KR20000039838A - Optical pickup device equipped dual focus prism - Google Patents

Abstract

PURPOSE: An optical pickup device equipped a dual focus prism is provided to solve a difficulty in a processing of lens according to a formation of dual focus and a difficulty in a production of optical pickup device according to an arrangement of many optical elements. CONSTITUTION: An optical pickup device is equipped: a hologram element(10) to detect an optical signal by emitting laser lights and to convert an optical path of emitting lights and receiving lights; a dual focus prism(20) to compatibly play a DAD(digital audio disk) and a DVD(digital video disk) by separating a wave width with converting the optical path of laser lights emitted from the hologram element(10); and an objective lens(30) to collect laser lights passed the dual focus prism(20) on an optical disk. Thereby a minimum optical element and the easily produced optical pickup device are offered by compatibly playing the DAD and the DVD because a numerical aperture is controlled by irradiating lights on disks differed each other with a different exterior projectile angle.

Description

Optical pickup device with dual focus prism

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup apparatus provided with a dual focus prism. In particular, the optical pickup device includes a dual focus prism capable of converting a laser beam from a single light source. The present invention relates to an optical pickup apparatus having a dual focus prism capable of forming an optimal optical spot in a digital audio and digital video disc.

In general, an optical data recording medium is divided into a digital audio disk (DAD) for music reproduction having a thickness of 1.2 mm and a digital video disk (DVD) having a thickness of 0.6 mm.

Conventionally, in the digital video disc, the track pitch on the disc is 0.74 탆 and the shortest length between the pit, which is the recording signal, is 0.4 탆, so that the track pitch is 1.6 탆 and the shortest length between the pit is 0.834 탆. Since the diameter of the optical spot must be different during reproduction, the spherical aberration of the objective lens does not match, so simultaneous reproduction is impossible.

In addition, optical aberration increases due to the 0.6mm thickness difference between the discs, which increases noise and increases the error rate. Therefore, the recorded information cannot be read accurately, so the optical pickup device can read only the recorded information of either 0.6mm or 1.2mm discs. It was supposed to be.

Therefore, a dual array of holographic optical lenses and objective lenses that correct mutual spherical aberration and focus two different spots on the disc to selectively read information recorded on a 1.2 mm disc and a 0.6 mm disc in recent years An optical pickup device using a focus lens has been developed.

As shown in FIG. 1, the conventional optical pickup device includes a laser diode 100 in which a laser beam having a predetermined wavelength is generated, and diffraction phenomenon of laser light formed on and incident on the laser diode 100. And a diffraction grating 105 which is separated into 0th order diffracted light and ± 1st order diffracted light, that is, a three beam, and has a predetermined slope at one side of the diffraction grating 105 to transmit incident light. A beam splitter 110 for reflecting the reflected light, a collimated lens 120 formed on the beam splitter 110 and having the linearly refracted light, and formed on the collimated lens 120 And collects linearly focused light and focuses the information recorded on a 0.6 mm disc 140 (hereinafter referred to as the first disc) for the digital video disc and a 1.2 mm disc (145 referred to as the second disc) as the digital audio disc. To read A dual focus lens 130 in which a hologram optical lens 132 and an objective lens 134 are arranged in combination, and an astigmatism generating lens for generating astigmatism for detecting a focus error in laser light with the recorded information ( 150 and a photodetector 160 which detects the light information passing through the astigmatism generating lens 150 and converts it into a current signal.

In the operation of the conventional optical pickup apparatus having such a configuration, first, laser light having a predetermined oscillation wavelength is incident on the diffraction grating 105 in the laser diode 100, and the incident laser light causes the diffraction grating 105 Transmitted and separated into 0th and ± 1st light, i.e., three beams. The three beams are used for focusing and tracking errors. The three beams penetrate the diffraction grating 105 and enter the beam splitter 110. The three beams are reflected and transmitted at a constant rate by the beam splitter 110. The reflected laser light is incident from the beam splitter 110 to the collimated lens 120, and the laser light passes through the collimated lens 120, thereby providing linearity. The laser light imparted with the linearity is incident from the collimated lens 120 to the hologram optical lens 132 of the dual focus lens 130, and the laser beam is corrected for optical spherical aberration by the hologram optical lens 132. Are diffracted at the same time.

The diffracted laser light is incident from the hologram optical lens 132 to the objective lens 134, and the diffracted laser light is collected by the objective lens 134 to be 0.6 mm in the first disk 140 and 1.2 mm in the second lens. The disk 145 is condensed into different airy shapes of 1.6 μm and 0.8 μm in diameter, respectively, and is irradiated onto the signal surface of the pit 142 of the first disk 140 or the second disk 145. Where the pit 142 is absent, it is almost reflected and returns to the objective lens 134. Where the pit 142 is located, the laser light is diffracted by the pit 142 and emitted outside the range of the objective lens 134. As a result, only a part of the incident light is returned, thereby generating a light quantity difference in the photodetector 160. This is because the depth of the pit 142 is set to λ / 4 of the wavelength, and the reflected light is canceled by interference due to different half wavelengths above and below the pit 142, thereby reducing the amount of light returned to the photodetector 160.

The modulated reflected light reflected from the first disk 140 or the second disk 145 is returned via the dual focus lens 130 and the collimated lens 120, and the reflected light is the collimated lens 120. Incident to the beam splitter 110, the reflected light is prevented from being irradiated back to the laser diode 100 by the beam splitter 110. The modulated reflected light is sent from the beam splitter 110 to the astigmatism generating lens 150, and the reflected light is generated by the astigmatism generating lens 150 to generate astigmatism for detecting a focus error, and thus the photodetector 110. The path of light is changed to the path where it is installed. The reflected light whose path is changed is sent to the photodetector 160 via the astigmatism generating lens 150, and the reflected light modulated by the disk is applied to the RF, focus error detection, tracking control and information by the photodetector. The converted current is demodulated by the control circuit (not shown) to reproduce the original signal.

Therefore, as described above, the laser beam emitted from the laser diode 100 is condensed in different airy shapes on the disc via the hologram optical lens 132, so that the beam focus is formed at different positions so that the disc is 1.2 mm thick. And can selectively read information recorded on a 0.6mm disc.

However, in the conventional optical pickup apparatus, the dual focus lens 130 for focusing the dual focus on the disk according to the thickness of the disk has an altitude in processing due to the combination of the hologram optical lens 132 and the objective lens 134. Because of the technical skills required, the production had a difficult problem.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has a dual focus that can solve the difficulty of processing a lens due to the formation of a double focus and a manufacturing difficulty of an optical pickup device due to the alignment of a plurality of optical elements. An object of the present invention is to provide an optical pickup device having a prism.

The present invention for achieving the above object is a hologram device for emitting a laser light to detect an optical signal and to convert the optical path of the emission light and the converged light, and the optical path of the laser light emitted from the hologram element by converting the optical width And a dual focus prism for compatible reproduction of digital audio discs and digital video discs, and a dual focus prism having an objective lens for focusing laser light on the optical disc via the dual focus prism. This is achieved by

1 is a configuration diagram of a conventional dual focus optical pickup device;

2A is a DVD playback state diagram of the optical pickup apparatus according to the present invention;

Figure 2b is a CD playback state of the optical pickup apparatus according to the present invention.

<Explanation of symbols for main parts of drawing>

1: laser diode 2: photodetector

5: diffraction grating 6: hologram lattice

10 hologram element 20 dual focus prism

22: selective reflection unit 24: the first prism

25: first reflector 26: second prism

27: second reflector 30: objective lens

40: DVD 45: Feet

50: CD

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

As shown in FIG. 2, the present invention provides a hologram element 10 for emitting laser light to detect an optical signal and converting an optical path between emitted light and convergent light, and a laser beam emitted from the hologram element 10. A dual focus prism 20 for converting a furnace to separate a wide width by converting a furnace, and a objective lens 30 for focusing a laser beam via the dual focus prism 20 on an optical disk. It consists of.

The hologram element 10 is, for example, a laser diode (1) for emitting laser light for 650 nm wavelength digital video, and a diffraction grating (5) for separating the laser light emitted from the laser diode (1) into a three beam (5). ), A hologram grid 6 that transmits the three beams diffracted by the diffraction grating 5 and changes the optical path of the reflected light, and the reflected light modulated by the optical information reflected by the optical disks 40 and 50 is collected. It consists of a photodetector 2.

The dual focus prism 20 forms a primary optical path of a laser beam, a first prism 24 having a first reflecting portion 25 formed on a lower surface thereof, and a second reflecting portion 27 formed on a side surface of the first prism 24. The second prism 26 constituting the optical path extending longer than the optical path of the prism 24, and the laser beam is reflected at a predetermined ratio on the attached oblique surface of the first prism 24 and the second prism 26 and It consists of the selective reflection part 22 which permeate | transmits.

Next will be described the operation of the present invention made as described above.

First, at the time of reproduction of the digital audio disc, that is, the CD 50, the laser light emitted from the laser diode 1 in the hologram element 10 is incident on the diffraction grating 5, as shown in FIG. 3A. The light is separated and radiated by the diffraction grating 5 into three beams of zero order light and ± 1 order light for focus and tracking error detection.

The three beams are irradiated from the hologram element 10 to the dual focus prism 20, and the irradiated laser light is reflected and transmitted at a constant rate by the selective reflection unit 22 after passing through the first prism 24.

Among the laser beams separated by the selective reflection unit 22, the laser light reflected downward is irradiated to the first reflection unit 25, and the laser light totally reflected by the first reflection unit 25 is directed toward the objective lens 30. do.

As described above, the laser beam passing through the dual focus prism 20 in a narrow width forms an optical spot with the outermost incident angle θ1 on the CD 50 by the objective lens 30 to the pit 45 on the CD 50. Is modulated by

The laser light modulated as described above is irradiated to the hologram element 10 via the objective lens 30 and the dual focus prism 20 through the same path.

The laser light irradiated to the hologram element 10 with the optical information as described above is irradiated to the hologram lattice 6 formed in the hologram element 10, and the irradiated laser light is fixed wavelength by the hologram lattice 6. While diffracted below, interference with laser light emitted from the laser diode 1 is prevented. The diffracted laser light is converted into the optical path from the hologram grating 6 to the photodetector 2 and converged. The converged laser light is modulated and reflected on the CD 50 to convert the digital audio signal into an original electrical signal. The signal is output and demodulated by the digital signal processor (not shown) to the original signal, thereby outputting an RF (RF) signal, a video signal recorded on a digital audio disc, a focus signal, an error detection signal, and a tracking signal.

On the other hand, when the digital video disc, ie, the DVD 40, is reproduced, as shown in FIG. 3B, the laser light is incident on the diffraction grating 5 from the laser diode 1 in the hologram element 10, and the laser light is diffracted. The grating 5 separates and emits three beams of zero order light and ± 1 order light for focus and tracking error detection.

The three beams are irradiated from the hologram element 10 to the dual focus prism 20, and the irradiated laser light is reflected and transmitted at a constant rate by the selective reflection unit 22 after passing through the first prism 24.

Among the laser beams separated from the selective reflection unit 22, the laser light, which is straight ahead, is irradiated to the second reflecting unit 27, and the laser light totally reflected by the second reflecting unit 27 is again the selective reflecting unit 22. Is investigated.

As described above, the laser light whose optical path is increased in the second prism 26 is partially reflected by the selective reflection unit 22, and the reflected laser light is irradiated toward the objective lens 30.

Since the optical path is increased as described above, the laser beam passing through the dual focus prism 20 is wider than the laser beam passing through the first prism 24, and the laser beam passing through the dual focus prism 20 is wider than the objective lens 30. By this, the outermost incident angle on the DVD 40 forms a light spot with θ2 and is modulated by the pit 45 on the DVD 40.

At this time, the outermost incidence angles of the laser beams irradiated onto different optical disks are different in narrow width and wider width, respectively, and the different outermost incidence angles are different in numerical aperture.

The adjustment of the numerical aperture adjusts the diameter of the light spot so that each of the optical disks having different thicknesses can be reproduced.

This is summarized as follows.

The crystallinity of the opening ratio N.A. for the outermost incident angles θ1 and θ2 is η when the refractive index of the medium is η,

N.A.1 = ηsinθ1 N.A.2 = ηsinθ2

Where the radius W of the beam with respect to the numerical aperture is K is a constant,

Since the diameter of the light spot is inversely proportional to the numerical aperture, the depth of focus D for the beam spot diameter is (R is a constant)

Therefore, the condition that the light spot becomes small is smaller as the wavelength of the laser light becomes smaller and becomes smaller as the numerical aperture is larger. Thus, the light spot is focused at the widest outermost angle of incidence through the first prism 24 and the second prism 26, respectively. The laser beam has a larger light spot focused at a narrower outermost angle of incidence via only the first prism 24.

That is, the optical path is increased so that the laser light via the second prism 26 has a diameter of the light spot suitable for reproducing the DVD 40.

Therefore, since the outermost incidence angle is adjusted due to the adjustment of the width of the laser light due to the difference in the optical paths, the numerical apertures and the diameters of the light spots are different, so that the discs having different thicknesses are compatible with each other.

The laser light modulated on the optical disks 40 and 50 through the above process is irradiated to the hologram element 10 via the objective lens 30 and the dual focus prism 20 through the same path.

The laser light irradiated to the hologram element 10 with the optical information as described above is irradiated to the hologram lattice 6 formed in the hologram element 10, and the irradiated laser light is fixed wavelength by the hologram lattice 6. While diffracted below, interference with laser light emitted from the laser diode 1 is prevented. The diffracted laser light is converted into the optical path from the hologram grating 6 to the photodetector 2 and converged, and the converged laser light is converted into a digital video signal by the laser light modulated and reflected on the CD 50. By outputting the signal and demodulating the original signal by a digital signal processing unit (not shown), an RF (RF) signal, a video signal recorded on a digital video disc, a focus signal, an error detection signal, and a tracking signal are output.

As described above, according to the present invention, the width of the laser light is adjusted due to the conversion and increase and decrease of the optical path, and since the outermost incident angle focused on the optical disc is different, the numerical aperture is adjusted so that the optical discs having mutually different thicknesses are compatible with each other. This becomes possible.

The optical pickup apparatus provided with the dual focus prism of the present invention includes a dual focus prism for increasing and decreasing an optical path, thereby varying the width thereof, and thereby controlling the numerical aperture by irradiating light on different optical discs at different outermost incidence angles. Therefore, the digital audio disc and the digital video disc can be reproduced interchangeably, thereby providing an optical pickup device with a minimum optical element and easy manufacturing.

Claims (2)

A hologram element 10 for emitting a laser light to detect an optical signal and converting an optical path between the emitted light and the converged light; A dual focus prism (20) for converting the optical path of the laser light emitted from the hologram element (10) to separate the width so that the digital audio disc and the digital video disc are compatible and reproduced; And An optical pickup device having a dual focus prism, characterized in that an objective lens (30) for condensing laser light via the dual focus prism (20) on an optical disc. The method of claim 1, wherein the dual focus prism 20, A first prism 24 forming a primary optical path of the laser light and having a first reflecting portion 25 formed on a lower surface thereof; A second prism 26 having a second reflecting portion 27 formed on a side thereof and constituting an optical path extending from the optical path of the first prism 24; And Optical pickup device having a dual focus prism characterized in that the selection reflecting portion 22 for reflecting and transmitting the laser light at a predetermined ratio on the attached oblique surface of the first prism 24 and the second prism 26 .