JP2006099844A - Optical head apparatus and optical disk apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical head apparatus and an optical disk apparatus by which coma aberration caused by tilt of an optical disk can be detected quantitatively by using a knife edge (Foucault) method. <P>SOLUTION: This optical head apparatus has a laser light source 20 emitting a laser beam, an objective lens 24 converging the laser beam emitted from this laser light source 20 on an information recording medium 1, and a photodetector 27 receiving reflected light from the information recording medium 1 through a condenser lens 25 converging it. A knife edge 26 is arranged at a converging position at which the reflected light is converged by the condenser lens 25, and tilt quantity of the information recording medium is detected based on an image projected by this knife edge 26. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical head device and an optical disc device for recording or reproducing information with respect to an optical disc. In particular, the coma aberration generated by tilting the optical disc is quantitatively determined using a knife edge (Fucault) method or the like. The present invention relates to an optical head device and an optical disk device that can be detected easily.

  As is well known, an optical disc (current generation DVD) having a single-sided capacity of 4.7 GB (gigabytes) has been put to practical use as an optical disc capable of recording information at high density. For example, there are a DVD-ROM (Digital Versatile Disk-Read Only Memory), a DVD-RW (Rewritable), a DVD-RAM (Random Access Memory), etc., which are read-only optical disks. However, in recent years, BS digital broadcasting and terrestrial digital broadcasting have begun, and a next-generation DVD (next-generation DVD) having several tens of gigabytes that can be recorded at the resolution of digital broadcasting has been developed and put into practical use. This next-generation DVD must realize a surface recording density of about 5 times that of the current DVD in order to be able to record at the resolution of digital broadcasting.

In order to increase the surface recording density, the beam spot diameter is generally narrowed by increasing the numerical aperture (NA) indicating the convergence performance of the objective lens as much as possible. This is because the spot diameter decreases in inverse proportion to the numerical aperture. Therefore, the smaller the beam spot diameter, the higher the surface recording density. On the other hand, when the optical disc is tilted in the radial direction with respect to the objective lens, the shape of the beam spot is disturbed by coma aberration caused by the substrate of the optical disc, so that the recording / reproducing characteristics are deteriorated. Since the coma aberration is proportional to the third power of the numerical aperture of the objective lens, the higher the numerical aperture of the objective lens, the narrower the margin of radial tilt (radial tilt) of the optical disc with respect to the recording / reproducing characteristics (when the tilt margin becomes narrower) , The mechanical error allowed for disc manufacturing and device assembly is extremely small, which is not very good). Therefore, in an optical head device or an optical disc device in which the numerical aperture of the objective lens is increased in order to increase the surface recording density, it is necessary to accurately detect and correct the optical disc radial tilt so as not to deteriorate the recording / reproducing characteristics. It is. For example, Japanese Patent Laid-Open No. 2003-016679 and Japanese Patent Laid-Open No. 2003-346365 detect such a tilt.
JP 2003-016679 A (paragraph number 0006, FIG. 3) Japanese Unexamined Patent Publication No. 2003-346365 (paragraph number 0013, FIG. 1)

  According to the technique described in the above-mentioned Patent Document 1, before the light is focused on the photodetector, the inner and outer sides of the light beam are condensed on separate photodetectors by the diffraction grating, and a spherical surface and a radial coma are calculated by respective calculations. Each aberration detection signal of the tangential coma is obtained. However, in Patent Document 1, for the purpose of tilt detection, the inner side and the outer side of the light beam are separately calculated, so that the optical system becomes complicated and the cost increases, and an eight-divided detector is required. There is a problem in that the S / N of the signal is lowered due to the increase in the signal.

  According to the technique described in Patent Document 2, the light source, the objective lens that condenses the light emitted from the light source on the optical recording medium, and the photodetector that receives the reflected light from the optical recording medium. A main beam and a sub beam having different intensity distributions when incident on the objective lens are used, a track error signal is detected from each of the main beam and the sub beam by a phase difference method, and the track error signal of the main beam and the track error of the sub beam are detected. A radial tilt of the optical recording medium is detected based on a phase shift from the signal. However, in Patent Document 2, since the amount of the recording / reproducing beam is reduced due to the use of three beams, the amount of tilt detection varies depending on the quality of the track error signal in order to detect the phase of the track error signal. There is.

  Accordingly, the present invention has been made to solve the above-described problems, and is a light that can quantitatively detect coma generated by tilting an optical disk using a knife edge (Fucault) method or the like. A head device and an optical disk device are provided.

  In order to solve the above-described problems, the present invention provides a laser light source that emits laser light, an objective lens that focuses the laser light emitted from the laser light source on an information recording medium, and the information recording medium. And an optical head device having a photodetector that receives the reflected light through a condensing lens, and a knife edge is disposed at a condensing position where the reflected light is collected by the condensing lens. A tilt amount of the information recording medium is detected based on an image projected by a knife edge.

  In order to solve the above-described problems, the present invention provides a laser light source that emits laser light, an objective lens that focuses the laser light emitted from the laser light source on an information recording medium, and the information recording medium An optical head device having a photodetector that receives the reflected light from the condenser lens that collects the reflected light from the diffractive element at a condensing position where the reflected light is collected by the condenser lens, A tilt amount of the information recording medium is detected based on a diffraction image diffracted by the diffraction element.

  In order to solve the above-described problems, the present invention provides a laser light source that emits laser light, an objective lens that focuses the laser light emitted from the laser light source on an information recording medium, and the information recording medium In the optical head device, comprising: a condensing lens that condenses the reflected light from the light; and a photodetector that receives light through a composite prism that transmits and reflects the reflected light collected by the condensing lens. The prism has a knife edge or a diffractive element, and the information is based on an image obtained by projecting the reflected light collected by the condenser lens by the knife edge or an image obtained by diffracting by the diffractive element. It is characterized in that the tilt amount of the recording medium is detected.

  According to the present invention, since the amount of tilt of the information recording medium is detected by arranging the knife edge or the diffraction element at the condensing position of the condensing lens of the light receiving optical system, it is not necessary to divide the light transmission system beam. The detector division of the light receiving system may be two divisions in one direction detection and four divisions at most in two directions, so that it is possible to detect tilt at low cost and high S / N.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram showing a schematic configuration of an embodiment according to an optical disc apparatus of the present invention. As shown in FIG. 1, an optical disc 1 is a disc-shaped information recording medium in which a reflective information recording layer is formed on a polycarbonate substrate having a thickness of 0.6 mm, for example. A short wavelength semiconductor laser light source 20 is used as the light source. The wavelength of the emitted light is, for example, in the violet wavelength band in the range of 400 nm to 410 nm. The outgoing light 100 from the semiconductor laser light source 20 is converted into parallel light by the collimator lens 21, passes through the polarization beam splitter 22 and the λ / 4 plate 23, and enters the objective lens 24. Thereafter, the light passes through the substrate of the optical disc 1 and is condensed on the information recording layer. The reflected light 101 from the information recording layer of the optical disc 1 passes through the substrate of the optical disc 1 again, passes through the objective lens 24 and the λ / 4 plate 23, is reflected by the polarization beam splitter 22, and then passes through the condenser lens 25. Then, it enters the photodetector 26.

  The light receiving part of the photodetector 27 is normally divided into a plurality of parts, and outputs a current corresponding to the light intensity from each light receiving part. The output current is converted into a voltage by an unillustrated I / V amplifier (current / voltage conversion) and then input to the arithmetic circuit 40. The input voltage signal is arithmetically processed by the arithmetic circuit 40 into a tilt error signal, HF signal, focus error signal, track error signal, and the like. The tilt error signal is for tilt control, the HF signal is for reproducing information recorded on the optical disc 1, the focus error signal is for focus control, and the track error The signal is used for tracking control.

  The objective lens 24 can be driven by the actuator 28 in the vertical direction, the disc radial direction, and the tilt direction (radial direction and / or tangential direction), and is controlled by the servo driver 50 so as to follow the information track on the optical disc 1. Is done. There are two types of tilt directions. There is a “radial tilt” that occurs when the disc surface tilts toward the center of the optical disc, and a “tangential tilt” that occurs in the tangential direction of the track. Of these, radial tilt is generally caused by warping of the disk. It is necessary to consider not only the tilt that occurs during disk manufacture, but also the tilt that occurs due to aging and sudden changes in the usage environment.

  The tilt sensor according to the present invention functions by arranging a knife edge 26 at the focal position of the condensing lens 25 of the light receiving optical system and detecting the image by the photodetector 27.

  FIG. 2 shows the arrangement relationship between the knife edge 26 and the photodetector 27.

  A knife edge 26 having an edge in the horizontal direction in the figure is installed at the focal position of the condenser lens 25, and the lower half of the light beam is shielded. An image by the knife edge 26 is projected onto the photodetector 27. When the optical disc 1 is tilted, coma aberration occurs in the reflected light beam 101 shown in FIG. Therefore, a so-called Foucault (knife edge) test is performed by placing the knife edge 26 at the focal position of the condensing lens 25, and the image reflects coma aberration. By doing so, since the recording / reproducing beam is used for detection, it is possible to accurately detect the tilt amount that directly affects the characteristics.

  FIG. 3 is a light beam image on the photodetector 27. It can be seen that when the optical disc 1 has no tilt, it is a simple semi-circular image (the center figure), whereas when the tilt is applied, an elliptical image is formed, which is divided into bright and dark depending on the tilt direction. Therefore, by monitoring the amount of light on the detector 27, a signal substantially proportional to the tilt can be obtained. That is, in the case of this example, when the tilt is applied in the minus direction (−0.6 degrees), the amount of light detected by the photodetector 27 decreases (left figure), and when the tilt is applied in the plus direction (0.6 degrees), light is emitted. The amount of light detected by the detector 27 increases (right figure). In this case, the plus direction and minus direction of the disc tilt are as shown in FIG. However, since it is necessary to correct the zero point, in this case, it is necessary to use a photodetector that is divided into two at the top and bottom in FIG. It is.

  The arrangement of the knife edge 26 in FIG. 2 is convenient for detecting a tilt occurring in the vertical direction in the figure. That is, when the vertical direction in the figure corresponds to the radial direction of the optical disk 1, for example, the radial tilt can be detected well by this arrangement. Conversely, when it is desired to detect the tilt of the optical disk 1 in the track extending direction (tangential direction), the knife edge may be rotated 90 degrees within the plane of the drawing.

  Further, as another embodiment, there is a method in which the knife edge of FIG. 1 is divided into upper and lower divided diffraction elements, that is, a so-called double knife edge type.

  FIG. 5 is a block diagram showing a schematic configuration of an embodiment of an optical disc apparatus including such a tilt sensor. FIG. 6 is a diagram showing an arrangement relationship between the diffraction element and the photodetector. FIG. 7 is a diagram showing that the diffractive element is vertically divided into two. FIG. 8 is a diagram showing a light beam image on the photodetector when a diffraction element is used. In addition, the same code | symbol is attached | subjected to the same component.

  As shown in FIGS. 5 to 8, a diffractive element 29 is disposed at the condensing position of the condensing lens 25 instead of the knife edge 26. As shown in FIG. 7, the diffraction element 29 is vertically divided into two, and the light beam that has passed through the upper part K1 has a diffraction image corresponding to the case where the lower part of the light beam at the condensing position is shielded by the knife edge. Projected on top. On the other hand, the light beam that has passed through the lower part K2 is projected on another region of the photodetector 27 as a diffraction image corresponding to the case where the upper part of the light beam at the condensing position is shielded by the knife edge. FIG. 8 shows an image on the photodetector 27 at this time. The light beam that has passed through K1 of the diffractive element 29 is guided onto the upper detector in FIG. 8, and a signal S_K1 is generated. Further, the light beam that has passed through K2 of the diffractive element 29 is guided onto the lower detector of FIG. 8, and a signal S_K2 is generated.

  When the tilt is 0, both produce the same image upside down. On the other hand, when the optical disc 1 is tilted as shown in the left and right diagrams of FIG. 8, an elliptical image is generated by reversing the brightness. Therefore, a signal proportional to the tilt can be directly detected by performing the calculation of Tilt = S_K1-S_K2. In this case, when the tilt is 0, the calculation of Tilt = S_K1−S_K2 becomes 0, and there is an advantage that correction of 0 point is not necessary.

  In the above description, the tilt is detected only in one direction. However, for example, by using a diffraction element 29 and a photodetector 27 as shown in FIG. It is also possible to detect disc tilt in the tangential direction. That is, when the diffraction element 29 is divided into four as shown in the figure, the vertical tilt in the figure is calculated as Tilt = (a + b) − (c + d), and the horizontal tilt in the figure is Tilt = (a + d) − (b + c). It is possible to detect simultaneously by performing the calculation. As described above, in the present invention, when detecting a disc tilt in one direction, a two-divided photodetector may be used, and when detecting a disc tilt in two directions, tilting is performed with high accuracy by using a quadrant photodetector. Can be detected.

  By the way, it may be difficult to adjust the knife edge 26 and the diffractive element 29 to be accurately arranged at the condensing position of the condensing lens 25. In this case, the adjustment as shown in FIG. 10 is easy. FIG. 10 is a structural diagram in which a photodetector and a composite prism are combined. As shown in FIG. 10, the composite prism 30 is mounted on the package 27 a of the photodetector 27. The light beam collected by the condensing lens 25 is incident on the half mirror surface 30a on the composite prism 30. The light beam is separated by the half mirror surface 30a into a light beam A for signal detection other than tilt such as an HF signal and a light beam B for tilt detection.

  The light beam A passes through the half mirror surface 30 a and enters the light receiving surface 27 b of the photodetector 27. On the other hand, the light beam B for tilt detection is reflected by the half mirror surface 30 a, further reflected by the mirror surface 30 b of the composite prism 30, and enters the light receiving surface 27 c of the photodetector 27.

  The focal length of the condenser lens 25 is such that the luminous flux A and the luminous flux B are condensed on the final surface 30c of the composite prism 30 when the luminous flux A is condensed on the light receiving surface 27b of the photodetector 27. Each optical path length of the composite prism 30 is designed. Therefore, by transferring the knife edge 26 to the final surface 30c of the composite prism 30, the light beam B for tilt detection can be used for tilt detection by the above-described method.

  Thus, by using the composite prism 30, the adjustment of the condenser lens 25 and the knife edge 26 in the horizontal direction (X direction) in the drawing is only adjusted so that the light flux A is condensed on the light receiving surface 27b of the photodetector 27. As a result, the adjustment efficiency is greatly improved. Further, a diffraction pattern having an effect equivalent to that of the diffraction element 29 may be imprinted on the final surface 30c. In that case, an effect equivalent to that of the configuration example of FIG. 5 can be expected.

  In addition, this invention is not limited to the said embodiment, In the implementation stage, it can change variously in the range which does not deviate from the summary.

1 is a block diagram showing a schematic configuration of an optical disc apparatus according to an embodiment of the present invention. The figure which shows the arrangement | positioning relationship between a knife edge and a photodetector. The figure which shows the light beam image on a photodetector. The figure which shows the tilt direction of an optical disk. The block diagram which shows schematic structure of the optical disk apparatus containing the tilt sensor by other embodiment of this invention. The figure which shows the arrangement | positioning relationship between a diffraction element and a photodetector. The figure which shows that the diffraction element is divided into 2 parts up and down. The figure which shows the light beam image on a photodetector when a diffraction element is used. The figure which shows the arrangement | positioning relationship between a 4-part diffraction element and a photodetector. FIG. 3 is a structural diagram in which a photodetector and a composite prism are combined.

Explanation of symbols

20 Semiconductor laser light source 21 Collimating lens 22 Polarizing beam splitter 23 λ / 4 plate 24 Objective lens 25 Condensing lens 26 Knife edge 27 Photo detector 27a Package 27b, c Light receiving surface 29 Diffraction element 30 Compound prism 30a Half mirror surface 30b Mirror surface 30c Final surface 40 Arithmetic circuit 50 Servo driver

Claims (8)

Via a laser light source that emits laser light, an objective lens that condenses the laser light emitted from the laser light source on an information recording medium, and a condenser lens that condenses the reflected light from the information recording medium In an optical head device having a photodetector for receiving light,
A light having a knife edge disposed at a condensing position where the reflected light is collected by the condensing lens, and detecting a tilt amount of the information recording medium based on an image projected by the knife edge. Head device. Via a laser light source that emits laser light, an objective lens that condenses the laser light emitted from the laser light source on an information recording medium, and a condenser lens that condenses the reflected light from the information recording medium In an optical head device having a photodetector for receiving light,
A diffractive element is disposed at a condensing position where the reflected light is collected by the condensing lens, and a tilt amount of the information recording medium is detected based on a diffracted image diffracted by the diffractive element. Optical head device. A laser light source that emits laser light, an objective lens that condenses the laser light emitted from the laser light source on an information recording medium, a condensing lens that condenses reflected light from the information recording medium, and In an optical head device having a photodetector that receives light through a composite prism that transmits and reflects the reflected light collected by a condenser lens,
The composite prism has a knife edge or a diffractive element, and is based on an image obtained by projecting the reflected light collected by the condenser lens by the knife edge, or an image obtained by diffracting by a diffractive element. An optical head device for detecting a tilt amount of the information recording medium.   The diffractive element and the photodetector are each divided into four, and the reflected light diffracted by the four-divided diffractive element is received by the four-divided photodetector, and the tilt amounts in two directions perpendicular to each other are simultaneously obtained. 4. The optical head device according to claim 2, wherein the optical head device is detected. Via a laser light source that emits laser light, an objective lens that condenses the laser light emitted from the laser light source on an information recording medium, and a condenser lens that condenses the reflected light from the information recording medium In an optical disc device that reproduces information from a photodetector that receives light and the reflected light received by the photodetector,
An optical disc, wherein a knife edge is disposed at a condensing position where the reflected light is collected by the condensing lens, and a tilt amount of the information recording medium is detected based on an image projected by the knife edge. apparatus. Via a laser light source that emits laser light, an objective lens that condenses the laser light emitted from the laser light source on an information recording medium, and a condenser lens that condenses the reflected light from the information recording medium In an optical disc device that reproduces information from a photodetector that receives light and the reflected light received by the photodetector,
A diffractive element is disposed at a condensing position where the reflected light is collected by the condensing lens, and a tilt amount of the information recording medium is detected based on a diffracted image diffracted by the diffractive element. Optical disk device. A laser light source that emits laser light, an objective lens that condenses the laser light emitted from the laser light source on an information recording medium, a condensing lens that condenses reflected light from the information recording medium, and In a photodetector that receives light through a composite prism that transmits and reflects the reflected light collected by a condenser lens, and an optical disc apparatus that reproduces information from the reflected light received by the photodetector,
The composite prism has a knife edge or a diffractive element, and is based on an image obtained by projecting the reflected light collected by the condenser lens by the knife edge, or an image obtained by diffracting by a diffractive element. An optical disc apparatus for detecting a tilt amount of the information recording medium. The diffractive element and the photodetector are each divided into four, and the reflected light diffracted by the four-divided diffractive element is received by the four-divided photodetector, and the tilt amounts in two directions perpendicular to each other are simultaneously obtained. 8. The optical disc device according to claim 6, wherein the optical disc device is detected.

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