400 Mbit/s optical heterodyne DPSK system experiment with in- line 1.5micron amplifiers.

We report a 400 Mbit/s Differential Phase Shift Keying (DPSK) heterodyne optical transmission system experiment using two in-line packaged resonant type amplifiers. The optical amplifier gave a 14.5dB net gain from fiber to fiber at lambda=1.488microns with no significant system penalty.