JPH0411331A - optical head - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] Industrial Field of Application The present invention relates to an optical head of an optical disk device that has an information recording medium and performs recording, retargeting, erasing, etc. of information by irradiating a light beam such as a laser beam. This relates to an optical head that can accurately and easily obtain tracking using a tracking error signal detection means.Conventional technology Although many reports have been made regarding technology regarding tracking error signal detection means in a conventional optical head, the drawings will be described below. Reference: A conventional optical head will be explained.

An example of a schematic configuration of a conventional optical head is shown in FIG.

In Figure 5, l is light #2 is a half mirror, 3 is an objective lens, 4 is an optical disk which is an information recording medium, and 5 is 2
Split photodetector 6 is a differential amplifier, 7 is a light spot, 5
a is a dividing line of the two-split photodetector 5. The present invention relates to tracking error signal detection means, and other means such as focus error signal detection means are omitted, but please refer to the drawings below. While explaining the operation of a conventional optical head, the light emitted from the light source 1 is reflected by the half mirror 2, passes through the objective lens 3, and forms a light spot on the optical disk 4. At this time, the light is recorded on the optical disk 4. The direction of the track is perpendicular to the plane of the paper.The reflected light from the optical disk 4 follows the opposite path, passes through the objective lens 3, passes through the half mirror 2, and forms a light spot 7 on the two-split photodetector 5. There is a dividing line 5a on the two-split photodetector 5.This is also a configuration in which the tracking error signal is detected by taking the difference between the electrical signals reproduced in the two light-receiving areas using the differential amplifier 6. This method is called the push-pull method and is widely put into practical use. There are many conventional examples in which the two-split photodetector 5 is miniaturized, that is, the optical head is miniaturized by having a configuration in which the reflected light passes through a lens before entering.
%Problems to be Solved by the InventionThe push-pull method of the conventional optical head mentioned above is a tracking error signal detection means with a simple structure. Generally, the objective lens is driven in the X direction (tracking direction) in FIG. 5 by an objective lens driving means (not shown) to follow a target track on the optical disk 4. In this case, the two-split photodetector 5 The upper light spot 7 moves in the X direction in response to the movement of the objective lens 3.

FIG. 6(A), FIG. 6(B), and FIG. 6(C) are diagrams showing the position of the light spot 7 on the two-split photodetector 5 and the state of the tracking error signal obtained thereby. Also 6th
Figure (A) shows the case where the objective lens 3 is at the neutral position of X, and the optical spot 7 is at a position approximately symmetrical with respect to the dividing line 5a.At this time, the optical disk 4 rotates and only the focus servo operates. (If the target voltage when the tracking servo is activated is 0, a signal that is almost symmetrical with respect to the voltage O can be obtained. In this case, the position of the light spot 7 on the two-split photodetector 5 moves and the symmetry with respect to the dividing line 5a is destroyed.Therefore, the tracking at this time The error signal ζ loses its symmetry with respect to voltage 0 and becomes a signal with a voltage offset of 1 V superimposed. Figure 6 (C) shows the case where the objective lens moves in the negative direction of the 3X direction. The obtained tracking error signal is a signal on which a voltage of -7■ is superimposed, contrary to the case shown in Fig. 6(B).In an optical disk device, when searching for a target track at high speed, the optical head is moved at high speed. A common method is to operate the tracking servo after the optical head is moved. At this time, if the objective lens 3 is moved from the neutral position in the X direction due to acceleration etc. when the optical head is moved, as shown in FIG. If you try to operate the tracking servo in these conditions, there is a very high probability that the servo will fail to pull in. Also, even if the servo pulls in, L target If the track has a large eccentricity (approximately 100 um or more), there is a drawback that the tracking performance is significantly degraded.In view of the above problems, the present invention aims to eliminate the offset of the tracking error signal due to the movement of the objective lens in the tracking direction. To provide an optical head that can significantly reduce An objective lens is used to converge information onto an information recording medium, and information signals are generated by reflected light from the information recording medium.

Focus error signal Tracking servo by detecting a tracking error signal and driving the objective lens in a focus direction that is approximately parallel to the optical axis direction of the objective lens and a tracking direction that is approximately perpendicular to the recording track and the focus direction. The means for detecting a tracking error signal transmits the reflected light from the information recording medium, and sets the center line substantially parallel to the recording track as the axis of symmetry in the cross section of the light beam, and detects the tracking error signal at the center including the axis of symmetry. A split convergence element spatially symmetrically splits and converges a light flux and two peripheral light fluxes that do not include the symmetry axis, and the transmitted light of the split convergence element is incident, and reflected light is reflected from the cross section of the light flux of the incident light. It has a two-divided light detection area divided by one linear dividing line that substantially coincides with the center line in the cross section of the light beam, and two light detection areas that exist independently from each other with this two-divided light detection area in between. It is composed of a multi-segment photodetector, and the positional relationship of the reflected light beam on the beam cross section is maintained on the multi-segment photodetector, and the central light beam including the axis of symmetry on the beam cross section of the reflected light beam is incident on the two-split photo detection area. The two peripheral light fluxes that do not include the axis of symmetry are incident on two photodetection areas that exist independently of each other, and each photodetection area of the multi-segment photodetector is electrically connected. The multi-split photodetector is a two-split photodetector, which includes two photodetection areas, a two-split photodetection area into which the central light beam is incident, which includes the axis of symmetry on the beam cross section of the reflected beam; In the two photodetection areas that existed independently of each other and into which two peripheral light fluxes are incident, the two photodetection areas that do not touch each other are combined on the photodetector to form a two-split photodetector. In addition, when the focus servo is applied and the objective lens is at the neutral position in the tracking direction, one dividing line is formed. In the cross-section of the beam, most of the reflected light is in the central portion of the beam that includes the axis of symmetry, with the center line approximately parallel to the recording track.With this configuration, the objective lens is aligned in the tracking direction. If the light spot on the photodetector moves from the neutral position of the movable range of
The tracking error signal obtained as an output is a high-quality signal with very little offset.Example: A first example of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is a light source, 2 is a half mirror, 3 is an objective lens/C, 4 is an optical disk serving as an information recording medium, 5 is a light receiving area 5p, 5q,
A four-split photodetector with 5r and 5s; 6 is a differential amplifier; 8 is a split converging element;
The first lens 8a transmits the reflected light from the first lens 8a, and in the cross-section of the beam, the center line that is approximately parallel to the recording track is the axis of symmetry, and the central part of the beam that includes the axis of symmetry enters the first lens 8a, and the periphery that does not include the axis of symmetry. Each of the two light beams incident on the second lens 8a and the second lens 8a has a focal length between the first lens 8a and the lens 8a. It is a composite element consisting of the third two lenses 8b and 8c, which spatially symmetrically divides and converges a light beam in the central part that includes the axis of symmetry and two light beams in the peripheral part that do not include the axis of symmetry. Q
&+ 9 b+ 9 C are three light spots formed on the four-split photodetector 5 by the split convergence element 8, 5a is the dividing line of the four-split photodetector 5, and the cross section of the beam reflected from the optical disk 4 A straight dividing line that is approximately parallel to the center line of the recording track in the recording track.
Further, 5b and 5c are also linear dividing lines that form the light receiving areas 5p and 5q.
The positional relationship on the beam cross section of the reflected beam from the optical disk 4 is shown in 4.
The present invention relates to tracking error signal detection means, and although other means such as focus error signal detection means are omitted, the following description will be made with reference to FIG. The operation of the optical head according to the first embodiment of the invention will be explained.The light emitted from the light source 1 is reflected by the half mirror 2, passes through the objective lens 3, and forms a light spot on the optical disk 4. The direction of the recording track on 4 is perpendicular to the paper surface. The objective lens 3 can be driven in the optical axis direction of the objective lens 3 by an objective lens driving means (not shown) to apply focus servo, and can be driven in the X direction (tracking direction) to apply tracking servo.
The reflected light from the mirror follows the opposite path, passes through the objective lens 3, and passes through the half mirror 2.
The light beam is spatially divided into three beams and placed on the four-split photodetector 5.
The force of forming three light spots 9a, 9b, 9c (here, the 4-split photodetector 5 has lenses 8a, 8b,
Even if the positional relationship on the beam cross section of the reflected light beam from the optical disc 4 is maintained on the four-split photodetector, the optical disc 4 is recorded on the beam cross section of the reflected light beam from the optical disk 4. With the center line approximately parallel to the track as the axis of symmetry, two peripheral light beams that do not include the axis of symmetry pass through the second lens 8b and third lens 8c of the split converging element 8 and reach the four-split photodetector 5. Incoming light receiving area 5
Light spots 9b and 9c are formed at p and 5s, respectively.
- Person The central beam including the axis of symmetry is the first of the split converging elements 8.
A light spot 9a is formed across the light-receiving areas 5q and 5r by passing through the lens 8a and entering the 4-split photodetector. When there is a dividing line 5a on the 4-split photodetector 5 and the objective lens 3 is at the neutral position in the X direction, the optical spot 9
a, 9b, and 9c are formed in each light-receiving area at substantially symmetrical positions with respect to the dividing line 5a. The tracking error signal is detected by taking the difference between the respective electric signals using a differential amplifier 6. FIGS. 9b and 9c are illustrated.
Although x indicates the intensity center position of the light spot 9a, the second
Figure (A) is a paper similar to Figure 1 and shows the case where the objective lens 3 is in the neutral position in the X direction.In this case, the light spot 9
The intensity center position 9X of a almost coincides with the dividing line 5a, and the tracking error signal (tomo) which is the output of the differential amplifier 6 is a signal without offset similar to the conventional example shown in FIG. 6(A). Similarly to the conventional example shown in FIG. 6(B), FIG. 2(B) shows light spots 9a, 9t when the objective lens 3 moves in the X direction in FIG. 1).

9c on the 4-split photodetector. In this state, the central beam including the axis of symmetry passes through the first lens 8a of the split converging element 8 and enters the 4-split photodetector 5.
The shape of the light spot 9a on the 4-split photodetector does not change, but the intensity center position 9X moves to the light receiving area 5q, and the amount of light received by the light receiving area 5q changes. In addition, the two peripheral light fluxes that do not include the axis of symmetry pass through the second lens 8b and third lens 8c of the split convergence element 8, enter the four-split photodetector 5, and enter the light receiving areas 5p and 5s. (respectively)
Although 9b and 9c are formed, the light spot 9c becomes smaller and the amount of light received by the light receiving area 5s decreases, and the light spot 9b becomes larger and the amount of light received by the light receiving area 5p increases. For the reflected light, the light receiving areas 5p and 5r are electrically connected.
8 are electrically connected. In this case, it is necessary to properly determine the divided areas of the lenses 8a, 8b, and 8c that form the divided converging element 8 in advance.
The amount of increase or decrease in light intensity can be made almost the same in the sum total of r and the sum total of light receiving areas 5q and 5s. The tracking error signal obtained by connecting the respective electrical signals with the differential amplifier 6 (different from the case shown in Fig. 6 (B)) is a signal with very little offset. Lens 3 is the first
In the first embodiment, the focus servo is applied and the objective lens is moved in the tracking direction (
In the cross-section of the beam reflected from the information recording medium, the split converging element directs most of the beam of reflected light from the center line that is approximately parallel to the recording track to the central portion that includes the axis of symmetry. Although it has been experimentally confirmed that a tracking error signal with the least offset can be obtained in the vicinity of this positional relationship as a luminous flux, the split converging element is Rather than combining composite elements, it splits the beam of reflected light from the information recording medium and changes the direction of the divided beam.
It goes without saying that the object of the present invention can also be achieved even if the configuration includes at least one deflection splitting prism that may have a lens convergence effect. It is not a single-image optical element that combines lenses, but at least one polarization splitter that splits the luminous flux of reflected light from the information recording medium, changes the direction of the divided luminous flux, and may have the convergence effect of a lens. It may also be composed of a complex element including a prism and at least one condenser lens that exists independently of the complex element.In this case, only the main part of tracking error signal detection is performed in the second embodiment of the present invention. An example is shown in FIG.

In FIG. 3, reference numeral 12 denotes a composite element that transmits the reflected light from the optical disk 4, and in the cross section of the light beam, the light beam in the central part including the axis of symmetry is set to the center line that is approximately parallel to the recording track. The incident parallel prism 12a and the deflection splitting prisms 12b, 12, into which each of the two light beams in the peripheral area that does not include the symmetry axis enter, change the directions of the two divided light beams into directions opposite to each other with respect to the symmetry axis.
A second embodiment of the present invention shown in FIG. 3 is shown in FIG. In this example, a light spot between the paths and the first embodiment of the present invention shown in FIG. 1. It goes without saying that the composite element constituting the split convergence element described in the second embodiment may be an integral element manufactured by press molding, etc., and is also effective in terms of transmittance of the element. Also number 1. It is clear that the composite element constituting the split convergence element described in the second embodiment may be a hologram element.
The four-segment photodetector 5 shown in the figure is used as an embodiment of the multi-segment photodetector of the present invention (the multi-segment photodetector may also be a two-segment photodetector (t) in this case. Only the two-split photodetector portion for tracking error signal detection is shown in FIG. 4 as a third embodiment of the present invention.

In FIG. 4, 2
On the split photodetector 14 Gζ On the beam cross section of the reflected light beam from the optical disk With the center line approximately parallel to the recording track as the axis of symmetry, the two peripheral beams that do not include the axis of symmetry enter the two-split photodetector 14. 9 b.

The central luminous flux including the axis of symmetry forming 9c & -X is 2
The light L enters the split photodetector 14 and forms a light spot 9a across the light receiving areas 5q and 5r.
The force (
When these three dividing lines are connected, they become one dividing line and constitute the two-divided photodetector 14, that is, the light receiving areas 5p, 5s and the light receiving area 5Q.

5r, the two light-receiving regions that do not touch each other, that is, the light-receiving regions 5p, 5r and the light-receiving regions 5q, 5s, are combined on the photodetector to form a two-split photodetector. Embodiment 1 This eliminates the need for electrical connections from each light-receiving area of the 4-split photodetector, which was necessary in Embodiment 2. Regarding tracking error signal detection,
It is clear that the same effect as in the first embodiment can be achieved through the same operation.4 As described above, the differences between the first to third embodiments of the present invention include the split converging element and the two-split light beam. Detector 14
Alternatively, with an extremely simple configuration of the 4-split photodetector 5, it is possible to significantly reduce the offset of the tracking error signal that conventionally occurs due to positional deviation of the objective lens 3 in the tracking direction. In the case where the objective lens 3 moves from the neutral position in the tracking direction due to acceleration etc. when moving the optical head, L
The retraction ability of the tracking servo is greatly improved, but if the target track has a large eccentricity (e.g. 100
When the L target track is larger than 10 μm), the followability to the L target track is greatly improved and stable tracking servo can be realized. an objective lens that focuses on an information recording medium having a track; a detection means that detects a tracking error signal using reflected light from the information recording medium; means (ML,
The means for detecting this tracking error signal transmits the reflected light from the information recording medium, and in the cross section of the light beam, the center line that is approximately parallel to the recording track is set as the axis of symmetry, and the light beam in the central part that includes the axis of symmetry does not include the axis of symmetry. A split convergence element spatially symmetrically splits and converges two light beams at the periphery, and the transmitted light of the split convergence element is incident, and the center line of the light flux cross section of the reflected light is Consisting of a multi-segment photodetector that has a two-split photodetection area divided by one linear dividing line that almost coincides with each other, and two photodetection areas that exist independently from each other with the two-split photodetection area in between. The positional relationship on the beam cross section of the reflected beam is maintained on this multi-segment photodetector, and the central beam that includes the axis of symmetry on the beam cross section of the reflected beam enters the two-split photodetection area, and the central beam that includes the axis of symmetry on the beam cross section of the reflected beam is The multi-segment photodetector ζ is also characterized in that the two peripheral light fluxes that are not present are incident on two photo-detection areas that exist independently of each other, and that the respective photo-detection areas of the multi-segment photodetector are electrically connected. It is a two-split photodetector, and includes two photodetection areas, a two-split photodetection area, into which the central light beam including the axis of symmetry on the beam cross section of the reflected beam enters, and two peripheral beams that do not include the axis of symmetry. In the two incident photodetection areas that existed independently of each other, the two photodetection areas that do not touch each other are combined on the photodetector and the two
It may be characterized in that one dividing line is formed to constitute a divided photodetector, and the divided converging element records information when the focus servo is applied and the objective lens is at a neutral position in the tracking direction. In a cross-section of the beam of reflected light from the medium, most of the beam of reflected light can be made into a central beam including a symmetry axis with a center line substantially parallel to the recording track. ! In the cross-section of the beam of reflected light from the information recording medium, with the center line approximately parallel to the recording track as the axis of symmetry, the first lens receives the beam in the central part that includes the axis of symmetry, and the peripheral part that does not include the axis of symmetry. The splitting and converging element splits the reflected light beam from the information recording medium. It may also be characterized by being a composite element including at least one deflection splitting prism that changes the direction of the split light flux and may have the converging effect of a lens. It is not an optical element, but a composite element that includes at least one deflection splitting prism that splits the beam of reflected light from the information recording medium, changes the direction of the split beam, and may have the convergence effect of a lens. The composite element may also be characterized by being composed of at least one lens that exists independently of the composite element. Moreover, the composite element may also be characterized as a hologram element. In an optical disk device, when the optical head is moved at high speed and the objective lens moves from the neutral position in the tracking direction due to acceleration etc. during the movement of the optical head, the retraction ability of the tracking servo is L: If the target track has a large eccentricity (about 100 μm or more) It is something that can be achieved.

[Brief explanation of the drawing]

FIG. 1 shows a schematic configuration of an optical head according to a first embodiment of the present invention. FIG. 2 (A) shows a schematic diagram of the main part of the embodiment. FIG. FIG. 4 is a schematic diagram of the main parts of the optical head in the third embodiment of the present invention. Main parts 2... half mirror 13... 4... optical disk drive 5... 4 minutes 5a, 5b, 5c...dividing line 5r, 5s...
Light-receiving area 6, 7, 9a, 9b, 9c...Light spot/split convergence element, 8a, 8b, 8-Lens, 12...Composite element, parallel prism 12b, 12c. Amo1... Side photodetector p, 5q, 5 differential amplifier, t, 8...c, 13...12a... Deflection split Brisbe two-split photodetector Fig.

Claims (8)

[Claims] (1) A light source, an objective lens that converges the light emitted from the light source onto an information recording medium having a recording track, and detecting an information signal, a focus error signal, and a tracking error signal by the reflected light from the information recording medium. a detection means, and a means for applying focus servo and tracking servo by driving the objective lens in a focus direction substantially parallel to the optical axis direction of the objective lens and in a tracking direction substantially perpendicular to the recording track and the focus direction; The means for detecting the tracking error signal transmits the reflected light from the information recording medium, and in the cross section of the light beam, a center line that is substantially parallel to the recording track is set as an axis of symmetry, and a center line that includes the axis of symmetry is provided. A dividing converging element that spatially symmetrically divides and converges a luminous flux in the area and two luminous fluxes in the peripheral area that do not include the axis of symmetry; 1, which substantially coincides with the center line in the beam cross section of the reflected light.
consisting of a multi-segment photodetector having a two-split photodetection area divided by a linear dividing line of a book, and two photodetection areas that exist independently of each other with the two-split photodetection area sandwiched therebetween;
The positional relationship of the reflected light beam on the light beam cross section is maintained on the multi-split photodetector, and the central light beam including the symmetry axis on the light beam cross section of the reflected light beam is incident on the two-split light detection area, An optical head characterized in that two peripheral light beams that do not include an axis of symmetry are respectively incident on two photodetection areas that exist independently of each other, and each photodetection area of the multi-segment photodetector is electrically connected. . (2) The multi-split photodetector is a two-split photodetector, and the two-split photodetection region is incident with a central light beam that includes the axis of symmetry on the cross section of the reflected light beam as set forth in claim 1. 2
Two photodetection areas that do not touch each other are combined on the photodetector in two photodetection areas that exist independently from each other and are incident with two peripheral light fluxes that do not include the axis of symmetry. 2. The optical head according to claim 1, wherein one dividing line is formed so as to constitute a two-divided photodetector. (3) When the focus servo is applied and the objective lens is at the neutral position in the tracking direction, the split converging element
In a cross-section of a beam of reflected light from an information recording medium, most of the beam of the reflected light is a beam of light in a central portion that includes an axis of symmetry with a center line that is substantially parallel to the recording track. The optical head according to item 1 or 2. (4) The split converging element has a first lens on which, in a cross-section of the beam of reflected light from the information recording medium, a center line including the axis of symmetry is incident, with a center line approximately parallel to the recording track as an axis of symmetry. , a composite element comprising two lenses, a second lens and a third lens, into which each of the two light fluxes in the peripheral portion not including the axis of symmetry enters, or The optical head according to item 3. (5) The splitting and converging element splits the reflected light beam from the information recording medium, changes the direction of the split light beam, and includes at least one polarizing splitting prism that may have the converging effect of a lens. 5. The optical head according to claim 4, wherein the optical head is a composite element including: (6) The split convergence element is not one optical element, but at least one split convergence element that splits the light beam reflected from the information recording medium, changes the direction of the split light beam, and may have the convergence effect of a lens. The optical head according to claim 4, characterized in that the optical head is constituted by a composite element including at least one deflection splitting prism, and at least one lens that exists independently of the composite element. . (7) The optical head according to claim 4, 5, or 6, wherein the composite element is an integral element manufactured by press molding or the like. (8) The optical head according to claim 4, 5, or 6, wherein the composite element is a hologram element.