Laboratoire Charles Coulomb UMR 5221 CNRS/UM2 (L2C)


Accueil > La Recherche > Axes & Equipes > Physique Appliquée > Spectroscopie THz


par Sébastien LAYSSAC - publié le , mis à jour le

The team is active in the Terahertz Research since more then 20 years. Its importance is based on collaboration of theoretical (guided by M. Dyakonov) and experimental (guided by W. Knap) groups. The THz group is one of the leading French teams of THz research with important facilities like THz sources and detectors coupled with high magnetic field allowing for cyclotron resonance and spin resonance related THz spectroscopy of solids.
The work of the team is supported by ANR program TeraGaN to study the possibility to use GaN High Electron Mobility Transistors as efficient THz sources with special geometries and architectures. The CNRS supports the team by offering guidance of the GDR, GDR-E and GDR-I projects “Semiconductor sources and detectors of THz frequencies” including Japan and twelve European countries. The team is also supported by the Region of Languedoc-Roussillon through the “Terahertz Platform”, to form a consortium on the use of THz radiations for medical, biological and physical purposes. STMicroelectronics is the strongest industrial partner of the team with the “Nano2012” program which is based on the study of ballistic effect and plasma wave effect in last generation of Silicon technology devices. The intention is to create at the end a complete device for THz real time imaging at room temperature. The team is also supported by the CEA-LETI through the “THz imaging on Si-MOSFTEs” project. This project has the goal to fabricate and to study a new architecture of transistors, amplifiers and antennas to obtain the best single pixel for THz detection. The JSPS International Fellowship Program for Research in Japan encourages the team with bilateral exchange of students and post-docs. The joint French-Lithuanian research program “Gilibert/EGIDE” and the joint French-Japanese research program “Sakura/EGIDE” also permit researchers to travel and to exchange knowledge and experimental facilities with these two countries.
Since very recently, the team is supported by ANR and JST for a French-Japanese action on the wireless Terahertz telecommunication with plasma wave devices as THz detectors. This program is one of the most important one worldwide in the field of data transfer in the THz frequency range. Effectively the strongly increasing demand for higher data rate wireless communication owing to the trend of a ubiquitous ICT society has led us to explore new frequency resources higher than any existing microwave/millimetre wave communication band, approaching the terahertz (THz) frequency range. In the 2008 Beijing Olympic Games, a Japanese research group (led by one of the members of the present consortium) demonstrated a 10Gbit/s wireless communication at a 120GHz carrier frequency for a 3km transmission of uncompressed high definition television (HDTV) data. In a near future super HDTV will become available for which over 40 Gbit/s transmissions is needed. Uncompressed data transfer requires a carrier frequency approximately ten or more times higher. This means the carrier frequency must be above 400GHz i.e. within sub THz or THz frequency range.
Although sub THz and THz radiation is severely absorbed by atmospheric vapour, there are several nice windows that can transmit those waves in free space with practical attenuation loss as low as 0.1dB/10m and good directivity. THz wireless communication is interesting also because it uses the directionality of optical links but it does not suffer from fog/smoke perturbations and has no danger for the eyes like high power optical or near infrared links. Therefore, such THz waves can be considered for a wide aspect of short distance free space high data rate communication purposes : like last mile internet or in house point to point wireless connections, secure multiple independent links for civilian and military purposes, as well as space communication. The additional interest in the development of sub THz communication is related to the fact that bands above 300 GHz are still free for use in most countries (in Japan and Europe neither band allocation nor regulation exist above 275 GHz).
The feasibility of very high data rate transmission with sub THz to THz carrier is still an open question. There are two main problems : i) how to generate and modulate the sub THz signals and ii) how to detect them. Showing the feasibility and demonstrating the first high date rate 40 Gbit/s communication prototypes at unexplored frequency bands (communication windows) in the frequency range from 400 to 900 GHz is one of the main goals of the present project. In order to break through the speed limit of conventional carrier transit type electron devices, we introduce the 2D (two-dimensional) plasmon resonance as a new physical principle of operation to realize i) frequency tunable, room temperature operating coherent monochromatic THz sources, ii) fast, coherent detection of coded THz carrier waves, and iii) 10 - 40Gbit/s intensity modulators for sub THz and THz carrier signals. These are the key scientific goals of the present project. The fundamental structure of those devices is based on the applicant’s original dual grating gate (DGG) high electron mobility transistors (HEMT’s). Novel ideas for advanced device structures and design/characterization methodology are pursued by collaborative research to develop these new functions into real device fabrications/demonstrations. Real test bed sub THz and THz wireless transmitter/receiver front end devices will be designed and integrated to demonstrate record 40 Gbit/s class wireless communications for the first time, verifying the feasibility of the ultrabroadband THz wireless communications.
Finally, the team is now merging with the GEHF team of the “Institut d’Electronique du Sud” via the “Groupement d’Interet Scientifique” (GIS) named Teralab steered by L. Varani. This GIS Teralab is an excellent opportunity to reinforce significantly the synergy between the two teams and to create a “pole of excellence” in this very competitive field of basic and applied research.