Optical information reproducing method

#The present invention relates to an optical information reproducing device for reproducing a signal from an optical information medium which carries digital or the like information recorded thereon in correspondence to edge positions of marks in accordance with a mark edge recording scheme.

#According to the mark edge recording scheme, digital information is recorded in the form of marks of different lengths with correspondence being established between bits “1” and “0 (zero)” on one hand and “presence” and “absence” of mark edges, respectively, on the other hand. A typical example of the reproducing method will be described below. When record marks are scanned therealong with a laser beam with a reflection beam being detected and converted into a reproduced signal by means of an optical detector, a reproduced signal is modulated in conformance with the record marks. By way of example, in the case of a CD-ROM disk and a phase-change disk or the like recording medium, when a light spot of the scan beam is positioned on the record mark, the reproduced signal assumes a low level, while it assumes a high level when the light spot is located in a space portion intervening between the record marks. On the other hand, when the light spot lies on an edge of the record mark, the reproduced signal assumes an intermediate level between the low and high levels. By setting a slice level at this intermediate level, an edge signal pulse is generated every time when the reproduced signal traverses the slice level. Thus, with the method described above, information recorded in conformance with the mark edge recording scheme can be reproduced.

#FIG. 5 is a view for illustrating a conventional information reading method which has heretofore been known. The length of a shortest record mark 52 and that of an inter-mark space, are represented by øm, while the length of a light spot 51 in the direction as viewed along the mark row is represented by øs. When the center of the light spot 51 is positioned on an edge 53 of the record mark 52 and when the length øm is shorter than a half of the diameter øs of the light spot, detection error of the edge 53 will be occurred under the influence of an adjacent record mark. Accordingly, the minimum length øm which allows the mark edge to be detected stably corresponds to a half of the diameter øs of the light spot (see FIG. 5(a)).

#FIG. 1 is a structural diagram showing an optical disk signal reproducing device according to an exemplary embodiment of the present invention.

#FIG. 2 is a view for illustrating the principle underlying reproduction of an information signal according to the present invention.

#FIG. 3 is a diagram showing a structure of an edge signal reproducing circuit according to an exemplary embodiment of the present invention.

#In the following, description will be made in detail of modes for carrying out the present invention by referring to the accompanying drawings.

#In the drawings, reference numerals indicate as follows.

#1 . . . semiconductor laser