This presentation is concerned with nanophotonic structures, especially with arrays of asymmetric split-ring resonator (ASRR) structures, that may be exploited in a variety of sensing applications. These applications include bio-medical sensing, organic material sensing more generally - and environmental sensing. Specific attention has been paid to the identification of molecules of interest via their bond-resonance spectral signatures.
Since their inception, metamaterial fishnet structures have frequently been used to exhibit a negative refractive index. Their shape and structure make it possible to independently produce both a negative permeability (μ) and a negative permittivity (ε). Fishnets that display this characteristic can be referred to as a double negative metamaterial. Although other techniques have been demonstrated, fishnets are commonly fabricated using electron-beam lithography (EBL) or focused ion-beam (FIB) milling. In this paper we demonstrate the fabrication of fishnets using nano-imprint lithography (NIL). Advantages associated with NIL include a shorter fabrication time, a larger feasible pattern area and reduced costs. In addition to these advantages, the quality of the fabricated structures is excellent. We imprint a stamp directly into a metal-dielectric-metal stack which creates the fishnet and, as an artifact of the technique, a periodic array of nanopillars. Two different designs of the fishnet and nanopillar structure have been fabricated and optical measurements have been taken from both. In addition to the experimental measurements the structures have also been extensively simulated, suggesting a negative refractive index with a real part as large in magnitude as five can be achieved.
The evaluation of electromagnetic material parameters from metamaterial structures has received much attention in the literature. Among others, one method is to retrieve the material parameters from the reflection and transmission measurements of the sample material. It has been found that the electromagnetic material parameters depend on the angle of incidence. Although based on the Nicholson-Ross-Weir technique, the proposed extraction technique has no limitations on the angle of incidence. The proposed extension of the NRW extraction technique is used to study a fishnet structure fabricated by nanoimprint lithography. Silver (Ag)- Magnesium Fluoride (MgF<sub>2</sub>) - silver (Ag) was deposited on the thick PMMA layer before directly imprinted by a stamp. The effective material parameters have been found to characterise the imprinted fishnet structure.
Optical metamaterials are able to achieve optical properties that do not exist in nature. Approaches to the homogenization of optical metamaterials are becoming more and more complex in the desire to achieve accurate representation. Here we propose to modify an existing retrieval approach for metamaterials to characterize their properties. To extract the effective refractive index and material parameters from reflection and transmission coefficients for double negative metamaterial in the optical regime, the modified Nicholson-Ross-Weir (NRW) method is used. In order to obtain a true picture of these metamaterials, as a function of angle of incidence of the illumination, it is important to present not only the effective parameters of permittivity and permeability but also some other important parameters such as coupling coefficients, that represent the inherent anisotropy.