JP2006236581A - Optical head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical head capable of detecting signals with a single optical head from two or more kinds of information recording media with different track pitches. <P>SOLUTION: The optical head is provided with a light source 1, a light quantity splitting means 2 for splitting a quantity of a light beam emitted from the light source into two or more beams of different angles, a condensing means 4 for condensing the two or more beams into light spots on an information recording medium 5, a light-shielding means for shielding a predetermined beam among the two or more beams reflected by the information recording medium, and a photo-detecting means 6 for detecting the beams reflected by the information recording medium. The light-shielding means is positioned in the luminous flux directly in front of the photo-detecting means, and selectively shields a predetermined beam among the two or more beams split by the light quantity splitting means according to the kinds of the information recording media. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  INDUSTRIAL APPLICABILITY The present invention is applied to an optical disc apparatus that records, reproduces, and erases information by irradiating an information recording medium with a light beam such as laser light and condensing a plurality of light spots on the information recording medium. It relates to a possible optical head.

  There have been many reports on conventional optical heads that can be used in optical disc apparatuses that record, reproduce, and erase information by focusing a plurality of light spots on an information recording medium. Hereinafter, a conventional optical head will be described with reference to the drawings.

  FIG. 5 shows the operation of the conventional optical head. The emitted light 7 emitted from the light source 1 made of a semiconductor laser chip enters the diffraction grating 2 and is divided into a plurality of beams having different angles. The 0th-order light 8a and the ± 1st-order diffracted light 8b, which are straight light beams, pass through the beam splitter 3, enter the objective lens 4, and are condensed on the information recording medium 5 as three light spots. The 0th-order light 8a and the ± 1st-order diffracted light 8b reflected by the information recording medium 5 pass through the objective lens 4 again, are reflected by the beam splitter 3, and are collected on the photodetector 6. A focus error signal, a tracking error signal, and an information signal of the information recording medium are obtained by the plurality of divided lights condensed on the photodetector 6. The 3-beam tracking method performs tracking servo by detecting the difference in the amount of reflected light of the ± first-order diffracted light 8b diffracted by the diffraction grating 2.

  However, in such a conventional optical head using the three-beam tracking method, the condensing position of the three beams is fixed, and a plurality of types of information recording media having different track pitches are detected by a single optical head. There was a problem that could not be done.

  The present invention provides an excellent optical head capable of detecting signals of a plurality of types of information recording media having different track pitches with a single optical head in view of such problems of the conventional optical head. It is the purpose.

  In order to achieve the above object, the present invention has the following configuration.

  That is, the optical head of the present invention includes a light source, a light amount dividing unit that divides light emitted from the light source into a plurality of beams having different angles, and a plurality of divided lights by the light amount dividing unit on an information recording medium. A light condensing means for forming a light spot, and a light detecting means for detecting reflected light from the information recording medium, and astigmatism, intervals of a plurality of light spots formed on the information recording medium, Further, at least one of the angles formed by the linearly aligned light spot rows and the tracks of the information recording medium is variable.

  The optical head according to the present invention includes a light source, a light amount dividing unit that divides the light emitted from the light source into a plurality of beams having different angles, and a plurality of light beams divided by the light amount dividing unit on an information recording medium. A light condensing means for forming a light spot, a light shielding means for shielding a predetermined beam among the plurality of beams divided by the light quantity dividing means, and a light detecting means for detecting reflected light from the information recording medium. It is characterized by having.

  The present invention has the advantage that signals can be detected from a plurality of types of information recording media having different track pitches with a single optical head.

  In the present invention, the light amount dividing means is constituted by a diffraction grating, is rotatable around the incident optical axis, is movable in parallel to the incident optical axis, and the distance from the light source is variable. In addition, the incident angle with respect to the incident optical axis may be variable. Further, a light quantity dividing means moving mechanism for changing the light quantity dividing means to a predetermined posture and / or position according to the type of the information recording medium may be provided.

  Further, the light shielding means is constituted by an optical filter or a liquid crystal shutter, or is constituted by a liquid crystal shutter, and among the plurality of beams divided by the light quantity dividing means, the type of the information recording medium is selected. Accordingly, it is characterized in that a predetermined beam is selectively shielded, located in front of the light detection means in the light beam, and integrated with a light detector constituting the light detection means. You may do.

  Hereinafter, the present invention will be specifically described with reference to the drawings by way of examples.

  FIG. 1A is a schematic configuration diagram of an optical head in one embodiment of the present invention. The optical path is the same as in FIG. That is, the emitted light 7 emitted from the light source 1 made of a semiconductor laser chip enters the diffraction grating 2 and is divided into 0th-order light 8a and ± 1st-order diffracted light 8b, which are straight traveling light. The 0th-order light 8a and the ± 1st-order diffracted light 8b pass through the beam splitter 3, enter the objective lens 4, and are condensed on the information recording medium 5 as three light spots. The 0th-order light 8a and the ± 1st-order diffracted light 8b reflected by the information recording medium 5 pass through the objective lens 4 again, are reflected by the beam splitter 3, and are collected on the photodetector 6. A three-beam tracking servo is performed by detecting a difference in reflected light amount of the ± first-order diffracted light 8b diffracted by the diffraction grating 2.

  FIG. 1B shows a plan view of the diffraction grating 2 of the present embodiment. As shown in the figure, in this embodiment, the diffraction grating 2 can be rotated only around the axis of the incident light 7, and other rotations and displacements are restricted by the optical base.

  FIGS. 1C and 1D show an example of the relationship between the tracks and the light spots of the 0th-order light 8a and the ± 1st-order diffracted light 8b irradiated on the surfaces of two types of information recording media 5 having different track pitches. As shown in the drawing, the diffraction grating 2 is rotated around the axis of the incident light 7 in accordance with the track pitches P1 and P2 on the information recording medium 5, and ± 1st order diffracted lights 8b linearly arranged on the information recording medium 5 are shown. The angle (θ 1, θ 2) formed by the light spot row by the track on the information recording medium 5 is changed. Accordingly, by discriminating the type of information recording medium and rotating the diffraction grating 2 around the incident optical axis so that the three beam spots correspond to a predetermined track pitch, a plurality of types of information recording media having different track pitches can be obtained. It is possible to detect a signal with one optical head.

  A mechanism for rotating the diffraction grating 2 will be described below with reference to FIG. As described above, the diffraction grating 2 can rotate only around the incident optical axis, and other rotations and displacements are restricted by the optical base. The pin portion of the eccentric pin 10 is inserted into the notch portion 9 of the diffraction grating 2, and the eccentric pin 10 itself is provided with a rotating means around the axis. By discriminating the type of the information recording medium and rotating the eccentric pin 10 around the axis according to the type, the diffraction grating 2 rotates around the incident optical axis to obtain a three beam spot corresponding to a predetermined track pitch. Is possible.

  As described above, in this embodiment, the diffraction grating is rotated around the incident optical axis, and the angle formed by a plurality of linearly aligned light spot arrays formed on the information recording medium and the track of the information recording medium is changed. I let you. As another means, it is possible to obtain a light spot interval corresponding to the track pitch of the information recording medium by moving the diffraction grating parallel to the incident optical axis to change the distance from the light source. Also, by changing the incident angle of the diffraction grating with respect to the incident optical axis, the light spot on the information recording medium has astigmatism, but it is possible to have astigmatism according to the type of information recording medium. is there. The means for changing the light spot by changing the attitude or position of the diffraction grating as described above may be used alone or in combination as appropriate depending on the type of the information recording medium.

  In the above-described embodiment, at least one of astigmatism of a plurality of light spots formed on the information recording medium, an interval, and an angle formed by the linearly aligned light spot array with the track of the information recording medium is variable. The case where a predetermined light spot is obtained according to the type of information recording medium has been described. On the other hand, the case where the light shielding means for shielding a predetermined beam among the plurality of beams divided by the light quantity dividing means is used will be described with reference to FIGS.

  An example using an optical filter as the light shielding means will be described with reference to FIG. The emitted light that is diffracted by the diffraction grating and divided into a plurality of beams having different angles is reflected on the information recording medium, and the 0th-order light 8a that is a straight traveling light is reflected on the light detection unit 6a of the light detector 6 and The ± first-order diffracted light 8b and the higher-order diffracted light 8c are collected on the light detection unit 6b. The diffraction grating is set so that each of the ± first-order diffracted light 8b and the higher-order diffracted light 8c can perform three-beam tracking servo on information recording media having different track pitches. Here, an optical filter 11 having a function of shielding predetermined diffracted light is provided immediately before the photodetector 6 in the light beam. Information with different track pitches can be easily selected without changing other optical elements by selecting the optical filter 11 so that only predetermined diffracted light is focused on the light detection unit 6b according to the type of information recording medium. An optical head corresponding to the recording medium can be obtained.

  An example in which a liquid crystal shutter is used as the light shielding means will be described with reference to FIG. In FIG. 4, when the light shielding means is the liquid crystal shutter 12, the type of the information recording medium is discriminated, and the liquid crystal shutter 12 is selectively opened and closed so that only predetermined diffracted light is condensed on the light detection unit 6b. It is possible to detect signals from a plurality of types of information recording media having different track pitches with a single optical head. For example, the diffraction grating is set so that ± first-order diffracted light 8b can perform 3-beam tracking servo on an information recording medium with a narrow track pitch and high-order diffracted light 8c on an information recording medium with a wide track pitch. . When an information recording medium having a wide track pitch is inserted, the liquid crystal shutter 12 blocks the ± first-order diffracted light 8b unnecessary for the tracking servo, and only the high-order diffracted light 8c necessary for the tracking servo is detected by the light detector 6b (same as above) Figure (a)). On the other hand, when an information recording medium with a narrow track pitch is inserted, an appropriate tracking servo signal can be obtained by shielding the high-order diffracted light 8c (FIG. 5B).

  Here, it goes without saying that any method may be used for the light shielding means without being limited to the above example. Further, it is obvious that the position of the light shielding means is not limited as long as a predetermined beam among the plurality of beams divided by the light quantity dividing means can be shielded. It is also possible to integrate the light shielding means with a photodetector constituting the light detecting means.

  As mentioned above, although the specific example at the time of using a diffraction grating for a light quantity dividing means was shown, it is clear that another optical element may be used for a light quantity dividing means.

  The field of application of the present invention is not particularly limited, and information recording medium is irradiated with a light beam such as laser light, and a plurality of light spots are condensed on the information recording medium, thereby recording, reproducing, and erasing information. It can be used in a wide range of optical disk devices that perform the above.

It is a schematic block diagram which shows one Example of the optical head of this invention. It is the schematic which shows the rotation mechanism of the diffraction grating in the optical head of FIG. It is the schematic which shows operation | movement of the light-shielding means in another Example of the optical head of this invention. It is the schematic which shows operation | movement of the light-shielding means in another Example of the optical head of this invention. It is a schematic block diagram which shows an example of the conventional optical head.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Diffraction grating 3 Beam splitter 4 Objective lens 5 Information recording medium 6 Photo detector 6a Photo detector 1
6b Photodetector 2
7 Emission light 8a 0th order light 8b ± 1st order diffracted light 8c High order diffracted light 9 Notch 10 Eccentric pin 11 Optical filter 12 Liquid crystal shutter

Claims (4)

A light source;
A light amount dividing means for dividing the light emitted from the light source into a plurality of beams having different angles;
Condensing means for condensing the plurality of beams on an information recording medium to form a light spot;
A light shielding means for shielding a predetermined beam among the plurality of beams reflected by the information recording medium;
A light detecting means for detecting a beam reflected by the information recording medium,
The light shielding means is located immediately before the light detection means in a light beam, and selectively selects a predetermined beam among the plurality of beams divided by the light quantity dividing means according to the type of the information recording medium. An optical head characterized by shielding light.   The optical head according to claim 1, wherein the light shielding unit includes an optical filter.   The optical head according to claim 1, wherein the light shielding unit includes a liquid crystal shutter.   The optical head according to claim 1, wherein the light shielding unit is integrated with a photodetector constituting the light detection unit.

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