Single- and alternating-polarization 170-gb/s transmission up to 4000 km using dispersion-managed fiber and all-Raman amplification

We demonstrate transmission of 170-Gb/s single- and alternating-polarization return-to-zero differential phase-shift keying signals in a recirculating loop using dispersion-managed fiber spans and all-Raman amplification. In the single polarization case, bit-error-ratio (BER) values of 5times10
^-9
and 1.6times10
^-4
were obtained after 960 and 2880 km, respectively. In the alternating polarization case, significantly larger transmission distances were achieved, with BER values of 2times10
^-9
after 1920 km and 5times10
^-5
after 4320 km, respectively