JPS6320735A - Optical head - Google Patents

Abstract

PURPOSE:To obtain a compact optical head by performing the photodetection after making the light reflected by either one of a focusing or tracking photodetector incident on the other photodetector. CONSTITUTION:The laser beams radiated from a semiconductor laser 50 are turned into parallel beams by a collimator lens 52 and converged on an optical disk 62 by an objective lens 60 after passing through a beam splitter 56. The half of the light beams reflected by an optical disk 62 is separated by the splitter 56 to produce the asigmatism by a lens 66 and a rod lens 68. Then a focus signal is detected by a photodiode 70. At the same time, the reflected light of the photodiode 70 travels back to pass through the splitter 56 and the polarized wave surface is turned by 45 deg. by a 1/2 wavelength plate 72. Then the reflected light is divided into two directions by a beam splitter 76 via a lens 72 and made incident on the photodiodes 78 and 80 of a tracking photodetectors.

Description

[Detailed Description of the Invention] [Field of Application for Sedentary Work] The present invention relates to an optical disc used in optical disc technology for non-contact recording/reproducing of information, and more specifically relates to an optical disc used in optical disc technology for recording/reproducing information in a non-contact manner. The present invention relates to an optical head that detects light with either a focussing or trafking light-receiving element, and detects the light by making the light reflected there enter the other light-receiving element.

[Prior Art] An optical head using a semiconductor laser is used to read information on an optical disk or write information on an optical disk. In this optical head, a laser beam is focused by an objective lens, irradiated onto a predetermined position on the signal surface of an optical disk, and the light from there is received to control the position of the objective lens.
In order to perform 4n, a light receiving element for focussing and tracking is provided.

FIG. 3 shows an example of an optical head used in a conventional magneto-optical disk device. A laser beam from a semiconductor laser 10 is focused by a collimator lens 12, and then passed through a shaping prism 1.
After shaping the irradiation spot into a circular shape in step 4, it passes through the first beam splinter 16, is reflected by the mirror 18, and is reflected by the objective lens 2.
The light is focused at zero and illuminates the signal surface of the magneto-optical disk 22. When such linearly polarized light is irradiated onto the magneto-optical disk 22, the plane of polarization of the reflected light is rotated due to the Kerr effect.

This reflected light passes through the objective lens 20, is reflected by the mirror 18 and the first beam splinter 16, and heads toward the light receiving system.This light is separated into two paths by the second beam splinter 24, one of which passes through the lens 26. The light passes through the cylindrical lens 28 and reaches a four-segment photodiode 30, which is a light receiving element for force focusing, and generates signals for force and lens control using an astigmatism method.

The other beam from the second beam splinter 24 is 17
The plane of polarization is rotated by 45 degrees with the two-wavelength plate 32, and the light is focused through the lens 34, split by the third beam splinter 36, and sent to the photodiode 38.4, which is a light receiving element for tracking.
It reaches 0.

The photodiodes 38 and 40 generate a recording information signal by their differential output, and also generate a tracking signal by a push-pull method.

[Problems to be Solved by the Invention] In the prior art, as described above, in order to perform signal detection for force fusing and tracking control, at least three
A combination of several beam splitters is required, and the large number of parts hinders miniaturization.

The purpose of the present invention is to eliminate the drawbacks of the prior art as described above,
An object of the present invention is to provide an optical head that can be easily miniaturized by reducing the number of beam splitters used.

[Means for Solving the Problems] The present invention, which can achieve the above objects, guides light reflected by either a focusing or tracking light receiving element to the other light receiving element. This is an optical head that performs optical detection.

Light sources for magneto-optical heads mainly use wavelengths of 0. The laser beam is in the 8 μm band, and a silicon photodiode is often used as the light receiving element. Silicon has a refractive index of approximately 3.5 at this wavelength and has a high reflectance (approximately 35%).
)have. In the conventional technology, only a part of the light that reaches the light receiving element is converted into electrical energy, and most of the remaining light is diffusely reflected and escapes in another direction. A major feature of this device is that it utilizes reflections from the surrounding cover glass and the like to guide light to the other light-receiving element and detect the light.

[The light sent from the working codisc first enters either a light receiving element for force sensing or tracking. Then, light detection is performed by the light receiving element. At the same time, the light reflected from that light receiving element is guided to the other light receiving element.

Necessary signals are detected by the focusing and tracking light-receiving elements, and lens positioning is performed based on these signals.

Since one of the light receiving elements operates like a half mirror, the number of installed beam splitters can be reduced.

[Embodiment] FIG. 1 is an explanatory diagram showing an embodiment of an optical head according to the present invention. Laser light from the semi-solid laser 50 is converted into parallel light by a collimator lens 52, passes through a first beam splinter 56, and is focused onto the signal surface of an optical disk 62 by an objective lens 60. The reflected light from the magneto-optical disk causes clockwise or counterclockwise Kerr rotation depending on the recorded information.

Half of the reflected light is separated by the first beam splitter 56, passes through a lens 66 and a cylindrical lens 68, and reaches a 4-split photodiode 70, which is a light receiving element for focusing. Lenses 66 and 68 create astigmatism, and a photodiode 70 detects a focus signal.

At the same time, the reflected light from the photodiode 70 travels backwards and passes through the first beam splitter 56. Then, the plane of polarization is rotated by 45 degrees by the 1/2 wavelength plate 72, passes through the lens 74, is split into two directions by the second polarization beam splitter 76, and reaches the photodiodes 78 and 80, which are light receiving elements for tracking. A recording information signal is generated in the photodiodes 78 and 80 by differential output, and a tracking differential output is generated by the push-pull method. At this time, the laser light from the semiconductor laser 50 is a beam spot.

A portion of the light is reflected by the mirror 56 and reaches the photodiodes 78 and 80, but since it is a constant amount of light that does not contain any signals, it does not cause any problem in tracking detection.

As is clear from the above description, the feature of the present invention is that the light reflected by the focusing light receiving element is actively directed to the trunking light receiving system, and is incident on the light receiving element to perform light detection. At the point. Of course, on the contrary, it is also possible to direct the light reflected by the tracking light-receiving element to the focusing light-receiving element for light detection.

The photodiode has a structure in which a silicon chip 92 is housed in a case 90 and covered with a bar glass 94, as shown in FIG. Light is used, and such a silicon photodiode is often used as the light receiving element.Silicon has a refractive index of about 3.5 at this wavelength and itself has a high reflectance (about 35%).

Therefore, by utilizing the reflection on the surface of the silicon chip 92, the optical path can be designed to guide the reflected light to the other light-receiving element.Also, it is possible to form an arbitrary reflective film on the surface of the cover glass. This also makes it possible to adjust the S/N of the optical head.

Although the above embodiment is an example of a head for a magneto-optical disk, the present invention can also be applied to an optical head for other optical disks.

[Effects of the Invention] As described above, the present invention is configured so that the light reflected by either one of the focus-length or tracking light-receiving elements is incident on the other light-receiving element to perform photodetection. One of the light-receiving elements acts like a half-mirror, and the number of installed beam splinters can be reduced, and the number of parts is small (and the structure is simplified and miniaturized).

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of an optical head according to the present invention, FIG. 2 is an explanatory diagram showing an example of a light receiving element, and FIG. 3 is an explanatory diagram showing an example of a conventional technique. 50...Semiconductor laser, 56.76...Beam splitter, 62...Magneto-optical disk, ? 0.78°80
···Photodiode. Patent Applicant Fuji Electrochemical Co., Ltd. Agent Shigemi) Takara No. 3
figure

Claims (1)

[Claims] 1. In an optical head that includes light receiving elements for focusing and tracking that receive light sent from the disk, and controls the position of the lens based on output signals from these, either the focusing or tracking light receiving element An optical head characterized in that light reflected by one light-receiving element is incident on another light-receiving element to perform light detection.