From Bulk Toward Micro-Structured TiO_2 Ceramics for All-Dielectric Metamaterials at Terahertz Frequencies

International audienceIn this study, we aimed to develop high permittivity TiO2 ceramics ideal for the fabrication of All-Dielectric Meta- materials operational in the terahertz frequency. TiO2 ceramic pellets are fabricated from a commercial powder. A comparative analysis was conducted between Spark Plasma Sintering (SPS) and conventional sintering process. Characterizations were then carried out in the range of 0.2 to 1.4 THz using THz time-domain spectroscopy. We observed that the samples fabricated by the spark plasma sintering and post-annealing treatment exhibit a high refractive permittivity associated with minimal loss (ε′ ≈ 100 and tan δ <0.015). These characteristics make these samples optimal candidates for achieving a negative refractive index in all-dielectric metamaterials. In addition, two micro-structuring processes were investigated for the realization of metamaterials operating in the terahertz range: micro-molding and direct TiO2 etching by Inductively Coupled Plasma (ICP)

Wavelength-Selective Diffraction from Silica Thin-Film Gratings

A reflective diffraction grating with a periodic square-wave profile will combine the effects of thin-film interference with conventional grating behavior when composed of features having a different refractive index than that of the substrate. A grating period of 700–1300 nm was modeled and compared for both silicon (Si) and silicon dioxide (SiO₂) to determine the behavior of light interaction with the structures. Finite element analysis was used to study nanostructures having a multirefractive index grating and a conventional single material grating. A multimaterial grating has the same diffraction efficiency as that of a grating formed in a single material, but had the advantage of having an ordered relationship between the grating dimensions (thickness and period) and the intensity of reflected and diffracted optical wavelengths. We demonstrate a color-selective feature of the modeled SiO₂ grating by fabricating samples with grating periods of 800 and 1000 nm, respectively. A high diffraction efficiency was measured for the green wavelength region as compared to other colors in the spectrum for 800 nm grating periodicity; whereas wavelengths within the red region of spectrum interfered constructively for the grating with 1000 nm periodicity resulting a higher efficiency for red color bandwidth. The results show that diffraction effects can be enhanced by the thin-film interference phenomenon to produce color selective optical devices

Design and realization aspects of 1-THz cascade backward wave amplifier based on double corrugated waveguide

The design and fabrication challenges in the first ever attempt to realize a 1-THz vacuum tube amplifier are described. Implementation of innovative solutions including a slow-wave structure in the form of a double corrugated waveguide, lateral tapered input and output couplers, deep X-ray LIGA fabrication process, and a cascade architecture of the backward wave amplifier are discussed. A new knowledge in the field of terahertz vacuum devices brought by intensive simulations and development of advanced fabrication and assembly processes of the micro structures is highlighted

Building blocks and concepts for THz remote sensing and communications

International audienceWe present technological building blocks and concepts under study which could ease the build-up of future THz remote sensing and communication systems. Critical issues regarding such systems mainly rely on the availability of sensitive and compact detectors together with powerful, large bandwidth and versatile sources