QCL with terahertz TEM-Horn Antennas

Quantum Cascade Lasers are one the most promising approach for the generation of THz waves and particularly in a double plasmon waveguide topology. Stripline resonators with a quasi-TEM mode are indeed interesting for THz-QCLs thanks to a high confinement factor combined with low losses. However they present two major drawbacks: the first is a poor outcoupling of the radiation, and the second is a highly divergent beam. In this communication we propose an original approach to solve simultaneously these two identified problems. It consists on the use of a metallic triangle connected at one end of the top metallic strip in order to realize with the ground plane a TEM- Horn Antenna (TEM-HA). We have first validated this approach with electromagnetic simulations based on a finite integration technique (FIT). The use of the TEM-HA improves the far-field radiation pattern, which presents a higher directivity in the direction of the antenna. We have also validated experimentally this concept on a QCL designed to emit at f=2 THz (lambda = 150 mum). The use of the antenna increases the collected power by a factor 2-to-3 compared to the case without antenna. We expect an even higher outcoupling by optimising the connection of the antenna to the QCL (electrical connection and position). Finally, as we believe that the realisation of a full monolithic device is the best approach to integrate the TEM-HA on the QCL, we will discuss on the technological issues raised by such a device.