JPH05258341A - Optical head - Google Patents

Abstract

(57) [Summary] [Purpose] To simplify adjustment in an optical head. A laser beam emitted from a laser diode 21 is converted into parallel light by a collimator lens 31.
The parallel light is reflected by the total reflection mirror 32 and further reflected by the beam splitter 33, and the objective lens 41
It is incident on the magneto-optical disk 42 via. The laser light reflected by the magneto-optical disk 42 is reflected by the objective lens 41.
The light that is incident on the beam splitter 33 through the beam splitter 33 passes through the half-wave plate 39, is partially reflected by the beam splitter 34, and is incident on the photodetector 37. Further, the light transmitted through the beam splitter 34 is reflected by the total reflection mirror 35, and the photo detector 38
Is incident on. An RF signal corresponding to the signal recorded on the magneto-optical disk 42 can be generated from the difference between the outputs of the photo detectors 37 and 38. Collimator lens 31, beam splitters 33 and 34, half-wave plate 3
9. The photo detectors 36 to 38 are the alignment unit 30.
Are integrated in.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head suitable for use in, for example, a magneto-optical disk device.

[0002]

2. Description of the Related Art FIG. 2 shows an example of the structure of an optical head in a conventional magneto-optical disk device. The laser light emitted from the semiconductor laser 1 is collimated by the collimator lens 2 and then incident on the objective lens 4 through the beam splitter 3 and focused on the magneto-optical disk 5. The laser light reflected by the magneto-optical disk 5 enters the beam splitter 3 via the objective lens 4. The laser light reflected by the beam splitter 3 is incident on the beam splitter 8 via the half-wave plate 13, and a part of the light is incident on the photodetector 10 via the condenser lens 9. The remaining light is incident on the photodetector 12 via the condenser lens 11.
A signal corresponding to the recorded information recorded on the magneto-optical disk 5 can be read from the difference between the outputs of the photo detectors 10 and 12.

On the other hand, a part of the light emitted from the semiconductor laser 1 and incident on the beam splitter 3 by the collimator lens 2 is reflected by the beam splitter 3 and is incident on the photodetector 7 via the condenser lens 6. A so-called APC servo can be applied so that the output of the semiconductor laser 1 becomes constant from the output of the photodetector 7.

[0004]

As described above, in the conventional optical head, the respective parts are arranged independently of each other. As a result, there is a problem that a lot of labor is required to adjust the optical axis of each optical component.

The present invention has been made in view of such a situation, and makes it possible to simplify the adjustment.

[0006]

The optical head of the present invention comprises a laser diode 21 for generating a laser beam, a collimator lens 31 for converting divergent light incident from the laser diode 21 into parallel light, and a collimator lens 31. Objective lens 4 for irradiating the emitted light on the magneto-optical disk 42
1, photodetectors 36 to 38 for receiving the light reflected by the magneto-optical disk 42, and a collimator lens 3
The light collimated by 1 is emitted toward the objective lens 41, and the light incident from the objective lens 41 is
An optical head including a beam splitter 33 that emits light toward the photodetectors 36 to 38 is characterized in that the collimator lens 31, the photodetectors 36 to 38, and the beam splitter 33 are integrally formed.

[0007]

In the optical head having the above structure, the collimator lens 31, the photodetectors 36 to 38 and the beam splitter 33 are integrally formed. Therefore, the size can be reduced.

[0008]

FIG. 1 is a sectional view showing the structure of an embodiment of an optical head of the present invention. As shown in the figure, the optical head of the present invention is composed of a light emitting / receiving section 20, an alignment section 30, and an objective lens 41.

The light emitting / receiving section 20 contains a semiconductor laser 21 and a photo detector 22 for focusing, and a hologram 23 having astigmatism or grating characteristics is attached to the surface thereof.

The alignment unit 30 includes a collimator lens 31, a total reflection mirror 32, a beam splitter 33,
34, a total reflection mirror 35, a photodetector 36 for APC control, photodetectors 37, 38 for detecting a magneto-optical signal, and a half-wave plate 39 are integrally formed. The substrate 40 of the alignment unit 30 has a structure in which a circuit for processing the outputs of the photo detectors 36 to 38 is incorporated.

The divergent laser light emitted from the semiconductor laser 21 is converted into parallel light by the collimator lens 31, reflected by the total reflection mirror 32, and incident on the beam splitter 33. The beam splitter 33 is composed of, for example, a half mirror. Therefore, a part of the light passes through the beam splitter 33 and is incident on the photodetector 36 for APC control. Further, a part of the light is reflected by the beam splitter 33, and focused on the magneto-optical disk 42 through the objective lens 41.

The laser light reflected from the magneto-optical disk 42 is incident on the beam splitter 33 via the objective lens 41, and the laser light transmitted therethrough is a half-wave plate 39.
And is incident on the beam splitter 34. The beam splitter 34 is, for example, a deflecting beam splitter, and a part of the light (for example, S wave component) is reflected and enters the photodetector 37. The remaining light (P wave component) passes through the beam splitter 34 and is totally reflected by the mirror 3.
5 and is reflected there and is incident on the photodetector 38.

A collimator lens 31, a total reflection mirror 32, beam splitters 33 and 34, a total reflection mirror 35, and a photodetector 36 housed in the alignment section 30.
All of the light beams from to 38 and the half-wave plate 39 are parallel light beams. As a result, these positional adjustments may be relatively rough, and the positional relationship once set is invariable because they are integrally fixed. As a result, the optical axis adjustment as the optical head is required only between the light emitting / receiving section 20, the alignment section 30, and the objective lens 41. Further, since the collimated light is incident on the photodetectors 36 to 38 as it is, a condenser lens is not required, the number of parts can be reduced, and the size and cost can be reduced.

Next, the operation will be described. The laser light emitted from the semiconductor laser 21 is a hologram 23.
And is incident on the collimator lens 31, where the divergent light is converted into parallel light. The parallel light is reflected by the total reflection mirror 32 and is incident on the beam splitter 33. Part of the light that has passed through the beam splitter 33 is incident on the photodetector 36 as parallel light. The output of the photodetector 36 is compared with a predetermined reference value, and the output of the laser diode 21 is controlled so that the difference becomes constant (AP
C control).

On the other hand, the laser beam reflected by the beam splitter 33 is passed through the objective lens 41 and the magneto-optical disk 4
2 is focused and illuminated. The laser light reflected by the magneto-optical disk 42 enters the beam splitter 33 via the objective lens 41. Part of the light is beam splitter 3
The light is reflected by the laser beam No. 3, is reflected by the total reflection mirror 32, and is incident on the collimator lens 31. Then, the laser light emitted from the collimator lens 31 enters the hologram 23.

As described above, the hologram 23 is provided with the characteristics of the grating and the astigmatism. Therefore, a part of the light is diffracted and given astigmatism, and is incident on the photodetector 22. Therefore, the focus error signal can be generated from the output of the photodetector 22 based on the so-called astigmatism method. Focus control is performed by driving a holder (not shown) that holds the light emitting / receiving unit 20, the alignment unit 30, and the objective lens 41 in the focus direction (vertical direction in the drawing) in response to the focus error signal.

On the other hand, a part of the light incident on the beam splitter 33 is transmitted therethrough and is transmitted through the half-wave plate 39, whereby the plane of polarization is rotated by 45 degrees. Then, a part (S wave component) of this laser light is polarized beam splitter 3
It is reflected at 4 and is incident on the photodetector 37. The rest (P-wave component) of the light incident on the beam splitter 34 is transmitted therethrough and is reflected by the total reflection mirror 35.
And is incident on the photodetector 38. The RF signal (P-wave component) corresponding to the magneto-optical information recorded on the magneto-optical disk 42 can be reproduced from the difference between the outputs of the photo detectors 37 and 38.

When the disc to be reproduced is a CD or an optical video disc, the half-wave plate 39, the beam splitter 34, the photodetector 37, etc. can be omitted.

In the present embodiment, the photodetectors 36 to 38 detect the laser light in the state of parallel light. When the diameter of the laser light is large, the diameters of the photo detectors 36 to 38 are also large. However, if these are increased, the stray capacitance makes it difficult to detect a high frequency signal. Therefore, it is preferable that the diameter of the laser light (the diameter of the objective lens 41 or the collimator lens 31) is 3 mm or less.

[0020]

As described above, according to the optical head of the present invention,
Since the collimator lens, the photodetector and the beam splitter are integrally formed, the adjustment becomes easy. In addition, miniaturization is possible.

[Brief description of drawings]

FIG. 1 is a sectional view showing a configuration of an embodiment of an optical head of the present invention.

FIG. 2 is a sectional view showing a configuration of an example of a conventional optical head.

[Explanation of symbols]

 20 light emitting / receiving section 21 laser diode 22 photodetector 23 hologram 30 alignment section 31 collimator lens 32 total reflection mirror 33, 34 beam splitter 35 total reflection mirror 36 to 38 photodetector 41 objective lens 42 magneto-optical disc

Claims (1)

[Claims] 1. A laser diode for generating laser light, a collimator lens for converting divergent light incident from the laser diode into parallel light, and an objective lens for irradiating the recording medium with the light emitted from the collimator lens. A photodetector that receives the light reflected by the recording medium; and a light that is collimated by the collimator lens, is emitted toward the objective lens, and the light that is incident from the objective lens is emitted by the photodetector. An optical head provided with a beam splitter which emits toward a detector, wherein the collimator lens, the photodetector and the beam splitter are integrally formed.