KR100211820B1 - An optical pick up device - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pick-up apparatus, in particular a laser diode that emits a laser beam polarized with normal light, and an inclined surface of two right-angle prisms facing each other at a predetermined distance from the laser diode and installed at right angles. A beam splitter is formed on an inclined surface of the prism, and a photodetector is formed at a central portion of one side of the first rectangular prism, and a reflective film is coated on one side of the second rectangular prism corresponding to the photodetector. The upper surface includes a prism of a cube having a phase hologram lattice formed thereon, and a lambda / 4 wavelength plate which is formed on the upper side at a predetermined distance from the prism and is incident on the circularly polarized light, and the circularly polarized light is converted into the abnormal light. The mechanical error between each optical element is reduced and the precision is not required between each component. Property is improved optical pick-up device can be reduced in size, and improves the optical efficiency by using a polarized beam in a normal light.

Description

Optical pickup

The present invention relates to an optical pick-up apparatus, and more particularly, a first rectangular prism and a second rectangular prism having a predetermined thickness are bonded to form a prism of a cube, and the apparatus is formed by forming a plurality of optical elements in the prism. The present invention relates to an optical pick-up apparatus capable of improving the light efficiency as well as reducing the size and light weight of the device.

In general, an optical pickup device includes an individual lens such as an objective lens, a beam splitter, a diffraction grating, a laser diode, and a photodetector. The optical pickup device irradiates light onto a pit shape of a disk and reads the signal. The digital audio disc (DAD) having a spot size diameter of 1.6 μm or the digital video disc (DVD) having a spot size diameter of 0.8 μm is widely used. In addition, optical pick-up devices require more precise precision to accurately read high-density and large-capacity information, and direct miniaturization of optical elements is becoming more and more compact in the trend of miniaturization of equipment.

Here, a general optical pick-up device used for a digital audio or video disc includes a laser diode 71 for generating a laser beam of a specific wavelength as shown in FIG. 1, and the laser diode 71. A diffraction grating 72 which separates a laser beam formed and incident on one side of the light into zero-order light and ± 1-order light, that is, a three-beam beam, and light formed by a predetermined inclination on one side of the diffraction grating 72 is fixed. Information recorded by focusing on the disk 75 by focusing on a beam 75 which reflects and transmits at a ratio and a beam splitter 73 formed on an upper side of the beam splitter 73 and incident due to a diffraction limit of a predetermined wavelength An objective lens 74 that reads an optical signal of the optical signal; and formed on a predetermined position below the beam splitter 73 and recorded on the disc 75 incident through the objective lens 74 and the beam splitter 73 Optical information signal constant electrical It consists of a photodetector 76 which outputs as a signal.

Referring to the operation of the optical pick-up device having such a conventional configuration, first, the laser diode 71 emits a laser beam of a predetermined oscillation wavelength, that is, about 780 nm, wherein the laser beam is located on one side of the radiation direction. It enters into the formed diffraction grating 72. Then, the light incident on the diffraction grating 72 is separately radiated into 0th order light and ± 1th order light due to the diffraction phenomenon. At this time, the 0th order light and the ± 1th order light that are separated through the diffraction grating 72 are for use for focus and tracking error detection and are commonly referred to as three beams.

That is, the light split into three beams by the diffraction grating 72 is incident on the beam splitter 73 having a constant reflectance and transmittance at a predetermined slope. Then, the light incident on the beam splitter 73 is reflected and transmitted at a constant rate, and the reflected beam is incident on the objective lens 74 and the beam is focused by diffraction phenomenon below a predetermined wavelength. Therefore, the beam focused by the objective lens 74 is sent on the audio or video disk 75 to focus on the disk 75, so that the information recorded on the disk 75 is reflected by a constant light and the objective It is incident on the lens 74.

That is, the light incident on the objective lens 74 is collected in an airy shape of several μm and irradiated onto the signal surface of the disk 75. The irradiated light is incident on a place where the pit 75a in which data is recorded is not present. The beam is reflected and returns to the aperture of the objective lens 74 almost intact, but where the pit 75a is present, light is diffracted by the pit 75a and emitted out of the range of the objective lens 74. Only part of the incident light is returned, thereby generating a light quantity difference in the photodetector 76. This is because the depth of the pit 75a is set to λ / 4 of the wavelength, and the reflected light is canceled by interfering with different half wavelengths above and below the pit 75a, so that the amount of light returned to the photodetector 76 is reduced.

On the other hand, the intensity of the light reflected back from the audio or video disc 75 is modulated by the pit 75a, and the modulated light information is transmitted to the photodetector 76 via the objective lens 74 and the beam splitter 73. ) Is outputted as a corresponding electrical signal, which is an audio signal recorded on the disc 75 by demodulating the original signal by a digital signal processor (not shown). RF) signal, an error detection focus signal, and a tracking signal, which are servo signals, are outputted.

However, such a conventional optical pick-up apparatus has been made independently of the mechanical errors generated during assembly as the optical pick-up apparatus is formed by assembling the optical components of the beam splitter, the diffraction grating, the laser diode, and the photodetector independently. As a result, the error occurrence rate during operation is high, and light emitted from the laser diode is finally incident to the photodetector so that the light cannot be efficiently used.

SUMMARY OF THE INVENTION The present invention has been made to solve the above disadvantages, and joins a first rectangular prism and a second rectangular prism to form a cube-shaped prism and a plurality of optical elements in the prism, and uses a laser beam polarized with normal light. The purpose of the present invention is to provide an optical pick-up apparatus that can reduce the mechanical error of each optical element, thereby contributing to the light and small size reduction of the optical pick-up apparatus, as well as improving the optical efficiency of the optical device.

As described above, the present invention provides a laser diode that emits a laser beam polarized with normal light, and a slope of the first rectangular prism and the second rectangular prism is fastened at a predetermined distance from the laser diode so that the slope acts as a beam splitter. A phase hologram grating is formed on the upper surface of the second rectangular prism for diffraction according to the polarization state of the incident beam, and the incident optical information is received at the center of one side of the first rectangular prism for detection as an electrical signal. A photodetector is formed, and on one side of the second rectangular prism that is parallel to the photodetector, a reflecting film is formed to totally reflect the beam of incident light, and the prism of which the shape is a cube, and the upper side at a predetermined distance from the prism. The normal light which is formed in the incident light is circularly polarized light, and the circularly polarized light is provided with a λ / 4 wavelength plate for wavelength conversion into an abnormal light It is characterized by.

1 is a block diagram of a conventional optical pick-up device,

2 is a block diagram of an optical pick-up apparatus according to the present invention;

3 is a plan view of a photodetector depicted for detecting focus error in accordance with the present invention.

* Explanation of symbols for the main parts of the drawings

1: laser diode 2: prism

3: first prism 4: second rectangular prism

5 beam splitter 6 phase hologram lattice

7: lambda / 4 wavelength plate 8: objective lens

9: disc 10: reflective film

11: photodetector

The optical pickup device according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 2 is an overall configuration diagram, and FIG. 3 is a perspective view of a prism, and an optical pick-up apparatus according to the present invention includes a laser diode 1 emitting a laser beam polarized with normal light, and the laser diode 1 and On the upper side at a certain distance, the prism formed with a beam splitter 5 on which the inclined planes of the first rectangular prism 3 and the second rectangular prism 4 are faced to face each other to reflect and transmit the beam incident on the inclined plane at a predetermined ratio. (2), a phase hologram lattice 6 formed on the upper surface of the second rectangular prism 4 corresponding to the laser diode 1 and diffracting according to the polarization state of the incident beam, and the prism A normal wavelength formed at the upper side at a predetermined distance from (2) and incident on the polarized light is a λ / 4 wavelength plate 7 for converting the wavelength into circularly polarized light, and the circularly polarized light into an abnormal light, and a predetermined position on the upper part of the prism 2 Formed on the disk to condense the beam (9) And an objective lens 8 for receiving a beam of optical information reflected from the disk 9, and a beam of optical information that is formed at a central portion of one side of the first rectangular prism 3 and is incident. It consists of a photodetector 11 for outputting as an electrical signal.

A reflective film 10 for total reflection of the incident beam is formed on one side of the second rectangular prism 4 corresponding to the photodetector 11 in parallel.

Meanwhile, referring to the operation of the optical pick-up device having such a configuration, first, the laser diode 1 emits a laser beam polarized by the normal light at a constant angle, and the emitted laser beam is the first rectangular prism 3. Is incident on the beam splitter 5 formed between the inclined surface of the and the inclined surface of the second rectangular prism 4. At this time, the laser beam of the normal light incident on the beam splitter 5 is reflected and transmitted at a predetermined ratio so that the double-transmitted laser beam is the phase hologram lattice 6 formed on the upper surface of the second rectangular prism 4 as it is. The light beam is transmitted through the λ / 4 wave plate 7 formed on the upper side at a predetermined distance from the prism 2, where the laser beam of the normal light passes through the λ / 4 wave plate 7 so that the shape of the beam is circularly polarized. Is focused on the objective lens 8, and the focused laser beam focuses on the pit 9a on the disk 9, which causes the information recorded on the pit 9a of the disk 9 to be fixed. Is reflected back into the objective lens 8 having a constant diffraction range.

On the other hand, the circularly polarized optical information beam focused on the objective lens 8 is wavelength-converted into the optical information beam of the abnormal light beam (S wave) by passing through the λ / 4 wavelength plate 7. The beam of optical information is incident on the phase hologram lattice 6 formed on the upper surface of the second rectangular prism 3. At this time, the phase hologram grating 6 performs diffraction according to the polarization state of the incident beam, i.e., the beam polarized by the extraordinary ray is diffracted by 0th order and ± 1st order light and irradiated to the beam splitter 5. Then, the beam incident on the beam splitter 5 is reflected and transmitted at a constant rate, and the double reflected beam is reflected on the reflecting film 10 and then reflected, and then passes through the beam splitter 5 again, so that the first rectangular prism 2 Irradiated by the photodetector 11 formed on one side is output as an electrical signal.

Here, the focus error is detected using the focal method. As shown in FIG. 3, the beam of optical information diffracted in the phase hologram grating 6 passes through the beam splitter 5, and thus, the normal five-segment photodetector 11. In this case, when the focus is located in front of the photodetector 11, each region of the photodetector 1 is irradiated in a beam shape as shown in FIG. In the latter case, the shape of the beam as shown in FIG. 3C is irradiated to each area of the photodetector 11. In the case where the focus is correctly made by the photodetector 11, the shape of the beam as shown in FIG. 3B is irradiated to each area of the photodetector 11. In this case, each area of the photodetector 11 is divided into A.B.C.D, and the focus error detection signal may be represented by the following equation.

[Equation 1]

F.E.S = A-B (where F.E.S is the focus error detection signal)

That is, the error is detected by using the difference in the amount of light in the differential amplifier (not shown) provided at the rear end of the beam irradiated to the photodetector 11 region of A and B, and the error is corrected by a controller not shown. .

In addition, in the present invention, the tracking error is detected by using the original beam method. When the beam irradiated to the pit 9a of the disk 9 deviates to the left and right sides of the pit 9a, as shown in FIG. There is a difference in the amount of light irradiated. Here, the tracking error detection signal may be represented by the following equation.

[Formula 2]

T.E.S = (A + C)-(C + D) (where T.E.S is the tracking error detection signal)

In other words, the difference in the amount of light irradiated to the two tracking detection regions is output as negative and positive values from the differential amplifier installed at the rear stage.

In addition, the beam of light information irradiated by the photodetector 11 may be represented by the following equation.

[Equation 3]

R.F = A + B + C + D (where R.F is the optical information signal)

In this way, the positional accuracy of the pickup device with respect to the disc 9, i.e., a focusing and tracking error signal, is generated from the shape of the beam irradiated to the photodetector 11, and in response to the signal, an unillustrated control device provides an objective lens 8 The optical pick-up device operates stably by applying a current to the coil of the actuator.

According to the present invention, a laser diode radiating a beam polarized with normal light and a slanted surface of two rectangular prisms are face-to-face bonded to form a prism of a cube, and a plurality of optical elements are provided in the prism to reduce the number of optical components. It is possible to improve the assemblability of the optical pickup device and to reduce the size and weight of the device.

Claims (4)

In the optical pick-up apparatus for receiving a laser beam reflected from the disk (9) by condensing the laser beam incident with a constant wavelength to the objective lens (8) and irradiated to the disk (9), A laser diode (1) emitting a laser beam polarized with normal light, and formed at an upper side with a constant distance from the laser diode (1) so that the inclined surfaces of the first rectangular prism (3) and the second rectangular prism (4) On the upper surface of the second rectangular prism 4 which is joined to face and parallel to the laser diode 1, a phase hologram lattice 6 is formed to diffract according to the polarization state and the first rectangular prism 2 is formed. The photodetector 11 which receives a beam of incident light information and outputs it as an electrical signal is formed at the central portion of the side of the prism 2 forming a cubic shape, and the upper side of the prism 2 at a predetermined distance. And a λ / 4-wavelength plate (7) for converting the normal light formed into a predetermined thickness into incident light into circularly polarized light and the circularly polarized light into abnormal light. The optical pick-up of claim 1, wherein a beam splitter (5) is formed on the inclined surfaces of the first rectangular prism (3) and the second rectangular prism (4) to reflect and transmit the incident beam at a predetermined ratio. Up device. The optical pickup apparatus according to claim 1, wherein a reflecting film (10) is coated on one side of the second rectangular prism (4) to reflect the incident beam at a predetermined angle. The optical pickup apparatus according to claim 1, wherein the phase hologram grid (6) transmits normal light as it is and diffracts abnormal light at a predetermined angle.