Coherent optical WDM systems for 1.6 Tb/s Ethernet over 40 km of single-mode fiber

Two 1.6 Tb/s coherent optical wavelength division multiplexed (WDM) systems targeting inter-data center links of up to 40-km reach over conventional single-mode fiber (CSMF) on C-band are proposed and numerically analyzed: a DP-QPSK-based 16 × 112 Gb/s system and a DP-16-QAM-based 8 × 224 Gb/s system. To satisfy the metro access space, noise and power transceiver characteristics are optimized, avoiding the use of any type of optical amplification or forward-error correction (FEC) scheme. Accordingly to the current Ethernet standard, feasibility of both 28 GBd architectures is hence numerically demonstrated at a very low bit-error-ratio (BER) threshold of 1 × 10−13, uncovering power sensitivities of −26.0 and −13.5 dBm and optical signal-to-noise ratio (OSNR) sensitivities of 35 and 40 dB for the first and second architectures, respectively. Negligible transmission OSNR and power penalties with respect to the back-to-back (BtB) case are calculated, thus demonstrating the effectiveness of the utilized DSP algorithms. Our simulation work also confirms that the 16-QAM-based scheme is more demanding in terms of OSNR and transmission power specifications than the 16-channel one, requiring approximately 12 dB more power and 5 dB more OSNR level at the transmitter laser outputs, with similar requirements at the receiver end. It is also demonstrated that laser linewidths of at most 1 MHz should be specified in both architectures, that the transmitter laser characteristics play a more appreciable role than those of the receiver laser, and that the frequency offset between these two lasers should be kept below 3 GHz. Our research work leverages the use of optical coherent technology at metro network level and claims for a necessary technological upgrade to such schemes for a forthcoming 1.6 Tb/s Ethernet standard to be feasible.