28 Gbaud PAM4 Real Time Optical Datacom Link up to 10 km

We present a forward error correction (FEC)-assisted, 10 km long, 28 Gbaud PAM4 optical link having error free performance over a wide dynamic range of -10 dBm to 0 dBm received optical power. The link was formed by driving a 1550 nm externally modulated laser with a commercial PAM4 transceiver chip. The optical signal was transmitted over 10 km long dispersion compensated fiber, fed to a low-noise 28 GHz linear receiver having variable gain, and routed back to the PAM4 transceiver chip. Real time bit error rate measurements demonstrate the advantage of employing linear receivers having automatic gain control (AGC).