Fig. 4

Demux of two QPSK-modulated channels. BER vs. angle for two channels at 280 GHz and 330 GHz, both modulated at 12.5 Gbaud (corresponding to 25 Gb/s in each channel), for an aggregate throughput of 50 Gb/s. To preserve the QPSK phase information, signals were detected using a Schottky-based sub-harmonic mixer with the output analyzed on a real-time high-bandwidth oscilloscope. In both cases, the optimum BER is well below the threshold for forward error correction. The insets show the constellation diagrams measured for each channel. The vertical dashed lines show the predicted positions of the BER minima for the two channels, according to Eq. (3)