A 2.4-m communication link operating at 3.9 THz based on a terahertz quantum cascade laser and a terahertz quantum well photodetector （THz QWP） are introduced. The lumped electrical models of THz QWP for small signals are presented. A discussion of the bandwidth limit of the detecting circuit is presented. Using direct on off-keying modulation and intensity detection, the transmission of digital video signal with a data rate of 2.5 Mb/s is demonstrated. Pseudo-random binary sequences are transmitted to investigate the bit-error rate （BER） at different rates. Result shows the error free transmission when the rate is below 5 Mb/s.
We demonstrate a wireless transmission link at 3.9 THz over a distance of 0.5 m by employing a terahertz （Hz） quantum-cascade laser （QCL） and a THz quantum-well photodetector （QWP）. We make direct voltage modulation of the THz QCL and use a spectral-matched THz QWP to detect the modulated THz light from the laser. The small signal model and a direct voltage modulation scheme of the laser are presented. A square wave up to 30 MHz is added to the laser and detected by the THz detector. The bandwidth limit of the wireless link is also discussed.
