KR100272086B1 - Beam adjusted type dual focus optical pickup device - Google Patents

Abstract

PURPOSE: A dual focus optical pickup device for regulating brightness, is provided to improve a technology in a dual focus lens condensing light to an optical disk with a dual focus, according to the thickness of the disk. And the device is provided to reduce the influence of spherical aberration by the use of a single objective lens, through the change of brightness. CONSTITUTION: A laser diode(5) emits vertical component of polarizing laser for a progressing direction of light in one side of a silicon plate(1), installed in parallel with a recorded layer of an optical disk. An optical detector(60) installed in a side of the laser diode(5) collects light reflected on the optical disk. An objective lens(40) condenses laser beam to the optical disk. An optical prism(10) installed in an acute angle with an upper surface of the silicon plate(1) selectively transmits and reflects laser beam, and receives parts of the reflective light. And the optical prism(10) generates a brightness gradient in a light speed boundary. A wavelength plate(20) installed between the optical prism(10) and the optical disk converts the phase of laser beam. And a light control plate(30) separately transmits laser beam passing the wavelength plate(20) in different transmission ratios according to the width.

Description

Dual Focus Optical Pickup Device

The present invention relates to a light intensity-controlled dual focus optical pickup device. In particular, a plurality of optical elements are integrally formed on a silicon substrate to induce miniaturization of the optical pickup device, and at the same time, the intensity distribution of the light beams is differently focused according to the width. The optical information is read on the digital audio disc and the digital video disc in different outward angles, so that the loss of the light amount is minimized.

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. A thick digital audio disc records data in multiple layers on one side, and a 0.6 mm thick digital video disc records data in multiple layers in the middle to record a large amount of data on a single disc.

Of the above two types of discs, the digital video disc is 1.2 mm thick and has a track pitch of 0.74 μm on the disc and a minimum length of 0.4 μm between the pit, which is a recording signal, for higher recording density than a 0.6 mm thick digital audio disc. When the information recorded from digital audio discs and digital video discs is read because the track pitch is different from that of digital audio discs with a track pitch of 1.6 μm and a shortest length of 0.834 μm, the diameter of the optical lens is different. Since spherical aberration does not match, simultaneous playback is impossible, and optical aberration increases due to the difference of 0.6mm thickness of discs, noise increases and error rate increases, making it impossible to read recorded information accurately. 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 laser light having a predetermined wavelength is generated, and formed and incident on the laser diode (a) A diffraction grating b which separates the zeroth order diffraction light and the first order diffraction light, that is, the three beams by using the diffraction phenomenon of the laser light, and the diffraction grating b is formed on one side of the diffraction grating b; A beam splitter (c) for transmitting incident light and reflecting reflected light, a collimator lens (d) formed above the beam splitter (c) so that the refracted light has a linearity, and an image side of the collimator lens (d) On a 0.6mm disk (h; hereinafter referred to as "first disk") for digital video disks and 1.2mm disk (i; referred to as "second disk" hereinafter) for digital video disk Information recorded by focusing Astigmatism for generating astigmatism for detecting a focus error in a dual focus lens g having a holographic optical lens e and an objective lens f arranged in a complex manner, and laser light accompanying the recorded information. 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 linearity is incident from the collimator lens (d) to the holographic optical lens (e) of the dual focus lens (g), and the laser light is corrected by the holographic optical lens (e) for optical spherical aberration. Are diffracted at the same time. The diffracted laser beam is incident from the hologram optical lens (e) to the objective lens (f), and the diffracted laser beam is collected by the objective lens (f). On the disk i are collected in different airy shapes of 1.6 μm and 0.8 μm, respectively, and irradiated to the pit (j) signal plane of the first disc h or the second disc i, and the laser beam 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 lambda / 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) and reproduced by 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 holographic ram optical lens (e), so that the beam focus is formed at different positions, so that the 1.2 mm disk and In this case, the information recorded on the 0.6mm disc can be selectively read.

However, in the above-described conventional dual focus optical pickup device, the dual focus lens g for condensing the optical disk with a double focus according to the thickness of the disk has a hologram optical lens e and an objective lens f, so that the processing is performed. It is difficult to manufacture due to the high level of technical skill, and the influence of spherical aberration is inevitably generated due to the use of a constant amount of light due to the difference in the thickness of the disk. Since it is located in the ultra plane, the design dimension between the optical elements is increased, there is a problem that the obstacle to miniaturization of the optical pickup.

The present invention has been invented in view of the above problems, and solves the manufacturing difficulties of the processing technology of the dual focus lens focusing on the optical disk with a double focus according to the thickness of the disk, and at the same time, a single object through the change of the light quantity. It is an object of the present invention to provide a light-controlling dual focus optical pickup device capable of reducing the influence of spherical aberration due to the use of a lens and integrating the arrangement between optical elements, thereby reducing the design dimension and miniaturizing the optical pickup device. .

The present invention for achieving the above object is provided with a laser diode which emits a polarization laser of a vertical component with respect to the traveling direction of the light from one side of the silicon substrate is installed in parallel with the recording surface of the optical disk, the installation side of the laser diode An optical pickup apparatus having a photodetector mounted on an optical disk for receiving reflected light reflected on an optical disk and an objective lens for focusing laser light on the optical disk, wherein the optical pickup device is installed at an acute angle with the upper surface of the silicon substrate to selectively transmit and reflect the laser light. A light prism for receiving a portion of reflected light and generating a light gradient in the light beam boundary, a wavelength plate provided between the optical prism and the optical disk to convert the phase of the laser light, and a laser light passing through the wavelength plate. It consists of a light control plate for separating and transmitting at different transmittances depending on the side Provided is a light control dual focus optical pickup device.

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.

3 (a) is a schematic diagram showing that the present invention reproduces a digital video disc.

3 (b) is a schematic diagram showing that the present invention reproduces a digital audio disc.

* Explanation of symbols for main parts of the drawings

1: silicon substrate 5: laser diode

10: optical prism 12: polarization separator

14: reflection type knife edge portion 20: wave plate

30: light control plate 32: outer plate

34: inner circular plate 40: objective lens

50: optical disk 55: recording surface

60: photodetector

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

In the present invention, as shown in FIG. 2, a silicon substrate 1 having an optical element provided thereon is provided in parallel with the recording surface of the optical disc 50. As shown in FIG.

An optical prism 10 is installed on the upper surface of the silicon substrate 1 at an acute angle on the silicon substrate 1. The optical prism 10 includes a polarization separator 12 for selectively transmitting and reflecting the laser beam at an upper slope according to the phase of the laser light, and a reflection type for totally reflecting a part of the reflected light at the lower slope and providing a light intensity gradient to the luminous flux boundary surface. It consists of a knife edge portion (14). The reflective knife edge portion 14 is coated with particles of a birefringent calcite component that can interfere with one side of the reflected light inside the rectangular lens part so that a light quantity gradient occurs in a portion of the reflected light, and is horizontal to the surface of the silicon substrate 1. Array is formed.

In addition, the polarization separator 12 transmits the laser light having a component parallel to the incident surface and reflects the laser light having a component perpendicular to the incident surface, thereby making the optical path of the incident light and the reflected light on the optical disc different.

In addition, a laser diode 5 is provided on the silicon substrate 1 so as to be spaced apart from the optical prism 10 at a predetermined distance, and the laser diode 5 is polarized with a component perpendicular to the traveling direction of the light, that is, S Emits a laser beam of constant wavelength, phase-shifted by a wave.

On the side of the laser diode 5, a photodetector 60, which is reflected on the optical disk 50 and receives the reflected light from which the optical information is read, is provided, and the photodetector 60 is a reflective type of the optical prism 10. In order to detect the focus error from the contrast difference generated in the knife edge portion 14, the bi-division photo detectors are formed on both sides.

On the other hand, the wavelength plate 20 is provided between the optical prism 10 and the optical disk 50 to change the polarization of the laser light, the laser light via the wavelength plate 27 on the upper side of the wavelength plate 20 The light control plate 30 is installed to separate the transmission at different transmittance. The light control plate 30 is composed of an inner circular plate 32 which transmits laser light at a first transmittance, and an outer plate 34 which is formed of an annular circular transmissive film and transmits laser light at a second transmittance. Thus, for example, the first transmittance is set to be larger than the second transmittance, for example, the inner circular plate 32 is formed of a combat film having a transmittance of 1, and the transmittance of the outer plate 32 is formed of a semi-permeable film having a 1/2. The incident light intensity distribution of the laser light focused on the optical disc 50 can be varied. Since the incident light intensity distribution thus varied is different in the light intensity of the laser light via the inner circular plate 34 and the outer plate 32, the angle of incidence of the outermost incident light of the laser light focused on the optical disc 50 is different according to the light intensity. It is possible to adjust the diameter and the depth of the light spot on 50).

In addition, an objective lens 40 for focusing the laser light via the light control plate 30 on the optical disk 50 is provided above the light control plate 30.

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

First, as shown in FIGS. 3 (a) and 3 (b), a laser beam having a constant wavelength is emitted from the laser diode 5, which is the incident surface with respect to the advancing direction of the laser light. Light, which is a component perpendicular to, for example, adjusts the phase of the laser light to emit the S-polarized light to emit the laser light. The polarized laser light is irradiated from the laser diode 5 to the polarization separator 12 formed on the upper surface of the optical prism 10. Since the polarization separator 12 is polarized split coating, It reflects S-polarized light, which is a vertical component, and transmits P-polarized light, which is a horizontal component, on the incident surface. Therefore, the laser beam is reflected by this polarization separating section 12, and the optical path is irradiated to the wave plate 20 side. In this way, the linearly polarized light is polarized by the wavelength plate 20 in the laser light irradiated. The laser light polarized by circularly polarized light is irradiated from the wavelength plate 20 to the light control plate 30, and the laser light is separated and transmitted by the light control plate 30. At this time, the laser light passing through the inner circular plate 34 of the light control plate 30 is a battle, and the laser light passing through the outer plate 32 is transflected so that the light intensity is separated and transmitted differently with respect to a single wide laser light. . The laser beam transmitted through the inner circular plate 34 among the laser beams separated and transmitted by the different light intensity distributions is confronted with each other and the outermost incident angle is focused on the optical axis via the objective lens 40, and the outer plate ( The laser beam passing through 32 is condensed at the outermost incident angle θ2 with respect to the optical axis via the objective lens 40. That is, the laser light passing through the light control plate 30 composed of the inner circular plate 34 and the outer plate 32 has different outer angles of incidence according to the amount of light, and thus the objective lens has different numerical apertures (NA: Numerical Aperture). The light is irradiated to 40 to be focused onto the optical disc 50.

However, the laser beams focused by the objective lens 40 via the light control plate 30 at different numerical apertures are different from each other because the outermost incident angles of the laser beams are different when they are incident on the optical disc 50. The numerical aperture, the diameter of the light spot, and the depth of focus are determined respectively.

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,

[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 34 and the outer plate 32 is thus obtained. The difference in the diameter of the light is smaller than the light transmitted through the outer plate 32 and collected through the inner circular plate 34.

Thus, for each optical disc 50, for example, when playing a digital video disc having a thickness of 0.6 nm as shown in FIG. 3 (a), the external plate 32 is polarized by being polarized at the wavelength plate 20. FIG. The semi-transmissive laser beam forms an optical spot of about 0.8 μm on the optical disc 50 at θ2 with respect to the optical axis by the objective lens 40, thereby interfering with the diffraction at the recording surface 55, thereby causing the amount of light and Optical information is read with or without light. At this time, in the present invention, since the lens for digital video disc is used, the recording surface 55 is accurately focused without generating spherical aberration.

When the digital audio disc having a thickness of 1.2 mm is reproduced, as shown in FIG. 3 (b), the laser light circularly polarized by the wave plate 20 is confronted by the inner circular plate 34 and is applied to the objective lens 40. The laser beam is smaller than NA1 in the above equation (1) on the optical disc 50 at? 1 with respect to the optical axis. 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 50, and n is the refractive index.

[Equation 4]

Is determined. At this time, the laser light around the optical axis with less occurrence of spherical aberration is battled with the inner circular plate 34 to reduce the numerical aperture, and the laser light transflecting the outer plate 32 transmits the numerical aperture through the inner circular plate 34. It becomes larger than the laser beam. Therefore, the laser light whose numerical aperture is reduced by combating the inner circular plate 34 while simultaneously playing the digital video disc with the objective lens 40 dedicated to digital video disc reproduction is adjusted so that the numerical aperture becomes NA1 by Equation 4 above. If possible, the spherical aberration is proportional to (NA) ⁴ so that the spherical aberration is significantly reduced. As a result, the numerical aperture becomes small 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 disc 50, that is, on the digital audio disc, so that the track pitch is 1.6 μm. On the digital audio disc having the shortest length of 0.834 μm, the recording surface 55 is interfered with diffraction on the recording surface 55 to read 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 50 in the above-described process is irradiated to the wave plate 20 via the objective lens 40 and the light control plate 30. In the laser beam, circularly polarized light is polarized by linearly polarized light when the wavelength plate 20 is transmitted. In this case, since the linearly polarized laser light is incident on the wavelength plate 20 when the circularly polarized light is reversed upon reflection on the optical disk 50, the P-wave straight line having a polarization direction orthogonal to the time of incidence upon the initial wave plate 20 is applied. It becomes polarized light. The inverted linearly polarized laser light is irradiated from the wave plate 20 to the polarization separator 12 on the upper surface of the optical prism 10, and the laser light of the linearly polarized light is transmitted and diffracted by the polarization separator 12. do. Since the transmission is polarized split coating so that the polarization separator 12 is transmitted with respect to the P wave, the laser beam transmits and diffracts the polarization separator 12. Thus, the laser light transmitted through the polarization splitting part 12 passes through the reflective knife edge part 14, and the laser light is reflected by the reflective knife edge part 14 to impart a light amount gradient to the boundary of the light beam. The provision of the light gradient is for detecting a focusing error on the optical disk 50, and is partially reflected from the reflective knife edge portion 14 and irradiated to the reflective knife edge portion 14, i.e., based on the optical axis. Thus, a transmissive surface is formed at one end of the reflective knife edge portion 14 so as to receive only one light beam and exclude the other light beam. Therefore, the partially received laser light becomes different from the incident light in the optical prism 10, and the focus error can be detected by the knife edge method by the generation of the light gradient, thereby passing through the optical prism 10. . The laser light totally reflected by the reflective knife edge portion 14 of the optical prism 10 has a focus error signal at a different light path than when it is emitted, and is divided between the laser diode 5 and the optical prism 10. It is irradiated with the photodetector 50 which is a photodetector of a system.

In this way, the laser light, which reads the optical information via each path, is diffracted, interfered and reflected and transmitted to output a digital audio signal and a digital video signal as an original electrical signal, 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 transmits the laser light through the optical control plate 30 having a different transmittance, so that the optical disk is focused on the objective lens 40 by transflecting the outer plate 32 of the optical control plate 30 when the digital video disc is reproduced. An optical spot is formed on the image 50 with a diameter of about 0.8 μm, and the digital video disc is reproduced. When the digital audio disc is reproduced, a laser beam strikes the inner circular plate 32 so that the light of the optical axis portion battles the objective lens ( 40 is condensed on the optical disc 50 and at the same time the outermost incident angle is smaller than that at the time of reproduction of the digital video disc, thereby greatly reducing spherical aberration caused by the thickness difference of the mutual optical discs 50. Since optical spots with diameters larger than the μm size are formed, digital audio discs with large recording surfaces can be reproduced accurately without loss of light.

The light intensity control dual focus optical pickup device of the present invention arranges the emitting portion and the receiving portion of the laser beam for reading optical information on the same plane, and reduces the occurrence of spherical aberration due to the thickness difference between the optical disks. Optical discs can be played at the same time, and the alignment of the optical elements can be simplified and can be fabricated integrally. Therefore, each optical element is arranged at the correct position. Therefore, the manufacturing cost of the optical pickup device can be reduced and reliability can be improved. Since the amount of light is adjusted and reproduced according to the optical disc, the function of the optical pickup device is improved by minimizing the loss of the amount of light.

Claims (6)

On one side of the silicon substrate 1, which is provided in parallel with the recording surface 55 of the optical disc 50, a laser diode 5 is provided which emits a polarized laser having a vertical component with respect to the traveling direction of the light, and the laser diode 5 An optical pickup apparatus having an optical detector 60 for receiving reflected light reflected on an optical disk 50 and an objective lens 40 for focusing laser light on the optical disk 50, wherein the silicon substrate is provided on an installation side of the silicon substrate. An optical prism 10 which is installed at an acute angle with the upper surface of (1) to selectively transmit and reflect the laser light and at the same time receive a part of the reflected light and generate a light gradient in the light beam boundary; and the optical prism 10 and A wavelength plate 20 interposed between the optical discs 50 to convert the phase of the laser light, and an optical control plate 30 for separating and transmitting the laser light through the wavelength plate 20 at different transmittances according to the width. Done Optical power control-type dual focus optical pickup apparatus is characterized in that. The polarization splitter 12 of claim 1, wherein the optical prism 10 transmits the laser light having a component parallel to the incident direction of the laser light at an upper slope and reflects the laser light having a component perpendicular to the incident surface. And a reflective knife edge portion 14 which receives a part of the laser light from the lower slope and totally reflects the light, and generates a light gradient in the light beam boundary. The light control plate 30 is composed of an inner circular plate 34 for transmitting a narrow laser light at a first transmittance, and an outer plate 32 for transmitting a wide laser light at a second transmittance. The light transmittance type dual focus optical pickup apparatus of claim 1, wherein the first transmittance is set larger than the second transmittance. The light quantity control dual focus optical pickup according to claim 3, wherein the inner circular plate 34 has a transmissive film of 1, and the outer plate 32 has a transmissive film of 1/2. Device. 4. The dual focus optical pickup apparatus of claim 3, wherein the outer plate (34) of the light control plate (30) is formed of an annular circular light-transmitting film. The optical focus control apparatus of claim 1, wherein the light control plate (30) adjusts the outermost incident angle of the laser light focused on the optical disc (50).

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