Fig. 4: HD-video streaming and perfect channel isolation in photoactive topological demultiplexer.

a THz communication experimental setup. Here two signals at different carrier frequencies (331.6 GHz and 344 GHz) were injected at the input port (highlighted as CH 1 + 2) of the Si-VPC chip. Due to the limited spacing between CH 1 and CH 2 couplers in the Si-VPC chip (shown in inset), we used a parabolic mirror to redirect the signal from CH 1 and collected it by using a horn antenna (a). Inset shows the optical image of fabricated Si-VPC chip with one input and two output ports. The red arrow highlights the input channel (CH 1 + 2), which further demultiplexed into two channels: CH 1 (green arrow) and CH 2 (orange arrow). b, d I–Q intensity constellation diagram recorded at channel 2 (CH 2; carrier frequency 344 GHz) of Si-VPC chip for PUMP OFF and ON case, respectively. Without photoexcitation (PUMP OFF case), we observe a clear constellation diagram corresponding to 40 Gbit/s data rate using QAM-16 with 10 GBaud symbol rate. With photoexcitation (PUMP ON case), the THz waves get attenuated. We observe fading in the constellation diagram. c, e Snapshot taken from real-time HD-video streaming transmitted via channel 1 (CH 1; carrier frequency 331.6 GHz) for pump OFF and ON case, respectively. The real-time streaming of HD video was uninterrupted even after attenuating the THz signal at CH 2 upon photoexcitation. This exhibits excellent isolation between the demultiplexed channels owing to the high-Q nature of the topological cavity. Please refer to the Supplementary Videos (Supplementary Movie “a” and Supplementary Movie “b”) to clearly illustrate THz channel demultiplexing.