JP3087586B2 - Optical head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head used for recording / reproducing an optical disk.

[0002]

2. Description of the Related Art A push-pull method is used for detecting a tracking error signal used for tracking control for causing a reproduction light to follow a recording track of an optical disk (for example, Japanese Patent Publication No. 4-1412). According to Japanese Patent Publication No. 4-1412, a track on the optical disc substrate 1 is used as a diffraction element 14 and light from the track is received by photodetectors 100 and 101 which are equivalently split in parallel with the track, and the differential light is received. From the tracking error signal.

However, this method has a drawback that when the objective lens moves in the horizontal direction, the light spots on the photodetectors 100 and 101 are shifted, so that the tracking error signal fluctuates in a DC manner.

In order to overcome such a drawback, a hologram diffraction element as a light amount branching means is provided together with an objective lens.
A method is conceivable in which the light is separated at the objective lens by being moved, and then received by a light receiving element (photodetector).

The principle of such an optical head will be described with reference to the drawings. FIG. 7 is a principle diagram of such an optical head. Reference numeral 1 denotes an optical disk. Light reflected from the optical disk 1 is diffracted and reflected by tracks on the optical disk 1.

Reference numeral 3 denotes an objective lens, which focuses light of a laser (not shown) on the optical disc 1.

The light reflected from the optical disk 1 is diffracted into 0-order light and ± 1st-order light by diffraction of tracks on the optical disk 1 and reenters the objective lens 3.

FIG. 8 shows the pattern of the diffracted light at this time.
It is possible to obtain a push-pull tracking error signal from the difference between the amounts of light on the −1st order light side and the + 1st order light side in the figure. In order to suppress the fluctuation, the light is separated immediately after the objective lens 3.

Returning to FIG. 7, reference numeral 4 denotes a hologram element as a light quantity splitting element, which follows the track (not shown) together with the objective lens 3 and moves in the direction of arrow A. Reference numeral 5 denotes a light receiving element, which receives the light branched by the hologram element 4.

FIG. 9 shows a detailed view of the hologram element 4 and the light receiving element 5. In FIG. 9, the hologram element 4 is divided into areas A and B in such a manner that the light spot of the objective lens 3 is divided. Light A1, B1 passing through A and B
The groove pitch of the hologram element 4 is manufactured so as to reach the P portion and the Q portion on the light receiving element 5.

The tracking error signal is expressed by the P
It can be generated by the differential between the section and the Q section.

As described above, the moving hologram element 4 separates the objective lens 3 from the objective lens 3 together with the objective lens 3 so that even if the objective lens 3 moves, the light is not reflected on the light receiving elements P and Q in FIG. Since the spot does not move, DC fluctuation of the tracking error signal due to the movement of the objective lens 3 is small.

However, in the case of an apparatus for recording information by efficiently irradiating a laser beam on the optical disc 1, the light passing through the objective lens 3 and the hologram element 4 has a light amount distribution according to the laser emission pattern. A light amount difference occurs according to the light amount distribution.

FIG. 10 is an explanatory diagram showing a light quantity distribution of the zero-order light reaching the light receiving element 5. The light amounts of the zero-order light of the lights A1 and B1 are A2 and B2, respectively.

The zero-order light reaching the light receiving element 5 has a Gaussian distribution known by the laser light emission pattern, and the light emission pattern has a solid line shape in FIG.

However, when the objective lens 3 is displaced rightward, the light emission pattern is displaced in the form of a broken line in FIG. The generated tracking error signal is shifted in terms of DC.

[0017]

As described above, in this conventional configuration, since the light emitted from the objective lens 3 has a light amount distribution, even if the light is separated and received by the hologram element 4 that moves with the objective lens 3. In addition, there is a problem that the tracking error signal fluctuates in a DC manner with the movement of the objective lens 3 due to the light amount distribution.

It is an object of the present invention to provide an optical head in which a tracking error signal does not fluctuate even if the light emitted from the objective lens has a light amount distribution.

[0019]

In order to achieve this object, an optical head according to the present invention uses a hologram diffraction element divided into a plurality of tracks in a track direction to form a distribution of light spots on a light receiving element for detecting tracking. In this configuration, light of a middle degree intersects and is received.

[0020]

[Effect] Even if there is a light amount distribution in the light amount of the objective lens, the middle light can cancel out the light amount distribution accompanying the movement of the objective lens, so that the fluctuation of the tracking error signal with respect to the lateral displacement of the objective lens can be suppressed. it can.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an optical head according to a first embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a configuration diagram of an optical head according to a first embodiment of the present invention. In FIG. 1, an optical disc 1,
The objective lens 3 has the same configuration as the conventional example. Reference numeral 9 denotes a hologram element which splits light toward the light receiving element 5.

FIG. 2 shows a configuration diagram of the hologram element 9 and the light receiving element 5. In FIG. 2, the hologram element 9 divides the light spot of the objective lens 3 so that B,
Divided into C and external A and D areas away from the center of the optical axis
Light spot is separated for each area to be irradiated
Is done.

Light passing through each part, A1, B
1, C1 and D1 reach the light receiving element 5. At this time, the light on the light receiving element 5, A 1 and C 1 are the first components of the light receiving element 5.
The light reaches the split element P , and B1 and D1
The respective pitches of the hologram element 9 are manufactured so as to reach the division element Q portion .

The tracking error signal is expressed by the P
It can be generated by the differential between the section and the Q section.

FIG. 3 is an explanatory diagram showing a light quantity distribution of the zero-order light reaching the light receiving element 5. The light amounts of the zero-order light of the lights A1, B1, C1, and D1 are A2, B2, C2, and D2, respectively.

The zero-order light reaching the light receiving element 5 has a Gaussian distribution known by a laser light emission pattern, and the light emission pattern has a solid line shape in FIG.

When the objective lens 3 is displaced to the right, the light emission pattern takes the form of a broken line in FIG. In part P, A
The light amount of C2 increases instead of the light amount of No. 2, and the light amount of D2 increases instead of the light amount of B2 decreases in the Q section. As described above, since the fluctuation in the light amount due to the movement of the objective lens 3 in the P section and the Q section is canceled out, DC fluctuation of the tracking error signal generated from the differential between the P section and the Q section is suppressed. can do.

As described above, the light receiving element 5 includes the objective lens 3
By passing the light passing near the center of the hologram element at B and C of the hologram element, it is possible to suppress the DC variation of the tracking error signal even if the objective lens 3 is displaced.

Next, a second embodiment will be described. FIG. 4 is a configuration diagram of an optical head according to a second embodiment of the present invention.

The light returning from the objective lens 3 is split by the hologram element 13 and received by the light receiving element 5.

FIG. 5 shows a configuration diagram of the hologram element 13 and the light receiving element 5. In FIG. 5, a hologram element 13 divides the light spot of the objective lens 3 into three parts,
B and external A and C regions distant from the center of the optical axis.
The light spot is divided for each area to be illuminated.
Separated.

Light passing through each of the parts A, B, and C;
A1 and C1 reach the P and Q portions of the light receiving element 5, respectively.
Each pitch of the hologram elements 13 is manufactured so that the light B1 reaches the boundary between the P portion and the Q portion.

Here, the light B1 passing through B is defocused compared with the lights A1 and C1 passing through A and C, and crosses by inverting the spot on the light receiving element 5. Such a defocusing method can be performed by so-called blazing of A, C, or B of the hologram element 13.

The first divisional element P of the light receiving element 5 receives half of the inverted spots of the lights A1 and B1 and receives the light.
The second split element Q of the child 5 receives half of the inverted spot of the light C1 and the light C1.

The tracking error signal is expressed by the P
It can be generated by the differential between the section and the Q section.

FIG. 6 is an explanatory diagram showing a light amount distribution of the zero-order light reaching the light receiving element 5. The light amounts of the zero-order light of the lights A1, B1, and C1 are A2, B2, and C2, respectively.

The zero-order light reaching the light receiving element 5 has a Gaussian distribution known by the laser light emission pattern, and the light emission pattern has a solid line shape in FIG.

When the objective lens 3 is displaced rightward, the light emission pattern has the shape of a broken line in FIG. 6, and the distribution of light at B2 is reversed left and right. Since the light amounts cancel each other, the tracking error signal detected by the differential between P and Q of the light receiving element 5 can suppress DC fluctuation with respect to the displacement of the objective lens 3.

As described above, the light receiving element 5 includes the objective lens 3
Is defocused at the portion B of the hologram element 13 and the spot on the light receiving element 5 is reversed to suppress DC fluctuation of the tracking error signal even if the objective lens 3 is displaced. it can.

After defocusing the light near the center,
Since the light is received near the center of the light receiving element 5 after the left and right inversion, the initial DC component of the tracking error signal, which cannot be sufficiently adjusted by the hologram element that moves together with the objective lens, can be adjusted by moving the fixed light receiving element 5 right and left. .

Although the present embodiment has been described by taking a hologram element of four divisions or three divisions as an example, the same applies even if the number of division methods is increased. Of course, instead of intersecting with the hologram element, the light receiving element may be divided to receive the light, but there is a disadvantage that the adjustment man-hour is required.

[0043]

As described above, since the light receiving element intersects and receives light near the center passing through the hologram element, it is possible to suppress a change in the light quantity distribution of the light due to the movement of the objective lens. As a result, it is possible to suppress DC fluctuation of the tracking error signal.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical head showing a first embodiment of the present invention.

FIG. 2 is a plan view of a hologram element 9 and a light receiving element 5 for explaining the operation of the first embodiment.

FIG. 3 is an explanatory diagram for explaining the operation of the first embodiment.

FIG. 4 is a configuration diagram of an optical head showing a second embodiment of the present invention.

FIG. 5 is a plan view of a hologram element 13 and a light receiving element 5 for explaining the operation of the second embodiment.

FIG. 6 is an explanatory diagram for explaining the operation of the second embodiment.

FIG. 7 is a configuration diagram of a conventional optical head.

FIG. 8 is a plan view for explaining the operation of the conventional example.

FIG. 9 is a plan view of a hologram element 4 and a light receiving element 5 for explaining the operation of the conventional example.

FIG. 10 is an explanatory diagram for explaining an operation of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical disk 3 Objective lens 5 Light receiving element 9, 13 Hologram element

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G11B ^7/ 09-7/095 G11B ^7/ 12-7/135

Claims (2)

(57) [Claims] 1. A light receiving element, an objective lens, and a hologram element that separates reflected light from an optical disk from the objective lens and is driven and moved together with the objective lens , wherein the hologram element emits light from the objective lens. Previous
A first divided element of the light receiving element for reflecting the reflected light from the optical disk;
And the light toward the second splitting element, and further, the light at the center of the optical axis of the optical disk reflected light,
The light is separated into external light separated from the optical axis center, and the light at the optical axis center and the external light are separated by the first component.
The split element and the second split element are different from each other.
Optical head that intersects and receives light at the divided elements to obtain a tracking error signal. 2. A light receiving element, an objective lens, and a hologram element that separates reflected light from an optical disk from the objective lens and that is driven and moved together with the objective lens , wherein the hologram element emits light from the objective lens. Previous
The reflected light of the optical disk is divided into the light at the center of the optical axis and the light in the optical axis.
The light is separated into external light separated from the core, and the external light is further directed to the first split element of the light receiving element.
Light and light directed to a second splitting element, and the first splitting element and the second splitting element are
The image of the light at the center is inverted with the light of the
An optical head that receives a tracking error signal from the head.