Downscaling at submicrometer scale of the gap width of interdigitated Ba0.5Sr0.5TiO3 capacitors.

The goal of this work was to study the influence of shrinking the gap width between the fingers of interdigitated tunable capacitors (IDCs). Voltage control of the capacitance was achieved with a 500-nm-thick Ba0.5Sr0.5TiO3 film which is in paraelectric state at room temperature. Eight devices with finger spacing ranging from 3 µm down to 0.25 µm were fabricated by the sol-gel deposition technique, electron beam patterning, and gold evaporation. The equivalent capacitance, quality factor, and tunability of the devices were measured subsequently by vector network analysis from 40 MHz to 40 GHz and for a dc bias voltage varying from -30 V to +30 V. This experimental study mainly shows that a decrease of the gap below 1 µm 1) introduces a frequency dependence of the capacitance caused by resonance effects with the finger inductance; 2) degrades the quality factor above 20 GHz, and 3) optimizes the tunability of the devices by enhancing the local electric field values. As a consequence, some trade-offs are pointed out related to the goal of ultra-thin ferroelectric film which can be voltage controlled by means of finger-shaped electrodes with deep submicrometer spacing.

Enhanced backscattering for infrared detection using photonic crystal based flat lens.

An n=-1 flat lens based on photonic crystal semiconductor technology is evaluated for infrared detection purposes. The idea consists in exploiting the backscattered waves of an incident plane wave impinging on a target placed in the focal region of a flat lens. It is shown that subwavelength detection of micronic dielectric targets can be obtained at 1.55 µm using the double focus of reflected waves induced by negative refraction. Complex relations among the intrinsic nature, the shape and size of the target, and detection efficiency are interpreted in terms of target eigenmode excitation. Reflectivity is modulated by the intrinsic mode nature, transverse, circular, or longitudinal, with an enhancement of the detection sensitivity in the case of whispering-gallery modes. It is believed that such a study paves the way to the definition of original noninvasive infrared sensors.

Electrically controllable fishnet metamaterial based on nematic liquid crystal.

A variable index metamaterial is demonstrated by embedding nematic liquid crystal inside fishnet layers' void at microwave frequencies. With an external electric field, the left handed passband can be reversibly shifted from 9.14 to 8.80 GHz, whereas the upper right handed passband is nearly unchanged. It is shown that during LC molecular reorientation, magnetic resonance is shifted to a lower frequency because of the permittivity increase between fishnet layers, leading to an effective index change of 1.1 within negative index regime.

Image reconstruction using a photonic crystal based flat lens operating at 1.55 µm.

We used an optimized photonic crystal based flat lens for target detection and image reconstruction of micrometer sized objects for an operating wavelength of 1.55 µm. Using numerical retrieval procedures inspired from tomography, the ability to detect subwavelength sized targets and to image metallic objects of complex shapes is shown. The relation between the reconstructed image quality and lens resolution is investigated.

Magnetically tunable left handed metamaterials by liquid crystal orientation.

The tunability of an omega-type left handed metamaterial was demonstrated at microwave frequencies via the magnetic control of liquid crystal (LC) orientation. From the experimental and simulation results, it is shown that the left handed pass-band can be tuned by 220 MHz by changing the orientation of LC molecules by 90 degrees. A maximum index variation of 0.25 was obtained in the negative index regime with a measured LC birefringence of 0.05 in the 10 - 12 GHz frequency band.

Optical near-field microscopy of light focusing through a photonic crystal flat lens.

We report here the direct observation by using a scanning near-field microscopy technique of the light focusing through a photonic crystal flat lens designed and fabricated to operate at optical frequencies. The lens is fabricated using a III-V semiconductor slab, and we directly visualize the propagation of the electromagnetic waves by using a scanning near-field optical microscope. We directly evidence spatially, as well as spectrally, the focusing operating regime of the lens. At last, in light of the experimental scanning near-field optical microscope pictures, we discuss the lens ability to focus light at a subwavelength scale.

An all-dielectric route for terahertz cloaking.

An original all-dielectric design that performs cloaking at 0.58 THz is demonstrated. The cloak consists of radially positioned micrometer-sized ferroelectric cylinders which exhibit under Mie theory a strong magnetic resonance. Full-wave simulations coupled with a field-summation retrieval technique were employed to adjust the rods magnetic plasma frequency; hence, the radial distribution in the permeability of the cloak. The behavior of the complete micro-structured device was simulated and results unambiguously show good reconstruction of the E-field wavefronts behind the cloak with high power transmission. This all-dielectric configuration provides an attractive route for designing cloaking devices at microwave and terahertz frequencies.

Photonic-crystal-based cloaking device at optical wavelengths.

We present a photonic crystal cloaking device at optical wavelengths based on the association of two lattices working in different regimes, namely, stop band and negative refraction. The idea is to reconstruct in phase an incident cut Gaussian modulated plane wave by using the photonic crystal dispersion properties to ensure that no light penetrates in the core of the device. It is believed that such a cloaking device could become a building block for future generations of 3D integrated optical circuits.