A simple equation which gives the crosstalk-free condition for land/gr
oove recording of optical discs is deduced. Making use of this equatio
n, the groove depth which minimizes the crosstalk from adjacent tracks
is easily calculated. For simultaneous suppression of both the on-gro
ove crosstalk and the on-land crosstalk, two practical approaches are
proposed for the phase modulation discs. This equation is also of use
in the signal estimation of optical discs.