JP2005310298A - Optical pickup and optical information processor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup wherein a detection system for detecting reflected lights obtained by reflecting a plurality of kinds of different wavelengths on optical recording media different in standards is simplified. <P>SOLUTION: An optical beam irradiated from a light source 1 is passed through a collimator lens 4 and a mirror 5, and converged on the recording surfaces 8 and 12 of optical media having different substrate thicknesses by an objective lens 7 according to the wavelength of the light source 1. A reflected light reflected on the recording surface 8 or 12 passes through the objective lens 7 to generate ± primary diffraction lights by a polarizing hologram element 6, and is received by a photodetector 2. The detection surface of the photodetector 2 is divided into two, the reflected light is focused between the detection surface and the collimator lens 4 on one photodetection surface, and focused in a position passed through the detection surface on the other detection surface. The focal position varies according to the wavelength of the optical beam irradiated from the light source 1. However, the focus error signals of the optical recording media having different substrate thicknesses are detected by the same photodetection system. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical information processing apparatus such as an optical disk, and more particularly to an optical pickup that records and reproduces signals on a plurality of types of optical disks of different standards and specifications.

  In recent years, as optical disk devices used for external storage devices of computers, video recorders, etc., for example, so-called CD disks such as CD-ROM disks, CD-R disks, CD-RW disks, DVD-ROM disks, DVD-RAM disks, DVDs. -Recording density / capacity and groove specifications / base material such as so-called DVD discs such as R discs, DVD-RW discs, DVD + R discs, DVD + RW discs, and BDs symmetric with blue laser light sources called Blu-ray discs A number of products for multi-disc applications that support a variety of recording media with different standards, such as thickness, with a single device are increasing.

  In such an apparatus, an optical pickup, which is an interface unit for recording / reproducing information on / from an optical disc, receives a laser light source having a different wavelength, or receives light reflected from the optical disc and outputs control signals such as an RF signal, focus, and tracking. A plurality of photodetectors and the like are mounted, and writing, erasing, and reading are performed on a medium suitable for each using a laser light source, a photodetector, and the like.

  In order to reduce the size and cost of the device while performing the recording and playback functions for various different standard discs in this way, adaptability to different types of discs and the optical system of the optical pickup Technology that balances downsizing is important.

  As one condition for obtaining adaptability to discs of different types, it is necessary to ensure the focus spot tracking control accuracy such as focus and tracking so that recording and playback compatibility can be achieved between different devices. In order to make it compact, it is necessary to reduce the number of optical components as much as possible and to configure it in a small space. An optical pickup corresponding to the plurality of recording media and having a compact optical system configuration is disclosed in Patent Document 1.

  FIG. 7 shows the configuration of the optical pickup in Patent Document 1 in a simplified manner with only the basic requirements. In FIG. 7, the optical pickup records and reproduces signals on various media having a substrate thickness of 0.6 mm, such as DVD-ROM as a reproduction medium and DVD-RAM, DVD-R, and DVD-RW as recording media. And a laser light source 101 that emits light having a wavelength of around 650 nm (wavelength λ1) used for the recording, a CD-ROM that is a reproduction medium, a CD-R that is a recording medium, a CD-RW, and the like. A laser light source 102 that emits light having a wavelength of about 800 nm (wavelength λ2) used for recording / reproducing signals on a 1.2 mm medium is separately provided.

  Further, near the laser light sources 101 and 102, photodetectors 112 and 115 for receiving light reflected by a medium suitable for light of each wavelength are provided. That is, the laser light source and the photodetector are configured as an integrated unit, and the optical pickup is configured using two types of units having laser light sources having different wavelengths. Hereinafter, a structure in which such a laser light source and a photodetector are integrated is referred to as a laser unit.

  Next, the operation of the conventional optical pickup shown in FIG. 7 having a plurality of laser units will be described. The linearly polarized light of wavelength λ1 emitted from the laser light source 101 is reflected by the wavelength selective prism 103 formed on the surface of the wavelength selective thin film 103a, becomes parallel light by the collimator lens 104, and bends the optical path by the rising mirror 105. Then, the light passes through a polarizing element 109 formed by combining a polarizing hologram 107 and a wave plate 108 mounted on the actuator 106. At this time, the light is transmitted without being diffracted due to the polarization dependence of the hologram 107.

  The wave plate 108 has a retardation of 5λ1 / 4 with respect to the light of wavelength λ1, and converts the light transmitted through the polarizing element 109 from linearly polarized light to circularly polarized light. This circularly polarized light is collected by the objective lens 110 onto the recording surface 111 of an optical disk having a substrate thickness of 0.6 mm such as a DVD. The light reflected from the recording surface 111 enters the polarizing element 109 again through the objective lens 110, but this time the circularly polarized light passes through the wave plate 108 in the opposite direction, so that the light from the laser light source side is polarized. It is converted into linearly polarized light having a polarization direction orthogonal to the direction, and is diffracted by the polarizing hologram 107. The diffracted light is reflected by the wavelength selection prism 103 via the collimating lens 104 and is incident on the photodetector 112 disposed in the vicinity of the laser light source 101, thereby obtaining a control signal such as focus and tracking, an RF signal, and the like. .

  On the other hand, the light having the wavelength λ2 emitted from the laser light source 102 is partially diffracted through a polarization-independent hologram 113 in which concave and convex gratings are formed on a transparent member such as a resin, and most of the light is zero order light. As transparent. The zero-order light passes through the wavelength selection prism 103, and after the diverging light is converged by the collimator lens 104, it passes through the rising mirror 105 and passes through the polarizing element 109. At this time, the light with the wavelength λ2 is transmitted without being diffracted as the light with the wavelength λ1 due to the polarization dependence of the polarization hologram 107.

  As described above, the wave plate 108 is a five-quarter wave plate for the light of the wavelength λ1 used in the DVD. That is, since the retardation of the wave plate is 650 × 5/4 = 812.5≈800 nm, it is almost a single wave plate for light of wavelength λ2 near 800 nm used for CD. For this reason, the light passes through the wave plate 108 with substantially linear polarization. The transmitted light is condensed by the objective lens 110 onto the recording surface 114 of the optical disk having a CD substrate thickness of 1.2 mm. Although not shown in the drawing, a wavelength-selective aperture limiting film is formed on the surface of the polarizing element 109, and the recording surface is made to have a low NA (Numerical Aperture) for light having a wavelength λ2 for CD. The upper spot diameter is set to be optimum.

  The light reflected from the recording surface 114 enters the polarizing element 109 again through the objective lens 110. At this time, since the wave plate 108 is a single wave plate as described above, it passes through the wave plate 108 in the linearly polarized state as it is in the return path. Therefore, the polarizing hologram 107 passes through without being diffracted. The transmitted light passes through the rising mirror 105, the collimating lens 104, and the wavelength selection prism 103, and is partially diffracted and split by a hologram 113 having no polarization dependency, and this diffracted light is disposed in the vicinity of the laser light source 102. By entering the detector 115, a control signal such as focus and tracking, an RF signal, and the like are obtained.

  Thus, by unitizing the laser light source and the photodetector, the optical system configuration of the optical pickup can be simplified as compared with the case where the light source and the photodetector are separate components. Further, since the relative positional relationship between the laser light source and the photodetector is determined by the mounting accuracy of the laser chip, the assembly adjustment of the pickup is simplified and the productivity is increased.

In an optical pickup as proposed in Patent Document 1, an optical pickup compatible with optical recording media of different standards can be configured compactly by integrating a laser light source and a photodetector. This is because the optical path from the laser light source to the optical recording medium (outward path) and the optical path from the optical recording medium to the optical detector (return path) are common, so that the configuration is branched in the reciprocating path, that is, the light source and the detector are separated. This is because the number of parts of the optical system can be reduced as compared with the case where the optical system is used, and the optical system can be stored in a small space. In addition, since it is configured to condense light of different wavelengths with one objective lens, the optical system from the wavelength selection prism to the optical disk is common to the two wavelengths. As a result, the number of optical components and the space can be reduced.
JP 2001-14714 A

  However, along with the growing demand for optical pickups, there is a need to further increase the productivity and further reduce the cost. For this purpose, it is necessary to further simplify the optical pickup. In the above-described optical pickup, two laser units having light sources having different wavelengths exist independently, so that optical adjustment is required for each. In order to further increase productivity, it is necessary to further reduce the number of components by integrating light sources having different wavelengths and reduce optical adjustment. Further, in the above optical pickup, there are wiring for flowing a laser driving current to the two laser units, wiring for guiding an electric signal received and converted by each photodetector to an LSI, etc. In many cases, the wiring pattern connecting them is complicated, and the flexible P board on which the wiring pattern is formed becomes large. In addition, for various optical disks that use light of different wavelengths, the photodetector pattern of the laser unit, the method of extracting signals, and the like are different, and the signal processing in the LSI becomes complicated.

  In recent years, laser light sources (hereinafter referred to as monolithic lasers) that emit laser beams of different wavelengths with a single chip and laser light sources (hereinafter referred to as hybrid lasers) that integrate multiple laser chips of different wavelengths have been newly developed, It is becoming. In such an optical pickup using a laser, the number of components can be increased by receiving laser beams of a plurality of wavelengths with a single photodetector, that is, by combining not only the light source but also the detector with respect to different wavelengths. Obviously, the optical system can be reduced and the optical system can be simplified.

  However, there has been no simple photodetection pattern that can be used for reflected light from optical information media of different standards using laser beams of a plurality of wavelengths. This is because a laser light source such as a monolithic laser generally has two light emitting points that generate relatively different wavelengths, and the imaging position on the photodetector also corresponds to each light emitting point. When the light is split relative to each other or when the light is branched to the photodetector using a diffraction element, the diffraction angle due to the diffraction element varies depending on the wavelength, so the detector pattern is completely shared at different wavelengths. This is due to reasons such as being difficult.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above-described conventional problems, and it is an object of the present invention to simplify a detection system for detecting reflected light reflected by optical recording media having different standards from a plurality of different wavelengths, and to reduce the cost of an optical pickup. .

  The invention according to claim 1 is a laser light source, a condensing lens for condensing light from the laser light source on the optical information medium, a branch element for diffracting and branching reflected light from the optical information medium, and light branched by the branch element. And a branching element that divides the light beam cross section of the light beam into two by a straight line passing through the center of the optical axis, and guides the light beam divided into two into the detection region. An optical pickup that converges to the side closer to the condenser lens than the photodetector surface, and converges the other light beam to the side farther from the condenser lens than the photodetector surface, and outputs multiple signals from each detection area. is there.

  According to the second aspect of the present invention, three detectors a, b, and c (where b is an area between a and c) in which a photodetector for performing focus error detection is divided into strips, and a strip Are divided into three detectors d, e, and f (where e is a region sandwiched between d and f), and each of the light beams obtained by dividing the light beam cross-section by a branching element into two parts. A and c, which are generated by changing the size of the light spot formed on the detector surface while receiving light by the combination of the photodetectors a, b and c and the combination of the photodetectors d, e and f. This is an optical pickup that outputs a plurality of signals of a change amount of the output sum of e and a change amount of the output sum of d, f, and b.

  According to the third aspect of the present invention, three detectors a, b, and c (in which b is an area between a and c) in which a photodetector for performing focus error detection is divided into strips, and a strip Are divided into two detectors d, e, and f (where e is a region sandwiched between d and f), and each of the light beams obtained by dividing the light beam cross-section by a branching element into two parts. Light received by the combination of the photodetectors a, b, and c and the combination of the photodetectors d, e, and f, and a and c generated by changing the size of the light spot formed on the detector surface. A value obtained by normalizing the change amount of the difference between the output sum and the output of b by the output sum of a, b, and c, and the change amount of the difference between the output sum of e and g and the output of f as d and e. The optical pickup outputs a plurality of signals B with a value normalized by the output sum of f and f.

  According to a fourth aspect of the present invention, there is provided the optical pickup according to any one of the first to third aspects, wherein a dividing line direction in which the branching element divides the beam cross section into two coincides with a direction corresponding to a track direction of the optical information medium.

  According to a fifth aspect of the present invention, the branch element is a polarization hologram, and is provided in a common portion between the forward path from the laser light source to the optical information medium and the return path from the optical information medium to the photodetector. The optical pickup according to claim 1, wherein the optical pickup is characterized in that

  According to the sixth aspect of the present invention, one of the + 1st order diffracted light and the −1st order diffracted light generated by the branch element is used for focus error detection, the other is used for tracking error detection, and a straight line passing through the center of the optical axis by the branch element. 6. The tracking error detection light obtained by dividing the light beam cross-section of the light beam into two separate detection areas, and a plurality of signals are output from the respective detection areas. The optical pickup described.

  The invention according to claim 7 further includes a diffraction grating for branching the laser beam emitted from the laser light source into a zero-order main beam and a ± first-order sub-beam, and the sub-beam light diffracted thereby 7. The optical pickup according to claim 1, further comprising a photodetector for receiving reflected light reflected by the optical information medium.

  The invention according to claim 8 is characterized in that the light of the sub-beam reflected from the optical information medium is branched by dividing the light beam section into two by the branch element, and the branched light is received by independent detectors. The optical pickup according to claim 7.

  The invention according to claim 9 is a monolithic laser light source that outputs light of different wavelengths or a laser light source in which a plurality of laser chips that output light of different wavelengths are arranged close to each other, and light from the laser light source. A condensing lens for condensing on the optical information medium; a branch element for diffracting and branching the reflected light from the optical information medium; and a photodetector for receiving the light branched by the branch element; The light beam cross section of the light beam is divided into two by a straight line passing through the center of the optical axis and guided to different detection areas, and one of the two divided light beams is converged on the side closer to the condenser lens than the photodetector surface. The optical pickup has an action of converging the other light beam to the side farther from the condenser lens than the light detector surface, and outputs a plurality of signals from each detection region.

  The invention described in claim 10 includes three detectors a, b, and c (in which b is an area between a and c) in which a photodetector for performing focus error detection is divided into strips, and a strip Are divided into three detectors d, e, and f (where e is a region sandwiched between d and f), and each of the light beams obtained by dividing the light beam cross-section by a branching element into two parts. A and c, which are generated by changing the size of the light spot formed on the detector surface while receiving light by the combination of the photodetectors a, b and c and the combination of the photodetectors d, e and f. 10. The optical pickup according to claim 9, wherein a plurality of signals of a change amount of an output sum of e and a change amount of an output sum of d, f, and b are output.

  The invention described in claim 11 includes three detectors a, b, and c (in which b is a region sandwiched between a and c) in which a photodetector for performing focus error detection is divided into a strip shape, and a strip shape. Are divided into two detectors d, e, and f (where e is a region sandwiched between d and f), and each of the light beams obtained by dividing the light beam cross-section by a branching element into two parts. Light received by the combination of the photodetectors a, b, and c and the combination of the photodetectors d, e, and f, and a and c generated by changing the size of the light spot formed on the detector surface. A value obtained by normalizing the change amount of the difference between the output sum and the output of b by the output sum of a, b, and c, and the change amount of the difference between the output sum of e and g and the output of f as d and e. 10. An optical pickup according to claim 9, wherein a plurality of signals B are output with a value normalized by an output sum of f and f. It is.

  The invention according to claim 12 is the optical pickup according to any one of claims 9 to 11, wherein the direction of a straight line passing through the center of the optical axis coincides with a direction corresponding to the track direction of the optical information medium.

  In the invention described in claim 13, the branching element is a polarization hologram, and is provided in a common part of the forward path from the laser light source to the optical information medium and the return path from the optical information medium to the photodetector. The optical pickup according to claim 9, wherein:

  The invention according to claim 14 is provided with a driving means for driving the condenser lens, and the branching element is integrated with the condenser lens and mounted on the driving means. The optical pickup described in 1.

  According to the fifteenth aspect of the present invention, one of the + 1st order diffracted light and the −1st order diffracted light generated by the branch element is used for focus error detection, the other is used for tracking error detection, and a straight line passing through the center of the optical axis by the branch element. 10. The tracking error detection light obtained by dividing the light beam cross-section of the light beam into two is guided to different detection areas, and tracking error detection is performed by subtracting outputs in the respective detection areas. The optical pickup according to -14.

  The invention according to claim 16 further includes a diffraction grating for branching the laser light emitted from the laser light source into a main beam of zero order light and a sub beam of ± first order light, and the light of the sub beam diffracted thereby 16. The optical pickup according to claim 9, further comprising a photodetector for receiving reflected light reflected by the optical information medium.

  In the invention according to claim 17, the reflected light obtained by reflecting the sub-beam light diffracted by the diffraction grating by the optical information medium is also split by the hologram element by dividing the light beam section into two in the radial direction of the optical information medium, Each of the light beams branched from the area is received by independent tracking detectors, and the difference between the output in the separate detection area for the main beam and the output difference in the separate detection area for the sub-beam are multiplied by a certain coefficient. 17. The optical pickup according to claim 16, wherein a tracking error signal is obtained based on a difference from the value.

  The invention described in claim 18 is characterized in that a photodetector is integrally formed adjacent to a monolithic laser chip that outputs light of different wavelengths or a plurality of laser chips arranged close to each other. An optical pickup and an optical information processing apparatus according to claim 17.

  The nineteenth aspect of the present invention is the optical pickup according to the eighteenth aspect, wherein a focus detector and a tracking detector are arranged on both sides of the light emitting point of the laser light source.

  According to a twentieth aspect of the present invention, when the direction of the line connecting the light emitting points of a plurality of laser beams having different wavelengths in the plane orthogonal to the optical axis direction of the optical pickup is the x direction, the x is sandwiched between the light emitting points. 20. The optical pickup according to claim 19, wherein a focus detector and a tracking detector are disposed in the direction.

  The invention according to claim 21 is characterized in that both the longitudinal direction of the strip of the focus detector and the diffraction direction by the hologram element coincide with the direction orthogonal to the track direction when viewed from the direction along the optical axis. The optical pickup according to any one of?

  The invention according to claim 22 is based on the optical pickup according to any one of claims 1 to 21, difference calculation means for calculating a difference between a plurality of signals output from the optical pickup, and the output of the difference calculation means. An optical information processing apparatus includes a focus control unit that controls a focus driving unit included in the optical pickup.

  According to the present invention, a photodetector for an optical pickup that records and reproduces optical information media having different substrate thicknesses and surface densities using light of different wavelengths is realized with a simple detection pattern, and further, a light source and a photodetector The optical pickup can be made a simpler structure by integration with, so that the productivity can be improved and the cost can be greatly reduced.

  In addition, a control algorithm for optimally controlling the relative position between the recording track of the optical information medium and the focused spot by the objective lens can be simplified, and the circuit scale of the optical information processing apparatus can be reduced.

  Further, the offset of the tracking error signal with respect to disturbance factors such as objective lens shift and disc tilt can be reduced, and stable recording / reproducing quality and high compatibility between apparatuses can be realized.

(Embodiment 1)
An embodiment of an optical pickup and an optical information processing apparatus according to the present invention will be described with reference to FIGS. In addition, the same number is attached | subjected about the same structure. FIG. 1 uses a laser unit 3 in which a monolithic laser chip 1 that emits light of a plurality of different wavelengths and a photodetector 2 formed adjacent to the laser chip 1 are integrated. In FIG. 1, red light having a wavelength of 650 nm or infrared light having a wavelength of 800 nm emitted from the laser chip 1 is converted into parallel light by the collimating lens 4, the optical path is bent by the rising mirror 5, and the polarization hologram elements 6 and ¼. It passes through the wave plate 9. At this time, light is not diffracted with respect to linearly polarized light emitted from the laser light source 1 due to the polarization dependence of the hologram 6. Further, the polarization hologram element 6 and the quarter wavelength plate 9 are mounted on the actuator 11 together with the condenser lens, and are moved integrally with the control movement of the objective lens.

  The light that has been circularly polarized by the quarter-wave plate 9 is condensed by the objective lens 7 and condensed on the recording surface 8 of the optical disk such as DVD or the recording surface 12 of the optical disk having a different substrate thickness such as CD. This is used for forming signal marks and reading pre-formed signals. In particular, when recording and forming signal marks, it is necessary to ensure compatibility with other devices, so it is important to maintain the relative position between the focused spot and the optical recording medium with high accuracy. . For this reason, the focus control for maintaining the distance from the objective lens 7 with respect to the recording surface 8 or 12 of the recording surface of the optical information medium, or the fluctuation of the recording track position accompanying the eccentricity of the optical information medium, follows. Detection accuracy of tracking control for positioning the focused spot on the track is required.

  When the light reflected by the recording surface 8 or 12 of the optical information medium passes through the wave plate 9, it is converted from circularly polarized light to linearly polarized light having a polarization direction orthogonal to the forward path. Unlike the optical pickup shown in the related art, in the case of this embodiment, any two different wavelengths are diffracted and branched into a plurality of light beams by the polarization hologram 6 in the return path. As will be described later, this is because light of different wavelengths is received by a common photodetector pattern and the same signal processing is performed. In addition, since the light path from the light emitting point to the optical disk is common for light of different wavelengths, it may not be possible to provide separate branch elements for each wavelength as in the optical pickup shown in the prior art. The plurality of diffracted light beams pass through the rising mirror 6 and the collimating lens 4 to be projected onto the photodetector 2 while being condensed.

  According to the present embodiment, the laser light source 1 that irradiates light of a plurality of wavelengths and the photodetector 2 are integrally formed, and not only the forward path and the return path of the optical system are common, but also light of different wavelengths. Since the optical path is common and the branch element on the return path supports both lights, the number of optical components is extremely small, and the optical system is extremely simplified. In addition, the number of optical adjustment axes is small, the productivity of the optical pickup is increased, and the cost is reduced.

  Furthermore, the pattern of the photodetector which implement | achieves the optical pick-up which is this embodiment is demonstrated using FIG. FIG. 2A shows a plan view of the polarization hologram element 6 viewed from the optical axis direction (perpendicular to the paper surface). The polarization hologram 6 has two regions D1 and D2 on the left and right in the drawing along a straight line Y1-Y2 passing through the optical axis center o, and the pitches of the diffraction gratings are different from each other in each region. For this reason, the return light from the optical disc is diffracted into + 1st order light and −1st order light at different angles at the part passing through D1 and the part passing through D2. Accordingly, both the + 1st order light and the −1st order light are guided to different photodetectors while the light beam cross section is divided into two in a semicircular shape. The straight line Y1-Y2 coincides with the track direction of the optical disc (direction orthogonal to the radial direction).

  FIG. 2B is a diagram showing a light beam diffracted by the polarization hologram goes to the photodetector. For the sake of simplicity, the rising mirror and the collimating lens are omitted in FIG. The detector is divided into two photodetectors 10a and 10b and two equally divided photodetectors 10c and 10d on both sides so as to sandwich the laser light source 1 therebetween. In the figure, for example, light diffracted to the photodetectors 10a and 10b side is + 1st order light, and light diffracted to the 10c and 10d side is -1st order light. A light beam indicated by a solid line indicates light having a wavelength λ1 for DVD, and a light beam indicated by a broken line indicates light having an infrared wavelength λ2 for CD. Of the + 1st order diffracted light, the light of wavelength λ1 diffracted in the region D1 is incident on the photodetector 10a. At this time, the semicircular light beam converges on the side farther from the surface of the photodetector 10a when viewed from the polarization hologram 6. The light of wavelength λ1 having a point P1 (P2 for light of wavelength λ2) and diffracting the region D2 is incident on the photodetector 10b. At this time, this semicircular light beam is detected by the polarization hologram 6. It has a convergence point P3 (P4 for light of wavelength λ2) closer to the surface of the vessel 10a. This difference in the position of the convergence point is due to the difference in the pitch of the hologram. When the optical distance between the optical disk and the objective lens changes due to some factor and enters a defocused state, the focal point imaging point (P1 to P4) by the return optical system moves in the optical axis direction.

  FIG. 2C shows a plan view of the photodetectors 10 a to 10 d and the laser light source 1. As shown in the figure, two light emission points of light having different wavelengths as viewed from the optical axis (direction orthogonal to the paper surface) are arranged on a straight line X1-X2, and detectors 10a, 10b and detectors 10c, 10d. Are also arranged on a straight line X1-X2. Each of the detectors 10a, 10b, 10c, and 10 is irradiated with a light beam divided and diffracted by the hologram 6, and geometrically semicircular spots 12a, 12b, 12c, and 12d (light having a wavelength λ2) by light having a wavelength λ1. Then, semicircular spots 13a, 13b, 13c, 13d) are formed. In the figure, photodetectors 10a and 10b divided into two are focus error detectors, and at the time of defocusing, for example, convergence points P1 and P3 of light of wavelength λ1 (convergence points P3 and P4 for light of wavelength λ2) are obtained. By moving in a direction far from the hologram, the spot size on the detector 10a increases, the amount of light kicked by the detector 10a increases, the output from 10a decreases, and conversely the spot on the detector 10b becomes Since the amount of light entering the detector 10b is increased by decreasing, the output increases. Therefore, a focus error signal can be obtained by taking the difference between these outputs. For the light of wavelength λ2, the position of the light emission point W2 is shifted on the straight line X1-X2 with respect to the position of the light emission point W1 of the light of wavelength λ1, and the diffraction direction of the hologram due to the wavelength error is the X direction. Therefore, semi-circular light spots 13a and 13b are formed on the photodetectors 10a and 10b, respectively, although they are slightly deviated from the light of wavelength λ1. Therefore, it is possible to obtain a focus error signal for light of different wavelengths with the same photodetector and the same output calculation.

In the figure, the two-divided photodetectors 10c and 10d are tracking error detectors, which can detect the light quantity balance with respect to the track center of the optical disc by taking the difference between the output of 10c and the output of 10d. Since this tracking detector is also on the straight line X1-X2, the difference in wavelength can be absorbed within 10c and 10d, respectively.
As shown in FIG. 1, if the polarization hologram 6 is mounted on the actuator together with the objective lens, it follows the fluctuation of the track position due to the eccentricity of the disk and the objective lens shifts in the radial direction of the optical disk. However, the dividing line of the hologram always coincides with the line passing through the center of the objective lens, and even if the polarization hologram moves, the divided light spots only shift in the photodetectors 10c and 10d, respectively. It does not appear as an error signal offset.

  As described above, according to the present embodiment, the laser light source that emits light of different wavelengths and the photodetector can be integrated, and the difference in wavelength and the difference in emission point position can be absorbed in the same detector. A focus error signal and a tracking error signal can be obtained by the same output calculation for different types of discs such as CDs and DVDs using light of different wavelengths. The RF signal can be obtained, for example, by taking the sum of outputs 10c and 10d. In the present embodiment, the tracking error detector is divided into two parts. However, it is generally detected by the phase difference method by further dividing the tracking error detector into two parts on the straight line X1-X2 in the vertical direction on the drawing. A tracking signal such as a DVD-ROM can also be obtained.

(Embodiment 2)
FIG. 3 is a diagram showing another embodiment of the focus side detector. In FIG. 3 (a), the focus detector is composed of six regions in which two pairs of detectors divided into three strips are arranged, and light beams from semicircular regions divided by holograms are respectively projected onto each group. The In the case of this configuration, as the focus error signal (FE) is obtained by taking the difference of the sum of the region where the light amount increases and the region where the light amount decreases as the spot diameter changes due to defocusing,
FE = (a + c + e) − (b + d + f)
It is obtained by the operation like

FIG. 6B shows the same detector pattern, but the calculation method is different. Generally, when a focused spot on an optical disk is scanned on a track during reproduction or overwriting, it passes over a mark that has already been formed. At this time, diffraction at the mark edge boundary in the track direction and a light amount balance difference occur in the track direction. Since this appears as a change in intensity in the y direction in the figure, this change is applied to the focus signal as a component other than the defocus component. Actually, the influence is small due to a frequency band difference or the like, but it is desirable to remove this error factor in order to further improve accuracy. More specifically, the difference in the amount of change that occurs between the three strip-shaped regions is normalized by the total amount of light for each semicircular spot. That is, for example, FE = (a + c−b) / (a + b + c) − (d + fe) / (d + e + f)
Perform operations like

  As a result, even if there is a light amount balance difference at the mark edge boundary, the component is normalized, so that it does not ride on the focus error signal as an error. For this reason, the stability of the focus control is improved, which is convenient when a high accuracy is required for forming the recording mark.

(Embodiment 3)
FIG. 4 is a diagram showing another embodiment of the present invention. FIG. 4A is a diagram illustrating a configuration of the optical pickup according to the present embodiment. The difference from the optical pickup of the first embodiment described above is that a diffractive element 15 that branches the laser light from the laser light source 1 into three beams of 0th order light and ± 1st order light is provided. That is, this embodiment shows that the present invention can be easily extended to a tracking detection method generally called a three-beam method or a DPP method (Differential Push-Pull method). The three beams generated by the diffractive element 15 are condensed on the recording surface 8 or 12 of the optical disc, respectively, to form three spots. Of the three spots, the spot of ± 1st order diffracted light is called a sub beam, and the 0th order diffracted light is called a main beam. These lights are incident on the photodetector 2 while the light beam is divided into regions by the polarization hologram element 6.

FIG. 4B separately includes detectors l and m that receive this sub beam. Therefore, the tracking error signal TE is set to TE = 1-m for a disk such as a CD-ROM that generally uses the 3-beam method.
For discs with guide grooves on CD-R / RW, DVD-R / RW, DVD-RAM and other disks, the far field for comparing the amount of groove diffraction on the inner and outer circumferences of the disk In law
TE = (g + h) − (i + k)
In a DVD-ROM device that is obtained by the above and the phase difference method is general, for example, TE can be detected by phase comparison between (g + k) and (i + h).

FIG. 4C shows that the sub-beam is also divided into two by the polarization hologram 6 at the center line in the track direction, so that the DPP tracking detection method can be performed. In the DPP method, even if the objective lens moves due to the eccentricity of the disk or the like, the offset of the tracking error signal caused by it can be canceled by the calculation of the main beam and the sub beam, so the tracking control accuracy is high. The sub-beam light receiving area is divided into two parts, n, p, q, and r, respectively. In this case, the tracking error signal of CD-ROM, CD-R / RW, and DVD-R / RW is DPP, that is, if K is an arithmetic coefficient, TE = (g + h) − (i + k) −K {(n + q) − (P + r)}
For DVD-RAM, the push-pull method is used.
TE = (g + h) − (i + k)
For a DVD-ROM, TE can be detected by phase comparison between (g + k) and (i + h).

  As described above, according to the present embodiment, an optimum tracking detection method can be selected and adopted for optical disks having different wavelengths and different specifications with a simple detector configuration. The diffractive element 15 may be an element that diffracts only one of lights having different wavelengths.

(Embodiment 4)
FIG. 5 is a diagram showing a pattern arrangement of light sources and photodetectors in another embodiment of the present invention. As shown in the figure, in this embodiment, the laser light source 51 emits light of three different wavelengths, such as a red laser for DVD, an infrared laser for CD, a blue laser for BD, and the like. To do. The respective light emitting points W1, W2, W3 viewed from the optical axis direction are arranged on a straight line X1-X2, and the detector pattern shown in the third embodiment is similarly formed on X1-X2. . A geometrically semicircular spot formed by diffracting and branching light of each wavelength by a polarization hologram element or the like and condensing on a photodetector is formed as shown in FIG. In this way, the light emission point position shift and the diffraction angle difference in the hologram are absorbed with respect to the three wavelengths, and the focus and tracking signals can be obtained by calculating the same output from all the same detectors. Can do.

(Embodiment 5)
FIG. 6 is a diagram showing another embodiment of the present invention. In the configuration of the optical pickup shown in FIG. 6A, the monolithic laser light source 21 that emits light of different wavelengths and the photodetector 23 that receives the light reflected from the recording surface 8 or 12 of the optical disk are composed of separate components. . The polarization beam splitter 22 branches the forward path and the return path of the optical system. Even with such a configuration, for example, the detector pattern described in the third embodiment can be applied. That is, in the same control signal detection method as that of the third embodiment, the light emission point divergence direction of light having different wavelengths on the coordinates viewed from the optical axis direction, the diffraction direction of the hologram, and the arrangement direction of the detector pattern are matched. Sharing for different wavelengths can be realized. In the detection pattern shown in FIG. 6B, strip-shaped photodetectors a, b, and c and d, e, and f are focusing photodetectors, g to r are tracking photodetectors, and the calculation method is as follows. The same as in the third embodiment.

The optical pickup according to the present invention is a device of an optical information recording apparatus that performs recording / reproduction on a plurality of different optical recording media with one apparatus, in particular by integrally forming a light source and a photodetector with different wavelengths. The present invention can be applied to uses such as a recordable optical disk device such as a CD, DVD, and Blu-ray that are required to be small and low cost.

1 is a configuration diagram of a main part of an optical pickup according to an embodiment of the present invention. Plan view of polarization hologram in the same embodiment Optical path diagram from hologram to photodetector in the same embodiment Light source-photodetector pattern diagram in the same embodiment FIG. 4 is a configuration diagram of a main part of another embodiment of the present invention, in which (a) illustrates an example of a photodetector pattern and a detection principle, and (b) illustrates another example of a photodetector pattern and a detection principle. Illustration to explain The principal part block diagram of the optical pick-up in another embodiment of this invention The figure explaining an example of the light source-photodetector pattern in the embodiment The figure explaining the other example of the light source-photodetector in the embodiment The figure explaining the example of the light source-photodetector pattern in other embodiment of this invention. The block diagram of the optical pick-up in another embodiment of this invention Photodetector pattern diagram in the same embodiment Main part configuration diagram of optical pickup in the prior art

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser light source 2 Photodetector 3 Laser unit 4 Collimate lens 5 Raising mirror 6 Polarization hologram element 7 Objective lens 9 Wave plate

Claims (22)

A laser light source, a condenser lens for condensing the light from the laser light source on the optical information medium, a branch element for diffracting and branching the reflected light from the optical information medium, and a photodetector for receiving the light branched by the branch element And the branching element divides the light beam cross section of the light beam into two by a straight line passing through the center of the optical axis and guides the divided light beam to another detection area, and collects one of the two divided light beams from the light detector surface. An optical pickup characterized in that the optical beam is converged to a side closer to, the other light beam is converged to a side farther from the condenser lens than the photodetector surface, and a plurality of signals are output from each detection region. Three detectors a, b, and c (in which b is an area between a and c), and three detectors d that are also divided into strips. , E, f (where e is a region sandwiched between d and f), and the light whose beam section is divided into two by the branching element is respectively detected by the photodetectors a, b, c. And the combination of the photodetectors d, e, and f, and the amount of change in the output sum of a, c, and e, which is generated when the size of the light spot formed on the detector surface changes. 2. The optical pickup according to claim 1, wherein a plurality of signals having a change amount of an output sum of d, f, and b are output. Three detectors a, b, and c (in which b is an area between a and c), and three detectors d that are also divided into strips. , E, f (where e is a region sandwiched between d and f), and the light beams obtained by dividing the light beam cross-section by the branching elements into the photodetectors a, b, c, respectively. And the combination of photodetectors d, e, and f, and the output sum of a and c and the output of b generated by the change in the size of the light spot formed on the detector surface. The value obtained by normalizing the change amount of the difference with the output sum of a, b, and c is normalized with A, and the change amount of the difference between the output sum of e, g, and the output of f is normalized with the output sum of d, e, and f. 2. The optical pickup according to claim 1, wherein a plurality of signals having the calculated value B are output. 4. The optical pickup according to claim 1, wherein a dividing line direction in which the branching element divides the beam cross section into two coincides with a direction corresponding to a track direction of the optical information medium. 5. The branching element is a polarization hologram, and is provided in a common portion between an outward path from the laser light source to the optical information medium and a return path from the optical information medium to the photodetector. The optical pickup according to any one of the above. One of the + 1st order diffracted light and the −1st order diffracted light generated by the branching element is used for focus error detection, the other is used for tracking error detection, and the light beam cross section of the light beam is divided into two by a straight line passing through the center of the optical axis by the branching element. 6. The optical pickup according to claim 1, wherein the tracking error detection light is guided to different detection areas and outputs a plurality of signals from each of the detection areas. The laser beam emitted from the laser light source further includes a diffraction grating that branches the main beam of zero-order light and the sub-beam of ± first-order light, and the reflected light reflected by the optical information medium by the sub-beam light diffracted thereby. The optical pickup according to claim 1, further comprising a photodetector for receiving light. 8. The light according to claim 7, wherein the light of the sub beam reflected by the optical information medium is branched by dividing the light beam section into two by the branch element, and each of the branched light is received by independent detectors. pick up. A monolithic laser light source that outputs light of different wavelengths or a laser light source in which a plurality of laser chips that output light of different wavelengths are arranged close to each other, and a light source that condenses the light from the laser light source onto an optical information medium An optical lens; a branch element that diffracts and branches reflected light from the optical information medium; and a photodetector that receives light branched by the branch element. The branch element is a light beam that passes through the center of the optical axis. The beam cross section of the beam is divided into two and led to different detection areas, and one of the two divided light beams is converged to the side closer to the condensing lens than the surface of the light detector, and the other light beam is irradiated with light. An optical pickup which converges on a side farther from the condenser lens than the detector surface and outputs a plurality of signals from each detection region. Three detectors a, b, and c (in which b is an area between a and c), and three detectors d that are also divided into strips. , E, f (where e is a region sandwiched between d and f), and the light whose beam section is divided into two by the branching element is respectively detected by the photodetectors a, b, c. And the combination of the photodetectors d, e, and f, and the amount of change in the output sum of a, c, and e, which is generated when the size of the light spot formed on the detector surface changes. 10. The optical pickup according to claim 9, wherein a plurality of signals having a change amount of an output sum of d, f, and b are output. Three detectors a, b, and c (in which b is an area between a and c), and three detectors d that are also divided into strips. , E, f (where e is a region sandwiched between d and f), and the light beams obtained by dividing the light beam cross-section by the branching elements into the photodetectors a, b, c, respectively. And the combination of photodetectors d, e, and f, and the output sum of a and c and the output of b generated by the change in the size of the light spot formed on the detector surface. The value obtained by normalizing the change amount of the difference with the output sum of a, b, and c is normalized with A, and the change amount of the difference between the output sum of e, g, and the output of f is normalized with the output sum of d, e, and f. 10. The optical pickup according to claim 9, wherein a plurality of signals with the value B are output. 12. The optical pickup according to claim 9, wherein the direction of a straight line passing through the center of the optical axis coincides with a direction corresponding to a track direction of the optical information medium. The branching element is a polarization hologram, and is provided in a common part between a forward path from the laser light source to the optical information medium and a return path from the optical information medium to the photodetector. 12. The optical pickup according to any one of 12 above. The optical pickup according to claim 9, further comprising a driving unit that drives the condenser lens, wherein the branch element is integrated with the condenser lens and is mounted on the driving unit. One of the + 1st order diffracted light and the −1st order diffracted light generated by the branching element is used for focus error detection, the other is used for tracking error detection, and the light beam cross section of the light beam is divided into two by a straight line passing through the center of the optical axis by the branching element. The light according to claim 9, wherein the tracking error detection light is guided to different detection areas, and the tracking error detection is performed by subtracting the outputs in the respective detection areas. pick up. The laser beam emitted from the laser light source further includes a diffraction grating that branches the main beam of zero-order light and the sub-beam of ± first-order light, and the reflected light reflected by the optical information medium by the sub-beam light diffracted thereby. An optical pickup according to claim 9, further comprising a photodetector for receiving light. The reflected light that is reflected by the optical information medium by the sub-beam light diffracted by the diffraction grating is also split by the hologram element by dividing the light beam cross section into two in the radial direction of the optical information medium. Received by an independent tracking detector, tracking error signal by the difference between the difference between the output of the main beam in different detection areas and the difference of the output of the sub-beams in different detection areas multiplied by a constant coefficient The optical pickup according to claim 16, wherein the optical pickup is obtained. The light according to any one of claims 9 to 17, wherein a photodetector is integrally formed adjacent to a monolithic laser chip that outputs light of different wavelengths or a plurality of laser chips that are arranged close to each other. pick up. 19. The optical pickup according to claim 18, wherein a focus detector and a tracking detector are disposed on both sides of the light emitting point of the laser light source. When the direction of the line connecting the light emitting points of a plurality of laser beams having different wavelengths in the plane orthogonal to the optical axis direction of the optical pickup is the x direction, the focus detector and tracking detection are in the x direction across the light emitting point. The optical pickup according to claim 19, wherein a vessel is arranged. 21. The light according to claim 9, wherein the longitudinal direction of the strip of the focus detector and the diffraction direction by the hologram element coincide with a direction orthogonal to the track direction when viewed from the direction along the optical axis. pick up. An optical pickup according to any one of claims 1 to 21, difference calculation means for calculating a difference between a plurality of signals output from the optical pickup, and focus drive means provided in the optical pickup based on an output of the difference calculation means. An optical information processing apparatus comprising: focus control means for controlling.

Images