| 摘要 |
It is intended that a read-out spot (V1) can be addressed quickly to a particular information part of the recording carrier (1). The tracks (2) of the recording carrier (1) are subdivided into two groups (a, b). The spacing (d1) between the tracks of the first group (a) is constant, as is the spacing (d2) between the tracks of the second group (b). The second spacing (d2) is greater than the first spacing (d1). The variation in the spacings (d1, d2) between the tracks (2) is about 10% of the average spacing. A read-out beam (11) of a laser (10) is focused by a lens (16) at the read-out spot (V1) on the recording carrier (1). After the reflection at the recording carrier (1), the read-out beam (11) is passed to a detector (14). In order to establish whether the read-out spot (V1) is addressed to the desired group of tracks, an auxiliary beam (l) is used. The auxiliary beam (l) is launched into the path of the read-out beam (11) and produces an addressing spot (V2) on the information carrier (1). The reflected part-beam (l+1) is reflected to two detectors (4, 5), which are connected to a differential amplifier (6). <IMAGE> |
