JP2005302084A - Optical information recording and reproducing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce cross talk from other layers caused when a multi-layers optical disk is read out and to reduce influence of other layers at write-in. <P>SOLUTION: A mirror is disposed at each of the converging positions of reflected light from a multi-layer medium, the mirror each having magnitude to the extent that reflected light corresponding to the layer is reflected and reflected light from the other layers are not shielded strongly, and thus each reflected light is separated. Since cross talk between layers of the reflected light separated by the minute mirror is removed, quality of a signal is improved. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical information recording / reproducing apparatus, and more particularly to a read / write optical system of an optical disc drive.

  A general outline of the optical system of the optical disk drive will be described with reference to FIG. Laser light emitted from the semiconductor laser 1 is converted into a parallel and circular beam by the collimator lens 23 and the triangular prism 2. Thereafter, the laser beam is reflected by the polarization beam splitter 31 and converted into circularly polarized light by the λ / 4 wavelength plate 21. This circularly polarized light is condensed on the optical disk 50 by 41 objective lenses. There is a guide groove inside the optical disc, and recording marks having different reflectivities are written along the groove. Since the optical disk is rotating, the recording mark at the laser light irradiation position moves, and the amount of reflected light changes with time. The length and interval of the recording mark are decoded according to the information to be recorded.

  The reflected light having information returns to the objective lens 41 and is converted from circularly polarized light to linearly polarized light by the λ / 4 wavelength plate 21. Since this polarization direction is orthogonal to the polarization direction of the light emitted from the semiconductor laser, it can be transmitted through the polarization beam splitter 31. This transmitted light is divided into two light beams by the half prism 32. The light passing through the condenser lens 42 is narrowed by the condenser lens, but the knife edge 22 is placed in front of the focal position, and half of the light beam is blocked. A two-divided detector 51 is installed at the focal position. When the focus of the irradiation light on the optical disc is deviated, the light quantity entering the two photodetectors of the two-divided photodetector 51 is unbalanced.

  This imbalance is detected as a differential signal by the electronic circuit 60 and used as a focus error signal 71. Using this focus error signal, the position of the objective lens 41 is adjusted by the actuator of 63 so that the focus position of the light emitted from the objective lens 41 is always aligned with the recording mark so as not to be defocused. On the other hand, the light reflected by the half mirror 32 is irradiated onto the two-divided photodetector 52 by the condenser lens 43. The electronic circuit 61 is a differential circuit, and its output is a tracking error signal 72. Further, the signal added by the electronic circuit 62 becomes a read data signal 73.

  The optical disk drive shown above is an example, and the focus error signal method is detected by a Foucault method, and the tracking error signal is detected by a method called a diffracted light differential type. In addition to these, various methods have been proposed. Typical examples of the focus error signal detection method include an astigmatism method and an image rotation method. The tracking error signal detection method includes a three-spot type and a wobbling type. These methods have advantages and disadvantages in optical adjustment or light use efficiency, and are used properly depending on the type of drive. These details are described in detail in (Non-Patent Document 1).

  Currently, transfer of large-capacity / high-speed data is becoming possible, and an optical disc as an information storage medium is required to have a high density in order to record large-capacity data such as moving image information. In order to achieve this, it is necessary to shorten the interval between the recording marks and the track pitch of the optical information recording medium, and the laser light has a shorter wavelength and the objective lens has a higher numerical aperture. As a result, the spot size of the laser beam for reading and writing to the optical information recording medium can be narrowed down to the diffraction limit of the lens aperture. Currently, the use of blue-violet laser light having a wavelength of around 405 nanometers or an objective lens having a numerical aperture of 0.85 is being studied. These values are almost technical limits, and it seems difficult to increase the density in this direction. Therefore, a method of multilayering is listed as a candidate, and a method of stacking recording information recording media in multiple layers is being studied.

  A problem that arises when the recording medium is multilayered is crosstalk from adjacent layers. In (Patent Document 1), in order to detect the reflected light from the adjacent layer, a method of dividing the reflected light into three or more and detecting the reflected light from the adjacent layer is adopted, and crosstalk is reduced by signal processing. A method has been filed.

JP 2001-273640 A

“Basics and Applications of Optical Disk Storage” (supervised by Yoshito Tsunoda, edited by the Institute of Electronics, Information and Communication Engineers)

  An object of the present invention is to reduce interlayer crosstalk without reducing the strength of the read signal. In FIG. 3, reference numeral 501 denotes a cross-sectional view of a two-layer optical information recording medium, where the first optical information recording medium layer is 511 and the second optical information recording medium layer is 512. It is assumed that the irradiation light 80 from the semiconductor laser is collected by the objective lens 41 and is focused on the first optical information recording medium layer 511. The reflected light including information passes through the objective lens 41 and the condenser lens 43 and enters the two-divided detector 52 in the state 81.

  As in FIG. 2, these signals are summed by the electronic circuit 62 to become a data signal. On the other hand, the reflected light 83 from the second optical information recording medium layer 512 passes through the objective lens 41 and the condensing lens 43, and then spreads as if it is emitted from the focal position at a distance twice the layer interval. The light detector 52 is irradiated as reflected light 84 in the focused state. The reflected light 84 becomes crosstalk with respect to the reflected light 81 from the originally intended first optical information recording medium layer, and reading may not be performed accurately. In Patent Document 1, the reflected light is divided into three parts, and the reflected light from each of the layers (the target readout layer and the two adjacent layers of the target layer) is detected at different focal positions. The method to do is adopted. In this method, since the reflected light is divided into three, there is a disadvantage that the light intensity is reduced and the signal-to-noise ratio is reduced.

  The problem to be solved by the present invention is that when reading a multilayer optical recording medium, noise caused by reflected light caused by other layers, so-called crosstalk, is reduced, and reduction in signal strength is suppressed. This is to reduce the probability that data cannot be read. Another object is to reduce the influence of the front layer (that is, closer to the objective lens) when recording.

  In order to achieve the above object, the reflected light from the multilayer optical disk is collected by a condenser lens, and the reflected light from each layer is a position corresponding to the size of each spot size at the position where the minimum spot is formed. A reflection mirror is installed and the reflected light from other layers is passed. The principle will be described with reference to FIG. Reference numeral 502 denotes a three-layer optical information recording medium. The minimum spot of the laser beam is assumed to be on the first optical information recording medium layer 511 by the objective lens 41. It is assumed that the second optical information recording medium layer 512 is far from the objective lens 41 and the third optical information recording medium layer 513 is in front.

  The reflected light from these layers returns to the objective lens 41, and is then condensed by the condenser lens 43 at positions 801, 821, and 831. Reference numeral 801 denotes a first optical information recording medium layer, 821 denotes a second optical information recording medium layer, and 831 denotes a condensing position of reflected light by the third optical information recording medium layer. Since the reflected light from other layers spreads at each reflected light condensing position, the amount of reflected light from other layers can be obtained by installing a reflector of appropriate size at the condensing position of the reflected light. It is possible to extract the reflected light from the corresponding layer without greatly affecting the thickness. In addition, since the reflection light from each layer can be separated by installing the reflecting mirror, it is possible to suppress interference during detection by the photodetector.

  The properties of the reflected light from each layer are as follows and can be used for signal processing. The irradiation light from the objective lens in FIG. 4 is focused on the first optical information recording medium layer 511. Accordingly, the reflectance changes depending on the presence or absence of a minute mark at the irradiation spot position. This reflected light is reflected light 801, which is the original signal readout signal. Since the reflected light from the second optical information recording medium layer 512 is transmitted through the mark of the first optical information recording medium layer, the intensity change also depends on the reflectance of the mark of the first optical information recording medium layer.

  Therefore, the reflected light from the second optical information recording medium layer 512 can also be used as a signal from the mark on the first optical information recording medium layer. Since the irradiation light greatly spreads on the second optical information recording medium layer 512, the reflectance of minute marks existing on the second optical information recording medium layer 512 is averaged and exists on the 512 layer. Since the mark to be applied does not significantly affect the amount of reflected light, it may be a signal from the first optical information recording medium layer.

  The reflected light 831 reflected by the third optical information recording medium layer 513 in the state of a large light spot reflects the average writing state of the third optical information recording medium layer. The average reflectance differs between the state in which nothing is written in the optical medium layer and the state in which it is written. For this reason, the amount of light transmitted to the first optical information recording medium layer 511 changes, and the writing power to the first optical information recording medium layer 511 varies. In order to avoid this, the amount of reflected light 831 is detected, and if the reflection is large, the writing power of the first optical information recording medium layer 511 is decreased, so the laser power for writing is increased and writing is performed. As a result, the shape of the written mark can be made good. As described above, the write power can be adjusted by detecting the reflected light 831.

  In addition, since the reflected light from the adjacent layer includes the reflectance state of the adjacent layer and data signal information, it can be used to control the write signal or improve the quality of the data signal. Therefore, the reflecting mirror which does not completely shield the reflected light from the information reading target layer on the optical axis for collecting the reflected light from the optical disc and reflects the reflected light from the adjacent layer located away from the objective lens. And a light detector for detecting the reflected light from the adjacent layer, or / and reflecting the reflected light from the information reading target layer and completely reflecting the reflected light from the adjacent layer close to the objective lens. It is preferable to install a reflecting mirror that does not block the light and a photodetector that detects the reflected light from the adjacent layer.

As described above, the effect of the present invention is that when reading data from a multilayer optical disk, crosstalk from other optical information recording medium layers can be reduced, and the reliability of the read signal is improved. . In addition, since the reflected light from each layer is detected separately, the use of this information recording makes it possible to reduce the influence of other layers during writing.

An embodiment of the present invention will be described below with reference to FIG.
Laser light emitted from the semiconductor laser 1 is divided into a main beam and two sub beams by the hologram element 27. This is to realize tracking called a differential push-pull method in which three light spots need to be formed on the disk surface. Only the main beam is shown in the figure. The three laser lights are collimated by the collimator lens 23 and then converted into a circular beam by the triangular prism 2. The laser light is reflected by the polarizing prism 31, is circularly polarized by the λ / 4 wavelength plate 21, and then narrowed down to a minute spot by the objective lens 41.

  Each sub beam illuminates an intermediate position between adjacent tracks on both sides. The multilayer optical disk 502 rotates at the focal position of the spot, and reflected light corresponding to the length and interval of the recording mark is generated from the optical information recording medium layers 511, 512, and 513. The reflected light returns from the objective lens 41, is converted into linearly polarized light by the λ / 4 wavelength plate 21, and passes through the polarizing prism 31.

  When the reflected light from different surfaces is narrowed down by the condenser lens 43, the position where the spot size is minimized is different. The reflected light from the optical information recording medium layer 511 is incident on the reflecting mirror 24, the reflected light from the optical information recording medium layer 512 is incident on the mirror 25, and the reflected light from the optical information recording medium layer 513 is incident on the mirror 26. And reflected in a right angle direction. Twenty-four mirrors are arranged side by side so as to reflect the sub-beams so as to correspond to the division into three light beams by the hologram element 27. The light reflected by the mirror group is irradiated on the photodetector 53 manufactured on the semiconductor substrate by the lens 44.

  A cylindrical lens 45 is an optical element necessary for detecting a focus error by the astigmatism method. The output from the light detector is processed by an electronic circuit 63 to generate a focus signal, a tracking signal, a read signal, and a control signal for writing to the laser light source 1. The light reflected by the mirror 25 becomes light in the state 822, the light reflected by the mirror 24 becomes light in the state 802, and the light reflected by the mirror 26 becomes light in the state 832. The position on the optical axis of the detection surface of the photodetector 53 is an intermediate point between two focal line positions due to the action of the cylindrical lens 45, and the beam is circular.

  FIG. 5 shows the shape of the detection surface of the photodetector 53. The light beam 802 is a main beam and is incident on the quadrant photodetector surface 11. The sub-beams are incident on the two-divided detector surfaces 12 and 13. A signal obtained by adding all the signals from the quadrant detector surface 11 becomes a readout signal. At the same time, a focus error signal can be generated from the output signal from the quadrant detector surface 11 and used for tracking the focal position. The quadrant detector surface can be used as a two-divided detector divided in the same direction as the two-divided detector surfaces 12 and 13. By combining the differential signals of the three two-divided detector surfaces, tracking by the differential push-pull method becomes possible.

  A beam indicated by 832 is incident on the photodetector surface 14. This light is from the optical information recording medium layer 513, and the writing state of this layer can be monitored. When a specific portion of this layer is written, the reflected light at that portion increases and the writing power to the optical information recording medium layer 511 decreases. If recording is performed with insufficient writing power, the mark shape becomes small, and the quality of the readout signal deteriorates. In order to avoid this, an optimum recording mark state can be realized by adjusting the recording power to be increased when the signal from the photodetector surface 14 is increased.

  The light 822 is incident on the photodetector surface 15. This light is reflected light from the optical information recording medium layer 512, and its intensity greatly depends on the state of the mark on the optical information recording medium layer 511 existing where the light is narrowed down. Since the optical information recording medium layer 512 is irradiated in a spread state, there is an influence of an average reflectance such as marks included in the range, but when there are a large number of marks, the reflectance may be almost constant. Therefore, the signal on the light detection surface 15 is transmitted light with respect to the signal added by the quadrant detector 11 and thus has an opposite phase. This can also be used as a read signal. Since this signal does not add the signal divided into four, it has a feature that the amplifier noise is small, and there is an advantage in terms of signal to noise ratio.

1 is a schematic diagram of a first embodiment of the present invention. It is the schematic of the conventional optical information recording / reproducing apparatus. It is the schematic for demonstrating the some reflected light generate | occur | produced with a multilayer optical information recording medium. It is the schematic which shows the solution means of this invention. It is a schematic diagram of the pattern of the photon detection surface of the photodetector used in an Example.

Explanation of symbols

1. Semiconductor laser 11.4 split detector pattern 12.13.2 split detector pattern 14.15. Undivided photodetector pattern2. Triangular prism 21. λ / 4 wave plate 22. Knife edge 23. Collimator lenses 24-26. Micro mirror 31. Polarizing beam splitter 32. Half prism 41. Objective lens 42.43.44. Condensing lens 45. Cylindrical lens 50. Single-layer optical disk 52.53. Photodetector 501.2 layer optical information recording medium, 502.3 layer optical information recording medium 511. First optical information recording medium layer 512. Second optical information recording medium layer 513. Third optical information recording medium layer 60.61.62.63. Electronic circuit 72. Tracking error signal 73. Read data signal 80. Irradiation light 81. Reflected light from the first optical information recording medium layer 82. Irradiation light to the second optical information recording medium layer 83.84. Reflected light from the second optical information recording medium layer 801. A condensing position 821. Of the reflected light from the first optical information recording medium layer. Condensing position 831 of the reflected light from the second optical information recording medium layer. Condensing position of reflected light from the third optical information recording medium layer 802. Reflected light from the first optical information recording medium layer 822. Reflected light from the second optical information recording medium layer 832. Reflected light from the third optical information recording medium layer.

Claims (3)

  In an optical disc information recording / reproducing apparatus having optical means for narrowing down laser light to an optical information storage medium and optical means for detecting reflected light from the optical information medium, the optical information medium is a multilayer, and the reflected light from the optical disc is One or more reflecting mirrors are installed on the optical axis to be collected, and the reflecting mirrors reflect the reflected light from the target medium layer and pass almost all the reflected light from the non-target medium layer. There is provided an optical information recording / reproducing apparatus.   2. The reflected light from an adjacent layer at a position away from the objective lens without reflecting the reflected light from the information reading target layer completely on the optical axis for collecting the reflected light from the optical disk. An optical information recording / reproducing apparatus comprising: a reflecting mirror that includes a photodetector that detects reflected light from the adjacent layer.   2. The light according to claim 1, wherein a reflection mirror that reflects the reflected light from the information reading target layer and that does not completely block the reflected light from the adjacent layer close to the objective lens is installed, and detects the reflected light from the adjacent layer. An optical information recording / reproducing apparatus comprising a detector.

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