KR100211819B1 - 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, and in particular, a first beam splitter and a second beam splitter are bonded to form a cube, and a photodetector is formed on one side of the first beam splitter and is parallel to the photodetector. A prism having a λ / 4 wavelength lattice plate formed on one side of the corresponding second beam splitter, a λ / 4 wave plate formed on the upper surface of the second beam splitter, and a polarizing coating layer formed on the slope of the first beam splitter; The provision of a laser diode to the prism for emitting a laser beam polarized with normal light makes the number of optical elements much smaller than that of a conventional optical pickup device, and as a result, the positioning and positioning of each optical element is very simple and easy. Can be. Therefore, the optical pickup device can be miniaturized, as well as the overall size of the device, and the light efficiency can be improved by using a polarized beam.

Description

Optical pickup

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pick-up apparatus, and more particularly, to joining a first beamsplitter and a second beamsplitter having a predetermined thickness to form a prism of a cube and forming a plurality of optical elements in the prism. The present invention relates to an optical pick-up apparatus capable of improving light efficiency as well as light and short size.

In general, an optical pickup device includes an object lens, a beam splitter, a diffraction grating, a laser diode, and a photodetector, in which individual parts are assembled. 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 is manufactured by the optical splitter, the diffraction grating, the laser diode, and the optical detectors independently, taking up a lot of space for assembly, and as the optical pick-up apparatus is configured, The error rate during operation is high due to mechanical errors generated during operation. In addition, since the light emitted from the laser diode is transmitted again through the beam splitter and finally irradiated to the photodetector, a beam of a large amount of optical information is lost.

Accordingly, the present invention has been made to solve the above-mentioned disadvantages, and forms a plurality of optical elements in a prism composed of a cube and reduces the mechanical error of each optical element by using a laser beam polarized with normal light. The purpose of the present invention is to provide an optical pick-up device that can contribute to light and short and small size of the device as well as improve the optical efficiency of the optical device.

The present invention is a laser diode that emits a laser beam polarized by the normal light, and the first beam splitter and the second beam splitter are coupled to the upper side at a constant distance from the laser diode and the polarizing coating layer on the slope of the first beam splitter A prism which is formed and has a cube shape, a photodetector formed at a central portion of one side of the first beam splitter to receive incident light information and detected as an electrical signal, and a second corresponding parallel to the photodetector Λ / 4 wavelength lattice plate which is formed on one side of the beam splitter and wavelength-transforms and diffracts the beam of incident light information and totally reflects it to a predetermined position, and the normal light which is formed on the upper surface of the second beam splitter with a predetermined thickness and is incident Silver circularly polarized light, the circularly polarized light is characterized in that the λ / 4 wavelength plate for converting the wavelength into the abnormal light.

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 shown for detecting a 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 beam splitter 4: second beam splitter

5: polarizing coating layer 6: lambda / 4 wavelength plate

7: objective lens 8: disc

9: lambda / 4 wavelength lattice plate 10: reflector

11: photodetector

The optical pickup device according to the present invention will be described in detail with reference to the accompanying drawings. 2 is an overall configuration diagram according to the present invention, Figure 3 is a perspective view of a prism according to the present invention is a diode diode (1) for emitting a laser beam polarized with normal light, and a constant distance from the laser diode (1) A prism 2 having a first beam splitter 3 and a second beam splitter 4 joined to an upper side thereof to form a cube and having a polarizing coating layer formed on a slope of the first beam splitter 3; Λ / 4-wavelength plate which is formed on the upper surface of the first beam splitter 3 corresponding to the laser diode 1 and has a predetermined thickness and converts normal light into circularly polarized light and circularly polarized light into abnormal light. (6), an objective lens (7) formed at an upper predetermined position of the prism (2), condensing a beam, irradiating the disk (8), and receiving a beam of light information reflected from the disk (8); In one side of the first beam splitter 3, a predetermined thickness therein The hologram lattice 9 is formed to diffract the beam of the incident optical information and convert it by 90 ° wavelength to reflect at a constant angle, and the λ / 4 wavelength lattice plate 9 and parallel to the λ / 4 wavelength lattice 9 The light detector 11 is formed on one side of the corresponding second beam splitter 4 to receive a beam of incident optical information and detect the beam as an electrical signal.

A reflective film 10 is formed on one side of the λ / 4 wavelength lattice 9 to totally reflect the beam of incident light information.

On the other hand, looking at the path of the polarized beam in the optical pick-up device having such a configuration as follows. First, the laser diode 1 emits a laser beam polarized with normal light at a constant angle, and the emitted laser beam is incident on the polarization coating layer 5 formed on the slope of the first beam splitter 3. At this time, the polarizing coating layer 5 transmits the incident normal light as it is and reflects the laser beam of the abnormal light at a predetermined angle so that the laser beam of the normal light is transmitted through the polarizing coating layer 5 as it is λ / 4. Incident on the wave plate 6. Therefore, the laser beam of the normal light passes through the λ / 4 wavelength plate 6, and the shape of the beam is in the state of circularly polarized light, and the light is collected by the objective lens 7. Focusing on 8a) causes the information recorded on the pit 8a of the disk 8 to be reflected by constant light and incident again into the objective lens 7 having a constant diffraction region.

On the other hand, the circularly polarized light information beam focused again by the objective lens 7 is polarized by 90 degrees through the λ / 4 wave plate 6 to form a beam of an abnormal light beam (S wave). The beam of optical information of is incident on the polarizing coating layer 5 formed on the slope of the first beam splitter 3. The extraneous light incident on the polarizing coating layer 5 is reflected at a predetermined angle and is incident on the? / 4 wavelength lattice plate 9 formed on one side of the hologram lattice. That is, the optical information beam of the abnormal light incident on the λ / 4 wavelength lattice plate 9 is converted into circularly polarized light and then reflected by the reflective film 10 and diffracted through the hologram lattice to form the λ / 4 wavelength lattice plate ( 9) is to be transmitted. Therefore, the beam of circularly polarized light passes through the λ / 4 wavelength lattice 9 so that the wavelength is changed to a normal light state and simultaneously diffracted at a constant angle to enter the polarizing coating layer 5. Then, the optical information beam of the normal ray is transmitted through the polarization coating layer 5 as it is and irradiated to the photodetector 11 formed on one side of the first beam splitter 3.

In this case, the focus error is detected by using a focal method. As shown in FIG. 3, a beam of optical information diffracted by the hologram grating is generally received in each area of the quadrature photodetector 11. In the case of the front of the detector 11, each beam of the photodetector 11 is irradiated in a beam shape as shown in FIG. 3A, and in the case of the focus of the back of the photodetector 11, it is shown in FIG. The shape of the beam as shown 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. 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 8a of the disk 8 deviates to the left and right sides of the pit 8a, the tracking error detection area 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)-(B + 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 8, 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 unshown control device 7 The optical pick-up device operates stably by applying a current to the coil of the actuator.

The present invention reduces the mechanical error between the optical elements by forming a laser diode that radiates a beam polarized with normal light, two beamsplitters and a cubic shaped prism and a plurality of optical elements in the prism. The optical pickup device can be miniaturized by improving the assemblability of the optical pickup device, and the S / N ratio of the servo signal or the information signal can be improved by using the polarized beam.

Claims (3)

In the optical pick-up apparatus for receiving a laser beam reflected from the disk (8) by condensing a laser beam incident with a constant wavelength with the objective lens (7) and irradiated to the disk (8), A laser diode (1) emitting a laser beam polarized with normal light, and the first beam splitter (3) and the second beam splitter (4) are bonded to each other at a predetermined distance from the laser diode (1) to form a shape. This cube forms a photodetector 11 on one side of the first beamsplitter 3 and a lambda / 4 wavelength lattice 9 on one side of the second beamsplitter corresponding to the photodetector 11 in parallel. And a prism 2 having a λ / 4 wave plate 6 formed on an upper surface of the second beam splitter 4 and a polarizing coating layer 5 formed on a slope of the first beam splitter 3. An optical pickup device, characterized in that. The optical pick-up device according to claim 1, wherein the polarizing coating layer (5) transmits a beam of normal light as it is and reflects a beam of abnormal light. According to claim 1, wherein one side of the λ / 4 wavelength lattice (9) is coated with a reflecting film 10 reflects the incident beam, and the λ / 4 wavelength lattice (9) has a hologram lattice formed is incident An optical pickup apparatus characterized by diffracting a beam at a predetermined angle.