Transceiver = Transmitter + Receiver. So this device is used on the receiver side to extract information at high bandwidth. Nice but now we need a transmitter D/A that can modulate a digital signal on a 200 GHz carrier. I think the unstated value of this may lie in measurement of physical systems, surveillance and instrumentation come to mind.
So I misread the 500 Gbps throughput as the sample rate, which is different. A typical parallel data vector might be 8 bits, which would reduce the sample rate to 62.5 GHz, and would require the bandwidth of the channel to be at least 150 GHz and excellent signal to noise ratio to get to 500Gbps data rate. Still, very impressive.