JPH0457225A - Optical head device - 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 [Field of Industrial Application] The present invention relates to a tracking sensor in an optical disk device that optically records and reproduces information.

[Prior art] Optical disk devices concentrically and
Alternatively, a tracking servo sensor method is required to record or reproduce signals in a spiral manner. Various methods have been proposed for this tracking servo sensor method.

One of these methods is a push-pull method that utilizes diffracted light from signal pits or guide grooves. In this method, the diffracted light distribution due to the guide groove formed on the information recording medium is projected onto a two-split photodetector, and a tracking servo sensor signal is obtained from the differential output of the two-split photodetector. is known to be affected by the depth of

FIG. 5 is a diagram showing the relationship between the guide groove depth and the push-pull signal in the push-pull method, and as is clear from the figure,
The groove depth is maximum when it is λ/8, and minimum when it is λ/4.

Another method is a three-beam method that uses sub-beams. In this method, the light beam is divided by a splitting means such as a diffraction grating, and a tracking servo sensor signal is obtained from the differential output of sub-beams located on both sides of the main beam for recording and reproduction. Because it exists,
During recording, the recording signal is disturbed by the sub beam and an offset occurs.

FIG. 6 is a diagram showing the appearance of spots on an information recording medium to explain the problems of the three-beam method. In the figure,
(8) is a recording track, which is assumed to be a guide groove.

(9) is the land part, (10), (11) are the spots focused on the information recording medium, (10) is the main beam, (l
la) and (llb) are the parts recorded by the sub beam, and (12) is the part recorded by the main beam (10).

FIGS. 6(a) and 6(b) both show a state in which the main beam is tracked on the guide groove. At this time, the secondary beam (
Looking at the differential outputs of (lla) and (llb), we see (
In case b), the same signal output is obtained for both the sub beams (lla) and (llb), so the differential output is zero and no offset occurs. However, in the case of figure (a), the leading beam (lla) passes through the non-recording area, while the trailing beam (llb) passes through the recording area, so the signals from both beams are The output will be different and an offset will occur.

As mentioned above, both methods have problems, and about λ/4
A single optical head device can stably record compact discs (hereinafter referred to as CDs) with bit strings formed at a depth of It is extremely difficult to reproduce.

FIG. 7 is a front view of the optical system of a conventional optical head device, in which (1) is a semiconductor laser as a light source;
2) is a collimator lens, (3) is a beam splitter for beam separation, (4) is an objective lens, and (5) is an information recording medium. (6) is reflected by the information recording medium (5),
The light beam deflected by the beam splitter (3) is sent to the photodetector (
7) is a convex lens for condensing light.

In this configuration, the tracking servo sensor signal is obtained by the push-pull method, so the offset that is a problem with the 3-beam method does not occur during recording, which is convenient when recording on a W10 disk with a groove depth of λ/8. It has a good tracking servo sensor system.

[Problems to be Solved by the Invention] Since the conventional optical head device is configured as described above, when playing a CD disc with a groove depth of λ/4, the tracking servo sensor signal decreases and the tracking There was a problem that the servo became unstable.

This invention was made to solve the above-mentioned problems, and it is an object of the present invention to provide an apparatus that can selectively switch between the push-pull method and the three-beam method depending on the type of disc.

[Means for Solving the Problems] An optical head device according to the present invention includes an objective lens that condenses a light beam from a light source and emits it to an information recording medium, and receives a reflected light beam from the information recording medium; a beam splitter that separates the emitted light flux from the light source and the reflected light flux;
In an optical head device having a photodetector for detecting a tracking support sensor signal that receives a light beam separated by the beam splitter, a mechanism for selectively arranging a flat plate and a diffraction grating between the light source and the objective lens. It is equipped with the following.

[Function] The optical head device according to the present invention can switch the tracking sensor method between the push-pull method and the three-beam method, so one optical head device can handle CD discs and W.
It is possible to record and play back 10 discs.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. The apparatus of the embodiment will be explained with reference to FIGS. 1 to 3. (13
) is a composite diffraction grating consisting of a diffraction grating part (13a) and a flat plate part (hereinafter referred to as the flat plate part) (13b) that has no diffraction effect, and is located near the boundary between the diffraction grating part (13a) and the flat plate part (13b) (part C). ) by rotating the semiconductor laser.
(1) and the collimator lens (2), the diffraction grating part (13a) of the composite diffraction grating (13) and the flat plate part (
13b) can be selectively inserted. The rest of the configuration is the same as the conventional example, so the explanation will be omitted.

Next, the diffraction grating part (13a) of the composite diffraction grating (13)
) and the flat plate portion (13b) into the emitted light beam will be explained with reference to FIGS. 2 and 3. FIG. 3 is a sectional view taken along the line ■--■ in FIG. 2. A composite diffraction grating (13) having a diffraction grating portion (13a) and a flat plate portion (13b) is bonded to a holder (14), and the holder (14) is attached to a housing (16) via a rolling bearing (15).
It is rotatably fixed to the In addition, the housing (16)
is made of a magnetic material, and has convex portions (18a) and (18b) facing the two magnets (17a) and (17b) attached to the holder (14). 18b) includes a driving coil (19a),
(19b) is wound.

Next, the operation will be explained.

First, as shown in Figures 1 and 2, when the flat plate part (13b) of the composite diffraction grating (13) is inserted into the light beam (E), the light emitted from the semiconductor laser (1) undergoes a diffraction effect. Therefore, one spot is focused on the information recording medium (5). Next, the coil (19a), (19b
) in a direction that repels the opposing magnets (18a) and (18b), a composite diffraction grating (
The holder (14) containing the holder (13) is rotated 180 degrees so that the diffraction grating portion (13a) is placed in the light beam (E), and is fixed in this state by magnetic attraction.

After the holder has been rotated 180 degrees and fixed, the coil (19
a), (19b) Even after de-energizing, the magnet (1
7a).

(17b) and the protrusions (19a) and (19b) because of the magnetic attraction force acting thereon, the holder (14) can remain fixed. In this way, the luminous flux (E)
When the diffraction grating section (13a) is inserted into the information recording medium (5), the emitted light from the semiconductor laser (1) is diffracted.
) on which multiple spots are focused. Moreover, since the thickness and material of the diffraction grating part (13a) and the flat plate part (13b) of the composite diffraction grating (13) are the same, the optical distance does not change even if the diffraction grating part (13a) and the flat plate part (13b) are replaced. It has become. Therefore, in a system equipped with the optical head device of the present invention, the tracking servo sensor signal is transmitted in a push-pull manner by selecting the flat plate portion (13b) during recording, and by selecting the diffraction grating portion (13b) during reproduction.
By selecting 3a), it is possible to obtain a three-frame system.

In the above embodiment, the composite diffraction grating (13) is used as a luminous flux (E)
I used a rotating mechanism to put it in and take it out, but the fourth
As shown in the figure, the composite diffraction grating (13) may be slid using a linear motor or the like.

[Effects of the Invention] As described above, according to the present invention, a compound diffraction grating having a diffraction grating portion and a flat plate portion can be replaced in the output beam, so that it is suitable for operation in one optical head device. A tracking servo sensor method can be used.

[Brief explanation of drawings]

FIG. 1 is a front view of an optical system of an optical head device according to an embodiment of the present invention, FIG. 2 is a front view of a rotation mechanism for moving the diffraction grating section and flat plate section, and FIG. ■-■ line sectional view, Figure 4 is a front view of the optical system showing another embodiment, Figure 5 is a diagram showing the relationship between guide groove depth and push-pull signal in the push-pull method, Figure 6 is 3-beam A diagram showing the appearance of spots on an information recording medium for explaining legal issues,
FIG. 7 is a front view of the optical system of a conventional optical head device. In the figure, (1) is a semiconductor laser, (3) is a beam splitter, (4) is an objective lens, (7) is a photodetector, (
13) is a composite diffraction grating having a diffraction grating portion and a flat plate portion. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] An objective lens that condenses a light beam from a light source and emits it onto an information recording medium and receives a reflected light beam from the information recording medium, and separates the output light beam from the light source and the reflected light beam. In an optical head device having a beam splitter and a photodetector for detecting a tracking servo sensor signal that receives the light beam separated by the beam splitter, a flat plate and a diffraction grating are selectively provided between the light source and the objective lens. An optical head device characterized by having a mechanism for arranging the head.