Rola Aylo

Co-sputtered SiC + Ag nanomixtures as visible wavelength negative index metamaterials

The fabrication and characterization of a novel metamaterial that shows negative index in the visible (blue) is reported. The real part of the negative index of this metamaterial at 405 nm, comprising co-sputtered SiC + Ag nanoparticle mixture on a glass substrate, is deduced from results of double Michelson interferometry setup which shows a negative phase delay. It is numerically verified that this metamaterial can yield near-field super-resolution imaging for both TE and TM polarizations.

Multilayer Periodic and Random Metamaterial Structures: Analysis and Applications

In recent years, multilayer photonic bandgap structures comprising stacks of alternating layers of positive and negative index have been proposed for a variety of applications, such as perfect imaging, filters, sensors, coatings for tailored emittance, absorptance, etc. Following a brief review of the history of negative index materials, the performance of such stacks is reviewed, with emphasis on analysis of plane wave and beam propagation, and possible applications in sensing. First, the use of the transfer matrix method to analyze plane wave propagation in such structures to determine the transmittance and reflectance is developed. Examples of cases where the Bragg bandgap and the so-called zero <;\(n \) > gap can be used for possible applications in sensing are illustrated. Next, the transfer matrix approach is extended to simulate the spatial evolution of a collection of propagating and nonpropagating TE and TM plane waves (or plane wave spectra) incident on such multilayer structures. The use of the complex Poynting theorem in checking the computations, as well as monitoring powers and the stored electric or magnetic energy in any section of the multilayer stack, is illustrated, along with its use in designing alternating positive and negative index structures with optimal gain to compensate for losses in the negative index material. Finally, the robustness of PIM-NIM stacks with respect to randomness in the dimensions of the PIM-NIM structure is examined. This should be useful in determining the performance of such structures when they are physically fabricated.

Perturbed multilayered structures of positive and negative index materials

In this work, we study the influence of disorder on the omnidirectional bandgap in a one dimensional stack of alternating positive and dispersive negative index materials. We achieve this through using the transfer matrix method to study wave propagation properties. In the case where the number of periods becomes infinitely large, the limit of the transmittance is derived from the trace of the matrix, and thus reducing the calculation complexity. The origin of the transmission resonances and their relation with the field localization for random systems are analyzed and compared with that of the periodic case. Our result shows that the zero average refractive index bandgap is not affected by small disorders in layer thickness or refractive index, and thus the multilayer stack is robust against fabrication. The finding is expected to achieve potential applications in optoelectronic sensor devices such as omnidirectional reflectors in airplane radomes. We also show that a random mixture of positive and dispersive negative index materials in an equal ratio always possesses a zero average refractive index bandgap.

Application of the transfer matrix method to reflection gratings in positive and negative index materials

The transfer matrix method (TMM) has been used to analyze plane wave and beam propagation through linear photonic bandgap structures. Here, we apply TMM to determine the exact spatial behavior of TE and TM waves in periodic refractive index structures of arbitrary thickness. First, we extend the TMM approach to analyze plane wave propagation through Kerr type nonlinear media. Secondly, we analyze second harmonic fields in a 1D nonlinear photonic crystal for arbitrary angle of incidence of the fundamental plane wave. This allows us to construct the overall transfer matrix of nonlinear waves for the whole nonlinear optical structure from all the individual layer transfer matrices. We extend this method to analyze the effect of second order nonlinearity to beam propagation by applying TMM to the angular spectral components of the beam(s).

Design of metamaterial based sensors for pressure measurement

Transmission and reflection spectra of periodic and random stacks comprising positive index materials and metamaterials have been extensively studied. In this paper we investigate the effectiveness of periodic stacks of PIM/NIM for use as a sensor. The transfer matrix method is used to find the transmittance and reflectance. Differences between the zero average refractive index bandgap and Bragg bandgap are illustrated. It is shown how these bandgaps can be used as the basis for designing sensors with minimal cross-sensitivity.

Tunable metamaterial binary nano-particle dispersed liquid crystal cells

Metamaterials with tunable properties are of great importance due to potential applications in super-resolution lensing and sensors. In this paper we study the feasibility of the fabrication of a metamaterial using binary nanoparticle-dispersed liquid crystal cell (NDLCC). Depending on the angle between the director axis of the LCC and the incident beam, types, radii, and volume filling fractions of the nanoparticles, a negative index of refraction cell is obtained in a certain range of frequencies. The effective index of refraction is calculated using the effective medium theory. The scattering, extinction, and absorption of such a NDLCC cell is also found. Finally, the influence of the various parameters to obtain such a negative index metamaterial has been investigated.

Baseband and envelope propagation in media modeled by a class of complex dispersion relations

We demonstrate that a class of simplified complex dispersion relations, which obey causality, can model baseband and envelope propagation in conventional and negative index materials. One such dispersion relation is a special case of the Drude model, another yields the Kuramoto-Shivashinsky equation, while a third, in the limit, yields the simplest dispersion for negative index materials.

Nanoparticle-dispersed metamaterial sensors for adaptive coded aperture imaging applications

We propose tunable single-layer and multi-layer (periodic and with defect) structures comprising nanoparticle dispersed metamaterials in suitable hosts, including adaptive coded aperture constructs, for possible Adaptive Coded Aperture Imaging (ACAI) applications such as in microbolometry, pressure/temperature sensors, and directed energy transfer, over a wide frequency range, from visible to terahertz. These structures are easy to fabricate, are low-cost and tunable, and offer enhanced functionality, such as perfect absorption (in the case of bolometry) and low cross-talk (for sensors). Properties of the nanoparticle dispersed metamaterial are determined using effective medium theory.

Propagation of a Gaussian beam through a stack of positive and negative refractive index materials

Propagation of a monochromatic Gaussian beam through a stack of alternating layers of positive-refractive-index dielectrics and negative-refractive-index metamaterials is analyzed using paraxial ray-optics approach. Expressions for the change of the spot-size of the Gaussian beam are derived. Sensors for measuring parameters that affect the thickness or refractive index of the metamaterials can be developed based on the change of the spot-size.

Application of up-sampling and resolution scaling to Fresnel reconstruction of digital holograms

Fresnel transform implementation methods using numerical preprocessing techniques are investigated in this paper. First, it is shown that up-sampling dramatically reduces the minimum reconstruction distance requirements and allows maximal signal recovery by eliminating aliasing artifacts which typically occur at distances much less than the Rayleigh range of the object. Second, zero-padding is employed to arbitrarily scale numerical resolution for the purpose of resolution matching multiple holograms, where each hologram is recorded using dissimilar geometric or illumination parameters. Such preprocessing yields numerical resolution scaling at any distance. Both techniques are extensively illustrated using experimental results.