Experimental comparison of transmission performance for Nyquist WDM and time-frequency packing

Several spectral efficient solutions for next-generation flexible optical networks are under investigation in order to cope with scalability issues while traffic demand is continuously increasing. Concerning transmission, Nyquist wavelength-division multiplexing (NWDM)-that confines the bandwidth within the Nyquist frequency of the signal-recently gained a momentum as one of the most suitable solutions for transmission over backbone networks and commercial solutions are available by now. Besides NWDM, other transmission techniques have been proposed to approach or overcome the Nyquist limit, thus further increasing the spectral efficiency (SE). Among them, time-frequency packing (TFP) is one candidate. This method builds a superchannel, whose subcarriers significantly overlap in frequency or time or both. This leads to an increased SE at the expenses of additional complexity within the transceiver to compensate for the introduced intersymbol interference. In this paper, we experimentally compare, for the first time, NWDM and TFP when employing the same identical test-bed. The experiment considered the two different terabit superchannels: a polarization multiplexed (PM)-16 quadrature amplitude modulation for the case of NWDM case, and a PM-quadrature phase-shift keying for TFP. The comparison and assessment of the results is carried out first in back-to-back configuration and, afterward, by propagating them over a recirculating loop consisting of a standard single-mode fiber, including spectrum selective switch to emulate node filtering