Performance Analysis of the Migration of a 400 Gb/S-NRZ Optical Ring to a 1.6 Tb/S-PAM4 Ring

In this paper, we aim to demonstrate the feasibility of upgrading the CELEC EP 40 channel, 400 Gb/s, NRZ, DWDM ring, using PAM-4 modulation with the same 40 channels transmitting each at 40 Gb/s, for achieving a total capacity of 1.6 Tb/s. To overcome the problem related to the dispersion sensitivity of PAM-4 in long-distance links, we employed a dual technique of compensation, in the optical and electrical domain, based on dispersion-compensating fibers and in electrical pre-distortion of the PAM-4 signal. Simulation results show that the upgrade to 1.6 Tb/s is feasible using low-complexity changes in the current infrastructure. In the shorter links of the ring, it is enough the use of optical dispersion compensation, and a BER = 10-9 is achievable with an optical received power of about −19 dBm, whilst in the longest links, the electronic pre-distortion is mandatory for avoiding a penalization of about 3 dB for getting the same goal BER if the pre-distortion is not used. We validated the simulations with a comparison with experimental results for the longest link, 165 km, of the ring. Experimental and simulations results show nearly de same values of non-pre-distortion penalty and receiver sensitivity, for achieving the same goal BER.