THz Optomechanics

Optomechanical QCL
Hybrid WGM-dipole antennna resonator. The prominent laser mode emits in a focused beam, whose far-field pattern is reported in the inset.

The consolidation of THz-based photonic technologies is an ambitious goal which would rapidly lead to the full commercial exploitation of THz electromagnetic radiation, in field that spans several topics, such as quality control, medical probes, security scanners and observational astrophysics. Among the most promising sources, Quantum Cascade Lasers (QCL) have a prominent role, thanks to their compactness, high power and electrical injection. Few challenges have yet to be addressed for the wide use of QCL as the best commercial source for applications: the low operating temperature, the limited tunability and the ill-shaped far field emission in standard ridge-waveguides. Combining mechanical elements with THz QCLs can reveal beneficial effects in terms of far-field shaping, frequency locking and sweeping. In a first design, we employed external mechanical resonators made with silicon nitride membranes which could be coupled to the THz laser via self-mixing and give a signature of the mechanical vibrations in the laser I-V characteristic and emission. A preliminary experiment using a solid-state infrared laser coupled to the mechanical membrane has shown very good displacement sensitivities [1]. An alternative approach considers the inclusion of mechanical elements direcly embedded within the THz laser cavity. To this end, combining concepts from the world of photonics and electronics, we designed a dipole antenna-whispering gallery mode hybrid resonator which results in a Continuous-Wave, high-power (300 mW) emission with a very focused far field (± 10°) [2]. The dipole antenna is a suspended, mechanically compliant string resonator, which we aim to use to obtain optomechanical interaction in this device geometry.

[1] L. Baldacci, A. Pitanti, L. Masini, A. Arcangeli, F. Colangelo, D. Navarro-Urrios and A. Tredicucci, Thermal noise and optomechanical features in the emission of a membrane-coupled compound cavity laser diode, Sci. Rep. (2016)

[2] L. Masini, A. Pitanti, L. Baldacci, M. S. Vitiello, R. Degl'Innocenti, H. E. Beere, D. A. Ritchie and A. Tredicucci, Continuous-wave laser operation of a dipole antenna terahertz microresonator, Light Sci. App. (2017)


  • Prof. Raffaele Colombelli, University of Paris VII