1. Only the first wavelength λ1 is transmitted by passing through the first light-transmitting portion 68, and the optical information of the transmitted first wavelength λ1 is transmitted to the beam split 65 having a predetermined thickness t. Is investigated.

At this time, the optical information of the first wavelength λ1 irradiated to the beam split 65 is reflected and transmitted by the beam split 65 at a predetermined ratio, and the double wavelength of the first wavelength λ1 is transmitted. The optical information of? Generates astigmatism for detecting a focus error due to the difference in thickness t of the beam split 65.

Therefore, the audio disc optical information including the astigmatism of the first wavelength [lambda] 1 transmitted by the beam split 65 is focused on the photodetector 62 formed on the upper surface of one side of the prism 66.

On the other hand, assuming that the disk 55 is a digital video disk, the optical information of the digital video disk focused and returned at an angle of θ2 is again transmitted through the objective lens 54 at the angle of θ2. By passing through the second light-transmitting section 69, only the second wavelength λ2 is transmitted, and the optical information of the transmitted second wavelength λ2 is irradiated to the beam split 65 having a predetermined thickness t. do.

At this time, the optical information of the second wavelength λ2 irradiated to the beam split 65 is reflected and transmitted at a predetermined ratio by the beam split 65, and the optical information of the transmitted second wavelength λ2 The optical information generates astigmatism for detecting a focus error due to the difference in thickness t of the beam split 65.

Therefore, the video disc optical information including the astigmatism of the second wavelength [lambda] 2 reflected by the beam split 65 is focused on the photodetector 62 formed on the upper surface of the silicon substrate 60.

Therefore, the photodetector 62 converts and outputs optical information of the disk into a current, and uses the output of the photodetector 62 to output an RF signal, a focus signal, and a tracking signal by a digital signal processor (not shown). By detecting and demodulating the signal into the original signal, audio signals recorded on digital audio and video discs are reproduced.

That is, in the structure of the present invention, the focus error detection is detected by the astigmatism method by the beam split 65 having a predetermined thickness t, and the tracking error detection is detected by the 3-beam method by the diffraction grating. .

According to the present invention, beam diameters of 1.6 μm and 0.8 μm in diameter are simultaneously formed on the disc, so that not only the digital audio disc but also the data recording capacity is many times larger than that of the audio disc. This can contribute to improving the reliability of the optical pick-up device.

Claims (1)

In an optical pick-up apparatus for condensing a beam using a laser beam as an objective lens, recording a signal on a disk, and reproducing the recorded information as an electric signal, a silicon substrate 60 in which a plurality of optical elements are placed; The two-wavelength laser diode 63 is formed inside the support 61 on one side of the silicon substrate 60 and simultaneously radiates beams of λ1 and λ2 having different wavelengths, and is formed on the other surface of the silicon substrate 60. A photo detector 62 for converting and returning optical information reflected by 55 into an electrical signal, and having a predetermined size formed on the upper surface of the silicon substrate 60 on which the photo detector 62 is formed to transmit a laser beam. The prism 66, a diffraction grating 67 formed on one side of the prism 66 to separate the incident beam into three beams, and formed in a central portion of the prism 66 at a predetermined thickness t in a diagonal direction to be incident Reflects and transmits the beam at a constant rate The beam split 65 generating the score difference and the first and second light transmitting portions 68 and 69 are formed on the upper surface of the prism 66 to selectively transmit only a beam having a specific wavelength so that the spot size on the disk can be improved. Optical pick-up device, characterized in that made of adjusting the beam size adjusting plate (70).