EP1062663A1 - Optical pickup device - Google Patents

Optical pickup device

Info

Publication number
EP1062663A1
EP1062663A1 EP99907875A EP99907875A EP1062663A1 EP 1062663 A1 EP1062663 A1 EP 1062663A1 EP 99907875 A EP99907875 A EP 99907875A EP 99907875 A EP99907875 A EP 99907875A EP 1062663 A1 EP1062663 A1 EP 1062663A1
Authority
EP
European Patent Office
Prior art keywords
light
laser source
diffracted light
recording medium
diffracted
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP99907875A
Other languages
German (de)
French (fr)
Inventor
Shinji Yamada
Hiroshi Miyazawa
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Kenwood KK
Original Assignee
Kenwood KK
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Kenwood KK filed Critical Kenwood KK
Publication of EP1062663A1 publication Critical patent/EP1062663A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • 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
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/085—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam into, or out of, its operative position or across tracks, otherwise than during the transducing operation, e.g. for adjustment or preliminary positioning or track change or selection
    • 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
    • G11B7/1365—Separate or integrated refractive elements, e.g. wave plates
    • 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
    • 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
    • G11B7/1365—Separate or integrated refractive elements, e.g. wave plates
    • G11B7/1369—Active plates, e.g. liquid crystal panels or electrostrictive elements
    • 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
    • G11B7/1381—Non-lens elements for altering the properties of the beam, e.g. knife edges, slits, filters or stops
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H2222/00—Light sources or light beam properties
    • G03H2222/31—Polarised light
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B2220/00—Record carriers by type
    • G11B2220/20—Disc-shaped record carriers
    • G11B2220/25—Disc-shaped record carriers characterised in that the disc is based on a specific recording technology
    • G11B2220/2537—Optical discs
    • 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
    • G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
    • G11B7/0045—Recording
    • 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
    • G11B7/14—Heads, e.g. forming of the optical beam spot or modulation of the optical beam specially adapted to record on, or to reproduce from, more than one track simultaneously

Definitions

  • the present invention relates to an optical pickup device for reading data from, and/or writing data into, an optical recording medium such as an optical disk and an optical card, and more particularly to an optical pickup device capable of high speed data read/ rite.
  • an optical pickup device of a multi-spot type In order to read data from an optical disk at high speed, an optical pickup device of a multi-spot type has been proposed in which light spots are applied at the same time to a plurality of tracks consecutively disposed in a radial direction of an optical disk.
  • the optical pickup device of the multi-spot type in order to generate a plurality of light spots, a plurality of semiconductor lasers disposed in line or laser light from a single laser light source is diffracted to generate imaginary light sources equivalent to semiconductor laser light sources.
  • a conventional optical pickup device for generating a plurality of imaginary light sources by utilizing diffraction of a diffraction grating cannot write data in an optical disk.
  • the reason for this is as in the following.
  • a light spot is formed on a track on which data is written.
  • a magneto-optical recording method in writing data, a record film of an optical disk is required to be heated to a Curie temperature or higher and the heated area is applied with a magnetic field generated by a magnetic coil. In this case, if a plurality of light spots are applied to a plurality of adjacent tracks, the same data is written in these tracks. This problem also occurs when a phase change method or other methods are used.
  • An optical pickup device (11) of this invention comprises the following constituents (a) to (d) : (a) a laser source (12); (b) light diffracting means (13, 36, 60) for generating light spot forming diffracted light by diffracting light supplied from the laser source (12);
  • diffracted light generation preventing means for preventing the light diffracting means (13, 36, 60) from generating the light spot forming diffracted light.
  • the optical recording medium (20) includes an optical card in addition to an optical disk (20) .
  • the different data positions (30) of the optical recording medium (20) are at different tracks in the case of concentric tracks and at the same track adjacent in the radial direction in the case of a spiral track.
  • Light from the laser source (12) is diffracted by the light diffracting means (13, 36, 60), and the diffracted light (16b, 16c) propagates as if it is emitted from an imaginary light source.
  • a plurality of light spots (32a, 32b, 32c) are formed on the optical recording medium (20) at the different data positions (30) by using non- diffracted light (16a) from the laser source (12) and the diffracted light (16b, 16c) from the light diffracting means (13, 36, 60).
  • the plurality of light spots (32a, 32b, 32c) are used for reading data at each of the data positions (30) .
  • the diffracted light generation preventing means (37, 42) prevents the light diffracting means (13, 36, 60) from generating the light spot forming diffracted light. Therefore, only the single light spot (32a) is formed on the optical recording medium (20) by using the non-diffracted light (16a) from the laser source (12). Data is written in the track where the single light spot (32a) is formed. Accordingly, data can be read at high speed from the optical recording medium (20) by using the plurality of light spots (32a, 32b, 32c) and also data can be written in the optical recording medium (20) by using the single light spot without any practical problem.
  • An optical pickup device (11) of the invention comprises the following constituents (a) to (d) : (a) a laser source (12); (b) light diffracting means (13, 36) for generating light spot forming diffracted light by diffracting light supplied from the laser source (12);
  • position changing means for changing a position of the light diffracting means (13, 36) so as to make the diffracted light (16b, 16c) from the light diffracting means (13, 36) enter the light spot forming means (15) during data read from the optical recording medium (20), and not to make the diffracted light (16b, 16c) from the light diffracting means (13, 36) enter the light spot forming means (15) during data write into the optical recording medium (20).
  • the light diffracting means (13, 36) includes a polarization hologram (36) in addition to a diffraction grating (13, 36).
  • Light from the laser source (12) is diffracted by the light diffracting means (13, 36), and the diffracted light (16b, 16c) propagates as if it is emitted from an imaginary light source.
  • the position of the light diffracting means (13, 36) is changed to a first position by the position changing means. Therefore, light from the laser source (12) diffracted by the light diffracting means (13, 36), i.e., diffracted light (16b, 16c), is also incident upon the light spot forming means (15).
  • the plurality of light spots (32a, 32b, 32c) are therefore formed on the optical recording medium (20) so that data can be read at the same time from the plurality of data positions (30) to thereby speed up data read.
  • the position of the light diffracting means (13, 36) is changed to a second position different from the first position by the position changing means. Therefore, the diffracted light (16b, 16c) from the light diffracting means (13, 36) is not incident upon the light spot forming means (15), but only the non-diffracted light (16a) from the laser source (12) is incident upon the light spot forming means (15) .
  • An optical pickup device (11) of the invention comprises the following constituents (a) to (d) : (a) a laser source (12); (b) a polarization hologram (36) for generating light spot forming diffracted light by diffracting light supplied from the laser source (12);
  • light spot forming means for forming a plurality of light spots (32a, 32b, 32c) on an optical recording medium (20) at different data positions (30), by using non-diffracted light (16a) from the laser source (12) and the diffracted light (16b, 16c) from the polarization hologram ( 36 ) ;
  • a half-wave plate (37) for providing a half-wave optical path difference between P-polarized light and S- polarized light supplied from the laser source (12) when the half-wave plate (37) is inserted into an optical path between the laser source (20) and the polarization hologram (36), the half-wave plate (37) being inserted into the optical path to prevent the polarization hologram (36) from generating the diffracted light during data write into the optical recording medium (20), and exited from the optical path to allow the polarization hologram (36) to generate the diffracted light during data read from the optical recording medium (20).
  • the half-wave plate (37) shifts an optical path difference between P- and S-polarized light from the laser source (12) by 90° so that it can output light incident upon the polarization hologram (36) by changing the polarization direction by 90 c .
  • the polarization hologram (36) can generate the diffracted light during data read from the optical recording medium (20), so that the plurality of light spots (32a, 32b, 32c) are formed on the optical recording medium (20) at the different data positions (30) to allow high speed data read.
  • the polarization hologram (36) does not generate the diffracted light so that only the single light spot (32a) of the non-diffracted light (16a) from the laser source (12) is formed on the optical recording medium (20) to thereby prevent any practical problem in writing data.
  • An optical pickup device (11) of the invention comprises the following constituents (a) to (d) :
  • a polarization hologram (36) for generating light spot forming diffracted light by diffracting light supplied from the laser source ( 12 ) ;
  • light spot forming means (15) for forming a plurality of light spots (32a, 32b, 32c) on an optical recording medium (20) at different data positions (30), by using non-diffracted light (16a) from the laser source (12) and the diffracted light (16b, 16c) from the polarization hologram (36);
  • a polarization direction changing liquid crystal element (42) for rotating a polarization direction of incidence light by 90° in accordance with a voltage applied to the element (42) inserted into an optical path between the laser source (20) and the polarization hologram (36), the element (42) preventing the polarization hologram (36) from generating the diffracted light during data write into the optical recording medium (20) and allowing the polarization hologram (36) to generate the diffracted light during data read from the optical recording medium (20), in accordance with a control of the voltage applied to the element (42) .
  • the polarization direction changing means (42) is, for example, liquid crystal molecules (48) of a TN twisted nematic mode, with opposing polarizers (50, 53) being removed.
  • Light output from the polarization direction changing means (42) has a polarization direction changed by 90° relative to the incidence light thereof, when no voltage is applied.
  • Light passes through the polarization direction changing means (42) without being rotated by 90° when a voltage is applied. If a laser ray from the optical recording medium (20) is an ordinary ray, the polarization hologram (36) generates the diffracted light when a voltage is applied to the polarization direction changing liquid crystal element (42), and it does not generate the diffracted light when no voltage is applied to the element (42) .
  • the polarization hologram (36) If a laser ray from the optical recording medium (20) is an extraordinary ray, the polarization hologram (36) generates the diffracted light when no voltage is applied to the polarization direction changing liquid crystal element (42), and it does not generate the diffracted light when a voltage is applied to the element (42) . With a control of the voltage applied to the polarization direction changing liquid crystal element (42), the polarization hologram (36) can generate the diffracted light during data read from the optical recording medium (20), so that the plurality of light spots (32a, 32b, 32c) are formed on the optical recording medium (20) at the different data positions (30) to allow high speed data read. During data write into the optical
  • the polarization hologram (36) does not generate the diffracted light so that only the single light spot (32a) of the non-diffracted light (16a) from the laser source (12) is formed on the optical recording medium (20) to thereby prevent any practical problem in writing data.
  • An optical pickup device (11) of the invention comprises the following constituents (a) to (c) : (a) a laser source (12); (b) a diffraction pattern displaying liquid crystal display (60) for displaying a diffraction pattern (61) during data read from an optical recording medium (20) and diffracting light supplied from the laser source (12) and for not displaying the diffraction pattern during data write from the optical recording medium (20); and
  • light spot forming means for forming a plurality of light spots (32a, 32b, 32c) on the optical recording medium (20) at different data positions (30), by using non-diffracted light (16a) and diffracted light (16b, 16c) supplied from the liquid crystal display (60).
  • the diffraction pattern displaying liquid crystal display (60) can display a desired pattern by controlling white and black of pixels to display the diffraction pattern (61) or make the display in a transmission state without displaying the diffraction pattern (61). While the
  • 11 diffraction pattern (61) is displayed, light from the laser source (12) is diffracted by the diffraction pattern (61) so that the diffracted light (16b, 16c) is formed, whereas while the diffraction pattern (61) is not displayed, light from the laser source (12) is not diffracted but is transmitted therethrough. Therefore, while the diffraction pattern displaying liquid crystal display (60) displays the diffraction pattern (61), the plurality of light spots (32a, 32b, 32c) are formed on the optical recording medium (20) at the different data positions (30) to allow high speed data read from the optical recording medium (20).
  • the diffraction pattern displaying liquid crystal display (60) does not display the diffraction pattern (61), only the single light spot (32a) of the non-diffracted light (16a) from the laser source (12) is formed on the optical recording medium (20) to write data in the optical recording medium (20) without any practical problem.
  • FIG. 1 is a schematic diagram showing the structure of an optical pickup device of a data read/write apparatus in a data read state.
  • Fig. 2 is a schematic diagram showing the main portion of the structure of the optical pickup device of the data read/write apparatus shown in Fig. 1 in a data write state.
  • Fig. 3 is a diagram illustrating light spots formed on an optical disk shown in Fig. 1.
  • Fig. 4 is a diagram showing the main portion of an optical pickup device in a data read state, the optical pickup device changing the number of light spots to be generated, by using a polarization hologram and a half-wave plate.
  • Fig. 5 is a diagram showing the main portion of the optical pickup device in a data write state, the optical pickup device changing the number of light spots to be generated, by using the polarization hologram and half-wave plate.
  • Fig. 6 is a diagram illustrating a principle of changing a polarization direction by a half-wave plate in which an optical path difference between P- and S-polarized light beams is 0.
  • Fig. 7 is a diagram illustrating a principle of changing a polarization direction by the half-wave plate in which an optical path difference between P- and S-polarized light beams is a half wavelength.
  • Fig. 8 is a diagram showing the main portion of an optical pickup device in a data read state, the optical pickup device changing the number of light spots to be generated, by using TN display mode liquid crystal without a polarizer.
  • Fig. 9 is a diagram showing the main portion of the optical pickup device in a data write state, the optical pickup device changing the number of light spots to be generated, by using the TN display mode liquid crystal without a polarizer.
  • Fig. 10 is a schematic diagram illustrating a principle of changing a polarization direction, in a state of absence of an electric field, of a TN display mode liquid crystal display which operates based upon the TN display mode liquid crystal without a polarizer shown in Figs. 8 and 9.
  • Fig. 11 is a schematic diagram illustrating a principle of changing a polarization direction, in a state of presence of an electric field, of the TN display mode liquid crystal which operates based upon the TN display mode liquid crystal without a polarizer shown in Figs. 8 and 9.
  • Fig. 12 is a schematic diagram showing the main portion of an optical pickup device in a data read state, the optical pickup device being capable of changing the number of light spots to be generated by using a liquid crystal display.
  • Fig. 13 is a schematic diagram showing the main portion of the optical pickup device in a data write state, the optical pickup device being capable of changing the
  • Fig. 1 is a schematic diagram showing the structure of an optical pickup device 11 of a data read/write apparatus 10 in a data read state
  • Fig. 2 is a schematic diagram showing the structure of the optical pickup device 11 of the data read/write apparatus 10 in a data write state
  • Fig. 3 is a diagram showing light spots 32a, 32b, and 32c formed on an optical disk 20 shown in Fig. 1.
  • a semiconductor laser 12 has a single laser light source.
  • a diffraction grating 13 is inserted between the semiconductor laser 12 and a beam splitter 14 in the data read state by an unrepresented actuator, whereas it is exited from between the semiconductor laser 12 and beam splitter 14 in the data write state.
  • Fig. 1 is a schematic diagram showing the structure of an optical pickup device 11 of a data read/write apparatus 10 in a data read state
  • Fig. 2 is a schematic diagram showing the structure of the optical pickup device 11 of the data read/write apparatus 10 in a data write state
  • Fig. 3 is a
  • two diffraction light beams 16b and 16c corresponding to two imaginary light sources are generated.
  • the number of imaginary light sources are not limited only to two, but the number may be set to 1 , 3, 4 , ... , n other than 2 by using a proper diffraction grating pattern of the
  • the diffraction grating 13 When the diffraction grating 13 is inserted between the semiconductor laser 12 and beam splitter 14, of the laser beam radiated from the semiconductor laser 12, the light beam not diffracted by the diffraction grating 13 propagates straightforward and becomes a non-diffracted light beam 16a, and the other light beams become diffracted light beams 16b and 16c.
  • the non-diffracted and diffracted light beams 16a, 16b, and 16c pass through the beam splitter 14 straightforward and propagate toward an objective lens 15.
  • the objective lens 15 diffracts the incident non-diffracted and diffracted light beams 16a, 16b, and 16c to form light spots 32a, 32b, and 32c (Fig.
  • a collimator lens between the beam splitter 14 and objective lens 15 is omitted in Figs. 1 and 2, it may be disposed therebetween.
  • the distance between the objective lens 15 of the optical pickup device 11 and the optical disk 20 is adjusted through a focus servo (not shown) by using light supplied from the collimator lens, to thereby form the proper light spots 32a, 32b, and 32c on the optical disk 20.
  • a plurality of tracks 30 extend at a predetermined pitch, each track 30 being formed with pits (or marks) corresponding to write data.
  • the light spots 32a, 32b, and 32c are formed on different
  • each light spot 32a, 32b, 32c propagates backward through the objective lens 15, is reflected at a right angle by the beam splitter 14, and becomes incident upon each photodiode 24a, 24b, 24c of a photodetector unit 23.
  • Each photodiode 24a, 24b, 24c supplies an electrical signal corresponding to an amount of the incident light to a signal processing unit 25.
  • the signal processing unit 25 derives data on each track 30 of the optical disk 20 from the electrical signal supplied from each photodiode 24a, 24b, 24c.
  • the diffraction grating 13 is exited from between the semiconductor laser 12 and beam splitter 14.
  • a laser light beam radiated from the semiconductor layer 12 is not diffracted by the diffraction grating 13 and becomes incident upon the beam splitter 14. Therefore, a light spot formed on the optical disk 20 is only a light spot 32a.
  • a data write area of the optical disk 20 applied with a light spot is heated to a Curie temperature or higher, and with a magnetic flux supplied from an unrepresented magnetic coil, the predetermined data is written without any practical problem.
  • Figs. 4 and 5 are diagrams showing the main portion of an optical pickup device in data read/write states, the optical pickup device changing the number of light spots to
  • Figs. 6 and 7 are diagrams illustrating a principle of changing a polarization direction by the half-wave plate 37 in which an optical path difference between P- and S-polarized light beams is 0 and a half wavelength, respectively.
  • a laser light beam is constituted of P- and S-polarized light beams having a polarization direction shift of 90°.
  • a laser light beam has a synthesized polarization direction which is a total of the P- and S- polarizations.
  • the polarization hologram 36 is inserted between the semiconductor laser 12 and an objective lens 15 (refer to Fig. 1).
  • the half-wave plate 37 is either inserted or exited from between the semiconductor laser 12 and polarization hologram 36 by an unrepresented actuator.
  • the light beams having the first and second polarization directions are called an ordinary ray and an extraordinary ray, respectively.
  • the laser beam radiated from the semiconductor laser 12 to be applied to the polarization hologram shown in Figs. 4 and 5 is the ordinary ray.
  • At least one imaginary light source is formed by using the laser beam from the semiconductor laser 12, i.e., diffracted light beams 16b and 16c are generated by the polarization hologram 36.
  • the half-wave plate 37 is exited from between the semiconductor laser 12 and polarization hologram 36, and the laser beam from the semiconductor laser 12 is made directly incident upon the polarization hologram 36 by maintaining the polarization direction Dl of the laser beam.
  • the half-wave plate 37 is inserted between the
  • the polarization direction of the laser beam supplied from the semiconductor laser 12 is equal to that of the ordinary ray of the polarization hologram 36. If the polarization direction of the laser beam supplied from the semiconductor laser 12 is equal to that of the extraordinary ray of the polarization hologram 36, the half-wave plate 37 is inserted in the data read state and exited in the data write state. Similar to the diffraction grating 13 shown in Figs. 1 and 2, the polarization hologram 36 may be inserted in the data read state to generate the diffracted light beams 16b and 16c, and exited in the data write state not to generate the diffracted light beams 16b and 16c. In this case, the half-wave plate 37 is not necessary.
  • Figs. 8 and 9 are diagrams showing the main portion of an optical pickup device in data read/write states, the optical pickup device changing the number of light spots to be generated, by using TN display mode liquid crystal 42 without a polarizer, and Figs. 10 and 11 are schematic
  • the TN display mode liquid crystal display 48 has a lamination structure made of a polarizer 50, glass plates 51 and 52, and a polarizer 53 stacked in this order from the side of incidence light 55. Between the glass plates 51 and 52, a liquid crystal layer is present which is made of liquid crystal molecules twisted by 90°. In an absence of an electric field, as shown in Fig.
  • an incidence light beam 55 whose polarization direction was aligned by the polarizer 50 passes through the liquid crystal layer by rotating its linear polarization by 90°, and reaches the polarizer 53, whereas in a presence of an electric field, as shown in Fig. 11, the incidence light beam 55 passes through the liquid crystal layer by eliminating the twist of the liquid crystal molecules 54 and maintaining the polarization direction of the incidence light beam 55, and reaches the polarizer 53.
  • the TN display mode liquid crystal 42 without a polarizer shown in Figs . 8 and 9 corresponds to the TN display mode liquid crystal display 48 shown in Figs. 10 and 11, with their polarizers 50 and 53 being
  • the TN display mode liquid crystal 42 without a polarizer changes the polarization direction of the laser beam of the semiconductor laser 12 by 90° in an absence of an electric field, and does not change it in a presence of an electric field.
  • the laser beam from the semiconductor laser 12 is an ordinary ray of the polarization hologram 36.
  • a switch 44 is turned on to apply a voltage from a d.c. power source 43 to the TN display mode liquid crystal 42 without a polarizer.
  • the laser beam from the semiconductor laser 12 passes through the TN display mode liquid crystal 42 without a polarizer by maintaining its polarization direction Dl, and becomes incident upon the polarization hologram 36.
  • the polarization hologram 36 is therefore supplied with an ordinary ray so that it generates a non-diffracted light beam 16a as well as diffracted light beams 16b and 16c.
  • the switch 44 is turned off so as not to apply an electric field to the TN display mode liquid crystal 42 without a polarizer. Therefore, the laser beam from the semiconductor laser 12 passes through the TN display mode liquid crystal 42 without a polarizer by changing its polarization direction by 90° from Dl to D2, and becomes incident upon the polarization hologram 36.
  • the polarization hologram 36 is therefore supplied with an extraordinary ray so that it generates only the non- diffracted light beam 16a without any diffraction.
  • the polarization direction of the laser beam supplied from the semiconductor laser 12 is equal to that of the ordinary ray of the polarization hologram 36. If the polarization direction of the laser beam supplied from the semiconductor laser 12 is equal to that of the extraordinary ray of the polarization hologram 36, the TN display mode liquid crystal 42 without a polarizer is applied with an electric field in the data read state, and not applied with an electric field in the data write state.
  • Figs. 12 and 13 are schematic diagrams showing the main portion of an optical pickup device 11 in data read/write states, the optical pickup device being capable of changing the number of light spots to be generated by using a liquid crystal display 60.
  • the liquid crystal display 60 is inserted between a semiconductor laser 12 and an objective lens 15 (refer to Fig. 1).
  • White/black of each pixel of the liquid crystal display 60 is controlled by an unrepresented controller to display a desired image.
  • a diffraction pattern 61 is formed by making predetermined black pixels, and in the data write state, all pixels are made white so as not to display a
  • the laser beam from the semiconductor laser 12 is not diffracted in the liquid crystal display 60 but passes therethrough to generate only a non-diffracted light beam 16a which is formed on the optical disk 20.

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
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Abstract

Data can be read at high speed from an optical disk (20) by using a plurality of light spots, and data can be written in the optical disk (20) by using a single light spot without any practical problem. In reading data from the optical disk (20), a diffraction grating (13) is inserted between a semiconductor laser (12) and an objective lens (15). A laser beam from the semiconductor laser (12) is diffracted by the diffraction grating (13) to generate diffracted light beams (16b, 16c) and form a plurality of light spots (32a, 32b, 32c) on a plurality of tracks (3) of the optical disk (20). In writing data in the optical disk (20), the diffraction grating (13) is exited from between the semiconductor laser (12) and objective lens (20). Only a non-diffracted light beam (16a) is incident upon the objective lens (15) to form a single light spot (32a) on the optical disk (20).

Description

DESCRIPTION OPTICAL PICKUP DEVICE
BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to an optical pickup device for reading data from, and/or writing data into, an optical recording medium such as an optical disk and an optical card, and more particularly to an optical pickup device capable of high speed data read/ rite. 2. Description of the Related Art
In order to read data from an optical disk at high speed, an optical pickup device of a multi-spot type has been proposed in which light spots are applied at the same time to a plurality of tracks consecutively disposed in a radial direction of an optical disk. In the optical pickup device of the multi-spot type, in order to generate a plurality of light spots, a plurality of semiconductor lasers disposed in line or laser light from a single laser light source is diffracted to generate imaginary light sources equivalent to semiconductor laser light sources.
A conventional optical pickup device for generating a plurality of imaginary light sources by utilizing diffraction of a diffraction grating cannot write data in an optical disk. The reason for this is as in the following. In writing data in an optical disk, a light spot is formed on a track on which data is written. For example, with a magneto-optical recording method, in writing data, a record film of an optical disk is required to be heated to a Curie temperature or higher and the heated area is applied with a magnetic field generated by a magnetic coil. In this case, if a plurality of light spots are applied to a plurality of adjacent tracks, the same data is written in these tracks. This problem also occurs when a phase change method or other methods are used.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an optical pickup device capable of solving the above problem.
It is another object of the present invention to provide an optical pickup device capable of switching between a single beam to a multi-beam in which data write to a recording medium is performed by using a single beam and data read from the recording medium is performed by using a multi-beam.
An optical pickup device (11) of this invention comprises the following constituents (a) to (d) : (a) a laser source (12); (b) light diffracting means (13, 36, 60) for generating light spot forming diffracted light by diffracting light supplied from the laser source (12);
(c) light spot forming means (15) for forming a plurality of light spots (32a, 32b, 32c) on an optical recording medium (20) at different data positions (30), by using non-diffracted light (16a) from the laser source (12) and the diffracted light (16b, 16c) from the light diffracting means (13, 36, 60); and
(d) diffracted light generation preventing means (37, 42) for preventing the light diffracting means (13, 36, 60) from generating the light spot forming diffracted light.
The optical recording medium (20) includes an optical card in addition to an optical disk (20) . The different data positions (30) of the optical recording medium (20) are at different tracks in the case of concentric tracks and at the same track adjacent in the radial direction in the case of a spiral track.
Light from the laser source (12) is diffracted by the light diffracting means (13, 36, 60), and the diffracted light (16b, 16c) propagates as if it is emitted from an imaginary light source. In reading data from the optical recording medium (20), a plurality of light spots (32a, 32b, 32c) are formed on the optical recording medium (20) at the different data positions (30) by using non- diffracted light (16a) from the laser source (12) and the diffracted light (16b, 16c) from the light diffracting means (13, 36, 60). The plurality of light spots (32a, 32b, 32c) are used for reading data at each of the data positions (30) . In writing data into the optical recording medium (20), the diffracted light generation preventing means (37, 42) prevents the light diffracting means (13, 36, 60) from generating the light spot forming diffracted light. Therefore, only the single light spot (32a) is formed on the optical recording medium (20) by using the non-diffracted light (16a) from the laser source (12). Data is written in the track where the single light spot (32a) is formed. Accordingly, data can be read at high speed from the optical recording medium (20) by using the plurality of light spots (32a, 32b, 32c) and also data can be written in the optical recording medium (20) by using the single light spot without any practical problem.
An optical pickup device (11) of the invention comprises the following constituents (a) to (d) : (a) a laser source (12); (b) light diffracting means (13, 36) for generating light spot forming diffracted light by diffracting light supplied from the laser source (12);
(c) light spot forming means (15) for forming a plurality of light spots (32a, 32b, 32c) on an optical recording medium (20) at different data positions (30), by using non-diffracted light (16a) from the laser source (12) and the diffracted light (16b, 16c) from the light diffracting means (13, 36); and
(d) position changing means for changing a position of the light diffracting means (13, 36) so as to make the diffracted light (16b, 16c) from the light diffracting means (13, 36) enter the light spot forming means (15) during data read from the optical recording medium (20), and not to make the diffracted light (16b, 16c) from the light diffracting means (13, 36) enter the light spot forming means (15) during data write into the optical recording medium (20).
The light diffracting means (13, 36) includes a polarization hologram (36) in addition to a diffraction grating (13, 36).
Light from the laser source (12) is diffracted by the light diffracting means (13, 36), and the diffracted light (16b, 16c) propagates as if it is emitted from an imaginary light source. In reading data from the optical recording medium (20), the position of the light diffracting means (13, 36) is changed to a first position by the position changing means. Therefore, light from the laser source (12) diffracted by the light diffracting means (13, 36), i.e., diffracted light (16b, 16c), is also incident upon the light spot forming means (15). The plurality of light spots (32a, 32b, 32c) are therefore formed on the optical recording medium (20) so that data can be read at the same time from the plurality of data positions (30) to thereby speed up data read. In writing data into the optical recording medium (20), the position of the light diffracting means (13, 36) is changed to a second position different from the first position by the position changing means. Therefore, the diffracted light (16b, 16c) from the light diffracting means (13, 36) is not incident upon the light spot forming means (15), but only the non-diffracted light (16a) from the laser source (12) is incident upon the light spot forming means (15) . A light spot (32a) corresponding to the laser source (12), i.e., only the single light spot (32a), is formed on the optical recording medium (20) . Therefore, desired data is written only at a single position (30) where the light spot (32a) is formed.
An optical pickup device (11) of the invention comprises the following constituents (a) to (d) : (a) a laser source (12); (b) a polarization hologram (36) for generating light spot forming diffracted light by diffracting light supplied from the laser source (12);
(c) light spot forming means (15) for forming a plurality of light spots (32a, 32b, 32c) on an optical recording medium (20) at different data positions (30), by using non-diffracted light (16a) from the laser source (12) and the diffracted light (16b, 16c) from the polarization hologram ( 36 ) ; and
(d) a half-wave plate (37) for providing a half-wave optical path difference between P-polarized light and S- polarized light supplied from the laser source (12) when the half-wave plate (37) is inserted into an optical path between the laser source (20) and the polarization hologram (36), the half-wave plate (37) being inserted into the optical path to prevent the polarization hologram (36) from generating the diffracted light during data write into the optical recording medium (20), and exited from the optical path to allow the polarization hologram (36) to generate the diffracted light during data read from the optical recording medium (20).
Light having a polarization direction diffracted by the polarization hologram (36) is called ordinary light, whereas light having a polarization direction perpendicular to that of the ordinary light, i.e. light not diffracted by the polarization hologram, is called extraordinary light. The half-wave plate (37) shifts an optical path difference between P- and S-polarized light from the laser source (12) by 90° so that it can output light incident upon the polarization hologram (36) by changing the polarization direction by 90 c . Assuming that light from the laser source (12) is ordinary light of the polarization hologram (36), if the half-wave plate (37) is inserted into the optical path, diffraction by the polarization hologram (36) is prevented, whereas if it is exited from the optical path, diffraction by the polarization hologram (36) is performed. Assuming that light at the data position (30) is extraordinary light of the polarization hologram (36), if the half-wave plate (37) is inserted into the optical path, diffraction by the polarization hologram (36) is performed, whereas if it is exited from the optical path, diffraction by the polarization hologram (36) is prevented. With such insertion and exit of the half-wave plate (37), the polarization hologram (36) can generate the diffracted light during data read from the optical recording medium (20), so that the plurality of light spots (32a, 32b, 32c) are formed on the optical recording medium (20) at the different data positions (30) to allow high speed data read. During data write into the optical recording medium (20), the polarization hologram (36) does not generate the diffracted light so that only the single light spot (32a) of the non-diffracted light (16a) from the laser source (12) is formed on the optical recording medium (20) to thereby prevent any practical problem in writing data.
An optical pickup device (11) of the invention comprises the following constituents (a) to (d) :
8 (a) a laser source (12);
(b) a polarization hologram (36) for generating light spot forming diffracted light by diffracting light supplied from the laser source ( 12 ) ; (c) light spot forming means (15) for forming a plurality of light spots (32a, 32b, 32c) on an optical recording medium (20) at different data positions (30), by using non-diffracted light (16a) from the laser source (12) and the diffracted light (16b, 16c) from the polarization hologram (36); and
(d) a polarization direction changing liquid crystal element (42) for rotating a polarization direction of incidence light by 90° in accordance with a voltage applied to the element (42) inserted into an optical path between the laser source (20) and the polarization hologram (36), the element (42) preventing the polarization hologram (36) from generating the diffracted light during data write into the optical recording medium (20) and allowing the polarization hologram (36) to generate the diffracted light during data read from the optical recording medium (20), in accordance with a control of the voltage applied to the element (42) .
The polarization direction changing means (42) is, for example, liquid crystal molecules (48) of a TN twisted nematic mode, with opposing polarizers (50, 53) being removed. Light output from the polarization direction changing means (42) has a polarization direction changed by 90° relative to the incidence light thereof, when no voltage is applied. Light passes through the polarization direction changing means (42) without being rotated by 90° when a voltage is applied. If a laser ray from the optical recording medium (20) is an ordinary ray, the polarization hologram (36) generates the diffracted light when a voltage is applied to the polarization direction changing liquid crystal element (42), and it does not generate the diffracted light when no voltage is applied to the element (42) . If a laser ray from the optical recording medium (20) is an extraordinary ray, the polarization hologram (36) generates the diffracted light when no voltage is applied to the polarization direction changing liquid crystal element (42), and it does not generate the diffracted light when a voltage is applied to the element (42) . With a control of the voltage applied to the polarization direction changing liquid crystal element (42), the polarization hologram (36) can generate the diffracted light during data read from the optical recording medium (20), so that the plurality of light spots (32a, 32b, 32c) are formed on the optical recording medium (20) at the different data positions (30) to allow high speed data read. During data write into the optical
10 recording medium (20), the polarization hologram (36) does not generate the diffracted light so that only the single light spot (32a) of the non-diffracted light (16a) from the laser source (12) is formed on the optical recording medium (20) to thereby prevent any practical problem in writing data.
An optical pickup device (11) of the invention comprises the following constituents (a) to (c) : (a) a laser source (12); (b) a diffraction pattern displaying liquid crystal display (60) for displaying a diffraction pattern (61) during data read from an optical recording medium (20) and diffracting light supplied from the laser source (12) and for not displaying the diffraction pattern during data write from the optical recording medium (20); and
(c) light spot forming means (15) for forming a plurality of light spots (32a, 32b, 32c) on the optical recording medium (20) at different data positions (30), by using non-diffracted light (16a) and diffracted light (16b, 16c) supplied from the liquid crystal display (60).
The diffraction pattern displaying liquid crystal display (60) can display a desired pattern by controlling white and black of pixels to display the diffraction pattern (61) or make the display in a transmission state without displaying the diffraction pattern (61). While the
11 diffraction pattern (61) is displayed, light from the laser source (12) is diffracted by the diffraction pattern (61) so that the diffracted light (16b, 16c) is formed, whereas while the diffraction pattern (61) is not displayed, light from the laser source (12) is not diffracted but is transmitted therethrough. Therefore, while the diffraction pattern displaying liquid crystal display (60) displays the diffraction pattern (61), the plurality of light spots (32a, 32b, 32c) are formed on the optical recording medium (20) at the different data positions (30) to allow high speed data read from the optical recording medium (20). While the diffraction pattern displaying liquid crystal display (60) does not display the diffraction pattern (61), only the single light spot (32a) of the non-diffracted light (16a) from the laser source (12) is formed on the optical recording medium (20) to write data in the optical recording medium (20) without any practical problem.
BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram showing the structure of an optical pickup device of a data read/write apparatus in a data read state.
Fig. 2 is a schematic diagram showing the main portion of the structure of the optical pickup device of the data read/write apparatus shown in Fig. 1 in a data write state.
12 Fig. 3 is a diagram illustrating light spots formed on an optical disk shown in Fig. 1.
Fig. 4 is a diagram showing the main portion of an optical pickup device in a data read state, the optical pickup device changing the number of light spots to be generated, by using a polarization hologram and a half-wave plate.
Fig. 5 is a diagram showing the main portion of the optical pickup device in a data write state, the optical pickup device changing the number of light spots to be generated, by using the polarization hologram and half-wave plate.
Fig. 6 is a diagram illustrating a principle of changing a polarization direction by a half-wave plate in which an optical path difference between P- and S-polarized light beams is 0.
Fig. 7 is a diagram illustrating a principle of changing a polarization direction by the half-wave plate in which an optical path difference between P- and S-polarized light beams is a half wavelength.
Fig. 8 is a diagram showing the main portion of an optical pickup device in a data read state, the optical pickup device changing the number of light spots to be generated, by using TN display mode liquid crystal without a polarizer.
13 Fig. 9 is a diagram showing the main portion of the optical pickup device in a data write state, the optical pickup device changing the number of light spots to be generated, by using the TN display mode liquid crystal without a polarizer.
Fig. 10 is a schematic diagram illustrating a principle of changing a polarization direction, in a state of absence of an electric field, of a TN display mode liquid crystal display which operates based upon the TN display mode liquid crystal without a polarizer shown in Figs. 8 and 9.
Fig. 11 is a schematic diagram illustrating a principle of changing a polarization direction, in a state of presence of an electric field, of the TN display mode liquid crystal which operates based upon the TN display mode liquid crystal without a polarizer shown in Figs. 8 and 9.
Fig. 12 is a schematic diagram showing the main portion of an optical pickup device in a data read state, the optical pickup device being capable of changing the number of light spots to be generated by using a liquid crystal display.
Fig. 13 is a schematic diagram showing the main portion of the optical pickup device in a data write state, the optical pickup device being capable of changing the
14 number of light spots to be generated by using the liquid crystal display.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the invention will be described with reference to the accompanying drawings .
Fig. 1 is a schematic diagram showing the structure of an optical pickup device 11 of a data read/write apparatus 10 in a data read state, Fig. 2 is a schematic diagram showing the structure of the optical pickup device 11 of the data read/write apparatus 10 in a data write state, and Fig. 3 is a diagram showing light spots 32a, 32b, and 32c formed on an optical disk 20 shown in Fig. 1. A semiconductor laser 12 has a single laser light source. A diffraction grating 13 is inserted between the semiconductor laser 12 and a beam splitter 14 in the data read state by an unrepresented actuator, whereas it is exited from between the semiconductor laser 12 and beam splitter 14 in the data write state. In Fig. 1, as a laser light beam passes through the diffraction grating 13, two diffraction light beams 16b and 16c corresponding to two imaginary light sources are generated. The number of imaginary light sources are not limited only to two, but the number may be set to 1 , 3, 4 , ... , n other than 2 by using a proper diffraction grating pattern of the
15 diffraction grating 13. When the diffraction grating 13 is inserted between the semiconductor laser 12 and beam splitter 14, of the laser beam radiated from the semiconductor laser 12, the light beam not diffracted by the diffraction grating 13 propagates straightforward and becomes a non-diffracted light beam 16a, and the other light beams become diffracted light beams 16b and 16c. The non-diffracted and diffracted light beams 16a, 16b, and 16c pass through the beam splitter 14 straightforward and propagate toward an objective lens 15. The objective lens 15 diffracts the incident non-diffracted and diffracted light beams 16a, 16b, and 16c to form light spots 32a, 32b, and 32c (Fig. 3) corresponding in number to that of real and imaginary light sources, on the optical disk 20. Although a collimator lens between the beam splitter 14 and objective lens 15 is omitted in Figs. 1 and 2, it may be disposed therebetween. The distance between the objective lens 15 of the optical pickup device 11 and the optical disk 20 is adjusted through a focus servo (not shown) by using light supplied from the collimator lens, to thereby form the proper light spots 32a, 32b, and 32c on the optical disk 20. In Fig. 3, a plurality of tracks 30 extend at a predetermined pitch, each track 30 being formed with pits (or marks) corresponding to write data. The light spots 32a, 32b, and 32c are formed on different
16 adjacent tracks 30. Light reflected from each light spot 32a, 32b, 32c propagates backward through the objective lens 15, is reflected at a right angle by the beam splitter 14, and becomes incident upon each photodiode 24a, 24b, 24c of a photodetector unit 23. Each photodiode 24a, 24b, 24c supplies an electrical signal corresponding to an amount of the incident light to a signal processing unit 25. The signal processing unit 25 derives data on each track 30 of the optical disk 20 from the electrical signal supplied from each photodiode 24a, 24b, 24c.
In writing data, as shown in Fig. 2, the diffraction grating 13 is exited from between the semiconductor laser 12 and beam splitter 14. A laser light beam radiated from the semiconductor layer 12 is not diffracted by the diffraction grating 13 and becomes incident upon the beam splitter 14. Therefore, a light spot formed on the optical disk 20 is only a light spot 32a. In writing data in the optical disk 20, a data write area of the optical disk 20 applied with a light spot is heated to a Curie temperature or higher, and with a magnetic flux supplied from an unrepresented magnetic coil, the predetermined data is written without any practical problem.
Figs. 4 and 5 are diagrams showing the main portion of an optical pickup device in data read/write states, the optical pickup device changing the number of light spots to
17 be generated, by using a polarization hologram 36 and a half-wave plate 37. Figs. 6 and 7 are diagrams illustrating a principle of changing a polarization direction by the half-wave plate 37 in which an optical path difference between P- and S-polarized light beams is 0 and a half wavelength, respectively. Referring first to Figs. 6 and 7, a laser light beam is constituted of P- and S-polarized light beams having a polarization direction shift of 90°. A laser light beam has a synthesized polarization direction which is a total of the P- and S- polarizations. If an optical path difference between P- and S-polarized light beams is 0, the synthesized polarization direction is a direction of y = - x in an x-y plane as shown in Fig. 6, whereas if an optical path difference between P- and S-polarized light beams is a half wavelength, the synthesized polarization direction is a direction of y = x in the x-y plane as shown in Fig. 7. It can therefore be understood that the polarization direction can be changed by 90° by the half-wave plate 37. Referring next to Figs. 4 and 5, the polarization hologram 36 is inserted between the semiconductor laser 12 and an objective lens 15 (refer to Fig. 1). The half-wave plate 37 is either inserted or exited from between the semiconductor laser 12 and polarization hologram 36 by an unrepresented actuator. The polarization hologram 36
18 diffracts an incidence light beam and outputs it if the polarization direction of the incidence light beam is a first direction, whereas it does not diffract an incidence light beam and outputs as it is if the polarization direction of the incidence light beam is a second direction perpendicular to the first polarization direction. The light beams having the first and second polarization directions are called an ordinary ray and an extraordinary ray, respectively. The laser beam radiated from the semiconductor laser 12 to be applied to the polarization hologram shown in Figs. 4 and 5 is the ordinary ray. In reading data from the optical disk 20 at high speed and generating a plurality of light spots on the optical disk 20, at least one imaginary light source is formed by using the laser beam from the semiconductor laser 12, i.e., diffracted light beams 16b and 16c are generated by the polarization hologram 36. In this case, as shown in Fig. 4, the half-wave plate 37 is exited from between the semiconductor laser 12 and polarization hologram 36, and the laser beam from the semiconductor laser 12 is made directly incident upon the polarization hologram 36 by maintaining the polarization direction Dl of the laser beam. In writing data in the optical disk 20 and generating a single light spot 32a on the optical disk 20, the half-wave plate 37 is inserted between the
19 semiconductor laser 12 and polarization hologram 36 as shown in Fig. 5 to change the polarization direction of the laser beam from the semiconductor laser 12 by 90° from Dl to D2 so that the extraordinary ray becomes incident upon the polarization hologram 36.
In the example shown in Figs . 4 and 5 , the polarization direction of the laser beam supplied from the semiconductor laser 12 is equal to that of the ordinary ray of the polarization hologram 36. If the polarization direction of the laser beam supplied from the semiconductor laser 12 is equal to that of the extraordinary ray of the polarization hologram 36, the half-wave plate 37 is inserted in the data read state and exited in the data write state. Similar to the diffraction grating 13 shown in Figs. 1 and 2, the polarization hologram 36 may be inserted in the data read state to generate the diffracted light beams 16b and 16c, and exited in the data write state not to generate the diffracted light beams 16b and 16c. In this case, the half-wave plate 37 is not necessary.
Figs. 8 and 9 are diagrams showing the main portion of an optical pickup device in data read/write states, the optical pickup device changing the number of light spots to be generated, by using TN display mode liquid crystal 42 without a polarizer, and Figs. 10 and 11 are schematic
20 diagrams illustrating a principle of changing a polarization direction, in a state of absence/presence of an electric field, of a TN display mode liquid crystal display 48 which operates based upon the display mode liquid crystal 42 without a polarizer shown in Figs. 8 and 9. Referring first to Figs. 10 and 11, the TN display mode liquid crystal display 48 has a lamination structure made of a polarizer 50, glass plates 51 and 52, and a polarizer 53 stacked in this order from the side of incidence light 55. Between the glass plates 51 and 52, a liquid crystal layer is present which is made of liquid crystal molecules twisted by 90°. In an absence of an electric field, as shown in Fig. 10, an incidence light beam 55 whose polarization direction was aligned by the polarizer 50 passes through the liquid crystal layer by rotating its linear polarization by 90°, and reaches the polarizer 53, whereas in a presence of an electric field, as shown in Fig. 11, the incidence light beam 55 passes through the liquid crystal layer by eliminating the twist of the liquid crystal molecules 54 and maintaining the polarization direction of the incidence light beam 55, and reaches the polarizer 53. The TN display mode liquid crystal 42 without a polarizer shown in Figs . 8 and 9 corresponds to the TN display mode liquid crystal display 48 shown in Figs. 10 and 11, with their polarizers 50 and 53 being
21 removed. The TN display mode liquid crystal 42 without a polarizer changes the polarization direction of the laser beam of the semiconductor laser 12 by 90° in an absence of an electric field, and does not change it in a presence of an electric field. In the TN display mode liquid crystal 42 without a polarizer shown in Figs. 8 and 9, the laser beam from the semiconductor laser 12 is an ordinary ray of the polarization hologram 36. In the data read state, a switch 44 is turned on to apply a voltage from a d.c. power source 43 to the TN display mode liquid crystal 42 without a polarizer. Therefore, the laser beam from the semiconductor laser 12 passes through the TN display mode liquid crystal 42 without a polarizer by maintaining its polarization direction Dl, and becomes incident upon the polarization hologram 36. The polarization hologram 36 is therefore supplied with an ordinary ray so that it generates a non-diffracted light beam 16a as well as diffracted light beams 16b and 16c. In contrast with the above, in the data write state, the switch 44 is turned off so as not to apply an electric field to the TN display mode liquid crystal 42 without a polarizer. Therefore, the laser beam from the semiconductor laser 12 passes through the TN display mode liquid crystal 42 without a polarizer by changing its polarization direction by 90° from Dl to D2, and becomes incident upon the polarization hologram 36.
22 The polarization hologram 36 is therefore supplied with an extraordinary ray so that it generates only the non- diffracted light beam 16a without any diffraction.
In the example shown in Figs. 8 and 9, the polarization direction of the laser beam supplied from the semiconductor laser 12 is equal to that of the ordinary ray of the polarization hologram 36. If the polarization direction of the laser beam supplied from the semiconductor laser 12 is equal to that of the extraordinary ray of the polarization hologram 36, the TN display mode liquid crystal 42 without a polarizer is applied with an electric field in the data read state, and not applied with an electric field in the data write state.
Figs. 12 and 13 are schematic diagrams showing the main portion of an optical pickup device 11 in data read/write states, the optical pickup device being capable of changing the number of light spots to be generated by using a liquid crystal display 60. The liquid crystal display 60 is inserted between a semiconductor laser 12 and an objective lens 15 (refer to Fig. 1). White/black of each pixel of the liquid crystal display 60 is controlled by an unrepresented controller to display a desired image. In the data read state, a diffraction pattern 61 is formed by making predetermined black pixels, and in the data write state, all pixels are made white so as not to display a
23 diffraction pattern 61 and make the liquid crystal display in a transmission state. While the diffraction pattern 61 is displayed, a laser beam from the semiconductor laser is diffracted by the diffraction pattern to generate diffracted light beams 16b and 16c on the optical disk 20. In contrast with the above, in the data write state, while the liquid crystal display 60 is in the transmission state, the laser beam from the semiconductor laser 12 is not diffracted in the liquid crystal display 60 but passes therethrough to generate only a non-diffracted light beam 16a which is formed on the optical disk 20.
24

Claims

1. An optical pickup device comprising:
(a) a laser source (12); (b) light diffracting means (13, 36, 60) for generating light spot forming diffracted light by diffracting light supplied from said laser source (12);
(c) light spot forming means (15) for forming a plurality of light spots (32a, 32b, 32c) on an optical recording medium (20) at different data positions (30), by using non-diffracted light (16a) from said laser source (12) and the diffracted light (16b, 16c) from said light diffracting means (13, 36, 60); and
(d) diffracted light generation preventing means (37, 42) for preventing said light diffracting means (13, 36,
60) from generating the light spot forming diffracted light .
2. An optical pickup device comprising: (a) a laser source (12);
(b) light diffracting means (13, 36) for generating light spot forming diffracted light by diffracting light supplied from said laser source (12);
(c) light spot forming means (15) for forming a plurality of light spots (32a, 32b, 32c) on an optical
25 recording medium (20) at different data positions (30), by using non-diffracted light (16a) from said laser source (12) and the diffracted light (16b, 16c) from said light diffracting means (13, 36); and (d) position changing means for changing a position of said light diffracting means (13, 36) so as to make the diffracted light (16b, 16c) from said light diffracting means (13, 36) enter said light spot forming means (15) during data read from the optical recording medium (20), and not to make the diffracted light (16b, 16c) from said light diffracting means (13, 36) enter said light spot forming means (15) during data write into the optical recording medium (20) .
3. An optical pickup device comprising:
(a) a laser source (12);
(b) a polarization hologram (36) for generating light spot forming diffracted light by diffracting light supplied from said laser source (12); (c) light spot forming means (15) for forming a plurality of light spots (32a, 32b, 32c) on an optical recording medium (20) at different data positions (30), by using non-diffracted light (16a) from said laser source (12) and the diffracted light (16b, 16c) from said polarization hologram (36); and
26 (d) a half-wave plate (37) for providing a half-wave optical path difference between P-polarized light and S- polarized light supplied from said laser source (12) when said half-wave plate (37) is inserted into an optical path between said laser source (20) and said polarization hologram (36), said half-wave plate (37) being inserted into the optical path to prevent said polarization hologram (36) from generating the diffracted light during data write into the optical recording medium (20), and exited from the optical path to allow said polarization hologram (36) to generate the diffracted light during data read from the optical recording medium (20).
4. An optical pickup device comprising: (a) a laser source (12);
(b) a polarization hologram (36) for generating light spot forming diffracted light by diffracting light supplied from said laser source (12);
(c) light spot forming means (15) for forming a plurality of light spots (32a, 32b, 32c) on an optical recording medium (20) at different data positions (30), by using non-diffracted light (16a) from said laser source (12) and the diffracted light (16b, 16c) from said polarization hologram (36); and (d) a polarization direction changing liquid crystal
27 element (42) for rotating a polarization direction of incidence light by 90┬░ in accordance with a voltage applied to said element (42) inserted into an optical path between said laser source (20) and said polarization hologram (36), said element (42) preventing said polarization hologram (36) from generating the diffracted light during data write into the optical recording medium (20) and allowing said polarization hologram (36) to generate the diffracted light during data read from the optical recording medium (20), in accordance with a control of the voltage applied to said element (42) .
5. An optical pickup device comprising: (a) a laser source (12); (b) a diffraction pattern displaying liquid crystal display (60) for displaying a diffraction pattern (61) during data read from an optical recording medium (20) and diffracting light supplied from said laser source (12) and for not displaying the diffraction pattern during data write from the optical recording medium ( 20 ) ; and
(c) light spot forming means (15) for forming a plurality of light spots (32a, 32b, 32c) on the optical recording medium (20) at different data positions (30), by using non-diffracted light (16a) and diffracted light (16b, 16c) supplied from said liquid crystal display (60).
28
6. An optical pickup device according to claim 2, wherein said position changing means is an actuator.
7. An optical pickup device according to claim 4, wherein said polarization direction changing liquid crystal element has a lamination structure sandwiched between glass plates between which a liquid crystal layer is intervened, the liquid crystal layer containing liquid crystal molecules twisted by 90
8. An optical pickup device according to claim 5, wherein displaying the diffraction pattern is performed by making predetermined pixels of said diffraction pattern displaying liquid crystal display have black color.
9. An optical pickup device according to claim 5 , wherein not displaying the diffraction pattern is performed by making all pixels of said diffraction pattern displaying liquid crystal display have white color to make said display in a transmission state.
29
EP99907875A 1998-03-11 1999-03-05 Optical pickup device Withdrawn EP1062663A1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
JP7644098 1998-03-11
JP7644098 1998-03-11
PCT/JP1999/001090 WO1999046767A1 (en) 1998-03-11 1999-03-05 Optical pickup device

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EP1062663A1 true EP1062663A1 (en) 2000-12-27

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EP (1) EP1062663A1 (en)
KR (1) KR20010041682A (en)
CN (1) CN1292917A (en)
DE (1) DE1062663T1 (en)
TW (1) TW548643B (en)
WO (1) WO1999046767A1 (en)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20020075783A1 (en) * 1998-02-20 2002-06-20 Amir Alon Switchable liquid crystal diffractive element
US6584059B1 (en) * 1999-02-17 2003-06-24 Matsushita Electric Industrial Co., Ltd. Information recording and reproducing apparatus
JP4107261B2 (en) * 2003-11-14 2008-06-25 セイコーエプソン株式会社 Printer with cutter mechanism

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Publication number Priority date Publication date Assignee Title
JPS6275942A (en) * 1985-09-27 1987-04-07 Nec Home Electronics Ltd Optical head
JPH01213627A (en) * 1988-02-20 1989-08-28 Fujitsu Ltd Optical head
JP3241781B2 (en) * 1991-08-22 2001-12-25 松下電器産業株式会社 Optical head device, optical information recording device, and optical information reproducing device
KR100206771B1 (en) * 1995-12-29 1999-07-01 구자홍 Optical pickup device

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9946767A1 *

Also Published As

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TW548643B (en) 2003-08-21
CN1292917A (en) 2001-04-25
KR20010041682A (en) 2001-05-25
DE1062663T1 (en) 2001-07-05
WO1999046767A1 (en) 1999-09-16

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