KR20110016271A - Optical pick-up apparatus - Google Patents

Optical pick-up apparatus Download PDF

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Publication number
KR20110016271A
KR20110016271A KR1020090073893A KR20090073893A KR20110016271A KR 20110016271 A KR20110016271 A KR 20110016271A KR 1020090073893 A KR1020090073893 A KR 1020090073893A KR 20090073893 A KR20090073893 A KR 20090073893A KR 20110016271 A KR20110016271 A KR 20110016271A
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KR
South Korea
Prior art keywords
light
recording medium
tracking
liquid crystal
wavelength
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KR1020090073893A
Other languages
Korean (ko)
Inventor
김인태
Original Assignee
엘지전자 주식회사
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Priority to KR1020090073893A priority Critical patent/KR20110016271A/en
Publication of KR20110016271A publication Critical patent/KR20110016271A/en

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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G02B5/1814—Diffraction gratings structurally combined with one or more further optical elements, e.g. lenses, mirrors, prisms or other diffraction gratings
    • G02B5/1819—Plural gratings positioned on the same surface, e.g. array of gratings
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/125—Optical beam sources therefor, e.g. laser control circuitry specially adapted for optical storage devices; Modulators, e.g. means for controlling the size or intensity of optical spots or optical traces
    • G11B7/127—Lasers; Multiple laser arrays
    • G11B7/1275—Two or more lasers having different wavelengths
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/13—Optical detectors therefor
    • G11B7/131—Arrangement of detectors in a multiple array
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1353—Diffractive elements, e.g. holograms or gratings
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1372—Lenses
    • G11B7/1374—Objective lenses
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1395—Beam splitters or combiners
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B2007/0003—Recording, reproducing or erasing systems characterised by the structure or type of the carrier
    • G11B2007/0006—Recording, reproducing or erasing systems characterised by the structure or type of the carrier adapted for scanning different types of carrier, e.g. CD & DVD

Abstract

PURPOSE: An optical pickup device is provided to efficiently generate tracking light for light of each wavelength when light of a different wavelength is selectively used. CONSTITUTION: An optical pickup comprises a light source(110), a tracking light forming unit(300), and a light detecting unit(190). The light source selectively emits light of a different wavelength. The tracking light forming unit includes a diffraction grating and a liquid crystal between diffraction gratings. The tracking light forming unit diffracts light of one of different wavelengths to divide. The light detecting unit detects the divided light. The tracking light forming unit divides one light of a selected specific wavelength into the main beam and two sub beams. The divided light has a diffraction angle in proportional to a wavelength.

Description

Optical pick-up apparatus

The present invention relates to an optical pickup apparatus, and more particularly, to an optical pickup apparatus capable of efficiently generating tracking light for light of different wavelengths.

An optical pickup apparatus generates light from a light source to form pit information on a surface of an optical disc as a recording medium or to reproduce recorded data using light reflected from the formed pit information.

In this case, there are various types of recording media, but CDs (CDs) and Digital Versatile Disks (DVDs) are generally used. Up to 27GB can be recorded using a blue laser having a short wavelength. Blu-ray Disks (BDs) are used.

1 is a view showing a general optical pickup device, Figure 2 is a view showing a tracking light forming portion of the optical pickup device for generating a light source of one wavelength. Referring to the drawings, a general optical pickup apparatus includes a light source unit 110 for generating light of a specific wavelength, a tracking light forming unit 120 for dividing the generated light, light transmitted to a recording medium, and light reflected from the recording medium. Optical separation unit 130 for separating, the collimating lens 140 to make the light source output from the light source on the path transmitted to the recording medium in parallel light, the path changing mirror 150 for changing the path of the light by reflection, recording the light Objective lens 160 for condensing the medium in the form of a spot, recording medium 170 for irradiating or reflecting light to the medium, and sensor lens 180 for condensing the light reflected from the recording medium to the cells of the photodetector in the form of spots And a light detector 190 for detecting the light reflected from the recording medium and reproducing the signal recorded on the recording medium. In this case, the tracking light forming unit 120 includes a substrate 122 and a diffraction grating pattern 120 to form a tracking light by dividing a light source having a specific wavelength into two beams, a main beam and a sub beam.

Meanwhile, since an optical pickup apparatus capable of recording and playing back all CDs, DVDs, and Blu-ray Discs is provided, it is possible to use CDs, DVDs, and Blu-ray Discs as one optical pickup apparatus.

Accordingly, as the light source unit of the optical pickup apparatus generates light having different wavelengths, a tracking light forming unit capable of forming tracking light corresponding to light of each wavelength is required.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical pickup apparatus capable of efficiently generating tracking light for light of each wavelength when selectively using light having a different wavelength such as CD light, DVD light, Blu-ray disc light, and the like. have.

An optical pickup apparatus according to the present invention for achieving the above object is provided with a liquid crystal between a light source unit for selectively emitting light of different wavelengths, a diffraction grating and the diffraction grating, to any one of the different wavelengths And a tracking light forming unit for diffracting and dividing the emitted light and a light detecting unit for detecting the divided light.

The tracking light forming unit divides one light emitted at a selected specific wavelength into a main beam and two sub beams.

The divided light is characterized by having a diffraction angle proportional to the wavelength.

The diffraction angle is increased in the order of diffraction angle when the CD light is input, the diffraction angle when the DVD light is input, and the diffraction angle when the Blu-ray disc light is input.

The liquid crystal is oriented in a specific direction, characterized in that the alignment direction is perpendicular to the direction oriented in accordance with the electric field.

The liquid crystal is rotated in the direction of the electric field according to the strength of the electric field, it characterized in that the refractive index is variable according to the rotation of the liquid crystal.

The optical pickup apparatus according to the present invention can efficiently generate tracking light for light of each wavelength when selectively using light of different wavelengths such as CD light, DVD light, Blu-ray disc light, and the like.

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

3 is a view showing the configuration of an optical pickup apparatus according to an embodiment of the present invention.

Referring to the drawings, the optical pickup apparatus according to an embodiment of the present invention, the light source unit 110 for generating light of different wavelengths, the tracking light forming unit for splitting the generated light having a specific wavelength among the light of different wavelengths (300), the optical separation unit 130 for separating the light transmitted to the recording medium and the light reflected from the recording medium, collimation lens 140 to make the light source output from the light source on the path transmitted to the recording medium in parallel light, A path changing mirror 150 for changing the path of the light by reflection, an objective lens 160 for condensing the light in the form of spots on the recording medium, a recording medium (not shown) to which light is irradiated or reflected, and a recording medium And a sensor lens 180 for condensing the light reflected from the cells of the photodetector in a spot form, and a photodetector 190 for detecting the light reflected from the recording medium and reproducing a signal recorded on the recording medium.

The light source unit 110 selectively generates light having different wavelengths corresponding to the CD, the DVD, and the Blu-ray Disc. To this end, the light source unit 110 may include three laser diodes that generate light having different wavelengths. That is, the light source unit 110 selectively generates light having different wavelengths for recording and reproducing in the CD, DVD, and Blu-ray Disc. At this time, the wavelength of light is about 780 nm for CD, about 660 nm for DVD, and about 405 nm for Blu-ray Disc.

On the path of the light generated by the light source unit 110, the CD light proceeds as it is, and the DVD light may further include a polarizer (not shown) for changing the polarization direction by 90.

The tracking light forming unit 300 may be provided on a path through which the light passing through the polarizer (not shown) moves, and divides the light into three, so that the light is accurately irradiated onto the track on the recording medium. Make it work.

In this case, the tracking light forming unit 300 includes a liquid crystal between the diffraction grating and the diffraction grating, diffracts and splits light emitted at a specific wavelength among different wavelengths, thereby converting one light into a main beam and two sub beams. That is, it can be divided into three beams. In this case, the divided light has a diffraction angle proportional to the wavelength. That is, the diffraction angle may increase in the order of the diffraction angle when the CD light is input, the diffraction angle when the DVD light is input, and the diffraction angle when the Blu-ray disc light is input.

In addition, the optical pickup device may further include a voltage adjuster (not shown) for adjusting the voltage across the diffraction grating to a voltage corresponding to the wavelength of the selected light.

The optical separation unit 130 changes the path of the light passing through the tracking light forming unit 300, transfers the light generated by the light source unit 110 to the recording medium, and transmits the light reflected from the recording medium to the photodetector 190. Can be delivered separately.

The collimating lens 140 may convert the light generated by the light source unit 110 into parallel light. Since the light generated by the light source unit 110 is scattered light, it is converted into parallel light so that it can be used for recording and reproducing on the recording medium. By making the collimating lens 140 into parallel light, signal recording to the recording medium can be performed more efficiently.

The path changing mirror 150 may change the path of the light in a direction in which the light generated by the light source unit 110 may be incident perpendicularly to the recording medium. Here, the path changing mirror 150 may be provided as a phase delay path changing mirror, which may cause a phase difference to occur at 90 degrees or 270 degrees with respect to vertical and horizontal polarization when light is incident at a specific angle. The phase delay path changing mirror generates a phase delay by forming a coating layer on the surface of the path changing mirror that changes the path of light. For example, when the light is circularly polarized using a phase delay path changing mirror, recording characteristics and noise characteristics are relatively improved.

The light whose path is changed in the path changing mirror 150 is focused on the recording medium by the objective lens 160. That is, the objective lens 160 may condense light on the recording medium in the form of spots. The light irradiated onto the recording medium by the objective lens 160 may form a pit on the recording medium to record data, or may be reflected by the formed pit.

The objective lens 160 may be provided in a bobbin (not shown) constituting an actuator of the optical pickup apparatus, and as the bobbin is moved for tracking and focusing operation, the objective lens 160 moves light to the recording medium. You can investigate.

On the other hand, the light reflected from the recording medium is transferred to the optical separation unit 130 in the reverse path of the path that the light is transmitted from the light source unit 110 to the recording medium. In the optical separator 130, the light is transmitted in a direction other than the direction of the light source unit 110.

The sensor lens 180 may be installed on a path through which light reflected from the recording medium and passed through the optical separation unit 130 is transmitted. The sensor lens 180 allows the light to be focused on the photodetector 190 in a spot shape.

The photodetector 190 detects light reflected from the recording medium, and a photodiode may be used. The photodetector 190 includes a plurality of cells to detect light collected by the sensor lens 180. Can be.

Hereinafter, the operation of the optical pickup apparatus according to the present invention having the configuration as described above will be described.

First, the light emitted by the light source unit 110 is diffracted while passing through the tracking light forming unit 300 so that one light is divided into three. When splitting the light by diffraction as described above, the tracking light forming unit 300 includes a liquid crystal between the diffraction grating and the diffraction grating, and diffracts and splits the light emitted at a specific wavelength among different wavelengths, thereby providing one light. Can be divided into a main beam and two sub-beams, that is, three beams.

Next, the light passing through the tracking light forming unit 300 is transmitted to the light separation unit 130. The light is reflected by the optical splitter 130 and transmitted to the collimator lens 140. As the light passes through the collimating lens 140, the light is changed from scattered light to parallel light.

The light that passes through the collimation lens 140 and becomes parallel light is changed by the path changing mirror 150 and transmitted to the objective lens 160. In this case, the path changing mirror 150 may be provided as a phase delay path changing mirror. When the light is incident at a specific angle when the path delay mirror 150 is provided, the phase difference is 90 degrees or 270 degrees with respect to the vertical and horizontal polarization. For example, when light polarized in the 45 degree direction is incident, the light is converted into circularly polarized light and reflected to the objective lens 160.

The light transmitted to the objective lens 160 is irradiated onto the signal recording surface of the recording medium as the bobbin moves. Light condensed on the recording medium through the objective lens 160 records a signal on the recording medium or reproduces the recorded signal. At this time, the light is recorded on the recording medium because the light irradiated on the recording medium forms the pit information on the signal recording surface of the recording medium. And, the reproduction of the signal in which the light is recorded on the recording medium is made by reflecting the pit information and passing it to the photodetector 190 through the path described below.

The light reflected from the recording medium passes through the objective lens 160, the path changing mirror 150, the collimation lens 140, and the optical separation unit 130 and is transmitted to the sensor lens 180. The sensor lens 180 condenses the light in the form of spots on the cells of the photodetector 190. The light detector 190 receiving the light may reproduce the signal recorded on the recording medium by using the collected light.

For example, the optical pickup apparatus of the present invention does not need to include all the various components shown in FIG. 3, and may be configured by selectively using the components according to design conditions. For example, if there is no problem in forming the optical path, the optical separator 130 may not be used. In the case of the sensor lens 180, light may be formed on the photodetector 190 without a sensor lens 180 in the form of a spot.

In addition, any one component having a plurality of functions may be used among the components shown in the illustrated embodiment, and the remaining components may each use one component having one function.

4 is a diagram illustrating a tracking light forming unit according to an exemplary embodiment of the present invention, and FIG. 5 is a diagram illustrating light divided for each of light having different wavelengths through the tracking light forming unit according to an exemplary embodiment of the present invention.

Referring to the drawings, the tracking light forming unit 300 according to an embodiment of the present invention is provided with ITO (Indum Tin Oxcide) or the like to form an electric field in the liquid crystal, the first transparent electrode 402, glass (glass), etc. And a liquid crystal 408 and a second transparent electrode 410 provided between the substrate 404, the diffraction grating pattern 406, and the diffraction grating pattern 406.

The liquid crystal 408 is aligned in a particular direction, and the alignment direction may be perpendicular to the direction in which the liquid crystals are oriented according to the electric field. In addition, the liquid crystal is rotated in the direction of the electric field according to the intensity of the electric field, the refractive index may be changed according to the rotation of the liquid crystal.

The tracking light forming unit 300 may split one light emitted at a selected specific wavelength into a main (0th order) beam and two sub (+ 1st order, -1st order) beams as shown in FIG. 5. .

At this time, the divided light has a diffraction angle θ proportional to the wavelength. That is, sin θ may be a wavelength / lattice interval. For example, as shown in FIG. 5, the diffraction angle (θ 1 ) at the input of the CD light of approximately 780 nm, the diffraction angle at the input of the DVD light of approximately 660 nm (θ 2 ), and the diffraction at the input of the Blu-ray Disc light of approximately 405 nm The diffraction angle may increase in the order of the angle θ 3 .

In addition, one light output by the light source unit is divided into a main beam and a sub beam through the tracking light forming unit 300. The main beam passing through the tracking light forming unit is a light detector, that is, the main cell of the light receiving element. two sub-beams, which are received by the cell and become a main push-pull (MPP) signal, and are diffracted by the tracking light forming unit, are received by the sub-cells of the photodetector, thereby receiving a first push-pull 1 (SPP1). ) And a second push-pull 2 (SPP2) signal.

6 is a view showing the optical properties of the liquid crystal, Figure 7 is a view showing a change in the arrangement of the liquid crystal according to the electric field.

Referring to the drawings, the liquid crystal 602 according to the exemplary embodiment of the present invention has a relatively high refractive index n 1 and one axis has a relatively high refractive index as shown in FIG. 6. Has a low refractive index n 2 .

In this case, the difference between n 1 and n 2 is different depending on the type of liquid crystal, and when the difference is large, the refractive index difference is about 0.2.

In addition, as shown in FIG. 7, when an electric field is applied in a solution state in which liquid crystal molecules are collected innumerably, all molecules may be arranged in a line in the electric field direction.

That is, the liquid crystal oriented in one direction is rotated in the electric field direction according to the intensity of the electric field, thereby changing the refractive index. This means that the refractive index of the liquid crystal layer changes according to the intensity of the electric field.

8 is a diagram illustrating a spectral ratio when three wavelengths are incident on a general diffraction grating, and FIG. 9 is a diagram illustrating a spectral ratio when three wavelengths are incident on a wavelength variable-corresponding diffraction grating according to the present invention.

Referring to the drawings, as shown in FIG. 8, when three wavelengths of the CD, the DVD, and the Blu-ray Disc enter the general diffraction grating, the spectral ratios are all different. For example, when the lattice depth is 190 nm, the spectral ratios of CD, DVD, and Blu-ray Disc are 13.5, 10, and 3, respectively, so that when one wavelength is matched, the spectral ratios of the other two wavelengths become very small or large. It cannot be used in the optical pickup device.

On the other hand, the refractive index difference for one liquid crystal due to the nature of the liquid crystal is 0.1 to 0.2 level. As shown in FIG. 9, when a liquid crystal having a refractive index difference of 0.2 is inserted into the gap between the lattice gaps, if the spot fits with a spectral ratio of 15 to 20, which is generally used, all three wavelengths may have a spectral ratio of about 16 at the lattice depth of 780 nm. Can be.

In addition, each time the wavelength is changed to CD, DVD, or Blu-ray Disc, the voltage across the diffraction grating is adjusted in three steps to create the refractive index of the liquid crystal for each wavelength. Can be. In this case, the grating depth may vary depending on the refractive index deviation of the liquid crystal used.

10 is a view showing a light detection cell provided in the light detection unit according to an embodiment of the present invention.

Referring to the drawings, the photodetector according to the embodiment of the present invention includes a first sub-beam photodetection cell 1100 and a fifth sub-beam, including the first to fourth light-receiving regions e1, f1, g1, and h1. A main beam photodetection cell 1200 including the eighth to eighth light-receiving areas A, B, C, and D, and a second including the ninth to twelfth light-receiving areas e1, f1, g1, and h1. And a photodetection cell 1300 for the subbeam.

The photodetector detects light reflected from the recording medium, and a photodiode may be used. That is, the light detecting unit has a total of 12 light receiving areas, and is used to detect CD light when recording or reproducing data on the CD, and to detect light for DVD when recording or reproducing data on the DVD. It can be used to detect light for Blu-ray Discs when recording or playing back data.

In this case, the spectral ratio may be calculated by the following equation.

Figure 112009049009881-PAT00001

Here, A, B, C, and D are light amounts condensed in each light receiving region of the main beam photodetection cell, and e1, f1, g1 and h1 are light amounts condensed in each light receiving region of the first subbeam photodetection cell, e2, f2, g2, and h2 are light amounts collected in each light receiving region of the second sub-beam photodetection cell, and cell gain is a preset gain value for the photodetection cell.

In addition, when the spectral ratio calculated through the equation is different from the desired spectral ratio, the spectral ratio may be adjusted by adjusting the voltage across the liquid crystal of the diffraction grating.

That is, in order to reproduce the data on the recording medium or to record the data on the recording medium in the optical pickup apparatus, it is necessary to perform accurate focus and tracking control based on the stable optical system structure.

To this end, the photodetector receives the laser light reflected from the recording medium and converts the laser light into an electrical signal, and performs focus and tracking control using the laser light received from the photodetector.

For focus and tracking control, a focusing error and a tracking error are detected by various methods. In general, a focus error (FE) is detected by astigmatism for focus control, and for tracking control. Tracking errors (TE) can be detected by the DPP (Differential Push Pull) method or the 3-spot method.

First, a focus error detection method based on astigmatism will be described. The photodetector has a main beam photodetection cell for receiving zero-order light from the return light and a subbeam photodetection cell for receiving primary light from the return light on the light-receiving surface. The cells are formed in a divided pattern in which the light receiving surface for receiving the return light is formed in a substantially rectangular shape, and each light receiving region divided into four sections by a set of orthogonal dividing lines through the center of the light receiving surface. The sub-beam photodetection cells may be formed at positions opposite to each other with the main beam photodetection cells interposed therebetween.

If the objective lens is in an optimal position with respect to the recording / reproducing surface of the recording medium and is in a just focus state coinciding with the recording / reproducing surface of the recording medium, The shape of the beam spot is circular. If the objective lens is too close to the recording / reproducing surface of the recording medium, or is too far away from the recording medium, the beam spot has an elliptical shape due to astigmatism of the returned light. Therefore, a focusing error can be obtained by comparing the received light output of the returned light by each light receiving area with each other.

On the other hand, in the case of the DPP method, a tracking error is obtained by using a difference signal between a spot caused by a main beam and a spot caused by a sub beam, and the photodetector unit receives a spot and a sub beam caused by a main beam received in each light receiving region of each cell. The tracking error can be obtained by obtaining the difference of the spot signals by.

As described above, in order to detect the tracking error, the optical system must be stabilized so as to accurately focus the cells of the photodetector, and the reliability of the thermal environment change of the photodetector must be high.

That is, the reason why the laser focus position on the cell of the photodetector is important is that this focus affects the servo performance of the optical pickup, and the photodetector cell is divided into four adjacent neighboring cell regions, for example. This creates the signal needed to perform servo in the focus and track direction.

However, if the laser focus is not accurately centered in the cell, the signals required for focus and track direction servos will be inaccurate, leading to a decrease in the overall optical pickup performance. It is desirable to make it relatively small. To this end, increasing the size of the cell and the size of the laser focal point on the cell ensures a relatively insensitive to thermal environment changes.

In addition, although the preferred embodiment of the present invention has been shown and described above, the present invention is not limited to the specific embodiments described above, but the technical field to which the invention belongs without departing from the spirit of the invention claimed in the claims. Of course, various modifications can be made by those skilled in the art, and these modifications should not be individually understood from the technical spirit or the prospect of the present invention.

1 is a view showing a general optical pickup device.

2 is a view showing a tracking light forming unit of an optical pickup apparatus for generating a light source of one wavelength.

3 is a view showing the configuration of an optical pickup apparatus according to an embodiment of the present invention.

4 illustrates a tracking light forming unit according to an embodiment of the present invention.

FIG. 5 is a view illustrating split light for each light having a different wavelength through a tracking light forming unit according to an exemplary embodiment of the present invention. FIG.

6 shows optical properties of liquid crystals;

7 is a view illustrating a change in arrangement of liquid crystals according to an electric field.

8 is a diagram illustrating a spectral ratio when three wavelengths are incident on a general diffraction grating.

9 is a view showing a spectral ratio when three wavelengths are incident on a wavelength tunable diffraction grating according to the present invention.

10 is a view showing a light detection cell provided in the light detection unit according to an embodiment of the present invention.

<Explanation of symbols on main parts of the drawings>

110: light source unit 300: tracking light forming unit

130: optical separation unit 140: collimation lens

160: objective lens 190: photodetector

Claims (11)

A light source unit selectively emitting light of different wavelengths; A tracking light forming unit having a liquid crystal between the diffraction grating and the diffraction grating, for diffracting and dividing the light emitted at any one of the different wavelengths; And And a photo detector for detecting the divided light. The method of claim 1, And the tracking light forming unit divides one light emitted at a selected specific wavelength into a main beam and two sub beams. The method of claim 1, And said split light has a diffraction angle proportional to the wavelength. The method of claim 3, The diffraction angle is increased in the order of the diffraction angle when the CD light input, the diffraction angle when the DVD light input, the diffraction angle when the Blu-ray disc light input. The method of claim 1, And the liquid crystal is aligned in a specific direction, and the alignment direction is perpendicular to the direction in which the liquid crystal is aligned in accordance with the electric field. The method of claim 1, The liquid crystal is rotated in the electric field direction according to the intensity of the electric field, the optical pickup device, characterized in that the refractive index is variable according to the rotation of the liquid crystal. The method of claim 1, And any one of the light having different wavelengths, the voltage adjusting unit adjusting the voltage across the diffraction grating to a voltage corresponding to the wavelength of the selected light. The method of claim 1, And an optical separation unit arranged on the path of the divided light to separate and transmit the light transmitted to the recording medium and the light reflected from the recording medium. The method of claim 8, And an objective lens for condensing the light passing through the optical separation unit in a spot form on the recording medium. The method of claim 1, And a sensor lens for condensing the light reflected from the recording medium to the cells of the photodetector in the form of spots. The method of claim 1, And the light detector detects the light reflected from the recording medium when the divided light is transmitted to and reflected from the recording medium.
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