
Differential Phase-Shift Keying (DPSK) is another modulation format which
has attract ed considerable attention for 40 Gbit/s applications. It incorporates
numerous phase jumps, which act similarly as above against intrachannel non-
linear effects, but we shall come back to this feature that later on. In contrast to all
the above formats, the information is carried by the phase itself. DPSK optical data
are generated by passing laser light into a electro-optic phase modulator, or pre-
ferably, into a Mach-Zehnder electro-optic amplitude modulator (see Figure 14.21,
lines 6–7), biased such that the intensity levels of the “1” and “0” symbols are