Fig. 1: Phototunable on-chip THz topological devices for 6G communication.
a Schematic of the topological interface showing two topologically distinct regions (black and gray regions). The domain wall is highlighted with a red dash line that hosts robust propagation of THz waves even at sharp bends. The red shaded regions show Wigner-Seitz and unit cell (rhombus-shaped). The central portion depicts the unit cell of VPC where the side of equilateral triangular air holes are marked with l1 and l2, respectively. The sign of Δl = l1 − l2 differentiate the Type A (Δl > 0) and Type B (Δl < 0) unit cells. The right panel shows the numerically calculated distribution of Berry curvature for both the unit cells. The Berry curvature is localized near the K and K′ valley, and Type A and Type B unit cells exhibit complementary distribution. b Optical image of fabricated straight (VPC-S) and bend (VPC-B) Si-VPC chips. An adiabatic tapered couplers were designed at both the input and output facets to efficiently in and out couple the THz waves from Si-VPC chips. The domain wall in Si-VPC chip is highlighted with a blue shaded region. The highest data rate recorded through VPC-S and VPC-B chips is 160 Gbit/s and 125 Gbit/s, respectively. Inset shows the I–Q constellation diagram corresponding to 160 Gbit/s using QAM-32 with 32 GBaud symbol rate through the VPC-S chip and reference (without the chip). The I–Q constellation diagram through the VPC-B chip is shown in Supplementary Information Fig. S8. c A schematic of an on-chip topological demultiplexer. Two differently modulated data signals at carrier frequencies fc1 and fc2 were injected into VPC waveguide, further demultiplexed into two separate channels: CH 1 and CH 2. The data signal with carrier frequency fc1 was modulated with an ON-OFF keying scheme for sending real-time HD video at 1.5 Gbit/s to CH 1 (coupled to waveguide via cavity, green arrow), while carrier frequency fc2 was modulated with QAM-16 (10 GBaud symbol rate) to achieve direct data transfer rate of 40 Gbit/s at CH 2 (orange arrow). The high Q nature of the topological cavity ensures excellent isolation between CH 1 and 2. It is verified by photoexciting (shown as λpump) the CH 2, which attenuated the 40 Gbit/s without affecting the real-time streaming of HD-video at CH 1. Please refer to the Supplementary Videos: Supplementary Movie “a” and Supplementary Movie “b” for a clear illustration of phototunable demultiplexing.
