JP2005108288A - Optical pickup and disk drive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure good signal quality by securing both of a sufficient S/N and a sufficient dynamic range at low costs. <P>SOLUTION: In an optical pickup, a plurality of laser beams having different wavelengths corresponding to disk recording media are emitted to the plurality of disk recording media 100a and 100b of different kinds, reproduction of information signals from the disk recording media of different kinds is made possible, and recording of an information signal is made possible at least on one kind of a disk recording medium. The optical pickup is provided with: a beam splitter 12 which reflects or transmits each emitted laser beam according to its advancing direction; at least one photodetector 16 receiving at least two kinds of laser beams having different wavelengths; and an element with a thin film 17 added thereto and having an optical filter function having wavelength selectivity and varied in transmittance according to the wavelength of a laser beam in the optical path of the laser beam from the beam splitter to the photodetector. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to the technical field of optical pickups and disk drive devices. More specifically, the present invention relates to a technical field for improving the performance of an optical pickup and a disk drive apparatus that record and reproduce information signals on different types of disk-shaped recording media.

  2. Description of the Related Art There is a disk drive device that records and reproduces information signals on a disk-shaped recording medium. Such a disk drive device moves in the radial direction of the disk-shaped recording medium mounted on a disk table and moves to the disk-shaped recording medium. And an optical pickup that records or reproduces an information signal by irradiating a laser beam through an objective lens.

  Some disk drive devices are capable of recording and reproducing information signals with respect to a plurality of disk-shaped recording media having different recording surface reflectivities and different laser beam outputs by one optical pickup.

  As the disc-shaped recording medium, in addition to the above-mentioned CD whose laser beam is used in the vicinity of 785 nm, a DVD (Digital Versatile Disc) whose used wavelength is around 660 nm, a Blu-ray disc whose used wavelength is around 405 nm, and the like. Exists.

  In an optical pickup capable of recording and reproducing information signals on a plurality of types of disc-shaped recording media having different use wavelengths as described above, for example, a dual layer disc having a plurality of recording layers (recording surfaces) When playing back a disk-shaped recording medium (DVD) having a low reflectivity, such as a disk-shaped recording medium called ± RW disk-shaped recording medium or a RAM (Random Access Memory) disk-shaped recording medium , The gain is low and the S / N (ratio of signal component to noise component) is deteriorated, which may adversely affect signal quality.

  Also, during high-speed recording, the amount of light incident on the light-receiving element is larger than that during playback, so that the dynamic range of the light-receiving element (difference between the maximum signal level and the minimum signal level) cannot be ensured. Saturation of the device occurs, which may also adversely affect the signal quality.

  The difference in the amount of incident light to the light receiving element as described above becomes larger as the recording speed increases, and tends to become larger in recent times of higher recording / reproducing speed.

  For example, when a signal is detected using a single light receiving element in an optical pickup capable of recording and reproducing information signals for CDs and DVDs, the signal frequency level of DVDs is higher than that of CDs. In particular, S / N tends to deteriorate during high-speed playback as compared to CD. In this case, it is possible to prevent S / N deterioration by increasing the output of the laser beam of the light emitting element (laser diode), but at the same time, the output at the time of reproducing the information signal also increases, and the recorded information This method is difficult to adopt because there is a risk of erasure of the image.

  In addition, since a CD has more specifications for recording an information signal at a high speed than a DVD, when a CD is recorded, the incident light amount to the light receiving element is larger than the DVD, and a DVD having a low reflectance is reproduced at a high speed. It is necessary to satisfy both the sufficient S / N and the sufficient dynamic range when recording a CD at a high speed, and if this is not possible, reproduction on a DVD with low reflectivity is required. As for recording on CDs, the high speed is limited.

  Therefore, a conventional optical pickup uses a filter whose transmittance is variable by a mechanical operation, such as a liquid crystal or a filter whose transmittance is electrically changed, such as an ND filter. There is one that ensures the range and improves the signal quality (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 11-73777

  However, in the above-described conventional optical pickup, in order to ensure the S / N and the dynamic range of the light receiving element, mechanical operations such as a filter such as a liquid crystal whose electrical transmittance is variable or an ND filter are used. Therefore, there is a problem that the driving power is required and the power consumption is large, and the liquid crystal itself is expensive, so that the cost is high.

  Further, since a driving circuit such as a liquid crystal or an ND filter is required, the cost is further increased.

  Furthermore, the use of a liquid crystal or an ND filter has a problem that the optical path of the optical system becomes longer and the optical pickup becomes thinner.

  Therefore, the optical pickup and the disk drive device according to the present invention overcome the above-described problems, and at the same time, ensure both a sufficient S / N and a sufficient dynamic range at a low cost to ensure a good signal quality. This is the issue.

  In order to solve the above-described problems, the optical pickup of the present invention is configured to emit a plurality of laser beams having different wavelengths corresponding to the respective disc-shaped recording media toward a plurality of different disc-shaped recording media. The information signal can be reproduced for each type of disc-shaped recording medium, and the information signal can be recorded for at least one type of disc-shaped recording medium. The traveling direction of each emitted laser beam A beam splitter that reflects or transmits the laser beam and at least one light receiving element that receives at least two types of laser beams having different wavelengths, and is provided in the optical path of the laser beam from the beam splitter to the light receiving element. A thin film with an optical filter function that has wavelength selectivity and different transmittance depending on the wavelength of the laser beam is attached. It is provided with a the device.

  In order to solve the above-described problems, the disk drive device of the present invention includes an optical pickup configured to emit a plurality of laser beams having different wavelengths corresponding to the type of the disk-shaped recording medium. Information signals can be reproduced for each disk-shaped recording medium, and information signals can be recorded for at least one type of disk-shaped recording medium. Accordingly, a beam splitter that reflects or transmits the laser beam and at least one light receiving element that receives at least two types of laser beams having different wavelengths are provided in the optical path of the laser beam from the beam splitter to the light receiving element. Thin film with optical filter function that has wavelength selectivity and has different transmittance depending on the wavelength of laser light It is provided with a the added element.

  Therefore, in the optical pickup and the disk drive device of the present invention, the transmission amount of the laser light incident on the thin film having the optical filter function changes according to the wavelength.

  An optical pickup according to the present invention includes a moving base that moves in a radial direction of a disk-shaped recording medium mounted on a disk table, and an objective lens driving device that is arranged on the moving base, to a plurality of different types of disk-shaped recording media. A plurality of laser beams having different wavelengths corresponding to the respective disk-shaped recording media, and reproducing information signals for the different types of disk-shaped recording media, and at least one kind of An optical pickup capable of recording an information signal on a disk-shaped recording medium, and having a wavelength different from that of a beam splitter that reflects or transmits the laser light according to the traveling direction of each emitted laser light. And at least one light receiving element for receiving at least two types of laser light, and from a beam splitter The optical path of the laser light to the optical element, and wherein the transmittance depending on the wavelength of the laser beam has a wavelength selectivity is provided an element obtained by adding a thin film having a different optical filter function.

  Therefore, it is necessary to ensure a sufficient S / N when reproducing a disk-shaped recording medium having a low reflectivity at a high speed and a sufficient dynamic range when recording another type of disk-shaped recording medium at a high speed. It is possible to achieve both at a low cost and to ensure good signal quality.

  Further, since a thin film is used, the optical path of the optical system is not lengthened, and the optical pickup can be thinned.

  In the invention described in claim 2, since the thin film having the optical filter function is provided on the exit surface of the beam splitter, it is usually provided on the exit surface where only AR coating for reducing reflection is applied. Thus, it is possible to easily form a thin film having an optical filter function.

  In the invention described in claim 3, since the light receiving element has a package that covers the light receiving portion that receives the laser beam, and a thin film having an optical filter function is provided in the package of the light receiving element, the light receiving element is formed in a normal plane. By providing on the surface of the package, a thin film having an optical filter function can be easily formed.

  The disk drive device according to the present invention includes a disk table on which a plurality of different disk-shaped recording media are individually mounted and rotated, and an objective lens drive disposed on a moving base that is moved in the radial direction of the disk-shaped recording medium. And an optical pickup configured to emit a plurality of laser beams having different wavelengths corresponding to the type of the disk-shaped recording medium, and reproduce information signals for the different types of disk-shaped recording media. A disk drive device capable of recording an information signal on at least one type of disk-shaped recording medium, wherein the optical pick-up is arranged according to the traveling direction of each emitted laser beam. A beam splitter that reflects or transmits laser light and at least two types of laser light having different wavelengths are received. And a thin film having an optical filter function that has wavelength selectivity and a different transmittance depending on the wavelength of the laser light in the optical path of the laser light from the beam splitter to the light receiving element. An element is provided.

  Therefore, it is necessary to ensure a sufficient S / N when reproducing a disk-shaped recording medium having a low reflectivity at a high speed and a sufficient dynamic range when recording another type of disk-shaped recording medium at a high speed. It is possible to achieve both at a low cost and to ensure good signal quality.

  Further, since a thin film is used, the optical path of the optical system does not become long, and the disk drive device can be miniaturized by reducing the thickness of the optical pickup.

  In the invention described in claim 5, since the thin film having the optical filter function is provided on the exit surface of the beam splitter, it is usually provided on the exit surface where only AR coating for reducing reflection is applied. Thus, it is possible to easily form a thin film having an optical filter function.

  In the invention described in claim 6, since the light receiving element has a package that covers the light receiving portion that receives the laser beam, and a thin film having an optical filter function is provided in the package of the light receiving element, the light receiving element is formed in a normal plane. By providing on the surface of the package, a thin film having an optical filter function can be easily formed.

  The best mode of an optical pickup and a disk drive apparatus according to the present invention will be described below with reference to the accompanying drawings.

  The disk drive device 1 is configured by arranging required members and mechanisms in an outer casing 2 (see FIG. 1), and the outer casing 2 has a disk insertion slot (not shown).

  A chassis (not shown) is disposed in the outer casing 2, and the disk table 3 is fixed to the motor shaft of a spindle motor attached to the chassis.

  Parallel guide shafts 4 and 4 are attached to the chassis, and a lead screw 5 that is rotated by a feed motor (not shown) is supported.

  The optical pickup 6 includes a moving base 7, required optical components provided on the moving base 7, and an objective lens driving device 8 disposed on the moving base 7, and is provided at both ends of the moving base 7. The bearing portions 7a and 7b are slidably supported by the guide shafts 4 and 4, respectively. When a nut member (not shown) provided on the moving base 7 is screwed into the lead screw 5 and the lead screw 5 is rotated by the feed motor, the nut member is sent in a direction corresponding to the rotation direction of the lead screw 5, The pickup 6 is moved in the radial direction of the disc-shaped recording medium 100 mounted on the disc table 3.

  As the disc-shaped recording medium 100, for example, a DVD 100a and a CD 100b are used.

  In the disk drive device 1 configured as described above, when the disk table 3 is rotated in accordance with the rotation of the spindle motor, the disk-shaped recording medium 100 mounted on the disk table 3, that is, the DVD 100a or the CD 100b is loaded. At the same time, the optical pickup 6 is moved in the radial direction of the disc-shaped recording medium 100 to perform a recording operation or a reproducing operation on the disc-shaped recording medium 100.

  As shown in FIG. 2, the optical pickup 6 includes, for example, a first light emitting element 9, a second light emitting element 10, an optical axis synthesizing element 11, a beam splitter 12, a collimator lens 13, an objective lens 14, and a multilens 15. And the light receiving element 16. The first light emitting element 9, the second light emitting element 10, the optical axis synthesizing element 11, the beam splitter 12, the collimator lens 13, the multilens 15, and the light receiving element 16 are disposed on the moving base 7. The objective lens 14 is provided in the objective lens driving device 8.

  As the first light emitting element 9, for example, a semiconductor laser that emits laser light having a wavelength of about 660 nm is used. As the second light emitting element 10, for example, laser light having a wavelength of about 785 nm is emitted. Semiconductor lasers are used. For example, when a Blu-ray disc is used as the disc-shaped recording medium 100, a light emitting element that emits laser light having a wavelength of about 405 nm is used.

  The optical axis synthesizing element 11 reflects, for example, the laser light emitted from the first light emitting element 9, transmits the laser light emitted from the second light emitting element 10, and is emitted from the first light emitting element 9. The laser beam and the optical axis of the laser beam emitted from the second light emitting element 10 are combined.

  The beam splitter 12 is formed by using a flat plate member such as glass as a base material. For example, the incident surface 12a of the laser beam is coated with a semi-transmissive mirror, and the output surface 12b is coated with an anti-reflection (AR) coating. .

  The collimator lens 13 has a function of converting the incident laser beam into a parallel beam.

  The objective lens 14 has a function of condensing incident laser light on the recording surface of the disk-shaped recording medium 100.

  The multi-lens 15 has a function of adjusting the amount of astigmatism and converting the optical magnification and condensing laser light on the light receiving element 16.

  A thin film 17 having an optical filter function is provided on the entrance surface or the exit surface of the multi lens 15. The thin film 17 having an optical filter function has a wavelength selectivity and a function of varying the transmittance of the incident laser light according to the wavelength of the laser light. The thin film 17 having an optical filter function is formed, for example, by laminating an optical thin film layer based on titanium oxide or silicon oxide on a support layer based on optical plastic. As shown in FIG. 3, the thin film 17 having an optical filter function has a high transmittance for a laser beam having a short wavelength near 660 nm and a transmittance for a laser beam having a long wavelength near 785 nm. Is formed to be low. For example, in the vicinity of a wavelength of 660 nm, the transmittance is such that sufficient S / N can be ensured at the time of high-speed reproduction of the DVD 100a, particularly DVD ± RW, DVD-RAM, etc. In the vicinity of 785 nm, the transmittance is such that a sufficient dynamic range of the light receiving element 16 at the time of high-speed recording of the CD 100b is secured and saturation of the light receiving element 16 does not occur.

  The light receiving element 16 includes a light receiving portion 16a covered with a package 16b formed of a transparent material.

  In the optical pickup 6 configured as described above, when laser light having a first wavelength (about 660 nm) is emitted from the first light emitting element 9, the emitted laser light is reflected by the optical axis synthesizing element 11. Subsequently, the light is reflected by the incident surface 12 a of the beam splitter 12, converted into a parallel light beam by the collimator lens 13, and condensed through the objective lens 14 onto the recording surface of the DVD 100 a mounted on the disk table 3. The laser beam condensed on the recording surface of the DVD 100a is reflected by the recording surface and enters the beam splitter 12 again through the objective lens 14 and the collimator lens 13 as return light. The return light incident on the beam splitter 12 is transmitted through the beam splitter 12, is emitted from the exit surface 12b, is incident on the light receiving element 16 via the multi lens 15, is photoelectrically converted, and is recorded on, for example, the DVD 100a. The signal is played back.

  On the other hand, when laser light having the second wavelength (about 785 nm) is emitted from the second light emitting element 10, the emitted laser light is transmitted through the optical axis synthesizing element 11 and subsequently incident on the beam splitter 12. The light is reflected by the surface 12a, is converted into a parallel light beam by the collimator lens 13, and is condensed on the recording surface of the CD 100b mounted on the disk table 3 via the objective lens 14. The laser beam condensed on the recording surface of the CD 100b is reflected by the recording surface and enters the beam splitter 12 again through the objective lens 14 and the collimator lens 13 as return light. The return light incident on the beam splitter 12 is transmitted through the beam splitter 12, is emitted from the exit surface 12b, is incident on the light receiving element 16 via the multi lens 15, is photoelectrically converted, and is recorded on, for example, the CD 100b. The signal is played back. At this time, the amount of the laser light incident on the light receiving element 16 is suppressed by the thin film 17 having an optical filter function with respect to the laser light traveling from the beam splitter 12 to the multi lens 15.

  FIG. 4 is a table showing an example of a change in the amount of light received by the light receiving element 16 depending on the presence or absence of the thin film 17 having an optical filter function.

  In FIG. 4, “MODE (double speed)” indicates the double speed during reproduction or recording, and “object emission (MAIN)” indicates the output of the primary light in the light emitted from the objective lens 14.

  As shown in FIG. 4, in the case of DVD-R, the amount of received light is 0.012 mW or 0.931 mW, regardless of the presence or absence of the thin film 17 having an optical filter function, and is not changed. On the other hand, in the case of the CD-R, when the thin film 17 having the optical filter function is not provided, the received light amount is 0.086 mW or 2.146 mW, and the thin film 17 having the optical filter function is provided. The received light amount is set to 0.069 mW or 1.717 mW, and the received light amount is reduced by about 20% by the thin film 17 having the optical filter function.

  As described above, in the disk drive device 1, the thin film 17 having an optical filter function in which the transmittance varies depending on the wavelength of the laser light in the optical path of the laser light from the beam splitter 12 to the light receiving element 16. Therefore, in the case of the CD 100b, the transmittance of the laser light is made lower than that in the case of the DVD 100a.

  Therefore, it is possible to satisfy both of sufficient securing of S / N when reproducing a low-reflectance DVD 100a at a high speed and sufficient securing of a dynamic range when recording a CD 100b at a high speed. Quality can be ensured.

  Moreover, unlike conventional optical pickups, a filter whose transmittance is variable by a mechanical operation such as a liquid crystal or an ND filter is not used. No power or drive circuit is required, and sufficient S / N and dynamic range can be secured without increasing costs.

  Further, since the thin film 17 having the optical filter function is used, the optical path of the optical system is not lengthened, and the optical pickup 6 can be thinned.

  In the above example, the thin film 17 having the optical filter function is provided on the multi-lens 15 disposed in the optical path between the beam splitter 12 and the light receiving element 16, but the thin film 17 having the optical filter function is provided. The position is not limited to this position, and any position from the beam splitter 12 to the light receiving element 16 may be provided.

  For example, when an adjustment lens for performing magnification conversion and a correction plate for correcting aberrations such as astigmatism and coma are disposed in the optical path between the beam splitter 12 and the light receiving element 16. These adjustment lenses and correction plates may be provided with a thin film 17 having an optical filter function.

  It is also possible to provide a thin film 17 having an optical filter function on the incident surface 12a or the exit surface 12b of the beam splitter 12. In particular, when a thin film 17 having an optical filter function is provided on the exit surface 12b of the beam splitter 12, since the exit surface 12b is usually only provided with an AR coating for reducing reflection, an optical filter function is provided. It is possible to easily form the thin film 17 having the.

  Further, as shown in FIG. 5, a thin film 17 having an optical filter function can be provided on the surface of the package 16 b of the light receiving element 16. The surface of the package 16b is normally formed in a flat surface, and the thin film 17 having an optical filter function can be easily formed.

  In the above, the disk drive device 1 using two types of disc-shaped recording medium 100, DVD 100a and CD 100b, is shown as an example. However, the type of disc-shaped recording medium 100 is not limited to DVD 100a and CD 100b. Other discs such as a Blu-ray disc may be used.

  In addition, the present invention can be applied to a disk drive device using two types of disk-shaped recording media 100 having different use wavelengths and an optical pickup provided in the disk drive device, as well as three or more types of disk-shaped recording media having different use wavelengths. The present invention can also be applied to a disk drive apparatus in which 100 is used and an optical pickup provided in the disk drive apparatus. In this case, for example, when three types of disc-shaped recording medium 100 are used, at least one light receiving element that receives at least two types of laser beams having different wavelengths is required.

  The specific shapes and structures of the respective parts shown in the above-described best mode are merely examples of the implementation of the present invention, and the technical scope of the present invention is limited by these. It should not be interpreted in a general way.

FIG. 2 to FIG. 5 show the best mode for carrying out the present invention, and this figure is a schematic perspective view of a disk drive device. It is a conceptual diagram which shows the structure of an optical pick-up. It is a graph which shows the relationship between the wavelength which injects into the thin film with an optical filter function, and the transmittance | permeability. It is a graph which shows an example of the change of the received light quantity of the light receiving element by the presence or absence of the thin film with an optical filter function. It is a conceptual diagram which shows the example in which the thin film with an optical filter function was provided in the package of the light receiving element.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Disc-shaped recording medium, 1 ... Disk drive apparatus, 3 ... Disk table, 6 ... Optical pick-up, 7 ... Moving base, 8 ... Objective lens drive device, 12 ... Beam splitter, 12b ... Output surface, 16 ... Light receiving element, 16a ... light receiving part, 16b ... package, 17 ... thin film with optical filter function

Claims (6)

A moving base that moves in a radial direction of a disk-shaped recording medium mounted on a disk table, and an objective lens driving device arranged on the moving base, each disk-shaped toward a plurality of different disk-shaped recording media A plurality of laser beams having different wavelengths corresponding to the recording medium are emitted, information signals can be reproduced for different types of disk-shaped recording media, and at least one type of disk-shaped recording medium can be reproduced. An optical pickup capable of recording information signals,
A beam splitter that reflects or transmits the laser light according to the traveling direction of each emitted laser light;
And at least one light receiving element for receiving at least two types of laser beams having different wavelengths,
In the optical path of the laser beam from the beam splitter to the light receiving element, an element to which a thin film having an optical filter function having a wavelength selectivity and a different transmittance depending on the wavelength of the laser beam is provided. Optical pickup. The optical pickup according to claim 1, wherein a thin film having an optical filter function is provided on an emission surface of the beam splitter. The light receiving element has a package that covers a light receiving portion that receives laser light,
The optical pickup according to claim 1, wherein a thin film having an optical filter function is provided in a package of the light receiving element. Disc-shaped recording having a disc table on which a plurality of disc-shaped recording media of different types are individually mounted and rotated, and an objective lens driving device arranged on a moving base moved in the radial direction of the disc-shaped recording medium And an optical pickup configured to emit a plurality of laser beams having different wavelengths corresponding to the type of the medium, the information signal can be reproduced for each of the different types of disc-shaped recording media, and at least 1 A disk drive device capable of recording information signals on various types of disk-shaped recording media,
The above optical pickup
A beam splitter that reflects or transmits the laser light according to the traveling direction of each emitted laser light;
And at least one light receiving element for receiving at least two types of laser beams having different wavelengths,
In the optical path of the laser beam from the beam splitter to the light receiving element, an element to which a thin film having an optical filter function having a wavelength selectivity and a different transmittance depending on the wavelength of the laser beam is provided. Disk drive device. The disk drive device according to claim 4, wherein a thin film having an optical filter function is provided on an emission surface of the beam splitter. The light receiving element has a package that covers a light receiving portion that receives laser light,
The disk drive device according to claim 4, wherein a thin film having an optical filter function is provided in a package of the light receiving element.

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