Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Patent
1985-12-11
1988-05-10
Richardson, Robert L.
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
369121, 369122, 346 76L, 346108, 350420, G11B 700
Patent
active
047440732
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an optical system for optical recording/reproducing.
BACKGROUND ART
Data recording on a medium, which can be optically accessed, e.g., an optical disk, requires about 10 mW power. However, a semiconductor laser, which is widely used as a light source for such recording has only low optical output of about 20 to 30 mW. For this reason, an optical output from a semiconductor laser must be effectively utilized, and high coupling efficiency is required for an optical system.
Meanwhile, when data is reproduced from an optical disk, higher reproducing performance can be obtained if light beams becomes incident to lenses more uniformly. FIG. 1 shows this phenomenon. An aperture 2A of a lens is smaller than a diameter 2W of a beam, and as A/W becomes smaller, MTF becomes higher.
In other words, high reproducing performance and high coupling efficiency are contrary requirements. Therefore, a recording/reproducing optical system which satisfies both the requirements and can cope with variations in optical constants of optical elements has not yet been known.
DISCLOSURE OF INVENTION
The present invention has been made in consideration of the above situation, and has as its object to provide a recording/reproducing optical system which has predetermined reproducing performance and coupling efficiency, and can cope with variations in optical constants of optical elements.
In order to achieve the above object, there is provided a recording/reproducing optical system, which comprises a semiconductor laser causing single transverse mode oscillation and having beam radiation angles of .theta..perp. and .theta..parallel. in planes normal and parallel to an active layer, respectively; a collimator lens having a focal length F.sub.c ; an anamorphic optical elemet having a magnification ratio of 1:.beta. in two directions crossing each other at right angles; and an objective lens having a focal length F.sub.0, a numerical aperture NA.sub.0 and an aperture 2A.sub.0, and in which ratios A.sub.0 /W.perp. and A.sub.0 /W.parallel. of the apertures to diameters 2W.perp. and 2W.parallel., on the planes normal and parallel to the active layer, of beams which are emitted from the semiconductor laser, pass through the collimator lens and the anamorphic optical element and are incident to the objective lens have the following relations with predetermined values fi.perp. and fi.parallel.: value.eta..sub.d : M=f.sub.c /f.sub.0 and .beta. satisfy the following relations: .theta..parallel..multidot.fi.parallel.) .theta..perp..multidot.sin .theta..parallel..multidot..eta..sub.d.sup.2)
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a graph showing the relationship between a ratio of a lens aperture and a beam diameter, and reproducing performance.
FIG. 2 is a schematic side view showing an embodiment of the present invention.
FIG. 3 is a graph showing the relationship between a ratio of a lens aperture and a beam diameter, and coupling efficiency.
FIG. 4 is a graph approximately showing the relationship shown in FIG. 3.
FIG. 5 is a graph showing an optical constant of the embodiment of the present invention.
BEST MODE OF CARRYING OUT THE INVENTION
An embodiment of the present invention will be described hereinafter with reference to FIGS. 2 to 5.
FIG. 2 shows an arrangement according to the embodiment. A semiconductor laser 1 causes single transverse mode oscillation. Beam intensity of light beams 2 radiated from the semiconductor laser 1 has a distribution approximate to the Gaussian distribution on a cross section normal to the optical axis.
Angles formed by the optical axis and light beams passing through a distal end of the beam radius of the beams 2 radiated from the semiconductor laser 1, i.e., a point at which the intensity thereof becomes 1/e.sup.2 of a value on the optical axis are .theta..perp. and .theta..parallel. (.theta..perp.>.theta..parallel.) in planes normal and parallel, respectively, to an active layer 3 of the semiconductor laser 1. In addition, a cross section of t
REFERENCES:
patent: 4318594 (1982-03-01), Hanada
patent: 4390235 (1983-06-01), Minoura
patent: 4466087 (1984-08-01), Cheng
patent: 4520471 (1985-05-01), Carlin
patent: 4520472 (1985-05-01), Reno
Eslinger Lewis H.
Richardson Robert L.
Sony Corporation
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