We significantly extended the frequency bandwidth of quantum cascade laser THz harmonic frequency combs to more than 1.1 THz, with still more than 800 GHz at high temperatures on fundamental comb state (90 K).In order to achieve this objective we optimised the technology for the fabrication of low-loss double-metal waveguides. We worked on the refinement of the wafer bonding process as well as on the copper deposition.
Exploiting such high-performance devices and optimised double-metal technology we pioneered a new planarized waveguide platform for integrated THz photonics that allowed the complete control of the laser dynamics with RF injection , switching from FM combs to AM combs, obtaining pulses as short as 4.4 ps.
The planarized approach allowed integration of optical elements as y-split, passive waveguides and antennas. We engineered planarized waveguides that allow control of the dispersion and realize broadband combs with them. The possibility to introduce anomalous dispersion proved essential for teh generation of THz solitons in coupled rings where we demonstrated THz optical solitons with pulse lengths as short as 12 ps.
Still exploiting the planarized devices and the integrated antennas we demonstrated a new way to detect THz radiation exploiting the regenerative amplification approach. THz detection up to 70 K has been demonstrated.
In the context of dual-comb spectroscopy, a topic that has been pursued since the beginning of the ERC grant was finally applied for patenting at the European patent office. The patent covers a new, fast delay line that can be used in different context for spectroscopy using laser systems. The delay line key component is a rotating, multi-faceted mirror inserted in a multi-reflecting cage. The PI G. Scalari is the main inventor and A. Forrer also significantly contributed to the invention. A publication exploiting the delay line as a core component in a single.comb high resolution high speed spectrometer has been recently accepted for publication in Communication Physics.
Concerning the high power and broadband extraction we implemented the concept of a broadband extractor by designing and fabricating a Vivaldi antenna for THz QCLs. The antenna is based on a polymer technology and successive metallization and mounted on the laser facet. Considerable improvement in the far field and polarization control have been achieved. By using the planarized approach already mentioned before we where able to ultimately obtain high power (> 15 mW) in a narrow beam from THZ QCL combs.
