Experiment of 2.56-Tb/s, polarization division multiplexing return-to-zero 16-ary quadrature amplitude modulation, 25 GHz grid coherent optical wavelength division multiplexing, 800 km transmission based on optical comb in standard single-mode fiber

Based on recirculating frequency shifter, we generate 20 high-quality multicarrier optical combs with a tone-to-noise ratio >25 dB . We also experimentally demonstrate 2.56-Tb/s , polarization division multiplexing return-to-zero 16-ary quadrature amplitude modulation, coherent optical wavelength division multiplexing transmission over 800 km standard single-mode fiber with 25-GHz channel spacing, and the spectrum efficiency is 5.1 b/s/Hz .