Discrete Multitone Transmission at Net Data Rate of 250 ${\text{Gb/s}}$ Using Digital-Preprocessed Analog-Multiplexed DAC With Halved Clock Frequency and Suppressed Image

We demonstrate the first single-lane intensity-modulated direct-detection (IMDD) optical transmission at a net data rate of 250 Gb/s. A discrete multi-tone (DMT) signal at a gross line rate of 300 Gb/s can be generated with a digital-preprocessed analog-multiplexed digital-to-analog converter (DP-AM-DAC), which consists of a digital preprocessor, two sub-DACs, and an analog multiplexer (AMUX). We show a new scheme to relax the required clock frequency to drive the AMUX in the DP-AM-DAC by half to make it easier to extend the bandwidth of the final output signal. The image signal in the final output is also suppressed by the new scheme. In the experiment, we drove the AMUX at 37.5 GHz to generate the DMT signal with a bandwidth of 61.5 GHz. As the optical transmitter, we used an O-band externally modulated laser with a 3-dB electrooptic bandwidth of >55 GHz. After transmission over a 10-km single-mode fiber with an optical fiber amplifier, the signal was received with a bit error rate below the threshold of 20%-overhead soft-decision forward error correction code.