Evidence of asymmetric beaming in a piecewise-linear propagation channel.

Asymmetric beaming in a piecewise-linear propagation channel is demonstrated for a single photonic-crystal prism at Gaussian-beam illumination. The used hybrid refraction-diffraction mechanism exploits oblique incidence, the first-negative-order deflection at the longer interface, and asymmetry in coupling at the exit interfaces and does not need blocking of transmission by dispersion in the backward illumination case. The Floquet-Bloch mode with left-handed behavior and nearly circular equifrequency dispersion contours is utilized. The outgoing waves may have significantly different spatial distributions for the forward and backward illumination cases, yielding asymmetry in the beaming regime.

Structural parameters and electronic properties of 2D carbon allotrope: Graphene with a kagome lattice structure.

In this paper, the electronic properties of a carbon allotrope, graphene with a kagome lattice structure, are investigated. Spin-polarized density functional theory (DFT) calculations with Grimme dispersion corrections were done. Bond lengths, electronic band structure, and projected density of states were calculated. Electronic band structure calculations show kagome flat-band formation with higher d-orbital contributed bonding behavior than the pristine graphene structure. The structural parameters and electronic band results of this 2D carbon allotrope show wider possible usage in many applications from desalination membranes to possible high-temperature superconductors.

Highly-Sensitive Refractive Index Sensing by Near-infrared Metatronic Nanocircuits.

In this work, we present a highly-sensitive refractive index sensor based on metatronic nanocircuits operating at near-infrared spectral range. The structure is designed based on simple nanorod geometry and fabricated by nanopatterning of transparent conducting oxides. The functionality of these polarization dependent metatronic nanocircuits is enhanced by applying tunable response. This feature is investigated by depositing NH2 (Amine) groups via plasma polymerization technique on top of indium-tin-oxide nanorods. The dielectric constant of Amine groups is a function of their thickness, which can be controlled by the RF power and the time duration of the applied plasma polymerization process. The resonance wavelengths of nanocircuits shift to higher wavelength, as the dielectric constant of the deposited material increases. An excellent agreement between the design and experimental results are obtained. Our metatronic based nanosensor offers a high-sensitive performance of 1587 nm/RIU with a satisfactory figure of merit for this class of sensors.

Asymmetric light propagation in chirped photonic crystal waveguides.

We report numerical and experimental investigations of asymmetric light propagation in a newly designed photonic structure that is formed by creating a chirped photonic crystal (PC) waveguide. The use of a non-symmetric distribution of unit cells of PC ensures the obtaining of asymmetric light propagation. Properly designing the spatial modulation of a PC waveguide inherently modifies the band structure. That in turn induces asymmetry for the light's followed path. The investigation of the transmission characteristics of this structure reveals optical diode like transmission behavior. The amount of power collected at the output of the waveguide centerline is different for the forward and backward propagation directions in the designed configuration. The advantageous properties of the proposed approach are the linear optic concept, compact configuration and compatibility with the integrated photonics. These features are expected to hold great potential for implementing practical optical rectifier-type devices.

Multi-gap individual and coupled split-ring resonator structures.

We present a systematic numerical study, validated by accompanied experimental data, of individual and coupled split ring resonators (SRRs) of a single rectangular ring with one, two and four gaps. We discuss the behavior of the magnetic resonance frequency, the magnetic field and the currents in the SRRs, as one goes from a single SRR to strongly interacting SRR pairs in the SRR plane. We show that coupling of the SRRs along the E direction results to shift of the magnetic resonance frequency to lower or higher values, depending on the capacitive or inductive nature of the coupling. Strong SRR coupling along propagation direction usually results to splitting of the single SRR resonance into two distinct resonances, associated with peculiar field and current distributions.

Surface morphology of Al0.3Ga0.7N/Al2O3-high electron mobility transistor structure.

We present surface properties of buffer films (AIN and GaN) and Al0.3Gao.zN/Al2O3-High Electron Mobility Transistor (HEMT) structures with/without AIN interlayer grown on High Temperature (HT)-AIN buffer/Al2O3 substrate and Al2O3 substrate. We have found that the GaN surface morphology is step-flow in character and the density of dislocations was about 10(8)-10(9) cm(-2). The AFM measurements also exhibited that the presence of atomic steps with large lateral step dimension and the surface of samples was smooth. The lateral step sizes are in the range of 100-250 nm. The typical rms values of HEMT structures were found as 0.27, 0.30, and 0.70 nm. HT-AIN buffer layer can have a significant impact on the surface morphology of Al0.3Ga0.7N/Al2O3-HEMT structures.

Subwavelength resolution in a two-dimensional photonic-crystal-based superlens.

We experimentally and theoretically demonstrate single-beam negative refraction and superlensing in the valence band of a two-dimensional photonic crystal operating in the microwave regime. By measuring the refracted electromagnetic waves from a slab shaped photonic crystal, we find a refractive index of -1.94 that is very close to the theoretical value of -2.06. A scanning transmission measurement technique is used to measure the spatial power distribution of the focused electromagnetic waves that radiate from a point source. The full width at half maximum of the focused beam is measured to be 0.21 lambda, which is in good agreement with the finite difference time domain method simulations. We also report a subwavelength resolution for the image of two incoherent point sources, which are separated by a distance of lambda/3.

A new detection method for capacitive micromachined ultrasonic transducers.

Capacitive micromachined ultrasonic transducers (cMUT) have become an alternative to piezoelectric transducers in the past few years. They consist of many small circular membranes that are connected in parallel. In this work, we report a new detection method for cMUTs. We model the membranes as capacitors and the interconnections between the membranes as inductors. This kind of LC network is called an artificial transmission line. The vibrations of the membranes modulate the electrical length of the transmission line, which is proportional to the frequency of the signal through it. By measuring the electrical length of the artificial line at a high RF frequency (in the gigahertz range), the vibrations of the membranes can be detected in a very sensitive manner. For the devices we measured, we calculated the minimum detectable displacement to be in the order of 10(-5) A/square root of Hz with a possible improvement to 10(-7) A/square root of Hz.

Tight-binding description of the coupled defect modes in three-dimensional photonic crystals

We have experimentally observed the eigenmode splitting due to coupling of the evanescent defect modes in three-dimensional photonic crystals. The splitting was well explained with a theory based on the classical wave analog of the tight-binding (TB) formalism in solid state physics. The experimental results were used to extract the TB parameters. A new type of waveguiding in a photonic crystal was demonstrated experimentally. A complete transmission was achieved throughout the entire waveguiding band. We have also obtained the dispersion relation for the waveguiding band of the coupled periodic defects from the transmission-phase measurements and from the TB calculations.

Scintigraphic evaluation of the Eustachian tube functions.

Eustachian tube (ET) dysfunction is one of the most important factors in the etiology of middle ear disease. There are several methods to assess the functions of ET which show the anatomic patency of the tube. However, functional patency of ET should be evaluated as well. For this reason, we used a scintigraphic method at 42 patients who had otitis media with effusion (study group) and traumatic perforation of the ear drum (control group) at 32 and 10 of them, respectively. After instillation of 100 microCi (100 microliters) Technetium 99m-macro-aggregated albumin (Tc99m-MAA) into the middle ear, 60 images were taken at 15 second intervals. Both groups were investigated as to whether there was radioactivity passage through ET and, the arrival time of the radioactivity to ET and to nasopharynx were calculated if the passage occurred. Radioactivity passage rates in the study and control groups were 5 (16%) and 10 (100%), respectively. The difference between both groups was statistically very significant (Chi-square, p < 0.001). Scintigraphy is a feasible tool for the assessment of ET functions. Scintigraphic methods should be improved and be used as a tubal function test in the future.

Terahertz spectroscopy of three-dimensional photonic band-gap crystals.

We have fabricated and built three-dimensional photonic band-gap crystals with band-gap frequencies larger than 500 GHz. We built the crystals by stacking micromachined (110) silicon wafers. The transmission and dispersion characteristics of the structures were measured by an all-electronic terahertz spectroscopy setup. The experimental results were in good agreement with theoretical calculations. To our knowledge, our new crystal has the highest reported photonic band-gap frequency.