Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Patent
1990-11-15
1992-12-15
Envall, Jr., Roy N.
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
369 4424, 369109, 369121, G11B 700
Patent
active
051723689
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns an optical reading device for an optical recording medium, more particularly an optical reading device that can be used especially in the reading heads of optical disks designated, in the market, by terms such as "compact disks", "video disks" or "digital optical disks".
In standard optical reading disks, the means generally used for splitting light energy consist of prisms or semi-transparent mirrors positioned so that the reflected beam emerging from the splitting device is directed along a line that is substantially perpendicular to the path of the extraction light beam. As a consequence the dimensions, notably the width of the reading device, are important. This is a hindrance to the reduction of the dimensions of the system as a whole.
To overcome these drawbacks, it has been proposed, notably in the French patent application No. 2 538 580, filed on behalf of the Pioneer Electronic Corporation, or in the French patent No. 2 597 249, filed on behalf of the present Applicant, that the splitting means used should consist of a diffraction grating or a birefringent grating. In this case, the beam reflected by the surface of the optical recording medium is reflected towards photosensitive detection means which are aligned with the light-emitting source substantially along one and the same axis perpendicular to the plane of the recording medium. Consequently, an optical reading device, far more compact than prior art devices, is obtained. However, to make it easy to set up the vertical servocontrol of the light beam on the recording medium, a diffraction grating is used giving an effect of astigmatism to the detection beam. In this case, the detection means are located in a plane close to the plane conjugate with the plane of the disk in the vicinity of the light emission source. The position of this plane should be defined very precisely. Indeed, this plane corresponds to the focal plane of the detection beam when the system is accurately focused. Since the position of the means is important, it follows therefrom that when the position settings are done, they should no longer be liable to modification which may be due, for example, to mechanical deformations of the reading device.
The present invention is therefore aimed at overcoming these drawbacks by proposing a novel optical reading device for an optical recording medium enabling the vertical servocontrol to be easily achieved.
Consequently, an object of the present invention is a device for the optical reading of an optical recording medium of the type comprising: a source for emitting a first light beam along a main optical axis; a splitter means to direct, along the main optical axis, the first beam towards the surface of the recording medium and to split a second beam obtained by reflection of the first beam on the surface of the recording medium so as to form a third beam directed along a secondary optical axis; a focusing means provided between the splitter means and the surface of the recording medium to focus the first beam on said surface; a mask to introduce a disymmetry in the third beam, and at least one detection device receiving at least one part of the third beam and giving at least one electrical signal expressing the detection made, characterized in that the mask is formed by at least one part of the external surface of the light-emitting source, the splitting means being positioned and made so that the mask is in the focusing plane of the third beam when the first beam is accurately focused.
According to a preferred embodiment, the light-emitting source is formed by a laser made in a semiconductor chip. Consequently, the mask is formed by one of the front edges of the chip, preferably a lateral edge. The mask may also be formed by one of the lower corners of the chip.
Furthermore, to prevent the third beam from being hidden by the upper or rear edge of the light-emitting source, the angle of deflection of the third beam is greater than the half-angle of aperture of the focusing means, seen from the light
REFERENCES:
patent: 4345321 (1982-08-01), Arquie et al.
patent: 4829506 (1989-05-01), Bresser et al.
patent: 4888760 (1989-12-01), Shikama et al.
patent: 4918675 (1990-04-01), Lee
patent: 5050155 (1991-09-01), Kurata et al.
patent: 5066138 (1991-11-01), Toide et al.
"Thomson-CSF"
Envall Jr. Roy N.
Hindi Nabil
Plottel Roland
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