Investigation of SOA nonlinearities on the amplification of DWDM channels with spectral efficiency up to 2.5 b/s/Hz

We have investigated and compared the effect of semiconductor optical amplifier (SOA) nonlinearities on the amplification of 14 dense wavelength-division-multiplexing channels using return-to-zero on-off keying [(RZ-OOK) 1 b/symbol], RZ differential quadrature phase-shift keying [(DQPSK) 2 b/symbol], and polarization (bit interleaved) multiplexed RZ-DQPSK (4 b/symbol) formats with aggregate data rates up to 50 Gb/s per channel. The channel spacing was 20 GHz with spectral efficiency from 0.625 up to 2.5 b/s/Hz. Our results have shown that while RZ-OOK format performs better at lower SOA input powers, RZ-DQPSK suffers less degradation from SOA nonlinearities at higher input powers. Overall, polarization-bit-interleaved RZ-DQPSK format was found to have the best tolerance to SOA nonlinearities.