FROM DEVICES TO APPLICATIONS

 

 

Our research is mainly devoted to the development of devices operating in the terahertz (THz) range, such as sources, detectors, transmission lines, antennas…. We also work on the application of THz radiation in the fields of spectroscopy, high bit-rate communications and near-field imaging.
More specifically our research is presently developing along the following main research lines:

 

– Conception, design and realisation of photomixers for the generation and detection of sub-mm and THz radiation using near infrared laser diodes (1550nm and 880m). We develop photomixers based on low-temperature grown (LT) GaAs and InGaAs, where both electrons and holes contribute to the photogenerated current, and also InGaAs-based uni-travelling-carrier photodiodes (UTC-PD) photomixers, where low-mobility holes are blocked using an appropriate potential barrier. Recently, using an original vertical cavity geometry, where the semiconductor is sandwiched between two metal mirrors, we have demonstrated the generation of 1.8mW in CW at 250GHz, corresponding to a record optical to mm-wave conversion efficiency of 0.7%. Presently funded projects related to this topic: PHENIX (ANR contract).

 

– Sub-mm wave and THz high-data rate communications. It is known that data traffic is increasing exponentially, with Internet protocol traffic expected to reach over > 100 exabytes per month by 2018. Since the fastest-growing part of data traffic is related to wireless channels, such an increase in network capacity requires much higher wireless transmission data rate links. Beyond the E-band (71-76 and 81-86 GHz) that will be rapidly saturated, the millimeter (D-band) and sub-millimeter range, between 275 and 400 GHz have a strong potential to develop these applications. To this end we are investigating high data-rate THz links using photonics-based THz emitters (UTC-PD) to down-convert optical fluxes to millimeter waves. Our recent advances include successful tests of single channels of 46 Gbit/s at 400 GHz (2 meters distance), of 32 Gbit/s at 385 GHz over 25 meter, and the first outdoor test over 1km range for Gbit/s data flows.

 

– Development of a new concept of THz gas laser. Optically pumped THz molecular lasers have been demonstrated since a long time, where a CO2 laser is used to create population inversion between rotational levels of a molecule. The main drawbacks of these lasers originate from the CO2 laser itself, which, besides being bulky and expensive it also emits on discrete lines, therefore heavily limiting the number of molecular transitions that can be efficiently pumped. We have recently shown that these limitations can be elegantly and efficiently overcome by replacing the CO2 pump laser with a mid-IR Quantum Cascade Laser (QCL). QCLs are operating in CW mode at room temperature; they are also monomode and can be continuously tuned in wavelength, with typical power levels in the 100’s of mW. By exploiting a QCL emitting at 10.3μm we have demonstrated the first THz gas laser pumped by a semiconductor laser source. Population inversion is obtained on the so-called “umbrella-mode” quantum transition of an ammonia (NH3) molecule, providing lasing on approximately 10 lines around 1THz. This research activity has lead to the spin-off of a startup company, thanks to the funding from Region Hauts-de-France

 

– THz optical isolators (under construction)

 

– THz spectroscopy of a single virus. The main objective of this novel research line is to demonstrate THz spectroscopy of a single virus by combining time domain spectroscopy with an existing THz scanning near-field microscope (SNOM) system that will be optimized for this specific application. The goal is to confine the electromagnetic THz field in a sub-wavelength region around the virus to be measured. In the first phase of this project we plan a systematic study based on FDTD simulations to design an ad hoc SNOM tip that maximizes the coupling with THz radiation. Finally we plan to work on the improvement of the detection sensitivity of the SNOM system by using a new type of coherent detection technique. The final objective will be the realisation of an optimized THz near-field instrument that will help answering fundamental questions in virology, such as the role played by the vibrations of the viral capsid (i.e. the protein shell around the virus).This research line is funded by Region Hauts-de-France. A post-doc position opening is now available and a description of the position can be found here.

 

– Antenna-based fast mid-IR detectors and photomixers. This is a new research line that aims at developing a new family of photonics devices based on intersubbad transitions in III-V semiconductor materials (GaAs and InGaAs). These devices will rely on plasmonic antennas for the coupling of mid-IR radiation to the intersubband transitions. On one side we target the realisation of ultra-fast mid-IR detectors (5-10μm range) operating at room temperature with a bandwidth exceeding 50GHz. On the other side we plan to exploit intersubbad transitions in multi-quantum well (QWIP) structures for the generation of sub-mm radiation through photomixing of mid-IR photons. This research line is presently funded by the ANR-Astrid project HISPANID, in collaboration with III-V Labs and mirSense.