Long-range plasmonic directional coupler switches controlled by nematic liquid crystals

A liquid-crystal tunable plasmonic optical switch based on a long-range metal stripe directional coupler is proposed and theoretically investigated. Extensive electro-optic tuning of the coupler's characteristics is demonstrated by introducing a nematic liquid crystal layer above two coplanar plasmonic waveguides. The switching properties of the proposed plasmonic structure are investigated through rigorous liquid-crystal studies coupled with a finite-element based analysis of light propagation. A directional coupler optical switch is demonstrated, which combines very low power consumption, low operation voltages, adjustable crosstalk and coupling lengths, along with sufficiently reduced insertion losses. © 2013 Optical Society of America

Time-domain modeling of dispersive and lossy liquid-crystals for terahertz applications

A numerical framework based on the finite-difference timedomain method is proposed for the rigorous study of electro-optically tunable terahertz devices based on liquid crystals. The formulation accounts for both the liquid-crystal full-tensor anisotropy and the dispersion of its complex refractive indices, which is described via modified Lorentzian terms. Experimentally characterized liquid-crystalline materials in the terahertz spectrum are fitted and modeled in benchmark examples, directly compared with reference analytical or semi-analytical solutions. In addition, the efficiency of broadband time-domain modeling of the proposed technique is also demonstrated by accurately reproducing time-domain spectroscopy measurements. © 2014 Optical Society of America

Ultrahigh-quality factor resonant dielectric metasurfaces based on hollow nanocuboids

In this work, a dielectric metasurface consisting of hollow dielectric nanocuboids, with ultrahigh quality factor, is theoretically proposed and demonstrated. The variation of the hole size of the cuboid allows for the tuning of the resonant anapole mode in the nanoparticles. The metasurface is designed to operate in two complementary modes, namely electromagnetically induced transparency and narrowband selective reflection. Thanks to the non-radiative nature of the anapole resonances, the minimal absorption losses of the dielectric materials, and the near-field coupling among the metasurface nanoparticles, a very high quality factor of =2.5×106 is achieved. The resonators are characterized by a simple bulk geometry and the subwavelength dimensions of the metasurface permit operation in the non-diffractive regime. The high quality factors and strong energy confinement of the proposed devices open new avenues of research on light-matter interactions, which may find direct applications, e.g., in non-linear devices, biological sensors, laser cavities, and optical communications.Research and Development Program through the Comunidad de Madrid (SINFOTON S2013/MIT-2790); Ministerio de Economia y Competitividad of Spain (TEC2013-47342-C2-2-R); mobility programs of Carlos III University and "Jose Castillejo" of the Ministerio de Educacion, Cultura y Deporte of Spain

Flexible terahertz wire grid polarizer with high extinction ratio and low loss

An aluminum-based THz wire grid polarizer is theoretically investigated and experimentally demonstrated on a sub-wavelength thin flexible and conformal foil of the cyclo-olefin Zeonor© polymer. THz time-domain spectroscopy characterization, performed on both flat and curved configurations, reveals a high extinction ratio between 40 and 45 dB in the 0.3-1 THz range and in excess of 30 dB up to 2.5 THz. The insertion losses are lower than 1 dB and are almost exclusively due to moderate Fabry-Perót reflections, which vanish at targeted frequencies. The polarizer can be easily fabricated with low-cost techniques such as roll-to-roll and/or large area electronics processes and promises to pen the way for a new class of flexible and conformal THz devices

Quality Coding by Neural Populations in the Early Olfactory Pathway: Analysis Using Information Theory and Lessons for Artificial Olfactory Systems

In this article, we analyze the ability of the early olfactory system to detect and discriminate different odors by means of information theory measurements applied to olfactory bulb activity images. We have studied the role that the diversity and number of receptor neuron types play in encoding chemical information. Our results show that the olfactory receptors of the biological system are low correlated and present good coverage of the input space. The coding capacity of ensembles of olfactory receptors with the same receptive range is maximized when the receptors cover half of the odor input space - a configuration that corresponds to receptors that are not particularly selective. However, the ensemble’s performance slightly increases when mixing uncorrelated receptors of different receptive ranges. Our results confirm that the low correlation between sensors could be more significant than the sensor selectivity for general purpose chemo-sensory systems, whether these are biological or biomimetic

Integrated optics nano-opto-fluidic sensor based on whispering gallery modes for picoliter volume refractometry

We propose and numerically investigate an integrated optics refractometric nano-opto-fluidic sensor based on whispering gallery modes in sapphire microspheres. A measurand fluid is injected in a micromachined reservoir defined in between the microsphere and an optical waveguide. The wavelength shift due to changes in the refractive index of the measurand fluid are studied for a set of different configurations by the finite element method and a high sensitivity versus fluid volume is found. The proposed device can be tailored to work with a minimum fluid volume of 1 pl and a sensitivity up of 2000 nm/(RIUnl). We introduce a figure of merit which quantifies the amplifying effect on the sensitivity of high quality factor resonators and allows us to compare different devices

Waveguided optical reflectors using liquid crystals and composites

We review several approaches to filter optical signals confined in waveguides by using either electro-optical or nonlinear optical effects in liquid crystals (LC) and composites

Guida d’onda ottica non lineare a cristallo liquido su silicio

The optical nonlinear transmission of a channel waveguide with E7 liquid crystal core infiltrated in a SiO2/Si V-groove is experimentally and theoretically investigated. Low input power excites optical nonlinearity due to optically induced reorientational effect