KR19980086185A - Dual Focus Optical Pickup - Google Patents

Abstract

The present invention relates to a dual focus optical pickup apparatus, which reduces the loss of light quantity of laser light, eliminates manufacturing difficulties, reduces manufacturing cost, and allows the optical pickup apparatus to be miniaturized, so that the recording surface of the optical disc 50 can be reduced. 55 and a prism 10 which is installed at an inclined angle and which transmits laser light, a laser diode 12 disposed at a bottom of one side of the prism 10 to emit laser light having a constant polarization, and the laser diode 12 ) A multi-segment photo detector 13 provided at both sides, a first reflecting portion 14 reflecting the laser light from the upper surface of the prism 10, and a laser beam reflected from the first reflecting portion 14 The second reflecting portion 15 formed on the lower surface of the prism 10 so as to be reflected again, the light control wavelength plate 20 formed on the upper surface of the prism 10 above the second reflecting portion 15, and Laser light via the optical control wavelength plate 20 to the optical disk 40 Including the objective lens 30 to belong to, the optical element is arranged in the correct position can reduce the manufacturing cost of the optical pickup device and improve the reliability, there is no loss in the control of the amount of light, so the function of the optical pickup device is improved It is effective.

Description

Dual Focus Optical Pickup

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dual focus optical pickup device, and in particular, a digital video disc having a thickness of 1.2 mm and a digital audio having a thickness of 0.6 mm because different diameters of light spots are changed by different transmittances of a single laser light. The present invention relates to a dual focus optical pickup apparatus capable of simultaneously reproducing information recorded on a disk and integrating optical elements of the optical pickup apparatus to improve assembling and induce miniaturization.

In general, an optical data recording medium, that is, an optical disk, is divided into a digital audio disk (DAD) for music playback having a thickness of 1.2 mm and a digital video disk (DVD) having a thickness of 0.6 mm, and has a thickness of 1.2 mm. Digital audio discs record data in multiple layers on one side, and 0.6 mm thick digital video discs record data in multiple layers in the middle to record a large amount of data on a single disc.

An optical pickup apparatus for reproducing data recorded on the above two types of discs reads information recorded on a 1.2 mm thick digital audio disc and a 0.6 mm thick digital video disc. Since the track pitch of the image is 0.74 µm and the shortest length between the pit, which is the recording signal, is 0.4 µm, the diameter of the optical spot must be different during playback because the track pitch is different from that of a digital audio disc having 1.6 µm and the shortest length between the feet is 0.834 µm. Because spherical aberrations do not match, simultaneous playback is impossible, and optical aberration is increased due to the difference of 0.6mm thickness of the discs. Only the recorded information on one of the 1.2mm discs could be read.

Therefore, a dual dual hologram optical lens and an objective lens are arranged to focus two different spots on a disc by correcting mutual spherical aberration so as to selectively read information recorded on a 1.2 mm disc and a 0.6 mm disc at the same time. A dual focus optical pickup device using a focus lens is being developed.

As an example of such a conventional dual focus optical pickup apparatus, as shown in FIG. 1, a laser diode (a) in which a laser light having a predetermined wavelength is generated, and a laser formed on and incident on the laser diode (a) A diffraction grating b that separates the zeroth order diffraction light and the ± 1st order diffraction light, that is, a three beam using a diffraction phenomenon of light, and a light having a predetermined slope formed on one side of the diffraction grating b; A beam splitter c for transmitting the reflected light and reflecting the reflected light, a collimator lens d formed above the beam splitter c so that the refracted light has linearity, and an upper side of the collimator lens d. Information formed by focusing linearly and focusing light on a 0.6 mm disc (h; first disc) for digital video discs and a 1.2 mm disc (i; second disc) for digital audio discs To read A dual focus lens g in which a hologram optical lens e and an object lens f are arranged in combination, and an astigmatism generating lens for generating astigmatism for detection of a focus error in a laser beam with the recorded information; k) and a photodetector 1 for detecting the light information passing through the astigmatism generating lens k and converting it into a current signal.

In the operation of the conventional optical pickup apparatus having such a configuration, first, a laser beam having a predetermined oscillation wavelength is incident on the diffraction grating b from the laser diode a, and the incident laser light receives the diffraction grating b. 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 b and enter the beam splitter c. The three beams are reflected and transmitted at a constant rate by the beam splitter c. The reflected laser light is incident on the collimator lens d from the beam splitter c, and the laser light passes through the collimator lens d, thereby providing linearity. The laser light imparted with the linearity is incident from the collimator lens (d) to the holographic optical lens (e) of the dual focus lens (g). Diffracted. The diffracted laser beam is incident on the objective lens f from the hologram optical lens e, and the diffracted laser beam is collected by the objective lens f, which is 0.6 mm in the first disk h and 1.2 mm in the second lens. On the disk i are collected in different airy shapes with diameters of 1.6 μm and 0.8 μm, respectively, and irradiated onto the pit (j) signal plane of the first disc h or the second disc i. Where there is no pit (j), it is reflected almost as it is and returns to the objective lens (f), but where there is a pit (j), the laser light is diffracted by the pit (j) and emitted outside the range of the objective lens (f). As a result, only a part of the incident light is returned, thereby generating a light quantity difference in the photodetector 1. This is because the depth of the pit j is set to λ / 4 of the wavelength, and the reflected light is canceled by interference due to the difference in half wavelengths above and below the pit j, thereby reducing the amount of light returned to the photodetector 1.

The modulated reflected light reflected from the first disk h or the second disk i is returned via the dual focus lens g and the collimated lens d, and the reflected light is reflected from the collimated lens d. Incident on the beam splitter c, the reflected light is prevented from being irradiated back to the laser diode a by the beam splitter c. The modulated reflected light is sent from the beam splitter c to the astigmatism generating lens k. The reflected light is generated by the astigmatism generating lens k to generate astigmatism for detecting a focus error, and thus the photodetector c. 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 1 via the astigmatism generating lens k, and the reflected light modulated by the disk is used for 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 light emitted from the laser diode (a) is condensed into different airy shapes on the disk via the hologram optical lens (e), so that the beam focus is formed at different positions, and thus the 1.2 mm disk and In this case, the information recorded on the 0.6mm disc can be selectively read.

In the conventional dual focus optical pickup device, the beam splitter (c) transmits light at a constant rate upon incidence of laser light by coating the polarizing film on two slopes of the rectangular prism in multiple layers to polarize the incident light by 90 ° to distinguish it from the reflected light. Due to the large amount of light loss, the dual focus lens (g) focuses the optical disk with a double focus according to the thickness of the disk. Therefore, a high degree of technical skill in processing due to the combination of the holographic optical lens (e) and the objective lens (f) is achieved. Because of this requirement, it is difficult to manufacture, and the arrangement of the installation position between the optical elements due to the different paths of the incident light and the reflected light is complicated. There is a problem that the manufacturing cost is increased by acting as an obstacle to the miniaturization of the optical pickup.

The present invention has been made in view of the above problems, and reduces the amount of light caused by transmitting and reflecting light at a constant ratio upon incidence of laser light, and has a high level of technical skill in processing according to a combination of holographic optical lenses and objective lenses. It provides a dual focus optical pickup device that can reduce the manufacturing cost by eliminating manufacturing difficulties, reduce the manufacturing cost by integrating the installation position arrangement between the optical elements, and simplify the design of the optical pickup device. Has its purpose.

In order to achieve the above object, the present invention provides a prism inclined with the recording surface of the optical disk, the prism through which the laser light is transmitted, a laser diode disposed at the bottom of one side of the prism, and the laser light is emitted, and installed on both sides of the laser diode. A multi-split photodetector, a first reflecting portion for reflecting the laser light on the upper surface of the prism, a second reflecting portion formed on the lower surface of the prism to reflect the laser light reflected by the first reflecting portion, and A hologram diffraction grating formed integrally on the upper surface of the prism on the upper side of the second reflecting portion, and an inner circular plate and a first transmissive film disposed between the prism and the optical disc on the upper side of the second reflecting portion and transmitting laser light at a first transmittance; Outer angle of incidence of laser light condensed on an optical disc, consisting of an outer plate which is a combat film that transmits at a second transmittance greater than the transmittance By providing a dual focus optical pickup apparatus comprising an optical control wavelength plate for adjusting and diffracting the reflected light reflected from the optical disk, and an objective lens which is an aspherical lens for focusing the laser light through the optical control wavelength plate on the optical disk. Is achieved.

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

2 is a layout view of a dual focus optical pickup apparatus according to the present invention;

Figure 3 is a schematic diagram showing the operating state of the present invention.

<Explanation of symbols for main parts of drawing>

10: prism 12: laser diode

14: first reflecting unit 15: second reflecting unit

16: phase hologram grating 20: light control wavelength plate

22: inner circular plate 24: outer plate

30: objective lens 40: optical disk

45: recording surface

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

As shown in FIG. 2, the optical prism 10 includes an optical element disposed thereon, and a laser prism 10 through which laser light is transmitted, and a laser diode 12 disposed on a bottom of one side of the transmission prism 10. The multi-segment photodetector 13 provided on both sides of the laser diode 12, the first reflecting portion 14 formed on the upper surface of the prism 10, and the second reflecting portion 15 formed on the lower surface of the prism 10. And a hologram diffraction grating 16 formed integrally with the upper surface of the prism 10 on the upper side of the second reflecting portion 15, and an optical control wavelength plate disposed between the prism and the optical disk on the upper side of the second reflecting portion ( 20) and an objective lens 30 arranged on the light control wavelength plate 20 to focus the laser light on the optical disk 40.

The transmissive prism 10 is inclined with the recording surface 55 of the optical disc 50, and the transmissive prism 10 is provided with a light transmissive prism having excellent light transmission efficiency. An optical control plate 20 is disposed between the upper portion of the transmissive prism 10 and the optical disk 50, and the refractive index of the anisotropic crystal is transmitted differently depending on the incident angle on the upper portion of the optical control plate 20 to change polarization. The objective plate 40 which consists of an aspherical lens so as to have a minimum spherical aberration of the wavelength plate 30 and the laser light to condense the laser light on the optical disk 50 is sequentially arranged.

The light control wavelength plate 20 disposed between the upper portion of the prism 10 and the optical disk 40 includes an inner circular plate 24 for transmitting laser light at a first transmittance and an outer plate for transmitting at a second transmittance ( 22), wherein the first transmittance is set smaller than the second transmittance, that is, the first transmittance of the inner circular plate 24 is 1/2, and the second transmittance of the outer plate 22 is 1 While adjusting the outermost angle of incidence of the laser light focused on the optical disk 50 with the combat film, the refractive index is transmitted differently according to the angle of incidence incident on the light control wavelength plate 20 to change the polarization.

In addition, an objective lens 40 is disposed on the optical control wave plate 20 so that the laser light is composed of an aspherical lens so as to have a minimum spherical aberration so as to focus the laser light on the optical disk 50.

The prism 10 is provided with a laser diode 12 which emits laser light of a predetermined wavelength on one side of the bottom, and a multi-segment photo detector 13 composed of a plurality of light receiving parts on both sides of the laser diode 12. Are arranged respectively. The configuration of the multi-segment photodetector 13 is for adopting the push pull method for the tracking error detection method, and at the same time, the beam size method is adopted for the focusing error detection method in the present invention.

In addition, a first reflecting portion 14 for totally reflecting the laser light toward the laser diode 12 is formed on the upper surface of the prism 10, and a second reflecting portion for totally reflecting the laser light on the lower surface of the prism 10 ( 15) is formed.

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

First, as shown in FIG. 3, a laser beam having a predetermined wavelength is emitted from the laser diode 12, which is a light component (for example, P-polarized light) parallel to the incident surface with respect to the traveling direction of the laser light. The polarization is adjusted so that it is emitted to emit laser light. The polarized laser light is reflected by the first reflecting portion 14 and the second reflecting portion 15 formed on the prism 10 on the laser diode 12, and the reflected laser light is reflected on each reflecting portion 14 15, the optical path is transmitted toward the hologram diffraction grating 16 and transmitted inside the prism 10. The totally reflected laser light is irradiated to the hologram diffraction grating 16 from the second reflecting portion 15, and the laser light is not diffracted from the hologram diffraction grating 16 so that the outside of the prism 10 does not change with the amount of light. Is released. The laser light passing through the hologram diffraction grating 16 is irradiated from the prism 10 to the light control wave plate 20, and the laser light is linearly polarized by circular light polarization by the light control wave plate 20. At the same time, the laser beam is separated and transmitted.

At this time, the laser light passing through the inner circular plate 24 of the light control wavelength plate 20 is transflected, and the laser light passing through the outer plate 22 is separated from the battle because the laser beam passes through the inner circular plate 24. The light is focused on the optical axis via the objective lens 30 to the outermost incident angle θ1, and the laser beam transmitted through the outer plate 22 has the outermost incident angle to the optical axis via the objective lens 30. It collects at θ2. That is, the laser light via the light control wavelength plate 20 composed of the inner circular plate 24 and the outer plate 22 has a different outer angle of incidence, so that the optical disk 40 has a different numerical aperture (NA: Numerical Aperture). Condensed on).

As described above, since the outermost incident angles of the laser light incident on the optical disc 40 are different, the numerical aperture, the diameter of the optical spot, and the depth of focus are respectively determined by the following equation.

The crystallinity of the aperture ratio N.A. with respect to the outermost incident angles θ1 and θ2 is η when the refractive index of the medium is

[Equation 1]

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,

[Equation 2]

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)

[Equation 3]

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 becomes larger. Thus, the light spot due to the difference in the outermost incidence angles respectively different through the inner circular plate 24 and the outer plate 22 is thus obtained. The difference in the diameter of the light is smaller than the light transmitted through the inner plate 22 and collected by the inner circular plate 24.

Thus, for each optical disk 40, for example, when playing a digital video disk having a thickness of 0.6 mm, the outer plate 22 is battled and about 2 on the optical disk 40 by the objective lens 30 with respect to the optical axis. The light spot having a size of 0.8 占 퐉 is formed to interfere with diffraction on the recording surface 45, thereby reading the optical information with an amount of light and the presence or absence of light. At this time, in the present invention, since a lens for digital video disc is used, the recording surface 45 is accurately focused without generating spherical aberration.

When the digital audio disc having a thickness of 1.2 mm is reproduced, the laser light transflected by the inner circular plate 24 is polarized by the wave plate 20 and focused by the objective lens 30, and the optical disc at θ1 with respect to the optical axis. On (40), the numerical aperture becomes small as NA1 of the above expression (1). This is because spherical aberration occurs because the digital audio disk and the digital video disk each have a thickness difference of 0.6 mm, so that Δd is the thickness of the optical disk 40, and n is the refractive index.

[Equation 4]

Since the laser light around the optical axis with less occurrence of spherical aberration is semi-transmissive to the inner circular plate 24 and the outer plate 22 is battled relatively, the laser light with large spherical aberration is small as NA1. Since the spherical aberration is adjustable in proportion to (NA) ⁴ , the spherical aberration is significantly reduced. As a result, the numerical aperture becomes smaller and the diameter of the optical spot is inversely proportional to the numerical aperture according to Equation 2, so that the diameter of the optical spot is larger than 1.6 µm on the optical disk 40, that is, on the digital audio disk, so that the track pitch is 1.6 µm. On the digital audio disc having the shortest length of the recording surface 45 is 0.834 占 퐉, the recording surface 45 interferes with diffraction and reads the optical information with the amount of light and the presence or absence of light.

Thus, the laser light that reads the optical information on each optical disk 40 in the above-described process is irradiated to the light control wavelength plate 20 via the objective lens 30, and the laser light is irradiated with the light control wavelength plate. Circularly polarized light is polarized by linear polarization (20). At this time, since the linearly polarized laser light is incident on the optical disk 40 when the inverted circularly polarized light is incident on the optical disk 40, the linearly polarized laser light has a polarization direction orthogonal to the time when the initial polarized laser light is incident on the optical disk 40. Linear polarization. The laser light of the inverted linearly polarized light is irradiated to the hologram diffraction grating 16 on the upper surface of the prism 10 from the light control wave plate 20, and the laser light of the linearly polarized light is diffracted by the hologram diffraction grating 16. . This is induced differently from the path of the laser light emitted from the laser diode 12 disposed on one side of the prism 10 and at the same time the diffracted laser light is used for the detection of the focus error. The laser light is diffracted and passes through the hologram diffraction grating 16 with a focus error signal in a different light path than when emitted. Thus, the laser light diffracted by the hologram diffraction grating 16 passes through the second reflecting portion 15 and the first reflecting portion 14 sequentially, and is totally reflected to form a multi-division scheme arranged on both sides of the laser diode 12. The photodetector 13 is irradiated.

In this way, the laser light, which reads the optical information via the respective paths, is diffracted, interfered and reflected and transmitted, and outputs the digital audio signal and the digital video signal as original electrical signals, and the output optical signal is a digital signal processor (not shown). Demodulated to the original signal to output an RF (RF) signal which is an audio signal recorded on the optical disc, a focus signal which is an error detection signal, and a tracking signal.

As described above, the present invention changes the polarization of the laser beam and passes the laser beam into the light control wave plate 20 having different transmittances, so that the external plate 22 of the light control wave plate 20 is reproduced when the digital video disc is reproduced. And the light is condensed by the objective lens 30 to form a light spot of about 0.8 탆 in diameter on the optical disk 40 to reproduce the digital video disk, and when the digital audio disk is reproduced, laser light is applied to the optical axis portion. The light is transmitted through the inner circular plate 24 to be condensed on the optical disk 40 by the objective lens 30, and at the same time, it greatly reduces the spherical aberration caused by the thickness difference between the optical disks 40. Since optical spots with diameters larger than 1.6 mu m are formed, digital audio discs with large recording surfaces can be accurately reproduced.

The dual focus optical pickup apparatus of the present invention is arranged on the same plane as the light emitting portion and the light emitting portion of the laser beam for reading optical information, and reduces the occurrence of spherical aberration due to the thickness difference between the optical disks. It can be reproduced and the alignment of the optical elements is simplified and can be manufactured at the same time. As each optical element is arranged at the correct position during manufacturing, it can reduce the manufacturing cost of the optical pickup device and improve the reliability. Since there is no loss, the function of the optical pickup device is improved.

Claims (7)

A prism 10 installed at an angle with the recording surface 55 of the optical disc 50 and transmitting laser light, and a laser diode 12 disposed at a bottom of one side of the prism 10 to emit laser light having a constant polarization. And a multi-segment photodetector 13 provided at both sides of the laser diode 12, a first reflecting portion 14 for reflecting a laser beam from an upper surface of the prism 10, and the first reflecting portion 14 The second reflecting portion 15 formed on the lower surface of the prism 10 so as to reflect back the laser light reflected by the light), and the light control wavelength formed on the upper surface of the prism 10 above the second reflecting portion 15. And a objective lens (30) for focusing the laser light via the optical control wavelength plate (20) onto the optical disc (40). 2. The light control wavelength plate 20 is composed of an inner circular plate 22 for transmitting laser light at a first transmittance and an outer plate 24 for transmitting at a second transmittance. A dual focus optical pickup apparatus characterized by being set smaller than the transmittance. 3. The dual focus optical pickup apparatus of claim 2, wherein the inner circular plate (22) has a transflective film of 1/2, and the outer plate (24) has a transmissive film of one. The dual focus optical pickup apparatus of claim 1, wherein the light control wave plate (20) diffracts reflected light without diffracting incident light. The dual focus optical pickup apparatus of claim 1 or 2, wherein the outer plate (24) of the light control wavelength plate (20) is formed of a circular light-transmitting film having an annular shape. 2. The dual focus optical pickup apparatus of claim 1, wherein the light control wavelength plate 20 adjusts the outermost incident angle of the laser light focused on the optical disc 40. The dual focus optical pickup apparatus of claim 1, wherein the laser diode (12) emits light polarized by a laser beam having a component horizontal to the incident surface.