Eli Lansey

Light localization, photon sorting, and enhanced absorption in subwavelength cavity arrays

A periodically patterned metal-dielectric composite material is designed, fabricated and characterized that spatially splits incoming microwave radiation into two spectral ranges, individually channeling the separate spectral bands to different cavities within each spatially repeating unit cell. Further, the target spectral bands are absorbed within each associated set of cavities. The photon sorting mechanism, the design methodology, and experimental methods used are all described in detail. A spectral splitting efficiency of 93-96% and absorption of 91-92% at the two spectral bands is obtained for the structure. This corresponds to an absorption enhancement over 600% as compared to the absorption in the same thickness of absorbing material. Methods to apply these concepts to other spectral bands are also described.

Photon sorting in the near field using subwavelength cavity arrays in the near-infrared

A frequency selective metasurface capable of sorting photons in the near-infrared spectral range is designed, fabricated, and characterized. The metasurface, a periodic array of dielectric cylindrical cavities in a gold film, localizes and transmits light of two spectral frequency bands into spatially separated cavities, resulting in near-field light splitting. The design and fabrication methodologies of the metasurface are discussed. The transmittance and photon sorting properties of the designed structure is simulated numerically and the measured transmission is presented.

Analytical analysis of the resonance response of subwavelength nanoscale cylindrical apertures in metal at near-ultraviolet, optical, and near-infrared frequencies

In this paper we analytically study the resonance response of cylindrical subwavelength apertures embedded in metal films at near-UV, optical, and near-IR frequencies. This analysis is concise, and allows accurate and intuitive prediction of both propagating and evanescent modes, which are key contributors to enhanced optical transmission through thin metal films. In this approach we do not analyze the detailed behavior of the fields inside the metal walls, but still obtain the effects of the implicit buildup of charges within those walls. We calculate the modal dispersion relation, cutoff dependence on cylinder radius, and waveguide attenuation for a cylindrical aperture embedded in metal. We support our findings with finite element simulations and find strong agreement with our theory.

Design of photonic metamaterial multi-junction solar cells using rigorous coupled wave analysis

We have developed a method to design multi-junction horizontally-oriented solar cells using single-layer photonic metamaterials. These metamaterial light harvesting templates are capable of separating white light into discrete wavelength ranges and trapping it efficiently into different, separately wired cavities. Any number of different wavelength-tailored charge separation complexes can be fixed to the walls of these tuned cavities. To design the metamaterials we have developed a coupled wave analysis of 2D periodic metamaterials. Past results with 1D gratings have shown that this is a very effective method for designing periodic structures and we have generalized the approach to 2D periodic cavities.

Measurement of Photon Sorting at Microwave Frequencies in a Cavity Array Metasurface

We present experimental results demonstrating the spatial sorting of incoming radiation in two spectral ranges. A metasurface composed of a periodically patterned metal of subwavelength thickness with dielectric inclusions concentrates and localizes electromagnetic fields near the surface. Light of the separate spectral bands is channeled into different geometrically tuned cavities within each spatially repeating unit cell. Excitation of cavity modes facilitates this simultaneous spatial- and spectral-selective absorption. The measured reflection and field profiles are presented and the spectral and spatial selectivity are shown. A method to apply these concepts to split radiation into three spectral bands is also proposed.

Dispersion analysis of subwavelength square apertures at optical frequencies

We present an analytical study of resonance properties of square subwavelength apertures at optical and near-IR frequencies. This approach allows accurate prediction of resonance responses, captures both propagating and evanescent modes, and can easily be implemented in other analytical techniques. In this approach we avoid analyzing the detailed behavior of the fields inside the metal walls, but still obtain the effects of the buildup of charges within those walls. We calculate the dispersion relation and find the cutoff frequencys dependence on cavity dimensions for a square aperture embedded in a silver film, and support our findings with finite-element simulations.

Rapidly optimizing optoelectronic devices using full wave 3D simulation software

Fabricating optoelectronic devices can be extremely costly due to the need for using high end fabrication methods such as photo lithography. Therefore, the importance of being able to accurately and rapidly prototype an optoelectronic device cannot be overstated. By using commercially available full wave 3D simulation software (FW3D), rapid prototyping can be achieved. A complete rapid prototyping process would require a discussion on simulation as well as fabrication work, however for this paper we will only focus on the simulation aspect which is rapid optimization. The bulk of our work will be to model and rapidly optimize an optoelectronic device which is currently of interest to many optoelectronic researchers. This structure is labeled as a frequency selective surface. By using two widely known numerical methods, we will demonstrate the modeling and simulation aspects needed for achieving rapid optimization and fully characterizing the optoelectronic performance of this device.

A Polarization-Independent Wavelength-Tuned Metamaterial for Solar Energy Applications

We present simulations of a polarization-independent, L-shaped cavity metamaterial using finite element techniques. These structures concentrate light in the cavities and have applications in high-efficiency solar energy devices.