JP2006236477A - Optical pickup and optical disk unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To generate three beams for obtaining tracking signals by diffracting light beams of different wavelengths by using a shared diffraction grating. <P>SOLUTION: This pickup has a 1st output section for emitting a light beam of a 1st wavelength, a 2nd output section for emitting a light beam of a 2nd wavelength, a 3rd output section for emitting a light beam of a 3rd wavelength, an objective lens 33 to focus the light beams outputted from the 1st-3rd output sections on the signal recording surface of an optical disk, a diffraction optical element 34 which is provided on the light path of the light beam of the 1st-3rd wavelengths and has a 1st diffraction part 34a formed on its one side and a 2nd diffraction part 34b formed on its other side, and a photo detector 35 to detect return light reflected on the optical disk. The 1st diffraction part 34a is formed by adhering materials having refraction indexes of different frequency characteristics. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical pickup and an optical disc apparatus for recording and / or reproducing information on a plurality of types of information recording media such as optical discs using light beams having different wavelengths.

  Currently, a next-generation optical disc format using a light source having a wavelength of about 400 to 410 nm by a blue-violet semiconductor laser is employed.

  In providing an optical pickup compatible with these next-generation optical discs, those having compatibility with optical discs having different formats such as conventional CD (Compact Disc) and DVD (Digital Versatile Disc) are desired. Thus, there is a need for an optical pickup and an optical disk apparatus that have compatibility between optical disks of different formats that have different disk structures and accompanying laser specifications.

  As an apparatus having compatibility between optical discs of different formats, a configuration in which light beams of different wavelengths emitted from the emission units provided in a plurality of light source units are condensed on the signal recording surface of each optical disc, or one Some have a configuration in which light beams of different wavelengths emitted from a plurality of emission units provided in a light source unit are condensed on a signal recording surface of each optical disc.

  In such an optical pickup, when a diffraction grating is provided to generate three beams for obtaining a tracking signal at the time of recording, if an optimum beam is selected for a light beam of a certain wavelength, a light beam of another wavelength is transmitted. There is a possibility that problems such as an extremely low rate may occur.

  As an optical pickup that generates three beams for obtaining tracking signals with respect to light beams having different wavelengths, for example, an optical pickup disclosed in Japanese Patent Application Laid-Open No. 2003-6891 is known (see Patent Document 1).

  The optical pickup shown in Patent Document 1 includes a diffraction grating for two wavelengths. However, such an optical pickup is not compatible with an optical pickup that realizes three-wavelength compatibility, and a sufficient diffraction efficiency cannot be obtained.

  Therefore, in the conventional optical pickup, in order to generate three beams for obtaining the tracking signal, it is necessary to arrange three light source units and three diffraction gratings in the vicinity of each light source unit. It became complicated and hindered miniaturization.

JP 2003-6891 A

  An object of the present invention is to diffract light beams of different wavelengths by a common diffraction grating to generate three beams for obtaining a tracking signal, which is a good signal for optical disks having different formats. An optical pickup capable of reading and writing data and an optical disc apparatus using the optical pickup are provided.

  In order to achieve this object, an optical pickup according to the present invention includes a first emitting unit that emits a light beam having a first wavelength, a second emitting unit that emits a light beam having a second wavelength, A third emission unit that emits a light beam having a wavelength of 3, an objective lens that focuses the light beams emitted from the first to third emission units on the signal recording surface of the optical disc, and first to third components A diffraction grating having a first diffractive part provided on one side and a second diffractive part provided on the other side, and return light reflected by the optical disc is detected on the optical path of the light beam having the wavelength of The first diffractive portion is formed by bonding bonding members having different frequency characteristics of refractive index.

  In order to achieve the above-described object, an optical disc apparatus according to the present invention includes an optical pickup that records and / or reproduces information on a plurality of different types of optical discs, and a disc rotation driving unit that rotates the optical disc. In the optical disc apparatus, the optical pickup includes a first emitting unit that emits a light beam having a first wavelength, a second emitting unit that emits a light beam having a second wavelength, and a light beam having a third wavelength. A third emission section that emits light, an objective lens that condenses the light beams emitted from the first to third emission sections on the signal recording surface of the optical disc, and the light beams of the first to third wavelengths A diffraction grating disposed on the road and having a first diffractive part provided on one side and a second diffractive part provided on the other side, and a photodetector for detecting return light reflected by the optical disk The first round Parts is formed by the frequency characteristic of the refractive index is different from the bonding member is bonded.

  The optical pickup according to the present invention can diffract light beams of different wavelengths by a common diffraction grating and generate three beams with optimum transmittance and diffraction efficiency, respectively, for optical disks having different formats. Since an optimal tracking signal can be obtained, good signal reading and writing can be performed on a plurality of types of optical discs, miniaturization and compatibility with a plurality of types of optical discs can be realized.

  The optical disk apparatus according to the present invention can diffract light beams of different wavelengths by a common diffraction grating and generate three beams with optimum transmittance and diffraction efficiency, respectively, for optical disks having different formats. Since an optimal tracking signal can be obtained, good signal recording and reproduction can be performed for a plurality of types of optical discs, compatibility with a plurality of types of optical discs can be realized, and the configuration can be simplified and miniaturized. .

  Hereinafter, an optical disk apparatus using an optical pickup to which the present invention is applied will be described with reference to the drawings.

  As shown in FIG. 1, an optical disc apparatus 1 to which the present invention is applied includes an optical pickup 3 for recording / reproducing information from / on an optical disc 2, a spindle motor 4 as a driving means for rotating the optical disc 2, and an optical pickup 3. And a feed motor 5 for moving the optical disk 2 in the radial direction. This optical disk apparatus 1 is an optical disk apparatus that realizes compatibility between three standards for recording and / or reproducing (hereinafter referred to as recording / reproducing) with respect to three types of optical disks 2 having different formats.

  The optical disk 2 used here is, for example, a CD (Compact Disc), a DVD (Digital Versatile Disc), a CD-R (Recordable) and a DVD-R (Recordable) that allow additional recording of information, and information can be rewritten. CD-RW (ReWritable), DVD-RW (ReWritable), DVD + RW (ReWritable), and other optical discs, and high-density recording using a semiconductor laser with a short emission wavelength of about 405 nm (blue-violet) It is a density recording optical disk, a magneto-optical disk, or the like.

  In particular, as the three types of optical discs in which information is reproduced or recorded by the optical disc apparatus 1 in the following, a high-density recording using a light beam having a protective substrate thickness of 0.1 mm and a wavelength of about 405 nm as recording / reproducing light is possible. Optical disk 11, a second optical disk 12 such as a DVD using a light beam having a protective substrate thickness of 0.6 mm and a wavelength of about 655 nm as recording / reproducing light, and a light beam having a protective substrate thickness of 1.2 mm and a wavelength of about 785 nm Will be described as being used with a third optical disk 13 such as a CD that uses the recording / reproducing light.

  In the optical disc apparatus 1, the spindle motor 4 and the feed motor 5 are driven and controlled in accordance with the disc type by a servo control unit 9 that is controlled based on a command from a system controller 7 that also serves as a disc type discriminating unit. The first optical disk 11, the second optical disk 12, and the third optical disk 13 are driven at a predetermined number of rotations.

  The optical pickup 3 is an optical pickup having a three-wavelength compatible optical system. The optical pickup 3 irradiates a recording layer of an optical disc having a different standard with a light beam having a different wavelength and detects reflected light from the recording layer of the light beam. The optical pickup 3 supplies a signal corresponding to each light beam from the detected reflected light to the preamplifier unit 14.

  The output of the preamplifier unit 14 is sent to a signal modulator / demodulator and an error correction code block (hereinafter referred to as a signal modulation / demodulation & ECC block) 15. The signal modulation / demodulation and ECC block 15 performs signal modulation, demodulation, and addition of ECC (error correction code). The optical pickup 3 irradiates the recording layer of the optical disc 2 rotating according to the signal modulation / demodulation and the command of the ECC block 15, and records or reproduces the signal on the optical disc 2.

  The preamplifier unit 14 is configured to generate a focus error signal, a tracking error signal, an RF signal, and the like based on a signal corresponding to a light beam detected differently for each format. In accordance with the type of the optical disk 2 to be recorded or reproduced, predetermined processing such as demodulation and error correction processing based on the standard of the optical disk 2 is performed by the servo control circuit 9, the signal modulation / demodulation, the ECC block 15, and the like. .

  Here, for example, if the recording signal demodulated by the signal modulation / demodulation & ECC block 15 is for data storage of a computer, it is sent to the external computer 17 via the interface 16. Thereby, the external computer 17 etc. can receive the signal recorded on the optical disk 2 as a reproduction signal.

  If the recording signal demodulated by the signal modulation / demodulation & ECC block 15 is for audio visual, it is converted from digital to analog by the D / A converter of the D / A and A / D converter 18 and supplied to the audio visual processor 19. Is done. Audio visual processing is performed by the audio visual processing unit 19 and transmitted to an external imaging / projection device (not shown) or the like via the audio visual signal input / output unit 20.

  In the optical pickup 3, for example, control of the feed motor 5 for moving to a predetermined recording track on the optical disk 2, control of the spindle motor 4, and two axes for holding an objective lens serving as light condensing means in the optical pickup 3 The servo control circuit 9 controls driving of the actuator in the focusing direction and driving control in the tracking direction.

  The laser control unit 21 controls the laser light source of the optical pickup 3. In particular, in this specific example, the laser control unit 21 performs control to vary the output power of the laser light source between the recording mode and the reproduction mode. Also, control is performed to vary the output power of the laser light source depending on the type of the optical disc 2. The laser control unit 21 switches the laser light source of the optical pickup 3 in accordance with the type of the optical disc 2 detected by the disc type determination unit 22.

  The disc type discriminating unit 22 can detect different formats of the optical disc 2 from the surface reflectance, the shape and the external shape difference between the first to third optical discs 11, 12 and 13.

  Each block constituting the optical disc apparatus 1 is configured to be able to perform signal processing based on the specification of the optical disc 2 to be mounted, according to the detection result in the disc type discriminating unit 22.

  The system controller 7 determines the type of the optical disk 2 based on the detection result sent from the disk type determination unit 22. As a method for discriminating the type of the optical disc, if the optical disc is of a type that is housed in a cartridge, there is a method in which a detection hole is provided in the cartridge and detected using a contact detection sensor or a push switch. In addition, the recording layer in the same optical disc is discriminated with respect to which recording layer is recorded / reproduced based on information by table information (TOC) recorded in premastered pits and grooves in the innermost circumference of the optical disc. Can be used.

  The servo control circuit 9 performs recording and / or reproduction by, for example, detecting the relative position between the optical pickup 3 and the optical disk 2 (including the case of detecting the position based on the address signal recorded on the optical disk 2). The area can be determined.

  The optical disc apparatus 1 configured as described above rotates the optical disc 2 by the spindle motor 4, drives and controls the feed motor 5 in accordance with a control signal from the servo control unit 9, and controls the optical pickup 3 on the optical disc 2. Information is recorded on and reproduced from the optical disc 2 by moving to a position corresponding to a desired recording track.

  Here, the recording / reproducing optical pickup 3 described above will be described in detail.

  As shown in FIG. 2, the optical pickup 3 to which the present invention is applied includes a first light source unit 31 having a first emitting unit that emits a light beam having a first wavelength, and a light beam having a second wavelength. A second light source part 32 having a second emission part for emitting and a third emission part for emitting a light beam of a third wavelength; and a light beam emitted from the first to third emission parts. An objective lens 33 that condenses on the signal recording surface of the optical disc 2, a first diffractive portion 34a that is disposed on the optical path of the light beam having the first to third wavelengths, and that is provided on one side, and is provided on the other side. A diffraction grating 34 having a second diffraction section 34b, and a photodetector 35 for detecting return light reflected by the signal recording surface.

  The optical pickup 3 is disposed between the first to third emission parts and the objective lens 33, and couples a coupling lens 36 that converts the divergence angle of the light beam emitted from the first to third emission parts. And an aberration correction unit 37 that is provided between the coupling lens 36 and the objective lens 33 and corrects the aberration based on the signal detected by the photodetector 35, and between the aberration correction unit 37 and the objective lens 33. A first beam splitter 38, and first and second light source sections as an optical path branching unit that is provided in the optical path and branches the optical path of the return light reflected by the signal recording surface from the optical path of the forward path light and guides it to the photodetector 35. 31 and 32 and the diffraction grating 34, and an optical path for combining the optical path of the light beam emitted from the first light source unit 31 and the optical path of the light beam emitted from the second light source unit 32. As a synthesis means, the second video And a beam splitter 39.

  The first light source unit 31 includes a first emission unit that emits a light beam having a first wavelength of about 405 nm to the first optical disc 11. The second light source unit 32 includes a second emitting unit that emits a light beam having a second wavelength of about 655 nm to the second optical disc 12 and a wavelength of about 785 nm to the third optical disc 13. And a third emission part for emitting the third light beam.

  The second beam splitter 39 has, for example, a mirror surface 39a having wavelength selectivity. The mirror surface 39a transmits the light beam emitted from the first emission part of the first light source part 31, and transmits the light beam emitted from the second and third emission parts of the second light source part 32. By reflecting, the optical paths of the respective light beams emitted from the first to third emission parts can be synthesized.

  The diffraction grating 34 generates ± first-order light for obtaining a tracking signal. That is, the light beam having the first to third wavelengths is divided into three main beams having a large amount of light and the light amount having a small amount of light. Generate side beams.

  That is, the first diffractive portion 34a provided on the output side surface of the diffraction grating 34 is formed in a lattice shape with a predetermined groove depth and width as shown in FIG. Thus, the joining members B having different refractive index frequency characteristics are joined together. The diffractive surface 34c is formed in a lattice shape, and the base material A and the joining member B are joined without a gap.

The first diffracting section 34a diffracts the light beams B ₁ and B ₃ having the first and third wavelengths, and makes a part of them ± 1st order diffracted lights B ₁₁ and B ₃₁ that become side beams, and the remaining large It is assumed that 0th-order diffracted lights B ₁₀ and B ₃₀ that pass through the portion and become the main beam. Further, the first diffractive portion 34a transmits almost the entire amount of the light beams B ₂₀ and B ₂₁ having the second wavelength.

  The first diffractive section 34a can diffract the light beams of the first and third wavelengths as side beams by the amount of light necessary for obtaining the tracking signal, and transmits almost all of the light beams of the second wavelength. Further, the material of the base material A and the joining member B and the lattice-like groove depth are determined.

  The second diffractive portion 34b provided on the incident side surface of the diffraction grating 34 is formed in a lattice shape with a predetermined groove depth and width, and the joining member is not joined. Note that the second diffractive portion may be configured to join a joining member in the same manner as the first diffractive portion, and an example in which the joining member is joined to the second diffractive portion will be described later.

Second diffractive portion 34b diffracts the light beam B ₂ of the second wavelength, and ± 1-order diffracted light B ₂₁ that a part of the side beams, the main beam is transmitted through the remaining majority 0-order diffracted light _{B 20.} In addition, the second diffractive portion 34b transmits almost all of the light beams B ₁ and B ₃ having the first and third wavelengths. The second diffractive section 34b can diffract the light beam of the second wavelength as a side beam by the amount of light necessary for obtaining the tracking signal, and transmits almost all of the light beams of the first and third wavelengths. Further, the material of the base material A and the lattice-like groove depth are determined.

  Next, the material of the base material A and the joining member B of the first and second diffractive portions 34a and 34b and the lattice-like groove depth will be described. In "Table 1", the refractive index with respect to each use wavelength of the material A of a base material and the material B of a joining member is shown.

FIG. 4 shows changes in the diffraction efficiency of the light beams having the first to third wavelengths when the groove depth of the first diffractive portion 34a joined by the base material A and the joining member B is changed. FIG. 5 shows the diffraction efficiencies of the light beams of the first to third wavelengths when the groove depth of the second diffractive portion 34b to which the joining member is not joined when the material A is the base material is changed. Showing change. 4 and 5, each curve indicates the ratio of the amount of each diffracted light emitted to the total light amount of the incident light beam, that is, the diffraction efficiency. The curves L ₁₀ and L ₁₁ are respectively The light beam 0th order diffracted light (transmission) and ± 1st order diffracted light with the first wavelength (405 nm) are shown, and the curves L ₂₀ and L ₂₁ are the 0th order diffracted light of the light beam with the second wavelength (655 nm), respectively. (Transmission) indicates ± 1st order diffracted light, and curves L ₃₀ and L ₃₁ indicate 0th order diffracted light (transmitted) and ± 1st order diffracted light of a light beam having a third wavelength (785 nm), respectively. .

  As described above, the first diffracting unit 34a can diffract the light beam having the first and third wavelengths as a side beam by the amount of light necessary for obtaining the tracking signal, and the light beam having the second wavelength can be diffracted. The groove depth is determined to be about 7.6 μm (7600 nm) so that substantially the entire amount can be transmitted. The second diffractive portion 34b can diffract the light beam of the second wavelength as a side beam by the amount of light necessary for obtaining the tracking signal, and transmits almost all of the light beams of the first and third wavelengths. The groove depth is determined to be about 1.4 μm (1400 nm). Table 2 shows the diffraction efficiencies of the first-order diffracted light when the first and second diffracting portions 34a and 34b are 7.6 μm and 1.4 μm, respectively.

  The diffraction grating 34 having the first and second diffracting portions 34a and 34b diffracts light beams of two different wavelengths by a diffractive portion provided on one surface when a light beam of different wavelengths is incident. As a result, a side beam for obtaining a tracking signal with an optimal amount of light can be obtained, and the remaining light beam of one wavelength can be transmitted, and is diffracted on one surface by a diffractive portion provided on the other surface. It is possible to obtain a side beam for transmitting a two-wavelength light beam and diffracting the remaining one-wavelength light beam to obtain a tracking signal with an optimum light amount. In other words, the diffraction grating 34 can diffract light beams having different wavelengths and generate three beams (main beam and side beam) with optimum transmittance and diffraction efficiency, respectively.

  The coupling lens 36 converts the divergence angle of the light beam emitted from each emission part of the first light source part 31 or the second light source part 32 and emits it as the substantially parallel light to the aberration correction unit 37 side.

  The aberration correction unit 37 is composed of, for example, a liquid crystal optical element that can change the refractive index by changing the voltage to be applied, and changes the refractive index based on the signal detected by the photodetector 35. Correct aberrations. In this embodiment, the liquid crystal optical element is provided as the aberration correction means. However, the present invention is not limited to this, and an actuator that moves the coupling lens 36 in the optical axis direction is provided as the aberration correction means. It may be configured. When the coupling lens actuator is provided, the generated aberration can be corrected by the actuator and the coupling lens.

  The objective lens 33 is a three-wavelength compatible objective lens. The numerical aperture of the objective lens 33 is 0.85 for the first wavelength, 0.60 for the second wavelength, and 0.45 for the third wavelength. The objective lens 33 can focus the light beam having the first wavelength whose divergence angle has been converted by the coupling lens 36 on the first optical disk 11 having the first protective substrate thickness. Further, the second wavelength light beam having the divergence angle converted by the coupling lens 36 is applied to the second disk 12 having the second protective substrate thickness, and the third protective substrate thickness is applied to the third disk. A light beam having a third wavelength whose divergence angle is converted by the coupling lens 36 can be focused on the optical disk 13. The objective lens 33 achieves compatibility with three different wavelengths by, for example, a so-called zone division type lens.

  On the incident side of the objective lens 33, an aperture filter 40 is provided as aperture limiting means for limiting the aperture of the light beam incident on the objective lens 33. The aperture filter 40 has a wavelength dependency in which the aperture diameter changes depending on the wavelength, and is 0.85 for the first wavelength, 0.60 for the second wavelength, 0.45 with respect to the wavelength of. As the aperture filter 40, for example, a hologram or the like is used.

  The first beam splitter 38 is provided on the optical path between the aberration correcting unit 37 and the objective lens 33, and the mirror surface 38a transmits the forward light to the objective lens 33 side, and the return light from the optical disc 2. Are branched off from the optical path toward the photodetector 35 and emitted. Between the first beam splitter 38 and the light detector 35, an optical element 41 such as a cylindrical lens for focusing the light beam branched in the optical path on the light receiving surface of the light detector 35 is provided.

  The photodetector 35 has, on its light receiving surface, a main beam photodetector for receiving the main beams of the first to third wavelength light beams divided into three beams by the diffraction grating 34, and a side for receiving the side beams. A beam photodetector. The photodetector 35 can obtain a tracking error signal from the side beam received by the side beam photodetector.

  Next, the optical path of the light beam emitted from the first and second light source units 31 and 32 in the optical pickup 3 will be described. First, an optical path when information is read or written on the first optical disc 11 will be described.

  The disc type discriminating unit 22 that discriminates that the type of the optical disc 2 is the first optical disc 11 emits a light beam having the first wavelength from the first emitting unit of the first light source unit 31.

  As shown in FIGS. 2 and 3, the light beam having the first wavelength emitted from the first emission part of the first light source part 31 is transmitted through the mirror surface 39a of the second beam splitter 39, and Incident on the diffraction grating 34. The light beam having the first wavelength incident on the diffraction grating 34 is transmitted through the second diffractive portion 34b provided on the incident side surface and is transmitted to the first diffractive portion 34a provided on the output side surface. When a part is diffracted and the rest is transmitted, it is divided into three beams of ± 1st order diffracted light that becomes a side beam and 0th order diffracted light that becomes a main beam and is emitted. Here, the light beam of the first wavelength is divided into three beams by the diffraction grating 34 with optimum diffraction efficiency.

  The light beam having the first wavelength divided into the three beams with the diffraction efficiency optimum for the diffraction grating 34 is made into substantially parallel light by the coupling lens 36, and the aberration generated on the signal recording surface of the optical disk by the aberration correction means 37. The light is corrected and incident on the first beam splitter 38.

  The light beam having the first wavelength incident on the first beam splitter 38 is transmitted through the mirror surface 38 a, the numerical aperture is set to 0.85 by the aperture filter 40, and the first optical disk 11 by the objective lens 33. Is appropriately condensed on the signal recording surface 11a.

  The light beam collected on the first optical disk 11 is reflected by the signal recording surface 11a, passes through the objective lens 33, is reflected by the first beam splitter 38, and is emitted to the photodetector 35 side. The light beam having the first wavelength branched by the first beam splitter 38 is focused on the light receiving surface of the photodetector 35 by the optical element 41 and detected. At this time, the main beam is incident on the main beam photodetector of the photodetector 35, and the side beam is incident on the side beam photodetector. A tracking error signal is obtained by the side beam incident on the side beam photodetector of the photodetector 35.

  Next, an optical path when information is read from or written to the second optical disk 12 will be described.

  The disc type discriminating unit 22 that discriminates that the type of the optical disc 2 is the second optical disc 12 emits a light beam having the second wavelength from the second emitting unit of the second light source unit 32.

  The light beam having the second wavelength emitted from the second emission part of the second light source part 32 is reflected by the mirror surface 39a of the second beam splitter 39 as shown in FIGS. Incident on the diffraction grating 34. The light beam having the second wavelength incident on the diffraction grating 34 is partly diffracted by the second diffractive portion 34b provided on the incident-side surface and is transmitted through the rest, thereby becoming a side beam. The beam is divided into three beams including ± first-order diffracted light and zero-order diffracted light serving as a main beam, and is transmitted through the first diffracting portion 34a and emitted. Here, the light beam of the second wavelength is divided into three beams by the diffraction grating 34 with the optimum diffraction efficiency.

  The light beam of the second wavelength divided into three beams with the optimal diffraction efficiency for the diffraction grating 34 is made into substantially parallel light by the coupling lens 36, and the aberration generated on the signal recording surface of the optical disk by the aberration correction means 37. The light is corrected and incident on the first beam splitter 38.

  The light beam having the second wavelength incident on the first beam splitter 38 passes through the mirror surface 38 a, has a numerical aperture of 0.60 by the aperture filter 40, and is set to the second optical disk 12 by the objective lens 33. Are appropriately condensed on the signal recording surface 12a.

  Since the optical path on the return path side of the light beam reflected by the signal recording surface 12a of the second optical disc 12 is the same optical path as the light beam having the first wavelength described above, description thereof will be omitted.

  Next, an optical path when information is read from or written to the third optical disc 13 will be described.

  The disc type discriminating unit 22 that discriminates that the type of the optical disc 3 is the third optical disc 13 emits a light beam having the third wavelength from the third emitting unit of the second light source unit 32.

  As shown in FIGS. 2 and 3, the light beam of the third wavelength emitted from the third emission part of the second light source part 32 is reflected by the mirror surface 39a of the second beam splitter 39, and Incident on the diffraction grating 34. The light beam of the third wavelength incident on the diffraction grating 34 is transmitted through the second diffractive portion 34b provided on the incident side surface and is transmitted to the first diffractive portion 34a provided on the output side surface. When a part is diffracted and the rest is transmitted, it is divided into three beams of ± 1st order diffracted light that becomes a side beam and 0th order diffracted light that becomes a main beam and is emitted. Here, the light beam of the third wavelength is divided into three beams by the diffraction grating 34 with optimum diffraction efficiency.

  The light beam of the third wavelength divided into three beams with the diffraction efficiency optimum for the diffraction grating 34 is made into substantially parallel light by the coupling lens 36, and the aberration generated on the signal recording surface of the optical disk by the aberration correction means 37 is corrected. The light is corrected and incident on the first beam splitter 38.

  The light beam of the third wavelength incident on the first beam splitter 38 is transmitted through the mirror surface 38 a, the numerical aperture is made 0.45 by the aperture filter 40, and the third optical disk 13 is made by the objective lens 33. Is appropriately condensed on the signal recording surface 13a.

  Since the optical path on the return path side of the light beam reflected by the signal recording surface 13a of the third optical disc 13 is the same optical path as the light beam having the first wavelength described above, description thereof will be omitted.

  The optical pickup 3 to which the present invention is applied diffracts the light beams of the first to third wavelengths, which are different wavelengths, by the common diffraction grating 34, and generates three beams with optimum transmittance and diffraction efficiency, respectively. Because it is possible to obtain an optimal tracking signal for optical discs with different formats, it is possible to read and write good signals to three different types of optical discs, miniaturization and compatibility with three wavelengths. To realize.

  In the optical pickup 3, the diffraction grating 34 is formed by bonding the first diffractive portion 34 a provided on one surface of the diffraction grating 34 to the bonding member. The diffractive portions provided on the surface may be formed by joining the joining members.

  Next, an example using the diffraction grating 44 shown in FIG. 2 and FIG. 6 in which the diffraction portions provided on both sides are joined by joining members as the diffraction grating constituting the optical pickup 3 will be described. To do.

  The diffraction grating 44 has a first diffractive part 44a provided on one side and a second diffractive part 44b provided on the other side, and generates ± first order light for obtaining a tracking signal. That is, the light beams having the first to third wavelengths are divided into three to generate a main beam with a large amount of light and a side beam with a small amount of light.

  That is, the first diffractive portion 44a provided on the exit side surface of the diffraction grating 44 is formed in a lattice shape with a predetermined groove depth and width as shown in FIG. The first joining members D having different refractive index frequency characteristics are joined together. The diffractive surface 44c is formed in a lattice shape, and the base material C and the first joining member D are joined without a gap.

The first diffracting section 44a diffracts the light beams B ₁ and B ₂ having the first and second wavelengths, and makes a part of them ± 1st order diffracted lights B ₁₁ and B ₂₁ that become side beams, and the remaining large It is assumed that 0th-order diffracted lights B ₁₀ and B ₂₀ that pass through the portion and become the main beam. The first diffractive portion 44a transmits substantially the entire amount of the light beams B ₃₀ and B ₃₁ having the third wavelength.

  The first diffracting unit 44a can diffract the light beam having the first and second wavelengths as a side beam by an amount of light necessary for obtaining the tracking signal, and transmits almost the entire light beam having the third wavelength. Further, the material of the base material C and the first joining member D and the lattice-like groove depth are determined.

  The second diffractive portion 44b provided on the incident-side surface of the diffraction grating 44 is formed in a grating shape with a predetermined groove depth and width, and has a refractive index frequency characteristic with respect to the substrate C. It is formed by joining different second joining members E. The diffractive surface 44d is formed in a lattice shape, and the base material C and the second joining member E are joined without a gap.

The second diffraction portion 44b, the third diffracts the light beam B ₃ wavelengths, and ± 1-order diffracted light B ₃₁ that a part of the side beams, the main beam is transmitted through the remaining majority 0-order diffracted light _{B 30.} The second diffractive portion 44b transmits substantially the entire amount of the light beams B ₁ and B ₂ having the first and second wavelengths. The second diffracting unit 44b can diffract the light beam of the third wavelength as a side beam by the amount of light necessary for obtaining the tracking signal, and transmits almost the entire amount of the light beam of the first and second wavelengths. Further, the material of the base material C and the second joining member E and the lattice-like groove depth are determined.

  Next, the specific substrate C of the first and second diffraction portions 44a and 44b, the materials of the first and second bonding members D and E, and the lattice-like groove depth will be described. Table 3 shows the refractive index of each of the base material C and the first and second joining members D and E with respect to each wavelength used. Here, the first and second joining members D and E are formed of the same material, but may be formed of materials having different refractive index frequency characteristics.

In FIG. 7, the groove depth of the first diffractive portion 44a (or the second diffractive portion 44b) joined by the base material C and the first joining member D (or the second joining member E) is shown. 6 shows changes in the diffraction efficiency of the light beams having the first to third wavelengths when is changed. In FIG. 7, each curve indicates the ratio of the amount of emitted diffracted light to the total amount of incident light beam, that is, the diffraction efficiency. The curves L ₁₀ and L ₁₁ are respectively the first wavelength zero-order diffracted light (transmitted) light beam (405 nm), is indicative of the ± 1-order diffracted light, the curve _{L 20, L 21} is 0-order diffracted light of the light beam of the respective second wavelength (655 nm) (transmission ), ± 1st order diffracted light, and curves L ₃₀ and L ₃₁ indicate 0th order diffracted light (transmission) and ± 1st order diffracted light of a light beam having a third wavelength (785 nm), respectively.

  As described above, the first diffracting unit 44a can diffract the light beam having the first and second wavelengths as a side beam by the amount of light necessary for obtaining the tracking signal, and the light beam having the third wavelength can be diffracted. The groove depth is determined to be about 8.7 μm (8700 nm) so that substantially the entire amount can be transmitted. Then, the second diffracting unit 44b can diffract the light beam having the third wavelength as a side beam by the amount of light necessary for obtaining the tracking signal, and transmits almost all of the light beams having the first and second wavelengths. The groove depth is determined to be about 8.0 μm (8000 nm). Table 4 shows the diffraction efficiencies of the first-order diffracted light when the first and second diffracting portions 44a and 44b are 8.7 μm and 8.0 μm, respectively.

  The diffraction grating 44 having the first and second diffracting portions 44a and 44b diffracts light beams having two different wavelengths by a diffractive portion provided on one surface thereof when a light beam having different wavelengths is incident thereon. As a result, a side beam for obtaining a tracking signal with an optimal amount of light can be obtained, and the remaining light beam of one wavelength can be transmitted, and is diffracted on one surface by a diffractive portion provided on the other surface. It is possible to obtain a side beam for transmitting a two-wavelength light beam and diffracting the remaining one-wavelength light beam to obtain a tracking signal with an optimum light amount. In other words, the diffraction grating 44 can diffract light beams having different wavelengths and generate three beams (main beam and side beam) with optimum transmittance and diffraction efficiency, respectively. Furthermore, since the diffraction grating 44 is formed by joining the diffractive portions on both sides thereof with joining members having different refractive index frequency characteristics, the diffraction grating 44 can be adapted to light beams of various operating wavelengths and is more optimal. The diffraction efficiency and transmittance can be set, and the degree of freedom in designing the optical pickup can be improved by improving the diffraction efficiency and transmittance.

  Next, the optical path of the light beam emitted from the first and second light source units 31 and 32 in the optical pickup 3 using the diffraction grating 44 will be described. The optical path until the light enters the diffraction grating 44 and the optical path after the light exits from the diffraction grating 44 are the same as in the case where the above-described diffraction grating 34 is used, and a description thereof will be omitted.

  First, a case where information is read from or written to the first optical disc 11 will be described. As shown in FIGS. 2 and 6, the light beam having the first wavelength incident on the diffraction grating 44 through the same optical path as described above is a second diffractive portion provided on the incident-side surface. The first diffracted light that becomes a side beam and 0 that becomes the main beam are transmitted through 44b, partially diffracted by the first diffractive portion 44a provided on the exit side surface and transmitted through the remainder. The light is divided into three beams composed of the next diffracted light and emitted. Here, the light beam of the first wavelength is divided into three beams by the diffraction grating 44 with the optimum diffraction efficiency. The light beam having the first wavelength emitted from the diffraction grating 44 is collected on the optical disc via the same optical path as described above, and the light beam reflected by the signal recording surface is reflected on the light receiving surface of the photodetector 35. Focused and detected.

  Next, a case where information is read from or written to the second optical disc 12 will be described. As shown in FIGS. 2 and 6, the second wavelength light beam incident on the diffraction grating 44 via the same optical path as described above is provided on the incident-side surface. The first diffracted light that becomes a side beam and 0 that becomes the main beam are transmitted through 44b, partially diffracted by the first diffractive portion 44a provided on the exit side surface and transmitted through the remainder. The light is divided into three beams composed of the next diffracted light and emitted. Here, the light beam of the second wavelength is divided into three beams by the diffraction grating 44 with optimum diffraction efficiency. The light beam having the second wavelength emitted from the diffraction grating 44 is condensed on the optical disc through the same optical path as described above, and the light beam reflected by the signal recording surface is reflected on the light receiving surface of the photodetector 35. Focused and detected.

  Next, a case where information is read from or written to the third optical disc 13 will be described. As shown in FIGS. 2 and 6, the light beam of the third wavelength incident on the diffraction grating 44 via the optical path similar to the above is the second diffraction section provided on the incident side surface. 44b is partially diffracted and transmitted through the remainder, so that the first diffracting portion 44a is divided into three beams of ± 1st order diffracted light that becomes a side beam and 0th order diffracted light that becomes a main beam. Transmitted and emitted. Here, the light beam of the third wavelength is divided into three beams by the diffraction grating 44 with optimum diffraction efficiency. The light beam of the third wavelength emitted from the diffraction grating 44 is condensed on the optical disc via the same optical path as described above, and the light beam reflected by the signal recording surface is reflected on the light receiving surface of the photodetector 35. Focused and detected.

  The optical pickup 3 using the diffraction grating 44 diffracts the light beams having the first to third wavelengths, which are different wavelengths, by the common diffraction grating 44 and generates three beams with optimum transmittance and diffraction efficiency, respectively. In addition, since an optimal tracking signal can be obtained for optical discs with different formats, it is possible to read and write good signals for three different types of optical discs, miniaturization and three wavelengths. Realize compatibility.

  In the optical pickup 3 described above, the first to third emission units are configured to be arranged in the first light source unit 31 or the second light source unit 32. However, the present invention is not limited to this. For example, The first to third light emitting units are arranged in one light source unit, and the light beams of three different wavelengths emitted from the one light source unit are respectively optimized by a common diffraction grating. You may comprise so that 3 beams may be generated with the transmittance | permeability and diffraction efficiency.

  Next, the optical pickup 50 shown in FIG. 8 including a light source unit having first to third emission units will be described. In the following description, portions common to the optical pickup 3 described above are denoted by common reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 8, an optical pickup 50 to which the present invention is applied includes a first emission part that emits a light beam having a first wavelength, and a second emission part that emits a light beam having a second wavelength. , A light source unit 51 having a third emission unit that emits a light beam of a third wavelength, and the light recording beam emitted from the first to third emission units of the light source unit 51 to the signal recording surface of the optical disc 2 The objective lens 33 that condenses on the top, the first diffractive part 34a provided on one side, and the second diffractive part provided on the other side, disposed on the optical path of the light beams having the first to third wavelengths. And a photodetector 35 for detecting return light reflected by the signal recording surface.

  The optical pickup 50 is disposed between the light source unit 51 and the objective lens 33, and converts the divergence angle of the light beam emitted from the first to third emission units, and the coupling lens. 36 and the objective lens 33, and is provided between the aberration correction means 37 for correcting the aberration based on the signal detected by the photodetector 35, and between the aberration correction means 37 and the objective lens 33. A first beam splitter 38 is provided on the incident side of the objective lens 33 as an optical path branching means for branching the optical path of the return light reflected by the recording surface from the optical path of the forward light and leading it to the photodetector 35. An aperture filter 40 that limits the aperture of the incident light beam, and is provided between the first beam splitter 38 and the light detector 35, and focuses the light beam on the light receiving surface of the light detector 35. And a university element 41.

  The light source unit 51 includes a first emission unit that emits a light beam having a first wavelength of about 405 nm to the first optical disc 11, and a second wavelength of about 655 nm to the second optical disc 12. And a third emission part for emitting a third light beam having a wavelength of about 785 nm to the third optical disk 13.

  Next, the optical path of the light beam emitted from the light source unit 51 in the optical pickup 50 will be described. First, an optical path when information is read or written on the first optical disc 11 will be described.

  The disc type discriminating unit 22 that discriminates that the type of the optical disc 2 is the first optical disc 11 emits a light beam having the first wavelength from the first emitting unit of the light source unit 51.

  The light beam having the first wavelength emitted from the first emission unit of the light source unit 51 is incident on the diffraction grating 34. The light beam having the first wavelength incident on the diffraction grating 34 is transmitted through the second diffractive portion 34b provided on the incident side surface and is transmitted to the first diffractive portion 34a provided on the output side surface. When a part is diffracted and the rest is transmitted, it is divided into three beams of ± 1st order diffracted light that becomes a side beam and 0th order diffracted light that becomes a main beam and is emitted. Here, the light beam of the first wavelength is divided into three beams by the diffraction grating 34 with optimum diffraction efficiency.

  Since the optical path of the light beam having the first wavelength after being divided into three beams with the diffraction efficiency optimum for the diffraction grating 34 is the same as that of the optical pickup 3 described above, the description thereof will be omitted.

  Next, an optical path when information is read from or written to the second optical disk 12 will be described.

  The disc type discriminating unit 22 that discriminates that the type of the optical disc 2 is the second optical disc 12 emits a light beam having the second wavelength from the second emitting unit of the light source unit 51.

  The light beam having the second wavelength emitted from the second emission unit of the light source unit 51 is incident on the diffraction grating 34. The light beam having the second wavelength incident on the diffraction grating 34 is partly diffracted by the second diffractive portion 34b provided on the incident-side surface and is transmitted through the rest, thereby becoming a side beam. The beam is divided into three beams including ± first-order diffracted light and zero-order diffracted light serving as a main beam, and is transmitted through the first diffracting portion 34a and emitted. Here, the light beam of the second wavelength is divided into three beams by the diffraction grating 34 with the optimum diffraction efficiency.

  Since the optical path of the light beam of the second wavelength after being divided into three beams with the diffraction efficiency optimum for the diffraction grating 34 is the same as that of the optical pickup 3 described above, the description thereof will be omitted.

  Next, an optical path when information is read from or written to the third optical disc 13 will be described.

  The disc type discriminating unit 22 that discriminates that the type of the optical disc 3 is the third optical disc 13 emits the light beam having the third wavelength from the third emitting unit of the light source unit 51.

  The light beam having the third wavelength emitted from the third emission unit of the light source unit 51 is incident on the diffraction grating 34. The light beam of the third wavelength incident on the diffraction grating 34 is transmitted through the second diffractive portion 34b provided on the incident side surface and is transmitted to the first diffractive portion 34a provided on the output side surface. When a part is diffracted and the rest is transmitted, it is divided into three beams of ± 1st order diffracted light that becomes a side beam and 0th order diffracted light that becomes a main beam and is emitted. Here, the light beam of the third wavelength is divided into three beams by the diffraction grating 34 with optimum diffraction efficiency.

  Since the optical path of the light beam of the third wavelength after being divided into three beams with the diffraction efficiency optimum for the diffraction grating 34 is the same as that of the optical pickup 3 described above, the description thereof will be omitted.

  The optical pickup 50 to which the present invention is applied diffracts the light beams of the first to third wavelengths having different wavelengths by the common diffraction grating 34 and generates three beams with optimum transmittance and diffraction efficiency, respectively. Because it is possible to obtain an optimal tracking signal for optical discs with different formats, it is possible to read and write good signals to three different types of optical discs, miniaturization and compatibility with three wavelengths. Is realized.

  In the optical pickup 50, as in the optical pickup 3, the diffraction gratings 44 formed by joining the diffractive portions provided on both sides are joined to the above-described diffraction grating 34. It may be configured.

  Since the optical disk apparatus 1 to which the present invention is applied includes the optical pickups 3 and 50 described above, the light beams having different wavelengths are diffracted by the common diffraction gratings 34 and 44, and three beams are obtained with the optimum transmittance and diffraction efficiency, respectively. And an optimal tracking signal can be obtained for optical discs of different formats, so that good signal recording and reproduction can be performed for a plurality of types of optical discs. In addition to realizing compatibility, the configuration can be simplified and downsized.

1 is a block circuit diagram showing a configuration of an optical disc apparatus to which the present invention is applied. It is an optical path diagram showing an optical system of an optical pickup to which the present invention is applied. It is sectional drawing explaining the structure of the diffraction grating which comprises the optical pick-up to which this invention is applied. 6 shows changes in transmittance and diffraction efficiency of zero-order light and ± first-order light of a light beam of each wavelength accompanying a change in groove depth of a first diffraction portion of a diffraction grating constituting an optical pickup to which the present invention is applied. FIG. The change of the transmittance | permeability of 0th-order light and +/- 1st-order light of the light beam of each wavelength accompanying the change of the groove depth of the 2nd diffraction part of the diffraction grating which comprises the optical pickup to which this invention is applied, and diffraction efficiency are shown. FIG. It is sectional drawing explaining the other structure of the diffraction grating which comprises the optical pick-up to which this invention is applied. Another example of the diffraction grating constituting the optical pickup to which the present invention is applied The transmittance of the 0th-order light and ± 1st-order light of the light beam of each wavelength accompanying the change of the groove depth of the first and second diffraction portions It is a figure which shows the change of diffraction efficiency. It is an optical path figure which shows the other example of the optical system of the optical pick-up to which this invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical disk apparatus, 2 Optical disk, 3 Optical pick-up, 4 Spindle motor, 5 Feed motor, 9 Servo control circuit, 22 Disk type discrimination | determination part, 31 1st light source part, 32 2nd light source part, 33 Objective lens, 34 Diffraction Grating, 35 photodetector, 36 coupling lens, 37 aberration correction means, 38 first beam splitter, 39 second beam splitter, 40 aperture filter, 41 optical element

Claims (7)

A first emission part for emitting a light beam of a first wavelength;
A second emission part for emitting a light beam of a second wavelength;
A third emission part for emitting a light beam of a third wavelength;
An objective lens for condensing the light beam emitted from the first to third emission portions on the signal recording surface of the optical disc;
A diffraction grating disposed on the optical path of the light beam having the first to third wavelengths and having a first diffractive portion provided on one side and a second diffractive portion provided on the other side;
A photodetector for detecting the return light reflected by the optical disc,
The first diffractive portion is an optical pickup formed by bonding bonding members having different refractive index frequency characteristics. The first wavelength is about 405 nm;
The second wavelength is about 655 nm;
2. The optical pickup according to claim 1, wherein the third wavelength is about 785 nm.   3. The optical pickup according to claim 1, further comprising a light source unit provided with the first to third emission units.   3. The optical pickup according to claim 1, wherein the second diffractive portion is formed by joining second joining members having different refractive index frequency characteristics. The first diffracting unit diffracts a part of the light beams having the first and third wavelengths and transmits the remaining light as ± first order diffracted light to form 0th order diffracted light, and the light having the second wavelength. Let the beam pass,
The second diffracting unit diffracts a part of the light beam having the second wavelength and transmits the remaining light as ± 1st order diffracted light to form 0th order diffracted light, and the light having the first and third wavelengths. The optical pickup according to claim 1 or 2, wherein the beam is transmitted. In an optical disc apparatus comprising: an optical pickup that records and / or reproduces information with respect to a plurality of different types of optical discs; and a disc rotation driving unit that rotationally drives the optical disc.
The optical pickup includes a first emission unit that emits a light beam having a first wavelength;
A second emission part for emitting a light beam of a second wavelength;
A third emission part for emitting a light beam of a third wavelength;
An objective lens for condensing the light beam emitted from the first to third emission portions on the signal recording surface of the optical disc;
A diffraction grating disposed on the optical path of the light beam having the first to third wavelengths and having a first diffractive portion provided on one side and a second diffractive portion provided on the other side;
A photodetector for detecting the return light reflected by the optical disc,
The first diffractive portion is an optical disc apparatus formed by joining joining members having different frequency characteristics of refractive index. 7. The optical disc apparatus according to claim 6, wherein the second diffractive portion is formed by joining second joining members having different refractive index frequency characteristics.

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