F. Gadot

Toward controllable photonic crystals for centimeter- and millimeter-wave devices

In this paper, we present several experimental and theoretical studies showing the feasibility of active photonic crystal controlled either by electrical elements or by light. The controllability of photonic crystals at centimeter wavelengths is proposed with the periodic insertion of diodes along the wires of a two-dimensional (2-D) metallic structure. For only three crystal periods with commercially available devices, more than 30 dB variations of the crystal transmission are predicted over a multigigahertz range by switching the diodes. From calculation models, a tight analogy is shown between these crystals and those consisting of discontinuous metallic rods with dielectric inserts. The numerical models as well as the proposed technology are validated by experimental measurements on 2-D crystals with either continuous or discontinuous metallic rods. The partial control of a 3-D layer-by-layer dielectric structure at millimeter wavelengths is also demonstrated in the second part of the work. A laser light is used to modulate the transmission level of defect modes by photo-induced free carrier absorption. The overall results are expected to contribute to further developments of switchable electromagnetic windows as well as to tunable waveguide structures in the microwave and millimeter wave domains.

Engineering resonances in infrared metamaterials

Engineering resonances in metamaterials has been so far the main way of reaching simultaneously negative permittivity and negative permeability leading to negative index materials. In this paper, we present an experimental and numerical analysis of the infrared response of metamaterials made of continuous nanowires and split ring resonators (SRR) deposited on low-doped silicon when the geometry of the SRRs is gradually altered. The impact of the geometric transformation of the SRRs on the spectra of the composite metamaterial is measured in the 20-200 THz frequency range (i.e., in the 1.5-15 microm wavelength range) for the two field polarizations under normal to plane propagation. We show experimentally and numerically that tuning the SRRs towards elementary cut wires translates in a predictable manner the frequency response of the artificial material. We also analyze coupling effects between the SRRs and the continuous nanowires for different spacings between them. The results of our study are expected to provide useful guidelines for the design of negative index metamaterials on silicon.

Photonic band gap materials for devices in the microwave domain

Materials with a periodically structured dielectric constant may exhibit forbidden photonic band gaps (PBG), that is, frequency domains where electromagnetic fields cannot propagate. The position and width of forbidden gaps can be controlled via the geometrical parameters of the structures and the contrast between the different permittivities. PBG materials have potential applications to a variety of devices in the microwave domain such as waveguides, couplers, reflectors and antenna substrate. This work reports on first experimental and theoretical studies of microwave guides and ring couplers based on PBG materials. Experiments are performed in the 27-75 GHz frequency range. Different coupling situations are given in illustration.

Large submillimeter and millimeter detector arrays for astronomy: development of NbSi superconducting bolometers

The achievement of the Planck and Herschel space missions in the submillimeter and millimeter range was made possible by a continuous effort on detector developments. Now limited by the intrinsic fluctuations of the radiation coming from the astronomical sources themselves, the sensitivity improvement requires the development of large arrays of detectors filling the focal plane of the telescopes. We present here the development of a TES array using NbSi sensors on SiN membranes. The readout electronics is based on SQUIDs and a cooled SiGe ASIC multiplexer. The detector is coupled with the input radiation by means of antenna. The present goal performance is adapted for the realisation of a ground based millimeter camera.

Full characterization of planar infrared metamaterials from far field diffraction pattern

Since the event of metamaterials, a considerable effort has been performed to fabricate them in the infrared and optical regimes. However, apart from the experimental demonstration and observation of H. J. Lezec et al based on surface plasma polariton, direct visualisation of negative refraction based on metal-dielectric resonances have not been performed experimentally so far in the infrared or visible regime (photonic crystals with periodicity on the order of the wavelength are not considered here). Very often only simulations have given the needed phase information for the retrieval methods in optical experiments. In this paper, a metamaterial composed of SRR (Split Ring Resonators) and a continuous wire is considered. We extract the phase information from the transmission and the reflection measurements through a diffraction grating made of the metamaterial to be characterized and silicon or gold. This retrieval allows a unambiguous retrieval of the effective parameters under conditions discussed in the paper at IR and visible wavelengths.

Conformable and Controllable Radome in X Band using Electromagnetic Band Gap Material

We report the study of the design and the simulation of a conformable and switchable radome in X band (around 10 GHz) based on a controllable electromagnetic band gap material (CEBG) [1-4]. This material consists of parallel periodic metallic wires forming a grid. The introduction of active electronic elements such as PIN diodes or photoconductors, allows the commutation between the electric state of continuous wires and the state of discontinuous ones. We switch from the forbidden gap of an EBG material made of the continuous metallic wires lattice to the forbidden band of the periodic discontinuous wires one, according to the voltage or the light intensity. This structure must present a commutation around 10 GHz and finds various applications in the aeronautic field.

Design and characterization of a controllable left-handed material at microwave frequencies

In this study, we present the conception, the simulation and the characterization of a controllable left-handed (CLHM) material operating between 7 and 16 GHz. This compact material, composed from metallic wires including p-i-n diodes and split-ring resonators is optimized to have a controllable permittivity and a fixed permeability. Changing the bias current of the p-i-n diodes controls the dielectric permittivity of the material, which is negative. This allows the tuning of the CLHM material from a reflection state to a transmission state. We have measured the transmission of the material between 7 and 16GHz, and its negative refraction index at oblique incidence, demonstrating the switching of the electromagnetic state of the material.

Robustness of the behavior of microstrip lines loaded with disordered complementary split ring resonators

In many papers, compact band-reject filters are realized by associating microstrip lines with complementary split ring resonators (CSRR). These studies assume that the periodicity of CSRR is perfect. However, a margin of error, related to the precision of manufacturing techniques, appears when operating these filters. In this paper, the robustness of the behavior of these filters is studied according to the degree of disturbance of the periodicity.

Design and simulation of an antenna-coupled TES bolometer

We present a new design of an antenna-coupled superconducting transition-edge sensor (TES) bolometer. The incident radiation is coupled to a membrane-based twin-slot antenna and then transmitted through lossless microstrip lines to lossy meander-like microstrip lines in which a NbSi film is located between strip and dielectric layer. The NbSi film serves as both power absorber and temperature sensor (thermometer). With the help of the electromagnetic simulation software High Frequency Structure Simulator (HFSS), we have studied the performance of the twin-slot antenna. The simulation results for radiation pattern and return loss show promising prospects for this TES bolometer design. The power absorption in NbSi film is another important aspect which will be modeled in the future.

Theoretical and experimental analysis of plasmonic resonances in infrared metamaterials under normal to plane incidence

Metamaterials have attracted much interest since their realization by Smith et al. [2]. A few research teams all other the world are making them a reality in the infrared and optical regime. Following the theoretical study of C. Rockstuhl et al. [4], we have fabricated various metamaterial structures derived from the combination of SRR (Split Ring Resonators) and nano-continuous wires by diminishing the size of the legs of the SRR perpendicular to the gap. This geometrical transformation shown in the SEM (scanning electron microscope) pictures of figure 1 allows an experimental understanding of the origin of resonances in metamaterials under normal incidence. The fabrication was performed by e-beam lithography, gold on silicon. Simulations were performed using a Drude model of the electromagnetic permittivity of gold. Both measurement and simulation results lead to an accurate analyze of the plasmonic resonances of the metamaterial and open the way to their control in infrared metamaterials under normal to plane propagation.