KR980011157A - Optical pick-up device - Google Patents

Abstract

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 by an electric signal, and more particularly to an optical pick-up apparatus for picking up a laser beam having a first wavelength and a second wavelength, Wavelength laser diode, a beam splitter formed integrally with a plurality of optical elements at a predetermined interval on one side of the two-wavelength laser diode, and a laser beam of a specific wavelength formed at a predetermined position above the beam splitter, The laser beam of the wavelength is reflected to adjust the spot size so that when a laser beam of a specific wavelength passes through the wavelength selective light transmitting portion, 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 is larger than that of the above-mentioned audio disc, so that the width of the pit is remarkably narrow It is possible to reproduce a digital video disc, which increases convenience in use, improves the assemblability, facilitates adjustment, and makes it possible to miniaturize the optical pick-up apparatus.

Description

Optical pick-up device

The present invention relates to an optical pick-up apparatus, and more particularly to a beam pick-up apparatus comprising a beam splitter integrally formed with a plurality of optical elements, and a wavelength selective light transmitting portion formed at a predetermined position between the beam splitter and the objective lens to selectively transmit two wavelengths (DAD) and a digital video disk (DVD) at the same time as well as contributing to ease of assembly and adjustment, light weight and shortening.

Generally, an apparatus for picking up recorded information is a system for detecting information on a disk surface by a mechanical change amount using a contact needle and a system for detecting information by changing a capacitance of a fine groove on a disk. However, , A beam splitter, a diffraction grating, a laser diode, a photodetector, or the like, was used to mount a digital audio disk (DAD) with a spot size of 1.6 μm or a digital video disk with a spot size of 0.8 μm A method of reproducing information recorded on a digital versatile disc (DVD) with an electric signal is widely used.

That is, the structure of an optical pick-up apparatus used in a digital audio disc generally includes a laser diode 70 for generating a laser beam of a specific wavelength as shown in FIG. 1, A diffraction grating 71 formed on one side of the diffraction grating 71 for separating the incident laser beam into zero-order and ± first-order light, that is, a three-beam using diffraction phenomenon, and a diffraction grating 71 formed on one side of the diffraction grating 71 at a predetermined slope A beam splitter 72 for splitting the incident beam into a predetermined ratio of reflected light and transmitted light, and a beam splitter 72 for condensing laser light incident on one side of the beam splitter 72 due to a diffraction limit of a certain wavelength, An objective lens 73 for reading the optical signal of the information recorded by focusing on the beam splitter 72, and an objective lens 73 for focusing the optical information recorded on the disk 74 formed at the predetermined position below the beam splitter 72, Convert to signal It comprises a detector 75.

The laser diode 70 emits a laser beam having a predetermined oscillation wavelength, that is, about 780 nm. The laser beam is emitted to one side in the radial direction The diffraction grating 71 is formed. Then, the light incident on the diffraction grating 71 is diffracted into 0-order light and ± 1-order light due to the diffraction phenomenon. At this time, the zero-order light and the ± first-order light separated through the diffraction grating 71 are generally used for focus and tracking error detection and are generally referred to as a three-beam (zero-order light, ± first-order light)

That is, the beam separated by the three-dimensional diffraction grating 71 is incident on the beam splitter 72 having a predetermined reflectance and transmittance at a predetermined slope. Then, the light incident on the beam splitter 72 is separated into a predetermined ratio of reflected light and transmitted light, and the reflected light is incident on the objective lens 73, and the beam is condensed by a diffraction phenomenon below a certain wavelength. Therefore, the beam condensed by the objective lens 73 is transmitted on the disk 74 to be focused, and the information recorded on the disk 74 is reflected by the constant light and incident on the objective lens 73.

At this time, the light incident on the objective lens 73 is condensed into an airy form of about several micrometers and is irradiated onto the signal surface of the disk 73. The irradiated light is incident on the pit 74a where the data is recorded, The beam is reflected and almost entirely returns to the aperture of the objective lens 73. Where the pit 74a is present, the light is diffracted by the pit 74a and emitted outside the range of the objective lens 73, So that only a part of the incident light is returned, thereby causing a light amount difference in the photodetector 75. This is because the depth of the pit 74a is set at? / 4 of the wavelength, and the amount of light returned to the photodetector 75 is reduced because the reflected light is canceled by the interference of the half wave at the upper and lower portions of the pit 74a.

On the other hand, the intensity of the light reflected and returned from the audio or video disk 74 is modulated by the pit 74a, and the modulated light information is passed through the objective lens 73 and the beam splitter 72 to the photodetector 75, And converted into a constant electric signal. Therefore, the converted electric signal is demodulated into an original signal by a digital signal processing unit (not shown), thereby converting an RF signal, which is an audio signal recorded on the disk 74, and an error signal, And a tracking signal is output.

However, since the optical components of the beam splitter, the diffraction grating, the laser diode, and the photodetector are independently manufactured by assembling the optical pick-up apparatus, the conventional optical pick-up apparatus has a mechanical error The digital audio disk (DAD) records and reproduces only audio signals, whereas the digital video disk (DVD) records and reproduces audio and video data, and thus the recording method is different. The optical pick-up apparatus has a problem in that only the information recorded on one disc is read but the data recorded on the two types of discs can not be selectively read.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to provide a two-wavelength laser diode which emits two different wavelengths, a beam splitter in which a plurality of optical elements are integrally formed at one side of the two- And a wavelength selective light-transmitting portion formed at a predetermined position between the beam splitter and the objective lens to selectively reflect the incident two-wavelength light, thereby miniaturizing the optical pick-up device, contributing to ease of assembly and adjustment, In addition, since the laser beam of two wavelengths passes through the wavelength selective light-transmitting portion, the beam focus of diameter of 1.6 mu m and 0.8 mu m is formed on the disc at the same time, so that the data recording density is higher than that of the digital audio disc A light which enables reproduction of a digital video disk having a significantly narrow pit width - it is an object to provide up device.

In order to achieve the above object, the present invention provides a two-wavelength laser diode which emits a laser beam of a first wavelength and a second wavelength, a plurality of optical elements integrally formed at one side of the two- A beam splitter formed at a predetermined position between the beam splitter and the objective lens so as to transmit a laser beam of a specific wavelength among laser beams of two wavelengths reflected by the beam splitter, A wavelength selecting and transmitting unit for reflecting a wavelength laser beam and adjusting a spot size on the disk; a reflection grating formed in a concavo-convex shape at the center of the lower surface of the beam splitter to totally reflect the incident optical information at a predetermined angle; The optical information is formed on one side of the upper surface of the splitter so that the light information totally reflected by the reflection grating is output as a constant electrical signal, Is characterized in that it is provided with a first photodetector, a second photodetector for converting is formed to one side of the center of the beam splitter the reflected light information from the first photodetector to an electrical signal.

FIG. 1 is a configuration diagram for explaining a conventional optical pick-up apparatus; FIG.

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

DESCRIPTION OF THE REFERENCE NUMERALS

1: 2 wavelength laser diode 2: beam splitter

4: wavelength selecting transparent part 5: first wavelength transparent part

6: second wavelength transmitting portion 7: objective lens

8: disc (DAD or DVD) 9: reflective grating

10: first photodetector 11: second photodetector

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIG. 2, the optical pick-up apparatus according to the present invention includes a two-wavelength laser diode 1 for emitting beams of a first wavelength lambda 1 and a second wavelength lambda 2 having different wavelengths, A beam splitter 2 having a predetermined slope on one side of the two-wavelength laser diode 1 and integrally formed with a plurality of optical elements, separating light incident at a predetermined ratio of reflectance and transmittance into reflected light and transmitted light, The laser beam of the other wavelength is selectively transmitted through the laser beam of two wavelengths formed at a predetermined position between the beam splitter 2 and the objective lens 7 and reflected by the beam splitter 2, A wavelength selective light-transmitting portion 4 composed of a first wavelength light-projecting portion 5 and a second wavelength light-projecting portion 6, A beam of a specific wavelength is focused on the disc 8 to form a beam focus Is composed of an objective lens (7).

The beam splitter 2 is provided with a concavo-convex reflective grating (not shown) for totally reflecting the optical information entered through the objective lens 7, the wavelength selective light-projecting portion 4 and the beam splitter 2, 8 are formed. A first side of the beam splitter 2 is connected to a first side of the beam splitter 2 for outputting optical information recorded on the audio and video disk 8 reflected by the reflective grating 9 as a constant electrical signal, A photodetector 10 is formed. A second photodetector 11 for outputting optical information reflected by the first photodetector 10 as an electrical signal is formed at a central portion of one side of the beam splitter 2.

The wavelength selective light-transmitting portion 4 includes a first wavelength transmitting portion 5 for transmitting only the first wavelength? 1 of the two wavelengths reflected by the beam splitter 2 and for reflecting the laser beams of all other wavelengths, , A second wavelength? 2 of the two wavelengths reflected by the beam splitter 2 is formed at a predetermined size on the outer circumferential surface of the first wavelength transmitting portion 5, and laser beams of all other wavelengths are reflected And a second wavelength light projecting part 6 for projecting the light.

Next, the operation of the present invention will be described.

First, the laser beams of the first wavelength lambda 1 and the second wavelength lambda 2 having different wavelengths are simultaneously emitted from the two-wavelength laser diode 1, and the laser beams of the first wavelength lambda 1 and the second wavelength lambda 2 The laser beam is incident on a beam splitter 2 having a constant ratio of reflectance and transmittance. The incident light is separated into reflected light and transmitted light, and the double reflected light is irradiated to the wavelength selective light-

The laser beams of the first wavelength lambda 1 and the second wavelength lambda 2 irradiated to the wavelength selecting and projecting portion 4 are transmitted to the first wavelength transmitting portion 5 and the second wavelength transmitting portion 6 by the first wavelength transmitting portion 5 and the second wavelength transmitting portion 6, And selectively reads the information recorded on the digital audio disk (DAD) or the digital video disk (DVD) according to the beam path difference.

That is, the laser beam of the first wavelength? 1 reflected by the beam splitter 2 passes through the objective lens 7 at the angle of? 1 only through the first wavelength transmitting portion 5 of the wavelength selecting and projecting portion 4 The laser beam of the second wavelength lambda 2 reflected by the beam splitter 2 is incident on the disk 8 at the same time as the laser beam of the second wavelength lambda 2 reflected by the beam splitter 2 passes through the second wavelength- Is focused via the objective lens 7 at an angle of [theta] 2 only through the objective lens 6 to form a beam focus on the disk 8. [ The first numerical aperture NA1 and the second numerical aperture NA2 are divided by the first wavelength transmitting portion 5 and the second wavelength transmitting portion 6 of the wavelength selecting and transmitting portion 4 , The size of the beam formed on the disk 6 is changed by the difference between the two numerical apertures, which causes a difference in light quantity.

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

NA1 =? Sin? 1, NA2 =? Sin? 2 (1)

(where? is the refractive index, refractive index in the air? = 1)

NA1 = Sin? 1, NA2 = Sin? 2 (2)

D = K x? / NA (3)

(D is a beam size, and K is a constant)

H = R x lambda / (NA) 2 (4)

(H is depth of focus, R is constant)

That is, as shown in the above equation, the beam size and the depth of focus are changed by changing the NA of the lens.

Therefore, the beam size and depth of focus formed on the disk 8, which are transmitted through the first wavelength transmitting portion 5 of the wavelength selective light-transmitting portion 4 and converged through the objective lens 7 at an angle of? 1, Is formed to be larger than the beam size and depth of focus formed on the disk (8) through the second wavelength transmitting portion (6) of the transparent portion (4) and converged through the objective lens (7) Therefore, the laser beam, which is transmitted through the first wavelength transmitting portion 5 of the wavelength selecting and projecting portion 4 and converged by the objective lens 7 at the angle of? 1, is formed on the disk 8 with a beam spot having a size of 1.6 mu m The data recorded on the digital audio disk DAD having a longer pit length 8a is read and transmitted through the second wavelength transmitting portion 6 of the wavelength selecting and transmitting portion 4 to be incident on the objective lens 7, the laser beam focused on the disk 8 is formed with a beam spot having a size of 0.8 mu m, thereby reading data recorded on a digital video disk (DVD) having a smaller pit length 8a.

That is, the laser beam formed at the angles of? 1 and? 2 by the first wavelength transmitting portion 5 and the second wavelength transmitting portion 6 of the wavelength selecting and projecting portion 4 is condensed in an airy form of 1.6 占 퐉 and 0.8 占 퐉 And the light is irradiated onto the signal surface of the digital video disk or the digital audio disk 8. This light returns almost as it is in the absence of the pit 8a on which the data is recorded but in the place where the pit 8a is located, Diffracted by the first photodetector 8a and emitted to the outside, so that only a part of the incident light is returned, resulting in a difference in light quantity between the first photodetector 10 and the second photodetector 11. [

In this state, the optical information of the digital audio disk 8 focused and read at the angle of? 1 is transmitted through the objective lens 7 to the first wavelength transmitting portion 5 of the wavelength selecting and transmitting portion 4 to have a constant reflectance and transmittance The beam splitter 2 having the beam splitter 2 is transmitted. At this time, the light information transmitted through the beam splitter 2 is incident on the reflective grating 9 formed in a concave-convex shape at the center of the lower surface of the beam splitter 2, and totally reflects at a certain angle. The light information totally reflected by the reflective grating 9 at a predetermined angle is incident on the first photodetector 10 formed on one side of the beam splitter 2 and is converted into a constant electrical signal, Is incident on the second photodetector 11 formed on one side of the beam splitter 2 to be converted into a corresponding electrical signal.

If the disc 8 is a digital video disc, the optical information of the digital video disc 8, which is focused and read at an angle of 2, is transmitted through the objective lens 7 to the second And is transmitted through the beam splitter 6 having a constant reflectance and transmittance through the wavelength transmitting portion 6. Then, the light information transmitted through the beam splitter 2 is incident on the reflection grating 9 formed in a concavo-convex shape on the lower surface of the beam splitter 2, and is totally reflected at a certain angle. The optical information reflected by the reflective grating 9 at a predetermined angle is incident on the first photodetector 10 formed on one side of the beam splitter 2 and converted into a constant electrical signal, And is incident on the second photodetector 11 to be converted into a corresponding electric signal.

That is, the intensity of the light reflected and returned from the audio or video disk 8 is modulated by the pit 8a, and the modulated light information is transmitted through the reflective grating 9 to the first photodetector 10 and the second light An electric signal which is transmitted to the detector 11 and is constantly converted is demodulated into an original signal by a digital signal processing unit (not shown), thereby converting an RF signal, which is an audio signal recorded on the disc 8, A focus signal and a tracking signal, which are error detection signals, are outputted. Here, the focus error is detected using the beam size method, and the tracking error is detected using the push-pull method using the original beam.

The present invention relates to a laser beam splitter which comprises a beam splitter integrally formed with a reflection grating, a first photodetector and a second photodetector, and a second beam splitter formed at a predetermined position between the beam splitter and the objective lens, Since the laser beam of all wavelengths is reflected and the wavelength selective light transmitting part capable of adjusting the spot size on the disk is provided, the assembling property due to no precision is required between the respective components is improved, and the ease of adjustment and the light picking Up device can be downsized and a laser beam of a specific wavelength is formed simultaneously with a beam focus of 1.6 mu m and 0.8 mu m so that the data recording capacity of the digital audio disk is higher than that of the audio disk and the width of the pit is remarkably narrow Digital video discs can be played back to increase convenience for users as well as improve reliability of products There are effective.

Claims (1)

1. An optical pick-up apparatus for condensing a laser beam with an objective lens (7) to record a signal on a disc and reproduce the recorded optical information, characterized in that two different first and second wavelengths lambda 1 and lambda 2 And a plurality of optical elements are integrally formed on one side of the two-wavelength laser diode 1 at a predetermined slope so as to reflect and transmit the incident beam at a predetermined ratio. The two-wavelength laser diode 1, A beam splitter 2 and a first wavelength transmitting portion 5 and a second wavelength transmitting portion 6 formed at predetermined positions between the beam splitter 2 and the objective lens 7 so as to be reflected by the beam splitter 2 A wavelength selecting and projecting unit 4 that transmits a laser beam of a specific wavelength among the plurality of beams and reflects laser beams of all other wavelengths to adjust a spot size; And a reflection grating for totally reflecting the optical information of the disk 8 A first photodetector 10 formed on an upper surface of the beam splitter 2 for outputting optical information totally reflected by the reflection grating 9 as an electrical signal and reflecting a part of the optical information at a predetermined angle, And a second photodetector 11 for outputting a part of the optical information reflected by the first photodetector 10 as an electrical signal. ※ Note: It is disclosed by the contents of the first application.