Broadband THz Switching with Extremely Low Insertion Loss and Superior Isolation

We report a novel high-performance terahertz (THz) switch using photoconductivity modulation. By using a Ge or Si thin film capacitively coupled across a coplanar waveguide (CPW), a non-contact shunt switch configuration offering extremely low insertion loss and superior isolation at THz frequencies can be achieved. Physics-based modeling and HFSS full wave simulation from 110–220 GHz for a Ge-based switch show that an insertion loss (IL)<0.3 dB and isolation (Iso)>70 dB can be achieved with an illumination light intensity of 100 W/cm². As a prototype to validate the approach, a micromachined Si chip of 73 µm thickness was mounted on top of D- and G-band CPWs on alumina substrates. To control the switch, an 808 nm wavelength fiber-coupled laser diode was used for illumination. On-wafer measurements over D- and G-bands agree with the simulations. At 170 GHz, the measured on-state IL was 0.4 dB, and the off-state isolation exceeded 32 dB. This outperforms most reported THz switches, across a range of technologies. The proposed THz switching is promising for developing high performance reconfigurable circuits required for more advanced THz sensing, imaging and communication applications.