JPH09282702A - Optical head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify an information signal reproducing system and a servo signal detecting system by integration and to detect a tracking error signal with good accuracy. SOLUTION: The laser beam separated by a beam splitter 25 is introduced through an optical system consisting of a Wollaston prism 26 and a diffraction grating 27 to photodetector 28. The two luminous fluxes among the three luminous fluxes separated by the Wollaston prism 26 are further separated by the diffraction grating 27. Information signals are reproduced by using the separated zero order diffracted light and ± first order diffracted light. The other one luminous flux is further separated by the diffraction grating and the focus error signal is detected by using the separated zero order diffracted light. The tracking error signal is detected by using the separated ± first order diffracted light. The photodetecting surface of the photodetector 28 is made smaller by setting the angle formed by the gratings of the diffraction grating 27 smaller than 45 deg. from the dividing line.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device for recording or reproducing information on a magneto-optical disk, and more particularly to an optical head for optically detecting information on the magneto-optical disk and converting it into an electric signal.

[0002]

2. Description of the Related Art An example of the structure of an optical head using a conventional technique will be described with reference to FIG. The laser light 2 emitted from the semiconductor laser 1 becomes a parallel light flux by the collimator lens 3, a part of which is reflected by the beam splitter 6 through the beam shaping prism 4 and the mirror 5 and reaches the photodetector 7 to output the laser light 2. To monitor. The laser beam 2 transmitted through the beam splitter 6 passes through a mirror 8 and is focused by an objective lens 9 on a recording film surface 11 of an optical disc 10.

The laser beam 2 reflected from the recording film surface 11 passes through an objective lens 9 and a mirror 8 and a beam splitter 6 partially passes through a convex lens 12 to reproduce an information signal reproducing system 13.
And reaches a part of the servo signal detection system 14. The information signal reproduction system 13 includes a polarization beam splitter 15 and a photodetector 1.
6 and the operation of this configuration is described in JP-A-5-217234.

The servo signal detection system 14 is a two-division diffraction grating 1
7, a convex lens 18, a cylindrical lens 19, and a photodetector 20. The operation of this structure is described in JP-A-6-162527 and will be described with reference to FIG. The two-divided diffraction grating 17 is composed of two regions, that is, a region A21 and a region B22, and a diffraction grating is formed symmetrically at an angle of 45 degrees with respect to the division line 23 in each region.

The photodetector 20 has a light-receiving surface 24 divided into eight parts a to h. The 0th-order diffracted light of the laser light 2 that has passed through the two-division diffraction grating 17 is incident on a to d of the light receiving surface 24 of the photodetector 20, and by the action of the convex lens 18 and the cylindrical lens 19, the so-called astigmatism method is used (a + c). ) −
A focus error signal can be obtained from the output of (b + d). The ± first-order diffracted light of the laser light 2 that has passed through the area A21 of the two-division diffraction grating 17 is e on the light-receiving surface 24 of the photodetector 20,
The ± first-order diffracted light of the laser light 2 that has entered g and passed through the region B22 of the two-division diffraction grating 17 is the light-receiving surface 2 of the photodetector 20.
It is possible to obtain a tracking error signal from the output of (e + g)-(f + h) by the so-called push-pull method by making the light incident on f and h of 4.

In the structure of the optical head as shown in FIG. 4, since the information signal reproducing system 13 and the servo signal detecting system 14 are separated, each signal can be accurately detected, but the number of parts is increased. There was a flaw.

Further, as an optical element for simplifying the detection system of the information signal and the servo signal, a three-beam Wollaston prism for splitting a light beam into three rays is, for example, Japanese Patent Publication No. 4-19.
No. 522 is proposed. An example in which the detection system is simplified by using this 3-beam Wollaston prism will be described with reference to FIG.

Laser light 2 emitted from a semiconductor laser 1
Is collimated by the collimator lens 3 to be a parallel light beam, which is partially reflected by the beam splitter 25 through the beam shaping prism 4 and reaches the photodetector 7 to monitor the output of the laser beam 2. The laser beam 2 transmitted through the beam splitter 25 passes through the mirror 8 and is focused by the objective lens 9 on the recording film surface 11 of the optical disc 10.

The laser beam 2 reflected from the recording film surface 11 passes through the objective lens 9 and the mirror 8 and the beam splitter 25.
A part of the light is reflected by the three-beam Wollaston prism 26, the convex lens 18, and the cylindrical lens 19 to reach the photodetector 31, where the information signal is reproduced and the servo signal is detected.

The operation of the three-beam Wollaston prism 26 will be described with reference to FIG. The laser beam 2 that has passed through the three-beam Wollaston prism 26 has three light beams 2a, 2b,
It is separated into 2c. The light beam 2a includes both P-polarized light component and S-polarized light component, and the light beam 2b includes P-polarized light component.
c is composed of an S-polarized component. The luminous fluxes 2b and 2c have the same intensity and form an angle of about 1 degree with respect to the luminous flux 2a.

The light beam 2a is a on the light receiving surface 24 of the photodetector 31.
To d, and the convex lens 18 and the cylindrical lens 1
By the action of 9, the so-called astigmatism method (a +
A focus error signal is obtained from the output of c)-(b + d). Furthermore, a tracking error signal is obtained from the output of (a + b)-(c + d) by the push-pull method. Light flux 2b, 2
c is incident on e and f of the light receiving surface 24, reproduces a magneto-optical signal by the output of (e−f), and reproduces a preformatted signal by the output of (e + f).

Although the detection system is simplified in the above configuration, the diameter of the light beam 2a on the photodetector 31 is, for example, about 0.
It is as small as 1 mm. Therefore, if the position of the light beam 2a is displaced, the tracking error signal is likely to be offset, and it is difficult to detect the tracking error signal with high accuracy.

[0013]

As described above, in the prior art, it has been difficult to integrate the information signal reproducing system and the servo signal detecting system in a simple and accurate manner. An object of the present invention is to provide an optical head capable of accurately detecting a tracking error signal while simplifying the information signal reproducing system and the servo signal detecting system by integrating them.

[0014]

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

A light source, an objective lens for condensing the laser light emitted from the light source on the recording film surface of the magneto-optical disk, and a part of the laser light reflected from the recording film surface is transmitted or reflected to be separated. In an optical head composed of a beam splitter for reproducing an information signal and a photodetector for detecting a servo signal, the laser beam separated by the beam splitter is composed of a Wollaston prism and a diffraction grating. Of the three light beams that have passed through the system and are guided to the photodetector and separated by the Wollaston prism, two light beams are further separated by a diffraction grating,
An information signal is reproduced by using the separated 0th-order diffracted light and ± 1st-order diffracted light, and the other one light flux is further separated by a diffraction grating, and a focus error signal is generated by using the separated 0th-order diffracted light. An optical head for detecting and detecting a tracking error signal by using the separated ± first-order diffracted light.

As described above, the present invention uses the three-beam Wollaston and the two-division diffraction grating at the same time to simplify the optical system by the three-beam Wollaston prism, and the tracking error by the push-pull method by the two-division diffraction grating. The signal is accurately detected.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of an optical head which is an embodiment of the present invention. Here, 1 is a semiconductor laser, 2 is a laser beam, 3 is a collimating lens, 4 is a beam shaping prism, 7 and 28 are photodetectors, 9 is an objective lens,
10 is an optical disk, 25 is a beam splitter, 26 is a three-beam Wollaston prism, and 27 is a two-division diffraction grating.

Laser light 2 emitted from semiconductor laser 1
Is collimated by the collimator lens 3 to be a parallel light beam, which is partially reflected by the beam splitter 25 through the beam shaping prism 4 and reaches the photodetector 7 to monitor the output of the laser beam 2. The laser beam 2 transmitted through the beam splitter 25 passes through the mirror 8 and is focused by the objective lens 9 on the recording film surface 11 of the optical disc 10.

The laser beam 2 reflected from the recording film surface 11 passes through the objective lens 9 and the mirror 8 and the beam splitter 25.
Part of the light is reflected by the three-beam Wollaston prism 26, the two-division diffraction grating 27, the convex lens 18, and the cylindrical lens 19 to reach the photodetector 28, which reproduces an information signal and detects a servo signal.

The operation of the three-beam Wollaston prism 26 and the two-split diffraction grating 27 will be described with reference to FIG. The laser beam 2 that has passed through the three-beam Wollaston prism 26 has three
The light beams 2a, 2b, 2c of the book are separated. Light flux 2a is P
Both the polarized light component and the S polarized light component are included, the light flux 2b is composed of the P polarized light component, and the light flux 2c is composed of the S polarized light component. Luminous flux 2
b and 2c have the same intensity and form an angle of about 1 degree with respect to the light beam 2a.

The two-divided diffraction grating 27 includes a region A29 and a region B.
It is composed of two areas of 30 and each area has a dividing line 23.
And a diffraction grating is formed symmetrically at an angle of about 20 degrees with respect to the V-shape. The light beam 2a is divided into two diffraction gratings 27.
The 0th-order diffracted light obtained by passing through is incident on a to d of the light receiving surface 24 of the photodetector 28, and due to the action of the convex lens 18 and the cylindrical lens 19, (a + c)-(b + d) by a so-called astigmatism method. The focus error signal is obtained from the output of.

Further, the ± first-order diffracted light obtained by passing the light beam 2a through the area A29 of the two-division diffraction grating 27 is the photodetector 2.
The first and second order diffracted light which is incident on e and g of the light receiving surface 24 of 8 and passes through the region B30 is incident on f and h of the light receiving surface 24 of the photodetector 28 and is (e + g) by the so-called push-pull method. )-(F + h) output to obtain the tracking error signal. As described above, the tracking error signal in the present invention is not obtained by the conventional method shown in FIG. 7 in which an offset easily occurs.

Similarly, the light beam 2 b is divided into two split diffraction gratings 27.
0th-order diffracted light obtained by passing through the area A29 and area B
All ± 1st-order diffracted light obtained after passing 30
The 0th-order diffracted light obtained by passing the light beam 2c through the two-division diffraction grating 27 and the ± 1st-order diffracted light obtained by passing through the areas A29 and B30 are all incident on the light-receiving surface 24j.
Incident on. The output of (i-j) reproduces the magneto-optical signal, and the output of (i + j) reproduces the preformatted signal.

As described above, the three-beam Wollaston prism 26 and the two-split diffraction grating 27 are used in combination, and the two-split diffraction grating 27 corresponds to the direction in which the light beam is separated by the three-beam Wollaston prism 26. It is possible to reduce the size of the light receiving surface 24 of the photodetector 28 by selecting the angle of the diffraction grating with respect to the dividing line 23 of FIG. Therefore, both the reproduction of the information signal and the detection of the servo signal can be performed by one photodetector 28 having a predetermined size.

The detection of the tracking signal by the push-pull method is performed by comparing the intensities of the portions of the light beam 2a passing through the regions A29 and B30 in the two-division diffraction grating 27, but at the position of the two-division diffraction grating 27, the light beam 2a is detected. Since the diameter of is equal to the diameter of the pupil of the objective lens and has a size of, for example, about 3 mm, the amount of offset generated in the tracking signal is small even with the positional deviation of the light beam 2a, and the tracking error signal can be detected accurately. Can be done.

The three-beam Wollaston prism 26
By changing the arrangement relationship between the two-division diffraction grating 27 and the arrangement shown in FIG. 2, the light receiving arrangement of the light receiving surface 24 of the photodetector 28 can be changed. That is, the two-division diffraction grating 27
The three-beam Wollaston prism 26 is rotated by 90 degrees about the laser beam 2 as a central axis while keeping the structure in which the dividing line 23 is horizontally arranged in FIG. Then,
The separated light beams 2a, 2b, 2c emitted from the three-beam Wollaston prism 26 are different from the horizontal separation in FIG.
It becomes vertical separation and has an orthogonal relationship with the dividing line 23 arranged horizontally. Therefore, the left and right i and j on the light receiving surface of FIG.
Have an upper and lower relationship. That is, the light receiving arrangement on the light receiving surface of FIG. 2 is rotated by 90 degrees. At this time, the size of the light receiving surface of the photodetector can be reduced by changing the angle of the diffraction grating with respect to the dividing line 23 from 45 degrees of the conventional technique to 70 degrees, for example.

FIG. 3 is a block diagram of an optical head according to another embodiment of the present invention. The same reference numerals as those in FIG. 1 indicate the same components. The difference from FIG. 1 is the shape of the beam splitter 32. A part of the laser beam 2 transmitted through the beam shaping prism 4 is reflected by the beam splitter 32 to reach the photodetector 7, and the other passes through the mirror 8 and the objective lens 9 to be collected on the recording film surface 11 of the optical disc 10. Be illuminated.

The laser beam 2 reflected from the recording film surface 11 passes through the objective lens 9 and the mirror 8 and the beam splitter 32.
After being reflected twice by the 3 beam Wollaston prism 2
The light reaches the photodetector 28 through the 6- and 2-division diffraction grating 27, the convex lens 18, and the cylindrical lens 19. Since the positions of the semiconductor laser 1 and the photodetector 28 are close to each other, there is an effect that the mounting area of components can be reduced as compared with FIG.

In the embodiment shown in FIGS. 1 and 3, the positions of the three-beam Wollaston prism 26 and the two-split diffraction grating 27 are exchanged so that the laser beam 2 passes through the two-split diffraction grating 27 and then the three-beam Wollaston prism is used. It may be arranged such that it passes through 26 and reaches the photodetector 28 through the convex lens 18 and the cylindrical lens 19. Further, in the embodiment of FIG. 1, the three-beam Wollaston prism 26 may be bonded to the beam splitter 25 to be integrated.
3 beam Wollaston prism 26
May be bonded to the beam splitter 32 to be integrated.

[0031]

As described above, in the present invention, the optical system is simplified and the tracking error signal by the push-pull method is accurately detected by simultaneously using the three-beam Wollaston and the two-division diffraction grating. It has the effect that

Further, by selecting the angle of the diffraction grating with respect to the dividing line 23 of the two-division diffraction grating 27 to be smaller than 45 degrees, which is the conventional technique, for example, about 20 degrees, the light receiving surface 24 of the photodetector 28 is selected. The size can be reduced, and the information signal reproduction and the servo signal detection can be performed by one detector.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram of the operation of FIG.

FIG. 3 is a configuration diagram of an optical head that is another embodiment of the present invention.

FIG. 4 is an example of a configuration of an optical head using a conventional technique.

5 is an explanatory diagram of the operation of FIG.

FIG. 6 is an example in which a detection system of an optical head using a conventional technique is simplified.

7 is an explanatory diagram of the operation of FIG.

[Explanation of symbols]

 1 semiconductor laser 2 laser light 3 collimating lens 4 beam shaping prism 6,25,32 beam splitter 7, 16, 20, 28, 31 photodetector 9 objective lens 10 optical disk 13 information signal reproduction system 14 servo signal detection system 15 polarized beam beam Splitter 17,27 Two-split diffraction grating 26 Three-beam Wollaston prism

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Toru Sasaki, Toru Sasaki 2880, Kozu, Odawara, Kanagawa Stock Company Hitachi Storage Systems Division (72) Inventor, Yasuo Kitada, 2880, Kozu, Odawara, Kanagawa Hitachi Storage Co., Ltd. System Division (72) Inventor Masachi Fukui 2880 Kozu, Odawara-shi, Kanagawa Hitachi Storage Systems Division (72) Inventor Yoshiro Konishi 2880 Kozu, Odawara, Kanagawa Hitachi Storage Systems Division

Claims (4)

[Claims] 1. A light source, and an objective lens for condensing laser light emitted from the light source on a recording film surface of a magneto-optical disk,
An optical head comprising: a beam splitter that transmits or reflects a part of the laser light reflected from the recording film surface to separate it, and a photodetector that reproduces an information signal and detects a servo signal, The laser beam separated by the beam splitter is passed through an optical system consisting of a Wollaston prism and a diffraction grating to be guided to a photodetector, and two of the three light beams separated by the Wollaston prism are The light flux is further separated by a diffraction grating, an information signal is reproduced by using the separated 0th order diffracted light and ± 1st order diffracted light, and the other one light flux is further separated by the diffraction grating,
An optical head, wherein a focus error signal is detected using the separated 0th order diffracted light, and a tracking error signal is detected using the separated ± 1st order diffracted lights. 2. The diffraction grating according to claim 1, wherein the grating pattern is divided into two parts, and the dividing line is parallel to the direction in which the light beam is separated by the Wollaston prism, and each grating with respect to the dividing line. Is
An optical head characterized in that its angle is set to be smaller than 45 degrees and is V-shaped. 3. The diffraction grating according to claim 1, wherein the grating pattern is divided into two, the dividing line is perpendicular to the direction in which the light beam is separated by the Wollaston prism, and each grating is divided with respect to the dividing line. Is
An optical head, characterized in that the angle formed is greater than 45 degrees and is V-shaped. 4. The optical system from claim 1 to the beam splitter,
An optical head characterized in that a light source and a photodetector are arranged close to each other by arranging a beam splitter, a Wollaston prism, and an optical system reaching the photodetector via a diffraction grating in parallel.