The hybrid Raman and erbium-doped fiber amplifier is investigated for a 16×40 Gbps differential phase-shift keying (DPSK) modulation system at different channel spacings. It is reported that the proposed hybrid optical amplifier (HOA) provides better gain, signal quality and induces lesser crosstalk even when 640 Gbps DPSK signals are transmitted over 100 km of pumped single mode fiber. Further, the proposed system performance is compared with the current state-of-the-art HOA schemes.