336 Gb/s in Direct Detection Below KP4 FEC Threshold for Intra Data Center Applications

We demonstrate direct detection of single polarization and dual polarization PAM4 signals delivering 168 and 336 Gb/s below the KP4 FEC threshold of 2.2×10
^-4
. The 84 Gbaud 2 bits and 4 bits per symbol transceivers operate at a bit error rate (BER) that is compliant to the RS(544, 514) FEC encoding for error-free operation, as considered for next generation PAM4 400GBase Ethernet standard targeting data center applications. For the DP-PAM4 format, we show that the BER is independent of the state of polarization of the optical signal. To the best of our knowledge, this is the first experimental demonstration of a single carrier delivering 336 Gb/s in direct detection at a BER compliant to the physical coding sublayer of 400GBASE interfaces. Finally, using an intensity modulator in series with a phase modulator, we demonstrate chromatic dispersion pre-compensation of 84 Gbaud PAM4 signals, producing a 40-fold BER improvement after 10 km of single-mode fiber.