JP2007280466A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device for easily constituting a compact photodetector and achieving a servo operation securely performing recording/reproducing operations to an information recording medium having a different recording density. <P>SOLUTION: The optical pickup device includes a semiconductor light receiving element 30, a first semiconductor laser 12 emitting a first laser beam LB1, a second semiconductor laser 13 emitting a second laser beam LB2, and an optical system defining an optical path of the first laser beam LB1 and the second laser beam LB2. The optical system includes a first hologram 17 and a second hologram 18. A hologram area of the second hologram 18 having different gratings separately is associated with a main beam of the second laser beam LB1 diffracted by the first hologram 17 and front and rear sub-beams, and irradiated therewith. Thus, the second hologram 18 corrects the optical path of the second laser beam P2, and the first laser beam LB1 and the second laser beam LB2 are received by a common light receiving part. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical pickup device used in an optical disc apparatus for optically recording or reproducing information on an information recording medium such as an optical disc.

  In recent years, information recording media such as optical disks and optical cards have attracted attention. Since these information recording media can record a large amount of information at a high density, their use is expanding not only as an external memory of a computer but also among various digital AV devices. An optical pickup device is used for writing information on the information recording medium and reading information from the information recording medium. A hologram is known as means for reducing the size, thickness and reliability of the optical pickup device.

  For example, in the optical pickup device disclosed in Japanese Patent Application Laid-Open No. 10-269588 (Patent Document 1), the optical pickup device is divided into two in the direction corresponding to the radial direction of the optical disc and further divided into two in the direction corresponding to the tangential direction of the optical disc. Thus, a hologram divided into a total of four hologram areas is used, and a separate grating is formed in each hologram area. In the pickup device, a focus error signal is detected by using a semicircular light beam diffracted in two adjacent hologram regions selected from the four divided hologram regions, and divided into four. A so-called phase difference signal (DPD) which is a track error signal (radial error signal) using a light beam diffracted in two non-adjacent hologram areas selected from the hologram area (that is, two hologram areas located diagonally opposite). Signal) is detected. For information reproduction, a light beam diffracted in all the four divided hologram regions is used.

  However, since the DPD signal used for the tracking servo uses the diffraction pattern of the reflected light from the already recorded pits, it is used for a read-only optical disk and a recorded optical disk on which information has already been recorded. It is effective for the tracking servo, but cannot be used for tracking servo for unrecorded discs. Therefore, a push-pull method or a differential push-pull method is used for tracking servo for an unrecorded disk. In these push-pull methods and differential push-pull methods, the detrack amount is detected by detecting the difference in the amount of light in a plurality of light receiving areas provided in the photodetector.

  For example, when the push-pull method is used, a difference in the light amount distribution of the light beam separated and diffracted by the hologram is detected by a two-divided photodetector, and a track error signal is generated based on this. However, when the objective lens moves in the radial direction and the optical axis of the reflected light from the optical disk is shifted or the optical disk is tilted, the center of the light beam is shifted to the position shifted from the light receiving center position of the two-part photodetector. In this case, an offset is generated in the differential signal output from the two-divided photodetector even though no tracking error has occurred, and it is determined that the signal is in the detrack state. There is a risk that.

Therefore, a differential push-pull method has been devised as a method for suppressing the occurrence of the offset. When the differential push-pull method is used, the light beam emitted from the light source is made into three beams using a diffraction grating into a main beam and two sub beams, and the front and rear sub beams with respect to the position of the main beam on the optical disk are changed. By shifting the position by ± 1 / 2n (n is an integer) track pitch, a track error signal is generated from the difference between the main beam signal and the sum of the front and rear sub-beam signals. As a result, a track error signal with no offset is obtained. An optical pickup device employing the differential push-pull method is disclosed in, for example, Japanese Patent Application Laid-Open No. 2001-273666 (Patent Document 2).

  When information is recorded on, for example, a DVD ± R disk using the differential push-pull method, it is necessary to set the grating direction (direction in which the grating extends) of the diffraction grating as follows. Considering the case where the grating direction of the diffraction grating is in the radial direction of the DVD ± R disc (that is, when the grating direction is perpendicular to the track), the front and rear sub-beams are diffracted in a direction orthogonal to the grating direction of the diffraction grating. Therefore, the position of the front and rear sub-beams on the DVD ± R disk is located on the same track as the position of the main beam on the DVD ± R disk. Therefore, if the grating direction of the diffraction grating is tilted by several degrees in the grating plane with respect to this state, the position of the front and rear sub-beams on the DVD ± R disk becomes the position of the main beam on the DVD ± R disk. On the other hand, it can be shifted by ± 1 / 2n (n is an integer) track pitch.

When the differential push-pull method is used, if the diffraction grating grating pitch is P and the wavelength of light emitted from the light source is λ, the diffraction angle θ of the front and rear sub-beams at the diffraction grating is θ = sin ^−1. It is represented by (λ / P). When the optical magnifications of the forward path and the backward path are equal, assuming that the distance from the light source to the diffraction grating is d, the distance g between the main beam and the front and rear sub beams on the light receiving surface of the photodetector is g = d × sin θ≈d × sin (sin ⁻¹ (λ / P)). The distance G between the main beam and the front and rear sub-beams on the DVD ± R disk is G = (d × λ) / (P × α), where α is the optical magnification of the forward path and the backward path. On the other hand, if the optical magnification is different between the forward path and the backward path, the optical magnification of the forward path is α, and the optical magnification of the backward path is β, the distance between the main beam and the front and rear sub-beams on the light receiving surface of the photodetector. Is g = (d × λ × β) / (P × α), and the distance G between the main beam and the front and rear sub-beams on the DVD ± R disc is G = (d × λ) / (P × α).

  Here, the optical magnification of the forward path refers to a ratio α = fcl / fo between the focal length fcl of the collimating lens and the focal length fo of the objective lens in the optical pickup device, and the optical magnification of the backward path is the optical pickup. It means the ratio α = fb / fo between the focal length fb of the detection system lens and the focal length fo of the objective lens in the apparatus. Therefore, when the collimating lens plays the role of the detection system lens in the return path, fcl = fb, and α and β are equal, and the optical magnifications of the forward path and the return path are equal.

  By the way, in recent years, an optical pickup device for the purpose of recording or reproducing information on two different optical disks represented by DVD and CD has been put into practical use. DVD and CD have not only different track pitches, but also different wavelengths of light beams used. For this reason, normally, two light sources that emit different wavelengths are mounted on the optical pickup device, and a differential push-pull method is employed to realize stable tracking servo. As a document disclosing the optical pickup device for the purpose of recording or reproducing information on the two different optical discs, for example, JP 2002-26996A (Patent Document 3) and JP 2003-317280 A (Patent Document). 4), JP-A-5-303757 (Patent Document 5), JP-A-2002-92933 (Patent Document 6), JP-A-2004-192976 (Patent Document 7) and the like are known.

Among these, in Patent Document 3, the distance of the first diffraction grating with respect to the first light source, the grating pitch of the first diffraction grating, the distance of the second diffraction grating with respect to the second light source, and the grating pitch of the second diffraction grating. It is described that the light receiving area of the photodetector provided corresponding to the front and rear sub-beams can be made common by adjusting. In Patent Document 4, information is recorded or reproduced on optical disks having different track pitches using a two-wavelength semiconductor laser that emits light beams having two different wavelengths and a diffraction grating having one diffraction period. Is described.

Patent Documents 5 and 6 describe that the diffracted light from the first hologram is diffracted again by the second hologram, and Patent Document 7 describes that the light emitted from the light source remains as one beam. It is described that a track error signal without the above-described offset is obtained by irradiating an optical disk and converting the reflected light into three beams in the return path.
JP-A-10-269588 JP 2001-273666 A JP 2002-269996 A JP 2003-317280 A JP-A-5-303757 JP 2002-92933 A Japanese Patent Laid-Open No. 2004-192776

  As described above, conventionally, a so-called phase difference method for detecting a DPD signal capable of generating a track error signal with only a main beam has been used for a read-only optical disc. However, as described above, it is necessary to use a servo mechanism that employs the differential push-pull method as a tracking servo for an optical disc that can be recorded and reproduced. In order to perform tracking servo using the differential push-pull method, it is necessary to use the above-mentioned front and rear sub-beams in addition to the main beam, and it is necessary to arrange a diffraction grating in the optical path to generate the front and rear sub-beams become.

  Therefore, in order to enable recording on optical discs having different recording densities using two different wavelengths, it is possible to separately arrange diffraction gratings suitable for the two different wavelengths. I need it. However, when two light sources are arranged close to each other or integrated, such as a two-wavelength semiconductor laser that derives light beams of two different wavelengths, it is possible to share one diffraction grating. Become. In such a configuration, the configuration of the optical system including the diffraction grating can be simplified, but on the other hand, the photodetector is increased in size and the configuration is complicated, resulting in an increase in manufacturing cost. This will be described in detail below.

  As described above, if the distance from the light source to the diffraction grating is d, the distance g between the main beam and the front and rear sub beams on the light receiving surface of the photodetector is g = (d × λ × β) / (P × α). At this time, when a diffraction grating having one period is used, the distance d and the pitch P are common to the light beams of the respective wavelengths, but naturally the wavelength λ is different. On the light receiving surface, the distances between the main beam and the front and rear sub beams of the light beams emitted from the respective light sources are different. Therefore, it is necessary to provide a light receiving area corresponding to each light beam having a different wavelength in the photodetector, and the size of the device increases with the increase in the light receiving area of the photodetector and the light receiving of the photodetector. As the number of regions increases, the configuration becomes complicated.

  Therefore, the present invention has been made to solve the above-described problems, and the photodetector can be configured to be small and simple, and recording / reproducing operations on information recording media having different recording densities can be performed. An object of the present invention is to provide an optical pickup device that realizes a servo operation that can be reliably performed.

  An optical pickup device according to the present invention includes a photodetector having a light receiving unit including a plurality of light receiving regions, a first light source that emits a first light beam, and a wavelength different from the wavelength of the first light beam. A light emitting unit including a second light source that emits a second light beam; and the light beam emitted from the light emitting unit is condensed on a recording surface of the information recording medium, and reflected light from the information recording medium is And an optical system that guides the light receiving area in association with the light receiving area. The optical system includes: a diffraction grating that branches each of the first light beam emitted from the first light source and the second light beam emitted from the second light source into a plurality of light beams; The recording surface of the information recording medium includes a plurality of light beams based on the first light beam branched by the diffraction grating and a plurality of light beams based on the second light beam branched by the diffraction grating. A plurality of light beams based on the first light beam reflected on the recording surface of the information recording medium and the second light reflected on the recording surface of the information recording medium A first hologram that diffracts each of the plurality of light beams based on the beam; and a second hologram that diffracts the plurality of light beams based on the second light beam diffracted by the first hologram.The plurality of light beams based on the second light beam diffracted by the first hologram are irradiated in correspondence with the hologram area of the second hologram in which different gratings are separately provided, Diffracted individually in different directions by the second hologram.

  With this configuration, the diffraction directions of the plurality of light beams based on the second light beam can be arbitrarily set by the plurality of hologram regions having different gratings provided in the second hologram. It becomes possible. Therefore, by appropriately adjusting the diffraction direction of these light beams, the photodetector can be made small and simple. Therefore, even when the differential push-pull method is adopted as a method for detecting a track error signal in an optical pickup device that records and reproduces information using two light beams having different wavelengths, the device can be reduced in size and simplified. It becomes possible. In addition, by optimizing the diffraction direction of each of the plurality of light beams based on the second light beam, aberration correction can be performed on these light beams irradiated on the light receiving unit of the photodetector. Since it becomes possible, the magnitude | size of the light beam irradiated on a light-receiving part can be made small. Therefore, noise can be reduced and high-speed response can be achieved, and a high-performance optical pickup device can be obtained.

  In the optical pickup device according to the present invention, the second hologram is diffracted by the plurality of light beams based on the first light beam diffracted by the first hologram and the first hologram. Of the plurality of light beams based on the second light beam, the plurality of light beams based on the first light beam diffracted by the first hologram are substantially transmitted without being diffracted, Preferably, only a plurality of light beams based on the second light beam diffracted by the first hologram are selectively diffracted.

  With this configuration, only the plurality of light beams based on the second light beam can be diffracted by the second hologram, so that the second hologram can be easily manufactured.

In the optical pickup device according to the present invention, each of the first light beam emitted from the first light source and the second light beam emitted from the second light source is emitted from the diffraction grating. Is preferably branched into a main beam and a plurality of sub beams. In that case, a light receiving region of the photodetector for receiving the main beam of the first light beam diffracted by the first hologram, and a light diffracted by the first hologram and further diffracted by the second hologram It is preferable that the light receiving region of the photodetector for receiving the main beam of the second light beam is shared, and the sub beam of the first light beam diffracted by the first hologram is received. At least a portion of the light receiving region of the photodetector and the light receiving region of the photodetector that receives the sub-beam of the second light beam diffracted by the first hologram and further diffracted by the second hologram Are preferably shared.

  In this way, by appropriately adjusting the respective diffraction directions of the plurality of light beams based on the second light beam by the plurality of hologram regions having different gratings provided in the second hologram, the first light The main beam of the beam and the main beam of the second light beam can be received by the same light receiving region, and at least a part of the sub-beam of the first light beam and the sub-beam of the second light beam are received. It is possible to receive light in the same light receiving region. Therefore, the photodetector can be remarkably reduced in size and simplified.

  In the optical pickup device according to the present invention, the first hologram includes two hologram regions divided by dividing lines extending in a direction corresponding to the radial direction of the information recording medium and separately provided with different gratings. In this case, it is preferable that the second hologram includes a hologram region divided into at least six or more separately provided with different gratings.

  With this configuration, the astigmatism method can be used as a focus error signal detection method.

  In the optical pickup device according to the present invention, the first hologram has a first dividing line extending in a direction corresponding to the radial direction of the information recording medium and a direction corresponding to the tangential direction of the information recording medium, and It is preferable to include a total of three hologram regions divided by a second dividing line extending from the first dividing line and provided with different gratings separately. In this case, the second hologram has different gratings separately. It is preferable that the hologram region divided into at least seven or more provided in is included.

  With this configuration, the knife edge method can be used as a focus error signal detection method.

  In the optical pickup device according to the present invention, it is preferable that the second wavelength is larger than the first wavelength.

  In this way, by setting the wavelength of the second light beam to be larger than the wavelength of the first light beam, each of the plurality of light beams based on the second light beam is individually diffracted in different directions. The second hologram can be easily manufactured.

  In the optical pickup device according to the present invention, it is preferable that the diffraction grating and the second hologram are arranged on the same plane.

  With this configuration, the diffraction grating and the second hologram can be integrated, so that the optical pickup device can be configured in a small size.

  In the optical pickup device according to the present invention, it is preferable that the diffraction grating, the first hologram, and the second hologram are formed on a single substrate.

  With this configuration, the diffraction grating, the first hologram, and the second hologram can be integrated, so that the optical pickup device can be made compact.

  According to the present invention, an optical pickup device capable of realizing a servo operation capable of reliably performing a recording / reproducing operation on an information recording medium having a different recording density, with which a photodetector can be configured to be small and simple. can do.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(Embodiment 1)
FIG. 1 is a conceptual diagram showing the configuration of the optical pickup device according to Embodiment 1 of the present invention, and FIG. 2 is an enlarged view of the integrated unit shown in FIG. As shown in FIG. 1, the optical pickup device 1 in the present embodiment mainly includes an integrated laser unit 10, a collimator lens 21, and an objective lens 22. As shown in FIG. 2, the integrated laser unit 10 includes a light emitting unit including a first semiconductor laser 12 that is a first light source and a second semiconductor laser 13 that is a second light source, and a diffraction grating 16 for tracking servo. The first hologram 17, the second hologram 18, and the semiconductor light receiving element 30 as a photodetector, and these components are integrated. Among the above components, the diffraction grating 16, the first hologram 17, the second hologram 18, the collimator lens 21, and the objective lens 22 condense the laser beam as a light beam on the recording surface of the optical disc that is an information recording medium. This corresponds to an optical system that focuses the reflected light on the light receiving portion of the semiconductor light receiving element 30.

  The first semiconductor laser 12 and the second semiconductor laser 13 are integrated or closely arranged. The first semiconductor laser 12 oscillates in a 650 nm band, for example, and emits a first laser beam LB1 having a wavelength of 650 nm, which is a first light beam. The second semiconductor laser 13 oscillates in the 780 nm band, for example, and emits a second laser beam LB2 having a wavelength of 780 nm, which is a second light beam. Thus, in the optical pickup device 1 according to the present embodiment, the wavelength of the second laser light LB2 is set longer than the wavelength of the first laser light LB1. Specifically, the first laser beam LB1 with a wavelength of 650 nm is used for reproducing a DVD, and the second laser beam LB2 with a wavelength of 780 nm is used for reproducing a CD.

  These semiconductor laser structures include a so-called monolithic type and a hybrid type. A monolithic semiconductor laser is a semiconductor laser that is integrally formed on the same semiconductor substrate. A hybrid semiconductor laser is a semiconductor laser that is closely disposed by bonding two semiconductor lasers together. In the present embodiment, a monolithic semiconductor laser designed so that the distance between the light emitting point of the first semiconductor laser 12 and the light emitting point of the second semiconductor laser 13 is 110 μm is illustrated.

  The diffraction grating 16 generates three light beams used for tracking servo with respect to each of the first laser light LB1 and the second laser light LB2. Specifically, the diffraction grating 16 branches the first laser light LB1 into a main beam that is 0th-order diffracted light and two sub-beams that are ± 1st-order diffracted light, and the second laser light LB2 is 0th-order diffracted light. The beam is branched into a main beam and two sub beams which are ± first-order diffracted light. Each of these ± 1st order diffracted lights becomes the front and rear sub-beams.

  The first hologram 17 diffracts the light beam in the return path (that is, the light beam reflected by the recording surface of the optical disk). As the light beam in the return path, the main beam and the front and rear sub beams of the first laser beam LB1 branched by the diffraction grating 16 described above, and the main beam of the second laser beam LB2 branched by the diffraction grating 16 described above, and There are a total of six light beams with the front and rear sub-beams. The first hologram 17 transmits the light beam in the forward path without substantially diffracting it. Details of the first hologram 17 will be described later.

  The second hologram 18 transmits the main beam and the front and rear sub-beams of the first laser beam LB1 out of the six light beams diffracted by the first hologram 17 in the return path without substantially diffracting the second laser beam. Only the main beam and front and rear sub-beams of LB2 are selectively diffracted. Details of the second hologram 18 will be described later.

  The semiconductor light receiving element 30 is diffracted by the first hologram 17 and diffracted by the first hologram 17 and the front and back sub-beams of the first laser beam LB1 transmitted without being diffracted by the second hologram 18 and the second hologram. A light receiving unit including a plurality of light receiving regions for receiving the main beam and the front and rear sub beams of the second laser light LB2 further diffracted by the light beam 18; The configuration of the light receiving unit will be described later.

  As shown in FIGS. 1 and 2, the first semiconductor laser 12, the second semiconductor laser 13, and the semiconductor light receiving element 30 are integrated as a laser package 11. The diffraction grating 16, the first hologram 17 and the second hologram 18 are integrated by forming a holographic pattern on the front and back surfaces of a single transparent substrate 15, and are mounted on the laser package 11 described above. ing. The integrated laser unit 10 is configured as described above.

  As shown in FIG. 1, the collimating lens 21 has a total of six first laser beams LB1 and second laser beams LB2 emitted from the first semiconductor laser 12 and the second semiconductor laser 13 and converted into three beams by the diffraction grating 16. Convert two light beams into parallel light. The objective lens 22 condenses a total of six light beams of the first laser beam LB1 and the second laser beam LB2 that have been collimated by the collimator lens 21 on the recording surfaces (that is, on the tracks) of the optical disc D1 or the optical disc D2. To do. Here, the objective lens 22 is fixed to the holder 23 of the optical pickup device 1.

  In addition to the objective lens 22, an aperture stop plate 25, a wave plate 26 and an actuator 24 are attached to the holder 23, and this is performed during focusing and tracking servo of the objective lens 22 with respect to the target track of the optical disks D 1 and D 2. The actuator 24 is integrally driven.

  The objective lens 22 is designed such that the first laser beam LB1 and the second laser beam LB2 are designed so that the aberrations on the recording surfaces of the optical disks D1 and D2 are small. For the first laser beam LB1, The center of the objective lens 22 is on the optical axis, and the center of the objective lens 22 is at a position shifted from the optical axis with respect to the second laser beam LB2.

  The aperture stop plate 25 has wavelength selectivity. When the wavelength of the first laser beam LB1 is set to the 650 nm band and the wavelength of the second laser beam LB2 is set to the 780 nm band as in the present embodiment, the first laser beam is set. For LB1, the aperture is limited so that the numerical aperture of the objective lens 22 is 0.65, and for the second laser beam LB2, the numerical aperture of the objective lens 22 is 0.5. It is a limitation.

  The wave plate 26 is designed to emit a phase difference as a quarter wave plate or a quarter + T (T is an integer) wave plate with respect to the first laser beam LB1 and the second laser beam LB2. Things are used.

With the above configuration, the first laser beam LB1 emitted from the first semiconductor laser 12 is branched by the diffraction grating 16 into a main beam that is 0th order diffracted light and front and rear subbeams that are ± 1st order diffracted light. The light passes through one hologram 17 and is condensed on the recording surface of the optical disc D1 by the objective lens 22 through the collimating lens 21. The return light is the objective lens 2
2. The light is diffracted by the first hologram 17 through the collimating lens 21, passes through the second hologram 18, and is guided to the light receiving portion of the semiconductor light receiving element 30. On the other hand, the second laser beam LB2 emitted from the second semiconductor laser 13 is branched by the diffraction grating 16 into a main beam that is 0th order diffracted light and front and rear subbeams that are ± 1st order diffracted light, and passes through the first hologram 17. Then, the light is condensed on the recording surface of the optical disc D2 by the objective lens 22 through the collimating lens 21. The return light passes through the objective lens 22 and the collimating lens 21 and is diffracted by the first hologram 17 and further diffracted by the second hologram 18 and guided to the light receiving portion of the semiconductor light receiving element 30.

  Here, a polarization hologram element is used as the first hologram 17, and a non-polarization hologram element is used as the second hologram 18. A polarization hologram element is a hologram element that selectively transmits and diffracts laser light depending on the polarization direction. A non-polarization hologram element always has a function of diffracting laser light regardless of the polarization direction. It is a hologram element.

  The first hologram 17 which is a polarization hologram element diffracts a plurality of beams of the first laser beam LB1 and the second laser beam LB2 on the return path. In the second hologram 18, by selecting the groove depth of the grating, the diffraction efficiency of the 0th-order diffracted light is larger than the diffraction efficiency of the ± 1st-order diffracted light with respect to the first laser light LB1, and the second laser light LB2 On the other hand, the hologram has a diffraction efficiency of ± 1st order diffracted light larger than that of 0th order diffracted light. In the present embodiment, since the wavelength selectivity is given to the second hologram 18, the second hologram 18 does not have a diffracting action on the first laser beam LB1 (the first hologram 18 is the first hologram 18). Laser light LB1 is transmitted), and the second laser light LB2 is set to have a diffractive action (± first-order diffracted light is generated).

  In the following, the optical path of the optical pickup device 1 and the relative relationship between the hologram and the light receiving unit in the present embodiment will be described in detail while paying attention to each of the first laser beam LB1 and the second laser beam LB2. The optical pickup device 1 according to the present embodiment is a case where an astigmatism method is employed for detecting a focus error signal.

  First, the first laser beam LB1 will be described. FIG. 3 is a diagram showing a state of the main beam and front and rear sub beams of the first laser light on the first hologram, and FIG. 4 is a diagram of the main beam and sub beam of the first laser light on the light receiving portion of the semiconductor light receiving element. It is a figure which shows a state.

  As shown in FIG. 1, the linearly polarized light in the x direction emitted from the first semiconductor laser 12 that emits the first laser beam LB1 of the integrated laser unit 10 is zero times in the diffraction grating 16 having the grating direction in the x direction. After being split into folded light (main beam) and ± 1st-order diffracted light (front and rear sub-beams), the polarization direction of each is converted into circularly polarized light by the wave plate 26 and is transmitted through the light transmission layer of the optical disc D1 and collected on the recording surface. To be lighted. On the recording surface of the optical disc D1, the sub beam is condensed with a shift of ± 1/2 × n (n is an integer) track pitch with respect to the main beam. The reflected light from the recording surface is diffracted by the first hologram 17 due to the difference in polarization direction because it is linearly polarized in the y direction, unlike the linearly polarized light emitted from the first semiconductor laser 12. The

As shown in FIG. 3, the first hologram 17 is divided into two semicircular hologram regions 17a and 17b by a dividing line 17x extending in a direction corresponding to the radial direction of the optical disc D1. Different holograms are formed separately in the hologram regions 17a and 17b. Therefore, when the x-axis is 0 degree in FIG. 3, astigmatism of 45 degrees in the hologram area 17a and -135 degrees in the hologram area 17b is given to the main beam LB1A and the front and rear sub-beams LB1B and LB1C, respectively. To diffract. Therefore, in the first hologram 17, a total of six light beams are generated by separating and diffracting the first laser beam LB1 in the return path.

  As shown in FIG. 4, the semiconductor light receiving element 30 includes a total of six rectangular light receiving regions 31a to 31 arranged in a matrix in a direction corresponding to the tangential direction of the optical disc D1 and a direction corresponding to the radial direction of the optical disc D1. 31f. Each of the light receiving regions 31a to 31f is divided into two by a dividing line extending in a direction corresponding to the radial direction of the optical disc D1, and as a result, the light receiving unit 31 is divided into two divided light receiving regions 31a1, 31a2, 31b1,. , 31f2 and 12 divided light receiving areas in total.

  The six light beams separated and diffracted by the first hologram 17 are received by the light receiving unit 31 of the semiconductor light receiving element 30. The above six light beams on the light receiving unit 31 are given astigmatism of 45 degrees in the hologram area 17a of the first hologram 17 and -135 degrees in the hologram area 17b, respectively. In the state shown in FIG. The separated beams LB1A1 and LB1A2 of the main beam LB1A of the first laser beam LB1 are respectively received by the two divided light receiving regions 31a1 and 31a2 of the light receiving region 31a and the two divided regions 31b1 and 31b2 of the light receiving region 31b, and the first laser light LB1 The separated beams LB1B1 and LB1B2 of the sub beam LB1B are respectively received by the two divided light receiving regions 31d1 and 31d2 of the light receiving region 31d and the two divided regions 31f1 and 31f2 of the light receiving region 31f, and the separated beams LB1C1 of the sub beam LB1C of the first laser beam LB1. LB1C2 is received by the two-divided light receiving regions 31c1 and 31c2 of the light receiving region 31c and the two divided regions 31e1 and 31e2 of the light receiving region 31e, respectively. The six light beams are condensed on the dividing lines of the light receiving regions 31a to 31f, respectively.

  If the output signals in the two-divided light receiving areas 31a1, 31a2, 31b1,..., 31f2 are A1, A2, B1,..., F2, respectively, the focus error signal FES is calculated by FES = (A1 + B2) ) − (A2 + B1), and the track error signal DPP is calculated by DPP = (A1 + B1) − (A2 + B2) −K {(C1 + D1 + E1 + F1) − (C2 + D2 + E2 + F2)} by the differential push-pull method. Can be obtained. Here, K is a constant. The reproduction signal RF can be obtained by calculating RF = (A1 + A2 + B1 + B2) using the entire beam spot of the main beam LB1A.

  Next, the second laser beam LB2 will be described. FIG. 5 is a diagram showing the state of the main beam and the front and rear sub-beams of the second laser light on the first hologram, and FIG. 6 is the state of the main beam and the front and rear sub-beams of the second laser light on the second hologram. FIG. 7 is a diagram showing the states of the main beam and the sub beam of the second laser light on the light receiving portion of the semiconductor light receiving element. FIG. 8 is a diagram showing the state of the main beam and the sub beam of the second laser light on the light receiving portion of the semiconductor light receiving element when the hologram region for the sub beam of the second laser light is not formed in the second hologram. .

As shown in FIG. 1, the linearly polarized light in the x direction emitted from the second semiconductor laser 13 that emits the second laser beam LB2 of the integrated laser unit 10 is zero times in the diffraction grating 16 having the grating direction in the x direction. After being split into folded light (main beam) and ± first-order diffracted light (front and rear sub-beams), the polarization direction of each is converted into circularly polarized light by the wave plate 26, and the light is transmitted through the light transmission layer of the optical disc D2 and collected on the recording surface. Lighted. On the recording surface of the optical disc D2, the sub beam is condensed with a shift of ± 1/2 × n (n is an integer) track pitch with respect to the main beam. The reflected light from the recording surface is diffracted by the first hologram 17 due to the difference in polarization direction because it is linearly polarized in the y direction, unlike the linearly polarized light emitted from the second semiconductor laser 13 in the x direction. The

  As shown in FIG. 5, the first hologram 17 is divided into two semicircular hologram regions 17a and 17b by a dividing line 17x extending in a direction corresponding to the radial direction of the optical disc D2 as described above. Different holograms are formed separately in the hologram regions 17a and 17b. Therefore, when the x-axis is 0 degree in FIG. 5, astigmatism of 45 degrees in the hologram area 17a and -135 degrees in the hologram area 17b is given to the main beam LB2A and the front and rear sub-beams LB2B and LB2C, respectively. To diffract. Therefore, in the first hologram 17, a total of six light beams are generated by separating and diffracting the second laser light LB2 in the return path.

  The light beam separated and diffracted by the first hologram 17 is diffracted again by the second hologram 18 to correct the optical path. As shown in FIG. 6, the second hologram 18 is divided by a dividing line 18y extending in a direction corresponding to the tangential direction of the optical disc D2 and a plurality of dividing lines 18x1 to 18x4 extending in a direction corresponding to the radial direction of the optical disc D2. Rectangular hologram regions 18a to 18f, and gratings are separately formed in the hologram regions 18a to 18f. The six light beams separated and diffracted by the first hologram 17 are irradiated in correspondence with these hologram regions 18a to 18f. Specifically, the separated beams LB2A1 and LB2A2 of the main beam LB2A of the second laser beam LB2 are respectively applied to the hologram regions 18a and 18b of the second hologram 18, and the separated beams LB2B1 of the sub beam LB2B of the second laser beam LB2 are irradiated. LB2B2 is applied to the hologram regions 18d and 18f of the second hologram 18, and the separated beams LB2C1 and LB2C2 of the sub-beam LB2C of the second laser beam LB2 are applied to the hologram regions 18c and 18e of the second hologram 18, respectively. Then, the six light beams irradiated in association with the hologram regions 18a to 18f are diffracted in different directions by the gratings provided in the regions.

  The six light beams diffracted in different directions by the second hologram 18 are received by the light receiving unit 31 of the semiconductor light receiving element 30. The six light beams on the light receiving unit 31 are rotated 90 degrees because they are given astigmatism of 45 degrees in the hologram area 17a of the first hologram 17 and -135 degrees in the hologram area 17b. The light receiving unit 31 receives light in the state shown in FIG. As shown in FIG. 7, the separated beams LB2A1 and LB2A2 of the main beam LB2A of the second laser beam LB2 are received by the two-divided light receiving regions 31a1 and 31a2 of the light receiving region 31a and the two divided regions 31b1 and 31b2 of the light receiving region 31b, respectively. The separated beams LB2B1 and LB2B2 of the sub beam LB2B of the second laser beam LB2 are respectively received by the two divided light receiving regions 31d1 and 31d2 of the light receiving region 31d and the two divided regions 31f1 and 31f2 of the light receiving region 31f, and the second laser light LB2 The separated beams LB2C1 and LB2C2 of the sub beam LB2C are received by the two divided light receiving areas 31c1 and 31c2 of the light receiving area 31c and the two divided areas 31e1 and 31e2 of the light receiving area 31e, respectively. The six light beams are condensed on the dividing lines of the light receiving regions 31a to 31f, respectively.

When the output signals in the two-divided light receiving regions 31a1, 31a2, 31b1,..., 31f2 are A1, A2, B1,..., F2, respectively, the focus error signal FES is calculated by FES = (A1 + B2) by the astigmatism method. ) − (A2 + B1), and the track error signal DPP is calculated by DPP = (A1 + B1) − (A2 + B2) −K {(C1 + D1 + E1 + F1) − (C2 + D2 + E2 + F2)} by the differential push-pull method. Can be obtained. Here, K is a constant. The reproduction signal RF can be obtained by calculating RF = (A1 + A2 + B1 + B2) using the entire beam spot of the main beam LB2A. Note that the DPD method can also be used as a track error signal for an optical disc on which information has already been recorded. In this case, the track error signal DPD performs an operation of DPD = (A1 + B1) − (A2 + B2). Can be obtained.

  Since the first hologram 17 is optimally designed with respect to the first laser beam LB1, the second laser beam LB2 diffracted by the first hologram 17 as in the present embodiment is generated by the semiconductor light receiving element 30. On the light receiving part 31, as shown by the broken line in FIG. Therefore, in the optical pickup device 1 according to the present embodiment, as described above, the second hologram 18 is disposed on the optical path of the second laser beam LB2 between the first hologram 17 and the semiconductor light receiving element 30. The optical path of the second laser beam LB2 is corrected, and the second laser beam LB2 is received in a light receiving region common to the light receiving region for receiving the first laser beam LB1.

  At that time, as a particularly important point, in order to diffract the main beam LB2A of the second laser beam LB2 necessary for the track error signal again by the second hologram 18, hologram regions 18a and 18b are provided in the second hologram 18. The diffraction direction is mainly in the x-axis direction, but in addition to that in the second hologram 18, the sub-beam LB2B is shifted in the -y-axis direction and diffracted, and the sub-beam LB2C is shifted in the + y-axis direction. The hologram regions 18d, 18f, 18c, and 18e are set so as to be diffracted. As described above, when the hologram regions 18d, 18f, 18c, and 18e for the sub-beams LB2B and LB2C of the second laser beam LB2 are not formed in the second hologram 18, as shown by a broken line in FIG. The main beam LB1A of the two laser beams LB2 is received by the light receiving regions 31a and 31b of the light receiving unit 31 (that is, the light receiving region where the main beam LB1A of the first laser beam LB1 is received). The sub beams LB2B and LB2C of the light LB2 are in the tangential direction of the optical disc D2 than the light receiving regions 31d, 31f, 31c and 31e of the light receiving unit 31 (that is, the light receiving regions where the sub beams LB1B and LB1C of the first laser beam LB1 are received). Is irradiated to the position shifted to, and received by these light receiving regions 31d, 31f, 31c, 31e. It becomes that there is no.

  As described above, in the optical pickup device 1 according to the present embodiment, a grating in which the main beam LB2A and the front and rear sub-beams LB2B and LB2C of the second laser beam separated and diffracted by the first hologram 17 are separately provided. The second hologram 18 diffracts the main beam LB2A and the front and rear sub-beams LB2B and LB2C of the second laser light individually in different directions by being irradiated in correspondence with the hologram regions 18a to 18f of the second hologram 18 It is configured as follows. Thereby, with respect to the main beam LB2A of the second laser beam LB2, the difference in diffraction angle caused by the wavelength difference between the main beam LB1A of the first laser beam LB1 generated by the first hologram 17 is corrected, and the second laser beam LB2A is corrected. The main beam LB2A of the light LB2 is focused on the light receiving regions 31a and 31b where the main beam LB1A of the first laser light LB1 is received. For the front and rear sub-beams LB2B and LB2C of the second laser light LB2, The difference in diffraction angle due to the difference in wavelength between the front and rear sub-beams LB1B and LB1C of the first laser beam LB1 generated by the first hologram 17, and the wavelength of the front and rear sub-beams LB1B and LB1C of the first laser beam LB1 generated by the diffraction grating 16 The difference in diffraction angle due to the difference is corrected, and the front and rear beams LB2B, L of the second laser beam LB2 are corrected. 2C is such that the first laser beam LB1 of the front and rear sub beam LB1B respectively, lb1c is condensed on the light receiving region 31d, 31f, 31c, 31e to be received. Therefore, the light receiving region can be shared, the semiconductor light receiving element 30 can be remarkably reduced in size, and at the same time, the configuration of the semiconductor light receiving element 30 can be simplified.

Further, when the second hologram 18 uses a common hologram region for the main beam LB2A of the second laser beam LB2 and the front and rear sub-beams LB2B and LB2C, if aberration correction is performed for the main beam LB2A, the front and rear sub-beams LB2B and LB2C On the contrary, aberration may occur. When aberration occurs in the front and rear sub-beams LB2B and LB2C, the size of the beam spot increases on the light receiving unit 31, and the beam spot protrudes from the light receiving region, making it difficult to detect the position with high accuracy. For example, when spherical aberration is given to the main beam LB2A, the front and rear sub-beams LB2B and LB2C are given spherical aberrations that are slightly off-axis, and therefore other aberrations (for example, coma and astigmatism). ) Occurs in the front and rear sub-beams LB2B and LB2C, making it difficult to detect the position with high accuracy. However, in the optical pickup device 1 according to the present embodiment, the optical path correction is performed on the main beam LB2A and the front and rear sub-beams LB2B and LB2C of the second laser beam LB2 individually in the separate hologram regions of the second hologram, so that aberration correction is performed. It will be possible to easily perform optimization.

  In the optical pickup device 1 according to the present embodiment, the second hologram 18 has wavelength selectivity, and is set so as not to diffract the first laser beam LB1. In this case, it is sufficient to adjust only the diffraction direction of the second laser beam LB2, and the second hologram 18 can be easily manufactured.

  In the optical pickup device 1 according to the present embodiment, the diffraction grating 16 and the second hologram 18 are arranged on the same plane, and the diffraction grating 16, the first hologram 17, and the second hologram 18 are arranged. Since it is formed on a single transparent substrate 15, it is suitable for integration, and downsizing of the device and ease of assembly are achieved.

  In the optical pickup device 1 according to the present embodiment described above, the second hologram 18 has a total of four separated sub-beams LB2B1, LB2B2, LB2C1, and LB2C2 that are diffracted in the second hologram. The case where separate hologram regions 18d, 18f, 18c, and 18e with different gratings are provided has been described as an example. However, it is necessary to diffract all these front and rear sub-beams LB2B1, LB2B2, LB2C1, and LB2C2 in different directions. In the case where there is no light, it is possible to diffract only a part of the light.

(Embodiment 2)
FIG. 9 is a conceptual diagram showing the configuration of the optical pickup device according to the second embodiment of the present invention, and FIG. 10 is an enlarged view of the integrated unit shown in FIG. In addition, the same code | symbol is attached | subjected about the structure similar to the optical pick-up apparatus in the above-mentioned Embodiment 1, and the description is not repeated.

  As shown in FIGS. 9 and 10, in the optical pickup device 1 according to the present embodiment, two transparent substrates 15 </ b> A and 15 </ b> B that are divided in the vertical direction are mounted on the laser package 11 of the integrated laser unit 10. The diffraction grating 16 and the second hologram 18 are formed on the lower surface of the transparent substrate 15A located below, and the first hologram 17 is formed on the upper surface of the transparent substrate 15B located above.

  With this configuration, the positional relationship between the first hologram 17 and the second hologram 18 can be variably set by changing the relative position between the transparent substrate 15A and the transparent substrate 15B. Therefore, the beam diameters of the first laser beam LB1 and the second laser beam LB2 on the first hologram 17 can be increased by bringing the first hologram 17 formed on the upper surface of the transparent substrate 15A closer to the collimator lens 21 side. Therefore, it is possible to relatively reduce the influence of the deviation of the emission point interval between the first semiconductor laser 12 and the second semiconductor laser 13.

(Embodiment 3)
The optical pickup device according to the third embodiment of the present invention has substantially the same configuration as that of the optical pickup device according to the first embodiment described above, and therefore is the same as the optical pickup device according to the first embodiment described above. The description of the portions is omitted, and only different portions are described.

  The optical pickup device in the present embodiment is different from the optical pickup device in the first embodiment described above in the configuration of the first hologram, the second hologram, and the semiconductor light receiving element, and the knife edge method is adopted for detecting the focus error signal. Is the case. Hereinafter, the relative relationship between the optical path of the optical pickup device and the hologram and the light receiving unit in the present embodiment will be described in detail while paying attention to each of the first laser beam LB1 and the second laser beam LB2.

  First, the first laser beam LB1 will be described. FIG. 11 is a diagram showing the states of the main beam and the front and rear sub beams of the first laser light on the first hologram, and FIG. 12 is a diagram of the main beam and the sub beam of the first laser light on the light receiving portion of the semiconductor light receiving element. It is a figure which shows a state.

  The linearly polarized light in the x direction emitted from the first semiconductor laser 12 that emits the first laser beam LB1 of the integrated laser unit 10 is converted into zero-order diffracted light (main beam) and ± by the diffraction grating 16 having a grating direction in the x direction. After being branched into first-order diffracted light (front and rear sub-beams), the polarization direction of each is converted into circularly polarized light by the wave plate 26, and the light is transmitted through the light transmitting layer of the optical disc D1 and condensed on the recording surface. On the recording surface of the optical disc D1, the sub beam is condensed with a shift of ± 1/2 × n (n is an integer) track pitch with respect to the main beam. The reflected light from the recording surface is diffracted by the first hologram 17 due to the difference in polarization direction because it is linearly polarized in the y direction, unlike the linearly polarized light emitted from the first semiconductor laser 12. The

  As shown in FIG. 11, the first hologram 17 includes a dividing line 17x as a first dividing line extending in a direction corresponding to the radial direction of the optical disc D1, and a center portion of the dividing line 17x as a base point. It is divided into two quarter-circular hologram regions 17a and 17b and one semicircular hologram region 17c by a dividing line 17y as a second dividing line extending in a direction corresponding to the local direction. Different gratings are separately formed in the hologram regions 17a to 17c. Therefore, the main beam LB1A and the front and rear sub-beams LB1B and LB1C of the first laser beam LB1 irradiated on the first hologram 17 are separated into a total of nine separated beams and diffracted in different directions.

  As shown in FIG. 12, the light receiving portion 32 of the semiconductor light receiving element 30 has a rectangular light receiving region 32a provided at a predetermined position and a rectangular shape arranged linearly in a direction corresponding to the radial direction of the optical disc D1. There are a total of seven light receiving areas including the light receiving areas 32b to 32g. In the light receiving region 32a, two divided light receiving regions 32a1 and 32a2 are formed by providing a dividing line extending in a direction corresponding to the tangential direction of the optical disc D1.

The nine light beams separated and diffracted by the first hologram 17 are received by the light receiving unit 32 of the semiconductor light receiving element 30. Specifically, the separated beams LB1A1, LB1A2, and LB1A3 of the main beam LB1A of the first laser beam LB1 are received by the light receiving regions 32c, 32b, and 32a, respectively, and the separated beams LB1B1 and LB1B2 of the sub beam LB1B of the first laser beam LB1. Are respectively received by the light receiving regions 32e and 32g, and the separated beams LB1C1 and LB1C2 of the sub-beam LB1C of the first laser beam LB1 are received by the light receiving regions 32d and 32f, respectively. The main beam L of the first laser beam LB1 described above.
The separated beam LB1A3 of B1A is collected on the dividing line of the light receiving region 32a.

  When the output signals in the two-divided light receiving areas 32a1, 32a2 are A1 and A2, respectively, and the output signals in the light receiving areas 32b, 32c,..., 32g are B, C,. The track error signal DPP is obtained by performing a calculation of FES = A1-A2 by the knife edge method, and the track error signal DPP is obtained by DPP = (BC) −K {(F + G) − (D + E)} by the differential push-pull method. It is obtained by performing the operation of Here, K is a constant. The reproduction signal RF can be obtained by calculating RF = (A1 + A2 + B + C) using the entire beam spot of the main beam LB1A.

  Next, the second laser beam LB2 will be described. FIG. 13 is a diagram showing the state of the main beam and the front and rear sub-beams of the second laser light on the first hologram, and FIG. 14 is the state of the main beam and the front and rear sub-beams of the second laser light on the second hologram. FIG. 15 is a diagram illustrating the states of the main beam and the sub beam of the second laser light on the light receiving portion of the semiconductor light receiving element.

  The linearly polarized light in the x direction emitted from the second semiconductor laser 13 that emits the second laser beam LB2 of the integrated laser unit 10 is converted into zero-order diffracted light (main beam) and ± by the diffraction grating 16 having a grating direction in the x direction. After being branched into first-order diffracted light (front and rear sub-beams), the polarization direction of each is converted into circularly polarized light by the wave plate 26, and is transmitted through the light transmission layer of the optical disc D2 and condensed on the recording surface. On the recording surface of the optical disc D2, the sub beam is condensed with a shift of ± 1/2 × n (n is an integer) track pitch with respect to the main beam. The reflected light from the recording surface is diffracted by the first hologram 17 due to the difference in polarization direction because it is linearly polarized in the y direction, unlike the linearly polarized light emitted from the second semiconductor laser 13 in the x direction. The

  As shown in FIG. 13, as described above, the first hologram 17 has a dividing line 17x extending in a direction corresponding to the radial direction of the optical disc D2 and the center of the dividing line 17x as a base point, and the tangential of the optical disc D2. A dividing line 17y extending in a direction corresponding to the direction is divided into two quarter-circle hologram regions 17a and 17b and one semicircular hologram region 17c. Different gratings are separately formed in the hologram regions 17a to 17c. Therefore, the main beam LB2A and the front and rear sub-beams LB2B and LB2C of the second laser light LB2 irradiated on the first hologram 17 are separated into a total of nine separated beams and diffracted in different directions.

  Here, since the first hologram 17 is optimally designed with respect to the first laser beam LB1, when the interval between the emission points of the first semiconductor laser 12 and the second semiconductor laser 13 is large, the second hologram 17 is used. The positional deviation between the beam center in the forward path of the laser beam LB2 and the dividing line 17y of the first hologram 17 cannot be ignored. In that case, it is necessary to change to a two-wavelength semiconductor laser in which the interval between the light emitting points of the first semiconductor laser 12 and the second semiconductor laser 13 is small, or to make the arrangement position of the first hologram 17 closer to the collimating lens 21 side. It is. In the case where the first hologram 17 is arranged close to the collimating lens 21 side, the configuration in the above-described second embodiment is preferable.

The light beam separated and diffracted by the first hologram 17 is diffracted again by the second hologram 18 to correct the optical path. As shown in FIG. 14, the second hologram 18 is divided by a dividing line 18y extending in a direction corresponding to the tangential direction of the optical disc D2 and a plurality of dividing lines 18x1 to 18x5 extending in a direction corresponding to the radial direction of the optical disc D2. Rectangular hologram regions 18a to 18g, and gratings are separately formed in these hologram regions 18a to 18g. The six light beams separated and diffracted by the first hologram 17 are irradiated in correspondence with these hologram regions 18a to 18g. Specifically, the separated beams LB2A1, LB2A2, and LB2A3 of the main beam LB2A of the second laser beam LB2 are respectively applied to the hologram regions 18b, 18c, and 18a of the second hologram 18, and the sub beams LB2B of the second laser beam LB2 are irradiated. The separated beams LB2B1, LB2B2, and LB2B3 are respectively irradiated on the hologram regions 18e, 18g, and 18a of the second hologram 18, and the separated beams LB2C1, LB2C2, and LB2C3 of the sub beam LB2C of the second laser beam LB2 The regions 18d, 18f, and 18a are respectively irradiated. The nine light beams irradiated in association with the hologram regions 18a to 18g are diffracted in different directions by the gratings provided in the regions.

  The nine light beams diffracted in different directions by the second hologram 18 are received by the light receiving unit 32 of the semiconductor light receiving element 30. Specifically, as shown in FIG. 15, the separated beams LB2A1, LB2A2, and LB2A3 of the main beam LB2A of the second laser beam LB2 are received by the light receiving regions 32c, 32b, and 32a, respectively, and are sub-beams of the second laser beam LB2. The separated beams LB2B1 and LB2B2 of LB2B are received by the light receiving regions 32e and 32g, respectively, and the separated beams LB2C1 and LB2C2 of the sub beam LB2C of the second laser beam LB2 are received by the light receiving regions 32d and 32f, respectively. The separated beam LB2A3 of the main beam LB2A of the second laser beam LB2 is condensed on the dividing line of the light receiving region 32a.

  When the output signals in the two-divided light receiving areas 32a1, 32a2 are A1 and A2, respectively, and the output signals in the light receiving areas 32b, 32c,..., 32g are B, C,. The track error signal DPP is obtained by performing a calculation of FES = A1-A2 by the knife edge method, and the track error signal DPP is obtained by DPP = (BC) -K {(E + G)-(D + F)} by the differential push-pull method. It is obtained by performing the operation of Here, K is a constant. The reproduction signal RF can be obtained by calculating RF = (A1 + A2 + B + C) using the entire beam spot of the main beam LB1A. For an optical disc on which information has already been recorded, the DPD method can be used as a track error signal. In this case, the track error signal DPD can be obtained by calculating DPD = BC. .

  Since the first hologram 17 is optimally designed with respect to the first laser beam LB1, the second laser beam LB2 diffracted by the first hologram 17 as in the present embodiment is generated by the semiconductor light receiving element 30. The light is irradiated on the light receiving unit 32 in a shifted manner. Therefore, in the optical pickup device according to the present embodiment, as described above, the second hologram 18 is arranged on the optical path of the second laser beam LB2 between the first hologram 17 and the semiconductor light receiving element 30 as described above. The optical path of the second laser beam LB2 is corrected, and the second laser beam LB2 is received in the light receiving region common to the light receiving region for receiving the first laser beam LB1.

  At this time, as a particularly important point, in order to diffract the main beam LB2A of the second laser beam LB2 necessary for the track error signal by the second hologram 18, hologram regions 18c, 18b, and 18a are formed in the second hologram 18. The diffraction direction is mainly in the x-axis direction, but in the second hologram 18, in addition to that, the sub-beam LB2B is shifted in the -y-axis direction and diffracted, and the sub-beam LB2C is in the + y-axis direction. The hologram regions 18e, 18g, 18d, and 18f are set so as to be diffracted by being shifted.

As described above, in the optical pickup device according to the present embodiment, the gratings different in the main beam LB2A and the front and rear sub-beams LB2B and LB2C of the second laser light separated and diffracted by the first hologram 17 are separately provided. Second hologram 1
The main hologram beam LB2A and the front and rear sub-beams LB2B and LB2C of the second laser beam are individually diffracted in different directions by the second hologram 18 by being irradiated in association with the eight hologram regions 18a to 18g. Yes. Thereby, with respect to the main beam LB2A of the second laser beam LB2, the difference in diffraction angle caused by the wavelength difference between the main beam LB1A of the first laser beam LB1 generated by the first hologram 17 is corrected, and the second laser beam LB2A is corrected. The main beam LB2A of the light LB2 is focused on the light receiving regions 32c, 32b, and 32a where the main beam LB1A of the first laser light LB1 is received, and the front and rear sub-beams LB2B and LB2C of the second laser light LB2 Is the difference in diffraction angle due to the difference in wavelength between the front and rear sub-beams LB1B and LB1C of the first laser beam LB1 generated by the first hologram 17, and the front and rear sub-beams LB1B and LB1C of the first laser beam LB1 generated by the diffraction grating 16 The difference in diffraction angle due to the difference in wavelength is corrected, and the front and rear beams LB of the second laser beam LB2 are corrected. B, LB2c comes to the first longitudinal sub-beam LB1B laser beam LB1 respectively, lb1c is condensed light receiving regions 32e, 32g, 32d, to 32f to be received. Therefore, the light receiving region can be shared, the semiconductor light receiving element 30 can be remarkably reduced in size, and at the same time, the configuration of the semiconductor light receiving element 30 can be simplified.

  In the optical pickup device according to the present embodiment described above, in the second hologram 18, four separated beams LB2B1, LB2B2, LB2C1, and LB2C2 used for track servo among a total of six front and rear sub-beams after separation. The case where separate hologram regions 18e, 18g, 18d, and 18f in which different gratings are formed in the second hologram so as to diffract all of the above has been described as an example. If the front and rear sub-beams LB2B1, LB2B2, LB2C1, and LB2C2 do not need to be diffracted in different directions, only a part of them may be diffracted.

  In the first to third embodiments described above, the case where a laser beam having a wavelength of 650 nm band is used as the first laser beam LB1 and a laser beam having a wavelength of 780 nm band is used as the second laser beam LB2 is exemplified. A laser beam having a wavelength of 410 nm may be used as the laser beam LB1, and a laser beam having a wavelength of 650 nm or a laser beam having a wavelength of 780 nm may be used as the second laser beam LB2.

  In the first to third embodiments described above, the case where the second hologram 18 is a wavelength-selective hologram element and the first laser beam LB1 is set to pass through without being diffracted is illustrated. Although described, the second hologram 18 may be configured to diffract both the first laser beam LB1 and the second laser beam LB2 without using the wavelength selective hologram element.

  In Embodiments 1 to 3 described above, ± first-order diffracted light is generated in the second hologram 18, but only the light beam actually used out of ± 1 diffracted light is generated by blazing the second hologram. Can be generated. In that case, it is possible to increase the light use efficiency in the second hologram 18.

  Thus, the above-described embodiments disclosed herein are illustrative in all respects and are not restrictive. The technical scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a conceptual diagram which shows the structure of the optical pick-up apparatus in Embodiment 1 of this invention. It is an enlarged view of the integrated unit of the optical pick-up apparatus in Embodiment 1 of this invention. It is a figure which shows the state of the main beam of the 1st laser beam on the 1st hologram of the optical pick-up apparatus in Embodiment 1 of this invention, and the front-back sub-beam. It is a figure which shows the state of the main beam and sub beam of a 1st laser beam on the light-receiving part of the semiconductor light receiving element of the optical pick-up apparatus in Embodiment 1 of this invention. It is a figure which shows the state of the main beam of the 2nd laser beam on the 1st hologram of the optical pick-up apparatus in Embodiment 1 of this invention, and the front-back sub-beam. It is a figure which shows the state of the main beam of the 2nd laser beam on the 2nd hologram of the optical pick-up apparatus in Embodiment 1 of this invention, and the front-back sub-beam. It is a figure which shows the state of the main beam and sub beam of a 2nd laser beam on the light-receiving part of the semiconductor light receiving element of the optical pick-up apparatus in Embodiment 1 of this invention. In the optical pickup device according to the first embodiment of the present invention, the main beam and the sub beam of the second laser light on the light receiving portion of the semiconductor light receiving element when the hologram region for the sub beam of the second laser light is not formed in the second hologram It is a figure which shows the state of. It is a conceptual diagram which shows the structure of the optical pick-up apparatus in Embodiment 2 of this invention. It is an enlarged view of the integrated unit of the optical pick-up apparatus in Embodiment 2 of this invention. It is a figure which shows the state of the main beam of the 1st laser beam on the 1st hologram of the optical pick-up apparatus in Embodiment 3 of this invention, and the front-back sub-beam. It is a figure which shows the state of the main beam and sub beam of a 1st laser beam on the light-receiving part of the semiconductor light receiving element of the optical pick-up apparatus in Embodiment 3 of this invention. It is a figure which shows the state of the main beam of the 2nd laser beam on the 1st hologram of Embodiment 3 of this invention, and the front-back sub-beam. It is a figure which shows the state of the main beam of a 2nd laser beam on the 2nd hologram of the optical pick-up apparatus in Embodiment 3 of this invention, and the front-back sub-beam. It is a figure which shows the state of the main beam and sub beam of a 2nd laser beam on the light-receiving part of the semiconductor light receiving element of the optical pick-up apparatus in Embodiment 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical pick-up apparatus, 10 Integrated laser unit, 11 Laser package, 12 1st semiconductor laser, 13 2nd semiconductor laser, 15, 15A, 15B Transparent substrate, 16 Diffraction grating, 17 1st hologram, 17a-17c Hologram area | region, 17x, 17y dividing line, 18 second hologram, 18a-18g hologram area, 18x1-18x5, 18y dividing line, 21 collimating lens, 22 objective lens, 23 holder, 24 actuator, 25 aperture stop plate, 26 wavelength plate, 30 semiconductor Light receiving element, 31 Light receiving part, 31a to 31f Light receiving region, 31a1, 31a2, 31b1,..., 31f2
2 divided light receiving areas, 32 light receiving portions, 32a to 32g light receiving areas, 32a1, 32a2 2 divided light receiving areas, D1, D2 optical disc, LB1 first laser light, LB2 second laser light.

Claims (8)

A photodetector having a light receiving portion including a plurality of light receiving regions;
A light emitting unit including a first light source that emits a first light beam and a second light source that emits a second light beam having a wavelength different from the wavelength of the first light beam;
An optical pickup device comprising: an optical system that focuses a light beam emitted from the light emitting unit on a recording surface of an information recording medium and guides reflected light from the information recording medium in association with the plurality of light receiving regions. And
The optical system is
A diffraction grating for branching each of the first light beam emitted from the first light source and the second light beam emitted from the second light source into a plurality of light beams;
The recording surface of the information recording medium includes a plurality of light beams based on the first light beam branched by the diffraction grating and a plurality of light beams based on the second light beam branched by the diffraction grating. An objective lens that focuses light on
A plurality of light beams based on the first light beam reflected by the recording surface of the information recording medium and a plurality of lights based on the second light beam reflected by the recording surface of the information recording medium A first hologram that diffracts each of the beams;
A second hologram that diffracts a plurality of light beams based on the second light beam diffracted by the first hologram,
The plurality of light beams based on the second light beam diffracted by the first hologram are irradiated in correspondence with the hologram region of the second hologram in which different gratings are separately provided. An optical pickup device that is diffracted individually in different directions by the second hologram.   The second hologram includes a plurality of light beams based on the first light beam diffracted by the first hologram and a plurality of lights based on the second light beam diffracted by the first hologram. Among the beams, a plurality of light beams based on the first light beam diffracted by the first hologram are substantially transmitted without being diffracted, and the second light diffracted by the first hologram The optical pickup device according to claim 1, wherein only a plurality of light beams based on the beam are selectively diffracted. The diffraction grating branches each of the first light beam emitted from the first light source and the second light beam emitted from the second light source into a main beam and a plurality of sub beams,
A light receiving region of the photodetector for receiving a main beam of the first light beam diffracted by the first hologram, and the second light diffracted by the first hologram and further diffracted by the second hologram. The light receiving area of the photodetector that receives the main beam of the light beam is shared,
A light receiving region of the photodetector for receiving a sub-beam of the first light beam diffracted by the first hologram, and the second light diffracted by the first hologram and further diffracted by the second hologram. The optical pickup device according to claim 1, wherein at least a part of the light receiving region of the photodetector that receives a sub beam of the beam is shared. The first hologram includes two hologram regions divided by dividing lines extending in a direction corresponding to the radial direction of the information recording medium and separately provided with different gratings.
4. The optical pickup device according to claim 1, wherein the second hologram includes a hologram region divided into at least six or more separately provided with different gratings. 5. The first hologram includes a first dividing line extending in a direction corresponding to the radial direction of the information recording medium and a second dividing line extending in a direction corresponding to the tangential direction of the information recording medium and extending from the first dividing line. Including a total of three hologram regions that are divided and provided with different gratings separately;
4. The optical pickup device according to claim 1, wherein the second hologram includes a hologram region divided into at least seven or more provided with different gratings separately. 5.   The optical pickup device according to claim 1, wherein the second wavelength is larger than the first wavelength.   The optical pickup device according to claim 1, wherein the diffraction grating and the second hologram are arranged so as to be included on the same plane.   The optical pickup device according to claim 1, wherein the diffraction grating, the first hologram, and the second hologram are formed on a single substrate.

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