A critical electromagnetic response of a self-complementary structure was investigated. The nearly perfect selfcomplementary checkerboard patterns were fabricated by the electron-beam lithography and their electromagnetic responses are measured in the terahertz region. The electromagnetic responses are affected drastically by the small structural difference even though the differences are less than 0.1% of the wavelength of the incident electromagnetic waves. The sample most close to the self-complementary checkerboard pattern shows a less frequency dependent response, which is expected for the self-complementary structures. In this sample, the metallic squares seem to be connected randomly from the SEM observation. The effect of the structural randomness in metal mesh structures is also investigated to obtain the common electromagnetic properties in randomly connected systems.
THz has become a wide field of investigation opening new opportunities in a growing number of domains of physics,
chemistry, and biology. Among the different techniques existing today to generate THz fields, heterodyning two optical
frequencies is a useful approach when tunability is required. Moreover, to address high-resolution spectroscopy or
metrology applications, a key point is the achievement of a narrow linewidth source. To this aim, two-propagation-axis
dual-frequency lasers have been already shown to provide narrow linewidth tunable beat notes up to 2 THz. We report in
this paper the demonstration of a narrow linewidth THz radiation source based upon this laser. Indeed the beat note
provided by the laser is sent into a unitravelling carrier photodiode (UTC-PD), and radiated by a transverseelectromagnetic-
horn antenna (TEM-HA). All components operate at room temperature. The emitted THz signal is
detected by a subharmonic mixer coupled to an electrical spectrum analyzer. The THz signal is observed and analyzed
thanks to a heterodyne detection. The measured dynamic range is 75 dB at 282 GHz, 50 dB at 500 GHz, 35 dB at
700 GHz and decreases to 20 dB at 1 THz. The decrease is due to the UTC-PD efficiency and conversion losses in the
sub-harmonic mixer. The measured linewidth is better than 30 kHz at any frequency from DC to 1 THz.
We have developed a new generation of optoelectronic large bandwidth terahertz sources based on TEM horn antennas
monolithically integrated with several types of photodetectors: low-temperature grown GaAs (LTG-GaAs) planar
photoconductors, vertically integrated LTG-GaAs photoconductors on silicon substrate and uni-travelling-carrier
photodiodes. Results of pulsed (time-domain) and photomixing (CW, frequency domain) experiments are presented.
At Terahertz (THz) frequencies metals are still excellent materials to guide and confine electromagnetic
radiation with relatively low losses. Therefore the concepts developed in the microwave range to design efficient
waveguides and resonators can be successfully transferred up to this frequency region. A successful example of such
"technology transfer" is the so-called metal-metal resonator, effectively used as a waveguide for THz Quantum Cascade
Lasers (QCLs). This type of resonator is essentially a downscaled version of a microstrip waveguide, widely used at
microwave frequencies. In this work we report on microwave impedance measurements of metal-metal ridge-waveguide
THz QCLs. Experimental data, recorded at 4K in the 100MHz-55GHz range, are well reproduced by distributed-parameter
transmission-line simulations, showing that the modulation cutoff is limited by the propagation losses that
increase for higher microwave frequencies, yielding a 3dB modulation bandwidth of ~70GHz for a 1mm-long ridge. By
using a shunt-stub matching we demonstrate amplitude modulation of a 2.3THz QCL up to 24GHz. In the last part of this
work we discuss the experimental evidence of a feedback-coupling between the intracavity THz field and the microwave
field generated by the beating of the Fabry-Perot longitudinal modes above the lasing threshold.
Biological applications require more and more compact, sensitive and reliable microsystems. We will present solutions in order to realize a "microspectroscopy" up to Terahertz frequencies of various biological entities (living cell, neurons, proteins...). We investigate these entities in liquid phase. In a recent work, we have demonstrated a solution to excite efficiently a single wire transmission line . The propagation mode is similar to a surface
plasmon and known as a Goubau-mode . The wire we used is extremely thin compared to other recent solutions at terahertz frequencies. There are three orders of magnitude in the size of the wire used by K. Wang and D.M. Mittleman. Typically the wire's width is 1μm compared to the 900μm diameter metal wire in . Moreover our solution is in a planar configuration which is more suitable for microfluidic applications. We benefit from the high confinement of the electromagnetic field around this very thin gold wire to optimize the sensitivity of these Terahertz BioMEMS. Microfluidic channels are placed below the strip in a perpendicular direction. We will first present some properties of the Planar Goubau-Line (PGL)  and the measurements results obtained with structures fabricated on glass and quartz substrates. In a last part resonant structures and Mach-Zehnder type interferometers will also be presented.
We investigate the way of detecting changes in dielectric function of biological entities in liquid phase such as living cell, neurons and proteins. These studies will be used to extract some biological mechanisms information. On this purpose, we have designed a one dimensional EBG (Electromagnetic BandGap) structure with a defect at terahertz frequencies. It is now well known that such a structure presents a transmission peak in the forbidden band with a high quality factor. Here the defect is a microchannel placed below a transmission line. We will show this BioMEMS in two configurations: (a) with classical transmission lines (CPW or Microstrip) and (b) with original transmission lines. We have recently demonstrated a way to excite a propagating mode (also known as Goubau mode) on a very thin single metal wire transmission line. For this propagating mode, the electromagnetic field is very highly confined around the metallic strip. We will briefly detail the properties of such a line and its excitation. We will then show the variations of the defect mode in the forbidden gap with the variation of the dielectric permittivity of the solution. The designed BioMEMS is in a planar topology with glass and quartz substrates.