• exceptional points
• microresonators
• quantum cascade laser
• terahertz

This thesis work describes the modelling, fabrication and characterization of a THz quantum cascade laser (QCL) whose resonant cavity is composed of whispering-gallery mode resonators combined with a linear dipole antenna. This peculiar configuration, when properly balanced by placing two microdisks in close proximity and connected by a suspended metallic bridge, allows to achieve vertical light emission; it represents a challenging task for THz QCLs, primarily originating from the electronic selection rules and subwavelength vertical confinement of light in double-metal waveguides.
In particular, I introduced an improved geometry for the electrical connection of the resonator, by considering a separate feeding of the two microdisks. This would simplify the device fabrication and, most interestingly, would be an ideal platform to investigate "exceptional points", obtained when the device is operated in full spatial and time symmetry. Changing the bias, the time-symmetry of the device can be modified, switching in and out of the conditions for the exceptional point, which is accompanied by a strong modification of the laser far field emission. The possibility to dynamically control the output beam, jointly with the expected high quality factor and low current threshold, make the device under consideration very promising for the development of miniaturized and monolithic THz sources.