KR19980058055A - Optical pickup - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pick-up apparatus, and more particularly, a laser diode that emits a laser beam polarized with normal light, and a vertical prism of the upper and lower sides connected to the upper and lower sides at a predetermined distance from the laser diode to be connected to the rectangular prism. A cubic prism having a polarization selective transmission layer formed on a slope, a phase hologram lattice diffracting according to a polarization state of an incident beam formed on an upper surface of the second rectangular prism, and a predetermined distance above the cubic prism And a second λ / 4 wavelength plate for converting the normal light incident to the circularly polarized light into the circularly polarized light and the circularly polarized light into the extraordinary light, and the beam of the extraordinary light formed on one side of the second rectangular prism. Wavelength-converted into normal light, one side of which is formed on a first lambda / 4 wavelength plate which is a reflecting plate, and on one side of the first rectangular prism facing the first lambda / 4 wavelength plate, It is equipped with a photo detector that receives a beam of optical information incident through the polarizing coating layer and outputs it as an electrical signal, thereby reducing mechanical errors between the optical elements and assembling as no precision is required between the components. The optical pick-up device can be miniaturized due to improved performance, and the light efficiency is improved by using a beam polarized with normal light.

Description

Optical pickup

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pick-up apparatus, and in particular, a laser diode emitting a beam polarized with normal light and a cuboid prism including two optical prisms joined to each other to facilitate assembly and adjustment of the device. In addition, the present invention relates to an optical pick-up apparatus that contributes to light and small size and improves light efficiency.

In general, a data reproducing and recording system using an optical disc such as a laser disc or a compact disc has been recently developed. An optical pickup apparatus is provided for irradiating a laser beam along a data recording track on the disc to reproduce or record information from such an optical disc, and for reproducing the data based on the beam reflected on the track. Such optical pick-up devices are usually assembled with individual parts such as an objective lens, a beam splitter, a diffraction grating, a laser diode, and a photodetector, so that more precise precision is required to accurately read high-density and large-capacity information. In the trend of miniaturization, the directing and simplification of optical elements is being made.

The optical pick-up device generally used here is a laser diode 71 that emits a laser beam of a specific wavelength, as shown in FIG. 1, and at a certain distance from the laser diode 71. A diffraction grating 72 for separating a laser beam formed and incident on one side into 0th order light and ± 1th order light, that is, three beams, and formed at a predetermined inclination on one side at a predetermined distance from the diffraction grating 72 The disk 75 reflects and transmits light at a predetermined ratio, and a beam splitter 73 formed at an upper side with a predetermined distance from the beam splitter 73 to collect incident laser light due to a diffraction limit of a predetermined wavelength. An objective lens 74 that reads an optical signal of information recorded by focusing on it, and is formed at a lower predetermined position with a predetermined distance from the beam splitter 73 to pass through the objective lens 74 and the beam splitter 73 Recorded on the disc 75 It consists of a photodetector 76 for outputting the optical information signal as a constant electrical signal.

On the other hand, the operation of the optical pick-up device having such a conventional configuration will be described. First, the laser diode 71 emits a predetermined oscillation wavelength, that is, a laser beam of about 780 nm, wherein the laser beam is emitted. Incident to the diffraction grating 72 formed on one side of the direction. 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 from the audio or video disc 75 and returned is modulated by the pit 75a, and the modulated light information is sequentially passed through the objective lens 74 and the beam splitter 73. 76, which is output as a corresponding electrical signal, which is an audio signal recorded on the disc 75 by demodulating the original signal by a digital signal processing unit (not shown). (RF) signal, an error detection focus signal and a tracking signal which are servo signals are outputted.

However, in the conventional optical pick-up device, since optical components such as a beam splitter, a diffraction grating, a laser diode, and a photodetector are independently manufactured, their assembly positions must be precisely installed at regular intervals between the components, thereby improving work efficiency. Falls. In addition, there is a limit to miniaturization of the device by installing the appropriate spacing between each component element and the disadvantage that the light emitted from the laser diode finally enters the photodetector to not use the light efficiently.

The present invention has been made to solve the above-mentioned disadvantages by combining two orthogonal prisms to form a cubic prism, having a plurality of optical elements in the cube prism and using a laser beam polarized with normal light, The purpose of the present invention is to provide an optical pick-up device that minimizes the mechanical error of the optical pickup device, thereby contributing to the light and shortening of the optical pick-up device, and makes the best use of the optical efficiency.

In order to achieve the above object, the present invention provides a laser diode that emits a laser beam polarized with normal light, and is formed on the upper side at a predetermined distance from the laser diode so that the slopes of the first rectangular prism and the second rectangular prism are joined to each other. A cubic prism including a plurality of optical elements, a polarization selective transmission layer that reflects and transmits according to a polarization state of a beam that is coated on an inclined surface of the first rectangular prism, and a predetermined thickness on an upper surface of the second rectangular prism A phase hologram grating diffracted according to the polarization state of the incident beam, a second λ / 4 wave plate for converting a beam formed at an upper side at a predetermined distance from the cubic prism by 90 °, and converting the incident beam; 90 ° wavelength conversion of the beam of abnormal light formed on one side of the second rectangular prism and reflected from the polarization selective transmission layer, and one side of which is coated with a reflector. A 1 λ / 4 wavelength plate and a circularly polarized light information beam formed on one side of the first rectangular prism facing the first λ / 4 wavelength plate and passing through the polarization selective transmission layer to receive and electrically A photodetector for outputting a signal is provided.

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 main parts of drawing>

1: laser diode 2: cubic prism

3: first right angle prism 4: second right angle prism

5: polarization selective transmission layer 6: phase hologram lattice

7: second lambda / 4 wavelength plate 8: objective lens

9: disk 10: first lambda / 4 wavelength plate

11: reflector 12: photodetector

The optical pickup device according to the present invention will be described in detail with reference to the accompanying drawings. Here, as shown in FIG. 2, the optical pick-up apparatus according to the present invention uses a laser diode 1 for radiating a laser beam polarized with normal light upwards, and an upper side with a constant distance from the laser diode 1. A cubical prism 2 formed in the first rectangular prism 3 and a slope of the second rectangular prism 4 coupled to each other and including a plurality of optical elements therein; and the first rectangular prism 3 Formed on an inclined surface of the polarization selective transmission layer 5 which reflects and transmits according to the polarization state of the incident beam, and is formed on the upper surface of the second rectangular prism 4 corresponding to the laser diode 1 The beam of the normal ray is transmitted as it is, and the abnormal ray is diffracted by the phase hologram lattice 6 and formed at a predetermined thickness on the upper side at a predetermined distance from the cubic prism 2 to avoid interference between the incident beam and the reflected beam. Fortune By using the refraction phenomenon, the normal light is circularly polarized light, and the circularly polarized light is formed at an upper predetermined position with a predetermined distance from the second lambda / 4 wavelength plate 7 and the cubic prism 2 to convert the wavelength into an abnormal light beam. Is focused on the disk 9 and irradiates the disk 9, and is formed on one side of the objective lens 8 for receiving a beam of optical information reflected from the disk 9 and the second rectangular prism 4, and transmits polarization selection. A first lambda / 4 wavelength plate 10 for converting wavelengths into beams of normal light by transmitting and reflecting an optical beam in the form of an extraordinary ray reflected and incident on the layer 5, and the first lambda / 4 wavelength plate ( It consists of a photo detector 12 formed on one side of the first rectangular prism 3 corresponding to (10) in parallel to receive the incident circularly polarized beam and output as an electrical signal.

One side of the first λ / 4 wavelength plate 10 is coated with a reflector 11 for reflecting a beam incident therein into the polarization selective transmission layer 5.

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. The polarization selective transmission layer (5) formed on the slope of the via, where the beam of the normal light incident on the polarization selective transmission layer (5) is transmitted through the phase hologram lattice formed on the upper surface of the second rectangular prism (4) It enters into (6). Then, the phase hologram lattice 6 performs diffraction according to the polarization state of the incident beam, so that the beam of the incident normal light beam passes through the phase hologram lattice 6 and enters into the λ / 4 wave plate 7. Here, the laser beam of the normal light passes through the lambda / 4 wavelength plate 7 so that the shape of the beam is wavelength-converted into the state of circularly polarized light and condensed by the objective lens 8. At this time, the laser beam focused by the objective lens 8 focuses on the pit 9a on the disk 9, and thus the information recorded on the pit 9a of the disk 9 is reflected by a constant light to give an objective. It is incident again to the lens 8.

On the other hand, the circularly polarized light information beam focused again by the objective lens 8 passes through the second lambda / 4 wavelength plate 7 so that the circularly polarized light beam is formed by the optical information beam of the abnormal light beam (S wave). The wavelength-converted beam of optical information, which is wavelength-converted, is diffracted by way of the phase hologram grating 6 formed on the upper surface of the second rectangular prism 4 to form a polarization selective transmission layer formed on the slope of the first rectangular prism 3. It enters into (5). Then, the beam of the abnormal light incident on the polarization selective transmission layer 5 is reflected at a predetermined angle and is incident on the first λ / 4 wave plate 10 formed on one side of the second rectangular prism 4. The beam transmitted through the first λ / 4 wave plate 10 has an optical information beam reflected by the reflecting plate 11 coated at one side of the first λ / 4 wave plate 10 with a wavelength of 90 °. The light passes through the second lambda / 4 wavelength plate 10 again, the wavelength of the beam is converted into a normal line, and is incident on the polarization selective transmission layer 5. At this time, the optical information beam of the normal light incident on the polarization selective transmission layer 5 is transmitted to the polarization selective transmission layer 5 and received by the photodetector 12 formed on one side of the first right prism 3. It is output as a constant electrical signal. At this time, the photodetector 12 is usually formed of four light-receiving elements, and detects an error by diffracting a predetermined amount of light of a beam to detect a focusing error and a tracking error together with a signal of optical information.

In the present invention, the focal method is used to detect the focus error. As shown in FIG. 3, the beam of optical information diffracted in the phase hologram grating 6 is received by each region of the ordinary five-segment photodetector 12. In this case, when the focus is brought to the front of the photodetector 12, each beam of the photodetector 12 is irradiated in a beam shape as shown in FIG. 3A, and the focus is brought to the rear of the photodetector 12. In this case, the shape of the beam as shown in FIG. 3 is irradiated to each area of the photodetector 12. In the case where the focus is correctly made by the photodetector 12, the shape of the beam as shown in FIG. 3B is irradiated to each area of the photodetector 12. At this time, each area of the photodetector 12 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 12 region of A and B, and the error is corrected by the 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)-(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 12 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 12, and in response to the signal, a control device not shown is provided. The optical pick-up device operates stably by applying a current to the coil of the actuator.

The present invention provides a laser diode that emits a beam polarized with normal light, and a cube including a plurality of optical elements in which a slope of a first rectangular prism and a slope of a second rectangular prism are coupled to an upper side at a predetermined distance from the laser diode. With the prism, the mechanical error in assembling each optical element is remarkably reduced, so that the assembly and light and small size of the device can be minimized, so that the optical pickup device can be miniaturized and the light efficiency can be increased by using a polarized beam. have.

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), The laser diode 1 emitting a laser beam polarized by the normal light, the slope of the first rectangular prism 3 and the slope of the second rectangular prism 4 at an upper side with a constant distance from the laser diode 1 The polarization selective transmission layer 5 is formed on the slopes of the first rectangular prism 3, and the phase hologram lattice 6 is formed on one side of the second rectangular prism 4 corresponding to the laser diode 1 in parallel. ) Is formed to a predetermined thickness and a photodetector 12 is formed at the central portion of one side of the first rectangular prism 1, and one side of the second rectangular prism 12 corresponding to the photodetector 12 in parallel with the photodetector 12. The cube prism (2) having the first lambda / 4 wavelength plate 10 for converting the 90 ° wavelength is formed in the upper part of the cubic prism (2) at a predetermined distance and the 90 ° wavelength conversion of the incident beam An optical pickup device characterized in that a 2? / 4 wavelength plate (7) is provided. 2. The optical pickup device according to claim 1, wherein the phase hologram grid (6) diffracts incident incident light and transmits normal light as it is. The optical pickup apparatus according to claim 1, wherein a reflecting plate (11) is provided at one side of the first λ / 4 wavelength plate (10) so as to totally reflect the incident beam to the polarization selective transmission layer (5). . The optical pickup apparatus according to claim 1, wherein the polarization selective transmission layer (5) transmits incident normal light as it is and reflects abnormal light.