Compatible recording and reproducing device

摘要

The device is compatible with a Super Density optical disc (SD) having a track spacing (P1) of 0.74 mu m, and with a compact disc (CD) having a track spacing (P2) of 1.6 mu m. The tracks are scanned with a main beam (M) and two auxiliary beams (E,F) from which a tracking error signal is derived. The midpoints of the scans are laterally spaced with a separation chosen as about 7/4 times the smaller track spacing, and about 3/4 of the greater track spacing. The tracks may be either spiral or parallel. The focal length of the scanner is proportional to the track spacing in each instance.